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topic 32179

Brown stain on aluminum alloy surface


Currently, our process line found a lot of brown stain on the surface of Aluminium alloy parts. The brown stain presented on Al alloy after cleaning and drying process. The parts are cleaned using detergent ADS902, then rinse by a lot of DI water. Finally, vacuum drying it at temperature 80-85C. The brown stain look like burn mark if visual check by naked eye. When analyst by SEM/EDX, the testing result shown that it's only contain Carbon and oxigen element. I would like to know is it the parts burn with carbon when the parts presented water in high temperature.

Thank you

Tan Christine
bearing catridge part - Balakong , Selangor, Malaysia


Because the part is not clean. A puddle of water can contain enough contaminate to cause the problem. A combination of spray rinses with immersion rinses can get a far better rinse than flowing thousands of gallons of DI water in one or two tanks. Take a look at Ted Mooney's article in the Metal Finishing Guidebook--The art and science of rinsing. Also try incorperating a blow off step prior to the drying step. Less retained water = less stain.

James Watts
- Navarre, Florida

First of two simultaneous responses -- 2004

I have encounterd this problems before. Try doing a small testing by using city water (JBA water) instead of DI water. Dry it at the same temperature. Inspect that any brown "burnmark" leave.

YC Chan
- Petaling Jaya, Malaysia

Second of two simultaneous responses -- 2004

Apparently the surfactant from the cleaning detergent is not coming off and when you bake it the organic ingredients break down into carbonacious compounds varing from brown to black, blacker with higher temperature.

To avoid this neutralize the remaining detergent by going through a deoxidizer and then more rinsing as Mr Watts said.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como
and co-author of The Sulfamate Nickel How-To Guide

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