JP5545798B2 - Method for producing aluminum alloy fin material for heat exchanger - Google Patents

Description

The present invention particularly relates to a method for producing an aluminum alloy fin material for a heat exchanger that is suitably 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 is an object of the present invention to provide a suitable method for producing an aluminum alloy fin material that can be suitably used.

To achieve the above Symbol purpose, the production method of the heat exchanger aluminum alloy fin material according to the first aspect of the present invention,
A method for producing an aluminum alloy fin material for a heat exchanger that is brazed without flux in a non-oxidizing gas atmosphere,
Si: 0.2-1.2% (mass%, the same shall apply hereinafter), Fe: 1.0-2.0%, Mg: 0. An alloy material containing 6 to 0.8%, Zn: 0.1 to 2.0%, Mn: 0.02 to 0.5%, the balance being Al and unavoidable impurities is twin-roll continuous casting and rolling Casting by the method
The Al—Fe—Mn—Si compound dispersed and precipitated by the casting remains.
It is characterized by that.

Moreover, the manufacturing method of the aluminum alloy fin material for heat exchangers according to the second aspect of the present invention includes:
A method for producing an aluminum alloy fin material for a heat exchanger that is brazed without flux in a non-oxidizing gas atmosphere,
Si: 0.2-1.2% (mass%, the same shall apply hereinafter), Fe: 1.0-2.0%, Mg: 0. 6 to 0.8%, Zn: 0.1 to 2.0%, Mn: 0.02 to 0.5%, Ti: 0.02 to 0.3%, Zr: 0.02 ~ 0.3%, Cr: 0.02 to 0.3%, V: 0.02 to 0.3% of one or more of the alloy material, the balance consisting of Al and inevitable impurities, twin rolls Cast by continuous casting and rolling method,
The Al—Fe—Mn—Si compound dispersed and precipitated by the casting remains.
It is characterized by that.

According to the present invention, a brazing property is satisfactory, and after brazing excellent strength, has a thermal conductivity and corrosion resistance, against the aluminum alloy fin material that can be particularly preferably used as a fin for a heat exchanger for motor vehicles And a suitable manufacturing method can be provided.

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 is strengthened by dispersion by forming Al-Fe-Si, Al-Mn-Si, Al-Fe-Mn-Si compounds together with Fe and Mn, or solid solution by dissolving in a matrix. Contributes to strength improvement by strengthening. 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. When the twin roll type casting and rolling method is used, the Al—Fe—Si based and Al—Fe—Mn—Si based compounds formed together with Si and Mn are finely dispersed, which contributes to improving the strength as dispersion strengthening. Fe has the effect of suppressing brazing diffusion by coarsening crystal grains after brazing due to the role of suppressing nucleation during brazing. The preferable content of Fe in this embodiment is 0.02 to 2.0%. If the Fe content is less than 0.02%, the effect becomes small. On the other hand, if the Fe content exceeds 2.0%, a giant intermetallic compound is produced during casting, which lowers the plastic workability. Further, when the Fe content exceeds 2.0%, the number of cathode sites increases, and the corrosion starting point increases, so that the self-corrosion resistance decreases. A more preferable Fe content is 0.05 to 1.8%.

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 Mn, Ti, Zr, Cr, and V.

  Mn is strengthened by dispersion by forming Al—Fe—Mn—Si, Al—Fe—Mn, and Al—Mn—Si compounds together with Fe and Si, or solid solution by dissolving in a matrix. Contributes to strength improvement as reinforcement. The preferable content of Mn in this embodiment is 0.02 to 0.50%. If the Mn content is less than 0.02%, the effect becomes small. On the other hand, if the Mn content exceeds 0.50%, the amount of solid solution in the matrix increases, and the thermal conductivity decreases. A more preferable Mn content is 0.10 to 0.40%.

  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 material having the above-described component composition is melted, and a plate-shaped ingot is produced by a twin roll type continuous casting and rolling method. The twin-roll continuous casting and rolling method is a method in which molten aluminum is supplied between a pair of water-cooled rolls from a refractory hot water supply nozzle, and a thin plate is continuously cast and rolled. The Hunter method and the 3C method are known. ing.

  In the twin roll type continuous casting and rolling method, the cooling rate at the time of casting is 1 to 3 orders of magnitude higher than that of the DC (Direct Chill) casting method. For example, the cooling rate in the DC casting method is 0.5 to 20 ° C./sec, whereas the cooling rate in the twin roll continuous casting and rolling method is 100 to 1000 ° C./sec. Therefore, crystallized substances such as Al-Fe-Si, Al-Fe-Mn, and Al-Fe-Mn-Si compounds produced during casting are characterized by being finely and densely dispersed as compared with the DC casting method. is there. The crystallized substance dispersed at high density promotes precipitation of elements dissolved in the matrix such as Mn and Si, and contributes to improvement in strength and thermal conductivity. Therefore, it was difficult to add Mn without reducing the thermal conductivity in DC casting, but in the case of the twin roll type continuous casting and rolling method, the strength without reducing the thermal conductivity by adding Mn. Can be improved.

  In addition, in the DC casting method with a low cooling rate during casting, coarse crystallized substances are formed during casting, and these crystallized substances can become recrystallization nuclei during brazing. May cause wax diffusion. However, in the twin roll type continuous casting and rolling method as in the present embodiment, since a fine crystallized material distribution is obtained, these crystallized materials do not become recrystallized nuclei at the time of brazing. In order to suppress the generation of crystal nuclei, the crystal grains after brazing become coarse. Therefore, brazing diffusion can be effectively suppressed by casting by a twin roll type continuous casting and rolling method. As a result, more Fe can be added than in the DC casting method, and it is possible to achieve both suppression of brazing diffusion and improvement in strength.

  Subsequently, the obtained plate-shaped ingot 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, and particularly the effect of Mg as a strengthening element and sacrifice of Zn. 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, aluminum alloys having the alloy compositions shown in Table 1 were cast by the casting methods shown in Table 2, respectively. In the alloy composition of Table 1, “−” indicates that it is below the detection limit, and “remainder” includes inevitable impurities.

  Test material No. cast by twin roll type continuous casting rolling method For 1 to 14, 17, and 18, the obtained plate-shaped ingot was cold-rolled, subjected to intermediate annealing at 370 ° C. × 2 h in a batch annealing furnace, and a final plate thickness of 0.06 mm (adjustment) Quality: H1n).

  Test material No. cast by DC casting method About 15 and 16, the homogenization process was not performed to the produced ingot, and after heating to 500 degreeC, it rolled to the desired thickness by hot rolling, and produced the board | 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 (test material No. 1-18), and the brazing heating was performed on the conditions shown in Table 2. Test material No. Only the test piece which evaluates a tensile strength and a fin joining rate only 18 was applied with flux, and brazing heating was performed. 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], and it was confirmed whether or not the fin 11 was diffused and melted. 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. 1 to 20, the tensile strength after brazing was as high as 120 N / mm ² or higher, the electrical conductivity was 45% IACS or higher, 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. Nos. 21, 24, and 31 had a tensile strength after brazing of less than 120 N / mm ² and were lower than those of the examples of the present invention. Test material No. In Nos. 21 and 24, the strength decreased because the contents of Si and Mg, which are strengthening elements, were small. Test material No. No. 31 satisfies the present invention example regarding the amount of element added, but since the brazing heating was performed after applying the flux, the strength was lowered because the Mg added to the flux reacted with the material and consumed. . Test material No. In Nos. 22 and 25, the amount of Si and Mg added was large, so the amount of solid solution in the matrix also increased, and the conductivity after brazing was low. Test material No. In No. 25, the amount of added Mg was not appropriate, so the fin joining rate was low. Test material No. No. 30 had a low fin bonding rate because the oxygen concentration in the furnace during brazing heat was high. In addition, test material No. In No. 31, 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 reduced. Test material No. In Nos. 22 and 25, since the amount of Si and Mg added was large, the solidus temperature decreased and melting occurred during brazing. Test material No. In No. 23, since the amount of Fe added was large, crystal grains after brazing became fine, and brazing diffusion occurred along the crystal grain boundaries. Test material No. In Nos. 28 and 29, the Fe addition amount satisfies the example of the present invention. However, since the Fe-based crystallized substance was coarsely distributed by the DC casting method, and became the core of the crystal grains, brazing was performed. The grain after the subsequent brazing became fine, and brazing diffusion occurred along the grain boundary. Test material No. In No. 27, since the amount of Zn added was large, the corrosion rate was fast, and the corrosion reduction amount was high. Test material No. In No. 26, the natural potential could not be sufficiently reduced due to the small amount of Zn added.

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

Claims (2)

A method for producing an aluminum alloy fin material for a heat exchanger that is brazed without flux in a non-oxidizing gas atmosphere,
Si: 0.2-1.2% (mass%, the same shall apply hereinafter), Fe: 1.0-2.0%, Mg: 0. An alloy material containing 6 to 0.8%, Zn: 0.1 to 2.0%, Mn: 0.02 to 0.5%, the balance being Al and unavoidable impurities is twin-roll continuous casting and rolling Casting by the method
The Al—Fe—Mn—Si compound dispersed and precipitated by the casting remains.
A method for producing an aluminum alloy fin material for a heat exchanger. A method for producing an aluminum alloy fin material for a heat exchanger that is brazed without flux in a non-oxidizing gas atmosphere,
Si: 0.2-1.2% (mass%, the same shall apply hereinafter), Fe: 1.0-2.0%, Mg: 0. 6 to 0.8%, Zn: 0.1 to 2.0%, Mn: 0.02 to 0.5%, Ti: 0.02 to 0.3%, Zr: 0.02 ~ 0.3%, Cr: 0.02 to 0.3%, V: 0.02 to 0.3% of one or more of the alloy material, the balance consisting of Al and inevitable impurities, twin rolls Cast by continuous casting and rolling method,
The Al—Fe—Mn—Si compound dispersed and precipitated by the casting remains.
The manufacturing method of the aluminum alloy fin material for heat exchangers characterized by the above-mentioned.

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