Corrosion Behavior of PEO Coatings on 6061 Al Alloy: Effect of Sodium Fluoride Addition to Aluminate based Electrolyte

The present work has studied the effect of sodium fluoride on properties of plasma electrolytic oxidation (PEO) coatings. PEO coatings were formed on 6061 Al alloy in aluminate based electrolytes with different sodium fluoride concentrations. The results indicated that addition of sodium fluoride to the electrolyte prepared ceramic coating with high quality and therefore improved the corrosion resistance in 3.5 wt% NaCl solution. Scanning electron microscopy (SEM) images were used to examine the cross sectional and surface morphology of the coatings. The corrosion behavior of the PEO coatings were evaluated using electrochemical impedance spectroscopy (EIS). The corrosion behavior of the coatings improved by adding 1 g/L sodium fluoride into the electrolyte, but the corrosion resistance of the coatings decreased while adding more than 1 g/L sodium fluoride in electrolyte solution. The prepared sample in the electrolyte with 1 g/L sodium fluoride showed the best morphology with the least porosity and more corrosion resistance compared with other coatings.