A new method is proposed to determine whether the effective stress for the viscous or quasi-viscous motion of dislocations exists or not in the deformation of crystalline materials. The crosshead speed is changed on the way of deformation and the work-hardening rate is measured immediately after the change. It is theoretically predicted that the work-hardening rate depends on whether the effective stress is negligible or not. Applying the method to high-temperature deformation of pure aluminum and Al-5.4 at.% Mg alloy, it is found that the effective stress is negligible in pure aluminum at all temperatures tested and in the alloy at temperatures where the dynamic strain aging occurs, while the stress is appreciable in the alloy at temperatures where the solute atmosphere dragging occurs.
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