Atomic-resolution energy dispersive X-ray spectroscopy mapping of η precipitates in an Al-Mg-Zn-Cu alloy

Energy-dispersive X-ray spectroscopy (EDS) mapping has been performed to determine the distributions of the component atoms of η-Mg(Zn,Cu)2 precipitates in an Al-Mg-Zn-Cu aluminium alloy. High-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) was concomitantly employed to recognize the configurations of atomic columns. Mg and Zn maps showed their alternating atomic columns. The Cu-map revealed that the Al matrix adjacent to the interfaces of (0001)η is segregated by Cu, giving an evidence of the effect of Cu additions on the precipitation and growth of η-Mg(Zn,Cu)2 precipitates. Furthermore, the elongated-hexagonal lattice defects located inside the zig-zag stacking configurations of (21¯1¯0)η are related to the Zn-depleted zones, which are presumably occupied by Mg atoms.