Preparation and Corrosion resistance of Cerium-based Chemical Conversion Coating on AZ91 Magnesium alloy
Cao Fa-he
Cite this article:
Cao Fa-he. Preparation and Corrosion resistance of Cerium-based Chemical Conversion Coating on AZ91 Magnesium alloy. Acta Metall Sin, 2008, 44(8): 979-985 .
Abstract In order to development an environmental friendly surface coating technology for magnesium, a chrome-free Ce-based process to form a conversion coating on AZ91 magnesium alloy was investigated. Electrochemical impedance spectroscopy (EIS) was chosen to evaluate corrosion resistance due to its low effect on electrochemical test system for getting high reproduction result. The effect of treatment time, temperature of electrolyte, concentration of Ce(NO3)3 and accelerant concentration on corrosion resistance was summarized, while a optimized technology was achieved, 0.02mol/l Ce(NO3)3, 4ml/l accelerant at 35℃ for 35 min. The results indicated that the chemical conversion formed in optimized technology presented yellow and impact surface by naked eye, while took on two layer structure with micro cracks on the outer layer. The content of Ce in inner layer was low than that of outer layer, while it was more impact. Tafel plots indicated that conversion film restrained the anodic and cathodic reaction on the interface, while the corrosion potential shifted anodic 240mV and corrosion current density decreased about 100 times.
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