Microstructure evolution and mechanical properties of a hot-rolled Ti alloy

The microstructure evolution and mechanical properties of a hot-rolled Ti-5.1Al-2.5Cr-0.5Fe-4.5Mo-1.1Sn-1.8Zr-2.9Zn titanium alloy sheet along the thickness direction were investigated. The results indicated that the hot-rolled titanium alloy sheet presented different microstructures along the thickness direction owing to the uneven distribution of stress and temperature during the hot rolling. The grains in central region underwent a larger deformation, leading to relative complete grain fragmentation and the formation of fine grains. During the air cooling process followed by hot rolling, the fraction of α phase precipitated in the central region was lower than that in the regions near the surface of the sheet. During hot rolling process, more deformation energy transformed to thermal energy and lower cooling rate in the central region promoted the α→β phase transformation, resulting in the increasing of the dynamic recrystallization in the β phase. By contrast, the dynamic recrystallization for α phase decreased. Distinct {0001}_α and {001}_β textures were observed, and these textures were markedly strengthened with the increasing distance from the central region. Due to the softening induced by dynamic recrystallization and the strengthening by concentrated dislocations, the surface of the sheet exhibits highest yield strength and lowest elongation.