Aluminum welding, edge-wise

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I keep having a problem welding a piece of aluminum on the end or edge.  This time i am trying to weld a .040 divider plate into an aluminum radiator tank.  I take a hacksaw and cut a slot in the tank, i make a patten and cut a .040 divider plate and slide it into the hacksaw cut and leave about .015 exposed above the tank.  The divider is a tight fit.  I clean as i would all other alminum welds but when i try to tig weld it is full of contamination, the aluminum never gets that bright shiney surface to it.  The tank metal looks ok but the divider sitting edgewise just fouls the works.  Anybody else have this problem, any suggestions?  I am an experienced welder and weld aluminum often, i have an old 330A/BP, i have 2% toungsten (1/8), straight argon, 9lbs.I seem to have this problem whenever i weld alum edgewise, in this case i have not purged the tank and the radiator is used and contaminated inside.  I have tried both 4043 &5356 rod, although the problem arises before i add the rod.Thanks, appreciate any suggestions  oj
Reply:probably not the answer you are looking for, but using a 1/8" tungsten for a .040" divider seems like a mismatch to me.  seems like you'd be able to get better starts with a significantly smaller Tungsten, like a 1/16" or a .040" tungsten.  just a thought, though.
Reply:Hello ojh, the first thing that comes to mind here is: "used radiator", being that aluminum is so porous and the coolants and other items that could have been present in this radiator are likely to have leached into the pores on the inside surface of the tank. This could cause these contaminants to show up as soon as the weld pool is initiated. I don't know the proximity of the seams of this radiator or whether it has been soldered together or tig welded, if it has been soldered then you might be fighting the solder being wicked into the weld pool due to heat and capillary action, kind of like trying to weld something that has been brazed or soldered without cleaning those materials off. Has this radiator been tanked or otherwise cleaned? A couple more items for you to consider. Best regards, Allanaevald
Reply:using a fresh hack saw blade made for aluminum? using dirty old,  oily blades with steel shavings will cause ferrous inclusions hence the weld metal will never be clean.aevald has a good point.  about the cleanliness of used tanks. Aluminum is very porous.I would check the cleanliness doing an edge weld shouldn't be any different than anything else  in fact they tend to be a little easier.
Reply:Thanks Burning, you're right the tig is large but i have better luck with a bigger knob for some reason.Allen, the radiator is from a race car, kinda new and has water only.  The tanks are welded and the fins are epoxied.I guess you guys have no problems welding edgewise.  I can see it happen, the edgewise metal turns to crud, almost like it wrinkles up turns grayish.  All this happens very quick, milliseconds kinda quick.
Reply:Metarinka i bet you're right!  Hacksaw blade!  I probably cut steel with it last and the small cutting are pounded right into the aluminum as i am sawing!  Good thinking.  I can clean the whole mess out, replace the .040 with .090 divider.  I'll get back tomorrow with results.  thanks again, oj
Reply:To finish this thread, i cleaned the intial weld and redidit, it isn't pretty but it held pressure so it is done.  On the second edgewise plate i did exactly as the first but cleaned the blade on the sawzall, paid extraspecail attention to cleaning the edges of the cut and drove in the same size plate as i used in the first cut.  It welded very nice, not pretty but i just moved right thru the joint with minimal hassle.  You guys were right, the saws' teeth held minute pieces of steel/contamination and that is what caused my problem.On the positive side, this problem lead me here and i might stick around for a while.  Thanks, oj
Reply:Originally Posted by ojhTo finish this thread, i cleaned the intial weld and redidit, it isn't pretty but it held pressure so it is done.  On the second edgewise plate i did exactly as the first but cleaned the blade on the sawzall, paid extraspecail attention to cleaning the edges of the cut and drove in the same size plate as i used in the first cut.  It welded very nice, not pretty but i just moved right thru the joint with minimal hassle.  You guys were right, the saws' teeth held minute pieces of steel/contamination and that is what caused my problem.On the positive side, this problem lead me here and i might stick around for a while.  Thanks, oj