JP2024082528A - Manufacturing method of brazing joined body - Google Patents

Abstract

To provide a manufacturing method of a brazing joined body, simplifying brazing treatment and improving brazability.SOLUTION: A manufacturing method of a brazing joined body, including a plurality of first members includes the steps of: performing chemical treatment on the first members having core materials, and brazing material layers disposed on the one surface or both surfaces of the core materials by an aqueous solution containing oxo acid as inorganic acid; performing washing treatment by pure water on the first members after the chemical treatment; and brazing the first members each other by performing brazing treatment without using a flux in a state of surrounding the brazing material layers of the first members after the washing treatment with screens under an inert gas atmosphere. The manufacturing method of the brazing joined body is such that: the brazing material layer contains 9.0-15.0 mass% of Si, 0.25-1.5 mass% of Mg, and 0.02 mass% or more of Bi, and comprises an aluminum alloy comprising balance aluminum and inevitable impurities; an average Feret's particle diameter of Si of the brazing material layer in the step of performing the chemical treatment is 3.5 μm or less; and electric conductivity of pure water used in the step of performing the washing treatment is 30 μS/m or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a solder joint.

For example, in various technical fields such as automotive parts, brazing is used to join multiple components. Brazing is broadly divided into (a) the CAB method (Control Atomsphere Brazing), which uses an inert gas (nitrogen, argon, etc.) and a fluoride-based flux under atmospheric pressure, and (b) the VB method (Vacuum Brazing), which uses no flux under high vacuum.

The CAB method, which is carried out under atmospheric pressure, requires the installation of a large-scale flux application process and measures to protect the working environment against flux dust. In addition, issues include the impact on the quality of brazed products, such as variations in brazing performance due to uneven flux application and appearance due to flux residue.

On the other hand, while the VB method does not cause problems related to flux, it is not suitable for mass production because it requires batch processing in a vacuum furnace, and the equipment tends to be expensive. For this reason, there has been a demand for a method that allows for simple brazing processing in the VB method without using a vacuum furnace.

For this reason, Patent Document 1 (JP Patent Publication No. 2017-505231) discloses a method for using an aluminum composite material in a thermal bonding method, the aluminum composite material being composed of an aluminum core alloy and an outer brazing layer, in which the aluminum brazing layer has an acid-washed surface, the aluminum composite material is used in a flux-free thermal bonding method, and the bonding method is carried out in the presence of a protective gas.

Patent Document 2 (JP 2020-15095 A) discloses a method for producing an aluminum composite material in which a core layer made of an aluminum core alloy is provided and an outer brazing layer made of an aluminum brazing alloy is bonded to one or both sides of the core layer, in which the aluminum brazing alloy has a specific composition and the aluminum composite material is washed with an alkaline or acid washing aqueous solution.

Patent Document 3 (JP Patent Publication 2021-122849A) discloses a method for brazing a heat exchanger in which multiple core plates formed into a shape with a tapered portion on the periphery using an aluminum alloy brazing sheet containing Mg are stacked so that the tapered portions are in contact with each other, the stack of core plates is surrounded by a screen, and the stack is heated and brazed in an inert gas atmosphere.

Patent Document 4 (JP Patent Publication 2021-122850A) discloses a brazing method in which a brazing sheet of three or more layers is used for brazing in an inert gas atmosphere without the need for flux, in which at least one surface of a core material is clad with an outermost brazing material layer via an intermediate layer, and the core material, intermediate layer, and brazing material layer are each made of an aluminum alloy having a specific composition, and the brazing sheet is laminated to assemble the heat exchange part of the heat exchanger, and then the portions of the plates that overlap each other during the lamination are brazed and joined.

JP 2017-505231 A JP 2020-15095 A JP 2021-122849 A JP 2021-122850 A

The methods of Patent Documents 1 to 4 have room for further improvement in terms of simplification of the brazing process and brazeability.
The present invention has been made in view of the above-mentioned problems, and has an object to provide a method for manufacturing a brazed joint having improved brazing properties and simplified brazing processing by performing brazing without using a flux or a vacuum furnace.

In order to solve the above problems, a method for producing a brazed joint according to the present invention is a method for producing a brazed joint including a plurality of first members, the method comprising the steps of:
A step of subjecting the first member having a core material and a brazing material layer provided on one or both sides of the core material to a chemical treatment using an aqueous solution containing an oxo acid, which is an inorganic acid;
performing a cleaning process with pure water on the first member after the chemical treatment;
performing a brazing process without using a flux in an inert gas atmosphere while the brazing material layer of the first member after the cleaning process is surrounded by a screen, thereby brazing and joining the first members together;
having
the brazing material layer is made of an aluminum alloy containing 9.0 to 15.0 mass% Si, 0.25 to 1.5 mass% Mg, and 0.02 mass% or more Bi, with the remainder being aluminum and unavoidable impurities;
The average Feret grain size of Si in the brazing material layer in the step of performing the chemical treatment is 3.5 μm or less,
The electrical conductivity of the pure water used in the cleaning process is 30 μS/m or less.

According to this aspect, the step of chemically treating with an aqueous solution containing an oxo acid, which is an inorganic acid, can easily and effectively remove impurities such as an aluminum oxide film formed on the surface of the brazing material layer, dust, dirt, and oil, and can make the surface of the brazing material layer clean. Next, in the step of performing a cleaning process, the aqueous solution containing an oxo acid remaining on the surface of the brazing material layer is removed with pure water. After this, in the brazing and joining step, the brazing process is performed on the first members without using a flux while the brazing material layer of the first member after the cleaning process is surrounded by a screen, thereby brazing the first members together. At this time, the brazing process can be simplified by performing the brazing process under an inert gas atmosphere without using a flux and without using a vacuum furnace. Since the brazing material layer contains 0.25 to 1.5 mass % of Mg, the aluminum oxide film remaining on the surface of the brazing material layer and adversely affecting the brazing process can be effectively removed. In addition, by performing the brazing process while the brazing layer of the first member is surrounded by a screen, an effective amount of Mg evaporated from the brazing layer during the brazing process remains near the surface of the brazing layer, capturing components that may inhibit brazing, such as O ₂ and H ₂ O, and thus brazing can be performed effectively. As a result, the brazing property can be improved. Furthermore, since the average Feret particle size of Si in the brazing layer in the chemical treatment process is 3.5 μm or less, the flowability of the brazing layer during the brazing process can be improved, and the brazing property can be improved. Since the electrical conductivity of the pure water used in the cleaning process is 30 μS/m or less, the pure water contains few impurities, and therefore the surface of the brazing layer can be effectively kept clean after the cleaning process.

The method for producing a brazed joint according to the present invention may further include at least one step selected from the group consisting of the following steps (a) and (b).
(a) forming a first component prior to performing a chemical treatment;
(b) A step of shaping the first member between the step of performing the cleaning treatment and the step of soldering. According to this aspect, by having step (a), step (b), or both steps (a) and (b), it is possible to obtain a soldered body having a desired shape by molding the first member into a desired shape.

The inorganic oxoacid is at least one acid selected from the group consisting of nitric acid, sulfuric acid, and phosphoric acid, and in the step of performing chemical treatment, the first member may be immersed in a liquid tank containing an aqueous solution containing an oxoacid whose pH is adjusted to -0.5 to 2.5 and whose liquid temperature is adjusted to 55°C to 85°C. According to this aspect, by using at least one acid selected from the group consisting of nitric acid, sulfuric acid, and phosphoric acid as the oxoacid, it becomes easy to obtain and prepare an aqueous solution containing an oxoacid, and since these acids have high oxidizing power, the surface of the brazing material layer can be effectively cleaned. In addition, by immersing the first member in a liquid tank containing an aqueous solution containing an oxoacid whose pH is adjusted to -0.5 to 2.5 and whose liquid temperature is adjusted to 55°C to 85°C, the surface of the brazing material layer can be effectively chemically treated to make the surface of the brazing material layer cleaner.

In the chemical treatment step, the surface potential (SHE: standard hydrogen electrode) of the brazing material layer may be adjusted to a range of -1100 mV to -850 mV. According to this embodiment, the strong aluminum oxide and magnesium oxide films formed on the surface of the brazing material layer during rolling are removed, leaving only the natural aluminum oxide film that is reformed after the chemical treatment, making it easier to destroy the oxide film due to the diffusion and evaporation of magnesium inside the brazing material, and further improving brazing properties.

The aluminum alloy may further contain at least one element selected from the group consisting of Na, Sr, Sb, and P in a total amount of 0.01 mass% or more. According to this embodiment, the brazeability can be further improved.

The first member may further have an intermediate layer between the core material and the brazing material layer, and the brazing material layer or the intermediate layer may contain at least one element selected from the group consisting of Zn and Na. According to this embodiment, it is possible to promote the destruction of the aluminum oxide film present on the surface of the brazing layer, and improve the fillet formation rate.

In the brazing step, the first member may be brazed to the second member. According to this aspect, a brazed body having a desired shape and including the first and second members can be obtained.

It is possible to provide a method for manufacturing a brazed joint that simplifies the brazing process and improves brazing properties.

3 is a flowchart showing a method for manufacturing a brazed joint according to an embodiment of the present invention. 1 is a cross-sectional view showing a first member used in a method for manufacturing a brazed joint according to an embodiment of the present invention. 3 is a cross-sectional view showing a brazing step in a method for producing a brazed body according to an embodiment of the present invention. FIG. 1 is a perspective view showing a heat exchanger including a brazed joint obtained by a method for producing a brazed joint according to an embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described. The embodiment of the present invention is a method for manufacturing a brazed joint having a plurality of first members, which includes a step of performing a chemical treatment on the first members having a core material and a brazing material layer provided on one or both sides of the core material with an aqueous solution containing an oxo acid, which is an inorganic acid, a step of performing a cleaning treatment on the first members after the chemical treatment with pure water, and a step of performing a brazing treatment without using a flux in an inert gas atmosphere with the brazing material layer of the first members after the cleaning treatment surrounded by a screen, thereby brazing the first members together. The brazing material layer of the first members is made of an aluminum alloy containing 9.0 to 15.0 mass% Si, 0.25 to 1.5 mass% Mg, and 0.02 mass% or more Bi, with the balance being aluminum and unavoidable impurities, and the average Feret's particle size of Si in the brazing material layer in the step of performing the chemical treatment is 3.5 μm or less, and the electrical conductivity of the pure water used in the step of performing the cleaning treatment is 30 μS/m or less. The term "oxo acid" refers to an inorganic acid that has an oxygen atom, at least one hydrogen atom bonded to the oxygen atom, and at least one other portion (one or more atoms, groups, main chains, etc.) and generates a conjugate base by releasing a hydrogen ion (proton). The term "average Feret particle size of Si in the brazing layer" refers to the average particle size measured as the longest distance between two parallel straight lines in the rolling direction in the Si on the brazing layer surface when performing a chemical treatment process. The "average Feret particle size of Si in the brazing layer" can be calculated as the average value of the Feret particle size of Si of 1 μm or more by measuring the brazing layer of a sample for observation that has been mirror-polished and coated with osmium in a range of ⁴⁸⁰⁰ μm2 using a field emission scanning electron microscope (FE-SEM) manufactured by Hitachi High-Technologies Corporation as a sample cross section. The Feret particle size does not depend on the rolling direction, so it was observed in the cross section in the rolling direction.

Figure 1 is a flowchart showing a method for manufacturing a brazed joint according to an embodiment of the present invention. Below, the method for manufacturing a brazed joint according to an embodiment of the present invention will be described with reference to the flowchart in Figure 1. First, as shown in Figure 1, a chemical treatment is performed on a plurality of first members having a core material and a brazing material layer provided on one or both sides of the core material using an aqueous solution containing an oxoacid, which is an inorganic acid (S1 in Figure 1). This chemical treatment process easily and effectively removes impurities such as aluminum oxide film formed on the surface of the brazing material layer, dust, dirt, and oil, and makes the surface of the brazing material layer clean.

The oxoacid is at least one acid selected from the group consisting of nitric acid, sulfuric acid, and phosphoric acid, and in the chemical treatment step, it is preferable that the first member is immersed in a liquid tank containing an aqueous solution containing an oxoacid whose pH is adjusted to -0.5 to 2.5 and whose liquid temperature is adjusted to 55°C to 85°C. An aqueous solution containing at least one acid selected from the group consisting of nitric acid, sulfuric acid, and phosphoric acid is easy to obtain and handle, so that the chemical treatment step can be simplified, and these acids have high oxidizing power so that the surface of the brazing material layer can be effectively cleaned. In addition, by immersing the first member in a liquid tank containing an aqueous solution containing an oxoacid whose pH is adjusted to -0.5 to 2.5 and whose liquid temperature is adjusted to 55°C to 85°C, the chemical treatment can be effectively performed to make the surface of the brazing material layer cleaner. The concentration of the oxoacid in the aqueous solution containing the oxoacid is preferably 5 g/L to 300 g/L, more preferably 10 g/L to 200 g/L, and even more preferably 50 g/L to 150 g/L. The pH of the aqueous solution containing the oxoacid is more preferably 0 to 1.0, and even more preferably 0.3 to 0.7. The liquid temperature of the aqueous oxoacid solution is more preferably 60°C to 80°C, and even more preferably 70°C to 80°C.

In the chemical treatment process, the surface potential (SHE: standard hydrogen electrode) of the brazing material layer is preferably adjusted to the range of -1100mV to -850mV. By having the brazing material layer have such a surface potential, the strong aluminum oxide and magnesium oxide film formed on the surface of the brazing material layer during rolling is removed, leaving only the natural aluminum oxide film that is reformed after the chemical treatment, making it easier to destroy the oxide film due to the diffusion and evaporation of magnesium inside the brazing material, and further improving brazing properties. The surface potential (SHE: standard hydrogen electrode) of the brazing material layer is more preferably -1000mV to -875mV, and even more preferably -950mV to -900mV. The surface potential (SHE: standard hydrogen electrode) of the brazing material layer can be measured using a potentiostat with a silver-silver chloride electrode as the reference electrode, a platinum plate electrode as the auxiliary electrode, and a 5% by weight NaCl aqueous solution at 23°C.

There are a plurality of first members used in the manufacturing method of the brazed joint according to the embodiment of the present invention, and the first members have at least a core material and a brazing material layer provided as an outermost layer on one or both sides of the core material, and may further have layers other than the core material and the brazing material layer. FIG. 2 is a cross-sectional view showing an example of a first member used in the manufacturing method of the brazed joint according to the embodiment of the present invention. In the first member shown in FIG. 2, a brazing material layer 21 is provided as the outermost layer on one side of the core material 23 with an intermediate layer 22 interposed therebetween. The intermediate layer 22 serves as a sacrificial layer for suppressing corrosion of the core material 23. In addition, a brazing material layer 24 is provided as the outermost layer on the other side of the core material 23. The brazing layers 21 and 24 are made of an aluminum alloy having a melting point lower than that of the core material 23. The composition of the aluminum alloy of the brazing layer 21 and the composition of the aluminum alloy of the brazing layer 24 may be the same or different, but both brazing layers 21 and 24 are made of an aluminum alloy containing 9.0 to 15.0 mass% Si, 0.25 to 1.5 mass% Mg, 0.02 mass% or more Bi, with the remainder being aluminum and unavoidable impurities. In addition, although FIG. 2 shows an embodiment in which the brazing layers 21 and 24 are provided on both sides of the core material as the outermost layers, the brazing layers may be provided as the outermost layer only on one side of the core material. The multiple first members may have different aluminum alloy compositions or the same aluminum alloy composition.

The brazing material layer is made of an aluminum alloy containing 9.0 to 15.0 mass% Si, 0.25 to 1.5 mass% Mg, 0.02 mass% or more Bi, the remainder being aluminum and unavoidable impurities. When the brazing material layers are provided on both sides of the core material, the aluminum alloy constituting each brazing material layer must satisfy the composition of 9.0 to 15.0 mass% Si, 0.25 to 1.5 mass% Mg, 0.02 mass% or more Bi, the remainder being aluminum and unavoidable impurities. The content of Si in the aluminum alloy is preferably 10 mass% to 14 mass%, more preferably 10 mass% to 12.5 mass%. By having the content of Si in the aluminum alloy within the above range, the melting point of the aluminum alloy can be lowered. The content of Mg in the aluminum alloy is preferably 0.5 mass% to 1.0 mass%, more preferably 0.5 mass% to 0.8 mass%. By the content of Mg in the aluminum alloy being within the above range, Mg diffused from the brazing material layer to the surface destroys the aluminum oxide film on the surface, facilitating the flow of the brazing material, and the evaporated Mg effectively stays near the surface of the brazing material layer, capturing components such as O ₂ and H ₂ O that may inhibit brazing, thereby enabling effective brazing. The content of Bi in the aluminum alloy is preferably 0.05 mass% or more, more preferably 0.1 mass% or more. If the content of Bi is 0.5 mass% or more, the effect is saturated. By the content of Bi in the aluminum alloy being within the above range, Bi moves to the brazing material layer by thermal diffusion during the brazing process, the flowability of the molten brazing material is improved, and the brazing property is stabilized, and the fillet formation rate and airtightness can be improved.

The average Feret particle size of the Si in the brazing material layer during the chemical treatment process is 3.5 μm or less, preferably 3.2 μm or less, and more preferably 3.0 μm or less. By having the average Feret particle size of the Si in the brazing material layer during the chemical treatment process within the above range, the fluidity of the brazing material layer during the brazing process can be effectively improved, thereby improving brazing properties.

The brazing material layer may contain elements other than Si, Mg, Bi, aluminum, and unavoidable impurities. In this case, the brazing material layer is made of an aluminum alloy containing 9.0 to 15.0 mass% Si, 0.25 to 1.5 mass% Mg, 0.02 mass% or more Bi, optional elements, and the remainder being aluminum and unavoidable impurities. It is preferable that the aluminum alloy contains at least one element selected from the group consisting of Na, Sr, Sb, and P in a total amount of 0.01 mass% or more as an optional element. According to this embodiment, it is possible to promote the destruction of the aluminum oxide film and improve the fillet formation rate.

The first member may further have an intermediate layer between the core material and the brazing material layer, and the brazing material layer or the intermediate layer may contain at least one element selected from the group consisting of Zn and Na. This can promote the destruction of the aluminum oxide film present on the surface of the brazing layer, thereby improving the fillet formation rate.

The core material is preferably made of an aluminum alloy, and although there are no particular limitations on the composition of the aluminum alloy that constitutes the core material, it is preferable that the aluminum alloy contains at least one element selected from the group consisting of 0.20 to 1.0 mass% Cu, 0.8 to 1.8 mass% Mn, and 0.25 to 1.5 mass% Mg, with the remainder being aluminum and unavoidable impurities.

The intermediate layer is preferably made of an aluminum alloy, and although there are no particular limitations on the composition of the aluminum alloy that constitutes the intermediate layer, it is preferable that the intermediate layer contains 0.20 mass% or less of Si, 0.20 mass% or less of Fe, 0.10 mass% or less of Cu, 0.10 mass% or less of Mn, and 0.10 mass% or less of Cr, with the remainder being aluminum and unavoidable impurities.

The first member can be manufactured, for example, by forming an aluminum alloy ingot in which the elemental components of the core material, intermediate layer, and brazing material layer are adjusted to predetermined contents, and then homogenizing the aluminum alloy, hot rolling, and cold rolling the aluminum alloy, and then integrating the core material, intermediate layer, and brazing material layer.

The brazing step may further include brazing the first member to the second member. The second member may or may not have a brazing material layer. The second member may or may not be formed into a predetermined shape. The second member may also be multiple members.

Next, after the step of performing the chemical treatment, the first member after the chemical treatment is subjected to a cleaning treatment with pure water (S2 in FIG. 1). In this step, the aqueous solution containing oxoacid remaining on the surface of the brazing material layer is removed by the pure water. The electrical conductivity of the pure water used in the cleaning treatment step is 30 μS/m or less. Since the electrical conductivity of the pure water is 30 μS/m or less, the amount of impurities in the pure water is small, so that the surface of the brazing material layer can be kept clean after the cleaning treatment. The electrical conductivity of the pure water is preferably 5 μS/m or less, and more preferably 1 μS/m or less. The electrical conductivity of the pure water is measured at 23° C. using a conductivity meter. The specific method of the cleaning treatment is not particularly limited, and examples include a method of immersing the first member in a pure water bath and leaving it still, a method of performing ultrasonic cleaning while the first member is immersed in a pure water bath, and a method of running pure water over the surface of the first member. However, a method of performing ultrasonic cleaning while the first member is immersed in a pure water bath is preferred.

Next, the brazing process is performed on the first member without using flux in an inert gas atmosphere with the brazing layer of the first member after the cleaning process surrounded by a screen, thereby brazing the first members together (S3 in FIG. 1). At this time, the brazing process can be simplified by performing brazing under an inert gas atmosphere without using flux and without using a vacuum furnace. Since the brazing layer contains 0.25 to 1.5 mass % Mg, the aluminum oxide film remaining on the surface of the brazing layer can be effectively removed. In addition, by performing the brazing process with the brazing layer of the first member surrounded by a screen, an effective amount of Mg evaporated from the brazing layer remains near the brazing layer surface, capturing components that may inhibit brazing, such as O ₂ and H ₂ O, and brazing can be effectively performed. Furthermore, since the average Feret particle size of Si in the brazing layer in the step of performing chemical treatment is 3.5 μm or less, the flowability of the brazing layer during the brazing process can be improved, thereby improving the brazing property. The screen may be arranged so as to cover at least a part of the brazing material layer, and may surround a part of the brazing material layer, the entire brazing material layer, a part of the first member other than the brazing material layer, or the first and second members. The screen may be arranged so as to leave a gap between the brazing layer and the screen, and the material, shape, and size of the screen are not particularly limited. The screen is preferably made of a thin metal plate of stainless steel or other heat-resistant metal having heat resistance sufficient to withstand the heating temperature during brazing, and has a cylindrical shape with a substantially rectangular cross section.

3 is a cross-sectional view showing an example of a brazing process according to a method for manufacturing a brazed joint according to an embodiment of the present invention, and shows an example of forming a core part 3, which is a part of a heat exchanger, as a brazed joint by brazing. As shown in FIG. 3, the core part 3, which is a laminate in which a large number of thin core plates 4 are stacked together with fin plates 5, is placed on a base plate 2. The core plate 4, fin plate 5, and base plate 2 are made of an aluminum alloy. Here, the core plate 4 corresponds to the first member, and the fin plate 5 and base plate 2 correspond to the second member. As shown in FIG. 3, the core plate 4 has a tapered portion 4a that rises obliquely on the periphery, and when each core plate 4 is stacked in the vertical direction, the respective tapered portions 4a overlap each other and are in close contact with each other. After the core plate 4 and the fin plate 5 are assembled in the predetermined state shown in FIG. 3 and held by a jig, the brazing material layer of the core plate 4 is surrounded by a screen 11 made of a metal plate, and the tapered portions 4a of the overlapping core plates 4 are brazed without using flux. At the same time, the fin plate 5 is brazed to the surface of the core plate 4, and the bottom surface of the lowest core plate 4 is brazed to the base plate 2. This brazing process is performed without using flux, and brazing can be performed in an inert gas atmosphere such as nitrogen or argon under pressure close to atmospheric pressure without using a high-vacuum vacuum furnace as in the conventional VB method, simplifying the brazing process and improving the environment at the manufacturing site. In addition, the brazing process can be performed using a continuous furnace that continuously heats the work while transporting it, improving the mass productivity of the brazed joint.

The core part 3, which is a brazed joint obtained in this way, is made by stacking a large number of shallow dish-shaped core plates 4 having the same basic rectangular shape together with fin plates 5, so that oil passages 6 and cooling water passages 7 are alternately formed between two adjacent core plates 4. The fin plates 5 are arranged in the oil passages 6. In addition, the overlapping tapered parts 4 of each core plate 4 are brazed to seal the periphery of the oil passages 6 and cooling water passages 7 of each stage, and the core part 3 is integrated as a whole. High-temperature oil is flowed through the oil passages 6, and low-temperature cooling water is flowed through the cooling water passages 7, so that heat exchange can be performed between the oil in the oil passages 6 and the cooling water in the cooling water passages 7. The base plate 2 also functions as an attachment part for attaching the heat exchanger to a desired position, and is made of a plate-shaped member that is larger and thicker than the core plates 4 so that it protrudes from the core part 3 to the periphery. A gap D is provided between the tapered portion 4a and the inner wall 11a of the side of the screen 11, and the gap D is preferably 0.5 mm to 5 mm, and more preferably 0.5 mm to 2 mm. The screen also has a ridge portion 12 that covers not only the side of the core portion 3 but also part of the upper portion of the core portion 3.

In the brazing process shown in Figure 3, the screen 11 prevents Mg vaporized from the brazing material layer of the core plate 4 from dissipating into the atmosphere, and instead keeps it near the brazing material layer of the core plate 4. This Mg effectively captures oxygen and moisture near the brazing surface that would hinder brazing.

The method for producing a brazed joint according to the present invention may further include at least one step selected from the group consisting of the following steps (a) and (b).
(a) forming a first component prior to performing a chemical treatment;
(b) A step of shaping the first member between the step of performing the cleaning treatment and the step of brazing. According to this aspect, by having the steps (a), (b), or (a) and (b), it is possible to obtain a brazed body having a desired shape by shaping the first member into a desired shape. The method of shaping the first member is not particularly limited, but examples thereof include stamping molding.

Although the embodiments of the present invention have been described above, the present invention is not limited to the manufacturing method of the brazed joint according to the above embodiment, but includes all aspects included in the concept of the present invention and the scope of the claims. In addition, each configuration may be appropriately and selectively combined to achieve at least some of the above-mentioned problems and effects. For example, the shape, material, arrangement, size, etc. of each component in the above embodiment may be appropriately changed depending on the specific usage mode of the present invention.

The aluminum alloys, in which the elemental components of the core material 1, intermediate layer 1, and brazing layers 1 to 10 were adjusted to the contents shown in Table 1, were ingot-formed, homogenized, hot-rolled, and cold-rolled, and then the core material, intermediate layer, and brazing layer were integrated to produce clad sheets 1 to 11 having a thickness of 0.6 mm, which have brazing layer A, intermediate layer, core material, and brazing layer B in this order from one outer surface to the other outer surface, as shown in Table 2. The clad sheet 11 was then annealed at 390°C to completely soften it by annealing. In Table 1, the numerical values are in mass%. In Table 1, "-" for Cu, Mn, Mg, and Zn indicates a concentration of unavoidable impurities less than 0.05 mass%, and "-" for Na and Bi indicates a concentration of less than 0.01 mass%.

The second component, a number of fin plates 5 with a corrugated cross section, and the base plate 2 were each made from A3003 material.

In Examples 1 to 7 and 9 to 15 and Comparative Examples 1 to 10, the clad sheets 1 to 11 were stamped to form a plurality of shallow dish-shaped core plates 4 having the same rectangular shape as the first member. Next, in Examples 1 to 7 and 9 to 15 and Comparative Examples 2 to 7, the core plate 4 made of the stamped clad sheets 1 to 11 was immersed in a liquid tank containing an aqueous solution containing an oxo acid under the conditions shown in Table 3, thereby performing a chemical treatment with an aqueous solution containing an oxo acid. In Comparative Examples 8 to 10, the core plate 4 was immersed in a liquid tank containing an aqueous solution containing an acid other than an oxo acid, which is an inorganic acid under the conditions shown in Table 3, thereby performing a chemical treatment. In Comparative Example 11, the core plate 4 was immersed in a liquid tank containing an alkaline aqueous solution under the conditions shown in Table 3, thereby performing a chemical treatment. In Comparative Example 1, no chemical treatment was performed.
On the other hand, in Example 8, a chemical treatment was performed using an aqueous solution containing an oxoacid by immersing a core plate 4 made of a clad sheet 1 in a liquid tank containing an aqueous solution containing an oxoacid under the conditions shown in Table 3. After that, the core plate 4 was stamped to produce a plurality of shallow dish-shaped core plates 4 having the same rectangular shape as the first member.

Next, the core plate 4 (first member) after the chemical treatment was subjected to a cleaning treatment under the conditions shown in Table 3. The electrical conductivity of water shown in Table 3 was measured at 23° C. using a conductivity meter. The "pH of aqueous solution (23° C.)" of Comparative Example 1 in Table 3 indicates the pH of the pure water used in the cleaning treatment.

After that, as shown in FIG. 3, eight core plates 4 and four fin plates 5 were stacked on the base plate 2 to assemble the core part 3. Also, as shown in FIG. 4, two connectors 9 communicating with the inside of the core part 3 were joined to the upper part of the core part 3 to assemble the heat exchanger 1. The heat exchanger 1 was fixed with a jig, and a cylindrical screen 11 with a substantially square cross section was installed to surround the core part 3. The screen 11 was a metal plate made of SUS303 and had a plate thickness of 1.0 mm. As shown in FIG. 4, the screen 11 is divided into two parts, a first half part 11A and a second half part 11B, so as to sandwich the core part 3 on the base plate 2 from both sides in the direction of the arrow A and surround the brazing layer of the core plate 4. The center of the two opposing sides is the dividing surface between the first half part 11A and the second half part 11B. The first half 11A and the second half 11B are arranged on the base plate 2 with their respective edges 13a and 14a, and 13b and 14b butted against each other. After the screen 11 is set on the base plate 2 as described above, the heat exchanger 1 is introduced into a brazing furnace to perform brazing. At this time, the core portion 3 is brazed under the conditions shown in Table 3 in an inert gas atmosphere without using flux, and the tapered portions 4a of the core plate 4 are brazed together, and the core plate 4 is brazed to the base plate 2 and the fin plate 5. A mesh belt type continuous aluminum brazing furnace is used as the brazing furnace, and nitrogen is used as the inert gas. At this time, the brazing process is performed under the conditions that the oxygen concentration in the temperature zone of the brazing furnace from 595°C to 605°C is 20 ppm to 30 ppm, and the dew point is -50°C to -40°C. The temperature conditions were as follows: the workpiece was measured, heated from room temperature to 577°C in 20 minutes, then heated to 600°C in 5 minutes, held at that temperature for 3 minutes, and then cooled from 600°C to 350°C in 7 minutes.

The brazed state was checked and an airtightness test was carried out on the heat exchanger 1 obtained as described above. The brazed state was measured as a fillet formation rate shown in the following formula.
Fillet formation rate (%) = length of the portion where the tapered portions 4a of the core plate 4 are actually brazed together / total perimeter length of the seven-stage fillet to be brazed at the portion where the tapered portions 4a of the core plate 4 are in contact with each other x 100
The fillet formation rate measured as described above was evaluated as follows: 0% or more and less than 50% was scored as "0", 50% or more and less than 75% was scored as "1", 75% or more and less than 90% was scored as "2", 90% or more and less than 95% was scored as "3", 95% or more and less than 98% was scored as "4", and 98% or more and less than 100% was scored as "5".

The airtightness test was carried out as follows. The heat exchanger 1 shown in Figure 4 was immersed in water, and with a sealing plug attached to the end 9b of the connector 9, air was allowed to flow into the end 9a of the connector 9 at a pressure of 0.5 MPa for one minute to check for the presence or absence of air bubbles from the brazed portion. At this time, the presence or absence of air bubbles from the brazed portion was evaluated as "present", and the absence or absence of air bubbles was evaluated as "absent".

In addition, the "average Feret particle size of Si in the brazing layer" was measured as the average particle size measured as the longest distance between two parallel straight lines in the rolling direction of the brazing layer surface in the chemical treatment process. Specifically, using a field emission scanning electron microscope (FE-SEM) manufactured by Hitachi High-Technologies Corporation, the brazing layer of the observation sample, which was mirror-polished and coated with osmium as a sample cross section, was measured in a range of ⁴⁸⁰⁰ μm2, and the average value of the Feret particle size of Si of 1 μm or more was calculated. Since the Feret particle size does not depend on the rolling direction, the observation was made on the cross section in the rolling direction this time. The surface potential of the brazing layer (SHE: standard hydrogen electrode) was measured using a potentiostat with a silver-silver chloride electrode as the reference electrode, a platinum plate electrode as the auxiliary electrode, and a 5% by mass NaCl aqueous solution at 23 ° C.

Table 4 shows the average Feret grain size (μm) of the Si in the brazing material layer, the surface potential (mV) of the brazing material layer, the fillet formation rate rating, and the airtightness of each example evaluated as described above.

In Examples 1 to 15, the fillet formation rate was scored as 4 or 5 and the airtightness was "present," whereas in Comparative Examples 1 to 11, the fillet formation rate was scored as 3 or less, and in Comparative Examples 1, 3, 4, and 8 to 10, the airtightness was "not present." Therefore, it can be seen that the manufacturing method of the brazed joint of the present invention can simplify the brazing process and improve the brazing properties.

1...Heat exchanger, 2...Base plate, 3...Core section, 4...Core plate, 4a...Tapered section, 5...Fin plate, 6...Oil passage, 7...Cooling water passage, 9...Connector, 9a, 9b...Connector ends, 11, 11A, 11B...Screen, 11a...Inner wall surface, 12...Ribbon section, 13a, 13b, 14a, 14b...Screen edges, 21, 24...Brazing layer, 22...Intermediate layer, 23...Core material

Claims (7)

A method for manufacturing a brazed joint including a plurality of first members, comprising the steps of:
A step of subjecting the first member having a core material and a brazing material layer provided on one or both sides of the core material to a chemical treatment using an aqueous solution containing an oxo acid, which is an inorganic acid;
performing a cleaning process with pure water on the first member after the chemical treatment;
performing a brazing process without using a flux in an inert gas atmosphere while the brazing material layer of the first member after the cleaning process is surrounded by a screen, thereby brazing and joining the first members together;
having
the brazing material layer is made of an aluminum alloy containing 9.0 to 15.0 mass % of Si, 0.25 to 1.5 mass % of Mg, and 0.02 mass % or more of Bi, with the remainder being aluminum and unavoidable impurities;
The average Feret grain size of Si in the brazing material layer in the step of performing the chemical treatment is 3.5 μm or less,
The electrical conductivity of the pure water used in the step of performing the cleaning treatment is 30 μS/m or less.
A method for manufacturing a brazed joint. 2. The method for producing a brazed joint according to claim 1, further comprising at least one step selected from the group consisting of the following steps (a) and (b):
(a) forming the first member prior to the step of performing the chemical treatment;
(b) forming the first member between the cleaning step and the brazing step; The oxoacid is at least one acid selected from the group consisting of nitric acid, sulfuric acid, and phosphoric acid;
3. The method for producing a brazed joint according to claim 1, wherein in the step of performing the chemical treatment, the first member is immersed in a liquid tank containing an aqueous solution containing an oxoacid, the aqueous solution having a pH adjusted to −0.5 to 2.5 and a liquid temperature adjusted to 55° C. to 85° C. The method for manufacturing a brazed joint according to claim 1 or 2, in which the surface potential (SHE: standard hydrogen electrode) of the brazing material layer is adjusted to a range of -1100 mV to -850 mV in the step of carrying out the chemical treatment. The method for manufacturing a brazed joint according to claim 1 or 2, wherein the aluminum alloy further contains at least one element selected from the group consisting of Na, Sr, Sb and P in a total amount of 0.01 mass% or more. The first member further includes an intermediate layer between the core material and the braze layer;
3. The method for producing a brazed joint according to claim 1, wherein the brazing material layer or the intermediate layer contains at least one element selected from the group consisting of Zn and Na. The method for manufacturing a brazed joint according to claim 1 or 2, further comprising brazing the first member to the second member in the brazing step.

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