The roles of Al2Cu and of dendritic refinement on surface corrosion resistance of hypoeutectic Al–Cu alloys immersed in H2SO4

Abstract: Al–Cu alloys castings can exhibit different corrosion responses at different locations due to copper content and to the resulting differences on microstructural features and on Al2Cu fractions. The aim of this study was to investigate the influence of Al2Cu intermetallic particles associated to the dendritic arm spacings on the general corrosion resistance of three different hypoeutectic Al–Cu alloys samples in sulfuric acid solution. The cast samples were produced using a non-consumable tungsten electrode furnace with a water-cooled copper hearth under argon atmosphere. The typical microstructural pattern was examined by using electronic microscopy techniques. In order to evaluate the surface corrosion behavior of such Al–Cu alloys, corrosion tests were performed in a 0.5M sulfuric acid solution at 25°C by using an electrochemical impedance spectroscopy (EIS) technique and potentiodynamic polarization curves. An equivalent circuit was also used to provide quantitative support for the discussions and understanding of the corrosion behavior. It was found that Al2Cu has a less noble corrosion potential than that of the Al-rich phase. Despite that, dendrite fineness has proved to be more influent on corrosion resistance than the increase on alloy copper content with the consequent increase on Al2Cu fraction. [Copyright &y& Elsevier]