Improved compromise between the electrical conductivity and hardness of the thermo-mechanically treated CuCrZr alloy

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.