I know aluminum does not rust all the way through but it does get surface rust on it as i have seen plenty of aluminum boats with surface rust on them.
Don't think I'd call it "rust." The only time aluminum really 'rusts' is when exposed to liquid Mercury. Otherwise, it is just minor oxidation, and it is better
at protecting the boat than paint is.
Aluminum is actually a highly reactive metal, with very poor qualities. In fact, most of the properties of aluminum make it virtually unsuitable for marine use. But, what makes it usable is the fact that it begins to oxidize within seconds of being exposed to air. It is this thin layer of aluminum oxide that makes aluminum the wonder metal. The oxide melts at around 3 times the heat that the aluminum does, which is why we have to TIG weld it on AC, and not DC (the AC current breaks the oxide layer up).