WO2022050030A1

WO2022050030A1 - Aluminum alloy extruded tube and heat exchanger

Info

Publication number: WO2022050030A1
Application number: PCT/JP2021/029860
Authority: WO
Inventors: 太一鈴木; 稜東森; 英敏熊谷
Original assignee: 株式会社Uacj
Priority date: 2020-09-02
Filing date: 2021-08-16
Publication date: 2022-03-10
Also published as: JP2022042318A

Abstract

An extruded tube of an aluminum alloy and for a heat exchanger and characterized by having a tube body comprising an aluminum alloy containing Mn, a Zn thermal sprayed layer formed on the outer surface of the tube body, and a coating film formed on the outer surface of the Zn thermal sprayed layer, wherein the coating film contains an Al-Si alloy brazing material powder, a fluoride flux powder that does not include Zn, and a binder, and in a heating test for measuring the average crystal grain size after holding at 600°C ±10°C for three minutes and then cooling to room temperature, the average crystal grain size of the tube body after the heating test is 150 μm or greater. By means of the present invention, it is possible to provide an aluminum alloy extruded tube that is for a heat exchanger for an automobile and that enables fins and the tube to be joined without reducing the wall thickness of the tube during brazing, and that has excellent brazing ability, and for which the fins do not easily detach over a long period of time, and that has excellent corrosion resistance due to protection from corrosion provided by the fins.

Description

Aluminum alloy extrusion tube and heat exchanger

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

Aluminum alloys that are lightweight and have high thermal conductivity are often used in heat exchangers made of aluminum alloys for automobiles such as evaporators and capacitors. The heat exchanger has a tube through which the refrigerant flows and fins for heat exchange between the refrigerant and the air outside the tube, and the tube and the fins are joined by brazing. Fluoride-based flux is often used for brazing between the tube and the fins.

Since the tube used in the heat exchanger for automobiles is joined to the fin by brazing in order to exchange heat as described above, it is necessary to provide a brazing material on the fin side or the tube side, so that the fin side or the tube A clad material in which a brazing material is clad on the side is often used, and there is a problem that the manufacturing cost and the material cost of the clad material are high.

When a clad material with a brazing material on the fin side is used, it is difficult to reduce the manufacturing cost and the material cost because the amount of the fin material used is larger than the amount of the tube material used. On the other hand, when the brazing material is provided on the tube side, it is not necessary to use a clad material for the fin material, so there is room for cost reduction.

As a conventional technique for providing a brazing filler metal on the tube side, for example, a technique for forming a flux layer containing Si (silicon) powder, a Zn-containing flux, and a binder on the outer surface of the tube has been proposed (patented). Document 1). In the flux layer having the above composition, all of the brazing filler metal component, Zn and the flux component can be simultaneously bonded in one bonding step. Further, since it is not necessary to provide a brazing material on the fin side, the fin can be manufactured using the bare fin material. As a result, cost reduction can be achieved.

Here, when a Zn-containing compound such as KZnF ₃ is used as the flux as in the flux layer of Patent Document 1, the flux component and Zn are generated by the following reaction formula.
6KZnF ₃ + 4Al → 3KAlF ₄ + K ₃ AlF ₆ + 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) of the tube, Zn is precipitated and potassium fluoroaluminate, which is a flux component, is generated. , Zn and functions as a flux component. Therefore, when a Zn-containing flux is used, the above reaction proceeds at the interface between the flux layer and the tube, that is, near the outer surface of the tube.

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

International Publication 2011/090059 JP-A-2018-118318

In recent years, in order to reduce the environmental load, there is an increasing demand to improve the fuel efficiency of automobiles by reducing the weight of components and to reduce the amount of materials used as products by extending the life of parts. Therefore, it is strongly required to use a tube thinner than the conventional one and to have a higher corrosion resistance than the conventional one in a heat exchanger using such a tube.

This not only allows the tube to be thinner, but also has a sacrificial anticorrosive effect on the tube itself, and at the same time, the fins do not fall off the tube surface even after being exposed to a corrosive environment for a long period of time. This means that the surface of the tube needs to be protected from corrosion.

However, in the method of Patent Document 1, since the pure Si powder contained in the paint is eutectic-melted with the aluminum on the tube surface to form a liquid phase wax of an Al—Si alloy, a part of the tube surface is about to try. It will be exhausted. Therefore, it is necessary to secure a certain thickness or more of the tube in order to prevent the tube from penetrating during the waxing heat, and it cannot be said that it contributes to the thinning of the tube.

Further, the pure Si powder contained in the paint is eutectic-melted with aluminum on the surface of the tube, and the liquid phase wax of the Al—Si alloy flows to the contact portion between the fin and the tube to form a fillet. .. At this time, if coarse Si particles are mixed, the liquid phase wax that is eutectic-melted with the aluminum on the surface of the coarse Si particles and the surface of the tube rapidly flows to the contact portion between the fin and the tube due to the capillary phenomenon. The periphery of the reduced Si grains is separated from the tube surface, a dent is formed on the surface of the tube from which the liquid phase wax has flowed out, and further eutectic melting proceeds at the bottom of the dent in contact with the Si grains. Then, a deep melting hole is formed, and there is a possibility that a through hole may be generated in the tube body.

In Patent Document 1, the content of coarse particles having a cumulative volume of particles having a particle size smaller than that, which is 5 times or more the particle size (99% particle size, D99), which is 99% of the total particles, is less than 1 ppm. We are trying to solve the above problem by using Si powder, but there is also a problem to reduce the mixing of coarse particles to less than 1 ppm.

Furthermore, since the reaction of Zn precipitation on the outer surface of the tube immediately before the formation of the liquid phase due to the above-mentioned flux reaction is proceeding, the generated liquid phase contains high-concentration Zn. This Zn diffuses to the outer surface of the tube to form a Zn diffusion layer, which functions as a sacrificial anticorrosion layer to improve the corrosion resistance of the tube, while concentrating in the fillet formed between the fin and the tube. In this case, since the potential of the fillet becomes the lowest, the fillet is preferentially corroded and consumed when exposed to a corrosive environment, causing the fins to fall off, resulting in early deterioration of heat exchange performance and fins. This means that the tube is no longer protected against corrosion, which can lead to premature penetration of the tube.

Further, in the method of Patent Document 2, Al—Si alloy powder is mentioned as an example as an alloy containing Si among the brazing filler metal powders. When Al-Si alloy powder is used as the brazing material for the coated tube, there is a concern that erosion will occur on the tube surface and the wall thickness will be reduced during brazing, unlike the case of pure Si powder. It is hard to say that it is practical.

Therefore, an object of the present invention is to eliminate the risk of forming through holes in the tube due to coarse Si particles during brazing, and to join the fins and the tube without reducing the tube wall thickness, and the brazing property is good. Aluminum alloy extruded tubes for automobile heat exchangers, which have excellent corrosion resistance mainly because the fins are hard to fall off for a long period of time and are mainly protected by the fins, and heat exchangers in which the aluminum alloy extruded tubes are used. Is to provide.

As a result of diligent studies to solve the above problems, the present inventors have made a tube body, a Zn sprayed layer formed on the outer surface of the tube body, and a coating film applied to the surface of the Zn sprayed layer. In a heating test in which the zinc alloy extruded tube is held at 600 ° C. ± 10 ° C. for 3 minutes and cooled to room temperature, the average crystal grain size is measured to be 150 μm or more. A brazing material made of an Al—Si alloy is adopted on the outer surface of the Zn sprayed layer by spraying Zn onto the tube body to form a Zn sprayed layer. By applying the powder and Zn-free fluoride-based flux powder, the tube surface is not melted during brazing, so that the tube wall thickness is not reduced during brazing and erosion is less likely to occur during brazing. Since the brazing property is good and it is difficult for Zn to concentrate in the fillet during brazing, it was found that Zn does not concentrate in the fillet after brazing, and the present invention has been completed.

The above-mentioned problem of the present invention is solved by the following invention.
That is, the present invention (1) is an aluminum alloy extruded tube used in an automobile heat exchanger.
A tube body made of an aluminum alloy containing Mn,
The Zn sprayed layer formed on the outer surface of the tube body and
The coating film formed on the outer surface of the Zn sprayed layer and
Have,
The coating film contains an Al—Si alloy brazing powder, a Zn-free fluoride-based flux powder, and a binder.
In a heating test in which the average crystal grain size is measured after holding at 600 ° C. ± 10 ° C. for 3 minutes and cooling to room temperature, the average crystal grain size of the tube body after the heating test is 150 μm or more. It provides an aluminum alloy extruded tube for a heat exchanger.

Further, in the present invention (2), the Mn-containing aluminum alloy contains 0.20 to 0.90% by mass of Mn, the Ti content is 0.10% by mass or less, and the balance Al and unavoidable. The present invention provides the aluminum alloy extrusion tube for a heat exchanger according to (1), which is an aluminum alloy composed of impurities.

Further, the present invention (3) is characterized in that the amount of Zn sprayed from the tube body is 3.0 to 8.0 g / m ² , and the aluminum alloy extruded tube for the heat exchanger according to (1) or (2). ..

Further, in the present invention (4), the coating amount of the Al—Si alloy brazing filler metal powder is 10.0 to 25.0 g / m ² , and the coating amount of the Zn-free fluoride-based flux powder is 3.0. Provided are the aluminum alloy extruded tubes for heat exchangers (1) to (3), wherein the amount is 12.0 g / m ² and the coating amount of the binder is 1.0 to 13.0 g / m ² . It is something to do.

Further, the present invention (5) is a brazing joint of an aluminum alloy extrusion tube for a heat exchanger according to any one of (1) to (4), fins made of an aluminum alloy containing Zn, and a brazing joint.
The average crystal grain size of the aluminum alloy forming the tube body is 150 μm or more.
It is intended to provide a heat exchanger characterized by.

According to the present invention, the fins and the tube are joined without reducing the tube wall thickness at the time of brazing, the brazing property is good, the fins are hard to fall off for a long period of time, and the fins prevent corrosion. Therefore, it is possible to provide an aluminum alloy extruded tube for an automobile heat exchanger having excellent corrosion resistance and a heat exchanger in which the aluminum alloy extruded tube is used.

It is a schematic diagram which shows the mini core produced in an Example.

The aluminum alloy extrusion tube of the present invention is an aluminum alloy extrusion tube used in an automobile heat exchanger.
A tube body made of an aluminum alloy containing Mn,
The Zn sprayed layer formed on the outer surface of the tube body and
The coating film formed on the outer surface of the Zn sprayed layer and
Have,
The coating film contains an Al—Si alloy brazing powder, a Zn-free fluoride-based flux powder, and a binder.
In a heating test in which the average crystal grain size is measured after holding at 600 ° C. ± 10 ° C. for 3 minutes and cooling to room temperature, the average crystal grain size of the tube body after the heating test is 150 μm or more. Aluminum alloy extrusion tube for heat exchanger.

The aluminum alloy extrusion tube for a heat exchanger of the present invention is formed of an aluminum alloy, and is a tube made of an aluminum alloy manufactured by extrusion molding the aluminum alloy. The aluminum alloy extruded tube of the present invention is used for a tube through which a refrigerant flows in a heat exchanger for automobiles by being brazed with fins or the like.

The aluminum alloy extruded tube of the present invention includes a tube body made of an aluminum alloy containing Mn, a Zn sprayed layer formed on the outer surface of the tube body, and a coating film formed on the outer surface of the Zn sprayed layer. , Have. That is, the Zn sprayed layer and the coating film are laminated in the order of the tube body-Zn spraying layer-coating film on the tube body formed of the aluminum alloy.

The tube body of the aluminum alloy extruded tube of the present invention is formed of an aluminum alloy containing Mn. Mn has an effect of improving the strength by being dissolved in the aluminum matrix, and also has an effect of making the electric potential noble.

The Mn-containing aluminum alloy forming the tube body contains 0.20 to 0.90% by mass of Mn, has a Ti content of 0.10% by mass or less, and is an aluminum alloy composed of the balance Al and unavoidable impurities. Is preferable.

The Mn content in the Mn-containing aluminum alloy forming the tube body is preferably 0.20 to 0.90% by mass, more preferably 0.30 to 0.80% by mass. When the Mn content in the Mn-containing aluminum alloy is within the above range, a sufficient strength improving effect and a potential nourizing effect in the deep part of the tube can be obtained. 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 effect, and if it exceeds the above range, Al—Mn precipitates are deposited in the matrix in the step before hot working described later. By suppressing the movement of grain boundaries, the crystal structure after brazing becomes finer, which may cause the above-mentioned brazing defects, and further, the workability in extrusion processing becomes low, and the tube body May reduce productivity.

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 at the time of casting can be made finer. On the other hand, if the Ti content in the aluminum alloy exceeds the above range, huge crystals may be formed during casting, which may make it difficult to manufacture a sound tube body, and in the case of an extruded multi-hole tube. , Crystallized Ti may cause friction with the die, which may reduce productivity and tool life.

The tube body is an aluminum alloy ingot adjusted to the chemical composition of the above Mn-containing aluminum alloy and cast, that is, 0.20 to 0.90% by mass, preferably 0.30 to 0.80% by mass. Mn is contained, the Ti content is 0.10% by mass or less, preferably 0.001 to 0.08% by mass, and the ingot of an aluminum alloy composed of the balance Al and unavoidable impurities is subjected to the following homogenization treatment. It is preferably hot-extruded using the aluminum alloy that has been subjected to the above.

Examples of the homogenization treatment include the following homogenization treatment of the first form and the homogenization treatment of the second form.

In the homogenization treatment of the first form, the aluminum alloy ingot having a predetermined chemical composition is held at 400 to 650 ° C. for 2 hours or more. The treatment temperature in the homogenization treatment of the first form is 400 to 650 ° C, preferably 430 to 620 ° C. When the treatment temperature of the homogenization treatment is within the above range, the coarse crystallized material formed during casting can be decomposed or granulated, and the non-uniform structure such as the segregated layer generated during casting can be homogenized. can. As a result, the resistance during extrusion processing can be reduced to improve the 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 lower than the above range, coarse crystallization and the above-mentioned non-uniform structure may remain, which may lead to a decrease in extrusion and an increase in surface roughness. Further, if it exceeds the above range, the ingot may be melted. The treatment time of the homogenization treatment is 2 hours or more, preferably 5 hours or more. When the processing time of the homogenization treatment is within the above range, the homogenization is sufficient. Further, the treatment time of the homogenization treatment is preferably 24 hours or less because the effect of homogenization is saturated even if it exceeds 24 hours.

In the second form of homogenization treatment, the aluminum alloy ingot having a predetermined chemical composition is held at 550 to 650 ° C. for 2 hours or more, and then the first homogenization treatment is performed, and then the first homogenization treatment is performed. The aluminum alloy ingot is subjected to a second homogenization treatment in which it is held at 400 to 550 ° C. for 3 hours or more.

The treatment temperature in the first homogenization treatment according to the second form of homogenization treatment is 550 to 650 ° C, preferably 580 to 620 ° C. When the treatment temperature of the first homogenization treatment is in the above range, the coarse crystallized material formed during casting can be decomposed or granulated, and can be positively re-solidified. On the other hand, if the treatment temperature of the first homogenization treatment is lower than the above range, it becomes difficult for the solid solution to proceed, and if it exceeds the above range, the ingot may be melted. The treatment time of the first homogenization treatment is 2 hours or more, preferably 5 hours or more. When the processing time of the homogenization treatment is within the above range, the above effect is sufficient. Further, the treatment time of the homogenization treatment is preferably 24 hours or less because the effect of homogenization is saturated even if it exceeds 24 hours.

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 that is solid-solved in the matrix can be precipitated and the solid solubility of Mn can be lowered. As a result, it is possible to reduce the deformation resistance in extrusion processing and improve the extrudability. On the other hand, if the treatment temperature of the second homogenization treatment is less than the above range, the amount of Mn precipitated is small, so that the effect of lowering the deformation resistance may be insufficient, and if it exceeds the above range, the effect may be insufficient. Since Mn is less likely to precipitate, there is a risk of lowering 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 becomes sufficient, and the effect of reducing the deformation resistance may be insufficient. Further, the treatment time of the homogenization treatment is effective because the reaction proceeds when it is long, but the effect is saturated even if it is too long, so that it is preferably 24 hours or less, and particularly preferably 15 hours or less.

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

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

The form of the tube body is not particularly limited, and is appropriately selected according to the application and required characteristics. Examples of the tube main body include an extruded flat multi-hole tube which is formed by extrusion processing, has a plurality of refrigerant flow paths inside, and has a flat cross-sectional shape perpendicular to the extrusion direction. Further, the tube body may have a simple cylindrical shape or the like. The tubular tube may be manufactured by extrusion.

The Zn sprayed layer according to the aluminum alloy extruded tube of the present invention is formed on the outer surface of the tube body. That is, in the aluminum alloy extruded tube of the present invention, the Zn sprayed layer is arranged between the tube body and the coating film. Zn sprayed on the outer surface of the tube body diffuses from the outer surface of the tube body to the deep part during brazing. Then, during brazing, the sprayed Zn diffuses from the outer surface of the tube body to the deep part to form a sacrificial layer, exerting a sacrificial anticorrosion effect as a single tube, and at the same time, Zn concentration in the molten wax is performed. It is reduced and has excellent corrosion resistance.

The amount of Zn sprayed is preferably 3.0 to 8.0 g / m ² , and particularly preferably 3.0 to 7.0 g / m ² . If an attempt is made to manufacture a product having a Zn sprayed amount less than the above range, stable arc discharge cannot be continued and manufacturing is difficult. If the Zn sprayed amount exceeds the above range, Zn is generated during brazing. However, the amount of Zn remaining on the outer surface increases without diffusing into the deep part of the tube body, so that Zn is concentrated in the fillet during brazing, and the corrosion resistance may be lowered.

The Zn spraying method for forming a Zn sprayed layer by spraying Zn on the outer surface of a tube body made of an aluminum alloy containing Mn is not particularly limited. As the Zn spraying method, a conventional thermal spraying method can be appropriately used. For example, two Zn wires are brought close to each other, a high-voltage current is applied, and an arc is discharged between the Zn wires to melt the tip of the Zn wire and blow off Zn zinc by blowing a high-voltage inert gas. This is a method of adhering molten Zn to the outer surface of the tube by passing the tube body through the tube body. As the wire used for thermal spraying, pure Zn wire is preferably used because it is easy to manufacture. Since the Zn wire is continuously sent as it melts, the arc discharge can be continued, so that a uniform Zn sprayed layer can be formed continuously in the longitudinal direction.

The coating film of the aluminum alloy extruded tube of the present invention is formed on the outer surface of the Zn sprayed layer. That is, in the aluminum alloy extruded tube of the present invention, the coating film is formed on the surface of the Zn sprayed layer opposite to the tube main body side. The coating film contains Al—Si alloy brazing powder, Zn-free fluoride-based flux powder, and binder.

Al-Si alloy brazing material powder is a powdery alloy of Al and Si. The Al—Si alloy brazing material powder is melted only by the Al—Si alloy brazing material powder itself by heating at the time of brazing, and liquid phase wax is generated 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 material powder contains Al, it is difficult for the brazing material to melt the outer surface of the tube during brazing.

The content of Si in the alloy of Al and Si constituting the Al—Si alloy brazing filler metal powder is preferably 5.0 to 20.0% by mass, and particularly preferably 7.0 to 15.0% by mass. When the Al content in the alloy of Al and Si is within the above range, the tube wall thickness is less likely to decrease due to melting of the outer surface of the tube during brazing, and the brazing property is improved.

The coating amount of the Al—Si alloy brazing filler metal powder is preferably 10.0 to 25.0 g / m ² , and particularly preferably 12.0 to 20.0 g / m ² . When the coating amount of the Al—Si alloy brazing material powder is within the above range, the brazing property is improved. 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 liquid phase brazing becomes insufficient and bonding failure is likely to occur, and if it exceeds the above range, the coating thickness becomes thick. It becomes excessively thick, the dimensional change of the core after brazing occurs, and the brazing property tends to be low.

The Zn-free fluoride-based flux powder functions as a flux during brazing and melts during brazing heat to destroy the Al—Si alloy brazing material powder and the oxide film on the outer surface of the tube. Allows immediate progress of brazing. The Zn-free fluoride-based flux powder is a fluoride that is in the form of powder and does not contain Zn. In the present invention, "Zn-free" and "Zn-free" mean that the amount of Zn is less than the lower limit of detection in the analysis by the electron probe microanalyzer.

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

The coating amount of the Zn-free fluoride-based flux powder is preferably 3.0 to 12.0 g / m ² , and particularly preferably 4.0 to 10.0 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 is insufficient, so that the oxide film is not sufficiently destroyed and the brazing property tends to be low. If it exceeds, the thickness of the coating film becomes excessively thick, the dimensional change of the core after brazing occurs, and the brazing property tends to be lowered.

The binder adheres Al—Si alloy brazing powder and Zn-free fluoride-based flux powder to the surface of the tube body. Examples of the binder include an acrylic resin and a urethane resin.

The amount of the binder applied is preferably 1.0 to 13.0 g / m ² . When the amount of the binder applied is within the above range, the Al—Si alloy brazing material powder and the Zn-free fluoride-based flux powder can be satisfactorily adhered 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 is likely to be peeled off, and if it exceeds the above range, the thermal decomposition of the binder becomes insufficient, and the undecomposed binder or the like is formed during brazing. May remain and the brazing property may decrease.

As a method of forming a coating film on the surface of the Zn sprayed layer formed on the surface of the tube body, for example, an Al—Si alloy brazing material powder, a Zn-free fluoride-based flux powder and a binder are mixed with a solvent. Then, a method of forming a coating film by applying the obtained paste to the surface of the Zn spraying layer and then drying and removing the solvent can be mentioned. Before mixing the Al—Si alloy brazing material powder and the Zn-free fluoride-based flux powder with the solvent, the Al—Si alloy brazing material powder and the Zn-free fluoride-based flux powder are mixed in advance. , Al—Si alloy brazing powder and Zn-free fluoride-based flux powder may be mixed, and then the obtained mixed powder may be mixed with a binder 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.

The aluminum alloy extruded tube for a heat exchanger of the present invention is held at 600 ° C. ± 10 ° C. for 3 minutes, and in a heating test for measuring the average crystal grain size after cooling to room temperature, the average crystal grain of the tube body after the heating test is performed. The diameter is 150 μm or more. That is, the aluminum alloy extruded tube for a heat exchanger of the present invention has a crystal structure in which the average crystal grain size of the tube body becomes 150 μm or more by holding at 600 ° C. ± 10 ° C. for 3 minutes and cooling to room temperature. Have. The average crystal grain size of the tube body is 150 μm or more when the aluminum alloy extruded tube for a heat exchanger is held at 600 ° C. ± 10 ° C. for 3 minutes and the average crystal grain size is measured after cooling to room temperature. As a result, so-called erosion in which the liquid phase wax erodes the crystal grain boundaries is less likely to occur during the wax addition heat, the tube wall thickness is less likely to decrease and the tube is less likely to penetrate, and bonding failure occurs due to the decrease in the wax amount. Since it becomes difficult, the waxability becomes good.

In the tube body of the aluminum alloy extrusion tube for a heat exchanger of the present invention having an average crystal grain size of 150 μm or more after the heating test, the average crystal grain size before the brazing heat addition is less likely to cause erosion during the brazing heat addition. Since it is large enough, erosion is unlikely to occur during wax addition heat. Therefore, in the heating test in which the average crystal grain size is measured after holding at 600 ° C. ± 10 ° C. for 3 minutes and cooling to room temperature, the heat of the present invention in which the average crystal grain size of the tube body after the heating test is 150 μm or more. Aluminum alloy extrusion tubes for exchangers are less prone to erosion during brazing heat addition.

In the heating test of the aluminum alloy extrusion tube for a heat exchanger of the present invention, first, the aluminum alloy extrusion tube for a heat exchanger of the present invention is heated to raise the temperature, and in the heating process, the holding temperature is 600 ° C. ± 10 ° C. Heated to This is a test for measuring the particle size. As a method for measuring the average crystal grain size of the tube body, a method of electrolytically polishing the test piece, obtaining a microscope image of each cross section with a polarizing microscope having a magnification of 50 to 100 times, and measuring the equivalent circle diameter is mentioned. Be done. Regarding the heating rate in the heating process of the heating test, the temperature range up to 500 ° C is an average heating rate of 30 ± 10 ° C / min, and the temperature range of 500 ° C or higher is an average of 10 ± 5 ° C / min. The rate of temperature rise.

The tube body having an average crystal grain size of 150 μm or more after the heating test according to the aluminum alloy extrusion tube for a heat exchanger of the present invention has the Mn content in the aluminum alloy ingot to be subjected to hot extrusion as a predetermined content. That is, an aluminum alloy containing 0.20 to 0.90% by mass of Mn, having a Ti content of 0.10% by mass or less, and being composed of the balance Al and unavoidable impurities is subjected to hot extrusion. It is introduced by using it as an ingot, more preferably, by subjecting the aluminum alloy ingot to the above homogenization treatment before subjecting it to hot extrusion, or by setting the ingot temperature at the time of hot extrusion to 480 ° C. or higher. It is obtained by reducing the machining strain.

The aluminum alloy extruded tube for a heat exchanger of the present invention has a higher strength than a tube whose tube body is made of pure aluminum because the tube body is made of an aluminum alloy containing Mn. Further, in the aluminum alloy extruded tube for a heat exchanger of the present invention, since the tube body is made of an aluminum alloy containing Mn, Mn is solidly dissolved in the aluminum matrix, so that the tube body is made of pure aluminum. In comparison, the potential becomes noble in the deep part, and the potential difference from the fin material and the tube surface tends to be large as described later, which is advantageous from the viewpoint of preventing corrosion penetration of the tube body.

In the aluminum alloy extrusion tube for a heat exchanger of the present invention, the coating film contains Al—Si alloy brazing filler metal powder and Zn-free fluoride-based flux powder, preferably Al—Si alloy brazing filler metal powder. A coating amount of 0.0 to 25.0 g / m ² , particularly preferably 12.0 to 20.0 g / m ² , and a Zn-free fluoride-based flux powder of 3.0 to 12.0 g / m ² . In particular, by containing it in a coating amount of 4.0 to 10.0 g / m ² , each powder exerts its respective function and interacts with each other to exert a synergistic effect. Has excellent waxing resistance and corrosion resistance.

In the aluminum alloy extrusion tube for a heat exchanger of the present invention, the Al—Si alloy brazing filler metal powder contained in the coating film is melted only by the Al—Si alloy brazing filler metal powder itself by heating at the time of brazing, and is outside the tube. Since liquid phase brazing is generated on the surface, the tube can be joined to fins and headers, and since the tube wall thickness is not reduced during brazing, the tube can be thinned.

From the above, the aluminum alloy extruded tube for heat exchanger of the present invention does not melt the outer surface at the time of brazing, so that the strength is high even if the wall thickness is thin.

In the aluminum alloy extrusion tube for a heat exchanger of the present invention, the Zn-free fluoride-based flux powder contained in the coating film is an oxide film on the surface of the Al—Si alloy brazed powder and oxidation of the outer surface of the tube during brazing. By breaking the film first, brazing is possible immediately after the Al—Si alloy powder is melted.

In the aluminum alloy extruded tube for heat exchanger of the present invention, during brazing, the sprayed Zn diffuses from the outer surface of the tube body to the deep part to form a sacrificial layer, and the tube itself exhibits a sacrificial anticorrosion effect. At the same time, Zn concentration in the molten brazing is reduced, and it has excellent corrosion resistance.

Further, in the case of a heat exchanger obtained by brazing a tube containing pure Zn powder or the like in a coating film, Zn in the molten brazing is concentrated at the time of fillet formation, and the potential of the fillet becomes the lowest. In this case, when the heat exchanger is exposed to a corrosive environment, the fillet portion is corroded fastest, so that the fillet disappears and the fins fall off from the tube. As a result, the heat exchange performance is greatly deteriorated, and further, the anticorrosion action of the tube by the fins is lost, so that the tube is likely to penetrate at an early stage.

On the other hand, in the aluminum alloy extruded tube for heat exchanger of the present invention, Zn is present on the outer surface of the tube body, but the Zn sprayed on the tube body is deeply formed from the outer surface of the tube body during brazing. Since it diffuses into, the amount of Zn present on the outer surface of the tube body immediately before the wax melts decreases. Therefore, in the aluminum alloy extrusion tube for heat exchanger of the present invention, Zn is not concentrated in the molten wax during fret formation. Therefore, in the heat exchanger obtained by brazing the aluminum alloy extruded tube for the heat exchanger of the present invention, the fillets do not preferentially corrode, so that the fins do not fall off from the tube surface for a long period of time, and the heat exchange performance is improved. Not only can the deterioration of the aluminum be prevented, but also the anticorrosion effect of the tube by the fins can be obtained for a long period of time. Therefore, the aluminum alloy extruded tube for a heat exchanger of the present invention has excellent corrosion resistance.

The heat exchanger of the present invention is a brazing joint of the aluminum alloy extrusion tube for the heat exchanger of the present invention and fins made of an aluminum alloy containing Zn.
The average crystal grain size of the aluminum alloy forming the tube body is 150 μm or more.
It is a heat exchanger characterized by.

In the heat exchanger of the present invention, the aluminum alloy extrusion tube for the heat exchanger of the present invention and fins made of an aluminum alloy containing Zn are joined by brazing.

The fin made of a Zn-containing aluminum alloy according to the heat exchanger of the present invention is formed of the aluminum alloy. The aluminum alloy forming the fin material is not particularly limited as long as it has sufficient strength and corrosion resistance for a heat exchanger, and for example, it has a Mn content of 0.8 to 1.5% by mass and a Zn content. Examples thereof include aluminum alloys having an amount of 0.5 to 2.5% by mass, a Cu content of 0.20% by mass or less, and the balance Al and unavoidable impurities. Further, the fin made of a Zn-containing aluminum alloy according to the heat exchanger of the present invention may be a known fin as long as it has sufficient strength and corrosion resistance for the heat exchanger.

In the heat exchanger of the present invention, fins made of an aluminum alloy containing Zn are brought into contact with the aluminum alloy extrusion tube for the heat exchanger of the present invention, and then other members such as a header are assembled and heated. It is produced by brazing. The heating temperature, heating time, and atmosphere at the time of brazing are not particularly limited, and the brazing method is also not particularly limited. The heating temperature of the brazing is, for example, 590 to 610 ° C., the heating time of the brazing is, for example, 15 minutes to 45 minutes, and the atmosphere of the brazing is, for example, a nitrogen gas atmosphere or argon. Gas atmosphere, etc.

Since the heat exchanger of the present invention is brazed using the aluminum alloy extruded tube for the heat exchanger of the present invention as the tube material, it is joined to the fins without reducing the tube wall thickness at the time of brazing. Is. Therefore, the heat exchanger of the present invention has high strength even if it is thin. Further, since the heat exchanger of the present invention is brazed using the aluminum alloy extruded tube for the heat exchanger of the present invention as the tube material, it is difficult for Zn to concentrate in the molten wax during fillet formation. The fins do not easily come off over a long period of time, and the fins protect them from corrosion, resulting in excellent corrosion resistance.

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

(Reference example and comparative example)
<Making a tube>
The billets having the chemical components shown in Table 1 were heated at 600 ° C. for 10 hours to perform a homogenization treatment, and then the billets having been homogenized were cooled to room temperature. Next, the billet was reheated to 450 ° C. and hot extrusion was performed to prepare a tube body having a flat cross section perpendicular to the extrusion direction and having a plurality of refrigerant channels.
Further, Al—Si alloy brazing powder, Zn-free fluoride-based flux powder and 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 form a coating film of the coating amount shown in Table 2, and the coating film was formed on the aluminum alloy extrusion tube for heat exchanger. Got
Next, the average crystal grain size after the heating test, the brazing property, and the corrosion resistance were evaluated. The results are shown in Table 3.

-Al-Si alloy brazing powder: Si content 12.0% by mass
-Zn-free fluoride-based flux powder: K-Al-F-based flux, Zn was below the lower limit of detection in Zn analysis by electronic microanalyzer analysis.
・ Binder: Acrylic resin

<Making fins>
A plate having a thickness of 0.1 mm made of an aluminum alloy having Mn: 1.2% by mass and Zn: 1.5% by mass was corrugated to prepare fins having a corrugated shape. The fin pitch was 3 mm and the fin height was 7 mm.

<Mini core fabrication and heating test>
As shown in FIG. 1, the fins were laminated so as to be sandwiched between tubes at the top and bottom, and assembled into a predetermined shape. In this state, the tubes and fins are heated in a nitrogen gas atmosphere, and the temperature rise rate is 30 ° C./min on average up to 500 ° C., and 10 ° C./min on average in the temperature range of 500 ° C. or higher. After raising the temperature to 600 ° C. and holding at 600 ° C. for 3 minutes, the temperature was lowered to room temperature and brazing was performed to join the tubes and fins to obtain a mini core simulating a heat exchanger.
The brazing property was evaluated using the obtained mini core. The results are shown in Table 3.
The heat history for producing the mini core corresponds to the heat history of the heating test.

<Evaluation of average crystal grain size and brazing property after heating test>
The cross section of the tube after brazing was observed, etching was performed, and the average crystal grain size was measured. The measurement was carried out by electrolytically polishing the test piece, obtaining a microscope image of each cross section with a polarizing microscope having a magnification of 100 times, and measuring the equivalent circle diameter.
In addition, by visual observation, it was confirmed whether or not the fins were joined, whether or not there was an appearance defect such as discoloration, whether or not the fins were melted, and whether or not there was erosion on the tube surface.

<Evaluation of corrosion resistance>
Each test piece was subjected to the SWAAT test specified in ASTM-G85-Annex A3 for 960 hours. By visually observing the test material after the test was completed, it was determined whether or not the fins were peeled off.

<Evaluation result>
In Reference Example 1, the average crystal grain size after brazing was sufficiently large at 400 μm or more, no brazing problem occurred, no erosion occurred, and the result was acceptable. Moreover, since the wall thickness of the tube after brazing did not change significantly as compared with the wall thickness before brazing, it was confirmed that no significant melting occurred. Further, as a result of the corrosion resistance test, the fins were not peeled off and had good corrosion resistance.
On the other hand, in Comparative Example 1, the average crystal grain size after brazing was sufficiently large, but the flux powder was insufficient, and the Al—Si alloy brazing powder and the oxide film on the outer surface of the tube were not sufficiently destroyed. Therefore, the fillet was not formed and it was rejected.
Similarly, in Comparative Example 2, the average crystal grain size after brazing was sufficiently large, but the Al—Si alloy brazing material powder was insufficient, and sufficient fillets could not be formed, resulting in a failure. ..
In Comparative Example 3, the average crystal grain size after brazing was as small as 120 μm, and erosion occurred around the fillet after brazing. Although the fillet was formed, its size was small and the joint strength of the fins was insufficient, so there was a concern that the fins would peel off at an early stage during actual use, so it was rejected. In addition, the result of the corrosion resistance test showed that the fins did not peel off and had good corrosion resistance.
The corrosion resistance test was carried out only in Reference Example 1 and Comparative Example 3 in which the fin and the tube were joined.

(Examples 1 to 4)
<Making a tube>
No. in Table 1 The billet having the chemical composition shown in 1 was heated at 600 ° C. for 10 hours to perform a homogenization treatment, and then the billet having been homogenized was cooled to room temperature. The billet was then reheated to 450 ° C. for hot extrusion. Next, immediately after the hot extrusion processing, Zn spraying was applied to the outer surface of the tube with the aim of spraying amount shown in Table 4, and the cross section perpendicular to the extrusion direction showed a flat shape, and a plurality of refrigerant flow paths were formed. In preparation for this, a Zn sprayed layer forming tube main body having Zn sprayed on the surface was produced.
Further, Al—Si alloy brazing powder, Zn-free fluoride-based flux powder and binder were mixed with a solvent to prepare a paste for forming a coating film. Next, the obtained paste was applied onto the Zn sprayed layer of the Zn sprayed layer forming tube body using a roll coater, and No. 1 in Table 2 was applied. A coating film having a coating amount shown in I was formed, and an aluminum alloy extruded tube for a heat exchanger on which the coating film was formed was obtained.
Next, fins were produced in the same manner as in the above reference example.
Next, as shown in FIG. 1, the fins were laminated so as to be sandwiched between tubes, and assembled into a predetermined shape. In this state, the tubes and fins are heated in a nitrogen gas atmosphere, and the temperature rise rate is 30 ° C./min on average up to 500 ° C., and 10 ° C./min on average in the temperature range of 500 ° C. or higher. After raising the temperature to 600 ° C. and holding at 600 ° C. for 3 minutes, the temperature was lowered to room temperature and brazing was performed to join the tubes and fins to obtain a mini core simulating a heat exchanger.
The brazing property was evaluated using the obtained mini core. The results are shown in Table 4.
The heat history for producing the mini core corresponds to the heat history of the heating test.

In Examples 1 and 2 of the present invention, Zn spraying was possible without any problem, the average crystal grain size after brazing was sufficiently large at 400 μm or more, no brazing problem occurred, no erosion occurred, and the results were acceptable. .. Moreover, since the wall thickness of the tube after brazing did not change significantly as compared with the wall thickness before brazing, it was confirmed that no significant melting occurred. Further, as a result of the corrosion resistance test, the fins were not peeled off and had good corrosion resistance.
On the other hand, in Comparative Example 1, since the target amount of Zn spraying was small, stable spraying was difficult, and a sample could not be prepared, resulting in a failure.
In Comparative Example 2, Zn spraying was possible without any problem, the average crystal grain size after brazing was sufficiently large at 400 μm or more, no brazing problem occurred, no erosion occurred, and the result was acceptable. However, after the corrosion resistance test, fin peeling occurred and the durability was unacceptable.

Claims

An aluminum alloy extruded tube used in automobile heat exchangers.
A tube body made of an aluminum alloy containing Mn,
The Zn sprayed layer formed on the outer surface of the tube body and
The coating film formed on the outer surface of the Zn sprayed layer and
Have,
The coating film contains an Al—Si alloy brazing powder, a Zn-free fluoride-based flux powder, and a binder.
In a heating test in which the average crystal grain size is measured after holding at 600 ° C. ± 10 ° C. for 3 minutes and cooling to room temperature, the average crystal grain size of the tube body after the heating test is 150 μm or more. Aluminum alloy extrusion tube for heat exchanger.
The aluminum alloy containing Mn is an aluminum alloy containing 0.20 to 0.90% by mass of Mn, a Ti content of 0.10% by mass or less, and the balance Al and unavoidable impurities. The aluminum alloy extrusion tube for a heat exchanger according to claim 1.
The aluminum alloy extruded tube for a heat exchanger according to claim 1 or 2, wherein the amount of Zn sprayed from the tube body is 3.0 to 8.0 g / m 2 .
The coating amount of the Al—Si alloy brazing filler metal powder is 10.0 to 25.0 g / m 2 , and the coating amount of the Zn-free fluoride-based flux powder is 3.0 to 12.0 g / m 2 . The aluminum alloy extrusion tube for a heat exchanger according to any one of claims 1 to 3, wherein the amount of the binder applied is 1.0 to 13.0 g / m 2 .
A brazed joint of the aluminum alloy extrusion tube for a heat exchanger according to any one of claims 1 to 4 and fins made of an aluminum alloy containing Zn.
The average crystal grain size of the aluminum alloy forming the tube body is 150 μm or more.
A heat exchanger featuring.