Li Addition Research Articles

Effect of Li on the deformation mechanisms of nanocrystalline hexagonal close packed magnesium

Addition of solutes such as lithium enhances ductility of hexagonal-close-packed (hcp) magnesium (Mg). However, the atomistic underpinning of Li addition on individual deformation mechanisms remain unclear and is the focus of the present work. We compared the deformation mechanisms in nanocrystalline (NC) and single crystal simulation systems of pure Mg and Mg-Li hcp alloys. Five deformation modes are observed in the pure NC Mg with randomly oriented grains – one basal {0001}〈112¯0〉, one pyramidal type-I {101¯1}〈112¯3〉, and three twinning slip systems {101¯2}〈101¯1〉,{101¯3}〈303¯2〉, and {101¯1}〈101¯2〉. Distributing 10at.% Li randomly to this NC Mg decreased its compressive yield strength by 14.5%. This also increases the ductility by activating non-basal deformation modes and by reducing the plastic anisotropy. We benchmarked these results by comparing the effect of Li addition on these deformation modes in Mg single crystals. Finally, we present a formability parameter (Fp) model based on unstable stacking fault energy, twin fault energy, and nucleation stress for dislocations (τNS). Quantifying the changes in Fp values for the Mg-Li alloys with respect to pure Mg in single crystal simulations explain the decrease in compressive yield strength and change in deformation mechanisms with Li additions. A sensitivity analysis study, comparing our CD-EAM results with a MEAM potential, shows that the effects of Li on the single deformation mechanisms are potential independent. Lastly, while results for Mg-10at.% Li random alloy are presented here, similar conclusions can be drawn for other compositions of this hcp Mg-Li alloy.

Strong luminescence enhancement of Li doped Y2O3:5 %Eu3+ phosphors

Y2O3:5 %Eu3+, x %Li+(x = 0, 2, 5, 8, and 10) phosphor have been synthesized by the sol–gel method. The microstructure and luminescent properties were also investigated for all samples by X-ray diffraction, scanning electronic morphology, and photoluminescence measurement. The Li addition is beneficial to the enhancement of luminescent intensity, and the optimal Li content is 8 % for Y2O3:5 %Eu3+. The enhancement could be attributed to three factors: one is the lattice shrinking due to smaller Li ionic radius, secondly, the appearance of the oxygen vacancies, and thirdly, the reducing number of OH− group by doping with Li+ ions.

Influence of Li Addition to Zn-Al Alloys on Cu Substrate During Spreading Test and After Aging Treatment

The spreading of Zn-Al eutectic-based alloys with 0.05 wt.%, 0.1 wt.%, and 0.2 wt.% Li on Cu substrate has been studied using the sessile drop method in presence of QJ201 flux. Wetting tests were performed after 1 min, 3 min, 8 min, 15 min, 30 min, and 60 min of contact at temperatures of 475°C, 500°C, 525°C, and 550°C. Samples after spreading at 500°C for 1 min were subjected to aging for 1 day, 10 days, and 30 days at temperature of 120°C, 170°C, and 250°C. The spreadability of eutectic Zn-5.3Al alloy with different Li contents on Cu substrate was determined in accordance with ISO 9455-10:2013-03. Selected solidified solder–substrate couples were, after spreading and aging tests, cross-sectioned and subjected to scanning electron microscopy, energy-dispersive spectroscopy (EDS), and x-ray diffraction (XRD) analysis of the interfacial microstructure. An experiment was designed to demonstrate the effect of Li addition on the kinetics of the formation and growth of CuZn, Cu5Zn8, and CuZn4 intermetallic compound (IMC) phases, during spreading and aging. The IMC layers formed at the interface were identified using XRD and EDS analyses. Increasing addition of Li to Zn-Al alloy caused a reduction in the thickness of the IMC layer at the interface during spreading, and an increase during aging. The activation energy was calculated, being found to increase for the Cu5Zn8 phase but decrease for the CuZn and CuZn4 phases with increasing Li content in the Zn-Al-Li alloys. The highest value of 142 kJ mol−1 was obtained for Zn-Al with 1.0 Li during spreading and 69.2 kJ mol−1 for Zn-Al with 0.05 Li during aging. Aging at 250°C caused an increase in only the Cu5Zn8 layer, which has the lowest Gibbs energy in the Cu–Zn system. This result is connected to the high diffusion of Cu from the substrate to the solder.

High-performance extruded Mg89Y4Zn2Li5 alloy with deformed LPSO structures plus fine dynamical recrystallized grains

The effects of the Li addition on the microstructure evolution of Mg94-xY4Zn2Lix (at.%, x=0, 1, 5, 9 and 13) alloys were systematically investigated. Little Li (<1at.%) addition facilitated the formation of 18R LPSO phases, but exceeded Li (>1at.%) addition inhibited the precipitation of 18R LPSO phases. While the (Mg, Zn)24Y5 eutectic phases increased gradually with the addition of Li. Microstructural refinement was significant when the content of Li was 5at.%. Li addition also changed the formation behavior of 14H LPSO phase of solid-solution Mg89Y4Zn2Li5 alloy only containing α-Mg and LPSO phases. The ultimate tensile strength and elongation of as-extruded Mg89Y4Zn2Li5 alloy reached to 385MPa and 14%, respectively. The coexistence of kinky block 18R LPSO phases and fine dynamical recrystallized (DRXed) grains surrounding bent lamellar 14H LPSO phases was responsible for the excellent mechanical properties.

Hot deformation behavior of Mg-4Li-1Al alloy via hot compression tests

Hot deformation behavior of rolled Mg–4Li–1Al sheets was investigated in the temperature range of 300–500 °C, and in the strain rate range of 1 × 10−3–1 × 10−1 s−1. No peak behavior was observed in the flow curves while micro-structures showed new equiaxed grains, shear bands and the dim boundaries distributed in the grains. Texture studies showed that prismatic slip was the main slip system. Thus, it was inferred that as geometrical softening or rotation of basal planes are the reasons for peak behavior, the dominance of prismatic planes instead of basal causes to no peak behavior. Also, according to the literature with Li addition, stacking fault energy of Mg alloys increases and self diffusion activation energy decreases; therefore, by considering flow curves and micro-structures, continuous dynamic recrystallization was suggested as the restoration mechanism for Mg-4Li-1Al alloy. Based on the constitutive analysis, it was found that a sine hyperbolic function could properly describe the hot deformation behavior of this material. Activation energy of 211 kJ/mol calculated from sine hyperbolic function indicates that prismatic slip becomes more frequent and cross slip becomes rate controlling mechanism, in accordance with the texture analyses.

Casting Fe–Al-based intermetallics alloyed with Li and Ag

Abstract

Influence of Li addition to passivity behavior of pure Al in NaCl acidic solution

The passive films on pure Al, Al‐1Li alloy, and Al‐2Li alloy were formed at a passive potential of −0.75 VSCE by potenyiostatic polarization for 30 min in 0.1 mol/L NaCl acidic solution (pH = 2). The corrosion resistances, semiconducting properties, and compositions of the passive films were, respectively, investigated by electrochemical impedance spectrum (EIS), Mott–Schottky (M–S) approach, and X‐ray depth photoelectron spectroscopy (XPS). The results showed that 1 and 2 wt% Li addition to pure Al improved its passivity resistance, especially for 2 wt% Li. Moreover, Li participated in the passive film formation process. The incorporation of Li2O by filling in the lattice interstitial position of Al2O3 could decrease oxygen vacancy concentration but did not change the n‐type semiconductor character of the passive films on pure Al. The increasing of passivity resistance was attributed to the decreasing of oxygen vacancy concentration and the increasing of Fermi energy of the passive films due to Li addition to pure Al.

Density, surface tension and viscosity of liquid ZnAl + X (X = Li, Na, Si) alloys

In this study, data for liquid ZnAl alloys with Li, Na and Si addition are presented. The thermophysical properties, viscosity, density and surface tension were measured using the discharge crucible method (DC). The experiments were conducted for Zn5.3Al alloys with 0.1, 0.2, 0.5, 1.0 and 3.0 wt% Na; 0.05, 0.1, 0.2, 0.5 and 1.0 wt% Li; and 0.5, 1.0, 3.0 and 5.0 wt% Si. The measurements were performed over a temperature range of 773–1023 K. The results show that the additions of Li and Na to eutectic ZnAl causes density and surface tension to decrease, and viscosity to increase. Addition of Si caused density, surface tension and viscosity to increase, in comparison to eutectic ZnAl alloy. The performed isotherms of density, surface tension and viscosity at 973 K show the influence of additions of Na, Li and Si to eutectic ZnAl.

Effect of Li on formation of long period stacking ordered phases and mechanical properties of Mg-Gd-Zn alloy

Alloys with composition of Mg96-xGd3Zn1Lix (at.%) (x=0, 2, 4, and 6) were prepared by conventional casting. The microstructures of these alloys under as-cast and solid-solution conditions have been observed, and the mechanical properties were investigated. The results showed that Li is an effective element to refine the grains and break the eutectic networks in as-cast MgGd3Zn1 alloy. During solid solution treatment, these broken eutectic networks are spheroidized and highly dispersed. In addition, plentiful lamellar long period stacking ordered (LPSO) phases are precipitated in an α-Mg matrix when the Li addition is not more than 4%. Solid-solution treated Mg92Gd3Zn1Li4 alloy exhibits an optimal ultimate tensile strength (UTS) of 226 MPa and elongation of 5.8%. The strength of MgGd3Zn1 alloy is improved significantly, meanwhile, the toughness is apparently increased.

Enhanced Stability of P2-Na2/3MnO2 through Li Addition

Energy storage technology plays a crucial role in the implementation of renewable energy and electrical vehicles. Na-ion battery, which relies on earth-abundant and low-cost Na resource, shows great potential for such applications. As an indispensable part of Na-ion battery, cathode materials with various structures have been extensively explored and investigated. Among them, layered Na2/3MnO2+σ with P2 structure is considered a promising candidate due to its high capacity, high volumetric energy density as well as spacious Na+ diffusion pathway. However, the original P2 structure in Na2/3MnO2+σ will transform through oxygen layer gliding at high charging voltage/low Na+ content, leading to serious capacity decay upon cycling. The multiple voltage plateaus during charge and discharge, which can be assigned to the ordering of Na+/vacancy in the structure, also brings adverse effect on cycle life. It has been reported that Li substitution in the transition metal sites (Na y [Li x M1-x ]O2) is effective in suppressing the structural transformation and relieving phase transitions for both P2 and O3 type layered transition metal oxides, thereby improving the cycle performance 1-6. Among these studies, it is worth to mention Xu’s surprising discovery from nuclear magnetic resonance (NMR) spectroscopy 2. They reported that the Li are not fixed in the transition metal sites. A majority of them will migrate to the Na layer when the cell is charged above 4.1 V to a higher potential of 4.4 V, while most Li diffuse back to the TM layer upon discharging to 2.0 V. The stability of the P2 structure with Li-substitution is attributed to the electrostatic attraction between adjacent TM layers induced by Li in the Na layer at high voltage. In other words, it is the Li reserve in the Na layers that hold the TM layers together. In this study, we investigate whether it is possible to stabilize the P2 structure by directly adding Li into Li x Na2/3MnO2+σ (0 ≤ x ≤ 0.2). Li x Na2/3MnO2+σ (0 ≤ x ≤ 0.2) were synthesized with the same Na/Mn ratio but with different Li content via conventional solid state method. The first benefit of Li addition is that the material is more stable in ambient conditions: Na2/3MnO2+σ undergoes structural change when left in air for a period of time, mainly due to reaction with moisture, while the Li-added samples remain unchanged. In addition, electrochemical behaviors are also changed. Li addition suppresses the phase transitions of Na2/3MnO2+σ. Even though the overall capacity is decreased with Li addition, cycle stability is improved. For example, capacity of Na2/3MnO2+σ decreases from 208.5 mAh/g to about 52.7 mAh/g (25.3% retention) after 100 cycles in the voltage range of 1.5~4.3 V at 15 mA/g. Li0.1Na2/3MnO2+σ on the other hand retains about 61.6% of its capacity after continuous Na+insertion/extraction for 100 cycles. Coulombic efficiency and rate performance are also improved with Li addition. Further structural characterizations to understand the reason for the improvements are underway and a detailed discussion will be presented at the meeting. Reference: (1) Van Nghia, N.; Ou, P.-W.; Hung, I. M. Electrochimica Acta 2015, 161, 63. (2) Xu, J.; Lee, D. H.; Clément, R. J.; Yu, X.; Leskes, M.; Pell, A. J.; Pintacuda, G.; Yang, X.-Q.; Grey, C. P.; Meng, Y. S. Chemistry of Materials 2014, 26, 1260. (3) Xu, J.; Liu, H.; Meng, Y. S. Electrochemistry Communications 2015, 60, 13. (4) Karan, N. K.; Slater, M. D.; Dogan, F.; Kim, D.; Johnson, C. S.; Balasubramanian, M. Journal of the Electrochemical Society 2014, 161, A1107. (5) Yabuuchi, N.; Hara, R.; Kajiyama, M.; Kubota, K.; Ishigaki, T.; Hoshikawa, A.; Komaba, S. Advanced Energy Materials 2014, 4. (6) Kim, D.; Kang, S.-H.; Slater, M.; Rood, S.; Vaughey, J. T.; Karan, N.; Balasubramanian, M.; Johnson, C. S. Advanced Energy Materials 2011, 1, 333. Figure 1

Characterization of ZnAl cast alloys with Li addition

The addition of Li to eutectic ZnAl alloy caused improved mechanical and thermal properties, with potential application in new design materials used in the automotive and aerospace industries. The alloys with 0.05, 0.1, 0.2, 0.5 and 1.0 Li (wt.%) content were studied using calorimetry, to determine the melting temperatures. Thermal linear expansion and electrical resistivity measurements were performed at temperatures of −50°C to 300°C and 30°C to 300°C. The microstructure of the specimens was analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Chemical microanalysis was performed using energy-dispersive X-ray spectroscopy (EDS) on SEM and TEM. The possibility of the occurrence of Al–Li, Li–Zn and Al–Li–Zn precipitates was studied by X-ray diffraction (XRDs) and selected area electron diffraction (SAED). The addition of Li to eutectic ZnAl alloy increased the electrical resistivity and the coefficient of thermal expansion; however, the melting point did not change. The mechanical properties, strain and microhardness increased with Li content in alloys.

Electrical Properties and Relaxor Phase Evolution of Li‐Modified BNT‐BKT‐BT Lead‐Free Ceramics

By conventional ceramics sintering technique, the lead‐free 0.85Bi0.5Na0.5(1−x)Li0.5xTiO3‐0.11Bi0.5K0.5TiO3‐0.04BaTiO3 (x =0–0.15) piezoelectric ceramics were obtained and the effects of Li dopant on the piezoelectric, dielectric, and ferroelectric properties were studied. With increasing Li addition, the temperature‐dependent permittivity exhibited the normal ferroelectric‐to‐ergodic relaxor (FE‐to‐ER) transition temperature (TFE‐ER, abbreviated as TF‐R) decreasing down to room temperature. The increasing Li content also enhanced the diffuseness of the FE‐to‐ER transition behavior. For composition with x = 0.15, a large unipolar strain of 0.37% ( = Smax/Emax = 570 pm/V) was achieved under 6.5 kV/mm applied electric field at room temperature. Both unipolar and bipolar strain curves related to the temperature closely, and when the temperature reached the TF‐R, the normalized strain achieved a maximum value (e.g., for x = 0.10, = 755 pm/V) owing to the electric‐field‐induced ER‐to‐FE state transition.

Elucidating the Effects of Additives on the Lipon/Electrode Interface, with a Focus on Mechanical Strain Effect

All-solid-state Li-ion batteries (ASSLIB), which replace the liquid electrolyte with solid materials, are expected to bring the improved chemical and structural stability and higher volumetric energy density than conventional Li-ion batteries. An emergent task for the next generation ASSLIB is to develop novel solid electrolyte material that has competitive Li-ion conductivity. The glassy lithium-phosphorus oxynitride (LiPON) has attracted attentions as a good candidate for that, however its practical rate capability in a full cell has been measured to be unexpectedly low, far below the computational predictions, which was attributed to the interface between solid electrolyte and cathode. Recently, one research team has reported that the rate capability of LiPON-ASSLIB could be highly improved by adding BaTiO3 (BTO) nanoparticles to the LiPON/electrode interface (Adv. Energy Mater. 4, 1301416). They hypothesized that that the space-charge layer formed in the interface area was the origin of low Li-ion conductivity and the strong dielectric behavior of BTO additive rectified it. However, the verification of the claimed hypothesis has not been made due to experimental difficulty in the measurements of the space-charge layer. Rigorous computational study at atomic scales will enable us to verify this hypothesis and understand the mechanism of the improved rate capability. In this work, we perform first-principles calculations to 1) model the LiPON/Ni-Mn spinel interface structure with and without BTO additive and 2) investigate the effects of BTO additive on the Li-ion conductivity. First, a model for the bulk LiPON is developed. There are several chemical compositions of LiPON (LixPOyNz; x=2y+3z-5). We select one sample structure, Li4PO3N, among them, for efficient study. The bulk Li4PO3N is obtained by substituting N ions for oxygen and adding extra Li ions to Li3PO4 crystal. Several ionic configurations that have different N substitution and Li addition are examined and the most stable one is identified. Next, the obtained bulk Li4PO3N is cropped and assembled with Ni-Mn spinel slab to create a model of the interface between LiPON electrolyte and Ni-Mn spinel cathode. We examine several combinations of different contacting facets and terminations, assuming that the interface structure will tend to have similar oxygen arrangement over Li4PO3N and Ni-Mn spinel parts, and find the most thermodynamically favorable one. Finally, we add BTO in the interface model to investigate its effect on the Li-ion conductivity. The activation energy barrier of Li-ion diffusion will be calculated in each case: bulk Li4PO3N, Li4PO3N/Ni-Mn spinel, and Li4PO3N-BTO/Ni-Mn spinel, and compared to investigate the effect of BTO additive on the Li-ion conductivity. From analysis on the ions distribution and electric charge distribution, we propose a structural distortion of the Li4PO3N part, which is ascribed to the lattice mismatch between the Li4PO3N and Ni-Mn spinel, can be more significant factor to determine the ionic conductivity than the space-charge layer. To support our suggestion, we calculate the activation energy barrier of Li-ion diffusion through the bulk Li4PO3N by applying different mechanical strains.

Improved the anisotropy of extruded Mg[sbnd]3Li[sbnd]3Al[sbnd]Zn alloy sheet by presetting grain re-orientation and subsequent annealing

Mg3AlZn alloy with 3 wt.% Li addition was extruded and its mechanical properties were examined. Otherwise than the typical strong basal texture obtained by ordinary Mg3AlZn extruded sheet, the Mg3Li3AlZn alloy showed a non-basal texture with its polar axis partial to the transverse direction completely. However, this type of texture would lead to strong planar anisotropy and did harm to the secondary metalworking. A simple but effective process named presetting grain re-orientation was carried out to improve the anisotropy of the Mg3Li3AlZn alloy sheet by introducing specific twins. The work hardening behavior of the initial sheet was deeply analyzed and it was used to guide the pre-deformation process. The research found that the macroscopic selection of the potential twinning planes can be feedback through the strain hardening curve. In addition, the variety and quantity of the introduced twins were confirmed to play an important role on the texture modification and property improvement of the Mg3Li3AlZn alloy sheet during the subsequent recrystallization annealing. The microstructure, texture, recrystallization and mechanical properties of various treated samples at different stages were also investigated in detail.

Effect of Li addition on the plastic deformation behaviour of AZ31 magnesium alloy

The enhancement in the workability, if any, of a dilute Mg alloy, AZ31, with the Li addition is investigated by examining the hot deformation behaviour of AZ31 alloyed with 1, 3 and 5wt% Li. Compression tests were conducted in the temperature, T, range of 150–400°C and strain rates, ε̇, ranging from 10−3 to 10+2s−1. Experimental results show that the deformation behaviour can be divided into three T regimes. In the low T regime (150–200°C), an increase in the Li content in AZ31 decreases the twin density with a concomitant enhancement in the non-basal or cross-slip activity. While high Li alloys exhibit low flow stress at low ε̇ in this regime, an increase in ε̇ increases strain hardening rate and twinning activity. Flow localization and shear band formation were observed in most of the alloys in this regime. Deformation in the intermediate T regime (250–300°C) leads to dynamic recovery (DRY) at low ε̇ and dynamic recrystallization (DRX) at high ε̇, which are the softening mechanisms in Li containing alloys. In high T regime (350–400°C), these alloys exhibit softening mechanisms similar to intermediate T regime but high Li alloys surprisingly exhibit higher flow stresses, which is attributed to the higher amount of Li in the solid solution, a result of the dissolution of Li containing precipitates. Non-basal slip and twinning at high ε̇ occur uniformly with homogeneous DRX. A low activation energy for deformation of high Li alloys indicates that the Friedel-Escaig (F-E) mechanism as the rate controlling deformation mechanism. The onset of twinning was examined by the appearance of first local maxima before peak strain in (d2σ/dε2) vs. ε curves. Mechanisms responsible for the dependence of critical stress for the onset of DRX on T and ε̇ are also discussed.

Effects of Li addition on microstructure and mechanical properties of Mg–6Al–2Sn–0.4Mn alloys

Effects of Li addition (2%, 5%, 8% and 11%) on microstructure and mechanical properties of the as-cast and as-extruded Mg–6Al–2Sn–0.4Mn-based alloys were investigated. Mg–xLi–6Al–2Sn–0.4Mn (x= 2, 5, 8 and 11, mass fraction, %) alloys were cast under an SF6 and CO2 atmosphere at 700 °C. After homogenization heat treatment at 350 °C, cast billets were extruded with a reduction ratio of 40:1 at 200 °C. Li addition to Mg–6Al–2Sn–0.4Mn resulted in the formation of MgSnLi2 and MgAlLi2 and/or AlLi intermetallic compounds and random basal texture. With increasing Li addition, β-Li phase was increased and the average area fraction of precipitates increased. Compression yield strength was increased from 212 to 235, 242 and 239 MPa as Li content was increased from 2% to 5%, 8% and 11%, respectively. Elongation was remarkably increased above 60% in 11% Li alloy. It is probable that Li-containing phases play a significant role in the enhanced mechanical properties by Li addition.

The synergistic effect of Li addition on microstructure, texture and mechanical properties of extruded Al–Mg–Si alloys

In the present work, 0, 1, 2 and 3 wt.% Li was added to conventional Al-0.9Mg-0.5Si alloy. The samples were extruded and aged to investigate the effect of Li addition on microstructure, texture and mechanical properties. The density of conventional alloy was reduced up to 7.8% while the ultimate tensile strength (UTS) increased by 62% with 3% Li addition. Electron backscatter diffraction (EBSD) revealed that Li addition effectively refined the grain size of the modified alloys. TEM/EDX and XRD analysis revealed the synergistic effect of Li addition which promoted the formation of nano-sized δ′(Al3Li) precipitates when Li content is higher then 1%. The ageing trend first decreased for 1 wt.% Li addition and then increased with increasing Li content from 2 to 3 wt.% at the expense of ductility. The intensity of texture increased with the gradual increase in Li content from alloy-1 to 4.

Record-low sintering-temperature (600 °C) of solid-oxide fuel cell electrolyte

One of the major problems arising with Solid-Oxide Fuel Cell (SOFC) electrolyte is conventional sintering which requires a very high temperature (>1300 °C) to fully densify the electrolyte material. In the present study, the sintering temperature of SOFC electrolyte is drastically decreased down to 600 °C. Combinational effects of particle size reduction, liquid-phase sintering mechanism and microwave sintering resulted in achieving full density in such a record-low sintering temperature. Gadolinium doped Ceria (GDC) nano-particles are synthesized by co-precipitation method, Lithium (Li), as an additional dopant, is used as liquid-phase sintering aid. Microwave sintering of this electrolyte material resulted in decreasing the sintering temperature to 600 °C. Micrographs obtained from Scanning/Transmission Electron Microscopy (SEM/TEM) clearly pointed a drastic growth in grain-size of Li-GDC sample (∼150 nm) than compared to GDC sample (<30 nm) showing the significance of Li addition. The sintered Li-GDC samples displayed an ionic conductivity of ∼1.00 × 10−2 S cm−1 at 600 °C in air and from the conductivity plots the activation energy is found to be 0.53 eV.

Structural transition region of liquid Mg–Li alloys

The local structural, dynamical, and thermodynamic properties of liquid Mg–Li alloys at 973K have been investigated using ab initio molecular dynamics simulation. The calculated pair-correlation functions agree well with the experimental results for pure Mg and Li. The local atomic structures have been characterized by the coordination number, bonded pair, and Voronoi polyhedron analysis. A structural transition region is found in the composition range from 12.5at.% Li to 31.25at.% Li: the close packing local atomic structures begin to transform to bcc type, which are dominated by the structural changes around Mg atoms on the effect of Li addition. The inflection point of calculated mixing enthalpy curve is also located in this region, supporting the transition of local atomic structures. Owing to the structural transition, the self-diffusion coefficients of Mg and Li change with different tendencies as Li content increasing. In addition, the interaction between Mg and Li atoms is evaluated by the quantity of charge transfer in liquid Mg–Li alloys. According to the quasi-chemical approximation model, charge transfer is confirmed as the key-factor of interaction energy.

Hafnium in Aluminum Alloys: A Review

Lots of the available literatures on hafnium in aluminum alloys are reviewed. The new binary Al–Hf phase diagram is simply assessed. Two ternary phase diagrams including Al–Hf–Zr and Al–Hf–Sc are accounted for, with emphasis on the aluminum rich part of the diagrams. The relationship between different structure Al3Hf and several different formation mechanisms including the probable phase transformation mechanisms is described. The continuous Al3Hf phase particles can serve as a grain refiner in the Al melt and a precipitate for controlling the grain structure of the alloy and a strengthening precipitate. A series of effects of Fe, Si, Zr, Sc and Li addition on the behavior of Al3Hf and Al alloys are given. Moreover, the effects of Hf on the microstructure and properties of Al alloys, such as hardness and creep, are reviewed. Finally, some views of Hf-containing Al alloys are summarized.