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Round White Spot after Anodising

May 6, 2010

Hi,

Recently, we discovered that after potassium dichromate seal, there is this little round spot, anodised, on the surface. There is no color tone in this round spot of ~0.4 inch dia. Our process as follow;

Alkaline clean
Rinse
Nitric acid dip
Rinse
Sulpho Chromic etch
2X rinse
sulfuric Acid Anodising
2X rinse
Potassium di-chromate seal @ 98 deg C
2X rinse
Air dry

Looking forward to your sharing

with Best Regards,

Jimmy Sim
plating shop employee - Singapore

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First of two simultaneous responses --

You did not say the alloy. If is is in the 5000 series the spot could be raw magnesium that did not "alloy". If the metal is an extrusion or has been "cold drawn" then this white spot is probably elongated "round". Come on back with some more information and let's give it a guess.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

May 10, 2010

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Second of two simultaneous responses --

To answer your query, we would atleast like to know what you are anodizing. A picture would speak a 1000 words and maybe someone here could definitely help you spot the problem.

Winston D'Souza
- Bombay, India
May 11, 2010

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My apology, the material is Al 6061 (I did try to upload the pic but it failed).

Jimmy Sim
- Singapore
May 17, 2010

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Ed. note: just attach the picture in email to mooney@finishing.com, Jimmy.