Mechanisms of plastification in multiaxially loaded textured magnesium

• Applicant: Professor Dr.-Ing. Otto Huber
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins ; Lightweight Construction, Textile Technology
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 438040004

Magnesium alloys are of increasing importance because of their high specific monotonic and cyclic mechanical strengths, ease of availability and economical manufacture, which give them high potential for lightweight energy saving structures. However, the hexagonal magnesium lattice has complex deformation behaviour under stress, which is not fully understood.Recent studies of textured Mg alloy sheets subjected to uniaxial and bending monotonic and cyclic loading have shown that macroscopic compressive strain manifests in twin-rich deformation bands that have a severe influence on the mechanical behaviour. Currently available phenomenological continuum models do not account for the discontinuous nature of these strain distributions, and experimental results for biaxial compression quadrants of the yield surface are not available due to complications of performing such tests.This fundamental research project will determine the relationship between microstructural deformation mechanisms and macroscopic yield and fatigue behaviour of textured magnesium (AZ31B alloy) subjected to complex multiaxial stress states through carefully designed and implemented mechanical tests and state-of-the-art microstructural analysis. It will significantly enhance our understanding of magnesium and the capability of modelling current industrial magnesium alloys as well as newly developed magnesium alloys.The range of tests will include in-plane biaxial monotonic and cyclic stress tests, SEM in situ compression tests and indentation. In each case the resulting microstructures will be characterised using TEM and EBSD, with particular focus on the initiation, growth and distribution of twins and their interaction with other defects such as grain boundaries and precipitates.Based on these complimentary studies, the complete yield surface of magnesium will be established and the strain-hardening behaviour characterised. This will then be used to develop an elastic-plastic constitutive model for FEM simulation to predict the stress and strain fields in engineering structures and to develop a fatigue model for cyclic biaxial loading.A novel cruciform specimen and anti-buckling guide will be designed using FEM simulation; SEM in situ mechanical testing will be made using a constraining device for biaxial compression; nanoindentation of magnesium TEM foils will be developed to explore fundamental microstructural deformation processes; new constitutive models for the cyclic behaviour of magnesium will be developed; an ultra-smooth core drilling machine and a miniature vibrational polisher will be built.

• DFG Programme: Research Grants
• International Connection: Austria
• Co-Investigator: Professor Dr.-Ing. Holger Saage
• Cooperation Partner: Lawrence Whitmore, Ph.D.