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"Round White Spot after Anodising"
May 6, 2010
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;
Nitric acid dip
Sulpho Chromic etch
Sulphuric Acid Anodising
Potassium di-chromate seal @ 98 deg C
Looking forward to your sharing
with Best Regards,
plating shop employee - Singapore
First of two simultaneous responses -- May 10, 2010
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
Second of two simultaneous responses -- May 11, 2010
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 17, 2010
My apology, the material is Al 6061 (I did try to upload the pic but it failed).Jimmy Sim
Ed. note: just attach the picture in email to email@example.com, Jimmy.