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In order to improve the corrosion resistance of brass, plasma electrolytic oxidation was performed on its surface, and the influence of Na2SiO3 electrolyte concentration on the performance of the oxide film was analyzed. The electrolyte with Na2SiO3·9H2O was prepared and NaOH as the main components, the forward voltage of 520 V, forward current of 1.4 A, pulse frequency of 2000 Hz, positive and negative duty ratio of 20% were set, and plasma electrolytic oxidation was performed on the brass specimen for 80 min. The influence of Na2SiO3 concentration on the microscopic morphology of the oxide film, thickness, roughness, chemical composition, bonding force and corrosion resistance was studied by field emission scanning electron microscope (SEM), surface roughness measuring instrument, eddy current thickness gauge, energy spectrometer (EDS), X-ray diffractometer (XRD), cross-cut adhesion tester, electrochemical workstation (potential polarization curve). The results show that the chemical composition of the film surface is composed of Cu, Zn, O, Si and other elements, and exists in the form of metal oxide and amorphous silicon dioxide. As the concentration of Na2SiO3 increases, the number of micropores on the surface of the film gradually increases, the size and distribution of the pores are becoming more and more uniform, the thickness of the film first increases and then decreases, and the surface roughness value first decreases and then increases. However, the excessive Na2SiO3 concentration increases the plasma electrolytic oxidation reaction and the surface melts, the quality of the film does not rise but falls. Plasma electrolytic oxidation can effectively improve the surface properties of brass. When the Na2SiO3 concentration is 8 g/L, the oxide film has the best corrosion resistance, and its self-corrosion current density is reduced by 2 orders of magnitude compared with the matrix.

A CeO2-doped plasma electrolytic oxidation (PEO) composite coating was prepared on the surface of Cu–Zn alloys by adding CeO2 nanoparticles into the mixed electrolytes of Na2SiO3·9H2O and sodium hydroxide. Surface microstructure and element composition of PEO coatings were studied by a scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). Microstructure analysis showed that CeO2 nanoparticles were uniformly deposited on the sample surface, and most of the particles were embedded into PEO coatings. Ce element found in the EDS and XRD analysis confirmed the successful incorporation of CeO2 nanoparticles. Furthermore, with the addition of CeO2 nanoparticles, the coating porosity decreased gradually, while the thickness and surface roughness of PEO coatings decreased and then increased. Corrosion resistance of PEO coatings was investigated by using a potentiodynamic polarization test. The results show that the addition of CeO2 nanoparticles has significantly improved the corrosion resistance of PEO coatings. Especially, the corrosion current density of the PEO coating with 4 g/L CeO2 concentration is 3 orders of magnitude more than that of the bare alloy substrate. [ABSTRACT FROM AUTHOR]