Effect of sodium benzoate on corrosion behavior of 6061 Al alloy processed by plasma electrolytic oxidation

The effect of sodium benzoate (NaBz) in an electrolyte on the corrosion behavior of a 6061 Al alloy coated by plasma electrolytic oxidation (PEO) was investigated. For this purpose, a PEO coating was performed on the present sample under alternating current conditions in an alkaline–aluminate electrolyte with and without NaBz. Regardless of the addition of NaBz, the microstructural observation showed that the coating layers consisted of outer and inner layers. When the alloy was coated in the electrolyte with NaBz, a higher fraction of α-Al2O3 was found in the coating film as compared to the sample coated in the electrolyte without NaBz. In addition, the coating of the sample processed in the electrolyte with NaBz became dense, which resulted in better corrosion resistance than the coating without NaBz. The potentiodynamic polarization test showed that the coating layer formed on the electrolyte with NaBz exhibited superior corrosion resistance to that without NaBz. The corrosion behavior of the PEO-coated sample could be explained using the equivalent circuit model. •Effect of NaBz on corrosion properties of Al alloy via PEO is significant.•Compact structure of coating layer is obtained with addition of NaBz.•Ratio of α-Al2O3/γ-Al2O3 increases as NaBz is added to the electrolyte.