Comparison of corrosion and antibacterial properties of Al alloy treated by plasma electrolytic oxidation and anodizing methods

Plasma electrolyte oxidation (PEO) and anodizing coatings were produced on 7075 Al alloy and compared together. Surface and cross section morphology of the coatings were studied by field emission scanning electron microscope. Phase compositions of coatings were analyzed by the X-ray diffraction Technique. Tafel polarization and immersion tests were done in 3.5.%wt NaCl solution to evaluate the corrosion properties of the coatings and substrate. The antibacterial activity of coatings was evaluated against E. coli bacterium. The PEO and anodized coatings had a completely different surface morphology and microstructure. The PEO coating was not affected by substrate surface features. Coatings cross sectional analysis showed that PEO coating had a dense barrier inner layer and a porous outer layer and it was less uniform in thickness than anodized coating. X-ray diffraction patterns of coatings demonstrated that PEO coating is mainly consisted of a crystalline γ-Al2O3 phase, while in the case of anodized coating no crystalline phase was observed which suggested that it composed of an amorphous phase. Corrosion resistance of 7075 Al alloy were improved after both coating treatments but PEO coating exhibited superior corrosion properties compared to anodized coating because of the crystalline barrier layer. Also, the presence of Silicon in PEO coating resulted in better antibacterial activity than anodized coating.