The γ" Phase in Mg-RE-TM Alloys: A Review on the Structure and Stability of the γ" Phase and Its Effect on Mechanical Properties

In magnesium-rare earth-transition metal (Mg-RE-TM) alloys, the gamma" phase (with a hexagonal structure with the space group P6 over bar 2m) is a critical strengthening phase that can significantly improve their mechanical properties. However, compared to other phases in Mg-RE-TM alloys, research on the gamma" phase is less documented, and an understanding of the gamma" phase is not well established. As a result, different models of the structure of the gamma" phase have been proposed. In this review, we summarize these structural models and find that the gamma" phase is different from the Guinier-Preston (G.P.) zone, as revealed via Cs-corrected high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) and density functional theory (DFT) calculations. In addition, we briefly summarize the stability of the gamma" phase and its effect on the mechanical properties of Mg-RE-TM alloys.