Zinc diffusion coating (zinc-infiltrating coating) is an anti-corrosion layer formed by diffusion of zinc on the surface of a steel matrix, and is widely used in industrial fields with high demand for anti-corrosion.
Excellent corrosion protection – Zinc diffusion coatings have excellent resistance to atmospheric corrosion due to the formation of an iron-zinc alloy. Studies have shown that galvanized coatings can improve the corrosion fatigue resistance of steel components, especially in environments containing hydrogen sulfide.
Protects the base metal – Zinc diffusion coatings effectively protect the steel substrate from corrosion, especially for long-term use in harsh environments.
The adhesion between the zinc diffusion coating and the base metal is strong, and as long as the process is properly controlled, the adhesion is very good.
Due to the penetration of iron in the coating, zinc diffusion coatings are harder than common electro-galvanized and thermal spray zinc coatings.
The zinc diffusion coating can be applied without a primer to achieve good adhesion and is suitable for subsequent coating treatment.
Since the coating is dominated by β phase (FeZn₃), cracking may occur when it is machined with a high elongation.
The zinc infiltration temperature affects the structure - the structure of the zinc diffusion coating is mainly composed of α phase, β phase, γ phase and ζ phase. At temperatures ranging from 400~600°C, these iron-zinc alloy phases exhibit different structures in the coating.
Effect of carbon content – An increase in the carbon content in the steel promotes the formation of β and ζ phases, which increases the thickness of the zinc layer.
The influence of other elements – the increased content of silicon, phosphorus, manganese and other elements in the steel promotes the interaction between the zinc and the steel matrix, resulting in a thicker zinc layer.
Powder zincification
The workpiece is heated (380~420°C) by embedding a mixed powder containing zinc powder. In this process, zinc powder works with alumina and other substances to promote the diffusion of zinc.
Pay attention to control the temperature to avoid melting or excessive oxidation on the surface of the zinc powder to ensure the diffusion effect.
Gas zincification
The workpieces are processed in a vacuum or in a reducing atmosphere. When the vapor pressure of zinc reaches a certain range, the zinc atoms are able to diffuse smoothly to the surface of the metal.
Liquid zinc seeping
Common methods of liquid galvanization include dry galvanizing and redox plating. The workpiece is pickled and fluxed and then immersed in zinc melt to form a zinc alloy coating.
Diffusion annealing (zinc)
The hot-dip galvanized coating is diffused and annealed in a protective atmosphere of 450~1020 °C to improve the uniformity and corrosion resistance of the coating.
Corrosion protection – Zinc diffusion coatings are widely used in steel pipes, springs, fasteners and other metal parts that need to be protected from corrosion, especially in the case of strict requirements for dimensional error.
Improved corrosion fatigue resistance – Galvanized coatings help improve the durability and service life of metal components in highly corrosive environments.
Zinc diffusion coatings occupy an important position in the field of metal surface treatment due to their excellent corrosion resistance and strong adhesion. With different galvanizing processes, the thickness, hardness and corrosion resistance of the coating can be tailored to the requirements. The coating is widely used in a variety of industries such as construction, automotive, and machinery, and meets various needs for high durability, corrosion resistance, and dimensional accuracy.