JP6431789B2 - Brazing method for hollow structure - Google Patents

Description

  The present invention relates to a method for brazing a hollow structure made of an aluminum material.

  As a heat exchanger made of an aluminum material, a laminated heat exchanger having a plate and an inner fin formed in a dish shape is known (for example, Patent Document 1). The laminated heat exchanger is manufactured by brazing a hollow structure in which plates and inner fins are alternately laminated.

  The hollow structure has a structure in which the edge portions of the plates overlap with each other and the inner fin is disposed in the hollow portion surrounded by the adjacent plates. Usually, the plate is composed of a brazing sheet in which a brazing material is clad on both sides of an aluminum alloy plate. Thereby, brazing of a hollow structure can be performed by one heating.

  Conventionally, as a brazing method for an aluminum material, a brazing material made of an Al—Si (aluminum-silicon) alloy is used, and after applying a fluoride-based flux on the brazing material, the workpiece is heated in a nitrogen atmosphere. The so-called flux brazing method is often used. The flux brazing method has low equipment costs and running costs, and has excellent production efficiency. In addition, the flux brazing method enables corrosion prevention treatment using Zn (zinc) diffusion, so that the aluminum material constituting the heat exchanger can be easily thinned, and thus the entire heat exchanger can be easily formed. The weight can be reduced.

  However, in recent years, as the heat exchanger is further reduced in size and weight, the refrigerant flow path inside the heat exchanger is miniaturized. For this reason, after brazing, there is a problem that the refrigerant flow path is clogged with flux residues. In addition, in the step of performing a surface treatment on the outer surface of the heat exchanger, the cost burden of the work of washing off the flux residue using acid or the like is regarded as a problem.

  Further, the fluoride flux used in the flux brazing method has a problem that it is consumed by reacting with Mg (magnesium) contained in the aluminum material, and the brazing property is deteriorated. Therefore, it is difficult for the flux brazing method to braze a high-strength material containing Mg. Further, since a high-strength material cannot be used, there is a limit to thinning the aluminum material.

  To solve these problems, a so-called fluxless brazing method has been proposed in which Mg or the like having an action of destroying an oxide film is added to a brazing material and brazing is performed in an inert gas atmosphere without using a flux. . For example, Patent Document 2 proposes a method of brazing without flux in a non-oxidizing gas atmosphere using an Al—Si—Mg alloy brazing material.

JP 2014-109388 A Japanese Patent Laid-Open No. 11-285817

  However, when brazing the hollow structure of the plate and the inner fin by the above-mentioned fluxless brazing method, the solder is drawn into the hollow structure at the joined portion between the edges of the adjacent plates, There is a problem that fillets are hardly formed on the outer surface. As a countermeasure, a method of promoting the formation of fillets by applying a fluoride-based flux to the outer surface of the edge has been studied. However, high-strength materials containing Mg cannot be used. There are problems such as instability, and the above problems cannot be solved.

  In addition, in order to improve the brazeability by the fluxless brazing method, a method such as increasing the purity of the inert gas to reduce the oxygen concentration and dew point, or using a high purity argon gas as the inert gas is also considered. It is done. However, these methods have problems in productivity and cost in addition to the effect of forming fillets on the outer surface of the edge, and are difficult to apply to mass production facilities.

  In addition, when brazing a conventional laminated heat exchanger by the fluxless brazing method, the fillet may not be uniformly formed even at the joined portion of the inner fin and the plate.

  As described above, the conventional fluxless brazing method has a problem that it is difficult to stabilize the quality of the brazing joint when brazing the laminated heat exchanger. As a result of repeated studies, the inventors have found that the cause of unstable brazed joint quality is the time transition of fillet formation.

  In the fluxless brazing method, brazing proceeds when an element such as Mg added to the brazing material or the core material breaks the oxide film present on the surface of the brazing material and the mating material. After the heating is started and until the temperature of the brazing material reaches the melting start temperature, Mg or the like diffuses in the solid brazing material and moves to the surface. Therefore, until the temperature of the brazing material reaches the melting start temperature, the destruction of the oxide film of the brazing material proceeds slowly, and the oxide film of the counterpart material is hardly destroyed.

  Immediately after the temperature of the brazing material reaches the melting start temperature and melting begins, neither the brazing material nor the counterpart oxide film is sufficiently destroyed. Therefore, the fillet formation proceeds slowly.

  At this time, in the hollow structure, oxygen in the atmosphere is reduced due to oxidation of the plate and the inner fins. In addition, since the inside of the hollow structure is isolated from the external space by the plate, the atmosphere hardly flows from the external space. As a result, the oxygen concentration in the atmosphere inside the hollow structure is lower than in the external space. Therefore, the destruction of the oxide film existing inside the hollow structure proceeds faster than the oxide film existing on the outer surface of the hollow structure. As a result, the brazing material existing inside the hollow structure can flow earlier than the outer surface.

  Further, in the joined portion of the inner fin and the plate, the inner fin is usually in contact with the plate or facing the plate with almost no clearance, but between the edges of the adjacent plates, A larger clearance may occur than between the fin and the plate. Therefore, the molten wax is easily drawn into the contact portion between the inner fin and the plate due to surface tension.

  When melting of the brazing material proceeds, the joined portions existing inside the hollow structure are connected via the brazing. Therefore, the flowable wax is supplied to the fillet inside the hollow structure, that is, the fillet on the inner side of the joint between the edges of the plate and the fillet of the joint between the plate and the inner fin. Fillets grow rapidly.

  On the other hand, since the destruction of the oxide film is delayed on the outer surface of the hollow structure compared to the inside, the molten wax is drawn into the inner surface of the hollow structure. As a result, a fillet is hardly formed on the outer surface of the hollow structure.

  As a result of further investigations based on the time transition of the fillet formation described above, the inventors have found a brazing method capable of suppressing the phenomenon in which the wax is drawn into the hollow structure.

  That is, the present invention aims to provide a brazing method that can stabilize the quality of brazing joint and is suitable for brazing of a hollow structure made of an aluminum material.

One aspect of the present invention includes a core material containing 0.2 to 1.3% (mass%, the same applies hereinafter) Mg, the balance having a chemical component composed of Al and inevitable impurities, and 7.5 to 13.0. 5. a first brazing material containing 1% Si and 0.004 to 0.1% Li with the balance being Al and inevitable impurities and clad-bonded to one surface of the core material; It contains 0 to 8.5% of Si and 0.004 to 0.1% Li in an amount of 1.0% or more less than the first brazing filler metal, with the balance being Al and inevitable impurities. Preparing a three-layer clad plate material comprising a second brazing material clad and joined to the other surface of the core material,
Prepare inner fins made of aluminum,
From the three-layer clad plate material, it has a flat portion and an edge portion that is provided on the outer peripheral edge of the flat portion and extends outward while extending toward the first brazing material in the thickness direction of the flat portion. Make a dish-shaped plate,
A plurality of the inner fins and the plurality of dish-shaped plates are alternately stacked so that the adjacent edge portions are in contact with each other and the inner fins are in contact with both of the adjacent flat portions. Assemble the body
The hollow structure is brazed by heating the hollow structure in an inert gas atmosphere.

  In the brazing method, the dish-shaped plate is made of a three-layer clad plate material having the specific layer configuration. The first brazing material in the three-layer clad material has a smaller temperature difference between the melting start temperature and the melting end temperature than the second brazing material. Therefore, when brazing by heating the hollow structure body, the wax derived from the first brazing material has a volume of the brazing as the temperature rises as compared to the brazing derived from the second brazing material. Increase quickly. As a result, the brazing derived from the first brazing material flows faster than the brazing derived from the second brazing material, and the inside of the hollow structure, that is, the first brazing material and the inner fins to be joined. A fillet is first formed on the inner side of the bonded portion between the portion and the edge portion.

  On the other hand, the second brazing material has a larger temperature difference between the melting start temperature and the melting end temperature than the first brazing material. Therefore, the volume derived from the second brazing material increases in volume more slowly than the first brazing material. As a result, the wax derived from the second brazing material stays in place until the wax derived from the first brazing material becomes flowable, and flows after the fillet is formed inside the hollow structure. Will be able to.

  And since the wax derived from the second brazing material flows after the fillet is formed inside the hollow structure, it is difficult to be drawn into the hollow structure. In addition, since the wax derived from the second brazing material can be supplied to the outer surface side of the joined portion between the edges, a fillet can be easily formed on the outer surface of the hollow structure.

  The brazing method can flow the first brazing material and the second brazing material at different timings. Thereby, a uniform fillet can be easily formed at the contact portion between the inner fin and the plate.

  In the conventional fluxless brazing, the brazing material inside the hollow structure starts to flow simultaneously. Therefore, the wax is drawn to the part where the plate and the inner fin are in contact with each other and the part where the clearance between the two is small, and the part where the clearance is large is not sufficiently supplied. There was a thing.

  On the other hand, in the brazing method, since the first brazing material and the second brazing material sequentially flow, the concentration of the brazing on the portion where the dish-shaped plate and the inner fin are in contact with each other is concentrated. Can be suppressed. As a result, it is possible to easily supply a sufficient amount of brazing to each bonded portion and form a uniform fillet.

  As mentioned above, according to the said brazing method, the quality of the brazing joining in the hollow structure which consists of aluminum materials can be stabilized.

Sectional drawing of the hollow structure before brazing in an Example. Sectional drawing of the hollow structure of the state in which the 1st brazing material flowed in the Example. Sectional drawing of the hollow structure in the state in which the 2nd brazing material flowed in the Example.

  The dish-shaped plate in the hollow structure is made of the three-layer clad plate material in which the first brazing material is clad-bonded to one surface of the core material and the second brazing material is clad-bonded to the other surface. Hereinafter, the chemical components of the core material, the first brazing material, and the second brazing material will be described in detail.

[First brazing material]
The first brazing filler metal contains Si and 0.004 to 0.1% Li, and the balance has chemical components composed of Al and inevitable impurities.

・ Si (silicon): 7.5 to 13.0%
By setting the content of Si in the first brazing material within the above specific range, it is possible to easily realize the brazing flow at a temperature lower than that of the second brazing material. In addition, by setting the Si content within the above specific range, a sufficient amount of brazing can be supplied to the bonded portion existing inside the hollow structure. As a result, the brazing property can be improved.

  When the Si content is less than 7.5%, the amount of brazing is insufficient and the brazing fluidity is low, so that the function as a brazing material is insufficient. On the other hand, when the Si content exceeds 13.0%, the amount of brazing is excessive and the amount of core material dissolved increases. In this case, the melting end temperature of the first brazing material becomes excessively high. Therefore, when the Si content is out of the specific range, the brazing property is lowered.

Li (lithium): 0.004 to 0.1%
Li has an action of destroying an oxide film present on the surface of the aluminum material. By setting the content of Li in the first brazing material within the specific range, fluxless brazing of the hollow structure can be easily performed. When the Li content is less than 0.004%, the effect of destroying the oxide film is low, and the brazing property inside the hollow structure is lowered. On the other hand, when the Li content exceeds 0.1%, the oxide of Li grows on the surface of the first brazing material, so that the brazing property is lowered.

Bi (bismuth): 0.01 to 0.3%
The first brazing material may further contain 0.01 to 0.3% Bi. Bi has an action of weakening an oxide film present on the surface of the aluminum material. Therefore, Bi can promote breakage of the oxide film and improve brazing properties by coexisting with Li. Moreover, since Bi has the effect | action which reduces the surface tension of a solder | brazing | wax, a brazing | wax will flow easily into the narrow clearance gap between to-be-processed objects. As a result, the reliability of brazing joint can be further improved.

  By making the Bi content in the specific range described above, the above-mentioned effects can be sufficiently obtained, and the brazing property of the hollow structure is further improved and the reliability of the brazing joint is further improved. Can do. When the Bi content is less than 0.01%, the above-described effects may be insufficient. On the other hand, when the Bi content exceeds 0.3%, it is difficult to obtain the effect of improving the brazing property commensurate with the Bi content. Further, when the Bi content is excessively large, the surface of the brazing material may be discolored, and in some cases, the brazing property may be deteriorated.

Mg (magnesium): 0.5% or less The first brazing material may further contain 0.5% or less of Mg. In this case, the hollow structure brazing property can be further improved by the action of destroying the Mg oxide film. When the Mg content exceeds 0.5%, the Mg oxide may grow on the surface of the first brazing material, which may cause a decrease in brazeability.

Sr (strontium), Sb (antimony), Fe (iron), Mn (manganese), Ti (titanium), Cu (copper), Zn (zinc)
The first brazing material may contain Sr, Sb, Fe, Mn, and Ti in order to adjust the fluidity of the brazing. The first brazing material may contain Cu and Zn in order to adjust the melting start temperature of the brazing material. The content of these elements can be appropriately set within a range that does not deteriorate the brazing property.

[Second brazing material]
The second brazing material contains 6.0 to 8.5% Si and 1.0% or more less than the first brazing material and 0.004 to 0.1% Li, with the balance being Al and It has chemical components consisting of inevitable impurities.

Si: 6.0 to 8.5% and 1.0% or more less than the first brazing material In order to realize the brazing method, the melting start temperature and the melting end temperature in the second brazing material It is necessary to increase the temperature difference to a certain degree so that the wax derived from the first brazing material flows at a lower temperature than the wax derived from the second brazing material. By setting the content of Si in the second brazing material within the specific range, a second brazing material suitable for the brazing method can be easily realized, and brazing properties can be improved.

  When the Si content is less than 6.0%, the amount of brazing is insufficient, and the brazing fluidity is low, so that the function as a brazing material is insufficient. Therefore, brazability is reduced. On the other hand, when the Si content exceeds 8.5%, the temperature difference between the melting start temperature and the melting end temperature becomes small. Therefore, the wax derived from the second brazing material can flow relatively early and is easily drawn into the hollow structure. As a result, the brazing property on the outer surface of the hollow structure is lowered.

  Further, when the difference in Si content between the second brazing material and the first brazing material is less than 1.0%, the temperature difference between the melting start temperature and the melting end temperature in the second brazing material is the first. The temperature difference is about the same as that of the brazing material. Therefore, the wax derived from the second brazing material may flow before the fillet formation in the hollow structure is completed. As a result, the wax derived from the second brazing material is easily drawn into the hollow structure, and the brazing property on the outer surface of the hollow structure is reduced.

Li: 0.004 to 0.1%
The second brazing material contains 0.004 to 0.1% of Li. The effect and limitation reason of Li are the same as those of the first brazing material.

Bi: 0.01 to 0.3%, Mg: 0.5% or less, Sr, Sb, Fe, Mn, Ti, Cu, Zn
The second brazing material may further contain Bi, Mg, Sr, Sb, Fe, Mn, Ti, Cu, and Zn. The effects and limitations of these elements are the same as in the first brazing material.

[Heart]
The core material contains 0.2 to 1.3% Mg, and the balance has chemical components composed of Al and inevitable impurities.

Mg: 0.2 to 1.3%
Mg contained in the core material diffuses into the first brazing material and the second brazing material by heating during brazing. Since Mg that has reached the surface of each brazing material breaks the oxide film, it is possible to easily flux-less braze the hollow structure. When the content of Mg in the core material is less than 0.2%, the amount of Mg that reaches the surface of the brazing material is reduced, resulting in a decrease in brazeability. On the other hand, when the Mg content exceeds 1.3%, the amount of Mg reaching the surface of the brazing material becomes excessive. As a result, Mg oxide grows on the surface of the brazing material, resulting in a decrease in brazeability.

Mn: 0.05 to 1.3%, Si: 1.0% or less, Fe: 1.0% or less, Cu: 0.9% or less, Zn: 6.5% or less, Ti: 0.2% Hereinafter, Zr (zirconium): 0.5% or less The core material is further made from 0.05 to 1.3% Mn, 1.0% or less Si, 1.0% or less Fe, 0.9% or less. It is preferable to include one or more selected from Cu, 6.5% or less of Zn, 0.2% or less of Ti and 0.5% or less of Zr. These elements can further improve the strength and corrosion resistance of the core material. When the content of these elements is excessively large, the material may be broken in the rolling process when the three-layer clad plate material is manufactured, and the productivity may be reduced.

  The inner fin in the hollow structure is preferably a brazing sheet in which a brazing material made of an Al—Si based alloy is clad on both surfaces of a core material made of an aluminum alloy. In this case, more wax can be supplied to the joined portion between the inner fin and the dish-shaped plate, and the fillet can be formed more easily. As a result, the wax derived from the second brazing material is less likely to be drawn into the hollow structure, and the fillet can be more easily formed on the outer surface of the joined portion between the edges of the dish-shaped plate.

  Similarly to the brazing material for the plate-like plate, elements such as Li and Bi may be added to the brazing material for the inner fin. Further, Mg may be added to the core material of the inner fin in the same manner as the brazing material of the plate-like plate. By adding these elements, the brazing property of the hollow structure can be further improved.

  Further, by using an Al—Si alloy having a low melting start temperature for the brazing material of the inner fin, sufficient brazing can be supplied to the fillet inside the hollow structure. As a result, a fillet can be more easily formed on the outer surface of the hollow structure.

  The brazing of the hollow structure is performed by heating a plurality of inner fins and a plurality of dished plates alternately stacked as described above and then pressing the stacked body from both sides in the stacking direction. Do.

  It is preferable that the hollow structure is brazed with the flat portion side of each of the dish-shaped plates facing upward. In this case, it can suppress that the wax originating in the 1st brazing material is drawn near to the to-be-joined part which exists under the inner fin. Further, in this case, the fillet can be formed first in the portion to be joined that exists above the portion to be joined between the plate-like plate and the inner fin. As a result, a uniform fillet can be more easily formed at the bonded portion between the plate-like plate and the inner fin.

  Further, a part of the wax derived from the first brazing material flows along the edge of the dish-shaped plate by gravity, and is supplied to the joined part between the edges. As a result, it is possible to further improve the brazability at the joined parts between the edges.

  As an atmosphere at the time of brazing, an inert gas that can be used industrially, such as nitrogen, argon, and a mixed gas of nitrogen and argon, can be used. From the viewpoint of improving the brazing property, the oxygen concentration of the inert gas is preferably as low as possible. In the brazing method, for example, an inert gas having an oxygen concentration of 50 ppm or less can be suitably used.

  The heating temperature during brazing is preferably 585 to 620 ° C, and more preferably 590 to 610 ° C. When the heating temperature is less than 585 ° C., the brazing fluidity becomes insufficient, and the brazing property may be lowered. On the other hand, when the heating temperature exceeds 620 ° C., there is a possibility that erosion that a part of the core material melts occurs. Moreover, it is preferable to make the temperature increase rate at the time of brazing as fast as possible from the viewpoint of suppressing the oxidation of the plate-like plate and the inner fin during the temperature increase.

  It is also possible to use a bare material made of an aluminum alloy as the inner fin.

(Example)
An example of the brazing method will be described with reference to the drawings. First, a three-layer clad plate material in which a first brazing material B is clad joined to one surface of the core material A and a second brazing material C is clad joined to the other surface, and an inner fin 2 made of an aluminum material are prepared. . The core material A contains 0.2 to 1.3% (mass%, the same applies hereinafter) of Mg, and the balance has chemical components composed of Al and inevitable impurities. The first brazing material B contains 7.5 to 13.0% Si and 0.004 to 0.1% Li, with the remainder having chemical components composed of Al and inevitable impurities. The second brazing material C contains 6.0 to 8.5% of Si and 1.04% or less less than the first brazing material B and 0.004 to 0.1% of Li, with the balance being Al. And chemical components composed of inevitable impurities.

  The inner fin 2 of this example is a corrugated fin made of an aluminum alloy bare material.

  Next, the three-layer clad plate material is subjected to press working to produce a plate-like plate 3 shown in FIG. The dish-shaped plate 3 includes a flat portion 31 and an edge portion 32 provided on the outer peripheral edge of the flat portion 31 and extending outward while extending toward the first brazing filler metal B side in the thickness direction of the flat portion 31. Have.

  Next, the plurality of inner fins 2 and the plurality of dish-shaped plates 3 are alternately overlapped so that the adjacent edge portions 32 are in contact with each other and the inner fins 2 are in contact with both of the adjacent flat portions 31. As a result, the hollow structure 1 is assembled. Then, brazing is performed by heating the hollow structure 1 in an inert gas atmosphere.

  For the sake of convenience, FIG. 1 shows a portion where there is a clearance between the edge portions 32 of the plate-like plate 3, but the adjacent edge portions 32 are in contact with each other at a portion not shown in the drawing. .

  Hereinafter, the time transition of fillet formation in the brazing method will be described in detail. In addition, in this example, the time transition of fillet formation in the case of brazing the hollow structure 1 in a state where the flat portion 31 side of each dish-shaped plate 3 is directed upward is shown.

  When the temperature of the hollow structure 1 reaches the melting start temperature of the first brazing material B due to the heating at the time of brazing, the first brazing material B gradually melts while remaining in place, and the brazing D is generated. When the temperature of the hollow structure 1 further rises, the volume of the wax D derived from the first brazing material B increases, and the wax D can flow. At this time, the second brazing material C is partially melted but cannot flow.

  Part of the wax D that has become flowable flows along the edge portion 32 of the plate-like plate 3 due to surface tension or gravity, and is supplied to the joined portion 321 between the edge portions 32 of the plate-like plate 3. As a result, as shown in FIG. 2, a fillet is formed on the inner side 321b prior to the outer surface side 321a of the joined portion 321 between the edge portions 32.

  Further, the wax D derived from the first brazing material B is also supplied to the bonded portion 21a between the plate-like plate 3 and the upper part of the inner fin 2, and forms a fillet.

  In the conventional fluxless brazing method, since the brazing material existing inside the hollow structure flows at the same time, the upper portion of the inner fin and the lower portion of the inner fin are connected via the brazing. . Therefore, the wax is biased downward due to gravity, and the wax supplied to the upper portion of the inner fin is likely to be insufficient.

  On the other hand, in the brazing method, as shown in FIG. 2, the upper bonded portion 21 a of the inner fin 2 and the lower bonded portion 21 b are not connected by the brazing D. Therefore, it is possible to suppress the brazing D derived from the first brazing material B from being attracted to the joined portion 21 b below the inner fin 2. Therefore, a sufficient amount of the wax D can be supplied to the bonded portion 21a at the upper part of the inner fin 2, and a uniform fillet can be easily formed.

  When the temperature of the hollow structure 1 is further increased, the wax E derived from the second brazing material C can flow. At this time, since the fillet formed in the upper bonded portion 21a of the inner fin 2 is separated from the second brazing material C, the wax D existing in the upper bonded portion 21a becomes the lower bonded portion 21b. It will not be attracted. In addition, in the joined portion 321 between the edge portions 32, since the fillet has already been formed on the inner side 321b of the hollow structure 1, the wax E generated on the outer surface of the hollow structure 1 is difficult to be drawn inside. Therefore, the brazing E derived from the second brazing material C, as shown in FIG. 3, is an outer portion of the joined portion 21 b between the dish-shaped plate 3 and the lower portion of the inner fin 2 and the joined portion 321 between the edges 32. It is supplied to the surface side 321a.

  As a result, when the brazing is completed, any one of the upper bonded portion 21a, the lower bonded portion 21b, the inner side 321b of the bonded portion 321 between the edges 32, and the outer surface side 321a is completed. In addition, a sufficient amount of wax D and E can be supplied to form a fillet. Therefore, according to the brazing method, the quality of the brazing joint in the hollow structure 1 can be easily stabilized.

(Experimental example)
This example is an example in which the brazing property is evaluated by changing the alloy type of the three-layer clad plate material constituting the dish-shaped plate 3. Hereinafter, a preparation method and an evaluation method of the specimen will be described.

[Preparation of specimen]
-Three-layer clad board material The alloy (alloy A1-A20) which has a chemical component shown in Table 1 was cast, and the obtained ingot was heated at 500 degreeC, and the homogenization process was performed. Subsequently, the ingot was hot-rolled to produce a brazing material plate having a thickness of 5 mm.

  Separately from the production of the brazing material plate, alloys (alloys B1 to B5) having chemical components shown in Table 2 were cast, and the resulting ingot was heated at 600 ° C. to perform a homogenization treatment. Thereafter, the ingot was chamfered to produce a core plate having a thickness of 40 mm.

  The brazing material plate and the core material plate obtained as described above were superposed in the combinations shown in Table 3, and clad rolled at 500 ° C. and joined together. Thereby, an intermediate material having a thickness of 2 mm was obtained. The obtained intermediate material was cold-rolled to a thickness of 0.4 mm and then annealed. Thus, a three-layer clad plate material was obtained. The clad rate of the first brazing material B and the second brazing material C in the three-layer clad plate material was 10%. The clad rate is the ratio of the thickness of each brazing material to the total thickness of the three-layer clad plate material.

-Assembling of the hollow structure 1 The three-layer clad plate material was pressed to produce the dish-shaped plate 3 shown in FIG. Corrugation was applied to a 1 mm plate material to produce an inner fin 2. The obtained plate-like plate 3 and inner fin 2 were alternately laminated as shown in FIG. 1 and fixed by a jig (not shown) to assemble the hollow structure 1 (Table 3, test bodies 1 to 21). .

-Brazing After installing the hollow structure 1 in the heating furnace with the flat portion 31 side of each dish-shaped plate 3 facing upward, the atmosphere in the heating furnace is replaced with nitrogen, and the oxygen concentration in the atmosphere Was 20 ppm or less. Thereafter, heating was performed while measuring the temperature of the hollow structure 1. Specifically, after raising the temperature so that the required time from the start of heating until the temperature of the hollow structure 1 reaches 600 ° C. is about 15 minutes, the temperature of the hollow structure 1 is kept at 600 ° C. Hold for 3 minutes to complete heating. After the heating was completed, the hollow structure 1 was cooled in the furnace and then taken out of the furnace.

[Evaluation]
The hollow structure 1 after brazing was cut as shown in FIG. 3, and the fillet on the inner side 321b and the fillet on the outer surface side 321a in the joined portion 321 between the edge portions 32 were visually evaluated. The results are shown in Table 3. In addition, the meaning of the symbol shown in the “Visual evaluation of fillet” column of Table 3 is as follows.

A: A continuous fillet was formed and the fillet size was uniform. B: A continuous fillet was formed, but there was some variation in the fillet size. C: The fillet was partially broken. Was not continuous

  As is known from Tables 1 to 3, in the test bodies 1 to 12, the first brazing material B, the second brazing material C, and the core material A have chemical components in the specific range. Therefore, in the test bodies 1 to 12, continuous fillets were formed on both the outer surface side 321 a and the inner side 321 b in the joined portion 321 between the edge portions 32.

Since the test body 13 had low Si content in both the first brazing material B and the second brazing material C, the fluidity of the brazing materials D and E was insufficient. As a result, both the fillet on the outer surface side 321a and the inner side 321b became discontinuous.
Since the test body 14 had a large Si content in the first brazing material B, the fluidity of the brazing D was insufficient. As a result, both the fillet on the outer surface side 321a and the inner side 321b became discontinuous.

Since the test body 15 had a high Si content in the second brazing material C, the second brazing material C flowed during the formation of the fillet on the inner side 321b. As a result, the fillet on the outer surface side 321a became discontinuous.
Since the difference between the Si content in the second brazing material C and the Si content in the first brazing material B is small in the test body 16, the second brazing material C is in the process of forming the fillet on the inner side 321b. Flowed. As a result, the fillet on the outer surface side 321a became discontinuous.
In the test body 17, since the Si content in the second brazing material C was higher than the Si content in the first brazing material B, the second brazing material C was formed before the fillet on the inner side 321 b began to be formed. Flowed. As a result, the fillet on the outer surface side 321a became discontinuous.

Since the test body 18 had little Li content in the 2nd brazing material C, the oxide film was not fully destroyed. As a result, both the fillet on the outer surface side 321a and the inner side 321b became discontinuous.
In the test body 19, since both the first brazing material B and the second brazing material C have a large content of Li, an oxide of Li grew excessively. As a result, both the fillet on the outer surface side 321a and the inner side 321b became discontinuous.

Since the test body 20 had a low Mg content in the core material A, the oxide film was not sufficiently destroyed. As a result, both the fillet on the outer surface side 321a and the inner side 321b became discontinuous.
Since the test body 21 had much Mg content in the core material A, the Mg oxide grew excessively. As a result, both the fillet on the outer surface side 321a and the inner side 321b became discontinuous.

  The above-described examples and experimental examples are examples of the brazing method, and the configuration can be appropriately changed without changing the gist thereof. For example, in the examples and experimental examples, the flat portion 31 of the plate-like plate 3 is shown as being completely flat. However, the flat portion 31 is curved as long as it can be brazed with the inner fin 2. It may be. It is also possible to provide protrusions or the like on the flat portion 31 for causing turbulent flow in the refrigerant.

DESCRIPTION OF SYMBOLS 1 Hollow structure 2 Inner fin 3 Dish plate 31 Flat part 32 Edge A Heart material B 1st brazing material C 2nd brazing material

Claims (5)

A core material containing 0.2 to 1.3% (mass%, the same shall apply hereinafter) of Mg, with the balance being a chemical component consisting of Al and inevitable impurities, and 7.5 to 13.0% Si and 0.004 A first brazing material containing a chemical component comprising -0.1% Li with the balance being Al and inevitable impurities, clad to one side of the core material; 6.0-8.5% and The other side of the core material having a chemical component containing Si and 0.004 to 0.1% Li in an amount of 1.0% or more less than the first brazing material, with the balance being Al and inevitable impurities. A three-layer clad plate material comprising a second brazing material clad and bonded to
Prepare inner fins made of aluminum,
From the three-layer clad plate material, it has a flat portion and an edge portion that is provided on the outer peripheral edge of the flat portion and extends outward while extending toward the first brazing material in the thickness direction of the flat portion. Make a dish-shaped plate,
A plurality of the inner fins and the plurality of dish-shaped plates are alternately stacked so that the adjacent edge portions are in contact with each other and the inner fins are in contact with both of the adjacent flat portions. Assemble the body
A method for brazing a hollow structure, wherein the hollow structure is brazed by heating in an inert gas atmosphere.   The method for brazing a hollow structure according to claim 1, wherein at least one of the first brazing material and the second brazing material further contains 0.01 to 0.3% Bi. .   The core material further comprises 0.05 to 1.3% Mn, 1.0% or less Si, 1.0% or less Fe, 0.9% or less Cu, 6.5% or less Zn, 0% The method for brazing a hollow structure according to claim 1 or 2, comprising one or more selected from Ti of 2% or less and Zr of 0.5% or less.   The hollow structure according to any one of claims 1 to 3, wherein the inner fin is a brazing sheet in which a brazing material made of an Al-Si alloy is clad on both surfaces of a core material made of an aluminum alloy. How to braze the body.   The hollow structure body according to any one of claims 1 to 4, wherein the hollow structure body is brazed in a state in which the flat portion side of each dish-shaped plate is directed upward. Brazing method.

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