STRAIN RATE SENSITIVITY AND TRANSIENT-BEHAVIOR IN AN AL-MG-SI ALLOY

The effect of strain rate changes on the flow stress of an Al-Mg-Si alloy at strains prior to the onset of the Portevin-Le Chatelier effect has been studied. Measurements of the instantaneous and steady state strain rate sensitivity of the flow stress and the flow stress transient period were carried out as a function of strain and strain rate. Negative values of the steady state strain rate sensitivity were reached prior to the onset of localised yielding, which occurred by the growth of local strain rate oscillations. The results are interpreted in terms of a constitutive flow model which takes into account time dependent changes in the local solute composition at dislocations accompanying a strain rate change.