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Accepted Manuscript
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doi: 10.12073/j.hjxb.20220426002
Abstract:
In order to study the influence of different scanning characteristic parameters on the surface morphology of selective laser melting (SLM), 316L stainless steel powder was taken as an example to carry out the single-layer and double-track numerical simulation at the mesoscopic scale. Based on the Discrete Element Method, the numerical model of powder bed is established. The Volume of Fluid method is used to calculate the melting, flow and solidification process of heated powder in powder bed. Considering the three scanning characteristic parameters of laser power, scanning speed and scanning spacing, the orthogonal experiment was designed and carried out to study the influence of selected scanning characteristic parameters on the tracks morphology on the surface of the formed part was studied from the two aspects of the tracks morphology and the tracks width.The effectiveness of numerical simulation was verified by actual printing and morphology observation experiments. The results show that in the range of linear energy density of 313 ~ 500 J / m and scanning interval of 50 ~ 90 μm, the morphology of melting tracks with smooth continuous local defects can be obtained, and the parameter combination in this interval is linearly corresponding in turn. In terms of the influence on the integrity of the weld morphology, scanning speed > scanning spacing > laser power.
In order to study the influence of different scanning characteristic parameters on the surface morphology of selective laser melting (SLM), 316L stainless steel powder was taken as an example to carry out the single-layer and double-track numerical simulation at the mesoscopic scale. Based on the Discrete Element Method, the numerical model of powder bed is established. The Volume of Fluid method is used to calculate the melting, flow and solidification process of heated powder in powder bed. Considering the three scanning characteristic parameters of laser power, scanning speed and scanning spacing, the orthogonal experiment was designed and carried out to study the influence of selected scanning characteristic parameters on the tracks morphology on the surface of the formed part was studied from the two aspects of the tracks morphology and the tracks width.The effectiveness of numerical simulation was verified by actual printing and morphology observation experiments. The results show that in the range of linear energy density of 313 ~ 500 J / m and scanning interval of 50 ~ 90 μm, the morphology of melting tracks with smooth continuous local defects can be obtained, and the parameter combination in this interval is linearly corresponding in turn. In terms of the influence on the integrity of the weld morphology, scanning speed > scanning spacing > laser power.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20221013001
Abstract:
The welding of TC4 titanium alloy plate was carried out by means of laser welding with filler wire and self-developed flux-cored wire, and the obtained welding joint was treated with 850 ° C heat preservation for 2 hours and then cooled and annealed with furnace, the microstructure and mechanical properties of the welded joint were compared with those of the welded joint. The results showed that the welded joint was composed of αp phase, αs phase and β phase, the α' martensite structure was not found in the as-welded joint, the strength of the as-welded joint decreased, but the elongation and impact toughness at room temperature increased, and the tensile fracture of the as-welded joint was surrounded by a large number of tearing lips, the dimples are deep and uniform, showing microporous polymerized ductile fracture. It was found by XRD that the as-welded joint was mainly composed of α' martensite, and a few weak multi-angle α phase diffraction peaks were observed, and the central angle of α phase diffraction peaks in the heat-treated joint was the same as that in the as-welded joint, in addition, a rather sharp diffraction peak of β phase (110) was found.
The welding of TC4 titanium alloy plate was carried out by means of laser welding with filler wire and self-developed flux-cored wire, and the obtained welding joint was treated with 850 ° C heat preservation for 2 hours and then cooled and annealed with furnace, the microstructure and mechanical properties of the welded joint were compared with those of the welded joint. The results showed that the welded joint was composed of αp phase, αs phase and β phase, the α' martensite structure was not found in the as-welded joint, the strength of the as-welded joint decreased, but the elongation and impact toughness at room temperature increased, and the tensile fracture of the as-welded joint was surrounded by a large number of tearing lips, the dimples are deep and uniform, showing microporous polymerized ductile fracture. It was found by XRD that the as-welded joint was mainly composed of α' martensite, and a few weak multi-angle α phase diffraction peaks were observed, and the central angle of α phase diffraction peaks in the heat-treated joint was the same as that in the as-welded joint, in addition, a rather sharp diffraction peak of β phase (110) was found.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220426001
Abstract:
In order to obtain high-quality laser cladding fabricated parts, a process optimization method targeting macroscopic and microscopic characteristics is proposed for 316L stainless steel as an example, based on the problem that existing studies only target geometric morphology for optimization.Firstly, an empirical statistical model of the geometric morphology and microstructure of the cladding layer and the main process parameters is constructed through full factorial design and regression analysis, and the influence of process parameters on the geometric morphology and the average intercept of microscopic grain is discussed. Then, the geometric morphology and the average grain intercept are selected as the indicators for evaluating the quality of cladding, and the optimal process parameters and suitable process range are determined by the composite desirability function. Finally, the feasibility and effectiveness of the method are verified. The results show that under the condition of the best process parameters, the statistical model of macroscopic and microscopic characteristics has high prediction accuracy. The prepared cladding samples not only have higher microhardness, but also have excellent tensile properties: the yield strength is 439 MPa, the tensile strength is 751 MPa, and the elongation is 26%. The process optimization of macroscopic and microscopic characteristics is achieved.
In order to obtain high-quality laser cladding fabricated parts, a process optimization method targeting macroscopic and microscopic characteristics is proposed for 316L stainless steel as an example, based on the problem that existing studies only target geometric morphology for optimization.Firstly, an empirical statistical model of the geometric morphology and microstructure of the cladding layer and the main process parameters is constructed through full factorial design and regression analysis, and the influence of process parameters on the geometric morphology and the average intercept of microscopic grain is discussed. Then, the geometric morphology and the average grain intercept are selected as the indicators for evaluating the quality of cladding, and the optimal process parameters and suitable process range are determined by the composite desirability function. Finally, the feasibility and effectiveness of the method are verified. The results show that under the condition of the best process parameters, the statistical model of macroscopic and microscopic characteristics has high prediction accuracy. The prepared cladding samples not only have higher microhardness, but also have excellent tensile properties: the yield strength is 439 MPa, the tensile strength is 751 MPa, and the elongation is 26%. The process optimization of macroscopic and microscopic characteristics is achieved.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220429002
Abstract:
In the ultra-narrow gap welding of the fed-in flux sheet constrained arc, the interaction between the continuously fed flux sheet and the arc affected the stability of the welding process. A method of rapidly interrupting the arc was used to obtain the shape of the molten pool and the instantaneous melting morphology of the flux sheet at the arc-extinguishing position . The relationship between the action length of the flux sheet on the arc and the degree of arc confinement was analyzed. The results showed that the feeding speed of the flux sheet was increased or the welding voltage was reduced , which could make the action length of the flux sheet on the arc increase. When it increased to a certain extent, the arc was effectively constrained at the bottom of the groove to uniformly heat the root of the side wall, and the flat weld with good root fusion was obtained. When the degree of restraint was weakened, the arc heating area was concentrated on the two side walls, and it was too difficult to form an effective molten pool at the root of the groove.Finally a hole weld was formed.
In the ultra-narrow gap welding of the fed-in flux sheet constrained arc, the interaction between the continuously fed flux sheet and the arc affected the stability of the welding process. A method of rapidly interrupting the arc was used to obtain the shape of the molten pool and the instantaneous melting morphology of the flux sheet at the arc-extinguishing position . The relationship between the action length of the flux sheet on the arc and the degree of arc confinement was analyzed. The results showed that the feeding speed of the flux sheet was increased or the welding voltage was reduced , which could make the action length of the flux sheet on the arc increase. When it increased to a certain extent, the arc was effectively constrained at the bottom of the groove to uniformly heat the root of the side wall, and the flat weld with good root fusion was obtained. When the degree of restraint was weakened, the arc heating area was concentrated on the two side walls, and it was too difficult to form an effective molten pool at the root of the groove.Finally a hole weld was formed.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220404001
Abstract:
5A06 aluminum alloy lock butt weld was used as the research object. Based on the laser beam oscillating, a laser power (power distribution) which is distributed along the oscillating path was added to achieve the dynamic control of power relative to the path. The fluid dynamics model of laser oscillating welding process was established by the finite element software FLUENT to research the effect mechanism of laser oscillating and power distribution on weld forming. The weld section morphology, molten pool dynamic behavior and porosity formation process were simulated and compared under two processes of equal power and power distribution. The results show that compared with the equal power weld, the better formed weld is obtained by power distribution and has no defects such as undercut and burn through. Due to the characteristics of power distribution, the average flow rate of molten pool is effectively reduced, the steady flow behavior of molten metal is exhibited, further improve the stability of the keyhole, and smaller depth-to-width ratio keyhole is obtained, effectively reduce the porosity of the weld (0.9 %).
5A06 aluminum alloy lock butt weld was used as the research object. Based on the laser beam oscillating, a laser power (power distribution) which is distributed along the oscillating path was added to achieve the dynamic control of power relative to the path. The fluid dynamics model of laser oscillating welding process was established by the finite element software FLUENT to research the effect mechanism of laser oscillating and power distribution on weld forming. The weld section morphology, molten pool dynamic behavior and porosity formation process were simulated and compared under two processes of equal power and power distribution. The results show that compared with the equal power weld, the better formed weld is obtained by power distribution and has no defects such as undercut and burn through. Due to the characteristics of power distribution, the average flow rate of molten pool is effectively reduced, the steady flow behavior of molten metal is exhibited, further improve the stability of the keyhole, and smaller depth-to-width ratio keyhole is obtained, effectively reduce the porosity of the weld (0.9 %).
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220425001
Abstract:
Seam tracking system is one of the key technology to realize intelligent welding. Aiming at the problems of welding seam tracking in narrow gap, such as the difficulty of real time seam tracking weld seam of sensor, a new multipole array capacitive sensor based on fringe electric field technology is designed. And the welding seam surface reconstruction is realized through the capacitive signal processing technology based on wavelet filtering and nonlinear mapping technology. Firstly, a mathematical model of multipole array capacitive sensing is established, and the capacitive sensor structure is optimized through theory calculation results and finite element simulation analysis. Subsequently,The capacitive signal of the sensor is extracted and optimized with the help of capacitance signal processing technology, the welding gun offset,and weld deviation are both obtained. The results show that the reconstructed weld surface is basically the same as the narrow gap weld in the experiment, and it is feasible for the multipole array capacitive sensor applying to narrow gap weld tracking, which is of great significance for narrow gap weld tracking.
Seam tracking system is one of the key technology to realize intelligent welding. Aiming at the problems of welding seam tracking in narrow gap, such as the difficulty of real time seam tracking weld seam of sensor, a new multipole array capacitive sensor based on fringe electric field technology is designed. And the welding seam surface reconstruction is realized through the capacitive signal processing technology based on wavelet filtering and nonlinear mapping technology. Firstly, a mathematical model of multipole array capacitive sensing is established, and the capacitive sensor structure is optimized through theory calculation results and finite element simulation analysis. Subsequently,The capacitive signal of the sensor is extracted and optimized with the help of capacitance signal processing technology, the welding gun offset,and weld deviation are both obtained. The results show that the reconstructed weld surface is basically the same as the narrow gap weld in the experiment, and it is feasible for the multipole array capacitive sensor applying to narrow gap weld tracking, which is of great significance for narrow gap weld tracking.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220328002
Abstract:
Extensive research was carried out on the microstructure and mechanical properties of the welded dual phase 12% Cr stainless steel (00Cr12Ni) composed of ferrite and martensite. Heat affected zone (HAZ) of weldment was subdivided to high and low temperature heat affected zones (HTHAZ & LTHAZ). HTHAZ was characterized by predominantly coarse ferritic grains, whereas LTHAZ contained mostly fine martensitic grains. The temperature profiles of both zones were monitored and recorded during Metal Active Gas (MAG) welding process. The experimental data were used to simulate the mechanical properties of each zone. The temperature profile of the entire weldment could be divided to from 1200 ℃ up to the melting point of the steel (HTHAZ) and from 800 to 1200 °C (LTHAZ). HTHAZ exhibited brittle behavior even at room temperature while LTHAZ was ductile at room temperature due to it fine martensitic structure. The microstructure and mechanical properties of welded joints with various characteristics obtained by three methods of MAG, plasma arc welding (PAW), and high-frequency induction welding (HFIW) are analyzed in this study. As the HAZ distribution of a MAG welded joint is at an angle to the weld centerline, the section is difficult to penetrate and fracture, so PWHT is not required. The coarse grains in the HTHAZ of PAW sample could be eliminated by austenization at 1000 °C. This was due to the formation of fine martensitic grains during subsequent cooling, therefore obtaining higher toughness. Although the HFIW resulted in fine martensitic grains, the toughness at room temperature was still low. The toughness of the joint was improved by further annealing.
Extensive research was carried out on the microstructure and mechanical properties of the welded dual phase 12% Cr stainless steel (00Cr12Ni) composed of ferrite and martensite. Heat affected zone (HAZ) of weldment was subdivided to high and low temperature heat affected zones (HTHAZ & LTHAZ). HTHAZ was characterized by predominantly coarse ferritic grains, whereas LTHAZ contained mostly fine martensitic grains. The temperature profiles of both zones were monitored and recorded during Metal Active Gas (MAG) welding process. The experimental data were used to simulate the mechanical properties of each zone. The temperature profile of the entire weldment could be divided to from 1200 ℃ up to the melting point of the steel (HTHAZ) and from 800 to 1200 °C (LTHAZ). HTHAZ exhibited brittle behavior even at room temperature while LTHAZ was ductile at room temperature due to it fine martensitic structure. The microstructure and mechanical properties of welded joints with various characteristics obtained by three methods of MAG, plasma arc welding (PAW), and high-frequency induction welding (HFIW) are analyzed in this study. As the HAZ distribution of a MAG welded joint is at an angle to the weld centerline, the section is difficult to penetrate and fracture, so PWHT is not required. The coarse grains in the HTHAZ of PAW sample could be eliminated by austenization at 1000 °C. This was due to the formation of fine martensitic grains during subsequent cooling, therefore obtaining higher toughness. Although the HFIW resulted in fine martensitic grains, the toughness at room temperature was still low. The toughness of the joint was improved by further annealing.
Effect of Ni content on microstructure and shearing property of 304/Sn-8Sb-4Cu-xNi/304 solder joints
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220325008
Abstract:
Effect of Ni content on melting property and microstructure of Sn-8Sb-4Cu-xNi (x=0, 0.5%, 1% and 2%, mass fraction) solders were investigated. 304 stainless steel were joined by Sn-8Sb-4Cu-xNi solders, and interfacial microstructure and shearing property of the solder joints were analyzed. The results showed that all of the Sn-8Sb-4Cu-xNi with different Ni content are near eutectic solders, with a melting point of 245 ℃. The microstructure of Sn-8Sb-4Cu solder was consisted of α phase, Sb2Sn3 + Cu6Sn5 + Sn composite phase and Cu6(Sn,Sb)5 phase. After the addition of Ni, the bulk Cu6(Sn,Sb)5 transformed into fine and uniformly distributed (Cu,Ni)6(Sn,Sb)5. When Ni content was less than 1%, the amount of composite phase and (Cu,Ni)6(Sn,Sb)5 phase increased with the increasing of Ni content. When Ni content increased to 2%, the amount of composite phase and (Cu,Ni)6(Sn,Sb)5 phase decreased with the increasing of Ni content, however, the Ni proportion in (Cu,Ni)6(Sn,Sb)5 phase increased to that of Cu. A diffusion layer with a thickness of about 1.5 μm formed at the Sn-8Sb-4Cu-xNi/304 interface, which was identified to be Fe2Sn by EDS. Only Cu6Sn5 type IMCs formed in the solders of 304/Sn-8Sb-4Cu-xNi/304 joints. Ni addition significantly improved the shearing strength of the 304/Sn-8Sb-4Cu-xNi/304 solder joints, when Ni content was 0.5%, the highest shearing strength was 66.9 MPa, increased by 60% compare with the joint without Ni addition. All of the joints were fractured within the solders.
Effect of Ni content on melting property and microstructure of Sn-8Sb-4Cu-xNi (x=0, 0.5%, 1% and 2%, mass fraction) solders were investigated. 304 stainless steel were joined by Sn-8Sb-4Cu-xNi solders, and interfacial microstructure and shearing property of the solder joints were analyzed. The results showed that all of the Sn-8Sb-4Cu-xNi with different Ni content are near eutectic solders, with a melting point of 245 ℃. The microstructure of Sn-8Sb-4Cu solder was consisted of α phase, Sb2Sn3 + Cu6Sn5 + Sn composite phase and Cu6(Sn,Sb)5 phase. After the addition of Ni, the bulk Cu6(Sn,Sb)5 transformed into fine and uniformly distributed (Cu,Ni)6(Sn,Sb)5. When Ni content was less than 1%, the amount of composite phase and (Cu,Ni)6(Sn,Sb)5 phase increased with the increasing of Ni content. When Ni content increased to 2%, the amount of composite phase and (Cu,Ni)6(Sn,Sb)5 phase decreased with the increasing of Ni content, however, the Ni proportion in (Cu,Ni)6(Sn,Sb)5 phase increased to that of Cu. A diffusion layer with a thickness of about 1.5 μm formed at the Sn-8Sb-4Cu-xNi/304 interface, which was identified to be Fe2Sn by EDS. Only Cu6Sn5 type IMCs formed in the solders of 304/Sn-8Sb-4Cu-xNi/304 joints. Ni addition significantly improved the shearing strength of the 304/Sn-8Sb-4Cu-xNi/304 solder joints, when Ni content was 0.5%, the highest shearing strength was 66.9 MPa, increased by 60% compare with the joint without Ni addition. All of the joints were fractured within the solders.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220909001
Abstract:
A new method of flexible control of unstable deformation in high-strength aluminum alloy 2A12 thin plate welding by using "high-speed gas flow field during welding" from the perspective of mechanics is proposed. The effectiveness and feasibility of this method in controlling deformation during welding are studied, and the influence of high-speed gas flow load on the stress evolution law of the thin plate is analyzed to elucidate its control of welding residual stress and deformation mechanism. The temperature field and stress field are analyzed based on the finite element method to determine the key factor of the distance between aerodynamic load and heat source, and to obtain the reasonable and effective range of gas pressure. Experiments are conducted on a self-developed high-speed gas flow field device during welding to verify the method. The results show that when the distance between aerodynamic load and heat source is 20 mm and the gas pressure is 30 MPa, the welding instability deformation is basically eliminated. The longitudinal residual tensile stress peak value on the cross section of the weld seam decreases by 77.73% compared to conventional welding, and the residual compressive stress peak value decreases by 69.23%. The maximum deflection of the plate edge deformation is only 0.9 mm, which is a decrease of 89.41% compared to conventional welding's 8.5 mm. The experimental results are in good agreement with the simulation results, verifying the correctness of the in-process control model based on the high-speed gas flow field.
A new method of flexible control of unstable deformation in high-strength aluminum alloy 2A12 thin plate welding by using "high-speed gas flow field during welding" from the perspective of mechanics is proposed. The effectiveness and feasibility of this method in controlling deformation during welding are studied, and the influence of high-speed gas flow load on the stress evolution law of the thin plate is analyzed to elucidate its control of welding residual stress and deformation mechanism. The temperature field and stress field are analyzed based on the finite element method to determine the key factor of the distance between aerodynamic load and heat source, and to obtain the reasonable and effective range of gas pressure. Experiments are conducted on a self-developed high-speed gas flow field device during welding to verify the method. The results show that when the distance between aerodynamic load and heat source is 20 mm and the gas pressure is 30 MPa, the welding instability deformation is basically eliminated. The longitudinal residual tensile stress peak value on the cross section of the weld seam decreases by 77.73% compared to conventional welding, and the residual compressive stress peak value decreases by 69.23%. The maximum deflection of the plate edge deformation is only 0.9 mm, which is a decrease of 89.41% compared to conventional welding's 8.5 mm. The experimental results are in good agreement with the simulation results, verifying the correctness of the in-process control model based on the high-speed gas flow field.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220325012
Abstract:
In this study, the ternary bees algorithm is innovatively applied to the optimization of process parameters for the engineering requirement, which aims to obtain better tensile strength in the laser welding process of 304 stainless steel flat plate. The proposed fast bees test method reduces the number of tests compared with the response surface method and can avoid to some extent the problems of insignificant response often encountered in the response surface method. With comparing the results among the response surface method, the bees algorithm optimization based on the response surface fitted equations and the fast bees test method, the optimal solutions predicted by the previous two methods were both approximately 688 MPa, while the fast bees test method obtained higher tensile strength of 733.7 MPa. The results show that the fast bees test method has clear and targeted optimisation characteristics and can be used as a low learning cost test method to help engineers for determining reasonable process parameters in the industrial sites.
In this study, the ternary bees algorithm is innovatively applied to the optimization of process parameters for the engineering requirement, which aims to obtain better tensile strength in the laser welding process of 304 stainless steel flat plate. The proposed fast bees test method reduces the number of tests compared with the response surface method and can avoid to some extent the problems of insignificant response often encountered in the response surface method. With comparing the results among the response surface method, the bees algorithm optimization based on the response surface fitted equations and the fast bees test method, the optimal solutions predicted by the previous two methods were both approximately 688 MPa, while the fast bees test method obtained higher tensile strength of 733.7 MPa. The results show that the fast bees test method has clear and targeted optimisation characteristics and can be used as a low learning cost test method to help engineers for determining reasonable process parameters in the industrial sites.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220308001
Abstract:
In this research, 785 MPa grade Fe-Cr-Ni-Mo deposited metals were prepared by tungsten inert gas (TIG) welding and metal active gas arc (MAG) welding processes, respectively. Scanning electron microscopy, transmission electron microscopy and electron backscatter diffraction were adopted to characterize the microstructure and crystallographic characteristics of the deposited metals. Results showed that the microstructure prepared by different welding processes composed of lath bainite. However, a large amount of coalesced bainite appeared in the microstructure of the TIG deposited metal (DM-TIG). In addition, there were a large number of inclusions in the MAG deposited metal (DM-MAG) due to the active shielding gas. After electron backscatter diffraction analysis, results indicated that the crystallographic orientation of DM-MAG was complex compared to DM-TIG due to the large number of autocatalytic nucleation. The results of the mechanical properties of different deposited metals indicted that the toughness of DM-TIG was significantly better than that of DM-MAG. This was due to the large-sized inclusions in DM-MAG, which became the source of cracks during the fracture process. In practical engineering application, welding method should be selected reasonably for components with high requirement of low temperature toughness.
In this research, 785 MPa grade Fe-Cr-Ni-Mo deposited metals were prepared by tungsten inert gas (TIG) welding and metal active gas arc (MAG) welding processes, respectively. Scanning electron microscopy, transmission electron microscopy and electron backscatter diffraction were adopted to characterize the microstructure and crystallographic characteristics of the deposited metals. Results showed that the microstructure prepared by different welding processes composed of lath bainite. However, a large amount of coalesced bainite appeared in the microstructure of the TIG deposited metal (DM-TIG). In addition, there were a large number of inclusions in the MAG deposited metal (DM-MAG) due to the active shielding gas. After electron backscatter diffraction analysis, results indicated that the crystallographic orientation of DM-MAG was complex compared to DM-TIG due to the large number of autocatalytic nucleation. The results of the mechanical properties of different deposited metals indicted that the toughness of DM-TIG was significantly better than that of DM-MAG. This was due to the large-sized inclusions in DM-MAG, which became the source of cracks during the fracture process. In practical engineering application, welding method should be selected reasonably for components with high requirement of low temperature toughness.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220325001
Abstract:
Research on the weldability of Twinning induced plasticity steels is essential for their applications in aerospace, automotive, natural gas transportation, nuclear energy and other fields. In this paper, the welding thermal simulation was performed on the forged high-Mn Twinning induced plasticity steel by setting different peak temperatures (850 °C, 950 °C, 1050 °C, 1150 °C, and 1250 °C) in each interval of the heat affected zone of the welded joint using the Gleeble3500 thermal simulation tester. The changes in the organization and properties of the forged base material after the thermal action of welding were analyzed. The results show that the organization of TWIP steel before and after the thermal action is all-austenitic with equiaxed grains, and the grain size firstly decreases and then increases with the rise of the peak temperature, but is still lower than that of the base material; The tensile properties in the heat-affected zone are better than those of the base material, mainly due to the occurrence of fine grain strengthening, the variation of impact toughness with peak temperature is consistent with the trend of grain size variation, it indicates that the grain size is related to the impact toughness of the twin-induced plasticity steel used in this study, and the finer the grain size, the worse the impact toughness. AlN particles were found at the bottom of the dimple fracture of the impact fracture.
Research on the weldability of Twinning induced plasticity steels is essential for their applications in aerospace, automotive, natural gas transportation, nuclear energy and other fields. In this paper, the welding thermal simulation was performed on the forged high-Mn Twinning induced plasticity steel by setting different peak temperatures (850 °C, 950 °C, 1050 °C, 1150 °C, and 1250 °C) in each interval of the heat affected zone of the welded joint using the Gleeble3500 thermal simulation tester. The changes in the organization and properties of the forged base material after the thermal action of welding were analyzed. The results show that the organization of TWIP steel before and after the thermal action is all-austenitic with equiaxed grains, and the grain size firstly decreases and then increases with the rise of the peak temperature, but is still lower than that of the base material; The tensile properties in the heat-affected zone are better than those of the base material, mainly due to the occurrence of fine grain strengthening, the variation of impact toughness with peak temperature is consistent with the trend of grain size variation, it indicates that the grain size is related to the impact toughness of the twin-induced plasticity steel used in this study, and the finer the grain size, the worse the impact toughness. AlN particles were found at the bottom of the dimple fracture of the impact fracture.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220325003
Abstract:
The droplet transition behavior in traditional MIG welding of aluminum alloy was detected and analyzed by CMOS high-speed camera. The transition frequency and velocity of the MIG droplets were determined. Based on the theoretical analysis of MIG welding heat source characteristics, thermal action mode and weld shape, the combined volume heat source model was proposed and developed from the macro welding heat process. The MIG arc was described as a double-ellipsoidal heat source, the droplet was described as a uniform-body heat source. In the developed droplet heat source model, the impact effect of the droplet on the weld pool was considered by accounting for its kinetic energy. Based on the above developed heat source model, the finite element calculation model of MIG welding of aluminum alloy was established. According to the simulation results of temperature field distribution of MIG build-up welding of thick plate aluminum alloy, it was found that the calculated weld bead geometry and fusion line shape showed excellent agreement with the experimental result. The results showed that the combined volume heat source model considering the droplet heat and kinetic energy could reasonably describe the heat process and finger melting depth characteristics of MIG welding. This research result has certain guiding significance for the numerical simulation and production application of MIG welding and hybrid welding of aluminum alloy.
The droplet transition behavior in traditional MIG welding of aluminum alloy was detected and analyzed by CMOS high-speed camera. The transition frequency and velocity of the MIG droplets were determined. Based on the theoretical analysis of MIG welding heat source characteristics, thermal action mode and weld shape, the combined volume heat source model was proposed and developed from the macro welding heat process. The MIG arc was described as a double-ellipsoidal heat source, the droplet was described as a uniform-body heat source. In the developed droplet heat source model, the impact effect of the droplet on the weld pool was considered by accounting for its kinetic energy. Based on the above developed heat source model, the finite element calculation model of MIG welding of aluminum alloy was established. According to the simulation results of temperature field distribution of MIG build-up welding of thick plate aluminum alloy, it was found that the calculated weld bead geometry and fusion line shape showed excellent agreement with the experimental result. The results showed that the combined volume heat source model considering the droplet heat and kinetic energy could reasonably describe the heat process and finger melting depth characteristics of MIG welding. This research result has certain guiding significance for the numerical simulation and production application of MIG welding and hybrid welding of aluminum alloy.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220418002
Abstract:
In this paper, the high chromium cast iron (HCCI) hardfacing layer is deposited on the surface of D32 low-alloy steel by electroslag surfacing method. Combined with the temperature field measurement of the heat-affected zone (HAZ) during the surfacing process, the microstructure and mechanical properties of the HAZ, composite interface and hardfacing layer are studied. The results show that: the heating and cooling rates are slower during the electroslag surfacing, and the temperature distribution in the low alloy steel substrate during the stabilizing stage is uniform; the maximum temperature gradient in the surfacing direction is 23.1 ° C / mm. The maximum thermal stress in the low-alloy steel substrate is 25.9 MPa, lower than its tensile strength, which effectively avoids the occurrence of cracks; the composite interface is smooth and clear, with an austenite band region, about 50 μm in width; The grains of HAZ have grown, whose microstructure is a mixture of ferrite and pearlite. The microstructure of HCCI hardfacing layer is composed of austenite, carbides and a small amount of martensite. The M7C3 type carbides are small and uniformly distributed in austenite grain boundaries. The bonding strength of the composite interface is 196 MPa; the impact energy (53 J) of the composite sample is significantly higher than that of the HCCI hardfacing layer (10.7 J). During abrasion, the HCCI hardfacing layer undergoes martensitic transformation under a large load, the hardness is improved, and an excellent performance in wear resistance was obtained.
In this paper, the high chromium cast iron (HCCI) hardfacing layer is deposited on the surface of D32 low-alloy steel by electroslag surfacing method. Combined with the temperature field measurement of the heat-affected zone (HAZ) during the surfacing process, the microstructure and mechanical properties of the HAZ, composite interface and hardfacing layer are studied. The results show that: the heating and cooling rates are slower during the electroslag surfacing, and the temperature distribution in the low alloy steel substrate during the stabilizing stage is uniform; the maximum temperature gradient in the surfacing direction is 23.1 ° C / mm. The maximum thermal stress in the low-alloy steel substrate is 25.9 MPa, lower than its tensile strength, which effectively avoids the occurrence of cracks; the composite interface is smooth and clear, with an austenite band region, about 50 μm in width; The grains of HAZ have grown, whose microstructure is a mixture of ferrite and pearlite. The microstructure of HCCI hardfacing layer is composed of austenite, carbides and a small amount of martensite. The M7C3 type carbides are small and uniformly distributed in austenite grain boundaries. The bonding strength of the composite interface is 196 MPa; the impact energy (53 J) of the composite sample is significantly higher than that of the HCCI hardfacing layer (10.7 J). During abrasion, the HCCI hardfacing layer undergoes martensitic transformation under a large load, the hardness is improved, and an excellent performance in wear resistance was obtained.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220401001
Abstract:
To solve the fusion welding problem of K4951 alloy is the key to realize the development of a new generation of aero-engine casing. Since the K4951 alloy contains the high content of refractory elements and the weldability is poor, this study designed seven kinds of welding wires by adjusting the precipitation-strengthening elements and solid-solution strengthening elements according to the composition characteristics of the alloy. The effects of alloying elements on crack sensitivity and creep properties of the welding joints were analyzed by means of Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Electro-Probe Microanalyzer (EPMA) and Thermal-calc software. Results show that when the content of B was increased from 0.005wt% to 0.04wt%, the crack sensitivity of the joint was significantly increased, and the weld metal is fractured. Increasing the Nb content can improve the healing ability of the liquid film in grain boundary, which can reduce the welding sensitivity of welding samples, and increase the creep life of joints from 15h to 40h. Reducing the content of Cr and Mo can increase the crack sensitivity of the alloy to a certain extent and increase the creep life of the joint. Increasing Al content and regulating the Nb, Cr, Mo and other elements can effectively inhibit crack formation and improve the high-temperature service performance of the welding joint. The results of this study can provide an important reference value for the subsequent research on weldability of precipitation strengthened nickel-based superalloy.
To solve the fusion welding problem of K4951 alloy is the key to realize the development of a new generation of aero-engine casing. Since the K4951 alloy contains the high content of refractory elements and the weldability is poor, this study designed seven kinds of welding wires by adjusting the precipitation-strengthening elements and solid-solution strengthening elements according to the composition characteristics of the alloy. The effects of alloying elements on crack sensitivity and creep properties of the welding joints were analyzed by means of Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Electro-Probe Microanalyzer (EPMA) and Thermal-calc software. Results show that when the content of B was increased from 0.005wt% to 0.04wt%, the crack sensitivity of the joint was significantly increased, and the weld metal is fractured. Increasing the Nb content can improve the healing ability of the liquid film in grain boundary, which can reduce the welding sensitivity of welding samples, and increase the creep life of joints from 15h to 40h. Reducing the content of Cr and Mo can increase the crack sensitivity of the alloy to a certain extent and increase the creep life of the joint. Increasing Al content and regulating the Nb, Cr, Mo and other elements can effectively inhibit crack formation and improve the high-temperature service performance of the welding joint. The results of this study can provide an important reference value for the subsequent research on weldability of precipitation strengthened nickel-based superalloy.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20211126003
Abstract:
The grain boundary parallel to the edge of the “Island-shaped zone” (ISZ) near the carbon steel fusion line of the dissimilar steel joint was studied. It was shown that the grain boundary parallel to the edge of the ISZ might be the migrated grain boundary or the solidified grain boundary. The ISZ had three kinds of structures, the first was consisted of the carbon steel base material and the composition transition region of its periphery, and the elements content in the composition transition region was between the carbon steel base material and the weld metal; the second was only consisted of the composition transition region, and the elements content in the composition transition region was also between the carbon steel base material and the weld metal; the third was only consisted of the composition transition region, but the Ni content in the composition transition region was higher than 5% ~ 6%.Only the ISZ with the first and second structures were possible to form the migrated grain boundary parallel to the edge of the ISZ, but the ISZ with the third structure could not form the migrated grain boundary parallel to the edge of the ISZ. The solidified grain boundary parallel to the edge of the ISZ was formed by the intersection of short cellular grains growing perpendicular to the ISZ surface with their adjacent subgrain bundles.
The grain boundary parallel to the edge of the “Island-shaped zone” (ISZ) near the carbon steel fusion line of the dissimilar steel joint was studied. It was shown that the grain boundary parallel to the edge of the ISZ might be the migrated grain boundary or the solidified grain boundary. The ISZ had three kinds of structures, the first was consisted of the carbon steel base material and the composition transition region of its periphery, and the elements content in the composition transition region was between the carbon steel base material and the weld metal; the second was only consisted of the composition transition region, and the elements content in the composition transition region was also between the carbon steel base material and the weld metal; the third was only consisted of the composition transition region, but the Ni content in the composition transition region was higher than 5% ~ 6%.Only the ISZ with the first and second structures were possible to form the migrated grain boundary parallel to the edge of the ISZ, but the ISZ with the third structure could not form the migrated grain boundary parallel to the edge of the ISZ. The solidified grain boundary parallel to the edge of the ISZ was formed by the intersection of short cellular grains growing perpendicular to the ISZ surface with their adjacent subgrain bundles.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220106002
Abstract:
In order to solve the problem of severe softening of duralumin alloy welded joints, 7075 aluminum alloy was selected as filler material for high assembly welding of 6061 aluminum alloy. The hardness of welded joints did increase, but thermal cracks occurred during welding. In this study, an ultrasonic assisted platform is designed to introduce ultrasonic vibration into the traditional tungsten argon arc welding to solve the problem of welding hot crack under the condition of ensuring the hardness of welded joint. The results show that the thermal crack disappears when the ultrasonic power is low, but the thermal crack occurs again when the ultrasonic power reaches 480 W. With the increase of ultrasonic power, the grain size and shape of the welded joint change, the columnar crystal in the fusion zone is broken and transformed into fine equiaxed crystal, and the equiaxed crystal in the weld center is refined. When p = 640 W, the average grain size in the weld center is the smallest. With the increase of ultrasonic power, the number of precipitates in the welded joint gradually increases and the distribution is gradually uniform, which has an impact on the welding thermal crack. Therefore, there is a range of ultrasonic power, which can solve the problems of welding joint softening and welding thermal crack at the same time.
In order to solve the problem of severe softening of duralumin alloy welded joints, 7075 aluminum alloy was selected as filler material for high assembly welding of 6061 aluminum alloy. The hardness of welded joints did increase, but thermal cracks occurred during welding. In this study, an ultrasonic assisted platform is designed to introduce ultrasonic vibration into the traditional tungsten argon arc welding to solve the problem of welding hot crack under the condition of ensuring the hardness of welded joint. The results show that the thermal crack disappears when the ultrasonic power is low, but the thermal crack occurs again when the ultrasonic power reaches 480 W. With the increase of ultrasonic power, the grain size and shape of the welded joint change, the columnar crystal in the fusion zone is broken and transformed into fine equiaxed crystal, and the equiaxed crystal in the weld center is refined. When p = 640 W, the average grain size in the weld center is the smallest. With the increase of ultrasonic power, the number of precipitates in the welded joint gradually increases and the distribution is gradually uniform, which has an impact on the welding thermal crack. Therefore, there is a range of ultrasonic power, which can solve the problems of welding joint softening and welding thermal crack at the same time.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220114003
Abstract:
In ultrasonic welding of polymers, the heating process can be considered as the process that the energy of sound field converts into the internal energy of polymers. According to the theory of second quantization, the energy flow of ultraosnic is equivalent to the phonons flow of a given flux. Phonons can only be absorbed as a complete unit by atoms. Atoms have separate energy levels and will absorb phonons in the transition from a lower level to a higher level. The total energy of these absorbed phonons is equal to the difference in energy of these two levels. According to this theory, in the process of one-vibrator welding, only the atomic vibrators with frequencies of an integer multiple of ultrasonic frequency can effectively absorb phonons. Whereas, in double-vibrator welding, besides the vibrators with the frequencies of integer multiples of these two ultrasonic frequencies, phonons can also be absorbed by the vibrators with the frequencies of the sum of integer multiples of the two ultrasonic freqiemcies. Therefore, the absorption capacity of phonons in double-vibrator ultrasonic welding is superior to that of single-vibrator welding, that is, the utilization rate of ultrasonic field energy in double-vibrator welding is much higher. The results of the corresponding experiments indicate that The double-vibrator system spends only 3/8 of the time of the single-vibrator system with half of the power in completing the same welding; and in the same welding time, the double-vibrator system with 12/13 of the power of single-vibrator system can accomplish the same welding.
In ultrasonic welding of polymers, the heating process can be considered as the process that the energy of sound field converts into the internal energy of polymers. According to the theory of second quantization, the energy flow of ultraosnic is equivalent to the phonons flow of a given flux. Phonons can only be absorbed as a complete unit by atoms. Atoms have separate energy levels and will absorb phonons in the transition from a lower level to a higher level. The total energy of these absorbed phonons is equal to the difference in energy of these two levels. According to this theory, in the process of one-vibrator welding, only the atomic vibrators with frequencies of an integer multiple of ultrasonic frequency can effectively absorb phonons. Whereas, in double-vibrator welding, besides the vibrators with the frequencies of integer multiples of these two ultrasonic frequencies, phonons can also be absorbed by the vibrators with the frequencies of the sum of integer multiples of the two ultrasonic freqiemcies. Therefore, the absorption capacity of phonons in double-vibrator ultrasonic welding is superior to that of single-vibrator welding, that is, the utilization rate of ultrasonic field energy in double-vibrator welding is much higher. The results of the corresponding experiments indicate that The double-vibrator system spends only 3/8 of the time of the single-vibrator system with half of the power in completing the same welding; and in the same welding time, the double-vibrator system with 12/13 of the power of single-vibrator system can accomplish the same welding.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb20220425003
Abstract:
Particle reinforced metal matrix composite structural parts have a wide range of prospects in aerospace, mechanical manufacturing, electronic and electrical fields. This study fabricated WC-reinforced TC4 matrix composites by laser selective melting technology. The effects of WC particle content and laser power on the microstructure and mechanical properties of the composite were investigated. The results show that: with the increase of WC particle content, the forming ability of composite samples decreases. When WC particle content is (0 ~ 15%), WC particles are evenly distributed, and no micro-pores and cracks are seen. When WC particle content is 20%, pores and cracks appear inside the material, making it difficult to form. At the interface of WC/matrix, an interface layer of TiC and W2C is formed, and the interface bonding performance is good. With the increase of particle content and laser power in the composites, the fracture strength and elongation of the composites decrease. The fracture mechanism is mainly the brittle fracture of WC particles and the lamellar tearing along the WC-W2C interface.
Particle reinforced metal matrix composite structural parts have a wide range of prospects in aerospace, mechanical manufacturing, electronic and electrical fields. This study fabricated WC-reinforced TC4 matrix composites by laser selective melting technology. The effects of WC particle content and laser power on the microstructure and mechanical properties of the composite were investigated. The results show that: with the increase of WC particle content, the forming ability of composite samples decreases. When WC particle content is (0 ~ 15%), WC particles are evenly distributed, and no micro-pores and cracks are seen. When WC particle content is 20%, pores and cracks appear inside the material, making it difficult to form. At the interface of WC/matrix, an interface layer of TiC and W2C is formed, and the interface bonding performance is good. With the increase of particle content and laser power in the composites, the fracture strength and elongation of the composites decrease. The fracture mechanism is mainly the brittle fracture of WC particles and the lamellar tearing along the WC-W2C interface.
Accepted Manuscript
, Available online ,
doi: 10.2073/j.hjxb.20220412001
Abstract:
Fe-Cr-C-B Fe based surfacing alloy was prepared by changing the addition of Ti or Nb. The microstructure and properties of surfacing alloy were tested and analyzed by means of scanning electron microscope, X-ray diffraction, Rockwell hardness tester and wear tester. The results show that in the surfacing alloy containing Ti or Nb, the primary austenite grain is refined, the eutectic structure is evenly distributed in a broken network, and black circular or massive TiC and rhombic or triangular NbC hard phase particles are formed respectively. The microstructure of the surfacing alloy with 5% Ti is the smallest. Tic or NbC hard phase particles are evenly dispersed in the structure and can be used as wear-resistant particles to form a wear-resistant skeleton with refined primary austenite and eutectic structure to jointly resist the wedging and cutting effect of wear particles. When the content of Ti is 5%, the surfacing alloy containing Ti achieves the best wear resistance, the hardness is 66HRC and the wear amount is 0.0487g; When the addition of Nb is 4%, the surfacing alloy containing Nb achieves the best wear resistance, the hardness is 65HRC and the wear amount is 0.0524g. Under the same conditions, the iron-based surfacing alloy containing an appropriate amount of Ti has better wear resistance.
Fe-Cr-C-B Fe based surfacing alloy was prepared by changing the addition of Ti or Nb. The microstructure and properties of surfacing alloy were tested and analyzed by means of scanning electron microscope, X-ray diffraction, Rockwell hardness tester and wear tester. The results show that in the surfacing alloy containing Ti or Nb, the primary austenite grain is refined, the eutectic structure is evenly distributed in a broken network, and black circular or massive TiC and rhombic or triangular NbC hard phase particles are formed respectively. The microstructure of the surfacing alloy with 5% Ti is the smallest. Tic or NbC hard phase particles are evenly dispersed in the structure and can be used as wear-resistant particles to form a wear-resistant skeleton with refined primary austenite and eutectic structure to jointly resist the wedging and cutting effect of wear particles. When the content of Ti is 5%, the surfacing alloy containing Ti achieves the best wear resistance, the hardness is 66HRC and the wear amount is 0.0487g; When the addition of Nb is 4%, the surfacing alloy containing Nb achieves the best wear resistance, the hardness is 65HRC and the wear amount is 0.0524g. Under the same conditions, the iron-based surfacing alloy containing an appropriate amount of Ti has better wear resistance.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220302001
Abstract:
The downstream area of seawater pipeline welds is a hot spot for corrosion. In order to explore the influence of weld reinforcements on the corrosion behavior of B30 pipes in the downstream area, the in-situ electrochemical testing device and the home-made circulating seawater-scouring device were used in four scouring-test nodes at 3 d, 7 d, 15 d, 30 d. The impedance spectra were tested with three simulated weld reinforcements (0 mm; 0.5 mm; 1.5 mm) in the adjacent heat-affected zone (HAZ) and 30-mm-downstream base-metal zone (BMZ). The corrosion morphology of the sample surface was observed by the scanning electron microscope (SEM), and the finite-element-simulation flow-model was established by using COMSOL software. The influence of weld reinforcements on the flow state of the medium was discussed. Results show that the impedance values in the HAZ and BMZ were smaller than those of the no-welding in the case of welding. The weld structure would accelerate the corrosion in the downstream zone. The larger the reinforcement, the greater the corrosion tendency. The corrosion rate in the HAZ was larger than that in the BMZ. The flow model showed that an eddy current appeared in the HAZ and accelerated the corrosion there. In this paper, the influence of simulated height on the erosion and corrosion properties of copper tube heat affected zone materials and base metal was evaluated by online electrochemical test technology, and the influence of simulated height on the surface flow pattern of the two materials was simulated by simulation software.
The downstream area of seawater pipeline welds is a hot spot for corrosion. In order to explore the influence of weld reinforcements on the corrosion behavior of B30 pipes in the downstream area, the in-situ electrochemical testing device and the home-made circulating seawater-scouring device were used in four scouring-test nodes at 3 d, 7 d, 15 d, 30 d. The impedance spectra were tested with three simulated weld reinforcements (0 mm; 0.5 mm; 1.5 mm) in the adjacent heat-affected zone (HAZ) and 30-mm-downstream base-metal zone (BMZ). The corrosion morphology of the sample surface was observed by the scanning electron microscope (SEM), and the finite-element-simulation flow-model was established by using COMSOL software. The influence of weld reinforcements on the flow state of the medium was discussed. Results show that the impedance values in the HAZ and BMZ were smaller than those of the no-welding in the case of welding. The weld structure would accelerate the corrosion in the downstream zone. The larger the reinforcement, the greater the corrosion tendency. The corrosion rate in the HAZ was larger than that in the BMZ. The flow model showed that an eddy current appeared in the HAZ and accelerated the corrosion there. In this paper, the influence of simulated height on the erosion and corrosion properties of copper tube heat affected zone materials and base metal was evaluated by online electrochemical test technology, and the influence of simulated height on the surface flow pattern of the two materials was simulated by simulation software.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220125001
Abstract:
The steel strip is made into steel tube by rolling and welding step by step. The hardness of the steel tube increases due to the early work hardening, which will significantly affect the secondary forming processing of the tube. In this paper, the effects of solution temperatures, solution cooling conditions and types of solution shielding gas on the microstructure and properties of 304 stainless steel thin-walled tube were studied by building an on-line solution treatment test platform in the 304 stainless steel tube production line. The results show that increasing the solution treatment temperature in the experimental temperature range will increase the grain size of the heat-affected zone and the base metal and promote the solid solution of carbides in and along the austenite grains, so as to significantly reduce the hardness of the heat-affected zone and the base metal. The ferrite distributed along the austenite grain boundary in the weld zone is partially dissolved, and the grain size increases to a small extent, so the hardness of the weld zone decreases slightly. However, adjusting the cooling conditions has little effect on the hardness of the weld and base metal. When argon is used as the solution treatment protective gas, the average hardness of the base metal of the tube can be reduced to 188.7 HV, which is 11.0% lower than that without solution treatment. When hydrogen is used as solution treatment protective gas, the average hardness can be reduced to 182.7 HV, which is 13.8% lower than that without solution treatment. Through microstructure observation, hardness test, flaring and flattening mechanical properties test, the solution-treated tubes under the two protective gas conditions all meet the national standards.
The steel strip is made into steel tube by rolling and welding step by step. The hardness of the steel tube increases due to the early work hardening, which will significantly affect the secondary forming processing of the tube. In this paper, the effects of solution temperatures, solution cooling conditions and types of solution shielding gas on the microstructure and properties of 304 stainless steel thin-walled tube were studied by building an on-line solution treatment test platform in the 304 stainless steel tube production line. The results show that increasing the solution treatment temperature in the experimental temperature range will increase the grain size of the heat-affected zone and the base metal and promote the solid solution of carbides in and along the austenite grains, so as to significantly reduce the hardness of the heat-affected zone and the base metal. The ferrite distributed along the austenite grain boundary in the weld zone is partially dissolved, and the grain size increases to a small extent, so the hardness of the weld zone decreases slightly. However, adjusting the cooling conditions has little effect on the hardness of the weld and base metal. When argon is used as the solution treatment protective gas, the average hardness of the base metal of the tube can be reduced to 188.7 HV, which is 11.0% lower than that without solution treatment. When hydrogen is used as solution treatment protective gas, the average hardness can be reduced to 182.7 HV, which is 13.8% lower than that without solution treatment. Through microstructure observation, hardness test, flaring and flattening mechanical properties test, the solution-treated tubes under the two protective gas conditions all meet the national standards.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220225001
Abstract:
Fiber-diode laser hybrid welding technology, which adequately combines the superiorities of both fiber and diode laser heat source, has great potential in the field of laser processing. In this paper, fiber-diode laser hybrid welding experiments were conducted for the 2195 Al-Li alloy. The effect of laser power on morphology and porosity was quantitatively investigated. The results show that fiber laser power has a significantly impact on the weld depth, while diode laser power has a significantly influence on the upper weld width. The regression model for predicting the cross-sectional area of weld seam was obtained. Besides, both fiber and diode laser play an important role in the control of porosity defects. The higher power of fiber laser is beneficial to reduce porosity. For 2195 Al-Li alloy with the thickness of 4mm, the high-temperature molten pool and large range of fiber-diode laser action region are formed at the fiber laser power of 3.0 kW and diode laser power between 2.5 kW and 3.0 kW, which results in the welded joint with the less porosity.
Fiber-diode laser hybrid welding technology, which adequately combines the superiorities of both fiber and diode laser heat source, has great potential in the field of laser processing. In this paper, fiber-diode laser hybrid welding experiments were conducted for the 2195 Al-Li alloy. The effect of laser power on morphology and porosity was quantitatively investigated. The results show that fiber laser power has a significantly impact on the weld depth, while diode laser power has a significantly influence on the upper weld width. The regression model for predicting the cross-sectional area of weld seam was obtained. Besides, both fiber and diode laser play an important role in the control of porosity defects. The higher power of fiber laser is beneficial to reduce porosity. For 2195 Al-Li alloy with the thickness of 4mm, the high-temperature molten pool and large range of fiber-diode laser action region are formed at the fiber laser power of 3.0 kW and diode laser power between 2.5 kW and 3.0 kW, which results in the welded joint with the less porosity.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220212001
Abstract:
In laser selective melting, the forming of powder bed will significantly affect the subsequent process and the quality of final products. In this paper, the dynamic numerical simulation of powder spreading behavior and forming quality in SLM forming process is carried out by using discrete element method (DEM). The influencing factors of powder bed quality are studied from two aspects of density and uniformity. The results show that the effect of powder spreading speed on the quality of powder bed is obvious. The powder spreading speed, powder spreading angle, scraper clearance height and powder particle size all have an important influence on improving the average density and uniformity of the powder bed. The lower the powder spreading speed, the higher the quality of powder bed and the lower the working efficiency. With the increase of the clearance height of the scraper, the density of the powder bed increases and the uniformity of the powder bed decreases to a lower value; The density of powder bed increases with the increase of powder laying angle, and then decreases. The structural uniformity of the whole powder bed also has a similar change trend. Increasing the particle size of powder will reduce the density of powder bed and the uniformity of powder bed structure. The powder spreading speed is 0.1m/s, and the clearance height of scraper is 90μm. The powder spreading angle is 15°, and the powder particle size is 15μm, the powder bed forming quality is the best. The research results of this paper will provide a valuable reference for the formation of high-quality powder bed in SLM process.
In laser selective melting, the forming of powder bed will significantly affect the subsequent process and the quality of final products. In this paper, the dynamic numerical simulation of powder spreading behavior and forming quality in SLM forming process is carried out by using discrete element method (DEM). The influencing factors of powder bed quality are studied from two aspects of density and uniformity. The results show that the effect of powder spreading speed on the quality of powder bed is obvious. The powder spreading speed, powder spreading angle, scraper clearance height and powder particle size all have an important influence on improving the average density and uniformity of the powder bed. The lower the powder spreading speed, the higher the quality of powder bed and the lower the working efficiency. With the increase of the clearance height of the scraper, the density of the powder bed increases and the uniformity of the powder bed decreases to a lower value; The density of powder bed increases with the increase of powder laying angle, and then decreases. The structural uniformity of the whole powder bed also has a similar change trend. Increasing the particle size of powder will reduce the density of powder bed and the uniformity of powder bed structure. The powder spreading speed is 0.1m/s, and the clearance height of scraper is 90μm. The powder spreading angle is 15°, and the powder particle size is 15μm, the powder bed forming quality is the best. The research results of this paper will provide a valuable reference for the formation of high-quality powder bed in SLM process.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220204002
Abstract:
In this paper, the laser butt welding experiment of CuCrZr and Inconel625 dissimilar material alloy tube was carried out, and the joint morphology, microstructure, chemical composition and mechanical properties of each sample were observed and analyzed. The experimental results show that the weld is in good shape under the laser power of 1100W-1300W, the defocus amount of + 20mm and the welding speed of 14.5mm/s, and the weld is in good shape when shielded by 99.9%Ar gas of 20L/min. The all-position welding of Inconel625/CuCrZr pipe can be realized, and the internal defects of the weld are less. However, the phenomenon of weld collapse is obvious with the increase of welding power. The transition of interface elements between Inconel625/CuCrZr weld and base metal is obvious. Due to the mutual solubility of Ni and Cu, there is mainly Ni-rich Ni/Cu solid solution inside the weld. In the process of laser welding, copper base metal is stirred by laser, and some copper base metal is "involved" in the weld, which remains in the weld after the workpiece is cooled. The tensile strength of laser welded joint of Inconel625/CuCrZr pipe is high, the main fracture position is the position of HAZ of coarse-grained copper, and the fracture form is mainly ductile fracture of copper base metal.
In this paper, the laser butt welding experiment of CuCrZr and Inconel625 dissimilar material alloy tube was carried out, and the joint morphology, microstructure, chemical composition and mechanical properties of each sample were observed and analyzed. The experimental results show that the weld is in good shape under the laser power of 1100W-1300W, the defocus amount of + 20mm and the welding speed of 14.5mm/s, and the weld is in good shape when shielded by 99.9%Ar gas of 20L/min. The all-position welding of Inconel625/CuCrZr pipe can be realized, and the internal defects of the weld are less. However, the phenomenon of weld collapse is obvious with the increase of welding power. The transition of interface elements between Inconel625/CuCrZr weld and base metal is obvious. Due to the mutual solubility of Ni and Cu, there is mainly Ni-rich Ni/Cu solid solution inside the weld. In the process of laser welding, copper base metal is stirred by laser, and some copper base metal is "involved" in the weld, which remains in the weld after the workpiece is cooled. The tensile strength of laser welded joint of Inconel625/CuCrZr pipe is high, the main fracture position is the position of HAZ of coarse-grained copper, and the fracture form is mainly ductile fracture of copper base metal.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220206001
Abstract:
In order to study the effect of rotating electrode contact force on discharge parameters and material transfer in electric-spark deposition (ESD), the automatic ESD experiments under different contact forces were carried out. The number of various discharge waveforms, discharge parameters such as average voltage and current of discharge pulses, transfer efficiency and deposition efficiency of ESD, surface morphology and cross-section morphology and surface roughness of the deposition layer under different contact forces were analyzed. The results show that the change of contact force affects the number and proportion of various discharge types during the automatic ESD process with rotating electrode. With the increase of contact force, the proportion of contact discharge decreases gradually while the proportion of short-circuit discharge increases gradually, and the average voltage and average power of discharge pulse decrease gradually while the average current increases gradually. The contact force has a great effect on the transfer efficiency and deposition efficiency of ESD, but has little influence on surface roughness. When the contact force is 1 N - 2 N, the proportion of contact discharge, transfer efficiency and deposition efficiency are higher in the automatic deposition process. The amount of material transfer caused by contact discharge is significantly higher than that caused by short-circuit discharge during the automatic ESD process with rotating electrode. Innovation point: With the increase of contact force, the proportion of contact discharge decreases gradually while the proportion of short-circuit discharge increases gradually, and the average voltage and average power of discharge pulse decrease gradually while the average current increases gradually. The amount of material transfer caused by contact discharge is significantly higher than that caused by short-circuit discharge, and the transfer efficiency and deposition efficiency are higher when the contact force is 1 N - 2 N.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220202001
Abstract:
X80 and X100 pipeline steels were welded together by hybrid laser-MIG welding method. The effects of laser power on weld geometry, microstructures, hardness, tensile strength and impact toughness of the hybrid welded joints were investigated. Results show that, when laser power is elevated from 2.0 kW to 3.5kW, both weld bead width and penetration of cap weld increase with a pronounced rise in laser zone penetration. Increasing acicular ferrite content and decreasing lath bainite content is obtained in the laser zone weld. The contents of lath bainite in coarse grained heat affected zone and fine grained heat affected zone of X100 steel side decrease. The contents of quasi-polygonal ferrite in coarse grained heat affected zone and fine grained heat affected zone of X80 steel side increase. Hardness distribution is asymmetrical with maximum hardness occurs in the fusion zone. Tensile strength of the hybrid welded joints barely changes with varying laser powers, and all the tensile specimens fractured at base metal of X80 steel side. Maximum hardness and impact toughness of the hybrid welded joint decrease with increasing laser power.
X80 and X100 pipeline steels were welded together by hybrid laser-MIG welding method. The effects of laser power on weld geometry, microstructures, hardness, tensile strength and impact toughness of the hybrid welded joints were investigated. Results show that, when laser power is elevated from 2.0 kW to 3.5kW, both weld bead width and penetration of cap weld increase with a pronounced rise in laser zone penetration. Increasing acicular ferrite content and decreasing lath bainite content is obtained in the laser zone weld. The contents of lath bainite in coarse grained heat affected zone and fine grained heat affected zone of X100 steel side decrease. The contents of quasi-polygonal ferrite in coarse grained heat affected zone and fine grained heat affected zone of X80 steel side increase. Hardness distribution is asymmetrical with maximum hardness occurs in the fusion zone. Tensile strength of the hybrid welded joints barely changes with varying laser powers, and all the tensile specimens fractured at base metal of X80 steel side. Maximum hardness and impact toughness of the hybrid welded joint decrease with increasing laser power.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220325005
Abstract:
Due to its harsh working environment, the superconducting conductor joint of ITER's internal coil has high requirements on weld quality. The performance of the joint will directly affect the normal operation of the internal coil. Due to the limitation of vacuum chamber space and the requirements of the surrounding environment, the final choice of copper pipe welding joint TIG welding method. In order to verify the welding process of oxygen free copper including preheating, arc preheating of oxygen free copper tube was carried out by TIG arc preheating method with open head to reach the temperature required for copper tube welding. Through nondestructive testing, macroscopic and microscopic inspection of copper welded joints and hardness measurement of weld, heat affected zone and base metal, the influence of arc preheating on heat affected zone is systematically evaluated. The results show that there is no significant difference between heat affected zone and base metal hardness, but there is a significant difference in microstructure, weld metal hardness is slightly higher, within the observation range, Arc preheating has no significant effect on the heat affected zone, which proves that arc preheating is feasible.
Due to its harsh working environment, the superconducting conductor joint of ITER's internal coil has high requirements on weld quality. The performance of the joint will directly affect the normal operation of the internal coil. Due to the limitation of vacuum chamber space and the requirements of the surrounding environment, the final choice of copper pipe welding joint TIG welding method. In order to verify the welding process of oxygen free copper including preheating, arc preheating of oxygen free copper tube was carried out by TIG arc preheating method with open head to reach the temperature required for copper tube welding. Through nondestructive testing, macroscopic and microscopic inspection of copper welded joints and hardness measurement of weld, heat affected zone and base metal, the influence of arc preheating on heat affected zone is systematically evaluated. The results show that there is no significant difference between heat affected zone and base metal hardness, but there is a significant difference in microstructure, weld metal hardness is slightly higher, within the observation range, Arc preheating has no significant effect on the heat affected zone, which proves that arc preheating is feasible.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220419001
Abstract:
Plasma spraying power supply usually adopts thyristor rectifier power supply or inverter power supply, which has problems such as low efficiency and large output current ripple. It is difficult to meet the special requirements of plasma spraying process. A high-power plasma spray chopper power supply was proposed based on an eight-phase interleaved parallel Buck converter in this paper. Firstly, the circuit topology of the chopper power supply was designed. The working principle and the current ripple generation mechanism of the chopper power supply were analyzed. The influence of the number of parallel phases and the duty cycle on the current ripple was clarified. The simulation verification was carried out. Then, based on the requirements of the plasma spraying process for power supply characteristics, a four-phase interleaved parallel module with power of 40 kW was designed. Under the cooperative control of the CAN bus, an 80 kW eight-phase interleaved parallel chopper plasma spraying power supply was formed. Finally, the plasma spraying chopper power supply prototype was built. Spraying experiments were carried out to test the output ripple and efficiency of the power supply. The experimental results show that, compared with the traditional thyristor rectifier power supply and inverter power supply, the current ripple rate of the chopper power supply was reduced by more than 50%, and the power efficiency was up to 94.5%.
Plasma spraying power supply usually adopts thyristor rectifier power supply or inverter power supply, which has problems such as low efficiency and large output current ripple. It is difficult to meet the special requirements of plasma spraying process. A high-power plasma spray chopper power supply was proposed based on an eight-phase interleaved parallel Buck converter in this paper. Firstly, the circuit topology of the chopper power supply was designed. The working principle and the current ripple generation mechanism of the chopper power supply were analyzed. The influence of the number of parallel phases and the duty cycle on the current ripple was clarified. The simulation verification was carried out. Then, based on the requirements of the plasma spraying process for power supply characteristics, a four-phase interleaved parallel module with power of 40 kW was designed. Under the cooperative control of the CAN bus, an 80 kW eight-phase interleaved parallel chopper plasma spraying power supply was formed. Finally, the plasma spraying chopper power supply prototype was built. Spraying experiments were carried out to test the output ripple and efficiency of the power supply. The experimental results show that, compared with the traditional thyristor rectifier power supply and inverter power supply, the current ripple rate of the chopper power supply was reduced by more than 50%, and the power efficiency was up to 94.5%.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220419002
Abstract:
In order to improve the energy utilization rate and reduce the energy dissipation, explosive welding was carried out with self-restraint structure explosive. T2 copper and Q345 steel were used as fly and base layers, respectively, and self-restraint structure explosive was adopted as welding explosive. The explosive welding process was simulated by ANSYS/AUTODYN code, and the copper/steel explosive welded clad plate was prepared. The welding quality was analyzed by mechanical property testing and microscopic morphology observation. The results show that self- restraint structure could reduce the dissipation of its own detonation products, which makes more explosive energy into kinetic energy of flyer layer and improves energy utilization rate. The collision velocity of copper/steel explosive welding is greater than the critical collision velocity of 345 m·s-1 after detonation distance is greater than 100mm away from the initiation end. The ultimate collision velocity at a detonation distance of 150 mm is 567 m·s-1. The initiation end of the copper/steel clad plate is of linear bonding, the bonding interface is transformed into wavy bonding as detonation distance increases. The shear strength of copper/steel clad plate is 237.0 MPa, and the fracture position is on the copper side. Copper layer existed work hardening after tension shear failure, and the farther measuring point from the interface is, the stronger the microhardness and plastic deformation is.
In order to improve the energy utilization rate and reduce the energy dissipation, explosive welding was carried out with self-restraint structure explosive. T2 copper and Q345 steel were used as fly and base layers, respectively, and self-restraint structure explosive was adopted as welding explosive. The explosive welding process was simulated by ANSYS/AUTODYN code, and the copper/steel explosive welded clad plate was prepared. The welding quality was analyzed by mechanical property testing and microscopic morphology observation. The results show that self- restraint structure could reduce the dissipation of its own detonation products, which makes more explosive energy into kinetic energy of flyer layer and improves energy utilization rate. The collision velocity of copper/steel explosive welding is greater than the critical collision velocity of 345 m·s-1 after detonation distance is greater than 100mm away from the initiation end. The ultimate collision velocity at a detonation distance of 150 mm is 567 m·s-1. The initiation end of the copper/steel clad plate is of linear bonding, the bonding interface is transformed into wavy bonding as detonation distance increases. The shear strength of copper/steel clad plate is 237.0 MPa, and the fracture position is on the copper side. Copper layer existed work hardening after tension shear failure, and the farther measuring point from the interface is, the stronger the microhardness and plastic deformation is.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220414001
Abstract:
The laser butt welding experiments of Inconel625 and 316LN dissimilar material alloy tubes were carried out, and the joint morphology, microstructure, chemical composition and mechanical properties of each sample were analyzed. The experimental results show that the weld is in good shape under the laser power of 1 100 to 1 300 W, the defocus of + 20 mm and the welding speed of 870 mm/min and 20 L/min 99.9%Ar gas protection, and the all-position welding of Inconel625&316LN thin-walled alloy pipe is realized with less internal defects. The transition of interface elements between Inconel625&316LN weld and base metal is obvious. Due to the mutual solubility of Fe and Ni, it is mainly composed of Fe and Ni solid solution with atomic ratio close to 1∶1 in the weld. The tensile strength of the laser welded joint of Inconel625&316LN pipe is higher. Due to the uniform distribution of Fe and Ni solid solution in the weld and the solid solution formed by the mutual dissolution of Fe and Ni elements in nickel and steel, the weld strength is higher, and it is not lower than that of the base metal, and it will not give priority to cracking under tensile test. With the increase of heat input, the crystal size in the weld gradually increases, the yield strength of the weld decreases gradually, and the fracture form is mainly the ductile fracture of the base metal.
The laser butt welding experiments of Inconel625 and 316LN dissimilar material alloy tubes were carried out, and the joint morphology, microstructure, chemical composition and mechanical properties of each sample were analyzed. The experimental results show that the weld is in good shape under the laser power of 1 100 to 1 300 W, the defocus of + 20 mm and the welding speed of 870 mm/min and 20 L/min 99.9%Ar gas protection, and the all-position welding of Inconel625&316LN thin-walled alloy pipe is realized with less internal defects. The transition of interface elements between Inconel625&316LN weld and base metal is obvious. Due to the mutual solubility of Fe and Ni, it is mainly composed of Fe and Ni solid solution with atomic ratio close to 1∶1 in the weld. The tensile strength of the laser welded joint of Inconel625&316LN pipe is higher. Due to the uniform distribution of Fe and Ni solid solution in the weld and the solid solution formed by the mutual dissolution of Fe and Ni elements in nickel and steel, the weld strength is higher, and it is not lower than that of the base metal, and it will not give priority to cracking under tensile test. With the increase of heat input, the crystal size in the weld gradually increases, the yield strength of the weld decreases gradually, and the fracture form is mainly the ductile fracture of the base metal.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220126001
Abstract:
The orthogonal test of plate surfacing was carried out by CMT Cycle Step welding process. The effects of the wire feeding speed, welding speed, CMT cycles, pause time interval on the fish-scal texture and forming size of weld surface were studied. The regression models of the process parameters on the step size (S) of fish-scale texture, weld width B and overlay thickness h were established. The results show that with the increase of the welding speed, CMT cycles, and pause time interval, the fish-scale step size (S) on the weld surface increases gradually. Properly reducing the welding speed and pause time interva can effectively reduce the height difference of weld surface Δh, and improve weld surface forming quality. With the increase of the wire feeding speed and CMT cycles, weld width B and overlay thickness h gradually increase; With the increase of the welding speed, weld width B and overlay thickness h gradually decrease. According to the theoretical analysis and regression analysis, the regression equations with high accuracy were obtained, which provided a theoretical basis for predicting the weld formation and optimizing the welding process parameters.
The orthogonal test of plate surfacing was carried out by CMT Cycle Step welding process. The effects of the wire feeding speed, welding speed, CMT cycles, pause time interval on the fish-scal texture and forming size of weld surface were studied. The regression models of the process parameters on the step size (S) of fish-scale texture, weld width B and overlay thickness h were established. The results show that with the increase of the welding speed, CMT cycles, and pause time interval, the fish-scale step size (S) on the weld surface increases gradually. Properly reducing the welding speed and pause time interva can effectively reduce the height difference of weld surface Δh, and improve weld surface forming quality. With the increase of the wire feeding speed and CMT cycles, weld width B and overlay thickness h gradually increase; With the increase of the welding speed, weld width B and overlay thickness h gradually decrease. According to the theoretical analysis and regression analysis, the regression equations with high accuracy were obtained, which provided a theoretical basis for predicting the weld formation and optimizing the welding process parameters.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220502001
Abstract:
Based on fluent 19.0 software, the heat flow coupling model of laser welding was established, and the effects of different surface tension temperature coefficients (negative values) on the flow field of molten pool were compared and analyzed. The results showed that with the decrease of surface tension temperature coefficient, the trend of clockwise flow vortex behind the molten pool gradually weakened or even disappeared, and the amount of welding spatter increased. With the decrease of surface tension temperature coefficient, the length of longitudinal section molten pool gradually increased, the maximum flow velocity of longitudinal section molten pool gradually increased, and the cross-sectional area of molten pool gradually decreased. When the temperature coefficient of surface tension was -2.5 × 10-4 N/(m·K), the average length of molten pool was 3.28 mm, the average maximum flow velocity of molten pool fluid was 2.89 m/s, and the average cross-sectional area of molten pool was 4.52 mm2. When the temperature coefficient of surface tension was -3.5 × 10-4 N/(m·K), the average length of molten pool was 3.73 mm, the average maximum flow velocity of molten pool fluid was 3.53 m/s, and the average cross-sectional area of molten pool was 4.03 mm2. When the temperature coefficient of surface tension was -4.9 × 10-4 N/(m·K), the average length of molten pool was 4.14 mm, the average maximum flow velocity of molten pool fluid was 4.09 m/s, and the average cross-sectional area of molten pool was 3.28 mm2.
Based on fluent 19.0 software, the heat flow coupling model of laser welding was established, and the effects of different surface tension temperature coefficients (negative values) on the flow field of molten pool were compared and analyzed. The results showed that with the decrease of surface tension temperature coefficient, the trend of clockwise flow vortex behind the molten pool gradually weakened or even disappeared, and the amount of welding spatter increased. With the decrease of surface tension temperature coefficient, the length of longitudinal section molten pool gradually increased, the maximum flow velocity of longitudinal section molten pool gradually increased, and the cross-sectional area of molten pool gradually decreased. When the temperature coefficient of surface tension was -2.5 × 10-4 N/(m·K), the average length of molten pool was 3.28 mm, the average maximum flow velocity of molten pool fluid was 2.89 m/s, and the average cross-sectional area of molten pool was 4.52 mm2. When the temperature coefficient of surface tension was -3.5 × 10-4 N/(m·K), the average length of molten pool was 3.73 mm, the average maximum flow velocity of molten pool fluid was 3.53 m/s, and the average cross-sectional area of molten pool was 4.03 mm2. When the temperature coefficient of surface tension was -4.9 × 10-4 N/(m·K), the average length of molten pool was 4.14 mm, the average maximum flow velocity of molten pool fluid was 4.09 m/s, and the average cross-sectional area of molten pool was 3.28 mm2.
Accepted Manuscript
, Available online
Abstract:
Accepted Manuscript
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Accepted Manuscript
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Abstract:
This paper studied the influence of a specification of electron beam welding on the structure of ‘rolled+ laser deposited’ TC4 welded joints, and analyzed the mechanical properties of the joints. Results show that on the rolled side, the microstructure of heat affected zone changes obviously, the shorter the distance away from welding center, the more amount of transformed β generates, and the columnar grain gradually transforms into equiaxed grain, with the appearance of clustered martensite α'. However, on the laser-deposited side, few changes are observed in the heat affected zone, β grain stays the shape of columnar, in which martensite α' generates, no equiaxed grain generates. The change trend of microhardness on both sides is similar, the closer the distance from the center, the higher the microhardness gets, the maximum hardness is around 400HV found in the fusion zone. The mechanical properties of welding joints are similar to that of forged TC4, all the fractures locate in the laser-deposited base metal region.
This paper studied the influence of a specification of electron beam welding on the structure of ‘rolled+ laser deposited’ TC4 welded joints, and analyzed the mechanical properties of the joints. Results show that on the rolled side, the microstructure of heat affected zone changes obviously, the shorter the distance away from welding center, the more amount of transformed β generates, and the columnar grain gradually transforms into equiaxed grain, with the appearance of clustered martensite α'. However, on the laser-deposited side, few changes are observed in the heat affected zone, β grain stays the shape of columnar, in which martensite α' generates, no equiaxed grain generates. The change trend of microhardness on both sides is similar, the closer the distance from the center, the higher the microhardness gets, the maximum hardness is around 400HV found in the fusion zone. The mechanical properties of welding joints are similar to that of forged TC4, all the fractures locate in the laser-deposited base metal region.
Accepted Manuscript
, Available online
Abstract:
In order to improve the precision and reliability of welding arc sensor in narrow gap, as well as to research the principle of arc sensor characteristic parameters influenced by the distance between welding torch and the side wall, by measuring the torch position using high precision laser displacement sensor, an experiment system for swing arc sensor which can simultaneously acquire welding voltage, welding current, welding torch swing position and arc image four signals was developed based on TMS320F2812 and Labview. Experiment was carried out by the welding method of P-GMAW. It was proved by the experiment that the established system is reliable and effective. The system has laid the necessary foundation for the further study of the characteristics of the narrow gap oscillating arc sensing.
In order to improve the precision and reliability of welding arc sensor in narrow gap, as well as to research the principle of arc sensor characteristic parameters influenced by the distance between welding torch and the side wall, by measuring the torch position using high precision laser displacement sensor, an experiment system for swing arc sensor which can simultaneously acquire welding voltage, welding current, welding torch swing position and arc image four signals was developed based on TMS320F2812 and Labview. Experiment was carried out by the welding method of P-GMAW. It was proved by the experiment that the established system is reliable and effective. The system has laid the necessary foundation for the further study of the characteristics of the narrow gap oscillating arc sensing.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.201940
Abstract:
The research on laser welding 5-mm thick T91 martensite heat-resistant steel with filler wires is conducted, and the effects on weld appearance, microstructures, and porosity are studied, also the weld mechanical properties of the optimal parameter are tested. The results show that when welding heat input increased by using same material wire to weld T91 steel, weld seam width, porosity decreased, and grain size changed a little, microstructure of weld zone and HAZ are tempered martensite. The weld seam can be pore-free with the parameter of power 5 600 w, speed 1.2 m/min, feeding speed 1.2 m/min, its microhardness is 300 HV, tensile strength is 697 Mpa, no cracks appear by 180° bending and back bending, and the impact properties are better than base metal at 20/0/–20 °C.
The research on laser welding 5-mm thick T91 martensite heat-resistant steel with filler wires is conducted, and the effects on weld appearance, microstructures, and porosity are studied, also the weld mechanical properties of the optimal parameter are tested. The results show that when welding heat input increased by using same material wire to weld T91 steel, weld seam width, porosity decreased, and grain size changed a little, microstructure of weld zone and HAZ are tempered martensite. The weld seam can be pore-free with the parameter of power 5 600 w, speed 1.2 m/min, feeding speed 1.2 m/min, its microhardness is 300 HV, tensile strength is 697 Mpa, no cracks appear by 180° bending and back bending, and the impact properties are better than base metal at 20/0/–20 °C.
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, Available online ,
doi: 10.12073/j.hjxb.20220304001
Abstract:
In this paper, the laser butt welding experiment of CuCrZr and 316LN dissimilar material alloy tube was carried out, and the joint morphology, microstructure, chemical composition and mechanical properties of each sample were observed and analyzed. The experimental results show that the weld is in good shape under the laser power of 1100 − 1400 W, the defocus amount of + 20 mm and the welding speed of 14.5 mm/s, and shielded by Ar gas of 20 L/min, which can realize all-position welding of CuCrZr/316LN pipe with less internal defects. However, the phenomenon of weld collapse is obvious with the increase of welding power. The transition of the interface elements between the CuCrZr/316LN weld and the base metal is obvious, and there is mainly Fe-rich Fe/Cu solid solution in the weld due to the mutual solubility of Fe and Cu. The tensile strength of the laser welded joint of CuCrZr/316LN pipe is higher, the main fracture location is the heat-affected zone of copper with coarse grain, the fracture form is mainly ductile fracture.
In this paper, the laser butt welding experiment of CuCrZr and 316LN dissimilar material alloy tube was carried out, and the joint morphology, microstructure, chemical composition and mechanical properties of each sample were observed and analyzed. The experimental results show that the weld is in good shape under the laser power of 1100 − 1400 W, the defocus amount of + 20 mm and the welding speed of 14.5 mm/s, and shielded by Ar gas of 20 L/min, which can realize all-position welding of CuCrZr/316LN pipe with less internal defects. However, the phenomenon of weld collapse is obvious with the increase of welding power. The transition of the interface elements between the CuCrZr/316LN weld and the base metal is obvious, and there is mainly Fe-rich Fe/Cu solid solution in the weld due to the mutual solubility of Fe and Cu. The tensile strength of the laser welded joint of CuCrZr/316LN pipe is higher, the main fracture location is the heat-affected zone of copper with coarse grain, the fracture form is mainly ductile fracture.
, Available online ,
doi: 10.12073/j.hjxb.20220310001
Abstract:
The Box-Benhnken Design (BBD) experimental design model, as one of the response surface methods, was designed to obtain the optimal parameters for laser cladding of Inconel 718 powder on Q690 high-strength steel plate. A mathematical model between input variables (laser power, scanning speed, powder delivery rate) and response values (dilution rate, heat affected zone depth, microhardness) was established. Principal component analysis method was used to establish the comprehensive evaluation index of cladding layer, and differential evolution algorithm was used to optimize and determine the optimal process parameters. The optimal process parameters were used for test verification, and the macro-morphology and microstructure of the specimen under the optimal process parameters were observed and analyzed, and the response values were compared with the optimized specimen. The results showed that the optimal processing parameters were laser power of 1 800 W, scanning speed of 28 mm/s, and powder feeding rate of 1.9 r/min, under which the heat affected zone depth was 294 μm, the dilution rate was 14.2%, and the microhardness was 276.6 HV0.5. The optimum specimens showed a 6.8% reduction in the depth of the heat affected zone, a 24.7% reduction in dilution, and a 21.7% increase in microhardness, and the optimum specimens showed small dendritic crystals with a small amount of cellular crystals.
The Box-Benhnken Design (BBD) experimental design model, as one of the response surface methods, was designed to obtain the optimal parameters for laser cladding of Inconel 718 powder on Q690 high-strength steel plate. A mathematical model between input variables (laser power, scanning speed, powder delivery rate) and response values (dilution rate, heat affected zone depth, microhardness) was established. Principal component analysis method was used to establish the comprehensive evaluation index of cladding layer, and differential evolution algorithm was used to optimize and determine the optimal process parameters. The optimal process parameters were used for test verification, and the macro-morphology and microstructure of the specimen under the optimal process parameters were observed and analyzed, and the response values were compared with the optimized specimen. The results showed that the optimal processing parameters were laser power of 1 800 W, scanning speed of 28 mm/s, and powder feeding rate of 1.9 r/min, under which the heat affected zone depth was 294 μm, the dilution rate was 14.2%, and the microhardness was 276.6 HV0.5. The optimum specimens showed a 6.8% reduction in the depth of the heat affected zone, a 24.7% reduction in dilution, and a 21.7% increase in microhardness, and the optimum specimens showed small dendritic crystals with a small amount of cellular crystals.
, Available online ,
doi: 10.12073/j.hjxb.20220327002
Abstract:
In order to solve the problem of double arc repulsion in the existing PAW−MIG hybrid welding process, a new welding process based on the regular change of MIG wire displacement was proposed, which combined MIG wire oscillation with plasma arc co-pool. The welding process test was carried out by adjusting the rotation (oscillation frequency) and amplitude of MIG welding wire motor. The results show that with the increase of rotational speed (oscillation frequency), the repulsion between plasma arc and MIG arc decreases and the coupling trend increases. Especially when the rotational speed is 2000 r/min(oscillation frequency 33 Hz), the co-pool welding effect is obvious. When the amplitude of MIG torch is 1mm, the arc shape is the most stable. When the oscillation frequency and amplitude are too large, it is not conducive to the stability of welding process. The oscillation speeds up the droplet transition frequency so that the tip of the welding wire presents a small droplet transition and reduces the welding splash. The mechanical properties of the butt test show that the tensile strength and bending strength increase first and then decrease with the increase of the oscillation frequency. The oscillation enhances the stirring ability of the molten pool metal and effectively improves the mechanical properties of the welded joint.
In order to solve the problem of double arc repulsion in the existing PAW−MIG hybrid welding process, a new welding process based on the regular change of MIG wire displacement was proposed, which combined MIG wire oscillation with plasma arc co-pool. The welding process test was carried out by adjusting the rotation (oscillation frequency) and amplitude of MIG welding wire motor. The results show that with the increase of rotational speed (oscillation frequency), the repulsion between plasma arc and MIG arc decreases and the coupling trend increases. Especially when the rotational speed is 2000 r/min(oscillation frequency 33 Hz), the co-pool welding effect is obvious. When the amplitude of MIG torch is 1mm, the arc shape is the most stable. When the oscillation frequency and amplitude are too large, it is not conducive to the stability of welding process. The oscillation speeds up the droplet transition frequency so that the tip of the welding wire presents a small droplet transition and reduces the welding splash. The mechanical properties of the butt test show that the tensile strength and bending strength increase first and then decrease with the increase of the oscillation frequency. The oscillation enhances the stirring ability of the molten pool metal and effectively improves the mechanical properties of the welded joint.
, Available online ,
doi: 10.12073/j.hjxb.20220909003
Abstract:
In order to obtain the corrosion process and mechanism of joints by electromagnetic pulse(EMP) welded with aluminum to steel in neutral salt spray medium of 5%NaCl, pull shear test was performed and the shear fracture morphologies were analyzed by scanning electron microscopy. The results showed that the shear strength of the welded joint decreased from 74 MPa to 33 MPa after 3 days in the neutral salt spray corrosion, which was 51.9% of the original shear strength, and the weld failed completely after 7 days of corrosion. At the periphery of the weld, particle flow impacted the oxides at the surface of the aluminum plate to form granular corrosion NaAlO2, and FeAl3 at the weld was broken, exposing the aluminum to be rapidly corroded into Al(OH)3. The craters created by the impact on the surface of the aluminum plate and the location of the sheet aluminum embedding on the surface of steel plate are the first to corrode. NaCl liquids accumulated and flowed under the surface metal for corrosion, and expanded along the direction of corrosion pit interconnection, and then extended to the joint zone where FeAl3 phase existed in the weld. When the oxides or weld was corroded by NaCl medium and lifted and broken, it was deeply corroded towards the aluminum matrix, forming many and deep gullies or pits, which became the main corrosion mechanism of rapid joint failure. When the oxide film or weld is lifted and broken by the NaCl medium corrosion, the corrosion turns to the deep direction of the aluminum substrate, forming many deep grooves or pits, which becomes the main corrosion mechanism of rapid joint failure.
In order to obtain the corrosion process and mechanism of joints by electromagnetic pulse(EMP) welded with aluminum to steel in neutral salt spray medium of 5%NaCl, pull shear test was performed and the shear fracture morphologies were analyzed by scanning electron microscopy. The results showed that the shear strength of the welded joint decreased from 74 MPa to 33 MPa after 3 days in the neutral salt spray corrosion, which was 51.9% of the original shear strength, and the weld failed completely after 7 days of corrosion. At the periphery of the weld, particle flow impacted the oxides at the surface of the aluminum plate to form granular corrosion NaAlO2, and FeAl3 at the weld was broken, exposing the aluminum to be rapidly corroded into Al(OH)3. The craters created by the impact on the surface of the aluminum plate and the location of the sheet aluminum embedding on the surface of steel plate are the first to corrode. NaCl liquids accumulated and flowed under the surface metal for corrosion, and expanded along the direction of corrosion pit interconnection, and then extended to the joint zone where FeAl3 phase existed in the weld. When the oxides or weld was corroded by NaCl medium and lifted and broken, it was deeply corroded towards the aluminum matrix, forming many and deep gullies or pits, which became the main corrosion mechanism of rapid joint failure. When the oxide film or weld is lifted and broken by the NaCl medium corrosion, the corrosion turns to the deep direction of the aluminum substrate, forming many deep grooves or pits, which becomes the main corrosion mechanism of rapid joint failure.
, Available online ,
doi: 10.12073/j.hjxb.20220908001
Abstract:
In this paper, the wetting and spreading process of 30% ~ 70% CuSn pre-alloyed powder composite silver solder on T2 copper matrix was studied, and the wetting and spreading mechanism of CuSn pre-alloyed powder composite silver solder on copper matrix was discussed. The results show that the initial contact angle decreases from 119° for 30% CuSn to 94° for 70% CuSn during the wetting and spreading process with the copper substrate. The final contact angle decreased from 15° for 30wt.% CuSn to 7 for 70wt.% CuSn. When the content of CuSn alloy powder in the powder core is 60 wt.%, the wetting area of the solder on the copper plate reaches 530.04 mm2, an increase of about 66% compared to when no CuSn alloy powder was added. The initial and final contact angles decreased with the increase of CuSn pre-alloy powder content due to the precursor wetting effect of the low melting point CuSn pre-alloy powder, which melted on the outer skin of BAg30CuZnSn brazing material during the brazing process, forming a thin layer of molten CuSn liquid alloy and reducing the solid-liquid interfacial tension. Subsequently, the molten BAg30CuZnSn foil strip spreads over the pre-melted Cu-Sn liquid thin layer and reacts with it by diffusion of solute atoms, eventually forming a liquid composite braze. The addition of the low melting point Cu-Sn pre-alloyed powder improves the wetting performance of the composite silver brazing material on copper significantly. The reaction wetting interface of the composite silver braze with the copper substrate is uniform and dense with the addition of 40% CuSn pre-alloyed powder, where the white rich (Ag) phases are interconnected and the Sn elements are mainly distributed in the Ag-rich phase and the surrounding tin bronze phase.
In this paper, the wetting and spreading process of 30% ~ 70% CuSn pre-alloyed powder composite silver solder on T2 copper matrix was studied, and the wetting and spreading mechanism of CuSn pre-alloyed powder composite silver solder on copper matrix was discussed. The results show that the initial contact angle decreases from 119° for 30% CuSn to 94° for 70% CuSn during the wetting and spreading process with the copper substrate. The final contact angle decreased from 15° for 30wt.% CuSn to 7 for 70wt.% CuSn. When the content of CuSn alloy powder in the powder core is 60 wt.%, the wetting area of the solder on the copper plate reaches 530.04 mm2, an increase of about 66% compared to when no CuSn alloy powder was added. The initial and final contact angles decreased with the increase of CuSn pre-alloy powder content due to the precursor wetting effect of the low melting point CuSn pre-alloy powder, which melted on the outer skin of BAg30CuZnSn brazing material during the brazing process, forming a thin layer of molten CuSn liquid alloy and reducing the solid-liquid interfacial tension. Subsequently, the molten BAg30CuZnSn foil strip spreads over the pre-melted Cu-Sn liquid thin layer and reacts with it by diffusion of solute atoms, eventually forming a liquid composite braze. The addition of the low melting point Cu-Sn pre-alloyed powder improves the wetting performance of the composite silver brazing material on copper significantly. The reaction wetting interface of the composite silver braze with the copper substrate is uniform and dense with the addition of 40% CuSn pre-alloyed powder, where the white rich (Ag) phases are interconnected and the Sn elements are mainly distributed in the Ag-rich phase and the surrounding tin bronze phase.
, Available online ,
doi: 10.12073/j.hjxb.20220309001
Abstract:
Due to the inaccuracy of the nominal strain approach in evaluating the low-cycle fatigue(LCF) properties of welded joints, a local strain approach considering mechanical heterogeneity of welded joints and based on elastic-plastic finite element analysis was proposed to evaluate the LCF properties of welded joints accurately. The LCF tests of smooth specimens of the welded joint of heat-resistant steel and the weld metal were conducted. The elastic-plastic finite element analysis of the smooth specimens of the welded joints during loading was calculated. The LCF properties of the welded joint were evaluated using the nominal and local strain approach. The results showed that the smooth specimens of the welded joint fractured at the softened weld zone. The LCF properties evaluated by the nominal strain approach were conservative. Since the mechanical heterogeneity of the welded joint was considered by the local strain approach, the LCF properties were evaluated based on the local strain in the fractured microzone. Therefore, the strain-life curve of the welded joint obtained by the local strain approach was close to the strain-life curve of the material of the fractured microzone.
Due to the inaccuracy of the nominal strain approach in evaluating the low-cycle fatigue(LCF) properties of welded joints, a local strain approach considering mechanical heterogeneity of welded joints and based on elastic-plastic finite element analysis was proposed to evaluate the LCF properties of welded joints accurately. The LCF tests of smooth specimens of the welded joint of heat-resistant steel and the weld metal were conducted. The elastic-plastic finite element analysis of the smooth specimens of the welded joints during loading was calculated. The LCF properties of the welded joint were evaluated using the nominal and local strain approach. The results showed that the smooth specimens of the welded joint fractured at the softened weld zone. The LCF properties evaluated by the nominal strain approach were conservative. Since the mechanical heterogeneity of the welded joint was considered by the local strain approach, the LCF properties were evaluated based on the local strain in the fractured microzone. Therefore, the strain-life curve of the welded joint obtained by the local strain approach was close to the strain-life curve of the material of the fractured microzone.
, Available online ,
doi: 10.12073/j.hjxb.20220306001
Abstract:
17-4PH stainless steel was fabricated by selective laser melting (selective laser melting, SLM). The microstructure of the as-built and solution heat treated 17-4PH was analyzed by backscatter electron diffraction (electron backscattered diffraction, EBSD) and transmission electron microscopy (transmission electron microscope, TEM). The relationship between microstructure dynamic fracture behavior was investigated by performing instrumented impact test. Absorbed impact energies related to crack initiation, stable and unstable propagation were calculated and the dynamic J-R curves were estimated.The results demonstrate that as-built 17-4PH mainly consists of coarse columnar δ ferrite grains growing along the building direction with <100> texture and fine martensitic grains with random orientation. A small amount of austinite can also be found in the as-built sample. As-built 17-4PH displays low resistance to crack initiation and propagation, resulting in marginally rising J-R curve and quasi-cleavage fracture. After solution heat treatment, the retained ferrite transforms into martensite and microstructural anisotropy can be eliminated. The impact toughness is 1 times higher than that in as-built conditions and the dynamic J-R curve rises steeply, indicating superior dynamic mechanical properties. Fracture surfaces revealed that the inferior dynamic fracture toughness of as-built 17-4PH can be attributed to the weak boundaries between the coarse δ ferrite grains and surrounding fine martensite grains.
17-4PH stainless steel was fabricated by selective laser melting (selective laser melting, SLM). The microstructure of the as-built and solution heat treated 17-4PH was analyzed by backscatter electron diffraction (electron backscattered diffraction, EBSD) and transmission electron microscopy (transmission electron microscope, TEM). The relationship between microstructure dynamic fracture behavior was investigated by performing instrumented impact test. Absorbed impact energies related to crack initiation, stable and unstable propagation were calculated and the dynamic J-R curves were estimated.The results demonstrate that as-built 17-4PH mainly consists of coarse columnar δ ferrite grains growing along the building direction with <100> texture and fine martensitic grains with random orientation. A small amount of austinite can also be found in the as-built sample. As-built 17-4PH displays low resistance to crack initiation and propagation, resulting in marginally rising J-R curve and quasi-cleavage fracture. After solution heat treatment, the retained ferrite transforms into martensite and microstructural anisotropy can be eliminated. The impact toughness is 1 times higher than that in as-built conditions and the dynamic J-R curve rises steeply, indicating superior dynamic mechanical properties. Fracture surfaces revealed that the inferior dynamic fracture toughness of as-built 17-4PH can be attributed to the weak boundaries between the coarse δ ferrite grains and surrounding fine martensite grains.
, Available online ,
doi: 10.12073/j.hjxb.20220617003
Abstract:
ER4047 wire and powdered Nocolok brazing flux were selected as filler materials, and two welding methods, laser fusion brazing and laser-CMT hybrid welding-brazing, were used to join 5A06 aluminum alloy and Ti6Al4V alloy. The microstructure and mechanical properties of the two welded joints were compared and analyzed. The results show that continuous and stable welded joints can be easily obtained by laser welding-brazing and laser-CMT hybrid welding-brazing under appropriate welding process. The microstructure of the middle part of the weld of aluminum/titanium laser welding-brazing and laser-CMT hybrid welding-brazing is α-Al solid solution and Al-Si eutectic structure. Both laser welding-brazing and laser-CMT hybrid welding-brazing have the thickest interface reaction layer on the upper surface of titanium alloy, with the thickness of <10 μm and < 6 μm respectively. The interface on the titanium side of the laser brazed weld is mainly serrated, and the interface on the titanium side of the laser-CMT composite brazed weld is mainly lamellar. The joints of laser welding-brazing and laser-CMT hybrid welding-brazing welding are fractured in the weld zone, and the average tensile strength of the joints are 252 and 209 MPa respectively. The tensile strength of laser welding-brazing is 20% higher than that of laser-CMT hybrid welding-brazing. The efficiency of laser-CMT hybrid welding-brazing is about 1.5 times higher than that of laser welding-brazing.
ER4047 wire and powdered Nocolok brazing flux were selected as filler materials, and two welding methods, laser fusion brazing and laser-CMT hybrid welding-brazing, were used to join 5A06 aluminum alloy and Ti6Al4V alloy. The microstructure and mechanical properties of the two welded joints were compared and analyzed. The results show that continuous and stable welded joints can be easily obtained by laser welding-brazing and laser-CMT hybrid welding-brazing under appropriate welding process. The microstructure of the middle part of the weld of aluminum/titanium laser welding-brazing and laser-CMT hybrid welding-brazing is α-Al solid solution and Al-Si eutectic structure. Both laser welding-brazing and laser-CMT hybrid welding-brazing have the thickest interface reaction layer on the upper surface of titanium alloy, with the thickness of <10 μm and < 6 μm respectively. The interface on the titanium side of the laser brazed weld is mainly serrated, and the interface on the titanium side of the laser-CMT composite brazed weld is mainly lamellar. The joints of laser welding-brazing and laser-CMT hybrid welding-brazing welding are fractured in the weld zone, and the average tensile strength of the joints are 252 and 209 MPa respectively. The tensile strength of laser welding-brazing is 20% higher than that of laser-CMT hybrid welding-brazing. The efficiency of laser-CMT hybrid welding-brazing is about 1.5 times higher than that of laser welding-brazing.
, Available online ,
doi: 10.12073/j.hjxb.20220330001
Abstract:
The finite element model for POP stacked solder joints was established. Analyzed stress distribution state and thermal fatigue life of solder joints under thermal cyclic load based on the ANAND constitutive equation. Based on the sensitivity method, studied the significance of the effect of POP package structure parameters on the thermal stress of solder joints. Used the response surface method to create a regression equation for the thermal stress of POP stacked solder joint with structural parameters and combined the particle swarm algorithm to optimize the structural parameters. Following the results, cracks will appear first at the point where the solder joint and copper pad touch. Upper solder joint height and lower solder joint height have a more significant effect on the thermal stress of POP stacked joints. The optimal structural parameter level combination is the upper solder joint height of 0.28mm, lower solder joint height of 0.35mm, and middle PCB thickness of 0.26mm. After optimization, the maximum thermal stress of the upper and lower solder joint is reduced by 0.816MPa and 1.271MPa respectively, which prolongs the thermal fatigue life of the POP stacked solder joints.
The finite element model for POP stacked solder joints was established. Analyzed stress distribution state and thermal fatigue life of solder joints under thermal cyclic load based on the ANAND constitutive equation. Based on the sensitivity method, studied the significance of the effect of POP package structure parameters on the thermal stress of solder joints. Used the response surface method to create a regression equation for the thermal stress of POP stacked solder joint with structural parameters and combined the particle swarm algorithm to optimize the structural parameters. Following the results, cracks will appear first at the point where the solder joint and copper pad touch. Upper solder joint height and lower solder joint height have a more significant effect on the thermal stress of POP stacked joints. The optimal structural parameter level combination is the upper solder joint height of 0.28mm, lower solder joint height of 0.35mm, and middle PCB thickness of 0.26mm. After optimization, the maximum thermal stress of the upper and lower solder joint is reduced by 0.816MPa and 1.271MPa respectively, which prolongs the thermal fatigue life of the POP stacked solder joints.
, Available online ,
doi: 10.12073/j.hjxb.20220418001
Abstract:
Sn35Bi0.3Ag/Cu welded joints were prepared at different welding time and temperature. The effects of welding time (1-9 min) and welding temperature (210 ℃-290 ℃) on the microstructure and mechanical properties of Sn35Bi0.3Ag/Cu welded joints were studyed by means of scanning electron microscope (SEM), universal tensile testing machine and ultrasonic scan machine. The results show that the Cu element diffuses into the welding interface and forms the (Cu5Sn6, Cu3Sn) interface layer. The Ag3Sn phase can inhibit the growth of interfacial layer. With the increase of welding time or welding temperature, the reaction layer thickens and the shear strength increases first and then decreases. The analysis of the fracture morphology of the welded joint shows that the fracture of the welded joint is jointly affected by Bi phase particles and Cu6Sn5 particles.The fracture of the welded joint occurs on the IMC / solder side. Bi phase particles and Cu6Sn5 particles affect the shear strength of the joint.In addition, when the welding time is 3 min and the welding temperature is 230 ℃, the brazing rate is the highest (99.14%)and the shear strength reaches the maximum value (51.8 MPa).
Sn35Bi0.3Ag/Cu welded joints were prepared at different welding time and temperature. The effects of welding time (1-9 min) and welding temperature (210 ℃-290 ℃) on the microstructure and mechanical properties of Sn35Bi0.3Ag/Cu welded joints were studyed by means of scanning electron microscope (SEM), universal tensile testing machine and ultrasonic scan machine. The results show that the Cu element diffuses into the welding interface and forms the (Cu5Sn6, Cu3Sn) interface layer. The Ag3Sn phase can inhibit the growth of interfacial layer. With the increase of welding time or welding temperature, the reaction layer thickens and the shear strength increases first and then decreases. The analysis of the fracture morphology of the welded joint shows that the fracture of the welded joint is jointly affected by Bi phase particles and Cu6Sn5 particles.The fracture of the welded joint occurs on the IMC / solder side. Bi phase particles and Cu6Sn5 particles affect the shear strength of the joint.In addition, when the welding time is 3 min and the welding temperature is 230 ℃, the brazing rate is the highest (99.14%)and the shear strength reaches the maximum value (51.8 MPa).
, Available online ,
doi: 10.12073/j.hjxb.20211114001
Abstract:
The high-efficiency welding of 6mm TA2 pure titanium plate was realized by using low power pulsed laser induced twin TIG hybrid welding heat source (LITTW). Based on the dynamic behavior of Ti particles, the effect of laser pulse on arc plasma was studied. The results show that the arc energy of LITTW is more concentrated than that of laser induced single TIG welding (LISTW). The welding energy consumption is only 50.9% of that of LISTW, but the welding speed is 2.3 times of that of LISTW. After the laser pulse action, there is a recovery time for the arc plasma to recover from the energy concentration state to the original arc shape. Under the experimental conditions, the recovery time of LITTW is 6.5 ms, which is 3 ms longer than that of LISTW. The stable keyhole morphology in LITTW provides conditions for the continuous transfer of Ti particles to arc plasma and prolongs the recovery time of plasma.
The high-efficiency welding of 6mm TA2 pure titanium plate was realized by using low power pulsed laser induced twin TIG hybrid welding heat source (LITTW). Based on the dynamic behavior of Ti particles, the effect of laser pulse on arc plasma was studied. The results show that the arc energy of LITTW is more concentrated than that of laser induced single TIG welding (LISTW). The welding energy consumption is only 50.9% of that of LISTW, but the welding speed is 2.3 times of that of LISTW. After the laser pulse action, there is a recovery time for the arc plasma to recover from the energy concentration state to the original arc shape. Under the experimental conditions, the recovery time of LITTW is 6.5 ms, which is 3 ms longer than that of LISTW. The stable keyhole morphology in LITTW provides conditions for the continuous transfer of Ti particles to arc plasma and prolongs the recovery time of plasma.
, Available online ,
doi: 10.12073/j.hjxb.20211208002
Abstract:
In order to accurately extract the characteristic parameters of the welding seams in the digital model of ship welding parts, and then to realize the adaptive and rapid matching and selection of welding processes in the robot database system, a feature parameter extraction algorithm of ship welds based on spatial position and contour distance is proposed. First, the spatial position relationship of the welded joint is determined by the recognition of the surface to be determined based on the Helen formula, and the weld feature is recognized through the combination of the minimum contour distance; then the feature points and lines at the weld groove are identified based on the total number of contour lines and the two end points with the smallest outline distance; finally, the final weld feature parameters related to the welding process are extracted based on the mathematical model built through the three types of welded joints. The test results show that the proposed welding seam feature parameter extraction algorithm can accurately identify 4 types of joint forms and 10 groove types, as well as accurately extract parameters such as weld gap, groove included angle and welded plate thickness, which is characterized by wide weld feature recognition and complete information extraction. Compared with other related recognition algorithms, the recognition rate of the proposed algorithm reaches 100%, and the recognition efficiency is increased by 16.06%, which further verifies the effectiveness of the algorithm.
In order to accurately extract the characteristic parameters of the welding seams in the digital model of ship welding parts, and then to realize the adaptive and rapid matching and selection of welding processes in the robot database system, a feature parameter extraction algorithm of ship welds based on spatial position and contour distance is proposed. First, the spatial position relationship of the welded joint is determined by the recognition of the surface to be determined based on the Helen formula, and the weld feature is recognized through the combination of the minimum contour distance; then the feature points and lines at the weld groove are identified based on the total number of contour lines and the two end points with the smallest outline distance; finally, the final weld feature parameters related to the welding process are extracted based on the mathematical model built through the three types of welded joints. The test results show that the proposed welding seam feature parameter extraction algorithm can accurately identify 4 types of joint forms and 10 groove types, as well as accurately extract parameters such as weld gap, groove included angle and welded plate thickness, which is characterized by wide weld feature recognition and complete information extraction. Compared with other related recognition algorithms, the recognition rate of the proposed algorithm reaches 100%, and the recognition efficiency is increased by 16.06%, which further verifies the effectiveness of the algorithm.
, Available online ,
doi: 10.12073/j.hjxb.20220222002
Abstract:
Aiming at the problems of low load duration, single power output mode, and poor consistency of welding joints of traditional transistor resistance spot welding power source, a variable polarity transistor micro resistance spot welding power source which can realize fast charge and discharge of the capacitor is designed. The load characteristics of the power supply are analyzed. The main circuit topology of the power supply based on the full-bridge inverter + H-bridge dual-phase chopper circuit is designed. The digital power control system based on the high-performance STM32 dual-core controller is designed. A multi-stage variable pulse width capacitor group fast charging method is proposed. The power output characteristic test and the copper-nickel sheet single-sided double-point process test are carried out. The test results show that the designed power supply output load persistence rate can reach more than 5%, and the polarity switching time can be as low as 0.1 ms or less. The variable polarity output mode can effectively solve the problem of different solder joint sizes caused by the polarity effect in the unipolar mode. The performance of the welded joint in the voltage control mode is better than that in the current control mode and the power control mode.
Aiming at the problems of low load duration, single power output mode, and poor consistency of welding joints of traditional transistor resistance spot welding power source, a variable polarity transistor micro resistance spot welding power source which can realize fast charge and discharge of the capacitor is designed. The load characteristics of the power supply are analyzed. The main circuit topology of the power supply based on the full-bridge inverter + H-bridge dual-phase chopper circuit is designed. The digital power control system based on the high-performance STM32 dual-core controller is designed. A multi-stage variable pulse width capacitor group fast charging method is proposed. The power output characteristic test and the copper-nickel sheet single-sided double-point process test are carried out. The test results show that the designed power supply output load persistence rate can reach more than 5%, and the polarity switching time can be as low as 0.1 ms or less. The variable polarity output mode can effectively solve the problem of different solder joint sizes caused by the polarity effect in the unipolar mode. The performance of the welded joint in the voltage control mode is better than that in the current control mode and the power control mode.
, Available online ,
doi: 10.12073/j.hjxb.20211231001
Abstract:
In order to realize automatic detection and classification of weld surface defects, an effective laser vision detection method for weld surface defects was studied. First, the weld image is collected by a laser vision sensor and preprocessed, including image segmentation, grayscale, smooth denoising and weld contour extraction. Then the feature vectors of laser stripe contour image of weld seam are extracted by means of Histogram of Oriented Gradient (HOG), the model parameters were optimized based on the five-fold cross-validation grid search method. Finally, an intelligent model of Support Vector Machine (SVM) was established to identify and classify weld surface defects. Different feature data were obtained by adjusting the weld contour extraction algorithm and HOG feature dimension, and then the identification effect of weld defects was analyzed by comparing each other. Under same experimental conditions, it is found that the recognition rate of SVM is higher than that of random forest classifier, k-nearest neighbor classifier and naive bayes classifier, reaching 97.86%. The proposed intelligent identification method of weld surface defects based on HOG-SVM can effectively improve the classification accuracy of weld defects (porosity, sag, undercut) and non-defects.
In order to realize automatic detection and classification of weld surface defects, an effective laser vision detection method for weld surface defects was studied. First, the weld image is collected by a laser vision sensor and preprocessed, including image segmentation, grayscale, smooth denoising and weld contour extraction. Then the feature vectors of laser stripe contour image of weld seam are extracted by means of Histogram of Oriented Gradient (HOG), the model parameters were optimized based on the five-fold cross-validation grid search method. Finally, an intelligent model of Support Vector Machine (SVM) was established to identify and classify weld surface defects. Different feature data were obtained by adjusting the weld contour extraction algorithm and HOG feature dimension, and then the identification effect of weld defects was analyzed by comparing each other. Under same experimental conditions, it is found that the recognition rate of SVM is higher than that of random forest classifier, k-nearest neighbor classifier and naive bayes classifier, reaching 97.86%. The proposed intelligent identification method of weld surface defects based on HOG-SVM can effectively improve the classification accuracy of weld defects (porosity, sag, undercut) and non-defects.
, Available online ,
doi: 10.12073/j.hjxb.20220325011
Abstract:
In order to improve the mechanical properties of M390 high carbon martensitic stainless steel and 304 austenitic stainless steel welded joints, especially the hardness of welded joints to meet the requirements of advanced knives production, different heat treatment processes of welded joints were performed for M390 high carbon martensitic stainless steel and 304 austenitic stainless steel jointts obtained by cold metal transfer welding. Tensile, Vickers microhardness tests and scanning electron microscopy (SEM) were used to characterize the mechanical properties and microstructure evolution of welded joints with different heat treatment processes, the carbide distributions of M390 base metal, M390 fine-grained region and M390 coarse-grained region in welded joints under different heat treatment processes were calculated, the fracture mechanism of welder joints under different heat treatment processes was studied. The research results show that the 1 150 S heat treatment process not only meets the hardness requirements of advanced knives, but also has good mechanical properties, and can be used as the best heat treatment process for M390/304 welded joints, the tensile strength and elongation of the corresponding welded joints reach 502 MPa and 20.8%, the tensile strength and elongation of the corresponding welded joints reach 98% and 95% of as-welded joint. The average size of carbides in M390 base metal, fine-grained region and coarse-grained region of 1 150 S heat treatment process is the smallest, and the carbide morphology is uniformly distributed in small blocks. With the increase of quenching temperature, both the tensile strength and elongation showed a trend of first decreasing and then increasing. With the decrease of cooling rate, both the tensile strength and elongation showed a decreasing trend. The the welded joint under different heat treatment processes is fractured at the interface between M390 coarse-grained region and weld metal, where the hardness varies greatly, and there is a phenomenon of uneven stress distribution.
In order to improve the mechanical properties of M390 high carbon martensitic stainless steel and 304 austenitic stainless steel welded joints, especially the hardness of welded joints to meet the requirements of advanced knives production, different heat treatment processes of welded joints were performed for M390 high carbon martensitic stainless steel and 304 austenitic stainless steel jointts obtained by cold metal transfer welding. Tensile, Vickers microhardness tests and scanning electron microscopy (SEM) were used to characterize the mechanical properties and microstructure evolution of welded joints with different heat treatment processes, the carbide distributions of M390 base metal, M390 fine-grained region and M390 coarse-grained region in welded joints under different heat treatment processes were calculated, the fracture mechanism of welder joints under different heat treatment processes was studied. The research results show that the 1 150 S heat treatment process not only meets the hardness requirements of advanced knives, but also has good mechanical properties, and can be used as the best heat treatment process for M390/304 welded joints, the tensile strength and elongation of the corresponding welded joints reach 502 MPa and 20.8%, the tensile strength and elongation of the corresponding welded joints reach 98% and 95% of as-welded joint. The average size of carbides in M390 base metal, fine-grained region and coarse-grained region of 1 150 S heat treatment process is the smallest, and the carbide morphology is uniformly distributed in small blocks. With the increase of quenching temperature, both the tensile strength and elongation showed a trend of first decreasing and then increasing. With the decrease of cooling rate, both the tensile strength and elongation showed a decreasing trend. The the welded joint under different heat treatment processes is fractured at the interface between M390 coarse-grained region and weld metal, where the hardness varies greatly, and there is a phenomenon of uneven stress distribution.
, Available online ,
doi: 10.12073/j.hjxb.20220121002
Abstract:
In order to research the influence of covering thickness on explosive welding, the explosive welding experiments under different covering thickness are simulated in three dimensions by using ANSYS/LS-DYNA software and combining the SPH-FEM coupling algorithm. The Q235 steel with the thickness of 20 mm and the 304 stainless steel with the thickness of 2.5 mm are used as the base plate and the flyer plate in the present study. The dynamic parameters in the welding process are calculated according to the corresponding material parameter theory, and an explosive welding window is established. The simulation results show that, compared to the explosive welding without covering, the impact velocity is increased by 39.3%, 58.1% and 68.8% respectively when the covering thickness is 15 mm, 30 mm and 45 mm. And the collision pressure is increased by 41.0%, 65.3% and 80.6% respectively. The simulation results approximately agree with the experimental results. The SPH method is used to carry out two-dimensional numerical simulation to obtain the composite interface between flyer plate and base plate when assembling covering. The simulation results show that the composite plate has a good waveform composite interface when the covering thickness is 15 mm, and the interface waveform is more consistent with the results of the metallographic analysis in the experiment.
In order to research the influence of covering thickness on explosive welding, the explosive welding experiments under different covering thickness are simulated in three dimensions by using ANSYS/LS-DYNA software and combining the SPH-FEM coupling algorithm. The Q235 steel with the thickness of 20 mm and the 304 stainless steel with the thickness of 2.5 mm are used as the base plate and the flyer plate in the present study. The dynamic parameters in the welding process are calculated according to the corresponding material parameter theory, and an explosive welding window is established. The simulation results show that, compared to the explosive welding without covering, the impact velocity is increased by 39.3%, 58.1% and 68.8% respectively when the covering thickness is 15 mm, 30 mm and 45 mm. And the collision pressure is increased by 41.0%, 65.3% and 80.6% respectively. The simulation results approximately agree with the experimental results. The SPH method is used to carry out two-dimensional numerical simulation to obtain the composite interface between flyer plate and base plate when assembling covering. The simulation results show that the composite plate has a good waveform composite interface when the covering thickness is 15 mm, and the interface waveform is more consistent with the results of the metallographic analysis in the experiment.
, Available online ,
doi: 10.12073/j.hjxb.20220106003
Abstract:
In this paper, Electron back scatter diffraction (EBSD) technique was used to study the grain boundary characteristic distribution of 316L stainless steel transverse tensile samples and normal tensile samples prepared by micron selective laser melting under 8%, 18% and 28% tensile strain. The results show that with the increase of tensile strain, the proportion of Σ3 grain boundaries of transverse and normal samples increased significantly, while the proportion of Σ9 and Σ27 grain boundaries decreased significantly. The connectivity of general high angle grain boundary network was effectively interrupted by Σ3 grain boundaries. The coherent/incoherent characteristics of special grain boundaries were measured by micro rectangular section method. When the transverse specimen was under 18% tensile strain, the special grain boundaries were mainly Σ3ic, accounting for about 60%. Under the same conditions, the special grain boundaries of normal tensile specimen were mostly Σ3c, accounting for about 73%. Further analysis pointed out that the migration of incoherent Σ3ic grain boundaries and the interaction with Σ9 grain boundaries were the reasons for the increase of the proportion of Σ3 special grain boundaries during the tensile strain.
In this paper, Electron back scatter diffraction (EBSD) technique was used to study the grain boundary characteristic distribution of 316L stainless steel transverse tensile samples and normal tensile samples prepared by micron selective laser melting under 8%, 18% and 28% tensile strain. The results show that with the increase of tensile strain, the proportion of Σ3 grain boundaries of transverse and normal samples increased significantly, while the proportion of Σ9 and Σ27 grain boundaries decreased significantly. The connectivity of general high angle grain boundary network was effectively interrupted by Σ3 grain boundaries. The coherent/incoherent characteristics of special grain boundaries were measured by micro rectangular section method. When the transverse specimen was under 18% tensile strain, the special grain boundaries were mainly Σ3ic, accounting for about 60%. Under the same conditions, the special grain boundaries of normal tensile specimen were mostly Σ3c, accounting for about 73%. Further analysis pointed out that the migration of incoherent Σ3ic grain boundaries and the interaction with Σ9 grain boundaries were the reasons for the increase of the proportion of Σ3 special grain boundaries during the tensile strain.
, Available online ,
doi: 10.12073/j.hjxb.20220123001
Abstract:
According to the requirements of robot welding motion simulation and multi-layer and multi-channel path planning, an open robot welding off-line programming system based on webgl is developed. Firstly, a robot MAG welding system based on laser vision sensing is built, and then a simulation platform is built by using JavaScript, webgl and other technologies. The three-dimensional point cloud data of weld bead is obtained through the sensor, and the point cloud processing technology is used to extract the weld bead feature information. On this basis, a multi-layer and multi pass path planning strategy for 20 mm thick V-groove steel plate is further proposed, Finally, the welding experiment of 4 layers and 10 passes of V-groove was completed. The results show that the system provides a reliable way to realize the key technologies of robot welding automation and intelligence.
According to the requirements of robot welding motion simulation and multi-layer and multi-channel path planning, an open robot welding off-line programming system based on webgl is developed. Firstly, a robot MAG welding system based on laser vision sensing is built, and then a simulation platform is built by using JavaScript, webgl and other technologies. The three-dimensional point cloud data of weld bead is obtained through the sensor, and the point cloud processing technology is used to extract the weld bead feature information. On this basis, a multi-layer and multi pass path planning strategy for 20 mm thick V-groove steel plate is further proposed, Finally, the welding experiment of 4 layers and 10 passes of V-groove was completed. The results show that the system provides a reliable way to realize the key technologies of robot welding automation and intelligence.
, Available online ,
doi: 10.12073/j.hjxb.20220123002
Abstract:
The thick-plates of AZ31B magnesium alloy with 9 mm thickness were joined successfully by Stationary shoulder friction stir welding (SSFSW) to explore the influence of stirring needle speed (500 – 1000 rpm) on the microstructure and mechanical properties of weld. The results show that the butt weld with smooth surface and no internal defects can be obtained at the rotation speed of 600 − 800 rpm under the given welding speed of 80 mm/min. When the rotation speed is 1000 rpm, discontinuous pits appear on the surface but there are still no defects in the weld. With the increase of rotating speed from 600 rpm to 1000 rpm, the weld nugget zone contour determined by the pin shape has little difference along the plate thickness. At 700 rpm, the grain size difference in the nugget zone is the smallest along the plate thickness. The inhomogeneity of hardness distribution in the WNZ decreases with the increase of rotational speed. The maximum difference of hardness in the middle of the plate thickness is 10.97 HV, and the minimum hardness is 47 HV at the interface between the heat affected zone and the nugget zone of the advancing side. The joint has the best mechanical properties at 700 rpm, the strength coefficient is 90.2% and the corresponding elongation is 69.3% of the BM. With the increase of rotational speed, the fracture mode changes from ductile-brittle mixed fracture to shear-ductile mixed fracture.
The thick-plates of AZ31B magnesium alloy with 9 mm thickness were joined successfully by Stationary shoulder friction stir welding (SSFSW) to explore the influence of stirring needle speed (500 – 1000 rpm) on the microstructure and mechanical properties of weld. The results show that the butt weld with smooth surface and no internal defects can be obtained at the rotation speed of 600 − 800 rpm under the given welding speed of 80 mm/min. When the rotation speed is 1000 rpm, discontinuous pits appear on the surface but there are still no defects in the weld. With the increase of rotating speed from 600 rpm to 1000 rpm, the weld nugget zone contour determined by the pin shape has little difference along the plate thickness. At 700 rpm, the grain size difference in the nugget zone is the smallest along the plate thickness. The inhomogeneity of hardness distribution in the WNZ decreases with the increase of rotational speed. The maximum difference of hardness in the middle of the plate thickness is 10.97 HV, and the minimum hardness is 47 HV at the interface between the heat affected zone and the nugget zone of the advancing side. The joint has the best mechanical properties at 700 rpm, the strength coefficient is 90.2% and the corresponding elongation is 69.3% of the BM. With the increase of rotational speed, the fracture mode changes from ductile-brittle mixed fracture to shear-ductile mixed fracture.
, Available online ,
doi: 10.2073/j.hjxb.20220410001
Abstract:
Aiming at the problems of low arc pressure and shallow weld penetration in Twin-electrode TIG (T-TIG) welding, a T-TIG welding method assisted by cusp magnetic fields with different polarities is introduced. A high-speed camera and an infrared camera were used to study the influence of cusp magnetic fields of different polarities on arc shape and weld characteristics, and a physical model was constructed to reveal the interaction mechanism between cusp magnetic fields and arc plasma. The results show that the external cusp magnetic field affects the shape of the T-TIG arc and the temperature field of the weld, and the cusp magnetic fields of both polarities can refine the structure of the heat-affected zone. Among them, under the action of a positive cusp magnetic field, the T-TIG arc shape changes more greatly, the weld temperature field is more concentrated, the penetration depth of the weld is increased by 37.1% compared with that without a magnetic field, and the energy utilization efficiency increases by 31.6%.
Aiming at the problems of low arc pressure and shallow weld penetration in Twin-electrode TIG (T-TIG) welding, a T-TIG welding method assisted by cusp magnetic fields with different polarities is introduced. A high-speed camera and an infrared camera were used to study the influence of cusp magnetic fields of different polarities on arc shape and weld characteristics, and a physical model was constructed to reveal the interaction mechanism between cusp magnetic fields and arc plasma. The results show that the external cusp magnetic field affects the shape of the T-TIG arc and the temperature field of the weld, and the cusp magnetic fields of both polarities can refine the structure of the heat-affected zone. Among them, under the action of a positive cusp magnetic field, the T-TIG arc shape changes more greatly, the weld temperature field is more concentrated, the penetration depth of the weld is increased by 37.1% compared with that without a magnetic field, and the energy utilization efficiency increases by 31.6%.
, Available online ,
doi: 10.2073/j.hjxb.20220412002
Abstract:
The main S-N curve method is a new method for fatigue calculation, which is widely used in fatigue analysis of welded structures. In order to predict the fatigue life of welded structures under the test load, firstly, the bench model is taken as the boundary condition to make the test load become the input of simulation analysis, and the more accurate dynamic response of weld is obtained through steady-state dynamic calculation. Second, in the master S - N curve method of quasi static calculation process, based on the introduction of dynamic structural stress based on modal structural stress superposition calculation method, the method to obtain the modal coordinates and calculated by the dynamic welding structure modal stress superposition structure, structure dynamic stress and the equivalent stress calculation, the method adopts the Lord S - N curve forecasting life assessment. Finally, the fatigue evaluation software of welded structure modal structure stress method is developed. The software is used to carry out the fatigue evaluation and fatigue test comparison. The results show that: This method can effectively identify the fatigue failure parts of the car body under dynamic loading, which verifies the effectiveness and superiority of this method in fatigue evaluation of welded structures under dynamic loading, and provides a technical basis for the study of fatigue life evaluation of welded structures and the expansion of the main S-N curve method..
The main S-N curve method is a new method for fatigue calculation, which is widely used in fatigue analysis of welded structures. In order to predict the fatigue life of welded structures under the test load, firstly, the bench model is taken as the boundary condition to make the test load become the input of simulation analysis, and the more accurate dynamic response of weld is obtained through steady-state dynamic calculation. Second, in the master S - N curve method of quasi static calculation process, based on the introduction of dynamic structural stress based on modal structural stress superposition calculation method, the method to obtain the modal coordinates and calculated by the dynamic welding structure modal stress superposition structure, structure dynamic stress and the equivalent stress calculation, the method adopts the Lord S - N curve forecasting life assessment. Finally, the fatigue evaluation software of welded structure modal structure stress method is developed. The software is used to carry out the fatigue evaluation and fatigue test comparison. The results show that: This method can effectively identify the fatigue failure parts of the car body under dynamic loading, which verifies the effectiveness and superiority of this method in fatigue evaluation of welded structures under dynamic loading, and provides a technical basis for the study of fatigue life evaluation of welded structures and the expansion of the main S-N curve method..
Display Method:
2022, 43(12): 1-11.
doi: 10.12073/j.hjxb.20220819001
Abstract:
Taking multiphase ceramics, fiber reinforced ceramic matrix composites and thermoelectric materials as examples, this paper discusses the researches published in recent years which focused on the composition design of filler metals, microstructure controlling of brazed interface, residual stress mitigation of brazed joints and performance evaluation of brazed joints. The results show that the wettability and interfacial bonding strength can be improved effectively by adding active elements to filler metals or modifying the surface of base metal. For the element diffusion of interface and the transitional dissolution of base metal, composite filler metals or barrier layer can be designed and prepared to solve these problems. The residual stress of brazed joint is greatly affected by the difference of thermal expansion coefficient of brazing materials. At present, various novel solutions have been proposed, such as adding porous interlayer, preparing gradient composite layer and machining of base metal surface. However, the application of research results is still limited to small size samples. The problem of relieving the residual stress of large size joints remains to be solved. Ultimately, the prospect of the interest in future research is concluded. It is expected to promote the domestic manufacturing of aerospace and weapons equipment.
Taking multiphase ceramics, fiber reinforced ceramic matrix composites and thermoelectric materials as examples, this paper discusses the researches published in recent years which focused on the composition design of filler metals, microstructure controlling of brazed interface, residual stress mitigation of brazed joints and performance evaluation of brazed joints. The results show that the wettability and interfacial bonding strength can be improved effectively by adding active elements to filler metals or modifying the surface of base metal. For the element diffusion of interface and the transitional dissolution of base metal, composite filler metals or barrier layer can be designed and prepared to solve these problems. The residual stress of brazed joint is greatly affected by the difference of thermal expansion coefficient of brazing materials. At present, various novel solutions have been proposed, such as adding porous interlayer, preparing gradient composite layer and machining of base metal surface. However, the application of research results is still limited to small size samples. The problem of relieving the residual stress of large size joints remains to be solved. Ultimately, the prospect of the interest in future research is concluded. It is expected to promote the domestic manufacturing of aerospace and weapons equipment.
2022, 43(12): 12-19.
doi: 10.12073/j.hjxb.20211212001
Abstract:
Single tungsten inert gas welding (STIG), double tungsten inert gas welding (DTIG), laser-single TIG arc hybrid welding (L-STIG) and laser-double TIG arc hybrid welding (L-DTIG) were used to weld TA2 titanium alloy butt joints with 6 mm thickness , and one-side welding with back formation were achieved. The results show that the arc energy of L-DTIG hybrid welding is more concentrated, and the welding speed can reach 680 mm/min. The heat input of L-DTIG hybrid welding is 605.5 J/mm, which is only 35.5% of DTIG and 59.0% of L-STIG. The grain size of L-DTIG weld zone is fine, and the microhardness can reach 229.5 HV. Tensile specimens fracture at the base material and the joint strength is better than that of the base material. After the addition of laser, the arc plasma central conductive zone of L-DTIG shrinks by 51.0% and 45.5% in the xOy and yOz planes, respectively, and the arc root shrinks by 75.0%. The measured arc pressure of the L-DTIG composite welding heat source on the workpiece was 3 465 Pa, which was 4.17 and 2.25 times higher than that of DTIG and L-STIG composite welding, respectively. The higher arc shrinkage ratio and arc pressure can significantly improve the welding efficiency and reduce the welding heat input.
Single tungsten inert gas welding (STIG), double tungsten inert gas welding (DTIG), laser-single TIG arc hybrid welding (L-STIG) and laser-double TIG arc hybrid welding (L-DTIG) were used to weld TA2 titanium alloy butt joints with 6 mm thickness , and one-side welding with back formation were achieved. The results show that the arc energy of L-DTIG hybrid welding is more concentrated, and the welding speed can reach 680 mm/min. The heat input of L-DTIG hybrid welding is 605.5 J/mm, which is only 35.5% of DTIG and 59.0% of L-STIG. The grain size of L-DTIG weld zone is fine, and the microhardness can reach 229.5 HV. Tensile specimens fracture at the base material and the joint strength is better than that of the base material. After the addition of laser, the arc plasma central conductive zone of L-DTIG shrinks by 51.0% and 45.5% in the xOy and yOz planes, respectively, and the arc root shrinks by 75.0%. The measured arc pressure of the L-DTIG composite welding heat source on the workpiece was 3 465 Pa, which was 4.17 and 2.25 times higher than that of DTIG and L-STIG composite welding, respectively. The higher arc shrinkage ratio and arc pressure can significantly improve the welding efficiency and reduce the welding heat input.
2022, 43(12): 20-26.
doi: 10.12073/j.hjxb.20211201001
Abstract:
In view of the insufficient toughness of the GPa-grade deposited metal, four groups of welding wires were designed to study the effects of Al and Mg elements on the microstructure and mechanical properties of metal cored welding wires. The microstructure of the deposited metal was characterized by scanning electron microscopy (SEM). The mechanical properties of the deposited metal were characterized by mechanical properties test. The results show that the deposited metal mainly consists of martensite and bainite. With the increase of Al and Mg contents from 0Al-0Mg to 0.3Al-0.9Mg, the content of O decreases from 0.030 8% to 0.014 3%, and the content of coalesced bainite decreases while that of lath martensite increases. and the inclusions were transformed from traditional oxides including Fe, Al, Si, Mn, etc. to spherical and fine particles mainly composed of Al and Mg oxides inclusions. Compared with 0Al-0Mg group, the average size of the inclusion in 0.3Al-0.9Mg group decreases by 0.13 μm, the tensile strength was increased by 152 MPa, and the impact absorption energy was increased by 11 J (−20 ℃).
In view of the insufficient toughness of the GPa-grade deposited metal, four groups of welding wires were designed to study the effects of Al and Mg elements on the microstructure and mechanical properties of metal cored welding wires. The microstructure of the deposited metal was characterized by scanning electron microscopy (SEM). The mechanical properties of the deposited metal were characterized by mechanical properties test. The results show that the deposited metal mainly consists of martensite and bainite. With the increase of Al and Mg contents from 0Al-0Mg to 0.3Al-0.9Mg, the content of O decreases from 0.030 8% to 0.014 3%, and the content of coalesced bainite decreases while that of lath martensite increases. and the inclusions were transformed from traditional oxides including Fe, Al, Si, Mn, etc. to spherical and fine particles mainly composed of Al and Mg oxides inclusions. Compared with 0Al-0Mg group, the average size of the inclusion in 0.3Al-0.9Mg group decreases by 0.13 μm, the tensile strength was increased by 152 MPa, and the impact absorption energy was increased by 11 J (−20 ℃).
2022, 43(12): 27-34.
doi: 10.12073/j.hjxb.20211208003
Abstract:
In waveguide devices, large-area and reliable low-temperature soldering bonding between the aluminum alloy shell and the microstrip circuit board were difficult because of the poor wettability of the Al alloy. In this study, Ag-15%Ni coating layer and Ni-5%Al/Ag-15%Ni composite coating layers with a thickness approximately of 80 μm were prepared on the surface of 5A06 Al alloy by arc spraying technology to improve the wettability of Sn-Pb alloy solder on the Al alloy surface. Comparable studies were performed on the microstructure, interfacial bonding behavior, low-temperature soldering behavior of the two kinds of coating layers, and the shearing failure mechanism of joints were investigated. Results showed that sound interfacial bonding was realized between the coating layer and the Al alloy substrate. Moreover, the two kinds of coating layers both exhibited good solderability at low-temperature. The bonding strength between the Ag-15%Ni coating layer and the Al alloy substrate was 40 MPa, and the shear strength of the soldering joint formed by the sprayed aluminum alloy substrate and T2 copper was 26 MPa. While, the Ni-5%Al/Ag-15%Ni composite coatings exhibited better bonding strength with the Al alloy substrate (42 MPa) and higher shear strength of the soldering joint (31 MPa) than the Ag-15%Ni single coating layer.
In waveguide devices, large-area and reliable low-temperature soldering bonding between the aluminum alloy shell and the microstrip circuit board were difficult because of the poor wettability of the Al alloy. In this study, Ag-15%Ni coating layer and Ni-5%Al/Ag-15%Ni composite coating layers with a thickness approximately of 80 μm were prepared on the surface of 5A06 Al alloy by arc spraying technology to improve the wettability of Sn-Pb alloy solder on the Al alloy surface. Comparable studies were performed on the microstructure, interfacial bonding behavior, low-temperature soldering behavior of the two kinds of coating layers, and the shearing failure mechanism of joints were investigated. Results showed that sound interfacial bonding was realized between the coating layer and the Al alloy substrate. Moreover, the two kinds of coating layers both exhibited good solderability at low-temperature. The bonding strength between the Ag-15%Ni coating layer and the Al alloy substrate was 40 MPa, and the shear strength of the soldering joint formed by the sprayed aluminum alloy substrate and T2 copper was 26 MPa. While, the Ni-5%Al/Ag-15%Ni composite coatings exhibited better bonding strength with the Al alloy substrate (42 MPa) and higher shear strength of the soldering joint (31 MPa) than the Ag-15%Ni single coating layer.
2022, 43(12): 35-40.
doi: 10.12073/j.hjxb.20211106001
Abstract:
The Ti-6Al-4V(TC4) filler wire was used to join 2 mm thick Ti-3Al-6Mo-2Fe-2Zr titanium alloy during laser welding process. Investigations concerning the influence of wire feeding rate on microstructure and tensile properties were conducted on laser welded Ti-3Al-6Mo-2Fe-2Zr joints with filler wire by optical microscope, scanning electron microscope, and X ray energy spectrometer and other analytical testing methods. The results show that, due to the decreasing heat effect from fusion line to base metal, the microstructure of the heat affected zone is divided as follows: single β region, primary α + matrix β region, and primary α + retained secondary α + matrix β region. Acicular α' phase is formed in the fusion zone, and the distribution is not uniform. As the wire feed speed increases, the number and size of acicular α' phase increases. The tensile strength and elongation of laser welded joints with filler wire are lower than those of the base metal. With the increase of wire feeding rate, the tensile strength of the joint increases and the elongation decreases. The reason is attributed to that, as the wire feeding rate increased, the [Mo]eq in the fusion zone decreased correspondingly, which led to the increment in the number and size of α' phase. When the wire feeding rate was higher than 1.0 m/min, the fracture location changed from fusion zone to heat affected zone because of the strengthening effects of α' phase.
The Ti-6Al-4V(TC4) filler wire was used to join 2 mm thick Ti-3Al-6Mo-2Fe-2Zr titanium alloy during laser welding process. Investigations concerning the influence of wire feeding rate on microstructure and tensile properties were conducted on laser welded Ti-3Al-6Mo-2Fe-2Zr joints with filler wire by optical microscope, scanning electron microscope, and X ray energy spectrometer and other analytical testing methods. The results show that, due to the decreasing heat effect from fusion line to base metal, the microstructure of the heat affected zone is divided as follows: single β region, primary α + matrix β region, and primary α + retained secondary α + matrix β region. Acicular α' phase is formed in the fusion zone, and the distribution is not uniform. As the wire feed speed increases, the number and size of acicular α' phase increases. The tensile strength and elongation of laser welded joints with filler wire are lower than those of the base metal. With the increase of wire feeding rate, the tensile strength of the joint increases and the elongation decreases. The reason is attributed to that, as the wire feeding rate increased, the [Mo]eq in the fusion zone decreased correspondingly, which led to the increment in the number and size of α' phase. When the wire feeding rate was higher than 1.0 m/min, the fracture location changed from fusion zone to heat affected zone because of the strengthening effects of α' phase.
2022, 43(12): 41-46.
doi: 10.12073/j.hjxb.20211219001
Abstract:
To exploring the causes and rules of rotary arc spatter, a combination method of multi threshold and BP neural network based on mask was proposed to identify welding spatter in accordance with the welding images of rotary arc flat surfacing collected by high-speed camera. The multi threshold method was used to obtain the spatter position and contour, and then the spatter was identified by establishing a BP neural network model with five characteristic values The recognition accuracy of this combined method can reach 95.76% for rotating arc spatter images with complex background. At the same time, through the phase analysis of spatter and welding wire position, the average phase of the maximum number of spatters is 241.4°, that is, about 0.14 cycle position after the end of welding wire enters the molten pool. This is mainly due to the current surge caused by the contact between the droplet at the end of welding wire and the molten pool, and the insufficient current suppression, The research results provide a basis for controlling spatter in rotating arc welding.
To exploring the causes and rules of rotary arc spatter, a combination method of multi threshold and BP neural network based on mask was proposed to identify welding spatter in accordance with the welding images of rotary arc flat surfacing collected by high-speed camera. The multi threshold method was used to obtain the spatter position and contour, and then the spatter was identified by establishing a BP neural network model with five characteristic values The recognition accuracy of this combined method can reach 95.76% for rotating arc spatter images with complex background. At the same time, through the phase analysis of spatter and welding wire position, the average phase of the maximum number of spatters is 241.4°, that is, about 0.14 cycle position after the end of welding wire enters the molten pool. This is mainly due to the current surge caused by the contact between the droplet at the end of welding wire and the molten pool, and the insufficient current suppression, The research results provide a basis for controlling spatter in rotating arc welding.
2022, 43(12): 47-52, 99.
doi: 10.12073/j.hjxb.20211216003
Abstract:
The root hump defect is easy to appear in the laser-MIG composite welding process. In order to realize the simultaneous prediction of the root hump defect in the welding process, this paper studies the algorithm of root hump defect prediction and analyzes the prediction results of different algorithm. The real-time visual sensing information of composite welding process is carried out by a high-speed camera, the time series characteristic information of the front weld pool and the keyhole in the welding process is extracted, and the characteristics signals are decomposed and reconstructed by wavelet packet decomposition (WPD). Then, the residual height of the back weld is obtained by a laser scanner, which is used as the basis for marking the hump status. Long short-term memory (LSTM) neural network was used to predict the status of root hump in the welding process. Experimental results show that the accuracy of WPD-LSTM algorithm for root hump prediction is 97.85%. Compared with other algorithms, the prediction accuracy of WPD-LSTM algorithm based on the temporal feature information of the front visual sensing in the welding process is higher, and the prediction results have higher continuity, which is conducive to realize the synchronous detection and control of root hump defects in welding process.
The root hump defect is easy to appear in the laser-MIG composite welding process. In order to realize the simultaneous prediction of the root hump defect in the welding process, this paper studies the algorithm of root hump defect prediction and analyzes the prediction results of different algorithm. The real-time visual sensing information of composite welding process is carried out by a high-speed camera, the time series characteristic information of the front weld pool and the keyhole in the welding process is extracted, and the characteristics signals are decomposed and reconstructed by wavelet packet decomposition (WPD). Then, the residual height of the back weld is obtained by a laser scanner, which is used as the basis for marking the hump status. Long short-term memory (LSTM) neural network was used to predict the status of root hump in the welding process. Experimental results show that the accuracy of WPD-LSTM algorithm for root hump prediction is 97.85%. Compared with other algorithms, the prediction accuracy of WPD-LSTM algorithm based on the temporal feature information of the front visual sensing in the welding process is higher, and the prediction results have higher continuity, which is conducive to realize the synchronous detection and control of root hump defects in welding process.
2022, 43(12): 53-63.
doi: 10.12073/j.hjxb.20220305001
Abstract:
In order to investigate the effect of Si content on the microstructure and properties of CoCrFeNiSix (x=0.5, 1.0, 1.5) high-entropy alloy coating, the high-entropy alloy coating was prepared by laser cladding technology. The phase composition, microstructure, element distribution, hardness value, wear resistance and corrosion properties of the coating were characterized by X-ray diffraction, scanning electron microscopy (SEM), energy dispersive spectroscopy, microhardness tester, friction and wear tester, and electrochemical workstation. The results show that with the increase of Si content, the alloy phase changes from single-phase face-centered cubic structure to face-centered cubic structure, silicon compound (σ) phase structure, and finally form face-centered cubic structure, body-centered cubic structure and σ mixed structure. The microstructure of the coating mainly changes from columnar crystals to dendritic crystals and finally to cellular crystals. At the same time, the hardness of the coating also increases. When the Si content is 1.5, the average hardness of the coating reaches 619.04 HV0.2, which is about 2.67 times that of the substrate. The wear amount and friction coefficient of the coating decreased with the increase of Si content, and the wear resistance of the coating increased significantly. In 3.5%NaCl solution, the corrosion performance of the coating increases first and then decreases with the increase of Si content. When Si content is 1.0, the corrosion performance of the coating is optimal.
In order to investigate the effect of Si content on the microstructure and properties of CoCrFeNiSix (x=0.5, 1.0, 1.5) high-entropy alloy coating, the high-entropy alloy coating was prepared by laser cladding technology. The phase composition, microstructure, element distribution, hardness value, wear resistance and corrosion properties of the coating were characterized by X-ray diffraction, scanning electron microscopy (SEM), energy dispersive spectroscopy, microhardness tester, friction and wear tester, and electrochemical workstation. The results show that with the increase of Si content, the alloy phase changes from single-phase face-centered cubic structure to face-centered cubic structure, silicon compound (σ) phase structure, and finally form face-centered cubic structure, body-centered cubic structure and σ mixed structure. The microstructure of the coating mainly changes from columnar crystals to dendritic crystals and finally to cellular crystals. At the same time, the hardness of the coating also increases. When the Si content is 1.5, the average hardness of the coating reaches 619.04 HV0.2, which is about 2.67 times that of the substrate. The wear amount and friction coefficient of the coating decreased with the increase of Si content, and the wear resistance of the coating increased significantly. In 3.5%NaCl solution, the corrosion performance of the coating increases first and then decreases with the increase of Si content. When Si content is 1.0, the corrosion performance of the coating is optimal.
2022, 43(12): 64-71.
doi: 10.12073/j.hjxb.20211219002
Abstract:
The 1060 aluminum tube/T2 copper rod are selected as the explosive composite rod preparation materials, and the T2 copper tube/Q235 steel tube are selected as the explosive composite pipe preparation materials. Using ANSYS/LS-DYNA software and combining the three algorithms of Lagrangian algorithm, ALE algorithm and SPH-FEM coupling algorithm, the numerical simulation of the explosive welding experiment of preparing two groups of explosive composite pipe and rod at one time is carried out. The simulation results show that the early modeling of Lagrange algorithm is the most concise, followed by the ALE algorithm. In the simulation process, SPH-FEM coupling algorithm takes the most time, and ALE algorithm takes the shortest time. The error between the collision velocity measured by the three algorithms and the theoretical calculation value is 0.9% − 5.3%. The error of SPH-EFM coupling algorithm is the smallest, and the error of Lagrange algorithm is the largest. The principle of energy accumulation inside the tubes is used to explain the diameter expansion of the external composite pipe during the welding process, and the pressure distribution at the composite interface of T2 copper tube/Q235 steel tube is used to verify this phenomenon.
The 1060 aluminum tube/T2 copper rod are selected as the explosive composite rod preparation materials, and the T2 copper tube/Q235 steel tube are selected as the explosive composite pipe preparation materials. Using ANSYS/LS-DYNA software and combining the three algorithms of Lagrangian algorithm, ALE algorithm and SPH-FEM coupling algorithm, the numerical simulation of the explosive welding experiment of preparing two groups of explosive composite pipe and rod at one time is carried out. The simulation results show that the early modeling of Lagrange algorithm is the most concise, followed by the ALE algorithm. In the simulation process, SPH-FEM coupling algorithm takes the most time, and ALE algorithm takes the shortest time. The error between the collision velocity measured by the three algorithms and the theoretical calculation value is 0.9% − 5.3%. The error of SPH-EFM coupling algorithm is the smallest, and the error of Lagrange algorithm is the largest. The principle of energy accumulation inside the tubes is used to explain the diameter expansion of the external composite pipe during the welding process, and the pressure distribution at the composite interface of T2 copper tube/Q235 steel tube is used to verify this phenomenon.
2022, 43(12): 72-78.
doi: 10.12073/j.hjxb.20211202004
Abstract:
The port stubs in China Fusion Engineering Test Reactor (CFETR) vacuum vessel are electron beam welded. Due to the large thickness of the plate, the residual stress after welding is large, and the microstructure of the weld from top to bottom is inhomogeneous, so it is necessary to adopt post-welding annealing to further improve the microstructure and properties. In order to explore an appropriate annealing process, a single temperature zone tubular furnace was used to anneal the electron beam welded sample of 50 mm thickness 316L stainless steel within the temperature range from 200 ℃ to 450 ℃. The grain structure of the heat affected zone and weld zone with different annealing processes was analyzed by electron backscattered diffraction (EBSD). In addition, tensile tests and microhardness tests were carried out on the top, middle and bottom areas of the joint under different annealing processes. The results show that the dislocation densities of weld zones and heat affected zones decrease with the increase of heat treatment temperature, and the third kind of internal stress caused by dislocation was released. After 300 ℃ heat treatment, the tensile strength and elongation after fracture of different areas of the joint are more excellent, and there are not too many precipitated particles in the fracture of each tensile sample. The variation trend of microhardness in each area of the joint at different annealing temperatures is approximately consistent with that of tensile strength.
The port stubs in China Fusion Engineering Test Reactor (CFETR) vacuum vessel are electron beam welded. Due to the large thickness of the plate, the residual stress after welding is large, and the microstructure of the weld from top to bottom is inhomogeneous, so it is necessary to adopt post-welding annealing to further improve the microstructure and properties. In order to explore an appropriate annealing process, a single temperature zone tubular furnace was used to anneal the electron beam welded sample of 50 mm thickness 316L stainless steel within the temperature range from 200 ℃ to 450 ℃. The grain structure of the heat affected zone and weld zone with different annealing processes was analyzed by electron backscattered diffraction (EBSD). In addition, tensile tests and microhardness tests were carried out on the top, middle and bottom areas of the joint under different annealing processes. The results show that the dislocation densities of weld zones and heat affected zones decrease with the increase of heat treatment temperature, and the third kind of internal stress caused by dislocation was released. After 300 ℃ heat treatment, the tensile strength and elongation after fracture of different areas of the joint are more excellent, and there are not too many precipitated particles in the fracture of each tensile sample. The variation trend of microhardness in each area of the joint at different annealing temperatures is approximately consistent with that of tensile strength.
2022, 43(12): 79-83.
doi: 10.12073/j.hjxb.20211214001
Abstract:
To address the problem of high residual stresses and high-temperature service requirements in the brazed joints of carbon/carbon (C/C) composites and niobium (Nb), vertically aligned few-layer graphene (VFG) coupled with the TiNi solder were used during the brazing process. VFG was prepared by plasma enhanced chemical vapor deposition (PECVD) method in this study. The microstructure and the chemical state of the surface of the VFG and the joint were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. Results revealed that the in-situ and uniform distribution of (Ti,Nb)2Ni particles and annular (Ti,Nb)C phases in the joint seam, effectively reduced the coefficient of thermal expansion of the joint seam and relieved the residual stresses in the joint. Meanwhile, the evenly distributed Nb solid solution endowed sound plasticity at high temperature to the joint seam. The shear strength of the joint at 1 000 ℃ reached 33 MPa, which is 450% higher than the directly brazed joint without interlayer.
To address the problem of high residual stresses and high-temperature service requirements in the brazed joints of carbon/carbon (C/C) composites and niobium (Nb), vertically aligned few-layer graphene (VFG) coupled with the TiNi solder were used during the brazing process. VFG was prepared by plasma enhanced chemical vapor deposition (PECVD) method in this study. The microstructure and the chemical state of the surface of the VFG and the joint were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. Results revealed that the in-situ and uniform distribution of (Ti,Nb)2Ni particles and annular (Ti,Nb)C phases in the joint seam, effectively reduced the coefficient of thermal expansion of the joint seam and relieved the residual stresses in the joint. Meanwhile, the evenly distributed Nb solid solution endowed sound plasticity at high temperature to the joint seam. The shear strength of the joint at 1 000 ℃ reached 33 MPa, which is 450% higher than the directly brazed joint without interlayer.
2022, 43(12): 84-89.
doi: 10.12073/j.hjxb.20211202002
Abstract:
The flat butt welding tests were carried out on 6061 aluminum alloy and AZ31 magnesium alloy with the thickness of 4 mm by introducing 0.05 mm Ni foil interlayer under the condition of constant travel speed and different rotation speeds using the friction stir welding (FSW) technology. The effects of rotation speeds on the distribution of Ni foil particles, the types and distribution of the intermetallic compounds (IMCs) and the strength of the joints were investigated by series of microstructure characterization and mechanical property tests. The results showed that compared to the joint without Ni, the introduction of Ni foil interlayer changed the types and distribution of IMCs in the weld nugget zone (WNZ). In WNZ, there was an obvious banded structure between magnesium alloy and aluminum alloy on which the flocculent Al12Mg17, granular Mg2Ni, lamellar Al3Mg2, and Ni foil particles of varying sizes were distributed. With the increasing of rotation speed, the distribution of Ni became more uniform, while the Al3Mg2 decreased relatively, and the distribution of the brittle Al3Mg2 gradually changed from continuous to intermittent. The tensile strength of the joint reached the maximum value when the rotation speed was 750 r/min. Compared to the joint without Ni, the tensile strength of the joint with the introduction of Ni foil interlayer was increased by 56 MPa, which was 56.9% of the strength of magnesium alloy.
The flat butt welding tests were carried out on 6061 aluminum alloy and AZ31 magnesium alloy with the thickness of 4 mm by introducing 0.05 mm Ni foil interlayer under the condition of constant travel speed and different rotation speeds using the friction stir welding (FSW) technology. The effects of rotation speeds on the distribution of Ni foil particles, the types and distribution of the intermetallic compounds (IMCs) and the strength of the joints were investigated by series of microstructure characterization and mechanical property tests. The results showed that compared to the joint without Ni, the introduction of Ni foil interlayer changed the types and distribution of IMCs in the weld nugget zone (WNZ). In WNZ, there was an obvious banded structure between magnesium alloy and aluminum alloy on which the flocculent Al12Mg17, granular Mg2Ni, lamellar Al3Mg2, and Ni foil particles of varying sizes were distributed. With the increasing of rotation speed, the distribution of Ni became more uniform, while the Al3Mg2 decreased relatively, and the distribution of the brittle Al3Mg2 gradually changed from continuous to intermittent. The tensile strength of the joint reached the maximum value when the rotation speed was 750 r/min. Compared to the joint without Ni, the tensile strength of the joint with the introduction of Ni foil interlayer was increased by 56 MPa, which was 56.9% of the strength of magnesium alloy.
2022, 43(12): 90-99.
doi: 10.12073/j.hjxb.20220303001
Abstract:
Homogeneous specimens of the double-pass laser-arc hybrid welding heat affected zone (HAZ) of low alloy high strength steels were prepared by welding simulation technology, the influence of second peak temperature on the microstructure and toughness of the simulated specimens was investigated. The results showed that the unaltered coarse grained HAZ (UACGHAZ) compose of coarse lath martensite (LM) with an average grain size between 84 − 98 μm. The supercritically reheated CGHAZ (SCRCGHAZ) is comprised of fine LM with an average grain size between 15.7 − 19.2 μm. The intercritically reheated CGHAZ (ICCGHAZ) compose of LM with blocky martensite-austenite constituents distributed along grain boundaries and subgrain boundaries. The subcritically reheated CGHAZ (SRCGHAZ) is comprised of LM with an average grain size between 79 − 88 μm. The instrumented impact test results showed that the ICCGHAZ specimens own the lowest resistance to crack initiation, and the ICCGHAZ and UACGHAZ had the poorest resistance to crack propagation.
Homogeneous specimens of the double-pass laser-arc hybrid welding heat affected zone (HAZ) of low alloy high strength steels were prepared by welding simulation technology, the influence of second peak temperature on the microstructure and toughness of the simulated specimens was investigated. The results showed that the unaltered coarse grained HAZ (UACGHAZ) compose of coarse lath martensite (LM) with an average grain size between 84 − 98 μm. The supercritically reheated CGHAZ (SCRCGHAZ) is comprised of fine LM with an average grain size between 15.7 − 19.2 μm. The intercritically reheated CGHAZ (ICCGHAZ) compose of LM with blocky martensite-austenite constituents distributed along grain boundaries and subgrain boundaries. The subcritically reheated CGHAZ (SRCGHAZ) is comprised of LM with an average grain size between 79 − 88 μm. The instrumented impact test results showed that the ICCGHAZ specimens own the lowest resistance to crack initiation, and the ICCGHAZ and UACGHAZ had the poorest resistance to crack propagation.
2022, 43(12): 100-104.
doi: 10.12073/j.hjxb.20211117001
Abstract:
In this paper, ultrasonic phased array technology was used to monitor the fatigue failure process of weathering steel butt joints. Based on the signal characteristics of ultrasonic probe, the fan-shaped scanning reflection process was studied, and a real-time scanning scheme was established for real-time monitoring of 10 mm thick weather resistant steel butt joints. The results show that when the fatigue life was 5 × 104 cycles, multiple cracks initiated at the weld toe of the butt joint and propagated along the plate thickness were detected by phased array. The cracks begin to expand rapidly when the fatigue life exceeded 3.5 × 105 cycles. Compared with the fatigue test fracture surface, it was found that the crack size based on the phased array detection was basically consistent with the test results, which validated the accuracy of the phased array crack dynamic detection. According to the relationship between the crack depth a, crack length c and cycle number N, the dynamic evolution of cracks was determined, the law of surface crack growth and evolution of weathering steel butt joint of medium and thick plate was built up.
In this paper, ultrasonic phased array technology was used to monitor the fatigue failure process of weathering steel butt joints. Based on the signal characteristics of ultrasonic probe, the fan-shaped scanning reflection process was studied, and a real-time scanning scheme was established for real-time monitoring of 10 mm thick weather resistant steel butt joints. The results show that when the fatigue life was 5 × 104 cycles, multiple cracks initiated at the weld toe of the butt joint and propagated along the plate thickness were detected by phased array. The cracks begin to expand rapidly when the fatigue life exceeded 3.5 × 105 cycles. Compared with the fatigue test fracture surface, it was found that the crack size based on the phased array detection was basically consistent with the test results, which validated the accuracy of the phased array crack dynamic detection. According to the relationship between the crack depth a, crack length c and cycle number N, the dynamic evolution of cracks was determined, the law of surface crack growth and evolution of weathering steel butt joint of medium and thick plate was built up.
2022, 43(12): 105-112.
doi: 10.12073/j.hjxb.20220408001
Abstract:
The cold crack sensitivity analysis of the copper backing outside root welding joints of X80M pipeline steel with large thickness and diameter under different assembly conditions was carried out. The effect of different assembly conditions on the cold cracking tendency of the joint was studied using the carbon equivalent method and stress field simulation. According to the results, the heat affected zone (HAZ) at the top cover layer and the root weld layer zone at the bottom of the X80M pipe steel weld joints are the weakest areas, which have the greatest cold crack tendency. When the butt gap is increased from 0 − 0.5 mm to 0.6 − 1 mm, the relative carbon equivalent of the root weld layer in the weld zone is also increased by 16.6%, which increases the cold cracking tendency. The increase in misalignment increases the hardenability of the heat affected zone of the joint cover layer and increases the susceptibility to cold cracking. The increase in the misalignment and the butt gap will lead to a further increase in the residual tensile stress after welding, and the increase in the misalignment will also lead to stress concentrations in the misalignment area of the joint, and the increase in the misalignment from 0 mm to 3 mm will result in a 52.4% increase in the peak residual stress at the concave corner of the root weld layer in the weld zone. Therefore, the X80M pipeline steel arc welding process needs to minimize the butt gap and the amount of misalignment to reduce the tendency of cold cracking.
The cold crack sensitivity analysis of the copper backing outside root welding joints of X80M pipeline steel with large thickness and diameter under different assembly conditions was carried out. The effect of different assembly conditions on the cold cracking tendency of the joint was studied using the carbon equivalent method and stress field simulation. According to the results, the heat affected zone (HAZ) at the top cover layer and the root weld layer zone at the bottom of the X80M pipe steel weld joints are the weakest areas, which have the greatest cold crack tendency. When the butt gap is increased from 0 − 0.5 mm to 0.6 − 1 mm, the relative carbon equivalent of the root weld layer in the weld zone is also increased by 16.6%, which increases the cold cracking tendency. The increase in misalignment increases the hardenability of the heat affected zone of the joint cover layer and increases the susceptibility to cold cracking. The increase in the misalignment and the butt gap will lead to a further increase in the residual tensile stress after welding, and the increase in the misalignment will also lead to stress concentrations in the misalignment area of the joint, and the increase in the misalignment from 0 mm to 3 mm will result in a 52.4% increase in the peak residual stress at the concave corner of the root weld layer in the weld zone. Therefore, the X80M pipeline steel arc welding process needs to minimize the butt gap and the amount of misalignment to reduce the tendency of cold cracking.
Since 1980 monthly
Supervisor: China Science and Technology Association
Sponsor: Chinese Mechanical Engineering Society
Editor-in-chief: Huiwen Zhang
Address: No. 2077, Chuangxin Road, Songbei District, Harbin
Postal Code: 150028
Telephone: 0451-86325919
Email: hjzzszjl@163.com
CN: 23-1178/TG
ISSN: 0253-360X
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