ThinkGeek is selling aluminum chain mail, bringing AC 5 to the masses (of geeks).
I don't see any reason why aluminum wouldn't be a good material for chain mail. Lighter and easier to maintain than teel or iron, even if not as strong. Where's the titanium chain mail?!












Titanium chain mail? I wants me some o' that!
Looking at that, it occurs to me that chain mail would involve a whole lot of padding underneath. The mail would (probably) stop the sharp end of a slashing or piercing weapon, but it wouldn't do much about the force itself. It wouldn't do anything against a hammer, for example. So you would need some padding to spread out the force and dull the impact.
BB: Yeah, chain mail was typically worn with lots of padding underneath, often layers of stiff leather. Just wearing the chain alone would protect from slashing injuries, but not piercing or crushing.