Seed alloy with core-shell structure, preparation method thereof and ultrafine-grained near-eutectic aluminum-silicon alloy

Abstract

The present invention provides a seed alloy with a core-shell structure, a preparation method thereof, and an ultrafine-grained near-eutectic aluminum-silicon alloy. The seed alloy includes an Al matrix and a plurality of seed crystals distributed on the Al matrix, and the plurality of seed crystals include SrB6@REB6 seed crystals with a core-shell structure, wherein SrB6 is the shell layer of the SrB6@REB6 seed crystal, and REB6 is the core of the SrB6@REB6 seed crystal. According to the present invention, efficient refinement of α-Al in the near-eutectic aluminum-silicon alloy can be achieved, and at the same time, the modification of eutectic Si can be promoted, so that the service mechanical properties and forming processing properties of the Al-Si alloy can be stably improved.

Description

Technical Field

[0001] The invention relates to the field of metal materials, and in particular to a seed alloy with a core-shell structure, a preparation method thereof, and an ultrafine-grained near-eutectic aluminum-silicon alloy. Background Art

[0002] Near-eutectic Al-Si alloys are widely used due to their excellent casting formability, specific strength, volume stability and heat resistance. Taking 4032 aluminum alloy as an example, it is used in the aerospace field to manufacture aircraft engine parts, guidance systems, rocket engine components and other parts that require heat resistance and high strength. In the automotive industry, it is often used in the manufacture of high-performance automobile engines, such as racing engines and engine parts for high-performance models.

[0003] Therefore, high-performance and high-quality Al-Si alloys have great engineering application value. Among them, grain refinement of alloys is the simplest and most effective way to improve the strength and plasticity, organizational density and surface quality of alloys. However, when the Si content in aluminum alloys exceeds 3wt%, the refining effect of commercial refiners such as Al-Ti-B on α-Al is greatly weakened. When the Si content exceeds 8wt%, Al-Ti-B is basically ineffective.

[0004] Therefore, for Al-Si alloys with high silicon content, especially near-eutectic Al-Si alloys, there is an urgent need for an efficient refiner that does not conflict with Si modification treatment. Summary of the invention

[0005] The present invention provides a seed alloy comprising SrB6@REB6 seed crystals of a core-shell structure, which can achieve efficient refinement of near-eutectic aluminum-silicon alloys and promote the modification of eutectic Si, thereby stably improving the service mechanical properties and forming processing properties of the near-eutectic aluminum-silicon alloys.

[0006] According to one aspect of the present invention, a seed alloy with a core-shell structure is provided, the seed alloy comprising an Al matrix and a plurality of seeds distributed on the Al matrix, the plurality of seeds comprising SrB6@REB6 seeds with a core-shell structure, wherein SrB6 is the shell layer of the SrB6@REB6 seeds, and REB6 is the core of the SrB6@REB6 seeds.

[0007] Optionally, RE in the SrB6@REB6 seed crystal includes at least one of La and Ce.

[0008] Optionally, the plurality of seed alloys further include independent SrB6 seeds and independent REB6 seeds.

[0009] Optionally, the SrB6@REB6 seed crystal, the independent SrB6 seed crystal, and the independent REB6 seed crystal are in-situ self-generated.

[0010] Optionally, based on 100wt% of the seed alloy, the content of Sr is less than or equal to 5.7wt%, the content of RE is less than or equal to 3.2wt%, and the content of B is less than or equal to 4.3wt%.

[0011] Optionally, based on 100wt% of the seed alloy, the total content of the SrB6@REB6 seed, the independent SrB6 seed, and the independent REB6 seed is less than or equal to 10.0wt%.

[0012] Optionally, the size of the SrB6@REB6 seed crystal is between 1 μm and 5 μm.

[0013] According to another aspect of the present invention, there is provided a method for preparing a seed alloy having a core-shell structure, the preparation method comprising: adding pure aluminum and Al-B alloy into a smelting furnace, heating to melt and raising the temperature to 750°C-950°C, and keeping warm for 10min-60min to obtain a first melt; adding Al-RE alloy to the first melt, stirring and keeping warm at 750°C-950°C for 3min-20min to obtain a second melt; adding Al-Sr alloy to the second melt, stirring and keeping warm at 750°C-950°C for 3min-20min to obtain a third melt.

[0014] Optionally, the preparation method further comprises: adjusting the temperature of the third melt to 730° C.-800° C., refining the third melt for 10 min-30 min, and finally pouring to obtain the seed alloy.

[0015] According to another aspect of the present invention, there is provided an ultrafine-grained near-eutectic aluminum-silicon alloy, which is produced by refining the near-eutectic aluminum-silicon alloy using a seed alloy having a core-shell structure, and the near-eutectic aluminum-silicon alloy includes titanium.

[0016] Optionally, the total amount of the seed crystal added is 0.002wt%-2wt% of the near-eutectic aluminum-silicon alloy. The near-eutectic aluminum-silicon alloy is a 4032 aluminum alloy, wherein, based on 100wt% of the near-eutectic aluminum-silicon alloy, the near-eutectic aluminum-silicon alloy includes 11wt%-13.5wt% Si, 0.05wt%-1.3wt% Cu, 0.8wt%-1.3wt% Mg, 0.5wt%-1.3wt% Ni, 0.01wt%-0.05wt% Ti, ≤1.0wt% Fe, ≤0.1wt% Cr, ≤0.25wt% Zn, and other unspecified elements each ≤0.05wt% and a total amount ≤0.15wt%.

[0017] Optionally, the average grain size of α-Al in the ultrafine-grained near-eutectic aluminum-silicon alloy measured by the KBI ring mold method or the TP-1 standard method is between 50 μm and 150 μm.

[0018] According to the present invention, efficient refinement of α-Al in near-eutectic aluminum-silicon alloys can be achieved, and at the same time, the modification of eutectic Si can be promoted, so that the service mechanical properties and forming processing properties of Al-Si alloys can be stably improved.

[0019] The method for preparing a seed alloy with a core-shell structure according to the present invention has low raw material cost, simple process, green environmental protection, and high industrialization potential. The seed alloy prepared thereby is suitable for simultaneously realizing the refinement of α-Al in a near-eutectic aluminum-silicon alloy and the modification of eutectic silicon. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description in conjunction with the accompanying drawings, in which:

[0021] Figure 1 The electron probe analysis of the crystal structure and composition of the seed alloy with a core-shell structure according to an embodiment of the present invention;

[0022] Figure 2 It is the macro grain structure (KBI ring die) of 4032 aluminum alloy before and after adding the refiner of the prior art and the seed alloy of the embodiment of the present invention.

[0023] Figure 3 The microstructure of the 4032 aluminum alloy before and after the seed alloy of the embodiment of the present invention is added. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0026] Hereinafter, embodiments of the present disclosure will be described as follows with reference to the accompanying drawings.

[0027] However, the present disclosure may be exemplified in many different forms and should not be construed as limited to the specific embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0028] It should be understood that when the terms “include” and / or “comprises” are used in the specification, they list the presence of stated materials and / or components, but do not preclude the presence or addition of one or more other materials and / or components.

[0029] A seed alloy with core-shell structure

[0030] According to an embodiment of the present invention, a seed alloy with a core-shell structure may include an Al matrix and a plurality of seeds distributed on the Al matrix. The plurality of seeds may include a SrB6@REB6 seed with a core-shell structure, wherein SrB6 is the shell layer of the SrB6@REB6 seed, and REB6 is the core of the SrB6@REB6 seed.

[0031] Figure 1 The crystal structure and composition of the seed alloy of the core-shell structure according to the embodiment of the present invention are analyzed by electron probe. Figure 1 The crystal structure and its corresponding component analysis show that the gray-black matrix in the crystal structure is an Al matrix, on which a plurality of block particles, i.e., a plurality of crystal seeds, are distributed. The plurality of crystal seeds may include SrB6@REB6 crystal seeds having a core-shell structure, wherein SrB6 is the shell layer of the SrB6@REB6 crystal seeds, and REB6 is the core of the SrB6@REB6 crystal seeds.

[0032] According to an embodiment of the present invention, the SrB6 shell layer may surround at least a portion of the REB6 core portion. For example, the SrB6 shell layer may surround the REB6 core portion as a whole, or may only surround a portion of the REB6 core portion. The present invention does not impose any specific restrictions on this. In addition, the present invention does not impose any specific restrictions on the specific shapes and sizes of the REB6 core portion and the SrB6 shell layer.

[0033] The size and distribution of the SrB6@REB6 seed crystal as described above are more controllable. In addition, the SrB6@REB6 seed crystal uses a cheap rare earth boride as the core, and forms a SrB6 shell on its surface. SrB6 plays a major role in nucleation. Since SrB6 is a shell, less amount is required, which is conducive to saving the cost of the seed alloy.

[0034] After the seed alloy according to the embodiment of the present invention is added to the near-eutectic Al-Si melt, the SrB6 shell in the SrB6@REB6 seed reacts in situ with the free titanium in the Al-Si melt to generate highly active TiB2 on the surface. * , which can resist Si poisoning and achieve efficient nucleation of α-Al. At the same time, the Sr released by the reaction of the SrB6 shell is also highly active and can effectively modify the eutectic Si in the near-eutectic Al-Si melt.

[0035] In addition, the core of REB6 can also react with titanium in situ to generate RE and highly active TiB2 * , achieving efficient nucleation of α-Al. At the same time, the RE released by the reaction in the core of REB6 can effectively transform the eutectic Si in the near-eutectic Al-Si melt together with Sr.

[0036] Therefore, the seed alloy containing SrB6@REB6 seeds can simultaneously achieve efficient refinement of α-Al and effective modification of eutectic Si, so that the service mechanical properties and forming processing properties of Al-Si alloys can be steadily improved.

[0037] like Figure 1 As shown, the seeds in the seed alloy may include independent SrB6 seeds and independent REB6 seeds in addition to the core-shell SrB6@REB6 seeds. Independent SrB6 seeds and independent REB6 seeds refer to seeds that exist independently without forming core-shell SrB6@REB6. Similar to the reaction between the SrB6 shell and the REB6 core, independent SrB6 seeds and independent REB6 seeds may also react in situ with free titanium in the Al-Si melt to form TiB2 and release Sr and RE, thereby refining the α-Al in the near-eutectic Al-Si melt and modifying the eutectic Si.

[0038] According to an embodiment of the present invention, SrB6@REB6 seeds, independent SrB6 seeds, and independent REB6 seeds can be in-situ self-generated. According to the present invention, the SrB6@REB6 seeds, independent SrB6 seeds, and independent REB6 seeds formed by in-situ reaction have high interface bonding strength with the Al matrix, and the scale and distribution are more controllable, which is more beneficial to subsequent reactions, refinement, and modification.

[0039] According to an embodiment of the present invention, RE may include at least one of La and Ce. For example, REB6 may be at least one of LaB6, CeB6 and (La, Ce)B6.

[0040] According to an embodiment of the present invention, based on 100wt% of the seed alloy, the content of Sr may be less than or equal to 5.7wt%, the content of RE may be less than or equal to 3.2wt%, and the content of B may be less than or equal to 4.3wt%. The lower limits of the contents of Sr, RE, and B may not be specifically limited. In addition, as an example only, based on 100wt% of the seed alloy, the content of Sr may be greater than or equal to 0.09wt%, the content of RE may be greater than or equal to 0.05wt%, and the content of B may be greater than or equal to 0.07wt%.

[0041] According to an embodiment of the present invention, based on 100wt% of the seed alloy, the total content of SrB6@REB6 seeds, independent SrB6 seeds, and independent REB6 seeds may be less than or equal to 10.0wt%. The lower limit of the content of the above three seeds may not be specifically limited. As an example only, the total content of SrB6@REB6 seeds, independent SrB6 seeds, and independent REB6 seeds may be greater than or equal to 0.05wt%. When the total content of the above three seed alloys contained in the seed alloy is small, when the near-eutectic Al-Si alloy is refined, the content of effective seeds can be increased by submitting the addition amount of seed alloy. Therefore, the total content of the above three seed alloys has no obvious effect on the refinement and modification effect achieved by the present invention.

[0042] According to an embodiment of the present invention, the size of the SrB6@REB6 seed can be between 1 μm and 5 μm. In addition, the size of the independent SrB6 seed and the independent REB6 seed can also be between 1 μm and 5 μm. According to the present invention, since the size distribution of the seed alloy is relatively concentrated, it can adapt to the narrow liquid-solid temperature range characteristics of the near-eutectic Al-Si alloy, and can efficiently nucleate within a relatively concentrated supercooling and temperature range, thereby ensuring its nucleation efficiency and refinement effect.

[0043] Preparation method of seed alloy with core-shell structure

[0044] According to an embodiment of the present invention, a method for preparing a seed alloy of a core-shell structure may include: adding pure aluminum and Al-B alloy to a smelting furnace, heating and melting and raising the temperature to 750°C-950°C, and keeping it warm for 10min-60min to obtain a first melt; adding Al-RE alloy to the first melt, stirring and keeping it warm at 750°C-950°C for 3min-20min to obtain a second melt; adding Al-Sr alloy to the second melt, stirring and keeping it warm at 750°C-950°C for 3min-20min to obtain a third melt.

[0045] According to an embodiment of the present invention, REB6 is generated in a second melt obtained after adding Al-RE alloy to the first melt and keeping it at 750℃-950℃ for 3min-20min. SrB6 is generated in a third melt obtained after adding Al-Sr alloy to the second melt and keeping it at 750℃-950℃ for 3min-20min, wherein a portion of SrB6 forms a shell with REB6 as the core to form SrB6@REB6 seeds, and another portion of SrB6 forms independent SrB6 seeds. In addition, a portion of REB6 remains as an independent REB6 seed. SrB6@REB6 seeds, independent SrB6 seeds, and independent REB6 seeds have been described above, and repeated descriptions will be omitted here.

[0046] The preparation method according to the embodiment of the present invention may further include adjusting the temperature of the third melt to 730° C.-800° C., refining the third melt for 10 min-30 min, and finally pouring to obtain a seed alloy with a core-shell structure.

[0047] The method for preparing a seed alloy with a core-shell structure according to an embodiment of the present invention has low raw material cost, simple process, green environmental protection, and high industrialization potential.

[0048] Ultrafine Grained Near-Eutectoid Al-Si Alloy

[0049] The present invention also provides an ultrafine-grained near-eutectic aluminum-silicon alloy produced by refining the near-eutectic aluminum-silicon alloy using the above-mentioned seed alloy with a core-shell structure.

[0050] According to an embodiment of the present invention, after the quasi-eutectic aluminum-silicon alloy is melted and heated to 720°C-750°C, a seed alloy with a core-shell structure according to an embodiment of the present invention is added, and then kept warm for 5min-60min to obtain an ultrafine-grained quasi-eutectic aluminum-silicon alloy.

[0051] According to an embodiment of the present invention, the near-eutectic aluminum-silicon alloy may include titanium. After the seed alloy is added to the near-eutectic Al-Si melt, the SrB6 shell in the SrB6@REB6 seed reacts in situ with the titanium in the Al-Si melt to generate highly active TiB2 on the surface. * It also releases highly active Sr, achieving efficient nucleation of α-Al and effective modification of eutectic Si. In addition, the core of REB6 can also react with titanium in situ to generate RE and highly active TiB2 * , achieving efficient nucleation of α-Al, and the released RE can, together with Sr, effectively modify the eutectic Si in the near-eutectic Al-Si melt.

[0052] In addition, similar to the reaction of SrB6 shell and REB6 core, independent SrB6 seeds and independent REB6 seeds can also react in situ with titanium in the Al-Si melt to form TiB2 and release Sr and RE, thereby refining the α-Al in the near-eutectic Al-Si melt and modifying the eutectic Si.

[0053] According to an embodiment of the present invention, the average grain size of α-Al in the ultrafine-grained near-eutectic aluminum-silicon alloy measured by the KBI ring mold method or the TP-1 standard method may be between 50 μm and 150 μm, thereby achieving effective refinement of α-Al.

[0054] According to an embodiment of the present invention, the total amount of seed crystals added is 0.002wt%-2wt% of the near-eutectic aluminum-silicon alloy. If the total amount of seed crystals added is less than 0.002wt% of the near-eutectic aluminum-silicon alloy, the seed content used for refining α-Al and modifying eutectic silicon is insufficient, which may affect the refinement and modification effects. If the total amount of seed crystals added is greater than 2wt% of the near-eutectic aluminum-silicon alloy, although the refinement and modification effects may not be affected, it will cause material waste.

[0055] According to an embodiment of the present invention, the near-eutectic aluminum-silicon alloy may be a 4032 aluminum alloy, wherein, based on 100wt% of the near-eutectic aluminum-silicon alloy, the near-eutectic aluminum-silicon alloy may include Si with a content of 11wt%-13.5wt%, Cu with a content of 0.05wt%-1.3wt%, Mg with a content of 0.8wt%-1.3wt%, Ni with a content of 0.5wt%-1.3wt%, Ti with a content of 0.01wt%-0.05wt%, Fe with a content of ≤1.0wt%, Cr with a content of ≤0.1wt%, Zn with a content of ≤0.25wt%, and other unspecified elements each with ≤0.05wt% and a total amount of ≤0.15wt%. However, the specific materials and contents of the near-eutectic aluminum-silicon alloy are not limited thereto.

[0056] Hereinafter, specific embodiments of the present invention will be described.

[0057] Example

[0058] 1. Preparation of seed alloy with core-shell structure

[0059] (1) Prepare the raw materials required for the seed alloy according to the following mass percentages: 1.0 strontium, 0.86 lanthanum, 1.14 boron, and the balance aluminum: pure aluminum, Al-B alloy, Al-La alloy, and Al-Sr alloy.

[0060] (2) Add pure aluminum and Al-B alloy into a smelting furnace, heat and melt, and raise the temperature to 790°C-800°C, and keep the temperature for 30 minutes to obtain a first melt.

[0061] (3) Adding Al-La alloy to the first melt, stirring and keeping the mixture at 790° C.-800° C. for 15 minutes to obtain a second melt.

[0062] (4) Adding Al-Sr alloy to the second melt, stirring and keeping the mixture at 790° C.-800° C. for 15 minutes to obtain a third melt.

[0063] (5) The temperature of the third melt is adjusted to 750° C., the third melt is refined for 20 min, and finally poured to obtain a seed alloy, wherein the total content of seeds in the seed alloy is 3 wt %.

[0064] 2. Preparation of ultrafine-grained near-eutectic aluminum-silicon alloy

[0065] 0.4wt% seed alloy was added into 4032 aluminum alloy at 730℃, kept warm for 15min and 30min respectively, and then poured into KBI ring mold.

[0066] Comparative Example

[0067] 0.4wt% of commercial Al-5Ti-1B alloy was added to 4032 aluminum alloy at 730℃, kept warm for 15min, and then poured into a KBI ring mold.

[0068] Figure 2 (a) is the macro grain structure of the unrefined 4032 alloy (KBI ring die). Figure 2 (b) is the macro grain structure (KBI ring die) of the 4032 alloy of the comparative example (4032 alloy + 0.4wt% Al-5Ti-1B) after being kept warm for 15 minutes; Figure 2 (c) and (d) are the macroscopic grain structures (KBI ring die) of the 4032 alloy of the embodiment (4032 alloy + 0.4wt% core-shell structure seed alloy) after being kept warm for 15min and 30min respectively.

[0069] like Figure 2 As shown in (a), it can be seen that the original 4032 alloy grains are abnormally coarse, with a grain size of about 5 mm. Figure 2 As shown in (b), adding 0.4wt% Al-5Ti-1B has little refinement effect. The millimeter-level matrix grains and developed dendrites will lead to long shrinkage feeding channels and large resistance, making it difficult to feed shrinkage between dendrites, causing casting defects such as segregation, shrinkage porosity, shrinkage pores, and snowflakes, which ultimately lead to poor overall performance of the casting and high scrap rate. Figure 2 As shown in (c) and (d), after adding the seed alloy of the core-shell structure of the present invention, the alloy grains are significantly refined to about 100 μm, and the refinement effect is basically the same after 15 minutes and 30 minutes of heat preservation, which reflects the anti-degradation property of the seed alloy of the present invention, and can fully match the process conditions and process window of 4032 production. After refinement, the flowability, forming performance of the alloy melt and the surface quality and consistency of the casting can be improved, the density can be improved, the defects such as shrinkage and shrinkage can be reduced, and finally the yield rate, processing performance and mechanical properties of the product can be improved.

[0070] Figure 3 (a) is the microstructure of the 4032 alloy before adding the core-shell structure seed alloy. Figure 3 (b) is the microstructure of the 4032 alloy after adding 0.4 wt % of the core-shell structure seed alloy according to the embodiment and keeping the alloy warm for 15 minutes.

[0071] from Figure 3 As can be seen from (a) before adding the core-shell structure seed alloy, the eutectic Si in the 4032 alloy has a coarse plate-like morphology. During service, stress concentration will form at the sharp corners of the eutectic Si, severely splitting the matrix, causing interface debonding or self-fracture, and ultimately leading to cracking and failure of the alloy. Figure 3 It can be seen from (b) that after adding the seed alloy with a core-shell structure, the morphology of eutectic Si in the 4032 alloy presents typical metamorphic characteristics, which are in the form of fine fibers, short rods or dots, which can reduce the stress concentration of the alloy during service and the effect of splitting on the matrix.

[0072] It can be seen that the core-shell structure seed alloy according to the embodiment of the present invention can not only efficiently refine α-Al, but also promote the modification of eutectic Si, thereby improving the service mechanical properties and forming processing performance of Al-Si alloys.

[0073] As described above, the present invention can achieve beneficial technical effects not limited to the following description.

[0074] According to the present invention, efficient refinement of α-Al in near-eutectic aluminum-silicon alloys can be achieved, and at the same time, the modification of eutectic Si can be promoted, so that the service mechanical properties and forming processing properties of Al-Si alloys can be stably improved.

[0075] The method for preparing a seed alloy with a core-shell structure according to the present invention has low raw material cost, simple process, green environmental protection, and high industrialization potential. The seed alloy prepared thereby is suitable for simultaneously realizing the refinement of α-Al in a near-eutectic aluminum-silicon alloy and the modification of eutectic silicon.

[0076] The seed alloy with a core-shell structure according to the embodiment of the present invention can refine the average grain size of α-Al in the near-eutectic aluminum-silicon alloy to between 50 μm and 150 μm.

[0077] While exemplary embodiments of the present invention have been described in detail with reference to examples, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the claims.

Claims

1. A seed alloy having a core-shell structure, characterized in that: The seed alloy includes an Al matrix and a plurality of seed crystals distributed on the Al matrix, wherein the plurality of seed crystals include SrB6@REB6 seed crystals having a core-shell structure, wherein SrB6 is a shell layer of the SrB6@REB6 seed crystal, REB6 is a core portion of the SrB6@REB6 seed crystal, and SrB6 surrounds at least a portion of REB6. Wherein, the seed alloy also includes independent SrB6 seeds.

2. The seed alloy having a core-shell structure according to claim 1, characterized in that: The RE in the SrB6@REB6 seed crystal includes at least one of La and Ce.

3. The seed alloy having a core-shell structure according to claim 1, characterized in that: The seed alloy also includes independent REB6 seeds.

4. The seed alloy having a core-shell structure according to claim 3, characterized in that: The SrB6@REB6 seed crystal, the independent SrB6 seed crystal, and the independent REB6 seed crystal are in-situ self-generated.

5. The seed alloy with a core-shell structure according to claim 3, characterized in that: Based on 100wt% of the seed alloy, the content of Sr is less than or equal to 5.7wt%, the content of RE is less than or equal to 3.2wt%, and the content of B is less than or equal to 4.3wt%.

6. The seed alloy with a core-shell structure according to claim 5, characterized in that: Based on 100wt% of the seed alloy, the total content of the SrB6@REB6 seed, the independent SrB6 seed, and the independent REB6 seed is less than or equal to 10.0wt%.

7. The seed alloy with a core-shell structure according to claim 1, characterized in that: The size of the SrB6@REB6 seed crystal is between 1 μm and 5 μm.

8. A method for preparing a seed alloy having a core-shell structure according to any one of claims 1 to 7, characterized in that: The preparation method comprises: Add pure aluminum and Al-B alloy into a smelting furnace, heat and melt, raise the temperature to 790°C-800°C, and keep the temperature for 10min-60min to obtain a first melt; Adding Al-RE alloy to the first melt, stirring and keeping at 790° C.-800° C. for 3 min-20 min to obtain a second melt, generating REB6; Add Al-Sr alloy to the second melt, stir and keep at 790℃-800℃ for 3min-20min to obtain a third melt to generate SrB6, wherein a part of SrB6 forms a shell with REB6 as the core to form SrB6@REB6 seed crystals, and the other part of SrB6 forms independent SrB6 seed crystals.

9. The preparation method according to claim 8, characterized in that: The preparation method further includes: adjusting the temperature of the third melt to 730° C.-800° C., refining the third melt for 10 min-30 min, and finally pouring to obtain the seed alloy.

10. An ultrafine-grained near-eutectic aluminum-silicon alloy, characterized in that: The ultrafine-grained near-eutectic aluminum-silicon alloy is produced by refining a near-eutectic aluminum-silicon alloy using a seed alloy having a core-shell structure according to any one of claims 1 to 7, wherein the near-eutectic aluminum-silicon alloy includes titanium.

11. The ultrafine-grained near-eutectic aluminum-silicon alloy according to claim 10, characterized in that: The total amount of the seed crystal added is 0.002wt%-2wt% of the near-eutectic aluminum-silicon alloy. The near-eutectic aluminum-silicon alloy is a 4032 aluminum alloy, wherein, based on 100wt% of the near-eutectic aluminum-silicon alloy, the near-eutectic aluminum-silicon alloy includes Si with a content of 11wt%-13.5wt%, Cu with a content of 0.05wt%-1.3wt%, Mg with a content of 0.8wt%-1.3wt%, Ni with a content of 0.5wt%-1.3wt%, Ti with a content of 0.01wt%-0.05wt%, Fe with a content of ≤1.0wt%, Cr with a content of ≤0.1wt%, Zn with a content of ≤0.25wt%, and other unspecified elements with each content of ≤0.05wt% and a total amount of ≤0.15wt%.

12. The ultrafine-grained near-eutectic aluminum-silicon alloy according to claim 10, characterized in that: The average grain size of α-Al in the ultrafine-grained near-eutectic aluminum-silicon alloy measured by the KBI ring mold method or the TP-1 standard method is between 50μm and 150μm.

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