Achieving High Strength Joint of Pure Copper Via Laser-Cold Metal Transfer Arc Hybrid Welding
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COPPER (Cu) and its alloys have been widely applied in industrial production because of excellent properties, such as high electrical and thermal conductivities, good ductility, and excellent corrosion resistance. However, commercial pure Cu is difficult to be joined by conventional arc welding linearly because of high thermal conductivity. Generally, preheating and great heat input (i.e., usually more than 850 kJ/m) are required, which leads to low welding efficiency and low-performance joint with remarkable grain coarsening within fusion zone (FZ) and heat-affected zone (HAZ), wide HAZ, low strength, and great distortion.[1–3] For example, Wang found that the maximum tensile strength of tungsten inert gas arc-welded Cu was only 142.6 MPa, not more than 50 pct of base metal (BM).[3] Since most of Cu parts need subsequent processing (such as rolling) after welding, the low-performance arc weld is hard to meet the requirement of modern industries. Laser welding of pure Cu is very difficult yet because of low laser absorptivity of pure Cu, although many assistant methods were employed. Biro et al.[4] found that increasing the oxygen content in argon assist gas increased the effective laser absorptivity of pure Cu, and then facilitated the process at much lower laser power and increased weld penetration depth. However, weld metal embrittlement due to excessive volume fraction of
YULONG CHEN, Master Student, CONG CHEN, Doctoral Student, and MING GAO, and XIAOYAN ZENG, Professors, are with the Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, P.R. China. Contact e-mail: [email protected] Manuscript submitted November 21, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
oxides was observed. Chen et al.[5] demonstrated that laser welding efficiency of pure Cu was significantly increased by using Cu-based nano-composite absorber. Gao et al.[6] succeed to join the bronzes by laser welding with filling Cu powder. The welds represented minor microstructure difference with the BM. Heider et al.[7] found that the keyhole in laser welding of Cu alloys was stabilized by power modulation, and the number of welding spatters and weld porosity were reduced effectively. Hess et al.[8] joined pure Cu by dual laser beams that combined a low power green laser beam with the wavelength of 515 nm and an infrared laser beam with the wavelength of 1030 nm. It was found that the green laser beam both increased the absorptivity and stabilized the keyhole, which facilitated the infrared laser welding of pure Cu at lower power. These studies improved laser weldability of pure Cu, but the complicated devices used or the possibly involved impurities limit their industrial applications. Presently, laser–arc hybrid welding has been considered as one of the most promising fusion welding methods in industry. By the laser–arc interaction, it has more advantages, such as better joint quality, higher welding stability, higher efficiency, and easier addition of welding wires.[9,10] It has succeeded i
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