When the galvanized steel sheet is exposed to the air, several types of conditions such as dry corrosion, wet and cold corrosion and wet corrosion are mainly caused.
Dry corrosion of galvanized steel refers to the corrosion of the surface layer of steel in ambient air with air humidity below 30% that does not produce a continuous electrolyte water film. Under such circumstances, the corrosion rate of steel is relatively slow, but there are few such natural environment standards.
Wet cold corrosion of galvanized steel refers to the corrosion of steel in ambient air with air humidity exceeding 30% and less than 100%. In such a case, there is dust on the surface of the steel, and there are micropores and gaps in the rust layer, which cause absorption by the microscope, resulting in shrinking water that cannot be seen by the human eye, and the principle of galvanic cells is generated in the shrinking water, and the corrosion rate is relatively fast. .
Wet corrosion of galvanized steel sheet refers to the corrosion of galvanized steel sheet in the humid and cold ambient air with air humidity exceeding 100%, and the surface layer has solidified shrinkage water that can be seen by the human eye. In such a case, the water on the surface of the steel shrinks and the water is thicker, so that the diffusion rate of oxygen to the outside of the steel surface after melting is relatively slow, which reduces the rate of corrosion. In fact, the corrosion of steel is closely related to the shrinking water of the surface layer between the two, and because of the presence of water, CO2 is dissolved in the water, so that iron produces a weak electrolyte, resulting in a series of weak electrolyte reactions.
The CO2 in the gas is continuously dissolved in the water, and the reaction is continuously carried out. Since the key product of the reaction is bright red, the material after iron air oxidation is generally called "red rust". The red rust is very loose and very easy to melt. It is impossible to protect the surface of the steel from being eroded again, so the corrosion of the steel will be carried out until it is completely etched. It is the characteristic of the steel. Because of this, steel must be
Other metal materials or the thickness of the protective layer of metal materials to reasonably avoid the corrosion of steel.