# First-Principles Investigation of Ag Doping Effects on Phase Stability and Mechanical Properties in Rare-Earth Magnesium Alloy Mg24(Gd,Y)5

## TL;DR

Adding silver to a rare-earth magnesium alloy improves its ductility without significantly reducing strength, as shown by combining computer simulations and experiments.

## Contribution

Reveals the atomic mechanism of Ag doping in Mg-Gd-Y alloys and provides a strategy to enhance ductility in high-strength rare-earth Mg alloys.

## Key findings

- Ag atoms occupy Mg sites and form bonds with rare-earth atoms, increasing phase stability.
- Ag doping raises fracture strain from 4% to 12%, significantly improving ductility with minimal strength loss.
- Combining DFT calculations and WAAM experiments clarifies microstructural and mechanical effects of Ag.

## Abstract

What are the main findings?
Ag preferentially occupies Mg sites in Mg24(Gd,Y)5 and segregates in rare-earth-enriched regions, validated by experiments.Ag forms covalent-ionic bonds with RE atoms via orbital hybridization, enhancing phase stability.Ag doping increases alloy ductility (fracture strain from 4% to 12%) with moderate UTS reduction, optimizing strength-plasticity synergy.First-principles calculations combined with WAAM experiments establish a micro-macro property correlation.

Ag preferentially occupies Mg sites in Mg24(Gd,Y)5 and segregates in rare-earth-enriched regions, validated by experiments.

Ag forms covalent-ionic bonds with RE atoms via orbital hybridization, enhancing phase stability.

Ag doping increases alloy ductility (fracture strain from 4% to 12%) with moderate UTS reduction, optimizing strength-plasticity synergy.

First-principles calculations combined with WAAM experiments establish a micro-macro property correlation.

What are the implications of the main findings?
Clarifies the atomic-scale mechanism of Ag doping in Mg-Gd-Y alloys, filling the gap in existing studies.Provides a novel strategy to improve ductility of high-strength rare-earth Mg alloys without severe strength loss.Offers theoretical and experimental basis for compositional design of Mg-Gd-Y-Ag-Zr alloys for additive manufacturing.Validates the effectiveness of integrating DFT calculations and WAAM technology in alloy performance optimization.

Clarifies the atomic-scale mechanism of Ag doping in Mg-Gd-Y alloys, filling the gap in existing studies.

Provides a novel strategy to improve ductility of high-strength rare-earth Mg alloys without severe strength loss.

Offers theoretical and experimental basis for compositional design of Mg-Gd-Y-Ag-Zr alloys for additive manufacturing.

Validates the effectiveness of integrating DFT calculations and WAAM technology in alloy performance optimization.

The limited ductility of the VW63K rare-earth magnesium alloy fabricated via cold metal transfer wire arc additive manufacturing (CMT-WAAM) was targeted in this work. An integrated approach that combines first-principles calculations with experimental characterization was employed to achieve this goal. This approach was used to systematically investigate how Ag doping alters the microstructure and mechanical properties of the alloy. First-principles calculations performed on the primary precipitate phase Mg24(Gd,Y)5 demonstrated that Ag atoms preferentially occupy the Mg lattice sites and form pronounced orbital hybridization with neighboring rare-earth atoms. These interactions were found to enhance critical mechanical parameters, including the Cauchy pressure, B/G ratio, and Poisson’s ratio, which are indicative of enhanced ductility and toughness of the phase. Experimental results indicate that the fracture strain of the VW63K-Ag alloy was increased from approximately 4% to above 12% following Ag doping. This resulted in a significant improvement in ductility. The ultimate tensile strength (UTS) underwent only a moderate reduction. Using a closed-loop approach integrating theoretical prediction and experimental validation, the microstructural modification and strengthening mechanisms of Ag in the VW63K alloy fabricated via CMT-WAAM were clarified. These findings offer a theoretical foundation and experimental evidence for compositional design and optimizing additive manufacturing (AM) processes for rare-earth magnesium alloys.