Effects of KMnO₄ on microstructure and corrosion resistance of microarc oxidation coatings on 2024 aluminum alloy

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.

Keywords

2024 aluminum alloy / KMnO₄ / microarc oxidation / microstructure / corrosion resistance

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