Effect of Fe3+ and F− on black micro‐arc oxidation ceramic coating of magnesium alloy

Abstract

AbstractThis study focuses on a black micro‐arc oxidation ceramic coating prepared on the surface of magnesium alloy by the technology of micro‐arc oxidation in the electrolyte containing F– and Fe3+ as well as its mechanism of F– and Fe3+. It needs coatings to experience detail analyses on their thickness, roughness, corrosion resistance, thermal control property, valence states of elements, phase composition, and morphology of coatings, respectively, through coating thickness gauge, roughness tester, electrochemical workstation, AE radiometer, X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), scanning electron microscope (SEM), and energy‐dispersive X‐ray spectroscopy (EDS). Results showed that with the help of F– in electrolyte, Fe3+ can be complexed and MgF2 can be obtained in the coating, which reduces the pores on the surface of micro‐arc oxidation coating. In addition, Fe3+ in the electrolyte contributes to the preparation of Fe2O3 and Fe3O4 in the coating, which can blacken the surface of the coating. Both F– and Fe3+ benefit to improve the corrosion resistance and thermal control performance of micro‐arc oxidation coating. There is higher iron oxide in the outer layer but higher fluoride in the inner layer of the coating.