Narrow Results

Hydrogen storage materials from Mg–Al alloy and Mg+Al mixture were prepared by reactive milling under H₂ atmosphere with carbonized anthracite as milling aid. The crystal structure of the materials and influence of Al location on hydrogen absorption/desorption kinetics were investigated. Results show that Mg partly got hydrided into β-MgH₂ and γ-MgH₂ during reactive milling. The average crystallite sizes of β-MgH₂ in the as-milled Mg–Al alloy and Mg+Al mixture were calculated by Scherrer equation to be 10 nm and 17 nm, respectively. In the process of hydrogen desorption, the catalytic ability of Al in Mg crystal lattice was not as effective as that on particle surface. The apparent activation energies for hydrogen desorption of the two materials were estimated by Kissinger equation to be 112.2 kJ/mol and 63.7 kJ/mol, respectively. Mg₁₇Al₁₂ reacted with H₂ to convert into MgH₂ and elemental Al during static hydrogenation at 300°C. For the hydrogenated Mg+Al mixture, the obvious increase of crystallite size resulted in a low rate of hydrogen absorption and a high temperature for hydrogen desorption.

The present study proposes a constitutive model for deformation twinning which takes into account the twin degrees of freedom via incompatibility tensor model based on Field Theory of Multiscale Plasticity (FTMP). The model is introduced in the hardening law in the FTMP-based crystalline plasticity framework, which is further implemented into a finite element code. Deformation analyses are made for pure single crystal magnesium with HCP structure, and the descriptive capabilities of the proposed model are confirmed based on critical comparisons with experimental data under plain–strain compression in multiple orientations, available in the literature. The simulated results are demonstrated to successfully reproduce the unique stress–strain responses induced by twinning. The evolution of the relative activities of the various slips, and twin mechanisms for each orientation are extensively examined.