During the Chalcolithic period (sort of a transition between Stone and Bronze Ages) people used copper knives. I think it's quite likely that the copper blades were primarily stabbers (daggers, spearheads, arrowheads) and that stone blades still did a lot of the cutting. So, I agree with knarfeng. For a stabber aluminum would work fine, but for cutting stuff I'd go with a cutlery grade steel.