Brazable high-strength rare earth aluminum alloy for battery liquid cooling plate and preparation method thereof

Abstract

This invention relates to a brazable high-strength rare-earth aluminum alloy for battery liquid cooling plates and its preparation method. The alloy composition and weight percentage are: RE (Ce,La): 4-7%; Mn: 0.8-1.8%, with the balance being Al. This invention is based on a design that simultaneously achieves second-phase strengthening and increases the alloy melting point through alloying with mixed rare-earth elements (RE) of Ce and La. By limiting the content of RE (Ce,La) and Mn elements, it forms fine-grained Al... 11 The RE(Ce,La)3 and Al6Mn phases act as second-phase strengthening agents and refine grains, improving the alloy's strength and plasticity. On the other hand, RE(Ce,La) elements have high chemical reactivity, purifying the melt and significantly improving ingot quality, thereby enhancing the mechanical properties and melting point of the aluminum alloy. Simultaneously, Mn elements can combine with impurity Fe elements, preventing the formation of harmful needle-like β-AlFe phases.

Description

Technical Field

[0001] This invention relates to the field of battery liquid cooling plate technology, specifically to a brazable high-strength rare earth aluminum alloy for battery liquid cooling plates and its preparation method. Background Technology

[0002] New energy vehicles represent a major direction for the global automotive industry's transformation, upgrading, and green development, and are also a strategic choice for the high-quality development of my country's automotive industry. The power battery is the heart of a new energy vehicle, and its operating status directly affects the vehicle's performance. To address the range and charging speed issues of new energy vehicles, the capacity and density of power batteries are continuously increasing, while their rated voltage is also rapidly rising. Consequently, the heat generated during battery operation accumulates quickly. If this heat cannot be dissipated effectively and promptly, it will lead to excessively high battery temperatures, severely impacting battery life and safety. Liquid cooling, with its advantages of high specific heat capacity and high heat transfer coefficient, is gradually surpassing air cooling and phase change cooling to become the mainstream cooling method for power batteries. The most crucial component of this cooling method is the liquid cooling plate.

[0003] One common manufacturing process for liquid cooling plates is to first prepare an upper plate containing flow channels by stamping, and then braze the upper plate to a flat lower plate. Currently, composite liquid cooling plates typically consist of an Al-Mn or Al-Mg-Si aluminum alloy core material (approximately 90%) as the upper / lower plate and an Al-Si alloy skin material (approximately 10%) as the brazing material. For example, the high-strength liquid cooling plate for power batteries published by Changzhou Changfa Refrigeration Technology Co., Ltd. (patent number 201820357789.X) uses 1006 or 3003 aluminum alloy for the upper plate and 6063 aluminum alloy for the lower plate; the composite aluminum alloy plate and its preparation method for liquid cooling plates for new energy power batteries published by Yinbang Metal Composite Materials Co., Ltd. (application number 202210482358.7) mainly includes an Al-Mg-Si core material layer and an Al-Mn protective layer, which are then brazed. However, the yield strength of current Al-Mn alloy core materials is only 40 MPa, and the tensile strength is only 110 MPa, which is insufficient to meet the requirements of liquid cooling plates to withstand the greater weight of batteries. In addition, the melting point of the brazing filler metal is around 580℃. Due to its low melting point, Al-Mg-Si alloy core materials are prone to melting, corrosion, and liquid film migration during brazing, which seriously impairs the corrosion resistance and mechanical properties of the liquid cooling plate.

[0004] Therefore, developing a brazable high-strength aluminum alloy with good load-bearing capacity, high melting point, and high stability, and developing its preparation process, to meet the rapidly growing demand of new energy vehicles, has become one of the key research directions for aluminum alloy materials used in power batteries. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a brazable high-strength rare-earth aluminum alloy for battery liquid cooling plates and its preparation method, so as to improve the strength and thermal stability of the core material layer and thus meet the requirements of liquid cooling plates for power batteries.

[0006] This invention is based on the design of alloying with rare earth elements such as Ce and La to simultaneously achieve second-phase strengthening and increase the alloy melting point. By limiting the content of Ce, La, mixed rare earth elements, and Mn, fine-sized Al atoms are formed. 11 The (Ce,La)3 phase and Al6Mn phase act as second-phase strengthening and grain refinement, improving the alloy's strength and plasticity. On the other hand, RE(Ce,La) elements have high chemical activity, purifying the melt and significantly improving ingot quality, thus enhancing the mechanical properties and melting point of the aluminum alloy. Simultaneously, Mn elements can combine with impurity Fe elements, preventing the formation of harmful needle-like β-AlFe phases. The aluminum alloy is manufactured through extrusion molding. The extruded alloy exhibits a yield strength ≥145MPa and a tensile strength ≥165MPa, representing increases of 260% and 50% respectively compared to existing levels of 40MPa and 110MPa, while also achieving an elongation ≥20% and a melting point above 635℃.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a brazable high-strength rare-earth aluminum alloy for battery liquid cooling plates, the composition and weight percentage of which are: RE(Ce,La): 4-7%; Mn: 0.8-1.8%, balance Al; other unavoidable impurity elements with individual content <0.05% and total content <0.15%.

[0009] In the brazable high-strength rare-earth aluminum alloy, the weight percentage of RE(Ce,La) element is preferably 4-6%, and the weight percentage of Mn element is preferably 0.9-1.6%.

[0010] The present invention also provides a method for preparing and forming the aforementioned brazable high-strength rare-earth aluminum alloy, comprising the following steps:

[0011] S1. Prepare materials according to the alloy composition ratio: pure aluminum, Al-RE master alloy, Al-Mn master alloy. First, melt the pure aluminum matrix to obtain molten aluminum.

[0012] S2. Heat the aluminum liquid, then add the dried Al-RE master alloy and Al-Mn master alloy to the aluminum liquid, stir to completely melt the master alloy, and keep it at the temperature to obtain a mixed melt.

[0013] S3. The mixed molten liquid is refined, degassed, and slag-removed; after cooling, it is poured and cooled to obtain an aluminum alloy ingot.

[0014] S4. Homogenize the aluminum alloy ingot.

[0015] S5. The homogenized aluminum alloy ingot is extruded and immediately water-quenched to obtain Al-Mn-RE(Ce,La) alloy rod, which is the brazable high-strength rare earth aluminum alloy.

[0016] In step S2, the aluminum liquid is heated to a temperature of 740–750°C. The holding time is 20–30 minutes.

[0017] In step S3, the cooling temperature is 690–710°C. After pouring, the mixture is air-cooled to room temperature.

[0018] In step S4, the homogenization treatment is carried out at a temperature of 350–450°C for 3–5 hours; after homogenization, the mixture is air-cooled to room temperature; this treatment can eliminate unevenness in composition and structure.

[0019] In step S5, the extrusion ratio is 10.0 to 13.0; the preheating temperature of the extrusion cylinder and extrusion die is 300°C, and the ingot is preheated at 300°C for 1 to 3 hours; the extrusion rate is 0.2 to 0.5 mm / s.

[0020] The microstructure of the extruded sample obtained in step (5) consists of α-Al grains, Al6(Mn,Fe) phase, and Al... 11 It is composed of RE(Ce,La)3 phase.

[0021] The present invention also provides an application of the aforementioned brazable high-strength rare earth aluminum alloy in the preparation of the core material layer for liquid cooling plates of power batteries.

[0022] This invention is based on a design that simultaneously achieves second-phase strengthening and increases the alloy melting point through RE(Ce,La) alloying. The maximum solid solubility of Ce and La in the Al matrix is ​​only 0.05 wt.%, therefore RE(Ce,La) mainly exists in Al as a second phase. When the RE(Ce,La) content is between 4 and 7 wt.%, it primarily forms Al... 11 The RE(Ce,La)3 phase is characterized by strong thermal stability and high hardness, effectively hindering dislocation movement under both room temperature and high temperature conditions. 11 The RE(Ce,La)3 phase can also act as a heterogeneous nucleus, increasing the number of heterogeneous nuclei and refining the alloy microstructure, thus playing a positive role in improving the alloy's strength and toughness. Furthermore, RE(Ce,La) elements have high chemical reactivity, capable of reacting and combining with H, O, N, S, and halogen elements in the melt, purifying the melt and significantly improving the quality of the casting, thereby enhancing the alloy's mechanical properties and melting point.

[0023] In this invention, the contents of Mn and RE(Ce,La) need to be controlled within a reasonable range. This is because the core material of the liquid-cooled plate needs to be rolled to a thickness of approximately 1 mm. This process requires that the alloy's plasticity not be too low; otherwise, it will cause problems such as cracking of the rolled part and poor surface quality, making it impossible to obtain a qualified liquid-cooled plate product. If the Mn content is too high, the Al6Mn phase becomes larger and is distributed in a continuous network on the grain boundaries, which is detrimental to the mechanical properties of the alloy. If the Mn content is too low, on the one hand, the Al6Mn phase content is insufficient, failing to provide an effective second-phase strengthening effect, which is detrimental to improving the alloy's strength; on the other hand, too little Mn cannot combine completely with the Fe element in the alloy. Fe is an unavoidable harmful element in aluminum alloys. The Fe-containing second phase, with its needle-like or lath-like morphology, cuts through the matrix, inducing stress concentration and severely reducing toughness. Adding an appropriate amount of Mn can transform the needle-like Fe-containing phase into a fine and rounded α-AlFeMn phase, greatly improving the alloy's toughness. If the RE(Ce,La) content is too high, Al... 11 The RE(Ce,La)3 phase becomes larger, forming coarse, strip-shaped primary Al. 11 The RE(Ce,La)3 phase is detrimental to the strength and plasticity of the alloy; if the RE(Ce,La) element is too low, it leads to the loss of Al, which has a strengthening effect and high thermal stability. 11 The insufficient amount of RE(Ce,La)3 phases prevents them from effectively strengthening the alloy as a second phase and increasing its melting point.

[0024] Compared with the prior art, this application has at least the following beneficial effects:

[0025] On the one hand, by rationally selecting the types and proportions of rare earth alloying elements, RE (Ce,La) elements and Al are introduced. 11 RE(Ce,La)3 phase: RE(Ce,La) elements significantly improve casting quality by purifying the melt, achieving a dual improvement in the alloy's mechanical properties and melting point; Al 11 The RE(Ce,La)3 phase can effectively act as a second-phase strengthening agent and a heterogeneous nucleation agent, thereby improving the mechanical properties of the alloy. On the other hand, the hot extrusion process allows Al... 11 The RE(Ce,La)3 phase breaks down, and compared with the as-cast state, the fine and dispersed second phase has a more significant strengthening effect, which can greatly improve the mechanical properties of the alloy.

[0026] A brazable high-strength rare-earth aluminum alloy suitable for use in liquid cooling plates for power batteries has been developed. The aluminum alloy prepared by this invention exhibits a yield strength ≥145MPa, tensile strength ≥165MPa, and elongation ≥20% under hot extrusion conditions; its melting point is higher than 635℃, which is more than 55℃ higher than the melting point of the brazing filler metal; and it does not undergo dissolution of the low-melting-point second phase during brazing, thus preventing overheating. Attached Figure Description

[0027] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0028] Figure 1 These are schematic diagrams of the aluminum alloy microstructures of Examples 1 and 2;

[0029] Figure 2 This is a schematic diagram of the microstructure of the aluminum alloy in Comparative Example 1;

[0030] Figure 3 This is a schematic diagram of the microstructure of the aluminum alloy in Comparative Example 2;

[0031] Figure 4 This is a schematic diagram of the microstructure of the aluminum alloy in Comparative Example 3;

[0032] Figure 5 This is a schematic diagram of the microstructure of the aluminum alloy in Comparative Example 4. Detailed Implementation

[0033] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0034] Example 1

[0035] This embodiment provides a brazable high-strength rare earth aluminum alloy for power battery liquid cooling plates and its preparation method, which is composed of the following alloying elements by mass percentage: Ce: 4.0%, Mn: 1.0%, other unavoidable impurity elements with individual content <0.05% and total content <0.15%, and the balance being Al.

[0036] The preparation method is as follows:

[0037] (1) Prepare materials according to the alloy composition ratio, first melt the base pure aluminum;

[0038] (2) When the temperature of the aluminum liquid reaches 745℃, add the dried Al-Ce master alloy and Al-Mn into the aluminum liquid, stir to make the master alloy completely melt, and keep it at the temperature for 25 minutes.

[0039] (3) Then, the aluminum liquid is refined, degassed and slag removed; the temperature of the aluminum liquid is reduced to 700℃ and then poured to obtain an aluminum alloy ingot, which is then air-cooled to room temperature.

[0040] (4) Homogenize the aluminum alloy ingot to eliminate uneven composition and structure. The homogenization temperature is 400℃, and the temperature is held for 4 hours. Then air cool to room temperature.

[0041] (5) The homogenized aluminum alloy ingot was extruded at an extrusion ratio of 12:1 to obtain Al-Mn-Ce alloy rods, which were immediately water-quenched after extrusion. The preheating temperature of the extrusion cylinder and extrusion die was 300℃, and the ingot was preheated at 300℃ for 2 hours; the extrusion rate was 0.3 mm / s.

[0042] The microstructure of the aluminum alloy prepared in this embodiment is as follows: Figure 1 As shown in the figure. It can be seen from the figure that Al 11 After extrusion, the Ce3 phase is distributed in a broken, strip-like pattern, which effectively acts as a second-phase strengthening agent, thus benefiting the mechanical properties of the alloy. Besides the Al6(Mn,Fe) phase and Al... 11 Apart from the Ce3 phase, no other microstructures were observed, indicating that Ce played a good role in purifying the melt, significantly improving the quality of the casting, and enhancing the mechanical properties and melting point of the alloy.

[0043] The mechanical properties and melting point of this alloy are as follows:

[0044] Yield strength: 148MPa, tensile strength: 168MPa, elongation: 24%, melting point: 638℃.

[0045] Example 2

[0046] The preparation steps in this embodiment are basically the same as those in Example 1, except that an Al-6Ce-1.6Mn aluminum alloy (i.e., Ce: 6 wt.%, Mn: 1.6 wt.%) is prepared. The microstructure of the aluminum alloy prepared in this embodiment is as follows: Figure 1 As shown. Similar to Example 1, except for the Al6(Mn,Fe) phase and Al... 11 No other microstructures were observed besides the Ce3 phase. The second phase fraction of the alloy in Example 2 was slightly increased compared to Example 1. The mechanical properties and melting point of this alloy are as follows:

[0047] Yield strength: 165MPa, tensile strength: 185MPa, elongation: 20.6%, melting point: 636℃.

[0048] Comparative Example 1

[0049] The preparation steps in this embodiment are basically the same as those in Example 1, except that an Al-4Ce-3Mn aluminum alloy (i.e., Ce: 4wt.%, Mn: 3wt.%) is prepared. The microstructure of the aluminum alloy prepared in this comparative example is as follows: Figure 2 As shown. Similar to Example 1, except for the Al6(Mn,Fe) phase and Al... 11No other structures were observed besides the Ce3 phase. Compared to Example 1, the Al6(Mn,Fe) phase was larger due to the excessive Mn content, resulting in a significant decrease in elongation.

[0050] The mechanical properties and melting point of this alloy are as follows:

[0051] Yield strength: 149 MPa, tensile strength: 157 MPa, elongation: 11.5%, melting point: 639℃.

[0052] Comparative Example 2

[0053] The preparation steps in this embodiment are basically the same as those in Example 1, except that an Al-4Ce-0.4Mn aluminum alloy (i.e., Ce: 4wt.%, Mn: 0.4wt.%) is prepared. The microstructure of the aluminum alloy in this comparative example is as follows: Figure 3 As shown, compared with Examples 1 and 2, the Al6(Mn,Fe) phase is significantly reduced, and long needle-like β-AlFe phase appears, which significantly reduces the alloy strength and elongation.

[0054] The mechanical properties and melting point of this alloy are as follows:

[0055] Yield strength: 132MPa, tensile strength: 147MPa, elongation: 10.5%, melting point: 637℃.

[0056] Comparative Example 3

[0057] The preparation steps in this embodiment are basically the same as those in Example 1, except that an Al-10Ce-1Mn aluminum alloy (i.e., Ce: 10 wt.%, Mn: 1 wt.%) is prepared. The microstructure of the aluminum alloy in this comparative example is as follows: Figure 4 As shown. Similar to Example 1, except for the Al6(Mn,Fe) phase and Al... 11 No other tissues were observed besides the Ce3 phase. Compared to Example 1, due to the excessive Ce content, Al... 11 Ce3 phases are larger and exhibit bulk formations. 11 The Ce3 phase significantly degrades the elongation of the alloy.

[0058] The mechanical properties and melting point of this alloy are as follows:

[0059] Yield strength: 170MPa, tensile strength: 181MPa, elongation: 9.7%, melting point: 635℃.

[0060] Comparative Example 4

[0061] The preparation steps in this embodiment are basically the same as those in Example 1, except that an Al-1Ce-1Mn aluminum alloy (i.e., Ce: 1 wt.%, Mn: 1 wt.%) is prepared. The microstructure of the aluminum alloy in this comparative example is as follows: Figure 5 As shown. Similar to Example 1, except for the Al6(Mn,Fe) phase and Al... 11 No other tissues were observed besides the Ce3 phase. Compared to Example 1, due to the insufficient Ce content, Al... 11 The Ce3 phase fraction was significantly reduced.

[0062] The mechanical properties and melting point of this alloy are as follows:

[0063] Yield strength: 124MPa, tensile strength: 143MPa, elongation: 23.2%, melting point: 640℃.

[0064] Table 1. Mechanical properties and melting point test results of a brazable high-strength rare-earth aluminum alloy for battery liquid cooling plates.

[0065] Alloy materials Yield strength (MPa) Tensile strength (MPa) Elongation (%) Melting point (°C) Example 1 148 168 24.0 638 Example 2 165 185 20.6 636 Comparative Example 1 149 157 11.5 639 Comparative Example 2 132 147 10.5 637 Comparative Example 3 170 181 9.7 635 Comparative Example 4 124 143 23.2 640

[0066] This invention has many specific applications, and the above description is only a preferred embodiment. It should be noted that the above embodiments are for illustrative purposes only and are not intended to limit the scope of protection of this invention. For those skilled in the art, several improvements can be made without departing from the principle of this invention, and these improvements should also be considered within the scope of protection of this invention.

Claims

1. A method for preparing and forming a brazable high-strength rare-earth aluminum alloy, characterized in that, Includes the following steps: S1. Prepare materials according to the alloy composition ratio: pure aluminum, Al-RE master alloy, Al-Mn master alloy. First, melt the pure aluminum matrix to obtain molten aluminum. S2. Heat the aluminum liquid, then add the dried Al-RE master alloy and Al-Mn master alloy to the aluminum liquid, stir to make the master alloy completely melt, and keep it at the temperature to obtain a mixed melt. S3. The mixed molten liquid is refined, degassed, and slag-removed; after cooling, it is poured and cooled to obtain an aluminum alloy ingot. S4. Homogenize the aluminum alloy ingot. S5. The homogenized aluminum alloy ingot is extruded and immediately water-cooled and quenched to obtain Al-Mn-RE alloy rod, namely the brazable high-strength rare earth aluminum alloy. The brazable high-strength rare earth aluminum alloy has the following composition and weight percentage: RE 4~6%; Mn 0.9~1.6%, balance Al; other unavoidable impurity elements have a single content of <0.05% and a total content of <0.15%; RE elements are one or more of Ce and La; In step S4, the homogenization treatment is carried out at a temperature of 350~450 ℃ for 3~5 h. In step S5, during extrusion, the extrusion cylinder and extrusion die are preheated to 300 ℃, and the ingot is preheated at 300 ℃ for 1~3 h; In step S5, the extrusion ratio is 10.0~13.0; the extrusion rate is 0.2~0.5 mm / s. The brazable high-strength rare-earth aluminum alloy obtained in step S5 has a microstructure consisting of α-Al grains, Al6(Mn,Fe) phase, and Al... 11 It consists of RE(Ce, La)3 phases.

2. The preparation and forming method according to claim 1, characterized in that, In step S2, the temperature of the molten aluminum is raised to 740~750 ℃.

3. The preparation and forming method according to claim 1, characterized in that, In step S3, the cooling temperature is 690~710℃.

4. The application of a brazable high-strength rare earth aluminum alloy obtained by the preparation and molding method as described in claim 1 in the preparation of the core material layer for liquid cooling plates of power batteries.

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