Abstract
Plasma electrolytic oxidation (PEO) of brass was carried out in aluminate electrolytes with the addition of NaH2PO4 (S1) and Na2SiO3 (S2), respectively, with the aim to investigate the effect of additives on the coating formation and corrosion resistance. For the PEO in S1 electrolyte, a mixed layer of AlPO4 and Al2O3 is formed at the initial stage, which leads to fast plasma discharges and formation of black coatings with the compositions of Al2O3, CuO, Cu2O and ZnO. However, in S2 electrolyte, plasma discharges are delayed and the coatings show a reddish color due to more Cu2O. Mott-Schottky tests show that the S1 coatings are p-type semiconductors; while the S2 coatings can be adjusted between n-type and p-type. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests show that the PEO treatment can significantly improve the corrosion resistance of brass, with protection efficiency up to 91.50% and the largest charge transfer resistance of 59.95 kΩ·cm2 for the S1 coating.
Published Version
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