Cold Working and Annealing of Copper

COLD WORKING AND ANNEALING OF COPPER

The aim of this experiment was to measure the change in hardness of pure copper as a function of the amount of cold work.

The Material we were testing (Pure copper) is a solid material and can be identified as a metal in the ‘Classification of materials’.

Metals are relatively dense and are a good conductor of both heat and electricity. They can be an element, compound or alloy. In this experiment we were dealing with pure copper which is an elementary metal.

Copper is used in many places, “It is used as a conductor of heat and electricity, a building material, and a constituent of various metal alloys”. Copper as a metal is very ductile, soft and malleable and in the experiment we were investigating how the more we elongated the copper how it affects the hardness of the material with time. This is only possible because copper is a metal and its “atoms are able to roll over each other into new positions without breaking the metallic bond”. However as the grain structure is flattened and elongated it causes hardness. “This rolling of layers of atoms over each other is hindered by grain boundaries because the rows of atoms don't line up properly. It follows that the more grain boundaries there are (the smaller the individual crystal grains), the harder the metal becomes”.

ANNEALING

“Controlling the size of the crystal grains

If you have a pure piece of metal, you can control the size of the grains by heat treatment or by working the metal.

Heating a metal tends to shake the atoms into a more regular arrangement - decreasing the number of grain boundaries, and so making the metal softer. Banging the metal around when it is cold tends to produce lots of small grains. Cold working therefore makes a metal harder. To restore its workability, you would need to reheat it.

You can also break up the regular arrangement of the atoms by inserting atoms of a slightly different size into the structure. Alloys such as brass (a...