Understanding Dislocation Motion and Plasticity via First Principles Simulations Towards Manufacturing of High Ductility Magnesium Alloys

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This grant supports fundamental research that facilitates manufacturing of ductile magnesium alloys. Magnesium alloys are the lightest structural materials and they are desirable for automotive and aerospace applications where improved energy efficiency becomes increasingly crucial. However, the limited room temperature ductility of magnesium alloys poses one of the major challenges to broad engineering application of these materials. Cold processing of magnesium at room temperature results in cracking or fracture. Hence, warm processing at elevated temperatures is typically used for industrial manufacturing, but this increases energy cost. To improve the ductility, expensive rare earth elements have been added to magnesium, but this is undesirable because of the high cost and uncertain availability of rare earths. This research project incorporates computational and experimental studies to search for inexpensive and readily available alloying elements for manufacturing new magnesium alloys with superior ductility. The results obtained from this work enables low-cost manufacturing of magnesium alloys which impacts the US economy and the environment. The project also promotes education of Integrated Computational Materials Engineering principles at undergraduate and graduate levels, as well as diversity by involving women and underrepresented minorities in disciplines of Science, Technology, Engineering and Math.Easy dislocation slip systems on the basal and prismatic planes in magnesium are unable to accommodate strain components along the c-axis of the hexagonal close-packed crystal structure. This leads to the limited ductility of magnesium at room temperature. The pyramidal c+a dislocations are able to accommodate c-axis strains, but their critical resolved shear stresses are one to two orders of magnitude higher than those of prismatic and basal dislocations. Consequently, under conventional deformation conditions, the density of c+a dislocations is insufficient to meet the criterion of strain accommodation. This project integrates first-principles hierarchical high-throughput-screening and experimental studies to identify alloying elements that are able to reduce the energy barrier to nucleation and glide of the c+a dislocations in Mg alloys. This is achieved by calculating through first principles simulations how alloying elements influence the landscape of generalized stacking fault energy which describes the energy barrier to dislocation glide. After suitable candidate elements are identified, magnesium alloys are synthesized by ingot casting. Channel die compression is carried out to fabricate samples with refined grains for tensile and compressive tests to determine their mechanical behavior. Dislocation structures are characterized by transmission electron microscopy. The project provides a new, physics-based strategy to develop novel high ductility magnesium alloys, which can be processed into components of useful shapes by rolling, drawing and stamping.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.