Mechanical properties and microstructure of ultra fine-grained copper prepared by a high-speed-ratio differential speed rolling

A high-speed-ratio differential speed rolling (HRDSR) process designed to introduce severe deformation into a sheet was found to be very effective in enhancing strength of the oxygen-free-copper (OFC). The deformation along the direction of thickness was fairly homogeneous and submicron grain size of 0.82 μm was obtained after the 65% thickness reduction in a single rolling pass. The fraction of high angle boundaries in the sample subjected to HRDSR for the 65% reduction was comparable to that measured in the Cu sample subjected to equal channel angular pressing (ECAP) after multiple pressings. The yield strength and tensile strength of the OFC sheet were 438 MPa and 475 MPa, respectively, which were higher by 10–20% than that of the Cu processed by other severe plastic deformation methods at room temperature. The high strength Cu produced by HRDSR also exhibited high electric conductivity.