The influence of solutes on flow stress plateaus, with emphasis on back stresses and the development of unified constitutive equations

To study the plateaus and peaks in the temperature dependence of the flow stress commonly observed in solid solution alloys, the flow stress of pure aluminum and three binary Al-Mg alloys has been measured at temperatures between 77 and 750 K and nonelastic strains between 0.02 and 20%. Both athermal and thermally activated processes were found to contribute to the observed behavior. Plateaus in the stress vs temperature response are largely due to the effects of solutes on the evolution of back stresses, an athermal process. Peaks in the stress-temperature response of the substitutional Al-Mg alloys are caused by the interaction of mobile solutes with dislocations, a thermally activated process which increases the effectiveness of the substructure as a barrier to dislocation motion. Based on these results. a physically plausible and simple method of incorporating solute strengthening within unified physical-phenomenological constitutive equations is outlined.