Zhou Dianwu

Study on H2 Adsorption and Dissociation Properties on Mg(0001) Surface

Abstract By the first-principles calculations method based on the density functional theory, H 2 adsorption and dissociation properties on clean, vacancy defective and Pd atom coadsorption Mg(0001) surfaces are investigated systematically. The calculation results show that the model of H 2 adsorption on clean surface is weak physisorption, and there is a high energy barrier, i.e., 1.3774 eV, when H 2 dissociates into two separate H atoms. Vacancy defect not only benefits enhancing of the physisorption interaction between H 2 and Mg surface, but also decreasing of the energy barrier, i.e., 1.2221 eV, of H 2 dissociation to some extent. For Pd atom coadsorption Mg(0001) surface, there is a strong chemisorption interaction between Pd atom and H 2 , and the energy barrier, i.e., 0.2860 eV, of H 2 dissociation is reduced significantly. Further analysis of electronic structures shows that the catalytic activity for H 2 adsorption and dissociation on three different surfaces is closely related to the bonding electrons number of s orbital of the topmost layer metal atoms which interact directly with H 2 around Fermi level.

MICROSTRUCTURE AND MECHANICAL PROPERTY OF STEEL/Al ALLOY LASER WELDING WITH Sn POWDER ADDITION

The laser welding test with Sn powder addition was carried out on DC56D+ZF galvanized steel with thickness 1.4 mm and 6016 aluminum alloy with thickness 1.2 mm. By using optical microscopy, scanning electron microscopy, X-ray diffraction and tensile test, the microstructure, fracture morphology, interface element distribution, main phase and mechanical properties of joints were studied. Elastic moduli and thermodynamic properties were calculated by using first-principles method based on density functional theory for FeAl and FeSn compounds. The results indicate that the morphology of welding surface can be improved and grain size is fine when the welding power is 2000 W, welding speed is 45 mm/s, the defocus distance is +2.0 mm, and Ar gas acts as the protection gas with flow rate 15 L/min. The average shear strength of the welding sample with Sn powder reaches 62.17 MPa. Compared to that without Sn powder addition, the average shear strength of weld joint increases by 1.46 times. Because of fine-grain strengthening and the improvement of the fluidity of the molten pool metal with Sn addition, it promotes the combination of the steel and aluminum interface