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

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.