A battery case and a method of manufacturing the same

Abstract

The application provides a battery shell and a preparation method thereof. The preparation method comprises the following steps: preheating a mold, adding a three-layer composite material into a mold cavity, the three-layer composite material comprising a core layer and outer layers arranged on both sides of the core layer, the outer layers being semi-solid aluminum alloy materials, the core layer being a semi-solid magnesium alloy material, the thickness of the core layer being 85-95% of the thickness of the three-layer composite material, and then performing die casting to obtain the battery shell; wherein the solid phase fraction of the semi-solid aluminum alloy material is 30-50%, the solid phase fraction of the semi-solid magnesium alloy material is 30-50%, the aluminum alloy material contains 4-6% of Si in terms of mass fraction, the magnesium alloy material contains 0-0.05% of Si in terms of mass fraction, and the magnesium alloy material contains a crystal refiner.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a battery casing and a method for preparing the same. Background Technology

[0002] With the increasing popularity of electric vehicles, lightweighting has become a major focus. The battery module accounts for a significant proportion of the overall vehicle weight, making its reduction a crucial research direction for electric vehicle lightweighting. Traditional lithium batteries primarily use aluminum alloy casings. While aluminum alloys offer superior corrosion resistance, thermal conductivity, and mechanical strength, their specific strength is lower than that of magnesium alloys. Furthermore, magnesium alloys possess better casting properties, achieving the same mechanical strength as 1.2mm thick aluminum alloys with a thickness of only 0.6mm. Therefore, using magnesium alloys for the casing better meets the demands of automotive lightweighting.

[0003] Semi-solid forming technology is a near-net-shape forming technology that can produce thin, high-strength castings, suitable for battery casing production. However, commercially available semi-solid aluminum and magnesium alloys contain high levels of silicon (Si). While Si can improve the fluidity of semi-solid materials and produce castings with low defects and high mechanical strength, it also significantly reduces the thermal conductivity of the material. For example, the theoretical thermal conductivity of AS21 magnesium alloy is approximately 68 W / (m*K). If AS21 is used to manufacture battery casings, it will not meet the heat dissipation requirements of the battery casing. If the Si content is reduced, the fluidity of the semi-solid material will not meet the requirements, and shrinkage cavities are prone to occur during solidification, further affecting the mechanical strength and thermal conductivity of the casting. Furthermore, magnesium alloys have poor corrosion resistance and cannot be directly used in battery casings, often requiring surface anti-corrosion treatment.

[0004] Therefore, there is an urgent need for a lightweight, high-strength, and thermally conductive battery casing and its manufacturing method to overcome the above-mentioned defects. Summary of the Invention

[0005] The purpose of this application is to provide a battery casing and a method for preparing the same.

[0006] The first aspect of this application provides a battery casing, comprising the following steps: preheating a mold, adding a three-layer composite material into the mold cavity, the three-layer composite material comprising a core layer and an outer layer disposed on both sides of the core layer, the outer layer being a semi-solid aluminum alloy material, the core layer being a semi-solid magnesium alloy material, the thickness of the core layer being 85-95% of the thickness of the three-layer composite material, and then performing die casting to obtain the battery casing.

[0007] The semi-solid aluminum alloy material has a solid phase fraction of 30-50%, the semi-solid magnesium alloy material has a solid phase fraction of 30-50%, the aluminum alloy material contains 4-6% Si by mass, the magnesium alloy material contains 0-0.05% Si by mass, and the magnesium alloy material contains a crystal refiner.

[0008] This application utilizes two semi-solid alloy materials to fabricate the battery casing. During the die-casting process, each layer of material maintains laminar flow, with only a small amount of liquid phase exchange at the interface. This results in a battery casing with a semi-solid magnesium alloy core layer and a semi-solid aluminum alloy outer layer. The aluminum alloy, with its high Si content, exhibits high fluidity, which facilitates the flow of the magnesium alloy during die-casting. Furthermore, it compensates for shrinkage cavities in the magnesium alloy during solidification, preventing a decrease in mechanical strength and thermal conductivity due to shrinkage. As an outer layer, it also protects the magnesium alloy from external corrosion, eliminating the need for nickel plating for corrosion protection. The magnesium alloy, with its low Si concentration, reduces the formation of the Mg2Si phase and possesses high thermal conductivity, improving heat dissipation. Adding a grain refiner further refines the grains, compensating for insufficient fluidity and enhancing mechanical strength. The magnesium alloy core layer, as the main component of the battery casing, further reduces the weight of the casing without compromising its strength.

[0009] Furthermore, the preparation methods for the semi-solid aluminum alloy material and the semi-solid magnesium alloy material are independently selected from one of the following methods: electromagnetic stirring, gas induction, ultrasonic stirring, mechanical stirring, or inclined plane method. All of the above preparation methods can be used for the preparation of semi-solid materials, and different preparation methods can be selected according to the different properties of the material. Even further, the preparation method for both the semi-solid magnesium alloy material and the semi-solid aluminum alloy material is a gas induction method. The gas induction method can prepare semi-solid materials with finer crystals, which can further improve the fluidity and mechanical strength of the semi-solid materials.

[0010] Furthermore, the crystal refiner contains Ca and / or Sr. Crystal refiners containing Ca and / or Sr can effectively promote the refinement of magnesium alloys, wherein Sr can improve the corrosion resistance of magnesium alloys.

[0011] Furthermore, the die-casting rate is 1200-1500 mm / min. A higher die-casting rate is used to avoid excessive solidification of the semi-solid materials in each layer during the die-casting process, which would reduce fluidity. This is especially important for the outer layer, as it is in direct contact with the inner wall of the mold and experiences a faster temperature drop. A die-casting rate that is too slow may cause the outer layer to detach from the core layer during the die-casting process, failing to form a complete coating on the core layer. If the die-casting rate is too fast, it is difficult for each layer to maintain a stable laminar flow state during the die-casting process, and air entrapment and oxidation doping are likely to occur.

[0012] Furthermore, the solid fraction of the semi-solid aluminum alloy material is 30%, and the solid fraction of the semi-solid magnesium alloy material is 50%. The outer layer of semi-solid aluminum alloy material is in direct contact with the inner wall of the mold and has a faster heat exchange rate. It needs to maintain a low solid fraction to avoid insufficient fluidity due to an increase in the solid fraction during die casting. The core layer of semi-solid magnesium alloy material has a higher solid fraction, thereby reducing the reduction in thermal conductivity and mechanical properties caused by shrinkage cavities generated during cooling.

[0013] Furthermore, the magnesium alloy material contains 0.5-1.5% Sr by mass fraction. A certain amount of Sr helps to improve the mechanical strength and fluidity of the magnesium alloy without causing a significant reduction in its thermal conductivity.

[0014] Furthermore, the semi-solid aluminum alloy material, the semi-solid magnesium alloy material, and the semi-solid aluminum alloy material are slowly added sequentially into the pressure chamber to form the three-layer composite material. Forming the three-layer composite material within the pressure chamber improves production efficiency and prevents changes in the solid fraction and crystal structure during the transfer of semi-solid materials. Slow addition also prevents the three-layer composite material from mixing.

[0015] Furthermore, the outer layer comprises a bottom layer near the lower mold and a top layer away from the lower mold, with a thickness ratio of (1-2):1 between the bottom layer and the top layer. The bottom layer has a longer contact time with the mold, requiring control of its thickness to prevent excessively thin bottom layers from solidifying too quickly during die casting, resulting in poor fluidity.

[0016] The second aspect of this application provides a battery casing, which is prepared by the above-described method, wherein the battery casing is made of aluminum alloy composite magnesium alloy.

[0017] The aforementioned battery casing has good mechanical strength and thermal conductivity. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the preparation method of this scheme.

[0020] Figure 2 This is a metallographic image of the battery casing of Example 1.

[0021] Figure 3 The image shows the metallographic structure of the battery casing in Comparative Example 3. Detailed Implementation

[0022] To facilitate understanding of this application, a more complete description will be provided below. This application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0023] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of the application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise explicitly specified.

[0024] 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 herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0025] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0026] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0027] Unless otherwise specified, the percentage content mentioned in this application refers to mass percentage for solid-liquid mixtures and solid-phase-solid mixtures, and volume percentage for liquid-phase-liquid mixtures.

[0028] Unless otherwise specified, all percentage concentrations mentioned in this application refer to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of that component.

[0029] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows for temperature fluctuations within the precision range controlled by the instrument.

[0030] The term "particle" as used in this application, or a substance with a defined particle size distribution, is not necessarily spherical in shape; it may be irregular and can be either primary or secondary particles. The particle size of irregular particles is calculated as the average of their maximum and minimum diameters.

[0031] The flowchart of the preparation method of this application is shown below. Figure 1 As shown. The solution of this application can be used to manufacture, for example... Figure 2 The square battery casing.

[0032] Example 1: A method for preparing a battery casing, comprising the following steps:

[0033] Semi-solid magnesium alloy materials and semi-solid aluminum alloy materials were prepared by gas-induced method. Inert gas argon was introduced into a pressure chamber preheated to 550°C, and then semi-solid aluminum alloy materials, semi-solid magnesium alloy materials, and semi-solid aluminum alloy materials were slowly added in sequence with a volume ratio of 1:8.5:0.5 to obtain a three-layer composite material. The thickness of the core layer was 85% of the thickness of the three-layer composite material, and the thickness ratio of the bottom layer to the top layer was 2:1.

[0034] The gas-induced method includes the following steps: introducing nitrogen gas at a rate of 5 L / min into a molten metal at a temperature 20°C above the liquidus line, and obtaining a semi-solid material after the solid fraction of the melt reaches the required range. The gas-induced methods in other embodiments and comparative examples are consistent with those in Example 1.

[0035] When poured into the pressure chamber, the solid fraction of the semi-solid magnesium alloy is 30%, and the solid fraction of the semi-solid aluminum alloy is 30%. The composition (mass fraction) of the semi-solid aluminum alloy is 6% Si, 0.30% Mg, 0.1% Fe, 0.1% Cu, 0.1% Mn, 0.05% Zn, 0.05% Ti, and the balance Al. The composition (mass fraction) of the semi-solid magnesium alloy is 2% Zn, 0.5% Sr, and the balance Mg.

[0036] The three-layer composite material is pressed into the cavity of a square battery mold by a pressure head for filling. The die-casting rate is 1200 mm / min, the pressure is 400 MPa, and the holding time is 20 s, thus obtaining the battery casing.

[0037] Example 2: A method for preparing a battery casing, comprising the following steps:

[0038] Semi-solid magnesium alloy materials and semi-solid aluminum alloy materials were prepared by gas-induced method. Inert gas argon was introduced into a pressure chamber preheated to 500°C, and then semi-solid aluminum alloy materials, semi-solid magnesium alloy materials, and semi-solid aluminum alloy materials were slowly added in sequence with a volume ratio of 0.3:9.5:0.2 to obtain a three-layer composite material. The thickness of the core layer was 95% of the thickness of the three-layer composite material, and the thickness ratio of the bottom layer to the top layer was 1.5:1.

[0039] When poured into the pressure chamber, the solid fraction of the semi-solid magnesium alloy is 30%, and the solid fraction of the semi-solid aluminum alloy is 30%. The composition (mass fraction) of the semi-solid aluminum alloy is 6% Si, 0.30% Mg, 0.1% Fe, 0.1% Cu, 0.1% Mn, 0.05% Zn, 0.05% Ti, and the balance Al. The composition (mass fraction) of the semi-solid magnesium alloy is 2% Zn, 0.5% Sr, and the balance Mg.

[0040] The three-layer composite material is pressed into the cavity of a square battery mold by a pressure head for filling. The die-casting rate is 1200 mm / min, the pressure is 400 MPa, and the holding time is 20 s, thus obtaining the battery casing.

[0041] Example 3: A method for preparing a battery casing, comprising the following steps:

[0042] Semi-solid magnesium alloy materials and semi-solid aluminum alloy materials were prepared by gas-induced method. Inert gas argon was introduced into a pressure chamber preheated to 550°C, and then semi-solid aluminum alloy materials, semi-solid magnesium alloy materials, and semi-solid aluminum alloy materials were slowly added in sequence with a volume ratio of 1:8.5:0.5 to obtain a three-layer composite material. The thickness of the core layer was 85% of the thickness of the three-layer composite material, and the thickness ratio of the bottom layer to the top layer was 2:1.

[0043] When poured into the pressure chamber, the solid fraction of the semi-solid magnesium alloy material is 50%, and the solid fraction of the semi-solid aluminum alloy material is 50%. The composition (mass fraction) of the semi-solid aluminum alloy material is 6% Si, 0.30% Mg, 0.1% Fe, 0.1% Cu, 0.1% Mn, 0.05% Zn, 0.05% Ti, and the balance Al. The composition (mass fraction) of the semi-solid magnesium alloy material is 2% Zn, 0.5% Sr, and the balance Mg.

[0044] The three-layer composite material is pressed into the cavity of a square battery mold by a pressure head for filling. The die-casting rate is 1200 mm / min, the pressure is 400 MPa, and the holding time is 20 s, thus obtaining the battery casing.

[0045] Example 4: A method for preparing a battery casing, comprising the following steps:

[0046] Semi-solid magnesium alloy and semi-solid aluminum alloy were prepared by electromagnetic stirring. Inert argon gas was introduced into a pressure chamber preheated to 550°C, and then semi-solid aluminum alloy, semi-solid magnesium alloy, and semi-solid aluminum alloy were slowly added in sequence at a volume ratio of 1:8.5:0.5 to obtain a three-layer composite material. The thickness of the core layer was 85% of the thickness of the three-layer composite material, and the thickness ratio of the bottom layer to the top layer was 2:1.

[0047] When poured into the pressure chamber, the solid fraction of the semi-solid magnesium alloy material is 30%, and the solid fraction of the semi-solid aluminum alloy material is 30%. The composition (mass fraction) of the semi-solid aluminum alloy material is 6% Si, 0.30% Mg, 0.1% Fe, 0.1% Cu, 0.1% Mn, 0.05% Zn, 0.05% Ti, and the balance Al. The composition (mass fraction) of the semi-solid magnesium alloy material is 2% Zn, 0.5% Sr, 0.15% Ca, and the balance Mg.

[0048] The three-layer composite material is pressed into the cavity of a square battery mold by a pressure head for filling. The die-casting rate is 1500 mm / min, the pressure is 400 MPa, and the holding time is 20 seconds, thus obtaining the battery casing.

[0049] Example 5: A method for preparing a battery casing, comprising the following steps:

[0050] Semi-solid magnesium alloy materials and semi-solid aluminum alloy materials were prepared by gas-induced method. Inert gas argon was introduced into a pressure chamber preheated to 550°C, and then semi-solid aluminum alloy materials, semi-solid magnesium alloy materials, and semi-solid aluminum alloy materials were slowly added in sequence with a volume ratio of 1:8.5:0.5 to obtain a three-layer composite material. The thickness of the core layer was 85% of the thickness of the three-layer composite material, and the thickness ratio of the bottom layer to the top layer was 2:1.

[0051] When poured into the pressure chamber, the solid fraction of the semi-solid magnesium alloy is 50%, and the solid fraction of the semi-solid aluminum alloy is 30%. The composition (mass fraction) of the semi-solid aluminum alloy is 6% Si, 0.30% Mg, 0.1% Fe, 0.1% Cu, 0.1% Mn, 0.05% Zn, 0.05% Ti, and the balance Al. The composition (mass fraction) of the semi-solid magnesium alloy is 2% Zn, 0.5% Sr, 0.25% Ca, and the balance Mg.

[0052] The three-layer composite material is pressed into the cavity of a square battery mold by a pressure head for filling. The die-casting rate is 1200 mm / min, the pressure is 400 MPa, and the holding time is 20 s, thus obtaining the battery casing.

[0053] Example 6: A method for preparing a battery casing, comprising the following steps:

[0054] Semi-solid magnesium alloy materials and semi-solid aluminum alloy materials were prepared by gas-induced method. Inert gas argon was introduced into a pressure chamber preheated to 550°C, and then semi-solid aluminum alloy materials, semi-solid magnesium alloy materials, and semi-solid aluminum alloy materials were slowly added in sequence with a volume ratio of 1:8.5:0.5 to obtain a three-layer composite material. The thickness of the core layer was 85% of the thickness of the three-layer composite material, and the thickness ratio of the bottom layer to the top layer was 2:1.

[0055] When poured into the pressure chamber, the solid fraction of the semi-solid magnesium alloy material is 30%, and the solid fraction of the semi-solid aluminum alloy material is 30%. The composition (mass fraction) of the semi-solid aluminum alloy material is 6% Si, 0.30% Mg, 0.1% Fe, 0.1% Cu, 0.1% Mn, 0.05% Zn, 0.05% Ti, and the balance Al. The composition (mass fraction) of the semi-solid magnesium alloy material is 2% Zn, 0.5% Sr, 0.05% Si, and the balance Mg.

[0056] The three-layer composite material is pressed into the cavity of a square battery mold by a pressure head for filling. The die-casting rate is 1200 mm / min, the pressure is 400 MPa, and the holding time is 20 s, thus obtaining the battery casing.

[0057] Comparative Example 1: A method for preparing a battery casing, comprising the following steps:

[0058] Semi-solid magnesium alloy materials are prepared by gas-induced method, in which semi-solid magnesium alloy materials are slowly added into the pressure chamber.

[0059] When the semi-solid magnesium alloy is poured into the pressure chamber (which is preheated to 550°C and purged with protective gas), the solid fraction of the semi-solid magnesium alloy is 30%, and the composition (mass fraction) of the semi-solid magnesium alloy is 2% Zn, 0.5% Sr and the balance Mg.

[0060] Semi-solid magnesium alloy material is pressed into the cavity of a square battery mold by a pressure head for filling. The die-casting rate is 1200 mm / min, the pressure is 400 MPa, and the holding time is 20 s, thus obtaining the battery casing.

[0061] Comparative Example 2: A method for preparing a battery casing, comprising the following steps:

[0062] Semi-solid aluminum alloy materials are prepared by gas induction method, in which semi-solid aluminum alloy materials are slowly added into the pressure chamber.

[0063] When the semi-solid aluminum alloy is poured into the pressure chamber (which is preheated to 550°C and purged with protective gas), the solid fraction of the semi-solid aluminum alloy is 30%. The composition (mass fraction) of the semi-solid aluminum alloy is 6% Si, 0.30% Mg, 0.1% Fe, 0.1% Cu, 0.1% Mn, 0.05% Zn, 0.05% Ti, and the balance Al.

[0064] Semi-solid aluminum alloy material is pressed into the cavity of a square battery mold by a pressure head for filling. The die-casting rate is 1200 mm / min, the pressure is 400 MPa, and the holding time is 20 seconds, thus obtaining the battery casing.

[0065] Comparative Example 3: A method for preparing a battery casing, comprising the following steps:

[0066] Semi-solid magnesium alloy material and semi-solid aluminum alloy material were prepared by gas-induced method. Semi-solid aluminum alloy material, semi-solid magnesium alloy material and semi-solid aluminum alloy material were slowly added to the pressure chamber in sequence with a volume ratio of 1:8.5:0.5 to obtain a three-layer composite material. The thickness of the core layer is 85% of the thickness of the three-layer composite material, and the thickness ratio of the bottom layer to the top layer is 2:1.

[0067] When poured into the pressure chamber, the solid fraction of the semi-solid magnesium alloy material is 30%, and the solid fraction of the semi-solid aluminum alloy material is 30%. The composition (mass fraction) of the semi-solid aluminum alloy material is 2% Si, 0.30% Mg, 0.1% Fe, 0.1% Cu, 0.1% Mn, 0.05% Zn, 0.05% Ti, and the balance Al. The composition (mass fraction) of the semi-solid magnesium alloy material is 2% Zn, 0.5% Sr, and the balance Mg.

[0068] The three-layer composite material is pressed into the cavity of a square battery mold by a pressure head for filling. The die-casting rate is 1200 mm / min, the pressure is 400 MPa, and the holding time is 20 s, thus obtaining the battery casing.

[0069] When poured into the pressure chamber, the solid fraction of the semi-solid magnesium alloy is 30%, and the solid fraction of the semi-solid aluminum alloy is 30%. The composition (mass fraction) of the semi-solid aluminum alloy is 6% Si, 0.30% Mg, 0.1% Fe, 0.1% Cu, 0.1% Mn, 0.05% Zn, 0.05% Ti, and the balance Al. The composition (mass fraction) of the semi-solid magnesium alloy is 2% Zn and the balance Mg.

[0070] The three-layer composite material is pressed into the cavity of a square battery mold by a pressure head for filling. The die-casting rate is 1200 mm / min, the pressure is 400 MPa, and the holding time is 20 s, thus obtaining the battery casing.

[0071] The tensile strength and thermal conductivity of the battery casings prepared in the above embodiments and comparative examples were tested, and the results are shown in Table 1. The tensile strength was measured according to the method disclosed in the national standard GB / T 228.1-2010 "Metallic materials, tensile testing - Part 1: Test at room temperature", and the thermal conductivity was measured according to the method disclosed in ISO 8301 AMD 1-2010.

[0072] Table 1

[0073]

[0074] According to the data in Table 1, the tensile strength and thermal conductivity of Examples 1-6 are better than those of Comparative Example 1. This is because this application uses two semi-solid alloy materials to prepare the battery casing. During the die-casting process, the materials of each layer maintain laminar flow, with only a small amount of liquid phase exchange at the interface, ultimately forming a battery casing with a semi-solid magnesium alloy material as the core layer and a semi-solid aluminum alloy material as the outer layer. The aluminum alloy material has a high Si content and high fluidity, which can drive the flow of the magnesium alloy material during die-casting. Furthermore, it can compensate for shrinkage cavities formed in the magnesium alloy during solidification, avoiding the reduction in mechanical strength and thermal conductivity due to shrinkage cavities. As an outer layer, it can prevent corrosion of the magnesium alloy by the external environment, thus eliminating the need for nickel plating for corrosion protection. The magnesium alloy material has a low Si concentration, which can reduce the formation of the Mg2Si phase. It has a high thermal conductivity, which can improve the heat dissipation effect of the battery casing. Additionally, by adding a grain refiner to promote grain refinement, it compensates for insufficient fluidity and improves its mechanical strength. Figure 2 As shown, no obvious pores were observed at the magnesium-aluminum interface of the battery casing, and the aluminum layer compensated for the defects in the magnesium layer. Comparative Example 2 used an aluminum alloy as the casing, whose density is more than 1.5 times that of magnesium alloy, thus failing to meet the requirements for lightweight design. Figure 3 As shown, Comparative Example 3 used an aluminum alloy with a lower Si content, which has poor fluidity. During solidification, many shrinkage cavities or even gaps are generated at the interface, resulting in a decrease in tensile strength and thermal conductivity.

[0075] Example 2 exhibits higher tensile strength and thermal conductivity compared to Example 1 because its core layer has a higher proportion, resulting in higher thermal conductivity and tensile strength in the core. Example 3 uses semi-solid magnesium alloy and semi-solid aluminum alloy with higher solids content, and its performance is slightly lower than that of Example 1. This may be because the high solids content magnesium alloy has fewer shrinkage cavities during cooling, while the high solids content aluminum alloy has lower fluidity during die casting, potentially leading to incomplete filling and porosity. However, its performance is still improved compared to Comparative Example 1. Example 5 exhibits better tensile strength and thermal conductivity than Example 1, possibly because it uses a semi-solid aluminum alloy with a lower solids content, which maintains better fluidity during die casting, while the higher solids content semi-solid magnesium alloy has fewer shrinkage cavities. Example 6 uses a magnesium alloy with a Si content of 0.05%, resulting in a slight increase in tensile strength.

[0076] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0077] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a battery casing, characterized in that, Includes the following steps: A preheated square battery mold is used to slowly add semi-solid aluminum alloy, semi-solid magnesium alloy, and semi-solid aluminum alloy materials into the preheated pressure chamber to form a three-layer composite material. The three-layer composite material includes a core layer and outer layers disposed on both sides of the core layer. The outer layers are semi-solid aluminum alloy materials, and the core layer is a semi-solid magnesium alloy material. The thickness of the core layer is 85-95% of the thickness of the three-layer composite material. The three-layer composite material is pressed into the cavity of the square battery mold by a pressure head for filling. After holding the pressure and cooling, the battery casing is obtained. The semi-solid aluminum alloy material has a solid phase fraction of 30-50%, the semi-solid magnesium alloy material has a solid phase fraction of 30-50%, the aluminum alloy material contains 4-6% Si by mass, the magnesium alloy material contains 0-0.05% Si by mass, and the magnesium alloy material contains a crystal refiner.

2. The preparation method according to claim 1, characterized in that, The preparation methods for the semi-solid aluminum alloy material and the semi-solid magnesium alloy material are independently selected from one of the following methods: electromagnetic stirring, gas induction, ultrasonic stirring, mechanical stirring, or inclined plane method.

3. The preparation method according to claim 2, characterized in that, The preparation method of the semi-solid magnesium alloy material is a gas-induced method, and the preparation method of the semi-solid aluminum alloy material is a gas-induced method.

4. The preparation method according to claim 1, characterized in that, The crystal refining agent contains Ca and / or Sr.

5. The preparation method according to claim 1, characterized in that, The die-casting rate of the pressure head is 1200-1500 mm / min.

6. The preparation method according to claim 1, characterized in that, The solid fraction of the semi-solid aluminum alloy material is 30%, and the solid fraction of the semi-solid magnesium alloy material is 50%.

7. The preparation method according to claim 1, characterized in that, The magnesium alloy material contains 0.5-1.5% Sr by mass fraction.

8. The preparation method according to claim 1, characterized in that, The outer layer comprises a bottom layer close to the lower mold and a top layer away from the lower mold, wherein the thickness ratio of the bottom layer to the top layer is (1-2):

1.

9. A battery casing, characterized in that, The battery casing is prepared by the preparation method according to any one of claims 1-8, wherein the casing is made of aluminum alloy composite magnesium alloy.

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