Evaluation of ultrasonic spot welded Al-Cu dissimilar sheets: Mechanical performance, microstructural changes and thermal analysis

Abstract

Automotive lithium-ion battery manufacturing industries are increasingly using ultrasonic welding (USW) to join thin dissimilar metals and foils. USW has good joint efficiency, no formation of the heat-affected zone, high production rate, shorter welding time, and sustainability over conventional fusion welding techniques. However, this process is less distinct and precise control of weld surface conditions to get good quality welds. In this regard, experimental and thermal analysis significantly helps to control the state of the weld interface during the joining process. In this study, the objective is to enhance the mechanical performance of aluminum (Al) and copper (Cu) joints under different surface conditions such as lubricating, normal, electrolytically, and emery polished. According to the lap shear tensile load result, the joint strength decreases significantly with the rise in weld time after 0.7 s. The lubricating surface provides the maximum lap shear tensile load of 1507 N among all other surface conditions. Fracture surface analyses are conducted to determine the quality of welds under varying surface conditions. Additionally, a three-dimensional (3D) finite element model (FE) for ultrasonic welding of two highly conductive metal sheets is also being investigated for the purposes of analysing the thermal behaviour around the weld interface. It reveals that the thermal profile of the interface differs depending on the surface condition. The numerical framework is confirmed by comparing the predicted interface temperature variations at different faying surface conditions with the experimental results.