I guess the place to start is a few notes on the material we are interested in here, aluminum and it's alloys. Because aluminum is not as strong as steel larger diameter tubes are generally needed to achieve the required strength. Lugs are generally not used and the frames are glued or TIG welded together.
There are a couple of major players in manufacturing aluminum tubing for bicycle construction. Italian manufacturer Dedacciai has be one of the leaders in tube production. Pez has a nice article on a visit to Dedacciai:
The other major player and innovator has been US manufacturer Easton.
I found this article by Easton about adding Scandium to Aluminum and why. I think there are a lot of misunderstandings when vendors use the term "Scandium" in their products.