Strengthening and plasticity mechanisms in Mg alloys with short range ordered clusters

• Applicants: Dr.-Ing. Henry Ovri; Dr.-Ing. Zhuocheng Xie
• Subject Area: Metallurgical, Thermal and Thermomechanical Treatment of Materials ; Computer-Aided Design of Materials and Simulation of Materials Behaviour from Atomic to Microscopic Scale ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 555365333

Magnesium (Mg) alloys hold promise for reducing CO2 emissions due to their high specific strength and recyclability. However, the applicability of traditional Mg alloys is significantly limited compared to other structural alloys due to their relatively poor ductility and low yield strength. Conversely, various experimental and computational efforts do confirm that low concentrations of rare earth (RE) in Mg significantly improve these properties. Evidently, an understanding of the micromechanisms underlying these improvements is critical for the optimization of existing Mg-RE based alloys and the development of new ones. Yet, our preliminary experimental investigation, performed on single crystals of Mg-Gd, demonstrates that existing mechanistic models cannot fully account for the observed improvements. Besides, our investigation indicated that the RE-rich short-range ordered (SRO) clusters in these alloy systems lead to a preferential strengthening of the basal orientation. This in turn leads to significant reduction in the pyramidal/basal critical resolved shear stress ratio, boosting pyramidal slip activities and consequently improving ductility. While our initial hypotheses appear well-founded, several key knowledge gaps remain to be addressed. To bridge these gaps, the proposed research program is structured around three overarching objectives: a) Addressing existing gaps in the experimental basis of the mechanistic model: we will firmly establish the type and morphology of the SRO clusters from directions orthogonal to the c-axis of the Mg crystal and validate their influence on strength and ductility in the basal, pyramidal and twinning orientations using a combination of in-situ scanning electron microscopy tensile testing, ex-situ micro-compression and high-fidelity microstructural characterization. b) Validation and refinement of the mechanistic model via atomic-scale modelling: We will refine and validate our mechanistic model by integrating the new experimental findings with insights gleaned from a combined approach of density functional theory calculations and atomistic simulations. c) Lay the groundwork for the development of industrially relevant Mg alloys: the refined model will form the basis for the development of a continuum model, which can accurately interpret the texture development and deformability of Mg alloys while considering the effects of SRO. By pursuing this approach, we aim to establish the foundation for next-generation, high-performance Mg alloys that meet the demanding strength and ductility requirements of critical applications.

• DFG Programme: Research Grants
• International Connection: France
• Cooperation Partners: Dr. Stéphane Berbenni; Julien Guénolé, Ph.D.