JP7650407B2 - Heat exchanger and its manufacturing method - Google Patents

Description

The present disclosure relates to a heat exchanger and a method for manufacturing the same.

Patent Document 1 discloses a method for brazing aluminum alloy members. In this brazing method, brazing is performed by carrying out the following steps. First, an aluminum alloy for brazing material is prepared to contain, by mass%, 0.2 to 3.0% Mg, 3 to 12% Si, and optionally 0.02 to 0.3% Bi, with the balance being Al and unavoidable impurities. In addition, an aluminum alloy for core material is prepared to contain, by mass%, 0.1 to 0.8% Mg, with the balance being Al and unavoidable impurities. Then, an aluminum alloy brazing sheet for heat exchangers is obtained in which an aluminum alloy brazing material is clad on one side of an aluminum alloy core material as a clad material in which a brazing material is superimposed and joined on one or both sides of a core material. The aluminum alloy brazing sheet and the brazing target member are arranged so that the aluminum alloy brazing material is interposed between the aluminum alloy core material and the brazing target member, and further, a coating film containing a paint containing a silane coupling agent and a water-soluble modified silicone oil is formed on the aluminum alloy brazing material. These are then assembled to form an aluminum alloy assembly for brazing. This allows the coating film to be interposed at the joint. The assembly is placed in a heating furnace in a non-oxidizing atmosphere without reducing pressure. The non-oxidizing atmosphere preferably has an oxygen concentration of 50 ppm or less by volume. In this atmosphere, for example, the brazing is performed by heating at a temperature rise rate of 10 to 200°C/min and heating to 590 to 610°C. It is said that this brazing method does not require the use of fluoride-based fluxes that remove oxides.

Patent Document 2 relates to a brazing method for an aluminum alloy brazing sheet and a manufacturing method for a heat exchanger, and in particular, discloses a brazing method that does not use flux, a so-called fluxless brazing method, and a manufacturing method for a heat exchanger using the fluxless brazing method. In this brazing method, brazing is performed on an aluminum alloy brazing sheet having a core material and a brazing material. In this brazing method, when the Si content of the brazing material is CSi mass%, the Bi content of the brazing material is CBi mass%, the Mg content of the brazing material is CMg-b mass%, the Mg content of the core material is CMg-c mass%, and CMg=CMg-b+CMg-c/2, the following conditions are satisfied: 3≦CSi≦13, 0.13CMg-0.3≦CBi≦0.58CMg0.45, CMg-b≧0.1, 0.2≦CMg≦1.1, and the aluminum alloy brazing sheet is brazed in an inert gas atmosphere at a heating temperature of 560 to 620°C without using any flux.

In this brazing method, the core material of the brazing sheet is made of an aluminum alloy containing 2.0 mass % or less (including 0 mass %) of Mg. Cited Document 3 states that such aluminum alloys can be Al-Cu alloys of JIS 2000 series, Al-Mn alloys of JIS 3000 series, Al-Mg alloys of JIS 5000 series, and Al-Mg-Si alloys of JIS 6000 series.

The core material of the brazing sheet in this brazing method may further contain Mn, Si, Cu, Fe, Ti, Cr, Zr, and Li. The brazing filler metal of the brazing sheet may further contain Mn, Ti, Cr, Zr, Zn, Sr, Na, Sb, rare earth elements, and Li.

In this brazing method, the core material may have an Mg content of 0% by mass or more and 2.0% by mass or less, an Mn content of 2.5% by mass or less, an Si content of 1.2% by mass or less, an Cu content of 3.0% by mass or less, an Fe content of 1.5% by mass or less, an Ti content of 0.5% by mass or less, an Cr content of 0.5% by mass or less, an Zr content of 0.5% by mass or less, and an Li content of 0.3% by mass or less. Also, the core material may contain one or more types of Ti, Cr, and Zr, i.e., not only one type, but two or more types, as long as the amounts do not exceed the upper limits described above. The unavoidable impurities in the core material are V, Ni, Ca, Na, Sr, etc., and may be contained in the following ranges: V: 0.05 mass% or less, Ni: 0.05 mass% or less, Ca: 0.05 mass% or less, Na: 0.05 mass% or less, Sr: 0.05 mass% or less, and other elements: less than 0.01 mass%.

In this brazing method, the brazing material may have a Mn content of 2.0 mass% or less, a Ti content of 0.3 mass% or less, a Cr content of 0.3 mass% or less, a Zr content of 0.3 mass% or less, a Zn content of 5.0 mass% or less, a Sr content of 0.10 mass% or less, a Na content of 0.050 mass% or less, an Sb content of 0.5 mass% or less, and a Li content of 0.3 mass% or less. As long as the upper limit values are not exceeded, the brazing material may contain one or more of Mn, Ti, Cr, and Zr, that is, not only one type, but also two or more types. As long as the upper limit values are not exceeded, the brazing material may contain one or more of Sr, Na, and Sb. Furthermore, when rare earth elements are contained in the brazing filler metal, one type may be contained or two or more types may be contained, for example, Sc, Y, La, Ce, Nd, Dy, etc. Also, as unavoidable impurities in the brazing filler metal, the following may be contained in the ranges: Fe: 0.35 mass% or less, Ca: 0.05 mass% or less, Be: 0.01 mass% or less, and other elements: less than 0.01 mass%.

Patent Document 3 discloses a fluxless brazing method for a heat exchanger having fine channel inner fins and an aluminum clad material used therein. In this brazing method, an aluminum clad material having an Al-Si brazing filler metal containing, by mass %, 0.1 to 5.0% Mg and 3 to 13% Si located on the outermost surface is used, and the contact and adhesion portion with the member to be brazed is joined by the Al-Si brazing filler metal at a heating temperature of 559 to 620°C in a non-oxidizing atmosphere without reduced pressure.

It is disclosed that the brazing material and core material of this aluminum clad material can be manufactured by a conventional method, and that the two or more materials, such as a sacrificial material, can be laminated together and then rolled to form a clad. It is disclosed that the composition of the core material of this clad material is one containing Si: 0.1-1.2%, Mg: 0.01-2.0%, one containing Mn: 0.2-2.5%, Cu: 0.05-1.0%, Si: 0.1-1.2%, Fe: 0.1-1.0%, or one containing Si: 0.1-1.2%, Mg: 0.01-2.0%, and further containing one or more of Mn: 0.2-2.5%, Cu: 0.05-1.0%, Fe: 0.1-1.0%, and optionally one or more of Zr: 0.01-0.3%, Ti: 0.01-0.3%, Cr: 0.01-0.5%, Bi: 0.01-1.0%.

Patent Document 3 discloses that although the inclusion of Bi in the brazing filler metal is not essential, the inclusion of Bi can improve the wettability of the brazing filler metal. It also discloses that the Bi content is preferably 0.01 to 1.0%, and that if it is less than 0.01%, the effect is insufficient, while if it exceeds 1.0%, the effect becomes saturated and the material cost increases, which is not preferable.

JP 2017-18959 A JP 2018-196895 A JP 2012-55895 A

In brazing aluminum alloys without using flux (hereinafter referred to as fluxless brazing), magnesium is added to the core material or brazing material to improve brazing properties. However, depending on the magnesium content in the core material and brazing material, the phenomenon in which the core material is eroded by the molten brazing material (hereinafter referred to as erosion) is likely to occur.

In heat exchangers for automobiles and the like, aluminum alloys are used to reduce weight. In such heat exchangers, brazing is used to join aluminum alloys together, as described in the above patent document. If fluxless brazing is performed, the removal of flux residue after brazing is not necessary, and the productivity of the heat exchanger can be improved. In heat exchangers for automobiles and the like, it is desirable to thin the members using aluminum alloys in order to reduce weight. However, in members made of thin aluminum alloys, when erosion occurs, problems such as through holes being formed in the members, or even if no through holes are formed, the durability of the heat exchanger being reduced may occur. Moreover, in general, the operating conditions for fluxless brazing that can realize brazing without erosion are narrow. Therefore, it may not be possible to manufacture a stable heat exchanger by fluxless brazing. Therefore, it may be difficult to improve the productivity, weight reduction, and durability of the heat exchanger.

The present disclosure has been made in consideration of the above circumstances, and has an object to provide a heat exchanger in which the occurrence of erosion is suppressed by fluxless brazing, and a manufacturing method thereof.

In order to achieve the above object, the heat exchanger according to the present disclosure comprises:
A plate-shaped flow path forming member is provided to allow a fluid to flow therethrough,
The flow path forming member is
A core layer;
A brazing material layer;
a diffusion layer formed between the core layer and the brazing material layer,
The core layer is
The magnesium content is 0.5% by mass or more and 0.75% by mass or less,
The manganese content is 1.0% by mass or more and 2.5% by mass or less,
The silicon content is 0.2% by mass or less,
It is an aluminum alloy of
The brazing material layer is
The magnesium content is 0% by mass or more and 0.9% by mass or less,
The manganese content is 1.0 mass% or less and is less than the manganese content of the core layer,
The silicon content is 8% by mass or more and 12.0% by mass or less,
It is an aluminum alloy of
The diffusion layer is a region in which the manganese content exceeds the manganese content of the brazing material layer and the silicon content exceeds the silicon content of the core material layer,
When the magnesium content (mass%) at a measurement point in the diffusion layer 45 μm away from the brazing material layer toward the core material layer is expressed as Ym and the silicon content (mass%) is expressed as Xs, the following relationship is satisfied.
Ym≦-0.31Xs+0.71...(1)
Ym≧-0.44Xs+0.58...(2)
Xs≦0.375Ym2-0.92Ym+0.994...(3)
Xs≧0.36...(4)

In order to achieve the above object, a method for manufacturing a heat exchanger according to the present disclosure includes:
A method for manufacturing a heat exchanger, comprising brazing a flow passage forming member having a brazing material layer disposed on one surface of a core material layer to a second member, the method comprising the steps of:
The core layer is
The magnesium content is 0.5% by mass or more and 0.75% by mass or less,
The manganese content is 1.0% by mass or more and 2.5% by mass or less,
The silicon content is 0.2% by mass or less,
The aluminum alloy is
The brazing material layer is
The magnesium content is 0% by mass or more and 0.9% by mass or less,
The manganese content is 1.0 mass% or less and is less than the manganese content of the core layer,
The silicon content is 8% by mass or more and 12.0% by mass or less,
The aluminum alloy is
The second member,
The magnesium content is 0.5% by mass or more and 0.75% by mass or less,
The manganese content is 1.0% by mass or more and 2.5% by mass or less,
The silicon content is 0.2% by mass or less,
The aluminium alloy layer is
The second member is heated while being in contact with the brazing material layer,
During the temperature increase, the temperature increase rate when increasing the temperature from 400° C. to 577° C. is set to be 50° C. per minute or more.

It is possible to provide a heat exchanger in which the occurrence of erosion is suppressed by fluxless brazing, and a manufacturing method thereof.

FIG. 2 is an enlarged view of a portion of the core of the heat exchanger according to the embodiment. 2 is a cross-sectional view taken along the line II-II of FIG. 1. 2 is a partially enlarged cross-sectional view of a brazed portion between a tube and a fin (part A in FIG. 1 ). FIG. FIG. 2 is an explanatory diagram of the layer structure of a brazing sheet. FIG. FIG. 4 is a partially enlarged view of a cross section of a second joint portion. FIG. FIG. 2 is an explanatory diagram of the structure of a test specimen. FIG. 13 is an explanatory diagram of a test piece after brazing treatment. 1 is a graph showing an example of the measurement results of manganese obtained by EPMA line analysis. 11 is a graph obtained by smoothing the graph in FIG. 10 . 12 is a graph showing approximate values of differential values obtained from the graph of FIG. 11 . 1 is an enlarged photograph of the diffusion layer of Reference Example 1. 1 is an enlarged photograph of the diffusion layer of Reference Example 2. 1 is an enlarged photograph of the diffusion layer of Reference Example 3. 1 is an enlarged photograph of the diffusion layer of Reference Example 4. FIG. 2 is a graph showing the relationship between the magnesium content and the silicon content at measurement points.

A heat exchanger and a manufacturing method thereof according to an embodiment of the present disclosure will be described with reference to the drawings.

Fig. 1 shows an enlarged view of a part of a core 100 of a heat exchanger according to this embodiment. Fig. 2 shows a cross-sectional view taken along line II-II in Fig. 1. As shown in Figs. 1 and 2, the core 100 has tubes 3 (an example of a flow path forming member) and fins 4 (an example of a flow path forming member, an example of a second member). The core 100 is formed by brazing the fins 4 to the tubes 3. Fig. 3 shows an enlarged view of the brazed portion (part A in Fig. 1) between the tubes 3 and the fins 4.

The tube 3 is a flow path forming member that forms a flow path 30 through which a fluid (heat medium) flows inside the tube 3. A flow path 40 through which a fluid (another heat medium) flows is formed outside the tube 3. The tube 3 is a heat transfer member that transfers heat of the fluid flowing through the flow path 30 to the fluid flowing through the flow path 40 via the fins 4. In this embodiment, examples of fluids that can serve as a heat medium include air, water, an aqueous solution (specific examples include antifreeze), an organic solvent, and oil.

As shown in FIGS. 1 and 2, the tube 3 is formed of an aluminum alloy brazing sheet (hereinafter simply referred to as the brazing sheet 1) having a core material layer 11 and a brazing material layer 12.

As shown in Fig. 2, the tube 3 is formed by folding the brazing sheet 1 into an annular shape, for example. The tube 3 is formed by folding the brazing sheet 1 so that the brazing material layer 12 (see Figs. 1 and 4) is disposed at a radially outer position in the annular shape. The tube 3 is formed by joining the first end 1a and the second end 1b of the brazing sheet 1 by brazing, with the brazing material layer 12 of the first (one) end 1a and the brazing material layer 12 of the second (other) end 1b being overlapped. Hereinafter, the portion of the tube where the first end 1a and the second end 1b are joined by brazing is referred to as a first joint portion 51.

1 and 2, the fins 4 are formed by bending, for example, an aluminum alloy plate material (see FIG. 5, hereinafter simply referred to as sheet material 2) into a corrugated shape. The fins 4 are so-called corrugated fins.

The fins 4 are disposed in the flow passages 40 (see FIG. 1 ). The fins 4 are heat transfer members that transfer heat from the tubes 3 to the fluid flowing through the flow passages 40, and are flow passage forming members that divide the flow passages 40.

In the core 100, the outer peaks 41 of the corrugated folded shape of the fins 4 are joined by brazing to the brazing material layer 12 (see FIGS. 1 and 4 ) side of the tubes 3. Hereinafter, the portion of the core 100 where the peaks 41 of the fins 4 are joined by brazing to the brazing material layer 12 side of the tubes 3 is referred to as a second joint 52.

In the core 100, the first joint 51 and the second joint 52 may be formed at the same or adjacent positions. That is, the top 41 of the fin 4 may be brazed to the radially outer position of the tube 3 in the first joint 51 to form the second joint 52. In this manner, the portion where the second joint 52 is formed in the first joint 51 and the tube 3 and the fin 4 are joined by brazing may be particularly referred to as the third joint 53. That is, the first joint 51 or the second joint 52 may include the third joint 53, and the third joint 53 is both the first joint 51 and the second joint 52. Hereinafter, the first joint 51, the second joint 52, and the third joint 53 may be collectively referred to simply as the joint.

At each joint, a fillet 34 is formed at the portion where the tube 3 and the fin 4 separate, as shown in Figures 1 to 3. The fillet 34 is formed by the surface tension of the brazing material when the brazing material of the brazing material layer 12 (see Figure 3) melts and flows, at the joint, at the portion where the tube 3 and the fin 4 separate. The formation of a fillet 34 of an appropriate size indicates that the brazing material flows appropriately, and thus indicates good brazing.

The brazing sheet 1 forming the tube 3 (see Figs. 1, 2 and 4), the tube 3, the sheet material 2 forming the fins 4 (see Fig. 5), the fins 4 and the joints will be described in detail below.

As shown in FIG. 4 , the brazing sheet 1 before brazing has a two-layer structure including a core layer 11 and a brazing material layer 12 disposed on one surface of the core layer 11 .

The core layer 11 is made of an aluminum alloy having a magnesium (Mg) content of 0.5 mass% or more and 0.75 mass% or less, a manganese (Mn) content of 1.0 mass% or more and 2.5 mass% or less, and a silicon (Si) content of 0.2 mass% or less.

In the core layer 11, the silicon content is preferably 0.05 mass % or less.

In addition to magnesium, manganese, and silicon, the core layer 11 may contain metal elements and impurities as additives.

The brazing material layer 12 is made of an aluminum alloy having a magnesium content of 0 mass% or more and 0.9 mass% or less, a manganese content of 1.0 mass% or less, which is less than the manganese content of the core material layer 11, and a silicon content of 8 mass% or more and 12.0 mass% or less.

The manganese content in the brazing material layer 12 is preferably 0.10 mass % or less. The manganese content in the brazing material layer 12 may be 0.05 mass % or more. Manganese is not an essential component in the brazing material layer 12.

The brazing material layer 12 may contain metals and impurities as additives in addition to magnesium, manganese, and silicon. For example, the brazing material layer 12 may contain bismuth as an additive. The content of bismuth in the brazing material layer 12 is preferably 0.1% by mass or more and 1.0% by mass or less. By containing bismuth in the brazing material at the above ratio, the wettability of the brazing material can be improved without elution from the material surface (the surface to be brazed). More preferably, the content of bismuth in the brazing material layer is preferably 0.20% by mass or more and 0.40% by mass or less.

The sheet material 2 shown in Figure 5 has an alloy layer made of an aluminum alloy having a magnesium content of 0.5 mass% or more and 0.75 mass% or less, a manganese content of 1.0 mass% or more and 2.5 mass% or less, and a silicon content of 0.2 mass% or less.

The alloy layer of the sheet material 2 may contain metals and impurities as additives in addition to magnesium, manganese, and silicon. The sheet material 2 may have a two-layer structure having a second alloy layer disposed on the surface of the alloy layer. The second alloy layer may be, for example, a layer similar to the brazing material layer 12 of the brazing sheet 1 (see FIG. 4). In the following description, a case in which the sheet material 2 is a single layer will be described as an example.

In the core 100 shown in Figs. 1 and 2, the brazing sheet 1 (see Figs. 1, 2, and 4) and the sheet material 2 (see Fig. 5), i.e., the tube 3 and the fin 4, are brazed through the brazing material layer 12. In the brazing heat treatment, the brazing sheet 1 forming the tube 3 diffuses metal components at the interface between the core material layer 11 and the brazing material layer 12 (see Fig. 4). Due to this diffusion, the layer structure of the brazing sheet 1 before brazing and the brazing sheet 1 after brazing (i.e., the tube 3) in the core 100 is changed. In the following description, the layer structure of the tube 3 is described, that is, the layer structure of the brazing sheet 1 after brazing. In the following description, the brazing sheet 1 after brazing is referred to as the tube 3. In addition, when the brazing sheet 1 is simply referred to as the brazing sheet 1, it refers to the brazing sheet 1 before brazing.

Fig. 6 shows a partially enlarged cross-sectional view of a second joint portion 52 which is a joint portion between the tube 3 and the fin 4. As shown in Fig. 6, the tube 3 has a diffusion layer 13 formed near the surface of the surface side of the core material layer 11 which contacts the brazing material layer 12. In the example shown in Fig. 6, the sheet material 2 forming the fin 4 and the tube 3 are made of an aluminum alloy similar to the core material layer 11, so that the fin 4 also has a diffusion layer 23 formed near the surface of the surface side which contacts the brazing material layer 12. The diffusion layer 23 is similar to the diffusion layer 13. In the following description, the description of the diffusion layer 13 also applies to the diffusion layer 23.

The diffusion layer 13 is a region in which the manganese content exceeds the manganese content of the brazing material layer 12 and the silicon content exceeds the silicon content of the core material layer 11 .

When the magnesium content (mass%) at a measurement point in the diffusion layer 13 of each joint, located 45 μm away from the brazing material layer 12 toward the core material layer 11, is represented as Ym and the silicon content (mass%) is represented as Xs, the following formulas (1) to (4) are satisfied at the measurement point. The measurement point is the same for all of the first joint 51, the second joint 52, and the third joint 53 (see FIG. 2).

Ym≦-0.31Xs+0.71...Formula (1)

Ym≧-0.44Xs+0.58...Formula (2)

Xs≦0.375Ym2-0.92Ym+0.994...Formula (3)

Xs≧0.36...Formula (4)

As shown in Figure 7, the measurement point was in a direction along the perpendicular line S to the boundary surface 14 between the brazing material layer 12 and the diffusion layer 13, and was a point 45 μm (distance d) away from the boundary surface 14 toward the core material layer 11 (the position indicated by the virtual line P in Figure 7).

In this embodiment, the measurement point is in the direction along the perpendicular line (same as perpendicular line S in Figure 7) to the boundary line (same as boundary surface 14 in Figure 7) between the brazing material layer 12 and the diffusion layer 13 on a cut surface of the tube 3 cut perpendicular to the core material layer 11, and is a point 45 μm away from the boundary line toward the core material layer 11.

In this embodiment, the magnesium content and silicon content in the diffusion layer 13 are values measured by scanning a cross section of the tube 3 cut perpendicular to the core layer 11 from the brazing material layer 12 side to the core layer 11 side using EPMA line analysis.

By using the brazing sheet 1 described above and brazing so that the above formulas (1) to (4) are satisfied at the measurement points, the occurrence of erosion due to fluxless brazing is suppressed in the core 100 shown in Figures 1 and 2, i.e., the heat exchanger according to this embodiment. By suppressing the occurrence of erosion in the tube 3 using the brazing sheet 1, it is possible to realize improvements in the productivity, weight reduction, and durability of the heat exchanger.

In the core 100, the above formulas (1) to (4) are satisfied even at the measurement points at the joints, so that the occurrence of erosion is suppressed at the joints as well. Furthermore, the durability of the heat exchanger is further improved by suppressing the occurrence of erosion at the joints.

The core 100 (heat exchanger) in which the occurrence of erosion is suppressed can be realized by, for example, a method for manufacturing a heat exchanger including the following brazing method. That is, the core 100 (heat exchanger) according to this embodiment can be manufactured by a method for manufacturing a heat exchanger including a brazing method in which the sheet material 2 is heated while being in contact with the brazing sheet 1, and the heating rate during heating from 400° C. to 577° C. is set to a temperature rise rate of 50° C. per minute or more. Note that a temperature rise rate of 50° C. per minute or more means that the temperature is raised at least 50° C. per minute.

A temperature rise rate of less than 50° C. per minute is not preferable because the brazing processing speed decreases, which reduces the productivity of the heat exchanger. Also, a temperature rise rate of less than 50° C. per minute is not preferable because it takes a long time to increase the temperature, which increases the amount of diffusion of metal components accompanying brazing at the interface between the core layer 11 and the brazing material layer 12 (see FIG. 4 ) (excessive diffusion), making it impossible to perform proper brazing.

In this method for manufacturing a heat exchanger, it is preferable to raise the temperature during brazing from room temperature to 577° C. or higher and 600° C. or lower. Note that room temperature in this embodiment refers to the temperature during storage or handling of the constituent materials of the heat exchanger (the brazing sheet 1 and the sheet material 2) at the manufacturing site of the heat exchanger (e.g., room temperature in a processing room), and is generally 0° C. to 50° C.

In an approximate evaluation based on a binary phase diagram of aluminum and silicon, the brazing material of the brazing material layer 12 specified in this embodiment begins to melt at 577° C., and it is considered that 60% to 80% of the entire brazing material melts at 577° C. In a similar evaluation, the brazing material layer 12 specified in this embodiment melts at 80% to 100% at 590° C., and it is considered that most of the brazing material can be used effectively.

By the way, in brazing, it is important that the core material of the core material layer 11 does not melt. In order not to melt the core material, it is advantageous to have a low brazing temperature. In the heat exchanger of this embodiment, the silicon content of the diffusion layer (for example, the measurement point) is about 0.65 wt% at most, the magnesium content is about 0.45 wt% at most, and it is considered that the melting point of the diffusion layer drops to around 600°C. That is, if the brazing temperature exceeds 600°C, the amount of silicon diffused from the brazing material further increases, the melting point of the diffusion layer further drops, and the high brazing temperature, combined with the high brazing temperature, leads to the melting of the core material. Therefore, the brazing temperature is appropriate to be 600°C or less.

Brazing is performed in a non-oxidizing atmosphere of an inert gas or reducing gas with an oxygen concentration of 10 ppm or less. Any inert gas that is used for joining aluminum alloys can be used, and nitrogen and argon are suitable examples.

An example of the heat exchanger according to this embodiment will be described below.

Test specimens simulating the joints of the heat exchanger according to this embodiment were prepared, and the brazing condition after the brazing process was evaluated for each test specimen with different brazing conditions (compositions of the core material and brazing material, and temperature conditions during brazing).

The specimens were prepared as follows.

Using the recipe of the aluminum alloy "A3003" as a guide, core materials were produced by changing the magnesium content and silicon content of the aluminum alloy. The magnesium content of the core material was set to 0 mass%, 0.30 mass%, 0.50 mass%, 0.60 mass%, 0.75 mass%, or 0.90 mass%, as described below. The silicon content of the core material was set to 0.05 mass% or less or 0.20 mass%, as described below. The manganese content of the core material was set to 1.0 mass% or more and 2.5 mass% or less, and fluctuations within this range were allowed. The copper content of the core material was allowed to be 0.05 mass% or more and 0.20 mass% or less. The zinc content of the core material was allowed to be 0.10 mass% or less. Other impurities in the core material were allowed to be 0.05 mass% or less as individual elements and 0.15 mass% or less as the total of impurities.

Next, brazing materials were prepared by changing the magnesium content and silicon (Si) content of the aluminum alloy based on the prescriptions of aluminum brazing materials "A-4045 (JIS standard: BA4045)" and "A-4043 (JIS standard: BA4045)". The magnesium content of the brazing material was set to 0 mass%, 0.50 mass%, 0.60 mass%, 0.75 mass%, 0.90 mass%, or 1.00 mass%, as described later. The silicon content of the brazing material was set to 8.0 mass%, 10.0 mass%, or 12.0 mass%, as described later. In addition, 0.1 wt% of bismuth (Bi) was prescribed for each brazing material. The manganese content was allowed to be 0.05 mass% or less. In addition, the copper content of the brazing material was allowed to be 0.30 mass% or less. In addition, the zinc and titanium contents of the brazing material were allowed to be 0.20 mass% or less, respectively. Other impurities in the brazing material were permitted to be up to 0.05% by weight for each individual element and up to 0.15% by weight for the total amount of impurities.

The core material was then clad with a brazing material to form a brazing sheet 1, and a flat test piece of a predetermined size was produced using the brazing sheet 1. This test piece had a core material layer with a thickness of 0.2 mm and a brazing material layer with a thickness of 0.05 mm.

The brazing material layer side of this test piece was placed facing an aluminum horizontal plate, and a spacer was sandwiched between the test piece and the aluminum horizontal plate (aluminum alloy "A3003") serving as the second component, leaving a gap of 1 mm at a position 45 mm away from the point of contact between the test piece and the aluminum horizontal plate, to form a specimen.

Fig. 8 shows the structure of the above-mentioned test specimen. Fig. 8 shows a test specimen 200 composed of a test piece 91, an aluminum horizontal plate 92, and a spacer 93. The test piece 91 and the aluminum horizontal plate 92 are in contact with each other at a contact point 94. A spacer 93 is inserted at a position 45 mm away from the contact point 94, forming a gap C of 1 mm between the test piece 91 and the aluminum horizontal plate 92.

Brazing was performed in a sealed atmosphere with an oxygen concentration of 10 ppm by heating the specimen at a constant heating rate of 50° C./min up to a predetermined temperature and holding the specimen at the temperature for a predetermined time. When brazing was performed, a fillet was formed from the contact point between the test piece and the horizontal aluminum plate of the specimen (hereinafter simply referred to as the contact point of the specimen) toward the spacer so as to fill the gap between the test piece and the horizontal aluminum plate.

As described below, the test pieces after the brazing process were visually observed for the components of the diffusion layer (magnesium, silicon, magnesium oxide (MgO)), the liquid phase rate of the brazing material as an example of an indication of the degree of melting of the brazing material, the presence or absence of brazing defects (the presence or absence of erosion), and the brazing material flow distance.

The brazing material flow distance was evaluated by measuring the length of the fillet formed in the test piece after the brazing process so as to fill the gap between the test piece and the horizontal aluminum plate (the length of the fillet extending from the contact point of the test piece to the spacer side along the horizontal aluminum plate). Hereinafter, the length of the fillet extending from the contact point of the test piece to the spacer side along the test piece and the horizontal aluminum plate is simply referred to as the brazing material flow distance. If the brazing material flow distance is 20 mm or more, it is considered to be good. If the brazing material flow distance is less than 20 mm, it is considered to be bad.

Fig. 9 shows a specimen after the brazing process when the brazing was performed well. As shown in Fig. 9, in the specimen 200, the brazing material flows from the test piece 91 to fill the gap C between the test piece 91 and the aluminum horizontal plate 92, and a fillet 95 is formed so as to extend from the contact point 94 to the spacer 93 side along the test piece 91 and the aluminum horizontal plate 92. In Fig. 9, the distance L is the brazing material flow distance.

The components of the diffusion layer are evaluated by measuring the components at a measurement point 45 μm away from the brazing layer toward the core layer in the test piece of the specimen after brazing treatment, that is, at a point 45 μm away from the boundary between the brazing layer and the diffusion layer toward the core layer, using an electron beam analyzer (EPMA). In the following examples, the contents of silicon and magnesium are evaluated. The distance from the boundary is the distance in the direction along the perpendicular line to the boundary, and in the observation of the cut surface, it is the same as the distance in the direction along the perpendicular line to the boundary between the brazing layer and the diffusion layer. When the test piece is flat, in the observation of the cut surface, the distance from the boundary is the same as the distance from the boundary between the brazing layer and the diffusion layer along the thickness direction of the test piece.

Here, the boundary surface and the diffusion layer are specified as follows. First, an EPMA line analysis (quantitative analysis) is performed on a cut surface of the test piece cut perpendicular to the core layer in the thickness direction of the test piece from the brazing material layer side to the core material layer side to measure the changes in the concentrations of silicon (Si), magnesium (Mg), and manganese (Mn). Hereinafter, the direction from the brazing material layer side to the core material layer side in the thickness direction of the test piece may be simply referred to as the depth or depth direction.

In the following examples, as shown in Fig. 9, EPMA line analysis was performed along a virtual line R that passes through the center of the fillet 95, i.e., a position Q that is 1/2 the distance L, which is the brazing material flow distance, from the contact point 94 of the test piece 200 along the aluminum horizontal plate 92 and is perpendicular to the test piece 91, i.e., along the depth direction of the test piece 91. Then, the boundary surface between the brazing material layer and the core material layer in the test piece 91 was identified, and a point G that is 45 µm away from the boundary surface toward the core material layer side was set as the measurement point. In other words, the measurement point was the intersection point of the virtual line P and the virtual line R.

For the EPMA line analysis, an electron probe microanalyzer (manufactured by JEOL Co., Ltd., model: JEOL JXA-8530F) was used. For the quantitative determination of elements, a calibration curve method was used. The acceleration voltage was 20 kV, and the current value of the sample current was 100 nA. For the analysis of magnesium, a TAP (thallium phthalate) crystal was used as the analyzing crystal, and the distance between the sample and the analyzing crystal was 107.513 mm. For the analysis of manganese, a LIF (lithium fluoride, LIFH) crystal was used as the analyzing crystal, and the distance between the sample and the analyzing crystal was 146.141 mm. The detection limit for light elements is 0.01 to 0.05% at the lower limit.

A supplementary explanation will be given regarding the determination of the boundary surface (boundary line) between the brazing material layer and the diffusion layer. FIG. 10 shows an example of the measurement results of EPMA line analysis performed along the depth direction of the test piece from the brazing material layer to the core material layer with respect to the concentration of manganese. In the graph of FIG. 10, manganese is represented as Mn. In the graph of FIG. 10, the horizontal axis is the depth of the test piece, and the vertical axis on the left is the count number in the EPMA line analysis. In addition, in the graph of FIG. 10, the vertical axis on the right is the concentration (weight %) of manganese derived from the count number. The boundary surface (boundary line) between the brazing material layer and the diffusion layer can be determined by smoothing this graph, further obtaining a differential value of the graph, and determining the depth position where this differential value is the largest, and this can be determined as the boundary surface (boundary line) between the brazing material layer and the diffusion layer. Smoothing can be performed, for example, by selecting the minimum value between 45 μm in the depth direction (measurements of 150 times of EPMA line analysis in the case of FIG. 10) and graphing it (see FIG. 11). The differential value of the graph may be obtained by mathematically differentiating an approximate function, and the differential formula may be graphed to obtain the position where the differential value is maximum. Alternatively, for example, a small section (e.g., 4.9 μm in the depth direction) may be set, and the slope of this small section may be obtained as an approximation of the differential value, graphed, and the position where the maximum value is obtained (see FIG. 12). In FIG. 12, part B in the figure is specified as the boundary surface. Figures 10 to 12 show the ranges of the brazing layer, core layer, and boundary layer specified based on the boundary surface obtained in FIG. 12. The boundary layer is the range of a peak in the graph that includes part B in FIG. 12, where the boundary surface is specified.

At the interface between the core layer and the brazing layer, magnesium diffuses and moves from the core layer to the brazing layer, and silicon diffuses and moves from the brazing layer to the core layer due to the brazing process. In contrast, manganese is an element that is difficult to diffuse and move due to the brazing process.

Silicon is an atom contained in a larger amount in the brazing material layer than in the core material layer, and therefore, when scanning in the thickness direction by EPMA line analysis, silicon from the brazing material layer is diffused to the core material layer side up to a depth position where more silicon is observed than in the core material layer before brazing.

Manganese is an atom contained in greater amounts in the core layer than in the brazing layer, and therefore, when scanning in the thickness direction by EPMA line analysis, the depth position at which the amount of detected manganese begins to increase is the interface between the core layer and the brazing layer.

That is, the diffusion layer in this embodiment is from the above-mentioned boundary surface to a depth position in the core material layer where more silicon is observed than in the core material layer before brazing.

The reason for evaluating the components of the diffusion layer at the above measurement point (a point 45 μm away from the boundary surface toward the core layer) is as follows. That is, prior to the evaluation of the examples, brazing was performed by changing the thickness of the brazing material layer of the test piece of the specimen, and the components of the diffusion layer of the specimen that was successfully brazed were evaluated by EPMA line analysis. As a result, even if the thickness of the brazing material layer was changed in various ways and the silicon content of the brazing material layer and the core material layer was changed, the silicon content showed the same value at a depth of 45 μm or more from the boundary surface even if the thickness of the brazing material layer was changed (however, the thickness of the brazing material layer was in the range of 10 μm to 150 μm). This is based on the results of the preliminary evaluation.

Since magnesium is a component that has the function of destroying the oxide film of aluminum during brazing, the evaluation of the components of the diffusion layer only requires the evaluation of the degree to which magnesium was easily diffused to the surface of the test piece (the surface on the brazing layer side, hereinafter simply referred to as the surface of the test piece). Therefore, it is sufficient to evaluate the magnesium content in the diffusion layer at any depth, for example, at a depth of 45 μm from the boundary surface where the silicon content is constant regardless of the thickness of the brazing layer. In this way, the measurement point was set to a point 45 μm away from the boundary surface toward the core layer.

The brazing filler metal liquid phase ratio (liquid phase ratio of the brazing filler metal during brazing) was approximately calculated from the binary phase diagram of the main components aluminum and silicon and the temperature reached by the specimen. If the brazing conditions are such that the brazing filler metal liquid phase ratio is 80% or more, it is considered that the heat input to the brazing filler metal during the brazing process is sufficient and the brazing filler metal can be sufficiently melted. On the other hand, if the brazing conditions are such that the brazing filler metal liquid phase ratio is less than 80%, it is considered that the heat input to the brazing filler metal is insufficient and the brazing filler metal cannot be sufficiently melted. Therefore, specimens under brazing conditions where the brazing filler metal liquid phase ratio is less than 80% are considered defective.

The occurrence of erosion was checked by observing the state of the diffusion layer of each test piece with an optical microscope. Brazing conditions in which erosion was clearly observed were considered to be good.

The confirmation of the occurrence of erosion using an optical microscope will be described below with reference to examples. Figures 13 to 16 are examples of enlarged photographs of the state of the diffusion layer formed by changing the components of the core material layer and the brazing material layer, observed with an optical microscope.

FIG. 13 is an enlarged photograph of the diffusion layer in a test specimen in which the core layer contained 0.75% by mass of magnesium and the brazing material layer contained 0.30% by mass of magnesium and 12% by mass of silicon, respectively, was heated at a heating rate of 50° C./min up to an ultimate temperature of 600° C., and then held at the ultimate temperature of 600° C. for 3 minutes for brazing (Reference Example 1).

14 is an enlarged photograph of the diffusion layer in the case where a test piece having a core layer containing 0.75% by mass of magnesium and a brazing layer containing 0.50% by mass of magnesium and 12% by mass of silicon was brazed by increasing the temperature to 600° C. at a heating rate of 50° C./min and then holding the temperature at 600° C. for 3 minutes (Reference Example 2). The specimen in Reference Example 2 was prepared under the same conditions as specimen 19 described later.

15 is an enlarged photograph of the diffusion layer in the case where a test piece having a core layer containing 0.75% by mass of magnesium and a brazing layer containing 0.75% by mass of magnesium and 12% by mass of silicon was heated at a heating rate of 50° C./min to an ultimate temperature of 600° C., and then held at the ultimate temperature of 600° C. for 3 minutes for brazing (Reference Example 3). The specimen in Reference Example 3 was prepared under the same conditions as specimen 8 described below.

Figure 16 is an enlarged photograph of the diffusion layer in a test specimen in which the core layer contained 0.75% magnesium by mass and the brazing material layer contained 1.00% magnesium by mass and 12% silicon by mass, respectively, was heated at a heating rate of 50°C/min up to an ultimate temperature of 600°C, and then held at the ultimate temperature of 600°C for 3 minutes for brazing (Reference Example 4).

In Reference Example 1 (see FIG. 13) and Reference Example 2 (see FIG. 14), crystal grains are not clearly visible from the brazing material layer to the core material layer, and erosion does not occur, but in Reference Example 3 (see FIG. 15) and Reference Example 4 (see FIG. 16), crystal grains are clearly visible from the brazing material layer to the core material layer, and erosion occurs. In this way, erosion can be directly observed by optical microscope photographs.

Tables 1-1 and 1-2 show the brazing conditions and evaluation results of the specimens evaluated. Table 1-1 shows the brazing conditions and evaluation results of specimens 1 to 10, and Table 1-2 shows the brazing conditions and evaluation results of specimens 11 to 22. Hereinafter, Tables 1-1 and 1-2 will be collectively referred to as Table 1.

In Table 1, magnesium is represented as Mg and silicon is represented as Si. The row "Components of test piece" shows the amount of magnesium in the core layer and the amounts of magnesium and silicon in the brazing layer.

In addition, the row "Components at measurement points" shows the temperature reached as the temperature conditions during brazing, and the silicon and magnesium contents at the measurement points as the measurement results after brazing. Although not shown in Table 1, as mentioned above, the heating rate for all specimens was 50° C./min, and the holding time after reaching the temperature was 3 minutes.

The "Results" row also shows the liquid phase rate of the brazing filler metal, the presence or absence of erosion, the flow distance of the brazing filler metal, and an overall evaluation.

The liquid phase rate of the brazing filler metal was marked "F (fail)" when it was less than 80% and judged to be defective, and marked "G (good)" otherwise.

Regarding the presence or absence of erosion, those in which the occurrence of erosion was obvious and judged to be defective were marked as "F (fail)" and others were marked as "G (good)."

The brazing filler metal flow distance indicates the measured brazing filler metal flow distance. If the brazing filler metal flow distance is less than 20 mm, it is determined to be defective.

In the overall evaluation, if any of the evaluation items, such as material flow distance, brazing material liquid phase rate, and the occurrence or non-occurrence of erosion, was rated as poor, it was judged as "F (fail)" and if a good result was obtained (if brazing was performed appropriately), it was judged as "G (good)".

From the overall evaluation, specimens 5-7, 10-12, 14, 15, 17, and 19-22 are examples of the present embodiment, and specimens 1-4, 8, 9, 13, 16, and 18 are comparative examples.

From the results in Table 1, the relationship between the magnesium content and the silicon content at the measurement points in the diffusion layer, which can realize brazing with suppressed erosion, i.e., a heat exchanger with suppressed erosion, can be derived as shown in the graph in Figure 17. In Figure 17, the range showing the magnesium content and silicon content of the diffusion layer that can realize a heat exchanger with suppressed erosion is shown as region X. The above-mentioned formulas (1) to (4) show the outer edge of the graph shown in Figure 14.

From the results in Table 1, the heat exchanger suppressing the occurrence of erosion and the manufacturing method thereof can be considered as follows. The graph shown in Fig. 17 and formulas (1) to (4) were derived as follows.

First, the basic concept for performing good brazing and the basic effects of additives in aluminum alloys will be explained.

In aluminum alloys (A3003, A4045, or A4343), the melting point decreases as the silicon content increases. In other words, in terms of the heating conditions (heat input) and melting of the brazing material (brazing material flow distance), a high silicon content in the brazing material layer is advantageous for brazing because the melting point of the brazing material decreases. As will be described later, when the silicon content of the diffusion layer (core material) increases, the melting point of the diffusion layer decreases, which may cause erosion.

Magnesium deficiency in brazing means a lack of magnesium to break down the aluminum oxide film.

Erosion occurs mainly when the melting point of the core material (diffusion layer) is lowered due to the diffusion of the brazing material components, causing the core material to melt. Of the additives that can be contained in the aluminum alloys A3003, A4045, and A4343, only magnesium and silicon affect the change in the melting point of these aluminum alloys, and the change in the amount of other additives added is sufficiently small compared to the effect of magnesium and silicon.

Excessive magnesium tends to cause magnesium oxide on the surface of the test piece, which becomes an inhibitor of wax flow.

For example, if the liquid phase rate is insufficient due to insufficient heat input or a change in the composition of the brazing material layer, the brazing material will not melt, the amount of liquid phase in the brazing material will be insufficient, and brazing will not be performed properly. The results in Table 1 will be considered in detail below.

As mentioned above, magnesium is a component that has the function of destroying the oxide film on aluminum during brazing, so the condition that is most unfavorable for destroying the oxide film on aluminum (the condition in which the amount of magnesium diffusing to the surface of the test piece is the smallest) is a material formulation in which magnesium is added only to the core layer.

The order of making and evaluating the specimens does not match the number of the specimens. In this example, specimens 8, 12, 15, 16, 17, 19, and 20 were made and evaluated in advance as a preliminary test, focusing on the magnesium content of the core layer. In this embodiment, the order of making and evaluating the specimens does not match the number of the specimens and is unrelated to them.

According to the results of specimens 15, 16, and 17, it can be seen that brazing is good when the magnesium content of the core layer is in the range of 0.5 wt% to 0.75 wt%. Based on the results of specimens 15, 16, and 17, the magnesium content of the brazing layer was increased as in specimens 8, 12, 19, and 20 to confirm whether brazing properties are improved. Specimens 12, 19, and 20 had good magnesium contents at the measurement points, and specimen 8 had a bad magnesium content of 0.43 wt%, which was the same. Specimen 8 had a magnesium content of 0.51 wt%, which was significantly higher than specimens 12, 19, and 20. It is considered that the magnesium content at the measurement point (boundary layer) is determined by the balance of the magnesium content between the core layer and the brazing layer. Therefore, it was determined that proper brazing could not be performed under brazing conditions in which the magnesium content of the core material layer or brazing material layer was increased compared to that of specimens 12, 19, and 20.

Based on the evaluation results of the above specimens 8, 12, 15, 16, 17, 19, and 20, the relationship between the silicon content and the appropriate lower limit of the magnesium content (magnesium deficiency) in the diffusion layer (measurement point) was examined as follows, leading to the above formula (2).

Based on the evaluation results of specimens 15 and 16, a boundary (lower limit) of the magnesium content at the measurement point at which brazing can be performed appropriately (no magnesium deficiency occurs) was determined when the silicon content at the measurement point was approximately 0.65 wt.%.

Specimens 10, 13, 14, 15, 16, 18, and 21 shown in Table 1 have a silicon content of 8 wt. % in the brazing material layer, and because the liquid phase fraction is low due to this silicon content, they are considered to be examples of specimens with the most severe brazing requirements.

Based on the evaluation results of the above specimens 8, 12, 15, 16, 17, 19, and 20, specimens 14 and 18, as well as specimens 10, 13, and 21, were produced and evaluated in which the silicon content of the brazing layer was set to 8 wt. % and the temperature reached during brazing was lowered to suppress diffusion of silicon from the brazing layer into the core layer.

Based on the evaluation results of specimens 14 and 18, a boundary (lower limit) of the magnesium content at the measurement point at which brazing can be performed appropriately (no magnesium deficiency occurs) was determined when the silicon content at the measurement point was approximately 0.5 weight percent.

Furthermore, based on the evaluation results of specimens 10, 13, and 21, a boundary (lower limit) of the magnesium content at the measurement point at which brazing can be performed appropriately (no magnesium deficiency occurs) was defined when the silicon content at the measurement point was approximately 0.36 wt.%.

In this manner, the above formula (2) was derived.

Next, the relationship between the silicon content and the appropriate lower limit of the magnesium content (magnesium deficiency) in the diffusion layer (measurement point) was examined as follows, leading to the above formula (3).

As described above, erosion occurs mainly when the melting point of the core material (diffusion layer) is lowered due to the diffusion of the brazing material components, causing the core material to melt, and it is magnesium and silicon that affect the change in melting point.

Specimens 8 and 19 are specimens that are most susceptible to erosion in terms of silicon content, that is, the brazing layer has the highest silicon content of 12 wt%, and silicon is most likely to diffuse into the core layer, causing the melting point of the core (diffusion layer) to decrease. Specimens 8 and 19 are also specimens that are most susceptible to the highest brazing temperature conditions, causing the core to melt. By comparing specimens 8 and 19, the boundary (upper limit) of the magnesium content at the measurement point at which brazing can be performed properly (no erosion occurs) was determined when the silicon content at the measurement point is about 0.65 wt%. The same boundary can be identified by further taking into account the results of specimens 12 and 20.

Since erosion occurred in specimen 8, specimen 7, which had a lower attained temperature than specimen 8, was fabricated and evaluated, and the boundary (upper limit) of the magnesium content at the measurement point at which brazing can be performed appropriately (no erosion occurs) was determined when the silicon content at the measurement point was approximately 0.59 wt.%.

For test pieces in which the silicon content of the brazing material layer was less than 12 weight percent for specimens 7, 8, and 19, and the magnesium content at the measurement point was equal to or less than that of these specimens, erosion was not expected to occur if the temperature reached was 600°C or less. Therefore, the production and evaluation of such specimens was omitted.

Based on the above results and the Al-Si-Mg ternary phase diagram, the above formula (3) was derived.

Next, the relationship between the silicon content and the appropriate upper limit of the magnesium content (the effect of magnesium oxide generation) in the diffusion layer (measurement point) was examined as follows, leading to the above formula (1).

As described above, if there is an excess of magnesium, magnesium oxide is likely to form on the surface of the test piece, and if the amount of magnesium oxide on the surface of the test piece increases, it becomes an obstruction to the flow of brazing material, resulting in poor brazing.

First, specimens 1 and 2 were produced using test pieces with a magnesium-added brazing layer used in conventional vacuum brazing methods, and the effect of magnesium was examined. The flow distance of the brazing material was small, and it was thought that the brazing was poor due to magnesium oxide. Therefore, specimens 5 and 6 were produced based on specimens 1 and 2, with the magnesium content of the brazing material layer slightly reduced compared to specimens 1 and 2, and the brazing was good. Based on the evaluation results of specimens 1, 2, 5, and 6, the boundary (upper limit) of the magnesium content at the measurement point where brazing can be performed appropriately was determined.

As described above, the magnesium content of the diffusion layer (measurement point) is determined by the balance of the magnesium content of the core material layer and the brazing material layer. In the combination of the core material layer and the brazing material layer in which the magnesium content of the diffusion layer (measurement point) is the same, the condition in which magnesium oxide is most likely to occur on the surface of the test piece and brazing is most likely to be defective is when magnesium is added only to the brazing material layer. Therefore, the boundary (upper limit) of the magnesium content can be appropriately identified by checking the test pieces 1, 2, 5, and 6 in which magnesium is only contained in the brazing material layer. Therefore, the trial production and evaluation of test pieces in which magnesium is contained in a balanced amount in the brazing material layer and the core material layer, which is more advantageous for brazing than these test pieces 1, 2, 5, and 6 in terms of the presence or absence of magnesium oxide generation, was omitted.

In addition, the brazing material layer of specimens 1, 2, 5, and 6 has a silicon content of 8 wt%, which is the most unfavorable condition for brazing in terms of the ease of melting the brazing material. In other words, if the brazing material layer has a higher silicon content than these specimens, it is considered that the brazing properties are more favorable than those of specimens 5 and 6. Therefore, all combinations of brazing material layers and core material layers in which the diffusion layers have the same magnesium and silicon contents as those of specimens 5 and 6 are more favorable for brazing than those of specimens 5 and 6, so the production and evaluation of specimens that are more favorable for brazing than those of specimens 5 and 6 were omitted.

In this manner, the above formula (1) was derived.

Finally, the relationship between the lower limit of the silicon content in the diffusion layer (measurement point) (balance with the liquid phase rate of the brazing material and heat input) was examined as follows, leading to the above formula (4).

As described above, when the brazing material layer has a high silicon content, the melting point of the brazing material is lowered, which is advantageous for brazing.

As the attained temperature increases and the heat input increases, the amount of silicon diffused into the diffusion layer increases. Based on the evaluation results of specimens 4, 5, 9, and 10, which had different attained temperatures and different heat inputs, the lower limit of the silicon content in the diffusion layer (measurement point) was set to 0.36 wt%. Note that specimens 5 and 10 have a brazing layer with a silicon content of 8 wt%, which is more disadvantageous for brazing. In specimens such as specimens 5 and 10, where the brazing layer has a silicon content of more than 8 wt%, brazing is considered to be advantageous in that the liquid phase rate of the brazing material is improved, so the production and evaluation of such specimens was omitted.

In this manner, the above formula (4) was derived.

In this manner, formula (4) was derived from formula (1) above, and region X was defined. As a confirmatory evaluation, specimens 3 and 11 were fabricated and evaluated. In specimen 3, where the silicon and magnesium contents at the measurement points were outside region X, rosion occurred and brazing was poor. In specimen 11, where the silicon and magnesium contents at the measurement points were within region X, good brazing without defects was achieved.

As a further confirmatory evaluation, a specimen 22 having a core material with a larger silicon content than the other specimens was produced and evaluated. In the specimen 22, the silicon and magnesium contents at the measurement points were within the region X, and good brazing without any defects was achieved.

As described above, from the evaluation results of the test specimens 3, 11, and 22, it was confirmed that if the silicon and magnesium contents at the measurement points are located within the region X, good brazing without defects can be performed, and if the silicon and magnesium contents at the measurement points are not located within the region X, the brazing will be defective.

Incidentally, in each of the above-mentioned test specimens, as described above, the brazing filler metal contains bismuth. In general, when the content of bismuth in the brazing filler metal for an aluminum alloy increases, it is possible to improve the wettability of the brazing filler metal (see, for example, Patent Document 3). It is known that the content of bismuth is preferably 0.01% by weight or more and 1.0% by weight or less, and that if it is less than 0.01% by weight, the effect is insufficient, and if it exceeds 1.0% by weight, the effect is saturated and the material cost increases, which is undesirable (see, for example, Patent Document 3). In this embodiment, similar to this knowledge, if the content of bismuth in the brazing filler metal is 1.0% by weight or less, even if the wettability of the brazing filler metal is improved and the brazing property is improved, the brazing filler metal flow distance cannot be expected to decrease, and there is no reason for the occurrence of erosion.

In this embodiment, other elements (e.g., Cu, Fe, Ti, Cr, Zr, Li, V, Ni, Ca, Na, Sr, etc.) that may be contained in the core material are considered not to affect brazeability at the content that may be contained, for example, in Patent Document 2, based on the technical common knowledge of those skilled in the art, for example, known phase diagrams of aluminum and each of the above elements. That is, even if these elements not mentioned in the above examples are contained in the core material in a predetermined amount, it is not expected that these elements will bind to magnesium or silicon in the core material or brazing material, hindering the diffusion of these magnesium and silicon and causing a decrease in brazeability.

In this embodiment, other elements (e.g., Ti, Cr, Zr, Zn, Sr, Na, Sb, Li, Sc, Y, La, Ce, Nd, Dy, Fe, Ca, Be, etc.) that may be contained in the brazing material are considered not to affect brazing properties at the content levels that may be contained, for example, in Patent Document 2, based on the technical common knowledge of those skilled in the art, for example, known phase diagrams of aluminum and each of the above elements. That is, even if these elements not mentioned in the above examples are contained in the brazing material in predetermined amounts, it is not expected that these elements will bind to magnesium or silicon in the core material or brazing material, inhibiting the diffusion of these magnesium and silicon, thereby causing a decrease in brazing properties.

Specifically, in this embodiment, the copper content of the core material is allowed to be 0.05% by mass or more and 0.20% by mass or less, the zinc content of the core material is allowed to be 0.10% by mass or less, and other impurities of the core material are allowed to be 0.05% by mass or less as individual elements and 0.15% by mass or less as the total of the impurities.

Specifically, in this embodiment, the copper content of the brazing filler metal is allowed to be 0.30% by mass or less, the zinc and titanium contents of the brazing filler metal are allowed to be 0.20% by mass or less, and the other impurities of the brazing filler metal are allowed to be 0.05% by mass or less as individual elements and 0.15% by mass or less as the total of the impurities.

In this way, it was shown that a heat exchanger having a brazed connection using a core layer and a brazing material layer having a predetermined silicon and magnesium content, where the silicon and magnesium content at the measurement point is located in region X, suppresses the occurrence of erosion.

In the method for manufacturing a heat exchanger in which brazing is performed at the joint where the silicon and magnesium contents at the measurement points are in region X, the production efficiency of the heat exchanger can be improved because the occurrence of erosion at the joint is suppressed. In addition, because the occurrence of erosion is suppressed, the heat exchanger can be easily made lighter and more durable.

In a manufacturing method for a heat exchanger in which brazing is performed where the silicon and magnesium contents at the measurement points are in region X, when a core material layer and a brazing material layer with predetermined silicon and magnesium contents are used, good brazing can be performed at an ultimate temperature range of 577° C. to 600° C., provided that the heating rate when heating from 400° C. to 577° C. is a temperature rise rate of 50° C. per minute or more. That is, in this manufacturing method for a heat exchanger, good brazing can be performed by controlling the ultimate brazing temperature in a wide range of 577° C. to 600° C. at the time of manufacturing, so that the burden of controlling brazing conditions during manufacturing of the heat exchanger can be reduced, which is efficient.

In this manner, it is possible to provide a heat exchanger in which the occurrence of erosion is suppressed and a manufacturing method thereof.

[Another embodiment]
(1) In the above embodiment, as shown in Fig. 2, a case has been described in which the tubes 3 are formed of the brazing sheet 1, and the fins 4 are a single layer and are formed of the sheet material 2, which is a plate material made of an aluminum alloy. However, the tubes 3 and the fins 4 are not limited to being formed of such materials. The tubes 3 may be formed of the sheet material 2, and the fins 4 may be formed of the brazing sheet 1. The tubes 3 and the fins 4 may be formed of the brazing sheet 1. The core 100 may have a form in which the tubes 3 and the fins 4 are brazed to each other via the brazing material layer 12 (see Fig. 4).

(2) In the above embodiment, as shown in FIG. 7, the case where the measurement point is located at a position in the diffusion layer 13 45 μm away from the brazing material layer 12 toward the core material layer 11 side has been described. However, the description of the measurement point located in the diffusion layer 13 is the same even when the measurement point is located in the diffusion layer 23 on the surface side of the sheet material 2 that is the fin 4 and is a joint and contacts the brazing material layer 12. That is, the measurement point in the diffusion layer 23 at the joint and located at a position 45 μm away from the brazing material layer 12 toward the core material layer 11 side is the same as the measurement point in the diffusion layer 13. However, the diffusion layer 23 near the portion where the tube 3 and the fin 4 are separated from each other may be excluded. In the core 100, it is sufficient that the formulas (1) to (4) described in the above embodiment are satisfied at any of the joints and at any of the measurement points in the diffusion layer 13 or the diffusion layer 23.

(3) In the above embodiment, it has been described that the tubes 3 are heat transfer members that transfer the heat of the fluid flowing through the flow passage 30 to the fluid flowing through the flow passage 40 via the fins 4, and that the fins 4 are heat transfer members that transfer the heat of the tubes 3 to the fluid flowing through the flow passage 40. However, it is also possible that the fins 4 are heat transfer members that transfer the heat of the fluid flowing through the flow passage 40 to the fluid flowing through the flow passage 30 via the tubes 3, and that the tubes 3 are heat transfer members that transfer the heat of the fins 4 to the fluid flowing through the flow passage 30.

(4) In the above embodiment, the brazing sheet 1 has a two-layer structure including the core layer 11 and the brazing material layer 12 arranged on one surface of the core layer 11. However, the brazing sheet 1 is not limited to this structure. For example, the brazing sheet 1 may have a three-layer structure including the core layer 11, the brazing material layer 12 arranged on one surface of the core layer 11, and another brazing material layer on the surface of the core layer 11 opposite to the surface on which the brazing material layer 12 is arranged.

(5) In the above embodiment, the brazing sheet 1 has a two-layer structure including the core layer 11 and the brazing material layer 12 disposed on one surface of the core layer 11. However, the brazing sheet 1 is not limited to this structure. For example, the core layer 11 may be formed of multiple layers. Similarly, the brazing material layer 12 may be formed of multiple layers. In this case, each of the layers constituting the core layer 11 or the brazing material layer 12 only needs to satisfy the requirements described in the above embodiment as the core layer 11 or the brazing material layer 12.

In addition, the configurations disclosed in the above embodiments (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, as long as no contradiction arises. Furthermore, the embodiments disclosed in this specification are examples, and the embodiments of the present disclosure are not limited thereto, and can be appropriately modified within the scope that does not deviate from the purpose of the present disclosure.

The present disclosure is applicable to heat exchangers and methods of manufacturing the same.

1: Brazing sheet 100: Core 11: Core material layer 12: Brazing material layer 13: Diffusion layer 14: Boundary surface 1a: First end 1b: Second end 2: Sheet material 200: Test piece 23: Diffusion layer 3: Tube 30: Flow path 34: Fillet 4: Fin 40: Flow path 41: Top 5: Test piece 51: First joint 52: Second joint 53: Third joint 91: Test piece 92: Aluminum horizontal plate 93: Spacer 94: Contact point 95: Fillet C: Gap G: Point L: Distance P: Virtual line Q: Position R: Virtual line S: Perpendicular line X: Area d: Distance

Claims (6)

A plate-shaped flow path forming member is provided to allow a fluid to flow therethrough,
The flow path forming member is
A core layer;
A brazing material layer;
a diffusion layer formed between the core layer and the brazing material layer,
The core layer is
The magnesium content is 0.5% by mass or more and 0.75% by mass or less,
The manganese content is 1.0 mass% or more and 1.5 mass% or less,
The silicon content is 0.2% by mass or less,
The copper content is 0.05% by mass or more and 0.20% by mass or less,
The zinc content is 0.10% by mass or less;
the balance being aluminum and impurities each of which is 0.05% or less, by weight, and the sum of which is 0.15% or less, by weight;
The brazing material layer is
The magnesium content is 0% by mass or more and 0.9% by mass or less,
The manganese content is 0.05 mass% or less and is less than the manganese content of the core layer,
The silicon content is 8% by mass or more and 12.0% by mass or less,
The copper content is 0.30% by mass or less,
The zinc content is 0.20% by mass or less,
The titanium content is 0.20% by mass or less;
the balance being aluminum and impurities each of which is 0.05% or less, by weight, and the sum of which is 0.15% or less, by weight;
The diffusion layer is a region in which the manganese content exceeds the manganese content of the brazing material layer and the silicon content exceeds the silicon content of the core material layer,
When the maximum value of the magnesium content (mass%) at a measurement point in the diffusion layer that is 45 μm away from the brazing material layer toward the core material layer is represented as Ym and the maximum value of the silicon content (mass%) is represented as Xs, the following relational expression is satisfied:
A heat exchanger , wherein the measurement point is in a direction along a perpendicular line to the boundary surface between the brazing material layer and the diffusion layer, and is a point 45 μm away from the boundary surface toward the core material layer .
Ym≦-0.31Xs+0.71...(1)
Ym≧-0.44Xs+0.58...(2)
Xs≦0.375Ym2-0.92Ym+0.994...(3)
Xs≧0.36...(4) The magnesium content and silicon content in the diffusion layer are
The heat exchanger according to claim 1 , wherein the value is measured by scanning a cross section of the flow path forming member cut perpendicular to the core material layer from the brazing material layer side to the core material layer side using EPMA line analysis. The heat exchanger according to claim 2 , wherein the brazing material layer has a bismuth content of 0.1 mass % or more and 1.0 mass % or less. A second member brazed to the flow passage member,
the flow passage forming member and the second member are brazed via the brazing material layer,
The second member is
The magnesium content is 0.5% by mass or more and 0.75% by mass or less,
The manganese content is 1.0 mass% or more and 1.5 mass% or less,
The silicon content is 0.2% by mass or less,
The copper content is 0.05% by mass or more and 0.20% by mass or less,
The zinc content is 0.10% by mass or less;
3. The heat exchanger of claim 2 comprising a layer of an aluminum alloy with the balance being aluminum and impurities not exceeding 0.05% by weight of each element and not exceeding 0.15% by weight in total . 5. The heat exchanger according to claim 4 , wherein the measurement point is located in the diffusion layer at a joint where the first flow passage forming member, the second flow passage forming member, and the second member are brazed. The flow path forming member is a tube formed by bending into a ring shape,
The tube is
the brazing material layer is disposed at a radially outer position of the annular shape,
a joint portion in which the first end portion and the second end portion of the flow passage forming member are joined together in a state in which the brazing material layer of the first end portion and the brazing material layer of the second end portion of the flow passage forming member are overlapped with each other,
The heat exchanger according to claim 4 , wherein the measurement point is located in the diffusion layer at the joint.

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