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Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20230417003
Abstract:
The traditional contour offset path planning strategy for wire arc additive manufacturing (WAAM) of medium-sized complex parts has a high degree of geometric fidelity. However, continuous offsetting can easily lead to underfilled regions and defects. To address this, a precise defect identification method based on Boolean operations is proposed. The defect region is obtained by calculating the Boolean difference between the original and backtracked polygons. This region is reconstructed into skeleton-filled areas through filtering and merging. The optimal zigzag path planning for each area is determined using minimum bounding boxes. And the contour offset path is optimized through segmentation, classification, partitioning and reorganization, which retains the advantages of the traditional method and reduces the times of arc starting or extinguishing. A propeller part was faced on a robotic WAAM system to validate this method, and the resulting parts met dimensional requirements with no surface defects.
The traditional contour offset path planning strategy for wire arc additive manufacturing (WAAM) of medium-sized complex parts has a high degree of geometric fidelity. However, continuous offsetting can easily lead to underfilled regions and defects. To address this, a precise defect identification method based on Boolean operations is proposed. The defect region is obtained by calculating the Boolean difference between the original and backtracked polygons. This region is reconstructed into skeleton-filled areas through filtering and merging. The optimal zigzag path planning for each area is determined using minimum bounding boxes. And the contour offset path is optimized through segmentation, classification, partitioning and reorganization, which retains the advantages of the traditional method and reduces the times of arc starting or extinguishing. A propeller part was faced on a robotic WAAM system to validate this method, and the resulting parts met dimensional requirements with no surface defects.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20221114001
Abstract:
The fabrication of large-size aerospace structures by additive manufacturing methods is limited by the processing efficiency and the maximum machining size of equipment. The development of composite manufacturing technology combining additive manufacturing and welding is expected to solve this problem. Therefore, the laser welding test of additive and forged TC11 titanium alloy was carried out. The weldability of additive TC11 titanium alloy (TC11-AM) and the weldability of "TC11-AM/forged TC11 (TC11-R)" joint and TC11-R/TC11-R joint were studied. EBSD observation for the microstructure of welded joints, Vickers hardness and tensile tests were conducted, and the fracture surface of tensile specimens was observed. It is found that no obvious porosity was found in the weld zone of TC11-R/TC11-R joint, TC11-AM/TC11-R joint, and TC11-AM/TC11-AM joint. Due to the large temperature gradient and fast cooling rate of the molten pool, the weld microstructure was coarse columnar grain with α' martensite phase inside. The tensile strengths of the three joints mentioned above were about 1594MPa, 1575MPa and 1688MP, respectively. The cross sectional microhardness of TC11-R/TC11-R and TC11-AM/TC11-AM joints shows Gaussian distribution, and the variation range ΔHV of hardness values was about ± 31HV and ± 6HV, respectively. Due to the obvious difference in microstructure in different regions of the joint, the microhardness of TC11-AM/TC11-R joint showed a step-like distribution with higher hardness in TC11-AM side and lower hardness in TC11-R side, and the range of hardness ΔHV was about ± 21HV. By comparing the tensile strength and elongation of the joint, TC11-AM/TC11-R joint and TC11-AM/TC11-AM joint have good laser beam welding weldability.
The fabrication of large-size aerospace structures by additive manufacturing methods is limited by the processing efficiency and the maximum machining size of equipment. The development of composite manufacturing technology combining additive manufacturing and welding is expected to solve this problem. Therefore, the laser welding test of additive and forged TC11 titanium alloy was carried out. The weldability of additive TC11 titanium alloy (TC11-AM) and the weldability of "TC11-AM/forged TC11 (TC11-R)" joint and TC11-R/TC11-R joint were studied. EBSD observation for the microstructure of welded joints, Vickers hardness and tensile tests were conducted, and the fracture surface of tensile specimens was observed. It is found that no obvious porosity was found in the weld zone of TC11-R/TC11-R joint, TC11-AM/TC11-R joint, and TC11-AM/TC11-AM joint. Due to the large temperature gradient and fast cooling rate of the molten pool, the weld microstructure was coarse columnar grain with α' martensite phase inside. The tensile strengths of the three joints mentioned above were about 1594MPa, 1575MPa and 1688MP, respectively. The cross sectional microhardness of TC11-R/TC11-R and TC11-AM/TC11-AM joints shows Gaussian distribution, and the variation range ΔHV of hardness values was about ± 31HV and ± 6HV, respectively. Due to the obvious difference in microstructure in different regions of the joint, the microhardness of TC11-AM/TC11-R joint showed a step-like distribution with higher hardness in TC11-AM side and lower hardness in TC11-R side, and the range of hardness ΔHV was about ± 21HV. By comparing the tensile strength and elongation of the joint, TC11-AM/TC11-R joint and TC11-AM/TC11-AM joint have good laser beam welding weldability.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20230414001
Abstract:
With the more extensive and in-depth application of additive manufacturing in various fields, more and more additive manufacturing products need fast and non-destructive quality inspection. Porosity as an important index to determine the mechanical properties of additive manufacturing products, its detection is the most important. In this paper, the laser power and scanning speed are adjusted to change the volume energy density, and the AlSi10Mg specimens with different porosities are obtained. The ultrasonic transverse and longitudinal waves were used to test the specimens, and the corresponding sound velocity and attenuation coefficient were obtained. The results show that the transverse and longitudinal sound speeds are inversely proportional to the porosity size, and the attenuation coefficients are directly proportional to the porosity size. When using sound velocity to characterize the porosity, the absolute value of longitudinal sound velocity is more variable, so the accuracy is better. Because the shear modulus of longitudinal sound velocity changes more than that of transverse sound velocity, the linearity is 23% higher than that of transverse sound velocity. When the attenuation coefficient is used to characterize the porosity, the accuracy of transverse wave is better than that of longitudinal wave because transverse wave of the same frequency is shorter in wavelength, and is more sensitive to the direction of polarization, so the linearity is 13% higher than that of longitudinal wave.
With the more extensive and in-depth application of additive manufacturing in various fields, more and more additive manufacturing products need fast and non-destructive quality inspection. Porosity as an important index to determine the mechanical properties of additive manufacturing products, its detection is the most important. In this paper, the laser power and scanning speed are adjusted to change the volume energy density, and the AlSi10Mg specimens with different porosities are obtained. The ultrasonic transverse and longitudinal waves were used to test the specimens, and the corresponding sound velocity and attenuation coefficient were obtained. The results show that the transverse and longitudinal sound speeds are inversely proportional to the porosity size, and the attenuation coefficients are directly proportional to the porosity size. When using sound velocity to characterize the porosity, the absolute value of longitudinal sound velocity is more variable, so the accuracy is better. Because the shear modulus of longitudinal sound velocity changes more than that of transverse sound velocity, the linearity is 23% higher than that of transverse sound velocity. When the attenuation coefficient is used to characterize the porosity, the accuracy of transverse wave is better than that of longitudinal wave because transverse wave of the same frequency is shorter in wavelength, and is more sensitive to the direction of polarization, so the linearity is 13% higher than that of longitudinal wave.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220621001
Abstract:
In the actual production process, arc additive manufacturing technology for repairing failed molds can cause poor formation problems such as missing flesh, depressions, and overstacking at the edges, which can lead to inconsistent thicknesses and large fluctuations in the melt layer, causing large errors in the accuracy of the additively manufactured parts. In order to reduce these defects, a variable layer thickness layered slicing algorithm is proposed, which mainly includes model pre-processing, determination of welding parameters, correction of the actual slicing thickness of the model, and completion of the final additive manufacturing process. The algorithm achieves accurate grasp of the layer thickness variation of the formed part by adjusting the lap rate during the cladding process, which improves the forming accuracy and reduces the above-mentioned defects such as poor forming. Finally, the variable layer thickness layered slicing algorithm proposed in this article was used to process the pyramid structure model, and cladding experiments were conducted. The results showed that the theoretically calculated filling path can fully fill the current layered surface. The actual cladding height and plane size have a small difference from the theoretical calculation values, and the forming accuracy can meet the requirements when the heat accumulation is small
In the actual production process, arc additive manufacturing technology for repairing failed molds can cause poor formation problems such as missing flesh, depressions, and overstacking at the edges, which can lead to inconsistent thicknesses and large fluctuations in the melt layer, causing large errors in the accuracy of the additively manufactured parts. In order to reduce these defects, a variable layer thickness layered slicing algorithm is proposed, which mainly includes model pre-processing, determination of welding parameters, correction of the actual slicing thickness of the model, and completion of the final additive manufacturing process. The algorithm achieves accurate grasp of the layer thickness variation of the formed part by adjusting the lap rate during the cladding process, which improves the forming accuracy and reduces the above-mentioned defects such as poor forming. Finally, the variable layer thickness layered slicing algorithm proposed in this article was used to process the pyramid structure model, and cladding experiments were conducted. The results showed that the theoretically calculated filling path can fully fill the current layered surface. The actual cladding height and plane size have a small difference from the theoretical calculation values, and the forming accuracy can meet the requirements when the heat accumulation is small
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20221121002
Abstract:
In order to solve the problem of deposited metal collapse caused by heat accumulation effect during the continuous process of wire arc additive manufacturing, the water-cooling aluminum plate was used on the back of the substrate. The 4047 aluminum alloy straight wall parts were prepared by two different processes: intermittent forming with water-cooling and intermittent forming without water-cooling and continuous forming with water-cooling. The straight wall parts which intermittent forming without water-cooling was used for benchmark specimen. By comparing the thermal cycle curve, grain morphology, tensile strength, hardness and elongation ratio, the effects of water-cooling conditions on the macroscopic morphology, microstructure and mechanical properties of the additive components were analyzed. The results show that the water-cooling condition can effectively reduce the heat accumulation, and the side walls of the structure are flatter. The straight wall additive structure has the best forming performance under the condition of continuous forming with water-cooling. There is no collapse at both ends of the structure and the forming efficiency is the highest. The grains at the bottom of the additive structures are mainly equiaxed crystals, while the other parts are mainly columnar and dendritic crystals. The grain size of the structure is the largest under continuous forming with water-cooling and the smallest under intermittent forming with water-cooling. The mechanical properties of all structures are equivalent to that of ZL102. The structure prepared by the intermittent forming with water-cooling have the best mechanical properties.
In order to solve the problem of deposited metal collapse caused by heat accumulation effect during the continuous process of wire arc additive manufacturing, the water-cooling aluminum plate was used on the back of the substrate. The 4047 aluminum alloy straight wall parts were prepared by two different processes: intermittent forming with water-cooling and intermittent forming without water-cooling and continuous forming with water-cooling. The straight wall parts which intermittent forming without water-cooling was used for benchmark specimen. By comparing the thermal cycle curve, grain morphology, tensile strength, hardness and elongation ratio, the effects of water-cooling conditions on the macroscopic morphology, microstructure and mechanical properties of the additive components were analyzed. The results show that the water-cooling condition can effectively reduce the heat accumulation, and the side walls of the structure are flatter. The straight wall additive structure has the best forming performance under the condition of continuous forming with water-cooling. There is no collapse at both ends of the structure and the forming efficiency is the highest. The grains at the bottom of the additive structures are mainly equiaxed crystals, while the other parts are mainly columnar and dendritic crystals. The grain size of the structure is the largest under continuous forming with water-cooling and the smallest under intermittent forming with water-cooling. The mechanical properties of all structures are equivalent to that of ZL102. The structure prepared by the intermittent forming with water-cooling have the best mechanical properties.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220630001
Abstract:
In order to achieve flexible manufacturing of aluminum-steel composite structures, this study proposed a new method of "arc + friction stir " hybrid additive manufacturing, first using BC-MIG welding to deposit a thin transition layer of aluminum alloy on the surface of galvanized Q235 steel, and then friction stir additive manufacturing for 6061 aluminum alloy and Q235 steel with transition layer.During the arc deposition of the transition layer, the galvanized layer and the bypass arc promoted the wetting and spreading of droplets on the steel surface, resulting in a flat surface profile.The subsequent friction stir additive manufacturing process eliminated porosity and cracking defects in the transition layer, resulting in a well-formed and defect-free aluminum-steel composite structure.The effects of different wire compositions (Al-Si and Al-Mg) on the microstructure and corrosion resistance of Al-steel composite structures were investigated.The results showed that the wire composition did not affect the weld formation but affected the thickness of the Fe-Al intermetallic compounds layer at the interface.At the same time, the corrosion resistance of Al-steel structures filled with Al-Si wire was better than that of Al-Mg wire, which was influenced by the intermetallic compounds at the interface, and electrical coupling corrosion occurred between the intermetallic compounds and the substrate, preferentially corroding the aluminum substrate and reducing the corrosion resistance of Al-steel composite structures.
In order to achieve flexible manufacturing of aluminum-steel composite structures, this study proposed a new method of "arc + friction stir " hybrid additive manufacturing, first using BC-MIG welding to deposit a thin transition layer of aluminum alloy on the surface of galvanized Q235 steel, and then friction stir additive manufacturing for 6061 aluminum alloy and Q235 steel with transition layer.During the arc deposition of the transition layer, the galvanized layer and the bypass arc promoted the wetting and spreading of droplets on the steel surface, resulting in a flat surface profile.The subsequent friction stir additive manufacturing process eliminated porosity and cracking defects in the transition layer, resulting in a well-formed and defect-free aluminum-steel composite structure.The effects of different wire compositions (Al-Si and Al-Mg) on the microstructure and corrosion resistance of Al-steel composite structures were investigated.The results showed that the wire composition did not affect the weld formation but affected the thickness of the Fe-Al intermetallic compounds layer at the interface.At the same time, the corrosion resistance of Al-steel structures filled with Al-Si wire was better than that of Al-Mg wire, which was influenced by the intermetallic compounds at the interface, and electrical coupling corrosion occurred between the intermetallic compounds and the substrate, preferentially corroding the aluminum substrate and reducing the corrosion resistance of Al-steel composite structures.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20221214003
Abstract:
In order to investigate the influence of heat input on the microstructure and properties of arc additive manufactured super duplex stainless steel, a single-walled test was conducted using ER2594 super duplex stainless steel wire with a diameter of 1.2 mm on a substrate of low carbon low alloy Q345 steel, with different heat inputs during MIG arc additive manufacturing. The microstructure and mechanical properties were analyzed. The results showed that when the heat input increased from 435.6 J/mm to 517.3 J/mm, the austenite content increased from 31% to 43%. This increase in austenite content was attributed to the higher heat input and slower cooling rate. When the heat input further increased to 599.0 J/mm, the austenite content decreased from 43% to 41% due to the reduced nitrogen content. With increasing heat input (from 435.6 J/mm to 599.0 J/mm), the microhardness initially decreased and then increased. This is because microhardness is positively correlated with ferrite content. The sample with the intermediate heat input value (517.3 J/mm) exhibited slightly better tensile performance due to its higher austenite content.
In order to investigate the influence of heat input on the microstructure and properties of arc additive manufactured super duplex stainless steel, a single-walled test was conducted using ER2594 super duplex stainless steel wire with a diameter of 1.2 mm on a substrate of low carbon low alloy Q345 steel, with different heat inputs during MIG arc additive manufacturing. The microstructure and mechanical properties were analyzed. The results showed that when the heat input increased from 435.6 J/mm to 517.3 J/mm, the austenite content increased from 31% to 43%. This increase in austenite content was attributed to the higher heat input and slower cooling rate. When the heat input further increased to 599.0 J/mm, the austenite content decreased from 43% to 41% due to the reduced nitrogen content. With increasing heat input (from 435.6 J/mm to 599.0 J/mm), the microhardness initially decreased and then increased. This is because microhardness is positively correlated with ferrite content. The sample with the intermediate heat input value (517.3 J/mm) exhibited slightly better tensile performance due to its higher austenite content.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20230403001
Abstract:
In this paper, the large thickness surfacing test was carried out by GTAW process, the welding hot crack of Inconel 625 alloy was studied, and the cracking mechanism of ERNiCrMo-3 welding wire surfacing metal was explained. It was indicated that the fabricated Inconel 625 sample consists of cellular dendritic which grew epitaxially from the substrate. Laves(Ni,Fe,Cr)2(Nb,Ti,Mo) phase, MC-type carbide and acicular δ(Ni3Nb) phases were also observed in the microstructure of as-welded sample. There are local crystal cracks in the microstructure of large thickness surfacing metal. The cracks are located between primary dendrites along the direction of columnar crystals. There is a large amount of δ(Ni3Nb) phases, near the cracks and on the fracture surfaces. δ phases is related to the formation of cracks. There are two solidification modes for 625 alloy surfacing: (1) and (2). At the end of crystallization, mode (2) with L → γ + δ eutectic reaction has greater sensitivity to thermal cracking, resulting in cracking of Alloy 625.
In this paper, the large thickness surfacing test was carried out by GTAW process, the welding hot crack of Inconel 625 alloy was studied, and the cracking mechanism of ERNiCrMo-3 welding wire surfacing metal was explained. It was indicated that the fabricated Inconel 625 sample consists of cellular dendritic which grew epitaxially from the substrate. Laves(Ni,Fe,Cr)2(Nb,Ti,Mo) phase, MC-type carbide and acicular δ(Ni3Nb) phases were also observed in the microstructure of as-welded sample. There are local crystal cracks in the microstructure of large thickness surfacing metal. The cracks are located between primary dendrites along the direction of columnar crystals. There is a large amount of δ(Ni3Nb) phases, near the cracks and on the fracture surfaces. δ phases is related to the formation of cracks. There are two solidification modes for 625 alloy surfacing: (1) and (2). At the end of crystallization, mode (2) with L → γ + δ eutectic reaction has greater sensitivity to thermal cracking, resulting in cracking of Alloy 625.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20230205002
Abstract:
At present, the reliability prediction of solder joints is mostly based on the combination of finite element simulation and single precision surrogate model, which has some problems such as long simulation time, low efficiency and poor accuracy. Therefore, a reliability prediction method for BGA (ball grid array) solder joints based on multi-fidelity model is proposed. Firstly, the convergence of different meshing schemes was verified, and then the high and low precision sample points were designed respectively for finite element analysis (FEA). Secondly, the reliability of solder joints was predicted based on the Co-Kriging model based on multi fidelity FEA data. Finally, the prediction results were compared with the single precision surrogate model, and NSGA algorithm was used to optimize the model to obtain the corresponding process parameters. The results show that with less simulation cost, the prediction effect of multi-fidelity model is better. Under the same prediction accuracy, the number of high-precision sample points of the variable reliability model is only 1/4 of that of the single precision model. At the same time, compared with the neural network prediction model, it converges faster in the optimization process. This paper provides some reference for the research of reliability prediction of solder joint with multi-fidelity model.
At present, the reliability prediction of solder joints is mostly based on the combination of finite element simulation and single precision surrogate model, which has some problems such as long simulation time, low efficiency and poor accuracy. Therefore, a reliability prediction method for BGA (ball grid array) solder joints based on multi-fidelity model is proposed. Firstly, the convergence of different meshing schemes was verified, and then the high and low precision sample points were designed respectively for finite element analysis (FEA). Secondly, the reliability of solder joints was predicted based on the Co-Kriging model based on multi fidelity FEA data. Finally, the prediction results were compared with the single precision surrogate model, and NSGA algorithm was used to optimize the model to obtain the corresponding process parameters. The results show that with less simulation cost, the prediction effect of multi-fidelity model is better. Under the same prediction accuracy, the number of high-precision sample points of the variable reliability model is only 1/4 of that of the single precision model. At the same time, compared with the neural network prediction model, it converges faster in the optimization process. This paper provides some reference for the research of reliability prediction of solder joint with multi-fidelity model.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20230614003
Abstract:
The flow behavior of the molten pool plays a decisive role in the distribution of coating elements in the weld seam. By establishing a three-dimensional transient numerical model of the laser welding molten pool, the flow behavior of the molten pool in laser welding of 22MnB5 high-strength steel with Al-Si coating and its influence on the distribution of Al elements in the weld seam were analyzed. In the welding experiment, The reliability of the numerical model was verified based on the scanning data of the welding joint using an energy spectrometer. The flow behavior of the laser welding melt pool and the distribution of Al element in the weld seam were studied by combining simulation and experimental results. The results showed that, according to the different energy and power density thresholds of the laser welding line, the morphology of the melt pool presented three characteristics: keyhole free, partially penetrated keyhole, and fully penetrated keyhole, with significant differences in temperature field, flow field Flow rate and stability; The keyless molten pool has the best stability due to its uniform flow velocity distribution and less vortex generation; The Al element in the coating is prone to segregation in the upper and lower weld toe areas of the welded joint. Compared to the upper surface coating, the Al element segregation phenomenon is more obvious when the lower surface coating enters the molten pool. Therefore, the homogenization distribution of the Al element in the upper part is significantly better than that in the lower part.
The flow behavior of the molten pool plays a decisive role in the distribution of coating elements in the weld seam. By establishing a three-dimensional transient numerical model of the laser welding molten pool, the flow behavior of the molten pool in laser welding of 22MnB5 high-strength steel with Al-Si coating and its influence on the distribution of Al elements in the weld seam were analyzed. In the welding experiment, The reliability of the numerical model was verified based on the scanning data of the welding joint using an energy spectrometer. The flow behavior of the laser welding melt pool and the distribution of Al element in the weld seam were studied by combining simulation and experimental results. The results showed that, according to the different energy and power density thresholds of the laser welding line, the morphology of the melt pool presented three characteristics: keyhole free, partially penetrated keyhole, and fully penetrated keyhole, with significant differences in temperature field, flow field Flow rate and stability; The keyless molten pool has the best stability due to its uniform flow velocity distribution and less vortex generation; The Al element in the coating is prone to segregation in the upper and lower weld toe areas of the welded joint. Compared to the upper surface coating, the Al element segregation phenomenon is more obvious when the lower surface coating enters the molten pool. Therefore, the homogenization distribution of the Al element in the upper part is significantly better than that in the lower part.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20221221001
Abstract:
Simulation method of fatigue crack growth considering material discontinuity was developed based on Abaqus, Zencrack and relevant user subroutines to accurately describe the fatigue crack growth behavior in welded structures. For initial embedded cracks located in weld region of a welded plate, faitigue crack growth simulations with different matching strengths between weld and base metal were carried out, and the influence of different matching strengths on fatigue crack growth life and characteristic for the welded structure were invesgated. It is found that distinct differences of SIF calculation results are obtained once the crack propagate from weld to base metals. Also, the difference gradually increases with increasing the crack size. As the values of crack growth parameters in weld are increasing, the relative crack growth rate of the crack located in the base metal decreases gradually and the crack shape transits from round to flat. In contrast, the relative crack growth rate in the base metal increases gradually, and the crack shape transits from round to ellipse. The present simulation method can provide an effictive way to accurately predict crack evolution in multi-materials of welded structures.
Simulation method of fatigue crack growth considering material discontinuity was developed based on Abaqus, Zencrack and relevant user subroutines to accurately describe the fatigue crack growth behavior in welded structures. For initial embedded cracks located in weld region of a welded plate, faitigue crack growth simulations with different matching strengths between weld and base metal were carried out, and the influence of different matching strengths on fatigue crack growth life and characteristic for the welded structure were invesgated. It is found that distinct differences of SIF calculation results are obtained once the crack propagate from weld to base metals. Also, the difference gradually increases with increasing the crack size. As the values of crack growth parameters in weld are increasing, the relative crack growth rate of the crack located in the base metal decreases gradually and the crack shape transits from round to flat. In contrast, the relative crack growth rate in the base metal increases gradually, and the crack shape transits from round to ellipse. The present simulation method can provide an effictive way to accurately predict crack evolution in multi-materials of welded structures.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20221011001
Abstract:
Reduced activation ferritic/martensitic (RAFM) steel was fabricated by wire and arc additive manufacturing (WAAM) technology. The microstructural evolution was investigated by optical microscope, scanning electron microscope and transmission electron microscope and the mechanical properties were tested by a tensile tester to study the effect of the heat treatment process on the microstructure and mechanical properties of WAAMed RAFM steel. The results showed that the microstructure of as-built RAFM steel consisted of dual phases of ferrite + tempered martensite and the average grain size was about 1.5-1.85 μm. After heat treatment, the grain size of RAFM steel did not increase significantly, and high-density dislocations were retained in the microstructure. In addition, after heat treatment, a high number of TiO2 secondary phase nanoparticles precipitated in the matrix and were dispersed in the matrix, with a size of 5-10 nm. The ultimate tensile strength (UTS) of WAAMed RAFM steel was significantly improved after heat treatment while the elongation after fracture was slightly reduced. The UTS of heat treated RAFM steel at room temperature was 1100 MPa and can still reach about 250 MPa when tested at 650 ℃.
Reduced activation ferritic/martensitic (RAFM) steel was fabricated by wire and arc additive manufacturing (WAAM) technology. The microstructural evolution was investigated by optical microscope, scanning electron microscope and transmission electron microscope and the mechanical properties were tested by a tensile tester to study the effect of the heat treatment process on the microstructure and mechanical properties of WAAMed RAFM steel. The results showed that the microstructure of as-built RAFM steel consisted of dual phases of ferrite + tempered martensite and the average grain size was about 1.5-1.85 μm. After heat treatment, the grain size of RAFM steel did not increase significantly, and high-density dislocations were retained in the microstructure. In addition, after heat treatment, a high number of TiO2 secondary phase nanoparticles precipitated in the matrix and were dispersed in the matrix, with a size of 5-10 nm. The ultimate tensile strength (UTS) of WAAMed RAFM steel was significantly improved after heat treatment while the elongation after fracture was slightly reduced. The UTS of heat treated RAFM steel at room temperature was 1100 MPa and can still reach about 250 MPa when tested at 650 ℃.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20230407003
Abstract:
There is a certain correspondence between the frontal molten pool and the penetration state. However, due to the numerous potential weld pool features related to the penetration state, how to remove redundant features and establish a concise knowledge model that reflects the corresponding relationship between weld pool features and penetration state is of great significance for achieving online control of welding penetration. A rough-fuzzy control method for welding penetration state is proposed and verified in variable gap MAG welding experiments. To solve the minimal feature set of the melt pool that characterizes the penetration state, we provide two attribute reduction algorithms based on variable precision rough sets. A decision information system for penetration state is established through variable gap-current welding experiments, and two shape parameters are introduced to describe the degree of sharpness at the tail of the molten pool. The classification rules of penetration status are obtained using rough set knowledge reduction and rule extraction algorithms. We establish a fuzzy control model for the width coefficient of the molten pool tail, and use the minimization of fuzzy entropy to construct membership functions of the error domain. The proposed control model is validated through two sets of variable gap welding experiments, and the results show that under closed-loop control, the weld back width is uniform and consistent, which can meet the requirements of welding specifications.
There is a certain correspondence between the frontal molten pool and the penetration state. However, due to the numerous potential weld pool features related to the penetration state, how to remove redundant features and establish a concise knowledge model that reflects the corresponding relationship between weld pool features and penetration state is of great significance for achieving online control of welding penetration. A rough-fuzzy control method for welding penetration state is proposed and verified in variable gap MAG welding experiments. To solve the minimal feature set of the melt pool that characterizes the penetration state, we provide two attribute reduction algorithms based on variable precision rough sets. A decision information system for penetration state is established through variable gap-current welding experiments, and two shape parameters are introduced to describe the degree of sharpness at the tail of the molten pool. The classification rules of penetration status are obtained using rough set knowledge reduction and rule extraction algorithms. We establish a fuzzy control model for the width coefficient of the molten pool tail, and use the minimization of fuzzy entropy to construct membership functions of the error domain. The proposed control model is validated through two sets of variable gap welding experiments, and the results show that under closed-loop control, the weld back width is uniform and consistent, which can meet the requirements of welding specifications.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20221212003
Abstract:
In order to study the temperature variation of the laser welding process of carbon fiber reinforced composite and aluminum alloy, this paper took 6061 aluminum alloy and carbon fiber reinforced Nylon 66 composite (CF/PA66) as the research object, established the finite element model based on heat conduction, and used SYSWELD software to conduct numerical simulation of the laser welding process of the two materials. The accuracy of the model was verified by experiments. On this basis, the influence laws of laser power, welding speed, lap width, cooling conditions and tooling thermal conductivity on the joint temperature field were studied. It is found that the size of aluminum alloy molten pool and the melting zone of PA66 resin increase with the increase of laser power and decrease with the increase of cooling rate. Under the same process parameters, the material lap size has no effect on the maximum melting width of interfacial resin. The water cooling condition can significantly reduce the melting pool size and the melting capacity of PA66 resin. The reduction of melt pool size and melting amount of PA66 resin is more significant.
In order to study the temperature variation of the laser welding process of carbon fiber reinforced composite and aluminum alloy, this paper took 6061 aluminum alloy and carbon fiber reinforced Nylon 66 composite (CF/PA66) as the research object, established the finite element model based on heat conduction, and used SYSWELD software to conduct numerical simulation of the laser welding process of the two materials. The accuracy of the model was verified by experiments. On this basis, the influence laws of laser power, welding speed, lap width, cooling conditions and tooling thermal conductivity on the joint temperature field were studied. It is found that the size of aluminum alloy molten pool and the melting zone of PA66 resin increase with the increase of laser power and decrease with the increase of cooling rate. Under the same process parameters, the material lap size has no effect on the maximum melting width of interfacial resin. The water cooling condition can significantly reduce the melting pool size and the melting capacity of PA66 resin. The reduction of melt pool size and melting amount of PA66 resin is more significant.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20221220001
Abstract:
In this paper, the dynamic behaviors of molten pool in autogenous laser welding and laser welding with filler wire were analyzed by high-speed camera online monitoring system, and the appearance of weld was compared and analyzed.The dynamic behaviors of molten pool under the action of autogenous laser welding and laser welding with filler wire were further analyzed by numerical simulation.The results showed that the surface of the molten pool behind the keyhole wall in autogenous laser welding, the flow from the keyhole opening to the tail of the molten pool occured, and the metal bulge appeared behind the keyhole opening. The size of the metal bulge was large, and the weld formation in autogenous laser welding was poor, and there were pits on the surface.The surface melt of the molten pool behind the keyhole wall in laser welding with filler wire flowed from the keyhole opening to the tail of the molten pool. But under the surface of the molten pool there was a flow from the tail of the molten pool to the keyhole. Although welding spatter would also occur, the size of welding spatter was relatively small, and due to the filling effect of liquid metal, the weld surface was not easy to appear concave defects, and the weld was well formed. Compared with the autogenous laser welding, the fluctuation of melt flow velocity behind the keyhole wall increased significantly after the liquid droplet entered the molten pool.
In this paper, the dynamic behaviors of molten pool in autogenous laser welding and laser welding with filler wire were analyzed by high-speed camera online monitoring system, and the appearance of weld was compared and analyzed.The dynamic behaviors of molten pool under the action of autogenous laser welding and laser welding with filler wire were further analyzed by numerical simulation.The results showed that the surface of the molten pool behind the keyhole wall in autogenous laser welding, the flow from the keyhole opening to the tail of the molten pool occured, and the metal bulge appeared behind the keyhole opening. The size of the metal bulge was large, and the weld formation in autogenous laser welding was poor, and there were pits on the surface.The surface melt of the molten pool behind the keyhole wall in laser welding with filler wire flowed from the keyhole opening to the tail of the molten pool. But under the surface of the molten pool there was a flow from the tail of the molten pool to the keyhole. Although welding spatter would also occur, the size of welding spatter was relatively small, and due to the filling effect of liquid metal, the weld surface was not easy to appear concave defects, and the weld was well formed. Compared with the autogenous laser welding, the fluctuation of melt flow velocity behind the keyhole wall increased significantly after the liquid droplet entered the molten pool.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20221226003
Abstract:
Welding joints with partial thickened structures are usually adopted in the design of aluminum alloy profiles to offset the thinning of the joint caused by the downward pressure of the shoulder in friction stir welding. However, after welding of such aluminum profiles, it will take a lot of hours to manually polish the thickened structures. In order to reduce the amount of grinding, a new type of aluminum profile without thickened structure is designed in this paper, ensuring non-thinning-welding by changing the structure of shoulder. In-depth research is carried out from the perspective of weld forming quality, mechanical properties and organizational structure, and key process parameters such as welding downforce are determined. Finally, combined with the characteristics of extrusion tolerance and assembly tolerance in industrial production, the influence of joint misalignment on welding quality is studied, and a reasonable joint tolerance range is determined.
Welding joints with partial thickened structures are usually adopted in the design of aluminum alloy profiles to offset the thinning of the joint caused by the downward pressure of the shoulder in friction stir welding. However, after welding of such aluminum profiles, it will take a lot of hours to manually polish the thickened structures. In order to reduce the amount of grinding, a new type of aluminum profile without thickened structure is designed in this paper, ensuring non-thinning-welding by changing the structure of shoulder. In-depth research is carried out from the perspective of weld forming quality, mechanical properties and organizational structure, and key process parameters such as welding downforce are determined. Finally, combined with the characteristics of extrusion tolerance and assembly tolerance in industrial production, the influence of joint misalignment on welding quality is studied, and a reasonable joint tolerance range is determined.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20221202001
Abstract:
Process performance, microstructure and corrosion properties of friction stir welded (FSW) joints of Zr-Sn-Nb-Cr-Fe zirconium alloys were studied in the present paper. The results indicate that the recommended zirconium alloys FSW joints with good shape and no welding defects were obtained by W-25%Re stir tool under the conditions of 250 rpm rotational speed, 40 mm/min welding speed, 10 kn axial force and argon protection. In stir zone (SZ), the severe plastic deformation leads to dynamic recrystallization, diffusion of alloying element and grain refinement and grain size increases with the increase of rotational speed. As the same time, a large number of irregularly shaped second phase particles were precipitated at the grain boundaries. These FSW joints prepared by different welding parameters exhibited black, bright and dense oxide film after being corroded in neutral water at 360 ℃, 18.6 MPa for 72 hours. However, the corrosion resistance of FSW joints decreases with the increase of rotational speed.
Process performance, microstructure and corrosion properties of friction stir welded (FSW) joints of Zr-Sn-Nb-Cr-Fe zirconium alloys were studied in the present paper. The results indicate that the recommended zirconium alloys FSW joints with good shape and no welding defects were obtained by W-25%Re stir tool under the conditions of 250 rpm rotational speed, 40 mm/min welding speed, 10 kn axial force and argon protection. In stir zone (SZ), the severe plastic deformation leads to dynamic recrystallization, diffusion of alloying element and grain refinement and grain size increases with the increase of rotational speed. As the same time, a large number of irregularly shaped second phase particles were precipitated at the grain boundaries. These FSW joints prepared by different welding parameters exhibited black, bright and dense oxide film after being corroded in neutral water at 360 ℃, 18.6 MPa for 72 hours. However, the corrosion resistance of FSW joints decreases with the increase of rotational speed.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20230105001
Abstract:
In present study, the effects of the resistance-assisted heating process on the formability of 2519-T87 friction stir welded joints were investigated by experiments and numerical simulations. Based on the coupled Eulerian-Lagrangian (CEL) method, a three-dimensional thermal mechanical coupling model of friction stir welding with a resistance-assisted heating process was established. The temperature field and material flow behavior were analyzed, and the mechanism of eliminating tunnel hole defects during resistance-assisted heating friction stir welding process was discussed. The results show that the auxiliary heating process increases the welding peak temperature from 483 ℃ to 549 ℃, increases the residence time at high temperature above 350 ℃, and expands the high-temperature distribution area. This reduces the material deformation resistance, and enhances the fluidity of materials from the retreating side of the nugget zone to the advancing side, leading to more sufficient backfilling of materials, thus eliminating the tunnel hole defects in the joint.
In present study, the effects of the resistance-assisted heating process on the formability of 2519-T87 friction stir welded joints were investigated by experiments and numerical simulations. Based on the coupled Eulerian-Lagrangian (CEL) method, a three-dimensional thermal mechanical coupling model of friction stir welding with a resistance-assisted heating process was established. The temperature field and material flow behavior were analyzed, and the mechanism of eliminating tunnel hole defects during resistance-assisted heating friction stir welding process was discussed. The results show that the auxiliary heating process increases the welding peak temperature from 483 ℃ to 549 ℃, increases the residence time at high temperature above 350 ℃, and expands the high-temperature distribution area. This reduces the material deformation resistance, and enhances the fluidity of materials from the retreating side of the nugget zone to the advancing side, leading to more sufficient backfilling of materials, thus eliminating the tunnel hole defects in the joint.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20221214002
Abstract:
High speed force arc MIG welding of TC4 Ti to 5A06 Al was carried out using SAl5183 filler. The effect of welding heat input E on the joint microstructures and properties were analyzed by SEM、XRD and tensile test. The results showed that E has a significant influence on the microstructure and mechanical properties under the test process conditions: lack of fusion occurred at the root part with the E lower than 0.93 kJ/cm, a single TiAl3 layer with the thickness of less than 1 μm was formed at the Ti/Al interface. Burn through occurred with the E exceeded 1.20 kJ/cm, a TiAl3 + Ti3Al double-layered structure with the thickness of 2.5 ~ 6 μm was formed at the top and middle parts, while a single TiAl3 layer with the thickness of about 1 μm was formed at other parts. When E is in the range of 1.02 ~ 1.11 kJ/cm, the joint was well formed and a TiAl3 layer with the thickness of about 0.7 ~ 1.5 μm was formed at the Ti/Al interface. In the selected processing range, the average tensile strength of the joint increases gradually with the increase of E, the ultimate tensile strength for the joints absent of forming defects can reach 232 MPa.
High speed force arc MIG welding of TC4 Ti to 5A06 Al was carried out using SAl5183 filler. The effect of welding heat input E on the joint microstructures and properties were analyzed by SEM、XRD and tensile test. The results showed that E has a significant influence on the microstructure and mechanical properties under the test process conditions: lack of fusion occurred at the root part with the E lower than 0.93 kJ/cm, a single TiAl3 layer with the thickness of less than 1 μm was formed at the Ti/Al interface. Burn through occurred with the E exceeded 1.20 kJ/cm, a TiAl3 + Ti3Al double-layered structure with the thickness of 2.5 ~ 6 μm was formed at the top and middle parts, while a single TiAl3 layer with the thickness of about 1 μm was formed at other parts. When E is in the range of 1.02 ~ 1.11 kJ/cm, the joint was well formed and a TiAl3 layer with the thickness of about 0.7 ~ 1.5 μm was formed at the Ti/Al interface. In the selected processing range, the average tensile strength of the joint increases gradually with the increase of E, the ultimate tensile strength for the joints absent of forming defects can reach 232 MPa.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20221025002
Abstract:
Nickel/tungsten carbide composite coating has high wear resistance, corrosion resistance, and high hardness characteristics, it is widely used in shield machine parts, rotary blade and other fields. In order to improve the service life of the hydraulic machinery overflow components, the nickel/tungsten carbide composite brazing coating was successfully prepared on the surface of austenitic stainless steel by thermal radiation brazing coating method in vacuum furnace using WC particles and nickel-based powder brazing alloys as coating materials. The microstructure and interfacial behavior of the brazing coating are analyzed with the aid of scanning electron microscopy, X-ray diffractometer, and metallographic microscopy. The result show that the interface bonding of WC hard-phase and nickel-based brazing alloy have mechanical occlusion and metallurgical bonding.There is a certain degree of component diffusion between the brazing coating and the steel substrate, and its narrower diffusion area is about 100 μm. When the WC content is lower than 25wt.%, the brazing coating has better wettability on the steel substrate, the internal denseness of the coating is good. Meanwhile, the composite coating with a minimum porosity of 1.08% is prepared.
Nickel/tungsten carbide composite coating has high wear resistance, corrosion resistance, and high hardness characteristics, it is widely used in shield machine parts, rotary blade and other fields. In order to improve the service life of the hydraulic machinery overflow components, the nickel/tungsten carbide composite brazing coating was successfully prepared on the surface of austenitic stainless steel by thermal radiation brazing coating method in vacuum furnace using WC particles and nickel-based powder brazing alloys as coating materials. The microstructure and interfacial behavior of the brazing coating are analyzed with the aid of scanning electron microscopy, X-ray diffractometer, and metallographic microscopy. The result show that the interface bonding of WC hard-phase and nickel-based brazing alloy have mechanical occlusion and metallurgical bonding.There is a certain degree of component diffusion between the brazing coating and the steel substrate, and its narrower diffusion area is about 100 μm. When the WC content is lower than 25wt.%, the brazing coating has better wettability on the steel substrate, the internal denseness of the coating is good. Meanwhile, the composite coating with a minimum porosity of 1.08% is prepared.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20230117001
Abstract:
Laser welding provides an effective technical method for power battery aluminum alloy sheet welding, but the traditional laser welding process is easy to produce spatter, porosity and other defects under the requirement of high welding speed, which will affect the service performance of component. In this paper, the regulation and control of laser lap welding of aluminum alloy sheet with adjustable ring spot are studied, and the influence law of center-ring laser power on weld forming was expounded. On this basis, the high-speed stable welding process window with no spatter, little porosity and large lap surface width was identified. In the range of the process window, the multi-objective optimization of process parameters was further carried out by taking small penetration fluctuation and large bonding width as targets. It has been proved that the welding speed is above 70mm/s, the welding width of the lap surface is increased by 8.89%, the fluctuation of the welding depth is less than 10%, there is no obvious forming defect, and the forming quality of the weld is further improved.
Laser welding provides an effective technical method for power battery aluminum alloy sheet welding, but the traditional laser welding process is easy to produce spatter, porosity and other defects under the requirement of high welding speed, which will affect the service performance of component. In this paper, the regulation and control of laser lap welding of aluminum alloy sheet with adjustable ring spot are studied, and the influence law of center-ring laser power on weld forming was expounded. On this basis, the high-speed stable welding process window with no spatter, little porosity and large lap surface width was identified. In the range of the process window, the multi-objective optimization of process parameters was further carried out by taking small penetration fluctuation and large bonding width as targets. It has been proved that the welding speed is above 70mm/s, the welding width of the lap surface is increased by 8.89%, the fluctuation of the welding depth is less than 10%, there is no obvious forming defect, and the forming quality of the weld is further improved.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20221208001
Abstract:
The Ni-Cr-Mo-B interlayer was used to perform transient liquid phase diffusion bonding of FGH98 superalloy. The effect of bonding time on the microstructure, mechanical properties and fracture behavior of the joint was investigated. The results indicated that the eutectic phases in the athermal solidification zone (ASZ) were Ni-rich borides and γ-Ni solid solution. The isothermal solidification zone (ISZ) was mainly composed of γ-Ni solid solution, and the diffusion affected zone (DAZ) contained boride with a variety of morphologies. With the increase of bonding time, the eutectic phase in ASZ gradually decreased and disappeared, the width of DAZ increased and the shear strength of the joint also gradually increased. Increasing the bonding time, the diffusion distance of boron element increased, resulting in a decrease in the density of boride precipitates in DAZ. When the joint was held for 120 min, it achieved complete isothermal solidification, reaching a shear strength of 724 MPa. The joint fracture occurred in DAZ, exhibiting a ductile fracture mode.
The Ni-Cr-Mo-B interlayer was used to perform transient liquid phase diffusion bonding of FGH98 superalloy. The effect of bonding time on the microstructure, mechanical properties and fracture behavior of the joint was investigated. The results indicated that the eutectic phases in the athermal solidification zone (ASZ) were Ni-rich borides and γ-Ni solid solution. The isothermal solidification zone (ISZ) was mainly composed of γ-Ni solid solution, and the diffusion affected zone (DAZ) contained boride with a variety of morphologies. With the increase of bonding time, the eutectic phase in ASZ gradually decreased and disappeared, the width of DAZ increased and the shear strength of the joint also gradually increased. Increasing the bonding time, the diffusion distance of boron element increased, resulting in a decrease in the density of boride precipitates in DAZ. When the joint was held for 120 min, it achieved complete isothermal solidification, reaching a shear strength of 724 MPa. The joint fracture occurred in DAZ, exhibiting a ductile fracture mode.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20230131001
Abstract:
The stability of droplet transfer is crucial for the quality of high current MAG welding. A high-speed camera system and electrical signal acquisition system were used to study the unstable droplet transfer process, arc morphology, and electrical signal of high current MAG. The formation mechanism of unstable droplet transfer was revealed, and the factors affecting the critical current value of unstable droplet transfer in high current MAG were analyzed. The results showed that the droplet transfer in high current MAG welding is an unstable transition mode consisting of swing and mixed transfer. The instability of the liquid cone due to strong electromagnetic force and deviation from the welding wire axis are the direct reasons. The arc rotation/swing frequency varies with the droplet transfer mode and arc shape. Dry elongation is the main factor affecting the critical current value of unstable droplet transfer, and the critical current value significantly decreases with the increase of dry elongation.
The stability of droplet transfer is crucial for the quality of high current MAG welding. A high-speed camera system and electrical signal acquisition system were used to study the unstable droplet transfer process, arc morphology, and electrical signal of high current MAG. The formation mechanism of unstable droplet transfer was revealed, and the factors affecting the critical current value of unstable droplet transfer in high current MAG were analyzed. The results showed that the droplet transfer in high current MAG welding is an unstable transition mode consisting of swing and mixed transfer. The instability of the liquid cone due to strong electromagnetic force and deviation from the welding wire axis are the direct reasons. The arc rotation/swing frequency varies with the droplet transfer mode and arc shape. Dry elongation is the main factor affecting the critical current value of unstable droplet transfer, and the critical current value significantly decreases with the increase of dry elongation.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20221211001
Abstract:
In the VPPA ( variable polarity plasma arc ) -MIG hybrid welding of aluminum alloy, when the welding current of VPPA is 130 A and the MIG welding current is 200 A, the MIG arc plasma is biased towards and connected with the VPPA plasma in the positive ( tungsten electrode is negative ) stage during the current base period, and does not connect with the VPPA plasma in the reverse polarity stage ( tungsten electrode is positive ), and the MIG arc voltage in the base stage is lower when the VPPA is positive. In order to clarify the above behavior mechanism, the hybrid arc was diagnosed by spectroscopy. Based on the Boltzmann diagram method and Stark broadening method, the average temperature and electron density of the VPPA-MIG hybrid arc at 2.5 mm above the test plate, the VPPA region, the coupling region, and the center of the MIG region are calculated. It is proved that the average state of the plasma at the above position is in a local thermodynamic equilibrium state. Based on the relationship between the emission coefficient and the plasma temperature, it is found that the high-temperature area of VPPA during the negative polarity period is larger than that during the positive polarity period by using Ar 794.8 nm narrow-band filtering combined with a high-speed camera. Moreover, the Al 396.1 nm spectral line in VPPA has higher radiation intensity and wider range during the reverse polarity period. It is proved that the decrease of MIG arc voltage in the base stage of hybrid welding mainly comes from cathode voltage drop rather than arc column voltage drop.
In the VPPA ( variable polarity plasma arc ) -MIG hybrid welding of aluminum alloy, when the welding current of VPPA is 130 A and the MIG welding current is 200 A, the MIG arc plasma is biased towards and connected with the VPPA plasma in the positive ( tungsten electrode is negative ) stage during the current base period, and does not connect with the VPPA plasma in the reverse polarity stage ( tungsten electrode is positive ), and the MIG arc voltage in the base stage is lower when the VPPA is positive. In order to clarify the above behavior mechanism, the hybrid arc was diagnosed by spectroscopy. Based on the Boltzmann diagram method and Stark broadening method, the average temperature and electron density of the VPPA-MIG hybrid arc at 2.5 mm above the test plate, the VPPA region, the coupling region, and the center of the MIG region are calculated. It is proved that the average state of the plasma at the above position is in a local thermodynamic equilibrium state. Based on the relationship between the emission coefficient and the plasma temperature, it is found that the high-temperature area of VPPA during the negative polarity period is larger than that during the positive polarity period by using Ar 794.8 nm narrow-band filtering combined with a high-speed camera. Moreover, the Al 396.1 nm spectral line in VPPA has higher radiation intensity and wider range during the reverse polarity period. It is proved that the decrease of MIG arc voltage in the base stage of hybrid welding mainly comes from cathode voltage drop rather than arc column voltage drop.
Investigation on fatigue life prediction approach of welded joints via integrated data-driven method
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20221116002
Abstract:
In this study, a novel intelligent fatigue life prediction approach was established via the integrated data-driven method (Borderline-Synthetic Minority Over-Sampling Technique, eXtreme Gradient Boosting, Deep Convolutional Neural Network). Among them, the Borderline-Synthetic Minority Over-Sampling Technique was used to enhance the data quality of the fatigue performance dataset, the eXtreme Gradient Boosting was used to realize the weight analysis of the influencing factors of fatigue life, and the Deep Convolutional Neural Network was used as the model framework to understand the multiple nonlinear relationships between fatigue life and its influencing factors. Based on the analysis of different technology combinations, it was found that weight analysis and data augmentation were both beneficial for improving prediction accuracy, with the former having better results than the latter. And by comparing with other novel prediction models, the accuracy and stability of the proposed method were verified.
In this study, a novel intelligent fatigue life prediction approach was established via the integrated data-driven method (Borderline-Synthetic Minority Over-Sampling Technique, eXtreme Gradient Boosting, Deep Convolutional Neural Network). Among them, the Borderline-Synthetic Minority Over-Sampling Technique was used to enhance the data quality of the fatigue performance dataset, the eXtreme Gradient Boosting was used to realize the weight analysis of the influencing factors of fatigue life, and the Deep Convolutional Neural Network was used as the model framework to understand the multiple nonlinear relationships between fatigue life and its influencing factors. Based on the analysis of different technology combinations, it was found that weight analysis and data augmentation were both beneficial for improving prediction accuracy, with the former having better results than the latter. And by comparing with other novel prediction models, the accuracy and stability of the proposed method were verified.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20221220003
Abstract:
At present, the traditional film photography is used to detect the welding seam of the bottom, barrel and ring parts of the launch vehicle, which has the disadvantages of low automation, complicated process and low digitization, and the negative film can't be preserved for a long time, so it can't meet the fast-paced development requirements of the current multi-type rockets. A robot-based multi-degree-of-freedom digital radiographic inspection system was developed by using the nondestructive inspection method combining X-ray and imaging board, using double seven-axis robot and synchronous lifting turntable as motion actuators, and using ADS multi-thread communication and Ethercat bus to realize the real-time communication among the controller, imaging inspection software, X-ray machine, robot and synchronous lifting turntable. Through the path planning of the motion actuator and the nondestructive inspection of weld seam imaging, the inspection automation of circumferential seam, longitudinal seam and variable curvature weld seam of products is realized. Compared with the traditional film photography, the inspection efficiency is increased by 5 times and the inspection accuracy is increased by 42%, which meets the current inspection work of multi-type rocket tanks.
At present, the traditional film photography is used to detect the welding seam of the bottom, barrel and ring parts of the launch vehicle, which has the disadvantages of low automation, complicated process and low digitization, and the negative film can't be preserved for a long time, so it can't meet the fast-paced development requirements of the current multi-type rockets. A robot-based multi-degree-of-freedom digital radiographic inspection system was developed by using the nondestructive inspection method combining X-ray and imaging board, using double seven-axis robot and synchronous lifting turntable as motion actuators, and using ADS multi-thread communication and Ethercat bus to realize the real-time communication among the controller, imaging inspection software, X-ray machine, robot and synchronous lifting turntable. Through the path planning of the motion actuator and the nondestructive inspection of weld seam imaging, the inspection automation of circumferential seam, longitudinal seam and variable curvature weld seam of products is realized. Compared with the traditional film photography, the inspection efficiency is increased by 5 times and the inspection accuracy is increased by 42%, which meets the current inspection work of multi-type rocket tanks.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20221212001
Abstract:
When conducting narrow gap all position welding of pipelines, welding defects are easy to occur near the overhead welding position, which restricts the quality and efficiency of pipeline construction. Aiming at the problem of poor formation and low reliability of overhead welding position in automatic pipe welding, this paper studies the influence of wire feeding speed, arc length correction, contact nozzle distance to molten pool and other factors on droplet transfer in P-GMAW process. It is found that increasing the arc length correction coefficient can increase the heat input of the arc to the side wall, which can alleviate the problem of poor side wall fusion, but will make the droplet transfer path difficult to control, Therefore, when the welding gun moves to the overhead welding position, short arc welding shall be adopted and the heat input to the side wall shall be supplemented by increasing the side stop time and swing; Increasing the wire feeding speed is conducive to obtaining smaller droplets, higher transfer frequency, reducing the distance between the contact tip and the molten pool, increasing the electromagnetic force and reducing the droplet size, which is more conducive to the transfer of droplets to the molten pool in overhead welding position. The research results have certain guiding significance for the process design of pipe narrow gap welding.
When conducting narrow gap all position welding of pipelines, welding defects are easy to occur near the overhead welding position, which restricts the quality and efficiency of pipeline construction. Aiming at the problem of poor formation and low reliability of overhead welding position in automatic pipe welding, this paper studies the influence of wire feeding speed, arc length correction, contact nozzle distance to molten pool and other factors on droplet transfer in P-GMAW process. It is found that increasing the arc length correction coefficient can increase the heat input of the arc to the side wall, which can alleviate the problem of poor side wall fusion, but will make the droplet transfer path difficult to control, Therefore, when the welding gun moves to the overhead welding position, short arc welding shall be adopted and the heat input to the side wall shall be supplemented by increasing the side stop time and swing; Increasing the wire feeding speed is conducive to obtaining smaller droplets, higher transfer frequency, reducing the distance between the contact tip and the molten pool, increasing the electromagnetic force and reducing the droplet size, which is more conducive to the transfer of droplets to the molten pool in overhead welding position. The research results have certain guiding significance for the process design of pipe narrow gap welding.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20230307001
Abstract:
Ti6Al4V/NiTi bionic function graded materials (BFGM) with dense and defect-free organization were prepared by laser additive manufacturing technology, and their interfacial microstructure, precipitation phase characteristics and mechanical properties were investigated. The results show that the Ti6Al4V/NiTi BFGM exhibits a non-uniform organization consisting of various grain morphologies and irregular and abnormal eutectic tissues, which are mainly titanium-rich and nickel-rich solid solutions and (Ti, Ni) compounds. As the content of NiTi alloy increases, the number and morphology of precipitated phases in the different deposition layers change significantly. The microstructure of BFGM undergoes a series of transformations: α + β biphasic organization → columnar crystals + irregular eutectic structure → columnar crystals → equiaxial crystals → equiaxial crystals + columnar crystals. Phase aggregation, segregation and segregation during solidification seriously affect the mechanical properties of BFGM, and the maximum microhardness of BFGM is 730.9 HV, which is attributed to the presence of brittle Ti2Ni phase. The tensile strength was 202 MPa and the elongation at break was 6.71%, which was significantly higher than that of the directly connected Ti6Al4V/NiTi heterogeneous material. The tensile fracture is characterized by brittle fracture with multiple secondary cracks extending along the crystal.
Ti6Al4V/NiTi bionic function graded materials (BFGM) with dense and defect-free organization were prepared by laser additive manufacturing technology, and their interfacial microstructure, precipitation phase characteristics and mechanical properties were investigated. The results show that the Ti6Al4V/NiTi BFGM exhibits a non-uniform organization consisting of various grain morphologies and irregular and abnormal eutectic tissues, which are mainly titanium-rich and nickel-rich solid solutions and (Ti, Ni) compounds. As the content of NiTi alloy increases, the number and morphology of precipitated phases in the different deposition layers change significantly. The microstructure of BFGM undergoes a series of transformations: α + β biphasic organization → columnar crystals + irregular eutectic structure → columnar crystals → equiaxial crystals → equiaxial crystals + columnar crystals. Phase aggregation, segregation and segregation during solidification seriously affect the mechanical properties of BFGM, and the maximum microhardness of BFGM is 730.9 HV, which is attributed to the presence of brittle Ti2Ni phase. The tensile strength was 202 MPa and the elongation at break was 6.71%, which was significantly higher than that of the directly connected Ti6Al4V/NiTi heterogeneous material. The tensile fracture is characterized by brittle fracture with multiple secondary cracks extending along the crystal.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20230304003
Abstract:
The finite element analysis method was used to numerically simulate the process of additive manufacturing of 2219 aluminum alloy by arc under additional ultrasonic impact, and the change of stress field and deformation was studied. The results show that the additional ultrasonic shock can reduce the stress concentration at the edge of the sediment and the area close to the sediment in the substrate during the multi-layer multi-channel deposition. Additional ultrasonic impact during multi-layer multi-channel deposition can effectively reduce the stress inside the sediment. After the additional ultrasonic impact, the stress range at the interchannel junction decreased from 156.1 ~ 211.6 MPa to 138.8 ~ 181.9 MPa, and the average residual stress on the surface decreased by 22.3%. Under the additional ultrasonic impact, the maximum deformation of multi-layer multi-channel arc additive components decreased from 0.61 mm to 0.53 mm, and the average deformation decreased from 0.33 mm to 0.27 mm. The stress distribution law of the upper surface of the multi-layer multi-channel sediment calculated by the finite element is similar to that measured in the actual experiment, which proves that the simulation results are reliable.
The finite element analysis method was used to numerically simulate the process of additive manufacturing of 2219 aluminum alloy by arc under additional ultrasonic impact, and the change of stress field and deformation was studied. The results show that the additional ultrasonic shock can reduce the stress concentration at the edge of the sediment and the area close to the sediment in the substrate during the multi-layer multi-channel deposition. Additional ultrasonic impact during multi-layer multi-channel deposition can effectively reduce the stress inside the sediment. After the additional ultrasonic impact, the stress range at the interchannel junction decreased from 156.1 ~ 211.6 MPa to 138.8 ~ 181.9 MPa, and the average residual stress on the surface decreased by 22.3%. Under the additional ultrasonic impact, the maximum deformation of multi-layer multi-channel arc additive components decreased from 0.61 mm to 0.53 mm, and the average deformation decreased from 0.33 mm to 0.27 mm. The stress distribution law of the upper surface of the multi-layer multi-channel sediment calculated by the finite element is similar to that measured in the actual experiment, which proves that the simulation results are reliable.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20230308002
Abstract:
Solid-state cold spray additive manufacturing (CSAM) technology has gradually become a research hotspot in many countries because of its advantages such as high deposition efficiency, fast deposition speed and very low thermal effect. However, due to the significant difference of its deposition principle with the traditionally well-developed laser additive manufacturing technology, the profile control of the deposit has become a difficulty in limiting its application. Based on the effect of cold spray conditions on deposit profile, numerical simulation methods have been used to predict and control the deposit morphology. In this paper, therefore, various effective simulation methods of profile prediction and control were elaborated in detail. Finally, the advantages and disadvantages of each method were summarized, and existing difficulties as well as future development directions of CSAM deposit simulation were prospected.
Solid-state cold spray additive manufacturing (CSAM) technology has gradually become a research hotspot in many countries because of its advantages such as high deposition efficiency, fast deposition speed and very low thermal effect. However, due to the significant difference of its deposition principle with the traditionally well-developed laser additive manufacturing technology, the profile control of the deposit has become a difficulty in limiting its application. Based on the effect of cold spray conditions on deposit profile, numerical simulation methods have been used to predict and control the deposit morphology. In this paper, therefore, various effective simulation methods of profile prediction and control were elaborated in detail. Finally, the advantages and disadvantages of each method were summarized, and existing difficulties as well as future development directions of CSAM deposit simulation were prospected.
Accepted Manuscript
, Available online
Abstract:
Using plasma arc as heat source, the additive fabrication of titanium alloy fuses layer by layer was carried out by AC assisted method. The influence of AC value on the microstructure and properties of the additive was studied. The influence of the auxiliary AC value on the droplet size and droplet transition was observed by high-speed photography, the roughness of the stack morphology was measured, the structure and microhardness of the stack were observed, and the influence of the auxiliary AC value on the compression performance of the stack was analyzed. The results show that a more obvious AC arc will be formed and the plasma arc will swing, which will oscillate the molten pool. The surface roughness and grain size of the additive are improved, and the grain size decreases with the increase of the applied auxiliary AC. When no AC is added to the AC value of 30A, the grain size is reduced by 26.4%. At the same time, the addition of auxiliary AC can significantly improve the hardness and plasticity of the additive. When the external auxiliary AC is 30A, the hardness is 454.15HV, and the compression strain is 0.28%. Without AC, the hardness is 406.45HV and the compressive strain is 0.11%, which is increased by 2.5 times.
Using plasma arc as heat source, the additive fabrication of titanium alloy fuses layer by layer was carried out by AC assisted method. The influence of AC value on the microstructure and properties of the additive was studied. The influence of the auxiliary AC value on the droplet size and droplet transition was observed by high-speed photography, the roughness of the stack morphology was measured, the structure and microhardness of the stack were observed, and the influence of the auxiliary AC value on the compression performance of the stack was analyzed. The results show that a more obvious AC arc will be formed and the plasma arc will swing, which will oscillate the molten pool. The surface roughness and grain size of the additive are improved, and the grain size decreases with the increase of the applied auxiliary AC. When no AC is added to the AC value of 30A, the grain size is reduced by 26.4%. At the same time, the addition of auxiliary AC can significantly improve the hardness and plasticity of the additive. When the external auxiliary AC is 30A, the hardness is 454.15HV, and the compression strain is 0.28%. Without AC, the hardness is 406.45HV and the compressive strain is 0.11%, which is increased by 2.5 times.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20221001001
Abstract:
In order to obtain the best performance of welded joints, dissimilar aluminum alloys of 2219-T87 and 5A06-H112 with a thickness of 5.5 mm was joined by pulsed VP-TIG butt welding. The L27(39) type orthogonal table with five process parameters and three levels were designed, and the interaction between three factors was considered at the same time. The influence of each factor on the tensile strength of the joints was analyzed, and the results show that the influence of the process parameters on the joint performance is in the order: welding speed > groove angle > peak current > pulse frequency > wire feeding speed. Through orthogonal optimization, an ideal defect-free welded joint was obtained. The mechanical properties, microstructure and corrosion properties of the optimized welded joint were tested. The results show that the fracture edge of the joint was near the fusion line on the 2219 side, where the strain was the largest and the hardness was the lowest. The corrosion resistance of the 2219 side fusion line and the weld area is the worst, and it is the location where pitting corrosion occurs preferentially.
In order to obtain the best performance of welded joints, dissimilar aluminum alloys of 2219-T87 and 5A06-H112 with a thickness of 5.5 mm was joined by pulsed VP-TIG butt welding. The L27(39) type orthogonal table with five process parameters and three levels were designed, and the interaction between three factors was considered at the same time. The influence of each factor on the tensile strength of the joints was analyzed, and the results show that the influence of the process parameters on the joint performance is in the order: welding speed > groove angle > peak current > pulse frequency > wire feeding speed. Through orthogonal optimization, an ideal defect-free welded joint was obtained. The mechanical properties, microstructure and corrosion properties of the optimized welded joint were tested. The results show that the fracture edge of the joint was near the fusion line on the 2219 side, where the strain was the largest and the hardness was the lowest. The corrosion resistance of the 2219 side fusion line and the weld area is the worst, and it is the location where pitting corrosion occurs preferentially.
Accepted Manuscript
, Available online ,
doi: 10.12073/j.hjxb.20220829001
Abstract:
Spot welding is one of the main connection methods of automobile parts, and the tensile and Shear strength of its joints are important factors to evaluate the connection quality. On the basis of preparing a large number of spot welding samples, this investigation conducted ultrasonic signal detection on the joints of each sample. Using signal processing methods to obtain time-domain, frequency-domain, and wavelet packet eigenvalues, a grading standard for the tensile and shear strength of spot welded joints was established by conducting tensile and shear tests on spot welded samples. According to the test data, BP neural network and neural network classifier based on Particle swarm optimization support vector machines (PSO-SVM) are trained. Finally, the accuracy of two neural network models for spot welding strength classification was compared by inputting feature value parameters with different data set. The experimental results show that the PSO-SVM neural network combined with 9 ultrasonic signal eigenvalues has a spot welding strength classification accuracy of 95%.
Spot welding is one of the main connection methods of automobile parts, and the tensile and Shear strength of its joints are important factors to evaluate the connection quality. On the basis of preparing a large number of spot welding samples, this investigation conducted ultrasonic signal detection on the joints of each sample. Using signal processing methods to obtain time-domain, frequency-domain, and wavelet packet eigenvalues, a grading standard for the tensile and shear strength of spot welded joints was established by conducting tensile and shear tests on spot welded samples. According to the test data, BP neural network and neural network classifier based on Particle swarm optimization support vector machines (PSO-SVM) are trained. Finally, the accuracy of two neural network models for spot welding strength classification was compared by inputting feature value parameters with different data set. The experimental results show that the PSO-SVM neural network combined with 9 ultrasonic signal eigenvalues has a spot welding strength classification accuracy of 95%.
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.20220810002
Abstract:
Due to low cost and good electrical performance, BGA packaging is widely used in integrate circuit (IC) industry. Finite element method (FEM) analysis was carried out for evaluation of stress distribution in the Ball Grid Array (BGA) solder joints, and the radial scale, the height, the spacing of the solder joints, the height of chip were selected as design factors. Response surface methodology (RSM) was used to generate 25 designs and finite element modeling was employed to simulate the response of the assemblies to reliability influencing simulation calculations. The equation regression was associated with genetic algorithm (GA) to search for an optimal combination of parameters that meet the thermal vibration quality characteristics. The confirmation results showed that the space played a role in the reliability, and the radical scale 0.28 mm, the height 0.20 mm, the spacing 0.4mm settings of produce optimal assembly which demonstrated potential of reducing equivalent stress of the best design by 7.51%, respectively. The aim of optimizing BGA solder joints parameters was succeeded.
Due to low cost and good electrical performance, BGA packaging is widely used in integrate circuit (IC) industry. Finite element method (FEM) analysis was carried out for evaluation of stress distribution in the Ball Grid Array (BGA) solder joints, and the radial scale, the height, the spacing of the solder joints, the height of chip were selected as design factors. Response surface methodology (RSM) was used to generate 25 designs and finite element modeling was employed to simulate the response of the assemblies to reliability influencing simulation calculations. The equation regression was associated with genetic algorithm (GA) to search for an optimal combination of parameters that meet the thermal vibration quality characteristics. The confirmation results showed that the space played a role in the reliability, and the radical scale 0.28 mm, the height 0.20 mm, the spacing 0.4mm settings of produce optimal assembly which demonstrated potential of reducing equivalent stress of the best design by 7.51%, respectively. The aim of optimizing BGA solder joints parameters was succeeded.
Accepted Manuscript
, Available online
Abstract:
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
, Available online
Abstract:
Accepted Manuscript
, Available online
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.
Articles in press have been peer-reviewed and accepted, which are not yet assigned to volumes /issues, but are citable by Digital Object Identifier (DOI).
Display Method:
, Available online ,
doi: 10.12073/j.hjxb.20221122001
Abstract:
This paper aims to study the microscopic mechanism of reheating cracks formed in the Coarse-grained heat-affected zone (CGHAZ) of the welded joint of T23 water-wall pipe without heat treatment in the process of service by means of high temperature aging method, and to reveal the internal reasons why the joint of T23 water-wall pipe without heat treatment in engineering is prone to cracking and leakage during short running after machine start-up. In this paper, the CGHAZ hardness, microstructure and precipitate equality of water-cooled wall welded joints after unaged and high-temperature aging were systematically studied by means of microhardness testing, metallographic structure (OM) observation, scanning electron microscope (SEM) morphology observation, energy dispersive spectroscopy (EDS) analysis and transmission electron microscope (TEM) phase analysis. The results show that after aging at 530 ℃ for 100h, the hardness of CGHAZ appears secondary hardening caused by intragranular dispersion strengthening. After that, the hardness of CGHAZ decreases gradually with the increase of aging (running) time, but after 1000h, the hardness of CGHAZ is still 319HV, which is higher than the standard requirements. When aging at 600 ℃, CGHAZ hardness decreases with the increase of aging time. These results indicate that the hardness reduction of CGHAZ caused by the microstructure recovery, recrystallization, martensitic slat widening, dislocation density reduction, and the precipitation of C and alloy elements from the matrix is higher than the hardness increase caused by the dispersion precipitation of MX carbides in the crystal.M23C6 carbon (nitrogen) compounds gradually precipitate and grow at grain boundaries and subgrain boundaries.The research results of this paper provide theoretical support for revealing the internal reasons of cracking and leakage of unheat treated T23 water-wall joint in short run after machine starting.
This paper aims to study the microscopic mechanism of reheating cracks formed in the Coarse-grained heat-affected zone (CGHAZ) of the welded joint of T23 water-wall pipe without heat treatment in the process of service by means of high temperature aging method, and to reveal the internal reasons why the joint of T23 water-wall pipe without heat treatment in engineering is prone to cracking and leakage during short running after machine start-up. In this paper, the CGHAZ hardness, microstructure and precipitate equality of water-cooled wall welded joints after unaged and high-temperature aging were systematically studied by means of microhardness testing, metallographic structure (OM) observation, scanning electron microscope (SEM) morphology observation, energy dispersive spectroscopy (EDS) analysis and transmission electron microscope (TEM) phase analysis. The results show that after aging at 530 ℃ for 100h, the hardness of CGHAZ appears secondary hardening caused by intragranular dispersion strengthening. After that, the hardness of CGHAZ decreases gradually with the increase of aging (running) time, but after 1000h, the hardness of CGHAZ is still 319HV, which is higher than the standard requirements. When aging at 600 ℃, CGHAZ hardness decreases with the increase of aging time. These results indicate that the hardness reduction of CGHAZ caused by the microstructure recovery, recrystallization, martensitic slat widening, dislocation density reduction, and the precipitation of C and alloy elements from the matrix is higher than the hardness increase caused by the dispersion precipitation of MX carbides in the crystal.M23C6 carbon (nitrogen) compounds gradually precipitate and grow at grain boundaries and subgrain boundaries.The research results of this paper provide theoretical support for revealing the internal reasons of cracking and leakage of unheat treated T23 water-wall joint in short run after machine starting.
, Available online ,
doi: 10.12073/j.hjxb.20221123001
Abstract:
Ti-Zr-Cu-Ni-Co amorphous filler metals were designed and prepared for vacuum brazing of TC4 titanium alloy to 316L stainless steel according to the dual-cluster model. The effect of Co content in filler metals on the microstructure, mechanical properties and fracture behavior of brazed joints was investigated. The results showed that the cross section of brazed joint could be divided into TC4/diffusion zone I/brazing seam center zone II/interface zone III/316L. The typical interfacial microstructure of the brazed joints was TC4/β-Ti + Ti2Cu/(Ti, Zr)2(Cu, Ni) + Ti2Cu + Ti2(Cu, Ni) + TiFe/(Fe, Cr)2Ti + α-(Fe, Cr) + τ + γ -(Fe, Ni) + σ/316L. The shear strength of brazed joints first increased, then decreased and then increased with the increase of Co content. The maximum shear strength of 310 MPa was obtained at 1.56 at.% Co. When Co element was not added, brazed joints fractured in the center of the brazing seam (zone II). And when the Co content was 1.56 ~ 6.24 at. %, brazed joints fractured near the interface zone (zone III) of 316L base metal. The fracture mode was typical cleavage fracture.
Ti-Zr-Cu-Ni-Co amorphous filler metals were designed and prepared for vacuum brazing of TC4 titanium alloy to 316L stainless steel according to the dual-cluster model. The effect of Co content in filler metals on the microstructure, mechanical properties and fracture behavior of brazed joints was investigated. The results showed that the cross section of brazed joint could be divided into TC4/diffusion zone I/brazing seam center zone II/interface zone III/316L. The typical interfacial microstructure of the brazed joints was TC4/β-Ti + Ti2Cu/(Ti, Zr)2(Cu, Ni) + Ti2Cu + Ti2(Cu, Ni) + TiFe/(Fe, Cr)2Ti + α-(Fe, Cr) + τ + γ -(Fe, Ni) + σ/316L. The shear strength of brazed joints first increased, then decreased and then increased with the increase of Co content. The maximum shear strength of 310 MPa was obtained at 1.56 at.% Co. When Co element was not added, brazed joints fractured in the center of the brazing seam (zone II). And when the Co content was 1.56 ~ 6.24 at. %, brazed joints fractured near the interface zone (zone III) of 316L base metal. The fracture mode was typical cleavage fracture.
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Display Method:
Analysis of stress distribution characteristics of Zr/Ni circumferential electron beam welded joints
2023, 44(9): 1-8.
doi: 10.12073/j.hjxb.20221219001
Abstract:
Zirconium has good mechanical properties, compatibility with nuclear fuel and radiation resistance, is widely used in the nuclear industry. Nickel has good mechanical properties and corrosion resistance, and is often used as a structural material. There are large differences in thermophysical properties and poor metallurgical compatibility between zirconium/nickel. There is currently no research on fusion welding of zirconium/nickel. In direct welding, the electron beam welded joint is composed of (γ-Ni+Ni5Zr) eutectic+Ni5Zr dendrite composite structure, which leads to welding cracks under residual stress. The tensile strength is only 36.4 MPa. In beam offset welding, the tensile strength of the joint increased to 189 MPa. The finite element simulation research on the stress field and temperature field of the joints under different welding parameters, combined with theoretical calculations, revealed that due to the structure of the weld, there is reheating phenomenon in the initial stage of welding, resulting in high residual stress. Electron beam deflects to Ni side effectively reduces the residual stress and thermal stress of the joint, which is the main reason for the disappearance of cracks.
Zirconium has good mechanical properties, compatibility with nuclear fuel and radiation resistance, is widely used in the nuclear industry. Nickel has good mechanical properties and corrosion resistance, and is often used as a structural material. There are large differences in thermophysical properties and poor metallurgical compatibility between zirconium/nickel. There is currently no research on fusion welding of zirconium/nickel. In direct welding, the electron beam welded joint is composed of (γ-Ni+Ni5Zr) eutectic+Ni5Zr dendrite composite structure, which leads to welding cracks under residual stress. The tensile strength is only 36.4 MPa. In beam offset welding, the tensile strength of the joint increased to 189 MPa. The finite element simulation research on the stress field and temperature field of the joints under different welding parameters, combined with theoretical calculations, revealed that due to the structure of the weld, there is reheating phenomenon in the initial stage of welding, resulting in high residual stress. Electron beam deflects to Ni side effectively reduces the residual stress and thermal stress of the joint, which is the main reason for the disappearance of cracks.
2023, 44(9): 9-15.
doi: 10.12073/j.hjxb.20221126001
Abstract:
In present work, the widely used Mg alloys ZK61, AZ31, AZ61 and AZ91 were selected for investigating the solidification cracking susceptibility during welding. Transverse motion weldability (TMW) test in two-speed mode was used to evaluate the susceptibility of Mg alloys to solidification cracking during welding. The critical transverse moving speed was obtained and considered as an index to estimate the solidification cracking susceptibility of Mg alloys as ranking: ZK61 > AZ31 > AZ61 > AZ91. The ranking is consistent with the results of one-speed test and predicted results based on │dT/d(fS)1/2│max. It was shown that two-speed test of TMW is effective to evaluate the susceptibility of Mg alloys to solidification cracking. According to the backfilled liquid at the tip of or near the solidification cracking, the intergranular backfilled liquid of ZK61 is discontinuous and the channel is narrow, which is difficult to heal the crack and increases the solidification cracking susceptibility. The liquid backfilling channel of AZ91 is the widest, which is conducive to intergranular liquid backfilling and reduces the solidification crack susceptibility.
In present work, the widely used Mg alloys ZK61, AZ31, AZ61 and AZ91 were selected for investigating the solidification cracking susceptibility during welding. Transverse motion weldability (TMW) test in two-speed mode was used to evaluate the susceptibility of Mg alloys to solidification cracking during welding. The critical transverse moving speed was obtained and considered as an index to estimate the solidification cracking susceptibility of Mg alloys as ranking: ZK61 > AZ31 > AZ61 > AZ91. The ranking is consistent with the results of one-speed test and predicted results based on │dT/d(fS)1/2│max. It was shown that two-speed test of TMW is effective to evaluate the susceptibility of Mg alloys to solidification cracking. According to the backfilled liquid at the tip of or near the solidification cracking, the intergranular backfilled liquid of ZK61 is discontinuous and the channel is narrow, which is difficult to heal the crack and increases the solidification cracking susceptibility. The liquid backfilling channel of AZ91 is the widest, which is conducive to intergranular liquid backfilling and reduces the solidification crack susceptibility.
2023, 44(9): 16-23.
doi: 10.12073/j.hjxb.20221201001
Abstract:
Fatigue life prediction under variable amplitude loading is an important issue in the integrity analysis of welded structures. Based on the fatigue damage zone concept proposed by Pavlou and the S-N curve recommended in BS7608 standard, an approach to predict fatigue lives of welded structures was realized by FEA heat transfer problem. Fatigue tests under two-level tensile loading block sequences were conducted for load-carrying cruciform welded joints, non-load- carrying cruciform welded joints and butt welded joints, respectively. The fatigue lives of the specimens were estimated according to Miner model, M-H model and Pavlou method. Results showed that the Pavlou method had higher prediction accuracy with more uniform distribution in the error scatter diagram of predicted life versus test life, which validated the rationality and effectiveness of the proposed method. Moreover, the influence of S-N curve survival probability on the life prediction accuracy is discussed. The S-N curve with 2.3% survival probability is suggested to be utilized to obtain satisfactory prediction results.
Fatigue life prediction under variable amplitude loading is an important issue in the integrity analysis of welded structures. Based on the fatigue damage zone concept proposed by Pavlou and the S-N curve recommended in BS7608 standard, an approach to predict fatigue lives of welded structures was realized by FEA heat transfer problem. Fatigue tests under two-level tensile loading block sequences were conducted for load-carrying cruciform welded joints, non-load- carrying cruciform welded joints and butt welded joints, respectively. The fatigue lives of the specimens were estimated according to Miner model, M-H model and Pavlou method. Results showed that the Pavlou method had higher prediction accuracy with more uniform distribution in the error scatter diagram of predicted life versus test life, which validated the rationality and effectiveness of the proposed method. Moreover, the influence of S-N curve survival probability on the life prediction accuracy is discussed. The S-N curve with 2.3% survival probability is suggested to be utilized to obtain satisfactory prediction results.
2023, 44(9): 24-29.
doi: 10.12073/j.hjxb.20221130001
Abstract:
In order to explore the morphology characteristics of the laser welded joint of Ti6Al4V alloy under low vacuum environment, non-penetration welding was performed under 5 Pa ambient pressure. The influence law of laser power and defocus amount on the weld morphology was studied, and the stability and formation interval of the typical joint morphology were analyzed. The results show that the weld bead quality can be obtained by changing the process parameters in a wide range under low vacuum ambient pressure, and the weld penetration increases linearly with the increase of output power. The geometric features of welded joints can be divided into two types: the U shape formed when the line energy utilization factor is less than 0.13 or greater than 0.14, and the V shape formed when the line energy utilization factor is between 0.13 and 0.14. V shape keyhole stability is poor, it is difficult to maintain the quasi steady state, weld penetration depth fluctuation is large, easy to form defects at the bottom of the weld.
In order to explore the morphology characteristics of the laser welded joint of Ti6Al4V alloy under low vacuum environment, non-penetration welding was performed under 5 Pa ambient pressure. The influence law of laser power and defocus amount on the weld morphology was studied, and the stability and formation interval of the typical joint morphology were analyzed. The results show that the weld bead quality can be obtained by changing the process parameters in a wide range under low vacuum ambient pressure, and the weld penetration increases linearly with the increase of output power. The geometric features of welded joints can be divided into two types: the U shape formed when the line energy utilization factor is less than 0.13 or greater than 0.14, and the V shape formed when the line energy utilization factor is between 0.13 and 0.14. V shape keyhole stability is poor, it is difficult to maintain the quasi steady state, weld penetration depth fluctuation is large, easy to form defects at the bottom of the weld.
2023, 44(9): 30-36.
doi: 10.12073/j.hjxb.20221119001
Abstract:
The fatigue tests of bobbin tool friction stir welding profile joints of 3.3 mm thick 6005A-T6 aluminum alloy with different dimensions were carried out to analyze the fatigue performance of the joints. Combined with the macroscopic forming and microstructure evolution of the joint under typical parameters, the fracture behavior of the bobbin tool friction stir welded joint was revealed. The results showed that the tensile fracture of the joint under typical parameters (rotation speed of 1 000 r/min, welding speed of 100 mm/min, width and thickness of parallel section of 11.8 mm and 3.1 mm) was located in the HAZ-RS. The grain structure characteristics in the TMAZ-AS of the joint could influence the fatigue cracks generation and propagation. The SEM analysis of fatigue fracture showed that no obvious defects were found. The fatigue cracks propagation and fracture zones showed typical fatigue fracture characteristics, and the fracture was located in the TMAZ-AS of the joint
The fatigue tests of bobbin tool friction stir welding profile joints of 3.3 mm thick 6005A-T6 aluminum alloy with different dimensions were carried out to analyze the fatigue performance of the joints. Combined with the macroscopic forming and microstructure evolution of the joint under typical parameters, the fracture behavior of the bobbin tool friction stir welded joint was revealed. The results showed that the tensile fracture of the joint under typical parameters (rotation speed of 1 000 r/min, welding speed of 100 mm/min, width and thickness of parallel section of 11.8 mm and 3.1 mm) was located in the HAZ-RS. The grain structure characteristics in the TMAZ-AS of the joint could influence the fatigue cracks generation and propagation. The SEM analysis of fatigue fracture showed that no obvious defects were found. The fatigue cracks propagation and fracture zones showed typical fatigue fracture characteristics, and the fracture was located in the TMAZ-AS of the joint
2023, 44(9): 37-43.
doi: 10.12073/j.hjxb.20221020001
Abstract:
Sandwich composite filler metal is an important technical means to realize reliable brazing connection between cemented carbide and steel. The microstructure of the composite layer and the interface layer between the composite layer and the matrix has an important influence on the mechanical properties. The microstructure evolution of brazing joint of gradient sandwich composite filler metal under different brazing temperature and time conditions was systematically studied, and the key factors affecting the mechanical properties were analyzed. The research results showed that the interfacial formation of gradient sandwich filler metal with steel and carbide matrix could be divided into four stages: interfacial structure formation, growth, fusion and rearrangement. The CuMn2 layer in the middle of the gradient filler metal gradually changed from the initial continuous shape to an isolated island surrounded by low Mn copper solid solution with the extension of holding time. As the holding time continued, CuMn2 layer disappeared and the whole brazing joint was composed of copper solid solution, silver solid solution and silver copper eutectic. The shear strength of the brazing joint reached the highest 285 MPa when the temperature was kept at 780 ℃ for 2.5 min. At this time, the Co and Ni elements had long range diffusion and accumulated near the CuMn2 interlayer, which improved the strength and toughness of the CuMn2 interlayer. The Co-based particle strengthening phase was distributed in the root of the fracture dimple. Further extension of holding time, Co, Ni and other brazing elements began to disperse, the brazing structure coarsened, the strength decreased.
Sandwich composite filler metal is an important technical means to realize reliable brazing connection between cemented carbide and steel. The microstructure of the composite layer and the interface layer between the composite layer and the matrix has an important influence on the mechanical properties. The microstructure evolution of brazing joint of gradient sandwich composite filler metal under different brazing temperature and time conditions was systematically studied, and the key factors affecting the mechanical properties were analyzed. The research results showed that the interfacial formation of gradient sandwich filler metal with steel and carbide matrix could be divided into four stages: interfacial structure formation, growth, fusion and rearrangement. The CuMn2 layer in the middle of the gradient filler metal gradually changed from the initial continuous shape to an isolated island surrounded by low Mn copper solid solution with the extension of holding time. As the holding time continued, CuMn2 layer disappeared and the whole brazing joint was composed of copper solid solution, silver solid solution and silver copper eutectic. The shear strength of the brazing joint reached the highest 285 MPa when the temperature was kept at 780 ℃ for 2.5 min. At this time, the Co and Ni elements had long range diffusion and accumulated near the CuMn2 interlayer, which improved the strength and toughness of the CuMn2 interlayer. The Co-based particle strengthening phase was distributed in the root of the fracture dimple. Further extension of holding time, Co, Ni and other brazing elements began to disperse, the brazing structure coarsened, the strength decreased.
2023, 44(9): 44-52.
doi: 10.12073/j.hjxb.20221214001
Abstract:
In order to achieve highly reliable connection of FGH96 and IN718 dissimilar high-temperature alloys for aerospace applications, to provide basic data and theoretical support for the safety evaluation and life prediction of aero-engines key components. Scanning electron microscopy and metallurgical microscopy were used to study the FGH96 and IN718 dissimilar high-temperature alloy inertia friction welding joint microstructure morphology and high-temperature tensile specimens fracture morphology and fracture location. Test results show that the weld zone FGH96 and IN718 were equiaxed grain organization, the grain size is about 2 μm, the weld zone γ′ and δ strengthening phase were completely dissolved, the heat-force affected zone FGH96 side of the grain γ′also was completely dissolved, the IN718 side δ strengthening phase occured partially dissolved, the short rod-like shape was disappeared, coarse and fine crystal organization coexisted. The welded joint 650 ℃ high temperature tensile specimens were fractured with the weld zone, but the average tensile strength up to 1 080.8 MPa, basically with IN718 parent material equal strength, the high-temperature tensile specimens crack location were in the edge of the sample weld zone, the crack from the weld zone was mainly due to γ′ and δ strengthening phase basically all dissolved, the strengthening effect disappeared, the performance was reduced. The crack was generated along the grain boundary from the weld fusion line to the specimen internal expansion, the crack from the specimen edge weld area around the same time to the specimen internal expansion, under the action of axial tension to form a "platform + crater" fracture characteristics, when the crack from the specimen edge weld area local location to the specimen internal expansion, under the action of axial tension to form "platform + shear" fracture characteristics.
In order to achieve highly reliable connection of FGH96 and IN718 dissimilar high-temperature alloys for aerospace applications, to provide basic data and theoretical support for the safety evaluation and life prediction of aero-engines key components. Scanning electron microscopy and metallurgical microscopy were used to study the FGH96 and IN718 dissimilar high-temperature alloy inertia friction welding joint microstructure morphology and high-temperature tensile specimens fracture morphology and fracture location. Test results show that the weld zone FGH96 and IN718 were equiaxed grain organization, the grain size is about 2 μm, the weld zone γ′ and δ strengthening phase were completely dissolved, the heat-force affected zone FGH96 side of the grain γ′also was completely dissolved, the IN718 side δ strengthening phase occured partially dissolved, the short rod-like shape was disappeared, coarse and fine crystal organization coexisted. The welded joint 650 ℃ high temperature tensile specimens were fractured with the weld zone, but the average tensile strength up to 1 080.8 MPa, basically with IN718 parent material equal strength, the high-temperature tensile specimens crack location were in the edge of the sample weld zone, the crack from the weld zone was mainly due to γ′ and δ strengthening phase basically all dissolved, the strengthening effect disappeared, the performance was reduced. The crack was generated along the grain boundary from the weld fusion line to the specimen internal expansion, the crack from the specimen edge weld area around the same time to the specimen internal expansion, under the action of axial tension to form a "platform + crater" fracture characteristics, when the crack from the specimen edge weld area local location to the specimen internal expansion, under the action of axial tension to form "platform + shear" fracture characteristics.
2023, 44(9): 53-59.
doi: 10.12073/j.hjxb.20221122003
Abstract:
In order to realize the automation of electric spark deposition (ESD), a closed loop control system of discharge parameters for ESD was developed. Discharge parameters during deposition are collected in real time. Based on the linear law that the average discharge pulse voltage is inversely proportional to the contact force, the closed-loop control of the average discharge pulse voltage is achieved by the feed motor and the feed slide adjusting the contact force between the workpiece and the electrode, and thus the automatic feed adjustment of electrode is realized. The analog circuit, digital control circuit and control software of the control system are designed by modular technology, which can shorten the development period, ensure the reliability and facilitate the upgrade and expansion. The test results of ESD show that the developed closed loop control system of discharge parameters can realize the stable contact between electrode and workpiece and obtain uniform and dense deposition layer, which is convenient to realize the automatic operation of ESD and is conducive to the popularization and application of ESD technology.
In order to realize the automation of electric spark deposition (ESD), a closed loop control system of discharge parameters for ESD was developed. Discharge parameters during deposition are collected in real time. Based on the linear law that the average discharge pulse voltage is inversely proportional to the contact force, the closed-loop control of the average discharge pulse voltage is achieved by the feed motor and the feed slide adjusting the contact force between the workpiece and the electrode, and thus the automatic feed adjustment of electrode is realized. The analog circuit, digital control circuit and control software of the control system are designed by modular technology, which can shorten the development period, ensure the reliability and facilitate the upgrade and expansion. The test results of ESD show that the developed closed loop control system of discharge parameters can realize the stable contact between electrode and workpiece and obtain uniform and dense deposition layer, which is convenient to realize the automatic operation of ESD and is conducive to the popularization and application of ESD technology.
2023, 44(9): 60-66.
doi: 10.12073/j.hjxb.20221120001
Abstract:
The weld metal of high manganese austenitic steel was prepared by submerged arc welding process with the main composition (wt.%) range of 0.30-0.50 C, 22.00-25.00 Mn, 3.50-5.50 Cr. The segregation behavior of alloying elements and the solidification characteristics of the molten pool of high manganese austenitic steel were studied by OM, EBSD, EPMA and other analysis methods. The analysis of microstructure and chemical composition shows that there are inhomogeneous mixed zone and partially melted zone (PMZ) in the fusion zone of high manganese austenitic steel welded joints prepared with the same composition system. The alloy element segregation zone of C, Mn and Cr produced by hot rolling in the test steel resulted in partial melting of the PMZ in the fusion zone of the welded joint, and further increases its degree of elemental segregation. The inhomogeneous mixed zone co-crystallizes in the PMZ in the form of cellular crystals, and the distribution of the alloy elements continues the distribution in the PMZ. The molten pool co-crystallizes in the form of cellular crystals on the protruding solid phase peninsula on the PMZ. The width of the initial cytosolic crystals correlates is intrinsically related to the spacing of the hot-rolled segregation bands of the base metal, which is produced by the segregation of alloying elements in the hot rolled strip in the partially melted zone and the concave solid-liquid interface formed by its partial melting.
The weld metal of high manganese austenitic steel was prepared by submerged arc welding process with the main composition (wt.%) range of 0.30-0.50 C, 22.00-25.00 Mn, 3.50-5.50 Cr. The segregation behavior of alloying elements and the solidification characteristics of the molten pool of high manganese austenitic steel were studied by OM, EBSD, EPMA and other analysis methods. The analysis of microstructure and chemical composition shows that there are inhomogeneous mixed zone and partially melted zone (PMZ) in the fusion zone of high manganese austenitic steel welded joints prepared with the same composition system. The alloy element segregation zone of C, Mn and Cr produced by hot rolling in the test steel resulted in partial melting of the PMZ in the fusion zone of the welded joint, and further increases its degree of elemental segregation. The inhomogeneous mixed zone co-crystallizes in the PMZ in the form of cellular crystals, and the distribution of the alloy elements continues the distribution in the PMZ. The molten pool co-crystallizes in the form of cellular crystals on the protruding solid phase peninsula on the PMZ. The width of the initial cytosolic crystals correlates is intrinsically related to the spacing of the hot-rolled segregation bands of the base metal, which is produced by the segregation of alloying elements in the hot rolled strip in the partially melted zone and the concave solid-liquid interface formed by its partial melting.
2023, 44(9): 67-73.
doi: 10.12073/j.hjxb.20221129006
Abstract:
Laser metal deposition is a widely used laser additive manufacturing technology. The fatigue tests of 304 austenitic stainless steel manufactured by laser metal deposition are carried out and the fatigue fracture mechanism is studied. According to the experimental results, the S-N curve of 304 austenitic stainless steel manufactured by laser metal deposition is drawn. The results show that the stress amplitude has an important effect on the fatigue fracture morphology. The larger the stress amplitude is, the coarser the fatigue fracture is. Under the higher stress amplitude, there are randomly distributed holes and cracks on the surface of the fracture specimen. Material defects such as oxide inclusions and pores are the main causes of fatigue crack initiation, and large local plastic deformation under the large stress amplitude (such as 275 MPa) is also one of the causes of fatigue crack initiation. With the increase of stress amplitude, the fatigue bands become clearer. Under the higher stress amplitude, the intersection of multiple slip systems leads to the expansion of fatigue bands in different plane, and the tire indentation appears in the crack propagation zone. With the increase of stress amplitude, the number of secondary cracks increases due to the increase of plastic deformation in the fatigue crack propagation zone.
Laser metal deposition is a widely used laser additive manufacturing technology. The fatigue tests of 304 austenitic stainless steel manufactured by laser metal deposition are carried out and the fatigue fracture mechanism is studied. According to the experimental results, the S-N curve of 304 austenitic stainless steel manufactured by laser metal deposition is drawn. The results show that the stress amplitude has an important effect on the fatigue fracture morphology. The larger the stress amplitude is, the coarser the fatigue fracture is. Under the higher stress amplitude, there are randomly distributed holes and cracks on the surface of the fracture specimen. Material defects such as oxide inclusions and pores are the main causes of fatigue crack initiation, and large local plastic deformation under the large stress amplitude (such as 275 MPa) is also one of the causes of fatigue crack initiation. With the increase of stress amplitude, the fatigue bands become clearer. Under the higher stress amplitude, the intersection of multiple slip systems leads to the expansion of fatigue bands in different plane, and the tire indentation appears in the crack propagation zone. With the increase of stress amplitude, the number of secondary cracks increases due to the increase of plastic deformation in the fatigue crack propagation zone.
2023, 44(9): 74-80.
doi: 10.12073/j.hjxb.20230329003
Abstract:
The evolution of microstructure and the initiation and propagation mechanism of microcracks during the tensile process of ERNiCrFe-13 welding wire deposited metal. The microstructure and fracture behavior of deposited metal were studied by in-situ tensile scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results show that the microstructure of ERNiCrFe-13 welding wire deposited metal is mainly composed of columnar dendrite γ phase (NiCrFe solid solution), Nb and Mo rich in Laves phase (Cr,Fe,Ni)2(Ti,Mo), MC carbides and eutectic structure in the interdendritic. The formation of Laves phase is mainly related to the segregation of Nb and Mo elements during solidification and has a size effect. Horizontal Laves phase size larger than 4 μm is prone to cracking. The fracture mechanism is the initiation of microcracks in the interdendrite precipitated phase under shear stress. Under the action of axial tensile stress, the connection is further extended along grain boundaries to fracture failure. The fracture is ductile and carbide segregation (NbC, TiC) and large Laves phase are the main causes of grain boundary cracks.
The evolution of microstructure and the initiation and propagation mechanism of microcracks during the tensile process of ERNiCrFe-13 welding wire deposited metal. The microstructure and fracture behavior of deposited metal were studied by in-situ tensile scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results show that the microstructure of ERNiCrFe-13 welding wire deposited metal is mainly composed of columnar dendrite γ phase (NiCrFe solid solution), Nb and Mo rich in Laves phase (Cr,Fe,Ni)2(Ti,Mo), MC carbides and eutectic structure in the interdendritic. The formation of Laves phase is mainly related to the segregation of Nb and Mo elements during solidification and has a size effect. Horizontal Laves phase size larger than 4 μm is prone to cracking. The fracture mechanism is the initiation of microcracks in the interdendrite precipitated phase under shear stress. Under the action of axial tensile stress, the connection is further extended along grain boundaries to fracture failure. The fracture is ductile and carbide segregation (NbC, TiC) and large Laves phase are the main causes of grain boundary cracks.
2023, 44(9): 81-87.
doi: 10.12073/j.hjxb.20221020002
Abstract:
Titanium/aluminum composite plate with excellent performance can be obtained by combining thin layer titanium alloy plate with aluminum alloy plate, which has broad application prospects. TC1/1060/6061 composite plate was successfully prepared by explosive welding technology. The interface morphology and interface elements of the two interfaces were tested, and the advantages of 1060 interlayer were analyzed. At the same time, the finite element model consistent with the test conditions was established, and the interface state and welding process were analyzed. Finally, tensile test and shear test were carried out to verify the bonding quality of interface. The results show that the TC1/1060 interface has a linear morphology, and the 1060/6061 interface has a large wavy interface, and each wave is accompanied by the vortex region. The element diffusion range at the TC1/1060 interface is 4.38 μm, and no Ti/Al intermetallic compounds are detected. The numerical simulation reproduces the jetting formation in the process of explosive welding. The interface temperature is distributed along the interface morphology, and the interface pressure reaches the maximum at the collision point, showing an elliptic distribution. The composite plate has high tensile strength and shear strength, which can meet the requirements of structure use.
Titanium/aluminum composite plate with excellent performance can be obtained by combining thin layer titanium alloy plate with aluminum alloy plate, which has broad application prospects. TC1/1060/6061 composite plate was successfully prepared by explosive welding technology. The interface morphology and interface elements of the two interfaces were tested, and the advantages of 1060 interlayer were analyzed. At the same time, the finite element model consistent with the test conditions was established, and the interface state and welding process were analyzed. Finally, tensile test and shear test were carried out to verify the bonding quality of interface. The results show that the TC1/1060 interface has a linear morphology, and the 1060/6061 interface has a large wavy interface, and each wave is accompanied by the vortex region. The element diffusion range at the TC1/1060 interface is 4.38 μm, and no Ti/Al intermetallic compounds are detected. The numerical simulation reproduces the jetting formation in the process of explosive welding. The interface temperature is distributed along the interface morphology, and the interface pressure reaches the maximum at the collision point, showing an elliptic distribution. The composite plate has high tensile strength and shear strength, which can meet the requirements of structure use.
2023, 44(9): 88-94.
doi: 10.12073/j.hjxb.20221129003
Abstract:
6056 aluminum alloy with 4mm thickness was welded by bobbin tool friction stir welding, and the non-uniform characteristics of microstructure and mechanical properties of different characteristic areas of the joint were studied. Results show that the equivalent strain of the cross section of the joint is dumbbell shape, which is consistent with the macro-morphology of the cross section of the weld. The plastic strain distribution along the left and right sides of the weld center is asymmetrical, and the plastic strain value at the advancing side of the joint is higher than that at the retreating side. The proportion of high angle grain boundary near the advancing side and the middle side is higher than that on the retreating side. The advancing side and middle side are mainly B-type\begin{document}$\{1 \overline 1{2}\} $\end{document} ![]()
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6056 aluminum alloy with 4mm thickness was welded by bobbin tool friction stir welding, and the non-uniform characteristics of microstructure and mechanical properties of different characteristic areas of the joint were studied. Results show that the equivalent strain of the cross section of the joint is dumbbell shape, which is consistent with the macro-morphology of the cross section of the weld. The plastic strain distribution along the left and right sides of the weld center is asymmetrical, and the plastic strain value at the advancing side of the joint is higher than that at the retreating side. The proportion of high angle grain boundary near the advancing side and the middle side is higher than that on the retreating side. The advancing side and middle side are mainly B-type
2023, 44(9): 95-105.
doi: 10.12073/j.hjxb.20221028006
Abstract:
SP2215 tube welded joints (WJ) were prepared by manual gas tungsten arc welding (M-GTAW) and ERNiCr-3 welding wire. The microstructure, mechanical properties and tensile fracture mechanism of the WJ after aging for different times at 650 ℃ were studied. The results show that the microstructure of SP2215 base metal (BM) is composed of austenite, a small amount of twins and primary NbN and Z phase in the as-welded condition, the weld metal (WM) was solidified into columnar dendrite with a completely austenitic structure, and Nb element was segregated between the dendrites and forms the NbC phase, which was distributed in a chain shape. After aging at 650 ℃ for 50 h, M23C6 began to precipitate at the austenite grain boundary of SP2215 BM and gradually coarsened with the extension of aging time, at the same time NbC phase gradually precipitated between dendrites and gradually formed into a cluster shape with the increase of aging time. The microhardness of BM and WM increases with the increasing of aging time, and reaches the maximum value at 500 h. The hardness of BM is always higher than that of WM. All the WJ with different aging time were fractured at the weld seam in a ductile manner at room temperature tensile test, however the fracture initiation position and fracture direction changed with the extension of aging time. When the aging time was 0-114 h, the fracture direction was transverse to the columnar dendrite direction, and the crack initiation position was the primary NbC particles between dendrites. When the aging time was 500-2012 h, the fracture direction was parallel to the columnar dendrite direction, and the crack initiation position is the dendritic core. The fracture position of the WJ changed from the weld seam to the SP2215 side with the increase of aging time at high temperature tensile test at 650 ℃. The WJ aging for 0-114 h fractured at the weld seam in a ductile manner, however the WJ aging for 2012 h fractured at the SP2215 side in a quasi-cleavage manner.
SP2215 tube welded joints (WJ) were prepared by manual gas tungsten arc welding (M-GTAW) and ERNiCr-3 welding wire. The microstructure, mechanical properties and tensile fracture mechanism of the WJ after aging for different times at 650 ℃ were studied. The results show that the microstructure of SP2215 base metal (BM) is composed of austenite, a small amount of twins and primary NbN and Z phase in the as-welded condition, the weld metal (WM) was solidified into columnar dendrite with a completely austenitic structure, and Nb element was segregated between the dendrites and forms the NbC phase, which was distributed in a chain shape. After aging at 650 ℃ for 50 h, M23C6 began to precipitate at the austenite grain boundary of SP2215 BM and gradually coarsened with the extension of aging time, at the same time NbC phase gradually precipitated between dendrites and gradually formed into a cluster shape with the increase of aging time. The microhardness of BM and WM increases with the increasing of aging time, and reaches the maximum value at 500 h. The hardness of BM is always higher than that of WM. All the WJ with different aging time were fractured at the weld seam in a ductile manner at room temperature tensile test, however the fracture initiation position and fracture direction changed with the extension of aging time. When the aging time was 0-114 h, the fracture direction was transverse to the columnar dendrite direction, and the crack initiation position was the primary NbC particles between dendrites. When the aging time was 500-2012 h, the fracture direction was parallel to the columnar dendrite direction, and the crack initiation position is the dendritic core. The fracture position of the WJ changed from the weld seam to the SP2215 side with the increase of aging time at high temperature tensile test at 650 ℃. The WJ aging for 0-114 h fractured at the weld seam in a ductile manner, however the WJ aging for 2012 h fractured at the SP2215 side in a quasi-cleavage manner.
2023, 44(9): 106-112.
doi: 10.12073/j.hjxb.20221213001
Abstract:
An efficient enhanced moving heat source model was developed based on the MSC. Marc finite element software platform. The thermo-elastic-plastic finite element method, along with the enhanced moving heat source model, was employed to numerically simulate the welding deformation of a large-scale long straight rolling stock structure measuring 13832 mm in length. Simultaneously, the welding deformation of the long and straight structure was measured experimentally and compared to the numerical simulation results. This comparison verified the accuracy and feasibility of the developed finite element calculation model for welding deformation in such structures. Subsequently, the developed computational method was used to investigate the impact of different welding sequences on the welding deformation of large long straight structures in rolling stock. The calculation results demonstrate that the welding sequence significantly affects both the mode and magnitude of welding deformation. By adjusting the welding sequence, substantial reduction in welding deformation can be achieved. This study provides guidance for the production of large long straight structures and reduces the process development cycle.
An efficient enhanced moving heat source model was developed based on the MSC. Marc finite element software platform. The thermo-elastic-plastic finite element method, along with the enhanced moving heat source model, was employed to numerically simulate the welding deformation of a large-scale long straight rolling stock structure measuring 13832 mm in length. Simultaneously, the welding deformation of the long and straight structure was measured experimentally and compared to the numerical simulation results. This comparison verified the accuracy and feasibility of the developed finite element calculation model for welding deformation in such structures. Subsequently, the developed computational method was used to investigate the impact of different welding sequences on the welding deformation of large long straight structures in rolling stock. The calculation results demonstrate that the welding sequence significantly affects both the mode and magnitude of welding deformation. By adjusting the welding sequence, substantial reduction in welding deformation can be achieved. This study provides guidance for the production of large long straight structures and reduces the process development cycle.
2023, 44(9): 113-117.
doi: 10.12073/j.hjxb.20220325005
Abstract:
The superconducting joint of the internal coil in the vacuum coil system of the device has a high requirement on weld quality because of its bad working environment. In order to verify the feasibility of welding oxygen free copper pipe with arc preheating method, the method of arc preheating with open head was adopted to preheat oxygen free copper pipe to reach the temperature required for welding copper pipe . Non-destructive testing , macroscopic and microscopic examination, and hardness measurement of weld, heat-affected zone and base metal are performed on copper welded joints. The influence of arc preheating on the heat-affected zone is evaluated. The analysis shows that there is no significant difference between the hardness of the heat affected zone and the base metal, but there is a significant difference in the microstructure. The hardness of weld metal is slightly higher.In the observation range, arc preheating has no significant effect on the heat-affected zone. The results show that arc preheating is feasible.
The superconducting joint of the internal coil in the vacuum coil system of the device has a high requirement on weld quality because of its bad working environment. In order to verify the feasibility of welding oxygen free copper pipe with arc preheating method, the method of arc preheating with open head was adopted to preheat oxygen free copper pipe to reach the temperature required for welding copper pipe . Non-destructive testing , macroscopic and microscopic examination, and hardness measurement of weld, heat-affected zone and base metal are performed on copper welded joints. The influence of arc preheating on the heat-affected zone is evaluated. The analysis shows that there is no significant difference between the hardness of the heat affected zone and the base metal, but there is a significant difference in the microstructure. The hardness of weld metal is slightly higher.In the observation range, arc preheating has no significant effect on the heat-affected zone. The results show that arc preheating is feasible.
2023, 44(9): 118-128.
doi: 10.12073/j.hjxb.20221025001
Abstract:
High nitrogen steel offers unique benefits including high strength, toughness, abrasion resistance, and corrosion resistance. The connectors have been widespread application in military equipment, medical instruments, and mining devices. The major domestic and foreign research reports in recent years on gas tungsten arc welding, gas metal arc welding, laser welding and laser-arc hybrid welding, friction stir welding and brazing of high nitrogen steel are summarized in detail.According to the three main classifications of fusion welding, solid-state welding and brazing, the paper systematically reviews the existing various types of high-nitrogen steel welding methods and process control from the aspects of shielding gas, heat input,process parameters and others, introducing the current status of the application of high-nitrogen steel materials in the field of medical devices, oil drilling collars, and armor protection. Finally, the review points out the shortcomings and aspects of the existing research on high nitrogen steel joining systems, expecting to provide information and theoretical basis for the research and application in the fields of high nitrogen steel welding, functional joining of high-strength materials and other related fields.
High nitrogen steel offers unique benefits including high strength, toughness, abrasion resistance, and corrosion resistance. The connectors have been widespread application in military equipment, medical instruments, and mining devices. The major domestic and foreign research reports in recent years on gas tungsten arc welding, gas metal arc welding, laser welding and laser-arc hybrid welding, friction stir welding and brazing of high nitrogen steel are summarized in detail.According to the three main classifications of fusion welding, solid-state welding and brazing, the paper systematically reviews the existing various types of high-nitrogen steel welding methods and process control from the aspects of shielding gas, heat input,process parameters and others, introducing the current status of the application of high-nitrogen steel materials in the field of medical devices, oil drilling collars, and armor protection. Finally, the review points out the shortcomings and aspects of the existing research on high nitrogen steel joining systems, expecting to provide information and theoretical basis for the research and application in the fields of high nitrogen steel welding, functional joining of high-strength materials and other related fields.
Since 1980 monthly
Supervisor: China Science and Technology Association
Sponsor: Chinese Mechanical Engineering Society
Editor-in-chief: Huiwen Zhang
Associate Editor: Zhenzhen Zhou
Address: No. 2077, Chuangxin Road, Songbei District, Harbin
Postal Code: 150028
Telephone: 0451-86323218
Email: hjzzszjl@163.com
CN: 23-1178/TG
ISSN: 0253-360X
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