Formation and characterization of Fe3+-/Cu2+-modified zirconium oxide conversion layers on zinc alloy coated steel sheets

Abstract

Please cite this article as: T. Lostak, S. Krebs, A. Maljusch, T. Gothe, M. Giza, M. Kimpel, J. Flock, S. Schulz, Formation and characterization of Fe 3+ -/Cu 2+ -modified zirconium oxide conversion layers on zinc alloy coated steel sheets, Electrochimica Acta (2013), http://dx. AbstractZirconium 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 2 O or Fe(NO 3 ) 3 9H 2 O 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 were studied by in-situ measurements of corrosion potential using potentiodynamic polarization technique.

Role of Intermetallics and Copper in the Deposition of ZrO2Conversion Coatings on AA6014

“…The presence of metallic Cu indicates a similar mechanism of deposition as proposed recently on hot-dip galvanized steel. 28 AFM analysis of different stages of the growth of the conversion coating shows instantaneous nucleation and a subsequent growth of the Cu-rich particles in lateral direction in at least two phases. No growth in height is observed, which may be attributed to the importance of the contact to the Al substrate for growth.…”

“…25,28 Coatings prepared by including copper in the solution were also shown to be thicker and showed enrichment of copper within the conversion film. 25,28 Painted cold-rolled steel pretreated with a Cu-containing ZrO 2 -based coating shows low frequency impedance moduli comparable to painted phosphate pretreated steel.25 Further, the mechanism was discussed of deposition of a Cu-containing ZrO 2 -based conversion coating on a variety of substrates including AA6014. 29 The presence of Cu was shown to be the driving force behind the increase in pH on the substrate which leads to a more homogeneous deposition.…”

“…[24][25][26][27] Inclusion of Cu II salts (or alternatively, Fe salts) in the bath has been shown to lead to higher overall growth rate of the film on cold rolled steel compared to the solutions without Cu II . 25,28 Coatings prepared by including copper in the solution were also shown to be thicker and showed enrichment of copper within the conversion film. 25,28 Painted cold-rolled steel pretreated with a Cu-containing ZrO 2 -based coating shows low frequency impedance moduli comparable to painted phosphate pretreated steel.…”

Review—Conversion Coatings Based on Zirconium and/or Titanium

“…The pH of 4.0 was used in the vast majority of reports. 6,36,37,42,51,52,[55][56][57]61,62,65,68,75,[85][86][87][88]94,98,108,109 although conversion was carried out at pH between 1.5 and 6. 30,32,46,48,49,53,64,66,[68][69][70]77,78,82,90,95,99,106,107,110 More extensive and thicker coating formation at pH 4.0 than at 2.9 was noticed for Gardabond X4707 coating on AA6060.…”

“…33,34,36,37,47,51,52,55,59,61,62,[64][65][66]69,70,72,78,82,84,87,90,92,94,95,98,99,101,102,104,[106][107][108]110,[112][113][114] Elevated temperatures were also studied, i.e. between 30 and 55…”