The effects of yttrium element on microstructure and mechanical properties of Mg-5 mass %Al-3 mass % Ca based alloys fabricated by gravity casting and extrusion process

The as-cast microstructure of Mg-5 Al-3Ca-xY alloy consists of dendritic a-Mg matrix, (Mg, Al)₂Ca eutectic phase and Al₂Y intermetallic compounds. These two kind of (Mg, Al)₂Ca compounds were observed: coarse irregular-shape structure at grain boundary and fine needle-shape structure in the α-Mg matrix grain. This (Mg, Al) ₂Ca phase of the extruded alloys was elongated to extrusion direction and size of this phase was refined comparing with that of as-cast alloys because of severe deformation during hot extrusion. Maximum yield and ultimate strength value of extruded alloys was 326 and 331 MPa at Mg-5Al-3Ca-3Y alloy, respectively. From these results, it is conclusively demonstrated that Y additions on Mg-5Al-3Ca alloy nave more ettect to improve mechanical properties.