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Bonding Anodized Aluminum?

Mot3s

Plastic
Joined
Oct 24, 2019
Could somebody please help me solve this issue with how to confidently bond 7075 aluminum to aluminum? The surface area of this bond is only about 1 sq. inch and my parts will be anodized (or they can probably mask the area I'm guessing, but I don't know what's better).

I have a screw clamping the surfaces as well, but the extra insurance of adhesive is what I would like. I'm seeing online that bonding aluminum is not as simple as it sounds, as the oxide layer is weak or something. Plus, I don't know how anodizing it changes anything with the sealed layer if I were to try epoxy or something.

Anyone have experience with this? Because I've already googled myself so I'm asking for someone that's had success with strong bonding between anodized aluminum surfaces, or bare aluminum surfaces, not just someone to tell me to use super glue because you think it will work.

Thanks a lot.
 
ideally you would mask the area before anodizing, and after anodizing is done, chromate conversion coating would be applied (alodine) to the bonding area (aluminum has to be bare, no oxides, conversion coating works on clean bare aluminum) - it sounds easier than actually getting it done well

alternatively you could simply skip masking, score the anodized area to be bonded with 60-80 grit sand paper and glue it, if there will be additional screws holding the joint in compression, it should hold, at least for some time

there are special structural glues (not epoxies necessarily) for bonding bare aluminum surfaces, but might not be available in small packaging

a while ago I had to repair a Heidenhain glass scale where the glass scale had separated from the anodized aluminum housing, I could use silicone glue there (forgot the exact type, can check later), but I suspect silicone might not have the right properties for OPs application, that particular silicone bonded to the anodized surface very well, it would break before releasing from the anodized surface
 
There are some double sided tapes from companies like 3M that are used to bond aluminium to aluminium and are quite strong but require a freshly bead blasted surface less than 30 minutes old to bond to.
 
Adhesives may work as long as moisture can never get to the area.

I was at an EAA meeting where a fellow gave a demonstration and talk about epoxy bonding of aluminum. The aircraft he was building used epoxy for much of the structure like wing assembly. He researched the subject and found boeing had a proprietary treatment process for similar attachments.

He brought some strips of aluminum that had been bonded together with just good cleaning processes. The strips were about an inch wide, 2 feet long and perhaps .025 thick. The last inch was not glued. Two volunteers were brought from the audience and each given a pair of pliers and told to pull on each of the unglued ends. Nothing happened. Then he took a spray bottle filled with water and sprayed a finely atomized cloud at strips. There was immediate failure with the strips peeling apart and the adhesive separating from the aluminum. The failure was so quick that it looked like a hoax. He had some strips that had been treated by Boeing and extreme pulling would cause the adhesive to split, the desired failure mechanism. He asked would you want to fly a plane into cloud with out treatment. I don't know how he pulled it off, but he actually got Boeing to treat his parts for a reasonable fee.

I do not know what the treatment is that Boeing uses but it prevents the rapid (almost instant) corrosion. This corrosion has almost no strength.
 
Any of thousands of "at least" vacuum-tube days tech have been soft-soldering Copper wire to Aluminium chassis for as long as aluminum has been used to MAKE equipment chassis. Aluminium to aluminium as well.

All it ever needed was a an ignorant razor blade and a spot of oil. Preferably a silicon "transformer" oil because you could keep it around for - what? 60 years already, my little bottle of it?

Johnson's "baby oil" from the local pharmacy worked fine, too.

Level the chassis so the oil dasn't run, pick your spot, apply a drop of oil. Scrape way the Oxide whilst razor blade is submerged in oil. Oxygen can't get to it to create a new layer.

Solder on a blob of ignorant 60/40, STILL working inside the drop of oil, add the ground wire, let it cool, wipe it clean, and go do whatever else is on your dance-card. That easy. Try it and see.

One could "tin" these two parts separately, then "sweat" them together?

Need greater strength? WELD them under an inert gas instead of soldering under oil.

Heliarc -> MiG -> TiG. Been going on and getting better and better and easier and easier ever since Aluminium first went cheap and available.

Any of that is "too difficult"?

Just use some other metal. Copper is a good 'un for conductivity, and dead-easy to furnace-braze.

Aluminium has "challenges", one of them being that it moves more than many other metals from temperature swings - which you have said NOTHING about for your application, not even the "normal" ambient temp it is designed to operate within.

Another that Aluminium is electrochemically rather more active than many "tamer" metals. "Rust" it does not, "Corrode" it assuredly can do, some forms of that eating away at bonds to even well-matched paints as well as even very good adhesives.
 
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Follow what thermite says about the oil. Aluminum is so aggressive that as soon as you clean it, it oxidizes. So, you either have to use a flux or work under a protective layer.

Tom
 
Follow what thermite says about the oil. Aluminum is so aggressive that as soon as you clean it, it oxidizes. So, you either have to use a flux or work under a protective layer.

Tom

Well. Yes. The puddle of oil. It wasn't there to make stuff slide more easily.

:)

The blade scrapes while submerged.
The soldering Iron tip melts the solder while submerged.

No oil handy? Make a puddle of solder, Scrape whilst IN it with the tip of the soldring Iron. Gradually, more of it adheres. BTDTGTTS.

Once there is a "spot" well-adhered, further joints don't even need the oil.
The solder has become the protective layer.

Doing this since forever-ago, so I haven't looked, but there may be a ham radio or audiophile who has made a You Tube on it.

BTW .. Aluminium is NOT all that "aggressive" or anodizers wouln't have a job. There actually is a brief but finite window of time when Oxide formation is not complete, particularly when temps are kept low. Work this time window smartly, the right flux is all you need.
 
Adhesives may work as long as moisture can never get to the area.

I was at an EAA meeting where a fellow gave a demonstration and talk about epoxy bonding of aluminum. The aircraft he was building used epoxy for much of the structure like wing assembly. He researched the subject and found boeing had a proprietary treatment process for similar attachments.

He brought some strips of aluminum that had been bonded together with just good cleaning processes. The strips were about an inch wide, 2 feet long and perhaps .025 thick. The last inch was not glued. Two volunteers were brought from the audience and each given a pair of pliers and told to pull on each of the unglued ends. Nothing happened. Then he took a spray bottle filled with water and sprayed a finely atomized cloud at strips. There was immediate failure with the strips peeling apart and the adhesive separating from the aluminum. The failure was so quick that it looked like a hoax. He had some strips that had been treated by Boeing and extreme pulling would cause the adhesive to split, the desired failure mechanism. He asked would you want to fly a plane into cloud with out treatment. I don't know how he pulled it off, but he actually got Boeing to treat his parts for a reasonable fee.

I do not know what the treatment is that Boeing uses but it prevents the rapid (almost instant) corrosion. This corrosion has almost no strength.

:Ithankyou::eek::wrong::willy_nilly: You have just identified the next move an aircraft company can use to save money building aircraft in the United States of America.
 
:Ithankyou::eek::wrong::willy_nilly: You have just identified the next move an aircraft company can use to save money building aircraft in the United States of America.

Luke AFB is dry... Renton, not so much. Maybe they should switch missions.
Buld 'em where they usta scrap 'em, and dissolve them where they usta build 'em?


Grateful as Hell the 2005 XJ8-L is stuck together with a brazillion "self piercing" loominum-alloy RIVETS, then, Iyam!

Were it glued, putting it through a car wash could have a similar effect as driving a Toy-Oder Crow-Roller past a ripe cornfield.

Motor parts slip their little-bitty harnesses and fly off for free lunch.
 
i thought 7075 was not weldable?

Anything as can be cast, electroformed, sputtered, deposited, or produced by powder metal technology can be welded "somehow", taking the physical meaning of "weld", not the machine it was done with..

What "somehow" costs to DO, or what the side-effects might be?

Ah, well.... that's a whole 'nuther entire pack of dogs, altogether!

"Not worth it" seems to be on the sons-of-bitches AKC registration papers more often than not.

Then again? Someone who didn't read the memo finds a way and fortunes are to be had.

:)
 
Thank you all for your replies. Interesting stuff. I should have mentioned I am not looking to do anything super fancy here and don't have the time or budget really. This is just a one time little deal here. I really just need confidence in a simple solution for bonding approximately 1 sq inch of anodized 7075 to itself, a section of 5/8x 3/16 bar to a flat surface. If I rough up the anodize and just use epoxy, would this suffice for having a shear strength of at least 100 lbs and last at least 1 year? Things like JB Weld 8265s claim 1800 lb shear strength, which would be fantastic, but that's gotta be dependent on what it's applied to. The bonded surfaces can't have much of a gap either, it's a small precision piece that needs to stay in place once applied and there's no room for adding another screw or changing the tolerance on the assembled part by more than a few thou.
I'm not looking for this thing to survive a nuclear blast. I just wanna have confidence that some adhesive with whatever prep work will be better than just the screw pressure itself. I don't understand the science to that extent to know how an adhesive would fail on an anodized surface. If I use a mechanical bond on sealed anodizing, then I can somewhat understand it not holding that well but what I wonder is if I rough an anodized surface, what specifically could then cause the mechanical bond to fail? I imagine it's a complicating science.
 
I'm definitely curious what Boeing came up with. You say as long as moisture can't get to the area. It sounds to me like that means moisture can't get to the adhesive at all, right? I can see moisture getting to the edges of the bond/adhesive layer, but not further than that. I'm not understanding that. Does moisture, even on the edge of bond, cause the onset of failure of the entire bonded surface, like a chain of failure type deal?
 
Just call this company,Epoxy Technology Inc. We bonded thousands of 6061, disks together after being 'hard anodized'.
The tech there will listen to your application requirements, and offer a few products. The sell small quantities ("Kits") to prove the process.

Regards,
Chris
 
For a very strong and permanent bond I would use 3M 5200 polyurethane adhesive after first cleaning with denatured alcohol.
I thought about 5200 also. I haven't found anything that shit doesn't stick to, and it's strong.

Stuff gets everywhere though, lol. I swear I can cut open a brand new tube and 2 seconds later it's on the bottom of my shoes... :willy_nilly:
 








 
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