By comparison with other metals such as Aluminum or Steel, Magnesium alloys present the remarkable advantage of having a very high specific strength. They are thus becoming increasingly relevant to industries within the automotive or aerospace sectors, as the incorporation of these alloys in vehicles opens new avenues towards the reduction of energy consumption and CO2 emissions.
Despite their rather ancient use, Magnesium alloys have been the subject of an intense research activity only in the last decade. For instance, the strong anisotropy and the coupled importance of twin and slip mechanisms in these metals are known to have a strong influence on the micromechanical deformation processes leading the macroscale evolution of full polycrystalline samples. It is consequently of prime importance to understand at the microscale the structural crystallographic evolution of the metal.
Experimental efforts have already established the behavior of Mg alloys at low strain rates, and a few studies are now tackling the dynamic behavior of these materials [1].With the rise of computational power in the last few years, it has now appeared necessary to couple these efforts to computational modeling. Such complementary approach can somehow be simplified in three steps: (1) model design, (2) model calibration, (3) model validation.
The modeling efforts accomplished in this direction in the present work consist specifically in using a continuum finite element framework with a detailed description of slip and twin activities, but also their interactions (slip-slip, twin-twin, slip-twin and twin-slip). Except for a few efforts [2], these specific interactions have been relatively ignored in continuum simulations. We consequently aim at describing the micromechanisms of crystallographic plastic deformation within one individual grain, as well as at the macroscale level through the use of supercomputing facilities, under the widest range of strain rates possible. The ongoing work is already yielding results of primary importance on the evolution of texture, stress concentration, and overall deformation as can be seen illustratively on Fig 1.
Such work will help complementing and supporting experimental efforts on Magnesium alloy by providing a numerical tool able to characterize the microstructural evolution of any polycrystalline sample in ways that experiments cannot or can difficultly reach (e.g. full 3D texture, individual slip/twin interaction activity, etc.) and at any loading rate.
Figure 1: Simulation of twinning in AZ31 Magnesium Alloy compression; Von Mises stress field, stress-strain curve, as well as texture evolution, are extracted from the simulation.
[1] I. Ulacia, N.V. Dudamell, F. Gálvez, S. Yi, M.T. Pérez-Prado and I. Hurtado, Mechanical behavior and microstructural evolution of a Mg AZ31 sheet at dynamic strain rates. Acta Materialia, 58: 2988-2998 (2010).
[2] A. Staroselsky and L. Anand, A constitutive model for hcp materials deforming by slip and twinning: application to magnesium alloy AZ31B. International Journal of Plasticity 19: 1843-1864 (2003).
By Ana Fernandez, Antoine Jerusalem and Teresa Perez-Prado
Computational Mechanics of Materials Group
