I’m just giving round numbers here. You can easily find the exact figures if you need them.
Aluminum is ⅓ the density of steel so for a given weight, Aluminum is 3x the thickness of steel. For bending moments the thickness is cubed, so Aluminum has the advantage of being 27x stiffer. BUT its modulus of elasticity is about ⅓ that of steel so the advantage is only 9x (or maybe 3x – i forget if it is a square term.)
It is difficult, if not impossible, to stamp Aluminum so it is usually milled.