Electrochemical behaviour of the Al-20Mg alloy in synthetic seawater with alkaline pH

Abstract

The corrosion of Al-(20 wt%) Mg alloy in artificial seawater solution at different pH, using potentiodynamic polarization, polarization resistance and electrochemical impedance spectroscopy techniques was assessed. The results showed that the effect of the pH of the artificial seawater solution promoted susceptibility to localized corrosion by dissolution of the oxide layer, which is naturally present on the surface of the aluminium alloy. X-ray diffraction analysis shows the presence of Al3Mg2 intermetallic phase which promotes the dissolution of the aluminium phase, and the evolution of hydrogen. The activation mechanism at the oxide-free zones and the diffusion through the corrosion products scale were associated with continuous formation of Al(OH)3 and Mg(OH)2 at the Al-Mg alloy interface, with minor protective effect as pH increases. The electrochemical behaviour of the Al-(20 wt%)Mg alloy in artificial seawater solution at pH 14 suggests potential application in hydrogen evolution due to its high surface catalytic activity. Results were complemented by scanning electron microscopy and X-ray diffraction characterization.