The Effect of iron re-deposition on corrosion of impurity-containing magnesium

Abstract

This article provides a contribution towards the mechanistic understanding of surface phenomena observed during corrosion of Mg-based substrates particularly in the low anodic polarization range. The concept considers recent literature explaining cathodic hydrogen evolution from noble acting areas even during global anodic polarization. Heavy metal impurities in the ppm range or intermetallics are always present even in highly pure magnesium. Their potential effect was investigated here in more detail. Experimental results contribute to understanding the role of iron impurities during dark area formation and suggest a way of linking the observed phenomena to recent literature. The shown enhanced cathodic activity of dark areas especially at the corrosion front and the superfluous hydrogen are linked to an iron re-deposition mechanism due to iron reduction. The proposed mechanism is based on results obtained from innovative characterisation techniques using magnetic fields, diffraction experiments and transmission electron microscopy, which show the formation of iron rich zones, especially at the corrosion front offering “in statu nascendi” metallic Fe films acting as active cathodes for hydrogen reduction.