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Effects of Current Density on the Properties of Microarc Oxidation Coatings Formed on Aluminum Alloy in Silicate-Na2MoO4 Electrolyte

Microarc oxidation (MAO) coatings on ZL108 aluminum alloy were prepared in the silicate-Na2MoO4 electrolytes with different current density. The MAO process was studied by measuring the voltage as a function of time. The microstructure, compositions, distribution of element and corrosion resistance of the MAO coatings were investigated by SEM, XRD, EDS, XPS and polarization curve, respectively. With the increasing of current density, the final voltage in the microarc discharge process increased. The results shown that the MAO coatings were mainly composed of mullite, γ-Al2O3, Si, little MoO2 and MoO3. The micropore size, thickness, compositions, distribution of element of the MAO coatings depended on the current density and the amount of MoO2 and MoO3. The corrosion resistance improved as the porosity of the MAO coatings decreasing.