Abstract
Solid solution copper alloys for connectors are required to have both strength and stress relaxation resistance. Stress relaxation resistance can be improved by low–temperature annealing after cold rolling because dislocations annihilate with recovery. The dislocations formed during deformation can be classified into SS (statistically stored) and GN (geometrically necessary) dislocations. Based on the thermal stability and mobility of each dislocation, it is necessary to investigate the effects of the changes in densities of SS and GN dislocations caused by the low–temperature annealing on the stress relaxation property. The changes in strength and stress relaxation resistance of solid–solution Cu–Mg and Cu–Sn alloys with the low–temperature annealing were investigated. The SS and GN dislocation densities of solid solution were analyzed by using both X–ray diffraction and EBSD (electron backscatter diffraction) methods, and the dependence of the SS and GN dislocation densities on the low–temperature annealing temperatures was clarified. It was confirmed that the SS dislocation density decreased with increasing the low–temperature annealing temperatures, while the GN dislocation density remained constant. Therefore, it was understood that the GN dislocations have little effect on the stress relaxation, while the SS dislocations are mainly responsible for the stress relaxation. also found that the stress relaxation resistance of the Cu–Mg alloy was superior to that of Cu–Sn alloy, and this was mainly due to the low SS dislocation density.
