Interaction of an Mg Basal Screw Dislocation and Mg17Al12 Precipitate Using Atomistic Simulations

Precipitation hardening in Mg-Al alloys mainly comes due to the interaction and competition between basal dislocations and Mg17Al12 precipitates. The precipitation hardening of Mg-alloys is considerably less effective compared to other metallic alloys, such as aluminum, a phenomenon attributed to geometric effects. Specifically, the Mg17Al12 precipitates tend to grow in thin plate-like or lozenge-shaped forms, or as elongated rods, all of which are aligned parallel to the basal plane. Nonetheless, there is a paucity of detailed atomistic simulations investigating the dislocation–precipitate interactions, particularly in the zero-temperature limit, to comprehensively assess the strengthening potential of these precipitates. This study focuses on the interaction between screw-type basal dislocations and precipitates in the athermal limit, employing molecular statics. Specifically, the critical resolved shear stress (CRSS) required to bypass the precipitates is elucidated as a function of precipitate size and juxtaposed with the predictions of classical continuum models. A detailed study to understand the role of precipitate orientation, dislocation offset from the precipitate, and multiple cutting mechanism are carried out in this paper. Atomistic microstructures reveal the shearing plane and shearing mechanism while the dislocations bypass the precipitate. These findings offer crucial insights into the precipitate hardening mechanisms and propose novel avenues for enhancing the mechanical properties of Mg-Al alloys.