Tesla Coil/Slayer Exciter : Aluminium or Copper wire?
The conductivity being only two thirds of that of copper wire of the same cross sectional area shouldn't be a problem, especially given a very low current application like a tesla coil secondary.  

Enamelled aluminum wire will thus be just fine electrically, but mechanically it is problematic: It won't wet with normal solder, be it lead free or not, unless you actually have copper clad aluminum wire. There are some fancy solder/flux combinations that strip the oxide layer and bond with aluminum, but they aren't exactly common. Even crimp connections of AL with copper/brass fittings are problematic, as such joints tend to corrode, but they should still be your best bet in this case. Another option is to terminate the AL wire with conductive epoxy.