Enhancing ultrasonic spot weldability of aluminum-copper alloy through surface modification techniques

Ultrasonic welding is a solid-state technique that is increasing​ly employed to join Li-ion battery interconnections in electric automobiles. Understanding the joint microstructure is essential for evaluating the performance and joint integrity. Surface modifications play a crucial role in affecting the friction and contact behavior at the joint interface. This investigation describes the effects of surface treatments and various welding energies on the ultrasonic weldability of aluminum/copper alloy joints using lubricated, normal, electrolytic, and emery-polished surfaces. The results demonstrated that lubricated surfaces facilitated improved plastic flow and mechanical interlocking, resulting in elevated tensile shear and T-peel failure loads of 642.37 N and 280.86 N, respectively, at a welding energy of 1950 J. The interface temperature of 420.66 °C was attained at this optimum weld energy. Microstructural analysis indicated that the lubricated surfaces exhibited a ductile fracture mode characterized by dimples, signifying mechanical interlocking and interface diffusion. Emery-polished surfaces exhibited the lowest mechanical performance. This decline is attributed to mixed-mode fracture, adhesive wear, and poor metallic bonding. Restricted interfacial sliding is considered responsible for the weakened bond. X-ray diffraction verified the existence of Al 2 Cu, Cu 5 Zn 8 , and Al 4 Cu 9 intermetallic compounds at the edge of the aluminum/copper alloy joints.