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Materials & Assembly

Aluminum Aerospace Coating May Replace Toxic Chromates

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Charles Murray
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Cost?
Charles Murray   11/15/2012 6:00:35 PM
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Ann, any idea how this coating would compare, cost-wise?

Rob Spiegel
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Nice development
Rob Spiegel   11/15/2012 8:08:54 PM
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Good story, Ann. It's good to see an environmentally friendly substance to replace the toxic coating. I also liked the "cool video."

TJ McDermott
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6061?
TJ McDermott   11/16/2012 10:50:18 AM
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Ann, you noted 7000 series and 2024 series specifically.  Will this process work for all aluminum alloys?

Dave Palmer
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Non-chromate coatings
Dave Palmer   11/16/2012 11:18:33 AM
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@Ann: Thanks for a good article on a timely topic.  It would be interesting to see polarization curves and salt spray testing results for the molybdate coatings.

There is a wide variety of non-chromate conversion coatings, including permanganates, zirconates, titanates, cerates, and others.  There are also conversion coatings based on trivalent chromium.  Some of these have been around for many years, while others are newer.  However, to the best of my knowledge, none of them provide corrosion resistance that is quite as good as that of hexavalent chromate.

Electrodeposited coatings can meet or exceed the performance of chromate, but it is challenging to coat internal passages with electrodeposited coatings, and they don't have the self-healing characteristics of conversion coatings.

The U.S. military has a great on-line database with information about alternatives to chromate conversion coatings.

Ann R. Thryft
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Re: Cost?
Ann R. Thryft   11/16/2012 11:41:33 AM
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Chuck, I wish we could get more cost info on some of these new technologies. As usual, not much is known yet until it's in use in industrial quantities. OTOH, the fact that it's non-toxic may be worth a cost differential.

Dave Palmer
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Re: 6061?
Dave Palmer   11/16/2012 1:53:35 PM
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@TJ McDermott: The same thing that makes 7075 and 2024 so much stronger than other aluminum alloys also makes them less resistant to corrosion: copper.  The copper-containing intermetallic particles that are responsible for these alloys' high strength create tiny galvanic cells within the material itself.

In general, if you can protect 7075 and 2024 against corrosion, 6061 will be easy.

Ann R. Thryft
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Re: 6061?
Ann R. Thryft   11/16/2012 3:29:57 PM
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TJ, I mentioned those specific alloys because the sources did, as the coating was developed specifically for mil/aero applications. But they also stated that this coating works on "all aluminum products." That sounds like all aluminum alloys.

Scott Orlosky
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Re: Cost?
Scott Orlosky   11/18/2012 7:07:46 PM
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Good discussions.  Non-toxic alternatives to chromate coatings of aluminum can move us closer to the overall environmental objectives of such programs as RoHS. Looking at overall lifecycle costs is important when considering a process change as you noted. Chromates consume resources in the disposal of spent coating residues.

Ann R. Thryft
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Re: Non-chromate coatings
Ann R. Thryft   11/19/2012 12:27:41 PM
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Thanks, Dave, for the summary and all those links. Performance is often the main issue with environmentally friendly substitutes, whether it's coatings or fuel, that are candidates for replacing toxic ones. This one sounds like it's pretty close.

Lee Wolfel
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Iron
Re: Non-chromate coatings
Lee Wolfel   11/29/2012 9:38:19 AM
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Hi Ann,

 

As a manufacturer of aluminum connectors for harsh environments the subject of what coating to use for corrosionprotection is a constant.  Especially today with RoHS and REACH activities.  Needless to say I am imensely interested and was hoping you can provide contact information for Chidambaram or a path to learn more?

 

THANKS,

Lee

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