Effect of Annealing Temperature on the Strength and Toughness of Ti-55531 Titanium Alloy After Multiple Heat Treatment

Herein, it is aimed to reveal the effect of annealing temperature on α microstructure parameters and mechanical properties of Ti-55531 alloy under the multiple heat-treatment process of “solution (855 °C) + annealing (700, 730, 760 °C) + aging (600 °C).” The microstructure is characterized by using optical microscopy, scanning electron microscopy, and transmission electron microscope. In the results, it is indicated that the annealing temperature does not change the volume fraction of the α_s phase of Ti-55531 alloy. The as-annealed precipitation-free zone α_s phase renucleates after aging treatment, resulting in a bimodal distribution of α_s phase in the matrix. The higher the annealing temperature, the larger the average size of α_s phase and the greater the heterogeneity in the alloy. Additionally, the heterogeneity of α_s phase affects further the plasticity and the crack propagation path of the alloy. With the increase of annealing temperature, the strength of Ti-55531 alloy decreases slowly, but the elongation and the impact toughness of the alloy increases rapidly resulting from the heterogeneity of α_s phase under multiple heat-treatment conditions.