Magnesium alloys have become increasingly important for various potential industrial applications, especially in energy storage, due to their outstanding properties. However, a clear under-standing of the dissolution mechanism of magnesium in the most common aqueous environments re-mains a critical challenge, hindering the broader application of magnesium alloys. To address pending key controversies in magnesium alloys research, the atomic-scale hydrogen evolution process and dis-solution mechanism of magnesium were investigated by combining machine learning molecular dy-namics with density functional theory. These controversies include the presence of magnesium reaction intermediates, the formation of uni-positive Mg+, the specific reaction steps involved in hydrogen evo-lution and magnesium dissolution, and the generation and growth mechanisms of the surface films. The results indicate that the intermediate species in the magnesium dissolution process is solid-phase MgOH, which exhibits an MgO-like structure. The magnesium in MgOH is identified as the widely recognized uni-positive Mg+. The intermediate film is formed, consisting primarily of the MgOH phase with a small amount of
The study of materials behavior under extreme conditions is fundamental to science and modern technology. Fast ramp compression is a unique method for exploring materials behavior and phase transformations under extreme conditions. One unexplored feature of this method is the nanoscale structure of the material under dynamic compression. This leaves a gap in understanding the details of phase transformations under fast ramp compression. Here, we made a first step in the exploration by applying the Williamson-Hall (WH) analysis to X-ray diffraction data (XRD) measured in magnesium subjected to fast ramp compression at four pressures. We found that at $P = 309 GPa$ magnesium in bcc-like phase has an average crystalline size $D = (2.2 \pm 0.7) nm$ and microstrain $\varepsilon = (-0.011 \pm 0.007)$. At $P = 409 GPa$, magnesium demonstrates $D = (4.5 \pm 3) nm$ with $\varepsilon = (-0.003 \pm 0.007)$. At $P = 563 GPa$, Fmmm magnesium has crystalline size $D = (2.6 \pm 0.5) nm$ with microstrain $\varepsilon = (-0.004 \pm 0.004)$. At $P = 959 GPa$, we revealed that sh-magnesium exhibits average size of $D > 12 nm$ and relatively high value of microstrain $\varepsilon = (0.011 \pm 0.002
A strategy to overcome sluggish hydrogenation/dehydrogenation of magnesium is demonstrated by creating magnesium-graphene interphase boundaries via high-pressure torsion (HPT). HPT reduces the grain size of pure magnesium from 1 mm to 850 nm, with 70% of grain boundaries having high misorientation angles. Graphene addition leads to even finer grain sizes of 10-500 nm with a bimodal morphology. The magnesium-graphene composites exhibit superior kinetics at 623 K while maintaining high air resistance. Kinetic modeling reveals that the rate-controlling mechanism transits from interfacial reaction in coarse-grained magnesium to atomic diffusion in magnesium-graphene nanocomposites. Kissinger analysis shows that the activation energy for hydrogen desorption remains unchanged at 145 +/- 2 kJ/mol, regardless of the presence of grain or interphase boundaries. However, the frequency factor (number of successful attempts to overcome the activation energy) increases with the generation of interfaces, which serve as sites for hydrogen diffusion and heterogeneous metal/hydride nucleation. These findings highlight the impact of interphase boundary engineering via severe plastic deformation for e
It is known that noble metals such as gold, silver and copper are not supercon- 1 ductors, so as magnesium. This is due to the weakness of the electron-phonon interaction 2 which makes them excellent conductors but not superconductors. As it has recently been 3 shown for gold, silver and copper, even for magnesium it is possible that in very particular 4 situations superconductivity may occur. Quantum confinement in thin films has been 5 consistently shown to induce a significant enhancement of the superconducting critical 6 temperature in several superconductors. It is therefore an important fundamental question 7 whether ultra-thin film confinement may induce observable superconductivity in non- 8 superconducting metals such as magnesium. We study this problem using a generalization, 9 in the Eliashberg framework, of a BCS theory of superconductivity in good metals under 10 thin-film confinement. By numerically solving these new Eliashberg-type equations, we 11 find the dependence of the superconducting critical temperature on the film thickness, L. 12 This parameter-free theory predicts superconductivity in very thin magnesium films. We 13 demonstrate that this is a fine-tuning
The wear resistance of magnesium and its alloys is very poor due to their inherent low hardness and poor tribological properties. Improving the wear resistance of magnesium and its alloys plays a significant role in expanding their application range. Various surface treatments have been used to produce protective coatings or layers for solving this problem. In this work, the Mg(OH)$_2$ layer with a thickness about 25 microns was directly formed on AZ91 magnesium alloy by oxidizing in superheated water vapor. SEM and XRD were employed to characterize the microstructure and phase composition of oxidized layer. The effect of oxidized layer on the friction and wear properties of magnesium alloy against the bearing steel ball were evaluated by using a reciprocating friction and wear test apparatus. The results showed that layer exhibited low friction coefficients and extremely small wear loss compared to the untreated substrate. Keywords: Magnesium alloy; Mg(OH)$_2$ layer; superheated water vapor; wear resistance.
The objective of this work is to assess computationally efficient coarse-grained plasticity models against high-fidelity crystal plasticity simulations for magnesium polycrystals over a wide range of textures and grain sizes. A basic requirement is that such models are able to capture {\it evolving} plastic anisotropy and tension-compression asymmetry. To this end, two-surface and three-surface plasticity models are considered. The two-surface constitutive formulation separately accounts for slip and twinning, while the three-surface model further apportions the contributions of basal and nonbasal slip. Model identification is based on stress-strain responses for loading along six orientations under both tension and compression. The evolution of overall plastic anisotropy, as well as microscale relative activities of slip and twin systems, is analyzed in detail. The prospects of using coarse-grained plasticity models in guiding the development of physically sound damage models for magnesium alloys are discussed.
Plastic work partitioning was investigated in extruded AZ31B magnesium alloy under loading orientations promoting slip- or twinning-dominated deformation. Slip-dominated deformation exhibits stable plastic flow with approximately 50$\%$ of plastic work dissipated as heat. In contrast, twinning-dominated deformation initially stores most plastic work, delaying dissipation and promoting rapid strain hardening and early strain localization. The distinct mechanical responses correlate with microstructural evolution, revealing deformation-mechanism-dependent energy storage behavior in HCP magnesium alloys.
Partial Table of Contents: ALLOY DEVELOPMENT. Development of Practical High Temperature Magnesium Casting Alloys (J. King). Creep Resistant Mg Alloy Development (K. Pettersen, et al.). New Magnesium Wrought Alloys (C. Jaschik, et al.). Phase Equilibria, Microstructure and Properties of Novel Mg-Mn- Y Alloys (A. Pisch, et al.). TEXTURE AND MICROSTRUCTURE. Texture Analysis as a Tool for Wrought Magnesium Alloy Development (S. Agnew, et al.). Influence of Texture on Deformation Behaviour of Magnesium Alloy AZ31 (R. Gehrmann, et al.). Magnesium Applications in Aerospace and Electronic Industries (B. Landkof). JOINING. Friction Stir Welding of Lightweight Materials (S. Kallee, et al.). MAGNESIUM MATRIX COMPOSITES. Thermal Fatgue of Magnesium Matrix Composites (F. Chmel?k, et al.). Possibilities of the Heat Treatment of MagnesiumMatrix Composites Reinforced with SiC Particles (K. Braszczynska). MECHANICAL DEVELOPMENT. Mechanical Properties of Extruded Magnesium Alloys (B. Closset). Fatigue Design with Cast Magnesium Alloys (C. Sonsino, et al.). Superplasticity of Magnesium-Based Alloys (U. Draugelates, et al.). APPLICATION. High-Speed-Drilling in AZ91 D Without Lubricoolants (F. Tikal, et al.). Cast Magnesium Alloys for Wide Application (P. Detkov, et al.). CORROSION AND SURFACE TREATMENT. Corrosion Properties of Die Cast AM Alloys (M. Videm, et al.). Corrosion Fatigue and Corrosion Creep of Magnesium Alloys (A. Eliezer, et al.). PROCESSING. Quality Index Charts for Mg-based Casting Alloys (C. C?ceres). Semi Solid Injection Molding of MagnesiumAlloys (A. Dworog, et al.). Hydrostatic Extrusion of Magnesium (K. Savage, et al.). Processing of Cellular Magnesium Alloy (Y. Yamada, et al.). PHYSICAL PROPERTIES. Damping in Magnesium and Magnesium Alloys (W. Riehemann). CREEP BEHAVIOUR. Creep of Mg-Zn-Al-Alloys (M. Vogel, et al.). The Microstructure and Creep of an Extruded Mg-Y-Nd Alloy (R. Azari-Khosroshahi). RECYCLING, MELTING, ENVIRONMENTAL. Remelting and Cleaning of Magnesium Scrap (U. Galovsky & M. K?hlein). SIMULATION. An Approach to Determine Solidification Curves of Commercial Magnesium Alloys (D. Mirkovic, et al.). Indexes.
Magnesium is one of the important elements in stellar physics as an electron donor and in Galactic Archaeology as a discriminator of different stellar populations. However, previous studies of Mg I and Mg II lines in metal-poor benchmark stars have flagged problems with magnesium abundances inferred from one-dimensional (1D), hydrostatic models of stellar atmospheres, both with or without the local thermodynamic equilibrium (LTE) approximation. We here present 3D non-LTE calculations for magnesium in FG-type dwarfs, and provide corrections for 1D LTE abundances. The 3D non-LTE corrections reduce the ionisation imbalances in the benchmark metal-poor stars HD84937 and HD140283 from $-0.16$ dex and $-0.27$ dex in 1D LTE, to just $-0.02$ dex and $-0.09$ dex respectively. We then applied our abundance corrections to 1D LTE literature results for stars in the thin disc, thick disc, $α$-rich halo, and $α$-poor halo. We find that the 3D non-LTE results show a richer substructure in [Mg/Fe]-[Fe/H] in the $α$-poor halo, revealing two subpopulations at the metal-rich end. These two subpopulations are also separated in kinematics, supporting the astrophysical origin of the separation. While th
Europa's tenuous atmosphere results from sputtering of the surface. The trace element composition of its atmosphere is therefore related to the composition of Europa's surface. Magnesium salts are often invoked to explain Galileo Near Infrared Mapping Spectrometer spectra of Europa's surface, thus magnesium may be present in Europa's atmosphere. We have searched for magnesium emission in Hubble Space Telescope Faint Object Spectrograph archival spectra of Europa's atmosphere. Magnesium was not detected and we calculate an upper limit on the magnesium column abundance. This upper limit indicates that either Europa's surface is depleted in magnesium relative to sodium and potassium, or magnesium is not sputtered as efficiently resulting in a relative depletion in its atmosphere.
We develop meanfield approximation and numerical quadrature schemes for the evaluation of Angular-Dependent interatomic Potentials (ADPs) for magnesium and magnesium hydrides at finite temperature (thermalization) and arbitrary atomic molar fractions (mixing) within a non-equilibrium statistical mechanical framework and derive local equilibrium relations. We numerically verify and experimentally validate the accuracy and fidelity of the resulting thermalized/mixed ADPs (TADPs) by means of selected numerical tests including free entropy, heat capacity, thermal expansion, molar volumes, equation of state and elastic constants. We show that the local equilibrium properties predicted by TADPs agree closely with those computed directly from ADP by means of Molecular Dynamics (MD).
We use first principles calculations to study the influence of thermomechanical loads on the energetics of precipitation in magnesium-aluminum alloys. Using Density Functional Theory simulations, we present expressions of the energy of magnesium-aluminum binary solid solutions as a function of concentration, strain and temperature. Additionally, from these calculations, we observe an increase in equilibrium volume (and hence the equilibrium lattice constants) with the increase in concentration of magnesium. We also observe an increase in the cohesive energy of solutions with increase in concentration, and also present their dependence on strain. Calculations also show that the formation enthalpy of $β$ phase solutions to be strongly influenced by hydrostatic stress, however the formation enthalpy of $α$ phase solutions remain unaffected by hydrostatic stress. We present an expression of the free energy of any magnesium aluminum solid solution, that takes into account the contributions of strain and temperature. We note that these expressions can serve as input to process models of magnesium-aluminum alloys. We use these expressions to report the influence of strains and temperature
Modeling deformation twin nucleation in magnesium has proven to be a challenging task. In particular, the absence of a heterogeneous twin nucleation model which provides accurate energetic descriptions for twin-related structures belies a need to more deeply understand twin energetics. To address this problem, molecular dynamics simulations are performed to follow the energetic evolution of $\{10\overline{1}2\}$ tension twin embryos nucleating from an asymmetrically-tilted grain boundary. The line, surface and volumetric terms associated with twin nucleation are identified. A micromechanical model is proposed where the stress field around the twin nucleus is estimated using the Eshelby formalism, and the contributions of the various twin-related structures to the total energy of the twin are evaluated. The reduction in the grain boundary energy arising from the change in character of the prior grain boundary is found to be able to offset the energy costs of the other interfaces. The defect structures bounding the stacking faults that form inside the twin are also found to possibly have significant energetic contributions. These results suggest that both of these effects could be cr
The Current State of Technology and Potential for Further Development of Magnesium Applications (K. Kainer & F. von Buch).Die-Casting Magnesium (R. Fink).Vacuum Die-Casting of Magnesium Parts with High Pressure (M. Siederslebnen).Squeeze-Casting and Thixo-Casting of Magnesium Alloys (K. Kainer & T. Benzler).Deformation of Magnesium (E. Doege & K. Droder).Manufacturing and Potential of Extruded and Forged Magnesium Products (J. Becker & G. Fischer).High-Temperature Properties of Magnesium Alloys (F. von Buch & B. Mordike).High-Tech Machining of Magnesium and Magnesium Composites (K. Weinert, et al.).Joining Magnesium Alloys (A. Schram & C. Kettler).Rapid Solidification and Special Processes for Processing Magnesium Alloys (T. Ebert & K. Kainer).Fibre-Reinforced Magnesium Composites (C. Fritze).Particle-Reinforced Magnesium Alloys (F. Moll & K. Kainer).Corrosion and Corrosion Protection of Magnesium (P. Kurze).Magnesium Corrosion - Processes, Protection of Anode and Cathode (H. Haferkamp, et al.).Electroless Nickel-Phosphor Alloy Coatings for Magnesium (F. Leyendecker).Recycling of Magnesium Alloys D. Scharf).Index.
A statistical theory is presented of the magnesium ion interacting with lysozyme under conditions where the latter is positively charged. Temporarily assuming magnesium is not noncovalently bound to the protein, I solve the nonlinear Poisson-Boltzmann equation accurately and uniformly in a perturbative fashion. The resulting expression for the effective charge, which is larger than nominal owing to overshooting, is subtle and cannot be asymptotically expanded at high ionic strengths that are practical. An adhesive potential taken from earlier work together with the assumption of possibly bound magnesium is then fitted to be in accord with measurements of the second virial coefficient by Tessier et al. The resulting numbers of bound magnesium ions as a function of MgBr2 concentration are entirely reasonable compared with densitometry measurements.
A critical issue in the asymptotic giant branch (AGB) self-enrichment scenario for the formation of multiple populations in Globular Clusters (GCs) is the inability to reproduce the magnesium isotopic ratios, despite the model in principle can account for the depletion of magnesium. In this work we analyze how the uncertainties on the various p-capture cross sections affect the results related to the magnesium content of the ejecta of AGB stars. The observed distribution of the magnesium isotopes and of the overall Mg-Al trend in M13 and NGC 6752 are successfully reproduced when the proton-capture rate by 25Mg at the temperatures 100 MK, in particular the 25Mg(p, gamma)26Alm channel, is enhanced by a factor 3 with respect to the most recent experimental determinations. This assumption also allows to reproduce the full extent of the Mg spread and the Mg-Si anticorrelation observed in NGC 2419. The uncertainties in the rate of the 25Mg(p,gamma)26Alm reaction at the temperatures of interest here leave space for our assumption and we suggest that new experimental measurements are needed to settle this problem. We also discuss the competitive model based on the super massive star nucleo
We use angle-resolved photoemission spectroscopy to investigate the electronic structure of bilayer graphene at high n-doping and extreme displacement fields, created by intercalating epitaxial monolayer graphene on silicon carbide with magnesium to form quasi-freestanding bilayer graphene on magnesium-terminated silicon carbide. Angle-resolved photoemission spectroscopy reveals that upon magnesium intercalation, the single massless Dirac band of epitaxial monolayer graphene is transformed into the characteristic massive double-band Dirac spectrum of quasi-freestanding bilayer graphene. Analysis of the spectrum using a simple tight binding model indicates that magnesium intercalation results in an n-type doping of 2.1 $\times$ 10$^{14}$ cm$^{-2}$, creates an extremely high displacement field of 2.6 V/nm, opening a considerable gap of 0.36 eV at the Dirac point. This is further confirmed by density-functional theory calculations for quasi-freestanding bilayer graphene on magnesium-terminated silicon carbide, which show a similar doping level, displacement field and bandgap. Finally, magnesium-intercalated samples are surprisingly robust to ambient conditions; no significant changes
We analyze the relations between the relative magnesium abundances in stars and their metallicities, Galactic orbital elements, and ages. The relative magnesium abundances in metal-poor ([Fe/H] < -0.4) thin-disk stars have been found to systematically decrease with increasing stellar orbital radii in such a way that magnesium over abundances ([Mg/Fe]>0.2 dex) are essentially observed only in the stars whose orbits lie almost entirely within the solar circle. At the same time, the range of metallicities in magnesium-poor stars is displaced from (-0.5<[Fe/H]<+0.3 dex) to (-0.7<[Fe/H]<+0.2 dex) as their orbital radii increase. This behavior suggests that, first, the star formation rate decreases with increasing Galactocentric distance and, second, there was no star formation for some time outside the solar circle while this process was continuous within the solar circle. The decrease in the star formation rate with increasing Galactocentric distance is responsible for the existence of a negative radial metallicity gradient (grad_{R}[Fe/H]=(-0.05 \pm 0.01) kpc^{-1}) in the disk, which shows a tendency to increase with decreasing age. At the same time the relative magn
We report new near ultraviolet HST/STIS observations of atmospheric absorptions during the planetary transit of HD209458b. We detect absorption in atomic magnesium (MgI), while no signal has been detected in the lines of singly ionized magnesium (MgII). We measure the MgI atmospheric absorption to be 6.2+/-2.9% in the velocity range from -62 to -19 km/s. The detection of atomic magnesium in the planetary upper atmosphere at a distance of several planetary radii gives a first view into the transition region between the thermosphere and the exobase, where atmospheric escape takes place. We estimate the electronic densities needed to compensate for the photo-ionization by dielectronic recombination of Mg+ to be in the range of 10^8-10^9 cm^{-3}. Our finding is in excellent agreement with model predictions at altitudes of several planetary radii. We observe MgI atoms escaping the planet, with a maximum radial velocity (in the stellar rest frame) of -60 km/s. Because magnesium is much heavier than hydrogen, the escape of this species confirms previous studies that the planet's atmosphere is undergoing hydrodynamic escape. We compare our observations to a numerical model that takes the s
The abundance of magnesium in the interstellar medium is a powerful probe of star formation processes over cosmological timescales. Magnesium has three stable isotopes, 24Mg, 25Mg, 26Mg, which can be produced both in massive and intermediate-mass (IM) stars with masses between 2 and 8 M_\odot. In this work, we use constraints on the cosmic star formation rate density (SFRD) and explore the role and mass range of intermediate mass stars using the observed isotopic ratios. We compare several models of stellar nucleosynthesis with metallicity-dependent yields and also consider the effect of rotation on the yields massive stars and its consequences on the evolution of the Mg isotopes. We use a cosmic evolution model updated with new observational SFRD data and new reionization constraints coming from 2018 Planck collaboration determinations. We find that the main contribution of 24Mg comes from massive stars whereas 25Mg and 26Mg come from intermediate mass stars. To fit the observational data on magnesium isotopic ratios, an additional intermediate mass SFRD component is preferred. Moreover, the agreement between model and data is further improved when the range of IM masses is narrow