Mechanical performance and fatigue fracture characterization of friction stir spot welded semi-solid metal 5083 aluminum alloy

The inherent structural weaknesses found in traditional cast aluminum parts are primarily caused by their dendritic formations. To counteract this, the Gas-Induced Semi-Solid (GISS) technique is utilized to facilitate a semi-solid state that yields nearly spherical, non-dendritic grains of consistent size, thereby enhancing the material's overall mechanical performance. As the automotive industry shifts toward electric vehicles, semi-solid cast aluminum is becoming a critical material for structural assemblies, often joined using Friction Stir Spot Welding (FSSW). Therefore, this work investigates the FSSW characteristics of semi-solid metal 5083 aluminum alloy (SSM5083), focusing on the mechanical properties and fatigue behavior of the joints. The experimental results showed that the best welding settings at 1600 rpm for the tool's rotation speed, 5 seconds for the dwell time, and 10 mm/min for the plunging feed rate produced a maximum lap shear strength of 4062 N. The hardness profiles showed values of 96.2 HV on the Advancing Side (AS) and 91.6 HV on the Retreating Side (RS), with an upward trend in hardness toward the stir zone boundary. Furthermore, the fatigue life equation was established for up to 2x10 6 cycles, determining an endurance limit of 757 N. Fractographic analysis via scanning electron microscopy (SEM) indicated that fatigue crack initiation predominantly occurred on the Advancing Side (AS), characterized by prominent beach marks and crack propagation features.