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How the Passivates Works?

Hello. Can Anybody explain me in which consist the chemical process of passivation. I'm looking for a method to improve the corrosion resistance of automotive suspension parts. I've thought about zinc plating. Ok. I understand how it works. But all the documentation that I've seen cited the passivates for improving the corrosion resistance. I only know that actually chrome particles are used but I don't know how it work. Any information will be very useful for me. THANK YOU.

ALFONSO BUSTOS GARCIA
- Valladolid SPAIN
2000

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Chromate conversion coatings passivate the zinc or zinc-alloy plating. It slows down the sacrificial corrosion of the plating so that the protection lasts longer. The conversion coating prevents white corrosion while the plating prevents red rust.

One major thing to point out, however, it that all current conversion coatings are based on hexavalent chromium. This material is about to be banned in the auto industry. I suggest you look at trivalent chrome conversion coatings instead.

Also, if zinc platings do not provide enough corrosion resistance, you might want to look at zinc-alloy platings like: zinc cobalt, zinc iron, and zinc nickel.

Tim Neveau
Rochester Hills, Michigan
2000

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Alfonso:

I am unsure of your question, but passivation is quite well explained in ASTM A967, with further clarification in the ASTM A380 document.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

2000