한국주조공학회

The high-temperature stability of Mg-8.0Zn-1.6Y (wt.%) alloys upon the addition of Ca has been investigated by characterizing the ignition temperature, microstructure, tensile and creep properties. The ignition temperature increases with an increase in the Ca content, indicating that an addition of Ca enhances the ignition resistance of the Mg-Zn-Y alloy. The as-cast microstructures of all tested alloys mainly consisted of the dendritic -Mg matrix and I-phase (Mg3Zn6Y) at the grain boundaries. In the Ca-added Mg8.0Zn added Mg8.0Zn-1.6Y alloys, the Ca2Mg6Zn3 phase forms, with this phase fraction increasing with an increase in the Ca contents. However, a high volume fraction of the Ca2Mg6Zn3 phase rather deteriorates the mechanical properties. Therefore, a moderate amount of Ca element in Mg-8.0Zn-1.6Y alloys is effective for improving the tensile and creep properties of the Mg-Zn-Y alloy. The Mg-8.0Zn1.6Y-0.3Ca alloy exhibits the highest tensile strength and the lowest creep strain among the alloys investigated in the present study. The creep resistance of Mg-Zn-Y-Ca alloys depends on the selection of the secondary solidification phase; i.e., when Ca2Mg6Zn3 forms in an alloy containing a high level of Ca, the creep resistance deteriorates because Ca2Mg6Zn3 is less stable than the I-phase at a high temperature.

Mg-Zn-Y alloys, Ca, I-phase, Ignition resistance, Creep resistance