A multiphase structure Mg-Ni-Nd hydrogen storage alloy based on in-situ activation method and its preparation method

Abstract

The present invention discloses a multiphase structure Mg-Ni-Nd hydrogen storage alloy based on in-situ activation method, and its component characteristics are that it simultaneously contains Nd4Mg 80 Ni8, Mg and Mg2Ni phases, and the volume fraction of the Nd4Mg 80 Ni8 phase is greater than 50%, the Mg phase is greater than 15%, and the sum of the Mg and Nd4Mg 80 Ni8 two phases is greater than 95%, and the rest is the Mg2Ni phase; the Nd4Mg 80 Ni8 phase decomposes in-situ during hydrogen absorption and desorption activation to form Mg, Mg2Ni and NdH 2.61 phase; among them, the Mg phase is a strip-shaped phase parallel to the extrusion direction, with a width of 2-5 μm; the Mg2Ni phase is a needle-shaped or granular phase, with a size of 0.5-2 μm, and is dispersedly distributed in the Nd4Mg 80 Ni8 matrix phase; the chemical formula satisfies Mg 100‑a‑b Ni a Nd b , 4.5 ≤ a < 9, 2 ≤ b < 4, a ≥ 2.25b. Its preparation method includes the following steps: 1. Melting of the Mg-Ni-Nd as-cast alloy; 2. Hot extrusion of the Mg-Ni-Nd as-cast alloy; 3. Filing and powder making of the Mg-Ni-Nd hot-extruded alloy; 4. Activation treatment of the Mg-Ni-Nd hot-extruded alloy powder. As an application of the hydrogen storage material, it has two hydrogen absorption and desorption platforms, the reversible hydrogen storage capacity is greater than 5.0 wt.%; at 300 °C, the hydrogen absorption and desorption cycle life is greater than 2900 times, and the capacity retention rate is greater than 80%.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogen storage materials, and particularly relates to a multiphase structure Mg-Ni-Nd hydrogen storage alloy based on an in-situ activation method and a preparation method thereof. Background Art

[0002] As a hydrogen storage material, metallic Mg has a hydrogen storage density as high as 7.6 wt.%, and is characterized by rich resources and low cost. However, such Mg-based hydrogen storage materials have the problem of poor cycling performance, that is, the hydrogen storage capacity and hydrogen storage kinetics decay during long-term hydrogen absorption and desorption cycles. The main reasons are that the key factor for the decay of the hydrogen storage capacity during the hydrogen absorption and desorption cycle is the oxidation of magnesium, the formation of thermodynamically inactive hydrides / metal phases, and the reduction of hydrogen absorption and desorption kinetics, resulting in the decay of the hydrogen storage capacity. The factor for the decay of hydrogen storage kinetics is the change in the microstructure of the material during the hydrogen absorption and desorption cycle, such as grain coarsening and the loss of catalytic phases of inactive sites during the high-temperature hydrogen absorption and desorption cycle, which causes the hydrogen absorption and desorption rate to slow down. To solve the above technical problems, common solutions are grain refinement and the introduction of catalysts.

[0003] The method of grain refinement has a certain effect on solving the problem of slow kinetics during the hydrogen absorption and desorption cycle. Its principle is to refine the particle and grain sizes of the Mg-based hydrogen storage material through a specific preparation process, increase the specific surface area of the reaction, and the formation of a high proportion of grain boundaries provides more hydrogen diffusion channels and reaction active sites for hydrogen absorption / desorption, significantly improving its hydrogen absorption and desorption kinetics. Currently, the common grain refinement methods include ball milling.

[0004] For example, in the existing literature 1, ("Hydrogen Storage Behavior and Performance of Multiple Cold-Rolled MgH2 / Nb2O5 Nanocomposite Powders", Processes, 2022, 10(5): 1017), a composite process of cold rolling and hydrogenation reaction ball milling is used to prepare ultrafine nanocrystalline MgH2 powder with a size of 8-18 nm. High-density lattice defects are introduced through cold rolling and ball milling processes to achieve nanocrystallization, improving the hydrogen absorption and desorption kinetic performance. Specifically, at 275 °C, the hydrogen storage capacity of MgH2 is 7.3 wt.% after 500 hydrogen absorption and desorption cycles.

[0005] The technical problems existing in this technical solution mainly include the following two problems:

[0006] 1. During the cycling process, the hydrogen absorption and desorption rate decays severely. It takes 600 hours to complete 500 hydrogen absorption and desorption cycles, that is, the average time for a single hydrogen absorption and desorption cycle is 1.2 hours. The reason is that grain refinement can be achieved through ball milling, enabling the grains to reach the nanoscale, which is the common concept of nanocrystallization in this field. Extremely high hydrogen absorption and desorption performance can be obtained during the first hydrogen absorption and desorption process. However, during long-term high-temperature hydrogen absorption and desorption cycles, the nanoscale grains will grow and coarsen into large grains, resulting in the disappearance of the nanocrystallization effect and further leading to a significant decrease in the hydrogen absorption and desorption rate.

[0007] 2. Due to the high energy consumption and complexity of the process caused by the ball milling method, high energy consumption is a common problem of the ball milling process. Moreover, this process requires cold rolling of Mg rods for 200 passes first, then hydrogenation reaction, followed by ball milling for 100 hours, and finally still requires cold rolling for 100 passes. Therefore, this technical solution has a particularly large number of steps, that is, the process is cumbersome.

[0008] Further analysis shows that Problem 1 and Problem 2 are highly correlated, that is, adopting the ball milling process will inevitably lead to technical problems such as nanocrystallization, high energy consumption, and a cumbersome process.

[0009] The method of introducing a catalyst has a certain effect on solving the problems of slow hydrogen absorption and desorption kinetics and poor cycling performance. The principle is that the introduced catalyst provides active sites for the hydrogen absorption and desorption reaction of Mg / MgH2, promotes the dissociation / recombination of hydrogen molecules, and increases the reaction rate; the catalyst can play a pinning role to ensure good structural stability of the material and improve the cycling performance.

[0010] For example, in the existing literature 2 (《Superior catalytic effect of nanocrystalline big-cube Zr2Ni metastable phase for improving the hydrogen sorption / desorption kinetics and cyclability of MgH2 powders》Energy, 2015, 91:274), first, Zr2Ni is annealed and then prepared into nanoparticles by ball milling for 150 h. At the same time, metallic Mg is hydrogenated by ball milling for 200 h to prepare nanocrystalline MgH2. Finally, using Zr2Ni as a catalyst, it is ball milled with MgH2 for 50 h to obtain a MgH2-10wt.% Zr2Ni composite material, achieving hydrogen absorption kinetics and cycling performance of absorbing 5.1wt.% hydrogen in 116 s and completely desorbing hydrogen in 613 s at 250°C. This technical solution shows that the introduction of a catalyst can effectively improve the hydrogen absorption / desorption kinetics and cycling performance. However, this technical solution is still based on the ball milling method, so there is still the inevitable problem of high energy consumption in the ball milling method. Specifically, this technical solution also has the technical problem of long duration - in the preparation process, only the ball milling process requires a total of 400 h to achieve the above performance.

[0011] In addition, the method of introducing a catalyst by the ball milling method also has the problem that the catalyst is distributed on the surface of metallic Mg. Therefore, during long-term cycling, the catalyst on the surface is prone to agglomeration and separation from the substrate, forming Mg / MgH2 particles without catalyst modification, resulting in a decrease in catalytic performance.

[0012] To overcome the problems of the above ball milling method, the preparation of hydrogen storage alloys based on the melting method can be adopted. First, the melting method has the characteristics of simple process and low cost. Moreover, the melting method can make alloying elements distributed inside the magnesium-based hydrogen storage material, playing a better catalytic role. However, the traditional conventional melting method has problems such as too large phase sizes and uneven distribution of elements inside the material.

[0013] In view of the problem of excessively large phase sizes in the above-mentioned traditional conventional smelting method, it can be solved by combining the smelting method with other processes. For example, in the existing literature 3, (《Improvement of hydrogen storage properties of Mg-Ni alloys by rare-earth addition》Materials Transactions, 2001, 42(4): 712), using pure Mg, pure Ni, and pure Nd powders as raw materials, through the process method of smelting - cold quenching - mechanical crushing, Mg 86 Ni 10 Nd4 hydrogen storage alloy was prepared. The obtained hydrogen storage alloy consists of a multiphase structure of Mg, Mg2Ni, and Mg 12 Nd. After hydrogenation, the Nd2H5 phase with a catalytic effect is in-situ formed; combining the cold quenching process significantly refines the phase size. After activation, 80% of the maximum hydrogen storage capacity can be dehydrogenated within 5 minutes at 300°C. Since this technical solution focuses on improving the hydrogen absorption and desorption kinetics performance, too much Ni and Nd elements are added, directly resulting in a small content of Mg elements, and further resulting in a reversible hydrogen storage capacity of only 4.80 wt.% for this magnesium-based hydrogen storage alloy, which cannot meet the application requirements; in addition, this magnesium-based hydrogen storage alloy also has the problem of poor cycling performance. After only 9 cycles, the hydrogen storage capacity significantly decays to 4.5 wt.%. The reason is that through this technical solution, only two binary phases, Mg2Ni and Mg 12 Nd, can be formed in the magnesium-based hydrogen storage alloy, which further leads to uneven distribution of Ni and Nd elements in the alloy due to the phase composition.

[0014] In view of the problem of uneven distribution of Ni and Nd elements in the alloy, it can be overcome by forming the Mg-Ni-Nd ternary intermetallic compound phase. For example, in the existing literature 4, (《The new ternary intermetallic NdNiMg5: Hydrogen sorption properties and more》Materials Research Bulletin, 2015, 61: 275), using pure Mg, pure Ni, and pure Nd as raw materials for smelting, and after the smelting is completed, annealing is carried out under the conditions of an annealing temperature of 600°C and an annealing time of 10 days. The Mg 72 Ni 14 Nd 14 alloy containing the ternary intermetallic compound phase NdNiMg5 was successfully prepared. Subsequently, during the hydrogen absorption and desorption process, NdNiMg5 is in-situ formed into NdH 2.61-Mg-Mg2Ni composite material. It realizes a maximum hydrogen storage capacity of 3.2 wt.% hydrogen absorption in 500 s at a temperature of 300 °C and a hydrogen pressure of 1 MPa, and a kinetic performance of complete hydrogen desorption in 300 s at a temperature of 300 °C. In order to form the Mg-Ni-Nd ternary intermetallic compound phase, a large amount of Ni element and Nd element are added in this technical solution. Therefore, the same technical problem as that in the aforementioned existing literature 3 appears - the relatively low content of Mg element results in a maximum hydrogen storage capacity of only 3.2 wt.%; in addition, since the formed Mg-Ni-Nd ternary intermetallic compound phase still cannot meet the uniform distribution of Nd element, this technical solution additionally adopts an annealing operation - as aforementioned, this annealing operation needs to be carried out at a high temperature of 600 °C for 10 days, resulting in a significant increase in energy consumption and time cost.

[0015] According to the prior art, the technical problems that need to be solved currently are manifested in the following three aspects in terms of performance:

[0016] 1. The reversible hydrogen storage capacity is higher than 5.0 wt.%;

[0017] 2. Maintain high hydrogen absorption and desorption kinetic performance during the hydrogen absorption and desorption cycle;

[0018] 3. Reduce the process difficulty, and reduce the raw material cost and time of production. Summary of the Invention

[0019] The object of the present invention is to provide a multiphase structure Mg-Ni-Nd hydrogen storage alloy based on in-situ activation method and its preparation method. Aiming at the prior art problems, the present invention constructs a thermodynamic phase diagram database of the Mg-Ni-Nd alloy system, selects a Mg-Ni-Nd hydrogen storage alloy with a specific composition. On the one hand, the content of Mg element in the Mg-Ni-Nd alloy is increased to improve the reversible hydrogen storage capacity. On the other hand, the ratio of Ni element and Nd element is adjusted to achieve the uniform distribution of elements, thereby improving the hydrogen absorption and desorption kinetic performance; at the same time, the process of refining the material grains is combined with melting to overcome the technical problems caused by high-time-consuming and high-energy-consuming processes such as annealing heat treatment and ball milling.

[0020] The basic principle of the present invention is as follows:

[0021] 1. According to the requirements of the hydrogen storage performance of the Mg-Ni-Nd alloy, combined with the knowledge of the thermodynamic phase diagram, select a rich Mg corner composition region that simultaneously contains Nd4Mg 80 Ni8, Mg and Mg2Ni phases. Increase the phase interface through the multiphase structure, and further increase the hydrogen atom transmission channels;

[0022] 2. Utilize the Nd4Mg 80 Ni8 phase can in-situ form NdH with catalytic effect after hydrogen absorption and desorption activation 2.61The characteristics of the Mg and Mg2Ni phases are utilized to increase the Nd and Ni elements, as well as the dispersion of the NdH 2.61 phase. Additionally, to ensure the above-mentioned dispersion, Nd4Mg 80 Ni8 in the Mg-Ni-Nd alloy for hydrogen storage must be the matrix phase, and the volume fraction of the phase should be greater than 50%;

[0023] 3. To increase the reversible hydrogen storage capacity of the Mg-Ni-Nd alloy for hydrogen storage, it can be overcome by increasing the content of the Mg phase with a high theoretical reversible hydrogen storage capacity. Specifically, the Mg phase needs to be greater than 15% to meet the requirement of a reversible hydrogen storage capacity greater than 5.0 wt.%. At the same time, to ensure the hydrogen absorption and desorption kinetics performance, the sum of the volume fractions of the Nd4Mg 80 Ni8 and Mg phases is greater than 95%;

[0024] 4. Based on the melting method, the combination of hot extrusion deformation + file filing powder-making process and activation treatment is used to reduce the process difficulty. Among them,

[0025] The hot extrusion deformation + file filing powder-making process can refine the sizes of the Mg and Mg2Ni phases in the Mg-Ni-Nd alloy, improving the hydrogen absorption and desorption kinetics performance of Mg-Ni-Nd; and introducing crystal defects such as vacancies, dislocations, and sub-grain boundaries as pinning sites, thereby enhancing the structural stability of the hydrogen storage alloy during the hydrogen absorption and desorption cycles, and further improving its cycling performance;

[0026] The activation treatment, as described above, can achieve in-situ decomposition to form Mg, Mg2Ni, and NdH 2.61 phases. While forming the catalytic NdH 2.61 phase, it increases the Nd and Ni elements, as well as the dispersion of the NdH 2.61 phase.

[0027] To achieve the above objectives, the present invention adopts the following technical solutions:

[0028] A multiphase structure Mg-Ni-Nd hydrogen storage alloy based on the in-situ activation method, the composition of the Mg-Ni-Nd hydrogen storage alloy contains, simultaneously, Nd4Mg 80 Ni8, Mg, and Mg2Ni phases, and the volume fraction of the Nd4Mg 80 Ni8 phase is greater than 50%, the Mg phase is greater than 15%, the sum of Mg and Nd4Mg 80 Ni8 is greater than 95%, and the rest is the Mg2Ni phase;

[0029] The Nd4Mg 80 Ni8 phase undergoes in-situ decomposition during hydrogen absorption and desorption activation to form Mg, Mg2Ni, and NdH 2.61 phase;

[0030] In the Mg-Ni-Nd hydrogen storage alloy, the Mg phase is a strip phase parallel to the extrusion direction, with a width of 2-5 μm, and the Mg2Ni phase is a needle-shaped or particle phase with a size of 0.5-2 μm, dispersed in the Nd4Mg 80 Ni8 substrate phase;

[0031] The chemical formula of the Mg-Ni-Nd hydrogen storage alloy satisfies Mg 100-a-b Ni a Nd b , a and b represent atomic ratio, 4.5≤a<9, 2≤b<4, a≥2.25b.

[0032] A method for preparing a multiphase structured Mg-Ni-Nd hydrogen storage alloy based on an in-situ activation method comprises the following steps:

[0033] Step 1, smelting of Mg-Ni-Nd cast alloy, selecting Mg, Mg-30Ni and Mg-50Nd as raw materials, and adding Mg as loss, under certain conditions, smelting Mg-30Ni, and adding Mg and Mg-50Nd to obtain alloy melt, and then, under certain conditions, keeping the alloy melt warm, casting and cooling naturally after the insulation is completed, so as to obtain Mg-Ni-Nd cast alloy, referred to as Mg-Ni-Nd-ca;

[0034] The composition requirement is to contain Nd4Mg 80 Ni8 phase, Mg phase and Mg2Ni phase; and Nd4Mg 80 The volume fraction of Ni8 phase is greater than 50%, the volume fraction of Mg phase is greater than 15%, and the volume fraction of Mg and Nd4Mg 80 The sum of the two Ni8 phases is greater than 95%, and the rest is the composition area of ​​the Mg2Ni phase;

[0035] The chemical formula is Mg 100-a-b Ni a Nd b , a and b represent atomic ratios, 4.5≤a<9, 2≤b<4, a≥2.25b

[0036] The smelting temperature of the smelting is 750°C; the insulation condition is that the insulation temperature is 700°C and the insulation time is 10-20min;

[0037] Step 2, hot extrusion of the Mg-Ni-Nd cast alloy, after machining the Mg-Ni-Nd-ca obtained in step 1 into a cylinder, preheating it under certain conditions, and after preheating, hot extrusion is performed under certain conditions to achieve hot extrusion deformation, and after hot extrusion, water quenching is immediately performed to obtain a block of Mg-Ni-Nd hot extruded alloy, referred to as Mg-Ni-Nd-ex;

[0038] The preheating conditions are: the preheating temperature is 400-450°C and the preheating time is 10-30min;

[0039] The hot extrusion conditions are as follows: the hot extrusion temperature is 400°C, the hot extrusion ratio is 12, and the hot extrusion speed is 0.4 m / s;

[0040] Step 3, filing and powdering of the Mg-Ni-Nd hot extruded alloy, after removing the surface oxide scale of the Mg-Ni-Nd-ex obtained in step 2, filing and powdering the blocky Mg-Ni-Nd-ex with a file in air to obtain the powder of the Mg-Ni-Nd hot extruded alloy, referred to as Mg-Ni-Nd-po;

[0041] Step 4, activation treatment of Mg-Ni-Nd hot extruded alloy powder, the Mg-Ni-Nd-po obtained in step 3 is subjected to hydrogen absorption activation under certain conditions to obtain a hydrogen absorbing Mg-Ni-Nd alloy, referred to as Mg-Ni-Nd-ab, and then, hydrogen is released under certain conditions to obtain a multiphase structure Mg-Ni-Nd hydrogen storage alloy based on the in-situ activation method.

[0042] The conditions for hydrogen absorption activation are: hydrogen absorption activation pressure of 4 MPa, hydrogen absorption activation temperature of 360°C, and hydrogen absorption activation time of 4 hours;

[0043] The hydrogen release condition is as follows: under vacuum conditions, the hydrogen release temperature is 360°C.

[0044] An application of a multi-phase structured Mg-Ni-Nd hydrogen storage alloy based on an in-situ activation method as a hydrogen storage material, wherein the Mg-Ni-Nd hydrogen storage alloy has two hydrogen absorption and desorption platforms, and a reversible hydrogen storage capacity of greater than 5.4wt.%;

[0045] The Mg-Ni-Nd hydrogen storage alloy absorbs more than 4.0 wt.% of hydrogen in 1 minute at 300°C and 3 MPa; and releases more than 5.0 wt.% of hydrogen in 5 minutes at 300°C and vacuum conditions;

[0046] When the hydrogen storage capacity of the Mg-Ni-Nd hydrogen storage alloy is maintained above 5.0wt.%, the number of cycles exceeds 1200 times;

[0047] When the capacity retention rate of the Mg-Ni-Nd hydrogen storage alloy is greater than 80%, the number of cycles exceeds 2900.

[0048] The technical effects of the present invention are as follows:

[0049] XRD analysis shows that the Mg-Ni-Nd hot extruded alloy contains Nd4Mg 80The Ni8 phase, Mg phase, and Mg2Ni phase. The contents of each phase were obtained by Rietveld refinement, and the measured results of the phase composition and content were consistent with the theoretical calculation results. The XRD results after hydrogen absorption and desorption activation showed that Nd4Mg 80 The Ni8 phase decomposed in-situ during hydrogen absorption and desorption to form Mg, Mg2Ni, and NdH 2.61 phase. Among them, the NdH 2.61 phase was an irreversible transformation and was uniformly distributed in the matrix, improving the hydrogen absorption and desorption kinetics and cycling performance of Mg-Ni-Nd as a catalyst and pinning site.

[0050] It can be seen from the SEM test that in the Mg-Ni-Nd hot-extruded alloy, Nd4Mg 80 The Ni8 phase was the matrix phase; the Mg phase was a strip-shaped phase parallel to the extrusion direction with a width of 2-5 μm; the Mg2Ni phase was extruded and broken into needle-shaped or granular phases with a size of 0.5-2 μm; and the Mg phase and Mg2Ni phase were dispersedly distributed in Nd4Mg 80 The Ni8 matrix phase.

[0051] It can be seen from the hydrogen storage performance test that the multiphase structure Mg-Ni-Nd hydrogen storage alloy based on the in-situ activation method has two hydrogen absorption and desorption platforms, a reversible hydrogen storage capacity greater than 5.0 wt.%, and a high hydrogen storage capacity; at 300 °C and 3 MPa, the hydrogen absorption amount in 1 min is greater than 4.0 wt.%; at 300 °C and under vacuum conditions, the hydrogen desorption amount in 5 min is greater than 5.0 wt.%, with a fast hydrogen absorption and desorption rate; at 300 °C, the hydrogen absorption and desorption cycle life is greater than 2900 times, and the capacity retention rate is greater than 80%, with a long cycle life.

[0052] The present invention has the following advantages compared with the prior art:

[0053] 1. According to the thermodynamic phase diagram database of the Mg-Ni-Nd alloy system, a Mg-Ni-Nd hydrogen storage alloy with a specific composition containing Nd4Mg 80 Ni8, Mg, and Mg2Ni phases is selected; and, Nd4Mg 80 The Ni8 phase in-situ forms catalytic NdH 2.61 after hydrogen absorption and desorption activation, realizing the dispersion of Nd elements and Ni elements, as well as the NdH 2.61 phase, and improving the hydrogen absorption and desorption kinetics and cycling performance of the Mg-Ni-Nd hydrogen storage alloy.

[0054] 2. The Mg-Ni-Nd hydrogen storage alloy prepared by the present invention based on the preparation method of induction melting, hot extrusion deformation, filing and powder making, and activation treatment. The hot extrusion deformation + filing and powder making process realizes the refinement of the material grains. The preparation process is simple, the operation is simple, suitable for mass production, and realizes the advantages of high capacity, fast rate, and long life of Mg-Ni-Nd. Brief Description of the Drawings

[0055] Figure 1 It is the isothermal section phase diagram and composition region of the Mg-rich corner of the Mg-Ni-Nd system at 400 °C;

[0056] Figure 2 It is the solidification path of the Mg-Ni-Nd alloy corresponding to Example 1 and Example 2 and the phase fraction changes of Mg, Mg2Ni, and Nd4Mg 80 Ni8 phases during solidification, where Figure 2 a is Example 1, Figure 2 b is Example 2;

[0057] Figure 3 a is the composition region to which Comparative Example 1 belongs, Figure 3 b is the solidification path of the Mg-Ni-Nd alloy corresponding to Comparative Example 1 and the phase fraction changes of Mg, Mg2Ni, and Nd4Mg 80 Ni8 phases during solidification;

[0058] Figure 4 a is the composition region to which Comparative Example 2 belongs, Figure 4 b is the solidification path of the Mg-Ni-Nd alloy corresponding to Comparative Example 2 and the phase fraction changes of Mg, Mg2Ni, and Nd4Mg 80 Ni8 phases during solidification;

[0059] Figure 5 It is the XRD pattern and Rietveld refinement results of the Mg-Ni-Nd hot-extruded alloy powder of Example 1;

[0060] Figure 6 It is the SEM micrograph of the Mg-Ni-Nd hot-extruded alloy of Example 1;

[0061] Figure 7 It is the PCT curve of Example 1 at 300 °C;

[0062] Figure 8 It is the hydrogen absorption and desorption kinetics of Example 1 at 300 °C, where Figure 6 a is the hydrogen absorption kinetics under a hydrogen pressure of 3 MPa, Figure 6 b is the hydrogen desorption kinetics under vacuum;

[0063] Figure 9 It is the cyclic life test results of Example 1 at 300 °C. Detailed Description of the Invention

[0064] The present invention further elaborates on the content of the present invention through examples in combination with the accompanying drawings of the specification, but it is not a limitation of the present invention.

[0065] In order to theoretically obtain the phases existing in the Mg-Ni-Nd alloy, first, the phase equilibrium relationship of the Mg-Ni-Nd system was experimentally determined, and a thermodynamic phase diagram database of the Mg-Ni-Nd system was constructed; based on the thermodynamic phase diagram database of the Mg-Ni-Nd system, the isothermal section phase diagram of the Mg-rich corner of the Mg-Ni-Nd system at 400 °C was obtained by thermodynamic calculation, and the composition regions meeting different requirements were marked.

[0066] Region 1, as Figure 1 shown by the composition region within the dotted line box in 80 , meets the following requirements: Region 1 simultaneously contains the Nd4Mg 80 Ni8 phase, the Mg phase, and the Mg2Ni phase; and, the volume fraction of the Nd4Mg 80 Ni8 phase is greater than 50%, the Mg phase is greater than 15%, and the sum of the two phases of Mg and Nd4Mg

[0067] Ni8 is greater than 95%, and the remaining is the composition region of the Mg2Ni phase. 88.5 Ni 8.1 Nd 3.4 Two compositions, namely Mg 91.5 Ni 6.0 Nd 2.5 and Mg 80 Ni Figure 2 a Figure 2 b, are selected within the above Region 1 and used as the compositions of Example 1 and Example 2 respectively; and, in order to clarify the solidification paths of the alloys corresponding to Example 1 and Example 2, the changes in the phase fractions of the Mg, Mg2Ni, and Nd4Mg

[0068] Ni8 phases during the solidification process are calculated using the thermodynamic phase diagram to obtain the equilibrium solidification path diagrams, as shown in

[0069] Region 2, as Figure 3 shown in 80 a, meets the following requirements: It simultaneously contains the Nd4Mg

[0070] Ni8 phase, the Mg phase, and the Mg2Ni phase; 80 However, the volume fraction of the Nd4Mg

[0071] One composition, namely Mg 94.0 Ni 5.0 Nd, is selected within the above Region 2 and used as the composition of Comparative Example 1; and, in order to clarify the solidification path of the alloy corresponding to Comparative Example 1, the Mg, Mg2Ni, and Nd4Mg 80The phase fraction change of the Ni8 phase is calculated using the thermodynamic phase diagram to obtain the equilibrium solidification path diagram. As shown in Figure 3 Figure b, the volume fractions of each calculated phase of the alloy corresponding to Comparative Example 1 at 400 °C are shown in Table 1.

[0072] Region 3, as shown in Figure 4 Figure a, meets the following requirements: It contains both the Nd4Mg 80 Ni8 phase, Mg phase, and Mg2Ni phase; however, the volume fraction of the Mg phase is less than 15%.

[0073] One composition is selected within the above Region 3, which is Mg 85.9 Ni 10.5 Nd 3.6 , as the composition of Comparative Example 2; and, in order to clarify the solidification path of the alloy corresponding to Comparative Example 1, during the solidification process, the phase fraction changes of the Mg, Mg2Ni, and Nd4Mg 80 Ni8 phases are calculated using the thermodynamic phase diagram to obtain the equilibrium solidification path diagram. As shown in Figure 4 Figure b, the volume fractions of each calculated phase of the alloy corresponding to Comparative Example 2 at 400 °C are shown in Table 1.

[0074] Table 1. Summary table of the types and volume fractions of phases in the Mg-Ni-Y-Nd alloy calculated by the thermodynamic phase diagram

[0075]

[0076] Example 1

[0077] A preparation method of a multiphase structure Mg-Ni-Nd hydrogen storage alloy based on the in-situ activation method with the chemical formula Mg 88.5 Ni 8.1 Nd 3.4 specifically includes the following steps:

[0078] Step 1, melting of the Mg-Ni-Nd as-cast alloy. Selecting within Region 1, meeting the condition of the chemical formula Mg 88.5 Ni 8.1 Nd 3.4 , using Mg, Mg-30Ni, and Mg-50Nd as raw materials, and additionally adding 8 wt.% of Mg as loss. Under the condition of a melting temperature of 750 °C, Mg-30Ni is melted, and Mg and Mg-50Nd are added to obtain an alloy melt. Then, under the conditions of a holding temperature of 700 °C and a holding time of 10 min, the alloy melt is held. After holding, it is cast and naturally cooled to obtain the Mg-Ni-Nd as-cast alloy, simply referred to as Mg-Ni-Nd-ca;

[0079] Step 2, hot extrusion of the Mg-Ni-Nd cast alloy, after machining the Mg-Ni-Nd-ca obtained in step 1 into a cylinder, preheating it at a preheating temperature of 400°C and a preheating time of 15 minutes, after preheating, hot extrusion is performed at a hot extrusion temperature of 400°C, a hot extrusion ratio of 12, and a hot extrusion speed of 0.4 m / s to achieve hot extrusion deformation, and immediately water quenching is performed after hot extrusion to obtain a block of Mg-Ni-Nd hot extruded alloy, referred to as Mg-Ni-Nd-ex;

[0080] Step 3, filing and powdering of the Mg-Ni-Nd hot extruded alloy, after removing the surface oxide scale of the Mg-Ni-Nd-ex obtained in step 2, filing and powdering the blocky Mg-Ni-Nd-ex with a file in air to obtain the powder of the Mg-Ni-Nd hot extruded alloy, referred to as Mg-Ni-Nd-po;

[0081] Step 4, activation treatment of the Mg-Ni-Nd hot extruded alloy powder, the Mg-Ni-Nd-po obtained in step 3 is hydrogen activated under the conditions of a hydrogen absorption activation pressure of 4 MPa, a hydrogen absorption activation temperature of 360°C, and a hydrogen absorption activation time of 4 hours to obtain a hydrogen-absorbing Mg-Ni-Nd alloy, referred to as Mg-Ni-Nd-ab. Then, under vacuum conditions, hydrogen is desorbed at a desorption temperature of 360°C to obtain a multiphase structure Mg-Ni-Nd hydrogen storage alloy based on an in-situ activation method, referred to as Mg-Ni-Nd-1#.

[0082] In order to prove the consistency between the measured results and the theoretical calculation results of the phase composition and content of the multiphase structure Mg-Ni-Nd hydrogen storage alloy based on the in-situ activation method, the Mg-Ni-Nd-po obtained in step 3 was subjected to XRD test and Rietveld refinement. The test results are shown in Figure 5 As shown in a, Mg-Ni-Nd-po contains Nd4Mg 80 The characteristic peaks of Ni8 phase, Mg phase and Mg2Ni phase; and, after calculation, the mass fractions are: Nd4Mg 80 The Ni8 phase is 78.53wt.%, the Mg phase is 18.99wt.%, and the Mg2Ni phase is 2.48wt.%. The test results show that the measured results of the phase composition and content are consistent with the theoretical calculation results.

[0083] In order to demonstrate the effect of activation treatment on the phase composition and content, XRD tests and Rietveld refinement were performed on Mg-Ni-Nd-ab and Mg-Ni-Nd-1# in step 4.

[0084] The XRD test results of Mg-Ni-Nd-ab are as follows Figure 5As shown in Fig. b, Mg-Ni-Nd-ab simultaneously contains the characteristic peaks of MgH2, Mg2NiH4, and NdH2 phases; and, through calculation, the mass fractions are as follows: the MgH2 phase is 58.39 wt.%, the Mg2NiH4 phase is 26.60 wt.%, and NdH 2.61 phase is 15.01 wt.%.

[0085] The XRD test results of Mg-Ni-Nd-1# are as Figure 5 shown in Fig. c. Mg-Ni-Nd-1# simultaneously contains the characteristic peaks of Mg, Mg2Ni, and NdH 2.61 phases. And, through calculation, the mass fractions are as follows: the Mg phase is 51.90 wt.%, the Mg2Ni phase is 31.18 wt.%, and NdH 2.61 phase is 16.92 wt.%.

[0086] The XRD test results of Mg-Ni-Nd-po, Mg-Ni-Nd-ab, and Mg-Ni-Nd-1# indicate that

[0087] during the hydrogen absorption activation process, the Mg phase absorbs hydrogen to form MgH2, the Mg2Ni phase absorbs hydrogen to form Mg2NiH4. At the same time, the Nd4Mg 80 Ni8 phase decomposes in-situ to form the MgH2 phase, Mg2NiH4 phase, and NdH 2.61 phase after hydrogen absorption;

[0088] during the hydrogen desorption activation process, the MgH2 phase desorbs hydrogen to form the Mg phase, the Mg2NiH4 phase desorbs hydrogen to form the Mg2Ni phase. However, the NdH 2.61 phase remains unchanged.

[0089] Therefore, the phase transformation reaction between the Mg phase and the MgH2 phase, and between the Mg2Ni phase and the Mg2NiH4 phase is reversible; the NdH 2.61 phase is an irreversible transformation and acts as a catalyst to improve the hydrogen absorption and desorption kinetic performance of the Mg-Ni-Nd hydrogen storage alloy.

[0090] To further prove the microstructure, phase morphology, and distribution of Mg-Ni-Nd-ex, SEM and EDS tests were carried out on Mg-Ni-Nd-ex obtained in step 2. The test results are as Figure 6 shown. In the Mg-Ni-Nd hot-extruded alloy, the Nd4Mg 80 Ni8 phase is the matrix phase; the Mg phase is a strip-shaped phase parallel to the extrusion direction with a width of 2 - 5 μm; the Mg2Ni phase is extruded and broken into needle-shaped or granular phases with a size of 0.5 - 2 μm; and, the Mg phase and the Mg2Ni phase are dispersedly distributed in the Nd4Mg 80 Ni8 matrix phase.

[0091] To prove the reversible hydrogen storage capacity of Mg-Ni-Nd-1#, PCT tests were conducted. The test results are as follows: Figure 7 As shown, Mg-Ni-Nd-1# has two PCT platforms for hydrogen absorption and desorption. This phenomenon indicates that there are two phases reacting with hydrogen during the hydrogen absorption and desorption processes;

[0092] The low PCT platform with a hydrogen storage capacity range of 0 - 4.35 wt.% is the hydrogen absorption and desorption platform of Mg / MgH2;

[0093] The high PCT platform with a hydrogen storage capacity range of 4.35 - 5.40 wt.% is the hydrogen absorption and desorption platform of Mg2Ni / Mg2NiH4;

[0094] Meanwhile, the PCT test results also show that at 300 °C, the reversible hydrogen storage capacity is 5.40 wt.%. Therefore, Mg-Ni-Nd-1# has a high reversible hydrogen storage capacity.

[0095] To prove the hydrogen absorption and desorption kinetic performance of Mg-Ni-Nd-1#, hydrogen absorption and desorption kinetic tests were conducted. The specific conditions for the hydrogen absorption and desorption kinetic tests are as follows: for hydrogen absorption, the temperature is 300 °C, the hydrogen pressure is 3 MPa, and the hydrogen absorption time is 30 min; for hydrogen desorption, the temperature is 300 °C, the hydrogen pressure is under vacuum conditions, and the hydrogen desorption time is 10 min.

[0096] The hydrogen absorption test results are as follows: Figure 8 as shown in Figure a and Table 2, the hydrogen absorption amount in 1 min at 300 °C and 3 MPa is 4.62 wt.%, and the total hydrogen absorption amount within 30 min is 5.18 wt.%, which is 96% of the reversible hydrogen storage capacity;

[0097] The hydrogen desorption test results are as follows: Figure 8 as shown in Figure b and Table 2, under 300 °C and vacuum conditions, the hydrogen desorption amount within 5 min is 5.12 wt.%,

[0098] The test results show that Mg-Ni-Nd-1# has good hydrogen absorption and desorption kinetic performance.

[0099] Table 2. Summary table of reversible hydrogen storage capacity and hydrogen absorption and desorption kinetics of Mg-Ni-Y-Nd alloys with different compositions

[0100]

[0101] Among them, C H,max is the maximum reversible hydrogen storage capacity; C ab 1min is the hydrogen absorption amount in 1 min; C ab 30min is the hydrogen absorption amount in 30 min;

[0102] C de 5minIt is the hydrogen release amount in 5 min.

[0103] To prove the cycling performance of Mg-Ni-Nd-1#, a cycling test was carried out. The specific method of the cycling test was to repeat the hydrogen absorption and desorption kinetics test. The test results are as Figure 9 shown.

[0104] At the 115th cycle, the hydrogen storage capacity of Mg-Ni-Nd-1# reached the maximum value, which was 5.44 wt.%;

[0105] At the 1220th cycle, the hydrogen storage capacity of Mg-Ni-Nd-1# was 5.01 wt.%, and the hydrogen storage capacity remained above 5.0 wt.%;

[0106] At the 2943rd cycle, the hydrogen storage capacity of Mg-Ni-Nd-1# was 4.39 wt.%, that is, the capacity retention rate was 80.6%;

[0107] The test results show that Mg-Ni-Nd-1# has good hydrogen absorption and desorption cycling stability, and the cycling life is more than 2900 times.

[0108] Based on the test results of Example 1, the following conclusions can be obtained:

[0109] 1. The measured results of the phase composition and content of the Mg-Ni-Nd alloy are consistent with the calculation results based on the thermodynamic phase diagram.

[0110] 2. When the Mg-Ni-Nd alloy satisfies the conditions of simultaneously containing the Nd4Mg 80 Ni8 phase, the Mg phase and the Mg2Ni phase; and, the volume fraction of the Nd4Mg 80 Ni8 phase is greater than 50%, the Mg phase is greater than 15%, the sum of the Mg and Nd4Mg 80 Ni8 two phases is greater than 95%, and the rest is the Mg2Ni phase in the composition region, the technical effects of both high hydrogen storage capacity, fast hydrogen absorption and desorption rate and long cycling life can be achieved.

[0111] 3. It should be particularly noted that the technical effect of long cycling life is obtained under the conditions of a specific hydrogen absorption time of 30 min and a hydrogen desorption time of 10 min, that is, good hydrogen absorption and desorption kinetics still exist during the cycling process.

[0112] To prove the influence of the alloy composition, that is, the selected composition region on the hydrogen storage capacity and hydrogen absorption and desorption kinetics, Comparative Example 1 and Comparative Example 2 are provided, which are Region 2 and Region 3 outside Region 1 respectively. The specific Comparative Example 1 is Mg 94.0 Ni 5.0 Nd, and Comparative Example 2 is Mg 85.9 Ni 10.5 Nd 3.6 .

[0113] Comparative Example 1

[0114] A preparation method of a Mg-Ni-Nd hydrogen storage alloy with the chemical formula Mg 94.0 Ni 5.0 Nd. The steps that are not specifically described in detail are the same as those in Example 1. The difference lies in that: the selected area in Step 1 is Area 2, and the satisfied chemical formula is Mg 94.0 Ni 5.0 Nd, and the obtained material is simply referred to as Mg-Ni-Nd-2#.

[0115] The PCT test results of Mg-Ni-Nd-2# are shown in Table 2. Under the condition of 300 °C, the reversible hydrogen storage capacity is 6.45 wt.%. Comparing with the test results of Example 1, it can be seen that the reversible hydrogen storage

[0116] capacity of Comparative Example 1 is increased by 1.05 wt.%. The reason is that the volume fraction of the Mg phase in Comparative Example 1 is higher than that in Example 1, reaching 66.8%, so the reversible hydrogen storage capacity is higher.

[0117] In the hydrogen absorption and desorption kinetic performance test results of Mg-Ni-Nd-2#

[0118] The hydrogen absorption test results are shown in Table 2. At 300 °C and 3 MPa, the hydrogen absorption amount in 1 min is 2.72 wt.%, and the total hydrogen absorption amount within 30 min is 4.49 wt.%, which is 69.6% of the reversible hydrogen storage capacity;

[0119] The hydrogen desorption test results are shown in Table 2. Under the conditions of 300 °C and vacuum, the hydrogen desorption amount within 5 min is 4.32 wt.%.

[0120] Comparing with the test results of Example 1, it can be seen that the hydrogen absorption amount in 1 min of Comparative Example 1 is reduced by 1.90 wt.%, the total hydrogen absorption amount within 30 min is reduced by 0.69 wt.%, and the hydrogen desorption amount within 5 min is reduced by 0.80 wt.%, that is, the hydrogen absorption and desorption kinetic performance of Comparative Example 1 is poor. The reason is that the volume fraction of the Nd4Mg 80 Ni8 phase in Comparative Example 1 is lower than that in Example 1, being 24.9%, resulting in limited in-situ formation of the NdH 2.61 phase during the activation treatment, and finally reducing the hydrogen absorption and desorption kinetics of the Mg-Ni-Nd hydrogen storage alloy.

[0121] Comprehensively comparing Example 1 and Comparative Example 1, it can be seen that although Comparative Example 1 can increase the reversible hydrogen storage capacity, the hydrogen absorption and desorption kinetics will be greatly reduced.

[0122] Therefore, when Nd4Mg 80When the volume fraction of the Ni8 phase is less than 50% and the Mg phase is the matrix phase, it directly leads to uneven distribution of Ni and Nd elements, fails to effectively play a catalytic role, and thus significantly reduces the hydrogen absorption and desorption kinetics of the Mg-Ni-Nd hydrogen storage alloy.

[0123] Comparative Example 2

[0124] A preparation method of a Mg-Ni-Nd hydrogen storage alloy with the chemical formula Mg 85.9 Ni 10.5 Nd 3.6 is the same as that of Example 1 for the steps not specifically described. The difference lies in that: the selected area in Step 1 is Area 3, and the satisfied chemical formula is Mg 85.9 Ni 10.5 Nd 3.6 , and the obtained material is simply referred to as Mg-Ni-Nd-3#.

[0125] The PCT test results of Mg-Ni-Nd-3# are shown in Table 2. Under the condition of 300 °C, the reversible hydrogen storage capacity is 4.93 wt.%. Comparing with the test results of Example 1, the reversible hydrogen storage capacity of Comparative Example 2 is reduced by 0.47 wt.%. The reason is that the volume fraction of the Mg phase in Comparative Example 2 is lower than that in Example 1, only 2.8%, so the reversible hydrogen storage capacity is lower.

[0126] In the hydrogen absorption and desorption kinetic performance test results of Mg-Ni-Nd-3#,

[0127] The hydrogen absorption test results are shown in Table 2. At 300 °C and 3 MPa, the hydrogen absorption amount in 1 min is 4.06 wt.%, and the total hydrogen absorption amount within 30 min is 4.82 wt.%, which is 95.8% of the reversible hydrogen storage capacity;

[0128] The hydrogen desorption test results are shown in Table 2. Under the conditions of 300 °C and vacuum, the hydrogen desorption amount within 5 min is 4.68 wt.%.

[0129] Comparing with the test results of Example 1, the hydrogen absorption amount in 1 min of Comparative Example 2 is reduced by 0.56 wt.%, the total hydrogen absorption amount within 30 min is reduced by 0.36 wt.%, and the hydrogen desorption amount within 5 min is reduced by 0.44 wt.%. That is, the hydrogen absorption and desorption kinetic performance of Comparative Example 2 is poor. The reason is that the reversible hydrogen storage capacity of Comparative Example 2 is reduced, resulting in a decrease in the hydrogen absorption and desorption amount per unit time, which will reduce the hydrogen absorption and desorption kinetics of the Mg-Ni-Nd hydrogen storage alloy.

[0130] Therefore, in terms of both the reversible hydrogen storage capacity and the hydrogen absorption and desorption kinetics, Example 1 is superior to Comparative Example 2.

[0131] Therefore, when the volume fraction of the Mg phase is less than 15%, the reversible hydrogen storage capacity of the Mg-Ni-Nd hydrogen storage alloy will be significantly reduced, resulting in a decrease in the hydrogen absorption and desorption amount per unit time, and further reducing the hydrogen absorption and desorption kinetics of the Mg-Ni-Nd hydrogen storage alloy.

[0132] Example 2

[0133] A preparation method of a multiphase structure Mg-Ni-Nd hydrogen storage alloy based on in-situ activation method with the chemical formula of Mg 91.5 Ni 6.0 Nd 2.5 The steps that are not specifically described in detail are the same as those in Example 1. The difference lies in that: the selected area in Step 1 is Area 1, and the satisfied chemical formula is Mg 91.5 Ni 6.0 Nd 2.5 , and the obtained material is simply referred to as Mg-Ni-Nd-4#.

[0134] The PCT test results of Mg-Ni-Nd-4# are shown in Table 2. Under the condition of 300 °C, the reversible hydrogen storage capacity is 5.92 wt.%.

[0135] In the hydrogen absorption and desorption kinetic performance test results of Mg-Ni-Nd-4#

[0136] The hydrogen absorption test results are shown in Table 2. At 300 °C and 3 MPa, the hydrogen absorption amount in 1 min is 4.16 wt.%, and the total hydrogen absorption amount within 30 min is 5.38 wt.%, which is 91.0% of the reversible hydrogen storage capacity;

[0137] The hydrogen desorption test results are shown in Table 2. Under the conditions of 300 °C and vacuum, the hydrogen desorption amount within 5 min is 5.22 wt.%.

[0138] Combining the test results of Example 1 and Example 2 can prove that the Mg-Ni-Nd alloy is located in Composition Region 1, that is, the chemical components of the Mg-Ni-Nd hydrogen storage alloy are in the composition region with an atomic ratio of Mg 100-a-b Ni a Nd b , where a and b represent the atomic ratio, satisfying 4.5 ≤ a < 9, 2 ≤ b < 4, and a ≥ 2.25b.

[0139] 1. It can achieve a reversible hydrogen storage capacity of the Mg-Ni-Nd hydrogen storage alloy greater than 5.0 wt.%;

[0140] 2. At 300 °C and 3 MPa, the hydrogen absorption amount in 1 min is greater than 4.0 wt.%;

[0141] 3. Under the conditions of 300 °C and vacuum, the hydrogen desorption amount within 5 min is greater than 5.0 wt.%;

[0142] 4. The technical effect of having a hydrogen absorption and desorption cycle life greater than 2900 times and a capacity retention rate greater than 80% at 300 °C.

Claims

1. A multiphase structure Mg-Ni-Nd hydrogen storage alloy based on in-situ activation method, characterized in that: The components of the Mg-Ni-Nd hydrogen storage alloy include Nd4Mg 80 Ni8, Mg and Mg2Ni phases, and Nd4Mg 80 The volume fraction of the Ni8 phase is greater than 50%, the Mg phase is greater than 15%, and the sum of the Mg and Nd4Mg 80 Ni8 two-phase is greater than 95%, and the rest is the Mg2Ni phase; The Nd4Mg 80 The Ni8 phase undergoes hydrogen absorption / desorption activation and in-situ decomposition to form Mg, Mg2Ni, and NdH 2.61 phases.

2. The multiphase structure Mg-Ni-Nd hydrogen storage alloy based on the in-situ activation method according to claim 1, wherein: In the Mg-Ni-Nd hydrogen storage alloy, the Mg phase is a strip-shaped phase parallel to the extrusion direction, with a width of 2-5 μm, and the Mg2Ni phase is a needle-shaped or granular phase, with a size of 0.5-2 μm, and is dispersedly distributed in the Nd4Mg 80 Ni8 matrix phase.

3. The multiphase structure Mg-Ni-Nd hydrogen storage alloy based on the in-situ activation method according to claim 1, wherein: The chemical formula of the Mg-Ni-Nd hydrogen storage alloy satisfies Mg 100-a-b Ni a Nd b , where a and b represent the atomic ratio, 4.5 ≤ a < 9, 2 ≤ b < 4, and a ≥ 2.25b.

4. A preparation method of a multiphase structure Mg-Ni-Nd hydrogen storage alloy based on in-situ activation method, characterized in that The following steps are involved: Step 1, smelting of Mg-Ni-Nd cast alloy, satisfying the conditions of the chemical formula, using Mg, Mg-30Ni and Mg-50Nd as raw materials, and adding Mg as a loss, smelting Mg-30Ni, and adding Mg and Mg-50Nd to obtain an alloy melt, then, keeping the alloy melt warm, casting and cooling naturally after the insulation is completed, so as to obtain a Mg-Ni-Nd cast alloy, referred to as Mg-Ni-Nd-ca; The component requirements are that Nd4Mg is included simultaneously 80 Ni8 phase, Mg phase and Mg2Ni phase; and, Nd4Mg 80 The volume fraction of the Ni8 phase is greater than 50%, the Mg phase is greater than 15%, and the sum of the two phases of Mg and Nd4Mg 80 Ni8 is greater than 95%, and the remaining is the composition region of the Mg2Ni phase; In the said step 1, the chemical formula is Mg 100-a-b Ni a Nd b , where a and b represent atomic ratios, 4.5 ≤ a < 9, 2 ≤ b < 4, and a ≥ 2.25b; In the step 1, the smelting temperature is 750° C.; the insulation condition is that the insulation temperature is 700° C. and the insulation time is 10-20 min; Step 2, hot extrusion of the Mg-Ni-Nd cast alloy, after machining the Mg-Ni-Nd-ca obtained in step 1 into a cylinder, preheating, hot extrusion after preheating to achieve hot extrusion deformation, and water quenching immediately after hot extrusion to obtain a block of Mg-Ni-Nd hot extruded alloy, referred to as Mg-Ni-Nd-ex; In step 2, the preheating conditions are: the preheating temperature is 400-450° C., and the preheating time is 10-30 min; The conditions of the hot extrusion are as follows: the hot extrusion temperature is 400°C, the hot extrusion ratio is 12, and the hot extrusion speed is 0.4 m / s Step 3, filing and powdering of the Mg-Ni-Nd hot extruded alloy, after removing the surface oxide scale of the Mg-Ni-Nd-ex obtained in step 2, filing and powdering the blocky Mg-Ni-Nd-ex with a file in air to obtain the powder of the Mg-Ni-Nd hot extruded alloy, referred to as Mg-Ni-Nd-po; Step 4, activation treatment of Mg-Ni-Nd hot extruded alloy powder, hydrogen absorption activation of Mg-Ni-Nd-po obtained in step 3, to obtain hydrogen absorption Mg-Ni-Nd alloy, referred to as Mg-Ni-Nd-ab, and then dehydrogenation, to obtain a multi-phase structure Mg-Ni-Nd hydrogen storage alloy based on in-situ activation method; In step 4, the conditions for hydrogen absorption activation are: hydrogen absorption activation pressure of 4 MPa, hydrogen absorption activation temperature of 360° C., and hydrogen absorption activation time of 4 h; The hydrogen release condition is as follows: under vacuum conditions, the hydrogen release temperature is 360°C.

5. The preparation method according to claim 4, wherein: The obtained multi-phase structure Mg-Ni-Nd hydrogen storage alloy based on the in-situ activation method has two hydrogen absorption and desorption platforms, and the reversible hydrogen storage capacity is greater than 5.4wt.%; The Mg-Ni-Nd hydrogen storage alloy absorbs more than 4.0 wt.% of hydrogen in 1 minute at 300°C and 3 MPa; and releases more than 5.0 wt.% of hydrogen in 5 minutes at 300°C and vacuum conditions; When the hydrogen storage capacity of the Mg-Ni-Nd hydrogen storage alloy is maintained above 5.0wt.%, the number of cycles exceeds 1200 times; When the capacity retention rate of the Mg-Ni-Nd hydrogen storage alloy is greater than 80%, the number of cycles exceeds 2900.

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