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The effect of Ni2+ on zinc phosphating of 2024-T3 Al alloy

TitleThe effect of Ni2+ on zinc phosphating of 2024-T3 Al alloy
Publication TypeJournal Article
Year of Publication2004
AuthorsAkhtar, AS, Susac, D, Glaze, P, Wong, KC, Wong, PC, Mitchell, KAR
JournalSurface & Coatings Technology
Date PublishedOct
Type of ArticleArticle
ISBN Number0257-8972
Keywordsaluminum alloy, ALUMINUM-ALLOY, Auger electron spectroscopy, chemical conversion, CHROMATE CONVERSION COATINGS, CORROSION PROTECTION, FILMS, Ni2+ additive, NICKEL, phosphating, photoelectron spectroscopy, STEEL, SURFACE, XPS

Zinc phosphate (ZPO) conversion coatings formed on 2024-T3 aluminum alloy, and on high-purity aluminum, after dipping in coating baths containing different amounts of Ni2+, have been studied by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, scanning Auger microscopy (SAM) and electrochemical measurements. Significant variations are observed in coating morphology and in stability against corrosion for the 2024-Al alloy as the amount of Ni2+ in the coating solution increases through the 0-2000 ppm range. By contrast, for high-purity Al, the most marked changes in coating morphology occur only as the Ni2+ concentration reaches 2000 ppm. The presence of additional elements, and especially Cu, in the 2024-Al samples results in an increase in the number of cathodic sites and hence more coating is formed for corresponding conditions. Additionally, the existence of second-phase particles in the 2024-Al sample leads to variations in the coatings at the microstructural level across the surface. These differences include local variations in the amount of Ni2+ in the coatings, as well as the local coverage. (C) 2004 Elsevier B.V. All rights reserved.

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