Comparison of corrosion behaviour of copper and copper alloys in aqueous chloride solution

A comparative corrosion study of Cu and Cu-Al, Cu-Al-Ni, Cu-Al-Mn and Cu-Al-Mn-Ni in 0.5 mol dm-3 NaCl solution was performed using an open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy measurements (EIS). Scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) analysis was used to evaluate corrosive damage on the sample surface after polarization measurements. The reported results suggest that the alloying elements have reduced cathodic and anodic current densities in the Tafel region, increased anodic currents at higher anodic potentials, and slightly displaced corrosion potential towards more positive values. Overall, impedance increased in the following order: Cu < Cu-Al < Cu-Al-Ni < Cu-Al-Mn < Cu-Al-Mn-Ni. This indicates that Cu alloys possess better corrosion resistance. SEM and EDS analysis after polarization measurements showed uniform dissolution of pure Cu, as well as the presence of a surface oxide layer, consisting of a mixture of the corresponding alloying elements, on all investigated alloys. Aggressive anodic polarization severely damaged the barrier layers on the Cu alloy specimens.