Study On The Mechanical Performance And Hydrogen Storage Mechanism Of Ca-Mg-Li Ternary Alloy

Mg-Li alloy and Mg-Ca alloy both are important magnesium alloy. Mg-Li alloy is the lowest density in the magnesium alloy, but it possesses relatively inferior work hardening capacity performance. Mg-Ca alloy can reduce the solid oxidation of alloys and improve creep resistance. Unfortunately, the Mg-Ca alloy is brittle. Ca-Mg-Li ternary alloy was studied for make up the shortcomings of the binary alloys and a complete ternary solution pases Ca(Mg,Li)2with the C14Laves phase structure is found. In order to understand the performance of the new ternary alloy system, theoretical investigations were performed to reveal the structural, elastic and electronic properties of ordered ternary Ca(Mg1-xLix)2(x=0,0.25,0.75,1) Laves phases with C14structure from First-principles calculations. The optimized lattice constants of the Ca(Mg1-xLix)2phase agreed well with the experimental data, and stabilities were lowered with increase in Li content. Elastic properties, including elastic constants, elastic moduli and elastic anisotropies, were studied in detail. The obtained results indicated that the ductility of ternary Ca(Mg1-xLix)2(x=0.25,0.75) phases were better, while the anisotropies were more significant comparison with binary Ca(Mg1-xLix)2(x=0,1) phase. The electronic structures were further investigated to uncover the underlying mechanism for structural stability and elastic properties.In addition, as an Mg-based hydrogen storage material, Ca-Mg-Li has the low density and high hydrogen content, it has drawn much attention. First-principles calculations were carried out to study the mechanism of hydrogen storage of CaLi1.5Mg0.5, such as the occupied sites of hydrogen. The results show that the tetrahedrons with large volume and metals with stronge affinity for hydrogen are preferential occupied by H. The second nearest-neighbor metal atoms of H also influence the preferential degree of sites of hydrogen. But the resultant spatial distribution of hydrogen is mainly influenced by the diffuse path of hydrogen and the H-H Coulomb repulsion. It is also clear from calculated electronic structures that charges transfer from the metal to the H atoms and the obvious ionic bond with part covalent contribution is formd between Metal-H. This also concurs with the characteristics of chemical bonding CaH2, LiH and MgH2. Moreover, the theoretical dehydrogenation path was in agreement with the experimental result.