Atomistic simulations of basal dislocations in Mg interacting with Mg17Al12 precipitates

Abstract

The mechanical properties of Mg-Al alloys are greatly influenced by the complex intermetallic phase Mg17Al12, which is the most dominant precipitate found in this alloy system. The interaction of basal edge and 30∘ dislocations with Mg17Al12 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 τc 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 Mg17Al12 precipitate increases both. These insights will help improve mesoscale models of hardening by incoherent particles.