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Seeing surface residue on Black Anodize finish after Autoclaving (a Mega Steambath)


Q. I am observing a dark "smokey looking" surface film forming over my black anodized (Type II, Class 2) 6061-T6 machined aluminum parts. The film forms after I run the parts through an AutoClave cycle. Autoclaving is a Steam/Pressure sterilization process commonly used in hospitals. The autoclave uses DI water. If I repeat a process of scrubbing the film off with Alcohol and autoclaving again, the film stops forming after the 3rd or 4th cycle. The parts look great and are spot free every time afterwards... I have sent before and after photos for review.


before before


after after after

Help! Time is money and we're not cheap ;-) Can anyone help me identify this film and recommend any process steps our plater can use to prevent filming after autoclaving? Autoclaves produce; 134 °C heated steam at 34 psi for 30 minutes.

I have tried using just Hot water sealed and Nickel/Hot water sealed processes with no success.

Joe Gruber
electrosurgical products - O'Fallon, Missouri, USA

simultaneous replies

First of two simultaneous responses -- 2006

I believe what you are seeing is seal-smut. Autoclaving will actually continue the sealing process that was not totally completed when the parts were anodized. Once the parts are completely sealed, the smut will cease to develop. This is probably not your coaters fault, as it can be difficult to get a "completely sealed" part through normal anodizing procedures.

The company I work for provided steam sealing (in an autoclave) as an option for the parts we manufacture that needed very good corrosion resistance. It's not a common practice in the USA, but is common, or was, in Japan.

Marc Green
Marc Green
anodizer - Boise, Idaho

Second of two simultaneous responses -- 2006

Joe, a wild guess. Some of the chemical plus dye stuff is still in the pores when sealed. Then the higher temp of the autoclave is forcing it to come out. Eventually, you are flushing it out.
Why not try hard anodize. The pores are a lot smaller. It would be a dark gray, but my guess is that it would be better looking than your after pictures. Try a half thou and a thou to see which one works best. No dye and no seal.
Your first run on the autoclave should seal it (which will slightly soften it)

James Watts
- Navarre, Florida



We currently hard black anodize parts that go through the autoclave cycle without your problem. I would suspect the sealing process.

Have you always experienced this problem? Is something 'new' in the process? Have you tried another supplier as a verification?

Willie Alexander
- Colorado Springs

Q. We are Medical devices Manufacturer. From our in-house manufacturing, I was able to do anodizing of Aluminium made Ster-lization boxes and instruments and also colored. Can someone guide me how to make colored (DIY) instruments autoclavable? I mean any surface treatment which I did in boiling water, or if any other suggestion would appreciate from seniors and Experts.

Rehan Mughal
Manufacturer - Pakistan
September 6, 2018

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