The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Re-heat treatment of zinc-plated parts

Does anyone have any insight into the potential ramifications of heat treating parts that are already zinc-plated? I have a situation where several thousand flat springs were found to be too soft, due to a problem with my vendor's heat treater...his solution is to simply send them back to him to be properly heat treated...but I am concerned because the parts are already plated.

Am I concerned for no reason? If not, what steps should be taken to do this correctly? Thanks in advance!

Scott Dupre
Lighting Manufacturer - Fall River, Massachusetts
2005

---

Zinc plating is cheap and not a big deal. Strip the plating, heat treat them, and replate them may be the best solution (although it is possible to ruin parts from repeatedly stripping followed by consequent over-pickling). I don't know what temperature and time you will need to restore the hardness, but virtually all zinc plated parts are chromated, and heat treat temperatures will usually destroy the chromate, I believe.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005

---

Good afternoon:
If you have a carbon steel spring that is too soft, the only way to make it harder by means of heat treating is to re-austenitize it. That involves temperatures over 1500F. The melting point of zinc is less than 800F. Bottom line: strip zinc plate before re-heat treating.

Steve Bizub
- St Louis, Missouri
2005

Thanks for the responses...out of curiousity, what could potentially happen as a result of heat treating the parts without stripping the zinc? Any thoughts? Thanks,

Scott Dupre
Lighting - Fall River, Massachusetts
2005

---

2005

First, you are going to have areas with no zinc and areas with thin zinc and worst of all is droplets of zinc at some of the edges. The metal will also oxidize differently making it a problem for reactivation.
I suspect that you will have a thin layer of zinc alloy in the steel surface.
Finally, you are going to have an ugly unworkable mess with squat for corrosion protection.

James Watts
- Navarre, Florida