Where is the dent, near the end? I used to straighten, and repair aluminum light poles. The make little hydraulic jacks about 1-1/2" high tha produce about 20,000 lbs of force. You put it inside between two blocks of wood and push the dent out.
If it is real close to the end you probably can do the same thing with 1/2" bolt of the right length and a coupling nut.