Corrosion resistance of an AlSi alloy (AS12) after sulfuric anodizing and MAO: Mechanisms and effect of sealing with sodium decanoate
Résumé
Al-Si alloys, widely used in moulded parts for industrial or domestic applications, may undergo an electrochemical finishing treatment in order to enhance their surface properties, especially their corrosion resistance. In the present study, anodic layers are grown on an AS12 alloy by conventional anodizing in sulfuric acid on the one hand and by microarc oxidation (MAO) on the other hand. While both aluminium and silicon are completely oxidized within the microarc layer, metallic silicon particles are embedded within the classic porous alumina layer formed in acidic medium, generating strains and resulting in a cracked coating.
Regarding the corrosion resistance, evaluated comparatively by electrochemical impedance spectroscopy (EIS) measurements performed in NaCl 0.1 M and salt spray test (SST), the results consistently show an improvement by microarc oxidation but not by sulfuric anodizing, since the corrosion mechanisms are mainly driven by galvanic coupling between silicon particles and aluminium matrix. A sealing post-treatment in sodium decanoate CH3(CH2)8CCONa is considered as well on both types of anodic layers. An enhancement of the anticorrosion performances is noticed in each case, more significantly for sulfuric anodizing.
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