Summary for electroless nickel thickness Discussion
Electroless nickel thickness vs. salt fog resistance is discussed in the context of plating steel parts to MIL-C-26074. The question asks how thickness affects salt spray performance. In the answer, George Shahin notes that surface roughness and phosphorus content strongly affect salt-spray resistance. Sara Michaeli adds that post-plating heating, while used to improve hardness, can sharply reduce corrosion resistance. She gives an example: about 25 microns of high-phosphorus electroless nickel may yield roughly 1000 hours in salt spray, but after heat treatment the resistance may drop to around 100 hours. The thread’s practical takeaway is that thickness alone does not determine performance; deposit chemistry, surface condition, and heat treatment all matter, and heat can significantly hurt corrosion resistance even when hardness improves.
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Q. We are looking to plate steel parts with
MIL-C-26074
[⇦ this spec on DLA] electroless nickel. Since the parts are steel, it is recommended that the Grade Coating be applied (0.0015-inch thick). We can only go up to 0.0008 inch, max. due to insertion requirements for the finished product. The question is: What kind of salt fog ( ASTM B117 ) resistance can we expect to get from coating a steel part with 0.0008-inch of electroless nickel? Can we achieve 48-hours? 200-hours? What about for 0.0005-inch (Grade B)?
Are there graphs available plotting electroless nickel plating thickness versus salt fog resistance (hours)? Thanks for your help.
Marc Pepi
US Army Research Lab – APG, Maryland, USA
2000
A. There are a lot of factors that effect the corrosion resistance, but the factors that have the greatest effect are surface roughness and %P in the EN. The lower the surface roughness the better the corrosion resistance. Also the higher the %P the better the corrosion resistance.
You should be able to get 48 hrs of salt spray from a high P EN deposit.
George Shahin
Atotech – Rock Hill, South Carolina
A. George is right, roughness, P content have a great effect on SS resistance but on top of that, heating which is done to improve hardness has also a great effect. For instance, 25 microns of high P EN should result in about 1000 hours in SS but if you heat it , the resistance will be reduced to about 100 hours.
Sara Michaeli
Tel-Aviv-Yafo, Israel