Corrosion behaviour of sol-gel Al₂O₃ coated Al-Si alloy in 3.5% NaCl solution

Abstract

Alumina sol was synthesized and coated on Al-Si alloy. The coated substrates were heated at 300ºC for sintering and precursor removal purposes. The cross-sectional examination of the coated specimens in SEM showed the presence of around 7 μm thick non porous and compact coating. XRD analysis confirmed the presence of αAl₂O₃ in the coated layer. The corrosion characteristics of the coating were evaluated in 3.5% NaCl solution by electrochemical measurements. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) analysis indicated that the coated substrate possesses an order of magnitude higher corrosion resistance as compared to uncoated substrate. EIS study has also indicated a significant decrease in diffusion phenomena of chloride ions through the coating/metal interfaces. The effect of heat treatment of Al-Si alloy on its corrosion properties has also been investigated.