Microstructural changes of Guinier–Preston zones in an Mg–1.5 at% Gd–1 at% Zn alloy studied by HAADF-STEM technique

Abstract

The microstructures of Guinier–Preston zones (GP-zones) precipitated in Mg 97.5Gd 1.5Zn 1 alloys annealed at 200 °C for various lengths of time have been thoroughly investigated by high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM) in combination with energy dispersive X-ray spectroscopy (EDS). The HAADF-STEM technique, which is capable of providing an atomic-scale Z-contrast image associated with heavier constituent elements in the alloys, has successfully allowed us to determine the atomic arrangement of Gd/Zn in the GP-zones. It is further evidenced that the GP-zones in the alloy have fairly variable microstructures with an advance of aging in the following way: wavy GP-zones → planar GP-zones → band-shaped (multi-layer) GP-zones (→ stacking faults).