Do you want just a hilt and scabbard to hang from your belt, or a blade that looks like metal?
It is hard to get a finish that looks like shiny metal and is durable, without using real metal. Though, perhaps you could be creative with aluminium tape so that the edges are on real edges of the sword.
If it would have been a Samurai sword, then there are swords for the sport "Iaido" that are made from aluminium that are very light. They are only for practising in the air, not intended to strike anything.
LARP'ers swords are usually oversized and cartoonish, but light, soft and durable. Made from soft rubbery foam coated with latex, with a fibreglass rod in the centre for stability. There are usually regulations for how to construct them so that they are safe. There are stores that sell kits for building them.
For the Lord of the Rings movies, some prop swords were supposedly made from aluminium, so save weight when they were just carried around. I don't know the specifics.