On the reversibility of dislocation slip during cyclic deformation of Al alloys containing shear-resistant particles

The cyclic deformation behavior of a model Al-4Cu-0.05Sn (wt.%) alloy containing a homogeneous and well-defined distribution of shear-resistant θ′ (Al₂Cu) precipitate plates was used to study the effect of precipitate state on the cyclic slip irreversibility. The precipitate spacing was controlled so that it was less than the self-trapping distance of dislocations. The cyclic deformation tests were conducted under constant plastic stain amplitude mode and the evolution of the cyclic stress and cyclic hardening rate with cumulative plastic strain were monitored. The deformed and undeformed microstructures were characterized using transmission electron microscopy. The cyclic deformation behavior and the corresponding dislocation structures depend on both precipitate state and imposed plastic strain amplitude. An expression for the cyclic slip irreversibility that explicitly depends on microstructural and deformation parameters was derived based on proposed mechanisms of interaction between the mobile dislocations and the precipitates. The cyclic deformation curve was calculated using the expression for the slip irreversibility and shown to describe most features of the cyclic deformation curves well, as a function of precipitate state and imposed plastic strain amplitude, as well as describing the results of plastic strain amplitude jump tests.