Superior energy absorption in porous magnesium: Contribution of texture development triggered by intra-granular misorientations

Abstract

The effect of the initial crystallographic texture and its development on the energy absorption capability of porous magnesium (Mg) with parallel cylindrical pores and a fiber texture was studied. The fiber texture, whose symmetrical axis is oriented along the longitudinal axis of pores, was modeled using crystal plasticity finite element method (FEM). Subsequently, the effect of the preferred orientation angle of the basal planes in Mg grains, denoted as the angle α, on the compressive deformation along the longitudinal axis of pores was analyzed. The analyses revealed that the orientation angle α of the basal planes strongly affects the development of the intra-granular crystallographic misorientations, which dominates the compressive deformation and energy absorption capability. When the angle α is low, a strong deformation constraint, originating from inter-granular interaction, occurs at the grain boundaries. Owing to the constraint, large intra-granular crystallographic misorientations occur during deformation. Consequently, the axial symmetry of the fiber texture becomes asymmetric, which causes the appearance of a plateau stress region, where compressive deformation proceeds with a small increase in stress. As a result, superior energy absorption is achieved for a low angle α. The crystal plasticity analyses also indicate that an ideal plateau stress region, where deformation proceeds with almost no increase in stress, appears by controlling the initial fiber texture using a compressive preloading on a porous Mg sample prepared via the present directional solidification process. Owing to the superior plateau stress region, the porous Mg achieves high energy absorption efficiency and capability simultaneously.