Effect of Deep Cryogenic Treatment on Microstructure and Properties of Pure Copper Processed by Equal Channel Angular Pressing

A new process combing equal channel angular pressing (ECAP) and deep cryogenic treatment (DCT) is proposed to balance the tensile strength and electrical conductivity of pure copper. The effect of the DCT on the microstructure and properties of pure copper processed by the ECAP is investigated. The optical microscopy (OM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) analyses are used to investigate the microstructure evolution. It shows that as a result of the ECAP, the shear bands are developed, the grains are obviously refined and the dislocation density increases. After the subsequent DCT, the grains are further refined and a large number of dislocations appear. With the increase of ECAP passes, the microhardness and tensile strength increase, however, the elongation to failure and electrical conductivity are degraded. The microhardness, tensile strength, elongation to failure, and electrical conductivity are enhanced by the DCT. The combination of tensile strength approximate to 423 MPa and electrical conductivity approximate to 97.9% international annealed copper standard (IACS) is simultaneously achieved after the ECAP (four passes) and DCT (24 h). Tensile properties can be improved by the DCT due to the increase of dislocation density and the grain refinement.