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Growth of permanganate conversion coating on 2024-Al alloy

TitleGrowth of permanganate conversion coating on 2024-Al alloy
Publication TypeJournal Article
Year of Publication2007
AuthorsKulinich, SA, Akhtar, AS, Wong, PC, Wong, KC, Mitchell, KAR
JournalThin Solid Films
Volume515
Pagination8386-8392
Date PublishedSep
ISBN Number0040-6090
Abstract

The growth of permanganate conversion coating on aluminum 2024-T3 alloy has been studied by characterizing, with scanning Auger microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy, the coatings formed by immersion of the alloy in the coating bath (containing KMnO4 and Na2B4O7, H-p 9-1) for different periods of time and at different temperatures. At room temperature, during the first 1-5 min of immersion, MnO2 deposits are formed only on the second-phase intermetallic particles (of Al-Cu-Mg and Al-Cu-Fe-Mn types), but the coating starts to develop on the Al matrix surface after 5-10 min. The coating slows down and stops after about 150 min, with a thinner deposit over the alloy matrix. The process is accelerated at higher temperatures, for example at 68 degrees C it self-limits after about 3 min. The electrochemical growth process appears to follow that established for the chromate conversion coatings, although XPS does not detect significant MnO4- incorporation into the permanganate coatings. (C) 2007 Elsevier B.V. All rights reserved.

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