Microstructure and mechanical properties of copper to nickel ultrasonic spot welds

Abstract Ultrasonic spot welding has been used for joining copper and nickel sheets. With increasing the welding time, the lap shear tensile load of Cu/Ni joints first increases up to the maximum (1879.1 ± 39.3 N), and then decreases. The hardness of the Cu side along the weld interface increases due to enhanced plastic deformation and element diffusion at the Cu/Ni interface. The microjoints expand from the weld interface below the peak of the sonotrode tip to the weld interface below the valley of the sonotrode tip. The joining mechanism is element diffusion, the generation and progressive expanding of microjoints, and mechanical interlocking.