Anodizing of AS12 alloy in alkaline media

[Display omitted] •Metallic silicon incorporates in the alumina anodic layer formed on AS12 in KOH.•Fluorides and silicates improve the efficiency of AS12 alkaline anodizing.•Micro-arc anodizing of AS12 is promoted by addition of fluorides and silicates.•Corrosion resistance of AS12 is enhanced micro-arc anodic layer. The anodizing of AS12 alloys in various alkaline media is investigated over a large potential range (0–600 V) in order to provide a deep understanding of the mechanisms involved and judiciously chose chemical conditions enabling efficient micro-arc anodizing. Combined in situ stationary electrochemical methods, electrochemical impedance spectroscopy and TEM observations reveal that silicon in the aluminium matrix modifies the composition and the electrochemical properties of the duplex nanostructure grown at the early stages of the anodizing, therefore hindering micro-arc anodizing initiation. The addition of fluorides to the electrolyte, or silicates to a lesser extend, reinforces the resistive properties of the internal anodic layer and favors the efficiency of the anodizing process. The corrosion resistance of AS12, evaluated in NaCl 0.1 M by electrochemical techniques and salt spray test, is improved by the presence of the oxide coating and the nature of the additive incorporated compounds as well.