Similar and Dissimilar Ultrasonic Spot Welding of 5754 Aluminum Alloy for Automotive Applications

摘要

Aluminum (Al) alloys are increasingly used in the transportation industry to reduce the weight of vehicles due to their high strength-to-weight ratio. These applications unavoidably involve similar and dissimilar joining of an automotive grade 5754 Al alloy to manufacture multi-material vehicle body structures and parts. Ultrasonic spot welding (USW), an emerging and promising solid-state joining technology, can be suitably applied to join Al alloys. In this study, 5754 Al alloy was welded in similar (Al5754-Al5754) and dissimilar (Al5754-ZEK100 Mg alloy, Al5754-HSLA steel) configurations at varying levels of welding energy. It was observed that USW had a strong effect on the interface microstructure, with fine grains present at the weld interface via dynamic recrystallization in the similar welding, while an interface diffusion layer formed in the dissimilar welding. The tensile lap shear strength increased with increasing welding energy, reached its optimum value, and then decreased with further increasing welding energy. The strength of dissimilar Al5754-ZEK100 and Al5754-HSLA steel joints was about 55% and 88% of that of the similar Al-Al joints, respectively. The dissimilar Al5754-HSLA steel joints exhibited the longest fatigue life due to the reduced stress concentration and additional strengthening arising from the brazing effect of the squeezed-out Al-Zn eutectic structure at the nugget edge.