Microstructure and Mechanical Properties of 7075 Al Alloy TIG-Welded Joint with 7075 Al Alloy Wire as Filler

Arc welding of Al–Zn–Mg–Cu (7xxx) high-strength Al alloys is an urgent problem to be solved. In this study, tungsten inert gas (TIG) welding of 7075 Al alloy with newly developed 7075 Al alloy wire as filler is successfully carried out and the full-penetration and defect-free joint is formed. The fusion zone (FZ) is consisted of fine and equiaxed α-Al dendrites and a narrow transition zone (TZ) with columnar α-Al grains is formed between the heat-affected zone (HAZ) and FZ. The minimum hardness is obtained in FZ in 7075 Al alloy-welded joints and post-weld heat treatment (PWHT, solid solutioned at 480℃ for 1 h and then aging at 120℃ for 24 h) induces significant hardening in both FZ and HAZ due to the precipitation of GP zones and η' phase. The yield strength, ultimate tensile strength and ductility of as-welded joint are 223 MPa, 374 MPa and 4.6%, and they are improved to 435 MPa, 533 MPa and 7.8%, respectively, after PWHT. The high-strength coefficient for 7075 Al alloy TIG-welded joint can be attributed to the 7075Al alloy wire filler, optimized TIG welding parameters and PWHT.