Aluminum alloy, preparation method thereof and automobile electric drive

Abstract

The invention provides an aluminum alloy, a preparation method thereof and an automobile electric drive, and belongs to the technical field of alloy materials. Wherein the aluminum alloy comprises 0.75 wt%-1.85 wt% of Fe, 0.9 wt%-1.2 wt% of Mg, 0.1 wt%-0.3 wt% of Mn and 0.1 wt%-0.3 wt% of M, and the M comprises at least one of Cr and Sr. The mechanical property of the aluminum alloy can be improved on the premise of high Fe content.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of alloy materials, in particular to an aluminum alloy, a preparation method thereof and an electric drive of an automobile. BACKGROUND

[0002] Die-casting aluminum alloy is a mainstream material for making electric drive housings of new energy vehicles and has the characteristics of lightweight. The most widely used die-casting aluminum alloy in the electric drive housing is ADC12 aluminum alloy of the AlSiCu system, which has the advantages of good fluidity and easy die-casting into complex-shaped parts.

[0003] However, the yield strength of ADC12 aluminum alloy is about 140 MPa, and the tensile strength is less than 300 MPa, which is difficult to meet the mechanical performance requirements of high-performance electric drives.

[0004] Although there is a high-toughness aluminum alloy with a yield strength of not less than 200 MPa and a tensile strength of not less than 350 MPa in the prior art, the aluminum alloy requires a low content of iron, which has a high requirement for the purity or impurity removal process of raw materials, thereby resulting in a high production cost. SUMMARY

[0005] In view of the above problems, the present application provides an aluminum alloy, a preparation method thereof and an electric drive of an automobile, aiming to improve the mechanical properties of the aluminum alloy under the premise of high Fe content.

[0006] In a first aspect, the present application provides an aluminum alloy, comprising 0.75wt%-1.85wt% of Fe, 0.9wt%-1.2wt% of Mg, 0.1wt%-0.3wt% of Mn and 0.1wt%-0.3wt% of M, wherein the M comprises at least one of Cr and Sr.

[0007] In an embodiment, the M comprises Cr and Sr, the mass fraction of Cr in the aluminum alloy is 0.08%-0.25%, and the mass fraction of Sr in the aluminum alloy is 0.02%-0.04%.

[0008] In an embodiment, the mass ratio of Fe to Cr is 4-8, and the mass ratio of Fe to Sr is 20-90.

[0009] In an embodiment, the aluminum alloy comprises the following mass fractions of components: Si 10%-12.5%, Cu 1.4%-3.4%, Fe 0.75%-1.85%, Mg 0.9%-1.2%, Mn 0.1%-0.3%, Cr 0.08%-0.25%, Sr 0.02%-0.04%, and the balance is Al.

[0010] In an embodiment, the mass ratio of Si to Mg is 9-13.

[0011] In an embodiment, in the metallographic structure diagram, the aluminum alloy comprises a Si-Al eutectic phase, and the average particle size of Si in the Si-Al eutectic phase is < 1 μm.

[0012] In an embodiment, in the metallographic structure diagram, the surface of the aluminum alloy comprises a grain refinement zone, the average size of the grains in the grain refinement zone is < 8 μm, and the width of the grain refinement zone is ≥ 100 μm.

[0013] In an embodiment, in the metallographic structure diagram, the aluminum alloy comprises a β-Fe phase, and the volume fraction of the β-Fe phase is < 0.01.

[0014] In an embodiment, the aluminum alloy further comprises at least one of Zn, Ni, Ti, La, Sn, and Pb; the mass fraction of Zn is ≤ 1.05%, and / or, the mass fraction of Ni is ≤ 0.4%, and / or, the mass fraction of Ti is ≤ 0.3%, and / or, the mass fraction of La is ≤ 0.05%, and / or, the mass fraction of Sn is ≤ 0.02%, and / or, the mass fraction of Pb is ≤ 0.2%.

[0015] In an embodiment, the yield strength of the aluminum alloy is ≥ 200 MPa, the tensile strength is ≥ 340 MPa, and the elongation at break is ≥ 2.4%.

[0016] In a second aspect, the present application provides a preparation method of an aluminum alloy, comprising:

[0017] providing raw materials, the raw materials comprising an Al source, an Mg source, an Mn source, and an M source, the M source comprising at least one of a Cr source and a Sr source; mixing the raw materials according to the following proportions: 0.9 wt% - 1.2 wt% of Mg, 0.1 wt% - 0.3 wt% of Mn, 0.1 wt% - 0.3 wt% of M, and the balance being Al; melting at a first temperature to obtain a first aluminum alloy melt; reducing the temperature to a second temperature, adding a refining agent to the first aluminum alloy melt under an inert atmosphere, stirring until uniform mixing, then skimming, and standing to obtain a second aluminum alloy melt; reducing the temperature of the second aluminum alloy melt to a third temperature, and die casting the second aluminum alloy melt, and obtaining the aluminum alloy after air cooling to room temperature.

[0018] In an embodiment, the step of providing the raw materials comprises: providing an Al source, the Al source comprising scrap aluminum, and under the condition that the Fe content in the scrap aluminum is < 0.75%, the raw materials further comprise an Fe source; heating the scrap aluminum to 580°C - 620°C, and removing the ferromagnetic impurities in the scrap aluminum by a magnetic separation process.

[0019] In an embodiment, the first temperature is 730°C - 750°C; and / or, the second temperature is 690°C - 710°C; and / or, the third temperature is 675°C - 685°C.

[0020] In an embodiment, the refining agent comprises the following raw materials in mass fraction: CaCl2 18%-22%, CaF2 12%-16%, graphite 3%-7%, LaCl3 2%-6%, B2O3 1%-3%, and the balance of KCl.

[0021] In an embodiment, the mass ratio of the refining agent to the first aluminum alloy melt is (0.1-0.3):100.

[0022] In an embodiment, the step of die casting the second aluminum alloy melt comprises: providing a die casting mold, heating the die casting mold to 125-145 DEG C, and controlling the negative pressure in the die casting mold to be 45-75 mbar; adding the second aluminum alloy melt into the pressure chamber of the die casting mold, controlling the injection pressure to be 80-120 MPa, the injection speed to be 5-8 m / s, and the injection time to be 2-5 s; and controlling the second aluminum alloy melt to be cooled to the same temperature as the die casting mold at a cooling rate of 120-170 DEG C / s during the die casting process.

[0023] In an embodiment, the step of providing raw materials comprises: providing scrap aluminum; heating the scrap aluminum to 580-620 DEG C, and removing impurities from the scrap aluminum by a magnetic separation process.

[0024] In a third aspect, the present application provides an automobile electric drive, comprising an electric drive shell made of the aluminum alloy of any one of the preceding claims or the aluminum alloy prepared by the method of any one of the preceding claims.

[0025] The aluminum alloy of the present application comprises Mg, which can be solid-solved in the Al matrix and helps to improve the strength of the aluminum alloy. The aluminum alloy of the present application further comprises Mn, which helps to generate α-Fe phase and reduce the precipitation of needle-like β-Fe phase, thereby helping to improve the ductility of the aluminum alloy. When the aluminum alloy of the present application comprises Cr, Cr and Fe can form more stable Al-Cr-Fe intermetallic compounds, reduce the precipitation of needle-like β-Fe phase, and promote the formation of more fine and uniform α-Fe phase, thereby reducing brittleness and improving the elongation of the aluminum alloy. When the aluminum alloy of the present application comprises Sr, Sr can be adsorbed on the surface of Fe phase, hinder its growth, and make the β-Fe and α-Fe phases more fine and dispersed, thereby helping to form a wider grain refinement band and improve the ductility of the aluminum alloy.

[0026] On the basis of high Fe content, the present application reduces the negative effects of Fe phase by adding Mg, Mn, Cr and / or Sr, thereby reducing the production cost of the aluminum alloy on the basis of improving the mechanical properties of the aluminum alloy. Therefore, the present application can improve the mechanical properties of the aluminum alloy on the premise of high Fe content. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Metallographic structure diagram of the aluminum alloy of some embodiments of the present application;

[0028] Figure 2 Metallographic structure diagram of the aluminum alloy of some embodiments of the present application;

[0029] Figure 3 Metallographic structure diagram of the aluminum alloy of some embodiments of the present application;

[0030] Figure 4 Metallographic structure diagram of the aluminum alloy of some embodiments of the present application. DETAILED DESCRIPTION

[0031] The following examples are for a more clear illustration of the technical solutions of the present application, and thus only serve as examples, and cannot be used to limit the protection scope of the present application.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in the specification herein is for describing particular embodiments only and is not intended to be limiting of the application; the use herein of terms such as “comprise” and “have” and any variations such as “comprises” and “has” is intended to cover the presence of stated features or objects and not to exclude the presence of one or more additional features or objects.

[0033] In the description of the embodiments of the present application, the technical terms “first”, “second”, and the like are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of “a plurality of” is two or more, unless otherwise explicitly and specifically limited.

[0034] Reference herein to “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The occurrence of the phrase in various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily independent or alternative embodiments to each other. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0035] In the description of the embodiments of the present application, the term “and / or” is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character “ / ” herein generally represents an “or” relationship between the associated objects before and after it.

[0036] In the description of the embodiments of the present application, the term "a plurality of" refers to two or more (including two), and similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of pieces" refers to two or more pieces (including two pieces). The term "at least one" refers to one or more.

[0037] The ADC12 aluminum alloy is a main material for a new energy vehicle electric drive shell and has the advantage of lightweight, but the yield strength of the ADC12 aluminum alloy is about 140 MPa, and the tensile strength is less than 300 MPa, and the mechanical strength cannot meet the demand of high-performance electric drive.

[0038] The prior art discloses a high-toughness Al-Si series die-casting aluminum alloy material, which comprises 0.08%-0.12% of Fe in terms of mass fraction. When waste aluminum is used as raw material to produce the aluminum alloy, due to the low Fe content defined in the aluminum alloy, higher requirements are put forward to the impurity removal process, resulting in the increase of production cost.

[0039] In order to solve the above problems, the present application provides an aluminum alloy, comprising 0.75wt%-1.85wt% of Fe, 0.9wt%-1.2wt% of Mg, 0.1wt%-0.3wt% of Mn and 0.1wt%-0.3wt% of M, wherein the M comprises at least one of Cr and Sr.

[0040] Mg can be solid-solved into the Al matrix, which helps to improve the strength of the aluminum alloy. In addition, Mg can promote the formation of a dense oxide film (Al2O3-MgO), thereby helping to improve the corrosion resistance of the aluminum alloy in harsh environments such as humidity and salt spray. Exemplarily, the mass fraction of Mg can be 0.9%, 0.95%, 1%, 1.03%, 1.05%, 1.07%, 1.1%, 1.13%, 1.15%, 1.18% or 1.2%.

[0041] Mn helps to generate alpha-Fe phase and reduce the precipitation of needle-like beta-Fe phase, thereby helping to improve the ductility of the aluminum alloy. Mn can form fine and dispersed manganese-containing phases (such as Al6Mn), hinder grain boundary migration and inhibit recrystallization. Exemplarily, the mass fraction of Mn can be 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, 0.23%, 0.25%, 0.28% or 0.3%.

[0042] Cr and Fe can form more stable Al-Cr-Fe intermetallic compounds, reduce the precipitation of needle-like beta-Fe phase, and promote the formation of finer and more uniform alpha-Fe phase, thereby reducing brittleness and improving the elongation of the aluminum alloy. Sr helps to form a wider grain refinement band, thereby helping to improve the ductility of the aluminum alloy.

[0043] The application reduces the negative effects of Fe phase by adding Mg, Mn, Cr and / or Sr on the basis of high Fe content, thereby reducing the production cost of the aluminum alloy on the basis of improving the mechanical properties of the aluminum alloy. Therefore, the application can improve the mechanical properties of the aluminum alloy under the premise of high Fe content. The aluminum alloy provided by the application can be applied to new energy automobile electric drive shells and other parts.

[0044] According to some embodiments of the application, M includes Cr and Sr, the mass fraction of Cr in the aluminum alloy is 0.08%-0.25%, and the mass fraction of Sr in the aluminum alloy is 0.02%-0.04%.

[0045] When the content of Cr is between 0.08% and 0.25%, it helps to refine the grains and indirectly suppresses the coarsening of the Fe phase. When the content of Sr is between 0.02% and 0.04%, it can increase the fluidity during smelting and better transmit pressure during pressure casting, which helps to form a wider grain refinement band.

[0046] Compared with using Cr or Sr alone, using Cr and Sr together can further improve the ductility of the aluminum alloy.

[0047] According to some embodiments of the application, the mass ratio of Fe to Cr is 4-8, and the mass ratio of Fe to Sr is 20-90.

[0048] The mass ratio of Fe to Cr can be any value between 4 and 8. For example, the mass ratio of Fe to Cr can be 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5 or 8. When the mass ratio of Fe to Cr is between 4 and 8, it can further reduce the precipitation of acicular β-Fe phase and promote the formation of finer and more uniform α-Fe phase.

[0049] The mass ratio of Fe to Sr can be any value between 20 and 90. For example, the mass ratio of Fe to Sr can be 20, 30, 40, 50, 60, 70, 80 or 90. When the mass ratio of Fe to Sr is between 20 and 90, it can further suppress the growth of Fe phase and help to form finer iron phase.

[0050] According to some embodiments of the application, the aluminum alloy includes the following components with the following mass fractions: Si 10%-12.5%, Cu 1.4%-3.4%, Fe 0.75%-1.85%, Mg 0.9%-1.2%, Mn 0.1%-0.3%, Cr 0.08%-0.25%, Sr 0.02%-0.04%, and the balance being Al.

[0051] Si can significantly reduce the melting point of the alloy and expand the solidification temperature interval, so that the molten metal remains flowable for a longer time before solidification, which is suitable for casting thin-walled or complex-shaped parts. When the content of Si is between 10% and 12.5%, Al and Si undergo eutectic reaction, and the uniform distribution of Si in the eutectic structure can alleviate stress concentration during solidification, reduce solidification shrinkage, and reduce the tendency of shrinkage and hot cracking, which helps to improve the mechanical strength of the aluminum alloy. In addition, Si can also generate Mg2Si strengthening phase with Mg to improve the strength of the alloy, and change the precipitation path of Fe phase. Exemplarily, the mass fraction of Si can be 10%, 10.2%, 10.5%, 10.8%, 11%, 11.3%, 11.5%, 11.7%, 12%, 12.2% or 12.5%.

[0052] Cu can form a substitutional solid solution in the Al matrix, forming a solid solution strengthening effect, thereby helping to improve the strength of the aluminum alloy. Exemplarily, the mass fraction of Cu can be 1.4%, 1.5%, 1.8%, 2.0%, 2.3%, 2.5%, 2.7%, 3.0%, 3.2% or 3.4%.

[0053] Cr can inhibit the precipitation of β-Fe phase. β-Fe phase usually exists in the form of needles, and this form of Fe phase is easy to cause the fracture of the aluminum alloy, is a harmful phase in the aluminum alloy, and can reduce the mechanical properties of the aluminum alloy, especially the plasticity and toughness. Sr can realize modification of eutectic silicon and Fe phase. Sr can refine eutectic silicon, improve the distribution of Fe phase, and inhibit the generation of β-Fe; Sr is adsorbed on the surface of Fe phase, hindering the growth of Fe phase, so that β-Fe and α-Fe phase are finer and more dispersed.

[0054] It should be noted that the aluminum alloy also includes some unavoidable impurity elements, and the content of the impurity elements is not more than 0.01%.

[0055] On the basis of high Fe content, the present application reduces the negative effects of Fe phase by adding Mg, Cr and Sr, thereby reducing the production cost of the aluminum alloy on the basis of improving the mechanical properties of the aluminum alloy. Therefore, the present application can improve the mechanical properties of the aluminum alloy on the premise of high Fe content.

[0056] According to some embodiments of the present application, the mass ratio of Si and Mg is 9-13.

[0057] The mass ratio of Si and Mg can be any value between 9 and 13. Exemplarily, the mass ratio of Si and Mg can be 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5 or 13. When the mass ratio of Si and Mg is between 9 and 13, not only the formation of β-Fe can be inhibited, but also the formation of Mg-Si-Fe composite phase can be reduced, thereby reducing the negative effects of Fe phase.

[0058] According to some embodiments of the present application, in the metallographic structure diagram, the aluminum alloy includes a Si-Al eutectic phase, and the average particle size of Si in the Si-Al eutectic phase is <1 μm.

[0059] The average particle size of Si in the Si-Al eutectic phase <1 μm means that the Si particles are more fine, and the fine Si particles can hinder the dislocation movement. When the aluminum alloy is subjected to external force, the dislocation is the main carrier of the slip of the crystal structure inside the material, and the dislocation movement easily leads to the deformation of the material, and the fine Si particles can act as “obstacles” to make the dislocation movement more difficult, and a larger external force is required to make the material deform, thereby improving the strength of the aluminum alloy.

[0060] According to some embodiments of the present application, in the metallographic structure diagram, the surface of the aluminum alloy includes a grain refinement zone, the average size of the grains in the grain refinement zone is <8 μm, and the width of the grain refinement zone is ≥100 μm.

[0061] The metallographic structure diagram is an image used to display the microstructure of a metal material, which can present the grain morphology, phase composition and distribution of the metal inside, and can be observed by an electron microscope.

[0062] The grain refinement zone refers to a region with an average grain size <8 μm, and the width of the grain refinement zone ≥100 μm means that there are more grains with an average size <8 μm in the aluminum alloy, and the more small-size grains, the higher the yield strength of the material. This is because the fine grains make the dislocation movement more easily blocked at the grain boundary, and a larger external force is required to make the dislocation continue to move, thereby improving the strength of the aluminum alloy. In addition, the fine-grained structure can make the stress distribution of the aluminum alloy more uniform when subjected to stress, reducing the stress concentration phenomenon. At the same time, the small grains make the crack propagation path more tortuous during crack propagation, consuming more energy, thereby helping to improve the toughness of the aluminum alloy.

[0063] According to some embodiments of the present application, in the metallographic structure diagram, the aluminum alloy includes a β-Fe phase, and the volume fraction of the β-Fe phase is <0.01.

[0064] The β-Fe phase usually exists in the form of needles, and this form of Fe phase easily causes the fracture of the aluminum alloy, is a harmful phase in the aluminum alloy, and can reduce the mechanical properties of the aluminum alloy, especially the plasticity and toughness. The volume fraction of the β-Fe phase <0.01 means that there is little β-Fe phase in the aluminum alloy, thereby helping to improve the strength and toughness of the aluminum alloy.

[0065] In some embodiments, the volume fraction of the β-Fe phase is calculated by using ImageJ software to analyze the metallographic image of the sample, and calculating the area ratio of the β-Fe phase (as an approximate value of the volume fraction); the statistical rule is to select at least 5 fields of view and take the average value. The volume fraction of the β-Fe phase = the area ratio of the β-Fe phase / the total measurement area. The above method conforms to the standard of ASTM E1245.

[0066] According to some embodiments of the present application, the aluminum alloy further comprises at least one of Zn, Ni, Ti, La, Sn, and Pb; the mass fraction of Zn is ≤1.05%, the mass fraction of Ni is ≤0.4%, and / or, the mass fraction of Ti is ≤0.3%, and / or, the mass fraction of La is ≤0.05%, and / or, the mass fraction of Sn is ≤0.02%, and / or, the mass fraction of Pb is ≤0.2%.

[0067] Zn can be solid-solved in the Al matrix, which helps to improve the strength of the alloy; Ni is beneficial to improve the high-temperature strength of the aluminum alloy; Ti can refine the grains; La has a modification effect on the eutectic silicon, which is beneficial to improve the elongation; Sn and Pb help to improve the forming performance of the aluminum alloy.

[0068] For example, the mass fraction of Zn can be 0.1%, 0.2%, 0.5%, 0.6%, 0.8%, 0.9%, 1.0% or 1.05%; the mass fraction of Ni can be 0.05%, 0.15%, 0.18%, 0.2%, 0.22%, 0.25%, 0.27%, 0.3%, 0.35% or 0.4%; the mass fraction of Ti can be 0.02%, 0.04%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25% or 0.3%; the mass fraction of La can be 0.01%, 0.02%, 0.03%, 0.04% or 0.05%; the mass fraction of Sn can be 0.01%, 0.012%, 0.014%, 0.016%, 0.018% or 0.02%; and the mass fraction of Pb can be 0.02%, 0.04%, 0.06%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18% or 0.2%.

[0069] When the contents of Zn, Ni, Ti, La, Sn and Pb are within the above ranges, the performance of the aluminum alloy can be fine-tuned, which can improve the mechanical properties of the aluminum alloy while avoiding a significant increase in the production cost of the aluminum alloy.

[0070] According to some embodiments of the present application, the yield strength of the aluminum alloy is ≥200 MPa, the tensile strength is ≥340 MPa, and the elongation at break is ≥2.4%.

[0071] Yield strength refers to the stress value corresponding to the time when the aluminum alloy starts to have obvious plastic deformation when the external force reaches a certain value during the tensile process. Tensile strength refers to the maximum tensile stress that the aluminum alloy can withstand until it is pulled apart during the tensile test. Elongation at break refers to the percentage of the length increase of the gauge length part of the aluminum alloy when it is stretched to break relative to the original gauge length.

[0072] When the performance of the aluminum alloy of the present application meets the above range, it means that the aluminum alloy has high mechanical strength and toughness, and can be applied to the electric drive shell, thereby reducing the weight of the electric drive shell.

[0073] In some embodiments, the yield strength, tensile strength and elongation at break of the aluminum alloy can be tested by a universal tensile testing machine.

[0074] According to some embodiments of the present application, the present application provides a preparation method of an aluminum alloy, comprising:

[0075] Providing raw materials, the raw materials comprising an Al source, a Mg source, a Mn source and an M source, the M source comprising at least one of a Cr source and a Sr source; mixing the raw materials according to the following proportions: Mg 0.9wt%-1.2wt%, Mn 0.1wt%-0.3wt% of Mn, M 0.1wt%-0.3wt%, and the balance being Al, melting at a first temperature to obtain a first aluminum alloy melt; reducing the temperature to a second temperature, adding a refining agent to the first aluminum alloy melt under an inert atmosphere, stirring until uniform, then skimming, and obtaining a second aluminum alloy melt after standing; reducing the temperature of the second aluminum alloy melt to a third temperature, and pressure casting the second aluminum alloy melt, and obtaining the aluminum alloy after air cooling to room temperature.

[0076] The Mg source, the Mn source and the M source can be added in the form of an element or in the form of an alloy. In order not to introduce impurities into the finished aluminum alloy, the Mg source, the Mn source and the M source can be added in the form of an aluminum alloy. In some embodiments, the raw materials can further comprise at least one of a Si source, a Cu source, a Zn source, a Ni source, a Ti source, a La source, a Sn source and a Pb source.

[0077] The melting of the raw materials can be carried out using a melting furnace, which can be an electric resistance furnace, an electric arc furnace, an electromagnetic induction furnace or a gas furnace. In some embodiments, the raw materials can be crushed to a particle size of ≤10mm before melting, and then the granular raw materials are melted, which helps to improve the melting efficiency.

[0078] The refining agent refers to an additive for removing gas and inclusions in the first aluminum alloy melt. In the smelting process, the first aluminum alloy melt is prone to absorbing hydrogen to form porosity defects, and non-metallic inclusions such as oxides and slag are also present in the first aluminum alloy melt. The refining agent can remove the gas and inclusions, so that the inclusions are gathered and floated to the surface of the melt, and then removed by slagging. The refining agent is added while stirring the first aluminum alloy melt to remove gas, and the time can be 10-20 minutes.

[0079] The inert atmosphere is mainly used to prevent the refining agent from failing. In some embodiments, the inert atmosphere can be at least one of nitrogen, argon, and helium, and the flow rate of the inert atmosphere can be 5-15 L / min.

[0080] The die casting process is a process in which the melt is injected into a steel mold, and the finished product is obtained after cooling and solidification. The die casting process has high production efficiency and can manufacture complex structures such as thin-walled, hollow, and threaded structures. The aluminum alloy of the present application is directly die cast without the need for heat treatment, which can further reduce production costs.

[0081] According to some embodiments of the present application, the step of providing raw materials includes: providing an Al source, the Al source including scrap aluminum, and under the condition that the Fe content in the scrap aluminum is <0.75%, the raw material further includes an Fe source; heating the scrap aluminum to 580-620°C, and removing ferromagnetic impurities in the scrap aluminum by a magnetic separation process.

[0082] Scrap aluminum refers to aluminum products or aluminum-containing materials of various sources that have been used or discarded, which can include construction scrap aluminum, industrial scrap aluminum, household scrap aluminum, packaging scrap aluminum, etc. Using scrap aluminum as an aluminum source can further reduce production costs.

[0083] Since the Fe content in the finished aluminum alloy product is 0.75-1.85%, when the Fe content in the scrap aluminum is <0.75%, an additional Fe source is needed.

[0084] Heating the scrap aluminum to 580-620°C can obtain semi-solid aluminum, which is convenient for magnetic separation. The magnetic separation process uses a magnet to attract ferromagnetic impurities in the scrap aluminum, including steel parts, iron oxides, Co, Ni, and other alloys.

[0085] In some embodiments, when the Al source includes scrap aluminum, an upper and lower two-stage smelting furnace can be used for smelting, i.e., the scrap aluminum is added to the upper smelting furnace, the scrap aluminum is heated in the upper smelting furnace to obtain semi-solid aluminum, then the ferromagnetic impurities are attracted out by a magnet, and the semi-solid aluminum is slowly poured into the lower smelting furnace after being left to settle the heavier impurities. The settled impurities are retained in the upper smelting furnace, and subsequent smelting is carried out in the lower smelting furnace.

[0086] According to some embodiments of the present application, the first temperature is 730-750 °C; and / or, the second temperature is 690-710 °C; and / or, the third temperature is 675-685 °C.

[0087] Exemplarily, the first temperature can be 730 °C, 735 °C, 740 °C, 745 °C or 750 °C, which is used to melt the raw materials. The second temperature can be 690 °C, 695 °C, 700 °C, 705 °C or 710 °C, when the second temperature is between 690 °C and 710 °C, the rapid decomposition of the refining agent can be reduced, which can reduce the premature consumption of the active ingredients, thereby helping to extend the action time of the refining agent. The third temperature can be 675 °C, 680 °C or 685 °C, when the third temperature is between 675 °C and 685 °C, the oxidation of the melt can be reduced, which can reduce the generation of oxidized inclusions, in addition, the die casting mold is usually made of alloy steel, which has a certain limitation in the working temperature range, controlling the second aluminum alloy melt at the third temperature can reduce the damage to the die casting mold, which helps to improve the service life of the die casting mold.

[0088] According to some embodiments of the present application, the refining agent comprises the following raw materials in mass fraction: CaCl2 18-22%, CaF2 12-16%, graphite 3-7%, LaCl3 2-6%, B2O3 1-3%, and the balance is KCl.

[0089] CaCl2(calcium chloride) can react with hydrogen in the first aluminum alloy melt to generate calcium chloride and hydrogen gas, which escapes from the aluminum liquid at high temperature, thereby achieving the purpose of degassing and reducing the porosity defects in the aluminum alloy. In addition, CaCl2 can reduce the surface tension of the first aluminum alloy melt, so that the impurities such as oxidized inclusions in the first aluminum alloy melt can more easily gather and float to the surface, which is convenient for removal. Exemplarily, the mass fraction of CaCl2 can be 18%, 18.2%, 18.5%, 19%, 19.5%, 20%, 20.5%, 21%, 21.5% or 22%.

[0090] CaF2(calcium fluoride) can reduce the melting point and viscosity of the refining agent, improve the fluidity of the refining agent in the first aluminum alloy melt, so that it can better contact with the first aluminum alloy melt and fully play the refining effect. The mass fraction of CaF2 can be 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5% or 16%.

[0091] Graphite can play a stirring role in the first aluminum alloy melt, so that the refining agent can be fully mixed with the first aluminum alloy melt, which can improve the refining effect and promote the removal of gas and impurities. The mass fraction of graphite can be 3%, 4%, 5%, 6% or 7%.

[0092] LaCl3(lanthanum chloride) can change the morphology and distribution of Si phase in the first aluminum alloy melt, making the Si phase more fine and uniform, thereby helping to improve the toughness and ductility of the aluminum alloy. The mass fraction of LaCl3may be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, or 6%.

[0093] B2O3(boron trioxide) can react with hydrogen in the first aluminum alloy melt at high temperature to generate boric acid and hydrogen gas, and the hydrogen gas escapes from the melt to achieve degassing. In addition, B2O3can form a dense protective film on the surface of the first aluminum alloy melt, preventing the melt from contacting air and reducing oxidation of the melt. The B2O3may be 1%, 1.5%, 2%, 2.5%, or 3%.

[0094] KCl(potassium chloride) helps to reduce the melting point of the refining agent, so that the refining agent can melt and uniformly distribute in the melt at a lower temperature, which can improve the refining efficiency. In addition, KCl also helps to improve the fluidity of the aluminum liquid, so that the gas and impurities in the aluminum liquid are more easily removed by the action of the refining agent. Exemplarily, the mass fraction of KCl can be 44%, 46%, 48%, 50%, 52%, 55%, 58%, 60%, or 64%.

[0095] According to some embodiments of the present application, the mass ratio of the refining agent to the first aluminum alloy melt is (0.1-0.3):100.

[0096] Exemplarily, the mass ratio of the refining agent to the first aluminum alloy melt can be 0.1:100, 0.15:100, 0.2:100, 0.25:100, or 0.3:100. When the mass ratio of the refining agent to the first aluminum alloy melt is (0.1-0.3):100, it can effectively remove impurities and gas, avoid the problem of uneven aluminum alloy caused by component segregation in the melt, and reduce the residue of the refining agent.

[0097] According to some embodiments of the present application, the step of die casting the second aluminum alloy melt comprises: providing a die casting mold, heating the die casting mold to 125-145℃, and controlling the negative pressure in the die casting mold to be 45-75 mbar; adding the second aluminum alloy melt into the compression chamber of the die casting mold, controlling the injection pressure to be 80-100 MPa, the injection speed to be 5-8 m / s, and the injection time to be 2-5 s; and controlling the cooling rate of the second aluminum alloy melt to be the same as the temperature of the die casting mold during the die casting process, and the cooling rate to be 120-170℃ / s.

[0098] Exemplarily, the preheating temperature of the die casting mold can be 125°C, 130°C, 135°C, 140°C, or 145°C. Preheating the die casting mold to 125°C-145°C can reduce the temperature difference between the second aluminum alloy melt and the surface of the mold cavity, reduce the heat loss of the second aluminum alloy melt during the filling process, and keep it with good fluidity, so as to fill the mold cavity more smoothly, help to form a clear profile and a good surface quality of the casting, and reduce the generation of defects such as cold shut and insufficient pouring. The negative pressure in the die casting mold can be 45 mbar, 50 mbar, 55 mbar, 60 mbar, 65 mbar, 70 mbar, or 75 mbar. When the die casting mold is maintained in a negative pressure environment of 45 mbar-75 mbar, it is helpful for the flow and filling of the second aluminum alloy melt in the mold cavity, and the gas (such as hydrogen) originally dissolved in the melt during the filling process can be more easily escaped, while the air entrained into the cavity can also be effectively reduced, thereby significantly reducing the number of pores and pinholes in the casting, and helping to improve the mechanical properties of the aluminum alloy.

[0099] Exemplarily, the injection pressure can be 80 MPa, 85 MPa, 90 MPa, 95 MPa, 100 MPa, 105 MPa, 110 MPa, 115 MPa, or 120 MPa, the injection speed can be 5 m / s, 6 m / s, 7 m / s, or 8 m / s, and the injection time can be 2 s, 3 s, 4 s, or 5 s. The injection pressure of 80 MPa-120 MPa can promote the second aluminum alloy melt to overcome the resistance in the mold cavity, quickly fill each corner of the mold, and the higher pressure can help the second aluminum alloy melt to perform feeding during the solidification process, effectively improve the internal defects such as shrinkage and porosity of the casting, and help to improve the mechanical properties of the aluminum alloy. The injection speed of 5 m / s-8 m / s can make the second aluminum alloy melt flow smoothly and quickly in the mold cavity, which helps to reduce the formation of pores and oxide inclusions. The injection time of 2 s-5 s provides sufficient filling time for the second aluminum alloy melt, which can fill the mold cavity under the joint action of pressure and speed, and avoids the problems caused by too long or too short injection time.

[0100] Exemplarily, the cooling speed can be 120°C / s, 130°C / s, 140°C / s, 150°C / s, 160°C / s, or 170°C / s. When the cooling rate is 120°C / s-170°C / s, it means that the cooling speed is relatively fast, which helps to form more crystal nuclei during the solidification process of the melt, thereby refining the grains. Fine-grained structure can improve the strength, hardness, and toughness of the aluminum alloy, and help to improve its mechanical properties.

[0101] According to some embodiments of the present application, the present application provides an automobile electric drive, comprising an electric drive shell, the electric drive shell is made of the aluminum alloy of any one of the above claims or the aluminum alloy prepared by any one of the above preparation methods.

[0102] Embodiment 1

[0103] The aluminum alloy comprises the following components by mass fraction:

[0104] Si 10.2%, Cu 1.8%, Fe 0.85%, Mg 1.05%, Cr 0.1%, Zn 0.95%, Mn 0.17%, Sr 0.036%, impurity elements not more than 0.01%, and the balance of aluminum. Among them, the content ratio of Si and Mg is 9.7, the content ratio of Fe and Cr is 8.5, and the content ratio of Fe and Sr is 23.6.

[0105] The preparation method of the aluminum alloy comprises:

[0106] (1) Impurities are removed from the waste aluminum by using two-stage melting furnaces: first, the waste aluminum is added to the upper melting furnace, heated to 600°C, and semi-solid aluminum is obtained; some impurities are absorbed by a magnet block; then, the semi-solid aluminum in the upper melting furnace is slowly poured into the lower melting furnace, and the settled heavy impurities are retained in the upper melting furnace. Subsequent melting is carried out in the lower melting furnace.

[0107] (2) The temperature of the lower melting furnace is heated to 730°C, and the required AlSi, AlCu, AlFe, AlMg, AlCr, and AlSr intermediate alloy is crushed to a particle size of 10mm and then added to the lower melting furnace, and stirred uniformly to obtain a first aluminum alloy melt.

[0108] (3) The temperature is reduced to 700°C, and 0.3% of a refining agent is added, the refining agent comprises the following raw materials by mass fraction: CaCl2 20%, CaF2 14%, graphite 5%, LaCl3 4%, B2O3 2%, KCl 35%, and the refining agent and the melt are fully mixed by stirring the melt. Argon is introduced at a flow rate of 10L / min, and the melt is slowly stirred at the same time, the aluminum melt is degassed while refining, the time is 10min; then the slag is removed. After standing for 8min, a second aluminum alloy melt is obtained.

[0109] (4) The temperature of the second aluminum alloy melt is controlled at 680°C; at the same time, the die casting mold is preheated, and the mold temperature is controlled at 130°C, and the mold negative pressure condition is 50mbar.

[0110] (5) Die casting: the injection time is 3s, the pressure is 90MPa, the injection speed is 6m / s, and the cooling rate is 120°C / s. After die casting, the aluminum alloy die casting material is taken out of the mold and air-cooled to room temperature.

[0111] Example 2

[0112] The aluminum alloy in this example includes the following components by mass fraction:

[0113] Si 12.5%, Cu 1.8%, Fe 0.85%, Mg 1.05%, Cr 0.1%, Zn 0.95%, Mn 0.17%, Sr 0.036%, impurity elements not more than 0.01%, and the balance of aluminum. The content ratio of Si and Mg is 12, the content ratio of Fe and Cr is 8.5, and the content ratio of Fe and Sr is 23.6.

[0114] The preparation method of the aluminum alloy in this example is the same as that in Example 1.

[0115] Example 3

[0116] The aluminum alloy in this example includes the following components by mass fraction:

[0117] Si 10.2%, Cu 1.8%, Fe 1.75%, Mg 1.05%, Cr 0.1%, Zn 0.95%, Mn 0.17%, Sr 0.036%, impurity elements not more than 0.01%, and the balance of aluminum. The content ratio of Si and Mg is 9.7, the content ratio of Fe and Cr is 17.5, and the content ratio of Fe and Sr is 48.6.

[0118] The preparation method of the aluminum alloy in this example is the same as that in Example 1.

[0119] Example 4

[0120] The aluminum alloy in this example includes the following components by mass fraction:

[0121] Si 10.2%, Cu 1.8%, Fe 0.85%, Mg 1.05%, Cr 0.1%, Zn 0.95%, Mn 0.17%, Sr 0.02%, impurity elements not more than 0.01%, and the balance of aluminum. The content ratio of Si and Mg is 9.7, the content ratio of Fe and Cr is 8.5, and the content ratio of Fe and Sr is 42.5.

[0122] The preparation method of the aluminum alloy in this example is the same as that in Example 1.

[0123] Example 5

[0124] The aluminum alloy in this example includes the following components by mass fraction:

[0125] Si 10.2%, Cu 1.8%, Fe 0.85%, Mg 0.9%, Cr 0.1%, Zn 0.95%, Mn 0.17%, Sr 0.036%, impurity elements not more than 0.01%, and the balance of aluminum. The content ratio of Si and Mg is 11.3, the content ratio of Fe and Cr is 8.5, and the content ratio of Fe and Sr is 23.6.

[0126] The preparation method of the aluminum alloy in this embodiment is the same as that in Embodiment 1.

[0127] Embodiment 6

[0128] The aluminum alloy comprises the following components by mass fraction:

[0129] Si 10.2%, Cu 1.8%, Fe 0.85%, Mg 0.9%, Cr 0.1%, Zn 0.95%, Mn 0.17%, Sr 0.036%, impurity elements not more than 0.01%, and the balance of aluminum. The content ratio of Si and Mg is 11.3, the content ratio of Fe and Cr is 8.5, and the content ratio of Fe and Sr is 23.6.

[0130] The preparation method of the aluminum alloy in this embodiment is the same as that in Embodiment 1.

[0131] Embodiment 7

[0132] Si 10.2%, Cu 1.8%, Fe 0.85%, Mg 1.05%, Cr 0.1%, Sr 0.036%, impurity elements not more than 0.01%, and the balance of aluminum. The content ratio of Si and Mg is 9.7, the content ratio of Fe and Cr is 8.5, and the content ratio of Fe and Sr is 23.6.

[0133] The preparation method of the aluminum alloy in this embodiment is the same as that in Embodiment 1.

[0134] Embodiment 8

[0135] The aluminum alloy comprises the following components by mass fraction:

[0136] Si 10.2%, Cu 1.8%, Fe 0.85%, Mg 1.05%, Cr 0.136%, impurity elements not more than 0.01%, and the balance of aluminum.

[0137] The preparation method of the aluminum alloy in this embodiment is the same as that in Embodiment 1.

[0138] Embodiment 9

[0139] The aluminum alloy comprises the following components by mass fraction:

[0140] Si 10.2%, Cu 1.8%, Fe 0.85%, Mg 1.05%, Sr 0.136%, impurity elements not more than 0.01%, and the balance of aluminum.

[0141] The preparation method of the aluminum alloy in this embodiment is the same as that in Embodiment 1.

[0142] Comparative Example

[0143] The comparative example uses an ADC12 aluminum alloy comprising the following components by mass fraction:

[0144] Si 10.3%, Cu 1.7%, Fe 0.85%, Mg 0.13%, Zn 0.94%, Mn 0.17%, Ni 0.06%, Ti 0.04%, Sn 0.01%, Pb 0.03%, impurity elements not more than 0.01%, and the balance of aluminum.

[0145] The preparation method of the aluminum alloy in the comparative example comprises:

[0146] (1) directly heat the ADC12 aluminum ingot to 730°C to melt, to obtain a first aluminum alloy melt;

[0147] (2) reduce the temperature to 700°C, add 0.3% of a refining agent comprising the following raw materials by mass fraction: CaCl2 20%, CaF2 14%, graphite 5%, LaCl3 4%, B2O3 2%, KCl 35%, and stir the melt to fully mix the refining agent and the melt. Argon is introduced at a flow rate of 10 L / min, while slowly stirring the melt, degassing the aluminum melt while refining, for 10 min; then remove the slag. Let stand for 8 min to obtain a second aluminum alloy melt.

[0148] (3) control the temperature of the second aluminum alloy melt at 680°C; at the same time, preheat the die casting mold, and control the mold temperature at 130°C, and the die casting mold negative pressure condition is 50 mbar.

[0149] (4) die casting: the injection time is 3 s, the pressure is 90 MPa, the injection speed is 6 m / s, and the cooling rate is 120°C / s. After die casting, the aluminum alloy die casting material is taken out of the mold and air-cooled to room temperature.

[0150] Performance test

[0151] The aluminum alloy standard dumbbell-shaped compression test bars were tested for yield strength, tensile strength and elongation at room temperature using MTS E45 universal tensile testing machine. The maximum tensile force of the tensile machine was 100 kN. The tensile rate was 2 mm / min. The gauge length of the specimen was 80 mm and the gauge diameter was 6.35 mm. The elongation at break was measured using an extensometer. The yield strength is the stress value at which plastic deformation begins, i.e. the engineering stress at 0.2% permanent set. The stress calculation method is tensile force / initial cross-sectional area of the gauge section. The tensile strength is the maximum engineering stress sustained by the material before tensile fracture, and the stress calculation method is tensile force / initial cross-sectional area of the gauge section. The elongation at break is the percentage plastic elongation of the gauge length after specimen fracture.

[0152] Test results

[0153] The test results in Examples 1-9 and Comparative Examples are shown in Table 1.

[0154] Table 1 Mechanical properties of the aluminum alloys in Examples 1-9 and Comparative Examples

[0155]

[0156]

[0157] As can be seen from Table 1, the yield strength of the aluminum alloys in the examples of the present application are all ≥ 200 MPa, the tensile strength is all > 340 MPa, and the elongation at break is all > 2.9%, i.e. the mechanical properties of the aluminum alloys in the present application are significantly better than those of the aluminum alloy ADC12 in the comparative examples, which shows that the introduction of Cr and / or Sr in the present application can reduce the harmful β-Fe phase, thereby helping to improve the mechanical properties of the aluminum alloy at high Fe content.

[0158] The metallographic structure of the aluminum alloys in Example 6 and Comparative Example was observed under a Leica S8 optical microscope, Figure 1 and 2 is the metallographic structure diagram of the aluminum alloy in Example 6, Figure 3 and 4 is the metallographic structure diagram of the aluminum alloy in the comparative example. By comparison Figure 1 and 3 It can be seen that the aluminum alloy in Example 6 of the present application has a grain refinement band with an average particle size of 7 μm (the grain size measurement uses the intercept method), and the width of the grain refinement band is 130 μm, while the grain refinement band of the ADC12 aluminum alloy in the comparative example is only 12 μm, and the wider grain refinement band helps to improve the strength of the aluminum alloy. By comparison Figure 2 and Figure 4It can be seen that the eutectic silicon in the aluminum alloy of the embodiment 6 of the present application is very fine, the size is less than 1 μm, and the harmful β-Fe phase in the form of needle cannot be observed in the metallographic graph, while the metallographic graph of the ADC12 aluminum alloy in the comparative example has coarse and long strip eutectic silicon and harmful β-Fe phase in the form of needle, which indicates that the fine eutectic silicon and the β-Fe phase with a volume fraction less than 1% are helpful to improve the strength and toughness of the aluminum alloy.

[0159] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the specification of the present application. Especially, as long as there is no structural conflict, each technical feature mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed in the text, but includes all technical solutions falling within the scope of the claims.

Claims

1. An aluminum alloy, characterized in that: The steel comprises 0.75wt%-1.85wt% of Fe, 0.9wt%-1.2wt% of Mg, 0.1wt%-0.3wt% of Mn and 0.1wt%-0.3wt% of M, wherein the M comprises at least one of Cr and Sr.

2. The aluminum alloy according to claim 1, wherein The M includes Cr and Sr, the mass fraction of the Cr in the aluminum alloy is 0.08%-0.25%, and the mass fraction of the Sr in the aluminum alloy is 0.02%-0.04%.

3. The aluminum alloy according to claim 2, wherein The mass ratio of Fe to Cr is 4-8, and the mass ratio of Fe to Sr is 20-90.

4. The aluminum alloy according to any one of claims 1 to 3, characterized in that The following components are included in the mass fraction: Si 10%-12.5%, Cu 1.4%-3.4%, Fe 0.75%-1.85%, Mg 0.9%-1.2%, Mn 0.1%-0.3%, Cr 0.08%-0.25%, Sr 0.02%-0.04%, and the balance is Al.

5. The aluminum alloy according to claim 4, wherein The mass ratio of Si to Mg is 9-13.

6. The aluminum alloy according to claim 4 or 5, characterized in that In the metallographic structure diagram, the aluminum alloy includes a Si—Al eutectic phase, and the average grain size of Si in the Si—Al eutectic phase is less than 1 μm.

7. The aluminum alloy according to any one of claims 1 to 6, characterized in that In the metallographic structure diagram, the surface of the aluminum alloy includes a grain refinement zone, the average size of grains in the grain refinement zone is less than 8 μm, and the width of the grain refinement zone is ≥100 μm.

8. The aluminum alloy according to any one of claims 1 to 6, characterized in that In the metallographic structure diagram, the aluminum alloy includes a β-Fe phase, and the volume fraction of the β-Fe phase is less than 0.

01.

9. The aluminum alloy according to any one of claims 1 to 8, characterized in that The aluminum alloy further includes at least one of Zn, Ni, Ti, La, Sn, and Pb; The mass fraction of Zn is ≤1.05%, and / or the mass fraction of Ni is ≤0.4%, and / or the mass fraction of Ti is ≤0.3%, and / or the mass fraction of La is ≤0.05%, and / or the mass fraction of Sn is ≤0.02%, and / or the mass fraction of Pb is ≤0.2%.

10. The aluminum alloy according to any one of claims 1 to 9, characterized in that The aluminum alloy has a yield strength of ≥200 MPa, a tensile strength of ≥340 MPa, and an elongation at break of ≥2.4%.

11. A method for preparing an aluminum alloy, characterized in that: include: Providing raw materials, wherein the raw materials include an Al source, a Mg source, a Mn source, and an M source, wherein the M source includes at least one of a Cr source and a Sr source; The raw materials are mixed according to the following ratio: 0.9wt%-1.2wt% of Mg, 0.1wt%-0.3wt% of Mn, 0.1wt%-0.3wt% of Mn, and the balance is Al, and smelted at a first temperature to obtain a first aluminum alloy melt; Lowering the temperature to a second temperature, adding a refining agent to the first aluminum alloy melt under an inert atmosphere, stirring until the mixture is uniformly mixed, then skimming and allowing to stand to obtain a second aluminum alloy melt; The temperature of the second aluminum alloy melt is lowered to a third temperature, the second aluminum alloy melt is die-casted, and then air-cooled to room temperature to obtain an aluminum alloy.

12. The method for preparing the aluminum alloy according to claim 11, wherein: The step of providing raw materials includes: Providing an Al source, wherein the Al source comprises scrap aluminum, and under the condition that the Fe content in the scrap aluminum is less than 0.75%, the raw material further comprises an Fe source; The scrap aluminum is heated to 580° C.-620° C., and ferromagnetic impurities in the scrap aluminum are removed through a magnetic separation process.

13. The method for preparing the aluminum alloy according to claim 11 or 12, wherein: The first temperature is 730°C-750°C; and / or, the second temperature is 690°C-710°C; and / or, the third temperature is 675°C-685°C.

14. The method for preparing the aluminum alloy according to claim 11 or 12, wherein: The refining agent includes the following raw materials by mass fraction: CaCl2 18%-22%, CaF2 12%-16%, graphite 3%-7%, LaCl3 2%-6%, B2O3 1%-3%, and the balance is KCl.

15. The method for preparing the aluminum alloy according to claim 14, wherein: The mass ratio of the refining agent to the first aluminum alloy melt is (0.1-0.3):

100.

16. The method for preparing the aluminum alloy according to claim 11 or 12, wherein: The step of die-casting the second aluminum alloy melt comprises: Providing a die-casting mold, heating the die-casting mold to 125° C.-145° C., and controlling the negative pressure in the die-casting mold to 45 mbar-75 mbar; Adding the second aluminum alloy melt into the pressure chamber of the die-casting mold, controlling the injection pressure to 80 MPa-120 MPa, the injection speed to 5 m / s-8 m / s, and the injection time to 2 s-5 s; During the die-casting process, the second aluminum alloy melt is controlled to cool to the same temperature as the die-casting mold, and the cooling rate is 120° C. / s-170° C. / s.

17. An automotive electric drive, comprising an electric drive housing, characterized in that: The electric drive housing is made of the aluminum alloy described in any one of claims 1 to 10 or the aluminum alloy prepared by the preparation method of any one of claims 11 to 16.

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