Titanium plates are widely recognized for their high strength, light weight and structural rigidity. The high-strength titanium alloy Ti-6Al-4V can be used not only in aerospace, but is also an important candidate for structural components used in other industrial fields such as automotive and chemical.
Ti-6Al-4V alloy sheet has very limited formability at room temperature and a large springback after forming, which poses many problems for conventional stamping and pressure forming. Although the forming limit of Ti-6Al-4V alloy sheet increases and the springback decreases at high temperatures, room-temperature forming has a great advantage in terms of cost savings. Roll forming is a forming method that uses rotating rolls to gradually deform a metal billet into a workpiece, suitable for forming structural parts with high strength and limited formability, and is increasingly used in the automotive industry, mainly for forming ultra-high-strength steels, high-strength steels and so on. Roll forming is an effective method for room-temperature forming of Ti-6Al-4V alloy plates because the angle of springback of the material is small during the rolling forming process and can be compensated by a simple and easy method of springback compensation. For this reason, Ossama et al. conducted a laboratory study on the forming and springback behavior of 2-mm-thick high-strength Ti-6Al-4V alloy plates annealed at 820°C at room temperature.
The pristine organization of the Ti-6Al-4V alloy sheet selected for the experiment consisted of 93.86% equiaxial α-phase and 6.14% β-phase, with an average grain size of 1.3 μm ± 0.7 μm. The results of the room-temperature tensile tests showed a large anisotropy, and the yield strength of the specimen was lowest when it was oriented at 45° to the direction of rolling, with a high elongation, and when it reached the ultimate strength, the specimen would quickly Fracture occurs quickly when the ultimate strength is reached. The forming limit tests were carried out on a machine equipped with a hemispherical punch with a diameter of 60 mm, and an optical strain measuring system “Autogrid Vario” equipped with four state-of-the-art CCD cameras was used to record the complete deformation history of each specimen. Different specimen shapes were designed to test the deformation behavior of different strain paths.
It was found that all the specimens fractured abruptly at the top of the hemispherical punch without any significant tightening before fracture, indicating that the room temperature formability of the alloy is very limited. The deformation behavior of Ti-6Al-4V alloy plates during room temperature bending and roll forming was analyzed comparatively. The results show that the minimum bending radius of the pendulum folding bending test and the V-die bending test is 9 mm, while the minimum bending radius of the roll forming is 7.51 mm, which is more than 15% higher. Roll forming can form smaller radius sizes and has less springback than simple bending. This is mainly due to rolling forming is a multi-step cumulative deformation process, gradual multiple deformation can inhibit the growth of cracks, and at the same time make the material deformation is more than the ordinary deformation of a full. In addition, the shape defects that often appear in the rolling process of high-strength steel are relatively few in the rolling and forming process of Ti-6Al-4V alloy. It can be seen that roll forming is a promising process solution for room temperature forming of high strength titanium alloy plates for aerospace and automotive structural components.
