Pitting in bright silver anodizing

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I am inquiring about bright silver anodizing on aluminum extrusions
We have had problems with bad pitting on the aluminum, we bring the metal in from china and have had that blamed but when we push the anodizer it gets done properly.
can you tell me why this happens.

Jeffrey James Stokes
aluminum partition systems - Sydney, NSW Australia

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Suspect chloride contamination in the line. Look for it in the deox, anodizing solution, and seal. IF the parts are racked on titanium and the seal tank is stainless steel, the galvanic current aggravates pitting, then in the presence the chloride pitting will be worse.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

Editor's note:
   Mr. Probert is the
   author of Aluminum How-To / Aluminio El Como