Due to the zinc in the dry air is not easy to change, in the humid air, surface can generate a very dense carbonate zinc film, the film can effectively protect the internal is no longer from corrosion. And when some reason make the coating damage and doesn't show much substrate, zinc and steel matrix form micro batteries, making fastener matrix cathode under protection. Widely used in the motor transport industry, but the need is trivalent chromium passivation coating, zinc nickel alloy plating closed), reduce harmful, toxic hexavalent chromium passivation layer.