Investigation of the performance properties of 99.95% copper after hydrostatic extrusion process for Electrical Discharge Machining (EDM) applications.
The change in material properties was possible by the strong refinement of the microstructure and texturization produced in the HE process.
The copper was hydrostatically extruded with a true strain ɛ=2.05 which corresponds to a reduction in cross section from Ø=70 mm to Ø=25 mm. The mechanical properties of the copper after HE improved significantly. The strength increase from 256 MPa in the initial state, to 410 MPa after the HE process and yield strength increase from the initial 210 MPa to 388 MPa after HE. These increases were accompanied by a decrease in ductility in the form of elongation, which decreased from 45% in the initial state to 12% after HE.
The mechanical properties are closely related to the characteristic structure of elongated grains generated in the HE process, forming a nanocrystalline equiaxial morphology on the cross-section with an average grain diameter of 298 nm. Microstructural studies revealed clear effects of the dynamic recrystallization process; recrystallized areas again saturated with defects, were present next to areas of enhanced grains.
In order to verify the functional properties, the authors carried out an analysis in the process of EDM with an electrode made of copper after the HE process. The subject of the analysis was the electrode wear as well as the quality of the machined surface in various machining variants. In all machining variants a significant reduction in wear was observed for copper electrodes after the HE process, up to 25%. The conducted tests also showed a significant improvement in the quality of the machined surface. The roughness decreased about 30% in the roughing process.
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