Speaking of Anodizing, it is a process which just speeds up what nature will do to aluminum.
The manufacturer can add dyes to it to make pretty colors but with, or without the colors it still is a process that creates Aluminum Oxide rapidly.
As I mentioned, even without Anodizing, the Aluminum Oxide will occure naturally from the reaction between the aluminum and the oxygen in the air.
Something to remember about Aluminum Oxide. It makes an excellent electrical resistor and more importantly to us Muzzleloaders, it makes great Sand Paper.
Aluminum Oxide is harder than steel and given a chanch it will wear the steel.
As others have mentioned, aluminum can also become contaminated with dirt/sand and grit, but then, so can wood.
If you use a rod guide, there is no problem with aluminum, but without it, IMO, your asking for trouble.
Another problem with aluminum is that most of the cleaning rods made from it do not use the high strength, heat treated alloys (like 6061-T6).
The softer, weaker aluminums threads will wear rapidly creating the possibility that a cleaning jag or ball screw can be lost down the bore.
In this reguard, brass is much better suited as a ramrod provided you keep it clean and use a muzzle guide with it.
(Just my 3 cents worth! (Inflation, don't you know?))
Me? I use stainless steel range rods with a nylon or brass muzzle protector.
Zonie