Sol-gel derived nanocomposite materials for corrosion protection of aluminium alloys

Abstract

Thermally curable nanocomposite coating materials have been developed to seal and protect copper-containing aluminium alloys against corrosion. The coating material was prepared via the sol-gel-process starting from epoxy functionalised silanes, nanoscaled silica and organic diole crosslinker. This coating matrix was additionally supplied with a varying content of cerium oxide (1-20 wt.%). The corrosion protective efficiency of these coatings was investigated on aluminium alloys Al 6013-T6 and AlCu4MgSi by salt spray test and electrochemical impedance spectroscopy (EIS), both on coatings with an artificial damage. Here, the pure coating matrix showed first corrosion attack by filiform corrosion and pitting after 10 days on Al 6013, and after 2 days on AlCu4MgSi. By additional incorporation of cerium oxide, on Al 6013 filiform corrosion and pitting could be effectively suppressed with a content of at least 20 wt.% CeO2 (related to solid content of the coating) and no corrosion attack (Ri=0, Wb=0= was observed over a period of 60 days (1440 h) of salt spray test. For AlCu4MgSi, which has a higher copper content and thus a higher corrosion sensitivity, the addition of cerium oxide in the coating matrix provided efficient protection against filiform and pitting corrosion on the artificial damage during a salt spray exposition of 14 days (336 h). EIS studies on the damaged coatings confirmed these results.