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

Abstract

The as-cast microstructure of Mg-5Al-3Ca-xY alloy consists of dendritic α-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 have more effect to improve mechanical properties.