THRESHOLD STRESS AND ITS TEMPERATURE-DEPENDENCE FOR HIGH-TEMPERATURE DEFORMATION OF A PRECIPITATION-HARDENED AL-0.7 AT-PERCENT-MN ALLOY

In order to clarify the originating mechanism of threshold stress for high temperature deformation of precipitation-strengthened alloys with incoherent dispersoids, the threshold stress was measured by the stress abruptly loading test (SAL test) and the creep test at 673, 623 and 573 K, using an Al-0.7 at%Mn alloy with incoherent Al6Mn precipitates. Further, the possibility of temperature dependence of threshold stress was discussed by estimating the activation energy for dislocations to detach the dispersoids. The main results are as follows. (1) At all the test temperatures, the threshold stress obtained by the SAL test decreased from the Orowan stress to the void-hardening stress as the time elapsed under load. (2) The relation of Zener-Hollomon parameter Z to the modulus-compensated creep stress in steady state could be expressed by a single master curve irrespective of the test temperature. (3) The calculated energy for a dislocation to detach the dispersoids was very high compared to the thermal energy, predicting that the threshold stress is almost independent of temperature, which agreed with the experimental observations. From the above results, it is concluded that the originating mechanism of the threshold stress is the Srolovitz's one, and the temperature dependence of the threshold stress is insignificant.