The experimental results show that the electrochemical protective effect of the galvanized layer on the non-coated steel surface is attenuated with distance. In the area adjacent to the galvanized layer, there is no corrosion of steel in this area. Outside part of the protection zone, there is no protection zone, this area steel serious occurrence.The corrosion is the same as that of bare steel, and the galvanized layer not far from it will not work in this area. Zinc/steel for foreign use,The results of atmospheric exposure test of "electric couple sample" show that the width of the complete protection zone is ~1mm, and the width of part of the protection zone is ~3.5 m. That is to say, the galvanized layer has a total protective distance of ~1mm, and a partial protective distance of ~4.5mm.So, whether the galvanized layer played a sacrificial anode protection, not depends on whether the area of the base steel exposed to cannot be dominated by the electrolyte (water film, for example), but depends on whether the area of the base steel exposed beyond the size of "reserve", or, if beyond the size of the "thoroughly reserve + part of the reserve". Beyond that, even if the water film is completely covered, the steel base also occurs.Corrosion,
The first case. Some metal coatings, such as tin coating (whether hot tin plating or tin plating), are only protective to the steel substrate in terms of polarity. If the tin plating layer is partially damaged, when there is an electrolyte cover, the tin becomes the cathode and the iron becomes the anode, which will aggravate the corrosion perforation of the steel substrate. Therefore, this kind of plating, the layer only before its own corrosion penetration, by isolation to protect the steel base.
The working life of anodized or cathodic coatings depends on the thickness of the coatings (the weight of coatings per unit area) and the ambient atmosphere. The thicker the coating, the heavier the plating, the longer its service life.Environmental atmosphere corrosive weak (such as rural atmosphere), coating service life long; Environmental atmosphere corrosive strong (such as industrial atmosphere, sea, "ocean atmosphere), the service life of the coating is short. The structure of the coating also has some influence on its corrosion resistance, such as the impurity in the pure zinc coating.Accelerate the corrosion rate of zinc layer.