Grain refinement and strengthening of a Cu-0.1Cr-0.06Zr alloy subjected to equal channel angular pressing

The grain refinement and mechanical properties of a Cu-0.1Cr-0.06Zr alloy subjected to equal channel angular pressing (ECAP) at a temperature of 673K were examined. The microstructure evolution was characterised by the development of a large number of low-angle subboundaries at small strains. An increase in the true strain resulted in gradual transformation of low-angle subboundaries into high-angle grain boundaries that was assisted by the deformation micro-banding. The development of new ultra-fine grains was considered as a kind of continuous dynamic recrystallization, the kinetics of which was characterised by a sigmoid-type dependence on strain and could be expressed by a modified Johnson-Mehl-Avrami-Kolmogorov equation. ECAP led to significant strengthening of the alloy. The yield strength increased from 105MPa in the initial state to 390MPa after 8 ECAP passes. A modified Hall-Petch relationship was applied to analyse the contributions of grain refinement and dislocation density to the overall strengthening. In spite of significant strengthening, the electro-conductivity remained at a level of 80% IACS.