Room temperature formability of high-strength titanium alloy sheet

Titanium plate is widely recognized for its advantages of high strength, light weight and good structural rigidity. High-strength titanium alloy Ti-6Al-4V can be used not only in the aviation field, but also in other industrial fields such as automobiles and chemicals.

Ti-6Al-4V alloy sheet has very limited formability at room temperature, and the springback after forming is large, which brings many problems to traditional stamping and pressure forming. Although the forming limit of Ti-6Al-4V alloy sheet will be increased and the springback will be reduced at high temperature, room temperature forming still has great advantages in terms of cost saving. Rolling forming is a forming method that uses a rotating roll to gradually deform the metal blank and make a workpiece, which is suitable for forming structural parts with high strength and limited formability, and is more and more used in the automotive industry, mainly used for forming ultra-high strength steel, high strength steel, etc. Due to the small springback angle of the material in the process of rolling and compensating for the springback by a simple and easy method, rolling forming is an effective method for forming Ti-6Al-4V alloy sheet at room temperature. To this end, Ossama et al. conducted laboratory research on the forming and springback behavior of 2mm thick high-strength Ti-6Al-4V alloy sheet after annealing at 820°C at room temperature. The original structure of the Ti-6Al-4V alloy plate selected for the experiment was composed of 93.86% equiaxed α phase and 6.14% β phase, and the average grain size was 1.3μm ±0.7μm. The room temperature tensile test results show that its anisotropy is large, and when it is 45° with the rolling direction, the yield strength of the specimen is the lowest, the elongation is high, and when the ultimate strength is reached, the specimen will quickly fracture. The forming limit test is performed on equipment equipped with a hemispherical punch with a diameter of 60 mm. The optical strain measurement system "Autogrid Vario" equipped with four advanced CCD cameras is used to record the complete deformation history of each specimen. The deformation behavior of different strain paths is tested by designing different specimen shapes. The experiment found that all the samples suddenly fractured at the top of the hemisphere punch, and there was no obvious necking phenomenon before the fracture, indicating that the room temperature formability of the alloy was very limited. The deformation behavior of Ti-6Al-4V alloy sheet during bending at room temperature and rolling was comparatively analyzed. The results show that the minimum bending radius of the pendulum folding bending test and the V-die bending test is 9mm, while the minimum bending radius of the rolled shape is 7.51mm, which is an increase of more than 15%. Rolled shapes can form smaller radius dimensions and have less springback than simple bending forming. This is mainly because rolling forming is a multi-step cumulative deformation process, and gradual multiple deformation can inhibit the growth of cracks, and at the same time make the deformation of the material more complete than the ordinary one deformation. In addition, the shape defects that often occur in the rolling process of high-strength steel are relatively rare in the forming process of Ti-6Al-4V alloy. It can be seen that rolling is a promising process solution for forming high-strength titanium alloy plates for aviation and automotive structural parts at room temperature.