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Speaking of MIG Aluminum - SOOT!

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  • Speaking of MIG Aluminum - SOOT!

    When I weld 6061 with 4043 it doesn't produce much soot, but when I welded 5052 (or 5086) with 5356 I get a lot of soot. Some folks critically acclaim its gas coverage and technique, but if that was the case wouldn't it soot up just as bad with 6061/4043?

    I seem to recall some folks when I was first learning how to chicken [email protected] aluminum together with my spool gun saying that was just the nature of the beast, but others have said no. Its gas coverage, setup and technique. So... what exactly is the difference then? Crank up the gas? Put some kind of gas diffuser inside the gun?
    *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

  • #2
    The 50** Al alloy group has higher content of magnesium in it's composition. Magnesium has a peculiar property of reacting with carbon dioxide/monoxide at higher temperature and reducing the gas to free carbon that forms as a very fine soot. In fact Mg burns in carbon dioxide, releasing a lot of sooty black residue. Magnesium being the stronger reducing agent robs carbon dioxide from the oxygen and leaves free carbon behind:

    2Mg+CO2-> 2MgO + C (soot)

    So if your shielding gas should contain carbon dioxide as a contaminant or part of the gas composition on purpose, then welding 50** group Al alloys shall produce a sooty residue. Also if your gas coverage is weak and the atmospheric CO2 content comes into contact with the welding puddle then it may also contribute to soot formation.


    • #3
      General opinion seems to be that its more or less normal deal when welding magnesium containing alloys. And correct technique can at least reduce it.
      Location: Helsinki, Finland, Europe