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topic 5417

What Does "Chromated" Mean?


(2000)

Q. What is Chromated? is there any difference between chromated and chromium plated? if so what is the difference? I want to include it my Project

Sheshagiri.K
Student - Bangalore, Karnataka, India


(2000)

A. Chromium plated means electroplated with chrome, such that the chrome is in metallic form. Chromated means treated with a solution of chromate, usually hexavalent (valence +6), as a corrosion-fighting passivation layer--usually applied to zinc and cadmium plated parts, or to aluminum. Chromium plating is usually bright and metallic, hard, low friction. Chromate coatings are a very thin gel.

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


July 23, 2008

Q. Chromate conversion coating to aluminium furniture
what is the advantage to applying before powder coat

What protection does it give.

Robert Lucas
- Hialeah Florida


July 25, 2008

A. Hi, Robert. Chromate (or a trivalent or chromate-free) conversion coating is essential. It is actually a several step process (cleaning, etching, desmutting, chromating) that leaves the surface of the aluminum properly prepared to accept paint; and the chromate is also important to keep corrosion from blooming and spreading in the event of a pinhole or scratch in the powder coating. Aluminum is a very active metal that oxidizes instantly; this oxidation layer is inconsistent in thickness & composition, and without a conversion coating the powder coating will be adhering to this rather than to aluminum.

Regards,

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


March 11, 2013

Q. Hi Ted,

Does chromating help with corrosion resistance before electroplating on high pressure die cast aluminium? Is this possible?

Many thanks,
Mike

Mike Durante
- Manly, NSW, Australia


March 11, 2013

A. Hi Mike. The answer to your question is no. Aluminum is never chromated before electroplating. Rather, aluminum is almost always zincated before electroplating. But I have to wonder if maybe the nomenclature is a bit off, and that's why you are confused on this?

Electroplating involves the electrodeposition of metals. There is a somewhat analogous process called electrocoating which involves the electrodeposition of organics (paints) . . . and chromating the aluminum before electrocoating is a conventional and very good practice.

Regards,

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


March 14, 2013

thumbs up signHi Ted, Thanks for clearing that up. Mike

Mike James
- Sydney, Australia



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