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Abstract

This project was aimed at developing and testing new thin organic coatings (TOC) based on Cr-free systems. The influence of the type of metallic substrate hot-dip galvanised - Galfan - Zn-Fe coating was also investigated. One standard Cr-containing TOC was compared with a newly developed Cr-free TOC technology using a blend of fluorometallate passivating agents with acid-resistant organic resins.

The main results are:
- Cr-free systems are already interesting for indoor applications for painted parts as well as unpainted parts;
- Cr-containing systems are still better performing for long-term corrosion protection in outdoor exposure;
- Corrosion results are greatly influenced by the nature of the substrate and by its roughness for a given TOC coating weight;
- Great care should be taken in the choice of accelerated ageing tests and the nature of media in electrochemical tests to assess comparative corrosion resistance between Cr- containing and Cr-free systems.

This study demonstrates that the role of Cr(VI) in thin organic coating formulations is very dependent on the way the product is tested - the type of substrate - which end-use property is considered. For long-term corrosion protection on unpainted panels, the Cr(VI)-containing product remains the most efficient and reliable solution. However, the level of corrosion protection which is possible with Cr-free systems is now high enough to meet the technical requirements for indoor applications of unpainted or post-painted panels. The limits of Cr-free systems in real processing conditions could be their chemical resistance in stringent degreasing conditions and the loss of paint adherence on highly deformed parts.

Additional information

Authors: MARQUAIS T, Sollac Atlantique - CED, Montataire (FR);STELLNBERGER K-H, Voest-Alpine Stahl GmbH, Linz (AT);WORMUTH R, Dortmunder Oberflächencentrum GmbH (DOC), Dortmund (DE);BARRANCO ASENSIO V, Centro Nacional de Investigaciones Metalúrgicas (CENIM), Madrid (ES);HARDY Y, CRM - Centre de recherches métallurgiques, Liège (BE);PUENTE MARTINEZ J M, Aceralia Corporación Siderúrgica, Aviles (ES);SANDER J, Henkel KGaA, Düsseldorf (DE)
Bibliographic Reference: EUR 20729 EN (2003), 75pp. Euro: 15
Availability: EUR-OP reference: KI-NA-20729-EN-S Available from EUR-OP sales agents URL: http://publications.eu/general/en/publications_en.htm
ISBN: ISBN: 92-894-5710-4
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