Effect of grain size on age hardening in AM60 magnesium alloy poured into various gravity molds

Abstract

Magnesium and its alloys are well-known as the lightest metallic structure material with excellent castability and specific strength. Those good mechanical properties are very attractive for industrial applications in automobile and portable electronic devices. Above all, AM60 magnesium alloy is manufactured from the pressure die casting process with chiefly high accuracy and productivity, but actual use and research using gravity casting with lower cooling rate is less than the die casting method, and there are a multitude of unknown things regarding solidification behavior and microstructure evolution. Our recent studies showed that continuous precipitation is covered by the whole of crystal grain with aging in AM60 magnesium alloy cast into permanent molds, which have the average grain size of 75–85 μm. On the other hand, continuous precipitation stays on the periphery of the crystal grain boundary with aging in the same cast into a sand mold, having the average grain size of 138–147 μm. It's thought that permanent mold castings have the age hardening behavior of intragranular precipitation participation type that is influenced by continuous precipitates. It's also thought that sand mold castings have the age hardening behavior of grain boundary participation type that is influenced by cellular precipitates. In this study, AM60 magnesium alloy with bigger grain size was used to detect the effect of grain size on age hardening behavior.