Formation of metastable phases during solidification of Al–3.2 wt% Mn

•During rapid solidification of Al–Mn alloys, expected phases do not always form.•This has been verified in this study.•Calculations of phase equilibria using thermodynamics can help to explain this.•‘Stable’ phases are shown to be kinetically inhibited from forming.

The solidification of the technologically important Al-rich Al–Mn alloys has been studied both experimentally and by calculation of the phase equilibria. The results of previous experimental studies, which indicated that one or more stable intermetallic phases are suppressed on solidification from the liquid, have been confirmed. It was shown that it is important to consider the formation of Al11Mn4 even though other intermetallic phases have a higher driving force for solidification. It is concluded that while an understanding of the thermodynamic properties of the phases is fundamental to modelling the formation of microstructure associated with solidification, it is necessary to take into account other effects such as the thermodynamic properties at interfaces and their effect on nucleation.