Hot tearing susceptibility of Mg-5Nd-xZn alloys

Abstract

Magnesium-neodynium-zinc (Mg-Nd-Zn) alloys are promising candidates as creep resistant alloys. Further, Nd is a rare earth (RE) addition with lower solid solubility and a relatively lower cost. Hence, the use of such alloys may result in a feasible and cost effective alternative for enhancing Mg alloy use in high temperature applications. Nevertheless, studies on the castability of Mg-Nd-Zn alloys are lacking. As such, the aim of this research was to investigate the hot tearing susceptibility of Mg-5Nd-xZn (x= 0, 3, 5, 7 wt%) alloys during permanent mold casting. Specifically, a constrained-rod casting mold equipped with a load cell was used to characterize hot tearing severity and determine the onset temperature of hot tearing. The onset solid fraction of hot tearing was subsequently determined via thermodynamic software. The results suggest that hot tearing severity increased initially with addition of Zn (up to 5 wt%), but then decreased with further addition to 7 wt%. This was likely attributed to both the low onset solid fraction of hot tearing (i.e. 0.5) recorded for this alloy, which enabled enhanced feeding and opportunity to heal developing hot tears, as well as the divorced eutectic structure observed which may have facilitated late stage feeding of eutectic liquid and hence limit the alloy's susceptibility to hot tearing.