Die structure optimization study for magnesium alloy wheel formed by backward extrusion

Abstract

The current magnesium (Mg) alloy wheel formed by backward extrusion (BE) often has upper rim cracking and coarse microstructure at the spokes to reduce the yield, and a reasonable die structure design is an important factor to improve the yield of the wheel, therefore, this poses new challenges on the die structure of Mg alloy wheels. The paper selected four parameters for the three positions of the wheel for optimizing the die structure by analyzing the forming characteristics and defects of Mg alloy wheels. Based on the actual extrusion conditions of the Mg alloy wheel, a numerical model of Mg alloy wheels formed by BE was established, and the effect of a single parameter on the physical field of the forming process was analyzed by numerical simulation in turn, and then the four parameters of the die structure were progressively combined and optimized to determine the better three positions of the Mg alloy wheel die, while an experimental trial was conducted to verify the accuracy of the results of this study. The results show that increasing the spoke thickness, decreasing the spoke inclination angle, increasing the punch fillet radius and increasing the inner fillet radius of the upper rim can effectively improve the metal flow and make the billet filling more smoothly. The optimized die structure can make the temperature at the wheel bottom lower and evenly distributed, the stress concentration at the window is relieved, the filling at the upper rim is complete, and the macroscopic tearing phenomenon disappears.