Mg-Li Alloy Research Articles

Plastic deformation and heat treatment of Mg-Li alloys: a review

• Review on plastic deformation and heat treatment behavior of Mg-Li alloys. • Aging softening and strengthening mechanism of Mg-Li-Al alloys is summarized. • Research emphasis of Mg-Li alloys in the future is prospected. As the lightest structural metallic materials, Mg-Li alloys have a bright development prospect in the fields of aerospace, weapon equipment, electronic technology and transportation. In this paper, the research progress of deformation processing and heat treatment of Mg-Li alloys is reviewed, with particular emphasis on the factors affecting the plastic deformation, the effects of plastic deformation on microstructural evolution and mechanical properties, and the heat treatment behavior of Mg-Li alloys. The problems existing in the scale application of Mg-Li alloys are pointed out, and the research focus of Mg-Li alloys in the future are also prospected.

Nanocrystalline strengthened Mg-Li alloy with a bcc structure prepared via heat treatment and rolling

Due to the low recrystallization temperature and rapid growth of recrystallized grains in high-lithium content Mg-Li alloy. Nanoscale high-lithium Mg-Li alloys are difficult to obtain by traditional processing. This paper found that the homogenization treatment of the as-cast Mg-14Li-0.5Ni alloy causes the transformation of the bcc structure to an hcp structure, which can effectively improve the strength and plasticity. After further rolling at room temperature, a nanocrystalline strengthened β-phase Mg-Li alloy was successfully prepared, and its strength was 150% higher than that of the as-cast alloy.

Grain boundary decohesion in body-centered cubic Mg-Li-Al alloys

Body-centered cubic (BCC) Mg-Li alloy can be effectively strengthened by Al addition. However, brittle fracture degrades the ductility. Further improvement in mechanical properties requires a deep understanding of the fracture mechanism. In this work, we investigate the fracture behaviour of BCC Mg-Li-Al alloys and probe underneath mechanisms. Three factors are likely responsible for the grain boundary decohesion: narrow precipitation free zones provide dislocations initiation and slip pathway; shearing of intragranular precipitates by planar slip will cause large stress concentration to GBs at the end of slip bands; grain boundary precipitates of Al-rich ordered phases weaken the interatomic bonding among grains. Once the stress locally exceeds GB cohesion, cracking nucleates and propagates along/through GBs and intergranular/cleavage fracture takes place.

Porosity Formation in Thin Welded Joints of Al-MG-LI Alloys.

This work is about the study of the correlation of pore formation in welded joints of Al–MG–LI alloy with zirconium additives with the state of the base metal, thermal vacuum treatment, and welding technologies MIG and EBW. Metallographic analysis has been carried out, the phase composition of the alloy and weld metal has been investigated, and thermal cycles of welding have been calculated, allowing to estimate the residence time of metal in the alloying zone and weld metal in the liquid state. The nature of the allocation of strengthening fine-dispersed phases in the welded joints of the alloy has been determined. The regularity and character of pore formation in welded joints depending on the applicable thermal vacuum treatment (TVT) and welding technology have been revealed. It was established that TVT with subsequent hardening and aging has no effect on the phase composition of the alloy. However, this type of treatment contributes to the formation of a more homogeneous and uniform nature of the separation of fine-dispersed strengthening phases. It was revealed that the MIG technology (metal with and without TVT) is characterized by a large length of the fusion zone, the high residence time of metal in the fusion zone and weld metal in the liquid state, and the formation of pores. Phase formation in the temperature range of the beginning and end of the alloy crystallization occurs not only in the weld at the final stage of crystallization but also in the fusion zone, which may induce pore formation, whereas EBW welding shows the opposite trend and no pores. It was found that EBW technology prevents pore formation and makes it possible to obtain welded joints of 1420 Al alloys of the required quality.

Fabrication of Ti-N and Ti-Al-N Coatings on Mg-Li Alloy by Smnat Under Nitrogen Atmosphere at Room Temperature

Fabrication of Ti-N and Ti-Al-N Coatings on Mg-Li Alloy by Smnat Under Nitrogen Atmosphere at Room Temperature

Cavity Nucleation Study during Quasi-Superplasticity of an Ultralight Coarse-Grained Rolled Mg-7.28Li-2.19Al-0.1Y Alloy

Cavity or cavitation is a phenomenon in superplasticity and creep and is significant to the prediction of cavity mechanism. However, compared to cavity growth, cavity nucleation is rarely reported in magnesium alloy, especially Mg-Li alloy. To investigate the cavitation nucleation, a novel Mg-7.28Li-2.19Al-0.1Y alloy has been fabricated by hot rolling and cold rolling; its flow stress and microstructural cavitation at elevated temperatures were investigated by optical microscopy and tensile tester.

Revealing the role of pyramidal slip in the high ductility of Mg-Li alloy

The high ductility of Mg-Li alloy has been mainly ascribed to a high activity of pyramidal <c+a> slip to accommodate plastic strain. In the present study, however, a quantitative analysis reveals that Li-addition can only slightly stimulate the activation of pyramidal <c+a> slip under compression along the normal direction of a hot-rolled Mg-4.5 wt.% Li plate, with a relative activity of approximately 18%. Although the limited activity of pyramidal <c+a> slip alone cannot accommodate a large plastic strain, it effectively reduces the number of {101¯1}−{101¯2} double twins, which are believed to be favorable sites for crack initiation. The evidently reduced activity of double twins leads to a lower cracking tendency, and therefore improves ductility.

Rolling texture development in a dual-phase Mg-Li alloy: The role of temperature

Dual-phase Mg-Li alloys sheets were rolled at four different temperatures ranging from liquid nitrogen to 300 °C to explore effect of rolling temperature on texture and mechanical properties of the material. Crystal plasticity simulation was utilized to illustrate the influence of slip activity on rolling texture development. The results show that the rolling texture is largely depended on deformation temperature. Unlike commercial Mg alloys, the critical resolved shear stress of basal slip in α-Mg phase of Mg-Li alloy decreased more significantly by increasing temperature compared to that of pyramidal <c+a> slip. Enhancement of basal slip by increasing temperature triggered a decrease of split angle of basal poles for the double-peak texture. Prismatic <a> slip largely enhanced by increasing temperature upon 200 °C, which induced a wider orientation spread along the transverse direction. For the β-Li phase, the promotion of {110}<111> slip system at elevated temperature triggered the enhancement of {211}<110> and {111}<211> texture components. The cryo-rolled sample exhibited the highest strength compared to the others due to a strong hardening behavior at this temperature. A two-stage hardening behavior was observed in these as-rolled dual-phase alloys. Strain transition at phase boundaries could be the reason for appearance of this two-stage hardening.

Numerical and experimental investigation of laser shock microhydroforming technology for microforming thin-walled LA103Z alloy foil with complex microfeatures

In this work, laser shock microhydroforming technology was further investigated. This technology employs liquid as the laser-induced shock wave transmission medium to microform a thin-walled LA103Z magnesium–lithium (Mg-Li) alloy foil with six bump features. A finite element model established by Hypermesh/LS-DYNA was used to illustrate the dynamic transmission of the liquid shock wave and the dynamic plastic deformation of the workpiece. The mechanism by which the liquid shock wave interacted with the closed liquid chamber to generate a homogenised shock wavefront was revealed. The dynamic loading form of the liquid shock wave and the characteristics of the microfeatures of the workpiece resulting from this dynamic loading form were also analysed mechanically. A comparison of the effects of liquid type and laser energy in this process showed that using castor oil as the liquid medium at threshold laser energy achieved the best plastic forming effect of the workpiece. Analysis of the thickness distribution of the workpiece revealed that the rupture was concentrated in the shear thinning region at the edge of the bump features caused by the transient large stress when the laser energy exceeded the threshold value.

Corrosion Initiation Behavior of Thermal Control Oxidation Film of LA103Z Alloy

The magnesium lithium thermal control oxidation is a commonly used conductive anti-corrosion treatment method for aerospace. The corrosion behaviors of thermal control oxidation films for LA103Z alloys were studied in 3.5% NaCl solution. The corrosion characteristics with different immersion time were characterized by using scanning electron microscopy, energy spectroscopy, and electrochemical methods. The results showed that the corrosion of Mg-Li alloy with chemical oxidation film starts from pitting corrosion, gradually expands in depth in the early stage, forms corrosion holes, and then gradually develops into river-like morphology. In the last stage, the increasing corrosion products slow down the corrosion rate and gradually covers the entire sample surface. The corrosion product mainly consists of MgO, LiF, and MgCl2. Combined with the electrochemical characteristics, the corrosion mechanism was investigated.

Synthesis and microstructure, properties characterization of Ni-Ti-Cu/Cu-Al functionally graded coating on Mg-Li alloy by laser cladding

The bottleneck challenge of preparing laser cladded coating on Mg-Li alloys is the evaporation and dilution of substrate, which seriously affect the performance of coatings. In order to solve these deficiencies, Ni-Ti-Cu/Cu-Al functionally graded coating was proposed in this work. The graded coating with excellent performance was successfully prepared on Mg-Li alloy. More remarkable, the top-layer was not affected by dilution and substrate evaporation. The top-layer was mainly composed of Ni3Ti and NiTi intermetallic compounds, as well as TiNi0.8Cu0.2 phase that dispersed on the surface of Ni3Ti. Typical hypoeutectic structure was found in the interlayer, which was composed of Li3Mg7 and CuMg2. Furthermore, the corrosion and wear resistance of Mg-Li alloy were greatly improved. Specifically, the wear volume of the top-layer and interlayer is reduced by 98.04% and 82.41% than that of substrate, respectively. The corrosion potential of the top-layer (-242 mV) and the interlayer (-991 mV) are 1311 mV and 562 mV higher than that of the substrate (-1553 mV), while the corrosion current density of the top-layer (2.71 × 10-7 A·cm−2) and the interlayer (1.93 × 10-6 A·cm−2) are about three and two orders of magnitude lower than that of the substrate (2.53 × 10-4 A·cm−2).

Co-Addition of Mg2Si and Graphene for Synergistically Improving the Hydrogen Storage Properties of Mg-Li Alloy.

Mg−Li alloy possesses a high hydrogen capacity. However, the hydrogenation and dehydrogenation performances are still far from practical application. In this work, Mg2Si (MS) and graphene (G) were employed together to synergistically improve the hydrogen storage properties of Mg−Li alloy. The structures of the samples were studied by XRD and SEM methods. The hydrogen storage performances of the samples were studied by nonisothermal and isothermal hydrogenation and dehydrogenation, thermal analysis, respectively. It is shown that the onset dehydrogenation temperature of Mg−Li alloy was synergistically reduced from 360°C to 310°C after co-addition of Mg2Si and graphene. At a constant temperature of 325°C, the Mg−Li−MS−G composite can release 2.7 wt.% of hydrogen within 2 h, while only 0.2 wt.% of hydrogen is released for the undoped Mg−Li alloy. The hydrogenation activation energy of the Mg−Li−MS−G composite was calculated to be 86.5 kJ mol−1. Microstructure and hydrogen storage properties studies show that graphene can act as a grinding aid during the ball milling process, which leads to a smaller particle size for the composites. This work demonstrates that coaddition of Mg2Si and graphene can synergistically improve the hydrogen storage properties of Mg−Si alloy and offers an insight into the role of graphene in the Mg−Li−MS−G composite.

Interfacial bonding mechanism and properties of HVOF-sprayed Fe-based amorphous coatings on LA141 magnesium alloy substrate

Due to poor corrosion and wear resistance, Mg-Li alloys often experience the premature failure during their service. In order to improve the corrosion and wear resistance of Mg-Li alloys, Fe-based amorphous coatings were firstly prepared on the LA141 magnesium alloy substrate by high velocity oxygen-fuel spraying technology (HVOF) in this study. It is noticed that by introducing the Ni60 interlayer with the thickness of 150 μm, the bonding strength of the Fe-based amorphous coating on LA141 alloy substrate can reach 56.9 MPa, which is currently the highest value of Fe-based amorphous coatings on magnesium alloys reported so far. It is found that the improvement of bonding strength is attributed to the localized metallurgical bonding at the interfaces of Fe-based amorphous coating/Ni60 and Ni60/LA141 and the compactness of Fe-based amorphous coatings. Moreover, the corrosion and wear resistance of the LA141 magnesium alloy with the Fe-based amorphous coatings are 34 times and 170 times higher than those of the bare LA141 magnesium alloy substrate, respectively. Finally, the failure mechanisms of the Fe-based amorphous coatings during tension and wear are discussed. This study can provide an alternative method for the surface protection of Mg-Li alloys.

High-Performance HVOF-Sprayed Fe-Based Amorphous Coating on LA141 Magnesium Alloy via Optimizing Oxygen Flow and Kerosene Flow.

To solve the problem of poor corrosion and wear resistance of Mg-Li alloys, Fe-based amorphous coatings were prepared by high velocity oxygen-fuel spraying technology (HVOF) on the LA141 magnesium alloy substrate with a Ni60 intermediate layer. The microstructure and performance of Fe-based amorphous coatings with different oxygen flow and kerosene flow were characterized and analyzed. The results demonstrate that there is an optimal oxygen/kerosene ratio where the porosity of Fe-based amorphous coating is the lowest. Moreover, the amorphous content increases with the decrease in the oxygen/kerosene ratio. In particular, when the oxygen flow is 53.8 m3/h and the kerosene flow is 26.5 L/h, the Fe-based amorphous coating possesses the lowest porosity (0.87%), the highest hardness (801 HV0.1), the highest bonding strength (56.9 MPa), and an excellent corrosion and wear resistance. Additionally, it can be seen that the Fe-based amorphous coating is composed of amorphous splats and amorphous oxides, but the Ni60 intermediate layer exhibits an amorphous and crystalline multi-phase structure. The high bonding strength of the coating is attributed to the low porosity of Fe-based amorphous coating and the localized metallurgical bonding between different layers. Finally, the mechanisms on corrosion and wear of Fe-based amorphous coatings are also discussed.

Lithium/yttrium cluster effect on {10[formula omitted]1} twin boundary migration in magnesium

The precipitate with a crystal structure different from the matrix usually plays a great role in the material strength. However, little is known about the contribution of precipitate similar to the matrix structure. Herein, the interaction of {101-1} twin and hexagonal close-packed (HCP) cluster has been investigated by molecular dynamics (MD) simulation and transmission electron microscopy (TEM) observation in magnesium. The sphere-/plate- shaped Li and Y clusters are respectively considered. The MD results show that twinning dislocation (TD) prefers to nucleate in the soft phase and can be pinned at the cluster/matrix interface for Mg-Li alloy and matrix/cluster interface for Mg-Y alloy. The higher stress and larger strain are required to pass through the upper half of Li cluster, signifying a stronger pinning effect in upper region. It is consistent with the experiment results. The twin boundary (TB) can also cut through the hard Y phase under shearing due to its HCP crystal structure and the accumulation of TDs with large Burgers vector. Compared with the different plate-shaped clusters, the strongest mechanical property is expressed on the sample with spherical phase. The finding of HCP-type cluster effect on {101-1} twin boundary migration gives a new insight into the precipitate strengthening mechanism.

High-temperature superplastic behavior and ECAP deformation mechanism of two-phase Mg-Li alloy

Fine grains of Two-phase Mg-Li alloy could be achieved by severe plastic deformation. The alloy exhibited a superplastic behavior with a maximum elongation of 306.6% at 623 K with an initial rate of 1.5 × 10−2 s−1. The value of the strain rate sensitivity under 623 K and 1.5 × 10−2s−1 is 0.36, and 121.6–160.0 kJ/mol. The dominant deformation mechanism in this alloy is grain boundary sliding accommodated by a slip which was controlled by lattice diffusion at 523–623 K.

A novel Ni2MnCuSnAl0.1 multi-principal element alloy coating to enhance the wear resistance and corrosion resistance of Mg-Li alloy

The evaporation and dilution of substrate are the key deficiencies that limit the performance of laser-cladded coatings on Mg-Li alloys (or Mg alloys). In order to overcome these drawbacks, in this work, a novel Ni2MnCuSnAl0.1 multi-principal element alloy (MPEA) coating and a multi-step ultrasonic assisted laser cladding technique were proposed. Dense metallurgical Ni2MnCuSnAl0.1 MPEA coatings were successfully synthesized on Mg-Li alloy. Typical gradient microstructure of low-diluted layer, diffusive layer and interfacial layer were obtained in the coating. The low-diluted layer was composed of BCC solid solution, Ni2MnAl and Ni2MnSn while the diffusive layer and interfacial layer showed an interactive microstructure of Mg-CuMg2 eutectic, Ni2MnAl, Li2MgSn/SnMg2 and Mg/Mg-Li substrate. The corrosion potential of Ni2MnCuSnAl0.1 MPEA coating (-108 mVSHE) was 1283 mVSHE higher than that of Mg-Li alloy (-1391 mVSHE), while the corrosion current density of the coating (5.85 × 10−7 A·cm−2) was about three orders of magnitude lower than that of Mg-Li alloy (1.12 × 10−4 A·cm−2). The micro-hardness gradually increased from the substrate to the coating, and the average micro-hardness of the coating was ~ 541.2 HV0.2, which is about 10 times higher than that of Mg-Li alloy (~57.8 HV0.2). The wear resistance of Mg-Li alloy was also improved approximately 10 times by cladding Ni2MnCuSnAl0.1 MPEA coating.

Difference in formation of plasma electrolytic oxidation coatings on MgLi alloy in comparison with pure Mg

In order to study the substrate lattice structure (Li addition) on the growth of plasma electrolytic oxidation (PEO) coatings, MgLi alloy (11.36 wt.% of Li, cubic) and pure Mg (hexagonal) were treated under a pulsed direct PEO mode in a phosphate electrolyte for different periods of time. The results revealed that the presence of Li and Li-rich phases in the cubic Mg alloy seems to be essential for the treatment result rather than the original lattice structure. A modified discharge behavior of MgLi alloy finally led to a different microstructure of the coating. The unstable coatings of MgLi alloy tended to dissolve rapidly though shared the similar composition to that of pure Mg. Li was incorporated only in the primary conversion products at the interface of coating/MgLi. In spite of the advanced efficiency of energy input during processing, the more porous and thinner PEO coatings on the MgLi alloy were less resistant to abrasion and corrosion. • PEO process exhibits a modified behavior in presence of Li in magnesium substrate. • Influence of Li on the growing of PEO coating is discussed. • Comparison of PEO coatings formed on MgLi alloy and pure Mg is achieved.

Role of extrusion temperature on the microstructure evolution and tensile properties of an ultralight Mg-Li-Zn-Er alloy

Role of extrusion temperature on the microstructure evolution and tensile properties of an ultralight Mg-10Li-5Zn-0.5Er alloy was studied. The results indicate that the second phases and grains are all refined after extrusion. It is firstly reported that there are two kinds of grains zone including micro-grained region and coarse-grained region in the as-extruded Mg-Li alloys with high Li content (≥ 9 wt%). As the extrusion temperature increases from 150 °C to 300 °C, the volume of micro-grained region decreases and finally almost disappears. The grain size of coarse-grained region increases as well. The amount of Mg-Li-Zn precipitates along the boundaries decreases and their quantity in the grains increases with grain coarsening. The strength rises slightly and the elongation decreases notably with the enhancement of extrusion temperature. As the extrusion temperature increases, the crack initiation appears from mainly around the bulky Mg-Zn-Er phases to mainly along the grain boundaries. Due to the grain refinement, the second phases strengthening, and the abundant slip systems of β-Li phase, the comprehensive properties of the as-extruded alloys have leading position in the field of wrought Mg-Li alloys and the optimum comprehensive tensile properties are gained in the alloy extruded at 275 °C.

Design of a Mg-7Li-2.6Al-0.4Si alloy with simultaneously improved strength and ductility

Mg-Li alloys have been widely applied in various engineering scenarios due to the ultralight feature. One of the key factors determining the applications of Mg-Li alloys is the strengthening methods, which have received much attention. In this paper, a new Mg-7Li-2.6Al-0.4Si (all in wt.%) alloy was designed and produced to improve the mechanical performance. The simultaneously outstanding mechanical strength and ductility have been demonstrated by nano indentation and tensile test, including a yield strength of 192 MPa, tensile strength of 250 MPa and elongation of 22 %. Based on the microstructural features characterized by optical microscopy, scanning electron microscopy and transmission electron microscopy, the excellent mechanical properties were attributed to the precipitates and refined grain size. The fracture morphology was also uncovered to further explain the good mechanical performance. Overall, this work yields a new Mg-7Li-2.6Al-0.4Si alloy with excellent properties, which suggest its great potential for various applications.