Chromate conversion on Chicago coatings are a type of conversion coating which is applied to passivate zinc, aluminum, cadmium, silver, copper, magnesium, tin and their alloys to slow corrosion. The process involves the use of various toxic chromium compounds which might include hexavalent chromium. The industry is now developing less toxic alternatives so as to comply with substance restriction legislation. One option is trivalent chromate conversion which is less environmentally damaging.

Chromating is normally used on zinc-plated parts to defend the zinc from white corrosion, which is mainly a cosmetic issue. It can't be applied directly to steel or iron, and it does not enhance zinc's anodic protection of the underlying steel from brown corrosion. It is also most commonly used on aluminum alloy parts in the aircraft industry where it is often called as chemical film. It also has an additional value as a primer for subsequent organic coatings, as any untreated metal, especially aluminium, is hard to paint or glue. A chromated part retains their electrical conductivity to varying degrees, depending upon the coating thickness. The process can also be used to add color for decorative or recognition purposes.