Tailoring the joint performance of friction stir welded AA6082-T6 through copper interlayer modification

This study investigates the influence of copper interlayer thickness on the mechanical performance and microstructural evolution of friction stir welded (FSW) AA6082-T6 aluminum alloy. Welding was conducted at rotation speeds of 710–1400 rpm, welding speeds of 14–56 mm/min, and copper interlayer thicknesses of 0.1 and 0.4 mm. Comprehensive analyses, including tensile, impact, hardness, macrostructural, microstructural (OM, SEM), and EDX characterization, were performed. Results revealed that incorporating a copper interlayer significantly enhanced joint strength and altered material flow. The best condition, using a 0.1 mm interlayer at 1400 rpm and 56 mm/min, produced the highest ultimate tensile strength (~168 MPa), a good balance of ductility, and better impact toughness. This was because Cu-rich particles and thin Al–Cu intermetallic compounds were evenly spread out, which helped with load transfer and grain refinement. In contrast, the 0.4 mm interlayer caused excessive IMC growth and Cu agglomeration, increasing brittleness. Hardness exhibited a characteristic W-shaped profile, and fracture analysis confirmed mixed ductile – brittle behavior under optimal conditions. Overall, the study highlights that optimizing interlayer thickness and heat input is essential for achieving strong and reliable FSW joints in Al–Cu systems.