Precipitates in an Al–Mg–Ge alloy studied by aberration-corrected scanning transmission electron microscopy

The precipitates present in an Al–0.59Mg–0.71Ge (at.%) alloy have been studied using aberration-corrected high-angle annular dark-field scanning transmission electron microscopy. Two types of needle-shaped precipitates growing along 〈0 0 1〉 Al were found: a phase isostructural to the trigonal U1 phase found in Al–Mg–Si alloys, and finer precipitates with a hexagonal arrangement of Ge columns. The study revealed the presence of a complex interface structure surrounding the U1-like precipitates, and an explanation based on interatomic distances is proposed.