Serrated flow in quenched duralumin alloy

Abstract

A model based on solute-dislocation interaction is proposed for dynamic strain ageing in substitutional alloys. Postulating on the basis of available experimental evidence that moving dislocations and their average velocity are dependent on the applied strain rate and test temperature T, a relation

is derived where t _cr is the time interval between the onset of plastic deformation and the appearance of first serration. This theory is applied to experimental observations of serrated flow in quenched duralumin alloy (D.T.D. 610 B): the effective activation energy (Q _M′ —H) for the dynamic strain ageing process, solute migration energy Q _M′ and an activation energy H associated with an intrinsic process of dislocation multiplication-motion are evaluated to be 0.23, 0.33 and 0.1 eV, respectively, for the alloy. It is suggested that copper-magnesium pair with a migration energy as the above value 0.33 eV causes necessary dislocation locking for the occurrence of serrated flow. In addition, the present analysis shows that during the dynamic strain ageing, moving dislocation density should decrease with increasing strain rate and decreasing test temperature.