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Copper and its alloys are widely used in high-speed railways, electronic devices, and lead frames due to their good electrical and thermal conductivity, as well as their excellent corrosion resistance. The pure copper used in this study has high electrical conductivity and excellent ductility, and is widely used in high-speed railways, electronic devices, and lead frames. However, its relatively low strength also limits its application in structural components. Severe plastic deformation(SPD) is a processing technology that significantly refines the grains of materials by applying extremely high plastic strain. Through multiple or continuous deformation passes, high-density dislocations and shear bands are generated within the material, promoting grain refinement to the sub-micron or even nano level. Among many SPD methods, equal channel angular pressing(ECAP), as a typical SPD technique, involves extruding material through a channel with a specific angle to achieve severe(pure) shear deformation. ECAP has been widely used to refine the grain size of metallic materials to the sub-micron or nano level and is one of the most effective methods for preparing bulk ultrafine-grained materials.In this study, the subject was as-cast pure copper with a purity of 99.996%. The pure copper underwent multiple ECAP deformations at room temperature, with an internal die angle Φ of 90°and an external arc angle Ψ of 20°. Butter and graphite were used as lubricants, the press rod speed was 2.5 mm·s-1, the number of extrusion passes was 8, and the extrusion path was the C-path. Optical microscopy and electron backscatter diffraction(EBSD) were used for microstructural analysis of the samples. The study investigated the microstructure, grain size, dislocation density, and degree of deformation of the as-cast pure copper after each ECAP pass. The results showed that after ECAP deformation, the microstructure exhibited mutually parallel and interwoven band-like structures. As the number of deformations passes increased, the bands thinned and gradually transformed into equiaxed grains. The as-cast pure copper exhibited large equiaxed grains with an average size of 89.5 μm. After the first pass of ECAP deformation, the grains were elongated and fragmented into band-like structures. These bands were oriented parallel to the shear direction and had an average width of approximately 17 μm. With increasing deformation passes, the band structures became finer and more uniform. After 4 passes, the bands were further refined, with an average width of about 2.7 μm, and some regions exhibited a more equiaxed morphology. By the 8 th pass, the microstructure consisted predominantly of equiaxed grains with an average size of 4.24 μm. The increase in dislocation density played a significant role in the strengthening of the material. The dislocation density increased dramatically with each pass of ECAP deformation, reaching a peak after 4 passes. The dislocation density increased from 2.9×1014 to 31.24×1014 m-2, a 997.24% increase compared to the original as-cast pure copper. Vickers hardness tester was used to measure the microhardness of the surface of each sample. The hardness reached a peak of HV 178.24 after 4 passes of ECAP deformation, indicating significant work hardening. The hardness of the pure copper after 8 passes of ECAP deformation was slightly lower at HV 173.6. A digital direct current(DC) low resistance tester was used to measure and calculate the electrical conductivity, with five measurements taken and averaged. The electrical conductivity of the material was also affected by ECAP deformation. As the grain size decreased and the dislocation density increased, the electrical conductivity decreased. The initial electrical conductivity of the ascast pure copper was 96.34%IACS, which decreased to 81.22%IACS after 8 passes of ECAP deformation. This reduction in electrical conductivity was attributed to the increased scattering of electrons by dislocations and grain boundaries, which impede the flow of electric current. A universal testing machine was used to conduct constant-speed room-temperature tensile tests on samples in different states, with a tensile speed of 0.37 mm·min-1. Each group of experiments was conducted twice to ensure the accuracy and reproducibility of the results for subsequent comparative analysis. The tensile strength reached a peak of 588.19 MPa after 4 passes of ECAP deformation, and the yield strength reached 617 MPa. The yield strength was theoretically calculated using the rule of mixtures, with the strengthening increment from ECAP deformation expressed as the sum of the initial material strength, dislocation strengthening increment, and grain refinement strengthening increment. Calculations based on these increments yielded results that were in good agreement with the experimental data. Additionally, a nonlinear fitting formula for the relationship between the number of deformations passes and the yield strength was obtained by fitting the yield strength curve. ECAP process was highly effective in refining the grain size of pure copper and significantly improving its mechanical properties. Four passes of ECAP could achieve a relatively optimal balance between strength(588.19 MPa) and conductivity(81.22%IACS), providing a process reference for the industrial application of high-strength and high-conductivity pure copper. Future work should focus on optimizing ECAP process parameters to further enhance the balance between strength and electrical conductivity, potentially leading to new applications for pure copper in industries where both properties are critical.
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Basic Information:
DOI：10.13373/j.cnki.cjrm.XY25080009
China Classification Code:TG146.11
Citation Information:
[1]Yang Xirong,Yan Kun,Liu Xiaoyan ,et al.Microstructure and Properties of Ultrafine-Grained Pure Copper Fabricated via ECAP[J].Chinese Journal of Rare Metals,2026,50(10):1602-1612.DOI:10.13373/j.cnki.cjrm.XY25080009.
Fund Information:
国家自然科学基金面上项目(51474170); 国家基金培育专项(X20240094); 陕西省自然科学基金面上项目(2023-JC-YB-312)资助
2026-10-15
2026-10-15