High-strength lightweight aluminum-based medium-entropy alloy and preparation method thereof

Abstract

This invention discloses a high-strength, lightweight aluminum-based medium-entropy alloy and its preparation method, relating to the technical field of lightweight medium-entropy alloy materials. The raw material composition of this aluminum-based medium-entropy alloy, expressed as Al in atomic percentage, can be... a Ti b Cr c M d The alloy comprises 45-65% Al, 10-30% Ti, 15-30% Cr, and 5-10% M, where M is one or more of Sc, V, and Mn, and a+b+c+d = 100. The specific preparation method is as follows: Pretreated raw materials are weighed according to the proportions and placed in a vacuum arc melting furnace or vacuum induction melting furnace. The alloy is melted under high-purity argon protection and held at a constant temperature to ensure uniform composition. The molten alloy is then poured into a preheated cast iron mold or water-cooled copper mold and allowed to cool naturally to room temperature to obtain an aluminum-based medium-entropy alloy ingot. The aluminum-based medium-entropy alloy prepared by this invention possesses both low density and high strength. Its as-cast microstructure is predominantly a solid solution phase, exhibiting excellent strength-plasticity matching. This allows for the fabrication of lightweight, high-performance cast structural parts without the need for complex thermomechanical processing.

Description

Technical Field

[0001] This invention relates to the field of metallic materials and their preparation technology, specifically to an aluminum-based medium-entropy alloy with aluminum as the main component, which has both low density and high strength, and its preparation method. Background Technology

[0002] Aluminum and aluminum alloys are widely used in transportation, aerospace, and equipment manufacturing due to their low density, high specific strength, good thermal and electrical conductivity, and excellent corrosion resistance. Traditional aluminum alloys generally use one main element (such as Al-Mg, Al-Cu, Al-Zn-Mg, etc.) and achieve solid solution strengthening or precipitation strengthening by adding small amounts of other elements. However, with the increasing demands for strength and service environment, traditional alloy systems have limitations in balancing low density, strength, corrosion resistance, and high-temperature stability. In the past two decades, the design concepts of high-entropy alloys and medium-entropy alloys have been proposed, providing new ideas for the development of multi-element alloys. By introducing multiple main elements and increasing the alloy configuration entropy, a simple solid solution structure can be stably formed under certain conditions, achieving higher solid solution strengthening and lattice distortion effects. Existing research mainly focuses on high-entropy or medium-entropy alloy systems dominated by transition metals such as Ni, Co, Fe, and Cr. Although these alloys have high strength, their high density is not conducive to lightweight structures. On the other hand, existing research on aluminum-based medium-entropy alloys mostly adopts systems such as Al-Cu-Mg-Zn and Al-TM (TM being a transition metal). These systems often require complex thermomechanical processing (hot rolling, cold rolling, forging, etc.) and strict aging heat treatment to obtain better comprehensive performance, which is not conducive to direct casting and limits their application in complex cast structural parts.

[0003] Therefore, there is an urgent need to develop an aluminum-based medium-entropy alloy system with aluminum as the main component, a reasonable composition design, and good comprehensive performance that can be obtained through a simple casting process. This system would achieve a balance between low density, high specific strength, and good casting processability, while simplifying the processing flow and reducing costs. Summary of the Invention

[0004] The purpose of this invention is to provide a high-strength, lightweight aluminum-based medium-entropy alloy. This alloy uses high-content aluminum as the main component, combined with elements such as Ti, Cr, and Sc / Mn / V. Through medium-entropy alloy design, it achieves high solid solution strengthening and lattice distortion strengthening, maintaining low density while possessing high strength. Furthermore, this invention provides a preparation method suitable for this alloy system, enabling the alloy to have good comprehensive properties in the as-cast state without the need for complex thermomechanical processing, making it suitable for direct casting.

[0005] The objective of this invention is achieved through the following technical solution: A high-strength, lightweight aluminum-based medium-entropy alloy, the composition of which is expressed as: Al a Ti b Crc M d (Atomic molar ratio), in the alloy expression a, b, c, d respectively represent the atomic percentage content of each corresponding main element, where M is one or more of Sc, V, Mn, and satisfies the following conditions: 45≤a≤65, 10≤b≤30, 15≤c≤30, 5≤d≤10, a+b+c+d=100.

[0006] Another objective of this invention is to provide a high-strength, lightweight aluminum-based medium-entropy alloy and its preparation method, the steps of which are as follows: (1) Ingredients: Select metals Al, Ti, Cr and M (one or more of Sc, Mn and V) with an industrial purity of not less than 99.9 wt.% as raw materials, according to the target composition Al a Ti b Cr c M d The required mass of each element was calculated based on its atomic percentage, and weighed using a precision electronic balance, with the weighing error controlled within ±0.5 at.%. Before weighing, the metal surface was mechanically polished and chemically cleaned to remove oxide scale, oil, etc., and then dried for later use.

[0007] (2) Melting: The pretreated metal raw materials are placed in graphite or ceramic crucibles in order of increasing melting point. The crucibles are then placed in a vacuum arc melting furnace or a vacuum induction melting furnace. The furnace cavity is evacuated using a mechanical pump and a molecular pump, and then filled with high-purity argon gas. Multiple evacuation / filling cycles are performed to further reduce the gas and impurity content. The arc or induction power supply is started under an argon protective atmosphere to melt the raw materials in the crucible into an alloy melt. After the melt is completely melted, the temperature is maintained to allow the alloying elements to fully diffuse and mix.

[0008] (3) Casting: The molten alloy with uniform composition is poured from the furnace into a pre-cleaned and preheated cast iron mold or water-cooled copper mold through a turning crucible or a funnel casting device. After casting, it is allowed to cool naturally to room temperature under static conditions to obtain an aluminum-based medium-entropy alloy ingot.

[0009] The vacuum condition in step (2) of this invention is: ≤5×10 -3 Pa.

[0010] In step (2) of the present invention, the purity of argon gas is ≥99.9 wt.%, and the argon gas pressure inside the smelting device is lower than the ambient gas pressure outside the device.

[0011] In step (2) of the present invention, the number of vacuuming / gas filling cycles is ≥2 times.

[0012] The heat preservation time in step (2) of the present invention is 5~10 min.

[0013] The cast structural component obtained in step (3) of the present invention is obtained by direct casting without the need for other complex thermomechanical processing.

[0014] The microstructure of the as-cast alloy described in this invention is mainly composed of a solid solution matrix phase, wherein the solid solution phase is HCP, and AlTi and / or Al3Ti intermetallic compound second phases are dispersed in the phase.

[0015] The as-cast alloy of the present invention has the following mechanical properties: compressive yield strength not less than 700 MPa, compressive strength not less than 2000 MPa, and fracture strain not less than 23%.

[0016] The principle of this invention: This invention relates to a high-strength, lightweight aluminum-based medium-entropy alloy. Al, Ti, and Cr, with relatively small differences in atomic radii, are selected as matrix phase elements, which improves the thermal stability and solid solubility of the matrix phase. To significantly increase the alloy's density, the aluminum content is designed to be at a high level of 45–65 at.%, while the content of Ti and Cr is adjusted to ensure the alloy exhibits a high mixing entropy, stabilizing the alloy's microstructure. Because the precise adjustment of Al, Ti, and Cr content greatly broadens the solid solubility of the matrix phase, compared to Al alloys (such as Al-Mn alloys) and other medium / high entropy alloys, the addition of rare earth and transition elements (such as Mn) can reach a higher level (5–10%). This provides higher medium-entropy solid solution strengthening, lattice distortion strengthening, and possible grain refinement strengthening, enabling the alloy to achieve high strength while maintaining low density. In terms of composition, the high Mn content and its high diffusion rate can promote the precipitation and uniform distribution of AlTi and / or Al3Ti intermetallic compound second phases in the matrix. Based on the above composition design, the high-strength lightweight aluminum-based medium-entropy alloy of the present invention can exhibit a composite microstructure composed of an HCP phase matrix and dispersed AlTi and / or Al3Ti intermetallic compound second phases, which has high thermal stability. This allows the alloy to exhibit excellent mechanical properties, with a compressive yield strength of not less than 700 MPa, a compressive strength of not less than 2000 MPa, and a fracture strain of not less than 23%. At the same time, the density of the alloy can be maintained at a low level: between 3.36 and 4.57.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) By designing the aluminum content to a high level of 45 to 65 at.%, the density of the alloy of the present invention is significantly lower than that of medium-entropy / high-entropy alloy systems mainly composed of Fe, Ni, Co, Cu, etc., which is beneficial to achieving weight reduction of structural parts. The density of the alloy is between 3.36 and 4.57.

[0018] (2) At the same time, Ti, Cr and transition group and rare earth elements such as Sc / V / Mn are introduced. By using medium entropy solid solution strengthening, lattice distortion strengthening and possible fine grain strengthening, the alloy can obtain high strength while maintaining low density. The compressive yield strength of the alloy is not less than 700 MPa, the compressive strength is not less than 2000 MPa, and the fracture strain is not less than 23%.

[0019] (3) The present invention adopts the Al-Ti-Cr-M four principal element design, and the alloy configuration entropy is in the range of medium entropy alloys, which is conducive to the formation of a phase structure dominated by simple solid solution under as-cast conditions. The microstructure of the alloy is dominated by HCP solid solution phase, and AlTi and / or Al3Ti intermetallic compound second phase are dispersed in the phase.

[0020] (4) The alloy system of the present invention is designed based on common industrial metals Al, Ti, Cr and a small amount of Sc / V / Mn. It does not contain precious metals and toxic elements. The raw materials are readily available and the cost is controllable.

[0021] (5) The preparation method proposed in this invention only requires smelting and casting processes, and does not require subsequent complex thermomechanical processing such as rolling and forging to obtain a high-performance as-cast structure, which is beneficial to the direct manufacturing of complex-shaped castings and cost reduction. Attached Figure Description

[0022] Figure 1 This is an optical microstructure of the high-strength, lightweight aluminum-based medium-entropy alloy prepared in Example 1 of the present invention.

[0023] Figure 2 The compression engineering stress-strain curves of the high-strength lightweight aluminum-based medium-entropy alloys prepared in Examples 2, 3 and 4 of this invention are shown.

[0024] Figure 3 The X-ray diffraction pattern is shown for the high-strength, lightweight aluminum-based medium-entropy alloy prepared in Example 3 of this invention.

[0025] Figure 4 This is a scanning electron micrograph of the high-strength, lightweight aluminum-based medium-entropy alloy prepared in Example 5 of the present invention. Detailed Implementation

[0026] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the contents described.

[0027] Example 1 A high-strength, lightweight aluminum-based medium-entropy alloy and its preparation method, specifically including the following steps: The alloy ingots are cast into alloys through electric arc melting or induction melting; the melting is carried out in a vacuum or argon protection, and magnetic stirring technology is used to mix the metal solution evenly during the melting process; the casting is carried out under vacuum or argon protection to form square or round ingots.

[0028] (1) Raw material pretreatment: Select metal Al, metal Ti, metal Cr, and metal Sc. The composition of the medium-entropy alloy is as follows (atomic percentage %): Al = 65.0, Ti = 10.0, Cr = 15.0, Sc = 10.0. Before weighing, mechanically grind and chemically clean the oxide scale and oil stains on the metal surface. Then, place the raw materials under a vacuum of 8.0 × 10 -2 Pretreatment was completed by vacuum deoxidation at 300 ℃ for 1 h under Pa conditions.

[0029] (2) Vacuum melting: The pretreated metal raw materials are placed in graphite or ceramic crucibles in order of increasing melting point. The crucibles are then placed in a vacuum arc melting furnace or a vacuum induction melting furnace. The furnace chamber is evacuated to a vacuum degree of 4.2 × 10⁻⁶ using a mechanical pump and a molecular pump. -3 Pa, then high-purity argon gas is introduced to 0.03 MPa, and two vacuum / gas filling cycles are performed to further reduce the gas and impurity content; under the argon protective atmosphere, an electric arc or induction power supply is started to melt the raw materials in the crucible into an alloy melt; after the melt is completely melted, it is kept at a constant temperature for 5 min to allow the alloy elements to fully diffuse and mix.

[0030] (3) Casting: After the alloy melt is completely melted in the melting furnace and the composition is uniform after heat preservation, the alloy melt is poured from the furnace into a pre-cleaned and preheated cast iron mold or water-cooled copper mold through a flipping crucible or a funnel casting device. After casting, the mold is placed in a static state and allowed to cool naturally in the air to room temperature. After demolding, an aluminum-based medium-entropy alloy square ingot is obtained.

[0031] Figure 1 The image shows a typical as-cast microstructure of the high-strength, lightweight aluminum-based medium-entropy alloy obtained in Example 1. Obvious dendritic crystals are visible, indicating that the material was directly solidified after melting without plastic deformation. The dendrites and interdendritic regions are clearly contrasted, and the interdendritic areas may be rich in gold elements or form a second phase, reflecting a certain degree of solidification segregation. The dendrite size is moderate, indicating a moderate cooling rate. The overall microstructure in the image is relatively dense and uniform. The density of the high-strength lightweight aluminum-based medium-entropy alloy obtained in this embodiment is shown in Table 1. The density of the medium-entropy alloy obtained in this embodiment is 3.36. The mechanical properties of the high-strength lightweight aluminum-based medium-entropy alloy obtained in this embodiment are shown in Table 1. The compressive yield strength of the medium-entropy alloy obtained in this embodiment is 703 MPa, the compressive strength is 2083 MPa, and the fracture strain is ~30.7%.

[0032] Example 2 A high-strength, lightweight aluminum-based medium-entropy alloy and its preparation method, specifically including the following steps: (1) Raw material pretreatment: Select metal Al, metal Ti, metal Cr, and metal V. The composition of the medium-entropy alloy is as follows (atomic percentage %): Al = 45.0, Ti = 30.0, Cr = 20.0, V = 5.0. Before weighing, mechanically grind and chemically clean the oxide scale and oil stains on the metal surface. Then, place the raw materials under a vacuum of 7.2 × 10 -2 Pretreatment was completed by vacuum deoxidation at 300 ℃ for 1 h under Pa conditions.

[0033] (2) Vacuum melting: The pretreated metal raw materials are placed in graphite or ceramic crucibles in order of increasing melting point. The crucibles are then placed in a vacuum arc melting furnace or a vacuum induction melting furnace. The furnace chamber is evacuated to a vacuum degree of 3.7 × 10⁻⁶ using a mechanical pump and a molecular pump. -3 Pa, then high-purity argon gas is introduced to 0.04 MPa, and three vacuum / gas filling cycles are performed to further reduce the gas and impurity content; under the argon protective atmosphere, an electric arc or induction power supply is started to melt the raw materials in the crucible into an alloy melt; after the melt is completely melted, it is kept at a constant temperature for 6 min to allow the alloy elements to fully diffuse and mix.

[0034] (3) Casting: After the alloy melt is completely melted in the melting furnace and the composition is homogeneous after heat preservation, the alloy melt is poured from the furnace into a pre-cleaned and preheated cast iron mold or water-cooled copper mold through a flipping crucible or a funnel casting device. After casting, the mold is placed in a static state and allowed to cool naturally in the air to room temperature. After demolding, an aluminum-based medium-entropy alloy square ingot is obtained.

[0035] The density of the high-strength, lightweight aluminum-based medium-entropy alloy obtained in this embodiment is shown in Table 1. The density of the medium-entropy alloy obtained in this embodiment is 4.18. The mechanical properties of the high-strength, lightweight aluminum-based medium-entropy alloy obtained in this embodiment are shown in Table 1, and the mechanical property curves are shown in Table 1. Figure 2 The medium-entropy alloy obtained in this embodiment has a compressive yield strength of 941 MPa, a compressive strength of 2945 MPa, and a fracture strain of ~36.1%.

[0036] Example 3 A high-strength, lightweight aluminum-based medium-entropy alloy and its preparation method, specifically including the following steps: (1) Raw material pretreatment: Select metals Al, Ti, Cr, and Mn. The composition of the medium-entropy alloy is as follows (atomic percentage %): Al = 45.0, Ti = 15.0, Cr = 30.0, Mn = 10.0. Before weighing, mechanically grind and chemically clean the oxide scale and oil stains on the metal surface. Then, place the raw materials under a vacuum of 6.5 × 10⁻⁶. -2Pretreatment was completed by vacuum deoxidation at 300 ℃ for 1 h under Pa conditions.

[0037] (2) Vacuum melting: The pretreated metal raw materials are placed in graphite or ceramic crucibles in order of increasing melting point. The crucibles are then placed in a vacuum arc melting furnace or a vacuum induction melting furnace. The furnace chamber is evacuated to a vacuum degree of 3.0 × 10⁻⁶ using a mechanical pump and a molecular pump. -3 Pa, then high-purity argon gas is introduced to 0.06 MPa, and two vacuum / gas filling cycles are performed to further reduce the gas and impurity content; under the argon protective atmosphere, an electric arc or induction power supply is started to melt the raw materials in the crucible into an alloy melt; after the melt is completely melted, it is kept at the temperature for 8 min to allow the alloy elements to fully diffuse and mix.

[0038] (3) Casting: After the alloy melt is completely melted in the melting furnace and the composition is homogeneous after heat preservation, the alloy melt is poured from the furnace into a pre-cleaned and preheated cast iron mold or water-cooled copper mold through a flipping crucible or a funnel casting device. After casting, the mold is placed in a static state and allowed to cool naturally in the air to room temperature. After demolding, an aluminum-based medium-entropy alloy square ingot is obtained.

[0039] The density of the high-strength, lightweight aluminum-based medium-entropy alloy obtained in this embodiment is shown in Table 1. The density of the medium-entropy alloy obtained in this embodiment is 4.57. The mechanical properties of the high-strength, lightweight aluminum-based medium-entropy alloy obtained in this embodiment are shown in Table 1, and the mechanical property curves are shown in Table 1. Figure 2 The medium-entropy alloy obtained in this embodiment has a compressive yield strength of 732 MPa, a compressive strength of 2317 MPa, and a fracture strain of ~32.3%.

[0040] Figure 3 The X-ray diffraction pattern of the high-strength lightweight aluminum-based medium-entropy alloy prepared in Example 3 is shown. The alloy is mainly composed of a solid solution phase with an HCP structure, which has the highest diffraction peak intensity and concentrated distribution, representing the matrix phase of the alloy. At the same time, weak AlTi and Al3Ti characteristic peaks appear at some 2θ angles, indicating that a small amount of Al-Ti intermetallic compounds precipitate under high Al and Ti content conditions, forming a multiphase structure. No obvious oxide or impurity phase diffraction peaks are observed, indicating that the melt has high purity.

[0041] Example 4 A high-strength, lightweight aluminum-based medium-entropy alloy and its preparation method, specifically including the following steps: (1) Raw material pretreatment: Select metals Al, Ti, Cr, V, and Mn. The composition of the medium-entropy alloy is as follows (atomic percentage %): Al = 58.0, Ti = 17.0, Cr = 17.0, V = 4.0, Mn = 4.0. Before weighing, mechanically grind and chemically clean the oxide scale and oil stains on the metal surface. The raw materials are then subjected to a vacuum of 5.5 × 10⁻⁶.-2 Pretreatment was completed by vacuum deoxidation at 300 °C for 1 h under Pa conditions.

[0042] (2) Vacuum melting: The pretreated metal raw materials are placed in graphite or ceramic crucibles in order of increasing melting point. The crucibles are then placed in a vacuum arc melting furnace or a vacuum induction melting furnace. The furnace chamber is evacuated to a vacuum degree of 2.0 × 10⁻⁶ using a mechanical pump and a molecular pump. -3 Pa, then high-purity argon gas is introduced to 0.05 MPa, and three vacuum / gas filling cycles are performed to further reduce the gas and impurity content; under the argon protective atmosphere, an electric arc or induction power supply is started to melt the raw materials in the crucible into an alloy melt; after the melt is completely melted, it is kept at the temperature for 9 min to allow the alloy elements to fully diffuse and mix.

[0043] (3) Casting: After the alloy melt is completely melted in the melting furnace and the composition is homogeneous after heat preservation, the alloy melt is poured from the furnace into a pre-cleaned and preheated cast iron mold or water-cooled copper mold through a flipping crucible or a funnel casting device. After casting, the mold is placed in a static state and allowed to cool naturally in the air to room temperature. After demolding, an aluminum-based medium-entropy alloy square ingot is obtained.

[0044] The density of the high-strength lightweight aluminum-based medium-entropy alloy obtained in this embodiment is shown in Table 1. The density of the medium-entropy alloy obtained in this embodiment is 3.78. The mechanical properties of the high-strength lightweight aluminum-based medium-entropy alloy obtained in this embodiment are shown in Table 1, and the mechanical property curves are shown in Table 1. Figure 2 The medium-entropy alloy obtained in this embodiment has a compressive yield strength of 783 MPa, a compressive strength of 2055 MPa, and a fracture strain of ~25.6%, exhibiting high strength and good plasticity.

[0045] Example 5 A high-strength, lightweight aluminum-based medium-entropy alloy and its preparation method, specifically including the following steps: (1) Raw material pretreatment: Select metals Al, Ti, Cr, Sc, V, and Mn. The composition of the medium-entropy alloy is as follows (atomic percentage %): Al = 55.0, Ti = 18.0, Cr = 18.0, Sc = 4.0, V = 2.5, Mn = 2.5. Before weighing, mechanically grind and chemically clean the oxide scale and oil stains on the metal surface. Then, place the raw materials under a vacuum of 5.0 × 10⁻⁶. -2 Pretreatment was completed by vacuum deoxidation at 300 °C for 1 h under Pa conditions.

[0046] (2) Vacuum melting: The pretreated metal raw materials are placed in graphite or ceramic crucibles in order of increasing melting point. The crucibles are then placed in a vacuum arc melting furnace or a vacuum induction melting furnace. The furnace chamber is evacuated to a vacuum degree of 1.0 × 10⁻⁶ using a mechanical pump and a molecular pump. -3Pa, then high-purity argon gas is introduced to 0.06 MPa, and three vacuum / gas filling cycles are performed to further reduce the gas and impurity content; under the argon protective atmosphere, an electric arc or induction power supply is started to melt the raw materials in the crucible into an alloy melt; after the melt is completely melted, it is kept at the temperature for 10 min to allow the alloy elements to fully diffuse and mix.

[0047] (3) Casting: After the alloy melt is completely melted in the melting furnace and the composition is uniform after heat preservation, the alloy melt is poured from the furnace into a pre-cleaned and preheated cast iron mold or water-cooled copper mold through a flipping crucible or a funnel casting device. After casting, the mold is placed in a static state and allowed to cool naturally in the air to room temperature. After demolding, an aluminum-based medium-entropy alloy square ingot is obtained.

[0048] The density of the high-strength lightweight aluminum-based medium-entropy alloy obtained in this embodiment is shown in Table 1. The density of the medium-entropy alloy obtained in this embodiment is 3.86. The mechanical properties of the high-strength lightweight aluminum-based medium-entropy alloy obtained in this embodiment are shown in Table 1. The compressive yield strength of the medium-entropy alloy obtained in this embodiment is 832 MPa, the compressive strength is 2254 MPa, and the fracture strain is ~23.7%.

[0049] Figure 4 The image shows a scanning electron microscope (SEM) image of the high-strength, lightweight aluminum-based medium-entropy alloy prepared in Example 5. It shows a typical dendritic structure with dendrites of about tens of micrometers in size and relatively uniform distribution. The contrast between light and dark areas in the dendrites and the interdendritic regions is obvious. A small amount of second phase or intermetallic compounds are enriched in the interdendritic regions, reflecting a certain degree of solidification segregation. The overall structure is dense, without obvious pores or inclusions, which provides the microstructure basis for the excellent mechanical properties of the alloy.

[0050] The testing methods for the mechanical properties and density of the high-strength, lightweight aluminum-based medium-entropy alloys in the above embodiments are as follows: (1) Compression mechanical properties: Compression tests were conducted using an electronic universal testing machine. The cylindrical specimens had dimensions of Ф6mm × 12mm, and the strain rate was 10. -3 / s; (2) Density test: The density of the alloy was tested using the Archimedes displacement method.

[0051] Table 1. Composition, compressive mechanical properties, and density of the examples. Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-strength, lightweight aluminum-based medium-entropy alloy, characterized in that, Its chemical composition, by atomic percentage, is Al. a Ti b Cr c M d Where: a is 45~65%, b is 10~30%, c is 15~30%, d is 5~10%, and a+b+c+d=100; M is one or more elements among Sc, V, and Mn.

2. The method for preparing the high-strength, lightweight aluminum-based medium-entropy alloy according to claim 1, characterized in that, Specifically, the following steps are included: (1) Batching and pretreatment: Select metal Al, metal Ti, metal Cr and M element metals with a purity of not less than 99.9 wt.%, weigh them according to the target atomic percentage, and control the weighing error of each element within ±0.5 at.%. After mechanical grinding and chemical cleaning, the raw materials are dried. (2) Raw material placement: The pretreated Al, Ti, Cr and M raw materials are placed in the vacuum melting device in order of increasing melting point; (3) Melting: The pretreated raw materials are loaded into a graphite crucible or a ceramic crucible and placed in a vacuum arc melting furnace or a vacuum induction melting furnace. After the vacuum is reached, high-purity argon is introduced and at least several vacuuming / gas filling cycles are performed. The raw materials are heated under argon protection to melt them completely and then kept at a constant temperature to make the alloy composition uniform. (4) Casting: The molten and homogeneous alloy melt is poured into a pre-cleaned and preheated cast iron mold or water-cooled copper mold to about 200 °C, and then naturally cooled to room temperature in the air to obtain an aluminum-based medium-entropy alloy ingot.

3. The method for preparing the high-strength, lightweight aluminum-based medium-entropy alloy according to claim 2, characterized in that, The vacuum condition in step (3) is: ≤5×10 -3 Pa.

4. The method for preparing the high-strength, lightweight aluminum-based medium-entropy alloy according to claim 2, characterized in that, In step (3), the purity of argon gas is ≥99.9 wt.%, and the argon gas pressure inside the smelting device is lower than the ambient gas pressure outside the device.

5. The method for preparing the high-strength, lightweight aluminum-based medium-entropy alloy according to claim 2, characterized in that, In step (3), the number of vacuuming / gas filling cycles is ≥2 times.

6. The method for preparing the high-strength, lightweight aluminum-based medium-entropy alloy according to claim 2, characterized in that, The heat preservation time in step (3) is 5~10 min.

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