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

Abstract

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 ZrO2 concentration, several microstructural changes were observed including; formation of cluster-type structure, damage to the inner layers (∼30 min) 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 (Rp ∼ 81.17 kΩ cm2) of the coatings was obtained for ZrO2 ∼ 2 g/L. However, higher concentration of the ZrO2 nanoparticles caused weak crystalline coating structure, due to unstable and lower intensity discharges, thus failed to offer high corrosion resistance performance. Keywords: Magnesium alloy, PEO coating, ZrO2, Corrosion, Nanoparticles addition