Dynamic Weld evolution during ultrasonic welding of Cu–Al joints

Abstract

Although ultrasonic welding of dissimilar metals has been widely applied in the automotive and electronic industries, the dynamic weld evolution, including deformation, breakage, and attachment, is still in a conjecture stage because of the short welding time, thin reaction layer and complex thermomechanical behavior. In this study, dissimilar welds of aluminum (Al) alloy 1060 to T2 copper (Cu) were comprehensively investigated via microstructural characterization, molecular dynamics simulations, and mechanical tests. It was found that micro-welds first formed at high asperities. Subsequently, the continuous relative friction at the interface induced severe plastic deformation on the Al side, resulting in the alternating fracture and formation of micro-welds, flattening of asperities, and attachment of Al on the Cu surface. The lap shear failure loads for the joints gradually increased with increasing welding time. The failure loads reached the maximum values of 0.9 ± 0.03 kN after a welding time of 0.29 s. Furthermore, the Cu asperities completely sunk into the Al matrix, presenting a macro-interlocking morphology at the interface. A swirl-like grain morphology with no deformation texture appeared simultaneously on the Al side. Analysis of the weld formation indicated that microstructural evolution of the joint, including material flow, grain morphology, and grain orientation, was mainly concentrated on the softer material side, providing a new understanding of the ultrasonic welding of dissimilar metals.