Influence of repair welding times on the microstructures and inhomogeneity mechanical properties of Al-Mg-Si welded joints

Repairing welded joints of defective aluminum alloy play an important role in improving the safety and reliability of the vehicle body. In this study, an equivalent welded joint model was established to accurately characterize the microstructure and mechanical properties of the heat-affected zone (HAZ) of a 6082-T6 aluminum alloy welded joint, specifically investigating the effects of repair welding times. The results revealed significant mechanical heterogeneity within the HAZ across repair times. The overall tensile strength, yield strength, and Vickers microhardness all followed a V-shaped variation trend characterized by initial decrease followed by increase, while the elongation demonstrated an L-shaped variation trend. The mechanical properties of the severely over-aging zone (SOAZ) 4 mm away from the fusion line were the weakest. For the SOAZ, the minimum tensile strength of the unrepaired original joint sample was the same as that of the once-, twice-, and thrice-repaired samples, which was 44.35 ± 1.61 % of the tensile strength of the parent material (321.2 MPa). However, after three repairs, the yield strength decreased by 17.25 % compared to that of the unrepaired original joint, and the minimum hardness (57.3 HV) decreased by 13.96 %. The softening behavior of the HAZ was primarily driven by the coarsening and decomposition of β" and β′ strengthening phases induced by multiple thermal cycles. Given the pronounced mechanical inhomogeneity arising from HAZ softening in multiply repaired joints, it is recommended that the number of repairs should not exceed two.