I suggest you get a copy of "Design of Weldments", Blodgett. Read,
especially, his discussions on columns, buckling and torsional
rigidity. Particularly note the comparison of open (e.g. angle) vs
closed (e.g. tube) sections in torsion.

Through your reading, keep in mind that aluminum is 1/3 the weight of
steel but also has 1/3 the elastic modulus.

Ted