Corrosion behaviour of rare earth ion-implanted hot-dip galvanised steel

The corrosion and oxidation behaviour of many metallic materials can be modified by ion beam bombardment of their top surface layers. Mechanical and chemical mechanisms co-operate to prevent the progress of corrosion. Rare earth ions have already been employed to avoid high-temperature oxidation of stainless steels and other technological alloys. This paper extends the use of lanthanides to improve the corrosion resistance properties of galvanic layers. By using a mass-analysed ion implanter, different doses of La+ and Ce+ have been implanted at 150 keV in two kinds of galvanic layers: hot-dip galvanised steel samples and galvannealed steel samples. Morphological changes were observed by scanning electron microscopy (SEM), and these are different depending on the substrate, the kind of ion and implanted dose. The study of polarisation curves in NaCl solutions shows that ion implantation clearly improves the corrosion behaviour of ion-implanted layers for the hot-dip galvanised layers, but not as clearly for the galvannealed, La+ implantation being the most effective means.