Physical field regulation of magnesium alloy wheel formed by backward extrusion process with multi-stage variable speed

To reduce the tonnage required during the forming process of magnesium (Mg) alloy wheels by backward extrusion (BE) and refine the grains at the wheel bottom, the multi-stage variable (MSV) speed process is proposed based on the characteristics of Mg alloy wheels formed by BE. A numerical model for the BE process of Mg alloy wheels using the Defrom-3D was constructed, and the effects of constant speed and MSV speed processes on the physical fields and DRXed grain size evolution during the forming of Mg alloy wheels were investigated. Lastly, the simulation results were indirectly verified by industrial trial production. The results show that constant speed extrusion has a small effect on the effective stress, but a large effect on the wheel temperature distribution, where the forming speed of the upper rim plays a decisive role in the final temperature distribution of the wheel. MSV speed process is used to regulate the physical field evolution during wheel forming based on the effect of constant speed on the physical field of the wheel. With the high-speed forming of the rim and low-speed forming of the upper wheel rim (9-9-1 mm/s), the temperature and effective stress distribution of the wheel blank are reasonable while reducing the forming tonnage and refining the grains at the wheel bottom.