Ultrasonic assistance for fatigue properties improvement of AA6061/Ti6Al4V dissimilar joints by resistance spot welding

Abstract

Replacing monolithic Ti components with Al-Ti hybrid structures is a promising way to achieve lightweight design and cost reduction; thus, it is highly desirable to manufacture Al-Ti hybrid structures using appropriate welding techniques. In this study, the robust joining of AA6061 to Ti6Al4V was enabled by the in-situ ultrasonic-assisted resistance spot welding (UaRSW) technique. More importantly, the correlation between the interface microstructure and the quasi-static and fatigue fracture behaviors of the UaRSW joints was elucidated by comparing them with the corresponding conventional resistance spot welding (RSW) joints. Ultrasonic vibrations can enhance heat transfer to form thinner, wavy intermetallic compound (IMC) layers. Moreover, the oxide film on the surface of AA6061 fragmented under ultrasonic action and was distributed in the heat-affected zone (HAZ). Compared to RSW joints, UaRSW joints had a significantly higher tensile shear strength and energy absorption capacity, as well as much higher fatigue limits of 45 %. The transition from interfacial failure to button pullout was attributed to the UaRSW-induced wavy IMC layers, which inhibited crack propagation along the interface. This work demonstrated that in-situ ultrasonic-assisted UaRSW can effectively improve the joining quality while ensuring high productivity, which had great potential for high-performance Al-Ti welding.