Stage weapons, at least ones that are going to be fought with, as opposed to merely brandished, need to be made with the same quality as a "real' sword.
I have made up a couple from aluminium, and bought a few that were retired from the Conan attraction at Universal. As a rule, our fight director prefers steel, it sounds right and dents less. But sometimes you need aluminium for an actor with limited strength that can't swing the steel sword.
Steel swords for stage use should be tempered firm enough to hit without denting, springy enough to flex without taking a set or breaking, and soft enough not to chip. All the swords onstage should the same hardness if possible. An edge dent in a soft steel sword raises a burr that is quite sharp and will give a painful shallow cut that will bleed freely. This will annoy both the actor and the costumer. The tang should be quite strong, ideally forged out and threaded, or at least a properly welded tongue and groove joint with a maximum of tang and a minimum of threads. And hilts and guards should be bronze, brass, or steel, not pot metal.