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The long-period stacking-ordered (LPSO) phases were demonstrated to be the predominant strengthening phases that can significantly improve the mechanical properties of Mg–Zn–Y alloys. However, the mechanism underlying this improvement has not been satisfyingly understood yet due to unclear characterization of the microstructures of these LPSO phases. We proposed the reliable structural model of Mg 142Zn 12Y 16 for 14H LPSO phase formed in Mg–Zn–Y alloys with first-principles calculations in this study. The space group of Mg 142Zn 12Y 16 is P6 3/mcm, with lattice dimensions a =  b = 11.168 Å, c = 36.408 Å, α =  β = 90°, and γ = 120°. And the atomic sites were given in this work. In contrast to other structural models proposed in previous studies, 14H LPSO phase was predicted to be thermodynamically stable on the basis of the present structural model, which can well account for the stability of 14H LPSO phases at higher temperature. Furthermore, the elastic constants and elastic moduli of 14H LPSO phase were also evaluated based on the present structural model. The calculated Young’s modulus of 14H LPSO phase agrees well with the available experimental values. The characteristics of 14H LPSO phase observed in experiments were successfully reproduced using the present structural model. The good match between the calculations and the experiments validates the reliability of the structural model proposed for 14H LPSO phase. [ABSTRACT FROM AUTHOR]

The strengthening mechanisms underlying the long period stacking order (LPSO) phases in Mg-Zn-Y alloys have largely remained unsolved due to unclear understanding of the local arrangements of Zn and Y atoms in the LPSO phases. The local arrangements of Zn and Y atoms in the LPSO structures are theoretically refined with first-principles method in this study. The calculations clearly demonstrate that Zn and Y atoms prefer clustering in the form of Zn6Y9 rather than arranging in random or ordered arrangements, or in the form of Zn6Y8 cluster, as proposed in previous experiments. The Zn6Y9 cluster, which leads to the formation of ABCA-type building block of the LPSO structures, can be particularly regarded as the ideal stoichiometric component of the LPSO structures. Various non-stoichiometric ZnmYn(Mg) clusters derived from the Zn6Y9 cluster can also easily exist in the LPSO structures. The non-stoichiometric ZnmYn(Mg) clusters may correspond to the arrangements of Zn and Y atoms in the LPSO phases with different Zn/Y ratios. This study indicates that the novel structures of the LPSO phases consisting of ABCA-type building blocks stem from the formation of the Zn6Y9 cluster and its derivative clusters, ZnmYn(Mg). [ABSTRACT FROM AUTHOR]