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Foundry Tech: Copper-based alloys

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In this edition, we’ll begin exploring copper-based alloys. They are a widely used family that has been around since around 3300 BC.

The copper family falls under the following main groups, which are further split into subgroups as different alloying elements are added:

  • Copper – greater than 99% Cupper (Cu)
  • High Copper Alloys – greater than 94% Cu
  • Copper-Nickels – Cu with nickel (Ni) as the principal alloying element
  • Copper-Nickel-Zinc – Cu with Ni and zinc (Zn) as the principal alloying element
  • Brasses – Cu with Zn as the principal alloying element
  • Bronzes – Cu with tin (Sn) as the usual alloying element

Copper

These grades are not intentionally alloyed, but usually contain traces of silver or deoxidizers. They are soft and ductile, and have extremely high electrical and thermal conductivities, while possessing very high corrosion resistance. They are used for electrical terminals and connectors, and in water-cooled equipment in high heat applications.

Copper microstructure, showing primary copper and cuprous oxide eutectic (globular features)

High Copper Alloys

These grades are used primarily for their combination of high strength and good conductivity. Chromium coppers are used for electrical contacts, clamps, welding gear and other electromechanical equipment.

Beryllium coppers have the highest tensile strengths of all the copper alloys. They are used in heavy duty mechanical and electromechanical equipment requiring ultrahigh strength and good electrical and/or thermal conductivity.

Beryllium copper microstructure

High copper alloy’s corrosion resistance is as good as, or better than that of pure copper. It is adequate for electrical and electronic products used outdoors or in marine environments, which generally do not require additional corrosion protection.

Copper Nickels

These alloys are also known as cupronickels, containing 10-30% nickel. Corrosion resistance and strength rises with nickel content. These can be heat treated when alloyed with small amounts of niobium and silicon. The copper-nickel alloys offer excellent resistance to seawater corrosion. This, combined with their high strength and good fabricability, has found them a wide variety of uses in marine equipment. Typical products include pump components, impellers, valves, tail-shaft sleeves, centrifugally cast pipe, fittings and marine products.

Copper nickel microstructure

Copper-Nickel-Zinc

Also known as nickel silvers, these alloys offer excellent corrosion, high castability and very good machinability. They have moderate strength. Among their useful attributes is their pleasing silvery lustre. Valves, fittings and hardware cast in nickel silvers are used in food and beverage handling equipment and as seals and labyrinth rings in steam turbines.

Nickel silver microstructure

In the next newsletter, we’ll finish looking at copper-based alloys when we look at brasses and bronzes.

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