Abstract: Effect of annealing on the microstructure and mechanical properties of TC17 titanium alloy welded joint was studied by means of metallographic microscope, scanning electron microscope, hardness tester, and tensile testing machine. The results show that dynamic recrystallization occurs in the weld seam of the TC17 titanium alloy, and metastable β grains are formed, and there is no obvious second phase in the grains, which leads to softening of the weld zone. As the distance from the weld seam gets closer, the aspect ratio of the primary α phase in the heat affected zone decreases and the secondary α phase dissolves gradually, resulting in a gradual decrease in microhardness. After annealing at 600 ℃ for 4 h, the hardness of weld seam is increased by 41% compared with that of the welded state, and the hardness of heat affected zone is increased by 12.8% compared with that of the welded state. Due to the fine and dispersed secondary α phase precipitated in the metastable β phase in both the weld and heat affected zone, the microhardness of weld and heat affected zone is increased significantly compared with the welded state. The properties of the welded joint are mainly determined by the size and quantity of α phase. After annealing, the α phase has obvious strengthening effect, the tensile strength of the welded joint is increased by 14% compared with that of the welded state, and the tensile strength of joint is higher than that of the substrate, thus the fracture position of the joint is on the substrate.

Key words: TC17 titanium alloy, electron beam welding, heat treatment, microstructure, mechanical properties