Pitting After Anodizing

Question:

We have a customer who is continuously sending us parts made from 7075-T6 that are pitted when we receive them. The customer asked us to anodize them anyway. We anodized them but, as expected, the pits left bare spots on the anodize surface. We stripped the parts, extended the time in the deoxidation tank, and reprocessed the parts. We were able to anodize approximately 75% with no bare spots but still lost about 25%. The customer refuses to believe that we cannot successfully anodize the pits. He is still sending us pitted parts, and although we have modified our process to include a longer deoxidation time, we are still having problems with failures. Do you have any documentation on anodizing a pitted surface that I could use either to better our process or help the customer understand the difficulty of his request? R.D.

Answer:

Do you know what caused the pitting in the first place?  I don’t know of a situation where the anodizing would cover up the pit, or even anodize it.  If your customer doesn’t want pits then they must mechanically remove them prior to sending the parts to you for anodizing.  You know the expression, “Garbage in, garbage out”. You can’t make good parts out of bad by anodizing them. Etching and anodizing a part can sometimes give the effect of hiding some scratches, scrapes, and perhaps “pits”, but anodizing does not actually remove surface defects..