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Letter 16049
Zinc vs Electroless Nickel for steel leaf
spring - breakage [Massachusetts]
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We are considering switching from a zinc plating to electroless
nickel for a leaf spring clip, .020" thick 1050 steel. In the past we
have seen cracking/breakage when the spring was press fit into a
housing. Our tests to date showed that nickel-plated parts show no
cracking during assembly, whereas the zinc plated parts cracked.
Hydrogen embrittlement was not found in any parts we tested, but we
can't rule it out as a potential problem. Furthermore, both the zinc
and nickel plating specs call for an embrittlement bakeout. Is there
any theoretical advantage to using a nickel plating over zinc for
this application??? Corrosion is not a significant factor to us in
our decision, but consistent as-plated appearance is important.
Mark Mozgowiec
- Cambridge, MA, USA
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Electroplated nickel is more ductile than electroless nickel.
Ductility may be a factor. I believe that hydrogen embrittlement is
the major cause of cracking. Zinc plating imparts a large amount of
hydrogen, and if not entirely removed in the baking cycle can and
does cause cracking. Electroplated nickel also produces some
hydrogen, but way less than zinc. Electroless nickel likewise
produces hydrogen. Electroless nickel requires a much longer bake
cycle with slow temperature ramping up to the final bake temperature.
The reason is that there are no grain boundaries for hydrogen to
follow. I recommend a longer higher bake temperature for the zinc
plated clips. If you choose to use nickel be aware of the baking
requirements. Each finish should be satisfactory. Costs zinc is the
lowest, then Electroplated nickel followed by EN.
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