Abstract: Cu-Cr-Zr-xSn alloys with different Sn contents were prepared by vacuum casting. Optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope(TEM) were used to analyze the microstructure evolution of the Cu-Cr-Zr-xSn alloys in the process of multi-stage thermo-mechanical treatment (rod blank→first drawing→950 ℃ solution treatment for 1 h→secondary drawing→peak aging at 450 ℃→room temperature drawing or cryogenic drawing→450 ℃ annealing), and the corresponding tensile strength and conductivity were measured. The effects of Sn element and cryogenic drawing on microstructure and properties of Cu-Cr-Zr alloy were mainly studied. The results show that both the Sn element and the cryogenic drawing can significantly improve the tensile strength of Cu-Cr-Zr alloy without causing too much loss of conductivity, where the Sn element will promote the formation of the Cr-rich primary phase. During the thermo-mechanical treatment process, the Cr-rich primary phase will be drawn into a fiber shape, which has the effect of fibre strengthening. Cryogenic drawing can improve the deformation resistance, resulting in a smaller deformed grain size, and also promote the Cr-rich primary phase to transform into a fibrous shape, which further improves the strength of the alloy.

Key words: Cu-Cr-Zr alloy, Sn element, cryogenic drawing, thermo-mechanical treatment, grain refinement