The posting about using baseball bats for tapers was one of the most
excellent ideas I've ever heard, and is the reason I love this list.  But
today as I've been cruising the web waiting for a test to finish, I found
out it was even better than I thought.

Aluminum ball bats (and tennis racket...and bikes) are often made with an
Aluminum-Scandium alloy.  Not only is it weldable, but it's weld will be
better than any other aluminum's weld.  There's even talk of welded aluminum
aircraft structures in the near future.

For those who can digest it:
http://home.no/al-sc/papers/Scandium%20in%20Aluminium%20Alloys%20-%20International%20Materials%20Reviews.pdf

It's a little over my head, but near the middle is a section that describes
how the Scandium will keep the allow pliable and avoid crystallization...and
other good stuff.  

It appears that baseball bats wouldn't just make good tapers, they would
also make great rotor housings.  The local used sports store might just make
for a ready source, expecially if you tell the owner that you'll pay for
anything that's not sellable as an actuall baseball bat.