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Electroless nickel is rusting in threaded area

we are doing high phos EN plating of 10 to 15 microns on threaded parts. the base material is steel (b7m/l7m). but we are getting rusting on thread portion. can anybody suggest solution for the problem.

Ajit G
manager - Hubli, Karnataka, India
April 7, 2009

ENP is not a sacrificial coating which means that if it is not absolutely pore-free it will not stop oxidation. Surface imperfections, burrs, crevices and rough machining always need a heavier coating than smooth surfaces to be entirely coated. Further on, these imperfections act as ideal sites to trap chemical residues, rinses and humidity which means corrosion.

Guillermo Marrufo
Monterrey, NL, Mexico
April 12, 2009

can anybody suggest suitable method nickel coating on studs & nuts? presently we are doing high phos nickel of 10 to 15 microns which is getting rusted.

Ajit V Godakhindi
- Hubli, Karnataka, India
April 15, 2009

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First of two simultaneous responses --

Ajit,

Your problem is not the nickel itself, but more likely the thickness of coating you are applying. As a minimum for corrosion resistance you should be applying 25 microns, even of high phos. If you want thinner coatings you will need to look at alternative technologies.

Brian Terry
Aerospace - Yeovil, Somerset, UK
April 16, 2009

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Second of two simultaneous responses -- April 16, 2009

Hi Ajith,

In my opinion we should not suspect on the coating immediately, suspect on the control as Mr.Guillermo Marrufo
rightly says. Observe your pre-treatment, judge whether the chemical /method feasible for that. Check for your rinsing, water quality, proper activation etc...

Is it rusting at the storage? Is it immediate? Or is it after usage (after threading?)

All the best.

Keshava Prasad M
- Chennai, Tamil nadu, India