Influence of zinc and silver additions on hot tearing susceptibility of Mg-14Gd-0.4Zr alloy

The effects of 1Zn and/or 2Ag additions on the hot tearing susceptibility (HTS) of Mg-14Gd-0.4Zr (wt%) alloy were studied. The HTS was evaluated by both theoretical predictions using Kou's criterion and experimental observations based on the in situ force-temperature recorded constrained rod casting (ISFTCRC) method. The results show that the order of HTS from high to low is Mg-14Gd-2Ag–1Zn-0.4Zr, Mg-14Gd-2Ag-0.4Zr, Mg-14Gd-1Zn-0.4Zr and Mg-14Gd-0.4Zr. Adding 1Zn and/or 2Ag changes the solidification path and the solidification interval, which affects the hot tearing susceptibility. Alloying elemental 1Zn slightly increases the solidification interval and the temperature range in the square root of the solid phase fraction (f _s ^1/2) range of 0.949–0.995, resulting in a slight increase in the hot tearing susceptibility. The addition of 2Ag drastically widens both the solidification interval and the temperature range in the f _s ^1/2 range of 0.949–0.995, thus significantly increasing the hot tearing susceptibility. Compared to the addition of 2Ag alone, the broadening degree of both the solidification interval and the temperature range in the f _s ^1/2 range of 0.949–0.995 is greater by adding the composite 2Ag/1Zn, which further promotes the occurrence of hot tearing. A narrower solidification interval and a temperature range in the f _s ^1/2 range of 0.949–0.995 result in a lower hot tearing susceptibility.