Structure and properties of hot-dip zinc coating

Steel with hot zinc plated widely used in the petrochemical industry, mechanical engineering, energy, industrial and civil construction, bridge building. Design engineers choose hot-dip galvanizing, because it provides unrivaled resistance to the harshest climates.

The hot zinc coating retains its protective properties for many years thanks to its three qualities:

  • high abrasion resistance;
  • uniform coating thickness;
  • complete protection of the entire surface of the product.

Hot Zinc Plated Structure

A unique feature of hot zinc coating is its structure of tightly interconnected intermetallic layers, which have high wear resistance.

On the picture 1 shows a cross-section of zinc coated steel, consisting of three intermetallic layers (Gamma, Delta and Zeta) and a top layer of pure zinc (And).

struktura-cinkovogo-pokrytiyaPicture 1 - Hot-dip zinc plated structure

When a steel product is immersed in molten zinc, a structure of these layers naturally forms as a result of a metallurgical reaction between iron in steel and zinc.. For each layer in the picture 1 indicated hardness in Vickers units. Can be seen, that all three intermetallic layers are harder, than base-steel, while the outer layer of Eta has low hardness and high ductility. This combination of zinc coating properties provides it with high wear resistance..

The high abrasion resistance of the hot-dip zinc coating gives it unrivaled resistance to damage in transit, installation on site or already in operation.

Uniform zinc coating thickness

Another important feature of hot zinc plating, which ensures his longevity, is its uniform thickness over the entire surface of the product, including outside and inside corners (picture 2).

zinc-coating-on-the-cornerPicture 2 - Hot zinc coating on the corner of the product

This eliminates the vulnerability to corrosion of the outer corners of the product., which is typical for most protective coatings, such as brushing or spraying.

Full corrosion protection of the entire surface

Hot-dip galvanizing is carried out by full immersion of the product in working solutions of degreasing and etching and, eventually, in a bath with molten zinc. This gives then, that all internal surfaces and cavities, as well as threads of steel fasteners - bolts, screws, nuts - get a full-fledged protective coating.

Since corrosion tends to proceed at an increased rate precisely inside hollow structures due to moisture condensation in them, then this advantage of hot zinc coatings is very useful.

Full protective coverage of steel fasteners is also important, as it works at connection points of structures, which are critical to ensure their strength and integrity.

Hot-dip zinc coating service life

Hot-dip galvanizing produces the thickest and most dense coating of any other galvanizing method. Requirements for the thickness or specific gravity of the coating depend on the operating environment of the product and on the specified service life.. Therefore, the thickness of the hot-dip zinc coating can be from 25 to 200 μm.

The service life of a hot-dip zinc coating before its first maintenance depends on the thickness of the coating and atmospheric conditions., in which it is operated (picture 3).

srok-sluzhby-cinkovogo-pokrytiya +Picture 3 - Service life of hot-dip zinc coating
before the first maintenance.
Received, that the need for maintenance of the zinc coating arises, when will it rust 5 % steel surface.

Source: http://www.galvanizeit.org