Effects of Er on Hot Cracking Susceptibility of Mg-5Zn-xEr Magnesium Alloys

Mg-Zn-Er casting magnesium alloys have good properties, such as high specific strength, high specific stiffness and remarkable temperature creep properties. Current researches mainly focused on the phases and mechanical properties at room and high temperatures. However, the effect of Er on hot cracking susceptibility of Mg-5Zn-xEr magnesium alloys was barely studied. In this work, a modified RDG (Rappaz-Drezet-Gremaud) model for predicting the hot cracking susceptibility of Mg-5Zn-xEr (x= 0.83, 1.25, 2.5, 5, mass fraction, %) ternary alloys was proposed, which considered the effects of phase and solidification temperature range on the hot cracking susceptibility of the multiphase alloys. And, the hot cracking susceptibility was evaluated by the experiment of constrained rod casting (CRC). The results indicated that the modified RDG model could accurately predict the hot cracking susceptibility of Mg-5ZnxEr magnesium alloys. The hot cracking susceptibility increased with the addition of Er up to 2.5%, and Mg-5Zn-2.5Er alloy showed the maximal hot cracking susceptibility; when the addition of Er increased to 5.0%, Mg-5Zn-5Er alloy exhibited the minimal hot cracking susceptibility. The calculated results were consistent with the experimental ones. Further analysis on the casting solidification curves, phases and microstructures showed that I-phase precipitated by peritectic reaction during solidification of Mg-5Zn-2.5Er alloy depleted liquid phases and extended the solidification temperature range of the alloy, leading to the hot cracking susceptibility increasing. The Mg-5Zn-5Er alloy underwent eutectic reaction of L→α-Mg+W during solidification, which reduced the solidification temperature range. Meanwhile, this process was beneficial to feeding the interdendritic hot cracking in the terminal period of solidification, which significantly decreased the hot cracking susceptibility of Mg-5Zn-5Er alloy.

Duke Scholars

Author Zhaohui Wang Pathology