Ultrasonic Welds between Brass Terminals and Aluminum Cables for Use in Electric/Hybrid Vehicles: An Electron Microscopy Investigation

The purpose of this project was to analyze two ultrasonic welds of aluminum cable to brass terminals which were supplied by a local company, where one weld sample was considered successful and the other was considered unsuccessful. The consideration of ``successful'' (sample 1) versus ``unsuccessful'' (sample 2) weld was determined by whether the weld passed the local company's shear test. The goal of the analysis was to understand the cable/terminal surface conditions and ultrasonic weld microstructural and chemical characteristics of ``successful'' and ``unsuccessful'' samples. Light and scanning electron microscopy analysis of the aluminum wires forming the cable showed significant roughness on the surface of the sample 1 wires, while the sample 2 have much smoother wire surfaces. Extended voids at the welded aluminum/brass interface of sample 2 were observed by combined high resolution SEM/TEM investigations. TEM analysis showed specific patterns in both materials for the length of the sample: highly deformed material along the interface, and an amorphous layer between the two metals. It was determined that ultrasonic weld performance depends on the surface condition of the starting materials.