Summary for type ii anodizing defects Discussion
Type II aluminum anodizing defects are the focus here: Katie Brown reports spots, areas missing color, and ink-like stains on machined parts that are cleaned and dried before anodizing, while the vendor blames the aluminum. Robert H. Probert advises that the pattern of defects is too varied to be explained by base-metal issues alone and suggests sending parts to an alternate shop for comparison. He notes that the white spots and ink stains appear too regularly spaced to be random processing defects and look more like parts that were packaged while still wet. The thread does not identify a single confirmed root cause, but it points toward a process/handling problem at the anodizer rather than simply bad aluminum.
August 4, 2020
Q. I am having issues with my type 2 anodized pieces. They have spots, areas missing color, and even ink like looking spots. The vendor is only saying that is issues with the aluminum and offering no other solutions or insights. The parts are machined, cleaned, and dried before anodizing. I am not very knowledgable with the anodizing process so I was looking for some suggestions to solutions in helping with these re-occurring issues.
Katie Brown
– St. Louis Missouri
A. Apologies that this didn’t get posted in a timely fashion, Katie. Once in a while a posting gets lost for this reason or that.
I think the answer here is to send some parts to an alternate shop. Problems with the base metal do happen of course, but I don’t believe the quality of the aluminum is the basic problem here: too many problems, too varied :-(
The white spots and ink stains in the last picture are too regularly spaced to be a random processing defect; looks to me like they were packaged while wet.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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February 2021
A. Some of the pictures show the possibility that, after good anodizing, some floating soil got in the pores and prevented the dye from getting in. You can detect this with a 10X magnify, look to see if the extrusion line goes right thru the bare spot, and looks properly anodized. Generally, spoken a little stronger than Ted above, seems poor workmanship. Another possibility, you did not identify the alloy, if it is in the 7000s and heat treated, then zinc molecules have come to the surface, fallen out, and left bare aluminum.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
February 24, 2021