grade of aluminum?

there are alloys

1XXX higher purity (very soft-electrical conducting)
2XXX copper alloyed -good for threading, usually a cast piece
3XXX silicon with copper and/or magnesium alloyed- cast
4XXX silicon alloyed -cast
5XXX magnesium alloyed
6XXX magnesium and silicon
7XXX zinc -aircraft alloys
8XXX tin or other- depends on wrought or cast
9XXX other
other designations for casting alloys
too much information?

I have seen brilliant 3003 alloys
sometimes they are "brite" dipped
in Hydroflouric acid and rinsed

ASM rated them all about the same for corrosion resistance
except 2XXX alloys

a good clear aluminum sealer would be a good idea