Microstructure and mechanical properties of Mg-Zn-Y cast alloys

Abstract

Recently the extruded Mg-Zn-Y alloy is known as attractive for automotive components with increased strength at elevated temperature. In order to achieve these attractive properties in cast component, we focused on grain refinement of Mg96Zn2Y2 (at%) cast alloy with long-period stacking ordered (LPSO) structures and investigated the effects of zirconium addition and cooling rate on microstructures and mechanical properties. Mg 96Zn2Y2 cast alloy with the addition of zirconium consisted of a-Mg phase, Mg12ZnY phase and Mg 3Zn3Y2 phase as well as the alloy without zirconium. However, the coarse dendritic structure was found to transform into fine equiaxed grains by an addition of 0.2at%Zr. Furthermore, the increased cooling rate led to the crystallization of the fine Mg3Zn 3Y2 and Mg12ZnY phases forming a net-like structure. Consequently, this alloy exhibited a tensile strength of 223MPa at 523 K, which is about twice that of A4032-T6 alloy and excellent fatigue property at high temperature of 473 K. Additionally, high elongation of 10.5% at room temperature was achieved even in the as-cast condition. This alloy also had thermal properties equivalent or higher than those of commercial magnesium alloys.