Effect of Y addition on the microstructure and high-temperature properties of extruded Mg-2.5Si-4Zn-0.7Ca alloy

Abstract The limited high-temperature performance of magnesium alloys has long been a key barrier to their widespread application. Among these, Mg-Si-based alloys show promise due to the high thermal stability of the Mg 2 Si phase and their low cost. However, in the as-cast state, the primary strengthening phase Mg 2 Si tends to be relatively coarse, which significantly deteriorates the mechanical properties of the alloy. Although approaches such as composite modification and hot extrusion have proven effective in enhancing both room-temperature and high-temperature mechanical properties, the specific role and underlying mechanism of combined Ca-Y addition together with hot extrusion in improving high-temperature performance have yet to be elucidated. This study systematically investigated the influence of Y content (0, 0.5, and 1.0 wt.%) on the microstructure and mechanical performance of the extruded Mg-2.5Si-4Zn-0.7Ca-xY alloy at both room and elevated temperatures. The findings reveal that as Y content increases from 0 to 1.0 wt.%, the Mg 2 Si phase undergoes gradual refinement and spheroidization, accompanied by a corresponding enhancement in mechanical properties across the tested temperature range. It was found that Y promotes the decomposition of Mg 2 Si to form the Y 2 Si 2 Mg phase, thereby refining the Mg 2 Si phase through both decomposition and mechanical fragmentation. The alloy containing 1.0% Y exhibited the best combination of room-temperature and high-temperature mechanical properties, reaching a tensile strength of 317.99 MPa with an elongation of 5.74% at room temperature; 227.43 MPa with 13.74% elongation at 150 °C; and 161.1 MPa with 19.17% elongation at 200 °C.