I just started welding not too long ago, and up until now ive only been learing to weld aluminum plate and so far i think im getting the hang or it. So i wanted to try out some aluminum piping. At my local srcap yard i found a bunch of 3" diameter x 3foot @ 1/16" thick Aluminum piping in their 6061 section.

Im having a real hard time trying to weld this stuff. everytime i make a puddle and start moving i can see a bunch of crap floating on the top of the puddle. this happens even after i hit it with a stainless steel brush real good. Maybe this stuff is annodized??? Or maybe a weird alloy? Anyone have any pointers for thin Al pipe.

Settings on Syncrowave 250
High frequency always on @ 70
3/32" 2% thoriated
100% argon @ 15CFM

Here are some pics.