Car wax or similar should keep it shiny for months after you've polished bare aluminium with a metal polish.
I think a metal polish like Autosol has some wax in it already, but perhaps the grinding action of the polish doesn't leave much wax on the newly polished surface, so giving it a good waxing should keep it shiny longer. But still, whenever I've polished an alu part with just the metal polish, it doesn't go dull within a few days.
I wouldn't say it's corrosion either. A bare aluminium surface will react with oxygen to form a very thin oxide layer, but the oxide will stop any further reaction. Anodising is just a thicker oxide layer applied by the manufacturer. Damaging corrosion is usually caused by salty water, either from road salt or sweat, it will eat away aluminium, both unanodised and anodised, by turning it into a white powder.