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The main task of yellow galvanic galvanizing of steel hardware (bolts, nuts, screws, fasteners ) - protection against corrosion and increased service life. The thickness of the coating, depending on the requirements, can range from 6 to 50 micrometers. Applying a layer less than 6 microns is impractical, because the protective characteristics of zinc will be unacceptably low. Thicknesses greater than 15 microns increase the risk of exceeding tolerances. For example, after coating the threaded part of a bolt with a thick zinc coating of 40 microns, the thread diameter  will increase in size by 0.08 mm and the standard nut may not fit onto the bolt. In the bell, coatings of 6-12 microns are usually applied, a larger layer is applied on pendants. The thickness of rainbow chromate film is 0.25-0.5 microns and does not affect the diameter of the product. The content of hexavalent chromium in it ranges from 80 to 220 mg/m2. The durability of yellow zinc in 5% salt spray is 200-300 hours. The corrosion rate of non-passivated zinc depends on pH:

Zinc corrosion rate

Galvanizing can be carried out using different technologies. Shiny coatings are more hard and less flexible than semi-shiny ones. The type of passivation has virtually no effect on microhardness. The electrical resistivity is slightly higher than that of metallurgical zinc due to the inclusion of carbon and sulfur from the electrolyte in the coating composition (up to 1%). It should be remembered that the contact resistance of zinc may vary depending on the passivation method. Rainbow film is of medium resistance, relatively colorless, olive or phosphate. In a bell or drum, galvanizing is more efficient, but the parts hit each other, which can lead to clogging of the thread.

You can order rainbow galvanizing of steel according to GOST 9.305-84 by phone and email indicated in the section "CONTACTS"


The main characteristics of zinc are given in the table

Designation (examples)



6-50 microns (optimal, greater thickness is possible)


490-1180 MPa

Electrical resistivity at 18oC

5.75×10-8 Ohm⋅m

Permissible operating temperature

300° C

Coating benefits:

  • Rainbow zinc on steel hardware provides excellent corrosion resistance, second only to khaki galvanizing. The coating is anodic with respect to iron and electrochemical protection is maintained in an aqueous neutral environment at temperatures up to  70° C. In hotter water, the coating becomes cathodic and protects hardware only mechanically.
  • Yellow zinc coating prevents contact corrosion when mating fasteners with parts made of aluminum and its alloys, ensures easy screwing of threaded parts of hardware, improves their appearance.
  • Yellow chromate film on zinc coating restores protective properties (self-heals) when scratched or small chips, which is especially important in the drum application method.
  • The zinc coating produced at our enterprise is ductile, withstands bending and flaring, thanks to the use of unique shine-forming additives in the electrolyte. It also has a high uniformity in thickness, which is confirmed by metallographic studies:

A microphotograph of a cross-section of the coating is shown below:


Disadvantages of galvanizing:

  • Iridescent chromate film on zinc is mechanically relatively weak. Chromated zinc coating loses its decorative appearance under constant mechanical influence (hands, tools).
  • Electrochemical galvanizing causes some loss of steel ductility due to hydrogenation. Steels with a tensile strength higher than 1400 MPa are not subject to galvanic galvanization.
  • Zinc has increased brittleness at temperatures above 250°C and below minus 70°C.
  • Rainbow chromated zinc has low chemical resistance to products released during aging of organic materials.