2023 年 62 巻 1 号 p. 17-22
Solid–solution copper alloys for connector terminals are required to improve stress relaxation resistance. The stress relaxation resistance is affected by grain size and low–temperature annealing condition. The smaller the grain size, the lower the stress relaxation resistance. This is deduced to be due to the increase in the dislocation density associated with the grain size. Dislocations are classified as GN (geometrically necessary) and SS (statistically stored) dislocations. It has been clarified that the low–temperature annealing improves the stress relaxation resistance mainly due to the recovery of the SS dislocations. On the other hand, the effect of the GN dislocations on the stress relaxation is not clearly understood. In general, the GN dislocation density depends on the grain size. Thus, the GN dislocation density was varied by changing the grain size, and its effect on the associated stress relaxation was investigated. The GN and SS dislocation densities of solid–solution Cu–Sn alloys were analyzed by a combination of XRD (X–ray diffraction) and EBSD (electron backscatter diffraction) methods. As the grain size decreased, the SS dislocation density changed little, while the GN dislocation density increased and the stress relaxation resistance deteriorated. The SS dislocations recovered by the low–temperature annealing whereas the GN dislocations did not. It was confirmed that the GN and SS dislocations have different effect on the stress relaxation.
