can you tig weld magnesium alloy to aluminum
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  1. #1
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    can you tig weld magnesium alloy to aluminum

    my guess is no. but if you can what rod would one use? specifically 6061 alum to cast 94%mag 6%aluminum

  2. #2
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    Re: can you tig weld magnesium alloy to aluminum

    No. Not possible because

    a) radically different melting temperature for alum alloys and mag alloys. Mag melts at a much lower temperature than aluminum. When you heat them with the torch, the mag will liquify long before the aluminum does.

    b) limited solubility for mag in aluminum and vice versa. It's like oil and water mixing.
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  3. #3
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    Re: can you tig weld magnesium alloy to aluminum

    Hmmm... and yet they somehow manage to get that 6% of aluminum to bond with that other 94% of magnesium to make the alloy in the first place... Something tells me this can be done...
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  4. #4
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    Re: can you tig weld magnesium alloy to aluminum

    lol thats what i figured...

  5. #5
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    Re: can you tig weld magnesium alloy to aluminum

    All I can say is, if you're going to try this....do it in a positive pressure vessel of some kind. The demands of magnesium are well known. The voodoo of mixing materials can have unintended consequences. Go with the known standards for welding magnesium, and my suggestion would be to get the highest mag. content filler you can find to attempt this.

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  6. #6
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    Re: can you tig weld magnesium alloy to aluminum

    No, but it's not because of melting temps or fire. The result of trying to weld magnesium directly to aluminium will just be a brittle mess

    Melting point of pure mag around 650C versus 660C for pure Al, obviously alloy contents alter things a little (580ish C for 4047 Al for example)
    Setting fire to a big chunk of mag is far from easy, mag swarf/dust on the other hand... Easier to start a mag fire machining the stuff than it is welding and still takes some effort (doing everything wrong)
    That 6% (or more) Al in a magnsium alloy isn't 'bonded' it's dissolved in the mag and as A Dab said there's a limit to how much can be dissolved (just like sugar or salt in water, copper in aluminium, carbon in iron etc etc.)

    The result of trying to weld magnesium directly to aluminium will just be a brittle mess

  7. #7
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    Re: can you tig weld magnesium alloy to aluminum

    Take a look at the attached picture for a minute. (Skip to the bottom if you want to bypass the technical mumbo jumbo...)

    I copied this phase diagram from:

    http://www.aluminiumlearning.com/htm...hase/Al_Mg.gif

    What this graph shows you is the amount of Magnesium that can be dissolved(like salt in water, as hotrodder said) in Aluminium(at equilibrium**). The bottom of the graph is %Magnesium(Mg), and the side of the graph shows temperature. The left side of the graph is pure aluminum, the right side is pure magnesium.

    Remember I said that magnesium has limited(not zero) solubility in aluminum. At the top of the graph, both elements are completely liquid; above 660.37°C. Draw an imaginary vertical line at 6% magnesium, and you'll see that line meets the highest line on the graph at around 650°. This is the temperature at which a mixture of 85%Al 15%Mg begins to solidify. Continue traveling down that imaginary line, and you'll meet another red line at about 525°C, this is the temperature at which 99%Al 1%Mg begins to solidify. Finally at about 451°C everything is solid. What you have at that temperature is a mixture of almost pure aluminum, and another phase(technical mumbo jumbo) that is made up of a aluminum and most of the magnesium that was present. If you were to polish this metal, etch it to bring up some details, and look at it under a microscope, you could see what looks like concrete. 'Cement' and 'rocks', or really 'aluminum+a little magnesium', and 'aluminum+a lot magnesium'. The exact amounts of magnesium in each phase are determined by how much magnesium is there to start with.

    **This graph assumes that the temperature of the metal mixture is changing very slowly. But it can give you an idea of how easy it is to mix these two elements together.


    Hopefully, I haven't put anybody to sleep yet....


    In reality, a weld would cool or freeze extremely rapidly, and it takes a different graph, that's a lot harder for me to explain, to illustrate what's happening. If you're curious about that sort of graph, search the internet for a T-T-T diagram(Time-Temperature-Transformation)

    Start here if you're skipping the techno-babble...


    Getting around to the point...Notice the middle of the graph is much more complicated. There's lots of intersecting lines and boundaries drawn. Without beating this to death, there's a lot that happens when you mix roughly equal parts of Al and Mg. Lots of different phases(mixtures of Al and Mg) that are solidifying at different temperatures. This is what's going on when you try to weld 6061(relatively pure aluminum) to 94/6 cast mag alloy. You get about a 50/50 mix of Alum, Mag, and a bunch of other stuff that really makes this much more complex.

    Everything is fine at welding temperatures, but as soon as the puddle starts to cool, parts of the molten liquid metal start to solidify, and some remains liquid. you get gas pockets trapped, oxide inclusions, a mushy zone(this is the real technical term), and generally speaking a big mess.

    All of this doesn't even take into account the fact that the OP wants to weld wrought 6061 to a cast magnesium part. The cast magnesium is likely going to be full of crap that would make it tough to join the cast part to even another magnesium part of the same composition.

    If you compare this to the phase diagram for Iron and Chromium, or Iron and Carbon, you'll see that the graphs are much simpler. Tin and Lead is one of the simplest, which reflects the reality that solders come in a wide variety of compositions, but other than slightly different melting temps, they all work relatively well because they mix together very well.

    Sometimes these complications can be overcome by adding the right filler metal to the weld. The filler metal changes the composition(the amount of each ingredient) in the molten puddle. You can 'push' the composition into a state that the materials being welded are very soluble with each other, and get a good weld. This is one reason that welding without filler metal often creates problems. Without the added ingredients from the filler metal you get a composition with lots of phases that aren't compatible with one another.

    Hoever, in this case, the base metals under discussion are too different in composition for any filler metal to overcome the poor solubility problem...

    Quote Originally Posted by DesertRider33 View Post
    Hmmm... and yet they somehow manage to get that 6% of aluminum to bond with that other 94% of magnesium to make the alloy in the first place... Something tells me this can be done...
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  8. #8
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    Re: can you tig weld magnesium alloy to aluminum

    wow guys thats alot of info..... just fyi 05+corvette subframes are made of this. good job gm!

  9. #9
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    Re: can you tig weld magnesium alloy to aluminum

    Help me out, are you saying that the '05 and newer corvette subframes are assembled by welding aluminum components to magnesium components?

    I'm skeptical, can you point me to some more info on the web about this? I'd like to know more details. What alloys, etc.

    Quote Originally Posted by turbotank View Post
    wow guys thats alot of info..... just fyi 05+corvette subframes are made of this. good job gm!
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  10. #10
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    Re: can you tig weld magnesium alloy to aluminum

    Hello A_DAB_will_do, from what I have seen of these, the sub-frames are magnesium, but not a combination of aluminum and magnesium, at least not a welded combination. They had a really good TV special on the Corvette where they discussed the completely newly designed ones and they followed the manufacturing process from start to finish. When they got done they took it out on the test track and gave the interviewer the ride of his life, over 200 mph I believe. Best regards, Allan
    aevald

  11. #11
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    Re: can you tig weld magnesium alloy to aluminum

    Thanks Aevald. A full magnesium sub-frame I can imagine. Just not a welded aluminum-magnesium assembly. I'll keep an eye out for that TV special you mentioned. I'm curious how GM deals with the corrosion issues with magnesium underbody pieces...

    Quote Originally Posted by aevald View Post
    Hello A_DAB_will_do, from what I have seen of these, the sub-frames are magnesium, but not a combination of aluminum and magnesium, at least not a welded combination. They had a really good TV special on the Corvette where they discussed the completely newly designed ones and they followed the manufacturing process from start to finish. When they got done they took it out on the test track and gave the interviewer the ride of his life, over 200 mph I believe. Best regards, Allan
    Mobile Welding at your worksite or place of business. Serving Dayton, Ohio and the surrounding metro areas.
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  12. #12
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    Re: can you tig weld magnesium alloy to aluminum

    yea nothing is welded to it its cast 94mag 6alum

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