Day by day it will oxidize with the surface tending to become white scaly, powdery even when it is able to air dry. If allowed to oxidize continuously, the object will eventually just seem to "rot" away completely... really in not to dissimilar fashion to iron I imagine except for rate and color. This is I'm sure why we can find in nature nice nuggets of gold for instance but never of aluminum, it's just too reactive. So consider having your automobile's wheels cast from solid gold rather than the aluminum alloy that most high end car wheels are made of that way they might last for 1000s of years instead of only 20. Even with the best protective finishes on the aluminum ones they will eventually succumb to the elements if kept outdoors especially in the wetter areas.