Trivalent chromium conversion coating formation on aluminium

The formation of a trivalent conversion coating on aluminium has been investigated using analytical electron microscopy, atomic force microscopy, ion beam analysis, glow discharge optical emission spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The coating is shown to comprise...

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Bibliographic Details
Published in:Surface & coatings technology 2015-10, Vol.280, p.317-329
Main Authors: Qi, J.-T., Hashimoto, T., Walton, J.R., Zhou, X., Skeldon, P., Thompson, G.E.
Format: Article
Language:English
Subjects:
Aluminium
Aluminum
Chromium
Coatings
Conversion coating
Electrochemical impedance spectroscopy
Formations
Raman spectroscopy
RBS
TEM
Trivalent chromium coating
XPS
Zirconium dioxide
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Summary:The formation of a trivalent conversion coating on aluminium has been investigated using analytical electron microscopy, atomic force microscopy, ion beam analysis, glow discharge optical emission spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The coating is shown to comprise a chromium- and zirconium-rich outer layer and an aluminium-rich inner layer. Zirconium and chromium are present in chemical states consistent with ZrO2, ZrF4, Cr(OH)3, Cr2(SO4)3, CrF3 and CrO3 or CrO42−. However, negligible amounts of Cr(VI) species occurred in coatings formed in de-aerated solution. Electrochemical impedance spectroscopy revealed that the inner layer provides the main corrosion protection during short-term tests in 0.1M sodium sulphate solution at room temperature. •Trivalent chromium conversion coatings are formed on aluminium.•Coatings are examined by TEM, revealing kinetics of growth and bi-layer morphology.•RBS, NRA and XPS are used to determine elemental concentrations and chemical states.•Raman spectroscopy indicates Cr(VI) is formed during coating growth.•Inner coating layer provides the main corrosion protection.
ISSN:0257-8972
1879-3347
DOI:10.1016/j.surfcoat.2015.09.024