Nuclear magnetic resonance, stored energy, and the density of dislocations in deformed aluminium

The mean-square width of the nuclear magnetic resonance absorption line and the density of dislocations observed by electron microscopy have been measured in specimens of cold-rolled aluminium. Cold rolling has been found to increase the mean-square line width by up to 120%, and the broadening is proportional to the density of dislocations. The stored energy has been calculated from the line broadening using a simple model, and the results are in reasonable agreement with the energy measured directly. The apparent energy of a dislocation in aluminium has been found to have the surprisingly high value of 18.8 × 10−4 erg/cm, and it is suggested that the density of dislocations observed in aluminium by electron microscopy does not represent the bulk value.