Influence of annealing temperature on microstructure evolution and strength-ductility trade-off in warm-rolled Ti-6Al-4V thin strips

This study investigates the effects of annealing temperature on the recrystallization behavior, microstructural evolution, and mechanical properties of Ti-6Al-4V alloy subjected to 90% large-reduction warm rolling. Progressive spheroidization and grain coarsening were observed with increasing annealing temperature. At 650°C, the microstructure retained elongated α and β phases with minimal spheroidization, resulting in the highest ultimate tensile strength of 1286 MPa but poor ductility. At 700°C, the α phase was partially spheroidized, achieving a moderate spheroidization fraction with fine equiaxed β grains uniformly distributed in the α matrix. This condition yielded the optimal combination of strength (tensile strength 1197 MPa, yield strength 1089 MPa) and ductility (elongation 13.2%). In contrast, annealing at 750°C caused significant grain coarsening, reducing strength but improving elongation. The growth of β occurs with the proceeding of α spheroidization, accompanied with the redistribution of V. The superior performance under the 700°C condition is attributed to a bimodal microstructure comprising ultrafine spheroidized grains and partially deformed grains, which synergistically enhance dislocation strengthening and deformation resistance, ensuring a balance between strength and ductility.