Structural and Mechanical properties of Magnesium Alloy Processed by Severe Plastic Deformation Method of Hydrostatic Cyclic Expansion Extrusion

Magnesium and its alloys have received much attention not only in the aerospace and electronics industry, but also in medical applications due to its low density, excellent physical properties, and biocompatibility. However, magnesium and its alloys have low ductility and poor strain hardening ability because of the hexagonal crystal structure with the limited number of slip systems at room temperature. Therefore, it seems necessary to improve their ductility and other mechanical properties via novel technologies. In this research, hydrostatic cyclic expansion extrusion has been used to produce ultrafine-grained magnesium rod. Properties of produced rods have been investigated morphologically and mechanically. The numerical investigation has also been performed to show the effects of hydrostatic pressure on strain distribution. Due to the brittleness of magnesium, the process has been conducted at elevated temperatures. Also, due to the fluid limitation at high temperatures, melted polyethylene has been used as the fluid in the process. The results showed that the yield and ultimate strength increased by 54% and 43% after only one pass of the hydrostatic cyclic expansion extrusion process, respectively. Also, elongation increased by 46%. Furthermore, microhardness has also increased with an average of 57 Hv to 70 Hv. The microstructure result showed that the grains become ultrafine-grained after only one pass of the process. Finite element investigation revealed that high hydrostatic pressure has a good effect on improving the strain distribution and the microstructure. This process seems very appropriate for industrial applications due to its ability to produce long ultrafine-grained rods.