Welding Tips and Tricks

i want to weld aluminum alloy windows which include many small square tube with side length 10mm and with thickness 1.5mm. the small square tube should be fillet welded on the large square tube with thickness 2mm.
how can i use Mig weld to achieve a sound weld?

I would recomend tig welding this if possible. Mig welding something that small will not looking that nice, especially mig welding al.