Effects of welding pressure on high-power ultrasonic spot welding of Cu/Al dissimilar metals

Abstract Although high-power ultrasonic welding (HPUSW) can provide better welding results about highly conductive materials, the welding mechanism is not well understood. In this study, the effects of welding pressure on dynamic process and joint characteristics (strength and fracture) of HPUSW were investigated. High pressure produces lower vibration amplitude of the upper and bottom specimens. Under excessive pressure, the vibration amplitude of sonotrode is significantly reduced, as compared to that under lower pressure during the initial welding period. The distribution of plastic strain follows the principle of crack growth and expansion. Excessive pressure results in the extrusion of trace elements from base material to the interface, which affects the process of interfacial diffusion. The maximum welding strength is obtained as the depth of penetration of sonotrode reaches its maximum value without the production of cracks. The results obtained in this work provide guidelines for optimizing the ultrasonic welding parameters.