Evaluation of high-cycle bending fatigue properties and fracture behaviors in AM60 magnesium alloy joints by friction welding

This study examines the microstructural and fatigue properties of AM60 magnesium alloy joints produced by rotary friction welding (RFW). Optical microscopy reveals significant microstructural changes, including grain refinement, reorientation of intermetallic phases, and redistribution of Mg₁₇Al₁₂ particles. The weld metal shows a dispersed needle-like intermetallic structure, while the heat-affected zone (HAZ) accumulates intermetallic phases at grain boundaries. Microhardness analysis indicates a high hardness value of 92.1 Hv at the weld interface, decreasing towards the base metal (BM) with hardness values between 50–60 Hv. Fatigue behavior studies demonstrate that higher interface angles reduce fatigue lifetime, with the 42° conical specimen showing the best performance. Fractography reveals a transgranular quasi-cleavage fracture mode, with cracks nucleating at the weld interface. Additionally, regression analysis was performed, and the suggested model was well-fitted. The study underscores the complex interplay of welding parameters, microstructure, and mechanical properties, offering insights for optimizing welding processes to enhance fatigue resistance of welded magnesium alloy joints.