Dissimilar ultrasonic spot welding of ZEK100 magnesium alloy to a clad AA7075 aluminum alloy: Tensile and fatigue properties.

The aim of this study was to examine the feasibility of joining ZEK100-O magnesium alloy to AA7072-clad high-strength AA7075-T6 aluminum alloy via solid-state ultrasonic spot welding (USW) and evaluate interfacial microstructures, tensile lap shear strength, and fatigue resistance. Distinctive "fishhook"- or "wave"-like mechanical interlocks were observed to form at the weld interface between the magnesium and aluminum alloys due to the presence of softer clad layer of AA7072 with ~ 1% Zn. This led to the enhanced tensile lap shear strength of the dissimilar welded joints, with the peak value emerging at a welding energy of 1000 J. Besides the mechanical bonding via effective interlock mechanism, a thin diffusion layer consisting of α-Mg + Al12Mg17 eutectic structure at 1000 J was also beneficial for attaining superior tensile lap shear strength and longer fatigue life, in comparison with other Mg/Al dissimilar joints without a clad layer. While interfacial failure predominated in the tensile lap shear tests, fatigue failure changed from the interfacial failure mode at the higher cyclic loading level, to a mixed mode of both interfacial and transverse through-thickness (TTT) failure at the intermediate loading level, and to full TTT failure at the lower loading level. [ABSTRACT FROM AUTHOR]