GUNMETAL-casting bronze-admiralty gunmetal-Gunmetal ingot-Modified gunmetalThe name for a casting bronze, C90500, containing 88% copper, 10 tin, and 2 zinc. It was originally used for small cannons, but is now used where the golden color and strong, crystalline structure are desired. It casts and machines well and is suitable for making steam and hydraulic castings, valves, and gears. It has a tensile strength of 32,000 to 45,000 lb/in2 (221 to 310 MPa), with elongation 15 to 30%. The specific gravity is 8.7, density 0.314 lb/in3 (8,719 kg/m3), and Brinell hardness 65 to 74. This alloy is similar to G bronze (C90300), which contains 88% copper, 8 tin, and 4 zinc. In England it is called admiralty gunmetal and is specified as BES No. 383 for sand castings. Gunmetal ingot may have the zinc replaced by 2% lead. Such an alloy is easier to machine but has less strength. Modified gunmetal contains lead in addition to the zinc. It is used for gears and bearings. A typical modified gunmetal contains 86% copper, 9.5 tin, 2.5 lead, and 2 zinc. It has a tensile strength up to 40,000 lb/in2 (276 MPa), elongation 15 to 25%, Brinell hardness 63 to 72, and density 0.31 lb/in3 (8,580 kg/m3).
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