I'd stick with steel.
Aluminum Alloy is 'brittle' almost like an exhaust manifold is (Cast metal). It is strong but if it's bent, it tears. And bending it back is a real hazzard.
With metal, if you smack a rock and want to bend it back, get a big hammer, with Aluminum...you will ruin the strength of the part.
'75 CJ5 ---Chevy HP 350 motor-- All Fiberglas---one piece tilt forward nose
1985 chevy stepside pickup, 300K on the clock: Original Owner
1989 Volvo 240 300K on the clock: Original Owner
the 1991 X is my newbie with 331K on the clock: bought OCT.'03 with 183K