Abstract
Windability of annealed pure copper wires, which depends on its stiffness was studied in relation to the effects of working conditions and other factors. Several kinds of hot-rolled copper wire rods were annealed after 90% cold drawing. Stiffnesses of annealing copper wires were evaluated by the spring elongation number (SEN) which can indicate a precise softening state with high sensitivity. Crystallographic textures of the annealed copper wires were examined by means of the X-ray diffraction method. Crystal grain sizes were measured by the intercepting method. The dislocation distribution of the annealed copper wires were observed by transmission electron microscopy. On the basis of these observations, the stress-strain curves were analyzed in relation to SEN.It was found that SEN of TPC1 (normal tough pitch copper) was the highest when copper wires were annealed at a lower annealing temperature for a shorter annealing time, and the copper wire specimens can be arranged as follows, according to the order of SEN by annealing:TPC1>OFC(Oxygen Free Copper)>SCR(Southwire Continuous Rod)>TPC2(Tough Pitch Copper with 16 ppm Pb and 11 ppm Sn). The relation between SEN and the reciprocal of the root of mean grain size gives a nearly straight line. On the other hand, the ratio of the texture component of annealed copper wires, Ir=(111)⁄{(111)+(100)}, shows a nearly constant value after annealing at various temperatures from 600 to 900 K. This indicates that anisotropic crystal structure does not develop after annealing.From these experimental results, we may conclude that SEN depends on the resistance of the grain boundary against dislocation movement, and that the higher the annealing temperature, the better becomes the windability of copper wires.
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