Dual composite rare earth modification method for harmful Fe-rich phase in secondary aluminum alloy

Abstract

The invention discloses a dual composite rare earth modification method for a harmful Fe-rich phase in a secondary aluminum alloy. The Y-La dual modification method is developed for the first time aiming at the industrial problem that the mechanical property of a needle-shaped beta-Fe phase is deteriorated due to the high Fe content in the regenerated aluminum alloy; adding a Y alterant at a high temperature, and synchronously introducing oxygen and magnetically stirring to promote formation of a large number of fine dispersed Y2O3 particles as heterogeneous nucleation sites of alpha-Fe; la modificator is added at medium-high temperature and is enriched at the liquid-solid front edge of alpha-Fe to inhibit growth of the alpha-Fe, and refining and spheroidizing of an iron-rich phase are achieved through double composite rare earth modification. According to the method, accurate regulation and control of the morphology of the Fe-rich phase are achieved through a synergistic mechanism that a Y2O3 high-temperature heterogeneous core promotes nucleation (refining) of the alpha-Fe phase and a La segregation phase interface inhibits growth (spheroidizing) of the alpha-Fe phase, and the industrial problem that deterioration of the harmful Fe phase in the high-Fe-content (0.8-1.6 wt.%) regenerated aluminum alloy is difficult to achieve through a traditional deterioration technology is solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aluminum alloy smelting treatment, and relates to a double-composite rare earth modification method for harmful Fe-rich phases in recycled aluminum alloy, that is, the Fe-rich phases in recycled aluminum alloy are regulated and controlled through double-composite rare earth modification, in particular to a method for cooperatively regulating the morphology of Fe-rich phases in recycled aluminum alloy through Y-La double modification, which is especially suitable for recycled aluminum alloy with high Fe content (0.8-1.6 wt.%). BACKGROUND

[0002] As a key material for resource recycling, the global production of recycled aluminum alloy accounts for more than 35% of primary aluminum. However, the uncontrollable enrichment of iron elements in waste aluminum raw materials, typically at a content of 0.8-1.6 wt.%, is caused by the mixed steel parts. When the iron content is high, needle-like β-Fe phases (Al5FeSi) with a length-diameter ratio greater than 8 will be precipitated in the melt, causing disastrous consequences: the elongation of the alloy decreases by more than 50% (the elongation is generally less than 3% when the Fe content is 1.2 wt.%). Industry research reveals a grim reality: 86% of recycled aluminum enterprises have insufficient elongation of less than 5% due to iron phase problems, and the iron content tolerance is low under the existing process.

[0003] Currently, the industry mainly uses manganese modification technology to realize harmful Fe phase modification (such as patent ZL200910272922.7), which promotes the transformation of β-Fe phase to α-Fe phase by adding 0.2-0.4 wt.% manganese elements. However, this technology has fundamental limitations: for recycled aluminum alloy with high iron content, the treatment effect is not obvious, the process window is narrow, and excessive manganese will generate Al6Mn brittle phase, which will further exacerbate the deterioration of mechanical properties. In addition, there are also a small amount of rare earth modification treatments (such as patent ZL201310038971.0): adding Ce, La and other light rare earth elements to form stable intermetallic compounds with Fe and change the Fe phase morphology. However, the effect of adding only light rare earth elements is limited and the treatment effect on aluminum alloy with high Fe content (>0.5 wt.%) is not ideal.

[0004] In summary, the core contradiction of high-value utilization of recycled aluminum alloy is that high iron content inevitably induces needle-like β-Fe phase, and the existing mainstream modification technology has limited treatment effect on high iron content, and the process window is narrow and difficult to control. Therefore, according to the growth mechanism of iron-rich phases in the solidification process, it is urgent to develop a new double-composite modification method with nucleation control and interface segregation functions. SUMMARY

[0005] In view of the problems that the high Fe content (0.8-1.6 wt.%) in the existing recycled aluminum alloy leads to the generation of needle-like β-Fe phase (Al5FeSi) which seriously deteriorates the mechanical properties, and the effect of the traditional modification technology is not obvious and the process window is narrow, a double composite rare earth modification method for the harmful Fe-rich phase in the recycled aluminum alloy is provided. The Fe-rich phase in the recycled aluminum alloy is regulated by the double composite rare earth modification. Specifically, the recycled aluminum alloy is prepared by adopting a double-stage holding process during smelting; in the first stage of high-temperature holding, Y modifier is added to the aluminum alloy melt to form Y2O3 heterogeneous core to promote the nucleation of harmless α-Fe phase; in the second stage of medium-high temperature holding, La modifier is added to enrich on the surface of the α-Fe phase to inhibit the growth of the α-Fe phase.

[0006] The purpose of the present application is achieved by the following technical solutions: The present application provides a method for regulating the Fe-rich phase in the recycled aluminum alloy by double composite rare earth modification. During the smelting process of the recycled aluminum alloy, Y modifier is added at high temperature, and oxygen is simultaneously introduced and magnetic stirring is performed, so as to promote the formation of a large number of fine dispersed Y2O3 particles as heterogeneous nucleation sites of α-Fe; La modifier is added at medium-high temperature to enrich on the liquid-solid front of α-Fe to inhibit the growth thereof, and the double composite rare earth modification realizes the refinement and spheroidization of the Fe-rich phase. In the recycled aluminum alloy, Y: 0.1-0.4 wt.%, La: 0.3-0.8 wt.%, and the balance is common elements and unavoidable impurities in the recycled aluminum alloy.

[0007] The present application introduces Y and La elements in a specific ratio to realize the double modification effect of the Fe-rich phase from the aspects of promoting nucleation (refining) and inhibiting growth (spheroidization): the double modification of the Fe-rich phase is realized by forming Y2O3 heterogeneous core to promote the nucleation of harmless α-Fe phase and by enriching La on the surface of the α-Fe phase to inhibit the growth thereof. The iron elements in the aluminum melt are consumed, thereby inhibiting the growth of harmful needle-like β-Fe phase and realizing the significant improvement of the elongation of the recycled aluminum alloy.

[0008] Specifically, the lower limit of the Y content is controlled at 0.1 wt.% to ensure the generation of sufficient fine Y2O3 nanoparticles, and lower than this value will result in insufficient α-Fe nucleation rate; the upper limit of the Y content is controlled at 0.4 wt.% to prevent excessive Y from forming coarse blocky Al2Y phase and leading to the decrease of mechanical properties. The lower limit of the La content is controlled at 0.3 wt.% because lower than this value will make it difficult to inhibit the growth of the Fe-rich phase; and the upper limit of the La content is controlled at 0.8 wt.% to avoid the generation of long needle-like Al 11 La3 phase and reduce the elongation of the alloy.

[0009] As an embodiment of the present application, the Fe content in the recycled aluminum alloy is 0.8-1.6 wt.%.

[0010] As one embodiment of the present invention, the ratio of Y content to Fe content is between 1:4 and 1:8; the ratio of La content to Fe content is between 1:2 and 1:3.

[0011] In one embodiment of the present invention, the high temperature is 800 ℃-820 ℃, the holding time is 10-20 min, and oxygen is continuously introduced into the bottom while magnetic stirring is performed during the holding period. The stirring speed selected for magnetic stirring is 2500-3500 r / min.

[0012] As one embodiment of the present invention, the medium-high temperature is 760 ℃-780 ℃, and the heat preservation time is 20-30 min.

[0013] As one embodiment of the present invention, the smelting and preparation of the recycled aluminum alloy includes the following steps: S1. Weigh the raw materials for recycling aluminum alloy scrap, Al-30Y, and Al-30La master alloys according to the proportions. S2, First stage of heat preservation: Heat the recycled aluminum alloy to melt and raise the temperature to 800 ℃-820 ℃, add Al-30Y master alloy, and keep it at this temperature for 10-20 minutes. During the heat preservation, oxygen is continuously introduced into the bottom of the melt through the vent pipe, and magnetic stirring is applied at a stirring rate of 2500-3500 r / min. S3, Second stage heat preservation: Cool the melt in S2 to 760 ℃-780 ℃, add Al-30La master alloy, and hold for 20-30 min; S4. Cool the melt in S3 to 735℃-745℃ and hold it there. After refining, remove the slag. S5. Cool the melt in S4 to 700℃-715℃ and hold it at that temperature. After removing the slag, pour the melt at 700℃-715℃ to obtain the casting. S6. The castings obtained in S5 are subjected to a two-stage heat treatment. The first step is solution treatment at 520-560℃, and the second step is aging treatment at 145-165℃.

[0014] In one embodiment of the present invention, in S4, the heat preservation time is 10-15 min and the refining time is 8-10 min; in S5, the heat preservation time is 15-25 min.

[0015] In one embodiment of the present invention, in S6, the solution treatment lasts for 6-7 hours and the aging treatment lasts for 3-4 hours.

[0016] In the method of this invention, during the first stage of heat preservation (S2), the added Y modifier forms fine Y2O3 nanoparticles in the high-temperature melt, which serve as heterogeneous nucleation sites (refinement) for the subsequent α-Fe phase. During the second stage of heat preservation (S3), the added La modifier is uniformly dispersed in the melt and accumulates on the surface of the α-Fe phase during subsequent solidification, reducing its surface energy and thus inhibiting growth (spheroidization). This dual composite modifier promotes the formation of fine spherical α-Fe phase in the microstructure, consuming the Fe element in the melt, thereby inhibiting the formation of harmful needle-like β-Fe phase.

[0017] The core idea of ​​this invention is to propose a dual strategy for the nucleation and growth process of high-temperature iron-rich phases: promoting nucleation through oxide heterogeneous nuclei and inhibiting growth through the enrichment of large rare earth elements at the interface. (1) Since the formation temperature of iron-rich phases is high, it is difficult to promote their nucleation by forming intermetallic compounds with higher temperatures and lower mismatch, which is one of the fundamental reasons why traditional modification techniques are unstable and have insignificant effects. (2) In addition, iron-rich phases are prone to grow into long needles along the preferred direction, which significantly deteriorates plasticity. Therefore, it is necessary to introduce large rare earth elements to inhibit their growth in the preferred direction, achieve spheroidization, and promote the formation of spherical and short rod-shaped iron-rich phases. To this end, this invention proposes a rare earth element functional partitioning synergistic control strategy, which achieves atomic-level reconstruction of iron-rich phases by precisely allocating the functions of Y and La rare earth elements. Based on oxidation thermodynamics, lattice mismatch theory (mismatch <15% indicates heterogeneous nucleation capability), and interface segregation theory (elements with low solid solubility and large atomic radii are easily enriched at the interface), ① high-temperature Y₂O₃ nanoparticles with a lattice mismatch of only 1.048% with the harmless α-Fe phase were calculated and screened to serve as heterogeneous nuclei to promote the nucleation of the α-Fe phase. During the high-temperature melting stage at 800-820 ℃, Y element was introduced, and the Y₂O₃ nanoparticles generated by its oxidation induced explosive heterogeneous nucleation of the harmless α-Fe phase, promoting the refinement of the iron-rich phase. Choosing a higher melting temperature of 800-820 ℃ helps to form more Y₂O₃ particles, thereby increasing the number of heterogeneous nuclei. If the melting temperature is too high, all elements are easily oxidized, forming oxidation inclusions; if the temperature is too low, sufficient Y₂O₃ nucleation sites cannot be formed. During the melting and holding period, oxygen is continuously introduced into the bottom of the melt through a vent pipe to promote the nucleation of Y₂O₃. Magnetic stirring is used to promote the uniform distribution of newly formed Y₂O₃. If the stirring rate is too low, uniform distribution cannot be achieved; if the stirring rate is too high, local high temperatures will be generated in the alloy melt, causing oxidation of other alloying elements and resulting in oxide inclusions. ② In the temperature range of 760-780 ℃, La is introduced. Due to its near-zero solid solubility and large atomic radius, it forms an adsorption layer at the iron-rich phase interface, effectively preventing the diffusion of Fe atoms, thereby inhibiting their preferential growth and promoting spheroidization of the iron-rich phase. A relatively low melting temperature is used in this stage, and La accumulates at the liquid phase front. If the melting temperature is too high, La will be uniformly distributed, resulting in insignificant spheroidization; if the temperature is too low, local agglomeration of La may occur.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1) It solves the problem that traditional technologies cannot effectively modify the harmful needle-like β-Fe phase in recycled aluminum alloys with high iron content.

[0019] 2) Compared to the strict Mn / Fe ratio requirement (close to 1:1) for Mn elements, the composite modifier of this invention is effective in a wider range of compositions, with a wider processing window and easier process control.

[0020] 3) The recycled aluminum alloy treated by this invention exhibits significantly improved strength and elongation. For example, compared to untreated A356 recycled aluminum, the strength increase after dual composite rare earth modification treatment is >20%, and the elongation increase is >130%. Attached Figure Description

[0021] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a mechanism diagram of rare earth composite metamorphic Fe phase; Figure 2 This is a schematic diagram of a smelting apparatus; Figure 3 (a) Metallographic photograph and (b) Schematic diagram of the microstructure of the alloy in Example 1; Figure 4 (a) Metallographic photograph and (b) Schematic diagram of the microstructure of alloy in Comparative Example 1; Figure 5 This is a schematic diagram of the microstructure of alloy 2 in Comparative Example; Figure 6 This is a schematic diagram of the microstructure of alloy 3 in Comparative Example; Figure 7 This is a schematic diagram of the microstructure of alloy 4 in Comparative Example; Figure 8 This is a schematic diagram of the microstructure of alloy 5 in Comparative Example; Figure 9 This is a schematic diagram of the microstructure of alloy 6 in Comparative Example; Figure 10 This is a schematic diagram of the microstructure of alloy 7 in Comparative Example. Detailed Implementation

[0022] The present invention will be described in detail below with reference to embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several adjustments and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0023] In all the following embodiments, the master alloy is made from recycled aluminum scrap A356, which has the following composition: Si: 6.8 wt.%, Fe: 1.1 wt.%, Mg: 0.3 wt.%, Cu: 0.15 wt.%, Mn: 0.10 wt.%, Zn: 0.08 wt.%, Ti: 0.15 wt.%, with the balance being Al and other unavoidable impurities.

[0024] Example 1 This embodiment provides a method for recovering aluminum from rare earth dual-composite modified A356 alloy. The alloy components are: Si: 6.8 wt.%, Fe: 1.1 wt.%, Y: 0.2 wt.%, La: 0.5 wt.%, with the balance being Al and other aforementioned trace elements and unavoidable impurities. The preparation method is as follows: S1: Material preparation: Weigh A356 recycled aluminum alloy, Al-30Y, and Al-30La intermediate alloy according to the proportions; S2: Preheating: First, grind and clean the recycled A356 crushed material, Al-30Y and Al-30La intermediate alloy, and then preheat at 220℃ for 3 hours to remove moisture; S3: Melting: Heat the A356 recycled material to melt and raise the temperature to 820 ℃, add Al-30Y master alloy, hold for 15 min, continuously introduce oxygen through a gas supply pipe, and perform magnetic stirring at a rate of 3000 r / min. During the process, use equipment such as... Figure 2 As shown; the melt was cooled to 770 °C, Al-30La master alloy was added, and the mixture was held at that temperature for 25 min; S4: Refining: Heat the melt to 740 ℃ and hold for 10 min. Refine with inorganic salt mixed refining agent for 8 min and remove slag. Then cool down to 710 ℃ and hold for 20 min.

[0025] S5: Casting: The melt obtained in S4 is subjected to gravity casting in a metal mold at 710 °C to obtain a casting.

[0026] S6: Heat treatment: The casting obtained from S5 is subjected to a two-step heat treatment: solution treatment at 540 °C for 6 hours followed by aging at 155 °C for 3 hours.

[0027] The microstructure and schematic diagram of the alloy obtained in this embodiment are shown below. Figure 3 As shown in the figure, the corresponding Fe phase is fine and dispersed, and is expected to have good mechanical properties.

[0028] Example 2 Compared with Example 1, the rare earth element content in this embodiment is adjusted to: Y: 0.25 wt.%, La: 0.4 wt.%, and the rest is the same as in Example 1. The microstructure of the alloy obtained in this embodiment is not significantly different from that in Example 1, and it still has good mechanical properties.

[0029] Example 3 Compared with Example 1, the rare earth element content in this embodiment is adjusted to: Y: 0.1 wt.%, La: 0.3 wt.%, and the rest is the same as in Example 1. The microstructure of the alloy obtained in this embodiment is not significantly different from that in Example 1, and it still has good mechanical properties.

[0030] Example 4 Compared with Example 1, the rare earth element content in this embodiment is adjusted to: Y: 0.4 wt.%, La: 0.8 wt.%, and the rest is the same as in Example 1. The microstructure of the alloy obtained in this embodiment is not significantly different from that in Example 1, and it still has good mechanical properties.

[0031] Comparative Example 1 Compared with Example 1, this comparative example did not add Y and La rare earth elements, but was otherwise the same as Example 1. The microstructure and schematic diagram of the alloy prepared in this comparative example are shown in Figure 4. It contains a large number of long needle-like β-Fe phases, which will result in very poor mechanical properties.

[0032] Comparative Example 2 Compared with Example 1, the Y content in this comparative example was reduced to 0.02 wt.%, while the rest was the same as in Example 1.

[0033] A schematic diagram of the microstructure of the alloy obtained in this comparative example is shown below. Figure 5 As shown, compared to Example 1, the generated Fe-rich phase is coarse and has poor mechanical properties.

[0034] Comparative Example 3 Compared with Example 1, the Y content in this comparative example was increased to 0.8 wt.%, while the rest was the same as in Example 1. A schematic diagram of the microstructure of the alloy obtained in this comparative example is shown below. Figure 6 As shown, compared to Example 1, the alloy microstructure of this comparative example shows the presence of coarse Al2Y phase, and the alloy elongation is reduced. Comparative Example 4 Compared with Example 1, the La content in this comparative example was reduced to 0.1 wt.%, while the rest was the same as in Example 1. A schematic diagram of the microstructure of the alloy obtained in this comparative example is shown below. Figure 7 As shown, compared to Example 1, the Fe-rich phase in the alloy structure of this comparative example is more slender, and the mechanical properties are significantly reduced.

[0035] Comparative Example 5 Compared with Example 1, this comparative example increases the La content to 1.0 wt.%, which is the same as in Example 1.

[0036] A schematic diagram of the microstructure of the alloy obtained in this comparative example is shown below. Figure 8 As shown, compared to Example 1, the comparative alloy microstructure exhibits additional long needle-like Al atoms. 11 The Ce3 phase impairs the mechanical properties of the alloy.

[0037] Comparative Example 6 Compared with Example 1, this comparative example replaces La with the same amount of Ce, and the rest is the same as Example 1.

[0038] A schematic diagram of the microstructure of the alloy obtained in this comparative example is shown below. Figure 9 As shown, compared to Example 1, the Fe-rich phase in the alloy structure of this comparative example is more slender, and the mechanical properties are significantly reduced.

[0039] Comparative Example 7 Compared with Example 1, this comparative example replaces element Y with the same amount of Ce, and the rest is the same as Example 1.

[0040] A schematic diagram of the microstructure of the alloy obtained in this comparative example is shown below. Figure 10 As shown, compared to Example 1, the generated Fe-rich phase is coarse and has poor mechanical properties.

[0041] Comparative Example 8 Compared with Example 1, the rare earth elements in this comparative example were added by adding Al-30Y and Al-30La together at 790℃, while the rest were the same as in Example 1.

[0042] Compared to Example 1, the Fe-rich phase in the alloy of this comparative example is more slender, the refining effect is not obvious, and the mechanical properties are significantly reduced.

[0043] Comparative Example 9 Compared with Example 1, the rare earth elements in this comparative example were added by adding Al-30Y and Al-30La together at 830 °C. The rest of the process was the same as in Example 1.

[0044] Compared to Example 1, the Fe-rich phase in this comparative alloy is coarser, the spheroidization effect is less obvious, and the mechanical properties are significantly reduced.

[0045] Comparative Example 10 Compared with Example 1, the temperature at which Al-30Y was added in the first stage was changed to 790 °C, while the rest was the same as in Example 1.

[0046] Compared to Example 1, the Fe-rich phase in the alloy of this comparative example is coarser, the refining effect is not obvious, and the mechanical properties are significantly reduced.

[0047] Comparative Example 11 Compared with Example 1, the temperature at which Al-30Y was added in the first stage was changed to 830 °C, while the rest was the same as in Example 1.

[0048] Compared to Example 1, the alloy in this comparative example exhibits blocky Y2O3 particles, resulting in a significant decrease in mechanical properties.

[0049] Comparative Example 12 Compared with Example 1, the temperature at which Al-30La was added in the second stage was changed to 750 °C, while the rest was the same as in Example 1.

[0050] Compared to Example 1, the Fe-rich phase in this comparative alloy has an uneven size distribution, insufficient La diffusion, and uneven spheroidization, resulting in mechanical properties that are inferior to those of Example 1.

[0051] Comparative Example 13 Compared with Example 1, the temperature at which Al-30La was added in the second stage was changed to 790 °C, while the rest was the same as in Example 1.

[0052] Compared to Example 1, the Fe-rich phase in this comparative alloy is coarser, the bonding between La and Fe-rich phase is poor, the spheroidization effect is not obvious, and the mechanical properties are significantly reduced.

[0053] Comparative Example 14 Compared with Example 1, this comparative example did not introduce oxygen during the first heat preservation period, but was otherwise the same as Example 1. Compared to Example 1, the Fe-rich phase in the alloy of this comparative example is coarser, the refining effect is not obvious, and the mechanical properties are significantly reduced.

[0054] Comparative Example 15 Compared with Example 1, the magnetic stirring rate of this comparative example was increased to 4000 r / min during the first heat preservation period, and the rest was the same as Example 1. Compared to Example 1, the alloy in this comparative example exhibits oxide inclusions, resulting in a significant decrease in mechanical properties.

[0055] Comparative Example 16 Compared with Example 1, the magnetic stirring rate of this comparative example was reduced to 2000 r / min during the first heat preservation period, while the rest was the same as Example 1. Compared to Example 1, the Y2O3 phase in this comparative alloy is coarse and unevenly distributed, with little refining effect and significantly reduced mechanical properties.

[0056] Performance testing Regarding the above embodiment 1 2 and Comparative Example 1 The prepared aluminum alloy was subjected to mechanical property testing. Tensile properties were tested on a Zwick Z100 universal testing machine at a tensile rate of 1 mm / min and a specimen marking length of 50 mm. Each data point represents the average of five valid tests. The performance test results are listed in Table 1. As shown in Table 1, compared to Comparative Example 1 without any treatment, the strength increase after the double composite rare earth modification described in this invention (Example) is >20%, and the elongation increase is >130%.

[0057] Table 1. Test results of mechanical properties and microstructure of recycled aluminum alloys

[0058] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A dual-composite rare earth modification method for harmful Fe-rich phases in recycled aluminum alloys, characterized in that, During the smelting of recycled aluminum alloys, Y modifier is added at high temperature, and oxygen is introduced and magnetic stirring is performed simultaneously to promote the formation of a large number of fine and dispersed Y2O3 particles as heterogeneous nucleation sites for α-Fe. La modifier is added at medium and high temperature to enrich the α-Fe liquid-solid front and inhibit its growth. The dual composite rare earth modification achieves the refinement and spheroidization of the iron-rich phase.

2. The method according to claim 1, characterized in that, The Fe content in the recycled aluminum alloy is 0.8-1.6 wt.%.

3. The method according to claim 1, characterized in that, The recycled aluminum alloy contains Y: 0.1-0.4 wt.%, La: 0.3-0.8 wt.%, and the balance consists of common elements and unavoidable impurities found in recycled aluminum alloys.

4. The method according to claim 3, characterized in that, The ratio of Y content to Fe content is between 1:4 and 1:8; the ratio of La content to Fe content is between 1:2 and 1:

3.

5. The method according to claim 1, characterized in that, The high temperature is 800 ℃-820 ℃, and the holding time is 10-20 min. During the holding time, oxygen is continuously introduced into the bottom and magnetic stirring is performed; the medium and high temperature is 760 ℃-780 ℃, and the holding time is 20-30 min.

6. The method according to claim 5, characterized in that, The stirring speed selected for magnetic stirring is 2500-3500 r / min.

7. The method according to claim 1, characterized in that, The smelting and preparation of the recycled aluminum alloy includes the following steps: S1. Weigh the raw materials for recycling aluminum alloy scrap, Al-30Y, and Al-30La master alloys according to the proportions. S2, First stage heat preservation: Heat the recycled aluminum alloy to melt and raise the temperature to 800 ℃-820 ℃, add Al-30Y master alloy, and simultaneously continuously introduce oxygen at the bottom and perform magnetic stirring, and keep it at this temperature for 10-20 min. S3, Second stage heat preservation: Cool the melt in S2 to 760℃-780℃, add Al-30La master alloy, and hold for 20-30 minutes; S4. Cool the melt in S3 to 735℃-745℃ and hold it there. After refining, remove the slag. S5. Cool the melt in S4 to 700℃-715℃ and hold it at that temperature. After removing the slag, pour the melt at 700℃-715℃ to obtain the casting. S6. The castings obtained in S5 are subjected to a two-stage heat treatment. The first step is solution treatment at 520-560℃, and the second step is aging treatment at 145-165℃.

8. The method according to claim 7, characterized in that, In S4, the holding time is 10-15 minutes and the refining time is 8-10 minutes; in S5, the holding time is 15-25 minutes.

9. The method according to claim 7, characterized in that, In S6, solution treatment lasts 6-7 hours; aging treatment lasts 3-4 hours.

10. The method according to claim 7, characterized in that, In the first stage of S2 heat preservation, the added Y modifier forms fine Y2O3 nanoparticles in the high-temperature melt and serves as heterogeneous nucleation sites for the subsequent α-Fe phase; in the second stage of S3 heat preservation, the added La modifier is uniformly dispersed in the melt and enriched on the surface of the α-Fe phase during the subsequent solidification process, reducing its surface energy and thus inhibiting growth.

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