Abstract: Aluminum-nickel is an important electrode material which has good application prospects to study the bonding mechanism and optimization technology of the joints. Ultrasonic welding of dissimilar metals, 1A99 aluminum alloy and N4 nickel alloy, were conducted in this research. The effect of welding energy on mechanical properties, macro morphology, atomic diffusion and fracture mode of the welded joints have been analyzed emphatically. The results show that under the high-frquency ultrasonic vibration, a sound aluminum to nickel ultrasonic welding joint is successfully obtained. The maximum tensile shear load of joint can reach 1121N at the welding energy of 600J. The hardness profile of aluminum side which is close to the sonotrode tip is decreased, while the hardness of nickel side is slightly increased during the welding process. By increasing the welding energy, the indentation depth on aluminum side is increased, and significant deformation of joints in the thickness direction is observed when the energy reaches 700J. The scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) analysis show that a 5.29μm thick transition layer in the faying interface between Al and Ni is found under the optimized welding parameters. And there is no intermetallic compound (IMC) formed in the joint. The brittleness problem of Al-Ni dissimilar metal joints caused by traditional fusion welding methods is solved in this study, which lays a theoretical foundation for promoting the development of Al-Ni electrode materials.

Key words: dissimilar metals； ultrasonic welding； welding energy； mechanical properties