New energy automobile motor shell aluminum alloy and preparation method of shell

Abstract

The invention discloses an aluminum alloy for a motor shell of a new energy automobile. The aluminum alloy comprises the following components in percentage by mass: 7.0 to 8.0 percent of Si, 0.75 to 0.80 percent of Fe, 0.35 to 0.45 percent of Mg, 0.015 to 0.025 percent of Sr, 0.05 to 0.1 percent of B, 0 to 0.05 percent of Ni, 0.01 to 0.1 percent of Ti and the balance of Al and impurities, wherein the content of Fe and Ni is in the range of 0.76-0.83, the ratio of (Si and Fe) to Ni is in the range of 165-800, and the total amount of other impurity elements is smaller than or equal to 0.3%. According to the motor shell prepared through the formula, the tensile strength is larger than or equal to 280 MPa, the yield strength is larger than or equal to 190 MPa, the elongation is larger than or equal to 5%, and the heat conductivity coefficient is larger than or equal to 165 W / m.K. The heat conduction and mechanical properties of the motor shell are better, the corrosion resistance and the high-temperature performance are both considered, expensive rare earth elements do not need to be added, the aging treatment time is short, and the comprehensive production cost is low.

Description

Technical Field

[0001] The invention belongs to the technical field of die-cast aluminum alloy machining, and mainly relates to an aluminum alloy for a motor housing of a new energy vehicle and a method for preparing the housing. Background Art

[0002] The motor housing of new energy vehicles is a component used to fix the stator and rotor windings, and plays a supporting and protective role. It is usually die-casted with alloys such as ADC12 and A380. As the overall development of motors is towards high integration, high speed, and high power density, the comprehensive performance requirements for housing materials are becoming increasingly stringent. Since various forms of loss (hysteresis loss, eddy current loss, mechanical loss, etc.) in the energy conversion process of the motor are presented in the form of heat, and the greater the motor power and the higher the integration, the more heat is generated. On the one hand, this will cause the normal service temperature of the parts to increase, and high-temperature deformation will affect the assembly conditions, generate noise, and even increase the risk of motor failure. On the other hand, if the generated heat cannot be dissipated in a timely and effective manner, and the temperature range exceeds the high-efficiency zone of the motor, it will also affect the power density of the motor and the service life of the internal materials. Therefore, high-power motors have increasingly higher requirements for the comprehensive performance of housing materials.

[0003] Prior art 1 (CN115537613B-A new energy vehicle motor housing aluminum alloy and its forming method) relates to a new energy vehicle motor housing aluminum alloy and a forming method, the aluminum alloy contains the following components by mass percentage: Cu0.5%-1.5%, Si9%-10.5%, Mn≤0.1%, Mg0.2%-0.45%, Fe0.5-0.7%, Zn≤0.1%, Sr0.015%-0.035%, Zr0.1%-0.35%, RE(La+Ce)0.03%-0.15%, the remainder is Al and impurities, wherein the total impurity content is not more than 0.25%. The tensile strength of the aluminum alloy component is 300-310MPa, the yield strength is 135-150MPa, the elongation after fracture is 5.5-7%, and the thermal conductivity is 125-135W / m·K. After T5 heat treatment, the tensile strength of aluminum alloy components is 310-330MPa, the yield strength is 150-185MPa, the elongation after fracture is 5-7%, and the thermal conductivity is 135-145W / m·K.

[0004] Prior art 2 (CN115961186A-die-cast aluminum alloy material, preparation method and application thereof) relates to a die-cast aluminum alloy material, preparation method and application thereof. The die-cast aluminum alloy material of the application includes, by weight: 8.0%-11.0% silicon, less than 0.5% iron, 1.0%-3.0% copper, 0.5%-2.5% magnesium, 0.5%-1.2% manganese, less than 1.3% zinc, 0.08%-0.15% titanium, 0.1%-0.2% zirconium, 0.02%-0.04% strontium and less than 1.0% impurities, wherein the mass ratio of the copper element to the magnesium element is (0.5-2.0):1. The die-cast aluminum alloy material has a yield strength of more than 230 MPa, a tensile strength of more than 360 MPa, an elongation of more than 3.0%, and a hardness of more than 115 HB.

[0005] Prior art 3 (CN116752018B-A die-cast aluminum alloy material exempt from heat treatment, its preparation method, and automobile structural parts) relates to a die-cast aluminum alloy material exempt from heat treatment, its preparation method, and automobile structural parts. Based on the total weight of the die-cast aluminum alloy material, the die-cast aluminum alloy material includes: 8.5-11.0 weight % Si, less than 0.2 weight % Fe, 1.8-3.0 weight % Cu, 1.0-2.0 weight % Mg, 1.0-2.0 weight % Zn, 0.1-0.3 weight % Ti, 0.02-0.07 weight % Sr, 0.03-0.06 weight % Zr, 0.2-0.8 weight % metal M and the balance Al, wherein M is selected from one or both of Mn and Mo. The bulk properties of the die-cast aluminum alloy material include: yield strength of more than 220 MPa, tensile strength of more than 330 MPa, and elongation of more than 2.3%.

[0006] As a motor housing material, it must first meet the die-casting forming performance, demolding performance, and mechanical properties to meet basic application requirements. On this basis, in order to meet the requirements of higher power density motors, it must also be able to take into account better thermal conductivity, high temperature resistance, and corrosion resistance. Finally, from the perspective of production cost, the selection of raw materials and the production process are also required to have low-cost advantages. After a large number of experiments and theoretical studies, it is found that to ensure the die-casting performance of parts, it is necessary to add a sufficient amount of Si elements (≥7wt.%) to ensure the flow performance; to ensure excellent demolding performance of parts, it is necessary to add a sufficient amount of Fe elements (≥0.8wt.%) to reduce the concentration difference between the melt and the mold, and the presence of coarse Fe-containing phases will affect the directional transmission efficiency of free electrons and reduce thermal conductivity; to improve the strength of the alloy, an appropriate amount of Mg elements (≥0.1wt.%) can be added to combine with Si elements to form Mg2Si strengthening phases to improve the strength of the alloy, but above 180°C, the Mg2Si strengthening phase will coarsen, resulting in a decrease in high-temperature strength, and if the Mg content is too high (≥0.6wt.%), the high-temperature aluminum alloy melt is easily oxidized and increases the tendency of hot cracking of die-cast parts; in addition, the addition of Cu elements can also have a strengthening effect, but because the electrode potential of Cu is higher than that of Al, it will cause aluminum to be continuously oxidized and corroded. To ensure that the parts have excellent corrosion resistance in actual service environments, the Cu content needs to be controlled below 0.1wt.%. It is difficult for existing technologies to meet these comprehensive performance requirements at the same time. For example, in the prior art 1, the content of Cu element is in the range of 0.5-1.5%, and a certain content of rare earth elements is added at the same time, and the corrosion resistance and production cost are difficult to guarantee; in the prior art 2, the content of Fe element is strictly controlled (<0.5%), and 0.5-1.2% of Mn element is added to improve the demolding performance. As a transition metal element, Mn is a peritectic reaction in its solidification process and has many vacancies in the outer electron layer, which easily increases free electron scattering and reduces the thermal conductivity of the alloy. In addition, 1.0-3.0% of Cu element is added to the alloy to reduce the corrosion resistance. In the prior art 3, a large amount of Cu element (1.8-3.0), Mn element (0.2-0.8) and other elements (1.0-2.0Zn, 0.1-0.3Ti, 0.2-0.8Mo) are also added, and the thermal conductivity and corrosion resistance of the alloy are not taken into account. Summary of the invention

[0007] The purpose of the present invention is to solve the above problems and provide an aluminum alloy suitable for a motor housing of a new energy vehicle and a method for preparing the housing.

[0008] The purpose of the present invention is achieved through the following technical solutions: A new energy vehicle motor housing aluminum alloy comprises the following components in mass percentage: Si: 7.0-8.0, Fe: 0.75-0.80, Mg: 0.35-0.45, Sr: 0.015-0.025, B: 0.05-0.1, Ni: 0-0.05, Ti: 0.01-0.1, and the balance is Al and impurities; wherein the Fe+Ni content is in the range of 0.76-0.83, the (Si+Fe) / Ni ratio is in the range of 165-800, and the total amount of other impurity elements is ≤0.3%.

[0009] A method for preparing a motor housing for a new energy vehicle comprises the following steps: S1. Furnace washing: clean the smelting furnace, add aluminum ingots and heat until melted, stir evenly and pour out the furnace washing material; S2. Smelting: adding Si, Fe, Ni and Mg raw materials with good proportions into a smelting furnace respectively, heating and melting and stirring evenly to obtain an alloy melt; S3, refining: degassing and refining the alloy melt obtained in step S2 to obtain a new alloy melt; S4, modification: modifying the alloy melt obtained in step S3, adding AlTiCB master alloy and Al-Sr master alloy with good proportions in sequence to obtain a new alloy melt; S5, die casting: feeding the alloy melt obtained in step S4 into a side furnace of a die casting machine, and after die casting, obtaining a motor housing casting; S6, aging: sending the motor housing casting obtained in step S5 into a heat treatment furnace for T5 treatment to obtain a motor housing casting; Among them, the aluminum alloy contains the following components in mass percentage: Si: 7.0-8.0, Fe: 0.75-0.80, Mg: 0.35-0.45, Sr: 0.015-0.025, B: 0.05-0.1, Ni: 0-0.05, Ti: 0.01-0.1, and the balance is Al and impurities; among them, the Fe+Ni content is in the range of 0.76-0.83, the (Si+Fe) / Ni ratio is in the range of 165-800, and the total amount of other impurity elements is ≤0.3%.

[0010] A further improvement of the present invention is that the total amount of Mn+Cr+V elements in the washed charge in step S1 is ≤0.02wt.%.

[0011] A further improvement of the present invention is that in step S2, Si, Fe, Ni elements are added simultaneously with Al, and after heating to complete melting, the temperature of the aluminum liquid is adjusted to within the range of 720-730°C, and then the Mg element is added.

[0012] A further improvement of the present invention is that in step S3, the degassing temperature is 720-730°C, the degassing time is 20-30 min, and the density of the alloy melt obtained in step S3 is ≥2.62 g / cm3.

[0013] A further improvement of the present invention is that in step S4, the transformation temperature is 715-725° C., Al-Sr master alloy is first added, and then AlTiCB master alloy is added after being stirred evenly.

[0014] A further improvement of the present invention is that in step S5, the die-casting temperature is 680-700°C and the mold temperature is 150-200°C.

[0015] A further improvement of the present invention is that in step S6, the aging temperature is 200-250°C and the aging time is 0.5-1h.

[0016] A further improvement of the present invention is that the tensile strength of the motor housing casting is ≥280 MPa, the yield strength is ≥190 MPa, the elongation is ≥5%, and the thermal conductivity is ≥165 W / m·K.

[0017] Compared with the prior art, the present invention has the following advantages: An alloy composition design that can take into account the comprehensive performance of forming performance, demoulding performance, mechanical properties, corrosion resistance, high temperature resistance and thermal conductivity. The main function of the Si element is to ensure the fluidity and mechanical properties of the alloy, but Si is a semiconductor, and the unmodified eutectic silicon is in the form of coarse lamellar layers, which has a great influence on the thermal conductivity of the alloy; the main function of the Fe element is to ensure the demoulding performance of the alloy, but the Fe element is also easy to combine with the Si element to form long needle-shaped β-Al 9 Fe 2 Si 2 phase, splitting the matrix while increasing the scattering effect on free electrons, reducing the mechanical properties and thermal conductivity of the alloy; Mg element mainly plays a strengthening role, and its excessive content also has an adverse effect on thermal conductivity; the addition of Ni element is to improve the long needle-shaped β-Al 9 Fe 2 Si 2 Phase morphology, using Ni element to replace part of β-Al 9 Fe 2 Si 2 The position of Fe atoms in the phase promotes the formation of polygonal Al 9 FeNi phase, thereby reducing the splitting effect of the long needle-shaped Fe-containing phase on the matrix and the scattering effect on free electrons, improving the mechanical properties and thermal conductivity of the alloy. On the other hand, the addition of Ni can also promote the high temperature strengthening phase Al 3The formation of Ni improves the high temperature resistance of the alloy. However, with the increase of Ni content in the alloy, Al 9 FeNi and Al 3 As the content of Ni phase increases, Al 9 The FeNi phase will absorb some Si atoms, thus deteriorating the overall performance of the alloy. Therefore, the content ratio of the three groups of elements Si, Ni, and Fe has a great influence on the Al content in the alloy. 9 FeNi phase, Al 9 Fe 2 Si 2 Phase and Al 3 The size, morphology and relative stability of the Ni phase have a very important influence. After a lot of research, the optimal ratio range to ensure the comprehensive performance of the alloy was found, that is, the Fe+Ni content is in the range of 0.76-0.83, and the (Si+Fe) / Ni ratio is in the range of 165-800.

[0018] A technical means to achieve the Ti-B-Sr composite modification and refinement effect. The main function of the Sr element in the alloy is to modify the eutectic silicon. The addition of Ti-B composite is to refine the α-Al matrix and improve the alloy strength. At the same time, it can also purify the melt and improve the thermal conductivity of the alloy. However, if the AlTiB master alloy is directly added, the Si in the melt will react with Ti first to form titanium silicon compounds, thereby weakening the TiB 2 The remaining B element in the alloy also reacts with Sr to form SrB 6 After a lot of experimental research, it was finally determined that Ti-B was added in the form of AlTiCB, and by controlling the addition amount, addition sequence and addition temperature of AlTiCB and Al-Sr master alloy, the poisoning reaction was avoided to ensure that the composite modification and refinement effect reached the expected level.

[0019] A method for preparing a motor housing for a new energy vehicle that takes into account both comprehensive performance and production cost. First, no expensive rare earth elements are added during the alloy composition design process. The several groups of alloy elements actually added are all from a wide range of sources, and the raw material cost is low. Secondly, in the process of parts production, according to the characteristics of the alloy design component elements, the optimized process parameters of each link are matched to reduce the energy consumption and duration of the production process. Finally, the heat treatment process of the parts is a low-temperature short-time aging process, and there will be no blistering and deformation due to excessive temperature. The surface quality is good, the yield is high, and the production cycle is fast and the cost is low. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The elements and features described in one embodiment of the present invention may be combined with the elements and features shown in one or more other embodiments. It should be noted that for the purpose of clarity, the representation and description of components and processes that are not related to the present invention and are known to those of ordinary skill in the art are omitted in the description. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0021] The present invention is further described below: A new energy vehicle motor housing aluminum alloy comprises the following components in mass percentage: Si: 7.0-8.0, Fe: 0.75-0.80, Mg: 0.35-0.45, Sr: 0.015-0.025, B: 0.05-0.1, Ni: 0-0.05, Ti: 0.01-0.1, and the balance is Al and impurities; wherein the Fe+Ni content is in the range of 0.76-0.83, the (Si+Fe) / Ni ratio is in the range of 165-800, and the total amount of other impurity elements is ≤0.3%.

[0022] A method for preparing a motor housing for a new energy vehicle comprises the following steps: S1. Furnace washing: clean the smelting furnace, add aluminum ingots and heat until melted, stir evenly and pour out the washing charge. The total amount of Mn+Cr+V elements in the washing charge is ≤0.02wt.%; S2. Melting: Add Si, Fe, Ni and Mg raw materials with good proportions into the melting furnace respectively, heat and melt them and stir them evenly to obtain alloy melt, that is, Si, Fe, Ni elements and Al are added at the same time, heated until completely melted, adjust the temperature of the aluminum liquid to the range of 720-730°C, and then add Mg element; S3, refining: degassing and refining the alloy melt obtained in step S2 to obtain a new alloy melt, wherein the degassing temperature is 720-730°C, the degassing time is 20-30 minutes, and the density of the alloy melt obtained in this step is ≥2.62g / cm3; S4, modification: modifying the alloy melt obtained in step S3, adding AlTiCB master alloy and Al-Sr master alloy with good proportions in sequence to obtain a new alloy melt, that is, the modification temperature is 715-725°C, first adding Al-Sr master alloy, stirring evenly and then adding AlTiCB master alloy; S5, die casting: feeding the alloy melt obtained in step S4 into a side furnace of a die casting machine, and after die casting, obtaining a motor housing casting, wherein the die casting temperature is 680-700°C, and the mold temperature is 150-200°C; S6, aging: sending the motor housing casting obtained in step S5 into a heat treatment furnace for T5 treatment to obtain a motor housing casting, wherein the aging temperature is 200-250° C. and the aging time is 0.5-1 h; Among them, the aluminum alloy contains the following components in mass percentage: Si: 7.0-8.0, Fe: 0.75-0.80, Mg: 0.35-0.45, Sr: 0.015-0.025, B: 0.05-0.1, Ni: 0-0.05, Ti: 0.01-0.1, and the balance is Al and impurities; among them, the Fe+Ni content is in the range of 0.76-0.83, the (Si+Fe) / Ni ratio is in the range of 165-800, and the total amount of other impurity elements is ≤0.3%.

[0023] The tensile strength of the motor housing casting is ≥280MPa, the yield strength is ≥190MPa, the elongation is ≥5%, and the thermal conductivity is ≥165W / m·K. The motor housing has better thermal conductivity and mechanical properties, while taking into account corrosion resistance and high temperature performance. It does not require the addition of expensive rare earth elements, and the aging treatment time is short, and the overall production cost is low.

[0024] Embodiment 1: A new energy vehicle motor housing aluminum alloy, the aluminum alloy contains the following components in mass percentage: Si: 8, Fe: 0.8, Mg: 0.45, Sr: 0.025, B: 0.05, Ni: 0.01, Ti: 0.01, and the remainder is Al and impurities. In the above preparation method, the Mg element addition temperature is 720°C, the degassing temperature is 720°C, the degassing time is 30min, the metamorphic temperature is 715°C, the die casting temperature is 680°C, the mold temperature is 150°C, and the aging system is 250°C*0.5h. The motor housing made by this formula has a tensile strength of 290, a yield strength of 200, an elongation of 5.4%, and a thermal conductivity of 170.

[0025] Embodiment 2: A new energy vehicle motor housing aluminum alloy, the aluminum alloy contains the following mass percentage components: Si: 7, Fe: 0.75, Mg: 0.35, Sr: 0.015, B: 0.1, Ni: 0.03, Ti: 0.05, the balance is Al and impurities. In the above preparation method, the Mg element addition temperature is 730°C, the degassing temperature is 730°C, the degassing time is 20min, the metamorphic temperature is 725°C, the die casting temperature is 700°C, the mold temperature is 200°C, and the aging system is 200°C*0.5h. The tensile strength of the motor housing made by this formula is 282, the yield strength is 193, the elongation is 6.7%, and the thermal conductivity is 178.

[0026] Embodiment 3: A new energy vehicle motor housing aluminum alloy, the aluminum alloy contains the following components in mass percentage: Si: 7.5, Fe: 0.78, Mg: 0.4, Sr: 0.02, B: 0.05, Ni: 0.05, Ti: 0.01, and the balance is Al and impurities. In the above preparation method, the Mg element addition temperature is 725°C, the degassing temperature is 725°C, the degassing time is 25min, the metamorphic temperature is 720°C, the die casting temperature is 690°C, the mold temperature is 180°C, and the aging system is 250°C*1h. The tensile strength of the motor housing made by this formula is 288, the yield strength is 196, the elongation is 5.2%, and the thermal conductivity is 175.

[0027] An alloy composition design with excellent comprehensive performance that can take into account forming performance, demoulding performance, mechanical properties, corrosion resistance, high temperature resistance and thermal conductivity. Ensure the optimal ratio range of the comprehensive performance of the alloy, that is, the Fe+Ni content is in the range of 0.76-0.83, and the (Si+Fe) / Ni ratio is in the range of 165-800. A technical means to achieve the Ti-B-Sr composite modification and refinement effect. Finally, it was determined that Ti-B was added in the form of AlTiCB, and by controlling the addition amount, addition order and addition temperature of AlTiCB and Al-Sr master alloy, poisoning reaction was avoided to ensure that the composite modification and refinement effect reached the expected effect. The optimized process parameters of each link were matched to reduce energy consumption and duration in the production process. Finally, the heat treatment process of the parts is low-temperature short-time aging, and there will be no blistering and deformation due to excessive temperature. The surface quality is good, the yield is high, and the production cycle is fast and the cost is low.

[0028] Finally, it should be noted that although the present invention and its advantages have been described in detail above, it should be understood that various changes, substitutions and transformations can be made without exceeding the spirit and scope of the present invention as defined by the appended claims. Moreover, the scope of the present invention is not limited to the specific embodiments of the processes, devices, means, methods and steps described in the specification. It will be readily understood by those skilled in the art from the disclosure of the present invention that existing and future processes, devices, means, methods or steps that perform substantially the same functions as the corresponding embodiments described herein or obtain substantially the same results as the corresponding embodiments described herein can be used according to the present invention. Therefore, the appended claims are intended to include such processes, devices, means, methods or steps within their scope.

Claims

1. A new energy vehicle motor housing aluminum alloy, characterized by: The aluminum alloy contains the following components in mass percentage: Si: 7.0-8.0, Fe: 0.75-0.80, Mg: 0.35-0.45, Sr: 0.015-0.025, B: 0.05-0.1, Ni: 0-0.05, Ti: 0.01-0.1, and the balance is Al and impurities; wherein the Fe+Ni content is in the range of 0.76-0.83, the (Si+Fe) / Ni ratio is in the range of 165-800, and the total amount of other impurity elements is ≤0.3%.

2. A method for preparing a motor housing for a new energy vehicle, characterized in that: The steps include: S1. Furnace washing: clean the smelting furnace, add aluminum ingots and heat until melted, stir evenly and pour out the furnace washing material; S2. Smelting: adding Si, Fe, Ni and Mg raw materials with good proportions into a smelting furnace respectively, heating and melting and stirring evenly to obtain an alloy melt; S3, refining: degassing and refining the alloy melt obtained in step S2 to obtain a new alloy melt; S4, modification: modifying the alloy melt obtained in step S3, adding AlTiCB master alloy and Al-Sr master alloy with good proportions in sequence to obtain a new alloy melt; S5, die casting: feeding the alloy melt obtained in step S4 into a side furnace of a die casting machine, and after die casting, obtaining a motor housing casting; S6, aging: sending the motor housing casting obtained in step S5 into a heat treatment furnace for T5 treatment to obtain a motor housing casting; Among them, the aluminum alloy contains the following components in mass percentage: Si: 7.0-8.0, Fe: 0.75-0.80, Mg: 0.35-0.45, Sr: 0.015-0.025, B: 0.05-0.1, Ni: 0-0.05, Ti: 0.01-0.1, and the balance is Al and impurities; among them, the Fe+Ni content is in the range of 0.76-0.83, the (Si+Fe) / Ni ratio is in the range of 165-800, and the total amount of other impurity elements is ≤0.3%.

3. A method for preparing a motor housing for a new energy vehicle according to claim 2, characterized in that: The total amount of Mn+Cr+V elements in the washed charge in step S1 is ≤0.02wt.%.

4. The method for preparing a motor housing for a new energy vehicle according to claim 2, characterized in that: In step S2, Si, Fe, Ni elements and Al are added simultaneously, and after heating to complete melting, the temperature of the aluminum liquid is adjusted to within the range of 720-730°C, and then the Mg element is added.

5. The method for preparing a motor housing for a new energy vehicle according to claim 2, characterized in that: In step S3, the degassing temperature is 720-730°C, the degassing time is 20-30 min, and the density of the alloy melt obtained in step S3 is ≥2.62 g / cm3.

6. A method for preparing a motor housing for a new energy vehicle according to claim 2, characterized in that: In step S4, the transformation temperature is 715-725° C., Al-Sr master alloy is added first, stirred evenly, and then AlTiCB master alloy is added.

7. A method for preparing a motor housing for a new energy vehicle according to claim 2, characterized in that: In step S5, the die casting temperature is 680-700°C, and the mold temperature is 150-200°C.

8. The method for preparing a motor housing for a new energy vehicle according to claim 2, characterized in that: In step S6, the aging temperature is 200-250° C., and the aging time is 0.5-1 h.

9. The method for preparing a motor housing for a new energy vehicle according to claim 2, characterized in that: The motor housing casting has a tensile strength of ≥280 MPa, a yield strength of ≥190 MPa, an elongation of ≥5%, and a thermal conductivity of ≥165 W / m·K.