Precipitate size evolution in an ultrafine-grained magnesium-manganese alloy

TL;DR

This study investigates how precipitate sizes evolve in a magnesium-manganese alloy subjected to high-pressure torsion, revealing that precipitate growth is limited by interfacial control rather than diffusion, despite increased manganese particle volume fraction.

Contribution

It provides new insights into precipitate size evolution mechanisms in ultrafine-grained magnesium alloys under severe plastic deformation.

Findings

Manganese volume fraction increases with strain.

Precipitate size remains constant during HPT.

Precipitate growth is interfacial, not diffusional.

Abstract

Precipitate size evolution during room temperature high-pressure torsion (HPT) of a Mg-1.35wt.%Mn alloy was studied using scanning transmission electron microscopy (STEM) and Small-/Wide-angle X-ray scattering (SAXS/WAXS). The volume fraction of the nm-scale $\alpha$-Mn particles increased with applied strain, however small angle X-ray scattering (SAXS) indicated that the majority of manganese remained in solution even after 10 HPT rotations, indicating that the reaction progress is still limited by the diffusivity of Mn. Analysis of the precipitate size distribution determined that the mean particle size did not increase over the course of HPT. This, in combination with the precipitate size distribution suggested that precipitate growth was subject to interfacial rather than diffusional control.