Study of initial stages of Al-Mg alloy corrosion in water, chloride and Cu(II) environment by a scanning Kelvin probe and XPS

Corrosion product layers formed during initial corrosion stages on Al-Mg alloy in water, 3.5% NaCl solution and 3.5% NaCl containing 50 ppm Cu(II) have been studied by scanning Kelvin probe (SKP) and X-ray photoelectron spectroscopy (XPS). The SKP spatio-temporal images reconstructed the solution-air boundary on corroded samples. The SKP sensitivity to detect the corrosion products layer on Al-Mg alloy was demonstrated to be in subnanometer scale. The Volta potential response on precorroded surfaces depended upon the immersion time (oxide layer thickness) and a kind of the solution used (oxide layer conductivity). The Volta potentials measured on the surfaces corroded in pure water were higher than those on the surfaces exposed to 3.5% NaCl or 3.5% NaCl + 50 ppm Cu(II) solutions. This difference has been explained in terms of higher conductivity of the corrosion product layers developed in the ion-containing media. (C) 2003 Elsevier Science B.V. All rights reserved.