Microstructure, electrical conductivity, and intergranular corrosion of AA6026/AA5183/AA6026 alloy welded joints after pulsed welding and post-weld heat treatment

Abstract

The present study examined the effect of heat input and T6 post-weld heat treatment on the microstructure, electrical conductivity, and intergranular corrosion of AA6026/AA5183/AA6026 welded joints. The samples were welded using pulsed MIG, pulsed TIG, and combined TIG&MIG procedures, and a portion of samples was subjected to the T6 condition (solution annealing, water quenching, and artificial aging). The results showed that lower heat input (pulsed MIG) reduced intermetallic precipitation along grain boundaries and thereby improved resistance to intergranular corrosion, while higher heat input (pulsed TIG) promoted more intensive precipitation and increased the risk of corrosion. The T6 treatment partially homogenized the microstructure but also likely promoted the precipitation of Mg₂Si along grain boundaries in the heat-affected zone of AA6026 and the formation of continuous β-Al₃Mg₂ films along grain boundaries in the weld metal of AA5183, which together increased susceptibility to intergranular corrosion of welded joints. The best resistance to intergranular corrosion was observed in joints produced by pulsed MIG welding with low heat input, while TIG&MIG joints, owing to even lower heat input, maintained stable intergranular corrosion resistance even after T6 treatment. In contrast, joints obtained by pulsed TIG welding with higher heat input suffered the most severe degradation of intergranular corrosion resistance in the T6 condition. These findings confirmed that heat input control was the decisive factor governing microstructural changes, electrical conductivity, and corrosion behavior of AA6026/ER5183/AA6026 welded joints.