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Crystal structure of the orthorhombic U2-Al4Mg4Si4 precipitate in the Al–Mg–Si alloy system and its relation to the β′ and β″ phases |
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| Authors: | SJ Andersen CD Marioara A Frseth R Vissers HW Zandbergen |
| Affiliation: | aSINTEF Materials Technology, Applied Physics, 7465 Trondheim, Norway bNTNU, Department of Physics, 7491 Trondheim, Norway cNational Centre for HRTEM, Laboratory of Materials Science, Delft University of Technology, Rotterdamseweg 137, 2628 AL Delft, The Netherlands |
| Abstract: | The atomic structure of a common precipitate in the Al–Mg–Si system has been determined. It is isotypic with TiNiSi (space group Pnma) and contains four units of MgAlSi in a unit cell of size a = 0.675 nm, b = 0.405 nm, c = 0.794 nm. EDS analyses support the composition. A model was based on the atomic structure of the β′ precipitate, electron diffraction and high-resolution transmission electron microscopy (HRTEM) images. A quantum mechanical refinement of the model removed discrepancies between simulated and experimental diffraction intensities. Finally, a multi-slice least square refinement confirmed the structure. The structural relation with β″ is investigated. A similar Mg–Si plane also existing in β″ and β′, can explain most coherency relations between the precipitate phases and with matrix. |
| Keywords: | Al–Mg–Si alloys U2-Al4Mg4Si4 precipitates High-resolution transmission electron microscopy Precipitate coherency relations |
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