[Antennas] Rusted and frozen steel pipe in aluminum tower top section.

[Raymond LaRue]

I have an aluminum tower top section with a steel pipe (taken from a
pushup mast) that has rusted within the aluminum collar (6061-T6?) and
will not budge.  
 
Anyone have any experience with how to remove the rusted pipe without
damaging the softer aluminum collar?
 
Your attention is appreciated.
 
Ray, W4BYG