Learning to weld aluminium

I was lucky enough to use a friend’s TIG welding setup earlier in the year to make a frame from stainless steel box section. Since I mostly machine aluminium in my workshop, I decided it was time to learn to weld pieces toegther, not just turn them into swarf. Here is my first attempt on a piece of 2mm thick sheet:

It took a couple of runs to get the current set to something reasonable, the early runs being just to the left of the torch. The longer weld is actually joining two pieces of sheet together; the reflections exaggerate the ripples. While this top side looks ok (pretty good I’d like to think for a first attempt), the weld doesn’t penetrate right through for most of the length so a bit more heat is needed next time. There is also some contamination of the weld visible (black holes), probably from something on the edges of the sheets, which I didn’t brush clean.