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Anodized Aluminum

05/25/2011 3:17 PM

I am a bit confused about what aluminum alloys are anodized and which are not. My understanding is: non-heat treatable alloys and temper 0 heat treatable alloys can be anodized, and the tempered alloys, T6, T5311, etc are not anodized. Am I correct in my assumption? This is a follow-up to the train wheel discussion. What I want to know is: will epoxy resin adhere to an anodized surface or should it be removed. I'm guessing 6061-T6 aluminum bar stock and tubing is not anodized. I tried googling, but it wasn't made clear.

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#1

Re: Anodized Aluminum

05/25/2011 5:31 PM

I'm not aware that any aluminum is anodized from the factory, unless ordered that way. If one cuts the Al to size the exposed surfaces will need treatment.

If it were mine, regardless of the grade, I'd use Alumiprep and Alodine (Not an endorsement) conversion coating and forget anodizing altogether. (Acid etch and conversion coat, in generic terms) This will give you the best possible adhesion for epoxy or paint. I can buy this at my local automotive paint store.

Anodizing would be my second choice, over nothing at all, because aluminum oxide forms very rapidly on freshly cleaned Al.

I would never sand, rinse with water and paint.

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#2

Re: Anodized Aluminum

05/25/2011 6:56 PM

I have T6061 anodized all the time.

If we do not anodize the part we will powder coat it.

Regular paint does not work very well and zinc chromate is what should be used as a primer, but it is very caustic.

Stock aluminum comes un-anodized. You need to anodize it after machining. Anodized surfaces are harder on tooling, so it is better to machine raw aluminum than parts with an anodized surface.

There are also different types of anodizing. Type II is the typical anodizing you find. Type III is a harder and somewhat thicker coat and uses a different process.

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#3
In reply to #2

Re: Anodized Aluminum

05/25/2011 7:04 PM

Actually, I don't want to anodize. I just want to know that the material I buy is not anodized. My application doesn't require a super hard surface. the tensile strength of 6061-T6 is adequate for my purpose. Thanks

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#4
In reply to #3

Re: Anodized Aluminum

05/25/2011 8:32 PM

All anodizing does is stop the surface from oxidizing, which it will do horribly if left untreated. It does not temper the actual aluminum, but does leave a hard coating (about 0.0005" thick) that prevents oxidation.

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#5
In reply to #4

Re: Anodized Aluminum

05/25/2011 11:37 PM

We build many things from 6061, all of it lives in the weather, and it is not "horribly oxidized" That is the reason we used it. It looks great 10 years after we left it, with a very thin layer of protective oxidation, excellent strength, with very light weight.

What are you referring to when you say "oxidized"

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#8
In reply to #5

Re: Anodized Aluminum

05/26/2011 9:37 AM

The surface finish will turn gray and it will also stain your hands during handling.

We use T6061 for military applications and anodize just about everything.

Anodizing is a form of controlled oxidation, but untreated aluminum will also oxidize, but in an uncontrolled fashion and it is also attacked by salts.

I have plenty of scrap pieces of unanodized aluminum around here. Stuff that is stored in a controlled environment looks pretty good. Stuff that is stored in sheds or other non-airconditioned/humidity controlled environments looks very much different.

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#9
In reply to #8

Re: Anodized Aluminum

05/26/2011 9:56 AM

So you are referring to cosmetic appearance, and the fact that some of the powder created by the surface oxidation can stain your hands. Horribly seems a little intense. We anodize when appearance and a little more surface hardness and smoothness is desired. The depth of color is quality enhancing as well.

The fact that the military anodizes just about everything is not surprising.

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#6

Re: Anodized Aluminum

05/26/2011 7:11 AM

What was the form of your aluminium? Extruded shapes can hang on to the lubricants used in manufacture as the surface is a little porous, also extruded shapes are often supplied with a brush anodised finish.

To attach epoxy I would sand & degrease the surface and leave a little time as possible before applying the epoxy.

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#7

Re: Anodized Aluminum

05/26/2011 7:36 AM

Check this out there is a lot of good info here.

give them a call they were very helpfull

www.ableelectropolishing.com

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#10

Re: Anodized Aluminum

05/26/2011 10:17 AM

We use 6061-T6 for high performance aircraft parts and the bar stock comes unfinished. In some cases where we need a cosmetic and electrically insulated coating, we employ a hard coat anodized finish per MIL-A-8625 which equally impregnates and coats the surface. We also epoxy electrical terminals to the anodized finish with excellent adherence. Otherwise we nickel plate it for high durability and severe environment corrosion prevention.

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