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Leaded Copper

Lead is frequently added to copper alloys to increase their machinability. The role of lead in copper alloys is two fold, it acts as a lubricant and, in the free machining grades, the lead assists in chip break up.

UNS C18700 leaded copper alloys are primary alloys that can be spot welded and seam welded to achieve hardness and electrical conductivity of 96% IACS. These alloys can be heat treated and cold worked. They are suitable for applications, which require high mechanical properties and deformation resistance at high temperature. Lead is added to many copper alloys, making all types of free machining alloys. Lead does not affect the structure and properties of copper because it is practically insoluble in solid copper. The pure copper solidifies first, leaving the lead to solidify last as almost pure lead globules at the grain boundaries or in the inter dendritic regions. The size and concentration of lead particles depends upon the concentration of lead in the alloy.

Leaded coppers are categorized as low lead alloys, or free machining alloys and high lead alloys. In the free machining alloys, the lead acts as chip breaker and lubricant making these alloys easier to machine than their non leaded counter parts. The high leaded copper alloys are used in bearing applications. In the bearing materials, the lead acts as a solid lubricant and the copper is the load bearing support. Lead is added to many of the copper alloys producing free machining brasses, bronzes and other copper alloys. The free machining brasses and other alloys are presented in the sections with the specific alloy types. The cast, high leaded copper alloys used for bearings are presented in this section. They are designated by UNS C98200 through C98840.

The microstructure of the as cast copper lead alloys consists of pure alpha copper dendrites, with lead globules in the boundaries between the dendrites. The higher the lead content of the alloy the more lead globules present in the structure. In the wrought structures, the lead is present as discrete particles between the alpha copper grains.

Applications

Resistance Welding Electrodes, Circuit Breaker Switches, Stud Bases for Power Transmitters, Electrical Conductor Material

Advantages

  • Greater corrosion resistance
  • Higher tensile strength
  • Brilliant polish
  • Excellent machine strength
  • High creep resistance
  • High temperature strenght
  • Excellent mechanical properties

Chemical Composition

Element Content (%)
Cu, Copper 99.0
Pb, Lead 1.0

Physical Properties

Properties Metric Imperial
Density 8.89 g/cm3 0.321 lb/in3
Melting point 953°C 1747°F

Mechancial Properties

Properties Metric Imperial
Hardness, Rockwell B (50.8 - 76.2 mm/2.00 - 3.00 in) 65 65
Hardness, Rockwell B (25.4 - 50.8 mm/1.00 - 2.00 in) 70 70
Hardness, Rockwell B (25.4 mm/1.00 in, heat treated) 75.0 75.0
Tensile strength at break (any thickness) 379 MPa 55000 psi
Yield strength (0.500%, any thickness) 379 MPa 55000 psi
Modulus of elasticity 117 GPa 17000 ksi
Poisson's ratio 0.181 0.181
Shear modulus 49.6 GPa 7200 ksi

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