Formation and characterization of Fe3+- / Cu2+- modified zirconium oxide conversion layers on zinc alloy coated steel sheets
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(NO3)2·3H2O or Fe(NO3)3·9H2O 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 Cu2+ or Fe3+ ions to the conversion solution. In addition, growth kinetics was studied by in situ measurements of corrosion potential using potentiodynamic polarization technique.