(1) The surface of the guardrail steel plate is covered with zinc coating as a whole, and the corrosion at this time is the corrosion of zinc in the atmosphere. Due to the protective effect of the products produced by zinc corrosion on itself, the corrosion speed is relatively slow. The zinc coating protects the steel from corrosion by physically isolating the steel from the atmosphere (corrosive environment).
(2) The alloy layer in the mirror zinc layer is partially exposed to the atmosphere due to corrosion and other reasons. At this time, the steel plate is still protected in the same form as the first case. Due to the difference of electrode potential, the pure zinc layer with negative potential will provide electrochemical protection to the alloy layer with positive potential and corrode first.
(3) When the galvanized layer is corroded, the pure zinc layer is completely corroded, but the alloy layer can still completely cover the steel plate surface. At this time, the role of the alloy layer is still the same as the first two cases, which is a form of physical protection in the isolation environment.
(4) When the partial defects of the coating (such as local corrosion, scratch, notch, punching, etc.) expose the steel plate in the zinc steel road guardrail to the air, the situation becomes more complex. In humid atmosphere, due to the existence of water, Zn, Fe Zn and Fe form electrodes and are in equilibrium.
(5) When the pure zinc layer is exhausted and the steel part is exposed in the atmosphere, the Zn Fe alloy layer still provides electrochemical protection for iron because the potential is negative compared with iron, but its potential is relatively positive, so the ability of electrochemical protection is poor.
(6) After the alloy coating is consumed as an anode in electrochemical protection, steel enters the process of air corrosion, and its service life is determined by its specific environment.
The protective effect of zinc coating on zinc steel guardrail is reflected not only in the case of atmospheric corrosion, but also in the case of electrochemical corrosion in electrolyte.
In short, because zinc coating has good protection results for zinc steel road guardrail, low production cost and controllable coating thickness, toughness and surface state, zinc coating treatment of iron and steel products has been more and more widely used in daily life.
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