Chromate and Non Chromate Conversion Coating
Chromate conversion coating is a type of conversion coating that can be applied to passivate aluminum and zinc die casting components. The basic purpose is as corrosion inhibitor, primer, decorative finish or to retain electrical conductivity.
Chromate conversion coatings on an aluminium substrate are known by the following terms: chemical film, yellow iridite, and the brand names Iridite, Bonderite , formerly known as Alodine, in the UK, Alocrom). It is also commonly used on aluminum alloy parts in the aircraft industry.
Iridite NCP is a non-chromium type of conversion coating for aluminium substrates.
The most commonly referred-to standard for applying chromate conversion coating to aluminium is MIL-DTL-5541 in the US, in the UK it is Def Stan 03/18.
The process is named after the chromate found in chromic acid, also known as hexavalent chromium, the chemical most widely used in the immersion bath process whereby the coating is applied. The treated component surface finish can usually be recognized by their distinctively iridescent, greenish-yellow color, hence the name gold alodine. However, hexavalent chromium is toxic, and it is non RoHS compliant. In Europe the RoHS (Restriction of Hazardous Substances) Directive is commonly referred to regarding elimination of hexavalent chromium in electrical and electronic equipment.