Abstract
Precipitates in an Al-Mg-Ge alloy similar to the β′ phase in Al-Mg-Si alloys were investigated using qualitative and quantitative aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM). The needle-shaped β′-Ge precipitates are coherent with the Al matrix along the needle direction which is parallel to a 〈0 0 1〉 Al direction, as well as one direction in the cross-section plane that is parallel to a 〈1 0 0〉 Al direction. This is linked to a smaller lattice parameter in the needle cross-section plane than that of coarser, less coherent β′ precipitates in Al-Mg-Si alloys, despite Ge having a larger atomic radius than Si. Quantitative HAADF STEM results show that the nominal Ge columns of the β′-Ge precipitates are not fully occupied by Ge, the intensity of these columns being consistent with an Al concentration of 30 ± 10%, or a vacancy concentration of 20 ± 10%. The coherent interface is atomically smooth, but with matrix columns containing Ge spaced periodically along the interface.
Original language | English (US) |
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Pages (from-to) | 3239-3246 |
Number of pages | 8 |
Journal | Acta Materialia |
Volume | 60 |
Issue number | 6-7 |
DOIs | |
State | Published - Apr 2012 |
Externally published | Yes |
Keywords
- Aluminium alloys
- High angle annular dark field
- Precipitation
- Scanning transmission electron microscopy
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Polymers and Plastics
- Metals and Alloys