Effect of Clad Rolling Process on Microstructure and Properties Evolution of Fine-Grain TC4 Alloy Sheet

The microstructure evolution of TC4 alloy plates with α martensitic as primary microstructure in dual-phase region during clad rolling and annealing were investigated. The relationship between microstructure evolution (grain size, texture) and strength of the alloy was discussed. The results show that β-quenched alloy exhibits fine lamellae α′ martensite which displays multi-scale and multi-variant distribution. The grain of β-quenched alloy is significantly refined with average grain size of 0.89 μm and //ND of Basal texture forms after two-phase cross rolling. However, a mixed structure, consisting of fine recrystallized grains and coarse deformed grains, is observed. During annealing process, the rolled samples undergo continuous static recrystallization, resulting in the formation of fine equiaxed grain (approximately 1.86 μm at 720 ℃). Meanwhile, annealing treatment do not change the texture type, while the intensity of Basal texture is slightly enhanced. The strong Basal texture makes the Schmidt factor of prismatic slip close to each other along the direction of TD and RD, which results in the decrease in strength difference between transverse and longitudinal direction. The strength of the sheet decreases with the increase in annealing temperature, which is due to the synergistic effect of the increase in grain size and the decrease in dislocation density. The result shows that the fine grained TC4 alloy with Basal texture can be fabricated by using α+β phase cross rolling and annealing, which provides a theoretical basis and technical support for the preparation of fine-grain titanium alloy plates for aerospace applications.