Thermodynamic stability of Al11RE3 intermetallic compounds from first-principles calculations

Abstract

Phase stability of Al-RE intermetallic compounds is crucial particularly for high temperature mechanical properties of Mg–Al–RE based alloys as well as the possibility of their commercial applications. For a long time, a controversial issue exists concerning whether Al11RE3 phase in heat-resistant Mg–Al–RE based alloys decomposes into Al2RE and Al when treated at high temperatures. Herein, we performed a systematically study to the relative phase stability of all Al11RE3 with single RE element compared with Al2RE at 0–1000K using the state-of-the-art first-principles density functional calculation method. The results indicate that Al11RE3 phases with RE=La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb are highly stable while those with RE=Ho, Er, Tm, Lu, Y, and Sc are always instable compared with the Al+Al2RE two-phase equilibrium at temperatures lower than 1000K. These calculations suggest that Al11RE3 phase in the Mg–Al–RE based alloys with Ce-rich misch metal or mixed RE elements would decompose into Al2RE and Al due to the instable Al11RE3 components, then decreased the alloy’s high temperature performances. The present work also provides important guidance for future optimization design of heat-resistant magnesium alloys.