Investigation on Influencing Mechanism of Processing Parameters on Corrosion Resistance and Zinc Content of Anodic Coatings Developed on Magnesium Alloys in Near-Neutral Solutions

In near-neutral solutions, the effects of NH4HF2, H3PO4, phytic acid (IP6), and EDTA-ZnNa2 concentration on corrosion resistance and the Zn amount of micro-arc oxidation (MAO) coatings were revealed by an orthogonal experiment. The influencing order of four factors on coating corrosion resistance is EDTA-ZnNa2 > NH4HF2 > IP6 > H3PO4, while the sequence on the Zn amount is ranked as EDTA-ZnNa2 > NH4HF2 > H3PO4 > IP6. The fabricated Zn-containing coatings exhibit excellent corrosion resistance, and their icorr values are two orders of magnitude lower than that of the WE43 substrate, while the highest Zn amount achieves 4.12 wt.%. P and F compete to take part in coating formation, and Zn ions enter into anodic coatings by diffusion. Coating corrosion resistance is jointly determined by surface characteristics, which will provide the important theoretical foundation for fabricating Zn-containing coating with high corrosion resistance.