Yes. Very difficult if you don't protect it. Road salt instantly ruins the finish. There are several ways to fight this problem, though.

One is to have the parts laquered. You get a hard, clear waterproof finish. Don't spill gasoline or oil on it, though. It also yellows if it gets too hot.

Another way is to find a powder coating shop and have a hard clearcoat baked on. More resistant to engine chemicals, and maintenance free... but over time, it can get dull from repeated temperature changes. I'm not a big fan of this idea, but it works for some people. I like the shine of the bare metal better than the plastic-like coatings. You can't bust out a can of Mother's metal polish and shine them back up once they're coated.

There's another product called Zoops Seal that seals aluminum from everything, and it's semi-permanent. It's not resistant to abbrasion, but it's resistant to anything else you'll find in an engine bay... fluids, gasses, etc... It's a polymer coating that is invisible once polished. It won't yellow or dull, and you can shine your parts back up with your favorite products if for some reason it ever does go dull, then seal it again. I'm going to try it since I've got so much stuff to seal. check it out... http://www.zoopseal.com This crap is expensive, but probably not in comparison to what it would cost to get 9 parts powder coated clear.