Chromating is the conversion coating process of depositing an oxide layer over a metal surface to enable the metal to react with the oxide layer. This forms a layer of passivated metal chromate on the surface.

Chromating is used to reduce the reactivity and to improve durability and surface finish of metals such as aluminium and zinc alloys.

The study of chromating is important because:

  • The layer acts as a cost-effective corrosion inhibitor, protecting vital components from material degradation.
  • It acts as primer.
  • It provides a decorative finish.
  • It improves electrical conductivity.


Chromating is commonly used on:

  • Hardware products
  • Tools
  • Aluminium alloy parts used in the aircraft industry
  • Phosphate coatings of ferrous surfaces


Chromating usually works like a coat of paint on zinc, protecting the zinc surface from white corrosion, and improving durability of zinc components several times over, depending on thickness of the coat. Darker coatings of chromate provide higher corrosion resistance, thus enhancing the lifespan.

Chromating solutions vary in composition, based on the metals to be coated and expected benefits like corrosion resistance. These coatings are initially gelatinous, but harden quickly to become hydrophobic by aging. Thickness of the coating can vary from a few nanometers to one or two micrometers.

Curing is required, which can be accelerated by providing heat less than 70°C, as higher temperatures can slowly damage the coating.


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