Zinc is a metallurgical reaction process. From the microscopic point of view, the process of hot dip galvanizing is two dynamic balance, heat balance and zinc iron exchange equilibrium. When the steel workpiece immersed in about 450 ℃ molten zinc liquid, room temperature liquid zinc absorption heat of the workpiece, reaching above 200 ℃, the interaction of zinc and iron became clear, zinc, iron penetrate the surface. As the temperature of the workpiece gradually approaching the temperature of molten zinc, workpiece surface formed with different proportion of zinc iron alloy layer, a hierarchical structure of zinc coating, with extended time, the growth of different alloy plating layer present different speed rate. From a macro perspective, the performance of the above process workpiece immersed in liquid zinc, zinc liquid boiling occurs when zinc, iron reaction gradually balance, zinc surface gradually calmed. Workpiece is made of zinc surface, the workpiece temperature is gradually lowered to below 200 ℃, the reaction was stopped by zinc, iron, hot dip galvanized coating has a thickness determined.
The thickness of the zinc coating main factors: a base metal component, the surface roughness of the steel, the steel of the active elements silicon and phosphorus content and distribution, the internal stress of the steel, the workpiece geometry, hot-dip galvanizing process. The current international and Chinese standards are divided into sections according to the steel thickness, thickness of zinc coating thickness and draw the local should reach the corresponding thickness, to determine zinc coating anticorrosion performance. Different steel thickness of the workpiece, to achieve thermal equilibrium, and zinc ion exchange equilibration at different times, the resulting coating thickness is different. The average thickness of the coating standard is based on the mechanism of the galvanizing experience in industrial production, the local thickness of the zinc coating thickness is taken into account the uneven distribution of the coating and corrosion protection requirements needed experience. Therefore, ISO standards, ASTM standards, JIS standards and Chinese standards zinc coating thickness requirement is slightly different, much the same.
The thickness of the zinc coating determine the performance of anticorrosion plating parts. For 3 mm below the thin steel plate surface is smooth, it is difficult to get a thicker coating in industrial production, in addition, it is not commensurate with the thickness of the steel zinc plating thickness and will affect the adhesion strength of the coating and the substrate and the coating appearance quality. A thick coating will cause the coating appearance of rough, easy peeling, plating parts can not stand the collision in the process of handling and installation. If there are more steels active elements of silicon and phosphorus, industrial production has been very difficult thinner coating, which is the silicon content of the steel in impact between the zinc-iron alloy layer growth mode.
Post time: Sep-10-2019