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Pitting in anodized aluminum

1" x 4" thick sulfuric dark grey anodized parts (waxed) in indoor environment are pitting slightly in one 3" x3" area only (out of approx. over 50' lineal ft.

No apparent chemical attack from the outside

Appears as slight pitting(less the .002 deep)whitish .

I believe it may be a form of sort of efflorescence in a porous section of alum and acids trapped during anodizing are working their way to surface?

If I wax it - spots momentarily disappear but soon reappear when dry.

I want know what it might be and what are some in situ repair ideas. Perhaps neutralize if acid and dye and seal with ?

Norm Stavin
- Amagansett, New York, United States
2004

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Please tell us the alloy, thickness of anodizing, and the kind of seal, and was the seal done under close control conditions. Also helpful would be to know the quantity in gm/L of dissolved aluminum in the sulfuric anodizing solution, temperature, current density. All of the above affect the pore size and the sealing reliability which leads to corrosion.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2004