2019年, 第28卷, 第4期　
刊出日期：2019-12-28

  

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  Effect of Ga on microstructure and properties of Sn-Zn-Bi solder for photovoltaic ribbon

  张敏, 许桓瑞, 王刚, 朱子越

  中国焊接. 2019, 28(4): 1-7. https://doi.org/10.12073/j.cw.20190917001

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  In this study, SEM, EDS, XRD and other test methods were used to study the effects of different Ga contents (0~2 wt.%) on microstructure, electrical conductivity, spreading area and mechanical properties of Sn-9Zn-3Bi solder. The results revealed that the microstructure of Sn-Zn-Bi-Ga solder alloy was mainly composed of β-Sn, Zn-rich, Bi-rich phase and Sn-Zn eutectic structure. The Ga can significantly improve the wettability of Sn-Zn-Bi on the pure copper, the maximum wetting area was 105.3 mm². With the increase of the Ga content the melting point of the solders decreased from 195 ℃ to 177 ℃. In addition, the Ga element can increase the oxidation resistance of solder. Its conductivity showed a decreasing trend with the gradual increase of the Ga content. With the increased of the Ga content the IMC (Intermetallic Compound) of Sn-Zn-Bi-xGa/Cu is only Cu5Zn8 and its thickness decreased remarkably.
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  Mechanism analysis of free formation of backing weld by the pulsed MAG-TIG double arc tandem welding

  刘黎明, 周彦彬

  中国焊接. 2019, 28(4): 8-15. https://doi.org/10.12073/j.cw.20190716002

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  Because of the presence of lower-level automation and efficiency in the backing welding of medium–thick plates, pulse-metal-active-gas–metal-inert-gas (MAG–MIG) dual-arc welding was applied to backing welding of 24-mm-thick Q235-B plate and the process and mechanism of root welding with back formation were investigated. The heating position of the MAG-arc at the front of the molten pool could be adjusted by using the electromagnetic force between the MAG-arc and the MIG-arc, and part of the arc energy could work on the root face directly. By combining the arc-discharge behaviour and analysis of flow in the molten pool, the shear stress of a tungsten inert gas (TIG) arc to the molten pool could make the liquid metal flow backwards. Thus, the quality of the front and bottom liquid metal were reduced, which favored the balance and stability. Continuous and stable back formation with uniform penetration could be achieved by using the pulse MAG–TIG dual-arc welding technology.
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  Cross section scan trace planning based on arc additive manufacturing

  孙清洁, 桑海波, 刘一博, 冯吉才

  中国焊接. 2019, 28(4): 16-21. https://doi.org/10.12073/j.cw.20190805002

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  In the context of additive manufacturing processes, the influence of specimen deformation from different welding paths is conducted by using CMT-AM. A least-squares method was used to quantitatively measure specimen deformation. The values of S (i.e., the sum of the distance from each feature point in a plane to the ideal plane)from different welding paths had significant influence on deformation of deposited layer.With the value of S increasing, the deformation of deposited layer gradually increased. With this result, a suitable welding trace plan was ascertained, which was successfully used to acquire well-formed and densely organized specimens during the arc-welding additive manufacturing process. Our results provide a foundation for experiments based on deposited layer scanning trace planning.
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  Underwater robot local dry welding system

  王振民, 谢芳祥, 冯允樑, 张芩

  中国焊接. 2019, 28(4): 22-27. https://doi.org/10.12073/j.cw.20190721002

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  To satisfy the demand for good quality underwater welding and maintenance of nuclear power stations, a set of local dry automatic welding systems has been developed. These systems were based on an underwater robot that consisted of a special high-power underwater welding power supply, diving wire feeder, mini drain cap, welding robot, and special underwater welding torch. With a digital signal controller microprocessor as its core and combined with a dual inverter topology, the welding power supply was characterized by full-digital construction and multi-waveform flexible output. A compact diving wire feeding device was designed, based on the armature voltage negative feedback and high-frequency chopping pulse width modulation.This device yielded a high-efficiency seal of the driving motor with the help of dynamic and static sealing technology. To overcome the difficulty of local protection and deslagging in the welding area, a mini drain cap (with a duplexgas structure) based on the principle of the convergent nozzle was designed. The practical tests and the underwater welding experiments revealed that the underwater robotic local dry welding system is quite feasible. That is, the system could strike the arc stably and reliably in the shallow water environment, and formed beautiful welding seams.
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  Analysis of weld pool vibration characteristics in pulsed gas metal arc welding

  吕小青, 张鹏, 沈俊

  中国焊接. 2019, 28(4): 28-32. https://doi.org/10.12073/j.cw.20190709002

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  Using highspeed camera image measuring and processing, the contour of the weld pool was extracted accurately in pulsed metal inert gas (P-MIG) welding. Based on this extraction method, time and frequency domain characteristics at different points along the contour of the weld pool were analyzed for one pulse one droplet and one pulse two droplets, respectively. The results show that, because of the wave super position that was created by the pulsed arc and droplet impacting the weld pool, the oscillation amplitude along the weld pool fluctuated and decreased with an increase in distance from the point to the arc center. The oscillation near the arc center was complex and intense for one pulse two droplets, and the amplitude were relatively small because the oscillation caused by the pulsed arc could be offset by the molten droplet impact. The weld pool oscillation that was caused by the pulsed arc was stronger than that caused by the droplet.
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  Graphene-coated copper foam interlayer for brazing carbon/carbon composite and niobium

  王泽宇, 霸金, 亓钧雷, 冯吉才

  中国焊接. 2019, 28(4): 33-38. https://doi.org/10.12073/j.cw.20190825002

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  Problems such as poor structural integrity, inhomogeneous dispersion, and agglomeration of graphene in the brazing seam are typically encountered for graphene additives in a brazed joint interface. To resolve these problems, a plasma-enhanced chemical vapor deposition process was employed for in-situ preparation of a high-quality graphene-coated copper (Cu) foam composite interlayer prior to be applied for brazing carbon/carbon composite and niobium. The prepared graphene and the brazed joints were characterized via Raman spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The results revealed that graphene was evenly distributed in the brazing seam with the help of the Cu foam, which was characterized by interconnected porosity. Simultaneously, the excellent chemical inertia of graphene inhibited the collapse of the Cu foam, based on which the thermal residual stress in the joint was effectively mitigated due to the synergistic reinforcement effect of the Cu foam (with good plastic deformation capacity) and graphene (with extremely low coefficient of linear expansion). This effect led to significant improvement in the average shear strength of the joint.
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  Combine S-N curve and fracture mechanics for fatigue life analysis of welded structures

  魏国前, OdsurenOchbileg, 岳旭东, 党章

  中国焊接. 2019, 28(4): 39-45. https://doi.org/10.12073/j.cw.20190623002

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  Based on the evolution of fatigue cracks in welded structures, the fatigue life of welded structures was defined as the sum of the crack initiation life N_i and the crack propagation life N_p. Correspondingly, a fatigue-life analysis method combining S-N curves and fracture mechanics theory was proposed. The equivalent structural stress method and the lower 99% boundary of the master S-N curve were used to evaluate N_i, and cracks at the end of the initiation stage were considered as semi-elliptical surface cracks. Moreover, Paris equation and the stress intensity factor range of the cracks were used to evaluate N_p. Furthermore, the fatigue test results obtained from the running girder of cranes were used as a reference for comparison and verification of the results. The results revealed that the equivalent structural stress is a good indicator for the crack initiation behavior of complex welded structures. In addition, the predicted fatigue life corresponded closely to the testing life.
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  Seam-tracking based on dynamic trajectory planning for a mobile welding robot

  洪宇翔, 都东, 潘际銮, 李湘文

  中国焊接. 2019, 28(4): 46-50. https://doi.org/10.12073/j.cw.20190717002

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  A new seam-tracking method based on dynamic trajectory planning for a mobile welding robot is proposed in order to improve the response lag of the mobile robot and the high frequency oscillation in seam-tracking. By using a front-placed laser-based vision sensor to dynamically extract the location of the weld seam in front of torch, the trend and direction of the weld line is roughly obtained. The robot system autonomously and dynamically performs trajectory planning based on the isometric approximation model. Arc sensor technology is applied to detect the offset during welding process in real time. The dynamic compensation of the weld path is done in combination with the control of the mobile robot and the executive body installed on it. Simulated and experimental results demonstrate that the method effectively increases the stability of welding speed and smoothness of the weld track, and hence the weld formation in curves and corners is improved.
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  Electron beam welding of SiCp/2024 and 2219 aluminum alloy

  陈国庆, 张秉刚, 杨勇, 冯吉才

  中国焊接. 2019, 28(4): 51-55. https://doi.org/10.12073/j.cw.20190713002

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  SiC_p/2024 matrix composites reinforced with SiC particles and 2219 aluminum alloy were joined via centered electron beam welding and deflection beam welding, respectively, and the microstructures and mechanical properties of these joints were investigated. The results revealed that SiC particle segregation was more likely during centered electron beam welding (than during deflection beam welding), and strong interface reactions led to the formation of many Al₄C₃ brittle intermetallic compounds. Moreover, the tensile strength of the joints was 104 MPa. The interface reaction was restrained via deflection electron beam welding, and only a few Al₄C₃ intermetallic compounds formed at the top of the joint and heat affected zone of SiC_p/Al. Quasi-cleavage fracture occurred at the interface reaction layer of the base metal. Both methods yielded a hardness transition zone near the SiC_p/2024 fusion zone,and the brittle intermetallic Al₄C₃compounds formed in this zone resulted in high hardness.
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  Fabrication of in-situ synthesized ceramic reinforced Ni-based alloy composite coatings by reactive braze coating processing

  裴新军, 刘文彬, 程铬, 潘新宇, 李爱娜, 李海深

  中国焊接. 2019, 28(4): 56-62. https://doi.org/10.12073/j.cw.20190911001

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  In-situ synthesized ceramic such as TiC, Cr7C3 and Cr5B3 reinforced Ni-based alloy composite coating was fabricated on the surface of mild steel substrate by reactive braze coating processing with colloidal graphite, Cr, Ni, ferro-boron, Si and titanium powders as the raw materials at low temperature of 1 000 ℃, and a new kind of coating materials was developed. By means of SEM, EDS, XRD and surface hardness tester, the microstructures, phases, hardness and wear-resistance of the coating were analyzed, respectively. The results revealed that the coating was mainly composed of the ceramic in-situ synthesized reinforcement phases of TiC, Cr7C3 and Cr5B3 and the binder phases in-situ synthesized of Ni31Si12 and (Ni, Fe) solid solution; The ceramic reinforcement phases of TiC, Cr7C3 and Cr5B3 were randomly distributed in the binder phases of Ni31Si12 and (Ni, Fe) solid solution; The coating had about 15vol% pores and can possibly be applied as a self-lubrication coating; The coating and the substrate were integrated together by metallurgical bonding; The coating had a hardness up to 91-94HR15N.