Mechanisms to inhibit corrosion of Al alloys by polymeric conversion coatings

We introduce a recently developed novel polypyrrole-based coating, which can be formed on the aluminium surface from an aqueous pyrrole solution of fluorozirconic and fluorotitanic acid neutralised with zinc oxide. The composite layer consists of polypyrrole (Ppy) chemisorbed on titanium and zinc oxides and exhibits advanced corrosion resistance. For the investigation of the structure and the corrosion mechanism of the composite corrosion resistant layer we use a photo-electron emission microscope (PEEM). PEEM is especially suitable because it can deliver topographic contrast as well as elemental contrast and chemical information in connection with a variable X-ray source. Additionally, in order to investigate further the corrosion mechanism, but also the role of the alloy in the corrosion process, we examine the aluminium samples with SEM/EDX. The structure of the corrosion resistant layer was investigated before and after accelerated corrosion tests. Our results pointed out the important role of titanium oxide and zinc in the corrosion resistance of our Ppy coating on aluminium.