Rolling and annealing of copper block.

Authors Avatar

Title:                         Rolling and annealing of copper block.

Abstract:

The hardness of a soft copper block was tested at City University, of increasing lengths and decreasing thickness after undergoing cold rolling. After the maximum length was obtained the copper a cut section was annealed to different temperatures. From the experiment it was found that as the block got thinner and longer the hardness increased. The experiment also shows that when the long copper section was annealed as the temperature was increased the breaking or tensile stress decreased.

Introduction:

The purpose of this Lab exercise is to investigate the effects of cold working and of annealing on the crystal structure and the hardness of a sample of copper (dimensioned at 50x25x5mm). The experiment is designed to allow us to see first hand the changes that take place in the material as it is subjected to varying degrees of work (deformation) and heat treatment.

Cold working uses the concept of “strain hardening”, to “temper” the metal, which is based on increasing the dislocation density within the material.  These dislocations are misalignments of atoms in the crystal lattice and interrupt the regular order of the slip planes along which the material will deform, since dislocations tend to be repulsive in the presence of other dislocations.

Prior to cold working, the crystal grains in copper will have consolidated into relatively large crystals that are equiaxial and the FCC structure provides 12 slip systems along which the metal can deform.  Thus it is soft, ductile, and easy to cold work.

During cold working, the copper sample is deformed (reshaped) which tends to deform and in some cases break down or re-orient the larger crystal grains in the axis (direction) of deformation.  The internal strain fields that result, act to inhibit the further movement of the atoms, and the sample becomes harder, stiffer, and more brittle as more work (% deformation) is performed.  This is the “strain hardening” due to cold working.

Join now!

Annealing is the process of heating a sample to allow the dislocations to move past each other via enhanced atomic diffusion at the higher temperature and relieve the stored energy in the strain fields.  This is termed recovery and allows the dislocations to relocate to sites producing low strain energies.   Continued exposure to the higher temperature allows recrystallization to occur.   During this process, new strain free and equiaxed crystals are formed into grains that have low dislocation densities and the mechanical properties like hardness and ductility revert to their pre-cold worked state.

Theory:

The main ...

This is a preview of the whole essay