The authoritative public forum
  for Metal Finishing since 1989
-----

Need mirror polish and corrosion resistance on 316

August 3, 2008

Hello,
I have an application where I am looking for both a mirror finish and corrosion resistance in a salt air environment. The part is a decorative bezel on an LED light mounted on the deck of a pleasure boat. The parts are machined from 316 SS. I polished them mechanically, then had them electropolished, but the finish is not good enough cosmetically. The customer wants a mirror polished surface. I buffed them post EP, but my understanding is that the electropolish is now gone... BUT, I have also been lead to believe that a mirror polish in itself will aid in fighting corrosion...
So my question: Are there any post polish processes that will aid corrosion resistance but won't knock the mirror finish off? This is a larger boat and regular maintenance (within reason) to polish these is not out of the question...
Thank you in advance for your help....

David Venhaus
Small biz owner - Wauwatosa, WisconsinI

---

Buffing followed by polish should produce a near mirror finish along with excellent passivation. I'd suggest you work with your electropolisher, or another electropolisher, to see what can be done. The parts may have been EP'd too long, or other factors, bath chemistry, temp, CD may not be optimum for brightness. Buffing followed by straight nitric acid passivation should work too. Jeffrey Holmes, CEF Spartanburg, South Carolina August 6, 2008 Humid and salty air is very aggressive, but a good copper+nickel+chrome multiple layer such as the one used for OEM car bumpers will last a good while without maintenance beyond washing it regularly. Its brightness will also be unbeatable. Guillermo Marrufo Monterrey, NL, Mexico August 6, 2008

---

Following up your polishing (either mechanical or EP) with passivation will increase your corrosion resistance. If you use citric acid passivation you won't have to worry about accidentally ruining the surface finish. Let us know if we can help.

Ray Kremer
Stellar Solutions, Inc.

McHenry, Illinois

August 26, 2008