Abstract
Aging reactions in Mg-RE alloys strengthen magnesium, due to the formation of metastable beta '' and beta' precipitates. We use first-principles calculations to critically assess binary Mg-RE (RE = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Y) aging reactions, metastable phases and interfacial energy. We find the following. (i) Our calculations correctly predict the formation of different variants of beta' phases for Mg-RE systems across the RE series. (ii) Surprisingly, the Mg/beta '' prismatic interfaces are unstable, with a negative interfacial energy. (iii) This interfacial instability implies the existence of a more energetically stable compound than beta '', which we show to be the beta' precipitate. By exposing the link between Mg/beta '' prismatic interfaces and the beta' structure, we propose that beta' phase formation is due to an energetic preference for an ordered arrangement of Mg and beta ''. (iv) Our Mg/beta '' interfacial energy results also indicate that atomically thin beta" planar Guinier-Preston zones can form as a precursor to beta' precipitation. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.