DC TIG on aluminum problems

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I had a job in the shop that was too thick for my tig machines. 6x1/2 tube welded to 5/8" plate. I tried to weld DC TIG using helium with horrible results. The helium was the best grade I could buy locally and tagged welding grade. Ultra high purity was special order and about $400 a bottle. The job had to be done before I could even get the ultra high purity so I went with the tested welding grade.  The plate was cleaned and brushed prior. I started with dc- and got lots of soot and odd colored deposits, worse on dc+. AC attempt is in the lower right. The plate tigs fine on AC with argon. I tried big cups small cups, gas lens, 20-35+ cfh flow out of an actual flow meter. I tried lantanated and ceriated tungstens. Some attempts were better than others, but all were awful.  The machine I was using is a Sync 250. I ended up welding the heavy sections with my spoolgun and 1/16" wire, then tigging the 1/4" plate caps on using ac and argon. I would still like to know where the fault lies though Attached Images
Reply:What filler are you using? Looks like  bad gas to me. Have you tried blending that helium into the argon at a 50℅ rate and welding AC?Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:Have you tried the helium on A/C?Miller Big 40GMiller HF-251 D High FreqVictor OA Lincoln 135 MigMK 3A CobramaticBridgeport J HeadCronatron OxylanceRadnor ACAG TorchWeldcraft TIG Torches1 blown knee and two 5 Gallon pails away from being a hero.
Reply:Originally Posted by Cape Cod GaryHave you tried the helium on A/C?
Reply:I am familar with a die repair shop that does aluminum on DC with straight industrial grade helium and 4043. The only issue they ever had was when they got some 5356 by mistake, it left some black spots that the wire mfg attributed to too much magnesium.I tried this at home and was amazed at how much heat a 1/16 tungsten could put into a block of aluminum.
Reply:Pre heat the parts.12v battery, jumper cables, and a 6013.I only have a facebook page. https://www.facebook.com/pages/VPT/244788508917829
Reply:5356 filler, after the first weld that little 1/4" plate was plenty warm. The lower right weld was a/c. I didnt think to try 4043 filler, but the job required 5356.
Reply:That should be no problem for the 250 on regular argon and AC. I've welded much thicker cylinder heads after pre heating with a 175.12v battery, jumper cables, and a 6013.I only have a facebook page. https://www.facebook.com/pages/VPT/244788508917829
Reply:what type of tungsten are you using? http://www.millerwelds.com/resources...ten-Selection/    Aluminum takes a certain tungsten.  http://www.millerwelds.com/resources...ints_tips.htmlGas Selection. http://www.millerwelds.com/resources...-for-beginnersDid you bring your tungsten to a balled end or a pointed end?
Reply:Originally Posted by AndrewDavenport89what type of tungsten are you using? http://www.millerwelds.com/resources...ten-Selection/    Aluminum takes a certain tungsten.  http://www.millerwelds.com/resources...ints_tips.htmlGas Selection. http://www.millerwelds.com/resources...-for-beginnersDid you bring your tungsten to a balled end or a pointed end?
Reply:No, I have not. Just throwing a couple ideas out there to look at. I am reading up on it more and more. I really like GTAW, only used it on steel for welding coupons on pipe (practicing). Haven't really mastered it yet. Still fooling around with it when I can get ahold of a tig rig. Thought those sites might be useful references for him to look at when I saw the thread.
Reply:You need to be in DCEN (straight polarity)  not DC+ as you said in your original post.   Our try a mix of argon and helium on AC.Tiger Sales:  AHP Distributor    www.tigersalesco.comAHP200x; AHP 160ST; MM350P,  Spoolmatic 30A; Everlast PowerTig 185; Thermal Dynamics 60i plasma.  For Sale:  Cobra Mig 250 w/ Push-pull gun.  Lincoln Wirematic 250
Reply:Originally Posted by AndrewDavenport89No, I have not. Just throwing a couple ideas out there to look at. I am reading up on it more and more. I really like GTAW, only used it on steel for welding coupons on pipe (practicing). Haven't really mastered it yet. Still fooling around with it when I can get ahold of a tig rig. Thought those sites might be useful references for him to look at when I saw the thread.
Reply:Aluminum should be welded dc- (negative) helium or argon or a mix will work. There is no cleaning action going on so it will look dirty. You must brush it after each bead. You also cant see a puddle because the aluminum oxide on the surface melts at a higher temp than the pure aluminum under it. The trick is to get enough heat in it that you should have a puddle and then start jamming filler through the oxide layer and into the molten pool underneath. Its dirty messy and easy to screw up but it does work.Btw just switching to 75/25 helium/argon mix will allow you to weld much thicker aluminum with AC. Its kinda blow your mind hot if you are used to straight argon.Lincolin Power Wave 450, Lincoln Powermig 255, Lincoln Pro Mig 140, Lincoln Squarewave Tig 275, Miller Big 40 G(with Hobart Hefty suitcase), Thermal Arc 95S and Esab PCM875 in an already full machine shop.
Reply:Originally Posted by MinnesotaDaveDC aluminum welding is a very different animal - when you've gotten good at AC aluminum it is good experience to try it in my opinion.I've done most of my DC experimenting on DC+ for thin stuff with Argon.  The thick stuff he is doing is welded on DC- with helium or AC with argon/helium.The run-of-the-mill data commonly listed only covers AC aluminum.
Reply:Originally Posted by AndrewDavenport89AHHHH I see what you mean Minnesota, thanks for clearing that up. I wasn't giving good info then. My bad. So how thick is too thick for DC+?  Like, when do you decide you need DC- or AC instead of DC+? Get where im going with that question?
Reply:I gotcha. well that clears that up for me! thanks dave! Learn something new every day!
Reply:I did play with it a bit more over the weekend. I was able to get some passable welds, and they were a bit sooty and needed brushing. #8 gas lens worked best for me at about 35 cfh. Very easy to drop the puddle on the floor. They were not AC appearance beads, but I could tell that with a wee bit of practice it would improve enough to be acceptable.
Reply:Originally Posted by walkerI did play with it a bit more over the weekend. I was able to get some passable welds, and they were a bit sooty and needed brushing. #8 gas lens worked best for me at about 35 cfh. Very easy to drop the puddle on the floor. They were not AC appearance beads, but I could tell that with a wee bit of practice it would improve enough to be acceptable.
Reply:The gauge I was using is calibrated for argon, so I am sure it is off a bit. I tried gas flows across the board, and that is what worked best with the helium. Less flow and I got that rusty colored deposit. Not saying it is right, but just what worked best. I dont think I am going to keep the cylinder, just return it and get the stupid lease deposit back, call it a good education and be done with it.