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Volta Potential Evolution of Intermetallics in Aluminum Alloy Microstructure Under Thin Aqueous Adlayers: A combined DFT and Experimental Study
RISE - Research Institutes of Sweden, Swerea, Swerea KIMAB. KTH Royal Institute of Technology, Sweden.
KTH Royal Institute of Technology, Sweden ; University of Science and Technology of Beijing, China.
KTH Royal Institute of Technology, Sweden.
University of Science and Technology of Beijing, China.
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2018 (English)In: Topics in catalysis, ISSN 1022-5528, E-ISSN 1572-9028Article in journal (Refereed) In press
Abstract [en]

In this work, first-principle density functional theory (DFT) was used to calculate the work function and Volta potential differences between aluminum alloy matrix and two intermetallic phases (Mg2Si and Al2Cu) with varying surface terminations as a function of adhering monolayers (ML) of water. The calculated data were compared with experimental local Volta potential data obtained by the scanning Kelvin probe force microscopy (SKPFM) on a commercial aluminum alloy AA6063-T5 in atmospheric environments with varying relative humidity (RH). The calculations suggest that the surface termination has a major effect on the magnitude and polarity of the Volta potential of both intermetallic phases (IMP’s). The Volta potential difference between the IMP’s and the aluminum matrix decreases when the surface is gradually covered by water molecules, and may further change as a function of adhering ML’s of water. This can lead to nobility inversions of the IMP’s relative to the aluminum matrix. The measured Volta potential difference between both IMP’s and their neighboring matrix is dependent on RH. Natural oxidation in ambient indoor air for 2 months led to a nobility inversion of the IMP’s with respect to the aluminum matrix, with the intermetallics showing anodic nature already in dry condition. The anodic nature of Al2Cu remained with the introduction of RH, whereas Mg2Si became cathodic at high RH, presumably due to de-alloying of Mg and oxide dissolution. The DFT calculations predicted an anodic character of both IMP’s in reference to the oxidized aluminum matrix, being in good agreement with the SKPFM data. The DFT and SKPFM data were discussed in light of understanding localized corrosion of aluminum alloys under conditions akin to atmospheric exposure. 

Place, publisher, year, edition, pages
2018.
Keywords [en]
Aluminum, Aqueous adlayer, DFT, Intermetallics, SKPFM, Volta potential, Aluminum corrosion, Anodic oxidation, Atmospheric corrosion, Atmospheric humidity, Binary alloys, Copper alloys, Dealloying, Density functional theory, Localized corrosion, Magnesium compounds, Matrix algebra, Metallic matrix composites, Molecules, Silicon alloys, Vapor deposition, Adlayers, Commercial aluminum alloys, First-principle density-functional theories, Localized corrosion of aluminums, Scanning Kelvin probe force microscopy, Volta-potential difference, Aluminum alloys
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Natural Sciences
Identifiers
URN: urn:nbn:se:ri:diva-33762DOI: 10.1007/s11244-018-0939-9Scopus ID: 2-s2.0-85045260197OAI: oai:DiVA.org:ri-33762DiVA, id: diva2:1204200
Available from: 2018-05-07 Created: 2018-05-07 Last updated: 2018-05-07Bibliographically approved

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