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How does hot-dip galvanizing coat steel with zinc?

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A labeled diagram of the periodic table entry for zinc, showing its atomic number 30, symbol Zn, atomic weight 65.38, electron configuration, name, hexagonal crystal structure, solid state at room temperature, and classification as a transition metal.
zinc

Hot-dip galvanizing is a process used to protect steel from corrosion by applying a zinc coating. The process generally involves the following steps:

  • Preparation: The steel is cleaned, often through pickling in acid, to remove impurities.12
  • Fluxing: The metal is treated with a flux, such as zinc-ammonium chloride, to prepare the surface for bonding.32
  • Dipping: The steel is submerged in a bath of molten zinc, typically maintained at approximately 440ā€“450 Ā°C (825ā€“840 Ā°F).14
  • Bonding: Upon contact with the molten zinc, a metallurgical reaction occurs where the zinc alloys with the iron in the steel, creating a strong, durable bond.4
  • Finishing: Excess zinc is removedā€”for example, by using gas-knives on steel stripsā€”to control the coating thickness.4

This method provides a protective barrier and offers sacrificial electrochemical protection, where the zinc corrodes in place of the steel if the coating is damaged.12