Electroless Nickel Thickness Vs. Salt Fog Resistance
We are looking to plate steel parts with Mil-C-26074 [linked by editor to free spec at Defense Logistics Agency, dla.mil] 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 [link by ed. to spec at TechStreet] ) 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
There are a lot of factors that effect the corrosion resistance,but the factors that have the greatest effect are surface roughness and%P of 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.
Atotech - Rock Hill, South Carolina
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 PEN should result in about 1000 hours in SS but if you heat it , the resistance will be reduced to about 100 hours.
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