alloy wheel cannot be removed upon a flat tire

Hi,
I own a peugeot rally '99 (16v 1.6l). Last year I have replaced the
original wheels with TSW alloys.

The problem is that when I have a flat tire, even when I take the
bolds out, I cann't remove the wheel. For some reason the aluminioun
alloy sticks to the metal (iron) surface. Each time I have a flat tire
I need to call road assistance, the mechanic cannot do anything and we
loading the car to the garage. When they eventyally managed to remove
the wheel (by punching it for more than half an houre wih a hummer)I
have noticed a bit of rust at the junction on iron and aluminioum,
whuch might cause the problem.

My question is very simple.

Does anybody experience similar problems with alloy wheels?
Is there anything I can do to prevent this unfortunate situation?

I have already tried to put some grass in an efford to protect the
surfaces from rust, by didn't work.

Any ideas are very wellcome.

thanks,
MemortIC.