Mechanical and microstructural evaluation of friction stir welded aluminum alloys under as-welded and heat-treated conditions

Abstract

Enhancing the strength and reliability of aluminium alloy joints remains a key challenge in industrial applications. Combining alloys with complementary properties offers the potential to optimize weight, strength, and corrosion resistance; however, joining dissimilar aluminium alloys is inherently difficult. Differences in chemical composition, thermal conductivity, and precipitation behavior often lead to microstructural incompatibilities, making it challenging to produce high‑quality, reliable joints. Friction stir welding (FSW) has emerged as a promising solid‑state joining technique for aluminium alloys. This study investigates the effect of post‑weld heat treatment (PWHT) on the mechanical properties, microstructure, and fracture behavior of friction stir welded dissimilar joints of AA6061‑T6 and AA5052‑H32 alloys. Microstructural analysis revealed fine equiaxed grains in the AW stir zone, which coarsened moderately post‑treatment, accompanied by improved precipitate distribution. Mechanical testing showed that PWHT significantly improved joint performance, increasing the ultimate tensile strength from 196.14 MPa in the as‑welded (AW) condition to 258.78 MPa, and enhancing joint efficiency to 32%. Fractographic analysis confirmed ductile fractures, and PWHT resulted in a more refined and uniformly distributed dimple morphology, as an indicative of enhanced plastic deformation capacity and improved fracture resistance. These results demonstrate that PWHT effectively mitigates localized softening, enhances ductility, and improves the structural integrity of dissimilar aluminium alloy FSW joints.