Earlier quoted context omitted.
You cannot weld aluminium, or at least not on the cheap. The only real "weldable aluminium" known today are scandium-aluminium alloys which are both hard to get, and expensive.
Cannondale bicycles would like to have a word with you. They started out making bikes out of 'aircraft aluminum' which if memory serves was [6061]( https://en.wikipedia.org/wiki/6061_aluminium_alloy ), which is magnesium silicon, not scandium. Do you mean you can't weld aluminum in an oxygen environment? I think you're right about that at least. I think they used argon, and then had a patented(?) annealing process to…
And you still have very painstaking process of finding the optimal welding recipe for the part, post-treatment, and defectoscopy.