Influence of Weld Energy on Microstructure and Mechanical Properties of Ultrasonic Spot Welded Al/CuNi Dissimilar Sheets

Solid-state welding is an emerging technique with the sole purpose of creating quality joints within a few seconds. Aluminum and cupronickel sheets are typically utilized in lithium-ion battery packs. Electric vehicles employ these materials due to their higher electrical and thermal conductivity. Ultrasonic welding is an energy-efficient process that produces effective bonds rapidly between two dissimilar thin materials. The weld interface temperature is comparatively low during the ultrasonic welding process, and negligible intermetallic compounds are formed at the bond region. In the present study, the weld strength and failure behavior of aluminum/cupronickel joints are investigated at various weld energies. The critical stress intensity factor is used to determine whether the joint is capable of withstanding the crack before its failure. The result disclosed that as the welding energy upsurges, the critical stress intensity factor increases gradually to its maximum level and then decreases with further increasing welding energy. The hardness of aluminum side is decreased by increasing weld energy because of enhanced plastic deformation and elemental diffusion at the bond interface. On the other hand, cupronickel surface hardness is not changed distinctly. Moreover, the cross-sectional and microstructural behavior of the joint interface is discussed to comprehend the complete bond quality.