Microstructure Evolution and Recrystallization of Ti6246 Alloy in Hot-Rolling and Annealing Processes

Herein, the Ti-6Al-2Sn-4Zr-6Mo (Ti6246)-casted alloy is treated with two different hot-rolling processes (3-pass and 5-pass), and the as-rolled alloy is subsequently annealed at different temperatures (780 and 850 °C). During hot rolling, obvious changes in the morphology and microstructure of the Ti6246 alloy occur. A large number of dislocations are generated in the rolling process, and their movement plays an important role in the microstructure evolution of the alloy. The 3-pass hot rolling results in a smaller grain size (0.43 μm) than that of the 5-pass rolled sample (0.68 μm), which can be attributed to the larger deformation degree of the single pass in the 3-pass rolling process. However, the larger deformation degree of the 3-pass rolling leads to higher dislocation density (34.29% of L_M above 1) and more microstructure defects in the Ti6246 alloy, which further result in easier initiation of the prismatic and pyramidal slips of the alloy. The 5-pass procedure can provide more deformation passes to promote the dynamic recrystallization (DRX) of the Ti6246 alloy and the fraction of DRX can reach 33.27%. In contrast, with the increase of the annealing temperature, the degree of recrystallization increases and the number of microstructure defects decreases.