Atomic scale investigation of a novel metastable structure in aged Mg–Nd alloys

Aged Mg-3.0 wt% Nd alloys were investigated by high angle annular dark-field scanning transmission electron microscopy. A hitherto unreported metastable phase designated β3 can always emerge at the endpoints of β1 particles. The crystal structure of β3 phase is determined to an orthorhombic lattice (space group Cmcm). With the {111}β1 planes acting as the basal plane of growth, β3 phase has three types of variants, which are related by a 120° rotation with respect to each other around the same [001]β3 axis. In addition, several peculiar morphologies and further evolution of β3 phase were also analyzed.