Microstructure characteristic and fracture failure behavior of Mg-Al-Zn alloy joint fabricated by oscillating laser-CMT hybrid welding

Abstract

The weldability of the newly developed corrosion-resistant Mg-Al-Zn alloy, characterized by concurrent high strength-toughness and corrosion resistance surpassing conventional magnesium alloys, becomes imperative for evaluating their overall utility and facilitating its integration into next-generation missile architectures. In this paper, the oscillating laser-cold metal transfer (CMT) hybrid welding was carried out to achieve high-quality Mg-Al-Zn alloy joints. The macro morphology, microstructure characteristic, and fracture failure behavior of Mg-Al-Zn alloy welded joint were researched. The in-situ observation during tensile test process for welded joint was employed to elucidate the complete expansion trajectory of the crack from its initiation to its final fracture. The influence mechanism of microstructure evolution on tensile property and its fracture failure behavior was revealed. The results indicates that 8-shaped and circular oscillations exert the most profound influence on the refinement and homogenization of the microstructure. The crack initiation exhibits a marked propensity for localization, wherein the failure mechanism is predominantly dictated by specific sites. In the absence of oscillation, cracks transition abruptly into the acceleration phase following initiation, resulting in a markedly diminished stable propagation zone. Conversely, under circular oscillation, crack propagation exhibits superior stability, characterized by a delayed onset of acceleration and a reduced growth rate. This behavior suggests an enhanced capacity for plastic coordination.