The Coating Classification Of Hot-dip Galvanizing Steel

The coating classification of hot-dip galvanizing steel


The continuous hot-dip galvanizing process offers a wide protection between the coating and the steel. These properties make zinc coatings well suitable to forming and demanding corrosive atmospheres. Because of the nature of the zinc, the coating provides corrosion protection for areas of exposed steel surfaces. Here well discuss the the coating classification of hot-dip galvanizing steel


According to the metallic property attached to the appearance of the steel, the coating can be divided into Pure Zinc Galvazinc and Zn-Fe Galvazinc alloy coating.

Pure Zine coating: Pure Zinc Galvazinc coated by hot dip galvanizing have a wide application are possible by selecting spangle or a post treatment and is usable from general processing to deep drawing according to application. Light coated steel have good weldability and formability. Heavy coated steel have superior corrosion resistance.

Zn-Fe alloy coating: Zn-Fe galvazinc alloy coated by hot dip galvanizing and annealing. Zn-Fe coating has superior paint adhesion and corrosion resistance and its weldability is superior to pure zine products. Corrosion protecting capacity of surface is same as Zn coating but superior paint adhesion provides higher corrosion resistance after painting. Galvanized steel with Zn-Fe alloy coating is mostly used for architecture, electric appliance, automobile and other application.


According to the thickness of zinc layer, hot galvanized steel coating can be divided into two types: Isopachous coating and differential coating.

Isopachous coating: Spot welding of metal coated material requires slightly higher current and electrode force than for uncoated steels due to the lower contact resistance of the coating. Similarly the increase in coating thickness increases slightly the required welding current.If there are no special requirements, it is generally available at the commercial board level of equal thickness steel, that is, the weight of two sides zinc layer is 275g/m2.

Differential coating: With the method of controlling the pressure of air knife, the thickness difference ratio of the two zinc layers is 1:3, making the thick layer of zinc coating a good corrosion resistance and a thin side weldability. In order improve weldability and achieve longer service life of welding electrodes, it is recommended to avoid unnecessarily thick coatings in welding applications. The steel plates with differential coating is mostly used in automobile manufacturing.


Galvanizing is economic and effective anti-corrosion method that drained around half of the world's zinc production. The successful forming of coated steels depends on selections made regarding the geometry of component, steel grade, metal coating type and thickness, surface quality and protection, and a tool used in the forming.


ASTM A 123 is the specification for Hot Dip Galvanizing. This specification covers the standard requirements for hot-dip galvanized zinc coatings on iron and steel products made from rolled pressed and forged shapes, castings, plates, bars, and strips. Any hot-dip Galvanized steel pipe needs, contact us for more details.