Effect of Al on microstructure and mechanical properties of HPDC Mg-6Y-3Zn alloys

The effect of Al on microstructure and mechanical properties is investigated in novel Mg-6Y-3Zn (WZ63) alloys produced by high-pressure die-casting (HPDC). The morphology of (Al,Zn)2Y phase varies from lamellar to flower-like and then to block shape with 0.4-1.0 wt% Al. The HPDC alloys exhibit fine grain sizes ranging from 4 mu m to 7.4 mu m, and significant grain refinement is obtained with Al as low as 0.4 wt%, which is different from that in gravity casting. The (Al,Zn)2Y phase is the crack source, and the dimple depth and elongation (EL) reduce with increasing Al content. Still, all the studied HPDC WZ63-xAl alloys maintain excellent tensile properties, keeping 256-274 MPa for tensile strength (UTS) and 7.4-9.7 % EL at room temperature and 188-213 MPa UTS and 10-35 % EL at 250 degrees C. Optimal mechanical properties are obtained with Al content around 0.4-0.5 wt%.