[genter]

How would you fabricate a frame from extruded tubing? Welding would destroy the grain structure.

[A_D_E_P_T]

That looks like it's an active research problem: https://www.sciencedirect.com/science/article/pii/S266633092...

At a glance, though, the problem doesn't seem insurmountable. FSW appears to work.

[le-mark]

Brazing has a long tradition in building bicycle frames.

[Scoundreller]

And lugs

[etrautmann]

Aren’t truck chassis increasingly made with epoxy or other adhesive bonds?