I've had good luck on non-critical aluminum joint applications using epoxy adhesives in combination with rivets. The rivets provide both positioning and clamping functions, while the epoxy provides additional strength and seals the joint. This is a "belt and suspenders" approach! In order to maintain a good bond line thickness, avoid squeezing too much of the adhesive out of the joint. To do so, you can use shims or a scrim cloth (screen).
FYI: Regarding the latest aluminum welding tech, google "friction stir welding". I saw sample parts at EWI (the Edison Welding Institute) back few years ago. Very cool, but probably not a DIY technology.
