Experimental Study of the Solidification Microstructure in the Mg-Rich Corner of Mg–Al–Ce System

The current lack of comprehensive understanding of the microstructure evolution in Mg–Al–Ce alloys hinders the accuracy of thermodynamic predictions. Our investigations have identified shortcomings within the published literature for the Mg-rich end of the Mg–Al–Ce phase diagram. In this study, the microstructure evolution in Mg–Al–Ce alloys has been studied by X-ray diffraction, scanning and transmission electron microscopy. The experimental results are compared with the Scheil-Gulliver prediction calculated using the CALPHAD method. The observed microstructure contains both the binary Al–Ce and Mg–Ce intermetallic phases in these alloys. The solidification sequence, invariant point and the phase boundaries in the liquidus projection of the Mg–Al–Ce phase diagrams that have been reported previously are inconsistent with this study. The hypoeutectic region is smaller compared to the current Mg–Al–Ce phase diagram. In addition, a hexagonal Al₅Ce₂ phase which is isostructural with Al₅La₂ has been identified in these alloys. The research addresses some of the current limitations in understanding the effect of Ce, when added in isolation, on microstructure development in Mg–Al based alloys.