BRUSH CASTING ALLOY 21C is a beryllium copper alloy of high strength with cobalt as the second alloying element (1.0 to 2.0% Co). Use is in age-hardened temper. This datasheet provides information on composition, physical properties, hardness, and tensile properties. It also includes information on casting, heat treating, and machining. Filing Code: Cu-575. Producer or source: Brush Wellman Inc..