Effect of Local Postweld Heat Treatments on Metal Inert Gas-Welded A7N01S-T5 Joints

T6, T7, and retrogression and reaging (RRA) postweld heat treatments (PWHTs) were redefined and deployed to restore MIG-welded A7N01-T5 aluminum alloy joints in train-body structures using an inductive heating device. After the PWHT, the microstructures and mechanical properties of the joints were studied by x-ray diffraction (XRD), electron backscattered diffraction (EBSD), and scanning electron microscopy (SEM). The results showed that the hardness and strength of the joints were improved by the T6 treatment, and the tensile strength of the joints reached 87.39% of the base metal. However, an improvement in the corrosion resistance was not observed. The T7-treated joints enhanced the toughness of the welded joints and improved their corrosion resistance. The RRA-treated joints improved the toughness and corrosion resistance and increased the strength and hardness. The RRA treatment had a more comprehensive effect on the improvement of the welded joint structure and performance and is more suitable for postweld heat treatment of the aluminum alloy welded joints in the body of high-speed trains.