A trivalent or hexavalent chromium layer is formed on the surface of a metal by the interaction of chromate solution with the metal. Because a large amount of trivalent chromium compounds in the passivation film are insoluble in water, the penetration of oxygen and water in the air is isolated, and the pores of the galvanized layer are closed (especially the electric galvanized layer).
A small amount of chromium 6 is distributed in the film, which can repair the passivation film that has been wiped off, and make the mildly torn film complete again.
Chromic acid passivation is the process of contacting the workpiece with an acidic solution containing hexavalent chromium to form a passivation film. The composition of chromic acid passivation liquid is also different with different workpiece materials.