JP2009058167A - Aluminum heat exchanger using tube having superior corrosion resistance and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a member for a heat exchanger used in manufacturing the heat exchanger, and having superior brazing property, corrosion resistance and heat exchanging performance for a long period. <P>SOLUTION: This member comprises a tube coated with Si powder of a maximum particle size of 30 μm or less together with fluoride flux not including Zn, and a fin, and the tube is composed of a material having a composition including Mn of 0.3-1.5%, Si of less than 0.10%, aluminum as remaining part, and unavoidable impurities, and having electric potential nobler than that of the fin by 30 mV or more after brazing. The brazing can be properly performed without local melting of the tube in brazing, by performing brazing by using fine Si powder. The tube can be sufficiently prevented from corrosion, as the tube is nobler than the fin by 30 mV or more, and a base layer is formed as a surface layer of the tube. Further, as the fillet hardly including Zn is formed, heat exchanging performance is not degraded even in use for a long period. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a member for an aluminum heat exchanger excellent in corrosion resistance and a method for manufacturing an aluminum heat exchanger excellent in corrosion resistance, which are used in the manufacture of an aluminum heat exchanger suitable for an air conditioner capacitor of an automobile. is there.

In aluminum heat exchangers manufactured by brazing, brazing sheets in which an Al-Si alloy brazing material is clad on an Al core material have been widely used so far. A product can be manufactured at a low cost by using a tube (extruded tube or the like) coated in the form of a mixture of a binder and a binder. Moreover, by using zinc-containing flux in this product, zinc diffuses from the tube surface to the inside due to heating during brazing, so the zinc concentration is high on the surface and low inside. A low and high potential gradient is formed inside. For this reason, although aluminum alloy is inherently prone to pitting corrosion, even if corrosion occurs, it is totally corroded, and it is possible to suppress leakage of refrigerant and strength reduction of the tube due to pitting corrosion, which has been a problem in the past. (For example, refer to Patent Document 1).
JP 2004-330233 A

  However, although the above-mentioned method certainly has good corrosion resistance of the tube, the zinc component in the flux is concentrated more in the fillet, which is the joint between the fin and the tube, during brazing, so the potential of this part Becomes the most base and the fillet is easily corroded. When the fillet is completely corroded, the tube is disconnected from the fin and the heat conduction from the tube to the fin is significantly reduced, so that the heat exchange performance is degraded relatively quickly. Further, in this type of brazing, since the Si powder is alloyed with surrounding aluminum to form an Al-Si alloy brazing during brazing, dents are caused by local melting of the tube. There may be a through hole. In addition, when the tube has a dent, corrosion may easily occur starting from this when the product is used.

  In order to solve the above-mentioned problems related to corrosion, the inventors have found that even if a zinc diffusion layer is not provided on the tube surface, an improvement effect can be obtained by using a combination in which the tube potential is no less than 50 mV from the fin. Yes. However, in the core made of this combination, the potential gradient is not formed in the tube, and the corrosion resistance depends only on the sacrificial anode effect of the fin, so that both the tube and the fin are made of water for a long time. When not in a wet state, the sacrificial anode effect is not exhibited, and there is a problem that pitting corrosion occurs in the tube.

  The present invention has been made against the background of the above circumstances, and is a member for a heat exchanger capable of obtaining a heat exchanger having good brazing properties and good corrosion resistance over a long period of time, and the manufacture of the heat exchanger. It aims to provide a method.

  The inventors of the brazing method of the above method, by suppressing the Si content with an Al-Mn alloy tube material, the tube after brazing was provided with a zinc diffusion layer that was low on the surface and high on the inside. The inventors have found that a similar potential gradient is formed and have completed the present invention.

  That is, among the aluminum heat exchanger members having excellent corrosion resistance according to the present invention, the first present invention includes a tube and a fin coated with Si powder having a maximum particle size of 30 μm or less together with a fluoride-based flux not containing Zn. The tube contains, by mass%, Mn: 0.3 to 1.5%, Si content less than 0.10%, and a composition composed of the balance aluminum and inevitable impurities, and brazing It is characterized in that it is made of a material that is no less than 30 mV nobler than the fin at the rear potential.

  The aluminum heat exchanger member excellent in corrosion resistance according to the second aspect of the present invention is the composition of the tube according to the first aspect of the present invention, further in mass%, Fe: 0.20-0.70%, Cu: It is characterized by containing one or more of 0.01 to 0.20% and Ti: 0.05 to 0.25%.

  The aluminum heat exchanger member excellent in corrosion resistance according to the third aspect of the present invention is characterized in that, in the first or second aspect of the present invention, the Si powder has an average particle size of less than 1 to 5 μm.

The aluminum heat exchanger member having excellent corrosion resistance according to the fourth aspect of the present invention is the member according to any one of the first to third aspects, wherein the fluoride flux contains potassium silicofluoride (K ₂ SiF ₆ ). It is characterized by that.

  The aluminum heat exchanger member having excellent corrosion resistance according to the fifth aspect of the present invention is any one of the first to fourth aspects of the present invention, wherein the fins are in% by mass and Mn: 0.8 to 1.50%. Zn: 0.3 to 5.0%, with the remainder having a composition composed of Al and inevitable impurities.

  The member for aluminum heat exchanger excellent in corrosion resistance according to the sixth aspect of the present invention is the composition of the fin according to any one of the first to fifth aspects, further comprising Cu: 0.01-0. One or more of 50%, Fe: 0.20 to 0.50%, and Si: 0.10 to 1.0%.

  According to a seventh aspect of the present invention, there is provided a method for producing an aluminum heat exchanger excellent in corrosion resistance, comprising a Si powder having a maximum particle size of 30 μm or less on the surface of a tube having the composition and material according to the first or second aspect of the present invention. Applying a coating containing a Zn-based fluoride flux and brazing the tube and fins by brazing, which is generated by the reaction of the coating with the Al component of the tube by brazing heating. It is characterized by.

  In the present invention, a finer Si powder is used, and when this is uniformly applied, a thin Al-Si alloy melting braze is formed on the entire tube surface by heating during brazing, and almost local melting of the tube occurs. Therefore, no dent is generated on the tube surface, the strength of the tube is sufficiently maintained, and deterioration of the corrosion resistance of the product due to the generation of the dent can be suppressed. When the particle diameter exceeds 30 μm, a through-hole due to the local melting is generated. Suitably, the average particle diameter of Si powder shall be less than 1-5 micrometers. This is because when the average particle size is less than 1 μm, the formation of the Al—Si alloy melt brazing is not sufficient, and the brazing property is remarkably lowered, and when it is 5 μm or more, a dent due to local melting occurs. is there.

  In addition, since zinc is not contained in the flux, a large amount of zinc is not contained in the fillet formed at the contact portion between the tube and the fin. Corrosion resistance is also sound. Therefore, the heat exchange performance is not deteriorated due to the early corrosion of the fillet.

As the flux, a potassium fluoride-based flux (KAlF ₄ + K ₃ AlF ₆ ) is usually sufficient, and this technique is widely used. However, when the Si powder becomes finer, the above effect is obtained with a potassium fluoride-based flux. Since it is not necessarily strong, sufficient joining may not be obtained unless the oxygen concentration in the brazing furnace atmosphere is lowered considerably, for example, 10 ppm or less. In such a case, by including K ₂ SiF ₆ as a flux, sufficiently satisfactory bonding is possible even in an oxygen concentration atmosphere of several hundred ppm. In this case, K ₂ SiF ₆ may be used alone or in combination with other fluoride fluxes.

  Furthermore, by using an Al—Mn alloy with a reduced Si content in the tube, an Al—Mn—Si compound is formed from Si and Al—Mn alloy diffused inward from the tube surface by brazing. As for the tube surface after brazing, the amount of solid solution Mn falls compared with the inside, and an electric potential falls. Such a phenomenon becomes more prominent as the amount of Si diffused is larger and closer to the surface, so that a potential gradient that becomes noble as the surface enters the interior with a lower base is formed. That is, the same effect as zinc diffusion is exhibited. This effect is sufficiently exhibited by an alloy having a Si content of less than 0.10% by weight. Due to such an effect, even if the tube surface is corroded, it does not become pitting corrosion but overall corrosion. In addition, since the sacrificial anode effect of the fin is acting by securing a potential difference of 30 mV or more between the tube and the fin, a double anticorrosion effect will be exhibited as a result. Corrosion will be suppressed.

  From the above viewpoint, it is desirable that the tube of the present heat exchanger is excellent in corrosion resistance and is an electrochemically noble alloy as much as possible. In addition to Mn, elements such as Cu, Ti, and Fe may be added. These elements also have the effect of improving the material strength. When Mn is contained in an amount of less than 0.3% by weight, the above-mentioned compound is not sufficiently formed, so that the effect is small. Reduce sex. Cu, Ti, and Fe are preferably one or two of Fe: 0.20 to 0.70%, Cu: 0.01 to 0.20%, and Ti: 0.05 to 0.25%. The above can be contained as needed. When these components are contained in an amount exceeding the upper limit, not only excellent properties can be imparted but also the workability of the material is deteriorated. On the other hand, if it is less than the lower limit, the desired characteristics cannot be imparted.

Similarly, the material of the fin included in the heat exchanger member is excellent in corrosion resistance, is an electrochemically base alloy as much as possible, has excellent high temperature strength that does not easily deform by heating during brazing, and is a product. Therefore, it is required that the alloy has excellent room temperature strength.
Zn is contained because corrosion resistance can be minimized and the potential can be effectively reduced. On the other hand, alloy elements of Mn, Cu, Fe, and Si are all contained for improving the high temperature and room temperature strength. Suitable contents are Mn: 0.8 to 1.50%, Zn: 0.3 to 5.0%, Cu: 0.01 to 0.50%, Fe: 0.20 to 0.50%, Si: 0.10 to 1.0%. When the content exceeds the upper limit, not only excellent properties can be imparted but also the workability of the material is deteriorated. On the other hand, if it is less than the lower limit, the desired characteristics cannot be imparted.

  As described above, according to the aluminum heat exchanger member excellent in corrosion resistance according to the present invention, it is provided with a tube and a fin coated with Si powder having a maximum particle size of 30 μm or less together with a fluoride-based flux not containing Zn, The tube contains, by mass%, Mn: 0.3 to 1.5%, Si content of less than 0.10%, a composition composed of the balance aluminum and inevitable impurities, and a potential after brazing. Since it is made of a material that is no less than 30 mV more than the fins, good brazing performance is obtained during brazing, and excellent corrosion resistance is exhibited over a long period of time after brazing. Deterioration of exchange performance can also be avoided.

  Further, according to the method for producing an aluminum heat exchanger excellent in corrosion resistance according to the present invention, Si powder having a maximum particle size of 30 μm or less is formed on the surface of the tube having the composition and material according to the first or second present invention. And a coating material containing a fluoride flux not containing Zn, and brazing the tube and the fin by brazing, which is generated by a reaction between the coating material and the Al component of the tube by brazing heating. Therefore, there is no local dissolution during brazing, and good brazing properties can be obtained. Further, the manufactured heat exchanger has excellent corrosion resistance, and the deterioration of the heat exchange performance with time due to fillet corrosion is also prevented.

Below, one Embodiment of this invention is described based on FIG.
The heat exchanger tube preferably contains Mn: 0.3 to 1.5%, and the Si content is less than 0.10%. If necessary, Fe: 0.20 to 0.70 %, Cu: 0.01 to 0.20%, Ti: 0.05 to 0.25%, or an Al alloy having a composition composed of Al and inevitable impurities with the balance being one or more. . The Al alloy is melted by a conventional method, and is usually formed into a tube 2 through an extrusion process. In this embodiment, the tube 2 has a multi-hole tube structure, and a plurality of passages 2a are formed therein.

Further, the heat exchanger fin preferably contains Mn: 0.8 to 1.50%, Zn: 0.3 to 5.0%, and further Cu: 0.01 to 0 as necessary. Al alloy having a composition containing one or more of 50%, Fe: 0.20 to 0.50%, Si: 0.10 to 1.0%, and the balance consisting of Al and inevitable impurities Is used. The Al alloy is melted by a conventional method, and the corrugated fins 3 are formed through a rolling process or the like. In addition, the manufacturing method of the tube 2 and the fin 3 is not specifically limited as this invention, A well-known manufacturing method can be employ | adopted suitably.
The tube 2 and the fin 3 are made of a material having a potential at which the tube 2 is no less than 30 mV nobler than the fin 3 in the potential after brazing.

The tube 2 is coated with an Si powder brazing material, a fluoride flux that does not contain Zn, and a coating material to which a binder and a solvent are added as necessary. The Si powder has a maximum particle size of 30 μm or less, and preferably has an average particle size of less than 1 to 5 μm. As the fluoride flux, one kind or two or more kinds of KAlF ₄ , K ₃ AlF ₆ , and K ₂ SiF ₆ can be used, and a K ₂ SiF ₆ simple substance or a flux containing this is preferably used. The size of the flux is not particularly limited in the present invention, but an average particle size of 10 μm or less is desirable. This is because if the thickness exceeds 10 μm, the thickness of the coating film increases, so that the center of the product shrinks during brazing, and the fins peel off after brazing. Moreover, a known thing can be used for a binder and an acrylic resin is used suitably. These materials are mixed with an appropriate solvent such as water or alcohol to obtain a coated product. The mixing ratio of these materials is not particularly limited in the present invention, but preferably the mixing ratio of Si powder: flux: binder: alcohol = 2-4: 7-15: 1-3: 13: 25 And

The coated material is applied to the tube surface by an appropriate method. The method for applying the coated material is not particularly limited, and a spray method, a shower method, a flow coater method, a roll coater method, a brush coating method, a dipping method, and the like can be appropriately employed.
In addition, as for the application quantity of a coated material, the range of 1-5 g / m < ² > is desirable for Si powder. If the amount is less than the lower limit, the amount of the molten solder formed is insufficient and the bonding strength is not sufficient, and if the upper limit is exceeded, the amount of melting of the tube increases and the wall thickness of the tube decreases, which is not preferable. .

The tube 2 and the fins 3 are assembled together with the header plate 4 and the like as necessary to constitute the heat exchanger member 1 and used for brazing. At the time of brazing, the brazing material is dissolved by heating to an appropriate temperature in an appropriate atmosphere such as an inert atmosphere. Examples of the heating temperature at this time include 580 to 620 ° C. Moreover, 1 to 10 minutes are mentioned as a heating holding time. However, these temperatures and heating times are exemplary, and the present invention is not limited to specific conditions.
At the time of brazing, a part of the matrix of the tube reacts with the coated material, and the members are brazed well. On the tube surface, an Al—Si—Mn compound is generated by brazing, and becomes lower than the inner surface of the tube.

In the brazing, the flux removes the surface oxide film of the brazing material, prevents oxidation during brazing heating, and further promotes the spreading and wetting of the brazing to improve the brazing property.
At the time of brazing, there is no local dissolution of the tube with Si powder, and good brazing is performed, and an appropriate fillet is formed between the tube and the fin. Further, in the brazed heat exchanger, the tube potential is no less than 30 mV higher than the fin, and the tube corrosion is effectively prevented. Furthermore, the tube surface layer is more base than the inside, and when the tube is corroded, it becomes a surface corrosion state to prevent pitting corrosion and improve corrosion resistance over a long period of time. In addition, there is no Zn supply from the brazing material or flux in the fillet, and the fillet is not preferentially corroded, thereby preventing a decrease in heat exchange efficiency over time.

  Tube alloys 1 to 4, chemical compositions (remaining Al and other unavoidable impurities) shown in Tables 1 and 2 were melted, comparative alloys, and fin alloys 1 to 3, respectively. After the homogenization treatment, the tube alloy was formed into a flat multi-hole tube having a thickness of 0.25 mm as shown in FIG. 1 by hot extrusion. On the other hand, after the soaking treatment, the fin alloy was formed into a plate having a thickness of 0.07 mm by hot rolling and cold rolling. The potentials after brazing of these alloys are shown in Tables 1 and 2, respectively.

Next, the tube was roll-coated with Si powder having a maximum particle size of 30 μm or less (average particle size 2.5 μm) and a fluoride flux as shown in Table 3 as a mixture of an acrylic resin and isopropyl alcohol, and dried. . The amount of Si powder applied was 3.0 g / m ² . As shown in FIG. 2, the mini-core is assembled as the aluminum heat exchanger member 1 by combining the tube 2 and the corrugated fin 3 with the header plate 4 and the like, and 600 ° C. for 3 minutes in a furnace with various oxygen concentrations in a nitrogen atmosphere. Brazing of holding was performed.

After the brazing, the bondability of the core was evaluated based on whether or not a sufficient fillet was formed between the tube and the fin. As a result, both cores were well bonded.
Furthermore, the core made of these various material combinations was subjected to a long-term corrosion test for 35 days in SWAAT, and the corrosion depth generated in the tube material after the test was measured. The results are shown in Table 3. Corrosion of the tube material occurred in both ends of the developed alloy cores 1 to 7 and the comparative material cores 9 and 10 at both end portions of the header plate where no fins were joined, whereas in the core 8, the corrosion occurred regardless of the position. Was. In any core, the corrosion of the tube-fin joint fillet was slight.

As shown in Table 3, the cores composed of the combinations satisfying the present invention have a potential difference between the surface and the interior of the tube and the potential of the tube is nobler than that of the fin. On the other hand, in the comparative core, it is clear that even if there is a potential difference between the fin and the tube, there is no potential difference in the tube, or the potential difference between the fin and the tube is reversed, so that the corrosion is severe.
As described above, in the heat exchanger that satisfies the conditions of the present invention, the corrosion resistance of the tube is very good, not only the occurrence of through-holes after long-term use, but also the pressure resistance strength of the product can be maintained practically, It is beneficial.

It is a figure which shows the tube contained in the member of one Embodiment of this invention. Similarly, it is a figure which shows the member for heat exchangers.

Explanation of symbols

1 Heat exchanger component 2 Tube 3 Fin

Claims (7)

  A tube and a fin coated with a Si-based powder having a maximum particle size of 30 μm or less together with a fluoride-based flux not containing Zn, the tube containing, by mass%, Mn: 0.3 to 1.5%, and Made of aluminum with excellent corrosion resistance, characterized in that the Si content is less than 0.10%, the composition is composed of the balance aluminum and unavoidable impurities, and the material is 30 mV or more noble than the fin at the potential after brazing. Heat exchanger component. In addition to the composition of the tube, by mass%, one or two of Fe: 0.20 to 0.70%, Cu: 0.01 to 0.20%, Ti: 0.05 to 0.25% The aluminum heat exchanger member excellent in corrosion resistance according to claim 1, comprising the above.   The average particle diameter of the said Si powder is less than 1-5 micrometers, The member for aluminum heat exchangers excellent in corrosion resistance of Claim 1 or 2 characterized by the above-mentioned. The member for aluminum heat exchanger excellent in corrosion resistance according to any one of claims 1 to 3, wherein the fluoride-based flux contains potassium silicofluoride (K ₂ SiF ₆ ).   The fin includes, by mass%, Mn: 0.8 to 1.50%, Zn: 0.3 to 5.0%, with the balance being composed of Al and inevitable impurities. Item 5. An aluminum heat exchanger member having excellent corrosion resistance according to any one of Items 1 to 4.   In addition to the composition of the fin, by mass%, one or two of Cu: 0.01 to 0.50%, Fe: 0.20 to 0.50%, Si: 0.10 to 1.0% The aluminum heat exchanger member excellent in corrosion resistance according to any one of claims 1 to 5, which is contained above.   A coating containing a Si powder having a maximum particle size of 30 μm or less and a fluoride-based flux not containing Zn is applied to the surface of the tube having the composition and material according to claim 1, and the tube and the fin A method for producing an aluminum heat exchanger having excellent corrosion resistance, wherein brazing is performed by brazing produced by a reaction between the coated material and the Al component of the tube by brazing heating.

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