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Radial Plastic Flow Machining (RPFM) is a novel severe plastic deformation process. By designing a specific plastic flow channel, the material is allowed to flow radially into the predetermined channel under the combined action of extrusion and cutting. A restricting ring is placed in the channel to form a copper terminal structure in one step. This study investigates in detail the formation mechanism, mechanical properties, and thermal stability of gradient structured copper terminals generated under different extrusion angles. It was found that as the extrusion angle increased, the high strain region slightly decreased, while the low strain region increased, allowing more material to be radially extruded. This indicates that tensile strength and toughness can be balanced by controlling different extrusion angle parameters. In performance testing, the study showed that the hardness of the copper terminals prepared by RPFM was more than double that of the original copper material, and the maximum tensile strength also doubled. Moreover, the performance of the copper terminals annealed at 150 ∘ C was similar to that of untreated copper terminals, demonstrating good thermal stability at this temperature. The study suggests that RPFM is not only an effective process for manufacturing gradient structured copper terminals in one step, but it also provides a new method for manufacturing copper terminals with excellent comprehensive performance. • Introduced Radial Plastic Flow Machining (RPFM) as a severe plastic deformation process. • Achieved one-step fabrication of gradient-structured copper terminals via RPFM. • Balanced high and low strain zones through varying extrusion angles. • Demonstrated significant improvement in hardness and tensile strength of copper terminals. • Confirmed good thermal stability at 150 °C for RPFM-prepared terminals. [ABSTRACT FROM AUTHOR]

Extrusion machining (EM) is an efficient and convenient method to prepare ultrafine-grained (UFG) materials. As a vital parameter in the EM process, tool rake angle (α) is critical to control the material's shear strain and grain size. The grains tend to refine with decreasing α , whereas a small α leads to difficult cutting, chip breakage, and poor surface quality. To achieve the controllable strain distribution, grain size adjustment, and improved formability of UFG pure copper strips, this paper proposed a novel design of the variable rake angle (VRA) tool. Combining experiments and finite element simulation, extrusion machining with variable rake angle tools (VRA-EM) was investigated. The results implied that a deviating angle (β) for the material flow existed during VRA-EM. The β increased as the cutting thickness (t c) increased, resulting in decreased plastic deformation, strain, and microhardness. The microstructure was also characterized by electron backscatter diffraction system (EBSD) and transmission electron microscopy (TEM) techniques. A dead metal zone was formed using the VRA tool, in which the material flow behavior was quite weak. The obtained UFG strip was further divided into the low-strain zone (LSZ) and high-strain zone (HSZ) based on strain distribution. And a new theoretical model of shear strain was established and conformed to experimental values. Accordingly, VRA-EM process was able to improve the mechanical properties and strain controllability, showing promising prospects for efficiently fabricating UFG materials. • A novel design of the variable rake angle (VRA) tool was proposed. • VRA-EM could achieve controllable strain distribution and grain size adjustment of UFG pure copper strips. • A deviating angle and a dead metal zone were formed during the VRA-EM. • The shear strain theoretical model of VRA-EM was established. [ABSTRACT FROM AUTHOR]