The wikipedia article on FSW is a pretty fascinating read: http://en.wikipedia.org/wiki/Friction_stir_welding http://en.wikipedia.org/wiki/Friction_stir_welding

The wikipedia article on FSW is a pretty fascinating read: http://en.wikipedia.org/wiki/Friction_stir_welding http://en.wikipedia.org/wiki/Friction_stir_welding Basically welding using a combination of joining pressure with a very high speed spinning steel bit that heats the aluminum joint via the friction created by it spinning on its surface. That spinning bit travels along the seam heating, and then it's pushed together when it's no longer quite solid, and spun together by the bit. Some interesting discussion of the crystal structure formed and the associated mechanical properties, as well.