Influence of Torsional Deformation and Annealing on Microstructure and Properties of Recycled Copper Rod

Torsional deformation at 720 ℃ and 500 ℃×60 min annealing treatment were carried out on the 8 mm diameter recycled copper rods prepared by fire refined high conductivity (FRHC) waste copper refining process and continuous casting and rolling process. The effects of torsional deformation and annealing treatment on the microstructure, mechanical properties and electrical conductivity of the copper rod were studied. The results show that twins were generated in the recycled copper rod structure during continuous casting and rolling process, and the twin crossover and the interaction between twins and dislocations caused by torsional deformation made the grains refined. The tensile strength of the recycled copper rod after torsional deformation increased from 215 MPa without torsional deformation to 273 MPa, but the elongation after fracture decreased from 40% to 21%;the hardness increased and the electrical conductivity decreased from 99.37%IACS to 86.78%IACS. After annealing treatment, the recycled copper rod had a structure with equiaxed crystals with more uniform size. The tensile strength was reduced to 208 MPa, while the elongation after fracture increased to 55%; the hardness decreased and the electrical conductivity increased to 98.21% IACS.