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

Abstract

Thcrmally curabic nanocomposite coating materials have bee n dcveloped to scal and protcct copper-containing aluminium alloys against corrosion. The coating matcrial was preparcd via the sol-gel-process starting fronr cpoxy functional ised si lanes, nanoscaled si l ica and organic diole crossl inker. This coatirrg nratr ix was addit ional ly supplied with a varying content of cerium oxide ( l-20 wt.%). The corrosion protective ff icicncy of thcsc coatings was invcstigated on aluminium alloys Al 6013-T6 and AlCu4MgSi by salt spray test and cle ctrochentical impedance spectroscopy (EIS), both on coatings with an artificiai damage. Herc, thc pure coating matrix showed first corrosion attack by filiform corrosion and pitting after l0 days on Al 6013, and after 2 days on AlCu4MgSi. By additional incorporation of cerium oxide, on Al 6013 filiform corrosion and pitting could bc cffcctively supprcsscd with a content of at lcast 20 wt.% CeO2 (related to solid content of the coating) and no corrosion attack (Ri=O, Wu=O) was observed over a period of 60 days (1440 h) of salt spray test. For AlCu4MgSi, rvhich has a higher coppcr content and thus a highcr corrosion sensitivity, the addition of cerium oxide in thc 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 thc damaged coatings confimed these results.