Abstract
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•The “unweldable” Al7075 alloy is successfully welded with a clad layer via USW.•Clad layer of AA7072 alloy contributes to the defect-free sound welded joints.•Tensile lap shear strength exceeds AWS D17.2 standards at higher energy levels.•The solid-state ultrasonic spot welded joints exhibit superior fatigue resistance.•Depending on cyclic load levels, two types of fatigue failure modes are observed.
The purpose of this study was to examine weldability of an AA7072-cladded high-strength AA7075-T6 via ultrasonic spot welding, focusing on the influence of welding energy on mechanical properties and failure mechanisms. Defect-free sound joints were achieved with robust bonding and grain refinement via dynamic recrystallization at the weld interface, leading to superior static and fatigue properties. The nominal tensile lap shear strength increased with increasing welding energy, and exceeded AWS D17.2 standards at higher energy levels. Interfacial failure at higher cyclic loads with distinctive elongated shear dimples and fatigue striations and transverse through-thickness failure at lower cyclic loads were observed.