Electroless nickel plating coats parts with a nickel-phosphorus alloy by a chemical reaction in a hot bath, with no electric current. Because no current is used, the coating builds up evenly on faces, edges, holes and threads. It gives good corrosion and wear resistance and can be hardened further by baking, so it is used on moulds, valves, pump parts, hydraulic parts and precision components.
Quick facts
- Coating
- Nickel with about 2–13% phosphorus
- Typical thickness
- About 10–50 µm; more for salvage
- Thickness evenness
- Very even, including in bores and threads
- Hardness as plated
- About 450–600 HV
- After heat treatment
- Up to about 900–1,000 HV
- Usually priced
- Per part or per square decimetre, by thickness
Low, medium or high phosphorus?
| Type | Phosphorus | Best for |
|---|---|---|
| Low | About 2–5% | Highest hardness and wear resistance |
| Medium | About 6–9% | General purpose, bright finish |
| High | About 10–13% | Best corrosion resistance, non-magnetic as plated |
How it is done
- Parts are degreased, pickled and activated to suit the base metal
- They are dipped in the hot nickel bath, around 85–90 °C, for a time set by the thickness needed
- They are rinsed and dried
- Optional baking for hydrogen relief, adhesion or extra hardness
- Thickness is checked by gauge or on a test coupon
What to send
- Base material (steel, stainless, aluminium, copper alloy)
- Thickness and phosphorus type, or the standard (for example ASTM B733)
- Whether hardening by heat treatment is needed
- Faces or threads to mask
- Tolerance on finished sizes (the coating adds on every face)
- Quantity and how parts can be hung or loaded in baskets
Need electroless nickel plating done?
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Questions
- ENP or hard chrome?
- ENP coats evenly into holes and threads and resists corrosion better. Hard chrome is harder and better for heavy sliding wear on shafts and rods, but builds up unevenly.
- Can aluminium be electroless nickel plated?
- Yes, with a special zincate pre-treatment. ENP is common on aluminium parts that need a hard, wear-resistant or solderable surface.
- How much does ENP add to a size?
- The coating thickness on each face, so a 25 µm coat adds about 0.05 mm (0.0020 inch) to a diameter. Machine parts undersize to allow for it.
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 22 October 2026.