Ultrasonic spot welding of magnesium-to-aluminum alloys with a copper interlayer: Microstructural evolution and tensile properties

Abstract

Ultrasonic spot welding of ZEK100-O Mg alloy to Al6022-T43 Al alloy with a Cu interlayer was successfully achieved, and relevant technical issues were investigated with focus on the microstructural evolution at Mg/Cu and Al/Cu interfaces and the tensile lap shear strength in relation to welding energy. While an interface diffusion layer occurred at both interfaces, the Mg/Cu interface diffusion layer mainly consisting of α-Mg and Mg2Cu eutectic structure grew much faster and became significantly thicker with increasing welding energy. A thin interface diffusion layer composed of primarily Al2Cu was present at the Al/Cu interface, alongside the formation of characteristic “barb”-like interlocks at lower energy levels and core-shell microstructures at higher energy levels. With increasing welding energy the tensile lap shear strength of the tri-dissimilar joints first increased, reached a peak value at an energy of 1500 J, and then decreased. The strength of ZEK100-Al6022 dissimilar joints was attained to be ∼35% higher with Cu interlayer than without Cu interlayer, reached ∼80% that of Al6022-Al6022 similar joints and almost the same strength level of ZEK100-ZEK100 similar joints. Interfacial failure was observed to occur at the Al/Cu interface at the lower energy and at the Mg/Cu interface at the higher energy.