Professor JAVIER LLORCA
IMDEA Materials Institute, c/ Eric Kandel 2, 28906 – Getafe, Madrid, Spain &
Department of Materials Science, Polytechnic University of Madrid, 28040 – Madrid, Spain
Mg and its alloys stand for the lightest structural metals and present high specific-strength, excellent bio-compatibility and reduced cost. One main limitation for the engineering application is the reduced ductility and formability at room temperature whose origin can be traced to the hcp lattice structure. Dislocation slip in hcp Mg crystals mainly occurs by basal and prismatic slip along < a > directions as well as by < c+a > dislocations on the pyramidal planes. However, as the Critical Resolved Shear Stress (CRSS) for pyramidal slip is very large, deformation along the < c > axis has to be accommodated by twinning, a polar mechanism which only takes place when the c axis of the hcp lattice is extended. Thus, the large differences in the CRSS values to activate plastic slip in the different systems in Mg as well as the polarity of twinning lead to the large plastic anisotropy of Mg alloys, that has very negative effects on the ductility.
Alloying with different elements is a natural strategy to improve the strength of different slip systems and modify the plastic anisotropy. However, the accurate determination of the effect of solute atoms and precipitates in the CRSS for each slip is very expensive because it requires the manufacturing of single crystals with different composition. This problem may be overcome by the combination of micropillar compression tests and high-throughput processing techniques based on the diffusion couples . This methodology requires a detailed analysis the effect of micropillar dimensions on the flow strength and can be easily extended to high temperature. Using this methodology, the effect of Al and Zn in solid solution on the CRSS for basal and pyramidal slip and twinning as well as of MgZn2 precipitates on basal and pyramidal slip was determined [1-3]. The results were compared with predictions from atomistic and/or continuum models and showed the effect of alloying on the strength and plastic anisotropy.
 J.-Y. Wang, N. Li, R. Alizadeh, M. A. Monclús, Y. W. Cui, J. M. Molina-Aldareguía, J. LLorca. Acta Materialia, 170, 155-165, 2019.
 R. Alizadeh, J. LLorca. Acta Materialia, 186, 475-486, 2020.
 J. Wang, J. M. Molina-Aldareguía, J. LLorca. Acta Materialia, 188, 215-227, 2020.
"Prof. Javier LLorca is scientific director and founder of the IMDEA Materials Institute and professor and head of the research group on “Advanced Structural Materials and Nanomaterials” at the Polytechnic University of Madrid. A Fulbright scholar, he is Fellow of the European Mechanics Society and of the Materials Research Society, member of the Academia Europaea and has held visiting positions at Brown University, Shanghai Jiaotong University, Indian Institute of Science and China Central South University. His research activities have been focused in the systematic application of multiscale modeling strategies and mechanical characterization techniques (in the range nm to m) to establish the processing-structure-properties relationships of structural materials."