Deformation behavior of anisotropic TA18 titanium alloy tube in hydroforming process at room temperature

While hydroforming of titanium alloy at room temperature is difficult due to its high strength, low hardening capacity, and significant springback, it is typically deformed into desired shape under high-temperature conditions exceeding 500°C, which increases the complexity of the process and raises costs. In this paper, the hydroforming method was used to manufacture TA18 titanium alloy variable-diameter tubular components at room temperature based on an innovative idea of useful wrinkles. The results show that the TA18 titanium alloy tube blank has a strong normal anisotropy of $\bar{r}$ = 5.2, which is conducive to developing wrinkles while preventing excessive thinning. When the pressure increases from 0.4 p_s (p_s is initial yield internal pressure) to 0.8 p_s, the number of wrinkles produced on the tube blanks gradually decreases from three to two, and their width increases. When the pressure exceeds p_s, wrinkles cannot be formed on the tube blanks, which will undergo bulging deformation. In the simulation, the wrinkling behavior of the tube blanks does not match the experiment when the Mises yield criterion was used. While using the anisotropic Hill48 yield criterion, the wrinkling trend and development of wrinkles can be well predicted. Furthermore, the wrinkled tubes can be completely flattened under 70 MPa during calibration, and their wall thickness distributions are consistent with the simulation results, with the maximum thinning ratio of the formed components at 6.2%. All of these results provide basic support for manufacturing titanium alloy tubular components with large cross-sectional differences at room temperature using the hydroforming process.