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topic 32735

Yellow residue after etching aluminum


My question is what might be the yellowish residue on aluminium parts that have been paint stripped (plastic media), then etched. Is the residue paint or anodize, organic or chemical.

Sonaca nmf Canada - ST-JANVIER, Quebec, CANADA


My first guess would be a chromate conversion coating, but that's only a guess and it assumes that the parts were chromate conversion coated in the first place. The part should have a processing history associated with it.

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey
Striving to live "Aloha"


My nickel bet is a zinc chromate primer.

James Watts
- Navarre, Florida


Interesting!, first I must say the paint is a fuel tank coating (organic) and which happens to be a bright yellow, then its mechanically stripped down to its original anodized finish(chromate seal), visually the part is beautiful, but once etched ,irregular yellow fadded stains appear. could it be paint residue or chemical?

Hope this helps!

Terrence Double
- Canada


Then it is very probably chromate that was trapped in the pores during the seal process. Tatchy because all of the pores re not exactly the same size and do not have to seal at the same rate.

James Watts
- Navarre, Florida

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