Room temperature formability of high strength titanium alloy wear-resisting plate
Titanium alloy wear-resistant plate has been widely recognized for its advantages of high strength, light weight and good structural rigidity. High-strength titanium alloy Ti-6Al-4V can not only be used in the aviation field, but also an important candidate material for structural parts in other industrial fields such as automobiles and chemicals. The formability of Ti-6Al-4V alloy wear-resistant plate at room temperature is very limited, and the rebound after forming is very large, which brings many problems to traditional stamping and pressure forming. Although the forming limit of Ti-6Al-4V alloy wear-resisting plate will be increased and the rebound will be reduced at high temperature, the room temperature forming has great advantages in cost saving. Rolling forming is a kind of forming method using rotating rolls to gradually deform metal billets and make workpieces. It is suitable for structural parts with high forming strength and limited formability. It is more and more used in the automobile industry, mainly for forming ultra-high strength steel and high strength steel. Because the springback Angle of the material is small and the springback compensation can be made by a simple and easy method during rolling forming, rolling forming is an effective method for forming Ti-6Al-4V alloy wear-resistant plate at room temperature. For this reason, Ossama et al. studied the forming and springback behavior of 2mm thick high-strength Ti-6Al-4V alloy wear-resistant plate annealed at 820℃ at room temperature.
The original structure of Ti-6Al-4V alloy wear-resistant plate is composed of 93.86% equiaxed α phase and 6.14% β phase, and the average grain size is 1.3μm±0.7μm. Tensile test results at room temperature show that the anisotropy is large. When the rolling direction is 45°, the yield strength of the sample is the lowest and the elongation is high. When the ultimate strength is reached, the sample will break quickly. The forming limit test was performed on equipment equipped with hemispherical punches with a diameter of 60mm. An optical strain measuring system "AutogridVario" with 4 advanced CCD cameras is used to record the complete deformation history of each sample. The deformation behavior of different strain paths is tested by designing different sample shapes.
It was found that all the samples suddenly broke at the top of the hemispherical punch, and there was no obvious necking phenomenon before the fracture, indicating that the formability of the alloy at room temperature was very limited. The deformation behavior of Ti-6Al-4V alloy wear-resistant plate during bending and rolling at room temperature was compared and analyzed. The results show that the minimum bending radius of pendulum folding bending test and V-mold bending test is 9mm, while the minimum bending radius of rolling forming is 7.51mm, which is increased by more than 15%. Rolling forms can be formed to smaller radius sizes and have less springback than simple bending forms. 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, the deformation of the material is more sufficient than the ordinary one deformation. In addition, the shape defects that often occur in the rolling process of high-strength steel are relatively few in the rolling process of Ti-6Al-4V alloy. It can be seen that rolling forming is a potential process scheme for forming high-strength titanium alloy wear-resistant plates for aviation and automobile structural parts at room temperature.
