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topic 6867

Rust formation on plated parts


Q. We manufacture speakers, and the outer frames & metal parts are zinc plated & passivated with yellow passivation.

What happens is after storing for a period of one to six months we find formation of rust. Plating thickness is 5 micron. Can any one suggest why this is happening and how we can prevent rust?

Ravi Janardanan
- Chennai, tamilNadu, India


A. Two quick possibilities, Mr. Janadanan:

1. Plating shops are very corrosive atmospheres, being extremely humid as they are, and with so much acid mist (designed to strip zinc) about. If you are storing the parts in a plating shop, I'm not surprised that they are rusting.

2. The parts have to be dry . . . absolutely dry, or they will rust in storage.

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


A. Aside from the "rust happens" truism, the plating thickness could be increased to give somewhat longer protection. Ten microns would be o.k.

Megan Pellenz
- Syracuse, New York

September 15, 2013

Q. How rust is formed on plated components, i.e., parts plated with zinc nickel trivalent black passivation

V.Swamy Nathan
- Chennai, Tamil nadu, South India

September 17, 2013

A. Hi Swamy. I think we'd need a paragraph or two of details to be able to address your question. Short of that, Megan's "Rust happens" is applicable, i.e., there is rustable steel underneath the zinc-nickel plating.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

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