I don't think there is a practical way to heat-treat aluminum at home. I think you need a pretty fancy (i.e. expensive) computer-controlled heat-treat oven.
I don't see any particular reason to do it, anyway. Buy the aluminum alloy with the properties you want to begin with. (6061 is probably not it. 2024 is fairly common, and harder.) The only reason we don't do that with steel is because hardened steel is too hard to machine readily...unless you're grinding it. But that's not a problem with aluminum.
Also, the stiffness of all aluminum alloys is probably about the same, give or take a little.
Check some of the websites of aluminum manufacturers (Alcoa, Kenametal, etc.) They probably have specs and application data online.
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