Abstract
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•Hybrid coatings with graphene oxide serve as alternative to chromate conversion coatings.•Graphene oxide cuts down moisture and oxygen diffusion through coatings.•Polysiloxane condensation of polar graphene oxide particles reduces coating performance.
This work evaluates the performance of hybrid coatings of polyurethane/polysiloxane filled with graphene oxide as replacement of chromate conversion coatings for protection of 2024-T3 aluminum alloys. The polysiloxanes in the hybrid coating form strong covalent bonds with the metal surfaces and inhibit corrosion, polyurethanes provide mechanical and optical properties, and graphene oxide and isocyanate-treated graphene oxide particles reduce oxygen and moisture diffusion through the coatings. The corrosion performance evaluated using electrochemical impedance spectroscopy and filiform corrosion test indicates the following trends. The hybrid coatings filled with isocyanate-treated graphene oxide particles show lower resistance to corrosion compared to hybrid coatings without graphene oxide, although oxygen diffusion and water vapor transmission are reduced by respectively 50% and 10% in the presence of only 0.67 wt.% graphene oxide. It is revealed that graphene oxide and isocyanate-treated graphene oxide particles promote polysiloxane condensation on particle surfaces, thereby effectively reducing a part of polysiloxanes that form continuous corrosion-protective layers on the aluminum alloy surface.