Using zinc coatings to protect the underlying steel substrate from corrosion, or to minimize it, has proven to be highly effective in typical atmospheric conditions. The corrosion protection principles mainly include the following aspects:
(1) A thin and dense layer of zinc oxide forms on the surface of the zinc coating. This zinc oxide layer is difficult to dissolve in water, thus providing a certain degree of protection to the underlying metallic zinc layer. However, it tends to peel off when its thickness reaches around 300 nanometers. The corrosion protection becomes even more effective if the zinc oxide reacts with other components in the atmosphere to form insoluble zinc salts.
(2) The zinc coating acts as a dense thin film covering the steel surface, preventing the steel substrate from coming into contact with any corrosive solutions and protecting it from corrosion.
(3) In cases where small areas of the steel substrate are not plated or parts of the surface are exposed due to corrosion, the zinc coating can create iron-zinc galvanic microcells under the electrolytic conditions formed by the surface water film. This allows the remaining zinc coating to repair the unplated and exposed areas, continuing to provide protective effects.
