Atomic structure of solute clusters in Al-Zn-Mg alloys

Scanning transmission electron microscopy imaging of Al-Zn-Mg alloys has provided new information on the atomic structures of solute rich clusters forming from a supersaturated solid solution at low temperatures. A unique unit of high Zn/Mg ratio is the fundamental cluster building block. The unit is essentially a partial substitution by Mg and Zn on the cubic aluminium cell and its surrounding truncated cube octahedral shell. A simple set of principles based on Frank-Kasper structures describes how the basic units arrange with respect to each other to form larger clusters. Density functional theory calculations, atom probe tomography and simulated diffraction patterns support the proposed atomic models. The results provide new insight into the very early stages of age-hardening in aluminium alloys. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. This is an open access article under the CC BY license

Automated summary

Scanning transmission electron microscopy imaging of Al-Zn-Mg alloys at low temperatures has revealed the atomic structures of solute-rich clusters, characterized by a unique unit with high Zn/Mg ratio. The arrangement of these basic units to form larger clusters is described by Frank-Kasper structures, supported by density functional theory calculations, atom probe tomography, and simulated diffraction patterns. These results provide new insight into the early stages of age-hardening in aluminum alloys.