Study on coarse grain refinement of Ti-6554 billet in hot extrusion process

The hot extrusion process can effectively refine the coarse grains of metastable β titanium alloy billet, thereby enhancing the material's internal microstructure and mechanical properties. This study explored the hot deformation behavior of as-cast Ti-6554 samples at temperatures ranging from 900 °C to 1150 °C and strain rates between 0.001 s^-1 and 1 s^-1 by a Gleeble-3500 tester. The Arrhenius constitutive model was established to simulated the hot extrusion process. Parameters such as the degree of deformation (x), metal plastic flow (μ), and deformation temperature (θ) were introduced to quantify the uniformity of distribution under various processes. Based on the simulation results, the optimal extrusion conditions were determined to be an extrusion ratio of 10, an extrusion angle of 60°, an extrusion velocity of 40 mm/s, a preheating temperature of 1100 °C, and an extrusion load of 2500 tf. Examination of the microstructure of the hot-extruded bar revealed that grain sizes consistently decreased from the centers towards the edges. The grains were refined from 2000~5000 μm to 100~200 μm after extrusion, demonstrating that the deformation degree, plastic flow and deformation temperature were well coordinated under these conditions.