Stacks

It's very possible but, they won't stay polished like chrome or polished stainless.

 

Ask @Straight Stacks .

 

I only run Dynaflex.

 

I've never seen or heard of aluminum being used. You can polish them as well as a fuel tank or rims but you'll be doing it often.

Some other problems I would expect:
1. They will get nicked and scratched easier (think when trying to remove bugs with a bristle brush).
2. If you apply a clear coat the heat might peel it off
3. Since Al conducts heat way better than steel, the pipe will be hotter.
4. The pipe will be hot all the way to the top
5. The pipe will take longer to cool
5. They will need to have a greater wall thickness....probably 3/16" I would guess.
6. And perhaps most importantly, because AL expands more than steel when heated, I would expect your connections to come loose and you'll have exhaust leaks.