Chromate and passivate are two different processes used for the surface treatment of metals, such as steel and aluminum.
A chromate is a conversion coating in which hexavalent chrome reacts with a zinc finish to convert that finish into a protective coating. Passivates were developed in response to the drive to trivalent passivates.
Passivates may be divided into two categories: thin and thick film. The passivate film thickness ranges from 1 micron or more for thick film passivates to less than half a micron for thin film passivates. Thin film trivalent passivates are specified to provide a thin trivalent chrome coating over the plated zinc finish. Normally, the thin film passivates produce a bluer appearance than the thick film passivates. Thick film passivates are typically heated and contain a higher concentration of metal salts. Because of their thickness, these passivates generally provide more corrosion resistance.