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Aluminum, back side of weld, what does this mean (have pics)

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  • Aluminum, back side of weld, what does this mean (have pics)

    What are we looking at, how can I make it go away?

    I've been teaching myself to TIG for personal pleasure. It's not a job, I just dabble and piddle. But I want to learn and better myself.

    Right now, I'm trying to learn how to get those real nice roundy corners on say a 90 degree corner with 2 pieces of 1/8" aluminum butted up. Something is freaky with the penetration on the back side. Is this normal? Anything to do with surface prep? I didn't do any on this, as I was just piddling.

    What are we looking at, how can I make it go away?



    Some other stuff I've piddled together in the last week.

    gague mount for race car.


    Catch can.

  • #2
    Thought I might add, that stuff in do in steel, has good penetration, in and out. The inside of say something like a 2" tube, looks the same as the outside, bonded metal. no seam, nothing that looks like the aluminum piece shown.

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    • #3
      What you're seeing is the deformation of the back side of your weld. The base material is completely fluid and you're pushing the puddle out on the back side when you add filler.

      Aluminum doesn't behave like steel. You can't fill a keyhole and be left with a smooth profile on either side of the joint (at least I can't).
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      • #4
        Originally posted by Fishy Jim View Post
        What you're seeing is the deformation of the back side of your weld. The base material is completely fluid and you're pushing the puddle out on the back side when you add filler.

        Aluminum doesn't behave like steel. You can't fill a keyhole and be left with a smooth profile on either side of the joint (at least I can't).
        Appreciate the time.

        Not so much the fact that the puddle is pushing through, but the line where one piece of metal met the other, like they pushed through but didn't fuse. The other side of the weld looks great. It did fuse just fine on the face.

        Looks weak and improperly done, to me. I'm not sure I'm explaining it right.

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        • #5
          A bit too much heat, move a little faster.

          If you have AC freq. adjustment turn it up higher than 120 Hz.

          Make sure your material is super clean, inside and out.

          Your welds look not too bad for a weekend warrior!

          For .102" Al. I was set at 100 Amps, Bal. 70, AC 120 Hz., 3/32" Lanthanated.

          Your mileage may vary...
          "If you build it, they will come!"

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          • #6
            You would need to clean the inside of the parts to be welded ,looks like a trash line.
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            • #7
              i agree with Fishy Jim, your pushing the metal out the back. Cleaning would help, and i think letting the filler melt in instead of pushing it strait in might help. maybe give back gassing a try? but i'm not sure that would help much with alluminum. I have used gas welding flux on the back side of alluminum tig welds, but it is messy, although the back did come together more smoothly. Since your making non structural stuff you can afford to experiment.
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              • #8
                Originally posted by fabricator View Post
                You would need to clean the inside of the parts to be welded ,looks like a trash line.
                There ya go, "trash line", I knew it must have a name of some kind. So cleaning the back would help that? As mentioned, I'm a weekend warrior, doing my best. and trying to improve.

                Originally posted by Laiky View Post
                i agree with Fishy Jim, your pushing the metal out the back. Cleaning would help, and i think letting the filler melt in instead of pushing it strait in might help. maybe give back gassing a try? but i'm not sure that would help much with alluminum. I have used gas welding flux on the back side of alluminum tig welds, but it is messy, although the back did come together more smoothly. Since your making non structural stuff you can afford to experiment.
                When I have the piece molten, the puddles moving, and usually about the time I get the filler rod in there, it's soft and instantly 'absorbs' right in. I wouldn't say there is any pushing happening at all. If anything, it could be sagging out due to gravity. But I'm willing to entertain all ideas to improve the work.

                Here's what I was working on last night, and why I want to make sure my joints are good. I wanted that cool 'roundy' look on the edge where the sides meet the top. I want to make sure the joint is sound so it won't leak fluid.



                Last edited by vectorsolid; 09-16-2008, 04:35 PM.

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                • #9
                  A little off topic, i like the projects, where are you getting the bungs especially the filler necks?
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                  • #10
                    Originally posted by Garage guy chris View Post
                    A little off topic, i like the projects, where are you getting the bungs especially the filler necks?
                    Actually, i like to help people looking for that kind of stuff because occasionally I need the favor returned when I'm looking for stuff.

                    Jegs does the filler cap with bung for $20, bet bang for the buck I've found for a product like that. The dimensions are odd though. The bung is just under 2", so if you put a 2" hole in something it falls through, and the lip for a nice surface fit is only .075 all the way around. I'd like to talk to somebody at Jegs about that some time. I'm sure it's that size for a reason. But it's thick and welds nice.

                    Summit and Jegs both sell lot's of little weld in bungs, for like NPT and -AN stuff. Most are under $5 in smaller sizes.

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                    • #11
                      The 'cleaning' action from the arc can't get to the back of the weld to take care of the oxide- remember Aloxide has a melting temp around 3 times that of Al. There will typically always be a 'witness line' or 'oxide line' on the root of a full pen Al weld (oxy fuel with flux aside) but it should be only noticable as a line of different 'colour'. Perhaps different 'shade' is a better term

                      Feeding some filler into the puddle helps the root profile- just touching the filler to the puddle can often result in the appearence you have. Don't add filler as soon as the puddle forms, wait for it very shiney and sink a little, then give it some filler. Obviously practice on some scrap first!

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