Conversion layer
Conversion layers are non-metallic , mostly inorganic , very thin layers on a metal surface, which are usually produced by the chemical reaction of an aqueous treatment solution with the metallic substrate.
effect
Conversion layers form a very good basis for the adhesion of subsequent coatings and significantly increase the corrosion resistance of the base material compared to untreated material surfaces. In addition, conversion layers have a very low electrical resistance. It is also technically possible to produce colored conversion layers for the production of decorative coatings.
electrolyte
The conversion layer is formed with an electrolyte . In the past, conversion views were often generated with chromium electrolytes based on the carcinogenic and SVHC- listed chromium (VI) oxide , known as chromating . This is used less and less due to strict legal requirements. Research is currently being carried out on suitable substituents. Alternatives to the classic chromium (VI) electrolyte are treatments based on chromium (III) oxide or complex fluorides ( titanium , zirconium compounds ). Another possibility for creating a conversion layer is phosphating using aqueous phosphate solutions.
literature
- Hansgeorg Hofmann, Jürgen Spindler: Process in coating and surface technology . Carl Hanser Verlag , 2nd edition, October 7, 2010, pp. 179ff, ISBN 978-3446423787 .
Individual evidence
Web links
- Chemical oxidation, chromating, phosphating of aluminum (accessed June 18, 2020)
- Pretreatment of aluminum and its alloys (accessed June 18, 2020)
- Conversion layers for metallic surfaces (accessed June 18, 2020)
- Electrochemical and surface chemical investigations on Zr-based conversion layers on galvanized strip steel (accessed on June 18, 2020)
- Combination of chemical conversion with water-based nanoparticle dispersions to build up improved corrosion protection layers on magnesium alloys (accessed on June 18, 2020)