WO2023021915A1

WO2023021915A1 - Aluminum alloy extruded tube and heat exchanger

Info

Publication number: WO2023021915A1
Application number: PCT/JP2022/028315
Authority: WO
Inventors: 稜東森; 太一鈴木
Original assignee: 株式会社Uacj
Priority date: 2021-08-16
Filing date: 2022-07-21
Publication date: 2023-02-23
Also published as: JP2023026898A

Abstract

Provided is an aluminum alloy extruded tube for a heat exchanger, characterized by having a tube body composed of an Mn-containing aluminum alloy and a coating film formed on the surface of the tube body, and the coating film being such that the coating amount of an Al-Si alloy brazing material powder is 9.0-25.0 g/m2, the coating amount of a Zn-containing fluoride-based flux powder is 1.0-9.0 g/m2, the coating amount of a Zn-free fluoride-based flux powder is 1.0-11.0 g/m2, and the coating amount of a binder is 1.0-13.0 g/m2, By using the present invention, it is possible to provide: an extruded tube that is to be used in a heat exchanger for an automobile, the extruded tube being joined to fins without any reduction in the wall thickness of the tube or with extremely little reduction in said wall thickness, having excellent brazing capabilities, having exceptional corrosion resistance, and being such that the fins do not readily fall out for a long period of time; and a heat exchanger in which said extruded tube is used.

Description

Aluminum alloy extruded tube and heat exchanger

The present invention relates to an aluminum alloy extruded tube used in a heat exchanger for automobiles and a heat exchanger made using the same.

Automotive heat exchangers such as evaporators and condensers often use aluminum alloys that are lightweight and have high thermal conductivity. The heat exchanger has tubes through which a refrigerant flows and fins for exchanging heat between the refrigerant and the air outside the tubes, and the tubes and the fins are joined by brazing. A fluoride-based flux is often used for joining the tube and the fin.

As mentioned above, the tubes used in automotive heat exchangers are joined to fins by brazing in order to perform heat exchange, and it is necessary to provide a brazing material on the fin side or the tube side. When a brazing filler metal is provided on the fin side, the fins are produced using a clad material clad with a brazing filler metal, making it difficult to reduce manufacturing costs and material costs. When a brazing material is provided on the tube side, for example, a technique has been proposed in which a flux layer containing Si powder, Zn-containing flux, and a binder is formed on the outer surface of the tube (Patent Document 1). The flux layer having the above composition can be deposited simultaneously with all of the brazing material component, Zn and flux component in one deposition step. Moreover, since there is no need to provide a brazing material on the fin side, the fin can be manufactured using a bare fin material. As a result, cost reduction can be achieved.

For example, when using a flux layer containing _KZnF3 as a Zn-containing flux, flux components and Zn are generated according to the following reaction formula.
6KZnF3 ₊ 4Al→ _3KAlF4 + _K3AlF6 + _6Zn (555°C or higher)

From the above reaction formula, the Zn-containing flux does not function as Zn and a flux component by itself, but by reacting with Al (aluminum) in the tube, Zn is precipitated and potassium fluoroaluminate, which is a flux component, is produced. , Zn and flux components.

Patent Document 2 also proposes a technique using an alloy powder containing Si as a brazing powder.

WO2011/090059 Patent No. 6294537

　In recent years, in order to reduce the environmental impact, there has been an increasing demand to improve the fuel efficiency of automobiles by reducing the weight of component parts, and to reduce the amount of materials used in products by extending the life of parts. From this point of view, it is strongly demanded to use thinner tubes than conventional ones and to have higher corrosion resistance than conventional ones in heat exchangers using such tubes. This means not only that the tube can be made thinner, but also that the tube itself has an excellent sacrificial anti-corrosion effect. This means that it is necessary to protect the tube surface from corrosion over a period of time.

However, in the method of Patent Document 1, the pure Si powder contained in the paint melts the tube surface to generate liquid phase brazing, so in order to prevent the tube from penetrating during brazing, the tube must have a certain thickness or more. It is difficult to say that it contributes to the thinning of the tube.

Furthermore, the pure Si powder contained in the paint forms a fillet when the Al-Si alloy liquid phase brazing produced by eutectic melting with the aluminum on the tube surface flows to the contact area between the fin and the tube. . At this time, if coarse Si grains are mixed, the liquid phase brazing eutectic melted with the aluminum on the surface of the coarse Si grains and the tube surface quickly flows to the contact portion between the fin and the tube due to capillary action. The surroundings of the Si grains that have become smaller are separated from the tube surface, forming depressions on the tube surface where the liquid phase brazing flows out, and further eutectic melting progresses at the bottom of the depressions that are in contact with the Si grains. If so, a deep melted hole is formed, and there is a possibility that a through hole is generated in the tube body.

In Patent Document 1, the content of coarse grains that is five times or more the grain size (99% grain size, D99) at which the cumulative volume of grains having a grain size below that is 99% of all grains is less than 1 ppm. An attempt has been made to solve the above problem by using Si powder, but there has also been a problem of reducing the contamination of coarse particles to less than 1 ppm.

In the method of Patent Document 2, an Al-Si alloy powder is cited as an example of an alloy containing Si among brazing powders. When Al--Si alloy powder is used as a brazing material for a coated tube, erosion occurs on the tube surface unlike the case of pure Si powder, and there is a concern that the tube may be thinned during brazing. Furthermore, a Zn-containing flux is used as the flux. Since the above-described flux reaction causes Zn to precipitate on the outer surface of the tube immediately before the liquid phase is generated, the generated liquid phase contains Zn at a high concentration. This Zn diffuses to the outer surface of the tube to form a Zn diffusion layer, which functions as a sacrificial anticorrosive layer to suppress the occurrence of pitting corrosion in the tube. In this case, the corrosion rate increases, and the thinning rate of the tube increases. Zn contained in the liquid phase during brazing also concentrates in the fillets formed between the fins and tubes. In this case, since the potential of the fillet becomes the most base, the fillet is preferentially corroded and worn when exposed to a corrosive environment, causing the fins to come off, resulting in early deterioration of the heat exchange performance and the fins. This means that premature penetration of the tube may occur due to the tube not being protected against corrosion. The present technology does not describe such countermeasures, and it is difficult to say that it is practical.

In addition, in Zn sprayed tubes, which are conventionally often used for heat exchanger tubes, the amount of surface Zn is usually 5 to 15 g/m ² , which reduces the potential difference between the tube surface and the tube depth and reduces the corrosion rate. Therefore, when the amount of Zn is set to 5 g/m ² or less in order to reduce the concentration of Zn on the fillet, it is difficult to spray Zn uniformly onto the tube surface.

Therefore, the object of the present invention is to join the fins and the tube without reducing the thickness of the tube during brazing or with a very small amount of reduction in thickness, and to have good brazeability and a long-term use. To provide an extruded tube made of an aluminum alloy used in a heat exchanger for an automobile, and having excellent corrosion resistance, and a heat exchanger using the extruded tube.

The present inventors have made intensive studies to solve the above problems, and as a result, in an aluminum alloy extruded tube having a tube body and a coating film applied to the tube surface, Al-Si is added to the outer surface of the tube. By applying specific coating amounts of the alloy brazing powder, the Zn-containing fluoride-based flux powder, and the Zn-free fluoride-based flux powder, the tube surface is not melted or melted during brazing. Therefore, the thickness of the tube is not reduced during brazing, or the amount of reduction is very small, and a Zn diffusion layer is formed on the outer surface of the tube during brazing, so corrosion is prevented by the sacrificial anticorrosive layer and fins on the tube surface layer. The present inventors have completed the present invention by discovering that the corrosion resistance is excellent.

The above problems of the present invention are solved by the following present invention.
That is, the present invention (1) is an aluminum alloy extruded tube used in a heat exchanger for automobiles,
a tube body made of an aluminum alloy containing Mn;
a coating film formed on the surface of the tube body;
has
The coating contains Al—Si alloy brazing powder, Zn-containing fluoride-based flux powder, Zn-free fluoride-based flux powder, and a binder,
The coating amount of the Al—Si alloy brazing filler metal powder is 9.0 to 25.0 g/m ² , the coating amount of the Zn-containing fluoride flux powder is 1.0 to 9.0 g/m ² , The coating amount of the Zn-free fluoride-based flux powder is 1.0 to 11.0 g/m ² and the coating amount of the binder is 1.0 to 13.0 g/m ² ;
To provide an aluminum alloy extruded tube for a heat exchanger characterized by:

The present invention (2) is characterized in that the aluminum alloy contains 0.20 to 1.20% by mass of Mn and 0.10% by mass or less of Ti, and the balance is Al and unavoidable impurities. The present invention provides an aluminum alloy extruded tube for a heat exchanger according to (1).

In the present invention (3), when a fin made of an aluminum alloy containing Zn is joined by brazing, in spontaneous potential measurement, the potential difference between the tube surface and the tube depth of the extruded tube (tube surface potential - tube depth potential) of -180 to -40 mV.

In the present invention (4), the average crystal grain size of the tube body after the heating test is held at 600° C.±10° C. for 3 minutes and cooled to room temperature to measure the average crystal grain size of 150 μm or more. An aluminum alloy extruded tube for a heat exchanger according to any one of (1) to (3) is provided.

The present invention (5) is characterized in that the heat exchanger aluminum alloy extruded tube according to any one of (1) to (4) and a fin made of an aluminum alloy containing Zn are joined by brazing. The present invention provides a heat exchanger that

The present invention (6) comprises an aluminum alloy extruded tube made of an aluminum alloy containing Mn, and a fin brazed to the aluminum extruded tube and made of an aluminum alloy containing Zn,
The aluminum alloy extruded tube has a Zn diffusion layer on the tube surface,
In spontaneous potential measurement, the potential difference between the tube surface and the tube depth of the aluminum alloy extruded tube (tube surface potential - tube depth potential) is -180 to -40 mV,
To provide a heat exchanger characterized by

According to the present invention, the fins and the tube are joined without reducing the thickness of the tube during brazing or with a very small amount of reduction in thickness, and the brazeability is good, and it can be used for a long time. The fins are difficult to fall off, and the Zn diffusion layer as a sacrificial corrosion protection layer is formed on the tube surface layer by brazing, and corrosion is prevented by the sacrificial corrosion protection layer on the tube surface layer and the fins, resulting in excellent corrosion resistance. It is possible to provide an aluminum alloy extruded tube used for and a heat exchanger using the extruded tube.

FIG. 4 is a schematic diagram showing a mini-core produced in an example.

The aluminum alloy extruded tube of the present invention is an aluminum alloy extruded tube used in a heat exchanger for automobiles,
a tube body made of an aluminum alloy containing Mn;
a coating film formed on the surface of the tube body;
has
The coating contains Al—Si alloy brazing powder, Zn-containing fluoride-based flux powder, Zn-free fluoride-based flux powder, and a binder,
The coating amount of the Al—Si alloy brazing filler metal powder is 9.0 to 25.0 g/m ² , the coating amount of the Zn-containing fluoride flux powder is 1.0 to 9.0 g/m ² , The coating amount of the Zn-free fluoride-based flux powder is 1.0 to 11.0 g/m ² and the coating amount of the binder is 1.0 to 13.0 g/m ² ;
An aluminum alloy extruded tube for a heat exchanger characterized by

The extruded tube for a heat exchanger of the present invention is made of an aluminum alloy, and is an aluminum alloy tube produced by extruding an aluminum alloy. The aluminum alloy extruded tube of the present invention is brazed with fins or the like to be used as a tube through which a refrigerant flows in a heat exchanger for automobiles.

(tube)
The tube body according to the aluminum alloy extruded tube of the present invention is made of an aluminum alloy containing Mn. Mn has the effect of improving the strength by forming a solid solution in the aluminum matrix, and also has the effect of making the potential noble.

The Mn-containing aluminum alloy that forms the tube body contains 0.20 to 1.20% by mass of Mn, has a Ti content of 0.10% by mass or less, and the balance is Al and inevitable impurities. is preferred.

In the Mn-containing aluminum alloy forming the tube body, the Mn content is preferably 0.20 to 1.20% by mass, particularly preferably 0.40 to 1.20% by mass. When the Mn content in the Mn-containing aluminum alloy is within the above range, it is possible to obtain a sufficient strength improvement effect and potential noble effect in the deep portion of the tube. On the other hand, if the Mn content in the aluminum alloy is less than the above range, it is difficult to obtain the above effects. By suppressing the movement of grain boundaries, the crystal structure after brazing becomes fine, which may cause brazing defects, and furthermore, the workability in extrusion processing is lowered, and the productivity of the tube body is reduced. is likely to be lower.

The Ti content in the Mn-containing aluminum alloy forming the tube body is preferably 0.10% by mass or less, more preferably 0.001 to 0.08% by mass. When the Ti content in the Mn-containing aluminum alloy is within the above range, the structure can be refined during casting. On the other hand, if the Ti content in the aluminum alloy exceeds the above range, large crystals may form during casting, making it difficult to produce a healthy tube body. , the crystallized Ti may cause friction with the die, which may reduce productivity and tool life.

As the tube main body, an aluminum alloy ingot adjusted to the chemical composition of the aluminum alloy containing Mn and cast, that is, 0.20 to 1.20% by mass, preferably 0.40 to 1.20% by mass of Mn, Ti content is 0.10% by mass or less, preferably 0.001 to 0.08% by mass, and the balance is Al and inevitable impurities An aluminum alloy ingot is subjected to the following homogenization treatment It is preferably an aluminum alloy subjected to hot extrusion.
The homogenization treatment includes the following first form of homogenization treatment and second form of homogenization treatment.

In the first form of homogenization treatment, an aluminum alloy ingot having a predetermined chemical composition is held at 400-650°C for 2 hours or longer. The treatment temperature in the first form of homogenization treatment is 400-650°C, preferably 430-620°C. When the treatment temperature of the homogenization treatment is within the above range, coarse crystallized substances formed during casting can be decomposed or granulated, and uneven structures such as segregation layers generated during casting can be homogenized. can. As a result, resistance during extrusion can be reduced to improve extrudability, and the surface roughness of the product after extrusion can be reduced. On the other hand, if the treatment temperature of the homogenization treatment is less than the above range, there is a risk that coarse crystallized substances and the uneven structure described above will remain, which may lead to deterioration in extrusion performance and increase in surface roughness. Moreover, if the above range is exceeded, there is a risk of inducing melting of the ingot. The treatment time for the homogenization treatment is 2 hours or more, preferably 5 hours or more. Homogenization becomes sufficient when the treatment time of the homogenization treatment is within the above range. Moreover, even if the treatment time of the homogenization treatment exceeds 24 hours, the effect of homogenization is saturated, so 24 hours or less is preferable.

In the second form of homogenization treatment, an aluminum alloy ingot having a predetermined chemical composition is subjected to a first homogenization treatment of holding at 550 to 650 ° C. for 2 hours or more, and after performing the first homogenization treatment, A second homogenization treatment is performed by holding the aluminum alloy ingot at 400 to 550° C. for 3 hours or longer.

The treatment temperature in the first homogenization treatment of the second form of homogenization treatment is 550-650°C, preferably 580-620°C. When the treatment temperature of the first homogenization treatment is within the above range, coarse crystallized substances formed during casting can be decomposed or granulated, and can be positively redissolved. On the other hand, if the treatment temperature of the first homogenization treatment is less than the above range, re-dissolution will be difficult to progress, and if it exceeds the above range, the ingot may melt. The treatment time of the first homogenization treatment is 2 hours or more, preferably 5 hours or more. When the treatment time of the homogenization treatment is within the above range, the above effects are sufficient. Moreover, even if the treatment time of the homogenization treatment exceeds 24 hours, the effect of homogenization is saturated, so 24 hours or less is preferable.

The treatment temperature in the second homogenization treatment according to the second form of homogenization treatment is 400 to 550°C. When the treatment temperature of the second homogenization treatment is within the above range, Mn dissolved in the matrix phase can be precipitated and the solid solubility of Mn can be reduced. As a result, deformation resistance in extrusion processing can be reduced, and extrudability can be improved. On the other hand, if the treatment temperature of the second homogenization treatment is less than the above range, the amount of precipitation of Mn is reduced, so the effect of reducing deformation resistance may be insufficient. Since it becomes difficult for Mn to precipitate, there is a risk of increasing the deformation resistance. The treatment time of the second homogenization treatment is 3 hours or more, preferably 5 hours or more. If the treatment time of the second homogenization treatment is less than the above range, the precipitation of Mn may be sufficient, and the effect of lowering the deformation resistance may be insufficient. The longer the homogenization treatment time is, the more effective the reaction progresses. However, even if the treatment time is too long, the effect is saturated.

In the second form of homogenization treatment, the first homogenization treatment and the second homogenization treatment may be performed continuously, or after performing the first homogenization treatment, the ingot is once After cooling, a second homogenization treatment may be performed. Note that performing the first homogenization treatment and the second homogenization treatment continuously means that after the first homogenization treatment is completed, the temperature of the ingot is set to a temperature lower than the treatment temperature of the second homogenization treatment It means that the second homogenization treatment is started when the treatment temperature of the second homogenization treatment is reached without cooling to . Further, after performing the first homogenization treatment, once the ingot is cooled and then the second homogenization treatment is performed, for example, after performing the first homogenization treatment, the ingot is heated to 200 ° C. After cooling to below, it is reheated and the second homogenization treatment is performed.

The method of hot-extrusion processing the aluminum alloy ingot that has been subjected to the first form of homogenization treatment or the second form of homogenization treatment is not particularly limited. The processing temperature for hot extrusion processing is, for example, 400 to 550°C.

The shape of the tube body is not particularly limited, and is appropriately selected according to the application and required properties. Examples of the tube main body include an extruded flat multi-hole tube formed by extrusion, having a plurality of coolant channels inside, and having a flat cross-sectional shape perpendicular to the extrusion direction. Further, the tube main body may have a shape such as a simple cylindrical shape, for example. The tubular tube may be manufactured by extrusion.

(Coating film)
The coating film according to the aluminum alloy extruded tube of the present invention is formed on the outer surface of the tube. The coating contains Al—Si alloy brazing powder, Zn-containing fluoride-based flux powder, Zn-free fluoride-based flux powder, and a binder.

The Al-Si alloy brazing powder is an alloy of powdered Al and Si. The Al--Si alloy brazing material powder melts by itself when heated during brazing, and produces liquid-phase brazing on the outer surface of the tube. This allows the tube to be joined to the fins and headers. Since the Al—Si alloy brazing filler metal powder contains Al, the outer surface of the tube is less likely to be melted by the brazing filler metal during brazing.

The content of Si in the Al-Si alloy constituting the Al-Si alloy brazing powder is preferably 5.0 to 20.0% by mass, particularly preferably 7.0 to 15.0% by mass. When the content of Si in the alloy of Al and Si is within the above range, it is difficult for the outer surface of the tube to melt during brazing to reduce the thickness of the tube, and the brazeability is improved.

The coating amount of the Al—Si alloy brazing powder is 9.0 to 25.0 g/m ² , preferably 12.0 to 20.0 g/m ² . When the amount of the Al—Si alloy brazing filler metal powder applied is within the above range, good brazeability is obtained. On the other hand, if the coating amount of the Al—Si alloy brazing material powder is less than the above range, the amount of the liquid phase brazing filler metal will be insufficient, and joint failure will easily occur. It becomes excessively thick, causing dimensional changes in the core after brazing, and the brazeability tends to be low.

　Zn-containing fluoride-based flux generates Zn by reacting with Al in the tube during brazing heat, forming a Zn diffusion layer on the tube surface. When Zn is produced from Zn-containing flux, Zn-free fluoride flux is produced at the same time. The Zn-free fluoride-based flux melts during the brazing heat and destroys the Al-Si alloy powder and the oxide film on the outer surface of the tube in advance, enabling brazing to proceed immediately after the formation of liquid phase brazing. do. In the present invention, the terms "containing Zn" and "containing Zn" indicate that the amount of Zn is detected (beyond the lower limit of detection) in analysis using an electron probe microanalyzer.

Examples of Zn-containing fluoride-based flux powders include KZnF ₃ and ZnF ₂ .

The coating amount of the Zn-containing fluoride-based flux powder is 1.0 to 9.0 g/m ² , preferably 2.0 to 8.0 g/m ² . When the coating amount of the Zn-containing fluoride-based flux powder is within the above range, the heat exchanger has excellent corrosion resistance. On the other hand, if the coating amount of the Zn-containing fluoride-based flux powder is less than the above range, the potential difference between the surface of the tube after brazing heat and the depth of the tube becomes small, resulting in an insufficient sacrificial anode effect. If the range is exceeded, the potential difference between the tube surface and the tube depth becomes excessively large, which increases the rate of thinning of the tube and increases the degree of Zn concentration in the fillet, resulting in a decrease in corrosion resistance.

The Zn-free fluoride-based flux powder functions as a flux during brazing, melts during brazing addition heat, destroys the Al-Si alloy brazing powder and the oxide film on the outer surface of the tube, and after the formation of liquid phase brazing, Allows brazing to proceed immediately. The Zn-free fluoride-based flux powder is powdery fluoride containing no Zn. In the present invention, "no Zn" or "no Zn" means that the amount of Zn is below the detection limit in analysis by an electron probe microanalyzer.

Examples of the Zn-free fluoride constituting the Zn-free fluoride flux powder include K--Al--F compounds such as KAlF ₄ , K ₂ AlF ₅ and K ₃ AlF ₆ . In addition to these, Zn-free fluorides include fluxes such as CaF ₂ and LiF.

The coating amount of the Zn-free fluoride-based flux powder is 1.0 to 11.0 g/m ² , preferably 3.0 to 11.0 g/m ² . When the coating amount of the Zn-free fluoride-based flux powder is within the above range, the effect of destroying the oxide film during brazing is sufficient. On the other hand, if the coating amount of the Zn-free fluoride-based flux powder is less than the above range, the flux component will be insufficient, resulting in insufficient destruction of the oxide film, and the brazability will tend to be low. If it exceeds, the coating thickness becomes excessively thick, the dimensional change of the core after brazing occurs, and the brazeability tends to deteriorate.

4. From the viewpoint of brazing properties, the total coating amount of the Zn-containing fluoride-based flux powder and the coating amount of the Zn-free fluoride-based flux powder is preferably 3.0 to 15.0 g/m ² . Particularly preferred is 0 to 13.0 g/m ² . Sufficient brazability can be obtained by setting the total coating amount of the Zn-containing fluoride-based flux powder and the coating amount of the Zn-free fluoride-based flux powder within the above range. On the other hand, if the total coating amount of the Zn-containing fluoride-based flux powder and the coating amount of the Zn-free fluoride-based flux powder is less than the above range, the flux component will be insufficient, resulting in insufficient destruction of the oxide film and soldering. In addition, if the above range is exceeded, the effect of destroying the oxide film described above is saturated, but the change in the coating thickness after melting the flux becomes excessively large, so the core during brazing dimensional change, and there is a concern that the brazeability may deteriorate.

The binder adheres Al-Si alloy brazing powder, Zn-containing fluoride-based flux powder, and Zn-free fluoride-based flux powder to the surface of the tube body. Examples of binders include acrylic resins and urethane resins.

The coating amount of the binder is 1.0 to 13.0 g/m ² . When the coating amount of the binder is within the above range, the Al—Si alloy brazing powder, the Zn-containing fluoride flux powder, and the Zn-free fluoride flux powder can be adhered well to the surface of the tube body. . On the other hand, if the coating amount of the binder is less than the above range, the coating film tends to peel off. may remain and the brazability may deteriorate.

As a method for forming a coating film on the surface of the tube body, for example, Al—Si alloy brazing powder, Zn-containing fluoride-based flux powder, Zn-free fluoride-based flux powder, and a binder are mixed with a solvent, A coating film can be formed by applying the obtained paste to the surface of the tube body and then drying and removing the solvent. Before mixing the Al—Si alloy brazing filler metal powder, the Zn-containing fluoride flux powder, and the Zn-free fluoride flux powder in the solvent, the Al—Si alloy brazing filler metal powder and the Zn-containing fluoride flux are mixed in advance. Powder and Zn-free fluoride-based flux powder are mixed to form a mixed powder of Al—Si alloy brazing powder, Zn-containing fluoride-based flux powder, and Zn-free fluoride-based flux powder. The mixed powder obtained may be mixed in a solvent together with a binder. For example, a roll coating method or the like is used to apply the paste to the surface of the tube body.

Preferably, when the aluminum alloy extruded tube of the present invention is joined to a fin made of an aluminum alloy containing Zn by brazing, in the self-potential measurement, the surface of the aluminum alloy extruded tube after brazing and the tube depth (tube surface potential-tube deep potential) is preferably -180 to -40 mV, particularly preferably -150 to -40 mV. In the aluminum alloy extruded tube of the present invention, a Zn diffusion layer is formed on the tube surface by the coating containing the Zn-containing fluoride-based flux powder, so that a potential difference is formed between the tube surface and the deep part of the tube. By being within the above range, a sufficient sacrificial anti-corrosion effect is exhibited, and the tube itself has excellent anti-corrosion performance. In the present invention, the electric potential at the tube depth of the aluminum alloy extruded tube refers to the electric potential at a depth of 150 μm or more from the surface of the aluminum alloy extruded tube after brazing.

The aluminum alloy extruded tube for a heat exchanger of the present invention is preferably kept at 600 ° C. ± 10 ° C. for 3 minutes, cooled to room temperature, and then cooled to room temperature. The average grain size is 150 μm or more. In other words, the aluminum alloy extruded tube for a heat exchanger has a crystal structure such that the tube body has an average crystal grain size of 150 μm or more when it is held at 600° C.±10° C. for 3 minutes and cooled to room temperature. there is The aluminum alloy extruded tube for a heat exchanger was kept at 600°C ± 10°C for 3 minutes, and after cooling to room temperature, a heating test was conducted to measure the average crystal grain size. Due to the above, during the brazing heat, the so-called erosion in which the liquid phase brazing erodes the crystal grain boundaries is difficult to occur, the decrease in the tube wall thickness and the penetration of the tube are difficult to occur, and the reduction in the amount of brazing Since defects are less likely to occur, brazeability is improved.

In the heating test related to the aluminum alloy extruded tube for heat exchanger, first, the aluminum alloy extruded tube for heat exchanger is heated to raise the temperature, and in the temperature raising process, it is heated to a holding temperature of 600 ° C. ± 10 ° C., and then In this test, a temperature of 600° C.±10° C. is maintained for 3 minutes, and then a heating test is performed by cooling to room temperature, and then the average crystal grain size of the tube body of the aluminum alloy extruded tube for heat exchanger is measured after the heating test. The method for measuring the average crystal grain size of the tube body includes a method of electropolishing a test piece, obtaining a microscopic image of each cross section with a polarizing microscope at a magnification of 50 to 100, and measuring the equivalent circle diameter. be done. In addition, regarding the temperature increase in the heating process of the heating test, the temperature range up to 500 ° C. is an average temperature increase rate of 30 ± 10 ° C./min, and the temperature range of 500 ° C. or higher is an average of 10 ± 5 ° C./min. is the rate of temperature rise.

The aluminum alloy extruded tube for a heat exchanger of the present invention has a tube main body made of the above specific aluminum alloy. Therefore, the aluminum alloy extruded tube for a heat exchanger of the present invention has higher strength characteristics than when a pure aluminum alloy is used for the tube body.

The coating film of the aluminum alloy extruded tube for heat exchangers of the present invention contains Al-Si alloy powder, Zn-containing fluoride flux powder, and Zn-free fluoride flux powder. These powders exert their respective characteristics and interact with each other to exert a synergistic effect, thereby easily realizing excellent brazeability and corrosion resistance.

That is, the Al—Si alloy powder contained in the mixed powder is melted by heating during brazing, and liquid phase brazing is generated on the outer surface of the tube. Thereby, the heat exchanger tubes and the fins can be joined. At this time, since liquid phase brazing is generated by the brazing material powder alone without melting the outer surface of the tube, the thickness of the tube should not be reduced during brazing, or the amount of reduction is very small, and a thinner tube should be used. can be done.

The aluminum alloy extruded tube for heat exchanger of the present invention contains 1.0 to 9.0 g/m ² , preferably 2.0 to 8.0 g/m ² of Zn-containing fluoride-based flux powder in the coating film. there is For example, in the case of heat exchanger tubes in which Zn is thermally sprayed on the tube surface, uniform Zn thermal spraying on the tube surface is difficult when the amount of Zn is small, and when the amount of Zn is large, Zn diffuses due to brazing. When a layer is formed, the potential difference between the surface of the tube and the depth of the tube increases, and the rate of thinning of the tube increases. Moreover, when the amount of Zn is large, the Zn concentration in the fillets, which are joints formed on the tube surface by brazing, increases, and the fillets are preferentially corroded, which may lead to premature detachment of the fins. On the other hand, in the case of a heat exchanger tube having a coating film formed by applying a paint containing Zn-containing fluoride-based flux powder, the tube surface should be uniformly coated regardless of the amount of Zn-containing fluoride-based flux. Therefore, an appropriate amount of Zn can be applied to the tube surface. As a result, due to the formation of the Zn diffusion layer, an appropriate potential difference is formed between the tube surface and the tube core, and the tube itself can have excellent anti-corrosion performance. In addition, Zn concentration in fillets is reduced, and corrosion resistance is improved.

The aluminum alloy extruded tube for a heat exchanger of the present invention contains a Zn-containing fluoride-based flux powder and a Zn-free fluoride-based flux powder in the coating film, and the Zn-containing fluoride-based flux powder and the Zn-free fluoride The system flux powder is melted by heating during brazing, and destroys the oxide film on the surface of the brazing material powder and the oxide film on the outer surface of the tube first, making it possible to braze immediately after melting the Al-Si alloy powder. do. In the aluminum alloy extruded tube for a heat exchanger of the present invention, the Zn-free fluoride-based flux powder is used to form the oxide film on the surface of the brazing material powder and the oxide film on the outer surface of the tube, which are insufficient with the Zn-containing fluoride-based flux powder alone. Since it replenishes the destructive action, the potential difference between the surface of the tube after brazing and the deep part of the tube can be made appropriate, and while the concentration of Zn in the fillet during brazing is reduced, the brazeability can be improved.

As described above, the aluminum alloy extruded tube for a heat exchanger of the present invention does not or hardly causes melting of the outer surface even if it is thinner, and has excellent brazeability. In the aluminum alloy extruded tube for heat exchangers, Zn-containing fluoride-based flux powder contained in the coating reacts with the tube during brazing addition heat to generate Zn, and Zn diffuses from the tube surface to sacrifice It has a layer and exhibits a sacrificial anti-corrosion effect as a single tube, and at the same time, Zn concentration in the fillet is reduced, and it has excellent corrosion resistance.

(Heat exchanger)
A heat exchanger according to a first aspect of the present invention is obtained by brazing fins made of an aluminum alloy containing Zn and extruded aluminum alloy tubes for a heat exchanger of the present invention.

The fins made of an aluminum alloy containing Zn according to the heat exchanger of the first embodiment of the present invention are made of an aluminum alloy. The aluminum alloy forming the fin material is not particularly limited as long as it has sufficient strength and corrosion resistance for use in heat exchangers. 0.50 to 2.50% by mass, a Cu content of 0.30% by mass or less, and the balance being Al and unavoidable impurities. The aluminum alloy for fin material may further contain 1.50% by mass or less of Si and/or 0.30% by mass or less of Zr. Further, the fins made of an aluminum alloy containing Zn according to the heat exchanger of the present invention may be known fins as long as they have sufficient strength and corrosion resistance for use in heat exchangers.

In the heat exchanger of the first aspect of the present invention, after contacting the aluminum alloy extruded tube for heat exchanger of the present invention with fins made of an aluminum alloy containing Zn, other members such as a header are assembled, It is produced by heating and brazing these. The heating temperature, heating time, and atmosphere for brazing are not particularly limited, and the brazing method is also not particularly limited. The heating temperature for brazing is, for example, 590 to 610° C., the heating time for brazing is, for example, 15 minutes to 45 minutes, and the atmosphere for brazing is, for example, nitrogen gas atmosphere, argon A gas atmosphere or the like.

In the heat exchanger of the first embodiment of the present invention, in self-potential measurement, the potential difference between the tube surface and the tube depth of the aluminum alloy extruded tube (tube surface potential - tube depth potential) is -180 to -40 mV, It is preferably -150 to -40 mV. Since the potential difference between the tube surface and the tube depth of the aluminum alloy extruded tube is within the above range, the Zn diffusion layer formed near the tube surface of the extruded tube exhibits a sufficient sacrificial anti-corrosion effect, making the tube excellent as a single unit. It has anti-corrosion performance.

The heat exchanger of the first aspect of the present invention is brazed using the aluminum alloy extruded tube for heat exchanger of the present invention as a tube material, so that the thickness of the tube is not reduced during brazing. It is joined to the fin with a very small decrease in thickness. Therefore, the heat exchanger of the present invention has high strength even if it is thin. In addition, since the potential difference between the surface of the tube after brazing and the depth of the tube is appropriate, pitting corrosion is suppressed by the sacrificial anode effect, but the rate of thinning of the tube is not too fast, providing excellent corrosion resistance.

In the heat exchanger of the first embodiment of the present invention, the heat exchanger tubes of the present invention and fins made of an aluminum alloy containing Zn are joined by brazing. A fillet is formed between the tube and the fins during brazing. In general, when pure Zn powder or the like is contained in the coating film, Zn in the molten brazing filler metal is concentrated during fillet formation as described above, and the potential of the fillet becomes the most negative. In this case, when the heat exchanger is exposed to a corrosive environment, corrosion progresses most rapidly in the fillet portions, and the disappearance of the fillets causes the fins to come off the tube surface. As a result, the heat exchange performance is greatly reduced, and furthermore, the anti-corrosion action of the tube by the fins is lost, so that the tube may penetrate at an early stage.

On the other hand, in the present invention, although the Zn component is contained in the coating film applied to the aluminum alloy extruded tube for heat exchanger, Zn concentration in the fillet does not occur as compared with the conventional technology. That is, since the fillets do not corrode preferentially, the fins do not fall off from the tube surface for a long period of time, and not only is it possible to prevent deterioration in heat exchange performance, but the fins provide a long-term anti-corrosion effect on the tube. Therefore, as described above, it has excellent corrosion resistance even when exposed to a severe corrosive environment.

A heat exchanger according to a second aspect of the present invention comprises an aluminum alloy extruded tube made of an aluminum alloy containing Mn, and a fin made of an aluminum alloy containing Zn, brazed to the extruded aluminum tube. and
The aluminum alloy extruded tube has a Zn diffusion layer on the tube surface,
The potential difference between the tube surface and the tube depth (tube surface potential - tube depth potential) is -180 to -40 mV,
A heat exchanger characterized by

The aluminum alloy extruded tube according to the second aspect of the heat exchanger of the present invention is made of an aluminum alloy containing Mn, and the Mn content in the aluminum alloy extruded tube according to the second aspect of the heat exchanger of the present invention is is preferably 0.20 to 1.20% by weight, particularly preferably 0.40 to 1.20% by weight. Further, the aluminum alloy extruded tube according to the second aspect of the heat exchanger of the present invention can contain Ti, and the Ti content in the aluminum alloy extruded tube according to the second aspect of the heat exchanger of the present invention is The amount is preferably 0.10% by weight or less, particularly preferably 0.001 to 0.08% by weight. Also, the aluminum alloy extruded tube according to the second embodiment of the heat exchanger of the present invention has a Zn diffusion layer on the tube surface.

The aluminum alloy forming the fin material of the heat exchanger according to the second embodiment of the present invention is not particularly limited as long as it has sufficient strength and corrosion resistance for heat exchangers. is 0.80 to 2.00% by mass, the Zn content is 0.50 to 2.50% by mass, and the Cu content is 0.30% by mass or less. The aluminum alloy for fin material may contain 1.50% by mass or less of Si and/or 0.30% by mass or less of Zr.

In the heat exchanger of the second aspect of the present invention, in the self-potential measurement, the potential difference between the tube surface and the tube depth of the aluminum alloy extruded tube (tube surface potential - tube depth potential) is -180 to -40 mV, It is preferably -150 to -40 mV. Since the potential difference between the tube surface and the tube depth of the aluminum alloy extruded tube is within the above range, the Zn diffusion layer formed near the tube surface of the extruded tube exhibits a sufficient sacrificial anti-corrosion effect, making the tube excellent as a single unit. It has anti-corrosion performance.

The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples shown below.

(Examples and Comparative Examples)
A tube body was produced using an alloy having the chemical components shown in Table 1, and then a coating film having a composition shown in Table 2 was formed on the surface of the obtained tube body to produce an aluminum alloy extruded tube. After that, using the obtained aluminum alloy extruded tube, a mini-core simulating a heat exchanger as shown in FIG. 1 was assembled, and the corrosion resistance of the obtained three types of mini-cores was evaluated.

<Production of tube body>
A billet having the chemical components shown in Table 1 was heated at 600° C. for 10 hours for homogenization. After the homogenized billet was cooled to room temperature, it was reheated to 450° C. and subjected to hot extrusion. As described above, a tube body having a width of 16 mm, a height of 1.0 mm, a flat cross section perpendicular to the extrusion direction, and a plurality of coolant channels was produced.

<Formation of coating film>
A paste for forming a coating film was prepared separately from the production of the tube body. Al--Si alloy brazing powder, Zn-free fluoride flux powder, Zn-containing fluoride flux powder and a binder were mixed with a solvent to prepare a paste for forming a coating film. Next, the obtained paste was applied to the flat surface of the tube body using a roll coater to obtain a coated tube. The composition of the paste after coating was as shown in Table 2.

The Al—Si alloy brazing filler metal powder has a Si content of 12.00% by mass, the Zn-free fluoride-based flux powder is a K—Al—F-based flux, and the Zn-containing fluoride-based flux is It was _KZnF3 and the binder was an acrylic resin.

<Fabrication of fins>
A 0.1 mm thick plate made of an aluminum alloy containing Mn: 1.20% by mass and Zn: 1.50% by mass was corrugated to produce a fin having a corrugated shape. The fin pitch was 3 mm and the fin height was 7 mm.

<Mini-core preparation and heating test>
The upper and lower fins were laminated in such a manner that they were sandwiched between aluminum alloy extruded tubes, and assembled into a predetermined shape shown in FIG. In this state, in a nitrogen gas atmosphere, the temperature of the tube and fins was raised to 600°C at an average heating rate of 10°C per minute in the region of 400°C or higher, and the temperature was maintained at 600°C for 3 minutes, and then cooled to room temperature. By brazing, the tube cut to a length of 40 mm and the fins were joined to obtain a mini-core simulating a heat exchanger.
Note that the thermal history for producing the mini-core corresponds to the thermal history of the heating test.

Using the three types of mini-cores (test specimens A to C) obtained above, brazeability evaluation, self-potential measurement, and corrosion tests were performed.

<Brazability evaluation>
The cross section of the brazed tube was observed, and by visual observation, the bonding state of the fins, the presence or absence of appearance defects such as discoloration, the presence or absence of melting of the fins, and the presence or absence of erosion on the tube surface were determined. Etching was also performed, and the average crystal grain size was measured. The average crystal grain size is measured by electropolishing the tube surface and then using a polarizing microscope with a magnification of 25 to obtain a microscopic image of a cross section at a depth of 10 μm or less from the tube surface. Three 1 mm line segments were drawn, and the average value obtained by dividing the 1 mm length of the line segment by the number of grain boundaries intersecting each line segment was taken as the average grain size.

<Spontaneous potential measurement>
After brazing, the self-potential of the tube surface and tube depth of each specimen was measured. Each site was cut to an appropriate size, masked with a sealant except for the area to be measured, immersed in a 5% NaCl solution for 24 hours, and the self-potential of each site was obtained from the average value from 18 hours to 24 hours. As for the potential at the deep portion of the aluminum alloy extruded tube, the potential at a depth of 150 μm from the outer surface of the aluminum alloy extruded tube was measured.
Regarding "tube surface potential (A) - tube deep potential (B)", -180 to -40 mV was "passed", and less than -180 mV or greater than -40 mV was "failed". .

<Corrosion test>
Each specimen was subjected to SWAAT specified in ASTM-G85-Annex A3 for 1320 hours. The presence or absence of peeling of the fins was determined by visually observing the test material after the completion of the test. In addition, for the maximum corroded portion of the tube selected by the depth of focus measurement, a cross section was obtained by mechanical polishing, and a microscope image of the cross section in the direction parallel to the longitudinal direction of the tube was obtained using a metallographic microscope with a magnification of 50 times, including the maximum corroded portion. The tube cross-sectional area reduction rate was obtained by dividing the tube cross-sectional area in a region of 2 mm in the longitudinal direction of the tube by the tube cross-sectional area before the corrosion test.
Regarding peeling of fins, if the tube and fins are fixed and force is applied, the tube and fins are fixed together. If the tube and fins are not separated from each other, even though the tube is partially peeled off, it is evaluated as "○: Passed, little fin peeling". A lot of fins come off."
When the tube cross-sectional area reduction rate was 20% or less, it was evaluated as "accepted", and when it exceeded 20%, it was evaluated as "failed".

<Evaluation results>
Table 3 shows the brazeability evaluation results.
Test Examples A, B, and C did not cause any brazing defects and passed the brazing properties. In addition, the average grain size of the post-brazing structure was sufficiently large as 150 μm or more, and no erosion occurred, which was acceptable. In addition, since the wall thickness of the tube after brazing did not change significantly compared to the wall thickness before brazing, it was confirmed that significant melting did not occur.

Table 4 shows the self-potential measurement results and the corrosion test results.
In test specimens A and B, the natural potential of the tube surface is 40 mV or more less noble than the deep part of the tube, the corrosion of the deep part of the tube can be prevented by preferential corrosion of the tube surface, and the natural potential of the tube surface and the natural potential of the deep part of the tube The difference was within 180 mV, the natural potential of the tube surface was not too base than the depth of the tube, and the potential difference was moderate. Further, in Test Example A, the peeling of the fins was extremely slight, and the sample passed the test. Specimen B was accepted because the fin peeling was slight. In all test specimens, the amount of Zn-containing flux in the coating was appropriate, and preferential corrosion of fillets was less likely to occur.
Specimen C had slight fin peeling and passed the test, but the corrosion rate of the tube was high because the difference between the natural potential of the tube surface and the natural potential of the deep part of the tube was greater than 180 mV. The reduction rate was greater than 20% and was unacceptable.

Claims

Aluminum alloy extruded tubes used in automobile heat exchangers,
a tube body made of an aluminum alloy containing Mn;
a coating film formed on the surface of the tube body;
has
The coating contains Al—Si alloy brazing powder, Zn-containing fluoride-based flux powder, Zn-free fluoride-based flux powder, and a binder,
The coating amount of the Al—Si alloy brazing filler metal powder is 9.0 to 25.0 g/m 2 , the coating amount of the Zn-containing fluoride flux powder is 1.0 to 9.0 g/m 2 , The coating amount of the Zn-free fluoride-based flux powder is 1.0 to 11.0 g/m 2 and the coating amount of the binder is 1.0 to 13.0 g/m 2 ;
An aluminum alloy extruded tube for a heat exchanger, characterized by:
2. The aluminum alloy according to claim 1, wherein the aluminum alloy contains 0.20 to 1.20% by mass of Mn and 0.10% by mass or less of Ti, and the balance is Al and inevitable impurities. Aluminum alloy extruded tube for heat exchanger.
When the fins made of an aluminum alloy containing Zn are joined by brazing, the potential difference between the surface of the extruded tube and the depth of the tube (potential on the surface of the tube - potential at the depth of the tube) is -180 to -180. 3. The aluminum alloy extruded tube for a heat exchanger according to claim 1, wherein the voltage is -40 mV.
In a heating test for measuring the average crystal grain size after cooling to room temperature after holding at 600° C.±10° C. for 3 minutes, the average crystal grain size of the tube body after the heating test is 150 μm or more. The aluminum alloy extruded tube for heat exchangers according to any one of claims 1 to 3.
A heat exchanger characterized by being a brazed joint of the extruded aluminum alloy tube for a heat exchanger according to any one of claims 1 to 4 and fins made of an aluminum alloy containing Zn.
An aluminum alloy extruded tube made of an aluminum alloy containing Mn, and a fin brazed to the aluminum extruded tube and made of an aluminum alloy containing Zn,
The aluminum alloy extruded tube has a Zn diffusion layer on the tube surface,
In spontaneous potential measurement, the potential difference between the tube surface and the tube depth of the aluminum alloy extruded tube (tube surface potential - tube depth potential) is -180 to -40 mV,
A heat exchanger characterized by: