Some Properties of Cu-Cr-Hf Alloys

Mechanical and electrical properties in various aged states of Cu-Cr-Hf alloys containing about 0.6%Cr and 0.14∼0.90%Hf were studied in comparison with those of Cu-Cr-Zr and Cu-Cr alloys. The relations between properties and microstructures were also studied by using the transmission electron microscope. The specimens were cast, hot-worked, solution-treated at 950°C for 1 hr, quenched and finally cold-reduced about 83% to 0.5 mm thick sheets.The results obtained were as follows. (1) Cu-Cr-Hf alloys were remarkably age-hardened in the temperature range of 400°∼450°C. (2) The age-hardenability was shown to be caused by the precipitation of two sorts of precipitates, i.e., Cr-rich phase and Cu-Hf compound. The Cu-Hf compound precipitated on the {111} habit plane of the matrix. (3) The alloys containing about 0.6%Cr and 0.2∼0.6%Hf exhibited properties of more than 60 kg/mm2 in strength and about 80% IACS in electrical conductivity, when aged at 400°∼450°C for about 3∼20 hr. (4) Therefore, the above alloys were considered to be superior to Cu-Cr alloys and equivalent or somewhat inferior to Cu-Cr-Zr alloys.