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Microstructural effects on the initiation of zinc phosphate coatings on 2024-T3 aluminum alloy

TitleMicrostructural effects on the initiation of zinc phosphate coatings on 2024-T3 aluminum alloy
Publication TypeJournal Article
Year of Publication2004
AuthorsSusac, D, Sun, X, Li, RY, Wong, KC, Wong, PC, Mitchell, KAR, Champaneria, R
JournalApplied Surface Science
Volume239
Pagination45-59
Date PublishedDec
Type of ArticleArticle
ISBN Number0169-4332
Keywords7075-T6, AA2024-T3, aluminum alloy, ATOMIC-FORCE MICROSCOPY, CONVERSION COATINGS, ELECTRON-MICROSCOPY, INTERGRANULAR CORROSION, LOCALIZED CORROSION, PERCENT CU ALLOY, phosphating, PITTING CORROSION, SAM, SEM, surface microstructure, TITANIUM PHOSPHATE, XPS
Abstract

The initiation of coatings deposited on to 2024-T3 aluminum alloy from supersaturated zinc phosphating solutions has been studied using scanning Auger microscopy (SAM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The alloy microstructure, especially associated with the second-phase particles, strongly affects the formation stages of the coating process, where etching of the substrate has a significant role. At the start, zinc phosphate (ZPO) crystals form on the Al-Cu-Mg second-phase particles, rather than on the matrix or on the Al-Cu-Fe-Mn particles, with the initial nucleation appearing at interfaces between Al-Cu-Mg particles and the matrix. In contrast, the formation of the ZPO coating is delayed on the cathodic Al-Cu-Fe-Mn particles, compared to those of the Al-Cu-Mg composition. When the coating process is completed, the whole sample surface is covered with ZPO although its thickness varies at the different micro-regions. (C) 2004 Elsevier B.V. All rights reserved.

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