PROPERTIES AND STRUCTURE OF WIRES EXTRUDED BY CYCLIC EXTRUSION COMPRESSION METHOD

摘要

The Cyclic Extrusion Compression method belongs to the group of severe plastic deformation processes (SPD) leading to the intense diminishing of microstructure to ultra-grained and nanograined sizes. Nowadays more frequent after the SPD processes, the additional deformation is exerted which purpose the continuation of the grain size is diminishing. The structural effect of the additional deformation process depends on the numerous parameters and its prediction not always is possible. The main purpose of the work was the analysis of the influence of additional deformation on the microstructure diminishing of AlMgSi alloy and pure copper deformed earlier by the CEC method. AlMgSi alloy was deformed in the range of true strains = 1.3÷16 (10/8.5 mm) by using the CEC method. The samples of AlMgSi alloy after the CEC deformation was directly extruded to wires from the previous diameter 10 mm to the diameter 3.2 mm. The additional deformation exerted in the successive extrusion had value phi = 2.3. The copper monocrystals were deformed by the CEC in the range of strains (p= 4.6÷13.9 (10/9 mm). The polycrystalline copper was deformed by CEC method in the range of strains phi = 1.3÷20.8 (10/8.5 mm). After the CEC the monocrystalline copper samples were directly extruded to wires with 3.2 mm in diameter. The additional strain in the successive extrusion achieved value phi = 2.3. Polycrystalline samples were extruded to 4 mm diameter wires, and additional deformation achieved value (p = 1.8. It was found that the combined deformation in the case of the AlMgSi alloy leads to the growth of grains, which mean size established at the level of about 200 nm. The effect of grain growth was reduction of microhardness of alloy of about 20 % in comparison to the microhardness after the CEC. The opposite phenomenon was found in the case of the copper wires, in which the mean size of grains diminished after the extra deformation; in monocrystals on the average of about 25 % and in polycrystalline samples of about 50% in comparison to the mean size after the CEC. It was found that the microhardness level increased in copper wire of about 9÷29 %. The results suggests that the differences in the stacking fault energy of the investigated materials, influence on the stored energy level, contribute to the proceed changes of microstructure and properties.