Chromatation (version 5)
N.B.: The information contained in this sheet comes from reliable sources. Nevertheless, it is provided without any guarantee, express or implied, of its accuracy.
Principle:
Chromating is a chemical conversion treatment that can be applied by spraying or dipping solutions containing hexavalent chromium to form complex oxide layers. The conversions with fluorides and possibly potassium ferricyanide induce an iridescent to yellow coloring of the layer.
The treatment time varies from 1 to 3 minutes and the maximum temperature of use is 70°C (to avoid significant cracking of the layer). The layers obtained are thin, about 0.5 μm thick, with a surface mass of about 1 g/m². The chromating layer is an excellent bonding base for organic finishes. It slightly increases the corrosion resistance of aluminum.
ASPECT: colorless / yellow / light brown
THICKNESS: 0 .05 to 0.5 μm, the notion of layer weight is more used: 0.05 to 1.3 g/m² depending on the application
MICRODURITY: 200 / 250 Hv 0.050
SURFACE CONDITION: micro-cracked and roughened layer ELECTRICAL CONDUCTIVITY: conductive
CORROSION RESISTANCE: 100 to 168 h depending on the alloy
SUBSTRATE:
All aluminum alloys. The alloy used has a strong influence on the performance level obtained.
VARIANTS:
Numerous processes have been developed and are often known by their trade name: alodine 1200, iridite 14-2, aluchrom 25, ardrox 4101...
Possibility of application with a pad
APPLICATIONS :
Corrosion resistance in a mildly aggressive environment
Bonding base for organic coatings (paints, glues, rubber...).
Local repair of damaged anodizing or painting treatments.
Storage under cover.
Applications: aeronautics, automotive, building, urban furniture ...
SELECTION CRITERIA - LIMITATIONS :
The intrinsic corrosion resistance is low and this treatment often requires an additional step of protection (painting...).
Environmental limitations: presence of hexavalent chromium.
ENVIRONMENTAL IMPACT:
The use of hexavalent chromium, toxic and carcinogenic, in surface treatments is tending to disappear. The
new regulations require the development of new chemical conversion processes without hexavalent chromium.
REFERENCE:
EN 2437 : aeronautical sector
ISO 9227-NSS : neutral salt spray test
EN 12 373-18 : Pitting corrosion rating system
ISO 8081: method of measuring the mass per unit area
EN 12 373-18 : Pitting corrosion rating system
Implementation
Main equipment (furnace, reactor, line, machine...)
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