Grain refiner, al-si alloy, and preparation method and use thereof

Abstract

The application discloses a grain refiner, an aluminum-silicon alloy, a preparation method and application thereof. The chemical composition of the grain refiner is Al, Nb, B, Eu and inevitable impurities, the content of Nb is 0.1-10wt%, the content of B is 0.1-10wt%, the content of Eu is 0.1-5.0wt%, and Al is the balance based on the total weight of the grain refiner. The grain refiner has small refining phase size, dispersed distribution and uniform composition, and has better refining effect when refining the aluminum-silicon alloy.

Description

Technical Field

[0001] This invention relates to a grain refiner, an aluminum-silicon alloy, its preparation method, and its uses. Background Technology

[0002] Cast aluminum-silicon alloys are widely used in industry due to their excellent mechanical properties and casting performance. Grain refinement of the alloy can result in a dense alloy microstructure, while also reducing the tendency for hot cracking and segregation in castings, decreasing porosity, and thus improving the overall performance of the alloy. The most common and effective grain refinement method is the addition of grain refiners.

[0003] Al-5Ti-B refining agent has been widely used. However, when refining high-silicon-content Al-Si alloys (Si≥5%), Si elements tend to accumulate on the surface of the refined phase TiB2 in the Al-5Ti-B refining agent, causing the refined phase TiB2 to lose its heterogeneous nucleation function, thus causing the refining agent to suffer from "Si poisoning".

[0004] Literature indicates that Al-Nb-B refining agents, due to the high reaction temperature of the NbB phase with Si (which generally does not react at aluminum alloy smelting temperatures), effectively "immunize" against Si poisoning. Therefore, Al-Nb-B alloys show great promise in Al-Si casting applications. However, the precipitation rate of Al-Nb-B alloys is very rapid during preparation and use, resulting in low Nb and B yields in the Al-Nb-B master alloy, making the proportions difficult to control and leading to unstable refining effects. Furthermore, Nb is expensive, and adding large amounts to increase yield would significantly increase refining costs.

[0005] In recent years, researchers have focused on developing novel grain refiners to address these issues. For example, CN104583429A discloses an Al-Nb-B master alloy for grain refinement, involving a novel Al-Nb-B grain refiner. This method uses pure Al, elemental Nb powder, and KBF4 powder as raw materials at 800–850°C for a reaction time of 2 hours, with stirring using a ceramic rod during the reaction. However, this method is costly, unsuitable for large-scale industrial production, and suffers from uneven microstructure and a decline in grain refinement effect. The grain size of the refined aluminum-silicon alloy remains relatively large, failing to meet the requirements for high-quality aluminum alloy products. CN109385542A discloses a method for preparing an aluminum-niobium-boron alloy rod for grain refinement, employing extrusion deformation to refine the refining phase in the Al-Nb-B alloy. This method improves the problem of declining grain refinement effect, but the composition of the extruded alloy rod remains uneven. CN111705232A discloses a method for preparing an aluminum-niobium-boron master alloy for grain refinement, and CN109022931A discloses an aluminum-niobium-boron master alloy, its preparation method, and its application. Both methods use an Al-Nb master alloy to prepare an Al-Nb-B grain refiner master alloy, which reduces the preparation cost of the grain refiner master alloy. In addition, both methods use different methods to optimize the uniformity of the microstructure and composition of the Al-Nb-B grain refiner master alloy, but the effect is still not ideal, and the problem of poor microstructure and composition uniformity still exists.

[0006] CN105624477A discloses a low-cooling-rate-sensitive, high-nucleation-capacity AlNbBRE grain refiner for cast aluminum alloys and its preparation method, and CN105648250A discloses the same. Both methods improve the sensitivity of the Al-Nb-B grain refiner to cooling rate and its grain refinement effect by introducing one or a mixture of La, Ce, Nd, Er, Gd, Yb, and Sc into the Al-Nb-B alloy. However, this method still does not solve the problem of uniform microstructure composition.

[0007] CN109385544A discloses an Al-MB grain refiner for cast aluminum-silicon alloys and its preparation method, wherein M in the Al-MB grain refiner represents Ti and Nb. This document mentions that the Al-MB grain refiner can be added to high-silicon-content aluminum-silicon alloys with a Si mass percentage of not less than 5.0 wt% to refine the α-Al grain size in the high-silicon-content aluminum-silicon alloy to no more than 700 micrometers. However, the grain size obtained in this patent document is still relatively large. Summary of the Invention

[0008] In view of this, one object of the present invention is to provide a grain refiner for casting aluminum-silicon alloys, which refines phases with small size, dispersed distribution, and uniform composition. When refining aluminum-silicon alloys, it can reduce the grain size of the refined aluminum-silicon alloy to approximately 220 μm, preferably to 198.15 μm. This can improve the mechanical properties of the refined aluminum-silicon alloy. Another object of the present invention is to provide a method for preparing the above-mentioned grain refiner, which has good process repeatability. A further object of the present invention is to provide a method for preparing aluminum-silicon alloys, which uses the grain refiner of the present invention for refining to obtain a refined aluminum-silicon alloy. Yet another object of the present invention is to provide an aluminum-silicon alloy. A still other object of the present invention is to provide an application of the grain refiner.

[0009] On one hand, the present invention provides a grain refiner for casting aluminum-silicon alloys, wherein the chemical composition of the grain refiner is Al, Nb, B, Eu, and unavoidable impurities.

[0010] Based on the total weight of the grain refiner, the Nb content is 0.1–10 wt%, the B content is 0.1–10 wt%, the Eu content is 0.1–5.0 wt%, and the Al is the balance.

[0011] According to the grain refiner of the present invention, preferably, the alloy nucleation phases of the grain refiner include NbAl3 phase, NbB2 phase, and Nb2Al phase. 20 One or more of Eu phase and EuAl phase, with the matrix phase being α-Al phase;

[0012] The size of the NbAl3 phase is less than or equal to 5 μm; Nb2Al 20 The size of the Eu phase is less than or equal to 5 μm; the size of the NbB2 phase is less than or equal to 2 μm; and the size of the EuAl phase is less than or equal to 2.5 μm.

[0013] According to the grain refiner of the present invention, preferably, the size of the NbAl3 phase is less than or equal to 2.5 μm; Nb2Al 20 The size of the Eu phase is less than or equal to 2.5 μm; the size of the NbB2 phase is less than or equal to 1.5 μm; and the size of the EuAl phase is less than or equal to 2.0 μm.

[0014] On the other hand, the present invention also provides a method for preparing the grain refiner according to the above description, comprising the following steps:

[0015] 1) Prepare a salt solvent melt from cryolite, sodium chloride, and potassium chloride;

[0016] 2) Add europium oxide and niobium pentoxide to the salt solvent melt of step 1), mix, and cool to obtain the precursor; wherein the total volume of europium oxide and niobium pentoxide is 1 to 50% of the volume of the salt solvent melt;

[0017] 3) Form aluminum melt from aluminum ingots; add potassium fluoroborate to the aluminum melt in batches and stir, then add the precursor obtained in step 2), continue stirring and reacting until complete, remove the salt solvent melt, and obtain an alloy solution;

[0018] 4) The alloy solution is sequentially refined, degassed, and slag removed to obtain a slag-removed alloy solution. The slag-removed alloy solution is further processed to obtain a grain refiner.

[0019] According to the preparation method of the present invention, preferably, the further treatment of the alloy solution after slag removal is optionally one of the following:

[0020] (a) Cast the alloy solution after slag removal into ingots to obtain a grain refiner;

[0021] (b) The alloy solution after slag removal is poured into a casting rod and then extruded into a fine rod to obtain a grain refiner;

[0022] (c) The alloy solution after slag removal is continuously cast and rolled into fine rods to obtain a grain refiner.

[0023] According to the preparation method of the present invention, preferably, based on the total weight of the salt solvent melt, cryolite is 20-60 wt%, sodium chloride is 20-40 wt%, and potassium chloride is 15-40 wt%.

[0024] According to the preparation method of the present invention, preferably:

[0025] In step 3), before adding potassium fluoroborate to the aluminum melt, the potassium fluoroborate is dried at 100-120°C to remove moisture, and then divided into multiple portions, each of which is wrapped in aluminum foil.

[0026] In step 3), the temperature for continued stirring is 850–950°C, and the reaction time is 30–60 min.

[0027] Furthermore, the present invention also provides a method for preparing an aluminum-silicon alloy, comprising the following steps:

[0028] Aluminum-silicon alloy raw materials with a silicon content of 5 wt% or more are melted to obtain aluminum-silicon alloy liquid; grain refiner as described above is added to the aluminum-silicon alloy liquid and mixed to obtain metal liquid; the metal liquid is refined, degassed, and slag is removed, then cooled, and then solidified and formed to obtain refined aluminum-silicon alloy.

[0029] The amount of the grain refiner added is 0.1 to 0.5% of the mass of the aluminum-silicon alloy liquid.

[0030] In another aspect, the present invention also provides an aluminum-silicon alloy, which is prepared by the preparation method described above.

[0031] In another aspect, the present invention provides the use of a grain refiner in refining the grain size of aluminum-silicon alloys, wherein the chemical composition of the grain refiner is Al, Nb, B, Eu, and unavoidable impurities.

[0032] Based on the total weight of the grain refiner, the Nb content is 0.1–10 wt%, the B content is 0.1–10 wt%, the Eu content is 0.1–5.0 wt%, and the Al is the balance.

[0033] The grain refiner of this invention produces grains with small, dispersed, and uniformly composed refinement phases. The preparation method of this grain refiner boasts a high yield of effective elements and exhibits superior refining effects compared to grain refiners prepared using existing technologies. This method involves the in-situ generation of an intermediate alloy of NbB2 and NbAl3 phases. The grain refiner prepared by this invention increases the number density of effective nucleation sites, improving refining efficiency. Compared to existing Al-Nb-B grain refiners, it allows for achieving the same refining effect with a smaller amount of refiner, thereby further reducing the cost of grain refiners. The grain refiner of this invention can refine high-silicon-content (Si content not less than 5 wt%) aluminum-silicon alloys, resulting in smaller grain sizes and improved mechanical properties. Attached Figure Description

[0034] Figure 1 This is a SEM image of the grain refiner obtained in Example 1 of the present invention.

[0035] Figure 2 This is an SEM image of the grain refiner obtained in Example 2 of the present invention.

[0036] Figure 3 This is a SEM image of the grain refiner obtained in Example 3 of the present invention.

[0037] Figure 4 for Figure 3 A magnified view of a portion of the image.

[0038] Figure 5 The image shows the macroscopic corrosion results of a blank aluminum-silicon alloy.

[0039] Figure 6 This is a macroscopic corrosion result diagram of the refined aluminum-silicon alloy obtained in Experimental Example 1 of the present invention.

[0040] Figure 7 This is a macroscopic corrosion result diagram of the refined aluminum-silicon alloy obtained in Experimental Example 2 of the present invention.

[0041] Figure 8This is a macroscopic corrosion result diagram of the refined aluminum-silicon alloy obtained in Experimental Example 3 of the present invention.

[0042] Figure 9 The image shows the grain size results of the blank aluminum-silicon alloy, Experimental Example 1, Experimental Example 2, Experimental Example 3, Comparative Experimental Example 1, and Comparative Experimental Example 2.

[0043] Figure 10 The tensile strength and elongation of the refined aluminum-silicon alloys obtained from the blank aluminum-silicon alloy, Experimental Example 1, Experimental Example 2, Experimental Example 3, Comparative Experimental Example 1, and Comparative Experimental Example 2 are plotted.

[0044] Figure 11 The image shows the SEM results of the refined aluminum-silicon alloy obtained in Experiment Example 3.

[0045] Figure 12 The image shows the SEM results of the refined aluminum-silicon alloy obtained in Experiment Example 1 for comparison.

[0046] Figure 13 The image shows the SEM results of the refined aluminum-silicon alloy obtained in Experiment Example 2 for comparison. Detailed Implementation

[0047] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0048] <Grain refiner>

[0049] The grain refiner of this invention can be used for refining aluminum-silicon alloys, especially for refining aluminum-silicon alloys with high silicon content. The chemical composition of the grain refiner is Al, Nb, B, Eu, and unavoidable impurities. Based on the total weight of the grain refiner, the Nb content is 0.1–10 wt%, the B content is 0.1–10 wt%, the Eu content is 0.1–5.0 wt%, and Al is the balance.

[0050] Based on the total weight of the grain refiner, the Nb content is preferably 0.5 to 5 wt%, more preferably 1.0 to 2.5 wt%, for example, 1 wt%, 1.2 wt%, 1.3 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, or 2 wt%.

[0051] Based on the total weight of the grain refiner, the B content is preferably 0.25 to 5 wt%, more preferably 0.3 to 4 wt%, for example, it can be 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.8 wt%, 1.0 wt%, 1.2 wt%, 1.5 wt%, 2.0 wt%, or 2.5 wt%.

[0052] Based on the total weight of the grain refiner, the Eu content is preferably 0.10 to 2.5 wt%, more preferably 0.20 to 2.0 wt%, for example, 0.10 wt%, 0.15 wt%, 0.20 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.8 wt%, 1.0 wt%, or 1.5 wt%.

[0053] This invention surprisingly discovers that using the rare earth element Eu and the grain refiner prepared by the method of this invention can better refine aluminum-silicon alloys, resulting in aluminum-silicon alloys with finer grains and more uniform microstructure. This invention believes this is because rare earth Eu atoms accumulate on the surface of the NbAl3 phase, preventing its growth, while excess Eu atoms combine with Al atoms to form the EuAl phase. During Al-Si alloy refinement, the EuAl phase dissolves, releasing rare earth Eu atoms. Rare earth Eu has a good modifying effect on eutectic silicon, thereby improving the mechanical properties of the refined aluminum-silicon alloy.

[0054] The alloy nucleation phases of the grain refiner of the present invention include NbAl3 phase, NbB2 phase, and Nb2Al phase. 20 One or more of Eu phase and EuAl phase, with the matrix phase being α-Al phase. Preferably, the alloy nucleation phase of the grain refiner of the present invention consists of NbAl3 phase, NbB2 phase, and Nb2Al phase. 20 Multiple compositions in Eu phase and EuAl phase.

[0055] The size of the NbAl3 phase is less than or equal to 5 μm, preferably less than or equal to 2.5 μm. Nb2Al 20 The size of the Eu phase is less than or equal to 5 μm, preferably less than or equal to 2.5 μm. The size of the NbB2 phase is less than or equal to 2 μm, preferably less than or equal to 1.5 μm. The size of the EuAl phase is less than or equal to 2.5 μm, preferably less than or equal to 2.0 μm.

[0056] <Preparation method of grain refiner>

[0057] The preparation method of the above-mentioned grain refiner of the present invention includes the following steps:

[0058] 1) Preparation of salt solvent melt; 2) Preparation of precursor; 3) Preparation of alloy solution; 4) Preparation of grain refiner. Optionally, it also includes: a drying step of potassium fluoroborate, and a material preparation step.

[0059] Existing technologies typically involve directly forming a melt from aluminum ingots and niobium-boron-containing raw materials, followed by casting, or directly forming a melt from aluminum ingots and niobium-boron-containing raw materials and then adding a covering agent (using a molten salt formed from sodium chloride and potassium chloride as the covering agent). This invention, however, adds niobium-europium-containing raw materials to a salt solvent melt, cools to form a precursor, then forms an aluminum ingot melt, adds potassium fluoroborate and the niobium-europium-containing precursor to the aluminum ingot melt, and finally removes the salt solvent melt to obtain an alloy solution. This method facilitates the dispersion of europium oxide and niobium pentoxide, improves reaction efficiency, and helps prevent the precipitation of the refining phase. This invention utilizes a fluoride salt reaction to reduce B atoms from potassium fluoroborate, followed by an aluminothermic reduction method to reduce rare earth Eu atoms from europium oxide and niobium pentoxide. The Nb atoms in the reaction solution react with Al and B atoms in situ to form fine NbAl3 and NbB2 phases, respectively, thereby improving the refining effect of the NbAl3 and NbB2 phases. Furthermore, rare earth Eu atoms accumulate on the surface of the NbAl3 phase, preventing its growth. Excess Eu atoms combine with Al atoms to form the EuAl phase. When refining Al-Si alloys using the grain refiner of this invention, the EuAl phase dissolves and releases rare earth Eu atoms. Rare earth Eu has a good modifying effect on eutectic silicon, thereby improving the mechanical properties of aluminum-silicon alloys.

[0060] Before step 1), the raw materials are prepared. The raw materials prepared in this invention include: aluminum ingots, potassium fluoroborate, europium oxide, niobium pentoxide, cryolite, sodium chloride, and potassium chloride. Specifically, B is added in the form of potassium fluoroborate, Nb in the form of niobium pentoxide, Eu in the form of europium oxide, and Al in the form of aluminum ingots. The actual amount of potassium fluoroborate added is 1.05 to 1.2 times the theoretical amount required for the target component, preferably 1.1 to 1.15 times. The actual amount of europium oxide added is 1.1 to 1.2 times the theoretical amount required for the target component, preferably 1.15 to 1.2 times. The actual amount of niobium pentoxide added is 1.1 to 1.2 times the theoretical amount required for the target component, preferably 1.1 to 1.15 times.

[0061] This invention uses cryolite, sodium chloride, and potassium chloride to form a salt solvent melt, which is then used as a solvent to form a precursor containing niobium and europium. This facilitates the dispersion of europium oxide and niobium pentoxide, improves reaction efficiency, and helps prevent the precipitation of the finer phase.

[0062] Based on the total weight of the salt solvent melt, cryolite comprises 20–60 wt%, sodium chloride 20–40 wt%, and potassium chloride 15–40 wt%. Preferably, based on the total weight of the salt solvent melt, cryolite comprises 30–60 wt%, sodium chloride 25–35 wt%, and potassium chloride 15–30 wt%. More preferably, based on the total weight of the salt solvent melt, cryolite comprises 50–60 wt%, sodium chloride 25–30 wt%, and potassium chloride 15–25 wt%.

[0063] The total volume of europium oxide and niobium pentoxide is 1 to 50% of the volume of the salt solvent melt, preferably 5 to 30%, and more preferably 10 to 20%.

[0064] In step 1), cryolite, sodium chloride, and potassium chloride are prepared into a salt solvent melt. Specifically, cryolite, sodium chloride, and potassium chloride are placed in a graphite crucible and heated to prepare the salt solvent melt. The temperature of the salt solvent melt is 800–850°C.

[0065] In step 2), europium oxide and niobium pentoxide are added to the salt solvent melt of step 1) and mixed, then cooled to obtain the precursor. Specifically, europium oxide and niobium pentoxide are added to the salt solvent melt of step 1) respectively, stirred to uniformly disperse europium oxide and niobium pentoxide, forming a liquid-solid mixture, then cooled to obtain the precursor.

[0066] In step 3), aluminum ingots are formed into aluminum melt; potassium fluoroborate is added to the aluminum melt in batches and stirred, then the precursor obtained in step 2) is added, and the reaction is continued to be stirred until complete. The salt solvent melt is removed to obtain an alloy solution.

[0067] In some embodiments, before adding potassium fluoroborate to the molten aluminum, the potassium fluoroborate is dried at 100–120°C to remove moisture, and then divided into multiple portions, each wrapped in aluminum foil. The aluminum foil-wrapped potassium fluoroborate is then added to the molten aluminum.

[0068] First, the precursor is crushed to a size ≤3cm, and then added to the molten aluminum in batches.

[0069] In some specific implementations, aluminum ingots are melted, with the molten aluminum temperature controlled at 850–950°C. Potassium fluoroborate wrapped in aluminum foil is added in batches. During the reaction, a graphite rotor of a degasser is used to continuously stir the solution at the top of the crucible. After the potassium fluoroborate is completely melted, the precursor is added. After the precursor has melted, the position of the graphite rotor is adjusted to stir the solution at the bottom of the crucible. After the reaction is complete, the salt solvent melt is removed. This invention has found that adjusting the position and rotation speed of the graphite stirring rod in the melt during the reaction can help prevent the precipitation of the grain-refining phase, thereby effectively maintaining the grain-refining effect of the grain refiner: during the fluoride salt reaction and the aluminothermic reaction, the graphite stirring rod is positioned near the interface between the molten salt and the aluminum liquid, far from the bottom of the crucible, and the rotation speed is increased, which helps to accelerate the reaction. When the reaction is complete and the heat preservation stage is in progress, adjust the position of the graphite stirring rod so that it is at the bottom of the crucible, 3-4 cm away from the bottom of the crucible. Reduce the speed appropriately and stir the bottom solution while ensuring that the upper molten salt is not stirred up to prevent the precipitation of the fine phase.

[0070] After adding the precursor, continue stirring at 850–950°C for 30–60 minutes until the reaction is complete.

[0071] In step 4), the alloy solution is sequentially refined, degassed, and slag removed to obtain a slag-removed alloy solution; the slag-removed alloy solution is further processed to obtain a grain refiner.

[0072] In some specific implementations, the argon valve of the degasser is opened for refining and degassing, followed by slag removal, cooling to 720±10℃, and then further processing. Argon gas is used for refining at a pressure of 0.1–0.4 MPa for 5–10 minutes. Refining, degassing, and slag removal can be performed using methods known in the art.

[0073] In this invention, the method for further processing the alloy solution after slag removal is selected from one of the following:

[0074] (a) Cast the alloy solution after slag removal into ingots to obtain a grain refiner;

[0075] (b) The alloy solution after slag removal is poured into a casting rod and then extruded into a fine rod to obtain a grain refiner;

[0076] (c) The alloy solution after slag removal is continuously cast and rolled into fine rods to obtain a grain refiner.

[0077] The diameter of the thin rod is about 9.5 mm.

[0078] In this invention, the average yield of Nb element in different parts of the Al-Nb-B-Eu grain refiner alloy is not less than 85%.

[0079] <Preparation Methods of Aluminum-Silicon Alloys>

[0080] This invention also provides a method for preparing an aluminum-silicon alloy, comprising the following steps:

[0081] Aluminum-silicon alloy raw materials with a silicon content of 5 wt% or more are melted to obtain aluminum-silicon alloy liquid; grain refiner as described above is added to the aluminum-silicon alloy liquid and mixed to obtain metal liquid; the metal liquid is refined, degassed, and slag is removed, and then cooled, preferably to 710-730°C, and then solidified and formed to obtain refined aluminum-silicon alloy.

[0082] In aluminum-silicon alloy raw materials, the silicon content is greater than or equal to 5 wt%, for example, it can be 10 wt%. The temperature of the aluminum-silicon alloy liquid can be 730-750℃.

[0083] The amount of the grain refiner added is 0.1-0.22% of the mass of the aluminum-silicon alloy liquid, preferably 0.15-0.21%, and more preferably 0.18-0.2%.

[0084] In some specific implementations, a refining agent is added to the molten metal, while an inert gas is introduced into the molten metal using a degassing machine to remove gas.

[0085] The refining agent can be any known in the art, for example, the refining agent can be selected from 25% Na3SiF6-12.5% ​​KCl-62.5% NaCl, 10% Na3AlF6-10% KCl-50% NaCl-30% NaF, or 15% Na3AlF6-45% NaCl-40% NaF.

[0086] Inert gases include, but are not limited to, argon.

[0087] Adding the grain refiner of the present invention to a silicon-aluminum alloy with a Si content of not less than 5 wt% can refine the α-Al grain size in the silicon-aluminum alloy to about 220 μm, for example, 198.15 μm. In the aluminum-silicon alloy raw material, the Si content can be greater than or equal to 5 wt% and less than or equal to 20 wt%, preferably greater than or equal to 7 wt% and less than or equal to 20%.

[0088] <Aluminum-Silicon Alloy>

[0089] This invention also provides an aluminum-silicon alloy, which is a refined aluminum-silicon alloy obtained according to the preparation method of aluminum-silicon alloy described above. Specifically, it is obtained by refining with the grain refiner of this invention. The eutectic silicon morphology of the refined aluminum-silicon alloy is fine fibrous or granular. The aluminum-silicon alloy of this invention basically does not have the problem of uneven microstructure composition. Uneven microstructure composition refers to the presence of microstructure segregation in the alloy, resulting in uneven distribution of the refining phase; some areas lack the refining phase, while others have a large distribution of the refining phase, or even agglomerate it. This will affect product performance and stability in practical applications.

[0090] <Application>

[0091] This invention also provides the use of the above-mentioned grain refiner in refining the grain size of aluminum-silicon alloys. The chemical composition of the grain refiner is Al, Nb, B, Eu, and unavoidable impurities. Based on the total weight of the grain refiner, the Nb content is 0.1–10 wt%, the B content is 0.1–10 wt%, the Eu content is 0.1–5.0 wt%, and Al is the balance. Such a grain refiner can refine aluminum-silicon alloys with high silicon content, resulting in a refined aluminum-silicon alloy with smaller grains and a more uniform microstructure. Further details about the grain refiner are provided above.

[0092] <Analytical Methods>

[0093] Elemental analysis: Analyzed using a Shimadzu ICPS-8100 inductively coupled plasma optical generator (ICPS).

[0094] SEM analysis: Microstructure analysis was performed using a Zeiss SIGMA500 microscope from Germany;

[0095] Macroscopic etching: Polish the surface to be observed with sandpaper until it is shiny and smooth. Etch the surface at room temperature with a 10-15% NaOH aqueous solution for 10-15 minutes, until the grain structure is clearly visible. After etching, rinse with water, then clean the surface with a 20-30% HNO3 aqueous solution, and finally rinse thoroughly with water and dry before proceeding to the next inspection step.

[0096] Grain size measurement: Grain size was measured using the metallographic image analysis software AON-STUDIO according to the standard for average grain size of metals (GB / T 6394-2017) - intercept method.

[0097] Determination of tensile strength and elongation: The tensile test shall be performed in accordance with GB / T 228.1-2010 Metallic materials, tensile testing - Part 1: Test method at room temperature, using an Instron universal testing machine (model INSTRON-5982); the elongation shall be measured using the attached extensometer accessories.

[0098] The following explains the sources of some of the raw materials: cryolite comes from Zhengzhou Gaojing Chemical Products Co., Ltd.; europium oxide and niobium pentoxide come from Shanghai Maclean Biochemical Technology Co., Ltd.

[0099] Example 1

[0100] The chemical composition of the target product grain refiner is: 96.5Al-1Nb-2B-0.5Eu. The preparation steps are as follows:

[0101] Prepare the raw materials, including aluminum ingots, potassium fluoroborate, europium oxide, niobium pentoxide, cryolite, sodium chloride, and potassium chloride. The amounts of aluminum ingots, potassium fluoroborate, europium oxide, and niobium pentoxide are calculated based on the chemical composition of the target product grain refiner. The actual amount of potassium fluoroborate added is 1.2 times the theoretical amount required for the target component, the actual amounts of europium oxide and niobium pentoxide added are 1.1 and 1.15 times the theoretical amounts required for the target component, respectively, and the actual amount of aluminum added is 1.1 times the theoretical amount required for the target component.

[0102] Cryolite, sodium chloride, and potassium chloride were placed in a graphite crucible and heated to prepare a salt solvent melt; wherein, based on the total weight of the salt solvent melt, cryolite was 60 wt%, sodium chloride was 25 wt%, and potassium chloride was 15 wt%; the total volume of europium oxide and niobium pentoxide was 20% of the volume of the salt solvent melt;

[0103] Europium oxide and niobium pentoxide were added to the salt solvent melt obtained in the previous step and stirred to form a liquid-solid mixture. The liquid-solid mixture was then cooled to obtain the precursor.

[0104] Aluminum ingots are formed into aluminum melt, and the temperature of the aluminum melt is controlled at 900℃. Dry potassium fluoroborate wrapped in aluminum foil is added to the aluminum melt in batches and stirred. During the reaction, a graphite rotor of a degasser is used to continuously stir the mixture at the top of the crucible. After the potassium fluoroborate is completely melted, the precursor obtained in the previous step is added. After the precursor is completely melted, the position of the graphite rotor of the degasser is adjusted so that the graphite rotor stirs the solution at the bottom of the crucible. The reaction is continued to be stirred until complete. The salt solvent melt is removed to obtain an alloy solution.

[0105] The alloy solution was successively refined and degassed, slag was removed, and the temperature was lowered to 730°C before being cast into ingots to obtain a product grain refiner.

[0106] Example 2

[0107] The only difference from Example 1 is the chemical composition of the target product grain refiner. The chemical composition of the target product grain refiner in Example 2 is: 95Al-2Nb-2B-1Eu. The actual amount of potassium fluoroborate added is 1.2 times the theoretical amount required for the target composition, the actual amounts of europium oxide and niobium pentoxide added are 1.2 times and 1.2 times the theoretical amounts required for the target composition, respectively, and the actual amount of aluminum added is 1.1 times the theoretical amount required for the target composition.

[0108] Example 3

[0109] The difference from Example 1 is that the chemical composition of the target product grain refiner is different and step 4) is different.

[0110] The chemical composition of the target product grain refiner in Example 3 is: 98.1Al-1.5Nb-0.3B-0.1Eu. The actual addition amount of potassium fluoroborate is 1.1 times the theoretical amount required for the target composition, the actual addition amounts of europium oxide and niobium pentoxide are 1.15 and 1.1 times the theoretical amounts required for the target composition, respectively, and the actual addition amount of aluminum is 1.1 times the theoretical amount required for the target composition.

[0111] Step 4) of Example 3 is as follows: The alloy solution is successively refined and degassed, slag is removed, and the temperature is lowered to 730°C to be cast into ingots. After being cast into cast rods, they are hot extruded into thin rods with a diameter of 9.5 mm. The extrusion temperature is 400°C and the extrusion speed is 20 mm / min to obtain a product grain refiner.

[0112] The chemical composition of the grain refiners obtained in Examples 1-3 was analyzed using inductively coupled plasma atomic emission spectrometry (ICP). The results are shown in Table 1.

[0113] Table 1

[0114]

[0115] The microstructure of the grain refiners prepared in Examples 1-3 was analyzed using scanning electron microscopy (SEM). SEM images of Examples 1 and 2 are shown below. Figure 1 , Figure 2 The SEM results for Example 3 are shown in the image below. Figure 3 and Figure 4 .

[0116] from Figure 1 and Figure 2 It can be seen that the large white particles in the grain refiner alloys prepared in Examples 1 and 2 are NbAl3 phase, and the fine dot-like phase is NbB2 phase. Both phases are evenly distributed and almost without agglomeration. The average size of the NbAl3 phase is 4.89 μm, and the average size of the NbB2 phase is 1.91 μm.

[0117] from Figure 3 It can be seen that the grain refiner alloy prepared in Example 3 has a more uniform and finer microstructure, with an average NbAl3 phase size of 2.43 μm and an average NbB2 phase size of 1.21 μm. From... Figure 4 It can be seen that, in addition to the NbAl3 and NbB2 phases, the grain refiner alloy also contains small amounts of EuAl and Nb2Al phases. 20 Eu phase.

[0118] Example 3 was repeated 3 times, and the chemical composition of each batch was the same (reasonable experimental error ±3% is allowed).

[0119] Comparative Examples 1-2

[0120] The difference between Comparative Example 1 and Example 3 lies in the chemical composition of the grain refiner of the target product. In Comparative Example 1, La was used instead of Eu to prepare 98.1Al-1.5Nb-0.3B-0.1La.

[0121] The difference between Comparative Example 2 and Example 3 lies in the chemical composition of the grain refiner of the target product. In Comparative Example 2, Ce was used instead of Eu to prepare 98.1Al-1.5Nb-0.3B-0.1Ce.

[0122] Application of grain refiners in Experimental Examples 1-3 and Comparative Experimental Examples 1-2

[0123] Example 1: An aluminum-silicon alloy raw material with a Si content of 10 wt% was melted to obtain an aluminum-silicon alloy liquid. The grain refiner prepared in Example 1 was added to the aluminum-silicon alloy liquid and mixed evenly to obtain a molten metal. A refining agent was added to the molten metal, and argon gas was simultaneously introduced into the molten metal using a degassing machine for 5 minutes to remove slag. The mixture was then cooled to 720°C and solidified to obtain a refined aluminum-silicon alloy. The mass of the grain refiner added was 0.2% of the mass of the aluminum-silicon alloy liquid.

[0124] The difference between Experimental Example 2 and Experimental Example 1 is that the grain refiner prepared in Example 2 was used. The difference between Experimental Example 3 and Experimental Example 1 is that the grain refiner prepared in Example 3 was used. The difference between Comparative Experimental Example 1 and Experimental Example 1 is that the grain refiner prepared in Comparative Example 1 was used. The difference between Comparative Example 2 and Experimental Example 1 is that the grain refiner prepared in Comparative Example 2 was used.

[0125] Macroscopic corrosion and grain size measurement were performed on the blank aluminum-silicon alloy (Al-10Si) and the refined aluminum-silicon alloy obtained from the experimental example.

[0126] The results of macroscopic corrosion observation of blank aluminum-silicon alloy are shown in the figure. Figure 5 The macroscopic corrosion results of the refined aluminum-silicon alloys obtained in Experiments 1, 2, and 3 are shown in the table below. Figure 6 , Figure 7 and Figure 8 .from Figures 5 to 8 The macroscopic corrosion diagram clearly shows that the microstructure of the aluminum-silicon alloy is significantly refined after being refined by the grain refiner obtained in this invention.

[0127] The grain size measurement results are shown below Figure 9 .from Figure 9 It can be seen that the grain size of the blank aluminum-silicon alloy (i.e., unrefined) reaches 2100 μm. However, the grain size of the aluminum-silicon alloy refined using the grain refiner of the present invention can be reduced to about 220 μm. Among them, the grain refiner prepared in Example 3 has the best refining effect, and the grain size of the refined aluminum-silicon alloy is reduced to 198.15 μm.

[0128] from Figure 9 and Figure 10 The test results showed that the grain size of Al-10Si alloy was refined by the grain refiners prepared in Comparative Example 1 and Comparative Example 2, but the grain size was still larger than that of alloy in Experimental Example 3.

[0129] from Figure 10The tensile strength and elongation of the refined Al-10Si alloy show that the strength and elongation of the Al-10Si alloy refined from the Al-Nb-B-Eu alloy are improved to varying degrees. Among them, the Al-Nb-B-Eu alloy rod prepared in Example 3 has the highest strength and elongation after refining the Al-10Si alloy, with strength and elongation reaching 184 MPa and 6.52%, respectively. Compared with the Al-10Si alloy, the strength is increased by 29.58% and the elongation is increased by 123.28%.

[0130] Furthermore, the mechanical property test results also showed that the alloy in Experimental Example 3 had better tensile strength and elongation. This indicates that the Al-Nb-B-Eu refining agent prepared in Example 3 has a better refining effect on Al-Si alloys than the Al-Nb-B-La and Al-Nb-B-Ce refining agents prepared in Comparative Examples 1 and 2.

[0131] from Figure 11-13 It can be seen that, compared to the Al-Nb-B-La / Ce alloy, the Al-Nb-B-Eu alloy has a better modification effect on eutectic silicon. The refined Al-Si alloy shows that the eutectic silicon phase changes from coarse lamellar to fine, fibrous. This indicates that rare earth Eu has a better effect on modifying eutectic silicon than rare earth La / Ce.

[0132] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A grain refiner for casting aluminum-silicon alloys, characterized in that, The grain refiner has the following chemical composition: Al, Nb, B, Eu, and unavoidable impurities. Based on the total weight of the grain refiner, the Nb content is 1.0–2.5 wt%, the B content is 0.3–2.5 wt%, the Eu content is 0.1–1.5 wt%, and the Al is the balance; The alloy nucleation phases of the grain refiner include NbAl3 phase, NbB2 phase, and Nb2Al phase. 20 One or more of Eu phase and EuAl phase, with the matrix phase being α-Al phase; The size of the NbAl3 phase is less than or equal to 5 μm; Nb2Al 20 The size of the Eu phase is less than or equal to 5 μm; the size of the NbB2 phase is less than or equal to 2 μm; and the size of the EuAl phase is less than or equal to 2.5 μm. The grain refiner is prepared by the following steps: 1) Prepare a salt solvent melt by mixing cryolite, sodium chloride and potassium chloride; wherein, based on the total weight of the salt solvent melt, cryolite is 20-60 wt%, sodium chloride is 20-40 wt%, and potassium chloride is 15-40 wt%; 2) Add europium oxide and niobium pentoxide to the salt solvent melt of step 1), mix, and cool to obtain the precursor; wherein the total volume of europium oxide and niobium pentoxide is 1 to 50% of the volume of the salt solvent melt; 3) Form aluminum melt from aluminum ingots; add potassium fluoroborate to the aluminum melt in batches and stir, then add the precursor obtained in step 2), continue stirring and reacting until complete, remove the salt solvent melt, and obtain an alloy solution; 4) The alloy solution is sequentially refined, degassed, and slag removed to obtain a slag-removed alloy solution. The slag-removed alloy solution is further processed to obtain a grain refiner.

2. The grain refiner according to claim 1, characterized in that, The size of the NbAl3 phase is less than or equal to 2.5 μm; Nb2Al 20 The size of the Eu phase is less than or equal to 2.5 μm; the size of the NbB2 phase is less than or equal to 1.5 μm; and the size of the EuAl phase is less than or equal to 2.0 μm.

3. A method for preparing the grain refiner according to claim 1, characterized in that, Includes the following steps: 1) Prepare a salt solvent melt by mixing cryolite, sodium chloride and potassium chloride; wherein, based on the total weight of the salt solvent melt, cryolite is 20-60 wt%, sodium chloride is 20-40 wt%, and potassium chloride is 15-40 wt%; 2) Add europium oxide and niobium pentoxide to the salt solvent melt of step 1), mix, and cool to obtain the precursor; wherein the total volume of europium oxide and niobium pentoxide is 1 to 50% of the volume of the salt solvent melt; 3) Form aluminum melt from aluminum ingots; add potassium fluoroborate to the aluminum melt in batches and stir, then add the precursor obtained in step 2), continue stirring and reacting until complete, remove the salt solvent melt, and obtain an alloy solution; 4) The alloy solution is sequentially refined, degassed, and slag removed to obtain a slag-removed alloy solution. The slag-removed alloy solution is further processed to obtain a grain refiner.

4. The preparation method according to claim 3, characterized in that, The alloy solution after slag removal can be further processed using one of the following methods: (a) Cast the alloy solution after slag removal into ingots to obtain a grain refiner; (b) The alloy solution after slag removal is poured into a casting rod and then extruded into a fine rod to obtain a grain refiner; (c) The alloy solution after slag removal is continuously cast and rolled into fine rods to obtain a grain refiner.

5. The preparation method according to claim 3 or 4, characterized in that: In step 3), before adding potassium fluoroborate to the aluminum melt, the potassium fluoroborate is dried at 100-120°C to remove moisture, and then divided into multiple portions, each of which is wrapped in aluminum foil. In step 3), the temperature for continued stirring is 850–950°C, and the reaction time is 30–60 min.

6. A method for preparing an aluminum-silicon alloy, characterized in that, Includes the following steps: Aluminum-silicon alloy raw materials with a silicon content of 5 wt% or more are melted to obtain aluminum-silicon alloy liquid; the grain refiner described in any one of claims 1 to 2 is added to the aluminum-silicon alloy liquid and mixed to obtain a metal liquid; the metal liquid is refined, degassed, and slag is removed, then cooled, and then solidified and formed to obtain a refined aluminum-silicon alloy. The amount of the grain refiner added is 0.1 to 0.5% of the mass of the aluminum-silicon alloy liquid.

7. An aluminum-silicon alloy, characterized in that, It is prepared by the preparation method described in claim 6.

8. The use of the grain refiner as described in claim 1 in refining the grain size of aluminum-silicon alloys.

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