Micro-arc oxidation behavior of fly ash cenospheres/magnesium alloy degradable composite and corrosion resistance of coatings

In order to reduce the degradation rate of fly ash cenospheres (FACs)/magnesium alloy (MA) degradable composite, the protective micro-arc oxidation (MAO) coatings were prepared on the composite. The corrosion resistance of the coatings was evaluated by immersion tests and potentiodynamic polarization tests in 3 wt% KCl solution. The results indicated that FACs and Mg2Si did not participate in the coating-forming reaction. During the initial period of MAO, the growth rate of the coating on α-phase was faster than that on β-phase. FACs and Mg2Si had a hindering effect on the growth of the coating and were gradually covered by the coating. With the extension of oxidation time, the thickness of the coating increased, and the growth mechanism changed from outward growth to simultaneous inward and outward growth. The microstructure of the coating changed from through-pores to complex porous structure with prolonged oxidation time. Both the immersion tests and the potentiodynamic polarization curves showed that the coating significantly improved the corrosion resistance of the composite, and the coating obtained with longer oxidation time showed better corrosion resistance.