Galvanizing is a metallurgical reaction process.

    Galvanizing is a metallurgical reaction process from the micro point of view, hot dip galvanizing process is two dynamic balances: thermal balance and zn-fe exchange balance.When the steel workpiece is immersed in molten zinc solution at about 450℃, the workpiece at room temperature absorbs the heat of zinc solution, reaching more than 200℃, the interaction between zinc and iron gradually becomes obvious, and zinc penetrates into the surface of the iron workpiece.As the temperature of the workpiece gradually approaches the temperature of the zinc solution, the alloy layers containing different proportions of zinc and iron are formed on the surface of the workpiece, which constitute the layered structure of the zinc coating. With the extension of time, different alloy layers in the coating show different growth rates.From a macro perspective, the above process shows that the workpiece is immersed in zinc liquid, and the zinc liquid surface appears boiling. When the reaction of zinc and iron gradually balances, the zinc liquid surface gradually calms down.The workpiece is taken out of the zinc liquid level, the temperature of the workpiece gradually decreases to below 200℃, the zinc and iron reaction stops, the hot-dip galvanized coating is formed, the thickness is determined.

    The main factors for the thickness of zinc coating are: matrix metal composition, steel surface roughness, active elements silicon and phosphorus content and distribution of steel, steel internal stress, workpiece geometry, hot dip galvanizing process.The current international and Chinese hot dip galvanizing standards are divided into sections according to the thickness of steel, zinc coating thickness and local thickness should reach the corresponding thickness, in order to determine the corrosion resistance of zinc coating.Different steel thickness of the workpiece, to achieve thermal balance and zinc iron exchange balance required time is different, the resulting coating thickness is different.The average coating thickness in the standard is based on the industrial experience value of the above mentioned galvanizing mechanism, and the local thickness is the experience value required to consider the uneven distribution of zinc coating thickness and the corrosion resistance requirements of the coating.Therefore, ISO standards, ASTM standards, JIS standards and Chinese standards in zinc coating thickness requirements are slightly different, much the same.