Anodic films containing polyaniline and nanoparticles for corrosion protection of AA2024T3 aluminium alloy

Anodic alumina films containing polyaniline and either TiO2 or ZrO2 nanoparticles were electrochemically synthesised on an AA2024T3 aluminium alloy by a single step anodising procedure in an oxalic acid electrolyte. The morphology and composition of the films were examined by SEM, TEM, GDOES and XPS. The resultant coatings, of thickness about 2.2 μm, displayed a nanoparticle-rich layer in the near surface-regions, of thickness in the range 100–250 nm. Potentiodynamic polarisation behaviour revealed that the polyaniline and TiO2-containing films on the AA2024T3 aluminium alloy show a passive current density two orders of magnitude lower than for films with ZrO2 nanoparticles and films without nanoparticles. The coatings with TiO2 nanoparticles, but without polyaniline, showed intermediate behaviour, with a passive current density one order of magnitude lower than the coatings with polyaniline and TiO2 nanoparticles. The improved barrier protection offered by the TiO2 nanoparticle containing coatings is attributed to the presence of the nanoparticle-rich layer formed on the outer part of the coating that blocks access to the pores of the anodic alumina film.