Effect of low-temperature quasihydroextrusion on the structure and physical properties of CuCrZr alloy

Abstract

The work is devoted to the study of changes in the structural and physical properties of the precipitation-hardened CuCrZr alloy under the influence of low-temperature (77 K) quasihydroextrusion with various degrees of deformation at liquid nitrogen temperature with subsequent aging. Prior to quasihydroextrusion, commercial alloy samples were annealed and quenched from the premelting temperature to obtain a supersaturated solid solution of alloying elements in the copper matrix. After quasihydroextrusion, the microstructure, lattice constant, pole densities, tensile strength and yield strength, microhardness (in different cross-sections of the extrudate), and electrical conductivity of the CuCrZr alloy were studied depending on the degree of deformation by quasihydroextrusion. It is shown that the deformation degree determines the kinetics of decomposition of the supersaturated solid solution and its structure. As a result of extrusion, an anisotropic structure of the matrix and precipitates is formed, which also determines the anisotropy of material properties. Subsequent aging leads to a significant decrease in the anisotropy of properties. With an increase in the deformation degree during extrusion (before aging), a significant monotonous increase in physical and mechanical properties occurs. However, in the range of deformation degrees of 40–50%, an anomalous “jump” of all measured properties and structural parameters is observed. The study proposes a physical mechanism that explains the experimental results. The mechanism is based on the occurrence of two kinetically differently directed processes: dynamic aging and its inhibition due to an increase in the defectiveness of the material. The latter process manifests itself essentially at low temperatures. In general, low-temperature quasihydroextrusion makes it possible to obtain a complex of sufficiently high mechanical and electrical characteristics of the CuCrZr alloy at relatively low degrees of deformation for one extrusion cycle, which is facilitated by low deformation temperature.