Self-healing anticorrosive hybrid sol-gel coatings based on loaded nanocontainers for 2XXX serie aluminium alloys

摘要

The 2XXX series aluminum alloys occupy a very important place in aerospace components, especially in the structure of an aircraft (70%) due to their lower density and their high mechanical properties. However, the presence of copper in the AA 2024-T3 alloy in order to improve the mechanical strength leds to an heterogeneous microstructure, which makes the alloy highly vulnerable to corrosion. Therefore, it is necessary to develop an efficient anti-corrosion system to protect it against atmospheric conditions. Since few years, great efforts have been made to research environmental friendly substitutes of hexavalent chromium which are the most efficient to protect aluminium alloys. In this way, hybrid sol-gel coatings of silica-epoxy have been developed as a barrier layer to protect against diffusion of corrosive agents such as water, oxygen and chloride ions at the coating/metal interface. In addition, when the coating is damaged, an active corrosion protection can be achieved with the incorporation of nanocontainers loaded with corrosion inhibitors. The nanostructured coating reveals enhanced long-term corrosion protection in comparison with the unloaded hybrid.In this work, we have investigated the development of sol-gel coatings with distinctive nanocontainers which include cerium(Ⅲ)) as an inorganic corrosion inhibitor. Coatings are deposited by dip-coating method on AA2024-T3 alloy. Our objective is to raise the amount of cerium physisorbed on nanocontainers to improve anticorrosion performances. The first step is the synthesis of nanoparticles presenting a high specific area: two kinds of nanoparticules have been evaluated, the first one based on silica and the second one on Boehmite in order to keep a chemical consistency with coating and substrate. Then the loading of the inhibitor was realized by physisorption in aqueous solution. The last step consists to evaluate by Electrochemical Impedance Spectroscopy (EIS) the inhibitor release of the loaded nanoparticles to highlight the nanocontainer effect involving in the active protection. Further characterizations to evaluate the morphology and the microstructure of the nanocontainers such as Scanning Electronic Microscopy, FEG-SEM, Transmission Electronic Microscopy (TEM), were undertaken. Anticorrosion performances of such nanocomposite coatings were evaluated by Electrochemical Impedance Spectroscopy (EIS) during immersion in a representative corrosive medium together with the resistance to accelerated corrosion test in neutral salt spray (NSS).