Structure-Dynamics Relationship in Al-Mg-Si Liquid Alloys

TL;DR

This study investigates how the atomic structure influences diffusion in Al-Mg-Si liquid alloys, revealing how Mg and Si modify local order and diffusion, which can inform alloy design.

Contribution

First principles molecular dynamics simulations reveal how Mg and Si alter local atomic order and diffusion in Al-Mg-Si alloys, providing new insights for alloy optimization.

Findings

Mg promotes icosahedral short-range order.

Si favors cubic local ordering.

Increasing Mg lowers diffusion; increasing Si enhances it.

Abstract

Enhancing properties and performances of aluminium alloys by a control of their solidification is pivotal in automotive and aerospace industries. The fundamental role of the structure-diffusion relationship is investigated for Al-Mg-Si liquid alloys taken as a prototype of Al-6xxx. For this purpose, first principles-based molecular dynamics simulations were performed for various Si and Mg content for Al-rich compositions, including the binary alloy counterparts. Results indicate that Mg and/or Si in alloys create a more compact ordering around Al than in pure Al, lowering diffusion. Mg promotes icosahedral short-range order, while Si displays a preference towards cubic local ordering, impacting diffusion based on their respective content. It suggests a mechanism whereby an increase in Mg content generally lowers the diffusion of each species, whereas an increase in Si content enhances their diffusion, providing insights for future alloy design.