Initial Aging Phenomena in Cu-Cr Alloy

The effects of quenching and aging temperatures on the initial aging curves of Cu-Cr alloy were examined mainly by means of electrical resistivity measurements. Three Cu-Cr alloy specimens having 0.24, 0.74 and 1.0% Cr were solution-treated at 950∼1050°C, quenched into ice-water and subsequently aged at 300∼500°C.The results obtained were as follows:(1) At the very early stage of aging (within about 30 sec), an abrupt decrease of resistivity with lowering aging temperatures (TA) and rising solution temperatures (Ts) was observed at TA up to about 400°C. In contrast, a transient increase of resistivity with rising TA and lowering Ts was observed at TA from about 450 to 500°C. These phenomena seem to be caused by a rapid formation of solute clusters and the reversion of clusters formed during quenching, which are enhanced by quenched-in vacancies, respectively.(2) The amount of precipitation increased at the latter stage of aging with rising Ts and TA as generally expected, where Ts was not so high as to form secondary defects.(3) As a result, the initial aging phenomena in Cu-Cr alloy were revealed to be complicated against expectations. This was considered to be due to the migration energy of vacanciesso larger in Cu-base alloys than that in Al-base alloys, that the clustering or reversion phenomena at the initial stage of aging could be detected.