Influence of decreased temperature on the plasticization effect in high-strength Al-Cu-Zr alloy

Abstract

The influence of deformation temperature of tensile test on the mechanical properties of ultrafine grained (UFG) Al-Cu-Zr alloy in three different states: after high pressure torsion (HPT), subsequent low-temperature annealing as well as after annealing and a small additional deformation has been studied for the first time. The UFG structure was formed by HPT processing. The temperature dependences of the yield stress and elongation to failure under uniaxial tension in the temperature range of 77–293 K were obtained for all three states. The effect of increasing ductility from ∼3–5 to 11 % (the plasticization effect) at room temperature while maintaining a high strength of ∼465 MPa was observed after deformation-heat treatment (DHT), consisting of annealing and additional deformation. The plasticization effect decreases monotonically with decreasing temperature of tensile test and completely disappears at ∼223 K. In the temperature range 223–293 K, the temperature sensitivity of the yield stress and the value of activation energy (Q) of plastic flow differ in all three states, which is related to the changes in the grain boundary (GB) structure (dislocation density, size and shape of Al2Cu nanoprecipitates). In the temperature range of 77–223 K, the temperature sensitivity of the yield stress does not depend on the state of GBs. The plasticization effect at room temperature is preserved when the strain rate is changed from 10−4 to 10−3 s−1 and sharply decreases as strain rate is further increased. The strain rate sensitivity coefficient (m) for the UFG Al-1.47Cu-0.34Zr (wt%) alloy was determined in the states before and after DHT. The results and relevant mechanisms are analyzed by using the resulting m valuе and Q values as well as the observations of specific features of GB structure.