Exploration of bonding phenomenon and microstructural characterization during high-power ultrasonic spot welding of aluminum to steel sheets with copper interlayer

Abstract

Lightweighting of automotive body structures involves the ultrasonic spot welding (USW) of dissimilar sheets because of its low energy consumption in comparison to the traditional fusion welding process. In this study, AA3003 aluminum alloy to AISI 304 stainless steel with a copper interlayer was joined using USW technique at different weld times. The tensile shear strength of Al-to-SS joint with Cu interlayer (95.9 MPa) exhibited a higher value of 20.17% than SS-to-Al joint with Cu interlayer (79.8 MPa). The softer Al side experienced interfacial failure (IF) modes at lower weld times and at higher weld times, it gradually transformed to nugget pull-out failure (NPF). A comparative lower hardness value was obtained in Al-to-SS joint with Cu interlayer, demonstrating the generation high interface temperature and rigorous plastic deformation. The precipitation of brittle intermetallic compounds (IMCs) on the fracture surfaces severely concedes the reliability of the weld joints. Keywords: Ultrasonic spot welding, Tensile shear failure load, Intermetallic compounds, Lap configuration, Interlayer, Nugget pull-out failure