Mechanisms of plastification in multiaxial loaded magnesium

Magnesium alloys are of particular importance for lightweight design structures due to their high strength- to-weight ratio and economical manufacture. The design of magnesium components relies upon our understanding of how the alloy behaves under various types and magnitudes of loading. In-depth study is required to correlate mechanical tests, such as tension, compression and shear, with deformation mechanisms at the microstructural scale. The hexagonal atomic structure of magnesium gives rise to complex deformation behaviour under stress. Magnesium sheets subjected to uniaxial compressive strain have been shown to deform through the formation and growth of bands of crystalline defects known as twins. These bands have a large influence on the mechanical properties, playing a significant role in strain-hardening and fracture initiation. Current theoretical models do not account for these strain distributions. Also, biaxial compressive deformation behaviour is not currently quantified due to the complications of performing such tests. This fundamental research project aims to characterise the relationship between microstructural deformation and macroscopic behaviour of the magnesium alloy AZ31B by a range of complex tests (including multiaxial compression, shear and nano-indentation) and state-of-the-art microstructural analysis. Particular focus will be placed upon the initiation, growth and distribution of twins, their interaction with other defects such as grain boundaries and precipitates, and their role in fracture initiation. The new JEOL JEM-F200 transmission electron microscope at the Paris Lodron University of Salzburg (PLUS) will be used to reveal the very earliest stages of deformation at the atomic scale. In situ uniaxial and biaxial compression tests in a scanning electron microscope will be carried out to investigate the deformation at the microstructural scale. Biaxial quasi-static and cyclic tests with cruciform specimens will be carried out at the University of Applied Sciences Landshut (UASL) to characterize and analyse the deformation behaviour and the fatigue behaviour at the macroscopic scale. Results from these tests will be used to develop an elasto-plastic constitutive model for the finite element method to calculate the macroscopic stress and strain fields and to develop a fatigue model for cyclic biaxial loading. Microstructural analysis will be carried out at the Department of Chemistry and Physics of Materials at PLUS by Dr. Whitmore, an experienced microstructural scientist and microscopist, while testing will mainly be made at the Competence Center for Lightweight Construction at UASL by Prof. Huber, an internationally recognized researcher in materials modelling and lightweight design and Prof. Saage, an experienced materials scientist.

No additional funding sources recorded.