Pitting potential of high purity binary aluminium alloys—I. AlCu alloys. Pitting and intergranular corrosion

Abstract

The effect of solute content on the pitting potential of Al-Cu alloys in 1M NaCl solutions was studied. In solution treated Al-Cu alloys the pitting potential of the alloy was found to increase with increasing Cu content. The maximum pitting potential value was limited by the solubility of Cu in the Al. It was found that, while the pitting potential of pure aluminium was ca. −0.52 V, the pitting potential of Al-5.22% Cu was −0.33 V. The ageing of the alloy affected the pitting potential. The pitting potential of the aged alloy was found to be determined by the copper content of the solute depleted zones formed during ageing. The formation of G.P. zones did not modify the pitting potential of the alloy. The formation of θ′′ phase, in an Al-3.5 Cu alloy, produced a decrease of 30 mV in the pitting potential, while the formation of θ′ phase produced a decrease of > 100 mV. As ageing was more rapid in the grain boundaries, there was a localized decrease in the pitting potential, which was followed by susceptibility of the alloy to intergranular corrosion.