Letter 1081

2024 Aluminium Hard Anodize Problem

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I would appreciate any help/information in regards to hard anodizing 2024 T3 aluminium to Mil-A-8625 [link is to spec at TechStreet] Type III black.

We are having a problem on some specific parts in which we are attempting to get a minimum of 1.2 mil applied to a bore on a machined part. The part is 5.000 inches OD by 4.250 inches long with a bore diameter that has steps in it from 1.9750 inches to 2.120 inches. Our tank temperature is 57 degrees F, aluminum content 1.0 , bath concentration 25.9 oz. per gallon. We were applying 16 volts with a initial amperage of 1100 amps.

Richard Johnson

Sir,

2024 is a hi copper alloy & can not be hardcoated in conventional hardcoat systems. Here in our facility we use 2 different hardcoat systems, Martin HC & Imperv-X HC. Martin will process most alloys BUT NOT hi copper ones. The Imperv-X system is specifically designed for high copper alloys and we hardcoat them daily with no problems. Please contact me if you would like more info or a quote on us finishing your pcs.

David A. Kraft Anacote Corporation Long Island City, NY

Richard,

Your information is not complete which makes an answer difficult or at least required an assumption to be made which is not good.

Al 1.0 Oz/gal or g/l or? Sulfuric Acid Oz by weight or fluid Oz ?

Normal hard anodize is 32 deg F. Are you using a proprietary or an additive? Straight DC or superimposed AC or pulse?

The high copper content in your alloy makes the anodizing more difficult, but you should be able to get 1 mill.

If your final voltage is 16, you are hard pressed to call it type III anodize, and 1 mil will be very hard to get.

Include all of the process variables and it will be easier for people that are more knowledgeable than me to help you.

Jim

James Watts
- FL

Your processing parameters are more appropriate for an anodize than a hardcoat. I doubt that this coating would meet the minimum wear requirements for a Type III hardcoating per MIL-A-8625. This could be contributing to your difficulties in achieving the desired thickness. Typical hardcoat anodizes utilize higher voltages and current densities with lower solution temperatures. The trade-off for these harder, thicker coatings is an increased tendency for "burning", particularly in the 2XXX series alloys. Special procedures and process controls can help minimize this phenomenon. Also, proper design and placement of auxiliary cathodes will help with coating uniformity.

Chris Jurey Luke Engineering & Mfg. Co. Inc. Wadsworth, OH

Dear Reader,

Hello. I am a searcher about "hard anodizing in ambient temperature". Please if you have a article or book about this, send me.

Thank you,

Mehdi Khandan
- Qom, Iran

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