Pitting corrosion of aluminum coated by ion beam assisted deposition of carbon with argon ions at different ion-to-atom arrival ratios

Aluminum and aluminum alloys have become increasingly important due to their low density and good corrosion properties, which arise from the dense oxide film that natural aluminum forms in contact with air. However, the passivity of aluminum and aluminum alloys fails when exposed to a wet environment in the presence of aggressive anions, such as chloride, when pitting corrosion occurs. To improve the overall corrosion resistance, aluminum was coated with amorphous carbon films at low temperature. The carbon films were formed by ion beam-assisted deposition under concurrent bombardment with argon ions. The corrosion behavior was evaluated by electrochemical polarization measurements carried out in neutral aqueous solutions containing sodium chloride. The results show that the films are able to considerably improve the corrosion resistance when a certain ion/atom arrival ratio is chosen.