Moat Pitting after Bright Dip of aluminum extrusion 1

[Colordude]

I know that there have been studies performed in the past concerning this topic and I would like to be able to gather some information concerning it. MOAT PITS

We have a customer that, we believe, is using the wrong type of coolant/lubricant on there cutoff saw operation which, at times, causes us to problems in the anodizing process. The phenomena is Castle and Moat Pitting.

Does anybody have any links to information on the formation of these pits? I would greatly appreciate any help provided.

 

[kenvlach]

A lubricant/cutting problem would be restricted to the surface & a very shallow depth. Take a part with the symptoms, photograph, mechanically polish, then reprocess. If the symptoms reappear, especially if in the same places, it is a material defect running through the material. Photos are very useful when talking to suppliers.

"Sounds like castle & moat pitting. It could be in the billet, but more likely in extrusion. It is a defect of metal homogenization and secondarily of cooling. Alloy metals precipitate differently in different portions of the extrusion leaving insoluble intrusion (castle) and easily dissolved aluminum around it (moat.)"

http://www.anodizing.org/

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