# Atomistic Simulations of Basal Dislocations Interacting with Mg$_{17}$Al$_{12}$ Precipitates in Mg

## TL;DR

This study uses atomistic simulations to understand how basal dislocations interact with Mg$_{17}$Al$_{12}$ precipitates in magnesium alloys, revealing mechanisms of dislocation passage and effects on material hardening.

## Contribution

It provides detailed atomistic insights into dislocation-precipitate interactions, including the role of dislocation absorption and the effects of different precipitate properties.

## Key findings

- Dislocation passage follows a logarithmic relation with precipitate size and spacing.
- Dislocations mainly deposit segments in the interphase boundary rather than shearing precipitates.
- Absorbed dislocations increase the stress needed for subsequent dislocations to pass.

## Abstract

The mechanical properties of Mg-Al alloys are greatly influenced by the complex intermetallic phase Mg$_{17}$Al$_{12}$, which is the most dominant precipitate found in this alloy system. The interaction of basal edge and 30$^\text{o}$ dislocations with Mg$_{17}$Al$_{12}$ precipitates is studied by molecular dynamics and statics simulations, varying the inter-precipitate spacing ($L$), and size ($D$), shape and orientation of the precipitates. The critical resolved shear stress $\tau_c$ to pass an array of precipitates follows the usual $\ln((1/D + 1/L)^{-1})$ proportionality. In all cases but the smallest precipitate, the dislocations pass the obstacles by depositing dislocation segments in the disordered interphase boundary rather than shearing the precipitate or leaving Orowan loops in the matrix around the precipitate. An absorbed dislocation increases the stress necessary for a second dislocation to pass the precipitate also by absorbing dislocation segments into the boundary. Replacing the precipitate with a void of identical size and shape decreases the critical passing stress and work hardening contribution while an artificially impenetrable Mg$_{17}$Al$_{12}$ precipitate increases both. These insights will help improve mesoscale models of hardening by incoherent particles.