Characterization of crystal structure and precipitation crystallography of a new MgxAl2-xGd phase in Mg97Al1Gd2 alloy

TL;DR

This study characterizes a new MgxAl2-xGd precipitate in Mg97Al1Gd2 alloy, revealing its crystal structure, composition, and orientation relationships using advanced electron microscopy techniques.

Contribution

It provides detailed crystallographic and compositional analysis of a novel MgxAl2-xGd phase, expanding understanding of phase transformations in Mg-Al-Gd alloys.

Findings

Precipitate composition Mg0.38Al1.62Gd

Crystal structure is fcc type Laves phase Mg2Gd/Al2Gd

Orientation relationship and habit plane identified

Abstract

The composition, crystal structure and precipitation crystallography of a newly found precipitate are characterized by a Cs-corrected scanning transmission electron microscopy (STEM). The composition of the plate-like precipitate could be expressed as MgxAl2-xGd (x = 0.38), and its crystal structure is the same as the fcc type Laves phases Mg2Gd and Al2Gd with the lattice parameter of 7.92 Angstrom (space group No. 227, Fd-3m). The orientation relationship between the matrix and precipitate is found to be (0001)m // (111)p and [10-10]m // [1-10]p, and the habit plane is parallel to (0001)m // (111)p plane. In addition, this preferred crystallography of phase transformation is well explained based on the atomic matching in the interface.