Effect of Hot-rolling Temperature on Microstructure and Dynamic Mechanical Properties of Ti-6Al-4V Alloy

The equiaxed Ti-6Al-4V alloys were rolled with an overall reduction ratio of 0.78 at 840, 870, 900 and 930 °C. The microstructure, texture and anisotropy of dynamic mechanical properties of the rolled alloy were investigated. Results show that the recrystallization and phase transformation do not occur until the rolling is performed at a temperature higher than 900 °C, and then the microstructure of the rolled alloy turns into bimodal, while the amount of lamellar α_s+β structure and recrystallized α grains shows an increasing tendency with the increased rolling temperature. Moreover, it is interesting to find that although the texture varies with the rolling temperature, the <0001> direction of α phase keeps parallel to the normal direction (ND) during the hot-rolling process at various temperatures. Based on the analyses of dynamic mechanical properties, Ti-6Al-4V alloy exhibits anisotropy of dynamic mechanical properties after hot-rolling at different temperatures. However, resulting from the rolling-temperature-depended texture and distribution of dislocation, the anisotropic tendency of dynamic mechanical properties varies with the rolling temperature. Moreover, with the increased rolling temperature, the dynamic flow stress loaded along ND decreases, while the adiabatic shearing failure strain slightly increases. The dynamic flow stress loaded along RD remains constant, while the adiabatic shearing failure strain exhibits an obviously decreasing tendency with the increased rolling temperature. The dynamic mechanical properties loaded along Transverse Direction (TD) remain constant when the rolling temperature is in the range of 840 °C to 900 °C, while the dynamic flow stress loaded along TD increases evidently when the rolling temperature reaches 930 °C, but the adiabatic shearing failure strain decreases greatly.