Inhibitor doped Sol-gel nanocomposite coatings for the corrosion protection of aircraft aluminum alloys

Aircraft aluminum alloys such as AA2024 are susceptible to severe corrosion in aggressive environments because of its heterogeneous microstructure. Chromate conversion coatings (CCC) are usually applied as the state of the art pre-treatment for corrosion protection of these alloys. However, since chromates are hazardous and carcinogenic, there is need for environmentally safe alternatives. Sol-gel coatings are environment-friendly barrier coatings that have been studied for corrosion protection of metals and alloys. In the present work, sol-gel nanocomposite coatings are developed using a mixture of methyltriethoxysilane (MTEOS) and colloidal silica. They are doped with an inorganic corrosion inhibitor like cerium nitrate and applied on Alclad AA2024 by spray-coating technique. The sol-gel process parameters were optimized to obtain a uniform pore-free and crack-free coating. Coated coupons were characterized by FESEM and EDX. Corrosion resistance of the sol-gel coatings in 3.5% NaCl solution was evaluated by potentiodynamic polarization technique, electrochemical impedance spectroscopy (EIS) and Neutral Salt Spray test