Study of the solute clusters/enrichment at early stage of ageing in Mg-Zn-Gd alloys by atom probe tomography

TL;DR

This study uses atom probe tomography to analyze the early-stage solute clustering and enrichment in Mg-Zn-Gd alloys during aging, revealing insights into LPSO structure formation and solute behavior.

Contribution

It provides a detailed 3D characterization of solute distribution and pairing in Mg-Zn-Gd alloys during aging, combining experimental data with first-principles calculations.

Findings

Zn-Gd solute pairs form two peaks at early aging stages.

The fraction of Zn-Gd pairs first increases then decreases due to LPSO precipitation.

Zn and Gd are synchronized in the LPSO structure, with no segregation of pure elements.

Abstract

The chemical enrichment/ordering of solute atoms in Mg matrix are crucial to understand the formation mechanism of long-period stacking ordered (LPSO) structures. In this study, three-dimensional distribution of solute elements in an Mg-Zn-Gd alloy during ageing process is quantitatively characterized by three-dimensional atom probe (3DAP) tomography. Based on the radius distribution function, it is found that Zn-Gd solute pairs in Mg matrix appear mainly in two peaks at early stage of ageing and the separation distance between Zn and Gd atoms is well rationalized by the first-principles calculation. Moreover, the fraction of Zn-Gd solute pairs increases first and decreases subsequently due to the precipitation of LPSO structures. Moreover, the composition of structural unit in LPSO structure and the solute enrichment around it are quantified. It is found that Zn and Gd elements are synchronized in the LPSO structure, and solute segregation of pure Zn or Gd is not observed at the transformation front of the LPSO structure in this alloy. In addition, the crystallography of transformation front is further determined by 3DAP data.