Unexpected capture of Guinier-Preston zone and γ″ phase in as-cast Mg-Gd-Y-Zn-Ni-Mn alloy: Atomic-scale insights

Highlights: • Cs-corrected HAADF-STEM is applied to directly image the solute-enriched structures. • G.P. zone and γ″ phase have been captured and their difference is reflected by different extents of segregation of Mn. • DFT calculations have confirmed that G.P. zone is the precursor of γ″ phase and predicted Mn atomic positions in γ″. -- Abstract: Cs-corrected high angle annular dark field - scanning transmission electron microscopy (HAADF-STEM) has been applied to characterize as-cast Mg-Gd-Y-Zn-Ni-Mn alloy. Atomic-scale images of Guinier-Preston (G.P.) zone and γ″ phase (hexagonal structure with space group P$\overline{6}$2 m) on the same plate have been captured unexpectedly, and the subtle difference between G.P. zone and γ″ is reflected by their different extents of segregation of Mn atoms. Density functional theory (DFT) calculations have confirmed that G.P. zone is the precursor of the γ″ phase and predicted the Mn atomic positions in γ″ phase.