This document discusses aluminum alloys, their designations, and properties. It focuses on the 2xxx series Al-Cu alloys which can be heat-treated for high strength and toughness through precipitation hardening. When quenched, these alloys form a supersaturated solid solution, and aging allows non-coherent precipitates to form, increasing strength. The addition of magnesium to Al-Cu alloys modifies the precipitation process for greater strengthening. Common applications of 2xxx series alloys include aircraft structures, pistons, and welding wire due to their high strength, toughness, and corrosion resistance.