Corrosion Performance of Nano-Alumina Coatings over Anodized Aluminum Alloy by Dip Coating Method

Abstract

Alumina coatings are widely used to enhance the wear, abrasion, and corrosion resistance of metal components. This investigation aims at studying the alumina sol-gel coating on the anodized aluminum alloy surface using a dip coating technique. A stable alumina coating was deposited over the anodized aluminum surface using oxime-modified aluminum(III) isopropoxide as sol-gel precursor. The scanning electron microscopy image of the coated anodized sample suggests deposition of a uniform and crack-free aluminum coating. The corrosion resistances of bare, anodized, and coated anodized aluminum alloy samples were investigated by electrochemical impedance spectroscopy and potentiodynamic polarization in 3.5 wt % aqueous NaCl solution. An appreciable shifting was observed in the equilibrium corrosion potential (E_corr) and the corrosion current density (i_corr) values of both anodized and coated anodized samples: i.e. E_corr: from –1377.11 mV (anodized) to –711.54 mV (coated anodized) and i_corr: from 80.37 μA/cm² (anodized) to 0.090 μA/cm² (coated anodized). The results clearly indicate the corrosion resistive behavior of nano-alumina coatings.