Bonding Anodized Aluminum?
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    Default Bonding Anodized Aluminum?

    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.

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    WEll,my car is held together with some kind of epoxy on anodized aluminum, so the anodize is not the issue

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    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

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    Check with Lord, might even suggest something other than epoxy.

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    Long tim ago I used lord versaloc acrylic . Lord was good to work with

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    Is it a production job?
    I would look to anodise, then mask yourself and bead blast the anodise off and then bond quickly (without the oxide layer forming).
    An araldite expoxy such as 2004 I would think would be a good place to start looking at specs

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    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.

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    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.

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    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.
    Last edited by thermite; 11-01-2019 at 02:50 AM.

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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

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    Quote Originally Posted by TDegenhart View Post
    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.

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    For a very strong and permanent bond I would use 3M 5200 polyurethane adhesive after first cleaning with denatured alcohol.

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    Quote Originally Posted by jz79 View Post
    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
    A tangent comment ref Alodine....In the UK, the trade name is Alocrom 1200.
    We used to run all military contracts here to Def Stans (Defence Standards) before they were all obsoleted, and the one for Alocrom is Def Stan 03/18.
    During a raise in issue of the standard, a paragraph was added regarding timescale for painting after Alocrom.

    Under Section 7 (Preparation, Coating and Supplementary Treatments) it says:-
    7.2.2.4 The primer or first coat of the specified paint scheme shall be applied to the dry chromate filmed surface within 16 hours.

    And that's it. No explanation or reason why for the specification change, and I haven't been able to find out why either.
    All I know is that it's a pretty much impossible thing to achieve, as a lot of the time, components are plated at one supplier, and painted at another.

    But there must be a reason. Because the process is not a plating but a conversion coating - it actually changes the layer of materials chemical composition to a high chrome content, so whether the Alocrom is still "open" (porous?) and thus more susceptible to paint adherence as it is getting "into" the surface, I don't know.
    I do know that Alocrom is considered "soft" for a 24hr period, as it takes time for the water to "migrate out", so after that, I assume the surface then "seals"?

    Which then also begs the question... you're effectively painting onto a surface that only "hardens" when the water is migrated out the surface.
    And if you're using oil based paint, the water can't migrate through so is the oil not trapping in the water (albeit only microscopic amounts?)

    Whether anyone can shed light on this?

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    Quote Originally Posted by Bill Simmons View Post
    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.
    I do hope Boeing have control of this process.
    It always worries me when such important (critical) processes are put into production because invariably they are run by the cheapest labour a company can find.
    I guess this is just another reason why I hate flying...

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    Quote Originally Posted by barbter View Post
    I guess this is just another reason why I hate flying...
    Flying ain't that bad. It's crashing I'm wanting to avoid.

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    Quote Originally Posted by Bill Simmons View Post
    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.
    You have just identified the next move an aircraft company can use to save money building aircraft in the United States of America.

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    Quote Originally Posted by Pathogen View Post
    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.

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    i thought 7075 was not weldable?

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    Quote Originally Posted by ernieflash View Post
    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.


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    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.


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