Chromating is a chemical surface treatment in which a thin protective layer is applied to metal (often galvanised steel or aluminium) by immersion in a chromium-based solution. This chromate layer protects against corrosion and improves paint adhesion.
How does it work?
During chromating the metal surface reacts with the chromium solution, forming an extremely thin (0.1-1 μm) but effective protective film. This layer:
- Passivates — makes the surface chemically inert
- Self-heals — small scratches in the layer repair themselves
- Improves adhesion — provides an excellent base for paints and coatings
Application
Chromating is used on:
- Galvanised steel products — bolts, nuts, fasteners
- Aluminium components — window frames, profiles, hardware
- Sheet steel — galvanised sheet for roof and facade panels
- Fasteners — screws and anchors for outdoor use
Types of chromating
- Yellow chromating — contains hexavalent chromium (Cr6+), very effective but environmentally harmful
- Clear/blue chromating — thinner layer, less protection
- Chrome-free passivation — modern, environmentally friendly alternatives based on trivalent chromium (Cr3+)
Note: Hexavalent chromium (Cr6+) is harmful to health and the environment. The EU has severely restricted its use under the REACH regulation.
Related terms
- Galvanising
- Corrosion
- Aluminium
- Steel
- Anodising
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