The yield and flow stress of dilute CuCd and CuMg alloys

Abstract

The results of tensile tests on dilute high conductivity CuCd alloys with a range of cadmium contents are presented. It is shown that, above about 0.6 wt.% Cd, dislocation pinning is strongly developed, giving apparently linear elastic deformation up to the sharp yield point. The strength of dislocation pinning is also reflected in a pronounced grain size dependence of the yield and flow stress which is maintained up to 30% strain. At lower cadmium contents the stress-strain behaviour is more like that observed in copper. The effect of the cadmium is associated with the degree of saturation of dislocation cores. Dislocation pinning also gives rise to strain-aging effects like those observed in iron alloys but, in contrast with iron, pinning has to compete with recovery at the high homologous aging temperature, thereby causing a peak in the aging curves. The strain hardening of CuCd is also marked at large strains in contrast with copper and, again, the effect is due to a combination of dislocation pinning and dynamic strain aging. For comparison, the results of tests on CuMg alloys are reported. Like cadmium, magnesium has a valency of 2, which is favourable to electrical conductivity, but it is shown that the dislocation pinning is not strongly developed in CuMg alloys.