If they are bare aluminum, you can get an aluminum brightener product from auto parts stores, you spray it on, scrub and then rinse. It is nasty stuff that contains phosphoric acid so you need to wear rubber gloves and eye protection. Here's the product at NAPA, but other stores carry similar products.
https://www.napaonline.com/en/p/MCR1458
If they are the newer style that are painted black the aluminum brightener product isn't a goos choice as it will remove the paint. You may want to look at something like Simple Green or Purple Power, those products will also damage the paint if left on for any amount of time so you need to be careful with them as well.
Worst case, you can get them glass beaded to clean them down to raw aluminum. Don't use sandblasting as it will leave a finish that doesn't look right.