Effect of electric-current pulses on structural changes in cold rolled copper at different initial temperatures

Abstract

The influence of external current electric fields on the mechanical properties of metals and alloys has been studied for a long time. The effects of electric-current pulses (ECPs) on materials structure were attributed to an increase in the mobility of dislocations in the presence of the electric current (an effect sometimes referred to as “electron wind”) and subsequent acceleration of the formation of recrystallization nuclei. At the same time, it has been demonstrated that the Joule heat induced by ECP has some impact on the recrystallization microstructure of the material. What makes the dominant contribution to the structural changes taking place in the material, Joule heating or "electron wind", remains still unclear. The aim of this work was to determine the effect of Joule heating by electric-current pulses on the evolution of grain structure at different initial temperatures in copper specimens. For this purpose, copper samples were rolled to a 90% thickness reduction and then pulsed at two initial temperatures of the specimens, 20°C and -170° C, the latter being achieved by cooling with liquid nitrogen. As the integral current densities 0.449 × 105 A2s mm-4 for initial room temperature and 1.052 × 105 A2s mm-4 for initial temperature -170oC were attained, the material was recrystallized completely. The microstructural changes are compared to similar observations for static recrystallization and explained in terms of Joule heating.