Kinetic analysis of dynamic point defect pinning in aluminium initiated by strain rate changes

Abstract

The role of point defect production during deformation was examined by sealing the vacancy sinks in the grain boundaries with solutes to magnify its effect upon instantaneous strain-rate changes. AA1100 aluminium sheets were thermal-mechanically treated to result in a grain size of about 25 µm and in grain boundaries that were not capable of acting as efficient vacancy sinks. Tensile tests at various temperatures ranging from 78 to 300 K showed that above 195 K, the pinning effect could be quantitatively analysed. A rate equation analysis for mono- and di-vacancy recovery was adopted to perform fits to the deduced change in flow stress with time after strain-rate change from which apparent activation energies were derived. This examination indicates that the migrating species are predominantly di-vacancies. It is concluded that point-defect atmospheres have the capacity to glide in unison with mobile dislocations and hence are sensitive to the magnitude of the strain rate and temperature.

Keywords:

• aluminium
• point-defect pinning
• di-vacancy kinetics
• jog dragging
• dislocation atmosphere

Acknowledgements

The authors thank the Natural Science and Engineering Research Council (Canada) for continuous support and General Motors Canada Ltd. and Novelis Inc. for providing materials-design situations, which require such basic understanding to implement solutions.