Vacuum die-cast motor rotor casting aluminum alloy and its preparation method

Abstract

The application discloses a vacuum die-casting motor rotor casting aluminum alloy and a preparation method thereof. According to mass percentage, the vacuum die-casting motor rotor casting aluminum alloy comprises the following components: 3.0-6.5% of Ni elements, 0.3-1.0% of Fe elements, 0.2-0.4% of Mg elements, 0.02-0.1% of B elements, 0.1-0.6% of Ce elements, and the rest is Al, and the rest is impurity elements; wherein, the content of a single impurity element is less than 0.03%, and the total content of the impurity elements is less than 0.2%.

Description

TECHNICAL FIELD

[0001] The present application relates to aluminum alloy materials and their application fields, and in particular to a vacuum die-casting motor rotor casting aluminum alloy and a preparation method thereof. BACKGROUND

[0002] With the increasing seriousness of energy and environmental problems, the development of new energy vehicles has attracted more and more attention. The motor is one of the core components of the new energy vehicle chassis, and the motor rotor is an important part of the motor. The traditional motor rotor mainly uses copper materials, but due to the high price of copper materials and the demand for lightweight of new energy vehicles, it is gradually replaced by aluminum materials. This can reduce the cost of raw materials and also achieve the goal of lightweight parts.

[0003] In the preparation method of the cast aluminum rotor for new energy vehicles, the conventional first remelting aluminum ingot Al99.50 b Although this type of motor rotor has relatively high plasticity, corrosion resistance, and electrical conductivity, it has low strength, with a tensile strength of only 60-80 MPa and a yield strength of only 25-65 MPa, and the heat treatment cannot achieve strengthening effect, and the machinability is not good.

[0004] Currently, the main forming methods for cast aluminum rotors are centrifugal casting and pressure casting processes. In the centrifugal casting rotor process, the equipment for centrifugal casting of aluminum is relatively simple, but there are many manual operation steps in the casting process, resulting in high labor intensity for the operators. Moreover, the defects of centrifugal cast aluminum rotors are diverse, mainly including rotor breakage, porosity, shrinkage and porosity, cracks, fine strips, incomplete filling and cold shut, too large rotor resistance, large stray loss, and many other defects. Although conventional high-pressure die casting has the advantages of high production efficiency, easy mechanization, automation, and reduced labor intensity, the main defect of the castings is that during high-speed filling of the metal liquid, the gas in the mold cavity is easily trapped and cannot be discharged in time, resulting in porosity of the part material, which reduces the strength and electrical conductivity of the die-cast aluminum alloy. Moreover, the currently used first remelting aluminum ingot Al99.50 b The alloying degree of the aluminum ingot material is not high, and there are disadvantages such as poor die-casting characteristics and die sticking. SUMMARY

[0005] In view of the above-mentioned deficiencies of the prior art, the purpose of the present application is to provide a vacuum die-casting motor rotor casting aluminum alloy and a preparation method thereof, which reduces the porosity of the parts, and improves the mechanical strength and electrical conductivity of the aluminum alloy material to solve the problems of complex processing steps, high labor intensity of the operators, many defects of the obtained cast aluminum rotor, and difficulty in meeting the needs of the mechanical strength and die-casting performance of the cast aluminum rotor in the prior art.

[0006] To solve the above technical problems, the present application adopts the following technical solutions:

[0007] A vacuum die-casting motor rotor casting aluminum alloy, according to mass percentage, comprises the following components: 3.0-6.5% of Ni element, 0.3-1.0% of Fe element, 0.2-0.4% of Mg element, 0.02-0.1% of B element, 0.1-0.6% of Ce element, and the rest is impurity element; wherein the content of single impurity element is less than 0.03%, and the total content of impurity elements is less than 0.2%; the rest is Al.

[0008] Preferably, the mass ratio of Ni and Fe is Ni:Fe=(3-22):1.

[0009] Preferably, the mass ratio of Ni and Mg is Ni:Mg=(7-33):1.

[0010] Preferably, the tensile strength of the aluminum alloy is at least 180MPa, the yield strength is at least 110MPa, the elongation is at least 10%, and the electrical conductivity is at least 45%IACS.

[0011] The present application also provides a preparation method of the vacuum die-casting motor rotor casting aluminum alloy.

[0012] Step 1: heat and melt aluminum ingot, control the temperature at 730-750℃, after uniform stirring, and stand for 5-10min;

[0013] Step 2: add aluminum-iron intermediate alloy and aluminum-nickel intermediate alloy for melting, after uniform stirring, stand for 10-15min;

[0014] Step 3: after cooling the aluminum liquid obtained in step 2 to 720℃, add AlCe10 intermediate alloy, magnesium ingot and AlB3 intermediate alloy, melt and stir uniformly, and stand for 15-20min;

[0015] Step 4: after refining and degassing the aluminum liquid obtained in step 3, stand for 20-25min;

[0016] Step 5: use the aluminum liquid in step 4 for vacuum die-casting to obtain a die-casting aluminum alloy casting, and then perform T6 heat treatment.

[0017] Preferably, in step 5, the die-casting is performed under the condition of vacuum degree of 10Kpa.

[0018] Preferably, the porosity of the die-casting aluminum alloy casting is less than 1.5%.

[0019] The present invention also provides an application of aluminum alloy for vacuum die casting of motor rotors, wherein the aluminum alloy obtained by the above preparation method is used to prepare motor rotors.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. This invention effectively improves the strength, heat resistance, and wear resistance of aluminum alloys by adding Ni to the Al matrix, laying the foundation for the basic properties of the aluminum alloy described in this invention. Simultaneously, the Al-Ni binary alloy has a high eutectic temperature (above 640℃), a narrow solidification range, and good casting performance. Ni has minimal impact on the electrical conductivity of the aluminum matrix, thus providing a basis for the high electrical conductivity of the aluminum alloy material.

[0022] 2. The addition of Fe to aluminum alloy in this invention has two advantages: first, it reduces die-casting sticking, extends mold life, and increases production efficiency; second, Fe can refine α-Al grains, making the α-Al+Al3Ni eutectic structure spheroidized. Grain refinement significantly improves the tensile strength and yield strength of Al-Ni alloys. At the same time, grain refinement and spheroidization of the eutectic structure increase the transport channels of free electrons and improve electrical conductivity.

[0023] 3. In this invention, Mg is added to the Al matrix. A small amount of Mg reacts with trace amounts of silicon impurities in the raw materials in the aluminum matrix to generate the strengthening phase Mg2Si. A small amount of Mg added to the aluminum matrix can form the strengthening second phase Al3Mg2. The precipitated alloy phase can enhance the tensile strength and yield strength of the material and enhance the electrical conductivity of the alloy.

[0024] 4. This invention effectively refines α-Al grains and improves the strength of the material by adding rare earth Ce to the Al matrix; at the same time, it also has a significant inhibitory effect on the acicular Fe phase in Al-Ni-Fe alloy, which can make the coarse acicular Fe become fine.

[0025] 5. In this invention, a trace amount of boron is added to the Al matrix. The boron element can react with the impurity elements in the aluminum matrix that affect thermal conductivity, causing them to precipitate at the bottom of the melt, thereby reducing the content of impurity elements, improving the electrical conductivity of the aluminum alloy, and significantly increasing the strength of the aluminum alloy. At the same time, the boron element can also increase the heat treatment hardening index of the aluminum alloy, so that the aluminum alloy still has high hardness and strength under high temperature conditions.

[0026] 6. This invention uses vacuum die casting to significantly reduce the porosity of the material, improve its mechanical and electrical properties, and provides a process for strengthening it through heat treatment such as T6. Detailed Implementation

[0027] This invention will describe the technical solutions of the embodiments of the invention clearly and completely. Obviously, the described embodiments are only some embodiments of the invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on this invention are within the scope of protection of this invention.

[0028] Unless otherwise specified in the specific circumstances, the numerical ranges listed in this invention include upper and lower limits, as well as all integers and fractions within that range, but are not limited to the specific values ​​listed when the range is defined.

[0029] I. A vacuum die-casting motor rotor made of aluminum alloy

[0030] In this invention, the vacuum die-cast motor rotor aluminum alloy comprises, by mass percentage, the following components: 3.0–6.5% Ni, 0.3–1.0% Fe, 0.2–0.4% Mg, 0.02–0.1% B, 0.1–0.6% Ce, with the remainder being impurity elements; wherein the content of a single impurity element is less than 0.03%, and the total content of impurity elements is less than 0.2%; the remainder is Al.

[0031] In some embodiments, the Ni content is controlled between 3.0% and 6.5%. Adding Ni to the Al matrix allows Ni and Al to form an aluminum alloy system based on an α-Al+Al3Ni eutectic structure. The Al3Ni alloy phase exhibits high hardness, good thermal stability, and a low coefficient of thermal expansion, effectively improving the strength, heat resistance, and wear resistance of the aluminum alloy material, thus establishing the fundamental properties of the aluminum alloy material described in this invention. Furthermore, this aluminum alloy system has a high eutectic temperature, reaching above 640°C, and a narrow solidification range, resulting in excellent casting performance. Therefore, the Ni content can be 3.0%, 3.10%, 3.15%, 3.53%, 4.05%, 4.45%, 5.02%, 5.56%, 6.02%, 6.45%, 6.38%, 6.46%, 6.5%, etc., as well as all ranges and sub-ranges between these values. It should be understood that, in embodiments, any of the above ranges can be combined with any other range.

[0032] In some embodiments, the Fe element content is controlled between 0.3% and 1.0%. Adding Fe serves two purposes: firstly, it reduces the occurrence of die-casting film adhesion, extends mold life, and increases production efficiency. Secondly, the addition of Fe forms an alloy phase structure dominated by the α-Al+Al3Fe / Al6Fe alloy phase with Al. The Al3Fe / Al6Fe alloy phase is a fine needle-like or lamellar structure. This alloy structure enhances the mechanical properties of the aluminum alloy, giving it sufficient strength. Furthermore, Fe can refine the α-Al grains and simultaneously spheroidize the α-Al+Al3Ni eutectic structure. Grain refinement significantly improves the tensile strength and yield strength of the alloy, while spheroidization of the eutectic structure increases the transport channels for free electrons, thereby improving the electrical conductivity of the alloy material. Therefore, the Fe content can be 0.30%, 0.31%, 0.32%, 0.45%, 0.51%, 0.61%, 0.65%, 0.72%, 0.81%, 0.95%, 0.96%, 0.97%, etc., as well as all ranges and subranges between these values. However, too low or too high a Fe content will cause these beneficial effects to disappear, especially the ratio of Ni to Fe. The mass ratio of Ni to Fe needs to be controlled between (3~22):1. Below this range, the proportion of Fe will increase, resulting in a large increase in acicular and lamellar structures of Al3Fe and Al9FeNi in the alloy system. Fe will have difficulty playing a spheroidizing role in the eutectic structure, which will have an adverse effect on the elongation and electrical conductivity of the alloy material. Above this range, the proportion of Fe in the system will be insufficient, which will not only have an adverse effect on the strength of the alloy material, but will also cause sticking during the die casting process, resulting in poor die casting formability of the material. Therefore, the mass ratio of Ni to Fe can be 3:1, 3.2:1, 6.6:1, 6.8:1, 7.3:1, 7.8:1, 7.9:1, 10.0:1, 10.2:1, 14.1:1, 16.5:1, 17.3:1, 18.6:1, 19.5:1, 20.2:1, 22:1, etc., as well as all ranges and sub-ranges between the above values. It should be understood that, in the implementation scheme, any of the above ranges can be combined with any other range.

[0033] In some embodiments, the content of Mg is controlled at 0.2% to 0.4%. After addition, Mg reacts with Si, an impurity element in the raw material, to form a strengthening phase Mg2Si, which is beneficial to the alloy. Simultaneously, it can also form a second phase, Al3Mg2, with Al, which has a strengthening effect. This alloy phase significantly enhances the tensile strength and yield strength of the alloy material. Furthermore, since the age-hardening effect of Fe and Ni elements in aluminum alloys is not significant, the addition of Mg can improve the age-hardening effect in Al-Ni-Fe matrix aluminum alloys. Therefore, the Mg content can be 0.20%, 0.21%, 0.22%, 0.23%, 0.25%, 0.31%, 0.32%, 0.35%, 0.38%, 0.39%, 0.4%, etc., as well as all ranges and sub-ranges between these values. Similarly, in the Al-Ni-Fe system, the ratio of Ni to Mg elements also needs to be controlled. The mass ratio of Ni to Mg is (7-33):1. If it is lower than this range, the proportion of Mg will increase. During the preparation process, Mg will undergo an oxidation reaction with oxygen, resulting in oxides in the alloy material, especially oxide inclusions and impurities. This can increase the porosity of the aluminum alloy material during the aluminum hydraulic casting process, ultimately harming the mechanical properties and electrical conductivity of the alloy material. If it is higher than this range, the proportion of Mg in the system will be insufficient, and Mg will not be able to play its original beneficial role, which is also detrimental to the mechanical properties and electrical conductivity of the alloy material. Therefore, the mass ratio of Ni to Mg can be 7:1, 7.9:1, 8.3:1, 9.5:1, 10.2:1, 13.8:1, 14.4:1, 15.7:1, 16.2:1, 17.0:1, 18.8:1, 20.3:1, 23.5:1, 26.7:1, 29.6:1, 31.5:1, 33:1, etc., as well as all ranges and sub-ranges between the above values. It should be understood that, in the implementation scheme, any of the above ranges can be combined with any other range.

[0034] In some embodiments, the content of element B is 0.02-0.1%. Element B mainly forms the α-Al+AlB2 phase in the Al matrix. This alloy phase can further refine the grain size of the alloy material. At the same time, element B can also react with impurity elements in the Al matrix that affect thermal conductivity. In particular, element B can react with transition metal elements such as Ti, V, and Mn dissolved in the aluminum melt. These transition metal elements are impurity elements introduced during the aluminum alloy preparation process and are difficult to avoid and remove. Therefore, after adding element B, it reacts with these impurity elements to generate high-density impurities such as TiB2 and VB2. These impurities will precipitate at the bottom of the melt, thereby reducing the impurity element content and improving the electrical conductivity of the aluminum alloy. Furthermore, element B can also enhance the heat treatment hardening index of the aluminum alloy, so that the aluminum alloy still has sufficiently high hardness and strength under high temperature conditions. Therefore, the content of element B can be 0.02%, 0.035%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, etc., as well as all ranges and sub-ranges between the above values. It should be understood that, in the implementation scheme, any of the above ranges can be combined with any other range.

[0035] In some embodiments, the Ce element content is 0.1% to 0.6%, and the addition of rare earth Ce element forms α-Al+Al with Al element. 11 The Ce3 alloy microstructure provides nuclei for the α-Al precipitated during the synthesis of the aforementioned eutectic structure. This prevents the initial dendrite formation of α-Al from growing due to its dense dendrites, thus suppressing the growth of coarse dendrites, effectively refining the α-Al grains, and improving the strength of the alloy material. Simultaneously, an appropriate amount of Ce also significantly inhibits the growth of the acicular Fe phase in the Al-Ni-Fe alloy system, making the coarse acicular Fe phase smaller, and also acts as a modifier, resulting in a long-lasting modification effect on the alloy material. However, the amount of Ce cannot exceed the range described in this invention; otherwise, these beneficial effects will develop into adverse effects. Therefore, the Ce content can be 0.1%, 0.15%, 0.35%, 0.37%, 0.42%, 0.45%, 0.46%, 0.48%, 0.49%, 0.53%, 0.55%, 0.58%, 0.60%, etc., as well as all ranges and sub-ranges between these values. It should be understood that, in the implementation plan, any of the above scopes can be combined with any other scopes.

[0036] In some embodiments, the aluminum alloy has a tensile strength of at least 180 MPa, preferably 180 MPa-240 MPa; a yield strength of at least 110 MPa, preferably 110 MPa-150 MPa; an elongation of at least 10%; and an electrical conductivity of at least 45% IACS, preferably 45% IACS-58% IACS.

[0037] II. A method for preparing aluminum alloy for vacuum die-casting motor rotors

[0038] The specific steps for preparing the above-mentioned vacuum die-casting motor rotor aluminum alloy are as follows:

[0039] Step 1: Heat the aluminum ingot to melt it, controlling the temperature at 730-750℃, stir it evenly, and let it stand for 5-10 minutes;

[0040] Step 2: Add aluminum-iron master alloy and aluminum-nickel master alloy to melt, stir evenly, and let stand for 10-15 minutes;

[0041] Step 3: After cooling the aluminum liquid obtained in Step 2 to 720℃, add AlCe10 master alloy, magnesium ingot and AlB3 master alloy, melt and stir evenly, and let stand for 15 to 20 minutes.

[0042] Step 4: After refining and degassing the aluminum liquid obtained in Step 3, let it stand for 20-25 minutes;

[0043] Step 5: Vacuum die casting is performed using the molten aluminum from Step 4 to obtain a die-cast aluminum alloy casting, followed by T6 heat treatment. The die casting process is as follows: the die-casting mold temperature controller maintains the temperature between 150℃ and 250℃, and the die-casting mold is equipped with an insulated barrel; during die casting, the barrel temperature is maintained at 200℃-280℃, the molten aluminum is die-cast into parts under a pressure of 50MPa-65MPa, the vacuum degree of the die-casting machine's mold cavity is below 10Kpa, and the aluminum is rapidly injected into the die-casting mold at an injection speed of 5-6m / s. After cooling and solidification, the die-cast aluminum alloy casting is demolded to obtain the die-cast aluminum alloy casting. The porosity of the die-cast aluminum alloy casting is less than 1.5%.

[0044] III. Examples and Comparative Examples

[0045] Table 1 (Unit: %)

[0046] Example Ni Fe Ni:Fe (mass ratio) Mg Ni:Mg (mass ratio) B Ce Al Example 1 3.15 0.31 10.2 0.22 14.3 0.03 0.15 remainder Example 2 3.53 0.45 7.8 0.25 14.1 0.04 0.35 remainder Example 3 4.05 0.51 7.9 0.35 11.6 0.06 0.42 remainder Example 4 4.45 0.61 7.3 0.31 14.4 0.08 0.46 remainder Example 5 5.02 0.65 7.7 0.31 16.2 0.07 0.48 remainder Example 6 5.56 0.72 7.7 0.35 15.9 0.08 0.55 remainder Example 7 6.02 0.81 7.4 0.32 18.8 0.06 0.58 remainder Example 8 6.45 0.95 6.8 0.38 17.0 0.09 0.53 remainder Example 9 6.38 0.96 6.6 0.21 30.4 0.07 0.49 remainder Example 10 6.46 0.32 20.2 0.21 30.8 0.08 0.45 remainder Example 11 3.10 0.31 10.0 0.39 7.9 0.05 0.37 remainder Example 12 3.15 0.97 3.2 0.23 13.7 0.06 0.35 remainder Comparative Example 1 6.25 0.92 6.8 3.10 2.0 0.08 0.41 remainder Comparative Example 2 6.35 0.91 7.0 0.08 79.4 0.08 0.52 remainder Comparative Example 3 6.28 3.18 2.0 0.31 20.3 0.05 0.42 remainder Comparative Example 4 6.32 0.09 70.2 0.32 19.8 0.07 0.44 remainder Comparative Example 5 6.28 3.32 1.9 3.25 1.9 0.06 0.43 remainder Comparative Example 6 6.21 0.15 41.4 0.05 124.2 0.06 0.43 remainder

[0047] Table 2

[0048]

[0049] Example 1:

[0050] Step 1: Heat and melt the aluminum ingot Al99.80 for remelting at 730℃-750℃, stir evenly, and let stand for 5-10 minutes.

[0051] Step 2: Add AlFe20 and AlNi5 aluminum master alloy to the melt obtained in Step 1 and melt it. After melting is complete, stir evenly and let it stand for 10-15 minutes.

[0052] Step 3: Cool the melt obtained in Step 2 to 720℃, and add AlCe10, Mg ingot, and AlB3 master alloy. Once melting is complete, stir thoroughly. Let stand for 15-20 minutes.

[0053] Step 4: After refining and degassing the aluminum liquid obtained in Step 3 with dry high-purity argon gas, let it stand for 20-25 minutes.

[0054] Step 5: Obtain the thermally insulated aluminum alloy solution from Step 4, press the aluminum alloy into the die-casting mold cavity, and mold to obtain the die-cast aluminum alloy casting.

[0055] Step 6: Preheat the die-casting mold temperature controller to 150℃-250℃. At the same time, the die-casting mold is equipped with an insulated barrel. During die casting, the barrel temperature is maintained at 200℃-280℃. The molten aluminum is die-cast into parts under a pressure of 50MPa-65MPa. The vacuum degree of the die-casting machine mold cavity is below 10Kpa. The injection speed is 5-6m / s to quickly enter the die-casting mold, cool and solidify, and then demold to obtain die-cast aluminum alloy castings.

[0056] Step 7: Perform T6 heat treatment on the die-cast aluminum alloy casting obtained in Step 6. This process involves heating the part from room temperature to 540℃±5℃, holding at 540℃±5℃ for 2-6 hours, and then quenching in hot water at 60℃-90℃. For the aging process, heat from room temperature to 225℃±5℃ and hold for 2-6 hours. Then air cool to room temperature.

[0057] Comparative Example 7:

[0058] The raw materials commonly used in the preparation of vacuum die-cast motor rotors using existing technologies (as shown in Table 2) are used to prepare the motor rotor using the method described in this invention. The specific steps are as follows:

[0059] Step 1: Remelt aluminum ingots Al99.50 b Heat to melt at 730℃-750℃, stir well; let stand for 5-10 minutes.

[0060] Step 2: Refine and degas the molten aluminum obtained in Step 1 using dry, high-purity argon gas, and let it stand for 20-25 minutes. Cool the molten liquid to 700℃-720℃.

[0061] Step 3: Obtain the thermally insulated aluminum alloy solution from Step 2, press the aluminum alloy into the die-casting mold cavity, and mold to obtain the die-cast aluminum alloy casting.

[0062] Step 4: Preheat the die-casting mold to 150℃-250℃ using a mold temperature controller. Simultaneously, equip the die-casting mold with an insulated barrel. During die casting, maintain the barrel temperature at 200℃-280℃, with the molten aluminum alloy casting in the barrel at 50MPa-65MPa. The vacuum degree of the die-casting machine's mold cavity is below 10Kpa. Use an injection speed of 5-6m / s to quickly enter the die-casting mold, cool and solidify, and then demold to obtain the die-cast aluminum alloy casting.

[0063] For step 5: Obtain aluminum ingots Al99.50 for remelting. b Die-cast aluminum alloy castings undergo T6 heat treatment. The process involves heating the parts from room temperature to 540℃±5℃, holding at 540℃±5℃ for 2-6 hours, and then quenching in hot water at 60-90℃. The aging process involves heating from room temperature to 225℃±5℃ and holding at that temperature for 2-6 hours. Finally, the parts are air-cooled to room temperature.

[0064] IV. Performance Testing

[0065] Based on the raw material ratios in Tables 1 and 2, aluminum alloy castings corresponding to Examples 2-12 and Comparative Examples 1-7 were prepared using the methods described in Example 1 and Comparative Example 7. These castings were then processed into standard samples according to the test standards for mechanical properties, electrical conductivity, and porosity for performance testing. The test results are shown in Table 3.

[0066] Table 3

[0067]

[0068] As can be seen from Tables 1-3:

[0069] (1) The motor rotor aluminum alloy prepared by using the element content and composition of the aluminum alloy described in this invention has excellent mechanical properties. Its tensile strength and yield strength can meet the requirements of high enough. The tensile strength is 180MPa-240MPa, the yield strength is 110MPa-150MPa, the elongation is greater than 10%, and the porosity is less than 1.5%. At the same time, the electrical conductivity meets the conductivity requirements of 45%IACS-58%IACS, and the electrical conductivity is good.

[0070] (2) In Comparative Example 1, the mass ratio of Ni to Mg was lower than the range described in this invention. This resulted in a significantly higher content of Mg in the alloy system described in this invention, leading to an increase in the Mg content in the alloy melt and a substantial improvement in the mechanical properties of the alloy material. However, the large amount of Mg in the aluminum melt is prone to oxidation with oxygen in the air. Further testing revealed a large amount of aluminum oxide in the die-cast aluminum alloy material obtained in Comparative Example 1, along with more oxide inclusions and impurities. At the same time, the porosity of the alloy also exceeded the range, ultimately causing a significant decrease in the elongation and electrical conductivity of the aluminum alloy.

[0071] (3) In Comparative Example 2, the mass ratio of Ni to Mg is much higher than the range described in this invention. This results in insufficient mass of Mg in the alloy system described in this invention, leading to a decrease in the content of Mg as a reinforcing phase. Consequently, the mechanical properties of the aluminum alloy material obtained in Comparative Example 2 show a very significant decrease.

[0072] (4) In Comparative Example 3, the mass ratio of Ni to Fe was too low, below the range described in this invention, which increased the Fe content in the system. Further observation of the alloy casting of Comparative Example 3 revealed a large number of needle-like and lamellar structures in the alloy casting. This indicates that a large number of Al3Fe and Al9FeNi alloy phases were formed in the alloy casting. The formation of these alloy phases not only made the strength of the alloy material too high, resulting in a significant decrease in elongation, but also hindered the transmission of electrons in the alloy material, leading to a decrease in the electrical conductivity of the alloy material.

[0073] (5) Comparative Example 4 has an excessively high mass ratio of Ni to Fe, which is higher than the range described in this invention. This results in a decrease in the Fe content in the alloy system. It can be seen that the mechanical properties of the casting obtained in Comparative Example 4 have decreased significantly, and sticking to the mold occurs during the die casting process. The die casting formability of the alloy material is very poor.

[0074] (6) In Comparative Example 5, the mass ratio of Ni to Mg and Fe is lower than that described in this invention, resulting in the mass of Fe and Mg being much higher than that described in this invention. This not only makes the elongation, porosity and electrical conductivity of the resulting casting lower than those of the Example, but also, a large amount of magnesium in the aluminum alloy forms a large amount of oxides during the die casting process. It can be observed that a large amount of slag and inclusions are formed in Comparative Example 5, which is also the reason for the increase in porosity of the alloy during the die casting process. Moreover, a large amount of needle-like or plate-like coarse structure can be observed in Comparative Example 5. These structures contain a large amount of iron. These coarse structures also lead to a further decrease in the elongation and electrical conductivity of the alloy material, thus making the elongation and electrical conductivity of the casting in Comparative Example 5 the lowest among all comparative examples.

[0075] (7) In Comparative Example 6, the mass ratio of Ni to Mg and Fe is higher than the range described in this invention, which makes the mass of Fe and Mg much lower than the requirements described in this invention. This results in a reduction of the strengthening phase in the alloy of Comparative Example 6, a sticking phenomenon in the die casting process, and a decrease in the mechanical strength of the final alloy, making it difficult to meet the requirements.

[0076] (8) In Comparative Example 7, the commonly used raw material for preparing the motor rotor using existing technology is high-purity aluminum Al99.50. b The aluminum alloy rotor is die-cast under vacuum conditions using the preparation method described in this invention. Compared with castings prepared using existing aluminum rotor forming methods (centrifugal casting and pressure casting), the casting prepared using the method described in this invention has a relatively low porosity, and the preparation method of this invention significantly enhances the material's electrical conductivity. However, because the raw material composition of Comparative Example 7 was not effectively adjusted, the material obtained in Comparative Example 7 does not contain heat-treated strengthening phases compared to the embodiments of this invention. Therefore, the mechanical strength of the casting is not significantly improved after heat treatment, resulting in low overall mechanical properties of the casting.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A vacuum die-casting aluminum alloy for motor rotors, characterized in that, Based on mass percentage, it includes the following components: 3.0~6.5% Ni, 0.3~1.0% Fe, 0.2~0.4% Mg, 0.02~0.1% B, 0.1~0.6% Ce, with the remainder being impurity elements; wherein the content of a single impurity element is less than 0.03%, and the total content of impurity elements is less than 0.2%; the remainder is Al. The mass ratio of Ni to Fe is Ni : Fe = (3~22): 1; The mass ratio of Ni to Mg is Ni : Mg = (7~33): 1; The vacuum die-casting motor rotor aluminum alloy is prepared by the following method: Step 1: Heat the aluminum ingot to melt it, controlling the temperature at 730~750℃, stir it evenly, and let it stand for 5~10 minutes; Step 2: Add aluminum-iron master alloy and aluminum-nickel master alloy to melt, stir evenly, and let stand for 10-15 minutes; Step 3: After cooling the aluminum liquid obtained in Step 2 to 720℃, add AlCe10 master alloy, magnesium ingot and AlB3 master alloy, melt and stir evenly, and let stand for 15~20 minutes. Step 4: After refining and degassing the aluminum liquid obtained in Step 3, let it stand for 20-25 minutes; Step 5: Vacuum die casting is performed using the molten aluminum from Step 4 to obtain die-cast aluminum alloy castings, which are then subjected to T6 heat treatment. The specific steps of the T6 heat treatment are as follows: the parts are heated from room temperature to 540℃±5℃, held at 540℃±5℃ for 2-6 hours, and then quenched in hot water at 60℃-90℃; aging process: the parts are heated from room temperature to 225℃±5℃ and held for 2-6 hours; then air-cooled to room temperature.

2. The vacuum die-casting motor rotor aluminum alloy according to claim 1, characterized in that, The aluminum alloy has a tensile strength of at least 180 MPa, a yield strength of at least 110 MPa, an elongation of at least 10%, and an electrical conductivity of at least 45% IACS.

3. The vacuum die-casting motor rotor aluminum alloy according to claim 1, characterized in that, In step 5, die casting is performed under a vacuum of 10 kPa.

4. The vacuum die-casting motor rotor aluminum alloy according to claim 1, characterized in that, The porosity of the die-cast aluminum alloy casting is less than 1.5%.

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