Preparation and characterization of micro-arc oxidation coating on hollow glass microspheres/Mg alloy degradable composite

Micro-arc oxidation (MAO) coatings on hollow glass microspheres (HGM) reinforced Mg alloy degradable composite were prepared in alkaline silicate electrolyte. The morphology, chemical composition and corrosion resistance of the coatings were investigated by SEM, EDS, XPS, XRD and electrochemical tests. The growth characteristics of the coatings and the effects of HGM on the MAO behavior were specially studied. The results showed that the main compositions of the coatings were MgO and Mg2SiO4 phases. The coatings possessed different growth behaviors on the different areas of the surface. The coatings exhibited faster growth rate on the α phase than the β phase. The HGM and Mg2Si particles hindered the growing of the coating in the early stage of MAO, but they would not disrupt the continuity of the coating, since they were gradually melted, reduced and disappeared, and translated into oxides of silicon and magnesium finally in the MAO process. The average thicknesses of the coatings obtained at MAO time of 10, 20, 30, and 40 min were 2.9 ± 0.9, 10.9 ± 0.8, 20.2 ± 1.2, and 22.7 ± 1.9 μm, respectively. Electrochemical tests showed the MAO coating obtained at MAO time of 30 min possessed the best corrosion resistance, the corrosion current density of which was approximately four orders of magnitude lower than that of the substrate.