Microstructure and Mechanical Properties of Copper Billets Fabricated by the Repetitive Extrusion and Free Forging Process

In the present study, with the aim of obtaining a weakened texture, grain refinement and improved mechanical properties, copper billets were successfully fabricated using the severe plastic deformation method of repetitive extrusion and free forging (REFF) without using any additional tools or devices. The evolution of the microstructure, texture and mechanical behavior of the ultrafine grain copper billets over an increasing number of REEF cycles was also systematically studied. Our results show that the effective strain per REFF process was e = 2.35. After two cycles of REFF process, the sum effective strain became e = 4.7, leading to high efficiency of grain refinement. The grain size was refined from 50 to 0.8 μm; the yield strength was increased to 462 MPa, and we obtained a weakened texture in the pure copper billets. By increasing the number of cycles, the grain refinement ability was decreased, and the texture was thus strengthened further. Therefore, two cycles of REFF were a reasonable process for producing ultrafine-grained copper billets.