Friction Stir Lap Welding with Pinless FSW Tool for Cu-Ni Alloy and Low-carbon Steel

  Cu-Ni alloy (C71000) and low-carbon steel (Q235) were joined by friction stir lap welding (FSLW) with pinless FSW tool with the help of nickel coating. The influence mechanism of the thickness of the nickel coating on the steel side on tension-shear strength of the weld was studied by means of tension-shear tests, SEM and EDS. Researches show that Ni coating could prevent Fe from oxidizing and reduce the micro-voids of the joint face of the weld. High interface temperature and contact pressure during the welding could promote diffusion of the Fe and Cu atom into the Ni coating through the interface and form seamless connection. Increasing the thickness of the nickel coating on the steel side could contribute to the improvement of the tension-shear strength of the weld. When the thickness of the Ni coating on Cu-Ni side and steel side reached 5μm and 20μm respectively, the maximum tension-shear strength of 295MPa was achieved, which was 2.76 times that of the weld without Ni coating and close to Cu-Ni alloy.