Optimization of heat-treatment parameters in hardening of titanium alloy Ti-6Al-4V by using the Taguchi method

Titanium alloys are widely applied in aircraft, nuclear, and military parts because of their high strength-to-density ratio, high toughness, and high corrosion resistance. However, achieving excellent mechanical properties of these alloys relies on appropriate heat-treatment processes. In this research, the prevalent alloy Ti-6Al-4V was used to investigate the optimization process parameters of heat treatment by using the Taguchi method. Hardness after aging and tensile strength (TS) were chosen as quality characteristics. Eight controllable factors were selected, comprising fan, solution temperature, duration time of solution treatment, protective gas, quench delay time, cooling rate, temperature, and duration time of aging treatment. The experiment was performed using orthogonal arrays of L-18(2(1) x 3(7)). The best combination condition of process parameters was obtained after a Taguchi quality analysis. The quality reproducibility was verified to be excellent through confirmation experiments. The results showed that the hardness after aging was higher than HRC 43 +/- 0.5, the TS of rod material higher than 169 ksi, and the TS of plate material higher than 157 ksi while using the best heat-treatment condition. The quality characteristics all met the AMS 4965 specifications of quality requirements for alloy Ti-6Al-4V.