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铁道科学与工程学报

JOURNAL OF RAILWAY SCIENCE AND ENGINEERING

Vol. 19    No. 3    June 2009

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Microstructure and formation mechanism of Ce-based chemical conversion coating on 6063 Al alloy
CHEN Dong-chu(陈东初)1, 2, LI Wen-fang(李文芳)1, GONG Wei-hui(龚伟慧)1,
WU Gui-xiang(吴桂香)1, WU Jian-feng(吴建峰)2

1. School of Materials Science and Engineering, South China University of Technology,
Guangzhou 510640, China;
2. School of Science, Foshan University, Foshan 528000, China

Abstract:In order to accelerate the conversion coating formation on 6063 Al alloy in the Ce(NO3)3 solution, accelerants of chloride  and ammonium salt were used. The coating morphology, composition and structure were analyzed with SEM/EDS, EPMA, XPS and XRD. The coating morphology is influenced by the composition, pH value and temperature of the treating solution. The coating composed of metal oxide, metal hydroxide and hydrate appears to be amorphous. The elements in the coating are Al, Ce, O, Mn and Mg, while the Ce element exists in the forms of Ce3+ and Ce4+. The accelerant of chloride can increase the compactness and Ce content of the coating, so the coating corrosion resistance is remarkably improved. A scheme for the electrochemical reaction in the coating formation was proposed, and the potential change in the coating formation was also studied. It is found that chloride can shorten the time period of the first and the second stages in coating formation.

 

Key words: aluminum alloy; conversion coating; rare-earth element

ISSN 1672-7029
CN 43-1423/U

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