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The study was concerned with improving the thermo-plastic treatment of the CuCrZr alloy so as to achieve a better compromise between its electrical conductivity and hardness. The experiments included severe plastic deformation (SPD), such as hydrostatic extrusion (HE), equal channel angular pressing (ECAP), and a combination of these processes, all followed by a precipitation hardening stage (solution treatment before the deformation and post-deformation ageing). The aim was to produce a material with a strongly refined microstructure (which is a factor promoting high hardness and high mechanical strength of the material) with the preservation of its high electrical conductivity. The material obtained had an ultrafinegrained structure ( d 2 = 200 nm) and a high ultimate tensile strength UTS = 630 MPa, values which are much higher than those of the reference commercial material used for the fabrication of the spot-welding electrodes. The optimization of the process parameters also permitted achieving a high electrical conductivity of 78% IACS. The CuCrZr alloy is commonly used as the material for the tips of the spot-welding electrodes, especially in the transportation industry. Therefore, the properties of the material obtained in the present study were verified from the applicative point of view i.e. some standardized spot-welding electrodes were fabricated of it and subjected to lifetime tests. The lifetime of the electrodes made of the material subjected to HE + post-deformation ageing appeared to be more than 6 times as long as that of the reference commercial electrodes. In the material treated by ECAP + HE, the result was much less advantageous which was because of the weaker morphological texture compared to that formed characteristically in the materials treated by HE alone. [ABSTRACT FROM AUTHOR]

CP 99.5% aluminium was processed by cryo-hydrostatic extrusion with true strains up to 3.4 in one pass. The aim was to refine its microstructure and improve its mechanical properties. The properties of the thus processed material were compared with those obtained after the same process but run at room temperature. Cooling the billet with liquid nitrogen combined with water cooling of the extruded wire enabled suppressing partially the dynamic and static structural processes. The grain size was reduced to ~400 nm in the cryo-extrusion, and to ~450 nm in the room-extrusion. In the cryo-extrusion the increase of the yield strength to 168 MPa and the hardness to 56 HV0.2 with the respective reduction of the elongation to fracture to 13.6% were obtained. The cryo-cooling effectiveness and the influence of the adiabatic heat generated during the plastic processing on the structure, mechanical properties, hardness, and tensile impact toughness just after hydrostatic extrusion, an also after the post deformation annealing are discussed. In view of the intensive adiabatic heating amounting to 0.57 T m no special improvement of the mechanical properties after the post-deformation annealing was observed. The cryo-cooling became effective at the true strain ε>2, where the extrusion pressures clearly differed from the room-extrusion pressures and the defect density substantially increased. After the cryo-hydrostatic extrusion the mechanical properties were comparable to the highest values reported in the literature for cryo-rolling but, since they were obtained in a single deformation step and with twice as large subgrains, the ductility of the extruded aluminium was higher. During the cryo-hydrostatic extrusion conducted at high strains the reduction in ductility of the aluminium is hindered and thanks to the beneficial role of the hydrostatic stress active in the material the structural and mechanical effects which occur during severe plastic deformation are enhanced. [ABSTRACT FROM AUTHOR]