Investigation of the non-equilibrium solidification microstructure of a Mg-4Al-2RE (AE42) alloy

The solidification microstructures of AE42 (Mg-4Al-2RE, wt%) alloys with three different cooling rates are investigated using CALculation of PHase Diagrams (CALPHAD) simulation and experimental validation. The results show that high cooling rates can refine the microstructure and decrease the formation of particulate Al2RE intermetallics. Particularly, the Mg17Al12 phase, predicted by CALPHAD simulation using the Scheil model, is not observed in the high-pressure die casting (HPDC) sample. The suppression of Mg17Al12 in HPDC AE42 alloy at high cooling rates and high pressure is likely due to the supersaturation of Al in (Mg), in addition to the preferential formation of Al11RE3 and Al2RE phases.