1Central Research Lab., Mitsubishi Metal Mining Co. Ltd., Omiya
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.
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