Stable preparation and characterization of yellow micro arc oxidation coating on magnesium alloy

The aim of this work is to obtain Sn-doped MAO coatings with yellow color on magnesium alloy in a new sodium stannate (Na2SnO3) electrolyte system, which is different from traditional micro arc oxidation (MAO) colored-coating with transition metal salt addition. The formation mechanism, microstructure and corrosion resistance of these yellow MAO coatings were comparatively investigated using SEM, EDS, XRD, XPS and electrochemical experiment. Results indicated that, although Sn element had been adsorbed on the sample surface with only Na2SnO3 addition, a high-impedance film could not be formed and the phenomenon of micro arc discharge did not occur. Yellow MAO coatings were obtained as adding Na2SiO3 into different concentrations of Na2SnO3 solution and the color was gradually deepened with the increase of Na2SnO3 concentrations. It had been proved that the obtained yellow MAO coating could be attributed to the formation of SnO2 phase under high temperature and high pressure. Compared with the white MAO coating, the yellow MAO coating with 15 g/L Na2SnO3 addition showed an excellent corrosion resistance. The stability of preparing yellow MAO coating and its superior anti-corrosion property made it a good candidate as decorative coating on magnesium alloy. (C) 2018 Elsevier B.V. All rights reserved.