A novel composited process of solution treatment-hot gas forming and stress relaxation aging for titanium alloys

A novel composited process including solution treatment-hot gas forming and stress relaxation aging is proposed in this paper to form titanium alloys component with high precision and improved strength simultaneously. Firstly, solution and aging treatments were carried out to study the effects of processing parameters on microstructure and properties. Secondly, uniaxial tensile tests at solution temperature were used to study the hot deformation. Thirdly, stress relaxation aging tests were performed to investigate the relation between stress relaxation and aging; Finally, sophisticated forming tools integrating air cooling channels were designed to validate this novel process by forming a TA15 alloy nozzle. Results show that Nano-scaled secondary α formed in the β matrix after the heat treatment at 950 °C/30 min/WQ + 600 °C/120 min/AC, which increased the ultimate strength of TA15 alloy by 11.8 %. Hot deformation at solution temperature of 950 °C could reduce the elastic strain by 50 % compared with that at 600 °C. The stress relaxation aging could not only further improve the strength of the sample but also increase the relaxation rate, which may result from more nucleation sites for the secondary α provided by the dislocations generated during the loading. A TA15 alloy nozzle was successfully formed by this novel composited process, and the final formed part obtained a diameter deviation less than 0.25 mm and post-form hardness improved by 8.6 %.