aluminum welding problem

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I have run into a problem now a total of six times in 200 procedures, where the test plates are acting like they have severe contamination (no pictures allowed) Very similar to welding on a aluminum salt box that has been in service for years.The high frequency arc changes sound noticeably and there is a combination of lumpy carbon bits and fine white oxide on the plate. This happens randonly on the plate for an inch or two and twice for the entire plate length, today it happened on pipe but only for a couple of inches then everything was perfect.material is 6061 to 6061 or 5052,3003 but 6061 is always the common material, filler is either 5356 or 4043thickness from 1/8" to 3/8" and three different mtr's.twice torches were rebuilt and gas flow confirmed on each occasion with no change in contamination. Electrode stickout is at most the cup diameter and gas flow for 3/8" cup averaging 20-25 CFH.All material is acid dipped and brushed before welding or blending wheel and wire brush; and cleaned with gun wash on one occasion to see if that helped.The aluminum is stored indoors at the supplier and at the shops,, both shops have steel welding occuring nearby, the tensiles do not indicate high levels of steel contamination in fact they are normal.There is antispatter spray available but not used on aluminum.Thought writing this out would help, I am missing something real simple I just know it. Any ideas before my last hair falls out?? johnLast edited by jnoon; 03-06-2012 at 07:47 PM.
Reply:Are you the one under the hood? If so describe what happens, more. Please. When the arc passes over this area.
Reply:Not me under the hood, but nearby, the arc sounds like half of the high frequency is gone and the weld gets lumpy (real word), fusion is poor at best and the back of the weld turns to a blob (partial joint penetration) and basically starts falling away.I would almost say there was some weird crap happening inside of the aluminum. The one thing not helping solve this so far is it happens in two shops and multiple suppliers.There is no visible porosity in the welds however three times the welds cracked full length (15") as soon as the weld was stopped.john
Reply:I have been allowed to take a couple of samples back to the office of the failures and so far the only thing that appears to be happening is a combination of small cup and having the torch at a poor angle, also the torch was offset in the groove and it looks like there may have been some air getting dragged into the joint along with the shielding gas.I will post pictures this weekend.john
Reply:New to welding aluminum myself, my problem was the tungsten sickout, try reducing it for a bead and see if she rolls. This was on a 1/16th ceriated tung about 17 cfh and a 7 cup. After I used less sickout, I  was rollin like a raver on 7 pills of X.14' PowerMig 210 MP13'Burntables 5x10 CNC Table14' SAE300 HE on a 12' Ram 4500 60 CA 4x4. Custom bed/bottles/reels.87' SA250d, 78 SA200,11' Ranger 250 GXT AC/DCThermal Dynamics Cutmaster 8112' Lincoln Precision Tig 22508' LN25
Reply:dirty buffing wheel / brush might be adding gremlins to the mix..............bw
Reply:Lack of good gas coverage or bad gas, is where I would start.  Too far of a stick-out would result in poorer gas coverage.Last edited by DLite; 03-15-2012 at 11:09 AM.
Reply:Originally Posted by jnoonNot me under the hood, but nearby, the arc sounds like half of the high frequency is gone and the weld gets lumpy (real word), fusion is poor at best and the back of the weld turns to a blob (partial joint penetration) and basically starts falling away.I would almost say there was some weird crap happening inside of the aluminum. The one thing not helping solve this so far is it happens in two shops and multiple suppliers.There is no visible porosity in the welds however three times the welds cracked full length (15") as soon as the weld was stopped.john
Reply:I'll take "What is parent material corrosion and voids full of acid" for $300, Alex.Two turn tables and a microphone.
Reply:that and a few other things, just have to convince them to run a lager cup when appropriate. Its hard enough convincing people backing gas is good for aluminum and too run over 15 CFM on the shielding gasjohn
Reply:Any chance the gas was actually turned up too high and the resulting turbulence was dragging air in at the sides? What about trying a gas lens to 'moderate' the flow and allow less gas to do the same job?
Reply:I use a gas lens 99% of the time, and have been doing so since the first time I used one back in the 80's.
Reply:#6 cup, with a gas lens and 20-25cfh don't really jive too well. Too high of a flow rate for a small gas lens.