Comparison of Single and Multilayer Coatings Based on Ormosil and Conversion Layers For Aluminum Alloy Corrosion Inhibition

By Olga Kachurina, Tammy L. Metroke, Elvira Stesikova, Edward T. Knobbe

Corrosion resistance behavior of single and mul-tilayer coatings based on ormosil, trivalent chromium conversion coating (tccc) and hexavalent chromium conversion coatings (hccc) on the surface of 2024-T3 aluminum alloy (AA) was investigated using potentiodynamic polarization curves and accelerated salt spray testing. The magnitude of the corrosion resistance for single layer coatings increased tccc < ormosil < hccc.

Multilayer ormosil/ormosil coatings are subject to phase separation, leading to poor performance in the electrochemical and accelerated salt spray testing. The presence of either hccc or tccc in the multilayer film was found to augment the inherent corrosion resistance of the ormosil barrier film. Multilayer coatings composed of either tccc/ormosil or hccc/ormosil were found to ex-hibit Rcorr values in the range 158-177 k
cm².

This implies that the environmentally-benign and nontoxic trivalent chromium conversion coating used in combination with an ormosil film may be a potential alternative for hexavalent chromium conversion coatings.