Intrinsic ductility enhancement in Mg alloys elucidated via large-scale ab-initio calculations

TL;DR

This study uses large-scale ab-initio calculations to understand how solute atoms like Y and Zn improve ductility in magnesium alloys by affecting dislocation behavior, aligning with experimental observations.

Contribution

It reveals the specific role of solutes in modifying dislocation energetics and slip mechanisms, providing new insights into ductility enhancement in Mg alloys.

Findings

Solute effects on dislocation glide are crucial for cross-slip in Mg-Y alloys.

Predictions match experimental results on slip transition and ductility.

Large-scale DFT captures dislocation energetics in Mg alloys.

Abstract

Magnesium is the lightest structural alloy, yet its practical use is limited by its low ductility. Recent studies suggest ductility enhancement in dilute Mg alloys may stem from favorable solute modification of <c+a> pyramidal I/II screw dislocation core energy difference, activating <c+a> slip via a double cross-slip mechanism. This work conducts large-scale DFT calculations, reaching ~6,000 atoms, of <c+a> dislocation energetics in Mg and Mg-Y/Zn alloys. We find that relative solute strengthening effects on pyramidal I and II screw dislocation glide are crucial for cross-slip enhancement in Mg-Y, in contrast to prior investigations, that find solute-mediated dislocation-core energy modification as the main driver. Our predictions align with single- and poly-crystal experimental results and also capture the transition from pyramidal II to I preferred slip in Mg-Y.