A conversion coating is a chemical treatment applied to aluminum. It is sometimes known as “passivating”, “chrome phosphate” or “alodine.”
Chrome-free conversion coatings are now available. This is usually done prior to painting or applying an adhesive, and is accomplished by immersing the aluminum in a conversion coating solution.
The finish provides some corrosion resistance, and more importantly, good adhesion. It is typically used as the base for an organic coating (i.e. paint) or for an adhesive.
There are many kinds of conversion coatings, some based on chrome and some used with other metals. Sometimes it is used as a final finish, but this requires the use of a very strong bath.
Unlike SAF, most paint applicators do not maintain a strong chrome bath because it is not required for paint pretreatment.