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Composition of beta'' precipitates in Al–Mg–Si alloys by atom probe tomography and first principles calculations

Abstract

The composition of beta'' precipitates in an Al–Mg–Si alloy has been investigated by atom probe  tomography, ab initio density functional calculations, and quantitative electron diffraction. Atom probe analysis of an Al-0.72% Si-0.58% Mg (at. %) alloy heat treated at 175 °C for 36 h shows that the beta'' phase contains ~20 at. % Al and has a Mg/Si-ratio of 1.1, after correcting for a local magnification effect and for the influence of uneven evaporation rates. The composition difference is explained by an exchange of some Si with Al relative to the published beta''-Mg5Si6 structure. Ab initio calculations show that replacing the Si3-site by aluminum leads to energetically favorable compositions consistent with the other phases in the precipitation sequence. Quantitative electron nanodiffraction is relatively insensitive to this substitution of Al by Si in the beta''-phase.

Category

Academic article

Language

English

Author(s)

Affiliation

  • SINTEF Industry / Materials and Nanotechnology

Year

2009

Published in

Journal of Applied Physics

ISSN

0021-8979

Publisher

AIP Publishing (American Institute of Physics)

Volume

106

Page(s)

1235271 - 1235279

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