Mg-Li Alloy Research Articles

Effect of AlLi phase on deformation behavior and dynamic recrystallization of Mg-Li alloy during hot compression

Hot deformation behavior of Mg−5Li−3Al−2Zn (LAZ532) alloy with AlLi phase was studied by using isothermal hot compression experiments at the deformation temperature of 473−623 K and the strain rate of 0.001−1 s−1. AlLi phase could significantly increase the peak stress of LAZ532 alloy during hot deformation because of its obstructing effect on the movement of dislocation. A relevant strain-compensated Arrhenius constitutive model was constructed to predict the hot deformation behavior of LAZ532 alloy, and the predicted results were in good agreement with experimental ones. The corresponding hot processing maps were established based on the Murty criterion, and the optimal processing domain was located in the range of 538−623 K and 0.001−0.01 s−1. At the high strain rate, AlLi phase was not beneficial for the flow stability and dynamic recrystallization of LAZ532 alloy during hot compression. In addition, deformation temperature would change the nucleation mechanism of the dynamic recrystallization of LAZ532 alloy.

High-Strength β-Phase Magnesium-Lithium Alloy Prepared by Multidirectional Rolling.

Magnesium-lithium alloys are popular in the lightweight application industry for their very low density. However, as the lithium content increases, the strength of the alloy is sacrificed. Improving the strength of β-phase Mg-Li alloys is urgently needed. The as-rolled Mg-16Li-4Zn-1Er alloy was multidirectionally rolled at various temperatures in comparison to conventional rolling. The results of the finite element simulations showed that multidirectional rolling, as opposed to conventional rolling, resulted in the alloy effectively absorbing the input stress, leading to reasonable management of stress distribution and metal flow. As a result, the alloy's mechanical qualities were improved. By modifying the dynamic recrystallization and dislocation movement, both high-temperature (200 °C) and low-temperature (-196 °C) rolling greatly increased the strength of the alloy. During the multidirectional rolling process at -196 °C, a large number of nanograins with a diameter of 56 nm were produced and a strength of 331 MPa was obtained.

Strengthening mechanism and corrosion behavior of friction stir welded LAZ933 magnesium-lithium alloy

In this study, friction stir welding (FSW) technique was applied to the LAZ933 magnesium-lithium (Mg-Li) alloy. Microstructure, mechanical properties and corrosion behaviors of friction stir welded LAZ933 magnesium-lithium alloy were analyzed by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffractometry (XRD), transmission electron microscopy (TEM), hardness, tensile, and electrochemical test. The experimental results indicated that FSW resulted in significant refinement of β phase, reduction of α phase content as well as dissolution of Mg17Al12 and AlLi (γ) precipitates in the nugget zone (NZ). The generated MgLi2Al (θ) precipitates in the NZ and heat-affected zone (HAZ) which had a coherent structure with the matrix could significantly strengthen the Mg-Li alloy. The ultimate tensile strength of the joint reached 163.5 MPa, and elongation reached 15.21%. In the weakest area of the weld (HAZ), the strengthening caused by the solid solution of α phases and formation of θ precipitates compensated the strength loss induced by the phase coarsening by thermal exposure in FSW, resulting in the joint fractured in the base metal (BM) and showed a ductile pattern. The corrosion current density changed from 4.831 × 10−5 A/cm2 to 2.054 × 10−5 A/cm2, which indicated that the weld had better corrosion resistance than the BM.

Microstructure and properties characterization of laser-cladded Cu[sbnd]Al alloy coatings on Mg[sbnd]Li alloy

MgLi alloys have a wide application in the lightweight structure materials on account of their ultra-light-weight, good machinability and high specific strength. However, the low strength, insufficient wear and corrosion resistances of MgLi alloys have become a critical problem that hinders their applications. In order to achieve excellent wear and corrosion properties, LC-Cu3Al, LC-Cu6Al and LC-Cu9Al coatings are designed and prepared on MgLi alloy substrates in this study. The phase structure, microstructure, hardness, wear and corrosion properties of CuAl alloy coatings are investigated in detail. The results show that a good metallurgical bond is achieved between the CuAl alloy coatings and the substrates. LC-Cu6Al coating's hardness, wear and corrosion properties are the best. Compared with the MgLi alloy substrate, the average hardness of LC-Cu6Al coating increases by 6.75 times, while the wear volume decreases by 88.32 % and the corrosion current density decreases by two orders of magnitude. The results suggest that using laser cladding CuAl alloy coatings is an excellent strategy to enhance the surface properties of MgLi alloy.

Improved electrochemical behavior of Mg-Li alloys by superhydrophobic layered double hydroxides/Ni-based composite coatings

As a lightweight material, the wide application of Mg-Li alloy is restricted by its corrosion resistance. Focusing on this, an innovative superhydrophobic composite coatings of nickel-based metal coupled with layered double hydroxides (LDHs) was prepared on Mg-Li alloy. The microstructure, hydrophobic property and corrosion resistance of coatings were investigated by SEM, TEM, XRD, FT-IR, AFM, contact angle tester and electrochemical test. The results indicated that the MgAl LDHs uniformly grown in situ on the NiP coating deposited on Mg-Li alloy through electroless plating and hydrothermal treatment. The MgAl LDHs with a complex honeycomb micro-nano structure improved the surface roughness of the composite coating to 126 nm. The two-step treatment achieved an excellent coupling between the metal-based coating and inorganic compounds. The low surface energy treatment of micro-nano structure on NiP coating surface with stearic acid (@SA) realized the superhydrophobic transition of the composite coating (WAC=154.27° ± 2.56°). Besides, MgAl LDHs showed better trapping properties for Cl-. Under the synergistic effect of anion capture and hydrophobic effect, the corrosion current density (1.35 ×10−7 A⋅cm−2) and impedance modulus of NiP/MgAl LDHs@SA coating were significantly better than those of NiP and NiP/MgAl LDHs coating. The superhydrophobic composite coating provided a better anticorrosion choice for Mg-Li alloy.

First-principles study of crystal structure search, stability and mechanical property of magnesium-lithium binary system

In this paper, the energetically stable and metastable crystal structures of Mg-Li binary system are searched throughout all possible Mg concentrations by using the first-principles calculations based on density functional theory (DFT). Three stable structures are found at compositions LiMg, LiMg2 and Li2Mg3. One metastable structure is found at composition LiMg3. The formation energy, phonon spectrum, and elastic constants are calculated to evaluate the energy, dynamic and elastic stabilities, respectively. At zero temperature, both the elastic moduli (include bulk modulus B, shear modulus G, Young’s modulus E, the Poisson’s ratio ν and B/G ratio) as a function of the Mg concentration in Mg-Li binary system and the spatial direction dependences of elastic moduli are analyzed. The temperature dependents of bulk modulus and thermal expansion coefficient are also analyzed to investigate the high-temperature mechanical properties of Mg-Li binary system. With the increase of temperature, the bulk modulus of Mg-Li alloys gradually decreases and the thermal expansion coefficient gradually increases. And the calculated results also show that LiMg2 can maintain excellent mechanical strength and mechanical stability at high temperature, and has the potential of application in the high-temperature fields.

An ultra-light Mg-Li alloy with exceptional elastic modulus, high strength, and corrosion-resistance

In this paper, a new Mg-Li alloy with exceptional Young’s modulus, great specific strength, and outstanding corrosion-resistance has been successfully developed, exceeding any reported values of elastic modulus of currently available for Mg alloys. The newly invented alloy reaches an elastic modulus of 60.83 GPa after heat treatment and a corrosion rate of 0.989 mm per year without any surface treatment. X-ray computed tomography and nanoindentation have proven the 3D distribution of hard secondary phases (AlLi and Al-X) with average equivalent diameters of 4.1 µm and 5.1 µm influencing modulus, hardness, and corrosion rate.

Effects of heat input on microstructures and mechanical properties of LAZ931 magnesium-lithium alloy by CO2 laser welding

LAZ931 magnesium-lithium (Mg-Li) alloy is a novel ultra-light alloy material. It is added with important alloying elements aluminum and zinc to form a quaternary Mg-Li alloy, which has high strength and low density, and improved mechanical properties. Due to the natural aging softening of multiphase Mg-Li alloys, their strength will decrease at room temperature. The welding research of LAZ931 Mg-Li alloy is only friction stir welding, and there is no report on laser welding. The industrial circle has put forward an increasingly urgent demand for the welding technique of LAZ931 Mg-Li alloy. CO2 laser welding of LAZ931 Mg-Li alloy with 2.15 mm in thickness was studied to explore a reasonable heat input range. CO2 laser welding can make the welded seam zone(WSZ) grain significantly refined. The base metal(BM) softening phase disappears after laser welding. Dispersion strengthening of the precipitated phase in the heat-affected zone(HAZ), resulting in enhanced strength of the HAZ. The WSZ is mainly composed of fine needle-like α-phase, granular α-phase, β-phase, and granular precipitation phase, and the grain interior and the grain boundary distribution of α-phase along β-phase; The width of the HAZ is narrow, and it partially melted to form a coarse needle-like α phase. The tensile strength of the welded joints obtained by laser welding is all fractured in the BM, indicating that improved strength after laser welding, and with the increase in heat input, the ultimate tensile strength and elongation rates of the welded joints show a descending trend; The microhardness of the WSZ is the highest, followed by the HAZ, and the microhardness of the BM is the lowest, and the microhardness of the WSZ is higher than that of the BMs under different heat inputs. With the increase in heat input, the WSZ grain becomes coarse, which in turn makes the mechanical properties of the welded joint decrease. The research results can provide a theoretical basis and technical support for the engineering application of this type of ultra-light Mg-Li alloy.

Investigation into thermodynamic behavior of LA103Z Mg[sbnd]Li alloy during turning based on modified Johnson–Cook model

The LA103Z MgLi alloy is a promising lightweight material for aerospace applications due to its superior performance. Its machining involves a complex thermal–mechanical coupling process during which the material undergoes high strain rate deformation. Thus, determining the precise constitutive model for accurately modeling the cutting is extremely important. To analyze the material flow behavior, Split Hopkinson Pressure Bar (SHPB) tests were conducted under strain rates of 1200–5000 s−1. By observing the microstructural characteristics of the material, adiabatic temperature rise (ATR) is found to be the dominant factor affecting the flow stress. Accordingly, a modified Johnson–Cook (J–C) constitutive model was derived by considering the effects of ATR on thermal softening and strain rate strengthening terms. The modified model was validated by SHPB measure data, the average relative error is 3.08 %. The finite element (FE) model was established based on the modified J–C model to predict the turning behaviors at various parameters. The predicted values coincide well with measured results, which proving the high-precision of FE model. The analysis results of the thermodynamic behaviors under different cutting parameters of MgLi alloy shows that the influences of cutting speed on temperature, and depth of cut on cutting forces (main cutting force Fc and feed force Ff) are the most significant. However, the effect of cutting speed on the cutting force is not evident due to the effect of temperature rise. The reasonable turning conditions of the large depth of cut and feed rate, and small cutting speed was suggested for studied LA103Z MgLi alloy to consider the machining quality and efficiency.

Microstructure and mechanical properties of refill friction stir spot welded Al–Mg-Li alloy joints

Microstructure and mechanical properties of refill friction stir spot welded Al–Mg-Li alloy joints

Unveiling the rolling texture variations of α-Mg phases in a dual-phase Mg-Li alloy

LZ91 Mg-Li alloy plates with three types of initial texture were rolled by 70% reduction at both room temperature and 200 °C to explore the rolling texture formation of α-Mg phase. The results showed that the rolling texture is largely affected by the initial texture. All the samples exhibited two main texture components as RD-split double peaks texture and TD-split double peaks texture after large strain rolling. The intensity of the two texture components was strongly influenced by the initial orientation and rolling temperature. Extension twinning altered the large-split non-basal orientation to a near basal one at low rolling strain. The basal orientation induced by twinning is unstable, which finally transmitted to the RD-split texture. The strong TD-split texture formed due to slip-induced orientation transition from its initial orientation. The competition between prismatic 〈a〉 and basal slip determined the intensity and tilt angle of the TD-split texture. By increasing the rolling temperature, the TD-split texture component was enhanced in all three samples. Limitation of extension twinning behavior and the promotion of prismatic slip at elevated temperature are the main reasons for the difference in hot and cold rolling texture.

Effect of air-formed film on corrosion behavior of magnesium-lithium alloys

It is recently suggested that air-formed film plays an important role in controlling corrosion resistance of Mg-Li alloys. However, the structure of the air-formed film and its effect on corrosion resistance of Mg-Li alloys has not been fully understood. Firstly, the air-formed films formed on α and β phases in a dual-phase LZ91 Mg-Li alloy after exposure to laboratory air for up to 48 h have been examined by SEM under the assistance of ultramicrotomy. Then, the effect of the air-formed film on surface potential and, consequently, corrosion/oxidation behavior of the alloy has been investigated. Finally, in order to exclude the influence from α phase, the structure of the air-formed film on β phase and its effect on corrosion/oxidation behavior of Mg-Li alloys have been studied based on a single-phase LA141 Mg-Li alloy. The results show that the air-formed film is thin and negligible on α phase but thick on β phase after prolonged exposure to laboratory air. The thick air-formed film on β phase has a multilayer structure with an inner layer consisting of MgO/Mg(OH)2 and outer layer consisting of Li2CO3, which greatly elevates the surface potential of β phase in air. Both LZ91 and LA141 Mg-Li alloys firstly undergo uniform corrosion and then filiform corrosion when immersed in NaCl solution and the pre-existed air-formed film on β-Li phase can retard the occurrence of filiform corrosion in the alloys.

Experimental study on friction stir modification of LA103Z Mg-Li alloy

Friction stir processing (FSP) is a method to produce severe plastic deformation (SPD) of materials, which can well improve and optimize the microstructure and mechanical properties of Mg-Li alloy. In this paper, the FSP experiment of LA103Z Mg-Li alloy was conducted, and the influence of process parameters on the microstructure, tensile strength, elongation after fracture and fracture morphology of the material was studied. The microstructure of the Mg-Li alloy after FSP was significantly refined. With the increasing rotational speed of the stirring head, the grain boundaries became clearer and more distinguishable, and the low angle grain boundaries transformed into the high angle grain boundaries. With the increasing feed speed of the stirring head, the grain refinement became more pronounced, and the dispersion of α-Mg phase in the stir zone became more uniform and distributed at the grain boundaries. When the rotational speed and the feed speed of the stirring head were 800-1000 r/min and 100-200 mm/min respectively, the comprehensive performance of the Mg-Li alloy plate after FSP was expected to be optimal.

A comparison of the microstructure-dependent corrosion of dual-structured Mg-Li alloys fabricated by powder consolidation methods: Laser powder bed fusion vs pulse plasma sintering

In this study, powder metallurgy methods were used to fabricate Mg-7.5Li-3Al-Zn alloys from repowdered extruded alloys. Extruded alloys were powdered using ultrasonic atomization, and then laser powder bed fusion (LPBF) and pulse plasma sintering (PPS) were used to consolidate the bulk materials. A comparison of the properties of the fabricated alloys with those of a conventionally extruded one was carried out using methods that characterized the microstructure and corrosion resistance. When compared to their conventionally extruded counterpart, LPBF and PPS materials exhibited refined microstructures with low enrichment in AlLi and coarse Al, Zn, Mn precipitates. The main drawback of the LPBF alloy, printed for the needs of this study, was its porosity, which had a negative effect on its corrosion. The presence of unrecrystallized particle boundaries in the PPS alloy was also unbeneficial with regard to corrosion. The advantage of the LPBF and PPS processes was the ability to change the proportion of α(Mg) to β(Li), which when the complete consolidation of the material is achievable, may increase the corrosion resistance of dual-structured Mg-Li alloys. The results show that powder metallurgy routes have a wide potential to be used for the manufacture of Mg-Li based alloys.

Investigation of crossed-twin structure formation in magnesium and magnesium alloys

In this work, the effect of alloying addition on the propensity for twin-twin interactions to transform into crossed-twin structures in magnesium alloys is investigated. A full-field elasto-viscoplastic fast Fourier transform (EVP-FFT) framework combined with a discrete twin model and dislocation density-based hardening law for slip strengths is used to calculate the micromechanical fields in the crystalline matrix around the interacting twins. AZ31 and MgLi alloys are selected along with pure Mg to study the influence of plastic anisotropy in connection with alloying elements. These alloys were selected since their plastic anisotropy measure, which is defined as the ratio between the critical resolved shear stress for pyramidal 〈c+a〉 and basal 〈a〉 slip modes, spanned a wide range. To quantify the role of twin thicknesses, we probe a range of impinging twin thicknesses while fixing the recipient twin thickness. The analysis reveals that: (i) the local driving stress for crossed twin structure formation generated from the interaction of the two twins is lower in a low plastically anisotropic material, like a MgLi alloy, than a high plastically anisotropic material like pure Mg and (ii) the critical impinging twin thickness needed to form the crossed twin structure in pure Mg, AZ31 and MgLi alloys is ∼0.5, ∼0.75 and ∼1.5 times the recipient twin thickness. We propose a relationship between the tendency for crossed twin structure formation and the experimentally observed higher ductility in MgLi alloys compared to pure Mg. One key implication of the findings is that crossed-twin structure formation can be hindered and the ductility of magnesium alloy thereby improved by properly choosing alloying elements that lower the slip strength for pyramidal c+a slip.

Experiment and Numerical Simulation on Bearing Properties of Mg-Li Alloy Thread

In order to verify the bearing performance of Mg-Li alloy thread connections, the tightening performance and axial pull-out performance of the Mg-Li alloy thread structure with wire thread insert were tested, and the failure load and mode were obtained. The finite element 2D axisymmetric model was used to numerically analyze the bearing properties of Mg-Li alloy threads. The reliability of the analysis model was verified by comparison with the experimental results and theoretical basis. The load distribution and stress distribution characteristics of the thread connection were studied, and the influence of boundary constraints on the axial pull-out performance was studied. The results show that the M5 Mg-Li alloy embeded wire threat insert with 8 rounds has sufficient connection strength under the action of tightening torque and axial pull-out load, and the failure mode is mainly bolts fracture. Boundary constraints will have an influence on the load distribution and performance of the Mg-Li alloy thread connection structure. The load-bearing ratio of each round thread changes obviously with the downward movement of the top of the boundary. As the top of the boundary moves downward, the location where the maximum load-bearing ratio will be transformed from the first thread to the last thread. The load-bearing ratio of the last thread gradually increases from 11.3% when the outer circumference fully restrained to 23.1% when the boundary area below 4 mm from the last thread. For the M5 Mg-Li alloy embeded wire threat insert with 8 rounds, the axial pull-out bearing capacity of M5 inserts is between 9.5 kN and 12 kN under different boundary conditions.

Grain refinement of Mg-14Li alloy by Sn addition and large strain rolling

Mg-Li alloy is the lowest density structural metal, which has great potential for various industrial applications. Although Mg-Li alloy has excellent plasticity, it has low strength and requires further strengthening. In this study, the grain size of Mg-14 wt% Li alloy was refined to 15.7 μm by the addition of 6 wt% Sn, the initial grain size of as-cast Mg-14Li alloy was 180 μm. Furthermore, the grain size of Mg-14Li-6Sn was further refined to 400 nm by the subsequent large strain rolling (LSR). The yield strength of the ultra-fine grained Mg-14Li-6Sn reached 160 MPa, and the elongation was not sacrificed but increased to 30% compared with the as-cast alloy (14%). The microstructural evolution was characterized by optical microscopy (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The high ductility of the ultra-fine grained Mg-14Li-6Sn is attributed primarily to the dynamic recovery, and the increase in strength is mainly due to the grain refinement.

Improved corrosion resistance of MAO coating on Mg-Li alloy by RGO modified silanization

The inherent micropores and microcracks in the micro-arc oxidation (MAO) film on the surface of Mg-Li alloy limit the corrosion resistance of the film in corrosive environments. In this work, the double-layer micro-arc oxidation/3-glycidoxypropyltrimethoxysilane (KH560) composite film was prepared on the surface of the LA103Z Mg-Li alloy by MAO and silanization treatments. Based on this, the modification with reduced graphene oxide (RGO) to the KH560 film was studied and the corrosion resistance of the film was investigated. The results show that the silane film prepared is uniform and complete which fills up the micropores and microcracks of the MAO film, enhancing the shielding effect of the film. Moreover, the RGO modification increases the thickness of the KH560 film and the corrosion resistance of the composite film significantly in 3.5 wt% NaCl solution.

Effect of Surfactants on the Corrosion Protectability of Calcium Phosphate Conversion Coatings on Duplex Structured Mg-8Li (in Wt.%) Alloy

Calcium phosphate chemical conversion coatings with the additions of sodium lauryl sulfate (SLS) and dodecanesulfonic acid sodium (DSS), respectively, were prepared on the surface of the Mg-8Li alloy. The surface and cross-sectional corrosion morphologies, compositions, and corrosion behavior of the coated surfaces in 3.5 wt.% NaCl solution were respectively investigated by using a scanning electron microscope (SEM), energy dispersive spectrometer (EDS), electrochemical workstation, hydrogen evolution apparatus, and optical microscope (OM). The results demonstrated that Ca-P coatings had a petal-like structure being composed of leaf-like particles. After being respectively performed for 30 min in conversion solutions containing SLS and DSS, the corresponding average film thicknesses of surface coatings were 27 μm and 7 μm. In addition, the corrosion current densities of coated surfaces by using the conversion solutions containing SLS and DSS were 1.438 × 10−5 A·cm−2 and 4.719 × 10−5 A·cm−2, respectively. The effect of surfactants on phosphate chemical conversion coating was discussed in detail.

Thermo-driven oleogel-based self-healing slippery surface behaving superior corrosion inhibition to Mg-Li alloy

Bioinspired by Nepenthes, lubricant infused surfaces (LIS) have attracted widespread attention in the field of anticorrosion. However, the lubricant coating has some disadvantages such as complex construction processing and easy loss of oil phase in air or dynamic water phase. In this study, oleogel is infused into a lotus leaf inspired super-hydrophobic matrix to form an oleogel infused surface (OIS) for enhancing corrosion resistance of active Mg-Li alloy. For reserving oleogel, firstly, a facile one-step electrodeposition method is used to construct super-hydrophobic surface (SHS) composed by samarium/myristic acid complex micro-nano flower structure onto Mg-Li alloy. The coating exhibits excellent superhydrophobic property at a static contact angle of 160° by applying 30 V electrolysis for 30 min. The protection efficiency of single SHS highly relates with the metal itself. For short period immersion in water phase, SHS can afford protection to Mg-Li alloy. However, the long-term immersion will see the rapid failure of SHS, and the high activity of Mg-Li alloy is one main reason. We assume that SHS cannot be a good choice for protecting Mg-Li alloy. Then, a Nepenthes inspired liquid coating is formed by infusing oleogel into the micro-nano structure by a spin-coating method. The liquid coating performs prominent corrosion resistance with Rct reaching as high as 1.51 × 1010 Ω cm². After the mechanical damage from the external environment, the liquid coating can realize self-repair through thermal assistance, and the liquid coating can still restore Rct up to 1.24 × 1010 Ω cm2 after healing. The corrosion resistance of the liquid coating remains strong by showing Rct as high as 1.14 × 109 Ω cm², even after immersion in representative corrosive 3.5 wt% NaCl solution for 30 d.