MSE 258:Physical Metallurgy of Non-Ferrous Metals

Dr. Emmanuel Kwesi Arthur

Department of Materials Engineering,

Kwame Nkrumah University of Science and Technology, Kumasi

2019

Lecture Five

Copper and Copper Alloys

Copper and its AlloysWhy Copper?

Copper alloys, bronze and brass, were the first alloys made by man

The second large class of nonferrous alloys is the Cu-based alloys.

Copper alloys enabled currency for trade because of its corrosion resistance and it is still used in this manner although diminishing because it is too expensive.

Copper is used for conducting electricity and thus for electronic interconnects

Copper is still widely used for marine applications because of its corrosion resistance

When is a copper coin not a copper coin?

When it is a copper-coated alloy!

Since 1992, UK copper coins have been made from copper-plated steel and are magnetic. A magnet can be used to separate copper coins by age.

Copper coins used to be made from pure copper but most ‘copper’ coins used around the world are now made from copper alloys.

Previously, as the value of copper increased, the metal used to make the coin became worth more than the actual coins. A melted-down, pure copper coin could have been sold for more than the face value of the coin!

Copper is also used in currency. In 1908 – 1992, the American penny was 95% copper.

Copper and its Alloys

Our modern world is inconceivable without copper.

Power supply, air-conditioning and refrigeration technology, transportation, telecommunications and electronics are taken for granted in today’s world.

Their high standard owes much to the consistent use of copper.

Cu has a variety of properties, which make it useful in many applications.

conductors of electricity

Copper and Copper Alloys

• Pure Copper - properties

Melting point 1083oC

Crystal structure Face Centered Cubic

Density 8.93 x 103 kg/m3

Young’s modulus, E 122.5 GPa

Tensile strength 220 MPa

Electrical resistivity 1.67 x 10-8 ohm meter at 20oC

Corrosion resistance Very good

Properties:

High thermal conductivity

High electrical conductivity which depends on its purity. (Silver (Ag) is the highest!)

Cu and most of its alloys are FCC; therefore toughness and ductility are retained at cryogenic temperatures.

Ease of fabrication (Good machinability)

Medium tensile strength

Non magnetic

Controllable microstructure – easily alloyed for higher strength

Easily soldered and joined, although it’s not easy to weld.

Relatively inexpensive

Copper and its Alloys

•Pure copper is red

•Zinc additions produce a yellow colour

• Nickel addition produce a silver colour

Good corrosion resistance

Copper is very uncorrosive so doesn’t rust easily. However, when it does rust, copper turns a blue-green colour. The statue of liberty is made out of copper.

Addition of zinc remarkably increases resistance to corrosion.

Copper and its Alloys

Copper does not react with water but it does slowly react with atmospheric oxygen to form a layer of brown-black copper oxide which, unlike the rust that forms on iron in moist air, protects the underlying metal from further corrosion (passivation).

•copper doesn’t show ductile-to-brittle transition temperature

Copper and its Alloys

At high temperatures, both of these have mobile dislocations, and thus they can sustain large plastic deformations without undergoing fracture.

At low temperatures however, while dislocations in BCC are no longer mobile, dislocations in FCC can still move very quickly. This lack of dislocation movement makes BCC brittle, while FCC stays ductile...

Copper trolley wires

Electronic products Copper plating

Copper and its alloys

Copper as a Heat Exchanger