Abstract: Cold-rolled Ti-6.5Al-2Zr-1Mo-1V(TA15) titanium alloy sheet was conventionally annealed at different temperatures ranging from 750 ℃ to 980 ℃ and dual-stage annealed, respectively, and the effect of different annealing treatments on the microstructure and hardness of the alloy was investigated. The results indicate that when the cold-rolled TA15 titanium alloy sheet is conventionally annealed at a temperature lower than the phase transformation point, an equiaxed primary α(α_P) phase can be obtained. After conventional annealing at a temperature close to the phase transformation point (965 ℃), a bimodal structure composed of α_P and lamellar α(α_S) phases is obtained. When the conventional annealing temperature is higher than the phase transformation point, the α_P phase disappears, and the microstructure consists of coarse Widmansttten α_W phase. After primary annealing near the phase transformation point and secondary annealing in the two-phase region, the cold-rolled TA15 titanium alloy sheet can obtain a tri-modal structure composed of α_P, α_W and α_S phases. Under conventional annealing, with the increase of annealing temperature, the hardness of the cold-rolled TA15 titanium alloy sheet first decreases and then increases. After the dual-annealing of 965 ℃×30 min, WQ+920 ℃×100 min, AC, due to the coarsening of α_S phase, the hardness is lower than that after the conventional annealing.

Key words: TA15 titanium alloy, annealing treatment, microstructure, hardness