On the Age-hardening of Cu-7%Al-1.5%Co Alloy

The age-hardening of the Cu-7%Al-1.5%Co alloy containing 0.01%P has been experimented by a variety of methods. The main results are as follows:(1) The age-hardening of the alloy, solution-treated by heating at 970°C for 2 hr and quenching in water, takes place when it reheated above 350°C. The behavior of hardness in the course of the age-hardening is such that is observed with usual precipitation hardening alloys.(2) The activation energy for the the hardening is 37.3 kcal/mol, being almost equivalent to that for the diffusion of Al in Cu.(3) The process of the age-hardening was examined by electron micrography, X-ray diffraction, electron probe micro-analysis. The results imply that the hardening is ascribed to the formation of G·P zones, where Al and Co are concentrated. At later stages of the heat treatment the zones grow into precipitates, whose electron microdiffraction indicates that they have a cubic structure.(4) Between 500°C and 600°C a heat evolution due to the formation of G·P zones is observed by the thermal analysis of the solution-treated specimens, and the evolved heat is determined to be 5.5 cal/g. Below 300°C another heat evolution is observed in the water quenched specimens, but the latter heat evolution seems to do nothing with the age-hardening of this alloy.