Metal finishing Q&As since 1989

-----

Black Anodized Aluminum Parts Change Color

We are a manufacturer of high speed test equipment for the integrated circuit industry. Lately we have been having problems with black anodized aluminum parts turning color. Some parts will start to change color when they are assembled onto the equipment. They do not seem to change when they are in closed boxes in the stockroom. Some will turn a mottled rosy color, while other parts from the same batch do not. Areas exposed to light and air will turn color while areas of the same part protected by fasteners, etc. remain black and unaffected. Sometimes finger prints are discernible in the affected areas.

Our fabricator has been using the same anodizer for some time and parts they build for other companies in similar businesses have not had problems. Are there any ideas out there as to what the problem is? We currently have parts at a lab being analysed and our fab shop will be sending some new parts to a different anodizer to see if this solves the problem, but I am still interested in the mechanism involved here.

David Williams
- Beaverton, Oregon
2000

---

Pretty easy one to answer...have your anodizer check his seal bath..sounds shot, to me. The fingerprints you see are being caused by the perspiration on someones fingers getting into the anodic pores, and partially sealing them. The reason the parts fade when out of the box is the light causes poorly sealed parts to fade. Other suspects would be too thin of a coating, and perhaps a dye that has lousy lightfastness, though, most of the blacks have excellent lightfastness. Hope this helps. Marc Green anodizer - Boise, Idaho 2000 Fading, fingerprints, color changes. I associate all of those things with a poor seal after the dye. Fingerprints especially. What type of solution are they sealing the parts in ? Boiling water, nickel acetate, nickel fluoride, some other sealing method, maybe steam? Other than that right there, there isn't much else that can cause those problems that I have seen or had experience with. Maybe the material, but I highly highly doubt it. Matthew Stiltner - Toledo, Ohio 2000

---

As a supplement to the responses above, you should check with the lab that is performing the evaluation to see if they can verify that the coating was sealed and determine the effectiveness of the seal. Ideally, you should let them know what type of sealing was specified as suggested by Mr. Stiltner's response.

Larry Hanke
Minneapolis, Minnesota
2000

---

---

Having a similar problem with my center caps, check out photo below, any more input?

Fernando Sanchez
- Chino Hill, California
December 31, 2011