Li Addition Research Articles

Dependence of defect susceptibility on microporosity variation in Mg-xLi-3Al-1Zn casting alloys

This study quantitatively describes relative contribution of microstructural characteristics and microporosity variation to the tensile properties of Mg-xLi-3Al-1Zn alloys from the perspective of defect susceptibility. The alloys were prepared by melting pure lithium, AZ31 alloy, and additional elements in two crucibles under an Ar atmosphere, and then mixing them to add Li in the range of 2–12 wt%. As the Li content increases, the Li-rich β phase forms along the grain boundaries of the Mg-rich α phase. At approximately 12 wt% Li, the entire matrix transitions to the Li-rich β phase, and the volume density decreases from 1.762 g/cm³ (AZ31 alloy) to a minimum of 1.435 g/cm³. Additionally, the yield strength continuously increased from 67 MPa (AZ31 alloy) to approximately 120 MPa with increasing Li content, while the tensile strength increased from 127 MPa (AZ31 alloy) to a maximum of 144 MPa at 6 wt% Li, and the elongation increased to 19 % at 10 wt% Li before decreasing at higher additions. The fracture mode during tensile deformation clearly depends on the fraction of α phase and β phase, varying with Li addition. However, all tensile properties, including yield strength, are fundamentally influenced by the fractographic porosity based on the fracture surface. The defect susceptibility coefficients on microporosity variation for tensile strength and elongation, and the maximum values achievable under defect-free conditions, are highest at 6 wt% Li and 10 wt% Li, respectively. Furthermore, the relative contributions of microporosity and microstructural components to the defect susceptibility of tensile properties can be described: tensile strength increases in the order of the mixed α+β phase, β phase, and microporosity, while the contribution of the β phase to elongation is relatively lower compared to the mixed α+β phase and microporosity.

Ionic conductivity and dielectric characteristics of a Li incorporated PVA electrolyte membrane and a study of a fully solid-state electrochromic device based on it

The construction and study of a fully solid state electrochromic (EC) device with cathodic coloration exhibiting very fast response times (< 1s) is reported using a WO3 EC layer and a poly (vinyl alcohol) (PVA)- Lithium acetate membrane electrolyte. Broadband dielectric studies on the polymer membranes with different Li concentrations show multiple relaxation mechanisms out of which a segmental relaxation prominent beyond a certain composition is strongly correlated with Li-ion conduction yielding better ionic conductivity and reversible coloration in the EC device. The relatively high Li conductivity in PVA has a direct correspondence with the lowering of the crystallinity of PVA and a decrease of the glass transition temperature, Tg with increasing Li addition. A simple model of the coloration process suggests that the short electrolyte diffusion length coupled with a high electric field and an interfacial emf that varies as ≈t−0.6 results in the swift current response of the film with an optimal performance at 20 wt.% Li in PVA, exceeding which irreversible coloration can occur on the surface. The transient current is crucial for the observed swift switching characteristics. Ageing studies for almost a month indicate potential stability of the EC device for over 150 cycles.

Effect of texture on bending behavior of Mg alloy sheets

The effect of Li elements on the microstructure and texture evolution of AZ31 alloy sheets during room-temperature three-point bending was investigated. The results showed that the conventional c-axis//ND basal texture of the extruded AZ31 sheet could be modified to a TD-elongated fiber texture with a 5 wt% Li addition. As a result, the room-temperature bendability of the Mg–3Al–5Li sheet was improved effectively, and this sheet showed a minimum bending radius of only 2 mm. The superior bendability exhibited surpasses the room-temperature bending capabilities commonly observed in the majority of commercial Mg alloys. The improvement in bendability of the Mg–3Al–5Li sheet was attributed to the TD-elongated texture distribution. This type of texture distribution may offer more effective deformation modes to alleviate thickness strain during bending in comparison to the texture in extruded AZ31 sheets. This study could provide insights into developing Mg alloys with high room-temperature bendability by tailoring texture distribution rather than texture weakening.

Achieving low hot tearing susceptibility in high-strength cast Al–Li alloys: Experimental investigation and simulation assessment

Due to the exceptional low density and high stiffness, cast Al–Li alloys are deemed suitable for structural applications. However, their economic benefits are limited by intolerable hot tearing susceptibility (HTS) during casting. This work aims to optimize alloy compositions that compromise low HTS and good mechanical properties. Six alloys (Alloys 1–6) with potentially high hot tearing resistance were selected by regulating Li, Cu and Mg additions based on the Kou's criterion and ProCAST simulation. Experimental results indicated that in contrast to Alloys 1–4, Alloys 5 & 6 containing higher solute contents show anomalously high HTS, significantly deviating from the predictions. It was further revealed that this phenomenon originates from a variety of Li-rich inclusions formed at interdendritic channels, which lead to strain localization and hinder residual liquid refilling. Then, Alloys 1–4 with low HTS were subjected to a tailored subsequent heat treatment to achieve optimal mechanical properties. Among the tested alloys, Alloys 3 & 4 exhibit comparatively lower ductility attributed to strain accumulation at the interface between coalesced Sʹ-Al2CuMg phases and Al matrix. In comparison, a good combination of strength and ductility (YS = 371 ± 14 MPa, UTS = 456 ± 19 MPa, EL = 2.5 ± 0.1 %) was successfully achieved in Al-2.5Li–2Cu–1Mg-0.15Zr alloy (Alloy 2) due to the synergistic reinforcement of δʹ-Al3Li and T1-Al2CuLi precipitates. Compared to other available cast Al–Li alloys, Alloy 2 possesses better hot tearing resistance while being highly competitive in strength. Our results are anticipated to contribute scientific guidance for developing high-performance cast Al–Li alloys with low HTS.

The Effect of Zr and Li on the Microstructure of AlMg5Si2Mn-Type Casting Alloys

AbstractIn the article, the authors present results of microstructural studies of Al-Mg-Si-Mn casting alloys with Zr, Li, and TiB2 additions on a broad scale. Zirconium content was set on two levels: 0.34 and 1.58 wt%, and Li was set 1.2 and 2.0 wt%. It was found that the addition of Zr shifts the eutectic melting temperature to a higher level, up to 611.3 °C at 1.6 wt% Zr. At the same time, Li addition leads to the depression of eutectic melting temperature: down to 587.2 °C at 2.0 wt% Li, what is a common effect of eutectic modification which was confirmed by means of structural examinations. The complex addition of Li and AlTi5B1 resulted in a eutectic melting temperature close to the equilibrium eutectic temperature for the Al-Mg-Si system (596.2 °C). The grain refinement effect of Zr is due to the nucleation of α-Al on the Zr(Al1−x, Six)3 phase. Crystals of this phase were detected in the grain centers of Zr-containing alloys. The Li addition does not affect α-Al grain size but changes the morphology of eutectic colonies from petal-like to fibrous. Observation of TiB2 particles inside the primary Mg2Si crystals gives direct experimental confirmation of nucleation of the primary phase on the surface of TiB2 in the alloy after adding Li and AlTi5B1. Natural aging of the alloys resulted in the formation of fine precipitates detected close to dislocations. The most apparent supposition is that the mechanism responsible for their formation is heterogeneous nucleation in the stress field of dislocations. Hardness tests showed adding 2.0 wt% of Li is very effective, increasing hardness up to 113 HV0.2 in naturally aged condition, which is nearly double that of commercial Al-Mg-Si die-casting alloy. Several effects were proposed which may synergistically contribute to the rise of hardness in Li-containing alloys, such as solid solution strengthening, formation of primary LiAlSi phase and natural aging.

The precipitation and corrosion behaviour of cast Al–Mg–(0.7, 1.3) Li–Cu alloys

Achieving the development of ultra-light Al–Li alloys with high strength and excellent corrosion resistance is always a challenge. In this study, the precipitation characteristics and electrochemical corrosion behaviours after isothermal aging of cast Al–Li alloys with two different Li contents were comparatively analysed. The results showed that the increase in Li content from 0.7 wt-% to 1.3 wt-% retarded the peak hardening and improved the Al–Li alloy hardness and strength by promoting the precipitation of the S′ (Al2CuMg) and T1 (Al2CuLi) phases. Besides, the galvanic coupling corrosion of the alloying element Cu with the aluminium matrix was reduced by more Li addition, thus improving the corrosion resistance of the alloy.

Improved ductility of hot extruded Mg-0.5Zn-0.5Zr-1RE alloy by Li addition

Mechanical properties of lean Mg-xLi-1RE-0.5Zn-0.5Zr alloys after hot working by the extrusion process were systematically investigated. By increasing Li content, the coarsening of the dynamic recrystallization (DRX) grain size (D) was recorded. This was ascribed to the decrease of the solidus temperature (TSolidus) by increasing Li content, and hence, the increase of the homologous temperature during hot deformation (T/TSolidus). As a result, the tensile yield stress (TYS), ultimate tensile strength (UTS), compressive yield stress (CYS), and ultimate compressive strength (UCS) decreased by increasing Li content. Accordingly, the Hall-Petch relationships of TYS = 145.8 + 69/√D and CYS = 69.3 + 100/√D were proposed, where TYS, CYS, and D are expressed in MPa, MPa, and μm, respectively. However, total elongation in the tension test and fracture strain in the compression test were significantly improved and the crystallographic texture intensity decreased by increasing the Li content. These improvements were found to be quite beneficial for overcoming and breaking the strength–ductility trade-off. The mechanical behavior of these alloys was compared to other competitive alloys for lightweight applications.

Role of Li and Sc Additions and Machining Conditions on Cutting Forces on Milling Behavior of A7075-Based Alloys

Role of Li and Sc Additions and Machining Conditions on Cutting Forces on Milling Behavior of A7075-Based Alloys

Effects of Li addition on the properties of biodegradable Zn–Fe–Li alloy: Microstructure, mechanical properties, corrosion behavior, and cytocompatibility

Biodegradable Zn-based alloys have excellent mechanical properties, a good corrosion rate, and favorable biocompatibility, which have broad application prospects. In this study, new biodegradable Zn-0.5Fe-xLi (x = 0, 0.2, 0.5, 0.8 wt%) alloys were successively prepared by melting and hot extrusion, and the effects of Li content on the microstructure, mechanical properties, corrosion behavior, and biocompatibility of the alloys were investigated. The formation of FeZn13 and eutectic LiZn4 phases in the Zn-0.5Fe-xLi alloys and the grain size of the Zn-0.5Fe-0.5Li alloys significantly reduced with an increase in Li content. The synergistic effect of solid solution and grain refinement of Li significantly improved the strength of the Zn-0.5Fe-0.5Li alloy and ensured the ductility of the alloy, which resulted in its optimum overall performance. The yield strength was 353.6 ± 6.8 MPa, the ultimate tensile strength was 441.9 ± 2.6 MPa, and the elongation was 26.8 ± 0.8%. In addition, the Zn-0.5Fe-0.5Li alloy showed excellent corrosion properties. The electrochemical corrosion rate was 0.735 mm/year, and the surface corrosion degradation morphology was uniform after immersion. The Zn-0.5Fe-0.5Li alloy also demonstrated the most favorable in vitro cytocompatibility in cellular experiments. Overall, the extruded Zn-0.5Fe-0.5Li alloy is a promising biodegradable implant material with excellent mechanical properties, a suitable corrosion rate, and good cytocompatibility.

Improved carrier collection efficiency in CZTS solar cells by Li‐enhanced liquid‐phase‐assisted grain growth

AbstractThe liquid‐phase‐assisted grain growth (LGG) process is a promising strategy to fabricate large‐grain pure sulfide Cu2ZnSnS4 (CZTS) layers that span the absorber thickness and improve the carrier collection efficiency in photovoltaic devices. Li doping is an effective route to promote such LGG process of Cu2ZnSn(S,Se)4 (CZTSSe) as it can provide liquid Li‐Se phase facilitating the growth of large‐grain CZTSSe. However, the detailed function of the added Li in grain growth has rarely been investigated in both CZTS and CZTSSe, as the reported in situ, and pre‐deposition doping strategies usually suffer from substantial Li losses during the spin‐coating process and/or the high‐temperature sulfurization process. Herein, by monitoring the temperature‐dependent Li loss during the sulfurization process, we demonstrate that a small proportion of the added Li can remain at the CZTS film from the early sulfurization stage and provide Li‐S flux to promote the LGG process. An encouraging efficiency of 10.53%, with a remarkably high short‐circuit current density of 22.6 mA/cm2 and open‐circuit voltage of 0.744 V, is achieved by a significantly enlarged grain size of 3 μm with Li addition. This work could enhance the knowledge of employing Li‐S as flux for growing large‐grain chalcogenide absorbers for high performance devices with better carrier transport.

Developing a High Ductility Mg Alloy Via Non-basal Slips and Intergranular Coordination Induced by Li and Er Addition

Developing a High Ductility Mg Alloy Via Non-basal Slips and Intergranular Coordination Induced by Li and Er Addition

Investigating electrical properties and crystal growth in NiO thin films by spray pyrolysis and electrostatic spray deposition

The control of the electrical properties and the growth mechanism of the NiO films were investigated by Li addition using the spray pyrolysis method. In addition, to enhance the uniformity and flatness of the NiO films, the electric field applied spray pyrolysis named electrostatic spray deposition (ESD) process was applied. Experimental results suggest that a certain amount of Li acts as an interstitial on the Ni sites in the NiO film and enhances crystal growth. Moreover, excessive Li additions resulted in Li segregation into NiO crystal defects, whereas the resistivity decreases and the promotion of crystal growth was not inhibited regardless of the presence of Li on the NiO film up to a Li concentration of 10 at.%. Furthermore, ESD was confirmed to deposit highly flat NiO films. These results represent the initial step toward the practical application of visible-light-transparent devices using spray deposition.

Enhancement effect of Li addition on nitriding reaction and combustion of Al-Li alloy in N2

For aluminum-based alloy particles, the addition of alloying element lithium (Li) with the properties of a high chemical activity and a low melting/boiling point can significantly improve the thermo-reactive properties of aluminum (Al) particles. To further reveal the combustion mechanism, this paper presents the nitriding reaction and combustion characteristics of Al-Li alloy in nitrogen (N2) through thermogravimetric analysis and differential scanning calorimetry (TG-DSC) analysis at a low heating rate and laser-induced ignition experiments at a high heating rate, considering the influences of two kinds of Li contents (1.0 wt% @ Al-1.0Li and 2.5 wt% @ Al-2.5Li) on these characteristics and making a comparison to the counterpart Al. Al-Li alloy powders as-prepared by gas atomization method showed the texture of the Li-rich eutectic phase compounds on the surface by scanning electron microscope (SEM) characterization. The TG-DSC results demonstrated that the thermal nitriding reaction of Al-Li alloy in N2 was significantly faster than that of pure Al. The nitriding reaction temperature decreased from 853 °C for pure Al to 245 °C for Al-2.5Li alloy with a reduction of 71 %. The final weight gain of Al-2.5Li alloy was almost three times higher than that of pure Al in N2. The SEM photograph of intermediate nitriding products revealed that the cracks and loose “island” structures in the Li-rich zone on the Al-Li surface were the key to preventing the formation of a “passivation effect” into Al and promoting N2 uptake during melting. In addition, Li also acts as a catalytic carrier and “oxygen absorber” to enhance the Al-N reaction. The combustion of single Al-Li alloy microparticles induced by laser showed two stages: preheating and rapid nitriding. Al-Li alloy particles were ignited more rapidly and showed typical gas-phase / surface combustion modes different from pure Al. According to these findings, the combustion mechanism was proposed to help guide the development of Al-based solid propellants containing Li and the synthesis of AlN/Al composites in nitrogen-rich environments.

Controlled Li Alloying by Postsynthesis Electrochemical Treatment of Cu2ZnSn(S, Se)4 Absorbers for Solar Cells.

Li-alloying of Cu2ZnSn(S, Se)4 (CZTSSe) absorbers is widely accepted for its beneficial influence on the performance of CZTSSe-based thin film solar cells. Given the degraded morphology characteristic of absorbers synthesized in the presence of excess Li concentrations, it is speculated that Li may be best incorporated into the absorber after synthesis. Here, we report an innovative method to add Li to synthesized CZTSSe by an electrochemical treatment using a liquid electrolyte. Our approach decouples Li addition from absorber synthesis, allowing one to possibly overcome morphology issues associated with high Li concentration. We show that Li is thereby transferred to the absorber and is incorporated into the crystal lattice. The resulting Li concentration in the absorber can be easily controlled by the treatment parameters. Using liquid electrolytes allows a straightforward disassembly of the lithiation setup and hence the fabrication of solar cells after electrochemical treatment. Electrochemically lithiated solar cells reached power conversion efficiencies of up to 9.0%. Further optimization of this innovative method is required to reduce expected interface issues resulting from the electrochemical treatment to demonstrate a gain in the power conversion efficiency of the CZTSSe solar cells. Finally, our results indicate strong lateral Li diffusion, which deserves further investigation. Moreover, the method could be transferred to other material systems, such as Cu(In, Ga)Se2 (CIGS), and adapted to treat layers with other alkali elements such as Na.

Influence of Gd and Li additions on the microstructural evolution and mechanical properties of hot-rolled AZ31 alloy

Thermomechanical processing and alloying are two common approaches to enhance the mechanical properties of Mg. Thus, the effects of Gd and Li elements, as two elements with various properties, on the microstructure and mechanical properties of a hot-rolled and consequently annealed AZ31 alloy were analyzed. The microstructure and texture was analyzed by scanning electron microscopy and electron back scattered diffraction. Accordingly, the mean grain size of 46 μm in the AZ31 alloy was reduced to 41 and 26 μm in the AZ31–2.9Gd and AZ31–2.3Li alloys, respectively. Grain refinement occurred due to continuous dynamic recrystallization and twinning-induced recrystallization in all of the alloys. Textural evolution showed that neither Gd nor Li could inhibit the occurrence of basal texture. Room temperature mechanical properties were assessed by using the shear punch test (SPT) method. The results exhibited that the strength of the AZ31 alloy was improved from 116 MPa to 139 MPa and 141 MPa by respective additions of Gd and Li. Strength enhancement was mainly attributed to the grain boundary strengthening and second-phase particles hardening. One promising observation was the simultaneous enhancement of shear strength and ductility by the addition of Gd and Li. This observation was ascribed to the more uniform distribution of second-phase particles and lower volume fraction of twins as potential sites for crack initiation. As long as mechanical strength is concerned, results favor the use of Li as alloying element in Mg, especially due to the more noticeable lightweighting potential compared to Gd.

The mechanism for Li-addition induced homogeneous deformation in Mg-4.5wt.% Li alloy

The mechanism by which Li additions induce a more homogeneous deformation was systematically investigated in this study by comparing the deformation behavior of pure Mg and Mg-4.5 wt.% Li using experiments, crystal plasticity simulations, and theoretical calculations. The results of the digital image correlation measurements showed that under tension along the transverse direction (TD), strong localized deformation bands with an angle of approximately 20° with respect to the TD were observed in pure Mg, but were absent in Mg-4.5 wt.% Li. Slip trace analyses indicated that basal slip was the predominant deformation mode for pure Mg, whereas that for Mg-4.5 wt.% Li was prismatic slip. A high relative activity of pyramidal 〈c+a〉 slip, approximately 17 %, was observed in Mg-4.5 wt.% Li at a high strain of 10 %. Contraction or double twins were hardly detected during the entire tension process. Crystal plasticity simulations revealed that the 4.5 wt.% Li addition dramatically reduced the critical resolved shear stress (CRSS) ratio of pyramidal 〈c+a〉 slip: prismatic slip: basal slip, which was 31.5:21:1 for pure Mg and 4.3:1.3:1 for Mg-4.5 wt.% Li. Theoretical calculations using the CRSS ratios determined by simulations revealed that easy and uniform deformation propagation induced by a dramatically reduced CRSS ratio of prismatic slip to basal slip played a more important role in improving the deformation homogeneity, in addition to the enhanced activity of pyramidal 〈c+a〉 slip. The mechanisms for how Li additions improve the ductility of Mg are also revisited in this paper.

Achieving ultra-high stiffness by solidifying and precipitating micro-compounds in HCP/BCC dual matrix of a new Mg-Li alloy

One of the major obstacles restricting the wide applications of Mg alloys is their low Young's modulus at ∼45 GPa, which is uncompetitive to Al alloy over 60 GPa. To resolve this issue, we proposed a new strategy of designing ultra-light Mg-Li alloys by employing the microscale compounds in both HCP and BCC grains to achieve high Young’s modulus. HCP or BCC alone cannot achieve a high modulus due to the segregation of solutes at the grain boundaries and the formation of brittle intermetallics in the interdendritic region. We designed chemistry that is so perfect to arrest the excess solutes inside the BCC matrix during solidification and engulf pre-solidified rare earth particles by HCP primary grains which have such a lean chemical composition that has almost no segregation. During solution heat treatment, the dissolution of solutes pushes the BCC boundary towards HCP grains by Ostwald ripening (BCC structures are interconnected but the HCP structures are isolated). During low-temperature aging heat treatment, nucleation of HCP structure on the rare earth particles inside the BCC grain is found, degrading the strength. Therefore, a novel Mg-Li-Al-Zn-Y-Mn-Gd (LAZWMV) alloy with a very high modulus was designed which reaches Young's modulus as high as 61.4 GPa. Micro-compounds (AlLi and Al-X) with average equivalent diameters of 3.76 µm and 6.55 µm were quantified in 3D using X-ray computed tomography and nanoindentation tests for establishing the microstructure-modulus correlation. The influence of Li addition on Mg-Mg was calculated by DFT calculations and the mechanism of modulus improvements has been proposed.

The Role of Lithium in the Aging Precipitation Process of Al-Zn-Mg-Cu Alloys and Its Effect on the Properties.

It is well known that the development of lightweight alloys with improved comprehensive performance and application value are the future development directions for the ultra-high-strength 7xxx series Al-Zn-Mg-Cu alloys used in the aircraft field. As the lightest metal element in nature, lithium (Li) has outstanding advantages in reducing the density and increasing the elastic modulus in aluminum alloys, so Al-Zn-Mg-Cu alloys containing Li have gained widespread attention. Furthermore, since the Al-Zn-Mg-Cu alloy is usually strengthened by aging treatment, it is crucial to understand how Li addition affects its aging precipitation process. As such, in this article, the effects and mechanism of Li on the aging precipitation behavior and the impact of Li content on the aging precipitation phase of Al-Zn-Mg-Cu alloys are briefly reviewed, and the influence of Li on the service properties, including mechanical properties, wear resistance, and fatigue resistance, of Al-Zn-Mg-Cu alloys are explained. In addition, the corresponding development prospects and challenges of the Al-Zn-Mg-Cu-Li alloy are also proposed. This review is helpful to further understand the role of Li in Al-Zn-Mg-Cu alloys and provides a reference for the development of high-strength aluminum alloys containing Li with good comprehensive properties.

Effect of Li addition on bending behavior of extruded Mg–2Zn alloy sheet

The effect of Li element on microstructure and texture evolutions of Mg–2Zn alloy sheet during three-point bending at room temperature were investigated. The results showed that the conventional c-axis//ND basal texture of the extruded Mg–2Zn sheet could be modified to a TD-elongated fiber texture with 3 wt.% Li addition. As a result, the room-temperature bendability of the Mg–2Zn–3Li sheet was improved effectively and this sheet showed a minimum bending radius of only 1.75 mm. Such an excellent bendability exceeds the room-temperature bending capacity of most commercial magnesium alloys. The improvement in bendability of the Mg–2Zn–3Li sheet was attributed to the TD-elongated texture distribution. This type of texture distribution could provide more efficient deformation modes to release the thickness strain during bending compared to the extruded Mg–2Zn sheet. This study could provide insights into developing Mg alloys with high room-temperature bendability by tailoring texture distribution rather than texture weakening.

New Solder Based on the Sn-Zn Eutectic with Addition of Ag, Al, and Li

New solder, based on Sn-Zn, with the addition of 1 at.% Ag, 1 at.% Al, and 0.5 at.% Li (SZAAL) was prepared. The influence of alloying elements on mechanical and electrical properties, microstructure, and melting point was investigated. The tensile test showed enhanced mechanical properties of SZAAL alloy compared to Sn-Zn eutectic and Sn-Zn-Ag. Investigated Al and Li additions improve the mechanical properties of the alloy, tensile strength and solder plasticity. Another positive effect is that those elements caused a decrease in the melting point, compared to Sn-Zn with 1 at.% Ag. Microstructural investigation revealed a fine Sn-Zn eutectic structure with the present epsilon phase (AgZn3). The addition of lithium and silver decreased the coefficient of linear expansion of the tested alloys. Li addition reduced significantly both the surface and interfacial tension, which translates into improved solder wettability. The surface tension of all solders decreased with temperature, but the interfacial tension increased with temperature. That is due to the weakening effect of the flux. Thus, the soldering temperature in the presence of the ALU33® flux should not exceed 250 °C.