Aluminum frames are made in both 6061 and 7005. 6061 requires high temperature heat treating to bring it back to full hardness after welding. 7005 requires only a low-temp aging process, has slightly higher strength but suffers from fatigue corrosion.
Butted tubes are not easily acquired and only available in a few profiles from chinese mfgrs. and usually aren't available in small quantities. Simply knowing the yield strength of a piece of material isn't a decent way to engineer a frame and most frame builders are more focused on the craft of frame building and selling rather than understanding a strange material. Aluminum builders will also make their own dropouts, BB shells, seat collars, head tubes and all the tooling required to construct and process a frame as well as some metallurgy and engineering skills. Usually these technologies can only be supported with great volume.
When Easton drove aluminum to low-market in 92 it became difficult for most good builders to continue. Chris Herting at 3D racing is very good.