Li Alloy Research Articles

Influence of tool velocity ratio on force-torque and mechanical properties of friction stir welded 2050-T84 Al-Li alloy plates

Aluminium-lithium (Al-Li) alloy is the most prominent alloy used in the aerospace industry’s internal structure and wings due to its improved physical and mechanical properties. The present study introduces a novel investigation into the joining of Al–Li alloy 2050-T84 using friction stir welding (FSW) at different tool velocity ratios (TVR) of 0.6, 0.8, and 1, respectively (i.e., the amalgamation of various process parameters like tool rotational speed (TRS of 600, 1000, and 1400 rpm and traverse speed of 60, 120, and 240 mm min−1) and constant tool tilt angle (1.5°). A threaded taper tool was used for joining the Al–Li alloy 2050-T84. This work aims to ascertain the effects of varying tool velocity ratios (TVR; rotational speed/traverse speed) on macrostructure, grain size distribution in the nugget zone, and mechanical strength of the welded specimens. The experimental results reveal that increasing the tool velocity ratio increases the grain size and decreases the welded specimen’s ultimate strength and hardness values. Higher tensile strength (403.2 MPa), micro-hardness values (122.15 HV0.1), and joint efficiency (75.49) of welded specimens are achieved at low TVR (0.6), and ductile failure is observed in all welded samples. Additionally, it is noticed that the stirred zone size increased with increasing the velocity ratio.

Developing Zn-2Cu-xLi (x < 0.1 wt %) alloys with suitable mechanical properties, degradation behaviors and cytocompatibility for vascular stents

Biodegradable Zn alloys show great potential for vascular stents due to their moderate degradation rates and acceptable biocompatibility. However, the poor mechanical properties limit their applications. In this study, low alloyed Zn-2Cu-xLi (x = 0.004, 0.01, 0.07 wt %) alloys with favorable mechanical properties were developed. The microstructure consists of fine equiaxed η-Zn grains, micron, submicron-sized and coherent nano ε-CuZn4 phases. The introduced Li exists as a solute in the η-Zn matrix and ε-CuZn4 phase, and results in the increase of ε-CuZn4 volume fraction, the refinement of grains and more uniform distribution of grain sizes. As Li content increases, the strength of alloys is dramatically improved by grain boundary strengthening, precipitate strengthening of ε-CuZn4 and solid solution strengthening of Li. Zn-2Cu-0.07Li alloy has the optimal mechanical properties with a tensile yield strength of 321.8 MPa, ultimate tensile strength of 362.3 MPa and fracture elongation of 28.0 %, exceeding the benchmark of stents. It also has favorable mechanical property stability, weak tension compression yield asymmetry and strain rate sensitivity. It exhibits uniform degradation and a little improved degradation rate of 89.5 μm∙year−1, due to the improved electrochemical activity by increased ε-CuZn4 volume fraction, and generates Li2CO3 and LiOH. It shows favorable cytocompatibility without adverse influence on endothelial cell viability by trace Li+. The fabricated microtubes show favorable mechanical properties, and stents exhibit an average radial strength of 118 kPa. The present study indicates that Zn-2Cu-0.07Li alloy is a potential and promising candidate for vascular stent applications. Statement of significanceZn alloys are promising candidates for biodegradable vascular stents. However, improving their mechanical properties is challenging. Combining the advantages of Cu and trace Li, Zn-2Cu-xLi (x < 0.1 wt %) alloys were developed for stents. As Li increases, the strength of alloys is dramatically improved by refined grains, increased volume fraction of ε-CuZn4 and solid solution of Li. Zn-2Cu-0.07Li alloy exhibits a TYS exceeding 320 MPa, UTS exceeding 360 MPa and fracture EL of nearly 30 %. It shows favorable mechanical stability, degradation behaviors and cytocompatibility. The alloy was fabricated into microtubes and stents for mechanical property tests to verify application feasibility for the first time. This indicates that Zn-2Cu-0.07Li alloy has great potential for vascular stent applications.

Effect of pre-deformation on microstructure and mechanical properties of 2050 Al−Li alloy

The microstructural evolution and mechanical properties of 2050 Al−Li alloy subjected to different rolling pre-strains (0−20%) and aging (T8) were studied. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to characterize the microstructure. The results show that the grains were significantly refined along the normal direction (ND) and the intragranular distortion increased with the increase of pre-strain level. The entanglement of defects, e.g., dislocations, provides a large number of nucleation sites for the precipitation of T1 phases. This leads to larger number of precipitates and narrower distance between precipitates, thus improving the hindering effects on dislocation motions and the strength of the alloy. When the pre-deformation level reaches 16%, the alloy shows the highest density of T1 phases and strength (the yield strength and tensile strength reach 568 and 584 MPa, respectively, and elongation is 8.6%). When the amount of pre-deformation is further increased to 20%, the atomic diffusion channels are reduced due to dislocation entanglement, and the reduction in the number of T1 phases eventually leads to a decrease in strength of the alloy.

Comparative Study on Microstructure, Corrosion Morphology, and Friction Wear Properties of Layered Double Hydroxide/Steam Coating Composite Coatings on Mg–Li Alloy

Mg alloy is the preferred material for the lightweight development of manufacturing industry. However, its application is limited due to the poor wear resistance and corrosion resistance. In this experiment, Mg–Al layered double hydroxide/steam coating (LDH/SC) composite coatings are prepared on the surface of LA43M Mg–Li alloy by steam treatment and in‐situ hydrothermal method for different times (12, 18, 24, 30, and 36 h). The morphology and structure of the coatings are characterized by scanning electron microscopy, energy dispersive spectrometry, and X‐ray diffractometer, and the friction wear test of the coatings is carried out. The corrosion resistance of the coatings is evaluated by immersion tests and hydrogen evolution experiments. The effect of hydrothermal time on the growth characteristics, wear resistance, and corrosion behavior of LDH/SC coatings in 3.5 wt% NaCl solution is systematically investigated. In addition, the growth mechanism and corrosion resistance mechanism of the LDH/SC coating are discussed. The results show that the composite coatings is mainly composed of LDH and Mg(OH)2 phases. Appropriately prolonging the hydrothermal reaction time is beneficial to the nucleation and growth of LDH. When the hydrothermal time is 30 h, the prepared coating has the best density, and the prepared coating can significantly improve the corrosion resistance and friction wear properties of the substrate.

Advanced design and optimization of tailored refining fluxes for the purification of Mg–Li alloys

This study systematically investigates the influence of integrating KCl into the refining flux on the purification efficiency of Mg–Li alloy. The findings reveal that an optimal purification effect is achieved with a 50 % addition of KCl to the refining flux, resulting in a remarkable 56 % reduction in volume fraction of inclusions to 0.17 % and an 80 % improvement in elongation to 29.1 %. The developed novel quaternary refining flux is composed of KCl + LiCl + LiF + CaF2 (3:3:1:2, wt.%). Based on thermodynamic calculation and analysis, the purification mechanism is elucidated, demonstrating that KCl enhances purification efficiency by reducing flux and melt viscosity, improving wettability, increasing contact area, and facilitating flux adsorption on inclusions. Excessive KCl addition hinders purification by decreasing flux density, slowing settling velocity, and affecting the purification process. The quaternary flux, applying to industrial Mg–Li alloy scrap, demonstrates outstanding purification performance with a 73 % reduction in inclusion volume fraction to 0.33 % and a remarkable 584 % increase in elongation to 17.1 %. The development and application of a novel Mg–Li alloy flux are of significant importance for promoting the industrial development of Mg–Li alloys.

Estimation of mode I quasi-static fracture of notched aluminum–lithium AW2099-T83 alloy using local approaches and machine learning

Aluminum–lithium (Al–Li) alloys offer superior performance under different conditions that involve mechanical loading, high temperature and corrosive environment. Therefore, Al–Li alloys are being used in the defense, aerospace, and aircraft industries, specifically in structural parts such as fuselage, empennage, and wings. By modifying the chemical composition, a third generation of Al–Li alloys has been introduced to overcome the mechanical and thermal shortcomings of previous Al–Li generations. As structural parts usually contain notches, it is of paramount importance to study the strength of the newly introduced alloys in the presence of such geometrical discontinuities to select the suitable alloy for a particular application. The aim of this work is to analyze the strength of U and V-notched specimens machined from extruded AW2099-T83 Al–Li alloys under quasi-static loading. The fracture stress of specimens with various notch radii and angles were estimated using strain energy density (SED) and the theory of critical distances (TCD) methods. A support vector machine (SVM) regression model was also implemented to assess the applicability of estimating fracture stress using machine learning approaches. The results show an average absolute discrepancy of 6.6 %, 7.8 % and 2.8 % for SED, TCD and SVM methods, respectively.

Li Alloys in All Solid-State Lithium Batteries: A Review of Fundamentals and Applications

Li Alloys in All Solid-State Lithium Batteries: A Review of Fundamentals and Applications

Strain-dependent heterogeneity of microstructure and mechanical properties of 2195 Al–Li alloy during power spinning and heat treatment

The effect of thickness reduction (20 % in each pass) on microstructure evolution and mechanical properties of 2195 Al–Li alloy during hot power spinning and the subsequent heat treatment were investigated. As a result, high-performance 2195 Al–Li alloy tube with a thickness of 1.56 mm was successfully fabricated. The results showed that the strain localization of spinning led to the heterogeneity of microstructure and mechanical property along the wall thickness direction of the spun tube. With the increase of thickness reduction, dynamical recrystallization set up from the outer surface and propagated to the inner surface, and thus refined the microstructure, improved the mechanical properties, and reduced the heterogeneity in the microstructure and mechanical properties of the spun tube. However, after heat treatment, abnormal grain growth appeared in the microstructure near the inner surface of the spun tube with a moderate thickness reduction, triggering a severer inhomogeneity in the microstructure and mechanical properties. A large enough thickness reduction could induce sufficient dynamic recrystallization, which led to the disappearance of abnormal grain growth of spun tube during heat treatment. Grain boundary strengthening and precipitation strengthening were the dominant strengthening mechanisms of 2195 Al–Li alloy spun tube.

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.

Influence of Surfactant Types on the Anti-Corrosion Performance of Phosphate Chemical Conversion Coated Mg-8wt.%Li Alloy

In this work, the morphology, anti-corrosion performance and degradation mechanisms of two phosphate chemical conversion coatings containing the AEO (fatty alcohol polyoxyethylene ether) and AES (fatty alcohol polyoxyethylene ether sodium sulfate) on an as-cast Mg-8wt.%Li alloy were explored and compared. Although two coating layers had a petal-shaped structure and were composed of leaf-shaped particles, the coating layer of the AES-coated sample was relatively dense due to the smaller size of the formed petal-shaped structure. Based on the electrochemical data and hydrogen evolution measurements, the corrosion protectability of the coating layer on the AES-coated sample was better than that on the AEO-coated sample. The determined corrosion current densities (icorr) of the AES-coated and AEO-coated samples in the 3.5 wt.% NaCl solution were, respectively, 7.8 mA·cm−2 and 11.7 mA·cm−2, whereas the icorr value of the coated sample without a surfactant was 36.2 mA·cm−2.

The effect of pre-deformation on the mechanical properties of Al–Li–Cu + TiC/TiB2 alloy

In this study, Al–Li alloys containing TiC + TiB2 particles were successfully prepared by mechanical stirring method. The alloy organisation and nanoparticles were investigated by scanning electron microscopy (SEM) and electron probe microanalyser (EPMA). The number of T1 phases in the alloy matrix after different pre-deformation was investigated by transmission electron microscopy (TEM). The results showed that TiC and TiB2 acted as nucleation plasmas for grains during solidification, promoting non-uniform nucleation and refining the grains in the 0.5 samples, the main recrystallisation mechanism of the alloy during solidification was the particle-stimulated nucleation (PSN) mechanism, and the incorporation of nanoparticles improved the recrystallisation resistance of the alloy, while the yield strength of the alloy firstly increased and then decreased as the amount of pre-deformation increased, and the best tensile properties occurred The yield strength and tensile strength of 0.5 samples after 5% pre-deformation were 580 MPa and 603 MPa, respectively.

Homogeneously Planar-Exposure LiB Fiber Skeleton Toward Long-Lifespan Practical Li Metal Pouch Cells.

LiB alloy is promising lithium (Li) metal anode material because the continuous internal LiB fiber skeleton can effectively suppress Li dendrites and structural pulverization. However, the unvalued surface states limit the practical application of LiB alloy anodes. Herein, the study examined the influence of the different exposure manners of the internal LiB fiber skeleton owing to the various surface states of the LiB alloy anode on electrochemical performance and targetedly proposed a scalable friction coating strategy to construct a lithiated fumed silica (LFS) functional layer with abundant electrochemically active sites on the surface of the LiB alloy anode. The LFS significantly suppresses the inhomogeneous interfacial electrochemical behavior of the LiB alloy anode and enables the exposure of the internal LiB fiber skeleton in a homogeneously planar manner (LFS-LiB). Thus, a 0.5Ah LFS-LiB||LiCoO2 (LCO) pouch cell exhibits a discharge capacity retention rate of 80% after 388 cycles. Moreover, a 6.15Ah LFS-LiB||S pouch cell with 409.3Whkg-1 exhibits a discharge capacity retention rate of 80% after 30 cycles. In conclusion, the study findings provide a new research perspective for Li alloy anodes.

Insights for the strength and ductility of precipitation hardening Al–Li–Sc alloys

Al–Li alloys with high elastic modulus, low density and high specific strength have been widely used in aerospace industry. However, although Al3Li precipitates enhance the strength significantly, the appearance of shearable Al3Li precipitates usually decreases the ductility, leading to the strength-ductility trade-off. In this study, the strategy of microalloying is applied to fabricate an Al–2.46 Li–0.2 Sc (wt.%) alloy with tunable precipitate sizes by heat treatment. This alloy exhibits a good combination of strength and ductility when the precipitate radius is smaller than 6.7 nm or larger than 16.4 nm. The strengthening mechanisms in Al–Li–Sc alloy with different precipitate sizes are quantitatively discussed. With the increase of precipitate size, the dominant precipitation strengthening mechanism changes. The influence of precipitate on ductility is mainly achieved by influencing the dynamic recovery rate of dislocation which can be illustrated by a dislocation-based model. When the precipitate size is relatively small or large, the Al–Li–Sc alloy exhibits a higher ductility owing to a lower dynamic recovery rate. This study provides insight for understanding the strength and ductility in Al–Li–Sc alloy as well as potential theoretical guideline for designing novel high-performance Al–Li based alloys.

Modeling Bauschinger effect through the reversibility of dislocation slip in an Al–Cu–Li alloy

Al–Cu–Li alloys are promising lightweight materials for extensive applications in aerospace. As aerospace components often experience strain path changes during service, understanding the resulting Bauschinger effect is crucial for optimizing the fatigue resistance and performance of these alloys. This study investigates the role of T1 precipitates in the Bauschinger effect in AA2099. The presence of shearable T1 precipitates has been found to significantly influence the Bauschinger effect by reducing the strengthening effect of T1 precipitates during reverse straining. An analytical expression for slip reversibility has been derived to quantify this phenomenon, and a microstructure-based constitutive model has been developed to accurately predict the Bauschinger effect in AA2099.

Electrically conductive and corrosion resistant coating on Mg[sbnd]Li alloys, Part I: Chemical conversion coating

MgLi alloys are one of the lightest structural materials, but suffer from severe corrosion due to the hyperactivity of Mg and Li. In this work, an electrically conductive and corrosion-resistant chemical conversion coating was fabricated on a duplex MgLi alloy LA103Z by two different routes: the first route using a conventional immersion treatment (Im-PCCs); and the second route using a brushing conversion treatment (Br-PCCs). Results demonstrate that chemical composition of conversion coatings remained, but surface morphology was altered. The Im-PCC depicts many lamellar CaHPO4 when the immersion time was longer than 60 s. The Br-PCC shows no lamellas on surface till a treatment time of 120 s. These lamellar crystals are detrimental to the electrical contact resistance (ECR), and the ECR for the Br-PCC was one order of magnitude lower than that for the Im-PCCs. Corrosion resistance for Br-PCCs, however, was slightly lower than Im-PCCs.

Enhanced fatigue crack propagation resistance of a new Al–Cu–Li alloy via different aging processes

The fatigue crack propagation (FCP) behavior of a new Al–Cu–Li alloy under different aging treatments including T3, T8, and non-isothermal aging (NIA) was investigated. It was detected that the T8-24h sample exhibited the highest FCP resistance and the best mechanical performance. Compared with the T3-40D sample, the crack paths of the T8-24h sample and the C150 (non-isothermal peak-aged) sample were more tortuous and the crack width was narrower. Furthermore, the T8-24 sample had the lowest decreased FCP rate by an order of magnitude at the stress intensity factor (ΔK) of 30 MPa·m1/2. A large number of nano-scale T1 phases were precipitated in the T8-24h sample and their number density was also increased compared with the other sample. The presence of the tiny T1 phase plays a crucial role in impeding crack propagation as it can be sheared by dislocations without accumulating damage. This resulted in a substantial improvement both in the mechanical and fatigue properties of the alloy. Moreover, in the Paris stage of FCP, factors such as the size and concentration of precipitates within the grain and grain boundary play a vital role in determining the extent of crack growth. The results of transmission electron microscopy (TEM) bright field images on grain boundaries (GBs) analysis show that the variations in strength between the grain boundary and intragranular regions have a direct influence on the alloy's susceptibility to fatigue and corrosion resistance.

Investigation of segregation behaviour in 2060 aluminium-lithium alloy during twin-roll casting

The utilization of the twin-roll casting process to fabricate aluminium (Al) - lithium (Li) alloys is regarded as an efficient and energy-saving strategy to meet the aerospace industry’s demands for reducing processing steps, cost-effectiveness, and corrosion resistance. This study successfully achieved the preparation of Al-Li alloy twin-roll cast slabs across various processing ranges to investigate the corrosion resistance differences in different processing conditions. Remarkable macro segregation phenomena were observed in the fabrication under high twin-roll casting speeds for TRC-3. By combining temperature and flow rate calculations, we comprehensively analysed the results of this segregation mechanism. The segregation is inherited into the final T6 state microstructure, exacerbating the precipitation of the T1 phases and deteriorating the ultimate corrosion resistance performance. We delved into a profound discussion regarding the mechanistic impact of segregation on corrosion behaviour. Ultimately, this study postulates a process parameter range for twin-roll casting of Al-Li alloys, aimed at attaining minimal segregation and maximal corrosion resistance.

Formability of 2195-T4 Al–Li alloy sheet by electromagnetic forming

This study explored the efficacy of electromagnetic forming in addressing the limited formability of aluminum–Lithium (AlLi) alloy at room temperature, focusing on the AA2195-T4 sheet. Comparative analyses were conducted to assess the formability. The results indicated that the limit strains obtained through electromagnetic forming were at least 50%, 10%, and 50% higher compared with those obtained through rigid punch forming under the uniaxial tension, plane strain, and biaxial tension. Upon utilizing forming limit diagrams, the failure processes during electromagnetic flanging were predicted. Notably, electromagnetic flanging enabled the creation of hole-flanging structures with a 60% increase in the flanging limit strain around the circumference, surpassing the capabilities of rigid punch flanging. Moreover, the maximum time window for electromagnetic flanging was extended to 168 h. Analysis of the flanging strain path indicated that cracks were prone to occur near round corners during electromagnetic flanging, contrasting with rigid punch flanging where cracks tended to form near the edges of straight walls. This study offered valuable insights for aerospace component formation utilizing Al–Li alloys at room temperature.

Effect of pre-rolling and aging temperature on the microstructure and mechanical properties of creep-aged 2050 Al–Li alloy

The influences of aging temperatures (160–200 °C) and 8% pre-rolling on the mechanical properties, and microstructures of the creep-aged AA2050 alloys were investigated. The results show that for the solid-solutioned alloys after the creep aging, the strength increased with an increase of aging temperatures. The ultimate tensile strength (UTS) and yield strength (YS) reached the highest value of 527 and 484 MPa at 200 °C, respectively, although the elongation (EL) reduced to 10.8%. At expense of σ phases, the temperature increase promoted the dislocation accumulation and the dense precipitation of θ′ and T1 phases, which increased the strength. It is noted that the strong oriented precipitation at 200 °C lost some strengthening effect. After the 8% pre-rolling, the strength of creep-aged alloys increased firstly and then decreased with the increase of temperature. The high strength (UTS = 574 MPa, YS = 535 MPa) at 180 °C was attributed to the dense precipitation of T1 phases under the action of diffusion kinetic and thermodynamic driving force. When the temperature reached 200 °C, the activated ledge mechanism significantly thickened T1 phases, thus decreasing the strength. The work revealed the critical roles of aging temperature and pre-rolling in tailoring precipitation behaviors and mechanical performance of Al–Li alloys, paving a way in designing creep-aged Al–Li alloys with the superb mechanical properties.

A novel high-strength Al–Li alloy printed by laser powder bed fusion: Microstructural evolution and strengthenin mechanism

This paper obtained an additively manufactured high-strength Al–Li alloy by laser powder bed fusion (LPBF) based on a third generation AA2195 alloy powder raw material. The relationship between the process optimization, microstructure evolution, and mechanical properties of the as-printed (AP) and heat-treated (HT) specimens was established for the first time to explain the intergranular fracture sensibility during LPBF and reveal the dominant precipitation strengthening mechanism induced by the subsequent heat treatment. The precipitation order of AP Al–Li alloy at the last stage of the solidification process was: L (Liquid phase) →T2 (Al6CuLi3) + θ′(Al2Cu) + δ′/β' (Al3(Li,Zr)) + T (LiAlSi) + Ω (AlCuMgAg). The micro-cracks caused by a relatively high grain boundary coverage of interconnected film-like eutectic phases, as well as micro-voids caused by the localized slip between the coarse T2-phases and soft precipitate-free zones, resulted in the high intergranular fracture sensibility. The well-designed T6 heat treatment of 515 °C/60 min solution treatment and 170 °C/6 h aging treatment was conducted to maximize the precipitation strengthening by T1-phases. The precipitation order of HT Al–Li alloy was supersaturated solid solution → GP zone + δ′/β' → θ′ + T1 (Al2CuLi) + ω (Al7Cu2Fe) + β′. The presence of continuously distributed T1-cells along the grain boundaries was not only capable of providing a pinning effect on dislocations movement and boundary migration, but also able to shorten the pile-up distance on the slip plane. Such phenomena improved the resistance ability of Al–Li alloys to mechanical damage and permitted a significant strength enhancement.