Establishment of a thermal damage model for Ti-6Al-2Zr-1Mo-1V titanium alloy and its application in the tube rolling-spinning process

Rolling-spinning of titanium alloy tubes is an advanced plastic forming technology that has been developed due to the urgent need for light-weight, high-precision, and high-reliability components in high-tech fields, such as aviation and aerospace. However, due to the complexity of the rolling-spinning process and the sensitivity of titanium alloy to temperature and strain rate, it is easy to crack, which severely restricts the improvement of the forming quality and forming limit of components. In this study, the critical deformation of Ti-6Al-2Zr-1Mo-1V was obtained by a hot compression test under various temperatures and strain rates. The damage threshold was obtained through FE simulation for the hot compression process under these temperatures and strain rates. The relationship among damage threshold, temperature, and strain rate was established by introducing the Zener-Hollomon factor. A thermal damage model for Ti-6Al-2Zr-1Mo-1V was established by combining the Oyane ductile fracture criterion with the relationship among damage threshold, temperature, and strain rate. By coupling this thermal damage model into the FE model for rolling-spinning of a Ti-6Al-2Zr-1Mo-1V tube, the damage prediction for the process was realized. The results show that the stress triaxiality at the top and bottom ends of the rolling zone is positive, the accumulation of damage is fast, and the strain rate is large in the zone. Thus, these ends are the zones most prone to damage in rolling process. The stress triaxiality at the local inner surface area of the spinning region is positive, the accumulation of damage is fast, and the strain rate is large in the zone. Therefore, the inner surface of the spinning region is the zone most prone to damage.