One note about aluminum: Unlike steel/iron where the corrosion is making holes in the surface, eventually leading to material erosion and failure, aluminum's oxidation process actually expands to seal and protect the underlying metal, so when you remove the oxidation, you remove the protection it furnishes.
The exception (there are always exceptions) to the above is that some alum alloys in constant saltwater exposure do corrode internally and waste away.
The later models of Hehr windows
have a black anodized finish of some sort that seems to hold up quite well.
Pete in the RatHaus, parked for a while at SoMineral Creek, near Silverton Colorado, where it's very cool