There are three methods for hardening copper: grain-size control, cold working, or alloying. When copper is hardened with tin, silicon, or aluminum, it generally is called bronze; when hardened with zinc, it is called brass. | CHAPTER 4_ COPPER AND ITS ALLOYS Howard Mendenhall Olin Brass East Alton Illinois Robert F. Schmidt Colonial Metals Columbia Pennsylvania COPPER 59 Introduction 60 Composition of Commercial Selection of Alloy 62 Copper 59 Fabrication 62 Hardening Copper 60 Mechanical and Physical Corrosion 60 Properties 68 Fabrication 60 Special Alloys 68 SAND-CAST COPPER-BASE ALLOYS 60 COPPER Howard Mendenhall Composition of Commercial Copper Specifications for copper generally accepted by industry are the ASTM standard specifications. These also cover silver-bearing copper. See Table 1 Low-resistance copper used for electrical purposes may be electrolytically or fire refined. It is required to have a content of copper plus silver not less than . Maximum permissible resistivities in international ohms meter gram are copper wire bars ingots and ingot bars . Mechanical Properties of Copper Annealed Cold Rolled or Drawn Cast Tensile strength psi MPa 30 000-40 000 210-280 32 000-60 000 220-400 20 000-30 000 140-210 Elongation in 2 in. 25-40 2-35 25-45 Reduction of area 40-60 2-4 Rockwell F hardness 65 max 54-100 Rockwell 30T hardness 31 max 18-70 Mechanical Engineers Handbook 2nd ed. Edited by Myer Kutz. ISBN 0-471-13007-9 1998 John Wiley Sons Inc. 59 60 COPPER AND ITS ALLOYS Physical Properties of Copper Density lb g cm3 Melting point 1981 F 1083 C Coefficient of linear F 68-212 F C 20-100 C thermal expansion F 68-392 F C 20-200 C F 68-572 F C 20-300 C Pattern shrinkage 14 in. ft 2 Thermal conductivity 226 Btu ft2 ft hr F 398 W m C at 68 F at 27 C Electric resistivity ohms circular mil ft microhm cm at 68 F at 20 C Temperature coefficient ohms F C of electric resistivity at 68 F at 20 C Specific heat J g C at 20 C Magnetic property Diamagnetic Optional property .
