Structural characteristics of β1′ precipitates in Mg–Zn-based alloys

β1′ precipitates in an Mg97Zn2.5Y0.5 alloy are shown to have a complex domain structure based on the structure of monoclinic Mg4Zn7 phase. All domains are oriented with [0 1 0]∥[0 0 0 1]Mg and one of the four planar matches with the matrix. Two of these orientations are related to two others by twinning on the (0 0 1) plane of the Mg4Zn7 phase. These orientations are brought about by crystallographic constraints from the matrix. An ordering of the domains creates a new structure.