Binary Al-Li Alloys Research Articles

The Influence of Aging Precipitates on the Mechanical Properties of Al–Li Alloys and Microstructural Analysis

In this work, the evolution of mechanical properties of binary Al–Li alloys with four approximately equal gradient Li contents (0.91–3.98 wt.%) under aging conditions is thoroughly investigated. The alloys undergo aging treatments at 175 °C for x hours (x = 0–120 h), and the peak-aged times of the four alloys are 6 h, 12 h, 48 h and 48 h, respectively, as the Li concentration increases. Both in the solution-treated and peak-aged states, the elastic modulus of binary Al–Li alloys exhibits an approximately linear increase with increasing Li content, consistent with trends predicted by density functional theory (DFT) calculations. Due to the presence of Al3Li precipitates, the modulus of higher-Li-concentration alloys in the peak-aged state increases by approximately 1.4–2.5% compared with that of alloys in the solution-treated state. Additionally, the study finds that increasing Li content significantly enhances the tensile strength and yield strength of the alloy but decreases its ductility, leading to a transition in fracture mode from ductile to brittle, as evidenced by a microscopic analysis of fracture surfaces. Under peak-aged (175 °C/48 h), the alloy with the highest Li content exhibits the maximum tensile strength of 341 MPa and a yield strength of 296 MPa, while its elongation is the lowest at 2.1%. These findings contribute to a deeper understanding of the effects of aging precipitates on the mechanical properties of Al–Li alloys, providing fundamental guidance for the design of future generations of Al–Li alloys.

Vanadium-Induced Structural Effects on the Corrosion and Tribological Properties of an Al-Li Binary Alloy

The influence of vanadium transition metal alloying on the structure, corrosion resistance and tribological properties of a binary Al-Li alloy containing 6wt% Li was investigated in this research. Varying vanadium contents of 0.05wt%, 0.1wt%, 0.5wt%, and 1.0wt% were examined. The results demonstrate that the addition of 1.0wt% vanadium optimally enhanced the corrosion resistance and wear resistance of the alloy. With 1.0wt% V, the wear rate decreased from 3.6 ± 0.50 ×10-2 m3/m to 1.5 ± 0.07 ×10-2 m3/m, the hardness increased from 51.7 ± 7.3 HV to 77.6 ± 4.1 HV, and the corrosion current density decreased from 43.6µA/cm2 to 3.9µA/cm2. Microstructural analyses revealed significant grain refinement induced by the addition of vanadium. The grain size decreased by 36.7%, and the dendrite arm spacing (DAS) decreased from 35µm to 8µm. Adding vanadium reduced the overall porosity of the alloy resulting from a peritectic reaction leading to the formation of vacancy-solute complexes at the grain boundaries. Phase and chemical composition analyses confirmed the formation and presence of δ (AlLi) strengthening phase within the interdendritic regions, particularly with the addition of 1.0wt% V. The presence of this phase strongly contributed to the observed improvements in corrosion resistance and tribological properties of the vanadium-modified alloy.

Assessment of atomic mobilities in the Al-Li fcc_A1 phase

Diffusion is one of the key factors that controls the precipitation of Al3Li metastable phase in Al-Li alloys. In this work, the diffusivity data in fcc Al-Li binary alloys available in the literature were comprehensively reviewed and critically evaluated, the diffusion mobilities of Al and Li in the Al-Li fcc_A1 phase were then assessed based on the reliable experimental data and empirical equations in the literature. An early relationship that correlates the diffusion activation energy and the melting temperature was revisited for group I elements, Li, Na, and K, and was used to predict the diffusivity of fcc Li. One set of self-consistent atomic mobility parameters for the Al-Li fcc_A1 phase was obtained. The limited reliable experimental diffusivity data can be generally reproduced by the present model parameters. In combination with the related thermodynamic description, the atomic mobility parameters were further verified by simulating the diffusion profiles of ion implanted Al samples at different annealing times. The model parameters were also used to simulate the concentration profiles of a cylindrical diffusion couple and the solidification process of an Al-3.5 wt.% Li alloy.

The Equilibrium α (Al-Li Solid Solution) and Metastable δ′ (Al3Li) Phase Boundaries in Aluminum–Lithium Alloys

Data on the equilibrium solubilities of the α Al-Li solid solution phase and the ordered metastable δ′ Al3Li (L12 crystal structure) precipitate phase are critically reviewed, and a new binary alloy phase diagram is proposed. The δ′ solvus, describing the equilibrium solubility of Li in the α phase, Xαe, in atom fraction Li, is given by the equation X_{alpha e} , = ,0.{6}00{text{86 exp}}left{ {{-}{8669}.{55}/{text{R}}T} right}, where R is the gas constant, and the temperature T is in K. The α solvus, i.e. the equilibrium solubility of Li in the δ′ phase, Xδ′e, is given by the equation X_{delta prime e} , = ,0.{18}0{9}, + ,{6}.{413}, times ,{1}0^{{{-}{4}}} {{T}}{-}{1}.{861}, times ,{1}0^{{{-}{6}}} T^{{2}} , + ,{1}.{4684}, times ,{1}0^{{{-}{9}}} T^{{3}} , which represents a compromise between previously published theoretical curves that predict retrograde behavior. It is emphasized that that all the data cited and re-analyzed exclusively involve binary Al-Li alloys. The new phase diagram eliminates data that were previously mis-attributed. Most importantly, it is informed by considerable re-analysis of previously published data, supplemented by the inclusion of data that were not previously considered, and eschews data on both Xαe and Xδ′e that are indubitably non-equilibrium in nature.

The Li stance on precipitation in Al\u2013Li-based alloys: an investigation by X-ray Raman spectroscopy

Decomposition and precipitation processes in a binary Al–Li alloy and a technical Al–Li–Cu–Mg alloy were investigated using differential scanning calorimetry and X-ray Raman spectroscopy (XRS). The formation of delta ’ and T1 precipitates in the Al–Li and the T8 heat-treated Al–Li–Cu–Mg alloy, respectively, was confirmed using DSC. The XRS measurements complemented by simulated spectra allowed for probing specifically Li and its environment within the Al matrix. Based on linear combination fits of the XRS spectra, the relative contributions of delta ' and T1 precipitates were quantified. These results are in agreement with estimates of the relative amount of Li taking part in the precipitation process. Difficulties and limitations of the application of XRS to Al alloy systems are also discussed.

Phase-field crystal study on the influence of nanoscale intergranular structures on grain boundary segregation

Grain boundary (GB) segregation can substantially affect the performance of materials by greatly changing the chemical compositions of GB. It is well known that GB segregation is essentially attributed to the structural differences between the bulk of grain and GB. Nevertheless, we still lack a clear understanding about the correlation between nanoscale intergranular structures and solute segregation. In this work, by using the phase-field crystal model, we performed atomic scale simulations to investigate the segregation of Li atoms to symmetric ⟨110⟩ tilt GBs in binary Al–Li alloys. It was found that the amount of segregated solute increases proportionally to GB misorientation angle in the case of low-angle tilt GBs, and converges at high-angle tilt GBs, except some special GBs with coincidence-site lattice. This is analogous to the dependences of GB energy and density on the misorientation angle. The correlations among GB structure, misfit strain around GBs and solute segregation are quantified at atomic scale. In low-angle tilt GBs, Li atoms are segregated to the compress zone around the core of intergranular dislocations to release the misfit strain energy. In the general high-angle tilt GBs, since the GB structure and misfit strain energy is uniform, the segregated atoms distribute homogeneously along GB. Particularly, the regular arrangement of structural units in some low Σ GBs lead to very low misfit strain energy, and accordingly to a periodically distributed and very low amount of solute segregation.

Examination of dendritic growth and microsegregation during solidification of Al–Li binary alloy using the phase-field simulation coupling CALPHAD data

Dendritic growth is one of the most important phenomena during the solidification of alloys. However, solute redistribution on the front of solid-liquid interface may result in nonuniform distribution of concentration between dendrite branches. This often causes microscopic segregation and undermines the properties of materials. In order to control the solidification microstructure of Al–Li alloy, we firstly need to understand in depth the morphological and concentration evolution during dendrite growth. Here, the KKS (S.G. Kim, W.T. Kim, T. Suzuki) phase-field model coupling CALPHAD data is employed. The dependences of the dendrite morphologies and growth kinetics on undercooling or initial solute concentration are qualitatively analyzed. Dendrite growth rate increases slowly when undercooling ΔT is approximately less than 25 °C, and steeply when ΔT>40 °C corresponding to the transition from diffusional dendrite growth into rapid solidification. Accordingly, the obtained morphologies change from dendrite into seaweed crystal. The increase of supersaturation influences dendrite growth similarly in terms of growth rate and morphology. Moreover, through simulation of columnar dendrites growth, we find that the microscopic segregation becomes more severely with decreasing undercooling, or increasing supersaturation. These results demonstrate the capability of the technology---phase-field simulation coupling to CALPHAD in the modelling of microstructure evolution during solidification of alloys.

Microstructural aspects of additive manufacturing of Al[sbnd]Li alloys with high Li content

Laser assisted powder bed fusion using a binary AlLi alloy with high Li content (Al–14 at.%Li) has been performed for the first time. The aim was to generate microstructures with extended concentration range of AlLi alloys in which the formation of the brittle δ–AlLi phase is avoided. From conventional casting processes it is known that the δ–AlLi phase is detrimental to mechanical properties and corrosion resistance. All processing steps from the production of ingots free of contamination, oxidation and macrosegregation to the synthesis of fine spherical powders appropriate for additive manufacturing to the powder bed fusion routine using ultra short pulses have been investigated. In comparison with as–cast microstructures, the fast cooling rate after laser assisted powder bed fusion leads to a uniform Li distribution in the primary α phase rather than to the formation of δ–AlLi, contributing to comparably high hardness of the samples.

Experimental Evaluation of Lithium Detection Limits by Windowless SDD EDXS and EELS in a Binary Al-Li Alloy Powder

Experimental Evaluation of Lithium Detection Limits by Windowless SDD EDXS and EELS in a Binary Al-Li Alloy Powder

Additive manufacturing of binary Al-Li alloys

Laser assisted additive manufacturing using binary Al-Li with increased Li content is presented. Al-Li alloys show high potential for future lightweight constructions due to increased stiffness at decreased mass. In particular, the elastic modulus significantly increases with increasing Li content. However, up to now, precipitation of the δ-AlLi limits the Li fraction to approximately 2 wt. %. In our approach, ultrashort laser pulses are used for powder fusion yielding increased cooling rates. As a result 3D printed parts of binary Al-Li with a Li content of 4 wt. % can be successfully demonstrated for the first time.

Incipient Bulk Polycrystal Plasticity Observed by Synchrotron In-Situ Topotomography.

In this paper, we present a comprehensive 4D study of the early stage of plastic deformation in a polycrystalline binary AlLi alloy. The entire microstructure is mapped with X-ray diffraction contrast tomography, and a set of bulk grains is further studied via X-ray topotomography during mechanical loading. The observed contrast is analyzed with respect to the slip system activation, and the evolution of the orientation spread is measured as a function of applied strain. The experimental observations are augmented by the mechanical response predicted by crystal plasticity finite element simulations to analyze the onset of plasticity in detail. Simulation results show a general agreement of the individual slip system activation during loading and that comparison with experiments at the length scale of the grains may be used to fine tune the constitutive model parameters.Dataset10.5281/zenodo.1412401

Laser-induced reversion of δ' precipitates in an Al-Li alloy: Study on temperature rise in pulsed laser atom probe.

The influence of tuning the laser pulse energy during the analyses on the resulting microstructure in a specimen utilizing an ultra-fast laser assisted atom probe was demonstrated by a case study of a binary Al-Li alloy. The decomposition parameters, such as the size, number density, volume fraction, and composition of δ' precipitates, were carefully monitored after each analysis. A simple model was employed to estimate the corresponding specimen temperature for each value of the laser energy. The results indicated that the corresponding temperatures for the laser pulse energy in the range of 10 to 80 pJ are located inside the miscibility gap of the binary Al-Li phase diagram and fall into the metastable equilibrium field. In addition, the corresponding temperature for a laser pulse energy of 100 pJ was in fairly good agreement with reported range of δ' solvus temperature, suggesting a result of reversion upon heating due to laser pulsing. Microsc. Res. Tech. 79:727-737, 2016. © 2016 Wiley Periodicals, Inc.

Bulk and Surface Properties of Liquid Al-Li and Li-Zn Alloys

Abstract Physicochemical properties like density, surface tension, and viscosity of liquid binary Al-Li and Li-Zn alloys have been measured using draining crucible method. The experimentally measured surface-tension values have been compared to theoretical results based either on the Butler model or the compound formation model assuming the existence of the most favored A 1 B 2 and A 2 B 3 clusters. Several models for viscosity calculation have been also applied and discussed in confrontation with measured data. Finally, the clustering effects in the liquid Al-Li and Li-Zn alloys have been examined using two microscopic functions, i.e., the concentration fluctuation function in the long-wavelength limit and the Warren-Cowley short-range order parameter.

Ostwald ripening in Al–Li alloys: A test of theory

AbstractExperimental characterization of microstructure evolution in three binary Al–Li alloys provides a quantitative test of diffusion screening theory. Particle size distributions, growth kinetics, and maximum particle sizes are obtained through quantitative, centered dark-field transmission electron microscopy. The dependences on δ′ precipitate volume fraction of the coarsening rate constant and maximum particle size are revealed, both of which have eluded determination for a half century. These experiments show that the diffusion screening theory for late-stage phase coarsening yields accurate predictions of maximum size of particle and relative coarsening constant.

Experimental, computational and theoretical studies of δ′ phase coarsening in Al–Li alloys

Experimental characterization of microstructure evolution in three binary Al–Li alloys provides critical tests of both diffusion screening theory and multiparticle diffusion simulations, which predict late-stage phase-coarsening kinetics. Particle size distributions, growth kinetics and maximum particle sizes obtained using quantitative, centered dark-field transmission electron microscopy are compared quantitatively with theoretical and computational predictions. We also demonstrate the dependence on δ′ precipitate volume fraction of the rate constant for coarsening and the microstructure’s maximum particle size, both of which remained undetermined for this alloy system for nearly a half century. Our experiments show quantitatively that the diffusion-screening theoretical description of phase coarsening yields reasonable kinetic predictions, and that useful simulations of microstructure evolution are obtained via multiparticle diffusion. The tested theory and simulation method will provide useful tools for future design of two-phase alloys for elevated temperature applications.

Superconducting State Parameters of Al-Li Binary Alloys

Theoretical computation of superconducting state parameters (SSP) viz. electron-phonon coupling strength \lambda , Coulomb pseudopotential \mu^* , transition temperature T_C , isotope effect exponent \alpha and effective interaction strength N_o V of face centered cubic Al_{1-C} Li_C binary alloys have been made extensively in the present work using a model potential formalism for the first time. A considerable influence of various exchange and correlation functions on \lambda and \mu^* is found from the present study. The present results of the SSP are found in qualitative agreement with the available experimental data wherever exist.

Effects of high magnetic fields on the microstructures and grain boundaries in binary Al–Li alloy

The effects of high magnetic fields on the as-cast microstructure and grain boundaries of binary Al-Li alloy were investigated. It was found that secondary dendrite arm spacing (SDAS) decreased and the distribution of the SDAS became uniform under high magnetic fields. The application of a high magnetic field had no effect on the type of precipitated phases in the alloy, although delta' (Al(3)Li) precipitates coarsened under the field of 11.5 T. Area fraction of grain boundary (AFGB) slightly decreased at first and then increased with increasing magnetic flux density under uniform magnetic fields, while it decreased under magnetic field gradients. (C) 2008 Elsevier B.V. All rights reserved.

Nonuniform Temperature Distribution in Adiabatic Shear Band Using Measured Shear Stress-Shear Strain Curve in Torsion of Thin-Walled Tube Aluminium Alloy Specimen and Gradient-Dependent Plasticity

Gradient-dependent plasticity where a characteristic length is involved to consider the microstructural effect (interactions and interplaying among microstructures due to the heterogeneous texture) and the measured nonlinear shear stress-shear strain curves for different loading strain rates are used to calculate the distribution of local temperature rise in adiabatic shear band (ASB) for aluminum-lithium alloy specimen of thin-walled tube in dynamic torsion test. ASB is assumed to initiate just at peak shear stress in the specimen. The temperature rise in ASB is decomposed into the uniform temperature rise in strain-hardening stage and the nonuniform temperature rise in strain-softening stage. The former depends on the measured nonlinear shear stress-shear strain curve prior to the peak, the density, the work to heat conversion factor and the heat capacity. The latter is related to the softening branch of the measured nonlinear shear stress-shear strain curve, the internal length parameter and the physical parameters. For binary Al-Li alloy, the predicted maximum temperatures in ASB are 413K at strain rate of 2000s-1 and 433K at strain rate of 2600s-1. These peak temperatures are lower than the recrystallization and phase transformation temperatures. Higher loading strain rate results in higher pre-peak and post-peak temperature rises, steeper profile of local temperature and higher peak local temperature in ASB. These predictions qualitatively agree with the previously analytical solution for ductile metal exhibiting linear strain-softening behavior beyond the peak shear stress based on gradient-dependent plasticity.

Length scales in phase coarsening: Theory, simulation, and experiment

The collective interactions occurring within a population of spherical precipitates dispersed throughout a contiguous matrix may be described on the basis of a diffusion screening length. This critical length scale is derived from the quasi-static theory of diffusion-limited phase coarsening of spherical precipitates. This theory predicts as functions of the dispersoid volume fraction the changes in diffusion screening length, the maximum particle size, the population’s coarsening rate, and, finally, the affine particle-size distribution. Furthermore, by considering fluctuations observed in the growth rates of individual particles, we formulate a stochastic theory of phase coarsening. Results obtained from simulating phase coarsening using multiparticle diffusion approaches and phase field model are then compared to the kinetic theories. Finally, particle-size distributions and the maximum radii predicted from theory and simulations are shown to agree well with experimental results obtained from measurements performed on δ′ (Al 3Li) precipitates in binary Al–Li alloys.

Microstructure and Mechanical Properties of Binary Al-Li Alloys Processed by ECAE

Microstructure and mechanical properties of two binary Al-0,7Li and Al-1,6Li alloys processed by equal channel angular extrusion (ECAE) up to strain of 9,2 were investigated. A significant grain refinement, from 300 μm toless than I μm, was achieved. The grain size reduction is more efficient in the alloy with higher Li content. In order to investigate the mechanical properties before and after ECAE deformation, the compression tests and microhardness measurements were performed. The strength of extruded material is more than two times higher. It was also found that the deformation in compression tests proceeds in a different way for ultrafine and coarse grain structure.