Repairing of exit-hole in friction-stir-spot welded joints for 2024-T4 aluminum alloy by resistance welding

The exit-hole in friction stir spot welded (FSSWed) 2024-T4 aluminum alloy joints was successfully repaired by using a three-phase secondary rectification resistance spot welding machine, which is termed as filling exit-hole based on resistance welding (FEBRW). The filling dynamic behavior of force was recorded by a device monitoring. Optical microscope (OM), electron backscatter diffraction (EBSD), and tensile shear tests and finite element modelling were conducted to investigate the repairing stages and bonding mechanisms of the repaired joints in detail. Results showed that exit-hole was completely filled and repaired experiencing three stages. Metallurgical bonding was achieved between plug and exit-hole wall in two forms, including melting bonding in the middle of the joints and partial diffusion bonding on both the upper and bottom of the joints. The highest tensile shear strength of the repaired joints was 7.43 kN, which was 36.3% higher than that of the as welded joints. Resistance welding paves an efficient way to repair the exit-hole in FSSWed joints.