[cptskippy]

The rear underbody of the Y is aluminum but it still has a steel chassis. Aluminum can never fully replace steel because it lacks the strength and rigidity.

Regardless, aluminum is expensive to extract and refine, requiring a tremendous amount of energy. In terms of cost, on average aluminum is more expensive than steel.

[robocat]

> Aluminum can never fully replace steel because it lacks the strength and rigidity.

Huh? The main reason is because Aluminium is expensive. The BWW i3 uses an Aluminium frame exactly because it reduces weight. https://www.marklines.com/en/report_all/Munro003_201710

[cptskippy]

None of what you said contradicts what you quoted. Steel is a stronger material than aluminum, the trade offs are that it's harder to form and weights more.