Grain size effect on thermal recovery during high temperature deformation of aluminum tested at constant true strain rates

For polycrystalline aluminum with several grain sizes of 170–730 μm, tensile deformation was carried out at true strain rates of 10−5–100 s−1 and a temperature of 553 K, and true stress σt–true strain εt curves were analyzed by computer simulation on the basis of dislocation dynamics to obtain important deformation parameters. These parameters could describe the experimental σt–εt curves well in the early stage of deformation, but the experimental curve started to depart to a lower stress from the theoretically simulated curve above a critical strain. This departure strain became smaller and the stress reduction during further straining became larger with decreasing grain size and strain rate. The departure was conclusively ascribed to the thermal recovery due to the annihilation of crystal lattice dislocations into the grain boundary.