The Effect of Additional Severe Plastic Deformation at Elevated Temperatures on the Microstructure and Functional Properties of the Ultrafine-Grained Al–0.4Zr Alloy

Abstract

The effect of severe plastic torsion deformation (SPTD) at elevated temperatures of 230 and 280°C on the microstructure, mechanical properties, and electrical conductivity of ultrafine-grained (UFG) Al–0.4Zr alloy samples is studied. The initial UFG structure in the material under study is preliminarily appeared in the SPTD process at ambient temperatures. It is shown that simultaneous significant increases in the strength from 140 to 230–280 MPa and in the electrical conductivity from about 47.5% to 52–54% IACS take place as a result of additional deformation of the UFG Al–0.4Zr alloy at elevated temperatures. The results are compared with the effect that annealing at the same temperatures exerts on the microstructure and properties of the UFG Al–0.4Zr alloy. It is established that severe plastic deformation at comparable temperatures leads to a more efficient, compared to annealing, formation of nanoscale precipitates of the Al₃Zr secondary phase and, consequently, to a larger decrease in the concentration of Zr in the solid solution, which ensures a significant increase in the electrical conductivity. Based on the obtained parameters of the microstructure, the contributions of various strengthening mechanisms to the general strengthening and electron scattering mechanisms to the electrical resistance are estimated. An comparative analysis of theoretical estimates with experimental results indicates that the strengthening in the UFG structure of the Al–0.4Zr alloy that is caused by additional SPD at elevated temperatures cannot be described by the action of only strengthening mechanisms traditional for UFG materials. Possible reasons for the obtained colossal strengthening are discussed.