Avaliação das propriedades protetivas e de blindagem eletromagnética de um sistema de pintura a base de tinta poliuretânica com nanotubos de carbono aplicados sobre a liga de alumínio AA7075

Abstract

The use of AA7075 aluminum alloys in the aerospace industry is increasing due to its good mechanical, corrosive and thermal resistance and is ideal for parts that suffer from high stress. An efficient method in the corrosion protection of these substrates, which is a point to be improved, are the chromate layers. However, these processes are being abandoned due to the use of hexavalent chromium, which is carcinogenic. Thus, environmentally favorable alternatives are being studied, among them the organic-inorganic hybrid coatings obtained through the sol-gel process were presented as an ecologically correct and promising alternative. In addition, for excellent corrosion resistance, the hybrid film has to be combined with a good organic coating (paint) and, further, to meet technological innovation, which are embedded in nanostructured materials that improve various properties and are contributing greatly to the development of areas such as aerospace, as they act as a barrier against electromagnetic pollution. In this context, the aim of the present work was to obtain a hybrid film from a precursor consisting of the precursors silanes 3- (trimethoxysilylpropyl) methacrylate - C10H20O5Si) and TEOS (Tetraethoxysilane - C8H20O4Si) on the aluminum alloy AA7075, and after that, to obtain a combined system of polyurethane paint and carbon nanotube (CNT), aiming at the protection of aluminum alloys against corrosion and electromagnetic shielding. The work had a sequence of tests, starting from the part of the pretreatment (hybrid film) which had curing temperature variation and multiple layers that, after evaluating its results, which guided the best pre-treatment performance on the alloy AA7075 considering varied conditions, it was started to apply the organic coating on the hybrid film. The organic coating was applied over the same pre-treatment variations and the best combination of hybrid film and paint was evaluated, which were subjected to mechanical and salt spray tests. The results only of hybrid film and hybrid film plus paint tended to the same result, and the best results were for the same D120 application (double application of hybrid film cured at 120 °C). Three different types of carbon nanotubes were incorporated in a polyurethane-based resin and apllied on the substrate with the best hybrid film. The results showed that the CNT functionalized with the amine group (NH2) presented a good interaction with the PU resin, favoring the formation of a level and uniform film. The samples presented low electromagnetic performance; however, with emerging potential for electromagnetic shielding.