JP2009139052A - Aluminum heat exchanger with superior corrosion resistance and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat exchanger with superior brazing characteristics and superior long term corrosion resistance. <P>SOLUTION: A tube having an alloy composition containing 0.05-0.50% of Mn, more than 0.10% and less than 0.50% of Si, and 0.01-0.10% of Cu, and the rest comprising aluminum and unavoidable impurity, and applied on a surface with a binder and a fluoric flux containing Si powder and zinc with a particle size of 30 μm or less is attached and brazed to a header, and a junction fillet wherein an electric potential of the tube surface is relatively 20 mV or more lower is formed between the header and the tube by brazing. By carrying out brazing by using fine Si powder, favorable brazing can be carried out without local melting of the tube during brazing, the tube surface becomes 30 mV or more lower than the fillet formed between the tube and the header, and corrosion of the fillet is sufficiently prevented. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an aluminum heat exchanger suitable for an air conditioner condenser of an automobile, and a method for manufacturing the heat exchanger.

  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.

  However, in brazing using Si powder, Si diffuses from the tube surface to the inside due to heating during brazing, so the Si concentration is high on the surface and low inside, and the tube has a high potential on the surface and a low potential on the inside. A gradient is formed. For this reason, when corrosion occurs in the tube, it becomes pitting corrosion, causing refrigerant leakage and strength reduction.

Therefore, by using a zinc-containing flux, a sacrificial layer formed by zinc diffusion during brazing is formed on the tube surface, and even when the tube is corroded, the entire surface is corroded and the generation of through holes is suppressed. There has been proposed a method capable of suppressing the refrigerant leakage and strength reduction of the tube due to (see, for example, Patent Document 1).
JP 2004-330233 A

  However, although the corrosion resistance of the tube is certainly good in the above method, the joint fillet of the tube and header is formed by the flow of the brazing material formed on the tube surface and the brazing material bonded to the header. By the zinc supplied from the flux containing zinc that has been applied, the potential becomes lower and the progress of corrosion is promoted. Since this fillet has a constant zinc concentration gradient as on the tube surface, if corrosion occurs, the progress to the fillet cannot be suppressed. Therefore, even if a through hole due to corrosion does not occur in the tube, a through hole is generated in this fillet, causing a problem due to refrigerant leakage.

  The present invention has been made against the background of the above circumstances, and an object of the present invention is to provide an aluminum heat exchanger in which good corrosion resistance is ensured even at a joint portion between a tube and a header, and a method for manufacturing the heat exchanger. And

  That is, among the manufacturing methods of the aluminum heat exchanger excellent in corrosion resistance of the present invention, the first present invention is Mn: 0.05 to 0.50% by mass%, Si: more than 0.10% to 0.00. Fluoride-based flux containing less than 50%, Cu: 0.001 to less than 0.10%, having an alloy composition consisting of the balance aluminum and inevitable impurities, and containing Si powder having a particle size of 30 μm or less and zinc on the surface And a tube coated with a binder are assembled to the header and brazed, and by this brazing, a joint fillet is formed between the header and the tube so that the potential of the tube surface is relatively lower than 20 mV. It is characterized by that.

The manufacturing method of the aluminum heat exchanger excellent in corrosion resistance according to the second aspect of the present invention is the first aspect of the present invention, wherein the zinc-containing fluoride-based flux is ² to 10 g / m ^{2 in} terms of zinc. It is applied to the tube.

  According to a third aspect of the present invention, there is provided a method for producing an aluminum heat exchanger excellent in corrosion resistance. In the first or second aspect of the present invention, the header is a clad material clad with a brazing material, and the zinc in the brazing material The concentration is mass% and is less than 2.0%.

  The manufacturing method of the aluminum heat exchanger excellent in corrosion resistance according to the fourth aspect of the present invention is the method according to any one of the first to third aspects of the present invention, wherein the zinc is added in an amount of 0.5-3. A sacrificial layer containing 0% is provided.

  The aluminum heat exchanger excellent in corrosion resistance of the fifth aspect of the present invention is Mn: 0.05 to 0.50% in mass%, Si: more than 0.10% to less than 0.50%, Cu: 0.001 to A tube and header containing less than 0.10% and having an alloy composition consisting of the balance aluminum and inevitable impurities are applied to the tube surface, and a fluoride flux and binder containing Si powder having a particle size of 30 μm or less and zinc. That the potential of the surface of the tube is more than 20 mV lower than the potential of the joint fillet formed between the tube and the header by the brazing. Features.

  The present invention relates to an aluminum heat exchanger, in which a tube and a header having a limited composition are combined. In addition, fins or the like can be joined and used as a heat exchanger. Here, what is made of aluminum includes, in addition to an aluminum alloy as a tube, a combination of members made of aluminum alloy, pure aluminum, or other materials.

  Next, the reason why the composition of the tube is limited will be described. In addition, all the following content is shown by the mass%.

Mn: 0.05 to 0.50%
Since Mn can improve the strength of the tube and adjust the potential of the tube, Mn is contained as an essential component. If the content is less than 0.05%, the effect is small, and a good potential relationship with respect to the fillet formed between the header and the header cannot be obtained. On the other hand, if the content exceeds 0.50%, the extrudability of the material is lowered.

Si: More than 0.10% to less than 0.50% Si, together with Mn, forms a fine Al-Mn-Si compound, effectively improves strength, and adjusts the potential of the tube. Therefore, it is contained as an essential component. However, if the content is 0.10% or less, the above effect is not sufficient, and a good potential relationship with the fillet cannot be obtained. On the other hand, when the content is 0.50% or more, the melting point of the alloy is lowered, and surface defects are caused by partial melting of the material during the extrusion process.

Cu: 0.001 to 0.10%
An appropriate amount of Cu has the effect of improving the corrosion resistance and strength of the tube. When Cu content is less than 0.001%, the corrosion resistance is not improved and the strength of the tube is lowered. On the other hand, if Cu content exceeds 0.10%, the corrosion resistance of the fillet formed between the tube and the header deteriorates.

  In addition, one or two of Ti and Fe may be added. These elements also have the effect of improving the material strength. When Ti and Fe are contained, the content is Fe: 0.10 to 0.50% and Ti: 0.01 to 0.20%. 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.

  Furthermore, in the present invention, a finer powder is used as the Si powder, and this is uniformly applied to the tube surface, so that a thin Al-Si alloy molten braze is formed on the entire tube surface by heating during brazing, and the tube Almost no local melting occurs. For this reason, there is no dent on the tube surface, the strength of the tube is sufficiently maintained, and deterioration of the corrosion resistance of the product due to the dent can be suppressed. When the particle size exceeds 30 μm, the dent due to the local melting occurs. Preferably, the average particle size of the Si powder is preferably less than 1 to 5 μm. This is because if the average particle size is less than 1 μm, the formation of the Al—Si alloy melt brazing is not sufficient, and the brazing performance is lowered, and if it is 5 μm or more, dents due to local melting tend to occur.

In addition, since zinc is contained in the flux, zinc diffuses into the tube during brazing, the surface zinc concentration is high and the inside is low, the potential on the surface of the tube is base, and the sacrificial layer with a potential gradient where the inside is noble Is formed. For this reason, even if corrosion occurs in the tube, it does not become a pitting corrosion form, and refrigerant leakage and strength reduction can be suppressed. As the flux, zinc potassium fluoride (KZnF ₃ ) alone or a mixture containing the same can be suitably used. The flux containing zinc, furthermore, can be exemplified such as ZnF _2. Examples of the flux that can be used by mixing with a flux containing zinc such as zinc potassium fluoride (KZnF ₃ ) include KAlF ₄ and K ₃ AlF ₆ .

When the brazing material formed on the tube surface flows between the tube and the header, and when the brazing material is bonded to the header, the brazing material flows together to form a joint fillet. The Although the brazing material on the tube surface contains zinc in the flux, the occurrence of corrosion in the fillet can be suppressed by making the fillet potential more noble than the tube surface. Suitably, the said effect | action is acquired reliably by setting it as 2-10 g / m < ² > as zinc conversion amount in a flux. When the zinc conversion amount in the flux is less than 2 g / m ² , the corrosion resistance of the tube is insufficient, and through holes are easily generated. ^{On the other hand} , if it exceeds 10 g / m ² , zinc is concentrated in the fillet and through holes are likely to be generated. In addition, when providing a brazing filler metal layer in a header, it can be provided either on the outer side or the inner side of the header.

Similarly, the occurrence of fillet corrosion can be suppressed by making the zinc concentration contained in the brazing material bonded to the header less than 2.0%. If it exceeds 2.0%, zinc will be concentrated in the fillet and through-holes are likely to be generated.
Further, a sacrificial layer containing 0.5 to 3.0% of zinc is provided on the outer side of the header, and the fillet can be sacrificial and corrosion-prevented by making the header surface potential lower than the fillet. Furthermore, by making the electric potential of the header surface lower than that of the tube surface, the header surface can sacrifice and prevent the fillet and the tube, and the corrosion resistance life of the heat exchanger can be further extended. If Zn contained in the sacrificial material is less than 0.5%, a sacrificial anticorrosive effect cannot be expected. If it exceeds 3.0%, the corrosion resistance of the header is lowered due to an excessive sacrificial anticorrosive effect. When providing the sacrificial layer outside the header, the brazing material layer can be provided inside the header.

  As described above, according to the present invention, by mass, Mn: 0.05 to 0.50%, Si: more than 0.10% to less than 0.50%, Cu: 0.001 to 0.10% A tube and header having an alloy composition consisting of the remaining aluminum and the inevitable impurities, and a coating containing Si powder with a particle size of 30 μm or less, zinc-containing fluoride-based flux and binder Since the electric potential of the tube surface is more than 20 mV lower than the electric potential of the joint fillet formed between the tube and the header by the brazing, the fillet is prevented from being corroded. Even if it is used for a long time, the effect of preventing refrigerant leakage due to corrosion is obtained.

Below, one Embodiment of this invention is described based on FIGS. 1-3.
The tube for heat exchanger contains Mn: 0.05 to 0.50%, Si: more than 0.10 to less than 0.50%, Cu: 0.001 to 0.10%, and if necessary An Al alloy containing one or two of Fe: 0.10 to 0.50% and Ti: 0.01 to 0.20%, with the balance being composed of Al and inevitable impurities is used. The Al alloy is melted by a conventional method, and is usually formed into a tube 1 through an extrusion process. In this embodiment, the tube 1 has a flat multi-hole tube structure, and a plurality of passages 2 are formed therein.

Moreover, the header 4 for heat exchangers is formed in a cylindrical shape as a whole by an aluminum alloy material, and has insertion holes 5 through 5 through which the tube 1 is inserted.
Further, as the heat exchanger fins 6, an Al alloy is melted by a conventional method, and a corrugated shape is prepared through a rolling process or the like. In addition, the manufacturing method of the tube 1, the header 4, and the fin 6 is not specifically limited as this invention, A well-known manufacturing method can be employ | adopted suitably.

The tube 1 is coated with an Si powder brazing material, a fluoride-based flux containing Zn, and a coating 3 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, a fluoride-based flux containing zinc such as KZnF ₃ is used. If desired, one or more of KAlF ₄ and K ₃ AlF ₆ may be used in combination. it can. The size of the fluoride-based flux is not particularly limited as 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 is preferably a mixing ratio of Si powder: flux: binder: alcohol = 1-5: 5-20: 1-4: 10-30. 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 in 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 Zn-containing flux is preferably ² to 10 g / m ^{2 in} terms of Zn.

The fins 6 are arranged between the tubes 1 and 1, and the end portions of the tubes 1 are inserted into the insertion holes 5 of the header 4 and assembled to each other 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 1 reacts with the coating 3 and the members are brazed well. On the surface of the tube 1, Zn in the flux diffuses by brazing and becomes lower than the inside of the tube 1.

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 melting of the tube with Si powder, and good brazing is performed, and an appropriate fillet 10 is formed between the tube 1 and the header 4.
The fillet 10 is nobler than the surface potential of the tube 1 after brazing, and the surface potential of the tube 1 is relatively lower than the fillet 10 by 20 mV or more. Thereby, the surface of the tube 1 is in a preferential corrosion state, and the fillet 10 is inhibited from corrosion. The heat exchanger obtained as described above does not cause refrigerant leakage due to corrosion even when used in a real environment for a long time.

  In addition, as shown to Fig.3 (a), the brazing | wax material layer 40 can be provided in the header 4 on the outer side through which the tube 1 is penetrated so that the said brazing may be performed reliably. At the time of brazing, the brazing material formed on the surface of the tube 1 and the brazing material by melting the brazing material layer 40 are melted together to form the fillet 10 between the tube 1 and the header 4. Braze well. In addition, by making the Zn content in the brazing filler metal layer 40 less than 2.0%, it is possible to avoid the Zn flowing from the brazing filler metal layer 40 from being concentrated in the fillet 10, and thereby, after brazing A state in which the surface potential of the tube 1 is 20 mV or more lower than that of the fillet 10 can be reliably obtained. When the Zn content of the brazing filler metal layer 40 is 2.0% or more, Zn is concentrated in the fillet 10 and through holes are generated early.

  As shown in FIG. 3B, the header 4 can be provided with a sacrificial material layer 41 on the outer side through which the tube 1 is inserted, and at that time, the brazing material layer 40 is provided on the inner side. The brazing may be surely performed. The sacrificial material layer 41 can prevent corrosion of the header 4 and can prevent the fillet 10 from being corroded for a long time with the surface of the header 4 as a base. In addition, it is more desirable that the surface potential of the header 4 be lower than the surface potential of the tube 1. The sacrificial material layer 41 preferably contains 0.5% or more of Zn in order to obtain a sufficient sacrificial effect. On the other hand, if the content exceeds 3.0%, Zn concentration in the fillet 10 occurs, and the corrosion resistance of the fillet 10 is reduced. Therefore, it is desirable that the Zn content of the sacrificial material layer be 0.5 to 3.0%. .

An aluminum alloy having a composition consisting of Mn: 0.30%, Si: 0.35%, Cu: 0.003%, the balance Al and inevitable impurities is melted as a tube material, and after homogenization treatment, hot extrusion is performed. A flat multi-hole tube having a wall thickness of 0.25 mm as shown in FIG. Thereafter, the tube is rolled with Si powder having an average particle size of 2.5 μm, a maximum particle size of 30 μm or less, and an application amount of 3 g / m ² and a fluoride flux shown in Table 1 as a mixture of an acrylic resin and isopropyl alcohol. It was applied and dried.

Next, materials were bonded together in combinations of the alloy compositions shown in Table 2, and a header material having a thickness of 1.2 mm was formed by hot rolling and cold rolling. After this header material was made into a semicircle by pressing, a hole for inserting a tube was provided by slot processing. A semicircular header material with or without slot processing was combined to form a cylindrical header pipe as shown in FIG. After the combination, the header pipe was immersed in an aqueous solution in which a fluoride-based flux was dispersed, and the flux was applied at 20 g / m ² .

As the fin alloy, an alloy obtained by adding 1.5% zinc to JIS3003 alloy was melted, and after homogenization, a plate having a thickness of 0.07 mm was formed by hot rolling and cold rolling. Thereafter, corrugation was performed to obtain a fin material.
The mini-core shown in FIG. 2 was assembled using the tube, header, and fin, and brazed at 600 ° C. for 3 minutes in a nitrogen atmosphere furnace. All cores were well bonded. Tables 1 and 2 show the tube surface and header surface potentials after brazing.
Moreover, the core which consists of these various material combination was used for the long-term corrosion test of SWAAT 38 days. After the test, the presence or absence of through-holes due to corrosion and the occurrence site were confirmed.

Table 3 summarizes the corrosion test results. According to Table 3, the cores composed of the combinations satisfying the present invention did not generate any through holes. On the other hand, in the core using the comparative material, through holes were generated in the tube or fillet, and sufficient pitting corrosion resistance could not be obtained. Table 3 further shows the potential difference between the tube surface and the fillet after brazing.
As described above, in the heat exchanger that satisfies the conditions of the present invention, the corrosion resistance is extremely good in all parts including the joint fillet of the tube and the header, and not only the occurrence of through holes after a long period of use, It was useful in practice, such as maintaining the pressure strength of the product.

It is a figure which shows the tube and header used for one Embodiment of this invention. Similarly, it is the figure which shows the heat exchanger which assembled | attached the tube and the header, and b section enlarged view. Similarly, it is a partial sectional view showing the configuration of the header.

Explanation of symbols

1 Tube 3 Application 4 Header 40 Brazing Material Layer 41 Sacrificial Material Layer 6 Fin 10 Fillet

Claims (5)

  Contains Mn: 0.05 to 0.50% by mass, Si: more than 0.10% to less than 0.50%, Cu: less than 0.001 to less than 0.10%, and consists of the balance aluminum and inevitable impurities A tube having an alloy composition and having a surface coated with a Si-based powder having a particle size of 30 μm or less and zinc-containing fluoride flux and a binder is assembled and brazed to the header, and the header and the tube are brazed by the brazing. A method for producing an aluminum heat exchanger having excellent corrosion resistance, characterized in that a joint fillet is formed in which the potential of the tube surface is relatively lower than 20 mV. The manufacture of an aluminum heat exchanger excellent in corrosion resistance according to claim 1, wherein the zinc-containing fluoride flux is applied to the tube in an amount of ² to 10 g / m ^{2 in} terms of zinc. Method.   The header is a clad material obtained by clad a brazing material, and the concentration of zinc in the brazing material is mass% and less than 2.0%, and is excellent in corrosion resistance according to claim 1 or 2. A method for manufacturing an aluminum heat exchanger.   The heat-made aluminum with excellent corrosion resistance according to any one of claims 1 to 3, wherein a sacrificial layer containing 0.5 to 3.0% of zinc is provided outside the header in mass%. Exchanger manufacturing method.   Contains Mn: 0.05 to 0.50% by mass, Si: more than 0.10% to less than 0.50%, Cu: less than 0.001 to less than 0.10%, and consists of the balance aluminum and inevitable impurities A tube having an alloy composition and a header are applied to the tube surface, and are brazed with a coating containing a Si powder having a particle size of 30 μm or less, a zinc-containing fluoride-based flux, and a binder. An aluminum heat exchanger having excellent corrosion resistance, wherein the potential is 20 mV or more lower than the potential of a joint fillet formed between the tube and the header by the brazing.

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