When the Galvanized Mild Steel sheet is exposed to the air, several types of conditions will occur, such as dry corrosion, wet corrosion, cold corrosion and wet corrosion.
The dry corrosion of galvanized sheet means that the steel surface in the ambient air with an air humidity of less than 30% will not produce continuous electrolyte water film corrosion. In this case, the corrosion rate of steel is relatively slow. However, such natural environmental standards are relatively few.
The wet and cold corrosion of Mild Steel sheet refers to the corrosion of steel in ambient air with an air humidity greater than 30% and less than 100%. In this case, there will be dust on the steel surface, and there will be micropores and crevices in the rust layer, causing the microscope to absorb and produce shrinkage water invisible to the naked eye. The principle of the primary battery is produced under the action of shrinking water, and its corrosion rate is relatively fast.
The wet corrosion of the Mild Steel sheet refers to the corrosion of the galvanized sheet when there is solidified shrinkage water on the surface of the galvanized sheet in a humid and cold environment where the air humidity exceeds 100%. In this case, the surface layer of the steel shrinks and the water becomes thicker. Therefore, the rate of oxygen diffusion to the surface of the steel layer after melting is relatively slow, thereby reducing the corrosion rate. In fact, the corrosion of steel is closely related to the surface shrinkage between the two. It is also due to the presence of water that carbon dioxide melts in the water, which makes the iron produce a weak electrolyte and a series of weak electrolyte reactions.
The carbon dioxide in the gas continues to melt into the water, and the reflection continues. Since the key product of reflection is bright red, the iron-air oxidized substance is usually called "red rust". Red rust is very loose and melts easily. The Galvanized Mild Steel sheet cannot keep the surface of the steel from being corroded, which promotes the corrosion of the steel until it is completely corroded. It is a characteristic of steel. Therefore, steel must be coated with other metal materials or the thickness of the protective layer of metal materials to avoid steel corrosion.
