Hot-dip galvanizing is a surface treatment technique in which steel products are immersed in a molten zinc solution (at a temperature of approximately 450°C) to form a dense alloy layer through a metallurgical reaction between iron and zinc.
Author: Anna
Analysis of hot-dip galvanizing principle
1. Basic definition
Hot-dip galvanizing is a surface treatment technique in which steel products are immersed in a molten zinc solution (at a temperature of approximately 450°C) to form a dense alloy layer through a metallurgical reaction between iron and zinc. The core of the process lies in the chemical bonding of zinc to the iron substrate, rather than a simple physical covering.
2. Reaction process
Zinc immersion: Steel is immersed in molten zinc after degreasing, pickling and other pre-treatments, and the zinc liquid penetrates the microscopic pores on the steel surface.
Alloy layer formation: iron and zinc undergo a diffusion reaction at high temperature, sequentially generating zinc-iron alloy layers such as Γ-phase (Fe₃Zn₁₀), δ-phase (FeZn₇), and ζ-phase (FeZn₁₃), which are usually 50-150 μm thick .
Outer layer of pure zinc: the outer alloy layer is covered with a pure zinc layer, which forms a metallic luster surface after cooling.
3. Plating protection mechanism
Physical barrier: The zinc layer isolates the steel from moisture and oxygen, blocking the oxidation reaction.
Electrochemical protection: Zinc acts as a sacrificial anode to prioritize corrosion and protect the iron substrate (even if the plating layer is locally broken, the protection can still be sustained).
Self-repairing: zinc corrosion products (e.g. zinc carbonate alkali) can fill the surface micro-cracks, delaying further corrosion.
4. Process advantages
Corrosion resistance: the coating life can be more than 50 years (under normal environment), far more than cold galvanizing (5-15 years).
Bonding strength: the alloy layer is metallurgically bonded to the substrate, and its resistance to mechanical impact and abrasion is significantly better than that of electro-galvanizing.
Economy: Suitable for mass production, the cost per unit area is lower than spraying and other processes.