Atomic structure of γ″ phase in Mg–Gd–Y–Ag alloy induced by Ag addition

ABSTRACT

Mg–Gd based alloys are typical high strength magnesium alloys owing to their outstanding age hardening behavior. The mechanical strength of aged Mg–Gd alloys is enhanced by high density prismatic-shaped precipitates in Mg matrix. Moreover, the addition of Ag has been found to enhance the strength of Mg–Gd based alloys further by forming a plate-shaped precipitate, named as γ″, on basal planes of Mg. However, the structure of this precipitate is not well understood due to the complex alloying system. In this work, the atomic structure of γ″ phase is investigated using atomic-resolution high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Based on the accurate atomic structure from three independent directions, e.g. in [0001]_Mg, [$\overline{2}$110]_Mg and [01$\overline{1}$0]_Mg zone axes, the unit cell of γ″ is well established. The γ″ phase has a hexagonal structure, and its lattice parameters are a = 0.55 nm and c = 0.42 nm. The orientation relationship between γ″ phase and Mg matrix is (0001)_γ″//(0001)_Mg and <$\overline{2}$110>_γ″//<$\overline{1}$010>_Mg.

KEYWORDS:

• Mg alloys
• precipitation
• HAADF-STEM
• microstructural analysis

Additional information

Funding

This work was supported by the National Key Research and Development Program of China [grant numbers 2017YFA0204403, 2017YFB0305501]; National Natural Science Foundation of China [grant numbers 51601003, 51401172, 51074106, 51374145]; Natural Science Foundation of Heilongjiang Province [grant number QC2017061]; Harbin Science and Technology Bureau [grant number 2017RAQXJ066].