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Metal finishing Q&As since 1989

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Clear chromate on Aluminum shows brown staining over time

We have been building some Aluminum metal frames for the past few months which are being rejected at our customer facility due to brown staining. Is this a normal reaction with Age? Is my plater not following the right plating process? Any suggestions?

Eran Lazarovich
Commodity Manager - Markham, Ontario
September 17, 2009

First of two simultaneous responses --

Not much information, so here is a wild guess. Your chem film applicator is staying in the tank for a longer period of time so he can always pass the salt spray test, which gives a darker color. For some reason, they are not rinsing adequately and spots of chem film remain on the part causing a very long reaction time which will give brown spotted parts.
Could be wrong and it would not be the first time.

James Watts
- Navarre, Florida
September 21, 2009

Second of two simultaneous responses --

Please give us more information. Is the application outdoor or indoor? Has the metal been blasted with media that has also been used on iron? Alloy?

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

September 21, 2009

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