Atomic scale interactions of basal dislocations and twin boundaries with ultrathin precipitates in magnesium alloys

D.F Shi,C.Y Wang,C.M Cepeda-Jiménez,M.T Pérez-Prado

doi:10.1016/j.actamat.2021.117442

D.F Shi, C.Y Wang + Show 2 more

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https://doi.org/10.1016/j.actamat.2021.117442

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Abstract

The aim of this work is to investigate the interaction of basal dislocations and twin boundaries with ultrafine basal disk-shaped precipitates at the atomic scale in the peak-aged Mg-1Mn-1Nd-3Zn (wt.%) alloy. With that goal, an experimental approach consisting on micropillar compression of two grains oriented favorably for basal slip and for tensile twin activation, respectively, as well as high resolution transmission electron microscopy, was put in place. First, a novel mechanism of interaction between particles and basal dislocations was observed. In particular, the movement of dislocations along basal planes led to the dissolution of the ultrathin basal precipitates in the nearby regions (within 80 nm) and to solute diffusion resulting in microsegregation of solutes at the slip lines. Hindering of basal slip due to such microsegregation prevented slip localization by promoting the consecutive activation of softer basal planes. Second, twin-precipitate interactions were found to be dependent on the twin boundary plane. In particular, bypassing of precipitates by coherent twin boundary segments were observed to lead to elastic rotations of the precipitate lattice, while the interaction of CTB/prismatic-basal intersections with precipitates resulted in precipitate shearing along prismatic planes.

Highlights

Vehicle lightweighting has become critical in recent years due to the urgent need to develop more sustainable transportation means [1,2]
A TEM Energy dispersive Xray spectroscopy (EDX)-based composition analysis was conducted in the region imaged in Fig. 3a, and the results are depicted in Fig. 3c–3f by means of single element compositional maps
Our work reveals that the interaction between the twin boundary and the precipitate is influenced by the specific nature (CTB or PB/BP) of the boundary segment traversing the precipitate

Summary

Introduction

Vehicle lightweighting has become critical in recent years due to the urgent need to develop more sustainable transportation means [1,2]. Significant research efforts have been invested in Mg alloys since the beginning of the century, a deeper understanding of physical metallurgy phenomena such as the interaction of particles, as potential hardening agents, with dislocations and twins, is still needed [7]. Recent studies have attributed this poor age hardening performance to the capacity of basal dislocations, which are the main strain carriers for most Mg alloys under a vast majority of testing conditions [7], to shear precipitates [10,11,12,13,14,15,16,17,18]. The capability of non-basal dislocations to shear precipitates has remained controversial. While some studies have reported the inability of c + a dislocations to shear c-axis rod precipitates in

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