http://www.staplaultrasonics.com/pro...eam-welder.htm

That url is for a company that makes ULTRASONIC WELDERS which work on
aluminum. I was reading in Wikipedia where the aluminum foil rolling
mills use ultrasonics to splice the rolled sheet back together when it
breaks in process.
The beauty of this method is that it generates very little heat and
so the al workpiece doesn't warp, which is a huge improvement over
thermal welding. Ultrasonics appear to be a lot simpler, with more
reliable seams, than the exotic Friction Stir Welding.
I haven't yet researched how adaptable this method, and its
machinery, is for homebuilders. It's just an exciting method to know
about. high cheers, Allen