trouble welding 6061

hey guys, i was recently welding some .25 6061 plate to .25 wall 6061 tubing in a fillet weld...welder is a 12 or so year old lincoln 255a machine...i tried green pure tungsten, red 2% lanth, and gold 1.5% thor all 3/32" with about 20 cfm flow and up to 230 amps AC...it gave me more trouble than a little. i couldnt get it to puddle for SHIT, and when i did it would blow out and a few times actually exploded all over me...i eventually got it done but not without great frustration.

prep was 150 grit hand sand and clean with denatured alcohol. material was sourced from mcmaster.

basically most of the welds look like a bag of smashed assholes and it pisses me off. a lot of them have blackish spots on them.

i have never run into this, granted i dont weld a ton of aluminum, but still what the hell.

any ideas?

I believe you need more amperage, especially if can't adjust the wave form. Try 90/10 ArHe blend and you still might have to preheat with oxyfuel torch. Blowout might be from outgassing-- you may need more venting inside the tubing.

Definitely have to preheat that. Could be some dirt somewhere on it. I'd try one another piece of al and see how it does. I had one event where I went to weld something in Al and couldn't get the damn thing to do anything good, oxidized the weld as if there was no gas flow, etc. Tried various things, searched what I could, and gave up on it. Never had that issue with it before but machine had been moved in the last 2yrs or so, and quite possibly something shaken loose or messed up inside. took a few pieces home and they welded great with my welder.

thanks guys...i just wanted to make sure i wasnt going crazy

1/4 inch is on the thick side for a 250 amp machine... but you can do it without preheating but it will take a while to get the pice up to heat. What machine is is?
Also, sand paper can be a bad thing. Glass beading is bad. Best thing to use is a stainless wire wheel thats never touched anything but aluminum. The aluminum oxide or glass embeds in the soft aluminum and ruins the weld. Also you have to make sure the peices are not clear anodized before you start.