Platelet precipitate in an age-hardening Mg-Zn-Gd alloy

The structure of a unique platelet precipitate with a three close-packed layer thickness, which occurred in a Mg-1 at.%Zn-2at.%Gd alloy aged at low temperatures (<similar to 500 K), has been determined based on scanning transmission electron microscopy and first principles calculations. The platelet precipitate is constructed by well-defined Gd networks that cause significant atomic displacements in the adjacent close-packed layer, in which the atomic sites are preferentially occupied by Zn atoms. Local Zn concentrations at the reconstructed-layer have been successfully tuned according to a similar manner of Vegard's law by reference to the local Gd-Gd interatomic distance along the c-axis. Therefore, the present platelet precipitate is found to be not a simple ordered hexagonal-close-packed Mg-Gd as previously reported, but a reconstructed ternary Mg-Zn-Gd structure. (C) 2018 Elsevier B.V. All rights reserved.