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铁道科学与工程学报

JOURNAL OF RAILWAY SCIENCE AND ENGINEERING

Vol. 19    No. 6    December 2009

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Microstructure and properties of oxalate conversion coating on
AZ91D magnesium alloy
JIANG Yong-feng(蒋永锋), ZHOU Hai-tao(周海涛), ZENG Su-min(曾苏民)

School of Materials Science and Engineering, Central South University, Changsha 410083, China

Abstract:The oxalate coating formed on AZ91D magnesium alloy by chemical conversion treatment methods in oxalate salt solutions was investigated. The surface morphologies and chemical composition of coating were examined using scanning electron microscopy (SEM) equipped with energy dispersive analysis of X-ray (EDX). Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves and salt spray tests were employed to evaluate corrosion protection of the coating to substrate in 5% NaCl solution. The mechanism of coating formations was also considered in details. The results indicate that a compact and dense surface morphology with fine particle clusters of the oxalate coating on magnesium alloy is presented, which mainly consists of oxide or/and organic of Mg, Al and Zn. And the anti-corrosion of the magnesium after oxalate conversion treatment is better than that of the magnesium substrate. The results of salt spray test for oxalate coating is evaluated as Grade 9 according to ASTM B117. The electric resistance of oxalate chemical conversion coating to substrate is below 0.1 Ω.

 

Key words: magnesium alloy; oxalate conversion coating; microstructure; corrosion

ISSN 1672-7029
CN 43-1423/U

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