Papers by Keyword: Mg-Li Alloy

Abstract: The effect of grain size on the initiation behavior of exfoliation corrosion in cold-rolled Mg-14mass%Li-3mass%Al alloy was examined. Exfoliation corrosion initiated after 30 minutes in the coarse-grained structure (279μm), whereas it was delayed to 60 minutes in the fine-grained structure (75μm) and further to 75 minutes in the ultrafine-grained structure (39μm). This delay is attributed to the suppression of shear band formation and localization during cold rolling with decreasing grain size, which enhances the uniformity of surface reactions in the corrosive environment and promotes faster and denser formation of the protective film at the early stage. Accordingly, the improved condition of the initial corrosion film is considered the primary factor responsible for the delayed onset of exfoliation corrosion.

Abstract: Mg-Li system alloys also has excellent cold-workability compared to commercial hcp-structured Mg alloys. However, Mg-Li alloys have poor corrosion resistance because not only that is Mg-based alloy but Li as a major alloying element is a less noble metal. For example, Mg-Li alloy sheet indicates high corrosion rate and exfoliation corrosion as a result of long-term corrosion test. The authors reported Mg-14 mass%Li-3 mass%Al alloy has the highest corrosion resistance in β-type solid solution alloy. Even though the optimized alloy composition, the alloy does not have enough corrosion resistance for practical use. In this study, anodized coating on Mg-Li alloy using phosphate solution was investigated. Anodizing of Mg-Li alloy facilitates the dissolution of substrate because of high Li concentration in this alloy. Therefore, the anodizing conditions were widely examined. As a result, the coating with approximately 15-20 μm of the surface layer was successfully formed. The surface layer was composed of MgAl₂O₄ and some phosphorus compounds. The thickness of anodized layer varied with the anodizing conditions. The dense surface layer was formed at a certain anodizing voltage and the corrosion resistance of anodized Mg-Li alloys was improved. However, the surface has some cracks and large flaky compounds. The formation mechanism of dense layer during anodizing were discussed.

Abstract: 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.

Abstract: Mg-Li alloys have much better formability than traditional Mg alloys. However, the corrosion resistance of Mg-Li alloys are low due to Li addition and cold-worked Mg-Li alloys sustain exfoliation corrosion, which is serious problem for practical use of Mg-Li alloys [1]. According to our previous report, the elongated grains may be the cause of the exfoliation corrosion. In this study, the exfoliation corrosion behavior of Mg-14mass%Li-1mass%Al (LA141) alloy processed by equal channel angular extrusion (ECAE) is characterized to see the corrosion morphology of the samples introduced more grains than rolling. The specimens processed by rolling showed only elongated grains and the ones processed by ECAE (Route A) at 2 and 4 times showed elongated grains and partially equiaxial grains and in the samples fabricated by ECAE (Route B_c) at 2 and 4 times, equiaxial grains were found by optical microscopy. In corrosion examination, the specimens of rolling and ECAE (Route A) developed exfoliation corrosions and the samples of ECAE (Route B_c) didn’t sustain exfoliation corrosion. This results were consistent with our previous report. Then the corrosion behavior of rolled and ECAEed samples were focused. The evaluation of the time until crack initiation and the number of cracks were employed to see the corrosion morphology of the samples

Abstract: A two-step deformation approach is proposed for the superplastic deformation (SPD) of Mg-9Li-1Al (LA91) alloy. This method has been successfully applied to titanium alloys and has induced enhanced superplasticity, and the feasibility of the method for the Mg-Li based alloy is explored. In a previous research, single-step SPD of LA91 alloy has been investigated, and the highest elongation of 563.7% was obtained by using the 8-pass equal channel angular extruded material, by the maximum strain rate sensitivity (Maxm) mode deformation. While in this research, the raw material in the as-extruded state is utilized. Constant velocity (Constv) and constant strain rate (CSR) modes are adopted for the first step of the deformation, respectively, with the elongation of the first step from 50% to 150%. The Maxm mode, in which the strain rate sensitivity m is always kept to be the maximum value, is applied to the second step. In addition, single-step tests by Constv, CSR and Maxm modes until fracture are conducted. The experimental temperature is 300°C, which was proved to be the optimum temperature for the SPD of this material in the previous research. The result shows that the 2-step method can greatly improve the superplasticity of the LA91 alloy, especially for the CSR mode deformation, and the maximum elongation obtained is 535.3%, by the CSR-Maxm mode, which is comparable to the optimum result in the previous research.

Abstract: This paper studies the effect of different solution temperature and quenching medium on Microstructure and hardness of Mg-9Li-4Al-1Zn-0.5Y alloy by means of optical microscope (OM), X-ray diffraction (XRD) and hardness testing. The results show that in the solution process, the higher of the solution temperature is, more of the second phase dissolved in β phase. In the quenching process, the higher of the cooling rate is, more of the second phase dissolved in the β phase precipitates from the super-saturation β matrix, which can greatly weaken the solution strengthening effect. The hardness of the investigated alloy reaches its highest value with solution treatment at 648K and water-quenched treatment, increased from 58HB to 108HB.

Abstract: Al-coated Mg-Li alloy rods and plates having a homogeneous coating layer of 180μm in thickness have been produced by hot extrusion of Mg-Li alloy billets together with Al disks. The Al-coated Mg-Li alloy exhibits an excellent corrosion resistance in a weight-loss test with a 0.5 mass% HCl aqueous solution, and it has been revealed by a potentiometric corrosion test with a 3 mass% NaCl aqueous solution that the Al-coated Mg-Li alloy has the same electric potential as that of pure Al. Al-coated Mg-Li alloy sheets produced by hot forging of the extruded plates exhibits good elongation of 22 %, 40 % and 130 % at room temperature, 200 °C and 300 °C, respectively.

Abstract: This work includes the comparison between corrosion resistance of MagLi4, MgLi7.5 and MgLi15 alloys in sodium chloride (0.15M NaCl) solution at 37°C. Results showed that the corrosion resistance is strongly determined by lithium content in the alloy. The worst corrosion resistance is typical for MgLi7.5 where the dual phase structure is observed. The magnesium - lithium alloys which contain less than 5% of Li and more than 11% (one phase structures) has got better corrosion resistance than dual phase structure magnesium – lithium alloys

Abstract: Casting Mg-Li alloy samples were subjected to annealing and aging treatment respectively, and the corrosion resistance of different samples was investigated by immersion test and electrochemical impedance spectroscopy measurement in 3.5% NaCl solution. The results show that the corrosion resistance of the as-cast sample is the best,the aged sample is the second, and the annealed sample is the worst to resist corrosion.

Abstract: The process of zinc immersion for Mg-Li alloy is researched in this paper. Through orthogonal experiments, the optimum process parameters are obtained. The microstructure and the composition of the Zn-dipped coating were measured with SEM, XRD, EDS and electrochemical testing. Results show that, the optimum process parameters are: concentration of main salt (ZnSO₄) is 40g/L; solution temperature is 60°C; dipping time is 5min. In addition, dipping time is the most influential factor, then is solution temperature, the last is the concentration of main salt.