2021年, 第30卷, 第1期　
刊出日期：2021-03-28

  

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  Texture and mechanical properties of metal inert gas welded 6082-T651 aluminum alloy joints

  祁广斌, 董红刚, 杨江, 郭柏征, 郝晓虎, 许晨玲

  中国焊接. 2021, 30(1): 1-12. https://doi.org/10.12073/j.cw.20201230001

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  Metal inert gas (MIG) welding was conducted with 12 mm thick 6082-T651 aluminum alloy plate to investigate the microstructure and mechanical properties of welded joint. The microstructure and element distribution of weld seam were characterized by electron backscattered diffraction (EBSD) and electron probe microanalysis (EPMA). The weld seam has typical cube texture ({001}<100>) characteristics. The closer to the center of weld seam, the weaker the texture feature, the higher the proportion of high-angle grain boundaries. The average tensile strength of joint was 232 MPa which is up to 72% of 6082 aluminum alloy base metal, and the bending angle for the root bend test sample reached 90° without cracks. The lack of strengthening phase and the existence of welding pores and inclusions in the weld seam caused the degradation of mechanical properties of resultant joint. The microhardness increased from the weld center to the base metal, but the overaging zone caused by welding thermal cycle was softening part of the joint, which had lower hardness than the weld seam.
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  Effect of alternating ultrasonic frequency electric signal on the distribution of pore in aluminum alloy weld

  陈琪昊, 唐健行, 王加友, 林三宝

  中国焊接. 2021, 30(1): 13-20. https://doi.org/10.12073/j.cw.20201004011

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  The application of ultrasonic vibration in the welding process can effectively suppress the pore defects of the weld. The different ultrasonic application methods own different effects on the weld pore. In this paper, the ultrasonic frequency vibration in the weld pool is excited by the coupling of the ultrasonic frequency electrical signal and the welding electrical signal. The influence of ultrasonic excitation voltage and excitation frequency on porosity, number, location, and size of pore in weld was investigated. The results show that the variation of ultrasonic excitation voltage and frequency has a direct influence on the pore distribution. The pore defects can be decreased by the coupling of ultrasonic frequency electrical signal with reasonable parameters or increased by the coupling of ultrasonic frequency electrical signal with unreasonable parameters. The ultrasonic excitation frequency is fixed at 30 kHz and the ultrasonic excitation voltage is changed. The porosity of the weld is close to that of the weld without ultrasonic action when the ultrasonic excitation voltage is 25 V and 75 V. The porosity of the weld is significantly lower than that of the weld without ultrasonic action when the ultrasonic excitation voltage is 50 V and 100 V. The ultrasonic excitation voltage is fixed at 100 V and the ultrasonic excitation frequency is changed. The porosity of the weld is the largest and exceeds that of the weld without ultrasonic action when the ultrasonic excitation frequency is 20 kHz. The porosity of the weld is lower than that of the weld without ultrasonic action when the ultrasonic excitation frequency is 25, 30, 35, and 40 kHz. The pores were mainly concentrated on the upper part of the weld and the number of pores of small size increased significantly after the coupling of an ultrasonic frequency electrical signal, indicating that ultrasonic promoted the rise and escape of bubbles in the weld pool.
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  Effect of heat treatment on microstructure and properties of VG10 and 3Cr13 dissimilar welded joints

  尹燕, 康平, 张瑞华, 路超, 肖梦智, 张圆

  中国焊接. 2021, 30(1): 21-29. https://doi.org/10.12073/j.cw.20200528008

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  Through laser swing welding of dissimilar steels, the microstructure and properties of welded joints of dissimilar steels under different heat treatment processes were investigated. In the test, the equilibrium phase diagrams of the base materials 3Cr13 and VG10 were calculated by JMATPro software. The microstructures of the different regions of the welded joints after the original and heat treatment were analyzed by XRD and SEM, and the changes of the microhardness were tested. The test results show that a martensite-like structure is generated at the base material on the 3Cr13 side of the original welded joint, and a non-convective mixing zone exists in the fusion zone on the VG10 side. At this location, a block-like, island-like structure is embedded in the base material. There were lamellar carbide formation on this structure. After heat treatment, the amount of carbides in the welded joints is reduced, but the primary carbides in the VG10 base metal are difficult to eliminate by heat treatment. In addition, the lamellar carbides in the VG10 side fusion zone are polymerized to form network carbides. The hardness of the base metal near the fusion line on both sides of the original welded joint is relatively large, and the hardness of the heat affected zone gradually decreases with increasing distance from the center of the weld. After heat treatment, the overall hardness of the welded joint has increased significantly. Among them, the hardness increase is greatest at the quenching temperature of 1050 ℃, and VG10 can reach about 830 HV.
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  Strength mismatch mechanism on friction stir welding joint of 7075 aluminum alloy

  朱浩, 董少康, 赵熠朋, 王晨霁, 王军, 朱绍金

  中国焊接. 2021, 30(1): 30-36. https://doi.org/10.12073/j.cw.20210114001

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  The precipitated phases in the WNZ, TMAZ, HAZ and BM of the friction stir welding (FSW) joint were observed using the transmission electron microscopy (TEM) and the lattice fringe spacing of the precipitated phases was measured. Combined with X-ray diffraction (XRD), the types of precipitated phases among the joint were confirmed and then the strength mismatch mechanism was revealed. The results show the precipitated phases of 7075 aluminum alloy FSW joint mainly consist of MgZn₂, AlCuMg and Al₂CuMg. The micro-zone of the joint experienced different thermal cycles, the types and sizes of precipitated phases are different and the strengthening effect is different. The strengthening effect of the AlCuMg and Al₂CuMg are better than that of MgZn₂. The precipitated phase in the WNZ mainly includes AlCuMg and Al₂CuMg, as well as the grain size is fine, the microhardness in this zone is pretty high. The number of precipitated phase AlCuMg and Al₂CuMg is smaller in the TMAZ and the MgZn₂ is relatively more, which lead the microhardness decrease. The number of precipitated phase MgZn₂ is relative larger in the HAZ, as well as the grain coarsening, the microhardness in this zone is lowest of the joint. At the same time, there are the precipitate free zones (PFZ) among the 7075 aluminum alloy FSW joint, which decreases the micro-hardness of the whole joint to some extent.
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  Study on resistance spot brazing process and joint performance of pure aluminum 1060 / galvanized steel

  张昌青, 刘晓, 金鑫, 王维杰, 王希靖

  中国焊接. 2021, 30(1): 37-42. https://doi.org/10.12073/j.cw.20200808002

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  Resistance spot brazing was used to perform the lap test of pure aluminum 1060 and SGCC hot-dip galvanized steel plate, the joint interface structure was studied, and the mechanical properties of the joint were tested. The results show that the aluminum-silicon (Al-Si) alloy solder used in the test has good wetting, and an intermetallic compound with a double-layer structure and uneven thickness is produced at the welded joint interface after welding. The thickness is <10 μm. The welding current is at 7.8 kA, the tensile shear load of the joint reaches a peak value of about 4.72 kN. Under the same process parameters, the tensile shear load of the resistance spot brazed joint is significantly higher than that of the spot welded joint. The joint fracture mostly occurs on the aluminum plate side, and mainly at the heat-affected zone and not at the welding point.It indicates that the quality of the spot brazed joint is good, but due to the local "unbrazed" defect on the aluminum side interface of the weld, tensile stress will occur at the weld interface and the stress effect on the intermetallic compound. It is easy to produce cracks.
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  Structure and mechanical property of TC17 linear friction welding joint

  季亚娟, 张田仓, 张连锋, 郭德伦

  中国焊接. 2021, 30(1): 43-47. https://doi.org/10.12073/j.cw.20200528002

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  TC17 titanium alloy which usually used on the fan and compressor disk were selected. Microstructure and mechanical property of joint were investigated. Microstructure character of different part of joint was analyzed also. Results showed that the joints included three zones, base metal (BM), thermal mechanical affected zone (TMAZ) and weld zone (WZ). The microstructure of joint middle part was equiaxial grains, but the bottom part was the elongated grains. Dynamic recrystallation happened at the weld zone. Tensile test result showed that joint tensile strength equal to that of the TC17 base metal. The average hardness value of the HAZ was 486 HV which was higher than that in the BM and WZ.
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  Study on asymmetric thermo-physical effect mechanism of intermediate frequency DC resistance spot welding for aluminum alloy

  韩立军, 林鹏宇, 张更伟, 钟丽慧

  中国焊接. 2021, 30(1): 48-56. https://doi.org/10.12073/j.cw.20210111001

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  The asymmetric thermo-physical mechanism of the resistance spot welding technique with intermediate frequency (2 kHz) and direct current (RSWIFDC) on the high strength aluminum (Al) alloy TL091 was studied here in view of the Peltier effect. On the basis of the analysis of the electrode cap surface erosion state and the shape-position of the nugget, it was concluded that asymmetric thermo-physical phenomenon occurred on both ends of the nugget, and even had an influence upon the shape-forming coefficient and the vertical position deviation of the nugget, and the erosion degree of the electrode caps. In this work, the relative thermo-physical model of the welding was established combined with the Peltier effect and the spot welding characteristics. Accordingly the relative welding phenomena, such as nugget center deviation and different erosion degree of the electrode cap surface, was explained clearly using the model related with the Peltier effect for the first time. This model provides important theoretical basis for future study and application of Al alloy spot welding, based on which, effective works may be done to promote the quality of the Al alloy welded joints and to obtain favorable control upon parameters of Al alloy welding for electrode caps.
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  The welding application of high strength steels used in engineering machinery

  崔冰, 严佩佩, 杜全斌, 杨德, 崔梦栓, 彭梦都

  中国焊接. 2021, 30(1): 57-64. https://doi.org/10.12073/j.cw.20201231001

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  With the rapid development of low alloy steel strength level, more problems caused by welding are exposed day by day. Recently, the efforts have been paid to improve or enchance the low toughness of heated affected zone and welded metal which can enchance the comprehensive mechanical properties that is the core scientific problems of its safe operation by researching crack initiation and crack propragation attracted a rapidly growing interest. This article focuses on the research status and progress of welding technology and joint microstructure and properties of advanced steel materials. The influence of shielding gas on the microstructure evolution of deposited metals，the effect heat input of welded joint performance, interpass temperature and alloy elements on welded joints microstructure and M-A constituent evolution and properties are reviewed in detail. And for the heat affected zone, the grain size and microstructure as well as the shape, size, and distribution of M-A constituent, have a significant impact on the impact toughness. This paper is an attempt to review the effect of different welding process parameters on welded metal and HAZ of HSLA steels.