The decisive impact of microstructure on the machinability of pure copper

Ultrafine-grained (UFG) materials have been of great attention due to their considerable behavior compared to coarse-grained counterparts. Also, the machinability of these UFG materials is of great importance because of the machining significance in manufacturing the final shape of industrial components. Hence, this study dealt with machinability in relation to the microstructure and mechanical properties of the UFG pure copper processed by the twist extrusion. The remarkable microstructure evolution through the dynamic recrystallization mechanisms improved the tensile strengths and hardness of the twist extrusion processed pure copper. Also, the reduction of ductility in the UFG copper compared to the initial state was related to the change of tensile fractography mechanism in which the large and deep dimples transformed into the combined small and shallow dimples with some cleavage planes in the UFG copper. Furthermore, the enhanced machinability of the processed sample was related to its lower thermal conductivity and the development of strain localization within the narrow shear bands which lead to the production of discontinuous short chips. Hence, the formation of the UFG structure is a suitable option to attain the enhanced machinability behavior of copper as one of the most used metals.