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Electroless nickel plating on cast iron parts

Q. Dear Sirs,

My name is George Ivanov and I'm heat treatment and coating technologist in company in Bulgaria. Our company manufactures hydraulic motors and steering units - www.ms-hydraulic.com . I suggest to my managers to put electroless nickel plating 20-25 microns onto our hydraulic motors.
After coating we carried out Salt Spray test (NSS - 400 hours) and the results were not so good. I have found that all steel and cast iron parts, which were machined (by turning or milling, they were perfect (without any corrosion). But the cast surfaces, which are not machined were coated with corrosion. Nickel plating coating is very uniform and without any cracks and defects.

That is my problem and I ask you to advise me :
1. How I can coat non-machined cast surfaces with nickel for corrosion protection ?
2. What do I have to do before coating to improve corrosion resistance of the nickel coating ?

George Ivanov
engineer - Kazanlak, Bulgaria
January 29, 2010

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February 2, 2010 On the cast surface, which is not machined, there is no rust or oxides, it seems to be sand blasted after casting process, but I will try sand blasting or shot peening again. About lubricants and cooling liquids during machining we have been using semi-synthetic liquids - Houghton products and after machining we clean these parts by alkaline solution in spraying washing machines and before assembling we have manganese phosphating process. I find out that maybe roughness of casting non-machined surfaces seems to be most important reason for this problem. Because where roughness is very high, there is rust on the nickel layer. I red in some articles that the roughness influences in opposite way, compared with painting process, where the adhesion is much better when the roughness is higher. George Ivanov - Kazanlak, Bulgaria George, Some basic questions first: What phosphorus content is in your Electroless nickel (low, e.g. 5% and below, medium, e.g. between 5 and 10% or high, e.g. 10-14%) What are your cleaning stages prior to plating? What does the salt spray failure look like (discreet failure points or a general covering of corrosion products)? My first thought is that your thickness of nickel is not sufficient to withstand 400 hours of salt spray. I would suggest a minimum thickness of 0.002" (50 microns) of high phosphorus nickel. Brian Terry Aerospace - Yeovil, Somerset, UK February 2, 2010

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February 16, 2010

Q. Dear Brian,

Sorry for this late answer, but I was in holiday last weeks.
About your questions:
1. We use middle phosphorus(5%)nickel plating process
2. prior stage of plating is alkaline degreasing by immersing - temperature 60°C
3. The rust looks like as many spots and small lines, there is no full surface coverage on the cast part. It mean that the rusted surface is about 15%.
Thank you for your advice, but we make this process in other company I have to ask this company to implement your suggestion.
If they couldn't make this process what is your advice ?

George Ivanov [returning]
- Kazanak, Bulgaria

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Q. I'm a student and I want to know some details for doing my project:
1. Does electroless nickel plating on cast iron have good corrosion resistance and heat withstanding properties?
2. If it is suitable, what's the composition of product?
3. Is electroless nickel plating powder enough for coating?
4. Which material composition is best for coating 20 cm dia cast iron
5. Or what coating Will best suit for cast iron?

Yogesh waran
- Chennai, tamilnadu, India
February 9, 2017