On the Structure, Transformation and Deformation of Long-Period Stacking Ordered Phases in Mg-Y-Zn Alloys

Ternary Mg-Y-Zn alloys have attracted considerable attention due to their unique microstructures and promising mechanical properties. The microstructure of these alloys contains predominantly intermetallic phases of 18R and/or 14H long-period stacking ordered (LPSO) structures, depending on the alloy processing conditions. Such 18R and/or 14H structures or similar LPSO structures are also found in other magnesium alloys such as Mg-Gd-Zn, Mg-Gd-Y-Zn, Mg-Dy-Zn, Mg-Ho-Zn, Mg-Er-Zn, Mg-Y-Cu, Mg-Y-Ni, and Mg-Y-Co. In addition, LPSO structures such as 24R and 10H have also been reported, even though they are less frequently observed. This paper provides a review of the current status on the characterization of the structure, thermal stability, transformation, and deformation of the LPSO structures using high-angle annular dark-field scanning transmission electron microscopy and electron diffraction. Unsolved issues on the LPSO structures are also highlighted and discussed. (C) The Minerals, Metals & Materials Society and ASM International 2014