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"Black Spots" after de-smutting, prior to anodizing

December 10, 2009

What would cause Black Spots during the de-smutting prior to anodizing?

Process and material specifics
- Material AMS4031(2219 alloy)
- Parts are resistance welded
- Anodizing is done per AMS2470 REV M

Black spots only occur in the weld zone.

Is this common for this type of material?

I've been told it is, but these are unacceptable to my customer.

Is there a fix for this, besides mechanically removing them by grinding?
In most instances these spots can be removed by grinding, but the parts then violate customer requirements because the welds have been ground thin.

Thanks
Scott

Scott Haenel
MFG Engineer - Ohio

You anodize only aluminum. 2027 is about 8% non-aluminum. What is in the welding rod? What are you using for a deoxidizer?

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

December 10, 2009

These parts are resistance welded, no filler.

I'll have to investigate the entire plating process and find out what processes are being used.

Scott Haenel
- Ohio
December 14, 2009

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