Characterization of ageing products in AA6111 using dynamic dislocation-defect analysis

In dynamic dislocation-defect analysis, the thermodynamic deformation-mode signatures are examined as the ageing proceeds. In this method, the activation volume (nu) and the mean slip distance (lambda) is simultaneously determined with the flow stress (tau) such that the inverse work-hardening slope (1/theta) can be plotted versus b(2)lambda/nu where b is the Burgers vector. The slope of this almost linear locus is directly proportional to the activation distance (d). Calibration with a model alumina-dispersed high conductivity copper reveals that punched-out loops are produced up to failure and is represented by a linear locus from 0.1 to 11% strain. Artificial ageing of AA6111 at 180 degrees C follows this pattern but the naturally-aged specimen manifest a distinctly different signature which shows a transition as the GP zone-type precipitates are sheared. Furthermore by selecting a suitable tensile-test temperature below 250K, the particle size and volume fraction can be determined if particle shearing does not take place. The optimum size and volume fraction necessary for sufficient strength and ductility can be assessed using this method.