Answer:
Aluminium will corrode easily with salt water or water in the atmosphere. There are many ways to stop it corroding, one of which is painting it. Paint will provide some corrosion resistance but will not help a lot if it is going to be going through a lot of wear and tear, as the paint will be scraped off and leave no protection. Another method is to just let the aluminum be in contact with air and it will almost instantly form a very thin layer of Al2O3 which then allows very little corrosion to occur, and if the Al2O3 is somehow removed it will almost instantly reform to provide resistance again.