Abstract
It has so far been reported that an addition of a small amount of tin makes it possible to omit the solution treatment for the aging of Cu-Cr alloy; i.e. the aging of Cu-Cr-Sn alloy water sprayed after hot rolling causes an increase in hardness comparable with the normal heat treatment. In the present work the effect of 0.16 mass%Sn addition on the age hardening kinetics in a Cu-0.6 mass%Cr alloy was studied using a heat treatment keeping specimens at 1123 K at different exposure times, so as to vary the solute chromium content prior to the aging.
Under a low supersaturated condition nucleation of homogeneous precipitation hardly occurred by aging at 723 K. While, the precipitation of chromium took place on the surface of the dispersed particles formed during hot-rolling, scarcely resulting in any increase in hardness. When the alloy was aged after cold-rolling at the same temperature, a noticeable increase in hardness was observed in the alloy containing tin by inhomogeneous precipitation on dislocations. The contribution to age hardening of work hardening due to the retained deformed matrix was clearly seen. The greater the amount of chromium content dissolved in the matrix after hot-rolling, the higher the increase in hardness after the aging. Retardation of recovery and recrystallization, which greatly affects age hardening, was attributed to the pinning effect of fine precipitates on climbing of dislocations. The addition of a small amount of tin not only retarded the precipitation of chromium occurring during hot-rolling, but also prevented the recovery pocess by means of segregation of tin to dislocations. Thus, the addition of tin to Cu-Cr alloy contributed simultaneously to the increase in precipitation hardening and improvement of heat resistance.
