THis is what we used to use the the Navy for repair aluminum castings regardless.

http://www.devcon.com/products/products.cfm?brand=Devcon&family=Aluminum%20Putty%20%28F%29

Does NOT look like aluminum when cured and it will not polish out. Dunno if you can powder coat over it either.

According to the MSDS information "Heating resin above 300 F in the presence of air may cause slow oxidative decomposition." so it may not be best.

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.