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Aluminum treatment


ErlendM

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Is it correct to assume that all parts of aluminum should be treated to avoid corrosion? I plan to use Alodine 1201 on all parts that are not pre-manufactured and treated.

 

The plans calls for 2024-T3 and I have ordered as pr. plans. However I spoke with an other builder (and flyer) - he says he used 6061-T6 all over, with no corrosion-protection. Does anyone have experiences with this? I feel more comfortable to stay to the plans, but if the other type is better, and doesn't need protection, than it will be easier to just use that.

Erlend Moen
Norway
Cozy MK IV #1556 - Chapter 16
http://cozy.ljosnes.no

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Is it correct to assume that all parts of aluminum should be treated to avoid corrosion? I plan to use Alodine 1201 on all parts that are not pre-manufactured and treated.

 

The plans calls for 2024-T3 and I have ordered as pr. plans. However I spoke with an other builder (and flyer) - he says he used 6061-T6 all over, with no corrosion-protection. Does anyone have experiences with this? I feel more comfortable to stay to the plans, but if the other type is better, and doesn't need protection, than it will be easier to just use that.

6061 is a better alloy for corrosion resistance but not as strong as 2024 t3 even in the t6 condition it can be used for many parts, it is a bit cheaper and easier to find just don't substitute it for structural parts like lift tabs or engine mounts

Evolultion Eze RG -a two place side by side-200 Knots on 200 HP. A&P / pilot for over 30 years

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Read this month's Sport Aviation on why you absolutely should NOT anodize any structural, control, or critical part. Significant reduction in fatigue life.

Perhaps it would be helpful to clarify that to anodize and to treat with alodine are different.

 

It is my understanding that all aluminum parts should be treated with alodine.

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Perhaps it would be helpful to clarify that to anodize and to treat with alodine are different.

 

It is my understanding that all aluminum parts should be treated with alodine.

... and that Alodine is the more common approach for home use. There's a lot of extra tools needed for Anodizing.

Drew Chaplin (aka the Foam Whisperer)

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www.Cozy1200.com - I'm a builder now! :cool:

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Brace for impact...

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  • 3 weeks later...

The Alumiprep is 33% Phosphoric acid. Someone more knowledgeable will have to state the suitability of Acetone.

 

Here is in Australia there is a solution at the local hardware super store that contains 25% Phosphoric acid. I hear that local builders use it as a substitute. I found this out just after paying $40 for one gallon of Alumprep when I only needed a couple ounces!!

Drew Chaplin (aka the Foam Whisperer)

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www.Cozy1200.com - I'm a builder now! :cool:

---

Brace for impact...

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Go to a hardware store or pool supply place and get a gallon of 25 %phosphoric or hydrochloric acid for WAY cheap. (Or just drink it from a can of Dr. Pepper!) Driveway cleaner or etching solution or muriatic acid if you ask the hardware store geeks. (Yeah, environMENTAL concerns may have changed the rules.) It's used to lower PH in pools. I paid less than three bucks ten years ago and I'm still using the same gallon. (Probably more $ now) It goes a long way in the proper dilution with water. Too much undiluted acid and the aluminum starts smoking and forming gas. It's Hydrogen and Chlorine gas!! Dont' get it on your skin or breath the fumes! Wear rubber gloves and goggles. Battery acid can be loads of fun too!

You can't always get a reaction. But the acid etches off the aluminum oxide layer and preps it for the flourine/chromate which is in the alodine. There is also cyanide and chromic acid in the alodine.

BTW Hydrochloric acid is also known as metal prep for wiping down auto metals prior to priming. You will find phosphoric acid in Naval Jelly for eating rust off of cars.

How does all this work? The acid etches the bad oxides off of the metal. The alodine/chromate creates a stable kind of oxide that the paint and epoxy can bond itself too. This oxide layer keeps the metal from corroding under the epoxy layers.

Hydrochloric acid is also on the list of chemicals used to produce Methanphetamine! So like ammonium nitrate fertilizer, or sudafed, don't be surprised if you have to sign for it.

I await corrections on my forgotten chemistry lessons.

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Go to a hardware store or pool supply place and get a gallon of 25 %phosphoric or hydrochloric acid for WAY cheap.

That's interesting! Hydrochloric Acid is in my hardware store. I even used it to rinse my concrete-floor prior to painting it!

 

The Hydrochloric Acid is 30%. Do I just submerge the parts in this fluid for 2 - 5 minutes, then rinse in water? Will this be adequate prior to Alodine?

 

Edit: If I am to use Alumiprep 33 I should use 25 parts Alumiprep to 75 parts water. I guess I should use the same mixture with HCl?

Erlend Moen
Norway
Cozy MK IV #1556 - Chapter 16
http://cozy.ljosnes.no

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That's interesting! Hydrochloric Acid is in my hardware store. I even used it to rinse my concrete-floor prior to painting it!

 

The Hydrochloric Acid is 30%. Do I just submerge the parts in this fluid for a couple of minutes, then rinse in water? Will this be adequate prior to Alodine?

Yes you will notice that the hydrochloric acid also makes the concrete etch just like aluminum!

 

You don't have to soak the aluminum parts at all. (Not a great idea, the acid will eat away at the structual integrity of the aluminum over time.) You can brush the acid on the aluminum and give it a light scrubbing or gentle brushing. The acid will take the oxides and oils off of the aluminum. RInse with water to decativate and dilute the acid. You can then brush on the Alodine while it's still wet and you will notice an amber color change as it forms the stable oxide coating. After it dries you are done. Of course don't get it dirty or oily before you bond your part into place. A quick wipe with acetone or paint thinner will remove any finger prints/oils before bonding or painting. This is after storing the part.

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Wasn't there just an article in, I believe, Kitplanes with regard to an anodized control rod snapping in a Safari helicopter which led to it's demise.

 

The article listed the strength degradation of the various types of aluminum treatments. A real eye opener.

 

I have to read it again (as most of my reading of mags is late at night while on the porcelain throne) but I walked away from the first read with the idea that any of the treatments that we use, including alodine, substantially weakens aluminum.

I Canardly contain myself!

Rich :D

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Wasn't there just an article in, I believe, Kitplanes with regard to an anodized control rod snapping in a Safari helicopter which led to it's demise.

 

The article listed the strength degradation of the various types of aluminum treatments. A real eye opener.

 

I have to read it again (as most of my reading of mags is late at night while on the porcelain throne) but I walked away from the first read with the idea that any of the treatments that we use, including alodine, substantially weakens aluminum.

It's also in EAA Sport Aviation

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There could be problems with anodizing thin parts, like the thin-walled control tubes referenced in the article in Sport Av.

Like elevator torque tubes for the Cozy/Long/Open/... ?

 

Rick

Rick Hall; MK-IV plans #1477; cozy.zggtr.org

Build status: 1-7, bits of 8-9, 10, 14 done! Working on engine/prop/avionics.
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Anodizing and Alodining are two completely different things. It's like an apples and oranges comparison.

 

Anodizing deposits a hard surface coating to the aluminum which changes the bending/vibration/hardness properties of the aluminum tube. That's also in the article you are discussing. Also in that article the tube in question is a long run control tube and the canard tube is much different in torque and vibration compared to that tube that failed in the article. But, I'm not saying to use anodizing.

 

The Alodining puts a stable oxide coating on the aluminum which preps the surface for bonding or painting. It doesn't change the physical properties of the metal. You will find that the surface of the aluminum parts when you get them from the vendors have a coating of 3003 aluminum which is pure aluminum to prevent oxidation. Alloyed aluminums are more susceptable to corrosion because of the doping elements present in the metal.

 

You will see in the plans that the tubes used for the canard elevators are required to be alodined before bonding in place. The CP issues also noted that there was corrosion in some elevators built back in the 70's that started to bubble up under the fiberglass and required rebuilding. Look up "intergranular corrosion" or "exfoliation corrosion." They were NOT alodined if memory serves me. Someone else can probably tell you which CP issue it was in.

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Not sure if it's mentioned in other plans, but the Cozy IV plans never say to alodine the elevator tubes (or any other tube). In fact, Chapter 11, Page 1, step 1 has you thoroughly sand the torque tubes with 220 grit.

 

I alodined my tubes and the sanding took the alodine right off. At least the inside is still coated.

Wayne Hicks

Cozy IV Plans #678

http://www.ez.org/pages/waynehicks

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Not sure if it's mentioned in other plans, but the Cozy IV plans never say to alodine the elevator tubes (or any other tube). In fact, Chapter 11, Page 1, step 1 has you thoroughly sand the torque tubes with 220 grit.

 

I alodined my tubes and the sanding took the alodine right off. At least the inside is still coated.

I didn't build a cozy so I don't know about the plans. Long-ez plans do specify, and yes, when you sand the tubes after alodining and it removes all the surface and alodine! You started from scratch, scratches, literally! :D

Sand, clean (acid, alumiprep), alodine, then bond. That should be your order. You started back on bare aluminum and took away the benefits of the alodine solution by sanding off the stable oxide coating.

Cozy girls use alodine on their parts before they ship them out. They sandblast some parts that will be bonded in place and THEN alodine them.

 

Believe it or not I actually repaired an aluminum tube on my home air conditioner that carried freon with this method. I used wet flox and Ezpoxy. It held freon for years. Yes, I know, envoiromentally unfriendly. I was young and stupid but oh so cheap! I was building an airplane, I needed my money for that! Of course I used to go right down the hardware store and buy my own R-22 freon so I could fill my own system. Those days are long gone!

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