MAGTWIN

Owing to its density approximately 4 times lower than that of steel, Magnesium has tremendous potential applications in both the automotive and aeronautics industries. Pure Mg, however, is of limited technological use due of its low yield stress, easy creep activation at low temperatures, and poor corrosion resistance. To circumvent these limitations, five different types of Mg-based alloys have been developed along with corresponding heat treatments. The addition of alloying elements has lead to significant improvements in terms of both strength and corrosive and creep properties. As a result, Mg alloys have been introduced in most industrial sectors, the major ones being the automotive and aeronautics industries. Currently, Mg alloys are mainly used to fabricate cast parts which are complex and costly. However, the bulk of potential applications of Mg alloys concerns the fabrication of parts by forming processes (e.g. cold rolling, hydroforming, etc). Unfortunately this alternative use of Mg alloys is currently not feasible because of the low ductility of wrought Mg alloys at room temperature. Fundamentally, the question of the limited ductility of Mg alloys at room temperature cannot be dissociated from the following underlying question: what are the plastic deformation mechanisms activated in pure and alloyed Mg during room temperature deformation? Few –if not no- comprehensive study encompassing both experiments and theory has been conducted on that topic such that many key aspects of the deformation of both pure and alloyed Mg are yet to be understood. For example, it is known that several deformation modes are simultaneously activated in Mg. However, the interactions between active modes are for the most part still unknown. Similarly, it is known that twinning can readily be activated within single crystal and polycrystalline Mg. Indeed, properly oriented, a Mg single crystal can entirely reorient by twinning. However, the driving force for twin activation has still to be identified. Also, microscopy revealed that the presence of second-generation twin lamellae –i.e. twin domains within primary twin domains- is observed in regions neighboring cracks. However it is not known what effects these second-generation twins have on plastic deformation, strain-hardening and ductility such that their role in plastic deformation is still today subject to speculation. Up to now, only a very limited number of studies have been dedicated to the development of physically based multi-scale models for the deformation and associated microstructure evolution of Mg. Among others, it was shown that while commonly used multi-scale approaches are acceptable to grossly predict the material response; these approaches can neither predict the relative contributions nor the role of second-generation twins, transmutations effects, etc. on the mechanical behavior of Mg alloys, owing to the fact that several key physical deformation processes are not well understood (e.g. twin nucleation, dislocation/twin interactions..) The proposed ANR addresses the aforementioned key points such as to allow control and prediction of the plastic behavior of Mg alloys during forming processes. The goal is to develop a comprehensive program investigating at the scales of interest -the atomistic scale, the crystal scale and the polycrystal scale- all critically important aspects of plastic deformation such as to obtain a predictive capability of the activation and effects of all mechanisms on plasticity of pure and alloyed Mg. The program will, by essence, balance experimental characterization and theoretical studies.