DC GTAW for Aluminum?

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Last evening had a buddy tell me that you dont need AC to TIG weld Aluminum...Ive been under the impression (from numerous sources) that you cannot weld Aluminum with DC due to its properties...So what's the REAL scoop?  Which of us is the ignorant one?ThermalArc 185MillerMatic 180 w/ AutosetVictor Cutskill Oxy/AcetyleneThermal Dynamics Cutmaster 38and spite!
Reply:not true, aluminum can be welded with DC -.  The reason AC is used is becuase it is both DC straight and DC reverse.  Dc reverse is used to help clean the metal as it is being welded, and on some welders when AC current is selected the machine will allow you to change your AC balance to give either more penetration DC -, or more cleaning DC +.
Reply:I tried it,  the oxides in the aluminum just sit there in the puddle.  Try it your self, you will only do it once even with really clean aluminum.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:i have done it, its not enjoyable, but it can be done.  The problem with aluminum is that oxide film melts at about 3600 degrees, where as aluminum melts at about 1300 degrees or so.  Unlike steel the oxide will not burn off under the heat of the arc, which is why aluminum must be wire brushed immediately before welding.  Even so the oxygen in the atmosphere begins to reform oxides immediately on the surface of the metal, which is why AC is used, for the cleaning action of DC+.If the metal were in an inert atmosphere the use of AC would not be needed because no oxides would be able to form
Reply:Originally Posted by drivethruboy54not true, aluminum can be welded with DC -.  The reason AC is used is becuase it is both DC straight and DC reverse.  Dc reverse is used to help clean the metal as it is being welded, and on some welders when AC current is selected the machine will allow you to change your AC balance to give either more penetration DC -, or more cleaning DC +.
Reply:sort of, but its actually the other way around.  Current that comes from the wall is AC 60 hz in the USA.  Most machines are transformer or transformer rectifiers.  The transformers inside the welder take the incoming power (high voltage low amperage) and change it to your welding power (low voltage high amperage)rectified current is AC that has already been transformed, and which is now selected to either be DC- or DC+.It looks like you have a dynasty 200dx, which by the way are very nice machines.  I had the privelage of using one of the new dynasty 700's when they were still being prototyped, let me tell you WORTH EVERY PENNY.  Back to your machine, its an inverter, which is completely different.  I dont remember exactly how they work, but i believe (correct me if im wrong) the AC input current is rectified first, transformed then re-rectified back to AC, and somehow does it all more efficiently than standard transformer machines.Maxstars are nice machines, but stay with the dynasty, they are the future of welding, and miller is the innovator of inverter technology and the dynasty series are at the head of the pack.Last edited by drivethruboy54; 02-25-2007 at 03:25 PM.
Reply:to tig aluminum with dc but you need helium then it will weld just fineChuckASME Pressure Vessel welder
Reply:I read that you need straight helium to do DC tig on aluminum.  Not sure if its true or not.Various GrindersVictor Journeyman torch200cf Acet. 250cf oxygenLincoln 175 plus/alpha2 gunLincoln v205t tigLincoln 350mpEsab 650 plasmaWhen you can get up in the morning, Its a good day.Live each day like its your last.
Reply:you can for real thick stuff but an argon mix is betterChuckASME Pressure Vessel welder
Reply:Originally Posted by DirtyLittleSecretYeah, as I understand it the AC units arent really AC at all but rather a DC that is being switched +/- very rapidly to create AC.  So how difficult is it to get REALLY good aluminum GTAW welds?  Is it more of a immediate clean thoroughly and weld immediately thing or is there more to it?  My same buddy might be essentially giving me his Maxstar 200DX, and since I cant justify two similiar TIG systems...
Reply:So, I could easily go with another smaller "mixed bottle" for whenever I need to do aluminum (if ever I get the hots to do so) and be fine?  Im totally new to this stuff, but dont want to make a mistake.ThermalArc 185MillerMatic 180 w/ AutosetVictor Cutskill Oxy/AcetyleneThermal Dynamics Cutmaster 38and spite!
Reply:Originally Posted by chopper5you can for real thick stuff but an argon mix is better
Reply:argon helps to maintain the arc .on thick aluminum straight helium is the way to go.so we have an disagreement lolit's all good zap ChuckASME Pressure Vessel welder
Reply:Most people keep forgetting  WHY Helium is needed when welding  THICK aluminum . Argon is "ABOUT"  10 times as dense as helium . therefore helium allows the heat penetration into the thick aluminum ,and quick melting of the aluminum. So, on thin aluminum , argon is needed to control penetration (and cleaning effect) helium is kinda "dirty" compared to argon, that's why some people think argon is all that's ever needed. WRONG  !!![SIZE="5"Yardbird"
Reply:Roy, how can helium be a dirty gas compared to argon? they're both inertyou can weld Al with DC, it's done all the time with MIG. Al oxide has a much higher melting temp than Al. using DC electrode +ve this isn't a problem as the flow of electrons breaks up the oxide layer. DC +ve is limited with the TIG process as the electron flow puts a lot more heat into the tungsten (about 2/3rds of the total arc heat occurs at the +ve electrode).TIG DC electrode -ve causes problems because of the difference in melting temp between Al and Al oxide (the oxide layer will not be removed by electron flow). using argon the result would be moulten Al covered by a solid film of Al oxide. pure helium gives a much hotter arc making it possible to melt the oxide sufficiently to get a sound weld. the process is more suited to welding thick sections.TIG AC gives the benefits of both worlds as AC is simply switching between DC-ve/DC+ve. pure argon is the usual choice of gas (easier arc starts and cheaper- need to flow more He as it's lighter than air). Ar/He mixs can be beneficial (easy arc starting of Ar/increased heat of He), albeit at increased cost
Reply:Originally Posted by chopper5argon helps to maintain the arc .on thick aluminum straight helium is the way to go.so we have an disagreement lolit's all good zap
Reply:Originally Posted by DirtyLittleSecretSo, I could easily go with another smaller "mixed bottle" for whenever I need to do aluminum (if ever I get the hots to do so) and be fine?  Im totally new to this stuff, but dont want to make a mistake.
Reply:Originally Posted by Roy HodgesMost people keep forgetting  WHY Helium is needed when welding  THICK aluminum . Argon is "ABOUT"  10 times as dense as helium . therefore helium allows the heat penetration into the thick aluminum ,and quick melting of the aluminum. So, on thin aluminum , argon is needed to control penetration (and cleaning effect) helium is kinda "dirty" compared to argon, that's why some people think argon is all that's ever needed. WRONG  !!!