Concurrent influences of tool offset and ultrasonic vibration on the joint quality and performance of dissimilar Al/Cu friction stir welds

Abstract

Dissimilar joints made of aluminium alloy (Al) and copper (Cu) have great prospective applications in the electrical and electronic industries. Still, it is a challenging task to join them and obtain good performance. In this study, dissimilar AA6061-T6 and C10100 joints were produced by friction stir welding (FSW) and ultrasonic vibration-assisted friction stir welding (UVaFSW) processes with three different tool offset degrees from the Al side to the Cu side. Tool offset towards Al base material and in the Al/Cu interface produced defect-free joints with sound strengths in both joints made with and without ultrasonic vibration. On the other hand, tool offset towards Cu base material produced unsound joints with defective features such as wormholes and a lack of surface fill in both joints made with and without ultrasonic vibration. Ultrasonic vibration addition favoured a drastic reduction in the intermetallic compound (IMC) layer thickness, particularly amongst the welds made with tool offset in the Al/Cu interface, than those made with tool offset towards Al base material. In addition, the influence of tool offsets and the ultrasonic vibration addition remarkably affects the sizes (particle areas and the minimum Feret diameters) and the concentration of the Cu particles distributed in the weld nugget. In the joints produced with tool offset towards Al base material, the particle areas and the minimum Feret diameters were decreased by ~73.3% and ~42.6%, respectively, with the ultrasonic vibration addition. On the other hand, ultrasonic vibration in the joints produced with tool offset in the Al/Cu interface resulted in decreased particle areas and the minimum Feret diameters by ~60.6% and ~24.6%, respectively. The joints made with ultrasonic vibration have higher tensile strength than those made by conventional FSW.