Ya know, theres this awesome website where you can find lots of info really quicky, its called GOOGLE!!!!!!!!!
An awful lot quicker to search for something like 'aluminum properties' or 'aluminum grades' than posting on a fourm and then waiting several hours for a responce; most if not all decent aluminum r/c parts are made from either 6061 or 7075m since they have the best properties for the intended use- gander at the info I found if you please:
http://en.wikipedia.org/wiki/Aluminium_alloy
you will probably need to read this to make more sense of the info on work hardening:
http://en.wikipedia.org/wiki/Work_hardened
Toodles....