What does a designation like Fe/Zn 12 mean?

It indicates an electroplated zinc coating on an iron or steel base metal with a minimum local thickness of 12 microns.

Is post-plating baking required for all steel parts?

No, it is specifically required for high-strength or highly stressed steel parts to prevent hydrogen embrittlement.

Why is chromate treatment applied after zinc plating?

To passivate the zinc surface, which significantly delays the onset of white rust and increases overall corrosion resistance.

IS 4994

: 1996

Electroplated Coatings of Zinc on Iron and Steel - Specification

CurrentSpecializedSpecificationMaterials Science · Aluminium and Non-Ferrous Metals

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This standard specifies the requirements for electroplated zinc coatings applied to iron and steel to provide protection against corrosion. It classifies coatings based on thickness and service conditions, and outlines necessary pre-treatments, post-treatments (like hydrogen embrittlement relief and chromate conversion), and testing procedures.

Specifies the requirements for electroplated zinc coatings on iron and steel articles for corrosion protection.

Quick Reference Values

mild service condition thickness5 microns (Fe/Zn 5)

moderate service condition thickness8 microns (Fe/Zn 8)

severe service condition thickness12 microns (Fe/Zn 12)

exceptionally severe condition thickness25 microns (Fe/Zn 25)

high tensile steel baking temp190°C to 220°C

Practical Notes

High-strength steel fasteners (tensile strength > 1000 MPa) must be baked to relieve hydrogen embrittlement shortly after plating to prevent brittle failure.

In salt spray tests, the appearance of white rust indicates the failure of the chromate passivation layer, whereas red rust indicates the failure of the underlying zinc coating and corrosion of the base steel.