Effect of aluminium content on the anodic behaviour of copper-aluminium alloys in 3.5 wt% NaCl solution

Anodic behaviour of heterogeneous Cu-Al alloys in 3.5 wt% NaCl solution has been investigated as a function of aluminium content by potentiodynamic polarization, cyclic voltammetry and potentiostatic current transient experiments and compared to pure Cu and homogeneous Cu-Al alloys. The specimens were subjected to various anodic potentials and subsequent analyses by scanning electron microscopy (SEM) supplemented with energy dispersion spectroscopy (EDS). The pure Cu and single -phase Cu-Al alloys showed that a relatively thick protective CuCl film forms at active-passive transition potentials and transforms into CuO or Cu(OH)₂ at the passivation potential, resulting in high limiting current densities. However, the Cu-10 wt% Al alloy is passivated to Al(OH)₃, impeding the transformation of the thick CuCl layer which contains AlCl or Al(OH)₂Cl salt into CuO or Cu(OH)₂. At high applied anodic potential, the Cu₂(OH)₃Cl phase forms on the deteriorated passive film Al(OH)₃.