New Yielding Phenomenon in Some Aluminium Alloys at High Temperatures

In Al-5.5 at%Mg, n=2,83.3 and U0=1.4eV. In Al-2.2at%Cu, n=4.5 and U0=1.5eV. (6) This yielding reappeared by annealing at the test temperatures. (7) No heterogeneous deformation related to this yielding phenomenon took place, the flow stress was independent of grain size. From these experimental results it may be concluded that under the condition where the high temperature yielding occurs, the plastic deformation is controlled by the viscous motion of dislocations which drag the solute atmosphere around them and thereby the increase in the mobile dislocation density during plastic deformation causes a remarkable yield drop, as proposed by Johnston. (Received July 29, 1964)

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