2016 Vol. 37 No. 3
2016, 37(3): 1-4.
Abstract：
Densetungsten carbide reinforced iron-based surface layer were prepared via casting-infiltration and heat treatment process. The microstructure of samples obtained by different heating time was researched.The results showed that dense tungsten carbide layer was generated on the surface.The thickness of the layer was increased with the heating time; the maximum thickness reached 148 μm. The micro-hardness of the layer was significantly higher thanthe iron matrix and it didn't change a lot with the varying heating time.The formation of dense tungsten carbide layer depended on the diffusion and the interaction in-situ of C and W atoms in the Fe-C-W system.
Densetungsten carbide reinforced iron-based surface layer were prepared via casting-infiltration and heat treatment process. The microstructure of samples obtained by different heating time was researched.The results showed that dense tungsten carbide layer was generated on the surface.The thickness of the layer was increased with the heating time; the maximum thickness reached 148 μm. The micro-hardness of the layer was significantly higher thanthe iron matrix and it didn't change a lot with the varying heating time.The formation of dense tungsten carbide layer depended on the diffusion and the interaction in-situ of C and W atoms in the Fe-C-W system.
2016, 37(3): 5-8.
Abstract：
In this work, the creep properties of China Low Activation Martensitic (CLAM) steel TIG welding joint have been carried out in the temperature of 823K and with the applied stress from 180 to 260 MPa. The creep curve and creepmechanism with mathematic model is analyzed. The results show that the TIG welding joints exhibited the typical three-stage creep curves; the minimum creep rate increasedat a constant temperature, the rupture time decreases with the stress increasing. The stress exponent n obtained by creep equation was higher than the typical values of 3~7, and the activation energy Q was about 436 KJ/mol.K, which is also higher than the self diffusion energy of Fe(300 KJ/mol·K) indicating a dislocation creep deformation mechanism.
In this work, the creep properties of China Low Activation Martensitic (CLAM) steel TIG welding joint have been carried out in the temperature of 823K and with the applied stress from 180 to 260 MPa. The creep curve and creepmechanism with mathematic model is analyzed. The results show that the TIG welding joints exhibited the typical three-stage creep curves; the minimum creep rate increasedat a constant temperature, the rupture time decreases with the stress increasing. The stress exponent n obtained by creep equation was higher than the typical values of 3~7, and the activation energy Q was about 436 KJ/mol.K, which is also higher than the self diffusion energy of Fe(300 KJ/mol·K) indicating a dislocation creep deformation mechanism.
2016, 37(3): 9-12.
Abstract：
Accurate seam tracking is a prerequisite for laser welding with good quality. A seam tracking method based on Kalman filtering with colored noises is proposed to predict the seam deviationsin micro butt joint whose width is less than 0.05 mm. In the experiment, the weldments were magnetized by usingan excitation magnetic field. Meanwhile, a magneto-optical sensor based on the principle of Faraday magneto effect was applied to acquire the magneto-optical image of the weld joint. By analyzing the magneto-optical images of weld joint, the joint center position was extracted and defined as the state vector. Then the state equation and the measurement equation based on the weld joint center position were established. Considering that the system process noise was colored noise, the Sage adaptive filtering was used to lessen the noise influence.The innovation series was used to estimate the process noise variance matrix, and the weld joint position could be predicted accurately. Experimental results show that seam tracking accuracy can be improved effectively with self-adaptive Kalman filtering method.
Accurate seam tracking is a prerequisite for laser welding with good quality. A seam tracking method based on Kalman filtering with colored noises is proposed to predict the seam deviationsin micro butt joint whose width is less than 0.05 mm. In the experiment, the weldments were magnetized by usingan excitation magnetic field. Meanwhile, a magneto-optical sensor based on the principle of Faraday magneto effect was applied to acquire the magneto-optical image of the weld joint. By analyzing the magneto-optical images of weld joint, the joint center position was extracted and defined as the state vector. Then the state equation and the measurement equation based on the weld joint center position were established. Considering that the system process noise was colored noise, the Sage adaptive filtering was used to lessen the noise influence.The innovation series was used to estimate the process noise variance matrix, and the weld joint position could be predicted accurately. Experimental results show that seam tracking accuracy can be improved effectively with self-adaptive Kalman filtering method.
2016, 37(3): 13-16,21.
Abstract：
The test blocks with welding defects were detected by the method of metal magnetic memory, and the testing ability of the metal magnetic memory technology on welding defects including crack, porosity, incomplete penetration, lack of fusion, slag inclusion was studied. For the welding defects such as cracking, porosity, incomplete penetration, lack of fusion, slag inclusion in welded joints, their average value Have and the maximum value Hmax of the magnetic field intensity, the area surrounded by the magnetic field intensity curve, the average value and maximum value of the magnetic field intensity gradient, the area surrounded by the magnetic field intensity gradient curve, were calculated and analyzed, respectively, which is also compared with the defect-free regions. The results show that、 of the welding defect are significantly different from parameters of the defect-free regions, whichcan accurately identify the location of welding defects. Whether it is a welding defect, or welding residual stress, itcan lead to changes of magnetic memory signal, but there are essential distinction between above two.
The test blocks with welding defects were detected by the method of metal magnetic memory, and the testing ability of the metal magnetic memory technology on welding defects including crack, porosity, incomplete penetration, lack of fusion, slag inclusion was studied. For the welding defects such as cracking, porosity, incomplete penetration, lack of fusion, slag inclusion in welded joints, their average value Have and the maximum value Hmax of the magnetic field intensity, the area surrounded by the magnetic field intensity curve, the average value and maximum value of the magnetic field intensity gradient, the area surrounded by the magnetic field intensity gradient curve, were calculated and analyzed, respectively, which is also compared with the defect-free regions. The results show that、 of the welding defect are significantly different from parameters of the defect-free regions, whichcan accurately identify the location of welding defects. Whether it is a welding defect, or welding residual stress, itcan lead to changes of magnetic memory signal, but there are essential distinction between above two.
2016, 37(3): 17-21.
Abstract：
Ni-WC/Cr3C2 coating was prepared on 45# steel surface by laser cladding technology, and the microstructure, phase and composition were studied by means of SEM and XRD, while the corrosion resistance and wear resistance were also studied. The results show that cellular dendrites were formed at the bottom of the laser cladding Ni-WC/Cr3C2 coating, while fine dendrites were at the middle and upper region of the coating. The cladding coating is mainly composed of γ-(Fe, Ni), M23C6 type carbides and undissolved WC particles. The microhardness is increased to 711HV0.1 due to the synergetic effect of fine grain strengthening, solid solution strengthening and carbides. Moreover, a reduction of the corrosion current density of about four times compared with 45# steel indicating the improved corrosion resistance. In addition, the weight loss of both the laser cladding coating and 45# steel was increased with the increase of wearing speed, and the weight loss of cladding coating is lower than that of 45# steel.
Ni-WC/Cr3C2 coating was prepared on 45# steel surface by laser cladding technology, and the microstructure, phase and composition were studied by means of SEM and XRD, while the corrosion resistance and wear resistance were also studied. The results show that cellular dendrites were formed at the bottom of the laser cladding Ni-WC/Cr3C2 coating, while fine dendrites were at the middle and upper region of the coating. The cladding coating is mainly composed of γ-(Fe, Ni), M23C6 type carbides and undissolved WC particles. The microhardness is increased to 711HV0.1 due to the synergetic effect of fine grain strengthening, solid solution strengthening and carbides. Moreover, a reduction of the corrosion current density of about four times compared with 45# steel indicating the improved corrosion resistance. In addition, the weight loss of both the laser cladding coating and 45# steel was increased with the increase of wearing speed, and the weight loss of cladding coating is lower than that of 45# steel.
Abstract：
Experiment of joining 6061 aluminum alloy and 304 stainless steel plate by molten-brazing operating at pulse-on-pulse welding mode was carried out and lap joints were obtained. The arc shape and welding current as well as voltage was acquired by high speed camera and electric signal acquisition synchronous system. The effect of the action mode of arc(inclination angle of torch and position of arc)on the weld formationand mechanical properties of the joint was conducted.The result showed that different action modes of arc actually had significant influence on the arc shape, weld formation and mechanical properties of the joint.When the anteversion angle is 20°and the heeling angle is 0°, the weld formation is sensitive to the position of arc. While with the anteversion angle of 20°and heeling angle of 0°, the weld formation is insensitive to the position of arc. Under the former condition, when L is -1 mm, 0 mm, 1 mm, the joint of aluminum and stainless steel has higher strength while under the later condition, the joint of aluminum and stainless steel has higher strength when L is 0 mm and 1 mm. The position the arc performs is the key factor to the shear strength of the joint and it also has effect on the thickness of the interface layer. The study of effect of the action way of arc on weld forming and mechanical properties helps us make effective control of the heat distribution in the process of joining aluminum and steel.
Experiment of joining 6061 aluminum alloy and 304 stainless steel plate by molten-brazing operating at pulse-on-pulse welding mode was carried out and lap joints were obtained. The arc shape and welding current as well as voltage was acquired by high speed camera and electric signal acquisition synchronous system. The effect of the action mode of arc(inclination angle of torch and position of arc)on the weld formationand mechanical properties of the joint was conducted.The result showed that different action modes of arc actually had significant influence on the arc shape, weld formation and mechanical properties of the joint.When the anteversion angle is 20°and the heeling angle is 0°, the weld formation is sensitive to the position of arc. While with the anteversion angle of 20°and heeling angle of 0°, the weld formation is insensitive to the position of arc. Under the former condition, when L is -1 mm, 0 mm, 1 mm, the joint of aluminum and stainless steel has higher strength while under the later condition, the joint of aluminum and stainless steel has higher strength when L is 0 mm and 1 mm. The position the arc performs is the key factor to the shear strength of the joint and it also has effect on the thickness of the interface layer. The study of effect of the action way of arc on weld forming and mechanical properties helps us make effective control of the heat distribution in the process of joining aluminum and steel.
Abstract：
A three dimensional finite element modal was established to analysis the welding residual stress of hybrid steel U-rib stiffened plate under different conditions. In this paper, a welding residual stress simulation method which was verified by large number of experiments, was used to identify the influence of thermal conductivity, specific heat capacity, density, modulus of elasticity, Poisson ratio and coefficient of thermal expansion to the distribution of the plate residual stress, respectively. The analysis results show that the coefficient of thermal expansion and Poission ratio have very little influence to the residual stress; the modulus of elasticity and thermal conductivity have most important influence; and the specific heat capacity and density have the moderate influence. As a result, the elastic modulus and thermal conductivity should be paid more attention in the welding residual stress numerical simulation on the hybrid steel U-rib stiffened plate in order to get the correct values.
A three dimensional finite element modal was established to analysis the welding residual stress of hybrid steel U-rib stiffened plate under different conditions. In this paper, a welding residual stress simulation method which was verified by large number of experiments, was used to identify the influence of thermal conductivity, specific heat capacity, density, modulus of elasticity, Poisson ratio and coefficient of thermal expansion to the distribution of the plate residual stress, respectively. The analysis results show that the coefficient of thermal expansion and Poission ratio have very little influence to the residual stress; the modulus of elasticity and thermal conductivity have most important influence; and the specific heat capacity and density have the moderate influence. As a result, the elastic modulus and thermal conductivity should be paid more attention in the welding residual stress numerical simulation on the hybrid steel U-rib stiffened plate in order to get the correct values.
2016, 37(3): 33-36.
Abstract：
The effect of Ga/Nd composite additive on the wettability and microstructure of n-0.3Ag-0.7Cu solder were investigated.The results indicated that the composite additive of Ga and Nd could greatly improve the wettability of solder, the optimal wettability of solder was obtained when the addition of Nd reached 0.1 wt.%. After adding moderate amount of Ga and Nd, the microstructure of solder was refined andthe shear strength of soldered joint was improved by 15%. Compared with the previous results that excessive amount of Nd was added, no obviously Sn-Nd phase observed in the solder, indicating that the composite additive of Ga and Nd could inhibit the formation of Sn-Nd phase to a certain extent.
The effect of Ga/Nd composite additive on the wettability and microstructure of n-0.3Ag-0.7Cu solder were investigated.The results indicated that the composite additive of Ga and Nd could greatly improve the wettability of solder, the optimal wettability of solder was obtained when the addition of Nd reached 0.1 wt.%. After adding moderate amount of Ga and Nd, the microstructure of solder was refined andthe shear strength of soldered joint was improved by 15%. Compared with the previous results that excessive amount of Nd was added, no obviously Sn-Nd phase observed in the solder, indicating that the composite additive of Ga and Nd could inhibit the formation of Sn-Nd phase to a certain extent.
2016, 37(3): 37-40.
Abstract：
The W-Fe-Ni alloy was diffusion bonded with HR2 steel using Ni as interlayer by hot isostatic pressing (HIP). The mechanical properties were evaluated by tensile tests. The microstructure of interface and the diffusion behaviors of different elements were analyzed through OM, SEM and EDS. Results show that, effective welding was obtained between W-Fe-Ni alloy and HR2 steel under the condition of 1200~1300℃, 130 MPa and holding time of 1 hour. The basemetal fractured during the tensile tests when stress raised to about 650 MPa but the interfaces still keep fine. There is no crack between W-Fe-Ni alloy and HR2 steel. Interdiffusion are sufficient through the base metal and interlayer. These elements including W, Co, Cr, Mn diffused to theopposite sides while Ni shows a tendency of diffusing to W-Fe-Ni alloy. The interface presents a good metallurgical binding.
The W-Fe-Ni alloy was diffusion bonded with HR2 steel using Ni as interlayer by hot isostatic pressing (HIP). The mechanical properties were evaluated by tensile tests. The microstructure of interface and the diffusion behaviors of different elements were analyzed through OM, SEM and EDS. Results show that, effective welding was obtained between W-Fe-Ni alloy and HR2 steel under the condition of 1200~1300℃, 130 MPa and holding time of 1 hour. The basemetal fractured during the tensile tests when stress raised to about 650 MPa but the interfaces still keep fine. There is no crack between W-Fe-Ni alloy and HR2 steel. Interdiffusion are sufficient through the base metal and interlayer. These elements including W, Co, Cr, Mn diffused to theopposite sides while Ni shows a tendency of diffusing to W-Fe-Ni alloy. The interface presents a good metallurgical binding.
2016, 37(3): 41-44.
Abstract：
Based on the British standard BS7910, the fracture assessment of level 2A was performed using the Crackwise4.0 software for the embedded flaw, which were formed when the submarine pipeline was installed, in the context of defects acceptance. The influence of fracture toughness, primary stress and mechanical properties on the critical crack size was analyzed using sensitive functions and factors, and the values of sensitivity were obtained respectively. Depended on the benchmark set in this paper, for a certain crack length the crack height was most affected by the yield strength at room temperature. As the critical crack length increased, the effect of primary stress on the critical crack height increased and the influence of fracture toughness as well as theyield strength at room temperature decreased relatively. However, the critical crack height was not sensitive to the tensile strength at all.
Based on the British standard BS7910, the fracture assessment of level 2A was performed using the Crackwise4.0 software for the embedded flaw, which were formed when the submarine pipeline was installed, in the context of defects acceptance. The influence of fracture toughness, primary stress and mechanical properties on the critical crack size was analyzed using sensitive functions and factors, and the values of sensitivity were obtained respectively. Depended on the benchmark set in this paper, for a certain crack length the crack height was most affected by the yield strength at room temperature. As the critical crack length increased, the effect of primary stress on the critical crack height increased and the influence of fracture toughness as well as theyield strength at room temperature decreased relatively. However, the critical crack height was not sensitive to the tensile strength at all.
Abstract：
According to the study on linear track and global distribution of plasma size signals in laser welding, it is found that the global signals distribution feature of plasma has a close relationship with the real laser welding conditions. As aresults anew method based on integral analysis for plasma size signals and its transform feature model has been established in this paper. The results show that this method can not only effectly remove the random noise signals and the negative influence of the signals fluctuation during data treating process, but also has special features on its repeatability and legibility. Therefore, it is a quick and accurate way in testing the change of plasma morphology in laser welding.
According to the study on linear track and global distribution of plasma size signals in laser welding, it is found that the global signals distribution feature of plasma has a close relationship with the real laser welding conditions. As aresults anew method based on integral analysis for plasma size signals and its transform feature model has been established in this paper. The results show that this method can not only effectly remove the random noise signals and the negative influence of the signals fluctuation during data treating process, but also has special features on its repeatability and legibility. Therefore, it is a quick and accurate way in testing the change of plasma morphology in laser welding.
2016, 37(3): 49-52.
Abstract：
The plasma underwater welding technology (PUW)was proposed and the welding process test was carried out on 304 stainless steel with a thickness of 5 mm. The optical microscopy, the super depth of field optical microscopy, tensile testing machine were applied to observe and to analyze the joint morphology as well as the mechanical properties. The results show that PUW can obtain stable arc and high-quality weld. The microstructure of weld metal mainly consisted of homogeneously distributed slightly coarsened dendritic crystal, some regions existed dense and uniform equiaxial dendritic crystal. The tensile strength of welded joints was about 77.56%. The fractured surface morphology presented typical ductile fracture. But the pores present on the weld surfaceaffect the mechanical properties of the weld.
The plasma underwater welding technology (PUW)was proposed and the welding process test was carried out on 304 stainless steel with a thickness of 5 mm. The optical microscopy, the super depth of field optical microscopy, tensile testing machine were applied to observe and to analyze the joint morphology as well as the mechanical properties. The results show that PUW can obtain stable arc and high-quality weld. The microstructure of weld metal mainly consisted of homogeneously distributed slightly coarsened dendritic crystal, some regions existed dense and uniform equiaxial dendritic crystal. The tensile strength of welded joints was about 77.56%. The fractured surface morphology presented typical ductile fracture. But the pores present on the weld surfaceaffect the mechanical properties of the weld.
2016, 37(3): 53-56,105.
Abstract：
Aiming at nonlinear and unstable characteristics of seam tracking signal of magnetic controlled arc welding, the paper proposed a characteristic signal extraction method of arc seam tracking by combining Matching Pursuit and the nonparametric basis function. Firstly, adaptive adjustment of template signal approximate one characteristic component of the original tracking signal is performed, then the optimal estimate of signal characteristic component matching the Template Signal is figured out by the extraction method of characteristic waveform based on nonparametric basis function. Secondly, the optimal estimationis used to update signal margin according to the principle of Matching Pursuit and then the optimal estimation of other characteristic component in the remaining signal was obtained. Finally, the process is repeated again and again until the energy of signal margin reach the preset threshold value.The feature signal extraction experiment on seam tracking platform based on magnetric controlled Arc sensor was verified that the method can extract signal scanning groove and the feature signal corresponding to short circuit transfer.
Aiming at nonlinear and unstable characteristics of seam tracking signal of magnetic controlled arc welding, the paper proposed a characteristic signal extraction method of arc seam tracking by combining Matching Pursuit and the nonparametric basis function. Firstly, adaptive adjustment of template signal approximate one characteristic component of the original tracking signal is performed, then the optimal estimate of signal characteristic component matching the Template Signal is figured out by the extraction method of characteristic waveform based on nonparametric basis function. Secondly, the optimal estimationis used to update signal margin according to the principle of Matching Pursuit and then the optimal estimation of other characteristic component in the remaining signal was obtained. Finally, the process is repeated again and again until the energy of signal margin reach the preset threshold value.The feature signal extraction experiment on seam tracking platform based on magnetric controlled Arc sensor was verified that the method can extract signal scanning groove and the feature signal corresponding to short circuit transfer.
2016, 37(3): 57-61.
Abstract：
The physical model of electron beam welding was established in consideration of all the thermal process and forces during electron beam welding. The molten pool behavior and weld shape of 304 stainless steel heated by stationary electron beam were studied by numerical simulation of the temperature field and fluid flow field. The results shown that the temperature gradient of top surface was higher than 106 K/m and the peak temperature of the molten pool fluctuated at boiling point of 304 stainless steel. The reaction force of metal vapor was the main driven force during heating stage. The top surface was depressed due to the impact of metal vapor and shacked with time. The Marangoni convection caused by surface tension gradient became the main driven force during cooling stage due to the reduction of metal vapor reaction force in the cooling stage. The weld width at the top and bottom surface was large than the center of thickness direction. The weld width at the top surface, bottom surface and the center were 1.9 mm, 1.8 mm and 1.6 mm respectively.
The physical model of electron beam welding was established in consideration of all the thermal process and forces during electron beam welding. The molten pool behavior and weld shape of 304 stainless steel heated by stationary electron beam were studied by numerical simulation of the temperature field and fluid flow field. The results shown that the temperature gradient of top surface was higher than 106 K/m and the peak temperature of the molten pool fluctuated at boiling point of 304 stainless steel. The reaction force of metal vapor was the main driven force during heating stage. The top surface was depressed due to the impact of metal vapor and shacked with time. The Marangoni convection caused by surface tension gradient became the main driven force during cooling stage due to the reduction of metal vapor reaction force in the cooling stage. The weld width at the top and bottom surface was large than the center of thickness direction. The weld width at the top surface, bottom surface and the center were 1.9 mm, 1.8 mm and 1.6 mm respectively.
Abstract：
In arc assisted activating TIG welding process, the base metal is pre-melted by an assisting arc along with mixture of argon and oxygen to form an oxide layer. After TIG welding, the weld penetration can be increased significantly. In this paper, two modes of uneven oxygen distribution at the surface of weld pool is proposed based on the experimental measurements; buoyance. A more sophisticated model of the weld pool in AA-TIG welding is developed, taking Lorentz force and surface tension into account. This model is developed to calculate the transportation hehavior of mass, momentum and energy in AA-TIG weld pool with the uneven oxygen distribution. In this paper, surface tension is a function of the temprerature coefficent and the concentration coefficient of the surface tension.The fluid flow in the weld pool is assumed to be turbulence and incompressible Newtonian fluid. The model is based on the RNG k-ε turbulence model. The experiments show that the calculated results agree well with measured value.
In arc assisted activating TIG welding process, the base metal is pre-melted by an assisting arc along with mixture of argon and oxygen to form an oxide layer. After TIG welding, the weld penetration can be increased significantly. In this paper, two modes of uneven oxygen distribution at the surface of weld pool is proposed based on the experimental measurements; buoyance. A more sophisticated model of the weld pool in AA-TIG welding is developed, taking Lorentz force and surface tension into account. This model is developed to calculate the transportation hehavior of mass, momentum and energy in AA-TIG weld pool with the uneven oxygen distribution. In this paper, surface tension is a function of the temprerature coefficent and the concentration coefficient of the surface tension.The fluid flow in the weld pool is assumed to be turbulence and incompressible Newtonian fluid. The model is based on the RNG k-ε turbulence model. The experiments show that the calculated results agree well with measured value.
2016, 37(3): 67-70.
Abstract：
The finite element model of welding in plate dryer was established. The residual deformation of different schema including forward welding, facing welding, backward welding, with total fifteen kinds of welding sequences were numerical simulated with the method of segmented moving heat source.The results show that the welding deformation of workpiece is bulging upward along the center, the welding deformation gradually increases from the outside tothe inside, the maximum deformation is in the inner part. The residual deformation of backward welding with aninterval of three rows is the minimum, which is 68% of that with forward welding with three rows interval and it is also 58.8% of the maximum residual deformation the fifteen kinds of welding sequences. The relative quantity of welding deformation in each optimized schemes is decreased appreciably while the diameter of plate dryer is bigger and the interval welding time of each rows is longer, the cooling time of each rows can be therefore shortened properly.
The finite element model of welding in plate dryer was established. The residual deformation of different schema including forward welding, facing welding, backward welding, with total fifteen kinds of welding sequences were numerical simulated with the method of segmented moving heat source.The results show that the welding deformation of workpiece is bulging upward along the center, the welding deformation gradually increases from the outside tothe inside, the maximum deformation is in the inner part. The residual deformation of backward welding with aninterval of three rows is the minimum, which is 68% of that with forward welding with three rows interval and it is also 58.8% of the maximum residual deformation the fifteen kinds of welding sequences. The relative quantity of welding deformation in each optimized schemes is decreased appreciably while the diameter of plate dryer is bigger and the interval welding time of each rows is longer, the cooling time of each rows can be therefore shortened properly.
Abstract：
Effect of welding segregation on retained austenitein regenerated weld for nanostructured bainite steel has been investigated by SEM, TEM and EBSD. Welding segregation resulted incoarse retained austenite that distributed at the boundary of the dendrite in the weld. The carbon content of coarse retained austenite is lower than that of the blocky-shape austenite, which reduces stability of the structure. The retained austenite in base metal is in submicronmeter size with a uniform distribution. By contrary, the size of retained austenite in the weld is in micronmeter, and the distribution is not uniform. As a result, the change of the retained austenite in the weld has important effect on the elongation rate of the weld.
Effect of welding segregation on retained austenitein regenerated weld for nanostructured bainite steel has been investigated by SEM, TEM and EBSD. Welding segregation resulted incoarse retained austenite that distributed at the boundary of the dendrite in the weld. The carbon content of coarse retained austenite is lower than that of the blocky-shape austenite, which reduces stability of the structure. The retained austenite in base metal is in submicronmeter size with a uniform distribution. By contrary, the size of retained austenite in the weld is in micronmeter, and the distribution is not uniform. As a result, the change of the retained austenite in the weld has important effect on the elongation rate of the weld.
2016, 37(3): 75-78.
Abstract：
Root shrinkage cavity in Al alloy electron beam welds is one special kind of welding defect, which results in stress concentration, induces the occurrence of crack and remarkablely decreases the carrying capacity, so it must be paid great attention. With the help of ANSYS APDL, by combining keyhole mode welding heat source model and interdendriticflowing theory as well as Niyama criterion, a set of defect criterion program based on temperature field was proposed to predict the root shrinkage cavity in 2219 Al alloy non-penetration electron beam overlaying weld. The results indicated that the simulated welding penetration has an error of 8.76%, the erros of simulated welding width is 13.28%, which werebasically in accordance with experimental samples. These results validated the exactness and feasibility of the defect criterion program developed in this paper.
Root shrinkage cavity in Al alloy electron beam welds is one special kind of welding defect, which results in stress concentration, induces the occurrence of crack and remarkablely decreases the carrying capacity, so it must be paid great attention. With the help of ANSYS APDL, by combining keyhole mode welding heat source model and interdendriticflowing theory as well as Niyama criterion, a set of defect criterion program based on temperature field was proposed to predict the root shrinkage cavity in 2219 Al alloy non-penetration electron beam overlaying weld. The results indicated that the simulated welding penetration has an error of 8.76%, the erros of simulated welding width is 13.28%, which werebasically in accordance with experimental samples. These results validated the exactness and feasibility of the defect criterion program developed in this paper.
2016, 37(3): 79-82.
Abstract：
The weighted average method is proposed to describethe relationship between the heat affected zone (HAZ) of laser tailor-welded blanks, the base metal and the weld.Based on the uniaxial tensile test, the mechanical properties of the base material and the weld were obtained. The prediction model is developed to determine the performance of the HAZ by ABAQUS software. By comparing the simulation results and the test, a reasonable weighting coefficient is determined, and the FEA model reliability is also proved.In addition, the performance of the HAZis also obtained by the mixing rule method, which is compared with the results by the weighted average method. There are only litter difference between the prediction results and the experiment. The prediction results by the weighted average method are closer to the test.
The weighted average method is proposed to describethe relationship between the heat affected zone (HAZ) of laser tailor-welded blanks, the base metal and the weld.Based on the uniaxial tensile test, the mechanical properties of the base material and the weld were obtained. The prediction model is developed to determine the performance of the HAZ by ABAQUS software. By comparing the simulation results and the test, a reasonable weighting coefficient is determined, and the FEA model reliability is also proved.In addition, the performance of the HAZis also obtained by the mixing rule method, which is compared with the results by the weighted average method. There are only litter difference between the prediction results and the experiment. The prediction results by the weighted average method are closer to the test.
2016, 37(3): 83-87.
Abstract：
The temperature field of single wire and tandem wires narrow gap submerged arc welding were calculated by using the special heat source model. The effectiveness of the simulation results was verified by the experiments. The simulation results show that the temperature field aredifferent between the single wire and tandem wires welding. The temperature field of the tandem welding is dissymmetric with largerweld width and smaller weld penetration on the sidewall. The influence of current fluctuation in the penetration of the sidewall is smaller in the tandem welding. With the same current and voltage,the tandem welding has higher deposition efficiency and a smaller tendency to produce overheated zone.
The temperature field of single wire and tandem wires narrow gap submerged arc welding were calculated by using the special heat source model. The effectiveness of the simulation results was verified by the experiments. The simulation results show that the temperature field aredifferent between the single wire and tandem wires welding. The temperature field of the tandem welding is dissymmetric with largerweld width and smaller weld penetration on the sidewall. The influence of current fluctuation in the penetration of the sidewall is smaller in the tandem welding. With the same current and voltage,the tandem welding has higher deposition efficiency and a smaller tendency to produce overheated zone.
2016, 37(3): 88-92.
Abstract：
With the DPMIG and TPMIG welding methods, the effect of different parameters on the welding performance of AA6061 aluminum alloy is studied in this paper. The stability of the welding process is verified with a wavelet analyzer, the microscopic structure and tensile property of the welding joint of the DPMIG and TPMIG methods is studied using a optical microscope and a electrical tensile test machine. The test results show that the welding processes of the TPMIG and DPMIG methods are both stable, and the voltage and current waves are both periodic and repeatable. But the variations of the dynamic resistance and intake energy of the TPMIG method are more ordered. The ripple weld seam of the TPMIG method is better than that of the DPMIG method, as well as less defect such as stoma and crack and better tensile property under different welding speed, showing that the TPMIG is a better welding method than the DPMIG method.
With the DPMIG and TPMIG welding methods, the effect of different parameters on the welding performance of AA6061 aluminum alloy is studied in this paper. The stability of the welding process is verified with a wavelet analyzer, the microscopic structure and tensile property of the welding joint of the DPMIG and TPMIG methods is studied using a optical microscope and a electrical tensile test machine. The test results show that the welding processes of the TPMIG and DPMIG methods are both stable, and the voltage and current waves are both periodic and repeatable. But the variations of the dynamic resistance and intake energy of the TPMIG method are more ordered. The ripple weld seam of the TPMIG method is better than that of the DPMIG method, as well as less defect such as stoma and crack and better tensile property under different welding speed, showing that the TPMIG is a better welding method than the DPMIG method.
2016, 37(3): 93-96.
Abstract：
Flip-Chip LEDs were reflow soldered to Cu/Ag and Cu/Ni/Au substrates using SAC305 solder paste. The microstructure evolutions of the two kinds of sample during high-temperature aging were investigated in this study. Experimental results indicated that there was some interactions between the microstructure on both side of the solder joints. Au layer on Cu/Ni/Au substrate was melted into the bulk solder during the reflow which depressed the growth of Au-Sn intermetallic compounds during aging. Meanwhile, the fast growth of Au-Sn layer on the chip side decreased the relative concentration of Sn in the bulk solder. Consequently, the relative concentration of other elements, including the elements having positive effect for the IMC growth on the substrate, was increased.Compared with the two kinds of sample, the samples on Cu/Ag substrates show poorer thermal aging resistance.
Flip-Chip LEDs were reflow soldered to Cu/Ag and Cu/Ni/Au substrates using SAC305 solder paste. The microstructure evolutions of the two kinds of sample during high-temperature aging were investigated in this study. Experimental results indicated that there was some interactions between the microstructure on both side of the solder joints. Au layer on Cu/Ni/Au substrate was melted into the bulk solder during the reflow which depressed the growth of Au-Sn intermetallic compounds during aging. Meanwhile, the fast growth of Au-Sn layer on the chip side decreased the relative concentration of Sn in the bulk solder. Consequently, the relative concentration of other elements, including the elements having positive effect for the IMC growth on the substrate, was increased.Compared with the two kinds of sample, the samples on Cu/Ag substrates show poorer thermal aging resistance.
2016, 37(3): 97-100.
Abstract：
Due to the fact that the parameter variety adaptability to MIG welding process was not sufficient in conventional digital PI control, an algorithm of adaptive control of on-line integral parameters was proposed. The control algorithm could obtain optimized integral parameters quickly and automatically by real-time detecting control quantity. Based on the control algorithmand the inherent minimum times of the rising edge and falling edge of the welding current, integral parameters can be divided into rising edge parameter and falling edge parameter. The adaptive controller for integral parameter was designed and implemented inside the welding equipment. The result indicated that using this algorithm and controller different initial values of integral parameters could be quickly searched for the adaptive value and a stable welding process can be achieved.
Due to the fact that the parameter variety adaptability to MIG welding process was not sufficient in conventional digital PI control, an algorithm of adaptive control of on-line integral parameters was proposed. The control algorithm could obtain optimized integral parameters quickly and automatically by real-time detecting control quantity. Based on the control algorithmand the inherent minimum times of the rising edge and falling edge of the welding current, integral parameters can be divided into rising edge parameter and falling edge parameter. The adaptive controller for integral parameter was designed and implemented inside the welding equipment. The result indicated that using this algorithm and controller different initial values of integral parameters could be quickly searched for the adaptive value and a stable welding process can be achieved.
2016, 37(3): 101-105.
Abstract：
The influence of constraint on welding deformation of Aluminum-Li alloy 5A90 T joint welded by dual-beam laser was studied. The constraint studied in this paper included two categories, one was applied to stiffener, and the other was applied to base plate. In the case of stiffener, the constraint was applied to the top and lateral face. The stiffener was fixed on the base plate by tack welding before the continuous welding began. Two situations were compared, one is that the constraint applied on the top and the lateral face were unloaded after tack welding, and the other was not. In the case of base plate, constraint was applied by pressing block, which was pressed on the base plate from two sides of the stiffener. The influence of the distance between the stiffener and the pressing block on welding deformation was studied. The computational result was validated by experiments. The deformation of stiffener during welding and after welding when constraint was applied on it was smaller than that condition that constraint was not applied. The longitudinal constraint applied to the base plate influenced the amount and the direction of bending deformation, but had little influence on the angle deformation of the T-joint. The constraint applied to the base plate in y direction during welding contributed to the reducation of angle deformation. The computational results of deformation direction and amount of bending deformation were consistent with experimental results.
The influence of constraint on welding deformation of Aluminum-Li alloy 5A90 T joint welded by dual-beam laser was studied. The constraint studied in this paper included two categories, one was applied to stiffener, and the other was applied to base plate. In the case of stiffener, the constraint was applied to the top and lateral face. The stiffener was fixed on the base plate by tack welding before the continuous welding began. Two situations were compared, one is that the constraint applied on the top and the lateral face were unloaded after tack welding, and the other was not. In the case of base plate, constraint was applied by pressing block, which was pressed on the base plate from two sides of the stiffener. The influence of the distance between the stiffener and the pressing block on welding deformation was studied. The computational result was validated by experiments. The deformation of stiffener during welding and after welding when constraint was applied on it was smaller than that condition that constraint was not applied. The longitudinal constraint applied to the base plate influenced the amount and the direction of bending deformation, but had little influence on the angle deformation of the T-joint. The constraint applied to the base plate in y direction during welding contributed to the reducation of angle deformation. The computational results of deformation direction and amount of bending deformation were consistent with experimental results.
2016, 37(3): 106-110.
Abstract：
Transient liquid phase diffusion bonding of Ti3Al-based alloy to TiAl intermetallic was conducted and a newly designed Ti-Zr-Cu-Ni-Fe alloy was used as interlayer. The joint microstructure was examined using a scanning electron microscope (SEM) equipped with an electron probe micro-analyzer (EPMA), the phase constitution was identified using an X-ray diffraction (XRD) spectrometer detected on the fractured surface. The results show that the Ti3Al/TiAl joint mainly consists of Ti-rich phase, Ti2Al layer, α2-Ti3Al phase and residual Al dissolved interlayer alloy dissolved with Al. The dissolution and inter-diffusion between base metal and interlayer become stronger with the increase of the bonding temperature. And meantime the Ti2Al is thickened and the amount of residual interlayer at the central part of the joint is decreased. The shear test results indicate that in the range of 880~1010℃ the increase of bonding temperature is beneficial to the joint strength. The maximum shear strength of Ti3Al/TiAl joint reached 502 MPa at room temperature and the shear strength was maintained at 196 MPa in 500℃.
Transient liquid phase diffusion bonding of Ti3Al-based alloy to TiAl intermetallic was conducted and a newly designed Ti-Zr-Cu-Ni-Fe alloy was used as interlayer. The joint microstructure was examined using a scanning electron microscope (SEM) equipped with an electron probe micro-analyzer (EPMA), the phase constitution was identified using an X-ray diffraction (XRD) spectrometer detected on the fractured surface. The results show that the Ti3Al/TiAl joint mainly consists of Ti-rich phase, Ti2Al layer, α2-Ti3Al phase and residual Al dissolved interlayer alloy dissolved with Al. The dissolution and inter-diffusion between base metal and interlayer become stronger with the increase of the bonding temperature. And meantime the Ti2Al is thickened and the amount of residual interlayer at the central part of the joint is decreased. The shear test results indicate that in the range of 880~1010℃ the increase of bonding temperature is beneficial to the joint strength. The maximum shear strength of Ti3Al/TiAl joint reached 502 MPa at room temperature and the shear strength was maintained at 196 MPa in 500℃.
2016, 37(3): 111-114,119.
Abstract：
The low temperature fracture toughness of welding metal is different for offshore platform steel when welded in horizontal and vertical positions. Several tests indicate that the toughness values of vertical welding position specimens with high heat input were higher than those of horizontal welding position specimens with low heat input, which are the reverse results of general consensus. Two groups of tests welded by FCAW were conducted, one is in horizontal position and the other one is in vertical position. After the CTOD (Crack Tip Opening Displacement) values were obtained, the macrographs, fracture surface morphologyand microstructure were analyzed. The result showed that the toughness values of vertical welding position specimens were higher than those of horizontal welding position specimens because of columnar crystal structure and slag inclusion.
The low temperature fracture toughness of welding metal is different for offshore platform steel when welded in horizontal and vertical positions. Several tests indicate that the toughness values of vertical welding position specimens with high heat input were higher than those of horizontal welding position specimens with low heat input, which are the reverse results of general consensus. Two groups of tests welded by FCAW were conducted, one is in horizontal position and the other one is in vertical position. After the CTOD (Crack Tip Opening Displacement) values were obtained, the macrographs, fracture surface morphologyand microstructure were analyzed. The result showed that the toughness values of vertical welding position specimens were higher than those of horizontal welding position specimens because of columnar crystal structure and slag inclusion.
2016, 37(3): 115-119.
Abstract：
Several thin-walled parts made by 20 overlayers were produced on base plates with different thicknesses. Results show that all the width of the overlaying weld canbe stable of 7.30 mm. Moreover, the stable weld width is not affected by the thickness of the base-plate. It is suggested that the various height from the weld to the base-plate heat sink ultimately contribute to the unstable-width varying weld near the base-plate. To adjust the weld width to anunstable-width zone, three kinds of control strategies were conducted. By using the optimized control strategy, the variance can be limited in 0.24. According to the parameters control curve, the heat sink effects exhibit a concave distribution along the height direction. Moreover, the radius of curvature increases with the increase of the thickness of base-plate.
Several thin-walled parts made by 20 overlayers were produced on base plates with different thicknesses. Results show that all the width of the overlaying weld canbe stable of 7.30 mm. Moreover, the stable weld width is not affected by the thickness of the base-plate. It is suggested that the various height from the weld to the base-plate heat sink ultimately contribute to the unstable-width varying weld near the base-plate. To adjust the weld width to anunstable-width zone, three kinds of control strategies were conducted. By using the optimized control strategy, the variance can be limited in 0.24. According to the parameters control curve, the heat sink effects exhibit a concave distribution along the height direction. Moreover, the radius of curvature increases with the increase of the thickness of base-plate.
2016, 37(3): 120-124.
Abstract：
The Fe-Nb-C-B-Ni-WC(30%)iron-based tungsten carbide wear resistant hardfacing alloy was deposited on the Q235 byargontungsten-arcwelding (TIG) using flux-cored wire. The effect of niobium content on the dissolution of tungsten carbide in the alloy was studied by changing the niobium content from 1.0% to 3.8%. The results show that niobium content has a great influence on the degree of dissolution of tungsten carbide in the alloy. The primarily precipitated fine NbC particles around the tungsten carbide inhibit the dissolution of tungsten carbide. The amount of fine NbC determines the intensity of the inhibitory effect on the dissolution of tungsten carbide. The alloy with 2.5% niobium effectively inhibit the dissolution of tungsten carbide in the alloy, the original tungsten carbide particles were reserved more completely.
The Fe-Nb-C-B-Ni-WC(30%)iron-based tungsten carbide wear resistant hardfacing alloy was deposited on the Q235 byargontungsten-arcwelding (TIG) using flux-cored wire. The effect of niobium content on the dissolution of tungsten carbide in the alloy was studied by changing the niobium content from 1.0% to 3.8%. The results show that niobium content has a great influence on the degree of dissolution of tungsten carbide in the alloy. The primarily precipitated fine NbC particles around the tungsten carbide inhibit the dissolution of tungsten carbide. The amount of fine NbC determines the intensity of the inhibitory effect on the dissolution of tungsten carbide. The alloy with 2.5% niobium effectively inhibit the dissolution of tungsten carbide in the alloy, the original tungsten carbide particles were reserved more completely.
2016, 37(3): 125-128.
Abstract：
In order to investigate the arc characteristic of local dry underwater welding, various pressure of compressed air was inflated into a chamber to simulate the various water depths. The arc signals were acquired and analyzed in time and frequency domain, respectively. Results show that the metal transfer mode of iron powder low-hydrogen potassium electrode is large droplet short circuiting transfer. The increase of the pressure results in the increase of droplet size. The average short circuiting time was changed from 5-7 ms under atmospheric pressure to 8-10 ms under pressure condition. Under pressured condition, the electrode melting rate increases and meanwhile the stable working point of the arc voltage feedback control system moves upward leading to the increase of arc voltage. The frequency domain analysis shows that the main characteristic frequency is less than 10 Hz under atmospheric pressure, whereas large amounts of the characteristic spectrums with frequency of more than 10 Hz appeared under high pressure condition, indicating an instability of the welding process.
In order to investigate the arc characteristic of local dry underwater welding, various pressure of compressed air was inflated into a chamber to simulate the various water depths. The arc signals were acquired and analyzed in time and frequency domain, respectively. Results show that the metal transfer mode of iron powder low-hydrogen potassium electrode is large droplet short circuiting transfer. The increase of the pressure results in the increase of droplet size. The average short circuiting time was changed from 5-7 ms under atmospheric pressure to 8-10 ms under pressure condition. Under pressured condition, the electrode melting rate increases and meanwhile the stable working point of the arc voltage feedback control system moves upward leading to the increase of arc voltage. The frequency domain analysis shows that the main characteristic frequency is less than 10 Hz under atmospheric pressure, whereas large amounts of the characteristic spectrums with frequency of more than 10 Hz appeared under high pressure condition, indicating an instability of the welding process.
