Mg-based Alloys Research Articles

Characteristics of hydride electrodes using Mg-Ti-Ni-Co-Al-based alloys synthesized by mechanical milling

For Ni-MH batteries, crystalline Mg-based alloys such as MgNi, Mg2Ni, REMg12, and La2Mg17 are regarded as hopeful negative electrode materials. Even though these alloys are inexpensive and have promising discharge capacity, they hardly ever electrochemically absorb or desorb hydrogen at room temperature. In this paper, the MgNi-based Mg50-xTixNi45Al3Co2 (x = 0, 1, 2, 3, 4) alloy electrodes were fabricated. The surface of the as-cast alloys was modified by mechanical Ni coating. The nanocrystalline and amorphous Mg50-xTixNi45Al3Co2 (x = 0, 1, 2, 3, 4) + 50 wt%Ni alloys for Ni-MH batteries were prepared using mechanical ball milling. The effects of Ti content and ball milling time on the structure and electrochemical hydrogen storage properties of the alloys were investigated. The electrochemical testing reveals that the as-milled alloys can electrochemically absorb and desorb hydrogen well at room temperature. Without any activation, the milled alloys can achieve maximum discharge capacity in the first cycle. With the extension of ball milling time and the increase of Ti content, the cycle stability and discharge capacity of the alloys are significantly enhanced. The electrochemical impedance spectrum, high rate discharge ability, potentiodynamic polarization curve, and potential-step measurement all indicate that the electrochemical kinetics of the prepared alloys initially increase and subsequently decrease with the increase of Ti content, while significantly improve with the prolongation of milling time.

Emergence of rapid solidification microstructure in additive manufacturing of a Magnesium alloy

Abstract Bioresorbable Mg-based alloys with low density, low elastic modulus, and excellent biocompatibility are outstanding candidates for temporary orthopedic implants. Coincidentally, metal additive manufacturing (AM) is disrupting the biomedical sector by providing fast access to patient-customized implants. Due to the high cooling rates associated with fusion-based AM techniques, they are often described as rapid solidification processes. However, conclusive observations or rapid solidification in metal AM — attested by drastic microstructural changes induced by solute trapping, kinetic undercooling, or morphological transitions of the solid-liquid interface — are scarce. Here we study the formation of banded microstructures during laser powder-bed fusion (LPBF) of a biomedical-grade Magnesium-rare earth alloy, combining advanced characterization and state-of-the-art thermal and phase-field modeling. Our experiments unambiguously identify microstructures as the result of an oscillatory banding instability known from other rapid solidification processes. Our simulations confirm that LPBF-relevant solidification conditions strongly promote the development of banded microstructures in a Mg-Nd alloy. Simulations also allow us to peer into the sub-micrometer nanosecond-scale details of the solid-liquid interface evolution giving rise to the distinctive banded patterns. Since rapidly solidified Mg alloys may exhibit significantly different mechanical and corrosion response compared to their cast counterparts, the ability to predict the emergence of rapid solidification microstructures (and to correlate them with local solidification conditions) may open new pathways for the design of bioresorbable orthopedic implants, not only fitted geometrically to each patient, but also optimized with locally-tuned mechanical and corrosion properties.

Study on degradation behavior of porous magnesium alloy scaffold loaded with rhBMP-2 and repair of bone defects

Magnesium (Mg) is abundant in humans. Studies have shown that Mg2+ significantly affects physiological processes such as osteogenesis, osteoblast adhesion and motility, immunomodulation, and angiogenesis. Mg-based alloy porous scaffolds have attracted increasing attention because of their degradability and mechanical properties. Hence, wire-cut EDM was used to fabricate porous scaffolds. In addition, fluoride treatment afforded an MgF2 coating, and racemic polylactic acid PDLLA was used as the carrier of rhBMP-2, which was evenly coated on the surface of the passivated porous alloy scaffold to slowly release growth factors and slow down the degradation rate. The rat femoral condyle defect model experiment was performed to study the in vivo bone regeneration capacity of porous scaffolds and compare the differences in the healing effect with or without rhBMP-2. The enhanced corrosion resistance of the porous scaffold was confirmed through in vitro immersion experiments. Micro-CT implied that porous scaffold with rhBMP-2 induced new bone formation and the new bone formation along the pores, as well as the histological examination in vivo. In summary, the porous scaffold promotes bone formation and has great potential for clinical translation.

MOF-derived Cu based materials as highly active catalysts for improving hydrogen storage performance of Mg-Ni-La-Y alloys

Higher initial (de)hydrogenation temperature and sluggish kinetics are the main bottlenecks to develop Mg-based hydrogen storage alloys with high hydrogen capacity. One of the effective methods of solving these problems is introducing additives to enhance (de)hydrogenation kinetics and decrease particle sizes to lower (de)hydrogenation temperatures. In this work, Mg85-Ni10-La4.5-Y0.5 alloy doped with Cu@C nanoparticles is prepared, which could enhance (de)hydrogenation kinetics via introducing Cu nanoparticles as a catalyst and reduce the alloy particle sizes via acting as a grinding agent to lower (de)hydrogenation temperature. The results indicate the dehydrogenation temperature of the modified Mg85-Ni10-La4.5-Y0.5 composite could be decreased to 308.5 °C, absorb 4.73 wt% H2 at 220 °C within 1 min and release 5.01 wt% H2 within 4 min at 300 °C. Moreover, the capacity retention could be maintained around 98.8% after 10 cycles at 300 °C, superior than those of Mg85-Ni10-La4.5-Y0.5 and milled-Mg85-Ni10-La4.5-Y0.5. DFT results and characterizations suggest that in-situ formed Mg2Cu could accelerate the dissociation of Mg-H bonds and the presence of amorphous carbon in Mg-Ni-La-Y-Cu system will further synergistically improve the (de)hydrogenation kinetics of Mg85-Ni10-La4.5-Y0.5. Reduced particle sizes under the aid of carbon frameworks also help introduce boundaries of the particles and shorten hydrogen diffusion pathways.

The semi-continuous (Mg,Al)2Ca second phase on Mg-Al-Ca-Mn alloys as an efficient anti-corrosion anode for Mg-air batteries

Developing high anti-corrosion and good discharge properties of magnesium based alloys for Mg-air batteries is still in challenge. In this work, a series of Mg-Al-Ca-Mn (AMX) alloys are prepared, and the second phases on AMX alloys are adjusting by varying the Al content. The AMX alloys with 3 wt% Al (denoted as AMX311) exhibits the excellent anti-corrosion behavior with a corrosion current density of 85.7 μA cm−2 and a low corrosion rate (4.1±0.21 mm y−1) in the 3.5 wt% NaCl solution. Furthermore, AMX311 shows lower hydrogen evolution volume (20.9±1 ml/cm2) and weight loss (5.8±0.3 mg) compared to other contrast samples. The outstanding electrochemical corrosion performance of AMX311 is attributed to the Al-rich oxide film which slowing corrosion at the initial stage and the formation of semi-continuous (Mg,Al)2Ca phase which can acts as a physical barrier to prevent the electrolyte from further corroding the magnesium matrix. Moreover, the AMX311 exhibits the highest discharge voltage (-1.471 V) and a peak specific energy of 1684.7±30.0 mW h g−1 at 20 mA/cm2, due to its superior corrosion resistance and reduced chunk effect. This work provides a good guide for designing advanced Mg-based alloys and an excellent insight into the effect of second phase on the corrosion and discharge performance of Mg-air batteries anode materials.

Design multifunctional Mg–Zr coatings regulating Mg alloy bioabsorption

Magnesium (Mg) alloys are widely used for temporary bone implants due to their favorable biodegradability, cytocompatibility, hemocompatibility, and close mechanical properties to bone. However, rapid degradation and inadequate strength limit their applicability. To overcome this, the direct current magnetron sputtering technique is employed for surface coating in Mg-based alloys using various zirconium (Zr) content. This approach presents a promising strategy for simultaneously improving corrosion resistance, maintaining biocompatibility, and enhancing strength without compromising osseointegration. By leveraging Mg's inherent biodegradability, it has the potential to minimize the need for secondary surgeries, thereby reducing costs and resources.This paper is a systematic study aimed at understanding the corrosion mechanisms of Mg–Zr coatings, denoted Mg-xZr (x = 0–5 at.%). Zr-doped coatings exhibited columnar growth leading to denser and refined structures with increasing Zr content. XRD analysis confirmed the presence of the Mg (00.2) basal plane, shifting towards higher angles (1.15°) with 5 at.% Zr doping due to lattice parameter changes (i.e., decrease and increase of “c” and “a” lattice parameters, respectively). Mg–Zr coatings exhibited “liquidphilic” behavior, while Young's modulus retained a steady value around 80 GPa across all samples. However, the hardness has significantly improved across all samples’ coating, reaching the highest value of (2.2 ± 0.3) GPa for 5 at.% Zr. Electrochemical testing in simulated body fluid (SBF) at 37 °C revealed a significant enhancement in corrosion resistance for Mg–Zr coatings containing 1.0–3.4 at.% Zr. Compared with the 5 at.% Zr coating which exhibited a corrosion rate of 32 mm/year, these coatings displayed lower corrosion rates, ranging from 1 to 12 mm/year. This synergistic enhancement in mechanical properties and corrosion resistance, achieved with 2.0–3.4 at.% Zr, suggests potential ability for reducing stress shielding and controlled degradation performance, and consequently, promising functional biodegradable materials for temporary bone implants.

Hot extrusion-induced Mg-Ni-Y alloy with enhanced hydrogen storage kinetics

In this work, the influence of the hot-extrusion method on the hydrogen storage kinetics of Mg-Ni-Y alloy was investigated. It was shown that the extruded Mg91.47Ni6.97Y1.56 alloy exhibits improved hydriding and dehydriding (H/D) kinetics, with a capacity of 3.5 wt.% H2 absorption within 60 s and 5.4 wt.% H2 desorption within 5 min at 573 K. The dehydrogenation activation energy of extruded alloy is 71.4 kJ mol−1, smaller than that of as-cast alloy (140.5 kJ mol−1). The enhancement of H/D kinetics is attributed to the microstructural refinement and increased grain/phase boundaries introduced by hot extrusion, as well as the catalytic effects from the in-situ generated and grain-refined Mg2Ni and YH2 particles during the H/D process. Furthermore, the dehydrogenated rate-determining step transforms from hydrogen diffusion in the hydride (as-cast alloy) to the surface penetration of hydrogen atoms (extruded alloy). These findings provide crucial insights for the design of Mg-based hydrogen storage alloys in the future.

Influence of the phase evolution and hydrogen storage behaviors of Mg-based alloy catalyzed by Gd-Fe compound

In order to further optimize the kinetic and thermal properties of Mg-based hydrogen storage alloy, the Mg + 10 wt% GdFe alloy is prepared by using vacuum induction melting. The XRD, SEM, EDS, TEM, PCT and TG-DTA are used to characterize the microstructure of the alloy and phase transition in the reaction process. The results show that the sample is composed of the main phase Mg and the remaining Mg5Gd. In addition, Fe elements are evenly distributed in dissolved in the Mg matrix. After hydrogen absorption, all these phases disappear and are transformed into MgH2 and GdH2. After hydrogen desorption, MgH2 transforms to Mg phase, but the GdH2 phase remains unchanged. During the reaction, Fe always exists in the Mg/MgH2 lattice in the form of simple substance, which is beneficial to the recombination and dissociation of hydrogen atoms. Meanwhile, the GdH2 phase also provides abundant the active sites and diffusion admittance. The alloy has a reversible hydrogen content of 5.8 wt% H2 and an activation energy of 144.1 kJ/mol. It also shows excellent kinetic properties, which can absorb 4.3 wt% H2 at 360 °C in 10 min, and complete hydrogen desorption at the same temperature requires only 18 min. The thermodynamics energy increases only slightly, but the initial hydrogen release temperature and peak temperature are much lower than those of Mg.

Enabling one-step regeneration of LiBH4 with self-sustaining hydrogen in its spent fuel – One pathway to storing renewable hydrogen

LiBH4 (LB in short) with a hydrogen capacity as high as 18.5 wt% and a low molecular weight (21.78 g mol−1) is among the most promising candidates for the hydrogen-based economy. However, current major technologies in (re)generation of LB rely heavily on energy-intensive processes, which greatly prohibits practical scaling-up of applications. Here we report a sustainable and effective approach to (re)generate LB via converting renewable H+ in crystalline water into H-, achieving a desirable yield of ∼50%. This one-step synthesis method relies on the reaction between spent fuels, specifically LiBO2·xH2O, and Mg-based alloys to form LB under ambient atmosphere. Notably, our approach surpasses the efficiency of other conventional method, such as LiH-B-H2 and MgH2-LiBO2 systems, which not only bypasses the energy-intensive dehydration procedure of LiBO2·xH2O (∼470 ℃) but also eliminates the use of costly hydrides or high-pressure H2. Our findings indicate that Mg participated in the regeneration process prior to Al in Mg-Al alloys and [BH4]- is gradually evolved from other intermediate species [BHx(OH)4-x]- (x = 0, 1, 2, 3). By combining hydrogen release and efficient storage of hydrogen-rich substrate in a closed materials cycle, this study may shed light on a promising step toward application of renewable hydrogen in a fuel cell-based hydrogen economy.

Optimization and analysis of sustainable magnesium-based alloy (Mg-Zn-Ca-Y) for biomedical applications

Due to strength and biodegradability, magnesium (Mg) and its alloys are potential biodegradable implant materials. However, pure Mg corrodes more rapidly in the physiological environment, causing rapid deterioration before bone repair. The discrepancy between bone healing and Mg implant deterioration encourages the development of new Mg alloys with other acceptable alloying elements to achieve the desired high corrosion resistance and mechanical properties. In this work, different concentrations of yttrium (Y), that is, Mg-4zn-0.2ca-xY, (x= 3,6,9,12% wt), are added to Mg-based alloys. The microstructure, mechanical characteristics, corrosion behavior, and biocompatibility of the alloys were carefully investigated. When Y concentrations are high, Mg alloys with Y change significantly. High Y concentrations in Mg alloys containing yttrium (Y) suppress intermetallic phases along grain boundaries and form chemically stable Y oxide layers on the surfaces, changing their microstructures and improving their corrosion resistance. Cytotoxicity analysis showed that human osteoblast cells were not significantly affected by the Y-containing Mg alloys. The benefits of using Y as an alloying element to simultaneously adjust Mg alloys with higher strength and slower deterioration are presented.

Ceramic metal oxide coatings formation by hybrid plasma electrolytic treatment: Interaction scenarios of ceramic NPs with oxide layers

Understanding the formation of protective ceramic metal oxide (CMO) coatings (layers) on the surface of light alloys remains a pressing task in light of products operating in extreme conditions. Plasma electrolytic oxidation (PEO) of light alloy surfaces has recently been modified by introducing various ceramic nanoparticles (NPs) into the electrolyte to perform hybrid plasma electrolytic treatment (HPET). In this work, the general and distinctive features of the interaction mechanisms of TiC, SiO2 and ZrO2 nanoparticles (NPs) with the CMO coating formed by HPET of Al–Si and Mg-based alloys were summarized and theoretically substantiated. The interaction of charged ceramic NPs accelerated by an electric field with the oxide layer is determined by transformation of the NPs kinetic energy into heating and plastic deformation, into phase transformations, as well as into the creation of new surface defects. One of the controlling factors is the ratio of the particle and the oxide layer hardnesses. In the case of SiO2 in Al–Si alloys, the formed coating is harder than the ceramic NPs while in other cases, the NPs are harder than the CMO coating, which determines the different scenarios for the interaction of NPs with the coating under HPET. In summary 7 different scenarios for the interaction of ceramic NPs added to the electrolyte with the СМO layer during its formation put forward, which depending on the ratio of the hardness of the CMO layer and the added particles, temperature/pressure conditions of the phase transformations in the NP (including its melting), the particles size distribution and the base PEO process parameters.

Investigation of hydrolysis properties of MgH2 in different anionic/cationic salt solutions

MgH2 is a promising metal hydride for high-density hydrogen storage, offering advantages such as operational safety, high hydrogen yield, and cost-effectiveness in hydrolysis-based hydrogen generation. However, challenges persist in this field, including reaction interruption caused by the formation of passivating layers and sluggish kinetics. In this study, MgH2 hydrolysis experiments were conducted, utilizing various solutions including 1 M AlCl3, Al2(SO4)3, Al(NO3)3, NiCl2, NiSO4, Ni(NO3)2, FeCl3, Fe2(SO4)3, and Fe(NO3)3 at different temperatures. The resulting hydrolysis products were analyzed using X-ray diffraction and scanning electron microscopy to examine their phases and morphology. Through comprehensive analysis of the hydrolysis mechanism and kinetics, chloride ion solutions were identified as highly efficient, demonstrating excellent rates and yields. Notably, AlCl3, NiCl2, and FeCl3 outperformed other solutions, exhibiting kinetic performance with hydrolysis activation energies of 17.3 ± 1.7, 24.2 ± 1.3, and 14.7 ± 1.7 kJ/mol, respectively. Furthermore, we extended our investigation to compare the hydrolysis effects of different cations, incorporating MnCl2, CoCl2, and CuCl2. Mechanistic analysis pinpointed Al3+ and Fe3+ as catalysts with exceptional hydrolysis performance and remarkable kinetic properties. The aforementioned remarkable MgH2 hydrolysis properties are of significant interest for investigating the corresponding Mg-based alloy hydrides, which are worthwhile to consider.

Effects of Ag, Cu or Fe addition on microstructure and comprehensive properties of biodegradable Zn-Mg alloy

In recent years, Zn-0.5 wt%Mg alloys have drawn a lot of attention as a potential candidate in biodegradable implant applications as it demonstrated more corrosion resistant property in comparison to Fe- and Mg-based alloys. Zn-0.5 wt%Mg based alloys were fabricated through powder metallurgy. This work examined the impact of the micro-alloying metals Cu, Fe, and Ag on Zn-Mg alloys. Moreover, the structure, absorbing properties, morphology, electrochemical properties, electrical properties, and wettability were also investigated. All fabricated Zn-0.5 wt%Mg alloys formed a primary phase of Mg2Zn11 and secondary phase of MgZn2. A minor phase of Zn was also identified in XRD analysis. Optical analysis showed that the Zn-0.5 wt%Mg-0.2 wt%Cu alloy gave a strong peak of absorbance at a short wavelength of 230 nm which is due to its colour. All alloys sintered at 350 ◦C displayed micro-needles having size in the range of 1.82–26.2 µm in SEM analysis. Zn-0.5 wt% Mg-0.2 wt% Cu alloy offered 140 Hv value of Vickers hardness. The electrochemical test findings measured corrosion resistance and most corrosion resistant material was Zn-0.5 wt%Mg-0.2 wt%Cu alloy with corrosion rate 0.0120 mm/year. Zn-0.5 wt%Mg-0.2 wt%Cu offered the conductivity with the least value of 7.45 ×10−12 Ω−1m−1and highest value of resistivity at 1.335 ×1011Ω-m, based on electrochemical study. All fabricated biodegradable Zn-0.5 wt%Mg alloys had an angle less than 90, indicating hydrophilicity as determined by wettability studies. Zn-0.5 wt%Mg-0.2 wt%Cu is the most suitable alloy in cardiovascular stent and orthopaedic implant applications.

Estimating dislocation density from electron backscatter diffraction data for an AZ31/Mg-0.6Gd hybrid alloy fabricated by high-pressure torsion

ABSTRACT The Geometrically Necessary Dislocation (GND) density was estimated from Electron Backscatter Diffraction (EBSD) data for an AZ31/Mg-0.6Gd (wt.%) hybrid material fabricated by high-pressure torsion (HPT) at room temperature through an equivalent strain range of ϵeq = 0.3–144 using Kernel Average Misorientation (KAM) and the Nye tensor approaches. The results show that generally the GND densities are significant at the beginning of the deformation (ϵeq = 0.3) and decrease in both alloys when ϵeq increases. The Mg-0.6Gd alloy exhibits a lower GND density due to rapid dynamic recrystallization. These results were compared to the GND densities measured in AZ31 and Mg-0.6Gd mono-materials processed separately by HPT under the same experimental conditions. In these mono-materials the GND densities increase with increasing equivalent strain up to 7 and then decrease with further straining. The Mg-0.6Gd and AZ31 regions of the hybrid material exhibit higher GND densities than the mono-materials particularly at low strain where the disc thickness and the bonding of the AZ31/Mg-0.6Gd interfaces cause more deformation heterogeneity in the hybrid material. It is shown that the GND density evolution as a function of ϵeq has the same tendency for the KAM and the Nye approaches but the average values are significantly higher with the Nye approach. An analysis suggests that the Nye approach overestimates the GND density of the Mg-based alloys.

Processing of different Mg-based multiphase alloys via a combined severe plastic deformation

In this study, cyclic extrusion compression angular pressing-forward extrusion was employed to develop binary magnesium-based multiphase alloys, and subsequently analysed the microstructural, mechanical and corrosional properties of the resulting samples. The findings demonstrate that the inclusion of alloying elements in the multiphase alloys significantly enhances their microstructural, mechanical and corrosional properties. Compared to pure Mg samples fabricated using the same method, the multiphase alloys produced by this technique exhibit finer grain structures. Mechanical analysis indicates that these multiphase alloys possess higher yield and ultimate strength compared to pure magnesium. Corrosion testing reveals that all produced alloys outperform pure magnesium in various aspects. Particularly, Mg–1Zn and Mg–1Mn alloys exhibit exceptional corrosion resistance in immersion, mass loss and polarisation tests.

Исследование структуры и свойств металл-интерметаллидного материала на основе (Ti – Al – Mg)/Ti, полученного методом самораспространяющегося высокотемпературного синтеза совмещенного с прессованием

The method of self-propagating high-temperature synthesis (SHS), combined with pressing, for the first time obtained a metal-intermetallic material based on gorenje products of the layered system (Ti – Al – Mg)/Ti. Exothermic synthesis from elementary powders was carried out at a pressure of 10 MPa, and pressing of the hot synthesis product at a pressure of 250 MPa. The paper demonstrates that as a result of SHS-pressing, an integral connection of the “intermetallic/metal” layers is formed. The main features of microstructure formation, phase composition and strength properties of transition zones at the boundary between reacting SHS compositions Ti – Al – Mg and Ti-substrate are investigated. The thickness of the transition zone between the layers was at least 15 µm. The results of energy dispersion analysis (EDA) showed that magnesium Mg in the synthesized alloy is mainly in the intergranular layers, in the form of a small amount of Ti – Al – Mg compound, which indicates incomplete reaction diffusion between Ti – Al and Al – Mg layers. The microhardness of Ti – Al grains in the synthesized alloy has an average value of 5820 MPa, and the matrix based on Al – Mg is 3980 MPa. The hydrostatic density is 3.3 g/cm3, with a porosity of less than 13 %. As a result, the method of SHS-pressing turned out to reduce the porosity of the resulting Ti – Al – Mg-based alloy by 3 times.

Interaction Regularity of Biomolecules on Mg and Mg-Based Alloy Surfaces: A First-Principles Study

Adsorbed molecules can modulate the behavior of magnesium (Mg) and Mg alloy in biomedical applications. The interaction regularity and mechanism of biomolecules (such as amino acids, dipeptides, and tripeptide) on a Mg(0001) surface, the influence of dipole correction, and the effects of alloying elements and electronic structure were investigated in this study using first-principles calculations. Specifically, the adsorption energy (Eads) of functional groups (-NH2, -COOH and -CN3H4), amino acids (arginine (Arg), glycine (Gly), and aspartic acid (Asp)), dipeptides (arginine–glycine (Arg-Gly), glycine–aspartic acid (Gly-Asp), and arginine–aspartic acid (Arg-Asp)), and arginine–glycine–aspartic acid (RGD) tripeptide were systematically calculated. Dipole correction slightly enhanced the interaction between molecules and Mg surfaces, but the Eads trend remained unchanged. The addition of alloying elements improved the interaction of molecules and Mg-based alloy surfaces. This study will be of fundamental importance in understanding the interaction regularity of molecules on Mg and Mg-based alloy surfaces and provide possibilities for surface modification design of biomedical materials.

(Digital Presentation) Designing New Complex Hydrides Based on Transition Metals for Hydrogen Storage Applications

The widespread implementation of the hydrogen economy demands access to materials with a high weight percentage of hydrogen. Mg-based hydrogen storage alloys have become a research hot-spot in recent years owing to their high hydrogen storage capacity, good reversibility of hydrogen absorption/desorption, low cost, and abundant resources. However, high decomposition temperature of Mg-based hydrideslimits their practical usage. Hydrogen is lightest of all elements, typically it need large volumes or high pressures to store appreciable amount of hydrogen.To overcome these challenges research activities are currently going on metal hydrides and complex hydrides based on transition metal. The main challenges come when endothermic decomposition enthalpy is considered. It becomes difficult to release the hydrogen at ambient thermodynamic conditions. On the other hand, the meta-stable hydrides are characterized by a low reaction enthalpy and a decomposition reaction that is thermodynamically favourable under the ambient conditions. The good kinetics along with evolution of hydrogen around the room temperature possessed by these materials offer much promise for underground storage and it can be used as a grid energy.The present research specifically focus on transition metal based complex hydrides such as NaMgMnH6 and NaMgFeH6 for hydrogen storage and especially predicted the crystal structure of the same using VASP simulation package. ABCX6 and AB2X6 were taken as reference composition A,B,C and X were substituted with Na, Mg, transition metals(Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu) and H, respectively.From the ICSD database search the corresponding structural variants were considered as trial structure to predict the ground state structure of these newly designed compounds. using the predicted ground state structure for these compounds, important properties like formation energy, hydrogen site energy, partial density of states(pDOS), electron density(ED), Mulliken effective charge(MEC), Bader electron charge(BEC), Born effective charge, ELF and COHP were calculated. the calculated properties of these compounds were compared with the well known reference compounds. We found that both NaMgMnH6 and NaMgFeH6 are stable with negative formation energy and als othey are semiconductors with the band gap value of 0.51eV and 1.01 eV, respectively. from the calculated electronic structure we found that both these materials are having indirect band behaviour. Analysing the electronic density of states, charge density and various charges mentioned above the chemical bonding behaviour was established as iono-covalent in nature. from the force as well as stress minimisation considering 53 structural variants as input the ground state structure, its space group, equilibrium lattice parameters and atom positions are listed. Also from the energy vs. volume curve for the ground state structure, the equilibrium volume, bulk modulus and pressure derivatives were found out. Among NaMgMnH6 and NaMgFeH6 our spin polarised calculation show that NaMgMnH6 is possesing spontaneous magnetic polarisation with substantial magnetic moment at the Mn site. Among the considered paramagnetic, ferromagnetic, as well as A-, C-,and G- antiferromagnetic configurations the G type antiferromagnetic configuration is found to be the ground state for NaMgMnH6.

High-resolution chemical and structural characterization of the native oxide scale on a Mg-based alloy

The structure and composition of the native oxide forming on the basal plane (0001) of the magnesium-based alloy Mg-2Al-0.1Ca was investigated by combining scanning transmission electron microscopy (STEM) and atom probe tomography (APT). While STEM measurements demonstrated the growth of a (111) MgO oxide layer with 3–4 nm thickness on the basal (0001) plane of the atom probe specimen, APT data further revealed the formation of an aluminum-rich region between bulk magnesium and the native oxide. The aluminum enrichment of up to ∼20 at% at the interface is consistent with an inward growth of the oxide scale.

Optimization of Anodizing Condition for Mg-14mass%Li-3mass%Al Alloy

Mg-Li system alloys also has excellent cold-workability compared to commercial hcp-structured Mg alloys. However, Mg-Li alloys have poor corrosion resistance because not only that is Mg-based alloy but Li as a major alloying element is a less noble metal. For example, Mg-Li alloy sheet indicates high corrosion rate and exfoliation corrosion as a result of long-term corrosion test. The authors reported Mg-14 mass%Li-3 mass%Al alloy has the highest corrosion resistance in β-type solid solution alloy. Even though the optimized alloy composition, the alloy does not have enough corrosion resistance for practical use. In this study, anodized coating on Mg-Li alloy using phosphate solution was investigated. Anodizing of Mg-Li alloy facilitates the dissolution of substrate because of high Li concentration in this alloy. Therefore, the anodizing conditions were widely examined. As a result, the coating with approximately 15-20 μm of the surface layer was successfully formed. The surface layer was composed of MgAl2O4 and some phosphorus compounds. The thickness of anodized layer varied with the anodizing conditions. The dense surface layer was formed at a certain anodizing voltage and the corrosion resistance of anodized Mg-Li alloys was improved. However, the surface has some cracks and large flaky compounds. The formation mechanism of dense layer during anodizing were discussed.