Effect of extrusion parameters on mechanical properties of Mg 97Zn1y2 alloys at room and elevated temperatures

Abstract

The effects of alloy extrusion parameters, such as extrusion ratio, temperature, and speed on the mechanical properties at room and elevated temperatures and the microstructure evolution were investigated in the production of high strength Mg-Zn-Y alloys. The alloy used is a Mg 97Zn1Y2 (at%) which is engineered to acquire a long-period stacking ordered (LPSO) structure phase to increase alloy-strength. The microstructure of the extruded Mg97Zn1 Y2 alloy consists of hot-worked and dynamically recrystallized (DRXed) α-Mg grains that includes a fiber-shaped LPSO phase elongated along the direction of extrusion. Whereas an increase in average equivalent strain promotes the DRX of αMg matrix and the dispersion of the fiber-shaped LPSO phase, an increase in average metal flow rate is conductive to the DRX of α-Mg grains, but is not to the dispersion of LPSO phase. The mechanical properties of the extruded Mg-Zn-Y alloys are affected by changes in the area fraction of the DRXed grains and the dispersion of the fiber-shaped LPSO phase. As the extrusion ratio and extrusion speed increase, overall DRX bringing grain growth in its train in the α-Mg matrix phase decreases the tensile strength of alloys, but the dispersed fiber-shaped LPSO phase remaining in the DRXed grains region makes good the adverse effect of overall DRX followed by grain growth. © 2010 The Japan Institute of Metals.