Evaluation of capabilities of ultrasonic vibration on the surface, electrical and mechanical behaviours of aluminium to copper dissimilar friction stir welds

Placement of the base materials in friction stir welding of aluminium to copper remains a significant aspect that influences the complete weld formation. Aluminium and copper were joined in different types of base material positions by friction stir welding and ultrasonic vibration-assisted friction stir welding. It was found that the roughness of the weld surfaces is reduced with the addition of ultrasonic energy during the welding, mainly in the type I joints. Besides, the aluminium/copper joint strength increased with a decrease in the intermetallic compounds layer thickness and sizes of the distributed copper particles in the type I and type II joints, respectively. The improvement of the strength seemed higher when copper was placed at the retreating side due to the aspect of mixing mechanisms between aluminium and copper in the stir zone, which established aspects of distributed copper particles. The digital image correlation technique was employed to investigate the major principal strain distribution along the cross-section of the welds as well as fracture step processes (strain evolution, crack inception, and dissemination) of friction stir welding and ultrasonic vibration-assisted friction stir welding joints. Welds performed with ultrasonic energy did not experience any form of improvement of the electrical conductivity. Nevertheless, the electrical conductivities of the friction stir welding and ultrasonic vibration-assisted friction stir welding joints are found to be within the range of the electrical conductivities of the base materials.