Interface microstructure and mechanical properties of copper/304 stainless steel dissimilar joint assisted by Ni transition layer using ultrasonic additive manufacturing (UAM)

The copper/304 stainless steel joints with high strength are obtained by preparing nickel transition layer on the steel surface using ultrasonic additive manufacturing (UAM) and pulsed TIG welding method. The results show that the addition of the nickel intermediate layer achieves metallurgical isolation between copper and steel, inhibits the infiltration of copper into steel grain boundaries and reduces joint stress, resulting in the formation of hybrid joints including fusion brazing (copper-nickel) and diffusion welding (nickel-steel). The weld and the vicinity of the interface are mainly composed of Cu-Ni solid solution and Ni-rich phase. The wavy texture produced by UAM on the nickel surface can form mechanical interlock at the interface to improve the joint strength, and finally all joints fracture near the fusion line on the copper side.