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Title: Initial stages of AZ91 Mg alloy micro-arc anodizing : Growth mechanisms and effect on the corrosion resistance
Author(s): D. Veys-Renaux, E. ROCCA, J. Martin and G. Henrion
Journal: Electrochimica Acta
Year: 2014
Volume: 124
Pages: 30-45
DOI: 10.1016/j.electacta.2013.08.023
Abstract: In the framework of the new ecological regulations, micro-arc oxidation (MAO) appears as an alternativeto usual processes in the field of corrosion protection of Mg alloys. In this work, the initial stagesof anodic layer growth in KOH-based electrolytes are studied up to and beyond the initiation of themicro-arc regime.The properties of the first anodized film preceding the occurrence of the dielectric breakdown (corre-sponding to the start of the micro-arc regime) are mainly determined by the incorporation of additives(fluorides or silicates) in the film, as shown by in situ electrochemical measurements. Scanning electronmicroscopy (SEM), X-ray photoelectron spectroscopy (XPS) and micro-Raman spectroscopy reveal boththe change of morphology and chemical state of silicate and fluoride in the anodized layer before andafter the micro-arc regime. In terms of electrochemical behaviour, investigated by stationary methodsand electrochemical impedance spectroscopy (EIS) in reference corrosive water, the anodic film grownin the silicate medium provides the best corrosion resistance thanks to a thick layer containing Mg2SiO4,whose degradation products seal the porosities of the coating.
Note: Département CP2S : ESPRITS

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