Ultrasonic Spot Welding of an Aluminum Alloy for Automotive Applications

Abstract

To reduce fuel consumption and the resulting environment-damaging, climate-changing, costly, human death-causing emissions, lightweight aluminum alloys have been increasingly used in the transportation industry due to their low density, high specific strength, superior ductility, machinability, recyclability, and environmental friendliness. The structural applications of such aluminum alloys in the automotive industry unavoidably entail welding and joining process. While it is challenging to weld aluminum sheets via the conventional resistance spot welding developed mainly for joining steel sheets, an emerging solid-state joining technology known as ultrasonic spot welding (USW) is promising for joining aluminum alloys. This study was aimed to examine the feasibility of welding a 6022 Al alloy similarly (AA6022-to-AA6022) and dissimilarly (AA6022-to-ZEK100) in relation to welding energy. It was observed that there was a significant change in the interface grain size in the similar welding, exhibiting a characteristic fine-grained “necklace”-like structure along the welding line, while an intermetallic diffusion layer was present in the dissimilar welding of aluminum-to-magnesium alloys, and its thickness increased as the welding energy increased. The tensile lap shear strength first increased, reached its peak value at a certain energy, and then decreased with increasing welding energy. The strength of the dissimilar welded joints was about 55% of that of the similar welded joints. Three different modes of interfacial failure, nugget pull-out, and transverse through-thickness (TTT) crack growth were observed in the similar welded joints, while only interfacial failure was present in the dissimilar welded joints.