Numerical simulation and process optimization for hot stretch bending of Ti-6.5Al-2Zr-1Mo-1V large-section extrusion

Abstract Ti-6.5Al-2Zr-1Mo-1V, as a nearly alpha-type titanium alloy with high Al element, is widely utilized to manufacture the main bearing structures of aircraft as frames and beams because of its high specific strength, outstanding resistance to high temperature and corrosion as well as its excellent mechanical and electrical compatibility with composite material. However, the traditional main bearing structures such as aircraft reinforced frame is large in size and complicated in shape. With the increasing demand for the structural efficiency and structural integrity of modern aircraft design. Hot stretch bending (HSB) is an effective technology to fabricate these kinds of curvature structures, which can not only improve the utilization rate of materials, but also reduce the production cycle and cost. However, compared with thin-walled extrusion profiles, thick-walled (sectional area≥1000 mm2) titanium alloy extrusion profiles are more difficult to form. On side, the large cross-sectional area is easy to cause uneven stress distribution and high level of residual stress. For another, HSB is a highly nonlinear process, whose parameters have a great impact on the forming accuracy of stretch bending parts. In this paper, the high temperature tensile mechanical properties of Ti-6.5Al-2Zr-1Mo-1V were measured experimentally. Then the coupled thermo-mechanical finite element (FE) model was completed by analyzing the effects of temperature, pre-stretch and stretch elongation on spring-back and stress distribution. Finally, when the temperature is 973 K, pre-stretch is 0.75% and the stretch elongation is 0.75%, which were the best process parameters combination from the perspective of spring-back.