Summary for blueish discoloration on hard anodized parts Discussion
Blueish discoloration on hard anodized parts was traced by the discussion toward contamination rather than the anodizing itself. Afiq Zainal said the parts were hard anodized to 35–45 µm with no sealing, and that the dryer sat near a spin-chip area with oil mist; Robert H Probert replied that oil mist was likely getting into the pores, especially in lower current-density areas where pores are larger. When Afiq reported the same bluish color on another anodizing line far from the spin-chip area, the follow-up answer said the defect was unlikely to be a normal hard-anodizing issue or an alloy problem, since it appeared recently and on two lines. The advice was to identify the alloy, then isolate whether the issue follows the material or the shop environment. The responder’s best guess was that the shop environment, not the alloy, was causing the discoloration.
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April 11, 2022
Q. Hello
I have issues with my hard anodized parts.
Thickness is between 35-45 µm.
No sealing is being used.
The hard anodizing dryer is located beside spin chip area where oil mist is around.
We are only having this problem recently. Can anyone help with this matter?
Afiq Zainal
– Johor Bharu Malaysia
A. Apparently the oil mist is getting into the pores, worse in the lower current density area where then pores are slightly larger.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
April 16, 2022
April 17, 2022
Thanks for the reply.
Q. We test run on another anodizing line.
Which is far away from the spin chip area.
But still we have the bluish colour.
Can suggest how to improve this visual defect?
Currently those cosmetic defects are accepted and released to end customer. Even washing on the parts could not eliminate the issue.
It can be wiped off with rubbing and IPA in the ID of the parts.
Afiq Zainal [returning]
– Johor Bharu Malaysia
A. Hi Afiq. I think Robert’s reply implied that a blue discoloration like this is not a known defect in hard anodizing. Therefore the chance that the alloy or something out of spec in the anodizing process, is the cause of the problem sounds extremely unlikely. On top of that, you didn’t have the problem until recently and it’s occurring on two distinct anodizing lines :-)
Please tell us the alloy and we can research whether there is anything special about it. But if you don’t accept that the problem is in the operating environment rather than the alloy or the anodizing process, the only way forward would be to get some material from a different supplier and see if the problem persists, and for the supplier to ship his material to a different shop and see if the problem persists there. The environment in your shop or that the parts are exposed to before they get to you is causing the problem, and my bet is your shop rather than before you receive the material. Best of luck!
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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April 2022