Enhanced Corrosion Resistance of Aluminium Alloy Using Hybrid Sol-gel Coating

Abstract

Aluminium (Al) alloy has excellent corrosion resistance due to the oxide layer films generated on its surface. The applications of this material, therefore, normally relate to the utilization under corrosive environments, such as, offshore and marine industries. However, the protective film could be damaged by chloride and fluoride ions, and alkalinity environment. This study aimed to improve the corrosion resistance property of Al alloy A5083 by coating with inorganic-organic hybrid films. The hybrid films were prepared by sol-gel method containing an inorganic precursor, Tetraethyl orthosilicate (TEOS) , and organic precursors, namely Octyltriethoxysilane (OTES) and Poly (methyl methacrylate) (PMMA). The surface structure, water contact angle, corrosion resistance and weathering resistance of the hybrid films were examined. Surprisingly, the film formed of TEOS and OTES in the ratio of 80:20 and PMMA 40% (40P) by volume showed the best corrosion resistance, around 0.37 x 10^-3 mm per year. The corrosion resistance test was done by potentiodynamic technique in 3.5 wt% NaCl. While, the TEOS and OTES film with PMMA 20% (20P) presented lower corrosion resistance around 0.53 x 10^-3 mm per year but the condition of the film was more stable. The QUV weathering resistance test exhibited that the 20P film had no defects up to 14 days, while the 40P film showed damaged surfaces within 7 days. In summary, the hybrid films composed of TEOS and OTES in the ratio of 80:20 and PMMA 20%. by volume was suitable to coat on Al alloy A5083 to increase corrosion resistance for marine environment applications.