"Proper" stripper is a mix of particularly nasty acids (NaOH is a base though and uses a different process), and unless you're a pro, you generally don't want to go through the effort of obtaining said chemicals, handling them, clean up, and responsibly disposing of them (or you could be one of those people that just dumps hazardous chemicals down the sewer because all this regulatory stuff is just a conspiracy). That looks rather dark and may have been etched by the cleaner. Aluminum is a soft metal, and one of the relatively aggressive metal polishes mentioned by others will put a very bright finish on aluminum in quick order with a little elbow grease.