Corrosion response of ultrafine-grained aluminium alloy processed by ECAP

Equal-channel angular pressing (ECAP) is one of Severe Plastic Deformation (SPD) techniques used to achieve ultrafine-grained materials in order to enhance mechanical properties of these materials. However, the deformation induced by these techniques generally deteriorate the material corrosion due to the modifications produced on its microstructure. In this study, the corrosion response of AA6012 aluminium alloy subjected to cryogenic and different heat treatments (solubilization and artificial aging) and then processed by ECAP was investigated. Electrochemical characterizations of this alloy in two different aerated and deaerated aqueous solutions at the same chloride concentrations (0.1 M NaCl) but at different pH (pH 2 and pH 6.5) were carried out by means of potentiodynamic polarization and electrochemical impedance spectroscopy. Before electrochemical tests, all specimens were embedded in an epoxy resin and subsequently some of them grinded with emery papers up to 4000 grit and others also polished with alumina (1 µm). SEM and TEM analyses were performed to study the evolution of the microstructure and the surface composition. The results show that in absence of aging, ECAP and cryogenic treatment influenced the corrosion behaviour of the AA6012 alloy. On the contrary the alloy subjected to artificial aging showed similar corrosion response.