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HaiGang Yunyi
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Tianjin Haigang Steel Coil
Service first, quality assured. More dedicated and focused on crafting even better boards.
01
2020
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09
Hot-dip galvanizing technology and process
Galvanized strip steel, also known as hot-dip galvanized strip steel, is a method of obtaining a metallic coating by immersing prefabricated steel components into molten zinc. In recent years, with the rapid development of high-voltage power transmission, transportation, and telecommunications, the requirements for the safety protection of steel components have become increasingly stringent, and the demand for galvanized strip steel has continued to rise.
Typically, the thickness of a phosphating treatment layer ranges from 5 to 15 μm, whereas the thickness of a hot-dip galvanized layer generally exceeds 65 μm, and can even reach up to 100 μm. Hot-dip galvanized strip steel boasts excellent processability, high coating density, and no impurities from organic compounds. As we all know, zinc’s resistance to atmospheric corrosion relies on both mechanical protection and electrochemical protection. Under atmospheric corrosion conditions, the surface of the zinc layer forms a protective film composed of ZnO, Zn(OH)2, and basic zinc carbonate, which provides a certain degree of corrosion mitigation. This protective film—also known as "white rust"—can be damaged, but new layers will promptly form to replace it. When the zinc layer is severely damaged and the underlying iron substrate is significantly exposed, zinc then exerts electrochemical protection on the substrate. With a standard electrode potential of -0.76 V for zinc and -0.44 V for iron, when zinc and iron form a microcell, zinc acts as the anode and dissolves, while iron serves as the cathode and remains protected. Clearly, hot-dip galvanizing offers superior resistance to atmospheric corrosion for the base metal, iron, compared to phosphating.
The entire process of hot-dip galvanizing involves the formation of an iron-zinc alloy layer between the iron substrate and the outermost pure zinc layer. During hot-dip coating, an iron-zinc alloy layer forms on the surface of the workpiece, which ensures excellent bonding between the iron substrate and the pure zinc layer. This process can be simply described as follows: When an iron workpiece is immersed in molten zinc, a solid solution of zinc in α-iron (body-centered cubic structure) initially forms on the surface. This is a crystalline phase in which iron, in its solid state, dissolves zinc atoms. The bond between these two metallic elements is relatively weak, with only modest attractive forces between the atoms. Once the solid solution reaches saturation, zinc and iron atoms begin to diffuse into each other. Zinc atoms that diffuse into (or penetrate) the iron substrate rearrange themselves within the substrate’s crystal lattice and gradually form an iron-zinc alloy. Meanwhile, iron atoms that diffuse into the molten zinc liquid react with zinc to form the intermetallic compound FeZn13, which settles at the bottom of the galvanizing bath as zinc slag. When the workpiece is removed from the zinc bath, a pure zinc layer—characterized by a hexagonal crystal structure—forms on its surface. The copper content in this pure zinc layer does not exceed 0.003%.
Strip steel, galvanized strip steel, cold-rolled hard strip steel, hot-dip galvanized strip steel, galvanized steel strip
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We primarily produce various products including galvanized strip steel, pickled strip steel, and cold-rolled strip steel. These products are widely used in industries such as construction, mechanical manufacturing, automotive, and household appliances.
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Shuangtang High-end Hardware Products Industrial Park, Jinghai District, Tianjin City
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