Abstract
Microarc oxidation (MAO) coatings were prepared on 2024 aluminum alloy in a Na2SiO3-KOH electrolyte with KMnO4 addition varying from 0 to 4 g/L. The microstructure and phases of the coatings were characterized by scanning electron microscopy (SEM) and X-ray diffractometry (XRD), respectively. The corrosion resistance of MAO coatings was evaluated by electrochemical potentiodynamic polarization in 5% (mass fraction) NaCl solution. The results show that when KMnO4 is added into base electrolyte, the growth speed of oxide coatings is increased obviously. The main phase of oxide coatings is Al2O3, and the contents of MnO2 and Mn2AlO4 phases are increased at the top of oxide coatings with increasing the concentration of KMnO4. The solute elements participate in forming the oxide coatings. When a proper concentration of KMnO4 (2.5 g/L) is added into the base solution, the micropores of the MAO coatings are small and compact, and the corrosion resistance of oxide coatings is increased largely.
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