Effects of Solid Solution, Cooling Rates and Aging Treatments on Microstructure and Mechanical Properties of TC4-DT Alloy

The changes of microstructure, strength and plasticity of Ti6Al4V-DT (TC4-DT) alloy were studied by metallographic microscope and tensile tester under different solid solutions, cooling rates and aging treatments. The results demonstrate that the main influencing factors of tensile strength and plasticity are solution temperature and cooling modes. Solid solution and aging treatment at 550 degrees C for 8 h in the alpha+beta phase and the single beta phase region can obtain the bimodal structure and the lamellar structure, respectively. When the solid solution temperature rises below the phase transition temperature, the amount of primary alpha phase obviously decreases; meanwhile, the strength and plasticity are better in the two-phase region. As the cooling rate decreases, the lamellar alpha phase becomes coarsened under the solution treatment above the phase transition temperature, and the tensile strength and yield strength gradually decrease. Moreover, the size of alpha phase increases as the aging temperature increases at the alpha+beta phase region. Furthermore, the dispersion strengthening of alpha phase makes the strength of the alloy higher at the lower aging temperature. In general, the strength and plasticity of TC4-DT alloy can be well matched, whose tensile strength can reach up to 1017 MPa and whose elongation is 22% under solid solution treatment at 860 degrees C for 1.5 h, aging treatment at 550 degrees C for 8 h and in the air-cooled state.