Rheological Behavior and Structure of a Bioresorbable Zn-Li Alloy under Uniaxial Compression and ECAP Processing

Abstract

The paper considers the rheological properties and structure formation of the new bioresorbable Zn-0.8Li alloy subjected to uniaxial compression at different initial temperature–velocity conditions and equal-channel angular pressing (ECAP). The rheological properties are investigated based on the results of the compression tests of cylindrical specimens at temperatures from 100 to 300°C and a strain rate of 1.6 s⁻¹. It has been found that at T_i = 100°C, the flow stress-strain curve of Zn-0.8Li is cyclical: first, the material hardens, then softens, and then hardens again. At T_i = 200°C, the flow stress-strain curve exhibits a horizontal section instead of a descending branch, followed by hardening. The maximum deformation–induced heating is observed at T_i = 100°C and reaches a value of 70°C. The lowest amount of dissipated energy is observed at T_i = 300°C. Structural analysis shows that at T_i = 100°C the regions of primary dendrites are plastically deformed, while the eutectic regions are more susceptible to mechanical fracture. An effective refinement of both phase regions occurs at temperatures above 300°C due to dynamic recrystallization. The average grain size in both areas reaches 4–5 μm. Based on the obtained data on the rheological behavior of the Zn-0.8Li alloy, a regime was selected and ECAP processing was performed at T_i = 300°C. Structural analysis of the obtained samples indicates refinement of the phases due to dynamic recrystallization. In the case of the eutectic region, the bulk of the grains is of recrystallization origin, and in the regions of primary dendrites, low–angle boundaries are formed and internal stresses accumulate. Due to an increase in the length of the intergrain boundaries, the ductility parameters increase by 7.5 times—the tensile elongation reaches 30% when the ultimate tensile strength of 520 MPa is reached.