What is the difference between zinc plating and galvanising?

Zinc plating is a thin electroplated layer (about 5–12 µm); hot-dip galvanising dips the part in molten zinc for a much thicker coat (often 50 µm or more) for outdoor steel.

What is yellow zinc plating?

Zinc plating with a yellow passivation coat, which adds corrosion resistance. Today trivalent passivations are used instead of the older hexavalent ones.

Why do hardened bolts need baking after zinc plating?

Plating can put hydrogen into high-strength steel and make it brittle; baking soon after plating drives the hydrogen out.

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Zinc plating

Also called: zinc electroplating, galvanising (electro), zinc plating job work, yellow zinc, blue zinc, trivalent passivation

Zinc plating deposits a thin layer of zinc on steel parts by electroplating, followed by a passivation coat. It protects fasteners, brackets and small parts from rust at low cost; the zinc corrodes first, protecting the steel underneath.

Quick facts

Method: Electroplating in rack or barrel lines
Typical thickness: About 5–12 µm (8 µm is common for fasteners)
Passivation colours: Clear / blue, yellow, black (trivalent today)
Corrosion test: Salt-spray hours depend on thickness and passivation
Works on: Steel and iron parts
Usually priced: Per kg (barrel) or per piece (rack)

Points to know

Electroplated zinc is much thinner than hot-dip galvanising: good for small parts indoors or mildly outdoors
High-strength steel parts (above about 32 HRC) can suffer hydrogen embrittlement: ask for baking after plating
Threads gain thickness: allow for it on tight fits
Zinc-nickel plating gives much better corrosion resistance for automotive parts

What to tell the shop

Thickness and passivation colour
Salt-spray hours required, if any
Hardness of the parts (for embrittlement baking)
Areas to mask
Quantity and part size (barrel or rack)

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Questions

What is the difference between zinc plating and galvanising?: Zinc plating is a thin electroplated layer (about 5–12 µm); hot-dip galvanising dips the part in molten zinc for a much thicker coat (often 50 µm or more) for outdoor steel.
What is yellow zinc plating?: Zinc plating with a yellow passivation coat, which adds corrosion resistance. Today trivalent passivations are used instead of the older hexavalent ones.
Why do hardened bolts need baking after zinc plating?: Plating can put hydrogen into high-strength steel and make it brittle; baking soon after plating drives the hydrogen out.

The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 8 October 2026.