Enhancing Joint Performance in Friction Stir Welding through Tailored Double-Butt-Lap Geometry

Abstract The study investigates the effectiveness of a novel joint configuration, the double-butt-lap (DBL), in friction stir welding (FSW) to join 6 mm thick AA 6061-T6 plates. Four welds, including a simple square butt (SSB) configuration and three DBL variations (with UB:LB ratios of 1:2, 1:1, and 2:1), were executed. Using consistent parameters, the investigation evaluates the force distribution, macrostructure, and mechanical properties of the joints. Results show varied force profiles; spindle torque and Z-force decrease notably in DBL configurations compared to SSB, while X-force decreases overall for all DBL variations. Macrostructural analysis indicates increased weld area and finer microstructures in DBL joints. A correlation between peak temperature, grain size, and hardness highlights larger grain sizes at higher temperatures, influencing joint hardness. The DBL configuration with a 2:1 ratio exhibits the highest joint efficiency (83.76%). Fractographic analysis indicates ductile failure in all samples. Bend testing reveals increased flexural strength and bend angles in two DBL-configured joints compared to SSB. The results indicate that using a 2:1 ratio for joining 6 mm AA6061-T6 plates through FSW is viable, providing valuable insights into enhancing mechanical properties by optimizing joint geometry.