Equal-channel angular pressing of copper rods: Comparative study of microstructure and hardness at different angles

The lack in previous works concerned with a full study of the deformation homogeneity, and how to reach a high level of deformation homogeneity in the different directions of equal-channel angular pressing (ECAP) processed Cu samples was the motivation of the current study. Therefore, reaching a high level of deformation homogeneity of the copper through optimizing the imposed strain according to the used ECAP die angles was investigated. ECAP was performed using three die angles 90 ^o , 110 ^o , and 130° up to 4 passes at room temperature. Microstructural characterization using optical and scanning electron microscopy revealed grain refinement across all die angles, with the 90° die producing the finest and most homogeneous fine-grained structure due to the highest-imposed shear strain. Grain size decreased from 31.3 µm in the annealed condition to 2.7, 4.8, and 7.2 µm after 4 passes using the angles 90°, 110°, and 130° respectively (pressing direction). Similarly, grain size decreased to 3.3, 5.8, and 7.4 µm after 4 passes using the 90, 110, and 130° dies, respectively (transverse direction). At the same time, refinement was comparatively less pronounced at higher die angles. Hardness mapping across ZY, YX, and ZX planes demonstrated significant strengthening and improved deformation homogeneity with increasing passes, with the 90° die consistently achieving the highest hardness values and lowest homogeneity index (H _index ). After 4 passes, hardness increased by 144.7, 115.1 and 95.6% (ZY plane), 129.3, 107.8 and 92.7% (YX plane), and 125, 104.3 and 91% (ZX plane) for 90°, 110°, and 130° dies, respectively. The mechanical properties of the 90° die deliver the highest strengthening (up to 403.7% in proof-strength and 70.3% in ultimate tensile strength), but with significant ductility loss. While the 110°and 130° dies show lower strengthening with relatively better ductility. Overall, the 90° angle provides the most effective processing route for producing fine-grained, high-strength Cu samples with excellent deformation homogeneity.