Method for manufacturing heat exchanger and method for manufacturing aluminum component

Abstract

This method for manufacturing a heat exchanger (100) comprises: a step for forming a zinc layer (20) on a surface (10a) of a heat-treated aluminum alloy material (10) constituting a heat exchanger body (1); a step for performing a first heat treatment in which the heat-treated aluminum alloy material having the zinc layer formed thereon is subjected to a heat treatment at a first temperature, thereby diffusing the zinc contained in the zinc layer into the heat-treated aluminum alloy material and solutionizing the heat-treated aluminum alloy material; and a step for cooling the heat-treated aluminum alloy material after the first heat treatment.

Description

Method for manufacturing a heat exchanger and method for manufacturing an aluminum part

[0001] The present invention relates to a method for manufacturing a heat exchanger and a method for manufacturing an aluminum part, and more particularly to a method for manufacturing a heat exchanger and a method for manufacturing an aluminum part by forming a zinc diffusion layer on the surface of an aluminum alloy material.

[0002] A method for manufacturing a heat exchanger and an aluminum part by forming a zinc diffusion layer on the surface of an aluminum alloy material is known in the art, as disclosed in, for example, Japanese Patent Laid-Open Publication No. 43-22166.

[0003] The above-mentioned Japanese Patent Laid-Open No. 43-22166 discloses a method for manufacturing a corrosion-resistant aluminum alloy material, in which a metallic zinc layer is formed on the surface of the aluminum alloy material and then heated to form a zinc diffusion layer on the surface of the aluminum alloy material in order to improve corrosion resistance. In the configuration disclosed in the above-mentioned Japanese Patent Laid-Open No. 43-22166, a zinc diffusion layer is formed on the surface of a 3000 series aluminum alloy material.

[0004] Japanese Unexamined Patent Publication No. 43-22166

[0005] Although not disclosed in the above-mentioned Japanese Patent Laid-Open Publication No. 43-22166, aluminum alloy materials are used as components constituting heat exchangers. For example, when a heat exchanger is used in an aircraft, a higher mechanical strength is required compared to a heat exchanger not used in an aircraft. Therefore, high mechanical strength is also required of the aluminum alloy material. However, the 3000 series aluminum alloy material disclosed in the above-mentioned Japanese Patent Laid-Open Publication No. 43-22166 is a so-called non-heat-treatable aluminum alloy material, the mechanical strength of which cannot be improved by heat treatment. Depending on the required mechanical strength, the 3000 series aluminum alloy material can also be used as a material for heat exchangers for aircraft. On the other hand, heat-treatable aluminum alloy materials such as 6000 series can be used as a material for heat exchangers that require higher mechanical strength than heat exchangers made of 3000 series aluminum alloy materials. However, when a heat exchanger is manufactured by forming a zinc diffusion layer on a heat-treatable aluminum alloy material using the manufacturing method disclosed in JP-A-43-22166, the heat-treatable aluminum alloy material is annealed. This makes it difficult to obtain an aluminum material with high mechanical strength. Therefore, there is a need for a technology for manufacturing a heat exchanger made of a heat-treatable aluminum alloy material with high mechanical strength while forming a zinc diffusion layer to improve corrosion resistance.

[0006] The present invention has been made to solve the above-mentioned problems, and one object of the present invention is to provide a method for manufacturing a heat exchanger and a method for manufacturing an aluminum part, which are capable of manufacturing a heat exchanger made of a heat-treatable aluminum alloy material having high mechanical strength while forming a zinc diffusion layer to improve corrosion resistance.

[0007] To achieve the above object, the present inventors conducted various experiments and intensive research, and found that by performing heat treatment at a predetermined first temperature, it is possible to form a zinc diffusion layer on the surface of a heat-treatable aluminum alloy material and simultaneously perform solution treatment of the heat-treatable aluminum alloy material. Based on this finding, a method for manufacturing a heat exchanger according to a first aspect of the present invention includes the steps of: forming a zinc layer on the surface of a heat-treatable aluminum alloy material constituting a heat exchanger body; performing a first heat treatment of the heat-treatable aluminum alloy material with the zinc layer formed thereon at a first temperature, thereby diffusing zinc contained in the zinc layer into the heat-treatable aluminum alloy material and solutionizing the heat-treatable aluminum alloy material; and cooling the heat-treatable aluminum alloy material after the first heat treatment. Note that solution treatment of the heat-treatable aluminum alloy material is a process of dissolving alloy components other than aluminum contained in the heat-treatable aluminum alloy material into the aluminum base material.

[0008] A method for manufacturing a heat exchanger according to a first aspect of the present invention includes a step of performing a first heat treatment on a heat-treatable aluminum alloy material having a zinc layer formed thereon at a first temperature, thereby diffusing zinc contained in the zinc layer into the heat-treatable aluminum alloy material and solutionizing the heat-treatable aluminum alloy material. This allows for the manufacture of a heat exchanger made of a heat-treatable aluminum alloy material having high mechanical strength while forming a zinc diffusion layer to improve corrosion resistance. The inventors have confirmed in experiments described below that a heat exchanger made of a heat-treatable aluminum alloy material having high mechanical strength while forming a zinc diffusion layer to improve corrosion resistance can be manufactured. Furthermore, since a single heat treatment can be used to perform zinc diffusion treatment and solutionizing the heat-treatable aluminum alloy material, the heat exchanger manufacturing process can be simplified. The mechanical strength of the heat-treatable aluminum alloy refers to tensile strength.

[0009] In the method for manufacturing a heat exchanger according to the first aspect, preferably, in the step of performing the first heat treatment, the heat treatable aluminum alloy material having the zinc layer formed thereon is heat treated at a first temperature, so that the mechanical strength of the heat treatable aluminum alloy material after the first heat treatment becomes higher than the mechanical strength of a 3000 series O aluminum alloy material, and a zinc diffusion layer is formed, in a depth range of 100 μm from the surface of the heat treatable aluminum alloy material after the first heat treatment, such that the zinc concentration decreases as it progresses from the surface of the heat treatable aluminum alloy material in a depth direction.

[0010] Here, in a zinc diffusion layer having a concentration gradient, a portion with a high zinc concentration corrodes before a portion with a low zinc concentration. Therefore, by forming a zinc diffusion layer so that the zinc concentration is highest at the surface and decreases in the depth direction (toward the center of the heat-treatable aluminum alloy material), corrosion is more likely to progress near the surface of the heat-treatable aluminum alloy material on which the zinc diffusion layer is formed. In this case, in a heat-treatable aluminum alloy material on which a zinc diffusion layer is formed, corrosion progresses along the surface of the heat-treatable aluminum alloy material where the zinc concentration is high, rather than in the depth direction of the heat-treatable aluminum alloy material where the zinc concentration gradually decreases. Therefore, the occurrence of pitting corrosion, which is localized pitting corrosion, can be suppressed in the heat-treatable aluminum alloy material. Therefore, by performing the first heat treatment at the first temperature as described above, a zinc diffusion layer having a concentration gradient in which the zinc concentration decreases in the depth direction from the surface of the heat-treatable aluminum alloy material is formed within a depth range of 100 μm from the surface of the heat-treatable aluminum alloy material, thereby improving the corrosion resistance of the heat-treatable aluminum alloy material. Furthermore, by performing the first heat treatment at the first temperature, the mechanical strength becomes higher than that of a 3000 series O aluminum alloy material. As a result, a heat-treatable aluminum alloy material having a mechanical strength higher than that of a 3000 series O aluminum alloy material can be obtained while ensuring corrosion resistance. The zinc concentration is expressed in terms of weight percent (wt%) of zinc contained in the zinc diffusion layer.

[0011] In this case, preferably, the heat treatable aluminum alloy material is formed of a 6000 series aluminum alloy material, and the first temperature is 460° C. or higher. With this configuration, it is possible to obtain a 6000 series aluminum alloy material having high mechanical strength required for aircraft heat exchangers and the like, while forming a zinc diffusion layer to improve corrosion resistance. Note that the fact that it is possible to obtain a 6000 series aluminum alloy material having high mechanical strength required for aircraft heat exchangers and the like, while forming a zinc diffusion layer to improve corrosion resistance, has been confirmed in experiments described below by the present inventors.

[0012] In the above-mentioned heat-treatable aluminum alloy material formed of a 6000-series aluminum alloy material, the first temperature is preferably 460°C or higher and 500°C or lower. Here, if the temperature is too high when forming the zinc diffusion layer, zinc diffusion proceeds more than necessary, making it difficult to form a zinc diffusion layer with a concentration gradient that has corrosion resistance. Furthermore, if the temperature is too low when solutionizing the 6000-series aluminum alloy material, the solutionization does not proceed, making it difficult to obtain an aluminum alloy material with high mechanical strength. Therefore, the present inventors conducted experiments while changing the temperature conditions and conducted extensive studies, and found that the temperature at which a zinc diffusion layer with a concentration gradient that has corrosion resistance and an aluminum alloy material with high mechanical strength can be formed is 460°C or higher and 500°C or lower. Based on this finding, by configuring the first heat treatment to be performed at a first temperature of 460°C or higher and 500°C or lower as described above, it is possible to perform the first heat treatment at a first temperature suitable for both forming a corrosion-resistant zinc diffusion layer with a concentration gradient and ensuring the required mechanical strength. As a result, a 6000 series aluminum alloy material can be obtained that both forms a corrosion-resistant zinc diffusion layer with a concentration gradient and ensures the required mechanical strength. The fact that a 6000 series aluminum alloy material can both form a corrosion-resistant zinc diffusion layer with a concentration gradient and ensures the required mechanical strength has been confirmed in experiments conducted by the present inventors, which will be described later.

[0013] In a configuration in which heat treatment at the first temperature increases the mechanical strength of the heat-treatable aluminum alloy material after the first heat treatment compared to that of a 3000-series O aluminum alloy material and forms a zinc diffusion layer having the concentration gradient within a depth range of 100 μm from the surface of the heat-treatable aluminum alloy material after the first heat treatment, preferably, in the step of performing the first heat treatment, the heat-treatable aluminum alloy material having the zinc layer formed thereon is heat-treated at the first temperature to diffuse zinc contained in the zinc layer so that the upper limit of the zinc concentration range in the concentration gradient of the zinc diffusion layer is 0.5% or more. Here, the present inventors conducted various experiments and conducted extensive research and found that when the zinc concentration in the zinc diffusion layer is 0.5% or more, it is possible to suppress the occurrence of pitting corrosion, which is localized pitting corrosion in the aluminum alloy material. Therefore, based on this finding, diffusing zinc contained in the zinc layer so that the upper limit of the zinc concentration range in the concentration gradient of the zinc diffusion layer is 0.5% or more can suppress the occurrence of pitting corrosion in the heat-treatable aluminum alloy material. The inventors of the present invention have confirmed in experiments described below that it is possible to prevent pitting corrosion when the upper limit of the zinc concentration range in the concentration gradient of the zinc diffusion layer is 0.5% or more.

[0014] In the method for manufacturing a heat exchanger according to the first aspect, preferably, in the step of forming the zinc layer, the zinc layer is formed by immersing the heat treatable aluminum alloy material in a zinc solution. With this configuration, the zinc layer can be easily formed on the entire surface of the heat treatable aluminum alloy material by immersing the heat treatable aluminum alloy material in the zinc solution.

[0015] The method for manufacturing a heat exchanger according to the first aspect preferably further comprises, after the step of cooling the heat-treatable aluminum alloy material, a step of performing artificial aging by a second heat treatment in which the heat-treatable aluminum alloy material is heat-treated at a second temperature lower than the first temperature. By performing the artificial aging, it is possible to obtain a T6 heat-treatable aluminum alloy material having a zinc diffusion layer formed thereon to improve corrosion resistance. As a result, it is possible to easily manufacture a heat exchanger that has corrosion resistance and is required to have the high mechanical strength of T6 material.

[0016] A method for manufacturing an aluminum part according to a second aspect of the present invention includes: a step of forming a zinc layer on a surface of a heat treatable aluminum alloy material; a step of performing a first heat treatment of heat treating the heat treatable aluminum alloy material on which the zinc layer has been formed at a first temperature to diffuse zinc contained in the zinc layer into the heat treatable aluminum alloy material and to solutionize the heat treatable aluminum alloy material; and a step of cooling the heat treatable aluminum alloy material after the first heat treatment.

[0017] A method for manufacturing an aluminum part according to a second aspect of the present invention includes a step of performing a first heat treatment on a heat-treatable aluminum alloy material having a zinc layer formed thereon at a first temperature, thereby diffusing zinc contained in the zinc layer into the heat-treatable aluminum alloy material and solutionizing the heat-treatable aluminum alloy material, as described above. This allows for the manufacture of an aluminum part made of a heat-treatable aluminum alloy material that has high mechanical strength while forming a zinc diffusion layer to improve corrosion resistance, similar to the method for manufacturing a heat exchanger according to the first aspect. Furthermore, since a single heat treatment can be used to perform the zinc diffusion treatment and the solutionizing of the heat-treatable aluminum alloy material, the manufacturing process for the aluminum part can be simplified.

[0018] According to the present invention, as described above, it is possible to provide a method for manufacturing a heat exchanger and a method for manufacturing an aluminum part, which are capable of manufacturing a heat exchanger made of a heat-treatable aluminum alloy material having high mechanical strength while forming a zinc diffusion layer to improve corrosion resistance.

[0019] FIG. 1 is a schematic perspective view showing a heat exchanger according to one embodiment of the present invention. FIG. 2 is a flowchart for explaining a method for manufacturing a heat exchanger according to this embodiment. FIG. 3 is a schematic view for explaining a configuration for manufacturing an aluminum part by forming a zinc layer on the surface of an aluminum alloy material and heat treating it. FIG. 4 is a schematic view for explaining a heat-treatable aluminum alloy material on which a zinc diffusion layer has been formed. FIG. 5 is a graph showing the gradient of zinc concentration in a zinc diffusion layer according to an example. FIG. 6 is a table showing experimental results of mechanical strength of a heat-treatable aluminum alloy material after heat treatment according to an example. FIG. 7 is a table showing experimental results of mechanical strength of a heat-treatable aluminum alloy material subjected to zinc diffusion treatment and solution treatment in parallel according to an example. FIG. 8 is an experimental result showing the concentration gradient of a zinc diffusion layer of a heat-treatable aluminum alloy material according to an example.

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0021] A method for manufacturing a heat exchanger 100 according to this embodiment will be described with reference to Fig. 1. The heat exchanger 100 is an example of the "aluminum part" of the present invention.

[0022] Specifically, the heat exchanger 100 of this embodiment shown in FIG. 1 includes a heat exchanger body 1. The heat exchanger body 1 includes a core section 2. The core section 2 includes a first flow path section 3 and a second flow path section 4, through which fluids flow, and a partition plate 5 joined to the first flow path section 3 and the second flow path section 4 and separating the first flow path section 3 and the second flow path section 4. Multiple first flow path sections 3, multiple second flow path sections 4, and multiple partition plates 5 are provided and stacked in a predetermined direction (Z direction) to form the core section 2 of the heat exchanger 100. The core section 2 is a portion of the heat exchanger 100 where heat exchange between multiple fluids occurs. Specifically, the core section 2 exchanges heat between the fluids flowing through the first flow path section 3 and the second flow path section 4, respectively.

[0023] The core portion 2 has openings that serve as inlet and outlet ports for the fluid, and is configured to allow the fluid to flow through and exchange heat. The structure of the core portion 2 is not particularly limited, but in this embodiment, the core portion 2 has a plate-fin structure. In this embodiment, the core portion 2 includes side bars 6 and fin members 7. The core portion 2 has a rectangular parallelepiped shape. The fluid flowing through the core portion 2 may be a gas or a liquid.

[0024] This embodiment illustrates an example of a heat exchanger 100 that exchanges heat between two types of fluids. That is, a first fluid flows through a first flow path section 3. A second fluid different from the first fluid flows through a second flow path section 4. The first fluid and the second fluid exchange heat via a partition plate 5. Heat transfers from the relatively high-temperature fluid of the first and second fluids to the relatively low-temperature fluid. In this embodiment, at least one of the first and second fluids is a corrosive fluid, or the heat exchanger 100 itself is used in a corrosive atmosphere. This embodiment illustrates an example in which the first fluid is a liquid and the second fluid is a gas. The first fluid may include, for example, water (electrolyte). The second fluid is, for example, air. In this embodiment, the heat exchanger 100 is used, for example, in a ship or the like.

[0025] The first flow path section 3 and the second flow path section 4 that constitute the plate-fin type core section 2 both have a flat (layered) shape and extend in planar directions (X and Y directions) that intersect with the stacking direction (Z direction).

[0026] The first flow path section 3, the second flow path section 4, and the partition plate 5 are each joined and integrated by brazing to form the core section 2. End plates 8 are provided on the outermost surfaces of the core section 2 in the stacking direction (Z direction). These end plates 8 are also integrated by brazing. The partition plate 5 is usually provided between layers, that is, at the boundary between the first flow path section 3 and the second flow path section 4 excluding the outermost portions in the stacking direction.

[0027] (Method of Manufacturing Heat Exchanger) Next, a method of manufacturing the heat exchanger 100 (see FIG. 1) according to this embodiment will be described with reference to FIGS. 2 and 3. FIG.

[0028] Fig. 3(A) shows the heat treatable aluminum alloy material 10 before the zinc diffusion layer 21 (see Fig. 4) is formed. In the example shown in Fig. 3(A), the heat treatable aluminum alloy material 10 has a plate shape.

[0029] In step S1, a zinc layer 20 (see FIG. 3(B)) is formed on a surface 10a (see FIG. 3(A)) of a heat-treatable aluminum alloy material 10 (see FIG. 3(A)) constituting the heat exchanger body 1 (see FIG. 1). In this embodiment, the zinc layer 20 is formed by immersing the heat-treatable aluminum alloy material 10 in a zinc solution. The zinc solution is a solution containing zinc oxide, sodium hydroxide, etc. That is, in this embodiment, the zinc layer 20 is formed on the entire surface 10a of the heat-treatable aluminum alloy material 10 by zincate treatment.

[0030] As a result, as shown in Fig. 3(B), a zinc layer 20 is formed on the heat treatable aluminum alloy material 10. In the example shown in Fig. 3(B), for convenience, the zinc layer 20 is illustrated on only one surface 10a of the heat treatable aluminum alloy material 10, but in reality, the zinc layer 20 is formed on all surfaces 10a of the heat treatable aluminum alloy material 10. After the zinc layer 20 is formed, the surface 20a of the zinc layer 20 becomes the surface 10a of the heat treatable aluminum alloy material 10.

[0031] Next, in step S2, the heat-treatable aluminum alloy material 10 having the zinc layer 20 formed thereon is heat-treated at a first temperature, thereby performing a first heat treatment in which the zinc contained in the zinc layer 20 is diffused into the heat-treatable aluminum alloy material 10 and the heat-treatable aluminum alloy material 10 is solutionized.

[0032] As a result, as shown in Fig. 3(C), the zinc layer 20 is diffused by the first heat treatment, and a zinc diffusion layer 21 is formed. Note that, for convenience, in Fig. 3(C), the zinc diffusion layer 21 is illustrated only on one surface 10a of the heat treatable aluminum alloy material 10, but in reality, the zinc diffusion layer 21 is formed on all surfaces 10a of the heat treatable aluminum alloy material 10. Also, in Fig. 3(C) to Fig. 3(E), a range of the heat treatable aluminum alloy material 10 where the zinc diffusion layer 21 is not formed is illustrated as an aluminum alloy material portion 10b where the zinc diffusion layer 21 is not formed.

[0033] In the present embodiment, the heat treatable aluminum alloy material 10 constituting the aluminum part (heat exchanger 100) is formed from a 6000 series aluminum alloy material. Specifically, the heat treatable aluminum alloy material 10 is formed from an A6951 (JIS standard) material or an A6063 (JIS standard) material. The A651 material and the A6063 material are Al-Mg-Si based aluminum alloy materials. Therefore, by subjecting the heat treatable aluminum alloy material 10 to a first heat treatment to be solutionized, Si (silicon) and Mg (magnesium) contained in the heat treatable aluminum alloy material 10 are dissolved in Al (aluminum) which is the base material.

[0034] By heat treating the heat treatable aluminum alloy material 10 having the zinc layer 20 formed thereon at the first temperature, the mechanical strength of the heat treatable aluminum alloy material 10 after the first heat treatment becomes higher than the mechanical strength of a 3000-series O aluminum alloy material. Also, by heat treating the heat treatable aluminum alloy material 10 having the zinc layer 20 formed thereon at the first temperature, a zinc diffusion layer 21 is formed in a depth range DR of 100 μm from the surface 10 a of the heat treatable aluminum alloy material 10 after the first heat treatment (see FIG. 4 ), which has a concentration gradient such that the zinc concentration decreases as the zinc concentration increases in the depth direction from the surface 10 a of the heat treatable aluminum alloy material 10.

[0035] In step S2, the substrate is held at a first temperature for a first time. The first temperature is 460°C or higher. Preferably, the first temperature is 460°C or higher and 500°C or lower. More preferably, the first temperature is 480°C or higher and 500°C or lower. The first time is 2 hours or higher and 6 hours or lower. Preferably, the first time is 3 hours or higher and 5 hours or lower.

[0036] In this embodiment, in step S2, the heat-treatable aluminum alloy material 10 having the zinc layer 20 formed thereon is heat-treated at a first temperature, thereby diffusing the zinc contained in the zinc layer 20 so that the upper limit of the zinc concentration range in the concentration gradient of the zinc diffusion layer 21 is 0.5% or more. Also, in this embodiment, the zinc contained in the zinc layer 20 is diffused so that the lower limit of the zinc concentration in the concentration gradient of the zinc diffusion layer 21 is 0.1%. The lower limit of the zinc concentration in the concentration gradient of the zinc diffusion layer 21 is a value determined by the following experiment.

[0037] Next, in step S3, the heat treatable aluminum alloy material 10 after the first heat treatment is cooled. In the present embodiment, the heat treatable aluminum alloy material 10 after the first heat treatment is left overnight at atmospheric temperature to cool the heat treatable aluminum alloy material 10 after the first heat treatment. Note that when cooling the heat treatable aluminum alloy material 10 after the first heat treatment, it may be cooled while blowing air with a blower.

[0038] This improves the mechanical strength of the heat treatable aluminum alloy material 10, as shown in Fig. 3(D). In this embodiment, the heat treatable aluminum alloy material 10 becomes a T4 material by cooling after the first heat treatment. In the example shown in Fig. 3(D), the difference in mechanical strength of the heat treatable aluminum alloy material 10 is represented by different hatching of the aluminum alloy material portion 10b of the heat treatable aluminum alloy material 10 that does not contain zinc.

[0039] Next, in step S4, artificial aging is performed by a second heat treatment in which the heat treatable aluminum alloy material 10 is heat treated at a second temperature lower than the first temperature. In step S5, artificial aging is performed by holding the heat treatable aluminum alloy material 10 at the second temperature for a second time. In this embodiment, the second temperature is 180°C to 200°C. The second time is 1 hour to 4 hours. For example, when the second temperature is 200°C, the second time is 1 hour. Thereafter, the treatment is completed.

[0040] This further improves the mechanical strength of the heat treatable aluminum alloy material 10, as shown in Fig. 3(E). In this embodiment, artificial aging is performed to turn the heat treatable aluminum alloy material 10 into a T6 material. In the example shown in Fig. 3(E), the difference in mechanical strength of the heat treatable aluminum alloy material 10 is represented by different hatching of the aluminum alloy material portion 10b of the heat treatable aluminum alloy material 10 that does not contain zinc.

[0041] In the present embodiment, by the treatment of the above-mentioned steps S1 to S4, it is possible to manufacture a heat exchanger 100 (aluminum part) made of a heat-treatable aluminum alloy material 10 of 6000 series T6 material having a zinc diffusion layer 21 formed on a surface 10a.

[0042] Next, with reference to FIG. 4, the heat-treatable aluminum alloy material 10 manufactured by the manufacturing method of this embodiment will be described.

[0043] As shown in FIG. 4 , a zinc diffusion layer 21 is formed in the heat treatable aluminum alloy material 10. Specifically, in a depth range DR of 100 μm from the surface 10 a of the heat treatable aluminum alloy material 10, the zinc diffusion layer 21 has a concentration gradient such that the zinc concentration decreases as the zinc concentration progresses from the surface 10 a of the heat treatable aluminum alloy material 10 in the depth direction (toward the center of the heat treatable aluminum alloy material 10). In this embodiment, the zinc diffusion layer 21 is defined as a range in which the zinc concentration is 0.1% or more. In the example shown in FIG. 4 , the zinc concentration gradient is represented by different hatching patterns in the zinc diffusion layer 21. Specifically, the smaller the hatching spacing, the higher the zinc concentration, and the wider the hatching spacing, the lower the zinc concentration. That is, in the example shown in FIG. 4 , the zinc diffusion layer 21 has a concentration gradient in which the zinc concentration decreases as the zinc concentration progresses in the depth direction within the depth range DR. The depth direction is the direction from the surface 10 a of the heat treatable aluminum alloy material 10 toward the center of the heat treatable aluminum alloy material 10 .

[0044] (Effects of this embodiment) In this embodiment, the following effects can be obtained.

[0045] In this embodiment, as described above, the manufacturing method of the heat exchanger 100 includes the steps of: forming a zinc layer 20 on the surface 10a of the heat-treatable aluminum alloy material 10 constituting the heat exchanger body 1; performing a first heat treatment of the heat-treatable aluminum alloy material 10 having the zinc layer 20 formed thereon at a first temperature, thereby diffusing zinc contained in the zinc layer 20 into the heat-treatable aluminum alloy material 10 and solutionizing the heat-treatable aluminum alloy material 10; and cooling the heat-treatable aluminum alloy material 10 after the first heat treatment. This makes it possible to manufacture a heat exchanger 100 made of a heat-treatable aluminum alloy material 10 having high mechanical strength while forming a zinc diffusion layer 21 to improve corrosion resistance. Furthermore, since the zinc diffusion treatment and the solutionization of the heat-treatable aluminum alloy material 10 can be performed by a single heat treatment, the manufacturing process of the heat exchanger 100 can be simplified. The inventors of the present invention have already confirmed in experiments described below that it is possible to manufacture a heat exchanger 100 made of a heat-treatable aluminum alloy material 10 having high mechanical strength while forming a zinc diffusion layer 21 to improve corrosion resistance.

[0046] Furthermore, in the present embodiment, as described above, in the step of performing the first heat treatment, the heat treatable aluminum alloy material 10 having the zinc layer 20 formed thereon is heat treated at the first temperature, whereby the mechanical strength of the heat treatable aluminum alloy material 10 after the first heat treatment becomes higher than the mechanical strength of a 3000 series O aluminum alloy material, and a zinc diffusion layer 21 is formed, which has a concentration gradient such that the zinc concentration decreases as it progresses in the depth direction from the surface 10 a of the heat treatable aluminum alloy material 10, in a depth range DR of 100 μm from the surface 10 a of the heat treatable aluminum alloy material 10 after the first heat treatment.

[0047] Here, in the zinc diffusion layer 21 having a concentration gradient, a portion with a high zinc concentration corrodes before a portion with a low zinc concentration. Therefore, by forming the zinc diffusion layer 21 so that the zinc concentration is highest at the surface and decreases in the depth direction, corrosion is more likely to proceed near the surface 10a of the heat-treatable aluminum alloy material 10 on which the zinc diffusion layer 21 is formed. In this case, in the heat-treatable aluminum alloy material 10 on which the zinc diffusion layer 21 is formed, corrosion proceeds in a direction along the surface 10a of the heat-treatable aluminum alloy material 10 where the zinc concentration is high, rather than in the depth direction of the heat-treatable aluminum alloy material 10 where the zinc concentration gradually decreases. Therefore, it is possible to suppress the occurrence of pitting corrosion, which is localized corrosion in the form of holes, in the heat-treatable aluminum alloy material 10. Therefore, as described above, by performing the first heat treatment at the first temperature, a zinc diffusion layer 21 having a concentration gradient such that the zinc concentration decreases as the zinc concentration increases in the depth direction from the surface 10a of the heat treatable aluminum alloy material 10 is formed in a depth range DR of 100 μm from the surface 10a of the heat treatable aluminum alloy material 10, thereby improving the corrosion resistance of the heat treatable aluminum alloy material 10. Furthermore, by performing the first heat treatment at the first temperature, the mechanical strength is increased compared to that of a 3000 series O-type aluminum alloy material. As a result, a heat treatable aluminum alloy material 10 having a mechanical strength higher than that of a 3000 series O-type aluminum alloy material can be obtained while ensuring corrosion resistance.

[0048] In the present embodiment, as described above, the heat treatable aluminum alloy material 10 is made of a 6000 series aluminum alloy material, and the first temperature is 460° C. or higher. This makes it possible to form the zinc diffusion layer 21 to improve corrosion resistance, while obtaining a 6000 series aluminum alloy material having high mechanical strength required for the heat exchanger 100 for aircraft and the like. Note that the fact that it is possible to form the zinc diffusion layer 21 to improve corrosion resistance, while obtaining a 6000 series aluminum alloy material having high mechanical strength required for the heat exchanger 100 for aircraft and the like, has been confirmed in experiments to be described later by the present inventors.

[0049] Furthermore, in this embodiment, as described above, the first temperature is 460°C or higher and 500°C or lower. This allows the first heat treatment to be performed at a first temperature suitable for both forming the zinc diffusion layer 21 with a concentration gradient having corrosion resistance and ensuring the required mechanical strength. As a result, a 6000 series aluminum alloy material can be obtained that both forms the zinc diffusion layer 21 with a concentration gradient having corrosion resistance and ensuring the required mechanical strength. The fact that a 6000 series aluminum alloy material can both form the zinc diffusion layer 21 with a concentration gradient having corrosion resistance and ensuring the required mechanical strength has been confirmed in experiments conducted by the present inventors, which will be described later.

[0050] In addition, in the present embodiment, as described above, in the step of performing the first heat treatment, the heat treatable aluminum alloy material 10 having the zinc layer 20 formed thereon is heat treated at the first temperature, thereby diffusing zinc contained in the zinc layer 20 so that the upper limit value of the zinc concentration range in the concentration gradient of the zinc diffusion layer 21 is 0.5% or more. This makes it possible to suppress the occurrence of pitting corrosion in the heat treatable aluminum alloy material 10. The fact that the occurrence of pitting corrosion can be suppressed when the upper limit value of the zinc concentration range in the concentration gradient of the zinc diffusion layer 21 is 0.5% or more has been confirmed in an experiment described later by the present inventors.

[0051] In the present embodiment, as described above, in the step of forming the zinc layer 20, the heat treatable aluminum alloy material 10 is immersed in a zinc solution to form the zinc layer 20. In this way, by immersing the heat treatable aluminum alloy material 10 in the zinc solution, the zinc layer 20 can be easily formed on the entire surface 10a of the heat treatable aluminum alloy material 10.

[0052] Furthermore, in this embodiment, as described above, after the step of cooling the heat treatable aluminum alloy material 10, a step of performing artificial aging by second heat treatment of heat treating the heat treatable aluminum alloy material 10 at a second temperature lower than the first temperature is further included. In this way, by performing artificial aging, it is possible to obtain a T6 material of the heat treatable aluminum alloy material 10 in which a zinc diffusion layer 21 for improving corrosion resistance is formed. As a result, it is possible to easily manufacture a heat exchanger 100 that has corrosion resistance and is required to have the high mechanical strength of a T6 material.

[0053] [Examples (Effect Confirmation Experiments)] (Example 1: Confirmation of Corrosion Resistance) In order to confirm the effects of the above-described embodiment, the following experiment (Example 1) was conducted. First, an experiment to confirm corrosion resistance was conducted. A zinc layer 20 was formed on a heat-treatable aluminum alloy material 10, and heat treatment was performed at 460°C, thereby forming a zinc diffusion layer 21 having a concentration gradient such that the zinc concentration decreases as the zinc concentration progresses in the depth direction from the surface 10a of the heat-treatable aluminum alloy material 10 up to a depth range DR of 100 µm. Thereafter, the cross section of the heat-treatable aluminum alloy material 10 on which the zinc diffusion layer 21 was formed was measured using an EPMA (Electron Probe Micro Analyzer) to measure the zinc concentration in the zinc diffusion layer 21.

[0054] Graph G1 shown in Fig. 5 is a graph showing the measurement results of the concentration of the zinc diffusion layer 21 of the heat treatable aluminum alloy material 10. In graph G1, the horizontal axis represents the diffusion depth (µm) and the vertical axis represents the zinc concentration (%).

[0055] In the graph G1, three curves are used to indicate the zinc concentrations in three regions of the zinc diffusion layer 21 of the heat treatable aluminum alloy material 10. That is, a solid line 80, a dashed line 81, and a dash-dotted line 82 each indicate the zinc concentration of the zinc diffusion layer 21 in a corresponding region among the three regions of the zinc diffusion layer 21 of the heat treatable aluminum alloy material 10.

[0056] As shown by the solid line 80, the dashed line 81, and the dashed dotted line 82, the zinc concentration was 1.0% or more at a position where the diffusion depth was 0 (surface 10a of the heat treatable aluminum alloy material 10) in all regions of the zinc diffusion layer 21 of the heat treatable aluminum alloy material 10. Furthermore, as shown by the solid line 80, the dashed line 81, and the dashed dotted line 82, the zinc concentration was 0.5% or more at a diffusion depth of 50 μm in all regions of the zinc diffusion layer 21 of the heat treatable aluminum alloy material 10.

[0057] As shown by the solid line 80, the dashed line 81, and the dashed-dotted line 82, when the diffusion depth exceeds 100 μm, saturation occurs in the measured value of the zinc concentration. This is because the zinc concentration contained in the heat-treatable aluminum alloy material 10 becomes low, and noise reduces the signal-to-noise ratio. Therefore, in the above embodiment, the depth range DR from the surface 10a of the heat-treatable aluminum alloy material 10 to 100 μm is defined as the zinc diffusion layer 21, and the lower limit of the zinc concentration in the concentration gradient of the zinc diffusion layer 21 is set to 0.1%.

[0058] A heat exchanger 100 manufactured using an aluminum part having a zinc diffusion layer 21 with a concentration gradient as shown in graph G1 was actually operated to confirm the corrosion state and thickness of the zinc diffusion layer 21. Specifically, a heat exchanger 100 manufactured using a heat-treatable aluminum alloy material 10 having a zinc diffusion layer 21 with a concentration gradient as shown in graph G1 was operated for a predetermined period of time, and the corrosion state and thickness of the zinc diffusion layer 21 were confirmed. In the heat exchanger 100, there were some locations where the thickness of the zinc diffusion layer 21 was reduced to approximately half (50 μm), but no pitting corrosion occurred. In other words, it was confirmed that the zinc diffusion layer 21 still maintained corrosion resistance even when its thickness was reduced to approximately half (50 μm). This confirmed that the upper limit of the zinc concentration range in the concentration gradient of the zinc diffusion layer 21 is preferably 0.5% or more.

[0059] (Example 2: Confirmation of mechanical strength after heat treatment by changing temperature) Next, as shown in Fig. 6 , an experiment (Example 2) was conducted in which the temperature during heat treatment was changed to confirm the mechanical strength of the heat-treatable aluminum alloy material 10 after the heat treatment. That is, in the example shown in Fig. 6 , in order to confirm the effect of temperature during solution treatment, heat treatment was performed at a plurality of temperatures without forming a zinc layer 20 on the surface 10a of the heat-treatable aluminum alloy material 10. In the example shown in Fig. 6 , the experiment was conducted on A6951 material and A6063 material as the heat-treatable aluminum alloy material 10.

[0060] As shown in Table T1 of Fig. 6, the A6951 material was subjected to heat treatment for 4 hours at temperatures of 460°C (Example 2-1), 470°C (Example 2-2), and 500°C (Example 2-3), and then the mechanical strength of each heat treatable aluminum alloy material 10 was measured. In addition, the A6063 material was subjected to heat treatment for 4 hours at a temperature of 500°C, and then the mechanical strength of the heat treatable aluminum alloy material 10 was measured.

[0061] As shown in Table T1, the mechanical strength of the A6951 material of Example 2-1, which was heat treated at 460°C for 4 hours, was 147 (MPa). The mechanical strength of the A6951 material of Example 2-2, which was heat treated at 470°C for 4 hours, was 147 (MPa). The mechanical strength of the A6951 material of Example 2-3, which was heat treated at 500°C for 4 hours, was 255 (MPa). The mechanical strength of the A6063 material of Example 2-3, which was heat treated at 500°C for 4 hours, was 250 (MPa).

[0062] The mechanical strength of each of the heat treatable aluminum alloy materials 10 according to Example 2-1, Example 2-2, and Example 2-3 shown in Table T1 was higher than the mechanical strength of the O material of A3003 (JIS standard) material in "JIS H4100," which is "95 or more and 135 or less." Therefore, as a result of performing heat treatment on the heat treatable aluminum alloy material 10 at a temperature of 460°C or more and 500°C or less, it was confirmed that the mechanical strength of the heat treatable aluminum alloy material 10 after the heat treatment was higher than the mechanical strength of the O material of 3000 series (A3003 material). In other words, even when the first temperature was 460°C or more and 500°C or less, it was confirmed that the mechanical strength of the heat treatable aluminum alloy material 10 after the heat treatment at the first temperature was higher than the mechanical strength of the O material of 3000 series.

[0063] (Example 3: Confirmation of mechanical strength when zinc diffusion and solution treatment are performed in parallel) Table T2 shown in Fig. 7 shows the mechanical strength of the heat treatable aluminum alloy material 10 according to Example 3 after the first heat treatment was performed on the heat treatable aluminum alloy material 10 after the zinc layer 20 was formed. That is, in Example 3, the table shows the mechanical strength of each of the heat treatable aluminum alloy materials 10 after the A6951 material (Example 3-1) and the A6063 material (Example 3-2) were heat treated under the conditions that the first temperature was 500°C and the first time was 4 hours.

[0064] After heat treatment under the conditions of a first temperature of 500°C and a first time of 4 hours, the mechanical strength of the A6951 material (Example 3-1) was 270 (MPa), and the mechanical strength of the A6063 material (Example 3-2) was 220 (MPa). That is, as a result of performing heat treatment at the first temperature on the heat treatable aluminum alloy material 10 after the zinc layer 20 was formed, it was confirmed that the mechanical strength of the heat treatable aluminum alloy material 10 according to Example 3 after the first heat treatment was higher than the mechanical strength of the 3000 series O material. Therefore, even when the heat treatable aluminum alloy material 10 after the zinc layer 20 was heat treated at the first temperature (500°C), it was confirmed that the tendency of the mechanical strength of the heat treatable aluminum alloy material 10 after the heat treatment did not change, as shown in Table T1 of FIG. 6 .

[0065] 8 is a graph showing a measurement result of the concentration of the zinc diffusion layer 21 according to Example 4 after the heat-treatable aluminum alloy material 10 having the zinc layer 20 formed thereon was subjected to a first heat treatment at 500°C for 4 hours. In the graph G2, the horizontal axis represents the diffusion depth (μm) and the vertical axis represents the zinc concentration (%).

[0066] As shown in graph G2, the zinc concentration was measured at five locations in total, at intervals of 10 μm, in the zinc diffusion layer 21 of Example 4, within the diffusion depth range of 0 μm to 40 μm. Each measurement result of the zinc concentration of the zinc diffusion layer 21 is shown by plot 83.

[0067] As shown in graph G2, it was confirmed that the concentration of the zinc diffusion layer 21 according to Example 4 after the heat treatable aluminum alloy material 10 having the zinc layer 20 formed thereon was 0.5% or more even at a diffusion depth of 40 μm after the first heat treatment under conditions of 500°C and 4 hours. Furthermore, as shown in the approximation curve 84 based on the plots 83, it can be estimated that the zinc concentration exceeds 0.2% in the zinc diffusion layer 21 having a diffusion depth of 100 μm. Therefore, it was confirmed that, as a result of the first heat treatment under conditions of 500°C and 4 hours of the heat treatable aluminum alloy material 10 having the zinc layer 20 formed thereon, a zinc diffusion layer 21 having a concentration gradient capable of ensuring corrosion resistance was formed in the heat treatable aluminum alloy material 10.

[0068] Therefore, it was confirmed from Table T2 shown in Fig. 7 and Graph G2 shown in Fig. 8 that the temperature at which the zinc diffusion layer 21 having a concentration gradient and having corrosion resistance can be formed and the temperature at which the heat treatable aluminum alloy material 10 can be solutionized so as to have high mechanical strength are 460°C or higher and 500°C or lower. In other words, it was confirmed that by performing the first heat treatment at the first temperature of 460°C or higher and 500°C or lower on the heat treatable aluminum alloy material 10 after the zinc layer 20 is formed, it is possible to form the zinc diffusion layer 21 to improve corrosion resistance and to manufacture a heat exchanger 100 constituted by the heat treatable aluminum alloy material 10 having high mechanical strength.

[0069] [Modifications] The embodiments and examples disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the description of the embodiments and examples above, and further includes all modifications (modifications) within the meaning and scope equivalent to the claims.

[0070] For example, in the above embodiment, an example of a method for manufacturing a heat exchanger 100 in which the first flow path portion 3, the second flow path portion 4, and the partition plate 5 are stacked and used in a ship or the like is shown, but the present invention is not limited to this. The present invention may be applied to the manufacture of a surface cooler for an aircraft engine, for example, as long as the heat exchanger is manufactured by performing a first heat treatment at a first temperature on the heat-treatable aluminum alloy material 10 after the zinc layer 20 is formed.

[0071] In the above embodiment, the heat treatable aluminum alloy material 10 is formed from a 6000 series aluminum alloy material, but the present invention is not limited to this. In the present invention, the heat treatable aluminum alloy material 10 may be formed from any one of a 2000 series, a 4000 series, and a 7000 series aluminum alloy material, for example.

[0072] In the above embodiment, an example of a configuration in which the upper limit of the zinc concentration range in the concentration gradient of the zinc diffusion layer 21 is 0.5% or more has been shown, but the present invention is not limited to this. For example, the upper limit of the zinc concentration range in the concentration gradient of the zinc diffusion layer 21 may be a value lower than 0.5% as long as it is a concentration at which pitting corrosion, which is localized pitting corrosion, does not occur in the heat treatable aluminum alloy material 10. However, in order to more reliably suppress the occurrence of pitting corrosion, which is localized pitting corrosion, in the heat treatable aluminum alloy material 10, the upper limit of the zinc concentration range in the concentration gradient of the zinc diffusion layer 21 is preferably 0.5% or more.

[0073] In the above embodiment, an example of a configuration in which the heat treatable aluminum alloy material 10 is immersed in a zinc solution in the configuration in which the zinc layer 20 is formed has been shown, but the present invention is not limited to this. For example, the zinc layer 20 may be formed by vapor-depositing zinc on the surface 10a of the heat treatable aluminum alloy material 10. Any method may be used as long as it is possible to form the zinc layer 20 on the surface 10a of the heat treatable aluminum alloy material 10.

[0074] In the above embodiment, an example of a configuration in which artificial aging is performed after cooling the heat treatable aluminum alloy material 10 after the first heat treatment has been shown, but the present invention is not limited to this. For example, in the present invention, artificial aging does not necessarily have to be performed.

[0075] In addition, in the above embodiment, the method for manufacturing the heat exchanger 100 has been described as an example of a method for manufacturing an aluminum part, but the present invention is not limited to this. The present invention may also be applied to a method for manufacturing an aluminum part other than the heat exchanger 100.

[0076] Reference Signs List 1 Heat exchanger body 10 Heat-treatable aluminum alloy material 10a Surface of heat-treatable aluminum alloy material 20 Zinc layer 21 Zinc diffusion layer 100 Heat exchanger

Claims

1. A method for manufacturing a heat exchanger, comprising: a step of forming a zinc layer on the surface of a heat-treatable aluminum alloy material constituting a heat exchanger body; a step of performing a first heat treatment on the heat-treatable aluminum alloy material on which the zinc layer has been formed at a first temperature, thereby diffusing zinc contained in the zinc layer into the heat-treatable aluminum alloy material and solutionizing the heat-treatable aluminum alloy material; and a step of cooling the heat-treatable aluminum alloy material after the first heat treatment.

2. A method for manufacturing a heat exchanger according to claim 1, wherein in the step of performing the first heat treatment, the heat-treatable aluminum alloy material having the zinc layer formed thereon is heat-treated at the first temperature, so that the mechanical strength of the heat-treatable aluminum alloy material after the first heat treatment becomes higher than the mechanical strength of a 3000-series O-type aluminum alloy material, and a zinc diffusion layer is formed in a depth range of 100 μm from the surface of the heat-treatable aluminum alloy material after the first heat treatment, the zinc concentration of which becomes lower as the zinc concentration increases in the depth direction from the surface of the heat-treatable aluminum alloy material.

3. The method for manufacturing a heat exchanger according to claim 2, wherein the heat-treatable aluminum alloy material is made of a 6000 series aluminum alloy material, and the first temperature is 460°C or higher.

4. A method for manufacturing a heat exchanger according to claim 3, wherein the first temperature is 460°C or higher and 500°C or lower.

5. A method for manufacturing a heat exchanger as described in claim 2, wherein in the step of performing the first heat treatment, the heat-treatable aluminum alloy material having the zinc layer formed thereon is heat-treated at the first temperature, thereby diffusing the zinc contained in the zinc layer so that the upper limit of the zinc concentration range in the concentration gradient of the zinc diffusion layer is 0.5% or more.

6. A method for manufacturing a heat exchanger according to claim 1, wherein in the step of forming the zinc layer, the zinc layer is formed by immersing the heat-treatable aluminum alloy material in a zinc solution.

7. The method for manufacturing a heat exchanger according to claim 1, further comprising, after the step of cooling the heat-treatable aluminum alloy material, a step of performing artificial aging by a second heat treatment in which the heat-treatable aluminum alloy material is heat-treated at a second temperature lower than the first temperature.

8. A method for manufacturing an aluminum part, comprising: a step of forming a zinc layer on a surface of a heat-treatable aluminum alloy material; a step of performing a first heat treatment on the heat-treatable aluminum alloy material on which the zinc layer has been formed at a first temperature, thereby diffusing zinc contained in the zinc layer into the heat-treatable aluminum alloy material and solutionizing the heat-treatable aluminum alloy material; and a step of cooling the heat-treatable aluminum alloy material after the first heat treatment.

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