Chromate conversion coatings are obtained by chemical reaction with the metal being treated to form a complex chromate film over the entire surface.The characteristics of the resulting surface offer the following benefits:
The coatings are suitable for use on all types of aluminium alloys including high-silicon pressure die-castings, which are difficult to anodise. In addition they can be used to treat zinc and magnesium alloys – particularly to promote good paint adhesion.
Chromate conversion is either carried out by immersion or by brush application.
A number of different coatings are available but the most commonly used products in the U.K. are alacrom1200 and alacrom 1000. In the USA the most commonly known is ‘alodine’.
Alacrom 1000 gives a clear coating and alacrom 1200 a colouration from champagne through to orange depending upon exposure time. The latter is by far the more common.