Sharif Digital Repository

A modified dislocation based model is introduced to explain the flow stress of Al-Mg alloys at different temperatures and strain rates considering solute alloying element concentration. The solute effect on flow stress is studied on the basis of storage and annihilation of dislocation. It is studied that how the increase of solute content can postpone the dislocation annihilation and how this can affect the storage phenomenon. It is found that the increasing of solute concentration can postpone the beginning of dislocation annihilation through deformation and also increase the critical strain that plateau occurs in plot of annihilation of dislocation versus shear strain. Thus, the plateau... 

Strain rate sensitivity (m-value) of ultrafine grain (UFG) AA 1050 and AA 5052 sheets processed by accumulative roll-bonding is investigated versus strain rate by stress relaxation (SR) test at ambient temperature. The results show a weak viscous nature of deformation for AA 5052 specimens as compared to AA 1050 ones. So that much less stress relaxation and negligible strain rate sensitivity are obtained for this material due to dislocation and grain boundary mobility limitation caused by Mg solute atoms. In order to formulate strain rate sensitivity of UFG aluminum as a function of strain rate, three phenomenological and two empirical models are developed and assessed by the experimental...