Outer Limits 4x4 Board

I'm about to buy some bash plates (front diff, sump & transfer case) for my GV.

I have the option of 5mm Alli or 3 mm steel. I imagine them to be run-of-the-mill grades not super bulletproof featherlite super $$$ grades. It looks to be flat plate not chequer. The alli plates are a little more expensive though.

Being a light'ish car which is better to use? I initially thought going steel since it doesn't grab like the alli plate would but then I got to thinking about the weight difference. Is there much of a weight difference between the two materials?

I've searched and people seem divided between weight vs strength.

I suppose the alli plate is better for rust resistance though

Cheers.

I'd tend to go for the Al plate, but I'm open to being proven wrong.

Approx values

density steel 7850 kg/m^3
density al alloy 2800 kg/m^3

thus 3 mill thick steel plate will be around 23.55 kg/m^2
and the alloy will be 14 kg/m^2

The strengths of either will be very comparable, as Al is weaker than steel, the thicker sheet will keep the plate to similar strengths.

Aluminium has poor resistance to fatigue :(

Aluminium age hardens naturally, and is accelarated by heat. Heat from engine, diffs etc, will rapidly over harden which weakens the material.

Aluminium is corrosion resistant.

If the steel does have issues, its easier to weld etc and doesn't look so bling bling.

EDIT: Thought I would provide a totally pointless fact (my opinion)
I would choose steel plate.
If weight was a big concern I would stop eating maccas.
If rust was a concern I wouldnt buy a zook.
Im a tight ass

Vibrations and heat isn't overly favourable for aluminium, especially when you do need its strength you dont want it to break.

I would go the steel, less likely to tear, and easier to repair or modify down the track if you need\want to.

I have a home made aluminium front bash plate, 5mm I think. Its taken a massive beating and I mean an absolute massive beating for years. Has big dents but has protected the diff and stuff nicely. Easy to bend back into shape if need be. Obviously no rust, there is no stress on it unless it takes an impact so (in my case anyway) the fatigue strength is negligble. IMO and experience 5mm al plate is fine for a bashplate. But then I don't really care about it cos I found the plate as scrap in my mates shed, so if it comes down to cost, go the cheaper option which would be steel. The weight is no concern, 2 tenths of bugger all effect, even on a zook.