Formation and characterization of Fe~(3+)-/Cu~(2+)-modified zirconium oxide conversion layers on zinc alloy coated steel sheets

摘要

Zirconium oxide conversion layers are considered as environmentally friendly alternatives replacing chromate-based passivation layers in the coil-coating industry. Based on excellent electronic barrier properties they provide an effective corrosion protection of the metallic substrate. In this work, thin layers were grown on HDG-steel-substrates by increasing the local pH at the surface and were characterized using potentiodynamic polarization technique. The influence of Cu(NO_3)_2·3H_2O or Fe(NO_3)_3·9H_2O on morphology and thickness of deposited protective layers were investigated by XPS, ToF-SIMS and FE-SEM. A significant film thickness increase was found by adding Cu~(2+) or Fe~(3+) ions to the conversion solution. In addition, growth kinetics was studied by in situ measurements of corrosion potential using potentiodynamic polarization technique.