JP5952995B2 - Aluminum alloy fin material for heat exchanger - Google Patents

Description

  The present invention particularly relates to an aluminum alloy fin material for a heat exchanger that is preferably used as a fin material for a heat exchanger such as a radiator, a heater, a condenser, and an intercooler.

  Aluminum alloys are lightweight and have high thermal conductivity, and are therefore used in automotive heat exchangers such as radiators, condensers, evaporators, heaters, intercoolers, and the like.

  In such heat exchangers, for example, corrugated aluminum alloy fins are conventionally brazed. As the aluminum alloy fin material, a pure aluminum alloy such as JIS1050 alloy having excellent thermal conductivity and an Al-Mn alloy such as JIS3003 alloy having excellent strength and buckling resistance have been generally used.

  By the way, in recent years, demands for weight reduction, size reduction, and high performance have been increasing for heat exchangers. Accordingly, it is particularly desired that the aluminum alloy fin material to be brazed and joined is thin and has excellent properties such as strength, thermal conductivity, and corrosion resistance.

  Patent Documents 1 and 2 propose a vacuum brazing fin material containing Si, Mn, and Mg as strengthening elements and added with In or Sn in order to give the fin a sacrificial anticorrosive action.

  Patent Document 3 proposes a fin material for CAB (Controlled Atmosphere Brazing) containing Mg, Si and Zn, and adding Mn, Cu and the like as necessary. The CAB method is a brazing method in which a non-corrosive flux (fluoride-based flux) is applied and heated in a non-oxidizing gas atmosphere.

  Patent Document 4 proposes a gas phase brazing fin material to which Mg, Si, Fe, Zn and the like are added. The gas phase brazing method is a brazing method performed in flux steam.

JP 57-098646 A JP-A-57-207153 Japanese Patent Laid-Open No. 62-182244 Japanese Patent Laid-Open No. 03-122238

  However, the above technique has the following problems.

  The vacuum brazing method has a demerit that Zn for providing sacrificial anticorrosive action to the fin cannot be used. This is because, since brazing is performed in a vacuum, even if Zn is added, it evaporates, and almost no Zn remains after brazing. Therefore, in the techniques disclosed in Patent Documents 1 and 2, In or Sn is added instead of Zn, but these elements greatly impair castability and rollability, and reduce productivity. There are drawbacks. In addition, since the aluminum alloys disclosed in Patent Documents 1 and 2 contain Mn, there is a disadvantage that the thermal conductivity of the fin is greatly reduced when Mn is dissolved. As a result, the heat exchanger is reduced in weight and size.

  The CAB method has a demerit that Mg as a strengthening element cannot be used. This is because the added Mg reacts with the non-corrosive flux used for removing the oxide film and inhibits the action of the flux to greatly reduce the brazing property. In addition, even if the flux application amount is increased to compensate for the reduction in brazing, in the case of a thin plate member such as a fin, most of the added Mg reacts with the flux and remains after brazing. Therefore, it does not contribute to strength improvement. In the aluminum alloy disclosed in Patent Document 3, Mg is added. However, for the reason described above, there is a drawback that the strength is hardly improved only by greatly reducing the brazing property.

  In the technique disclosed in Patent Document 4, the mechanism for removing the oxide film in the gas phase brazing method is the same as that in the CAB method, and only the flux supply method is different. For this reason, Mg is also added to the aluminum alloy disclosed in Patent Document 4, but the action of Mg is the same as that in the CAB method even in vapor phase brazing, so that brazing properties and strength are also lowered. There are drawbacks.

  The present invention has been made in view of such problems, has good brazing properties, and has excellent strength, thermal conductivity and corrosion resistance after brazing, particularly as a heat exchanger fin for automobiles. It aims at providing the aluminum alloy fin material which can be used conveniently.

In order to achieve the above object, an aluminum alloy fin material for a heat exchanger according to the present invention,
An aluminum alloy fin material for a heat exchanger having no brazing material, which is brazed without flux in a non-oxidizing gas atmosphere having an oxygen concentration of 10 ppm or less and has a tensile strength of 120 N / mm ² or more after brazing. ,
Si: 0.2-1.2% (mass%, the same shall apply hereinafter), Fe: 0.02-0.5%, Mg: 0.1-0.8%, Zn: 0.1-2.0% And the balance consists of Al and inevitable impurities,
It is characterized by that.

Moreover, the aluminum alloy fin material for other heat exchangers of the present invention is
An aluminum alloy fin material for a heat exchanger having no brazing material, which is brazed without flux in a non-oxidizing gas atmosphere having an oxygen concentration of 10 ppm or less and has a tensile strength of 120 N / mm ² or more after brazing. ,
Si: 0.2-1.2% (mass%, the same shall apply hereinafter), Fe: 0.02-0.5%, Mg: 0.1-0.8%, Zn: 0.1-2.0% Further, Ti: 0.02-0.3%, Zr: 0.02-0.3%, Cr: 0.02-0.3%, V: 0.02-0.3% Containing one or more of them, the balance consisting of Al and inevitable impurities,
It is characterized by that.

  According to the present invention, there is provided an aluminum alloy fin material that has good brazing properties and has excellent strength, thermal conductivity and corrosion resistance after brazing, and can be suitably used particularly as a fin of an automotive heat exchanger. can do.

It is a perspective view which shows typically the structure of the core for evaluation of a fin joining rate.

  As a result of studying the above problems, the present inventors have met the purpose by brazing a fin material having a specific alloy composition under low oxygen partial pressure without using a flux (hereinafter also referred to as “no flux”). I found out. Hereinafter, embodiments of the present invention will be specifically described.

  First, the reason and range of addition of the component elements of the aluminum alloy fin material of this embodiment will be described.

Si contributes to strength improvement by dispersion strengthening by forming an Al—Fe—Si based compound with Fe or by solid solution strengthening by dissolving in a matrix. Moreover, Si precipitates as fine Mg ₂ Si together with Mg, and improves the strength. The preferable content of Si in the present embodiment is 0.20 to 1.20% (mass%, the same in the description of the embodiment below). When the Si content is less than 0.20%, the above effect is reduced. Further, if the Si content exceeds 1.20%, the solidus temperature (melting point) of the material is lowered and the possibility of melting at the time of brazing is increased, and the amount of solid solution in the matrix is increased. Conductivity decreases. A more preferable Si content is 0.30 to 1.0%.

  Fe has the effect of increasing the high-temperature strength and preventing deformation during brazing heating. Fe forms an Al—Fe—Si based compound with Si and contributes to strength improvement as dispersion strengthening. The preferable content of Fe in this embodiment is 0.02 to 0.50%. When the Fe content is less than 0.02%, the effect of improving the strength is small. Further, when the Fe content exceeds 0.50%, a large amount of intermetallic compounds of a size that can be recrystallized nuclei during brazing are dispersed, so that the crystal grains after brazing become fine and brazing diffusion may occur. is there. A more preferable Fe content is 0.05 to 0.40%.

Mg dissolves in the matrix and contributes to strength improvement as solid solution strengthening. Further, Mg precipitates as fine Mg ₂ Si together with Si and improves the strength. In addition, Mg has the effect of lowering the oxygen concentration around the brazed joint by evaporating part of the added during brazing, and brazing properties by removing the oxide film on the material surface Is effective. The preferable content of Mg in the present embodiment is 0.10 to 0.80%. When the Mg content is less than 0.10%, the above effect is reduced. On the other hand, if the Mg content exceeds 0.80%, a strong MgO oxide film is formed on the surface of the material, so that the brazing property is lowered. Furthermore, when the content exceeds 0.80%, the solidus temperature (melting point) of the material is lowered, and the possibility of melting at the time of brazing increases, and the solid solution amount of Mg in the matrix increases. Therefore, thermal conductivity is reduced. A more preferable Mg content is 0.15 to 0.60%.

  Zn has the effect of lowering the natural potential of the fin and improving the sacrificial anticorrosive effect. The preferable content of Zn in the present embodiment is 0.10 to 2.0%. When the Zn content is less than 0.10%, the above effect is reduced. On the other hand, if the Zn content exceeds 2.0%, the corrosion rate increases and the self-corrosion resistance of the fins decreases. Furthermore, when the content exceeds 2.0%, the solid solution amount of Zn in the matrix increases, so that the thermal conductivity decreases. A more preferable Zn content is 0.30 to 1.5%.

  The fin material of this embodiment may further contain a predetermined amount of one or more of Ti, Zr, Cr, and V.

  Ti, Zr, Cr and V are all effective in improving the strength. The preferred contents of Ti, Zr, Cr and V are 0.02 to 0.30%, respectively. When the content of the element is less than 0.02%, the above effect is reduced. On the other hand, if the content exceeds 0.30%, a giant intermetallic compound is produced during casting to lower the plastic workability, and the amount of solid solution in the matrix increases, so that the thermal conductivity decreases.

  Next, the manufacturing method of the aluminum alloy fin material of the present invention will be described.

  First, an aluminum alloy having the above component composition is melted and cast into a slab, and then homogenized as necessary. The casting method is not particularly limited, but DC (Direct Chill) casting is desirable. The homogenization treatment may not be performed, but when it is performed, the treatment temperature is preferably 450 to 550 ° C. When the homogenization treatment temperature is less than 450 ° C., the homogenization effect for eliminating segregation during casting becomes small. When the homogenization temperature exceeds 550 ° C., the intermetallic compound crystallized or precipitated at the time of casting is coarsened, which may cause wax diffusion due to the refinement of crystal grains of the fin material.

  Then, the slab which performed the homogenization process as needed is hot-rolled at the temperature of 380-550 degreeC, and produces a 2-5 mm board | plate material. If the temperature during hot rolling is less than 380 ° C., the deformation resistance of the slab is high and it is difficult to crush. When the temperature at the time of hot rolling exceeds 550 ° C., as described above, there is a possibility that wax diffusion due to the refinement of crystal grains of the fin material may occur.

  Subsequently, the obtained plate material is cold-rolled and annealed as necessary to obtain a fin material. The final plate thickness of the fin material is not limited to this, but is about 0.04 to 0.10 mm. In the case of carrying out intermediate annealing in which annealing is performed in the middle of cold rolling, the final cold rolling rate is 5 to 50%. For the annealing, either a batch annealing furnace or a continuous annealing furnace (CAL) may be used. The annealing temperature is preferably 150 to 450 ° C. when performing batch annealing, and 350 to 550 ° C. when performing in a continuous annealing furnace (CAL).

  Next, a preferable brazing method for the aluminum alloy fin material of the present embodiment having the above-described alloy composition will be described. In the present embodiment, brazing is performed in a non-oxidizing gas atmosphere with a furnace oxygen concentration of 10 ppm or less and without flux. The reason is as follows.

  In order to perform brazing of an aluminum alloy, it is necessary to destroy the oxide film present on the surface of the object to be brazed and bring the brazing material and the object to be brazed into metal contact. For example, in the vacuum brazing method, the oxide film is removed by Mg added to the brazing material, and in the CAB method, the oxide film is removed by flux.

  On the other hand, in this embodiment, the flux is not used in the non-oxidizing gas atmosphere, and the oxide film is removed by Mg added to the fin material that is to be brazed. Here, as the non-oxidizing gas used at the time of brazing, industrially used nitrogen gas, argon gas, or the like can be used.

  By brazing by the above method, a part of Mg added to the fin material evaporates in the atmosphere at the time of brazing and floats in the vicinity of the joint portion with the brazed object. And Mg floating in the atmosphere destroys the oxide film present on the surface of the brazed object by the reducing action and prevents reoxidation of the metal aluminum exposed after the oxide film is removed.

  In addition, since brazing is performed in a non-oxidizing gas atmosphere, it is possible to use Zn, which is difficult to use by the vacuum brazing method. In the brazing method of this embodiment, the oxide film is removed with Mg added to the fin material. However, since the removal action of Mg itself is considered to be smaller than the flux used in the CAB method, it is non-oxidized. The oxygen concentration in the reactive gas atmosphere has a significant effect on the brazeability. In the present embodiment, the preferable oxygen concentration in the furnace is 10 ppm or less. When the oxygen concentration exceeds 10 ppm, the metal aluminum exposed after removal of the oxide film is re-oxidized and the brazing property is lowered. A more preferable furnace oxygen concentration is 5 ppm or less.

  As described above, according to the present embodiment, since a non-corrosive flux is not used, good brazing properties can be obtained even when Mg is added. The anticorrosion effect can be used effectively. Also, high thermal conductivity can be obtained. Therefore, a fin material that can be suitably used as an aluminum alloy fin material for thin heat exchangers is obtained.

  Next, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

  First, an aluminum alloy having the alloy composition shown in Table 1 was cast by a DC casting method and finished by chamfering both surfaces. In the alloy composition of Table 1, “−” indicates that it is below the detection limit, and “remainder” includes inevitable impurities.

  Thereafter, the produced ingot was not homogenized and heated to 500 ° C., and then rolled to a desired thickness by hot rolling to produce a plate material. Subsequently, the obtained plate material was cold-rolled and subjected to intermediate annealing at 370 ° C. × 2 h in a batch annealing furnace to produce a fin material (tempered: H1n) having a final plate thickness of 0.06 mm.

  And each produced fin material was made into the test material (alloy No. 1-9), and the brazing heating was performed. Table 2 shows the conditions regarding the oxygen concentration in the furnace and the presence or absence of flux application to the test material when brazing is performed. Test material No. Only the test piece which evaluates a tensile strength and a fin joining rate only 13 was flux-applied, and the brazing heating was implemented. The flux was applied by immersing the test piece in a suspension in which the fluoride flux was adjusted to 5% concentration. Then, evaluation about intensity | strength, electrical conductivity, brazing property, and corrosion resistance was performed with respect to each test material by the method shown below, and those results were shown in Table 3. Here, the measurement of electrical conductivity is for evaluating the thermal conductivity of the fin material. In the case of an aluminum alloy, it can be determined that the higher the electrical conductivity, the better the thermal conductivity. In this specification, “brazing heating” refers to the temperature and time assumed to be the actual brazing of the fin material, and heating the specimen alone unless otherwise specified. To do.

[A] Tensile strength after brazing (N / mm ² ):
The specimen was brazed and heated at 600 ° C. × 3 min, then cooled at a cooling rate of 200 ° C./min, and then allowed to stand at room temperature for 1 week to obtain a sample. Each sample was subjected to a tensile test at room temperature in accordance with JIS Z2241 under conditions of a tensile speed of 10 mm / min and a gauge length of 50 mm.

[B] Conductivity (% IACS):
The specimen was brazed and heated at 600 ° C. × 3 min, and then cooled at a cooling rate of 200 ° C./min to obtain a sample. And the electrical conductivity was calculated | required by measuring an electrical resistance with respect to each sample according to JISH0505 in a 20 degreeC thermostat. Note that the unit% IACS represents the conductivity defined in JIS H0505 in this specification.

[C] Fin joint ratio (%):
First, as shown in FIG. 1, a corrugated specimen (fin 11) and a brazing sheet 12 having a plate thickness of 0.3 mm in which JIS 3003 is a core material 13 and 10% of JIS 4045 brazing material 14 is clad on one side thereof. And prepared each. Thereafter, the evaluation core 10 shown in FIG. 1 is formed by combining the fin 11 and the surface of the brazing sheet 12 on the brazing material 14 side, and the evaluation core 10 is brazed and heated at 600 ° C. for 3 minutes. . And about the core 10 for evaluation after brazing heating, this was evaluated by making the ratio of the number of the fins joined with respect to the total number of the fins 11 into a fin joining rate. As the evaluation, those having a fin joint ratio of 95% or more were evaluated as “B” having good brazing properties, and those having a fin joint ratio of less than 95% were evaluated as “x” having insufficient brazing properties.

[D] Presence / absence of fin diffusion and melting:
Microscopic observation of the cross section was performed on the evaluation core 10 produced in the above [c] to confirm the presence or absence of fin diffusion and melting of fins. In the evaluation, those having neither wax diffusion nor melting were evaluated as “good”, and those having either or both of wax diffusion and melting were evaluated as “x”.

[E] Self-corrosion resistance evaluation (corrosion reduction (%) measurement):
The specimen was brazed and heated at 600 ° C. × 3 min, and then cooled at a cooling rate of 200 ° C./min to obtain a sample. And after performing the salt spray test for 200 hours with respect to each sample according to JISZ2371, the corrosion reduction amount was measured.

[F] Natural potential (mV):
The specimen was brazed and heated at 600 ° C. × 3 min, and then cooled at a cooling rate of 200 ° C./min to obtain a sample. Each sample was evaluated by measuring the natural potential of the fin (vs Ag / AgCl) in a 5% NaCl aqueous solution at 25 ° C. As an evaluation, if the natural potential is lower than −720 mV, it is “good”, and if it is nobler than −720 mV, it is “x”.

Test material No. which is an example of the present invention. In Nos. 1 to 16, the tensile strength after brazing was as high as 120 N / mm ² or more, the electrical conductivity was 45% IACS or more, and the thermal conductivity was evaluated as good. Also, there was no problem with the fin bonding rate, brazing diffusion and melting, and the brazing property was good. Furthermore, the amount of decrease in corrosion was less than 4.0%, and the natural potential was lower than -720 mV, and the sacrificial anticorrosive effect was secured.

On the other hand, the results of the comparative example were as follows. Test material No. In Nos. 17, 20, and 25, the tensile strength after brazing was less than 120 N / mm ² , which was lower than that of the examples of the present invention. Test material No. Nos. 17 and 20 had lower strength because the contents of Si and Mg as strengthening elements were small. Test material No. No. 25 satisfies the example of the present invention with respect to the element addition amount, but since the brazing heating was performed by applying the flux, the strength was lowered because the Mg added to the flux reacted with the material and consumed. . Test material No. Nos. 18 and 21 had a large amount of Si and Mg added, so the amount of solid solution in the matrix also increased and the conductivity after brazing was low. Test material No. In No. 21, the amount of Mg added was not appropriate, so the fin joining rate was low. Test material No. No. 24 had a low fin bonding rate because the oxygen concentration in the furnace during the brazing heat was high. In addition, test material No. In No. 25, since flux was applied and brazed and heated, the flux and Mg reacted, and neither the film removal effect due to Mg nor the film removal effect due to flux was sufficient, and the fin bonding rate was lowered. Test material No. Nos. 18 and 21 had a large amount of Si or Mg added, so that the solidus temperature decreased and melting occurred during brazing. Test material No. In No. 19, since the amount of Fe added was large, the crystal grains after brazing became fine, and brazing diffusion occurred along the crystal grain boundaries. Test material No. In No. 23, the amount of Zn added was large, so that the corrosion rate was high, and the corrosion reduction amount was high. Test material No. No. 22 could not make the natural potential sufficiently low because the amount of Zn added was small.

10 Evaluation Core 11 Fin 12 Brazing Sheet 13 Core Material 14 Brazing Material

Claims (2)

An aluminum alloy fin material for a heat exchanger having no brazing material, which is brazed without flux in a non-oxidizing gas atmosphere having an oxygen concentration of 10 ppm or less and has a tensile strength of 120 N / mm ² or more after brazing. ,
Si: 0.2-1.2% (mass%, the same shall apply hereinafter), Fe: 0.02-0.5%, Mg: 0.1-0.8%, Zn: 0.1-2.0% And the balance consists of Al and inevitable impurities,
An aluminum alloy fin material for heat exchangers. An aluminum alloy fin material for a heat exchanger having no brazing material, which is brazed without flux in a non-oxidizing gas atmosphere having an oxygen concentration of 10 ppm or less and has a tensile strength of 120 N / mm ² or more after brazing. ,
Si: 0.2-1.2% (mass%, the same shall apply hereinafter), Fe: 0.02-0.5%, Mg: 0.1-0.8%, Zn: 0.1-2.0% Further, Ti: 0.02-0.3%, Zr: 0.02-0.3%, Cr: 0.02-0.3%, V: 0.02-0.3% Containing one or more of them, the balance consisting of Al and inevitable impurities,
An aluminum alloy fin material for heat exchangers.

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