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Surface effects in chromate conversion coatings on 2024-T3 aluminum alloy

TitleSurface effects in chromate conversion coatings on 2024-T3 aluminum alloy
Publication TypeJournal Article
Year of Publication2001
AuthorsSun, X, Li, R, Wong, KC, Mitchell, KAR, Foster, T
JournalJournal of Materials Science
Volume36
Pagination3215-3220
Date PublishedJul
Type of ArticleArticle
ISBN Number0022-2461
KeywordsCOPPER IONS, CU ALLOY, FILMS, GROWTH, MECHANISM, mobility
Abstract

Chromate conversion coatings formed on samples of 2024-T3 aluminum alloy, which had been given different pre-treatments, were examined by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and corrosion tests. Two pre-treatments were considered, namely a simple mechanical polish, and polishing followed by an etch in a HF-H2SO4 solution. The latter treatment leads to significant Cu enrichment at the oxide-alloy interface, and this in turn can lead to a deleterious effect on the corrosion protection afforded by a subsequently applied chromate coating. Discussions are given of the behaviour of Cu in the coating formed on the sample that received an acid etch in the pre-treatment. This involves both migration through the coating and a non-uniform redeposition of Cu on to the coating surface. By contrast, the sample that initially was given just the mechanical polish in the pre-treatment does not show a Cu enrichment in the surface region, and the subsequently applied coating appeared stable after a 24 h immersion in a NaCl test solution. (C) 2001 Kluwer Academic Publishers.

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