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Based on the density functional theory, the stability of three possible Mg3Nd(001) surfaces is investigated, and the structural and electronic properties of O adsorption on the most stable Mg3Nd(001) surface are studied. The calculated results show that the most favorable adsorption site is the (2Nd+Mg) hollow site, and the adsorption energy decreases as the coverage increases. At low coverage O atoms prefer Nd atoms to Mg atoms as nearest neighbors. When the coverage increases to a full monolayer, some O atoms sink into the alloy surface and stay between Nd and Mg atoms. The electronic structures of the adsorption system show that for all coverage the interaction between O and the alloy surface mainly arises from the hybridization of O 2p states and Nd 5d states, while the interaction between Mg 3s states and O 2p states becomes noticeable at the high coverage. The present study reveals that during the initial oxidation stage of the alloy, Nd atoms can get a priority of oxidation, followed by Nd rich oxide film. [ABSTRACT FROM AUTHOR]

The minimum creep rate and microstructures of aged samples of Mg-Gd-Zr alloys, with and without alloying additions of Zn and/or Y, have been investigated in the present work. The creep tests were performed at 523 K (250 °C) and under 80 to 120 MPa, and the microstructures before and after creep tests were characterized using scanning electron microscopy, transmission electron microscopy, and the high-angle annular dark-field imaging technique. It is found that dislocation creep predominates in the steady-state creep stage for all alloys. The Mg-2.5Gd-0.1Zr (at. pct) alloy, strengthened by the β′ precipitates, has minimum creep rates in the range 1.0 × 10 to 3.8 × 10 s under 80 to 120 MPa. The addition of 1.0 at. pct Zn to the Mg-2.5Gd-0.1Zr alloy reduces the 0.2 pct proof strength and increases the minimum creep rate, resulting from the formation of γ′ basal plates at the expense of β′ precipitates. The replacement of 1.0 at. pct Gd by Y in the Mg-2.5Gd-1.0Zn-0.1Zr alloy leads to a substantial reduction in the minimum creep rate, even though it does not cause much change to the 0.2 pct proof strength. The reduced minimum creep rate is attributed to a much lower diffusivity of Y atoms than Gd in the solid magnesium matrix. An increase in the Gd content from Mg-1.5Gd-1.0Y-1.0Zn-0.1Zr to Mg-2.5Gd-1.0Y-1.0Zn-0.1Zr leads to a denser distribution of precipitates, a higher 0.2 pct proof strength, and a further reduction in the minimum creep rate. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the effect of rotating gas bubble stirring treatment on the microstructures of semi-solid AZ91-2Ca alloy was investigated. The semi-solid slurry was produced by injecting fine gas bubbles into the melt through a rotating steel diffuser during solidification, and the samples of semi-solid slurry were taken by the rapid quenching method. The results show that fine and spherical α-Mg particles can be obtained under rotating gas bubble stirring treatment. The process parameters such as gas flow rate, cooling rate and rotation speed have significant influence on the morphology of primary solid particles. After rotating gas bubble stirring treatment, the higher the particle density, the finer and rounder the primary α-Mg particles. The formation of numerous solid particles is due to the combination mechanisms of copious nucleation and dendrite fragmentation. [Copyright &y& Elsevier]

Abstract: First-principles calculations within generalized gradient approximation have been performed to investigate ideal strengths of anti-fluorite structured Mg2X (X = Si, Ge, Sn and Pb) compounds. The present calculations showed that the ideal tensile strengths of Mg2X occur in the [111] directions while the ideal shear strengths appear in the (111) [11-2] systems. Both ideal tensile strength and shear strength of Mg2X (X = Si, Ge, Sn and Pb) decreased gradually with the increase of atomic number of X. The microscopic process and inherent mechanisms of mechanical properties were discussed from the evolution of electronic structures during strain. [Copyright &y& Elsevier]

In this study, the influence of T5 heat treatment on tensile and fatigue behavior of hot-extruded Mg–10Gd–3Y (wt%) magnesium alloy has been investigated. High cycle fatigue tests were carried out at a stress rate (R) of -1 and a frequency of 100 Hz using hour-glass-shaped round specimens with a gauge diameter of 5.8 mm. The results show that fatigue strength (at 107 cycles) of Mg–10Gd–3Y magnesium alloy increases from 150 to 165 MPa after T5 heat treatment, i.e., the improvement of 10% in fatigue strength has been achieved. However, the crack growth resistance is lowered by T5 heat treatment. Results of microstructure observation and scanning electron microscopy-energy dispersive x-ray (SEM-EDX) analysis suggest that the fatigue strength in the Mg–10Gd–3Y magnesium alloy is determined by the threshold stress of basal slip, which is induced by solid solution hardening and precipitation hardening. [ABSTRACT FROM AUTHOR]

A new flux was developed specially for recycling of scrap magnesium alloy AZ91 with high iron content. JDMJ in the flux could effectively remove inclusions from the recycled magnesium alloy and its proper addition was about 2.0 wt%. Excessive addition of the flux would result in flux inclusion in the recycled magnesium alloy. B2O3 in the flux made the iron concentration in the scrap magnesium alloy decrease from 0.044 wt% to about 0.002 wt% during recycling and its optimal addition was 0.3 wt% by Gaussian Fitting. The tensile properties of the recycled magnesium alloy were greatly improved by about 35%. Weight loss measurement, potentiodynamic study and pitting morphology examination revealed that the corrosion resistance of the recycled magnesium alloy was also greatly improved. The mechanisms of inclusion removing and iron reducing in the scrap magnesium alloy during recycling were discussed thermodynamically and formation of FeB was confirmed as the main reason for iron reducing in the recycled magnesium alloy AZ91 by XRD analysis. [ABSTRACT FROM AUTHOR]

Abstract: Theoretical investigations of the effect of Y and Zn atom substitution on elastic properties of 6H-type ABCBCB LPSO structure in Mg97Zn1Y2 alloy have been performed from density function theory. Elastic properties, including elastic constants and elastic modulus were investigated, and the influence of Y and Zn substitution were discussed in detail. Elastic anisotropies were analyzed by several methods, and the results show that the anisotropy in compression is almost negligible, whereas the anisotropy in shear is relatively large. Furthermore, the shear anisotropy becomes larger with Zn substitution than Y substitution. The electronic characteristics indicate that the Mg–Y and Mg–Zn bonds exhibit covalent feature due to hybridization, so the interactions of Mg with Y and Zn are enhanced. [Copyright &y& Elsevier]

Abstract: The stacking faults of 17 B2-structured magnesium alloys have been studied systematically by means of first-principles calculations. After structure optimization and stability analysis, the generalized stacking fault energy surfaces for two possible slip planes {001} and {110} have been calculated using a super-cell tilling technique, and the main feature of generalized stacking fault energy surfaces was analyzed. Then the most likely slip directions were determined, and the stable and unstable stacking energies were obtained. The dissociation of perfect dislocation was further discussed. The electronic structures were also investigated to reveal the underlying mechanism for stability and stacking faults. [Copyright &y& Elsevier]

Multi-stacking fault structures in pure magnesium similar to long-period stacking ordered phases of Mg–Y–Zn alloys have been investigated systematically from first-principles calculations. Based on stacking fault energy, the favorable multi-stacking fault structures are in general accordance with experimental observations. Furthermore, the present investigations indicate that inter-transformation occurs mainly between long-period stacking ordered structures with the same type of stacking faults when their lower stacking fault energies are closer. Calculated electronic structures reveal two different mechanisms for I 1–I 1 and I 2–I 2 interactions. [ABSTRACT FROM AUTHOR]

Abstract: The structural, elastic and electronic properties of Mg(Cu1−x Zn x )2 alloys (x =0, 0.25, 0.5,and 0.75) were investigated by means of first-principle calculations within the framework of density functional theory (DFT). The calculation results demonstrated that the partial substitution of Cu with Zn in MgCu2 leaded to an increase of lattice constants, and the optimized structural parameters were in very good agreement with the available experimental values. From energetic point of view, it was found that with increase of Zn content the structural stability of Mg(Cu1−x Zn x )2 alloys decreased apparently. The single-crystal elastic constants were obtained by computing total energy as a function of strain, and then the bulk modulus B, shear modulus G, Young''s modulus Y and Poisson''s ratio ν of polycrystalline aggregates were derived. The calculated results showed that among the Mg(Cu1−x Zn x )2 alloys, MgCuZn exhibited the largest stiffness, while Mg2Cu3Zn showed the best ductility. Finally, the electronic density of states (DOSs) and charge density distribution were further studied and discussed. [Copyright &y& Elsevier]

Abstract: The crystal structure of the 10H-type long-period stacking order structure in Mg–Y–Zn alloy was investigated by first-principle calculations. The calculated results show that the accurate positions and distinctive arrangement of Zn and Y atoms in the most stable 10H-type LPSO phase exhibit mirror symmetry with respect to the atomic layer C6, which agrees well with the experimental observations. Theoretical calculations still indicate that the mirror symmetry 10H-type ABACBCBCAB phase is not distorted, the lattice distortion of other LPSO phases may originate from the asymmetry of Zn element in the chemical order and stacking order. The obtained electronic density of states (DOS) reveals the underlying mechanism for mirror symmetry of 10H-LPSO phase. [ABSTRACT FROM AUTHOR]

Abstract: The structural, electronic and elastic properties of typical hexagonal-close-packed MgZn2 and ScZn2 phases in Mg–Sc–Zn alloy were investigated by means of first-principles calculations within the framework of density functional theory (DFT). The calculated lattice constants were in good agreement with the experimental values. The obtained cohesive energy and formation enthalpy of both phases are negative, showing their structural stability from energetic point of view. The five independent elastic constants were calculated, and then the bulk modulus B, shear modulus G, Young''s modulus E and Poisson''s ratio ν of polycrystalline aggregates were derived. The ductility and plasticity of the MgZn2 and ScZn2 phases were further discussed. The elastic anisotropy of the two phases was also analyzed. Finally, the electronic density of states (DOS) and charge density distribution were also calculated to reveal the underlying mechanism of structural stability and mechanical properties. [Copyright &y& Elsevier]

Abstract: The β′ phase precipitate in Mg–Gd alloy system has been investigated by means of first-principles calculation within the generalized gradient approximation. The lattice parameters are determined theoretically by structural optimization of full relaxation, and the Mg7Gd is found to be energetically more stable compared with the Mg15Gd from the calculated formation energy. The nine independent elastic constants are calculated, indicating the proposed Mg15Gd structure in literature is mechanically unstable. Then the polycrystalline bulk modulus B, Young''s modulus E, shear modulus G, Poisson ratio ν of Mg7Gd are gained by the Voigt–Reuss–Hill (VRH) approximation. The ductility and plasticity, especially elastic anisotropy are discussed in details. Based on the electronic density of states and charge density distribution, the covalent bonding and metallic bonding are exhibited in Mg7Gd compound. Last, the Debye temperature is also calculated for the investigation in the future. [Copyright &y& Elsevier]

Abstract: First-principles calculations have been carried out to investigate the electronic structure and mechanical properties of the main binary Laves phase CaMg2, CaAl2 and MgAl2 with C14, C15 and C36 structures in Mg–Al–Ca alloy, respectively. The optimized structural parameters were in very good agreement with the experimental values. The calculated heat of formation and cohesive energy showed that the C15-CaAl2 Laves phase was of the strongest alloying ability and structural stability. The electronic density of states (DOS) and charge density distribution were given. The elastic parameters Cij were calculated, then the bulk modulus, shear modulus, Young''s modulus, Possion''s ratio and anisotropy value were derived. The ductility and plasticity were discussed in comparison with the previous experimental and theoretical data. The results showed that C14-MgAl2 is of the best ductility and C15-MgAl2 is of the best plasticity in the investigated binary alloys. [Copyright &y& Elsevier]

Abstract: First-principles calculations were performed to study structural, elastic and electronic properties of typical face-centered cubic (fcc) precipitates of Mg-based alloys (Mg3Gd, Mg3Gd0.5Y0.5 and Mg3Zn3Y2) within the generalized gradient approximation. The calculated results show that the substitution of part of the Gd with Y in Mg3Gd leads to a slight decrease in the cell volume (0.35%), and the lattice parameters obtained after full relaxation of crystalline cells are in good agreement with the experimental data. The calculated negative formation enthalpies and the cohesive energies show that these typical fcc precipitates of Mg-based alloys have good alloying ability and structural stability. According to the calculated density of states of these phases, it is found that the highest structural stability of Mg3Zn3Y2 is attributed to an increase in the bonding electron numbers below the Fermi level. In addition, the elastic constants Cij of these phases were also calculated, and the bulk modulus B, shear modulus G, Young’s modulus E, Poisson’s ratio ν and anisotropy value A of polycrystalline materials were derived from the elastic constants. The mechanical properties are further discussed. [Copyright &y& Elsevier]

Abstract: The corrosion behaviors of Mg–6wt.%Gd–3wt.%Y–0.4wt.%Zr (GW63K) alloy in 5wt.% NaCl aqueous solutions have been investigated in both as-cast and T6 heat treatment conditions by immersion test and electrochemical techniques. The corrosion products and their morphologies formed in the solution after immersing various time have been analyzed by FE-SEM and XRD. It was found that the morphologies of the film of corrosion products varied with immersion time and changed from honeycomb into porous structure composed of tiny erect flaks after immersing 60min. The phenomena of undermining and falling away of the noble second phase particles observed in the test can be used as an evidence to support the Mechanism II explaining the mechanism of negative difference effect (NDE) about magnesium and its alloys. It was indicated that the E CORR of GW63K alloy in T6 condition (−1.71V) is little nobler than that in as-cast (−1.73V). It was shown by pitting scans that GW63K alloy has tendency to pit whether in as-cast or in T6 condition and the tendency in T6 condition is more serious than that in as-cast. An equivalent circuit was proposed based on the EIS experimental data and the honeycomb or porous characteristics of the corrosion products formed on the surface of GW63K alloy. [Copyright &y& Elsevier]