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Letter 16049
Zinc vs Electroless Nickel for steel leaf
spring - breakage
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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, Massachusetts
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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.
June 11, 2009
Is it a good idea to zinc plate leaf springs? I have heard it is
not a good idea because of hydrogen embrittlment. The springs are
going on a salt water boat trailer and I was planning on zinc plating
them then doing a two stage powder coat on top.
Brady Cherry
hobbyist - Newport Beach, CA, USA
July , 2009
Hi, Brady. I would clean them and then spray them with
Cold Galvanizing Compound / Zinc Rich Paint [link is to product info]. You would probably have to search for a zinc plater to do them since most would probably be unwilling to because the springs can break in the plating tank before they even get a chance to bake out the hydrogen.
Regards,
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Ted Mooney, P.E.
finishing.com
Brick, New Jersey
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