Effects of pre-temper conditions of base metal on microstructure and strength-ductility performance of AA7075 friction stir welding joints

This study explores the impact of different pre-temper conditions of the base metal (BM) on the microstructure and strength-ductility performance of AA7075 welded joints, aiming to identify effective processing approaches for aluminum alloy forming. The findings reveal that in comparison to the average grain size (AGS) in the weld nugget zone (NZ) of the AA7075-T6 joint (approximately 2.85 mu m), the grain refinement is more pronounced in the NZ of the AA7075-O joint (approximately 2.09 mu m). Concerning mechanical performance, the AA7075-T6 joint experiences softening in the welding region, demonstrating significantly lower tensile properties than the BM, with an ultimate tensile strength of 416 MPa and an elongation of 4.4 %. Conversely, the AA7075-O joint undergoes hardening in the welding region, displaying higher tensile strength than the BM, with an elongation of 8.7 %. Three-point bending destructive experiments results indicate that the AA7075-O joint can withstand larger bending angles, displaying more thorough plastic deformation and superior forming performance.