Abstract
The spring elongation number (SEN) indicates a softening state with high sensitivity, and the windability of the annealed pure copper wires can be evaluated by the SEN. The SEN characteristics of the copper wires were studied in relation to the electrical conductivity and metallurgical structure of the wire rods. The hot-rolled copper (tough pitch copper) wire rods were heat-treated at 673-1073 K in 1.33×10−3 Pa within 86.4 ks, and they were cold drawn to about 89.8% and finally annealed at temperatures up to 673 K. The annealed copper wires were subjected to the SEN test, tesile test, electrical conductivity measurement and structural observation.
When the wires are annealed after heat-treatment at 873 K, the copper wires increase in SEN from the lowest annealing temperature. Completely softened copper wires have high electrical conductivity when the half-softening temperatures were low. The size of Cu2O particles in the copper wire rod increases with rise of heat-treatment temperature.
It is concluded from these results that the decrease in half-softening temperature of the cold-drawn copper wire after the heat-treatment at 873 K is due to the precipitation of impurities in the copper matrix and the growth of Cu2O particles.
