Non-equilibrium hot stamping process for fully martensitic titanium alloy thin-walled components

Non-equilibrium hot stamping (NEHS) process generating non-equilibrium microstructure by rapid heating, can enhance both the formability and post-form strength of titanium alloy. It could reduce the cycle time dramatically from traditionally ∼20 min to ∼2 min by using cold forming dies. In this study, uniaxial tensile tests at elevated temperatures were used to study the deformation behavior of titanium alloy under NEHS conditions. The evolution of martensitic microstructure was studied by scanning electron microscope. NEHS of Ti-6Al-4V alloy U-shaped components were used to investigate the effects of heating rate, temperature, and holding force on the formability, springback, and mechanical properties. Results show that the deformation behaviors at temperatures below and above β-transus are quite different. With the temperature increasing, dynamic softening gradually transforms into dynamic hardening, and the elongation initially increases, then decreases, and finally rises again upon entering the single-phase region. Rapid heating to the single-phase region results in a fine martensitic microstructure, which could overcome the traditional strength-ductility trade-off in titanium alloys. The synergistic control of heating rate, temperature, and holding force during forming is critical for defect suppression and dimensional precision of the components. Specifically, U-shaped components formed under the optimal regime exhibit a ‌15.0% increase in tensile strength compared to the as-received alloy sheet, coupled with an elongation no less than 6.5% and a springback angle no more than 0.2°, demonstrating the advantage of NEHS in simultaneously enhancing mechanical performance and dimensional precision‌.