Electroless Nickel Plating (ENP)
Electroless nickel plating (ENP) chemically deposits a nickel-phosphorus alloy at a perfectly even thickness over every surface, including bores, threads and internal passages. It gives hard, wear- and corrosion-resistant coatings on steel, aluminium and copper alloys.
What it is
Unlike electroplating, ENP uses no electric current. A reducing agent in the bath deposits nickel-phosphorus wherever the solution touches the part, so thickness is uniform, typically within about ±10%, even on complex shapes.
The phosphorus content changes the properties. Low phosphorus (1–5%) is hardest; medium phosphorus (6–9%) is the general-purpose choice; high phosphorus (10–13%) gives the best corrosion resistance and is non-magnetic. Heat treatment after plating can raise hardness considerably.
Typical applications
- Hydraulic and pneumatic valve bodies, spools and manifolds
- Pump components, shafts and impellers
- Moulds and dies needing wear resistance and easy release
- Precision parts with bores or threads that must be coated evenly
- Aluminium parts that need a hard, solderable surface
Suitable materials
- Carbon and alloy steels
- Aluminium alloys
- Copper, brass and bronze
- Stainless steel
- Cast iron (with care)
Points to consider
- Because thickness is uniform, machining can allow for it precisely; state the finished size before or after plating.
- High-phosphorus ENP is preferred for corrosion resistance; low or medium phosphorus with heat treatment for maximum hardness.
- Heat treatment for hardness (around 400 °C) is not suitable for parts that would lose their own temper or hardness at that temperature.
- Surface roughness is reproduced, not hidden, so finish the part to the final Ra before plating.
Frequently asked questions
Why choose ENP over normal nickel plating?
ENP coats bores, threads and recesses at the same thickness as outer surfaces and is harder. Electrolytic nickel is cheaper but builds up unevenly on complex parts.
Does ENP work on aluminium?
Yes. Aluminium is given a zincate pre-treatment first, after which ENP adheres well and gives a hard, wear-resistant, solderable surface.
How hard is electroless nickel?
Typically around 500–600 HV as plated. Heat treating at about 400 °C can raise it to roughly 900–1,000 HV, close to hard chrome.