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-----Black spots on aluminum from anodizing
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Q. Dear sir,
We are facing problems after Anodising: some black pits & patches, but they're not there before anodising. Please help me sir.
Employee - Chennai Tamil nadu
April 6, 2022
A. Hi Karthik!
Readers have already suggested possible porosity, poor quality castings, poor cleaning, and lack of proper de-oxidizer/desmutter as the most likely causes ... but without pictures, or a listing of your process steps, or knowing the alloy and type of parts, there probably isn't much more to say :-(
Please send pics to [email protected] along with alloy and part type, and treatment sequence. Thanks!
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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April 2022
April 11, 2022
Q. Dear sir,
Thanks for your reply.
We are Facing the problem for black pits found only in particular area in vision camera & boroscope inspection.
Before Anodising the part is visually inspected through cutting section & penetrant test part will be OK
But After Anodising we face that problem in particular area
Regards
Employee - Chennai Tamil nadu
⇩ Similar, related, Q&As -- oldest first ⇩
2007
Q. We do AC2A and we are doing anodizing after machining.
Anodizing process:
Temp 8 °C
sulfuric acid :150 g/litre
Precleaning : non alkaline degreasing agent
Current density 1.5A/dm2
Using distilled water with pH 6.5 ~ 7.5
TDS <30 PPM
We face a peculiar problem of black spots after anodizing on our brake parts.
Why is this happening and what could be the countermeasures?
- Chennai, Tamilnadu, India
|
A. Guess #1 is a porous and poor quality casting. - Navarre, Florida 2007
A. Does the spot happen on any parts you do or just only happen on a certain part? - Singapore 2007 |
A. Degreasing alone as pretreatment for anodize is totally inadequate. All aluminum alloys have a natural occurring oxide layer on them that must be removed prior to building a fresh, dense aluminum oxide (i.e. anodize) layer. These are typically acid mixtures such as nitric / bifluoride or chromic / sulfuric. Without one of these etches, deoxidizers, and / or desmutters, you'll get a patchy, non-uniform, spotted anodize!
Milt Stevenson, Jr.
Plating shop technical manager - Syracuse, New York
2007
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