Prediction of shear strength of cluster-strengthened aluminum with multi-scale approach describing transition from cutting to bypass of precipitates by dislocations

We investigate the deformation of aluminum alloy containing copper in the form of fine Al-Cu clusters 1-4 nm in diameter with multiscale approach. A part of these precipitates (clusters of 1-2 nm in diameter) reproduce that were experimentally obtained by (Sun et al., 2019) by cyclic dynamic loading of aluminum alloy. At the first stage, molecular dynamics (MD) reveals that main mechanism of interaction of dislocation with the copper-containing cluster are cutting of precipitate for 1 nm cluster and bypass by Orowan mechanism for clusters with diameters above 1.4 nm. Single events of climb are observed in MD, frequency of which increases with a temperature raise. The stresses level realized for the climb mechanism practically do not differ from that of the basic mechanism for the considered inclusion diameters. Also, the results of MD simulations show that the strength of the cluster depends on the presence of enough number of copper atoms on the slip plane of dislocation and does not directly depend on the concentration of copper when it varies in the range of 20-100% inside the precipitate. Reduction of copper concentration below 20% decreases the precipitate resistance, and the system behavior converges to the case of pure aluminum at 0%. These results are supported by MD calculations of generalized stacking fault energy, which demonstrate a weak dependence of unstable stacking fault energy on copper concentration in the range of 30-70%. A continuum model of dislocation motion in aluminum containing the copper-containing cluster is proposed, which considers the kinetics of dislocation-precipitate interaction and accounts for the transition from cutting to bypass. Parameters of the model are fitted to MD data with Bayesian algorithm. Model of dislocation motion and dislocation-precipitate interaction is implemented into 2D discrete-dislocation dynamics (DDD). Flow stress of alloy predicted with DDD demonstrates reasonable agreement with the experimental data. Calculations show that the cluster-strengthened alloy demonstrates much less inhomogeneity of plastic deformation in comparison with the alloy with a comparable flow stress and volume fraction of typical phases precipitated during classical aging, which is also in line with the experiment.

Automated summary

The study reveals that the strength of clusters in aluminum alloy with copper content ranging from 20-100% depends on the number of copper atoms rather than the direct influence of copper concentration. Introducing copper-containing clusters into aluminum alloy can reduce the inhomogeneity of plastic deformation and aligns with experimental results.