Probably not the best idea to use an aluminum kettle. The problem is aluminum is a reactive metal, and when any food or liquid that doesn't have a neutral pH, so anything slightly acidic or alkali, is in contact with it metallic and other off flavors can be produced. The reason being because what you basically create is a primitive battery, and really, who wants to drink battery acid? Although, I know some of my brews have ended up tasting like battery acid regardless of the type of kettle, haha.
Anyway, it's best to go with a "non-reactive" pot/kettle. So, Stainless steel of course is the best option. Technically anodized aluminum, and can definitely work, it's just finding one of the right size can be problematic.
I hope this info helps a bit, and that I haven't come off too much like an arrogant ass. Haha.