Chemical Conversion Coating
Definition - What does Chemical Conversion Coating mean?
A chemical conversion coating is a coating that is produced by electrochemical or chemical reaction of metals, giving a superficial layer which contains the metal compound.
It offers economical protection against corrosion and a surface suitable for powder coating and painting. It also preserves electric conductivity, in contrast to anodizing which produces coatings that are non-conductive.
Unlike anodizing, chemical conversion coatings do not need electricity, making production more cost effective. It can be colored or clear, depending on preference.
A chemical conversion coating is also known as chromating, chromate conversion and alodining.
Corrosionpedia explains Chemical Conversion Coating
Conversion coatings are applied on metal parts for corrosion protection. These are acidic in order to transform a metal substrate to a zinc phosphate or iron surface. It is the chemical reaction that makes the metal surface improve field performance and paint adhesion.
Chemical conversion coatings can go through either electro-chemical or chemical processes, which may include any of the following:
- Chromate conversion - Mainly utilized on aluminum surfaces
- Zinc and iron phosphate conversion - Mainly applied on steel substrates
- Anodizing - Used primarily on aluminum
This type of coating is utilized to provide a surface for paint to adhere to throughout the process of curing. Without it, metal and other surfaces would have paint that only sits on top of the surface rather than being bonded to it mechanically. Due to this, paint may undergo delamination or flaking from the steel surface, especially in cases of inadequate or no conversion.
Chemical conversion coatings that are distributed evenly are a thin film of crystals that overlaps throughout the pre-treatment period. When properly prepared, such coating offers a very solid base for adhesives and paints.