The role of aluminum distribution on the local corrosion resistance of the microstructure in a sand-cast AM50 alloy

•Site-specific analytical electron microscopy was performed on corroded AM50.•Areas close to eutectic microstructure show less corrosion damage.•Eutectic Mg grains develop an Al-rich layer between the alloy and corrosion product.•We demonstrate, using low-loss EELS, that the Al-rich layer is metalli...

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Bibliographic Details
Published in:Corrosion science 2013-12, Vol.77, p.151-163
Main Authors: Danaie, Mohsen, Asmussen, Robert Matthew, Jakupi, Pellumb, Shoesmith, David W., Botton, Gianluigi A.
Format: Article
Language:English
Subjects:
A. Alloy
A. Magnesium
Aluminum
Aluminum base alloys
Applied sciences
B. STEM
B. TEM
Corrosion
Corrosion environments
Corrosion products
Exact sciences and technology
Magnesium base alloys
Magnesium oxide
Mathematical analysis
Metals. Metallurgy
Solid solutions
Thin films
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Summary:•Site-specific analytical electron microscopy was performed on corroded AM50.•Areas close to eutectic microstructure show less corrosion damage.•Eutectic Mg grains develop an Al-rich layer between the alloy and corrosion product.•We demonstrate, using low-loss EELS, that the Al-rich layer is metallic in character.•Primary α-Mg grains, with lower Al content, do not develop the Al-rich layer and corrode severely. Site-specific analytical electron microscopy was performed on a corroded sand-cast AM50 alloy. Areas close to partially divorced eutectic were the regions with less corrosion damage. The corrosion product layer in these areas consisted of a columnar section of predominantly amorphous MgO. At the alloy interface, an aluminum-rich layer was identified. Electron energy-loss spectroscopy suggests this layer is metallic in character. The corrosion product film on the primary α-Mg grains possessed a bi-layer morphology: a thin columnar film and a thicker, porous sub-layer. The formation of the Al-rich layer depends on the Al content in solid solution at a specific location.
ISSN:0010-938X
1879-0496
DOI:10.1016/j.corsci.2013.07.038