Cтруктура и прочность мелкозернистой меди после криогенной прокатки и обработки однократными импульсами тока различной мощности

Abstract

The effect of a treatment combining isothermal cryogenic rolling and single electro-pulsing on the structure and hardness of M1 grade copper with an initial grain size of 10 –15 μm was investigated. Copper was deformed at liquid nitrogen temperature by multi-pass rolling with a total reduction of 90 %. Subsequent electro-pulse treatment (EPT) was carried out in the interval of integral current densities (Kj) from 3.5 ×104 to 8.1×104 A2 s / mm4. Nearly two-fold strengthening of Cu under rolling was found due to the formation of a heavily deformed (sub)grain structure with a crystallite size of the order of 1 μm and a fraction of high-angle boundaries of about 30 %. With further EPT with an energy of 3.5 ×104 A2s / mm4, the processes of recovery predominantly occur, resulting in slight softening with a simultaneous strong decrease in micro-distortions of the crystal lattice and dislocation densities. Processing with higher energies resulted in a sharp drop in the hardness of Cu owing to an activation of in-situ continuous static recrystallization, forming regions of new fine defect-free grains, whose fraction increased with Kj, and intensified the formation of annealing twins. As a result of EPT with Kj in the range of 5×104 – 7×104 A2s / mm4, a uniform fine-grained structure with a grain size of near 2 μm and a fraction of high-angle boundaries of about 90 %, a third part of which were twins of Σ3, was obtained. With a further increase in pulsing energy to 8.1×104 A2s / mm4, normal grain growth to 4 μm with minor changes in the angular parameters of the structure were observed. The nature of structural and mechanical behavior of copper is discussed. A conclusion is made on the viability of the use of combination of cryogenic rolling and EPT to manufacture ultrafine- and fine-grain sheets of different strength out of copper.