Basal dislocation/precipitate interactions in Mg-Al alloys: an atomistic investigation

TL;DR

This study uses atomistic simulations to investigate how edge basal dislocations interact with Mg17Al12 precipitates in Mg alloys, revealing mechanisms consistent with experimental observations and theoretical models.

Contribution

It introduces a new atomistic modeling strategy for precipitate insertion and details the dislocation-precipitate interaction mechanisms in Mg alloys.

Findings

Dislocations bypass precipitates via Orowan loops entering the precipitate.

Dislocation shearing occurs after multiple dislocations overcome the precipitate.

Initial shear stress matches Bacon-Kocks-Scattergood model predictions.

Abstract

The interaction between edge basal dislocations and $\beta$-Mg$_{17}$Al$_{12}$ precipitates was studied using atomistic simulations. A strategy was developed to insert a lozenge-shaped Mg$_{17}$Al$_{12}$ precipitate with Burgers orientation relationship within the Mg matrix in an atomistic model ensuring that the matrix/precipitate interfaces were close to minimum energy configurations. It was found that the dislocation bypassed the precipitate by the formation of an Orowan loop, that entered the precipitate. Within the precipitate, the dislocation was not able to progress further until more dislocations overcome the precipitate and push the initial loop to shear the precipitate along the (110) plane, parallel to the basal plane of Mg. This process was eventually repeated as more dislocations overcome the precipitate and this mechanism of dislocation/precipitate interaction was in agreement with experimental observations. Moreover, the initial resolved shear stress to bypass the precipitate was in agreement with the predictions of the Bacon-Kocks-Scattergood model.