2020年, 第29卷, 第4期　
刊出日期：2020-12-28

  

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  Influence of two-step aging on structure and stress corrosion sensitivity of friction stir welded 7050-T7451 aluminum alloys

  张华, 郭启龙, 赵常宇, 林三宝, 石功奇

  中国焊接. 2020, 29(4): 1-6. https://doi.org/10.12073/j.cw.20200601002

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  3 mm thick 7050-T7451aluminum alloy joint was obtained by friction stir welding, and the two-step aging treatment was performed at 121 °C × 5 h + 163 °C × 27 h after welding. Microstructure, hardness profiles and stress corrosion sensitivity of the joint were measured and studied. The results indicate that through the two-step aging, the grain size is coarsened, the age-hardening precipitates and PFZ become wider at the same time, which results in the discontinuous grain boundary; the microhardness of the FSW joints decreased, but the heat-affected zone significantly narrowed, which increased the uniformity of the microhardness of the FSW joints; and the two-stage aging effectively reduced the stress corrosion sensitivity of the FSW joints. The joints with aging treatment were not broken after 60 days, however all the joints without aging treatment were broken within 1 day.
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  Evolution of microstructural and mechanical properties of AISI 316 during continuous drive friction welding process

  Jabbar Hassan Ammar, Boukharouba Taoufik, Miroud Djamel, Titouche Nacer-Eddine, Ramtani Salah

  中国焊接. 2020, 29(4): 7-12. https://doi.org/10.12073/j.cw.20200310001

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  The aim of present study is introducing a method by subdividing friction welding phases into three steps according to the temperature change during continuous drive friction welding operation. Thermal curve allowable subdividing of the friction welding phase’s time into three distinct periods, while the microstructure evolution during friction welding goes through three different situations. The effects of three distinct periods were achieved by macro-microscopy, microhardness HV_0.1, tensile tests and scanning electronic microscopy (SEM). The results clearly show that the microstructure during the friction phase goes through three completely different situations which mechanically influenced on microstructure, tensile strength and ductility of the welded joint.
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  Research on the influence mechanism of brazing seam geometry on gas pores in brazed joints

  程战, 龙伟民, 薛松柏, 傅玉灿, 吴铭方

  中国焊接. 2020, 29(4): 13-18. https://doi.org/10.12073/j.cw.20200804001

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  Gas pore is a common defect in brazed joint. It lowers the brazing rate and affects the properties of joint. Experimental results show that the application of unequal-gap brazing seam effectively decreases the amount and volume of gas pores, and increases brazing rate. This paper establishes a force model of unequal-gap brazing seam, and proposes the constitutive relationship between expulsion force and curvature. The force condition of gas bubble in geometrically different brazing seams were calculated, and the results were verified with experiments. The results show that the expulsion force of gas bubble is positively correlated to the curvature of the seam geometry. The gas bubble tends to move towards the direction with large curvature and wider gap. The directional bubble movement is obtained through varying the configuration of gas-liquid interface to meet geometric conditions. Gas bubble accelerates to expulse with arc, hyperbola and cycloid brazing seams, in which the best drainage effects of gas bubble occur for cycloid seams.
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  Weld shape and microstructure of TC4 laser welding with activating flux of Na₂SiF₆

  侯继军, 董俊慧, 白雪宇, 韩旭, 杨虎

  中国焊接. 2020, 29(4): 19-24. https://doi.org/10.12073/j.cw.20200404002

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  Na₂SiF₆ was used as surface activating flux for laser welding of TC4 titanium alloy. The effect of Na₂SiF₆ on TC4 titanium alloy laser welding was determined by observing the weld surface. The morphological characteristics of the high temperature plasma above the workpiece was observed and analyzed by using high-speed digital camera system. The variation of weld depth,width and microstructure were analyzed by optical microscope. The experimental results show that laser weld of TC4 titanium alloy has good appearance with activating flux of Na₂SiF₆, weld penetration increases by about 0.8%–12%, while weld surface width decrease by about 10%–29%, the depth to width ratio is effectively improved. The inhomogeneity of weld microstructure was improved, and the crystallization direction of β columnar crystals on the upper part of the weld was changed, the grain size and microstructure of the weld were refined by Na₂SiF₆.
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  Evolution behavior of phase and performance in Ni-based coating layer based on high temperature thermal field

  秦建, 黄俊兰, 龙伟民, 于德庆, 吴铭方, 王裕昌

  中国焊接. 2020, 29(4): 25-32. https://doi.org/10.12073/j.cw.20200526001

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  Effect of post-welding heat treatment on the microstructure and properties of BNi-2 brazing coating was analyzed. The phase transformation in the heat treatment process was analyzed by high temperature metallographic microscope, scanning electron microscope and X-ray diffraction, and the microhardness after the post heat treatment was tested by microhardness tester. The results show that the microstructure of brazing BNi-2 brazing coating is mainly CrB phase, Ni solid solution phase and eutectic phase of Ni₃B and Ni₃Si. After brazing, the overall hardness value is higher, generally higher than 510 HV, and the microhardness in some areas is higher than 700 HV. After quenching, the solid solution phase of Ni increased, and the eutectic phase of Ni and Ni₃Si decreased, leading to the softening of the brazing coating, the area whose microhardness in the range of 342 HV–454 HV increased. After tempering the brazed coating samples, the eutectic phases of Ni and Ni₃Si grew and the hardness recovered, but the overall hardness distribution was still lower than the brazing one. The results of the brazing post-heat treatment test show that the post-welding heat treatment will bring adverse effects on the hardness distribution of the coating, which may affect the wear resistance of the coating.
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  Relation between viscoplastic flow, periodic feature and Joule heat validity for electrically assisted friction stir welding

  耿海滨, 罗键, 高建军, 项俊锋

  中国焊接. 2020, 29(4): 33-40. https://doi.org/10.12073/j.cw.20200606010

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  Electrically assisted friction stir welding is a promising way to improve liquidity of viscoplastic metal. However, this local heat source only can take into effect in a certain contact interface status. Semi-analytical model and FEM are adopted to analyze materials flow in electrically assisted FSW. Semi-analysis results show that Joule heating is validity with rotation speed 1400 r/min and travel speed 400 mm/min. The maximum flow velocity is 0.033 m/s when travel speed is 400 mm/min, and it increases to 0.043 m/s with current assistant. Visco-plasticizing efficiency is a key factor to decide whether Joule heat is significant, and viscoplastic flow can periodically make circuit short. Periodic torque, axial force and onion rings surface show dynamic flow process, which can be used to illustrate the dynamic contact resistance feature and correct the calculation equation of Joule heat. This paper is aim to point out the potential relation between viscoplastic flow, periodic torque and Joule heating validity.
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  Quality evaluation of laser welds based on air-coupled ultrasound

  常俊杰, 李媛媛, 汤永辉, 邬瑞峰

  中国焊接. 2020, 29(4): 41-47. https://doi.org/10.12073/j.cw.20200325002

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  With the wide application of laser welding technology in automobiles and rail transportation, the non-destructive testing technology for laser welding seams is also getting better. Aiming at the laser welding seam of two-layer metal sheet below 3 mm, the possibility of laser welding seam detection by air-coupling ultrasonic detection technology is discussed. By numerical analysis and experimental analysis, Lamb wave is excited on aluminum plate in air. Through the propagation simulation of Lamb wave in laser weld specimen, the influence of laser weld width and weld quality on reflectivity and transmittance is analyzed. The propagation law of Lamb wave in laser weld specimen is clarified. The results show that the quality of laser weld can be evaluated by the mode of Lamb wave A0.
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  Effect of aluminium element on microstructure and properties of weld metal of 960 MPa steel

  裘荣鹏, 冯旭

  中国焊接. 2020, 29(4): 48-53. https://doi.org/10.12073/j.cw.20200602009

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  A kind of self-protective flux cored wire has been developed for joining 960 MPa high strength steel. Weld metal containing different aluminium elements contents was obtained by changing the content of aluminum powder in the composition of the flux core. The strength and toughness of weld metal were tested by tensile test and impact test at different temperatures, and the influence mechanism of aluminium element on the microstructure and mechanical properties of weld metal was analyzed by means of metallographic microstructure observation and scanning electron microscope observation. The results show that aluminium element content on impact ductility of weld metal of 960 MPa high strength steel is great, but the influence on tensile strength and elongation of weld metal is little. With increasing aluminium element contents of weld metal, the impact energy of weld metal increases at first and then decreases, the best aluminium element content of weld metal is 0.2 wt.%. Aluminium oxide is easy to be formed in weld metal with low aluminium element contents, and the aluminium oxide can easily become nucleation particle for acicular ferrite. It is conducive to formation more acicular ferrite and will improve impact absorbing energy of weld metal. Aluminium nitride will easily formed in weld metal with high aluminium element content, and the coarse ferrite microstructure appears in weld metal and reduces impact energy of weld metal.
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  Study on sensitivity of Nb to high-temperature ductility dip crack of inconel 690

  王吉孝, 王黎, 王君, 金国

  中国焊接. 2020, 29(4): 54-59. https://doi.org/10.12073/j.cw.20200603001

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  Sensitivity of Nb to high-temperature ductility dip crack (HTDDC) of deposited metal of Inconel 690 welding wire was studied in detail. Strain to fracture test and high-temperature tensile test were selected as the test methods to study the sensitivity of HTDDC. The deposited metals of four kinds of welding wire were observed and analyzed by OM and SEM. Experiment results show that Nb can effectively improve the ability of Inconel 690 to resist HTDDC and reduce the crack sensitivity of deposited metal. The mechanism of HTDDC is the grain boundary strength of deposited metal is lower than the intragranular strength. The (Nb, Ti) C can effectively block the grain boundary sliding and improve the resistance to deformation of the grain boundary.
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  Joining of activated graphite to 6063 aluminum alloy with Al-Cu-Si-Ni-Mg filler metal

  元琳琳, 黄晓猛, 陈晓宇, 齐岳峰

  中国焊接. 2020, 29(4): 60-64. https://doi.org/10.12073/j.cw.20200419001

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  In this work, 6063 aluminum alloy-graphite joint intended for thermal conductive application were realized by applying Al-Cu-Si-Ni-Mg brazing filler metal and Ag-Cu-Ti pasted on high density graphite substrate to ensure wetting during the brazing process. The interface reactions during brazing and mechanical properties were studied using scanning electron microscopy (SEM) and shear test device. TiC was formed at the graphite/active Ag-Cu-Ti paste interface due to the reaction between Ti and C, and thus the wettability on the graphite was improved.It is shown that joint with a good quality can be produced at a brazing temperature of 550 ℃ for 10 min.The average tensile strength of the joint is 21MPa. thus the wettability on the graphite was improved.It is shown that joint with a good quality can be produced at a brazing temperature of 550 ℃ for 10 min.