Summary for electroless nickel cracking Discussion
Electroless nickel plating cracking is discussed in the context of a swaging operation that locks a 316 stainless female threaded part onto a 1215 steel male threaded part plated with medium-phosphorus EN per MIL-C-26074. The questioner is seeing cracking and is trying to adjust thread engagement before folding the female edge over the male threads. Jeffrey Holmes notes that not all electroless nickel deposits behave the same: some are more corrosion resistant, some more ductile, and some harder as plated. He suggests trying a slightly thinner deposit because more thickness is not helping when crimping on threads. He also mentions a possible EN strike, which uses an alkaline bath, as an outside possibility. James Watts adds that sulfamate nickel would be softer, but it would not plate into thread valleys nearly as well as EN, reducing corrosion resistance, and he suggests experimenting with a soft Permatex-type dip if it could perform as well as the EN.
April 10, 2015
Q. I’m developing a product that uses a swaging operation to lock two threaded components relative to one another. We are adjusting the thread engagement, then folding over the edge of the female threaded component (316 S.S.) onto the male threaded component (1215 Steel Electroless Nickel Plated Medium Phosphorus MIL-C-26074
[⇦ this spec on DLA] 12-20 µ). Mechanically it’s working great! The problem arises when we do our corrosion testing. The swaging operation causes the thread peak of the male threaded component to deform. This deformation cracks the Nickel Plating, which creates a corrosion site. Is there a post baking process that can improve the adhesion and ductility of the nickel plating? Or, maybe nickel plating is not the best coating for this application?
Thanks!
Brett Nagel
Mechanical Engineer – Shelton, Connecticut, USA
A. 12L15 contains lead, so the pretreatment process needs to include a fluoboric acid step to get good adhesion. Most EN platers already know this, but you could check if yours does.
AFAIK there’s no heat treating process which will improve ductility of EN. In fact if temperatures are very high, the EN will get harder.
If possible, either a conventional Watts nickel bath or sulfamate bath can produce softer deposits than EN.
Jeffrey Holmes, CEF
Spartanburg, South Carolina
April 13, 2015
April 16, 2015
All ENs are not equal. Some are more corrosion resistant and some are more ductile and some are harder as plated.
You might try a bit less thickness to see if that would help. You are crimping on threads and more is not helping.
There is an outside possibility that you could get by with an EN strike (which is an alkaline bath vs. a normal acid one)
While a sulfamate nickel would be softer, it will not plate into the valley of the threads anywhere near as well as the EN, so less corrosion resistance.
I would experiment with a soft permatex type dip to see if it would work as well as the EN.
James Watts
– Navarre, Florida