Improvement in metallurgical reaction and mechanical properties of Mg/Al ultrasonic spot welding by introducing a pure Ni interlayer

Sound AZ31B magnesium alloy/1060 pure aluminum ultrasonic spot welding joints were successfully fabricated through the introduction of a pure Ni (N4) interlayer at the interface. Characterization results showed that, under identical welding parameters, the Ni interlayer slightly reduced the peak interfacial temperature while greatly improving plastic deformation. A large number of AlNi intermetallic particles were observed on the Mg side, whereas a small quantity of Al 3 Ni particles appeared on the Al side. The migration distance of AlNi particles was also notably longer. Continuously distributed intermetallic compounds (IMCs) were formed, consisting of a 6.15 μm-thick Mg 2 Ni layer at the Mg/Ni interface and a 5.14 μm-thick Al 3 Ni phase at the Al/Ni interface. These IMCs effectively suppressed the formation of brittle Al 3 Mg 2 and Al 12 Mg 17 phases commonly found in conventional Mg/Al ultrasonic joints. The presence of the Ni interlayer expanded the weld zone, raising the average maximum tensile shear strength to 673.3 N, which was 32% higher than joints without the interlayer. All fractures displayed ductile-brittle hybrid behavior, characterized by both dimple rupture and cleavage facets.