A low-cost, high-strength, lightweight high-entropy alloy and its preparation method

Abstract

The present invention discloses a low-cost, high-strength, lightweight high-entropy alloy and a preparation method thereof. The atomic ratio expression is: Al a CoCrFeNi b O c , where 0.7 ≤ a ≤ 1.5, 1.8 ≤ b ≤ 2.4, and 0.001 ≤ c ≤ 0.05. The steps are as follows: selecting a lightweight high-entropy alloy system, performing first-principles calculations, calculating phase diagrams, designing alloy compositions, and preparing alloy ingots. Its microstructural characteristics consist of primary FCC phase dendrites and eutectic lamellar structures. The eutectic lamellar structures are composed of FCC and BCC phases. The O element is dissolved in the primary FCC phase dendrites and the FCC phase in the eutectic lamellar structures. Nano-Al2O3 phases are dispersed in the FCC phase within the primary FCC phase dendrites and the eutectic lamellar structures and at their phase interfaces. The room-temperature tensile strength of this alloy reaches 2 GPa, and the elongation reaches 5%. Compared with the existing AlCoCrFeNi 2.1 alloy (deformed state), the tensile strength is increased by nearly 1 time.

Description

Technical Field

[0001] The present invention belongs to the field of lightweight high-entropy alloy materials, and particularly relates to a low-cost, high-strength lightweight high-entropy alloy and a preparation method thereof. Background Art

[0002] Facing the increasingly severe energy and environmental problems, the research on lightweight structural materials is particularly important. So far, lightweight materials have been widely developed and applied. For example, lightweight alloy materials such as magnesium alloys, aluminum alloys, and titanium alloys have partially replaced steel materials and are widely used in fields such as automobiles and aerospace. However, the high manufacturing cost and limited performance of existing lightweight alloy materials limit their wider application in practical engineering.

[0003] Compared with traditional lightweight alloys, lightweight high-entropy alloys have excellent properties such as high hardness and strength, good high-temperature resistance and corrosion resistance. Among them, AlCoCrFeNi 2.1 high-entropy alloy is a typical eutectic high-entropy alloy, composed of an FCC soft phase and a BCC hard phase, showing excellent strength and toughness at room temperature, and the tensile strength can reach 1 GPa. However, the strength of the FCC phase is relatively low, resulting in relatively lower strength of the material compared to other high-entropy alloys. Researchers use precipitation strengthening means to improve the mechanical properties of lightweight high-entropy alloys. For example, some elements such as Ti and Cu are added on the basis of high-entropy alloys to form dispersed precipitation phases, and at the same time, hot working processes are used to improve the distribution and size of the precipitation phases, further improving the strength of the alloy. However, the above processes are complex, time-consuming and laborious. At the same time, to obtain the designed eutectic structure, high-purity raw materials are required, and alloy materials must be prepared in a high-vacuum environment to avoid introducing elements such as oxygen to damage the material structure, resulting in harsh production and manufacturing conditions and high costs. For example, the literature 1 "A promising new class of high-temperature alloys: eutectic high-entropy alloys" reports that AlCoCrFeNi 2.1 high-entropy alloy requires high-purity raw materials (Al, Co, Ni: 99.9 wt.%, Cr: 99.5 wt.%, Fe: 99.6 wt.%), and under high-vacuum conditions (pumped to 6×10 -2 Pa, and then filled with argon with a purity ≥ 99.999%), the room-temperature strength of the prepared material is 944 MPa, the elongation is 25.6%, and after cold rolling with a deformation of 8%, the room-temperature strength of the material is 1145 MPa, and the elongation is 10%. This process not only has high requirements for raw materials and preparation conditions, but also has limited improvement in material performance. Therefore, it is urgent to develop new low-cost, high-strength lightweight high-entropy alloy materials and technologies. Summary of the Invention

[0004] The object of the present invention is to provide a low-cost, high-strength, lightweight high-entropy alloy and its preparation process. This lightweight high-entropy alloy not only has high tensile strength but also large elongation. This material is particularly suitable for industrial production and preparation, can be produced with low-purity raw materials and under low-vacuum conditions, and the preparation process is simple, with low cost, and is easy to promote and popularize.

[0005] The technical solution to achieve the object of the present invention is: a low-cost, high-strength, lightweight high-entropy alloy, and its alloy element atomic expression is: Al a CoCrFeNi b O c , where 0.7 ≤ a ≤ 1.5, 1.8 ≤ b ≤ 2.4, 0.001 ≤ c ≤ 0.05.

[0006] Furthermore, the microstructural characteristics of this high-strength lightweight high-entropy alloy material are: it is composed of primary FCC phase dendrites and eutectic lamellar structures. The eutectic lamellar structure is composed of FCC phase and BCC phase. The O element is dissolved in the primary FCC phase dendrites and the FCC phase in the eutectic lamellar structure. The nano-Al2O3 phase is dispersedly distributed in the FCC phase in the primary FCC phase dendrites and the eutectic lamellar structure and at their phase interfaces.

[0007] Furthermore, the lightweight high-entropy alloy material has excellent room-temperature tensile properties, with its tensile strength reaching 1600 - 2000 MPa and its elongation reaching 5 - 10%.

[0008] A method for preparing the above-mentioned low-cost, high-strength, lightweight high-entropy alloy material includes the following steps:

[0009] The first step: Select a lightweight high-entropy alloy system. According to the equilibrium solidification phase diagram, for the Al a1 (CoCrFe) b1 Ni c1 quinary alloy, where, in terms of atomic ratio, when a1 = 1, b1 = 1, c1 = 2.1, it reaches the eutectic point and precipitates FCC and BCC eutectic structures. FCC is the soft phase and BCC is the hard phase. To further strengthen the FCC phase, O element is introduced. O is dissolved in the primary FCC phase dendrites and the FCC phase in the eutectic lamellar structure to achieve solid-solution strengthening. At the same time, O reacts with aluminum to generate nano-Al2O3 particles, which are dispersedly distributed in the FCC phase and at its phase interfaces to achieve second-phase strengthening. Use Thermal-Calc software to calculate the alloy composition of obtaining eutectic or near-eutectic structures under near-equilibrium solidification conditions as Al a CoCrFeNi b O c (atomic ratio), where 0.7 ≤ a ≤ 1.5, 1.8 ≤ b ≤ 2.4, 0.001 ≤ c ≤ 0.05;

[0010] Step 2: Weigh the metal raw materials of Al, Co, Cr, Fe, and Ni according to the component ratio in Step 1;

[0011] Step 3: Put the raw materials of Al, Cu, Ni, Cr, and Fe into a water-cooled copper crucible in sequence according to the alloy component ratio, cover the furnace lid and pump down to a low vacuum below 10 Pa, and then fill the furnace with argon at 0.04 - 0.06 MPa to prepare alloy ingots by using a water-cooled copper crucible suspension melting furnace;

[0012] Step 4: Carry out melting for 3 - 4 passes to obtain a high-strength lightweight high-entropy alloy ingot with uniform mixing.

[0013] Further, in Step 1, O element is introduced by using the oxide impurities, surface oxide scales in the metal raw materials and the oxygen impurities contained in the low-vacuum melting atmosphere.

[0014] Further, in Step 1, the Gibbs free energy of reaction of each element with oxygen in the alloy is calculated by using the first-principles method, and the temperature for generating dispersed nano-Al2O3 particles is determined to be 700 - 2000 °C.

[0015] Further, in Step 2, the purity (weight percentage) of the metal raw materials is above 99%, and the rest are impurity components containing oxides.

[0016] Further, in Step 3, the purity (mole percentage) of argon is above 99%, and the rest are impurity components containing oxygen.

[0017] Further, in Step 4, the melting power is 20 - 30 kW.

[0018] Compared with the prior art, the present invention has the following advantages: (1) The microstructure is composed of primary FCC phase dendrites and eutectic lamellar structures. The eutectic lamellar structure is composed of FCC phase and BCC phase, and the material has both high strength and plasticity; (2) O element is dissolved in the primary FCC phase dendrites and the FCC phase in the eutectic lamellar structures, and nano-Al2O3 phases are dispersed in the FCC phase and at its phase interfaces in the primary FCC phase dendrites and the eutectic lamellar structures, and solid-solution strengthening and second-phase strengthening are used to enhance the FCC phase; (3) The room-temperature mechanical properties of the lightweight high-entropy alloy are significantly improved; (4) The requirements for the purity of alloy raw materials and the preparation vacuum degree are low, and harmful O element is transformed into a strengthening element; (5) There is no need to remove the surface oxides of raw materials and pump to a high vacuum degree, and the preparation process is simple, efficient and low-cost, being suitable for large-scale industrial production. Description of the Drawings

[0019] Figure 1 is the preparation flow chart of the low-cost high-strength lightweight high-entropy alloy material of the present invention.

[0020] Figure 2 is the schematic diagram of the microstructure of the low-cost high-strength lightweight high-entropy alloy material. Detailed implementation manners

[0021] In order to better understand the technical content of the present invention, specific embodiments are given below in conjunction with the accompanying drawings for illustration.

[0022] The preparation steps of the following embodiments are as shown in the Figure 1 flow schematic diagram.

[0023] The concept and principle of the present invention are as follows: According to the equilibrium solidification phase diagram, for the Al a1 (CoCrFe) b1 Ni c1 quinary alloy, wherein, in terms of atomic percentage, when a1 = 1, b1 = 1, and c1 = 2.1, the eutectic point is reached, and the eutectic structure of FCC and BCC is precipitated. FCC is the soft phase and BCC is the hard phase. However, the strength of the FCC phase is relatively low, resulting in relatively lower strength of the material compared to other high-entropy alloys. To further enhance the FCC phase and improve the alloy strength, O element is introduced (using the oxide impurities in the metal raw materials, the surface oxide scale, and the oxygen impurities in the low-vacuum melting atmosphere to introduce the O element), so that O is dissolved in the primary FCC phase dendrites and the FCC phase in the eutectic lamellae, realizing interstitial solid solution strengthening. At the same time, O reacts with aluminum to form nano-Al2O3 particles, which are dispersed in the FCC phase and its phase interface, realizing second-phase strengthening. The Gibbs free energy of reaction of each element with oxygen in the alloy is calculated by the first-principles method, and it is determined that the temperature for generating the dispersed nano-Al2O3 particles is 700 - 2000 °C. Using the Thermal-Calc software to calculate the alloy composition for obtaining the eutectic or near-eutectic structure under the condition of near-equilibrium solidification is Al a CoCrFeNi b O c (atomic ratio), wherein, 0.7 ≤ a ≤ 1.5, 1.8 ≤ b ≤ 2.4, 0.001 ≤ c ≤ 0.05. To further reduce costs and facilitate production and preparation, the O element is introduced using the oxides in the raw materials and the oxygen in the melting atmosphere, converting the harmful O element into a strengthening element and reducing the requirements for the purity of the alloy raw materials and the vacuum degree of the preparation.

[0024] Example 1

[0025] (1) Design the alloy composition

[0026] Select a heat-resistant aluminum alloy system. According to the equilibrium solidification phase diagram, Al a1 (CoCrFe) b1 Ni c1A quinary alloy, where, in terms of atomic ratio, when a1 = 1, b1 = 1, c1 = 2.1, it reaches the eutectic point, and a eutectic structure of FCC and BCC precipitates, with FCC being the soft phase and BCC being the hard phase. To further strengthen the FCC phase, O element is introduced. O dissolves in the primary FCC phase dendrites and the FCC phase in the eutectic lamellae to achieve solid-solution strengthening. At the same time, O reacts with aluminum to form nano-Al2O3 particles, which are dispersed in the FCC phase and its phase interface to achieve second-phase strengthening. The Gibbs free energy of reaction of each element with oxygen in the alloy is calculated using the first-principles method, and the temperature for generating the dispersed nano-Al2O3 particles is determined to be 700 - 2000 °C. The alloy composition for obtaining a near-eutectic structure under near-equilibrium solidification conditions is calculated using the Thermal-Calc software as AlCoCrFeNi 2.1 O 0.02 (atomic ratio).

[0027] (2) Selection of raw materials

[0028] The purity of each metal component selected for preparing the alloy ingot in the present invention is shown in Table 1, and the alloy composition is AlCoCrFeNi 2.1 O 0.02 ;

[0029] Table 1 Purity of metal components selected for preparing the alloy ingot (wt.%)

[0030]

[0031] (3) Preparation of alloy ingot

[0032] An alloy ingot is prepared using a water-cooled copper crucible suspension melting furnace, and the specific procedure is as follows:

[0033] a. Prepare materials according to the designed composition ratio; put the prepared materials into the water-cooled copper crucible in the melting furnace according to a weight of about 200 g per ingot, cover the furnace lid and evacuate to 5 Pa; fill the furnace with argon (99%) at a certain pressure, and the argon pressure range is 0.04 MPa. The O element is introduced using the oxide impurities in the metal raw materials, the surface oxide scale, and the oxygen doped in the low-vacuum melting atmosphere;

[0034] b. Melt for 3 passes to obtain a uniformly mixed alloy ingot, and the melting power is 30 kW.

[0035] (4) Microstructure and property testing

[0036] The schematic diagram of the microstructure of the prepared material is as Figure 2As shown: It consists of primary FCC phase dendrites and eutectic lamellar structures. The eutectic lamellar structures are composed of FCC phase and BCC phase. Element O is dissolved in the primary FCC phase dendrites and the FCC phase in the eutectic lamellar structures. Nano-Al2O3 phases are dispersedly distributed in the FCC phase within the primary FCC phase dendrites and the eutectic lamellar structures and at their phase interfaces. The results of mechanical property tests show that the tensile strength and elongation of the prepared material reach 1833 MPa and 7% respectively, and the tensile strength is 60% higher than that of the alloy in Document 1.

[0037] Example 2

[0038] The alloy prepared in this example has a composition of AlCoCrFeNi 2.1 O 0.001 (atomic ratio). Before melting, the vacuum is pumped to 1 Pa, and then 0.05 MPa of argon gas is filled. Other steps are the same as those in Example 1. The alloy microstructure consists of primary FCC phase dendrites and eutectic lamellar structures. The eutectic lamellar structures are composed of FCC phase and BCC phase. Element O is dissolved in the primary FCC phase dendrites and the FCC phase in the eutectic lamellar structures. Nano-Al2O3 phases are dispersedly distributed in the FCC phase within the primary FCC phase dendrites and the eutectic lamellar structures and at their phase interfaces. The results of mechanical property tests show that the room-temperature tensile strength and elongation of the prepared material reach 1685 MPa and 9% respectively.

[0039] Example 3

[0040] The alloy prepared in this example has a composition of AlCoCrFeNi 2.1 O 0.05 (atomic ratio). Before melting, the vacuum is pumped to 10 Pa, and then 0.04 MPa of argon gas is filled. Other steps are the same as those in Example 1. The alloy microstructure consists of primary FCC phase dendrites and eutectic lamellar structures. The eutectic lamellar structures are composed of FCC phase and BCC phase. Element O is dissolved in the primary FCC phase dendrites and the FCC phase in the eutectic lamellar structures. Nano-Al2O3 phases are dispersedly distributed in the FCC phase within the primary FCC phase dendrites and the eutectic lamellar structures and at their phase interfaces. The results of mechanical property tests show that the room-temperature tensile strength and elongation of the prepared material reach 1922 MPa and 6% respectively.

[0041] Example 4

[0042] The alloy prepared in this example has a composition of Al 1.5 CoCrFeNi 2.4 O 0.05(Atomic ratio). Before melting, evacuate to 10 Pa under vacuum, and then fill with 0.04 MPa argon. Other steps are the same as in Example 1. The alloy microstructure consists of primary FCC phase dendrites and eutectic lamellar structures. The eutectic lamellar structures are composed of FCC phase and BCC phase. Element O is dissolved in the primary FCC phase dendrites and the FCC phase in the eutectic lamellar structures. Nano-Al2O3 phases are dispersed in the FCC phase within the primary FCC phase dendrites and the eutectic lamellar structures and at their phase interfaces. The mechanical property test results show that the tensile strength and elongation of the prepared material at room temperature reach 2016 MPa and 5% respectively.

[0043] Example 5

[0044] The alloy prepared in this example has a composition of Al 1.5 CoCrFeNi 2.4 O 0.001 (Atomic ratio). Before melting, evacuate to 1 Pa under vacuum, and then fill with 0.05 MPa argon. Other steps are the same as in Example 1. The alloy microstructure consists of primary FCC phase dendrites and eutectic lamellar structures. The eutectic lamellar structures are composed of FCC phase and BCC phase. Element O is dissolved in the primary FCC phase dendrites and the FCC phase in the eutectic lamellar structures. Nano-Al2O3 phases are dispersed in the FCC phase within the primary FCC phase dendrites and the eutectic lamellar structures and at their phase interfaces. The mechanical property test results show that the tensile strength and elongation of the prepared material at room temperature reach 1952 MPa and 6% respectively.

[0045] Example 6

[0046] The alloy prepared in this example has a composition of Al 0.7 CoCrFeNi 1.8 O 0.05 (Atomic ratio). Before melting, evacuate to 10 Pa under vacuum, and then fill with 0.04 MPa argon. Other steps are the same as in Example 1. The alloy microstructure consists of primary FCC phase dendrites and eutectic lamellar structures. The eutectic lamellar structures are composed of FCC phase and BCC phase. Element O is dissolved in the primary FCC phase dendrites and the FCC phase in the eutectic lamellar structures. Nano-Al2O3 phases are dispersed in the FCC phase within the primary FCC phase dendrites and the eutectic lamellar structures and at their phase interfaces. The mechanical property test results show that the tensile strength and elongation of the prepared material at room temperature reach 1759 MPa and 7% respectively.

[0047] Example 7

[0048] The alloy prepared in this example has a composition of Al 0.7 CoCrFeNi 1.8 O 0.001(Atomic ratio), evacuated to 1 Pa before melting, and then filled with 0.05 MPa argon. Other steps are the same as in Example 1. The alloy microstructure consists of primary FCC phase dendrites and eutectic lamellar structures. The eutectic lamellar structures are composed of FCC and BCC phases. O element is dissolved in the primary FCC phase dendrites and the FCC phase in the eutectic lamellar structures. Nano-Al2O3 phases are dispersed in the primary FCC phase dendrites, the FCC phase in the eutectic lamellar structures, and their phase interfaces. The mechanical property test results show that the tensile strength and elongation of the prepared material at room temperature reach 1612 MPa and 10% respectively.

[0049] Example 8

[0050] The alloy prepared in this example has a composition of AlCoCrFeNi 2.2 O 0.02 (Atomic ratio), evacuated to 5 Pa before melting, and then filled with 0.05 MPa argon. Other steps are the same as in Example 1. The alloy microstructure consists of primary FCC phase dendrites and eutectic lamellar structures. The eutectic lamellar structures are composed of FCC and BCC phases. O element is dissolved in the primary FCC phase dendrites and the FCC phase in the eutectic lamellar structures. Nano-Al2O3 phases are dispersed in the primary FCC phase dendrites, the FCC phase in the eutectic lamellar structures, and their phase interfaces. The mechanical property test results show that the tensile strength and elongation of the prepared material at room temperature reach 1836 MPa and 7% respectively.

[0051] Example 9

[0052] The alloy prepared in this example has a composition of AlCoCrFeNi 2.2 O 0.001 (Atomic ratio), evacuated to 1 Pa before melting, and then filled with 0.05 MPa argon. Other steps are the same as in Example 1. The alloy microstructure consists of primary FCC phase dendrites and eutectic lamellar structures. The eutectic lamellar structures are composed of FCC and BCC phases. O element is dissolved in the primary FCC phase dendrites and the FCC phase in the eutectic lamellar structures. Nano-Al2O3 phases are dispersed in the primary FCC phase dendrites, the FCC phase in the eutectic lamellar structures, and their phase interfaces. The mechanical property test results show that the tensile strength and elongation of the prepared material at room temperature reach 1774 MPa and 8% respectively.

[0053] Example 10

[0054] The alloy prepared in this example has a composition of Al 0.7 CoCrFeNi 2.1 O 0.001(Atomic ratio). Before melting, the vacuum was pumped to 1 Pa, and then argon gas with a pressure of 0.05 MPa was filled. Other steps were the same as those in Example 1. The alloy microstructure consisted of primary FCC phase dendrites and eutectic lamellar structures. The eutectic lamellar structures were composed of FCC and BCC phases. Element O was dissolved in the primary FCC phase dendrites and the FCC phase in the eutectic lamellar structures. Nano-Al2O3 phases were dispersed in the FCC phase within the primary FCC phase dendrites and the eutectic lamellar structures and at their phase interfaces. The mechanical property test results showed that the room-temperature tensile strength and elongation of the prepared material reached 1665 MPa and 9% respectively.

[0055] Example 11

[0056] The alloy prepared in this example had a composition of Al 0.7 CoCrFeNi 2.1 O 0.05 (Atomic ratio). Before melting, the vacuum was pumped to 10 Pa, and then argon gas with a pressure of 0.04 MPa was filled. Other steps were the same as those in Example 1. The alloy microstructure consisted of primary FCC phase dendrites and eutectic lamellar structures. The eutectic lamellar structures were composed of FCC and BCC phases. Element O was dissolved in the primary FCC phase dendrites and the FCC phase in the eutectic lamellar structures. Nano-Al2O3 phases were dispersed in the FCC phase within the primary FCC phase dendrites and the eutectic lamellar structures and at their phase interfaces. The mechanical property test results showed that the room-temperature tensile strength and elongation of the prepared material reached 1785 MPa and 8% respectively.

[0057] Comparative Example 1

[0058] Literature 1 “A promising new class of high-temperature alloys: eutectic high-entropy alloys” reported that for AlCoCrFeNi 2.1 high-entropy alloys required high-purity raw materials (Al, Co, Ni: 99.9 wt.%, Cr: 99.5 wt.%, Fe: 99.6 wt.%), and under high-vacuum conditions (pumped to 6×10 -2 Pa, and then filled with argon gas with a purity ≥99.999%). The room-temperature strength of the prepared material was 944 MPa and the elongation was 25.6%. After cold rolling with a deformation amount of 8%, the room-temperature strength of the material was 1145 MPa and the elongation was 10%.

[0059] The alloy compositions and properties in the examples and comparative examples were compared as shown in Table 2.

[0060]

[0061] Although the present invention has been disclosed above in its preferred embodiments, it is not intended to limit the present invention. Those of ordinary skill in the art to which the present invention pertains may make various modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A low-cost, high-strength, lightweight high-entropy alloy, characterized in that, The atomic expression of its alloying elements is: Al a CoCrFeNi b O c , where 0.7 ≤ a ≤ 1.5, 1.8 ≤ b ≤ 2.4, 0.001 ≤ c ≤ 0.05; The microstructure characteristics of the high-strength lightweight high-entropy alloy are as follows: It consists of primary FCC phase dendrites and eutectic lamellar structures. The eutectic lamellar structures are composed of FCC and BCC phases. Element O is dissolved in the primary FCC phase dendrites and the FCC phase in the eutectic lamellar structures. Nano-Al2O3 phases are dispersedly distributed in the FCC phase within the primary FCC phase dendrites and the eutectic lamellar structures and at their phase interfaces. It is prepared by the following steps: Step 1: Select a lightweight high-entropy alloy system. According to the equilibrium solidification phase diagram, Al a1 (CoCrFe) b1 Ni c1 quinary alloy. Among them, when the atomic ratio is a1 = 1, b1 = 1, c1 = 2.1, the eutectic point is reached, and the eutectic structure of FCC and BCC is precipitated. FCC is the soft phase and BCC is the hard phase. To strengthen the FCC phase, O element is introduced. O is dissolved in the primary FCC phase dendrites and the FCC phase in the eutectic lamellae to achieve solid solution strengthening. At the same time, O reacts with aluminum to form nano-Al2O3 particles, which are dispersed in the FCC phase and its phase interface to achieve second-phase strengthening. Use Thermal-Calc software to calculate the alloy composition of the eutectic or near-eutectic structure obtained under near-equilibrium solidification conditions as Al a CoCrFeNi b O c , where 0.7 ≤ a ≤ 1.5, 1.8 ≤ b ≤ 2.4, 0.001 ≤ c ≤ 0.05; Step 2: Weigh the metal raw materials of Al, Co, Cr, Fe, and Ni according to the component ratio in Step 1. Step 3: Sequentially put the raw materials of Al, Cu, Ni, Cr, and Fe into a water-cooled copper crucible according to the alloy component ratio, cover the furnace lid and evacuate to vacuum, then fill the furnace with argon gas, and use a water-cooled copper crucible suspension melting furnace to prepare an alloy ingot. Step 4: Melt for 3 - 4 passes to obtain a uniformly mixed alloy ingot. Among them, in Step 1, element O is introduced by using the oxide impurities in the metal raw materials and the oxygen impurities contained in the melting atmosphere.

2. The high-strength lightweight high-entropy alloy according to claim 1, characterized in that, The lightweight high-entropy alloy has excellent room-temperature tensile properties, with its tensile strength reaching 1600 - 2000 MPa and elongation at break reaching 5 - 10%.

3. A method for preparing a high-strength lightweight high-entropy alloy as described in any one of claims 1-2, characterized in that, It includes the following steps: Step 1: Select a lightweight high-entropy alloy system. According to the equilibrium solidification phase diagram, Al a1 (CoCrFe) b1 Ni c1 quinary alloy. Among them, when the atomic ratio is a1 = 1, b1 = 1, c1 = 2.1, the eutectic point is reached, and the eutectic structure of FCC and BCC is precipitated. FCC is the soft phase and BCC is the hard phase. To strengthen the FCC phase, O element is introduced. O is dissolved in the primary FCC phase dendrites and the FCC phase in the eutectic lamellae to achieve solid solution strengthening. At the same time, O reacts with aluminum to form nano-Al2O3 particles, which are dispersed in the FCC phase and its phase interface to achieve secondary phase strengthening. Use the Thermal-Calc software to calculate the alloy composition of the eutectic or near-eutectic structure obtained under near-equilibrium solidification conditions as Al a CoCrFeNi b O c , where 0.7 ≤ a ≤ 1.5, 1.8 ≤ b ≤ 2.4, 0.001 ≤ c ≤ 0.05; Step 2: Weigh the metal raw materials of Al, Co, Cr, Fe, and Ni according to the component ratio in Step 1. Step 3: Sequentially put the raw materials of Al, Cu, Ni, Cr, and Fe into a water-cooled copper crucible according to the alloy component ratio, cover the furnace lid and evacuate to vacuum, then fill the furnace with argon gas, and use a water-cooled copper crucible suspension melting furnace to prepare an alloy ingot. Step 4: Melt for 3 - 4 passes to obtain a uniformly mixed alloy ingot.

4. The method according to claim 3, wherein In Step 1, the Gibbs free energy of reaction of each element with oxygen in the alloy is calculated by using the first-principles method, and the temperature for generating dispersed nano-Al2O3 particles is determined to be 700 - 2000 °C.

5. The method according to claim 3, wherein In Step 2, the purity of the metal raw materials is above 99 wt%.

6. The method according to claim 3, wherein In Step 3, the purity of the argon gas is above 99 mol%.

7. The method according to claim 3, characterized in that, In Step 3, evacuate to below 10 Pa after covering the furnace lid, and then fill the furnace with argon gas at 0.04 - 0.06 MPa.

8. The method according to claim 3, characterized in that, In Step 4, the melting power is 20 - 30 kW.

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