Effects of Annealing Temperature on Microstructure and Properties of Pure Copper Wires Containing Unidirectional Fibrous Crystals

Effects of annealing temperature on microstructure and properties of pure copper wires containing unidirectional fibrous crystals fabricated by unidirectional continuous casting process and heavy deformation below recrystallization temperature were investigated. The copper wire was annealed in a vacuum firing furnace for 1 h at 200, 300, 400 and 500℃ respectively, then was cooled down in the furnace. By observing the microstructure and analyzing the mechanical properties and electrical conductivity of the copper wires before and after annealing treatment, it is shown that at the annealing temperature below 300℃, the microstructure of the wires still remains fibrous crystals without evident changes, the tensile strength decreases slightly, and the elongation increased a little. After annealing at 400℃, the wires were fully recrystallized and compound twins could be found. After annealing at 500℃, the recrystallized grains coarsened. When the annealing temperature was higher than 400℃, the tensile strength decreased apparently and the elongation increased greatly. When the annealing temperature ranges from 200 to 400℃, the electrical conductivity increases by a small percentage (lower than 2%).