What to use for exhaust pipe?

Anybody use aluminum NPT pipe? I've had the problem with iron NPT pipe rattling and chewing the threads out of my flathead Briggs & Stratton blocks, which are aluminum also. I'm thinking of a snug aluminum adapter fitting (something stubby) first installed in the block and then extended with more aluminum pipe and end adapter to receive a Briggs muffler. Could sort of patch the thread problem at the block, and relieve the stress from weight of iron pipe.