Preparation and application of a composite modified high-performance aluminum-silicon alloy

Abstract

This application belongs to the field of aluminum alloy recycling technology, and more specifically, relates to the preparation and application of a composite modified high-performance aluminum-silicon alloy. This invention uses a La and Ce element composite modification of graphene combined with an ultrasonic dispersion process to prepare graphene into a composite powder, thereby reducing the contact angle between graphene and the aluminum alloy melt. Simultaneously, by controlling the Cr-Mn-Er element ratio, the Fe-rich phase is transformed from needle-like to short rod-like / granular, achieving a synergistic effect between the strengthening effect of graphene and the regulation of the Fe-rich phase. This solves the technical problem in existing technologies where graphene-modified aluminum alloys easily undergo interfacial diffusion in high-temperature melts, generating a brittle Al4C3 phase, leading to a severe decrease in alloy toughness.

Description

Technical Field

[0001] This application belongs to the field of aluminum alloy recycling technology, and more specifically, relates to the preparation and application of a composite modified high-performance aluminum-silicon alloy. Background Technology

[0002] Aluminum-silicon alloys, with their excellent castability, reliable corrosion resistance, and significant cost advantages, have achieved large-scale applications in key automotive components, precision housings for electronic devices, and structural parts for industrial machinery. Graphene, as a two-dimensional nanomaterial, possesses ultra-high strength, modulus, and excellent thermal and electrical conductivity. Introducing it into aluminum alloy systems can strengthen the matrix and enhance functional properties. In existing technologies, graphene is often added directly as raw powder. However, due to the inertness of graphene's surface and poor wettability with molten aluminum alloys (contact angle > 50°), and the presence of numerous Fe impurities and oxide particles in recycled aluminum alloy melts, graphene is easily adsorbed, forming large agglomerates with a size > 10 μm. Furthermore, single stirring and dispersion processes (such as mechanical stirring) can only achieve macroscopic mixing and cannot break down the microscopic agglomerations of graphene, resulting in extremely uneven distribution of graphene in the alloy. Ultimately, this leads to performance fluctuations exceeding 25%, making it difficult to meet the stability requirements of industrial production.

[0003] Existing technologies lack targeted control over interfacial reactions: graphene and the aluminum matrix readily diffuse into the high-temperature melt, forming a brittle Al4C3 phase (high hardness and brittleness). This phase accumulates with increasing melting cycles in recycled aluminum alloys, fracturing the matrix and causing stress concentration, resulting in a decrease in alloy toughness exceeding 25%. The repeated melting processes of recycled aluminum alloys further exacerbate the formation and growth of the Al4C3 phase, severely weakening the strengthening effect of graphene. Recycled aluminum alloy raw materials inevitably introduce Fe impurities (typically 0.5-1.2%). Existing technologies lack targeted phase control schemes, easily forming coarse needle-like / skeleton-like Al-Si-Fe phases. These phases not only fracture the alloy matrix but also adsorb graphene agglomerates, leading to a dual stress concentration of "phase defects + graphene agglomeration," significantly reducing the synergy between alloy toughness and strength. Simultaneously, without suitable elemental ratio control strategies, the morphology of the Fe-rich phase cannot be improved, completely negating the strengthening effects of graphene, such as fine grains and load transfer. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this application is to provide a La-Ce composite rare earth coupling agent, its preparation method, and a method for preparing high-performance aluminum-silicon alloys based on this coupling agent combined with Cr-Mn-Er ternary element regulation. This aims to solve the technical problems of existing technologies where graphene and aluminum alloys easily undergo interfacial diffusion in high-temperature melts, generating brittle Al4C3 phases, resulting in large fluctuations in alloy properties and unstable strengthening effects when graphene is used to modify aluminum alloys.

[0005] To achieve the above objectives, in a first aspect, this application provides a method for preparing a composite modified high-performance aluminum-silicon alloy, comprising the following steps: S1. The pretreated aluminum-silicon alloy raw material is preheated and then heated to 780~800℃ to melt, obtaining the first melt; the temperature is lowered to 740-760℃, Al-10Cr, Al-10Mn, and Al-10Er master alloys are added, electromagnetic stirring is started, and after stirring evenly, slag is removed to obtain the second melt; argon gas is introduced into the second melt for rotary degassing to remove gas and fine impurities from the melt; S2. Cool the second melt to 720~730℃, add rare earth-modified graphene powder, simultaneously start electromagnetic stirring, and introduce argon gas for protection, so that the rare earth-modified graphene powder is uniformly dispersed in the melt to obtain the third melt; monitor the melt viscosity using an online viscosity sensor and control it at 1.2~1.5 Pa. s, temperature maintained at 720~730℃; S3. Pour the qualified third melt into a preheated mold and die-cast it using a vacuum casting process to obtain an aluminum-silicon alloy casting; The rare-earth modified graphene powder is obtained by modifying graphene with a La-Ce composite rare-earth coupling agent; the preparation method of the La-Ce composite rare-earth coupling agent includes the following steps: (1) Prepare a composite rare earth salt solution of lanthanum and cerium, wherein the solvent used to dissolve the rare earth salt contains an alcohol organic solvent; (2) After dissolving stearic acid in an alcoholic organic solvent, add alkaline solution dropwise and heat and stir to carry out saponification reaction to obtain sodium stearate saponified solution; (3) The composite rare earth salt solution is added dropwise to the sodium stearate saponification solution, heated and stirred to react and generate a white flocculent crude La-Ce composite rare earth stearic acid coupling agent; after washing and purification, it is dried and ground to obtain powdered La-Ce composite rare earth coupling agent.

[0006] Preferably, the method for preparing the rare earth modified graphene powder includes the following steps: dispersing graphene in an alcohol-based organic solvent to obtain a graphene dispersion, mixing it with the La-Ce composite rare earth coupling agent, ultrasonically dispersing the mixture, and then drying it to obtain rare earth modified graphene powder; wherein the mass of the La-Ce composite rare earth coupling agent is 5-10% of the mass of the graphene.

[0007] Preferably, step (1) specifically involves dissolving lanthanum and cerium chloride salts in a molar ratio of 2.5:2 to 3.5:2 in a mixed solvent of an alcohol organic solvent and deionized water to obtain the lanthanum and cerium composite rare earth salt solution.

[0008] Preferably, the alcohol organic solvent in steps (1) and (2) is one or more of anhydrous ethanol, methanol, 95% ethanol and isopropanol.

[0009] Preferably, in step (2), alkali solution is added dropwise until the pH of the system is 8-9, and the saponification reaction is carried out at a constant temperature of 60℃-65℃ for 30-40 minutes to obtain sodium stearate saponification solution.

[0010] Preferably, in step (3), the molar ratio of rare earth ions in the composite rare earth salt solution to sodium stearate in the sodium stearate saponification solution is 1:3.2-1:3.5; the mixture is heated to 80-85°C and stirred at 200-400 r / min for 60-150 min to obtain the white flocculent La-Ce composite rare earth stearic acid coupling agent crude product.

[0011] Preferably, in step S1, Al-10Cr, Al-10Mn, and Al-10Er master alloys are added, and the mass ratio of Cr to Mn is 0.5 to 0.8, and the mass ratio of Mn to Er is 12 to 25.

[0012] Preferably, the mass of the rare earth modified graphene powder in step S2 is 0.1-0.3 wt% of the mass of the second melt.

[0013] According to another aspect of the present invention, an application of a composite modified high-performance aluminum-silicon alloy in the preparation of automotive structural parts is provided, wherein the composite modified high-performance aluminum-silicon alloy is prepared by the aforementioned preparation method.

[0014] Overall, the technical solutions conceived in this application have the following beneficial effects compared with the prior art: (1) This invention constructs a metallic active interface layer and prepares micron-level composite powder by directionally combining La and Ce rare earth elements with the surface defects of graphene. This solves the problem of poor wettability of graphene with recycled aluminum alloy melt and easy formation of large agglomerates, thereby reducing the contact angle and reducing the fluctuation of alloy performance from 25%+ to below 8%.

[0015] (2) The present invention utilizes the metallic interface layer formed by La and Ce modification to block the diffusion of Al atoms into the graphene interlayer, which solves the problem that the alloy toughness decreases by more than 25% due to the generation of a large amount of brittle Al4C3 phase at high temperature. After multiple smeltings, the Al4C3 phase content is still ≤0.2%, ensuring the strengthening effect.

[0016] (3) By precisely matching the ternary elements Cr-Mn-Er (Cr / Mn=0.5~0.8, Mn / Er=12~25), the present invention transforms the needle-like / skeleton-like Al-Si-Fe phase into short rod-like / granular phases, solving the problem of double stress concentration caused by the superposition of Fe impurity phase and graphene agglomerates, and achieving synergistic improvement of strength and toughness.

[0017] (4) This invention combines La-Ce modified graphene with Cr-Mn-Er-regulated Fe enrichment to form a bidirectional promoting effect, which solves the problem that the existing technology is not adapted to the impurity enrichment characteristics of recycled aluminum alloys, eliminates the negative effect of "impurity-graphene", and expands the application of graphene in low-quality recycled materials. Attached Figure Description

[0018] Figure 1 This is a schematic flowchart of the method for preparing graphene-modified high-performance aluminum alloys provided in the embodiments of this application; Figure 2 This is a comparison of the as-cast microstructure of aluminum alloys prepared in the embodiments and comparative examples of this application. Content (a) is the microstructure of the comparative example 1, and content (b) is the microstructure of the aluminum alloy prepared in Example 1. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0020] This invention provides a method for preparing a La-Ce composite rare earth coupling agent, comprising the following steps: (1) Prepare a composite rare earth salt solution of lanthanum and cerium, wherein the solvent used to dissolve the rare earth salt contains an alcohol organic solvent (to improve the miscibility of the rare earth salt solution with the sodium stearate saponification solution). (2) After dissolving stearic acid in an alcoholic organic solvent, add alkaline solution dropwise and heat and stir to carry out saponification reaction to obtain sodium stearate saponified solution; (3) The composite rare earth salt solution is added dropwise to the sodium stearate saponification solution, and heated and stirred to react and generate a white flocculent La-Ce composite rare earth stearic acid coupling agent crude product; it is washed and purified to remove free Cl. - Na + Unreacted raw materials were dried and ground to obtain powdered La-Ce composite rare earth coupling agent.

[0021] In some embodiments, step (1) specifically involves dissolving lanthanum and cerium chloride salts in a molar ratio of 2.5:2 to 3.5:2 in a mixed solvent of an alcohol organic solvent and deionized water to obtain the lanthanum and cerium composite rare earth salt solution; the alcohol organic solvents in steps (1) and (2) are one or more hydrophilic alcohols such as anhydrous ethanol, methanol, 95% ethanol (v / v) and isopropanol.

[0022] Preferably, the alkaline solution in step (2) also contains the alcohol organic solvent, which is also used to improve the miscibility of the rare earth salt solution and the sodium stearate saponification solution.

[0023] In some embodiments, step (2) involves adding alkali solution dropwise until the system pH reaches 8-9, and then maintaining a constant temperature of 60℃-65℃ for 30-40 minutes to induce a saponification reaction, thereby obtaining a sodium stearate saponified solution. Suitable saponification conditions ensure complete saponification of stearic acid.

[0024] In some embodiments, the molar ratio of rare earth ions in the composite rare earth salt solution to sodium stearate in the sodium stearate saponification solution in step (3) is 1:3.2-1:3.5; the mixture is heated to 80-85°C and stirred at 200-400 r / min for 60-150 min to obtain the white flocculent La-Ce composite rare earth stearic acid coupling agent crude product.

[0025] Preferably, the washing and purification in step (3) specifically involves: centrifuging the crude white flocculent La-Ce composite rare earth stearic acid coupling agent, removing the supernatant, collecting the bottom precipitate, and washing it repeatedly with anhydrous ethanol. After each washing, the supernatant is discarded by centrifugation to remove free Cl. - Na + Unreacted raw materials should be removed to avoid residual chloride ions, sodium ions, etc., from affecting the properties of the aluminum alloy. The drying process is vacuum drying at a temperature of 65-80℃ for 3-6 hours.

[0026] The present invention also provides a La-Ce composite rare earth coupling agent prepared by the preparation method described above, and a rare earth modified graphene powder, which is obtained by modifying graphene with the La-Ce composite rare earth coupling agent described above.

[0027] In some embodiments, the rare earth modified graphene powder of the present invention is prepared by the following steps: dispersing graphene in an alcohol-based organic solvent to obtain a graphene dispersion, mixing it with the La-Ce composite rare earth coupling agent, ultrasonically dispersing the mixture, and then drying it to obtain rare earth modified graphene powder.

[0028] In some embodiments, the mass of the La-Ce composite rare earth coupling agent is 5-10% of the mass of graphene; the ultrasonic dispersion power is 300-500W, and the dispersion time is 40-60min.

[0029] This invention utilizes the aforementioned rare-earth-modified graphene powder to prepare high-performance aluminum-silicon alloys, and therefore also proposes a method for preparing graphene-modified high-performance aluminum-silicon alloys, comprising the following steps: S1. The pretreated aluminum-silicon alloy raw material is preheated and then heated to 780~800℃ to melt, obtaining the first melt; the temperature is lowered to 740-760℃, Al-10Cr, Al-10Mn, and Al-10Er master alloys are added, electromagnetic stirring is started, and after stirring evenly, slag is removed to obtain the second melt; argon gas is introduced into the second melt for rotary degassing to remove gas and fine impurities from the melt; S2. Cool the second melt to 720~730℃, add the rare earth-modified graphene powder, simultaneously start electromagnetic stirring and introduce argon gas for protection, so that the rare earth-modified graphene powder is uniformly dispersed in the melt to obtain the third melt; monitor the melt viscosity using an online viscosity sensor and control it at 1.2~1.5 Pa. s, temperature maintained at 720~730℃; S3. Pour the qualified third melt into a preheated mold and die-cast it using a vacuum casting process to obtain high-performance recycled aluminum alloy castings.

[0030] In some embodiments, step S1 involves adding Al-10Cr, Al-10Mn, and Al-10Er master alloys, with the mass ratio of Cr to Mn being 0.5 to 0.8 and the mass ratio of Mn to Er being 12 to 25.

[0031] In a preferred embodiment, the electromagnetic stirring speed in step S1 is 300-500 r / min, the magnetic field strength is 0.15-0.25 mT, and the stirring time is 5-10 min; argon gas is introduced into the second melt for degassing by rotation for 8-12 min at a speed of 200-320 r / min; the electromagnetic stirring speed in step S2 is 200-350 r / min, the magnetic field strength is 0.08-0.12 mT, and the stirring time is 8-12 min; in step S3, the mold is preheated to 200-250℃, and a vacuum die-casting process is adopted, with a vacuum degree of 60-100 mbar, a casting pressure of 50-60 MPa, and a punch speed of 0.1-0.3 m / s at low speed and 3-5 m / s at high speed.

[0032] In a preferred embodiment, the magnetic field strengths in steps S1 and S2 are slightly different. Step S1 requires rapid homogenization of the composition and promotion of degassing and impurity removal, while step S2 has already completed degassing. If strong stirring continues, it will cause violent fluctuations in the melt, entraining air and causing secondary oxidation and hydrogen absorption, thus destroying the purification effect. Therefore, the magnetic field strength in step S1 is slightly greater than that in step S2.

[0033] In some embodiments, the mass of the rare earth modified graphene powder in step S2 is 0.1-0.3 wt% of the mass of the second melt.

[0034] The method for preparing graphene-modified high-performance aluminum-silicon alloys of the present invention is applicable to the preparation of various aluminum-silicon series casting alloys (such as A356, C611, etc.). Therefore, the raw materials for its preparation include, but are not limited to, alloy elements, intermediate compounds or recycled aluminum-silicon alloy raw materials.

[0035] In some embodiments, the pretreatment steps of the aluminum-silicon alloy raw material in step S2 include: grinding to remove the surface oxide layer and oil stains, crushing into 50-100mm blocks, and calcining at 400-500℃ for 2-4 hours to remove the organic coating.

[0036] This invention prepares graphene into composite powder by modifying graphene with La and Ce elements (forming a metallic interface layer) and using an ultrasonic dispersion process, thereby reducing the contact angle between graphene and molten aluminum alloy. At the same time, by controlling the Cr-Mn-Er element ratio (Cr / Mn=0.5~0.8, Mn / Er=12-25), the Fe-rich phase is transformed from needle-like / skeleton-like to short rod-like / granular, achieving a synergistic effect between the strengthening effect of graphene and the control of the Fe-rich phase.

[0037] This invention improves the dispersibility and alloy performance stability of graphene in recycled aluminum alloys. Through La and Ce rare-earth composite modification, a metallic active interface layer is constructed on the graphene surface, preparing it as a micron-sized composite powder, thus solving the agglomeration problem caused by traditional direct addition. The contact angle between graphene and the melt decreases, and the fluctuation range of alloy performance is reduced from over 25% to below 8%, significantly improving the reliability of industrial production. Simultaneously, it adapts to the impurity characteristics of recycled materials, expanding the application scenarios of graphene.

[0038] This invention suppresses the formation of brittle Al4C3 phase while ensuring alloy toughness. It utilizes an interface layer formed by La and Ce modification to block the diffusion channels of Al atoms, thus inhibiting interfacial reactions at the source. Compared to traditional technologies that result in a more than 25% decrease in alloy toughness, this invention ensures that the Al4C3 phase content of the recycled aluminum alloy remains ≤0.2% after multiple smeltings. This avoids the brittle phase tearing the matrix, ensures the full utilization of graphene's strengthening effect, and overcomes the performance degradation bottleneck under high-temperature smelting.

[0039] This invention achieves a synergistic improvement in the mechanical properties of alloys. By precisely proportioning the ternary elements Cr-Mn-Er (Cr / Mn=0.5~0.8, Mn / Er=12~25), the needle-like / skeletal Al-Si-Fe phase in recycled materials is transformed into short rod-like / granular phases. This transformation eliminates the dual stress concentration caused by Fe impurities and graphene agglomerates, releasing the fine-grain strengthening and load-transfer functions of graphene. It solves the problem of "strengthening and deterioration offsetting each other" in traditional technologies, achieving simultaneous improvement in strength and toughness.

[0040] This invention optimizes process adaptability and reduces production and application costs. It constructs a synergistic system of "graphene modification + Fe-rich phase regulation" and adopts mature processes such as ultrasonic dispersion, electromagnetic stirring, and vacuum die casting, without requiring large-scale modifications to existing production lines. In some embodiments, the raw materials consist of primary and secondary Al-7Si recycled materials. Combined with an online viscosity monitoring mechanism, the process cycle is shortened and the smelting efficiency is improved. This not only increases the utilization rate of low-quality recycled materials but also provides a guarantee for large-scale production.

[0041] The composite modified high-performance aluminum-silicon alloy provided by this invention can be used to manufacture automotive structural parts.

[0042] The embodiments of the present invention are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally in accordance with conventional conditions.

[0043] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0044] In some embodiments of the present invention, a high-performance recycled aluminum alloy modified with graphene is provided, which solves the problems of performance degradation and poor compatibility of graphene modification in existing aluminum-silicon series casting alloys, such as (A356, C611, etc.) recycled aluminum alloys due to Fe impurities, and achieves a dual improvement in the mechanical properties and functional characteristics of recycled aluminum alloys.

[0045] The embodiments of this application are described below with reference to the accompanying drawings. Unless otherwise specified, all percentages mentioned in the following embodiments of the present invention are mass percentages.

[0046] In the following examples, primary and secondary Al-7Si-0.3Cu-0.2Mg-0.6Mn-0.1Ti-0.03La-0.02Ce-0.02Sr-0.05Zr (also abbreviated as Al-7Si) aluminum alloy recycled materials are mixed at a weight ratio of 7:3 as raw materials for preparing graphene-modified high-performance aluminum alloys. The primary material is the material near the flow channel, and the secondary material is the slag bag material. After mixing the primary and secondary materials at a weight ratio of 7:3, the components by weight percentage are as follows: Si content 6~8%, Cu content 0.2~0.4%, Mg content 0.1~0.3%, Mn content 0.5~0.7%, Ti content 0.05~0.2%, La content 0.02~0.05%, Ce content 0.02~0.05%, Sr content 0.02~0.05%, Zr content 0.02~0.1%, Fe content 0.5~1.2%, and the balance is Al.

[0047] The following are examples and comparative examples.

[0048] Example 1 A method for preparing graphene-modified high-performance aluminum alloy, such as... Figure 1 As shown, it includes the following steps: Preparation of S1.La-Ce composite rare earth coupling agent: Weigh out LaCl3 according to the La:Ce molar ratio of 3:2. 6H2O, CeCl3 Add 7H2O to anhydrous ethanol-deionized water mixed solvent (volume ratio 1:1) to prepare a 0.25 mol / L solution. Stir at 25℃ and 300 r / min for 30 min until completely dissolved to obtain a La-Ce composite rare earth salt solution. Simultaneously, weigh stearic acid according to a rare earth ion to stearic acid molar ratio of 1:3.5 and dissolve it in anhydrous ethanol. Stir at 60℃ and 400 r / min until dissolved, then slowly add 1 mol / L... The pH of the system was adjusted to 8-9 with NaOH ethanol solution, and the saponification reaction was carried out at 60℃ for 30 min to obtain sodium stearate saponification solution. Both solutions were reserved. Subsequently, rare earth salt solution was added dropwise to the sodium stearate saponification solution at 60℃ at a rate of 5 drops / second. After the addition was completed, the temperature was raised to 85℃, and the reaction was carried out at 350 r / min with stirring for 2 h to generate a milky white flocculent crude La-Ce composite rare earth stearic acid coupling agent. After the system was allowed to cool naturally to room temperature, it was centrifuged at 8000 r / min for 10 min and the supernatant was discarded. The bottom precipitate was collected and washed repeatedly with anhydrous ethanol three times, with centrifugation each time to remove free Cl. - Na + The unreacted raw materials were then placed in a vacuum drying oven and dried at 80°C for 6 hours. After being ground through a 200-mesh sieve using an agate mortar, the pure La-Ce composite rare earth coupling agent (La:Ce=3:2) was obtained in powder form and stored in a sealed container for later use.

[0049] S2. Graphene pretreatment: Graphene was added to anhydrous ethanol at a solid-liquid ratio of 1g:100mL, and La-Ce composite rare earth coupling agent (La:Ce=3:2) at 7% of the mass of graphene was added. The mixture was ultrasonically dispersed for 50min (power 350W) and then vacuum dried at 80℃ for 2h to obtain rare earth modified graphene powder.

[0050] S3. Pretreatment of recycled materials: Mix primary and secondary Al-7Si recycled materials in a weight ratio of 7:3, grind to remove surface oxide layer and oil stains, crush into 50~100mm blocks, calcine at 480℃ for 3h to remove organic coating, and set aside.

[0051] S4. Melting and Element Modification: The pretreated recycled material is added to a graphite crucible, preheated to 400℃, and then heated to 780~800℃ to melt, obtaining the first melt; the temperature is lowered to 750℃, and Al-10Cr, Al-10Mn, and Al-10Er master alloys are added, wherein the elemental mass ratio of Cr to Mn is 0.5, and the elemental mass ratio of Mn to Er is 20; electromagnetic stirring is started for 5 minutes (300 r / min, magnetic field strength 0.2 mT), and after stirring evenly, slag is removed to obtain the second melt; argon gas is introduced into the second melt for rotary degassing (250 r / min) for 10 minutes to remove gas and fine impurities from the melt.

[0052] S5. Graphene Composite Addition: The second melt is cooled to 720~730℃, and 0.1wt% of pretreated rare earth modified graphene powder is added. Simultaneously, electromagnetic stirring is started for 8 minutes (speed reduced to 280 r / min, magnetic field strength 0.1 mT), and argon gas is introduced for protection, ensuring the rare earth modified graphene powder is uniformly dispersed in the melt to obtain the third melt. The melt viscosity is monitored using an online viscosity sensor and controlled within 1.2~1.5 Pa. s, keep the temperature at 720~730℃.

[0053] S6. Die casting: Pour the qualified third melt into the barrel, preheat the mold to 250℃, and use vacuum die casting process (vacuum degree 80mbar), casting pressure 60MPa, punch low speed 0.2m / s, high speed 4.5m / s, to die cast high-performance recycled aluminum alloy castings.

[0054] Example 2 The rest is the same as in Example 1, except that the mass of rare earth modified graphene powder added in step S5 is 0.2% of the mass of the second melt. During the preparation of the rare earth modified graphene powder, the amount of rare earth coupling agent added is 10% of the graphene mass.

[0055] Example 3 The rest is the same as in Example 1, except that in step S4, an Al-10Cr, Al-10Mn, and Al-10Er master alloy is added, wherein the mass ratio of Cr to Mn is 0.8 and the mass ratio of Mn to Er is 12. In step S5, the mass of rare earth modified graphene powder added is 0.3 wt% of the mass of the second melt. During the preparation of rare earth modified graphene powder, the amount of rare earth coupling agent added is 5% of the mass of graphene.

[0056] Comparative Example 1 The rest is the same as in Example 1, except that in step S5, rare earth modified graphene was not added, and Al-10Cr, Al-10Mn, and Al-10Er master alloys were not added.

[0057] Comparative Example 2 The rest is the same as in Example 1, except that the graphene added in step S5 is unmodified graphene and no Al-10Cr, Al-10Mn, or Al-10Er master alloys are added.

[0058] Comparative Example 3 The rest is the same as in Example 1, except that rare earth modified graphene was not added in step S5.

[0059] Comparative Example 4 The rest is the same as in Example 1, except that Al-10Cr, Al-10Mn, and Al-10Er master alloys are added, wherein the mass ratio of Cr to Mn is 0.3.

[0060] Comparative Example 5 The rest is the same as in Example 1, except that Al-10Cr, Al-10Mn, and Al-10Er master alloys are added, wherein the mass ratio of Cr to Mn is 1.

[0061] Comparative Example 6 The rest is the same as in Example 1, except that an Al-10Cr, Al-10Mn, and Al-10Er master alloy is added, wherein the mass ratio of Mn to Er is 10.

[0062] Comparative Example 7 The rest is the same as in Example 1, except that an Al-10Cr, Al-10Mn, and Al-10Er master alloy is added, wherein the mass ratio of Mn to Er is 30.

[0063] The mechanical property testing standard for the alloys prepared in the above embodiments and comparative examples is GB / T228.1. The test results for 2021 are recorded in Table 1. Ten specimens were tested for the mechanical properties of each alloy, and the average value was taken.

[0064] Table 1. Mechanical property test results of alloys prepared in the examples and comparative examples.

[0065] As can be seen from Table 1, in the embodiments of the present invention, graphene was modified using a synthesized La-Ce composite rare earth coupling agent and then introduced into the smelting and casting process of aluminum alloys. By comparing with the comparative examples, it can be seen that compared with the absence of graphene (regardless of whether Cr-Mn-Er is introduced) or the absence of modification of the composite rare earth coupling agent of the present invention with the introduced graphene, the aluminum alloys obtained show significant improvements in various mechanical properties, especially in the ultimate tensile strength. In addition, the fluctuation range of mechanical properties is reduced from 25%+ to below 8%, which may be due to the directional bonding of La and Ce rare earth elements with the defects on the surface of graphene, constructing a metallic active interface layer and making micron-sized composite powder, thus solving the problems of poor wettability of graphene with recycled aluminum alloy melt and easy formation of large agglomerates.

[0066] Figure 2 Content (a) shows the metallographic structure of the alloy prepared in Comparative Example 1, in which the dark dendritic phase is the Al-Si eutectic phase, and the bright white skeletal and blocky large-sized phase is the Fe phase, which is unevenly distributed and has obvious aggregation in some areas. Figure 2 Content (b) shows the metallographic structure of the aluminum alloy prepared in Example 1, in which the Fe phase is bright white, fine, short rod-shaped and granular, with only trace amounts of needle-shaped Al4C3 phase. Large bulk secondary phases are almost absent in the structure, resulting in a more uniform overall distribution. Therefore, from Table 1 and... Figure 2 It can also be seen that the embodiments of the present invention, through the precise ratio of Cr-Mn-Er ternary elements (Cr / Mn=0.5~0.8, Mn / Er=12~25), transform the coarse needle-like / skeleton-like Al-Si-Fe phase into short rod-like / granular phases, solving the problem of double stress concentration caused by the superposition of Fe impurity phase and graphene agglomerates, and achieving a synergistic improvement in strength and toughness; moreover, in the embodiments of the present invention, the Al4C3 phase content is still ≤0.2% after multiple meltings of the alloy, which is also significantly lower than that of the comparative example. This may also be due to the use of the metallic interface layer formed by La and Ce modification, and the precise ratio of Cr-Mn-Er ternary elements to prevent Al atoms from diffusing into the graphene interlayer, thus solving the problem of generating a large amount of brittle Al4C3 phase at high temperatures.

[0067] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a composite modified high-performance aluminum-silicon alloy, characterized in that, Includes the following steps: S1. The pretreated aluminum-silicon alloy raw material is preheated and then heated to 780~800℃ to melt, obtaining the first melt; the temperature is lowered to 740-760℃, Al-10Cr, Al-10Mn, and Al-10Er master alloys are added, electromagnetic stirring is started, and after stirring evenly, slag is removed to obtain the second melt; argon gas is introduced into the second melt for rotary degassing to remove gas and fine impurities from the melt; S2. Cool the second melt to 720~730℃, add rare earth-modified graphene powder, simultaneously start electromagnetic stirring, and introduce argon gas for protection, so that the rare earth-modified graphene powder is uniformly dispersed in the melt to obtain the third melt; monitor the melt viscosity using an online viscosity sensor and control it at 1.2~1.5 Pa. s, temperature maintained at 720~730℃; S3. Pour the qualified third melt into a preheated mold and die-cast it using a vacuum casting process to obtain an aluminum-silicon alloy casting; The rare-earth modified graphene powder is obtained by modifying graphene with a La-Ce composite rare-earth coupling agent; the preparation method of the La-Ce composite rare-earth coupling agent includes the following steps: (1) Prepare a composite rare earth salt solution of lanthanum and cerium, wherein the solvent used to dissolve the rare earth salt contains an alcohol organic solvent; (2) After dissolving stearic acid in an alcoholic organic solvent, add alkaline solution dropwise and heat and stir to carry out saponification reaction to obtain sodium stearate saponified solution; (3) The composite rare earth salt solution is added dropwise to the sodium stearate saponification solution, heated and stirred to react and generate a white flocculent crude La-Ce composite rare earth stearic acid coupling agent; after washing and purification, it is dried and ground to obtain powdered La-Ce composite rare earth coupling agent.

2. The preparation method according to claim 1, characterized in that, The method for preparing the rare earth modified graphene powder includes the following steps: dispersing graphene in an alcohol-based organic solvent to obtain a graphene dispersion, mixing it with the La-Ce composite rare earth coupling agent, ultrasonically dispersing the mixture, and then drying it to obtain rare earth modified graphene powder; wherein the mass of the La-Ce composite rare earth coupling agent is 5-10% of the mass of the graphene.

3. The preparation method according to claim 1, characterized in that, Step (1) specifically involves dissolving lanthanum and cerium chloride salts in a molar ratio of 2.5:2 to 3.5:2 in a mixed solvent of an alcoholic organic solvent and deionized water to obtain the lanthanum and cerium composite rare earth salt solution; and / or, The alcoholic organic solvents mentioned in steps (1) and (2) are one or more of anhydrous ethanol, methanol, 95% ethanol and isopropanol.

4. The preparation method according to claim 1, characterized in that, Step (2) Add alkali solution dropwise until the pH of the system is 8~9, and keep the temperature at 60℃~65℃ for 30-40 minutes to carry out the saponification reaction to obtain sodium stearate saponification solution.

5. The preparation method according to claim 1, characterized in that, In step (3), the molar ratio of rare earth ions in the composite rare earth salt solution to sodium stearate in the sodium stearate saponification solution is 1:3.2-1:3.5; heat to 80-85℃ and stir at 200-400r / min for 60-150min to obtain the white flocculent La-Ce composite rare earth stearic acid coupling agent crude product.

6. The preparation method according to claim 1, characterized in that, Step S1 involves adding Al-10Cr, Al-10Mn, and Al-10Er master alloys, with the mass ratio of Cr to Mn being 0.5~0.8 and the mass ratio of Mn to Er being 12~25; and / or, In step S1, the electromagnetic stirring speed is 300-500 r / min, the magnetic field strength is 0.15-0.25 mT, and the stirring time is 5-10 min; argon gas is introduced into the second melt for rotary degassing for 8-12 min at a speed of 200-320 r / min; and / or, The electromagnetic stirring speed in step S2 is 200-350 r / min, the magnetic field strength is 0.08-0.12 mT, and the stirring time is 8-12 min; and / or, In step S3, the mold is preheated to 200~250℃ and a vacuum die-casting process is adopted, with a vacuum degree of 60-100mbar, a casting pressure of 50~60MPa, and a punch speed of 0.1-0.3m / s at low speed and 3-5m / s at high speed.

7. The preparation method according to claim 1, characterized in that, The mass of the rare earth modified graphene powder in step S2 is 0.1-0.3 wt% of the mass of the second melt.

8. The application of a composite modified high-performance aluminum-silicon alloy in the manufacture of automotive structural parts, characterized in that, The composite modified high-performance aluminum-silicon alloy is prepared by the preparation method described in any one of claims 1 to 7.

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