Computational Modeling Advances Design of Magnesium Alloys Free of Rare Earth Elements

Bi-Cheng Zhou, UVA assistant professor of materials science and engineering, published path-finding research in Physical Review Materials, reporting on phase stability and early-stage precipitation in magnesium-tin alloys. His paper, co-authored with his Ph.D. students Du Cheng and Chu-Liang Fu and postdoctoral fellow Kang Wang, is among the editors’ suggested readings in the prediction, synthesis, processing structure, properties and modeling of a wide range of materials.

“Computational modeling helps us understand the material properties of an important material system,” Zhou said. As the lightest of all structural metals, magnesium alloys have great potential for applications in which weight is critical to performance and efficiency, such as the automotive, rail and aerospace industries. These alloys are highly castable, meaning they can be pooled in a liquid form and cooled into a die-cast shape.

Whereas many magnesium alloys are made with rare earth elements, Zhou’s team focused on an alloy composed with tin, a ubiquitous and comparatively inexpensive element that enhances magnesium’s electrochemical and corrosion resistance.

The team employed computational modeling to understand the magnesium-tin alloy’s precipitation sequence, which controls mechanical properties such as strength and ductility. Precipitation is the formation of secondary particles inside the material through atomic movement. These movements are very small, quick, transient and variable.

“What’s unique about our approach is that we combined first principles of quantum mechanical calculations with a statistical mechanical approach called cluster expansion. Rather than synthesizing a material to meet specific, known parameters, we model how atoms interact to see what is possible,” Zhou said. This approach enables true prediction of potential metastable precipitates at the early stage of precipitation, which are extremely difficult to characterize experimentally.

Zhou’s computational modeling suggests a new precipitation sequence to design magnesium alloys free of rare earth elements. The team’s next step is to apply similar methods to other magnesium alloys such as those containing zinc and calcium. The modeling will be validated through electron microscopy experiments with physical materials conducted by James M. Howe, Thomas Goodwin Digges Professor of Materials Science and Engineering. A grant from the National Science Foundation’s Designing Materials to Revolutionize and Engineer our Future program supports their research.