Study of methods to improve the corrosion behaviors of aluminium foam

Engineer and designer are always looking for new materials to produce products with ever-higher properties. Among the new materials appeared over the last decade metal foams seem to be the most promising materials. In fact, this material combines excellent mechanical properties, typical of metals, with a very low density, typical of expanded polymeric materials. Aluminium foams are those that are most interesting for the ease and the limited cost of production. There are several production methods. One of the most promising is the Alporas method. From big foamed block flat panels were obtained by cutting without shape limit. However, during the production process, open cells are created. Aluminium shows enough corrosion behaviour on several environment due to the native passive layer formed on surface. In more aggressive conditions, as chloride ions presence or low pH, different solutions permits to increase the corrosion behaviour. Considering the aluminium foam the situation results more critical due to the very strange and complex surface geometry which favours the localised of corrosion like pitting and crevice phenomena. In this work, different methods to improve the corrosion behaviours are considered. The deposition of paint by cathaphoretic could be a solution due to the possibility to create a coating also with complex geometry. The vitreous enamel with a thin or very thick deposit could guarantee the corrosion protection maintaining the fire and high temperature resistance. In case of thin layer the opened cells result very critical probably connected with a high dimension of enamel frits particles. In this case, the enamel deposit guarantee an enough behaviour only in case a less aggressive environment. Finally, also the anodising process, which produce a protective oxide layer, could enhance the behaviour of aluminium foam. In this last case, a critical aspect results the microstructures of the alloy, which show influence on the growth of the state. In particular precipitates made by titanium, calcium and aluminium are able to hinder the uniformity of oxide layer and favour the formation of defect with reduction of protection properties. To evaluate the corrosion protection properties of the selected systems both accelerated corrosion tests (acetic salt spray test) and electrochemical tests (polarisation curves and electrochemical impedance spectroscopy) tests were carried out