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

Abstract 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 pre-corroded 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.