Investigation of ZrO2 nanoparticles concentration and processing time effect on the localized PEO coatings formed on AZ91 alloy

AZ91 Mg alloy was treated through a new localized PEO (Plasma Electrolytic Oxidation) coating approach, using electrolyte solutions with varying ZrO2 nanoparticles concentration (2-8 g/L) and processing times. With increase in the ZrO(2 )concentration, several microstructural changes were observed including; formation of cluster-type structure, damage to the inner layers (similar to 30min) and sealing of defects. Corrosion analysis of the final coatings was carried out using potentiodynamic polarization, electrochemical impedance spectroscopy and post-corrosion analysis. It was explored that highest corrosion resistance (R-p similar to 81.17 k Omega cm(2)) of the coatings was obtained for ZrO2 similar to 2 g/L. However, higher concentration of the ZrO(2 )nanoparticles caused weak crystalline coating structure, due to unstable and lower intensity discharges, thus failed to offer high corrosion resistance performance. (C) 2019 Published by Elsevier B.V. on behalf of Chongqing University.