well to add on my previous post, I supose if one could get the durafix flux sticks which I use for brazing/soldering aluminium thin enough it could be done,
the problem is (tried some foil just for fun) you need to heat up all 3 parts the: to weld pieces and the flux to 400degrees using a propane burner. but the foil is allready gone before the fluxstick even wants to melt. you may not hold the fluxstick itelf into the flame because you'll loose strength in the joint. the flux stick you normaly get from durafix are quite thick 3mm or so, but you can strecht them out pretty good which makes them thinner.
thicker alloy brazing is pretty easy once you had some practice and I think it's a nice alternative for Tig on non structural parts, and you can even use this as a form of helicoil, fill the destroyed hole up and rebore and tap. it is really strong of the parts are perfectly clean, just don't use it on parts that go over 370degrees celcius.
I also have never actaly met anyone who did tig foil together but I am sure it can be done, question remains on the purpose of such skill but hey, why not if you can.
grtz Thomas