Aluminum alloy clad plate strip for heat exchangers and method of making the same

Abstract

The application discloses an aluminum alloy composite plate strip for a heat exchanger and a preparation method thereof, and belongs to the technical field of aluminum alloy composite plate strips.The aluminum alloy composite plate strip comprises a core material layer and a cladding layer.The core material layer comprises Si, Fe, Cu, Ti, Mg+Mn and rare earth elements.The cladding layer comprises Si, Fe, Cu, Ti, Zr, Mg+Mn and rare earth elements.The mechanical strength, corrosion resistance and high-temperature resistance of the core material layer and the cladding layer are simultaneously improved by adding different contents and proportions of rare earth elements and Mg+Mn into the core material layer and the cladding layer.The microstructure is further improved by improving the process conditions, so that the mechanical strength and the thermal cracking resistance are further improved.The prepared aluminum alloy composite plate strip has excellent comprehensive performance and can meet the performance requirements of high strength, corrosion resistance and high-temperature resistance.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloys, and in particular to an aluminum alloy composite plate and strip for heat exchangers and its preparation method. Background Technology

[0002] A heat exchanger is a device used to transfer heat from a hot medium to a cold medium to meet specified process requirements; it is an industrial application of convective heat transfer and heat conduction. Heat exchangers are widely used in air conditioning, automobiles, trucks, aerospace, and other fields. Aluminum alloys, due to their light weight and high thermal conductivity, are a key material for manufacturing aluminum heat exchangers.

[0003] In recent years, with the continuous development of technology, the power of heat exchangers has been increasing. Conventionally used aluminum alloys, due to limitations in strength and corrosion resistance, are increasingly unable to meet the requirements. Chinese Patent CN 106827712 B discloses a brazed aluminum alloy composite plate, core material, and preparation method for heat exchangers. This technology improves corrosion resistance by compositing a corrosion-resistant aluminum alloy onto one side of the core material, and enhances the strength of the core material by appropriately increasing the content of Cu, Mn, Fe, and Si elements, while simultaneously reducing costs.

[0004] However, in the process of implementing the inventive technical solution in the embodiments of this application, the inventors of this application discovered that the above-mentioned technology has at least the following technical problems:

[0005] 1. The outer layer of corrosion-resistant aluminum alloy will soften and deform before the core layer of aluminum alloy during the brazing process;

[0006] 2. Cracks may occur during brazing or use. Summary of the Invention

[0007] This invention provides an aluminum alloy composite plate / strip for heat exchangers and its preparation method, thereby solving the aforementioned defects of aluminum alloy materials in the use of heat exchangers in the prior art.

[0008] To solve the above-mentioned technical problems, the present invention provides an aluminum alloy composite plate and strip for heat exchangers, comprising: a core layer and a cladding layer; wherein, the core layer comprises the following components by weight percentage: Si 0.8-1.2%, Fe≤0.45%, Cu 0.6-0.9%, Ti 1.35-1.45%, Mg+Mn 1.0-1.5%, rare earth elements 0.05-0.1%, and the remainder being Al and unavoidable impurities; the cladding layer comprises the following components by weight percentage: Si 1.5-2.0%, Fe≤0.45%, Cu 0.3-0.5%, Ti 0.8-1.2%, Zr 0.65-1.0%, Mg+Mn 1.5-2.0%, rare earth elements 0.15-0.2%, and the remainder being Al and unavoidable impurities.

[0009] In a preferred embodiment of the present invention, the Mg / Mn ratio in the core material layer is 5 to 3:1.

[0010] In a preferred embodiment of the present invention, the Mg / Mn ratio in the coating layer is 4 to 2:1.

[0011] In a preferred embodiment of the present invention, the rare earth element is at least one of Ce or Nd.

[0012] In a preferred embodiment of the present invention, the rare earth element is a mixture of Ce and Nd in a mass ratio of 1:1 to 2.

[0013] To solve the above-mentioned technical problems, the present invention provides a method for preparing aluminum alloy composite plates and strips for heat exchangers, comprising the following steps:

[0014] (1) Preparation of core material layer: According to the formula amount of core material layer, the alloy components of the core material layer are successively smelted, refined, cast, milled, hot rolled and heat treated to obtain the core material layer;

[0015] (2) Preparation of coating layer: According to the formula amount of coating layer, the alloy components of the coating layer are successively subjected to melting, refining, casting, milling, hot rolling and heat treatment to obtain the coating layer;

[0016] (3) Composite and rolling: The cladding layer prepared in step (2) is wrapped around the core material layer prepared in step (1), welded together, and then hot rolled, annealed once, cold rolled and annealed twice to obtain the aluminum alloy composite plate and strip for heat exchangers.

[0017] In a preferred embodiment of the present invention, the thickness of the core material layer obtained in step (1) is 3 to 5 times the thickness of the coating layer prepared in step (2).

[0018] In a preferred embodiment of the present invention, in step (3), the hot rolling process conditions are as follows: first, the temperature is raised to 500-550°C at a rate of 20-30°C / min, then kept at a constant temperature for 30-60 minutes, and then rolled. The thickness after hot rolling is 30-50% of the thickness before hot rolling.

[0019] In a preferred embodiment of the present invention, in step (3), the process conditions for the first annealing are: annealing temperature of 250-300°C and holding time of 5-7 hours.

[0020] In a preferred embodiment of the present invention, the process conditions for the secondary annealing in step (3) are as follows: first, the temperature is raised to 200-300°C at a rate of 15-25°C / min and held for 2-3 hours; then, the temperature is raised to 350-380°C at a rate of 10-15°C / min and held for 1-2 hours; finally, the temperature is raised to 400-420°C at a rate of 5-10°C / min and held for 3-5 hours.

[0021] The beneficial effects of this invention are as follows: This invention provides an aluminum alloy composite plate and strip for heat exchangers and its preparation method. On the one hand, by simultaneously adding different contents and ratios of rare earth elements and Mg and Mn composite components to the core layer and the cladding layer, the mechanical strength, corrosion resistance, and high-temperature resistance of the core layer and the cladding layer are improved. On the other hand, by improving the process conditions, the microstructure is further improved, thereby further enhancing the mechanical strength and thermal crack resistance. The prepared aluminum alloy composite plate and strip has excellent comprehensive performance and can meet the performance requirements of high strength, corrosion resistance, and high temperature resistance. Attached Figure Description

[0022] Figure 1 This is a cross-sectional structural schematic diagram of a preferred embodiment of an aluminum alloy composite plate strip for a heat exchanger according to the present invention;

[0023] Figure 2 This is a schematic diagram of the process for preparing an aluminum alloy composite plate and strip for a heat exchanger according to the present invention.

[0024] The components in the attached diagram are labeled as follows: 1. Core material layer, 2. Covering layer. Detailed Implementation

[0025] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0026] Please see Figure 1 and Figure 2 The embodiments of the present invention include:

[0027] The present invention discloses an aluminum alloy composite plate and strip for heat exchangers, comprising: a core layer 1 and a cladding layer 2.

[0028] The core layer comprises the following components by weight percentage: Si 0.8–1.2%, Fe ≤0.45%, Cu 0.6–0.9%, Ti 1.35–1.45%, Mg + Mn 1.0–1.5%, with a Mg / Mn ratio of 5–3:1, rare earth elements 0.05–0.1%, and the remainder being Al and unavoidable impurities. Mg strengthens the aluminum alloy, while the addition of Mn serves as an auxiliary strengthening agent and also reduces thermal cracking and improves corrosion resistance. Through the combined addition of Mg and Mn and the design of a low Mn ratio, the tensile strength of the aluminum alloy in the core layer is significantly improved, while the corrosion resistance is appropriately enhanced.

[0029] The coating layer comprises the following components by weight percentage: Si 1.5–2.0%, Fe ≤0.45%, Cu 0.3–0.5%, Ti 0.8–1.2%, Zr 0.65–1.0%, Mg+Mn 1.5–2.0%, with Mg / Mn ratio of 4–2:1, rare earth elements 0.15–0.2%, and the remainder being Al and unavoidable impurities.

[0030] The rare earth elements in the core layer and the cladding layer respectively comprise a mixture of Ce and Nd in a mass ratio of 1:1 to 2. The rare earth elements react in the aluminum alloy to form a network of high-hardness rare earth compounds distributed at the grain boundaries. This network structure refines the crystal structure of the aluminum alloy, hinders grain boundary movement, thereby stabilizing the matrix structure, preventing deformation, and contributing to improved high-temperature resistance of the aluminum alloy, preventing thermal deformation during brazing.

[0031] Compared with the core layer, by adding a combination of Mg and Mn, reducing the proportion of Mg and increasing the proportion of Mn in the Mg and Mn combination, the coating strength is improved to a certain extent while significantly improving its corrosion resistance.

[0032] This invention, through the formulation design of the core material layer and the cladding layer, simultaneously improves the mechanical strength and corrosion resistance of both the core material layer and the cladding layer, thereby enhancing their overall strength and corrosion resistance. Furthermore, by designing a low Mn ratio in the Mg / Mn combination of the core material layer and a high Mn ratio in the Mg / Mn combination of the cladding layer, it prioritizes improving the strength of the core material layer and the corrosion resistance of the cladding layer, thus comprehensively enhancing the performance of the entire aluminum alloy composite strip and meeting the requirements for high strength and high corrosion resistance.

[0033] In addition, the addition of rare earth elements to the core layer and the cladding layer effectively improves their high-temperature resistance and prevents them from deforming due to heat during the brazing process.

[0034] The formulation design of the core layer and the cladding layer of the present invention can simultaneously improve the strength, high temperature resistance and corrosion resistance of the core layer and the cladding layer. The three aspects of performance complement each other, fundamentally improving the comprehensive performance of aluminum alloy composite plates and strips for heat exchangers.

[0035] The specific steps for preparing the aluminum alloy composite plate and strip for the above-mentioned heat exchanger are as follows:

[0036] According to the formula amount of the core material layer and the formula amount of the cladding layer, the alloy composition of the core material layer and the alloy composition of the cladding layer are respectively subjected to smelting, refining, casting, milling, hot rolling and heat treatment to obtain a core material layer with a thickness of d1 and a cladding layer with a thickness of d2, and the casting and rolling process is controlled so that d1 is 3 to 5 times d2.

[0037] The cladding layer prepared in the above steps is applied to the outside of the core material layer, welded together, and then subjected to hot rolling, primary annealing, cold rolling, and secondary annealing to obtain the aluminum alloy composite plate and strip for the heat exchanger.

[0038] The hot rolling process conditions are as follows: first, the temperature is raised to 500-550℃ at a rate of 20-30℃ / min, then held at the temperature for 30-60min, and then rolled. The thickness after hot rolling is 30-50% of the thickness before hot rolling.

[0039] The process conditions for the first annealing are: annealing temperature of 250-300℃, holding time of 5-7 hours.

[0040] The process conditions for the secondary annealing are as follows: first, the temperature is increased to 200-300℃ at a rate of 15-25℃ / min and held for 2-3 hours; then, the temperature is increased to 350-380℃ at a rate of 10-15℃ / min and held for 1-2 hours; finally, the temperature is increased to 400-420℃ at a rate of 5-10℃ / min and held for 3-5 hours.

[0041] The preparation method of this invention employs a rolling process of hot rolling followed by cold rolling. On the one hand, hot rolling utilizes the preheating from heat treatment, saving energy; on the other hand, it achieves good rolling results and high rolling efficiency. Through the design of primary and secondary annealing, especially the design of the secondary annealing process conditions, rolling stress is effectively removed, ensuring sufficient grain growth and shaping in the aluminum alloy after rolling, which helps to further improve the overall performance of the aluminum alloy composite strip.

[0042] Example 1

[0043] (1) Preparation of the core layer:

[0044] The core layer formulation includes the following components by weight percentage:

[0045] The composition is as follows: Si 0.8%, Fe 0.35%, Cu 0.6%, Ti 1.35%, Mg+Mn 1.2% with a Mg / Mn ratio of 5:1, a mixture of Ce and Nd 0.05% with a Ce to Nd mass ratio of 1:1, and the remainder being Al and unavoidable impurities.

[0046] The alloy components of the above formula were successively smelted, refined, cast into ingots, milled, hot rolled, and heat treated to obtain the core material layer. Melting was carried out in an aluminum melting furnace at a melting temperature of 730°C. After the alloy components were completely melted, the slag was removed, and then the core material was transferred to a refining furnace for refining for 30 minutes, followed by standing for 10 minutes. Then, the core material was cast into ingots, milled, and hot rolled into a core material layer with a thickness of 27 mm. The core material was then placed at 630°C for 8 hours for homogenization treatment and set aside for later use.

[0047] (2) Preparation of the coating layer:

[0048] The coating layer comprises the following components in weight percentage:

[0049] The coating consists of 1.5% Si, 0.45% Fe, 0.3% Cu, 0.8% Ti, 0.65% Zr, 1.5% Mg+Mn with a Mg / Mn ratio of 4:1, 0.15% Ce and Nd mixture with a Ce to Nd mass ratio of 1:1, and the remainder being Al and unavoidable impurities. By designing the amount of rare earth elements added to the coating layer to be greater than that added to the core layer, the high-temperature resistance of the coating layer is significantly improved, thereby strengthening the protection of the core layer.

[0050] The alloy components of the above formula were successively subjected to melting, refining, ingot casting, milling, hot rolling and heat treatment to obtain the coating layer. The melting was carried out in an aluminum melting furnace at a melting temperature of 735℃. After the alloy components were completely melted, the slag was removed, and then the mixture was transferred to a refining furnace for refining for 30 minutes, then allowed to stand for 10 minutes. The mixture was then cast into an ingot, milled, and hot rolled into a coating layer with a thickness of 9 mm. The coating layer was then placed at 630℃ for 8 hours for homogenization treatment and set aside for later use.

[0051] (3) Composite and rolling: The cladding layer prepared in step (2) is wrapped around the core material layer prepared in step (1), and welded together. Then, composite hot rolling, first annealing, cold rolling and second annealing are performed to obtain the aluminum alloy composite plate and strip for the heat exchanger.

[0052] The process conditions for composite hot rolling are as follows: heating to 500℃ at a rate of 30℃ / min, holding for 45min, and controlling the composite thickness after rolling to be 30% of the composite thickness before rolling.

[0053] The process conditions for the first annealing are: annealing temperature of 300℃ and holding time of 5 hours;

[0054] The cold rolling process conditions are: two-pass cold rolling, and the thickness after rolling is 15% of the thickness after hot rolling;

[0055] The process conditions for the secondary annealing are as follows: first, the temperature is increased to 200℃ at a rate of 15℃ / min and held at that temperature for 3 hours; then, the temperature is increased to 350℃ at a rate of 10℃ / min and held at that temperature for 2 hours; finally, the temperature is increased to 400℃ at a rate of 5℃ / min and held at that temperature for 5 hours.

[0056] Example 2

[0057] (1) Preparation of the core layer:

[0058] The core layer formulation includes the following components by weight percentage:

[0059] The composition is as follows: Si 1.2%, Fe 0.3%, Cu 0.9%, Ti 1.45%, Mg+Mn 1.5% with a Mg / Mn ratio of 3:1, a mixture of Ce and Nd 0.1% with a Ce to Nd mass ratio of 1:1, and the remainder being Al and unavoidable impurities.

[0060] The alloy components of the above formula were successively smelted, refined, cast into ingots, milled, hot rolled, and heat treated to obtain the core material layer. Melting was carried out in an aluminum melting furnace at a melting temperature of 730°C. After the alloy components were completely melted, the slag was removed, and then the core material was transferred to a refining furnace for refining for 30 minutes, followed by standing for 10 minutes. Then, the core material was cast into ingots, milled, and hot rolled into a core material layer with a thickness of 27 mm. The core material was then placed at 630°C for 8 hours for homogenization treatment and set aside for later use.

[0061] (2) Preparation of the coating layer:

[0062] The coating layer comprises the following components in weight percentage:

[0063] The composition is as follows: Si 2.0%, Fe 0.45%, Cu 0.5%, Ti 1.2%, Zr 1.0%, Mg+Mn 2.0% with a Mg / Mn ratio of 2:1, a mixture of Ce and Nd 0.2% with a Ce to Nd mass ratio of 1:1, and the remainder being Al and unavoidable impurities. By designing the amount of rare earth elements added in the coating layer to be greater than that in the core layer, the high-temperature resistance of the coating layer is significantly improved, thereby strengthening the protection of the core layer.

[0064] The alloy components of the above formula were successively subjected to melting, refining, ingot casting, milling, hot rolling and heat treatment to obtain the coating layer. The melting was carried out in an aluminum melting furnace at a melting temperature of 735℃. After the alloy components were completely melted, the slag was removed, and then the mixture was transferred to a refining furnace for refining for 30 minutes, then allowed to stand for 10 minutes. The mixture was then cast into an ingot, milled, and hot rolled into a coating layer with a thickness of 9 mm. The coating layer was then placed at 630℃ for 8 hours for homogenization treatment and set aside for later use.

[0065] (3) Composite and rolling: The cladding layer prepared in step (2) is wrapped around the core material layer prepared in step (1), and welded together. Then, composite hot rolling, first annealing, cold rolling and second annealing are performed to obtain the aluminum alloy composite plate and strip for the heat exchanger.

[0066] The process conditions for composite hot rolling are as follows: heating to 500℃ at a rate of 30℃ / min, holding at that temperature for 45min, and controlling the composite thickness after rolling to be 30% of the composite thickness before rolling.

[0067] The process conditions for the first annealing are: annealing temperature of 300℃ and holding time of 5 hours;

[0068] The cold rolling process conditions are: two-pass cold rolling, and the thickness after rolling is 15% of the thickness after hot rolling;

[0069] The process conditions for the secondary annealing are as follows: first, the temperature is increased to 200℃ at a rate of 15℃ / min and held at that temperature for 3 hours; then, the temperature is increased to 350℃ at a rate of 10℃ / min and held at that temperature for 2 hours; finally, the temperature is increased to 400℃ at a rate of 5℃ / min and held at that temperature for 5 hours.

[0070] Comparative Example 1

[0071] The difference from Example 1 is that the secondary annealing process involves placing the cold-rolled sheet directly into an annealing furnace at 400°C for 5 hours.

[0072] Comparative Example 2

[0073] The difference from Example 1 is that no Mn was added to the core layer and the coating layer.

[0074] Comparative Example 3

[0075] The difference from Example 1 is that no rare earth elements were added to the core layer and the coating layer.

[0076] The aluminum alloy composite plates prepared in Examples 1 and 2, as well as Comparative Examples 1-3, were subjected to performance tests, including tensile strength, SWAAT salt spray corrosion resistance, brazing hot deformation, and brazing cracking. The brazing conditions were: heating to 650℃ for 30 minutes, holding at that temperature for 10 minutes, with argon as the protective atmosphere. The tensile strength and SWAAT salt spray corrosion resistance were measured before brazing. The test results are shown in the table below.

[0077]

[0078]

[0079] As can be seen from the data in the table above, the aluminum alloy composite sheet and strip with the improved formula of this invention can effectively improve mechanical strength and enhance heat resistance, corrosion resistance, and other properties, resulting in excellent overall performance. Through process improvement, the microstructure can be perfected, thereby increasing the matrix strength and preventing thermal cracking.

[0080] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. An aluminum alloy composite plate / strip for a heat exchanger, characterized in that, include: The material comprises a core layer and a cladding layer; wherein the core layer comprises the following components by weight percentage: Si 0.8–1.2%, Fe ≤0.45%, Cu 0.6–0.9%, Ti 1.35–1.45%, Mg+Mn 1.0–1.5%, rare earth elements 0.05–0.1%, and the remainder being Al and unavoidable impurities; the cladding layer comprises the following components by weight percentage: Si 1.5–2.0%, Fe ≤0.45%, Cu 0.3–0.5%, Ti 0.8–1.2%, Zr 0.65–1.0%, Mg+Mn 1.5–2.0%, rare earth elements 0.15–0.2%, and the remainder being Al and unavoidable impurities; In the core material layer, the Mg / Mn ratio is 5 to 3:1; in the coating layer, the Mg / Mn ratio is 4 to 2:

1.

2. The aluminum alloy composite plate and strip for a heat exchanger according to claim 1, characterized in that, The rare earth element is at least one of Ce or Nd.

3. The aluminum alloy composite plate and strip for a heat exchanger according to claim 2, characterized in that, The rare earth element is a mixture of Ce and Nd in a mass ratio of 1:1 to 2.

4. A method for preparing an aluminum alloy composite plate / strip for a heat exchanger as described in claim 1, characterized in that, Includes the following steps: (1) Preparation of core material layer: According to the formula amount of core material layer, the alloy components of the core material layer are successively smelted, refined, cast, milled, hot rolled and heat treated to obtain the core material layer; (2) Preparation of coating layer: According to the formula amount of coating layer, the alloy components of the coating layer are successively smelted, refined, cast into ingots, milled, hot rolled and heat treated to obtain the coating layer; (3) Composite and rolling: The cladding layer prepared in step (2) is wrapped around the core material layer prepared in step (1), welded together, and then hot rolled, annealed once, cold rolled and annealed twice to obtain the aluminum alloy composite plate and strip for heat exchangers.

5. The method for preparing an aluminum alloy composite plate / strip for a heat exchanger according to claim 4, characterized in that, The thickness of the core material layer obtained in step (1) is 3 to 5 times the thickness of the coating layer prepared in step (2).

6. The method for preparing an aluminum alloy composite plate / strip for a heat exchanger according to claim 4, characterized in that, In step (3), the hot rolling process conditions are as follows: first, the temperature is raised to 500-550℃ at a rate of 20-30℃ / min, then kept at a constant temperature for 30-60min, and then rolled. The thickness after hot rolling is 30-50% of the thickness before hot rolling.

7. The method for preparing an aluminum alloy composite plate / strip for a heat exchanger according to claim 4, characterized in that, In step (3), the process conditions for the first annealing are: annealing temperature of 250-300℃ and holding time of 5-7 hours.

8. The method for preparing an aluminum alloy composite plate / strip for a heat exchanger according to claim 4, characterized in that, In step (3), the process conditions for the secondary annealing are as follows: first, the temperature is raised to 200-300℃ at a rate of 15-25℃ / min and held for 2-3 hours; then, the temperature is raised to 350-380℃ at a rate of 10-15℃ / min and held for 1-2 hours; finally, the temperature is raised to 400-420℃ at a rate of 5-10℃ / min and held for 3-5 hours.

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