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

Abstract

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 α-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 Cu 2(OH) 3Cl phase forms on the deteriorated passive film Al(OH) 3.