Effects of material combination for ultrasonic spot welding on microstructure and strength of Al/Al, Al/Cu, and Al/Ni dissimilar joints

Abstract

The dissimilar joining of Al/Cu and Al/Ni is required to reduce the weight of electronic and electrical devices. Ultrasonic spot welding (USW) is expected to be applied to dissimilar materials because of the low heat input during the joining process. However, to obtain high strength via USW, the relationship among the welding parameters, joining strength, and microstructure for different material combinations must be investigated. In this study, Al/Al, Al/Cu, and Al/Ni are joined via USW by systematically varying the welding parameters; subsequently, their tensile shear load and microstructure are investigated. Results show that the vibration amplitude and welding time impose greater effects on the joint strength than the welding pressure for all material combinations. High-strength joints that fractured at the Al upper plate are obtained by optimizing the welding parameters for each material combination. Al/Ni bonding had a narrower margin of welding time to obtain a higher tensile shear load compared with other material combinations. This is due to the high heating rate and maximum temperature of Al/Ni joints, which cause the excessive deformation of the Al upper plate during prolonged welding. Texture analysis showed that recrystallized grains with GOSS orientation was remained in the high-strength dissimilar joints.