Red Copper

Red copper (aka Minecraft Grade Copper) is an alloy of Redstone and Copper. It is probably one of the first alloys you'll need to make after steel. Its primary use is to make wires in Red Copper Cables at least at this point. It is very useful in a multitude of places, mainly electrical components of machines. The hardest part is acquiring lots of Redstone, but once you do, you can mass-produce red copper for all its uses.

Obtention
Blasting redstone with copper

Uses
Numerous electrical and technological uses