Electrochemical Oxidation of Al–Mg–Si–Sc Alloys with Small Amounts of Zirconium and Manganese in 3% NaCl Solution

Abstract

The electrochemical oxidation of α - Al–Mg₂Si–Sc alloys with small amounts of Zr and Mn in 3% NaCl solution is studied using the method of potentiodynamic anodic polarization curves, quantitative Auger electron spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and atomic absorption spectroscopy. It is established that there are two regions of anodic potential (from stationary potential to –0.71 V and higher) and, accordingly, two stages of corrosion: (i) formation of protective films containing α - Al₂O₃, SiO₂, and silicon solid phases on the samples and transition of Mg²⁺ - and SiO₃^2- -ions into a solution and (ii) formation of lower magnesium silicide, MgSi, in the region of higher polarization besides the above solid phases. It is shown that zirconium and manganese serve as cathodic areas and substantially slow down the corrosion of the alloys at the second (basic) stage (especially at Zr and Mn aggregations).