I've done some alu brazing recently during a O/A course I took. It is freaking difficult (for me), and I believe you would want to heat treat afterwards, but it does work, and seemed really strong - we were t joining 1/16" alu plates. I think we were using harris alu brazing rods and flux.
I bet you could do a bike out of this stuff. Someone should braze up some alu joints, then braze them. If the tube breaks first.....