Laser Welding For Copper-Steel Joint

In this paper, dissimilar materials laser welding of carbon steel and T1 copper was comprehensively and systematically researched, and a new method of dissimilar materials laser welding of copper-steel was proposed. Firstly, dissimilar materials welding weldability of copper-steel was analyzed by welding metallurgy and molten pool solidification process. Because of the high reflectivity of copper to CO2 laser beam, the scarf joint geometry was used, i.e., the sides of the copper and steel were in obtuse and acute angles, respectively. During the welding process, the laser beam was fixed on the steel side and the dilution ratio of copper to steel was controlled by properly selecting the deviation of the laser beam. Secondly, Copper-steel butt joints with different copper dilution ratio were welded. To improve the adaptability of technology, copper-steel butt joint with nickel added in also were welded. Finally, Mechanical properties, composition and microstructure of joints were measured and analyzed. According to the analysis result, the formation process of interface between intermixing zone and copper plate was discussed.The dilution ratio of copper has great influence on the mechanical property and microstructure of copper-steel joint. When the dilution ratio of copper is much higher than that of steel, there are a large amount of mesophase particles on the copper matrix and many gas pores in the weld. The tensile sample was fractured at the weld, and the tensile strength is 250.7Mpa; When the dilution ratio of copper is close to steel's, there are a large amount of mesophase particles which are on the intergranular and many gas pores and cracks in the weld. The tensile sample was fractured at the weld, and the tensile strength is 139.3Mpa; When the dilution ratio of copper is much lower than that of steel, there are less mesophase particles on the upper side of interface between the intermixing zone and copper plate. the vortex phenomenon that weld invade into the copper matrix was found on the lower side. There is no obvious defect in the weld. The upper side of tensile sample was fractured at the interface between intermixing zone and copper plate, and the lower side was fractured at the copper plate. The tensile strength is 251.3Mpa.In this paper, copper-steel joints, which added nickel with different dilution ratio of copper, were welded. When the dilution ratio of copper is higher, there are many gas pores in the weld, The tensile sample was fractured at the weld, and the tensile strength is 249Mpa; When the dilution ratio of copper is lower, there are less gas pores in the weld. The tensile sample was fractured at the copper plate, and the tensile strength is 250.9Mpa.The copper-steel joints'mechanical properties and microstructure were analyzed by tensile testing machine, OM, SEM and TEM. The result show that when the dilution ratio of copper is low, a joint without gas pore and crack can be welded, and the tensile strength of the joint is higher than copper plate's. The weld's formation process was made up of three steps. Firstly, the laser beam was fixed on the side of steel, the steel was melted, and formed a keyhole. Secondly, the copper near the interface between EH36 and copper plate was melted due to the heat transfer. The copper and steel were mixed at the upper side of the interface, and the steel's turbulent liquid flow invaded into the copper matrix, which was melted or critical melted. Finally, the molten pool was solidified.