JP2009046705A - Extruded flat perforated pipe for heat exchanger having excellent corrosion resistance, and heat exchanger - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an extruded flat perforated pipe for a heat exchanger which has excellent corrosion resistance and sufficient strength, and can be made thin in thickness, and to provide a heat exchanger. <P>SOLUTION: The extruded flat perforated pipe for the heat exchanger is composed of an aluminum alloy having a composition containing, by mass, 0.01 to 0.30% Si, 0.01 to 0.30% Fe, 0.05 to 0.40% Cu and 0.05 to 0.30% Mn, further comprising 0.05 to 0.30% Ti, or comprising 0.05 to 0.25% Zr, or comprising 0.05 to 0.25% Zr and 0.05 to 0.25% Ti, and in which the total of Zr and Ti is ≤0.3%, and the balance Al with inevitable impurities. As for grains with a grain area of ≥1.0 μm<SP>2</SP>dispersed into a matrix, the occupancy area ratio of an AlFeSi stable phase is 0.1 to <0.5%. The outer surface is coated with a composition for brazing obtained by mixing Zn-containing flux, Si powder and a binder. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an extruded flat multi-hole tube for a heat exchanger excellent in corrosion resistance and a heat exchanger that can be suitably used for an automotive heat exchanger such as a car air conditioner.

  Conventionally, tubes and flat multi-hole tubes made by extruding pure aluminum or aluminum alloys have been used in automotive heat exchangers such as condensers and evaporators of car air conditioners.

  In general, as shown in FIG. 2, the heat exchanger is made of a pair of left and right tubes called header pipes 5, and an aluminum alloy provided between the header pipes 5 so as to be spaced apart from each other in parallel. It is composed of a large number of tubes 1 and fins 6 provided between the tubes 1 and 1. Then, the internal space of each tube 1 and the internal space of the header pipe 5 are communicated, the medium is circulated between the internal space of the header pipe 5 and the internal space of each tube 1, and heat can be exchanged efficiently through the fins 6. It is like that.

  Each tube 1 constituting this heat exchanger has a flux containing brazing filler metal powder on the surface of an Al alloy extruded tube 3 having a flat cross section having a plurality of refrigerant passage holes 4 as shown in the perspective view of FIG. It is known that it is manufactured using an extruded flat multi-hole tube 11 for heat exchanger in which a flux layer (coating layer) 2 is formed by applying It is also known that powders, Al—Si based alloy powders, or Al—Si—Zn based alloy powders are used.

  In order to fabricate a heat exchanger using the extruded flat multi-hole tube 11 for heat exchanger, the extruded flat multi-hole tube 11 for heat exchanger is installed at right angles to the header pipes 5 provided at intervals in parallel to each other. Then, the end of each extruded flat multi-hole tube 11 for heat exchanger is inserted into an opening (not shown) provided on the side surface of the header pipe 5, and a corrugated shape is formed between the extruded flat multi-hole tubes 11 for the heat exchanger. When the fins 6 are arranged and assembled, and the resulting assembly is charged into a heating furnace and heated, the header pipe 5 and the tube 1 are brazed and fixed by the brazing material of the extruded flat multi-hole tube 11 for heat exchangers. A heat exchanger in which corrugated fins 6 are brazed and fixed between the tubes 1 and 1 is obtained.

  Generally, the thickness of the tube 1 constituting the heat exchanger is thinner than that of the header pipe 5 and the like from the viewpoint of efficiently performing heat exchange. For this reason, when the tube 1 and the header pipe 5 corrode at substantially the same speed, there is a possibility that the tube 1 has a hole first and the medium leaks from there. Therefore, in the heat exchanger, the anticorrosion measure of the tube 1 is an important issue.

  In addition, the extruded flat multi-hole tube 11 for heat exchanger is required to satisfy predetermined conditions with respect to assembling property, brazing property, heat exchanger strength / corrosion resistance, and the like. Furthermore, such an extruded flat multi-hole tube 11 for a heat exchanger is generally formed into a cross-sectional shape having a width of 5 to 50 mm and a height of 1 to 5 mm, and satisfies a predetermined dimensional accuracy and surface roughness. Is required.

  Examples of the material that can realize the extruded flat multi-hole tube 11 for heat exchanger that satisfies such conditions include pure aluminum with good extrudability and aluminum alloys containing a small amount of Cu, and are widely used. (For example, patent document 1).

The addition of Cu increases the strength of the product, while reducing the deformation resistance at high temperatures by controlling the addition amount to an appropriate level, thereby contributing to the improvement of extrudability.
On the other hand, when the extruded flat multi-hole tube 11 for heat exchangers is used in a corrosive environment, local corrosion such as pitting corrosion may occur, but it is relatively early especially when the recent reduction in weight and thickness is achieved. There was a possibility that a through-hole was formed in the case and could not be used.
Regarding this corrosion resistance problem, a method is used in which Zn is coated on the tube surface and diffused to the inner surface of the tube by heating at the time of brazing of the product. The so-called sacrificial anode effect was used to minimize the progression to local corrosion. As a method for imparting the sacrificial anode effect, there is a method of providing Zn on the tube surface by a method such as Zn spraying or Zn flux coating.
For example, Patent Document 2 describes a heat exchanger tube in which a flux layer containing Si powder and Zn-containing flux is provided on the surface.
JP 2001-26832 A JP 2004-330233 A

  However, it is difficult for Zn spraying to control the amount of spraying accurately, and deterioration in corrosion resistance due to large variations in the amount of spraying is inevitable. In addition, although Zn flux coating generally adopts a roll coating method, it is difficult to stably and uniformly apply this, and corrosion resistance deterioration due to non-uniform Zn concentration is inevitable.

  In addition, when the tube thickness is less than 0.3 mm, the material strength significantly decreases even with local corrosion that could be overlooked with the conventional wall thickness, and the internal pressure of the heat exchanger refrigerant causes the deformation due to this local corrosion to proceed easily. There is a tendency to break. Therefore, further improvement in corrosion resistance has been demanded.

  Currently, alloys that are widely used include alloys in which a small amount of Cu is added to pure aluminum. However, Cu that had been dissolved until then changes due to aging or heating, and the corrosion resistance is significantly deteriorated due to intergranular corrosion. Cases leading to (early through-hole generation) have been a problem.

  Accordingly, the alloy additive elements and addition amounts were reviewed, and tube materials with better corrosion resistance than the current one were studied. As described above, reduction of the amount of Cu added, which causes deterioration of corrosion resistance, was examined. However, when the amount of Cu added is reduced, it directly leads to a decrease in mechanical properties, so that it is essential to supplement strength with multiple elements.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an extruded tube having excellent corrosion resistance, sufficient strength, and capable of being thinned, and an extruded flat multi-hole tube for a heat exchanger. .
Furthermore, an object of the present invention is to provide a heat exchanger that is excellent in corrosion resistance and has sufficient strength, using the extruded tube or the multi-hole tube for heat exchanger.

  In order to solve the above-mentioned problems, the present inventor has intensively studied the above-described strength-complementing element. And Ti and Zr can not only complement the mechanical properties, but also form Al-Ti and Al-Zr compounds, respectively, to exhibit the mold cleaning effect during extrusion, and to flatten the tube structure It has been found that there is an effect of delaying the generation of through holes due to pitting corrosion. In addition, the inventors have invented a means for further improving the corrosion resistance improvement effect of Ti by controlling the amount of Cu solid solution. And in order to provide further corrosion resistance, the method of coat | covering Zn was devised, and it came to complete this invention. That is, the present invention has the following configuration.

(1) The extruded flat multi-hole tube for heat exchanger of the present invention is Si: 0.01 to 0.30%, Fe: 0.01 to 0.30%, Cu: 0.05 to 0.40 in mass%. %, Mn: 0.05 to 0.30%, Ti: 0.05 to 0.25%, or Zr: 0.05 to 0.25%, or Zr: 0.05 -0.25% and Ti: 0.05-0.25%, the total of Zr and Ti is 0.3% or less, the balance is made of an aluminum alloy consisting of Al and inevitable impurities, and the matrix Among the particles having a particle area of 1.0 μm ² or more dispersed therein, the area ratio occupied by the AlFeSi stable phase is 0.1% or more and less than 0.5%, Zn-containing flux, Si powder, binder, And a brazing composition mixed with

(2) The heat exchanger extrusion flat multi-hole tubes of the present invention, the Zn flux layer can be made of _{ZnF 2,} ZnCl 2, any one of KZnF ₃ or 2 or more kinds.

(3) Moreover, the heat exchanger of this invention was equipped with the extrusion flat multi-hole pipe for heat exchangers as described in either (1) or (2).

According to the extruded tube and the multi-hole tube for heat exchanger of the present invention, Si: 0.01 to 0.30%, Fe: 0.01 to 0.30%, Cu: 0.05 to 0.40 in mass%. %, Mn: 0.05 to 0.30%, Ti: 0.05 to 0.25%, or Zr: 0.05 to 0.25%, or Zr: 0.05 -0.25% and Ti: 0.05-0.25%, the total of Zr and Ti is 0.3% or less, the balance is made of an aluminum alloy consisting of Al and inevitable impurities, and the matrix Among the particles having a particle area of 1.0 μm ² or more dispersed therein, the area ratio occupied by the AlFeSi stable phase is 0.1% or more and less than 0.5%, Zn-containing flux, Si powder, binder, The brazing composition mixed with In addition to reducing the amount of Cu that causes corrosion resistance deterioration, and containing Ti and Zr as strength supplemental elements to prevent deterioration of mechanical properties due to Cu reduction, corrosion resistance and extrudability are not deteriorated. Complements mechanical properties. Furthermore, since an Al—Ti-based compound and an Al—Zr-based compound are formed, a mold cleaning effect during extrusion is exhibited. Moreover, it has the effect of promoting flattening of the tube structure and suppressing the generation of through holes due to pitting corrosion.

  Next, by reducing the amount of Cu solid solution as much as possible, the intergranular corrosion due to subsequent changes with time and heating is prevented, and the effect of improving the corrosion resistance by Ti is further effective. Reducing the amount of Cu solid solution means that Cu is precipitated, and the generation of an AlFeSi stable phase is used as a means for precipitating this Cu. Since Cu behaves similarly to Si, building an AlFeSi stable phase is common to building an AlFeSi (Cu) stable phase. Thus, corrosion resistance can be improved by precipitating Cu and reducing the amount of solid solution in the alloy.

  Also, by applying a brazing composition in which Zn-containing flux, Si powder and binder are mixed, the brazing composition forms a molten brazing during brazing and promotes uniform Zn diffusion and distribution. Eliminates the uniformity that occurs during application. Further, when Zn diffuses into the Al substrate, the sacrificial anode effect is exhibited. On the other hand, Si is dissolved in the matrix by diffusion, and the sacrificial anode effect due to Zn is hindered. Therefore, in the present invention, it is anticipated that Si will diffuse in the stage before brazing, and by generating nuclei that form an AlFeSi phase, at the time of brazing, the nuclei and the diffused Si are combined to form an AlFeSi phase. This suppresses the solid solution of Si in the matrix, makes the sacrificial anode effect due to Zn more effective, and improves the corrosion resistance and brazing function.

  Further, the heat exchanger of the present invention includes the above-described extruded flat multi-hole tube for heat exchanger, so that the corrosion resistance can be improved by the combination of the alloy and the sacrificial anode layer.

Hereinafter, the extruded flat multi-hole tube for a heat exchanger and the heat exchanger excellent in corrosion resistance according to the present invention will be described in detail with examples.
The extruded flat multi-hole tube for heat exchanger having excellent corrosion resistance according to this embodiment is Si: 0.01 to 0.30%, Fe: 0.01 to 0.30%, Cu: 0.05 to 0% by mass. .40%, Mn: 0.05 to 0.30%, Ti: 0.05 to 0.25%, or Zr: 0.05 to 0.25%, or Zr: 0 0.05 to 0.25% and Ti: 0.05 to 0.25%, and the total of Zr and Ti is 0.3% or less, and the balance is made of an aluminum alloy composed of Al and inevitable impurities. In the particles having a particle area of 1.0 μm ² or more dispersed in the matrix, the area ratio occupied by the AlFeSi stable phase is 0.1% or more and less than 0.5%, Zn-containing flux, Si powder, A brazing composition mixed with a binder was applied to the outer surface And features.

[Component composition of aluminum alloy]
The component composition of the aluminum alloy used for the extruded flat multi-hole pipe for heat exchangers excellent in corrosion resistance according to the present invention will be described. Unless otherwise specified, the content of each element described below is mass%.

"Si" 0.01-0.30%
In the extruded flat multi-hole tube for a heat exchanger constituting the present invention, an AlFeSi stable phase can be generated and Cu can be precipitated by containing Si. Since Cu behaves similarly to Si, building an AlFeSi stable phase is common to building an AlFeSi (Cu) stable phase. And the intergranular corrosion by subsequent temporal change and a heating is prevented, and the corrosion-resistance improvement effect by Ti is made still more effective.
If the Si content is less than 0.01%, the effect of generating an AlFeSi stable phase in the matrix cannot be sufficiently obtained, and Cu precipitation becomes insufficient, so that the corrosion resistance cannot be sufficiently improved. There is a case. Moreover, since intensity | strength will become inadequate that content of Si is less than 0.01%, it is unpreferable. On the other hand, when the Si content exceeds 0.30%, a low melting point compound is likely to be formed, and pickup due to the heat of extrusion processing at high speed extrusion is likely to occur.

"Fe" 0.01-0.30%
In the extruded flat multi-hole tube for a heat exchanger constituting the present invention, an AlFeSi stable phase can be generated in the matrix by containing Fe in the aluminum alloy. Moreover, while Fe improves the strength of the aluminum alloy by dispersion strengthening, it tends to generate coarse crystallized products, which may increase the corrosion rate of the alloy and reduce the corrosion resistance. Moreover, since the produced crystallized substance becomes the nucleus of recrystallization by containing Fe, the recrystallization at the time of brazing becomes fine, and brazing erosion resistance may fall. For this reason, as for content of Fe, it is desirable that it is 0.01-0.30 by mass%. By setting the Fe content to 0.01 to 0.30, the strength can be improved without deteriorating the corrosion resistance and the brazing property.

"Cu" 0.05-0.40%
In the extruded flat multi-hole tube for heat exchangers constituting the present invention, Cu has the effect of improving the strength, corrosion resistance, and extrudability of the extruded flat multi-hole tube for heat exchangers.
If the Cu content is less than 0.05%, the strength and corrosion resistance of the extruded flat multi-hole tube for heat exchangers are insufficient, which is not preferable. Further, if the Cu content exceeds 0.40%, a low melting point compound is likely to be formed, the deformation resistance at the time of extrusion rises, and there is a possibility that high speed extrusion becomes difficult. Since picking up due to the generated aluminum flaws is likely to occur, it is not preferable. On the other hand, when the Cu content exceeds 0.40%, a low-melting-point compound is likely to be formed, and pickup due to aluminum soot generated by the heat of extrusion processing during high-speed extrusion tends to occur.

"Mn" 0.05-0.30%
In the extruded flat multi-hole tube for heat exchangers constituting the present invention, Mn has an effect of improving the strength and corrosion resistance of the extruded flat multi-hole tube for heat exchangers.
If the Mn content is less than 0.05%, the strength and corrosion resistance of the extruded flat multi-hole tube for a heat exchanger are insufficient, which is not preferable. On the other hand, if the Mn content exceeds 0.30%, deformation resistance at the time of extrusion increases, which may cause difficulty in high-speed extrusion. On the other hand, if the Mn content exceeds 0.30%, pickup tends to occur during high-speed extrusion.

"Zr" 0.05-0.25%
In the aluminum alloy constituting the present invention, Zr improves the strength of the alloy and improves the extrudability by the cleaning effect on the mold, and at the time of high-speed extrusion of the contact portion between the mold and the alloy of the extrusion apparatus. It has the effect of improving lubricity and suppressing the occurrence of pick-up and improving the wear of the mold.
If the Zr content is less than 0.05%, the strength of the alloy becomes insufficient. Further, when the Zr content is less than 0.05%, there is a possibility that a sufficient cleaning effect on the mold cannot be obtained, and that the occurrence of pickup during high-speed extrusion cannot be sufficiently suppressed. On the other hand, if the content of Zr exceeds 0.25%, it is not preferable because castability is deteriorated and cracks are easily generated. Furthermore, if the content of Zr exceeds 0.25%, a coarse Zr compound is likely to be generated, the components in the aluminum alloy become non-uniform, and the quality of the material is impaired.

"Ti" 0.05-0.25%
In the aluminum alloy constituting the present invention, Ti improves the strength and durability of the alloy, improves the lubricity at the time of high-speed extrusion of the contact portion between the mold of the extrusion device and the alloy, and suppresses the occurrence of pickup. Is.
If the Ti content is less than 0.05%, the effect of improving the strength and durability of the alloy may not be obtained sufficiently, which is not preferable. Further, if the Ti content is less than 0.05%, the effect of improving the lubricity during high-speed extrusion cannot be sufficiently obtained, and the effect of suppressing the occurrence of pickup during high-speed extrusion cannot be improved. There is a fear. On the other hand, if the Ti content exceeds 0.25%, deformation resistance at the time of extrusion is increased, which may cause difficulty in high-speed extrusion. Further, if the Ti content exceeds 0.25%, a coarse Ti compound is likely to be generated, and the quality of the material is impaired.

The aluminum alloy constituting the present invention has a mass% in which Zr is 0.05 to 0.25%, Ti is 0.05 to 0.25%, and the total content of Zr and Ti is 0. When it is in the range of not more than 3%, both Zr and Ti can be contained.
If the content of Zr and Ti is less than 0.05%, the strength of the alloy becomes insufficient. In addition, there is a possibility that the cleaning effect on the mold cannot be sufficiently obtained, and there is a possibility that the occurrence of pickup during high-speed extrusion cannot be sufficiently suppressed. On the other hand, if the total content of Zr and Ti exceeds 0.3%, it is not preferable because castability is lowered and cracks are easily generated. Furthermore, coarse Zr compounds and Ti compounds are likely to be generated, the components in the aluminum alloy become non-uniform, and the quality of the material is impaired.

[AlFeSi stable phase]
In the extruded flat multi-hole tube for heat exchanger of the present invention, the area ratio occupied by the AlFeSi stable phase is 0.1% or more and less than 0.5% among particles having a particle area of 1.0 μm ² or more dispersed in the matrix. It is preferable that In such an aluminum alloy, Si in the matrix is precipitated as an AlFeSi (Cu) stable phase together with the AlFeSi stable phase. Here, particles having a particle area of less than 1.0 μm ² dispersed in the matrix have a small volume of particles, so that Si solidification can be easily performed by heating (preheating, processing heat, frictional heat) during extrusion. Since dissolution occurs and Si cannot be effectively precipitated as an AlFeSi stable phase, it is not preferable. If the area ratio is less than 0.1%, the effect of precipitating Si as an AlFeSi stable phase and the effect of precipitating Cu as an AlFeSi (Cu) stable phase cannot be sufficiently obtained, which is not preferable. Further, even if the area ratio is 0.5% or more, the effect of precipitating Si or Cu is saturated, so that the corrosion resistance is not improved.

The AlFeSi phase includes not only an AlFeSi stable phase but also an AlFeSi metastable phase. Even if the particle area of the AlFeSi metastable phase is 1.0 μm ² or more, since the solid solution of Si is easily generated by heating during extrusion, the Si concentration in the matrix is improved. It is disadvantageous for the purpose.
Here, the “AlFeSi stable phase” is a ratio of Fe and Si atom concentrations (= Fe atom concentration / Si atom concentration) measured by EDX (Energy Dispersive X-ray Spectroscopy). Means less than .5.
The “AlFeSi metastable phase” means that the ratio of Fe and Si atom concentrations (= Fe atom concentration / Si atom concentration) measured by EDX is 3.5 to 7.0.

When Cu is dissolved in the matrix, various problems occur. First, it precipitates with Si by heating or aging, and forms a Cu-Si deficient phase in the vicinity of the grain boundary to cause grain boundary corrosion. In addition, the potential of the matrix becomes noble, and there are problems that the potential difference cannot be obtained with the AlZr and AlTi particles and that the sacrificial anode effect due to Zn flux is hindered. For these reasons, early through holes are generated in the extruded tube, and the corrosion resistance is deteriorated.
Therefore, reduction of the solid solution amount of Cu was studied, and a method of depositing AlFeSi, that is, AlFeSi (Cu) was adopted as a means for depositing Cu. Of the particles having a particle area of 1.0 μm ² or more dispersed in the matrix, if the area ratio occupied by the AlFeSi stable phase is less than 0.1%, the effect cannot be obtained, which is not preferable. Moreover, it saturates that the area ratio which an AlFeSi stable phase occupies is 0.5% or more. Therefore, it is preferable to use an aluminum alloy in which the area ratio occupied by the AlFeSi stable phase is 0.1% or more and less than 0.5%.

  By this method, Cu precipitation due to heating or aging can be prevented, and intergranular corrosion can be prevented. Moreover, since a potential difference from AlZr and AlTi particles is obtained and layer corrosion is promoted, pitting corrosion can be prevented. Moreover, the sacrificial anode effect by Zn Flux also increases. Therefore, the corrosion resistance in the extruded tube can be improved.

  Then, the manufacturing method of the aluminum alloy which comprises this invention is demonstrated. However, this is an example, and the present invention is not limited to the following manufacturing method.

[Production method of aluminum alloy]
In the present embodiment, in the step of homogenizing the aluminum alloy, the first heat treatment, the cooling step, and the second heat treatment are sequentially performed.
"First heat treatment"
In the first heat treatment, the aluminum alloy is held at a temperature in the range of 560 ° C. to 620 ° C., more preferably in the range of more than 590 ° C. to 610 ° C. for 1 hour to 18 hours, more preferably 3 hours to 10 hours. To do.
By performing the first heat treatment, low melting point elements such as Cu and Si contained as an inevitable impurity can be uniformly distributed, and the element that generates the pickup during high speed extrusion can be dissolved to suppress the generation of the pickup. . Further, Zr that is difficult to uniformly diffuse in the aluminum alloy can be uniformly diffused in the aluminum alloy.

  When the processing temperature of the first heat treatment is lower than the above range or when the processing time is shorter than the above range, the distribution of elements such as Si, Cu, Zr, etc. becomes non-uniform, or pickup is generated during high speed extrusion There is a possibility that the solid solution of the elements becomes insufficient and the occurrence of pickup during high-speed extrusion cannot be sufficiently suppressed. In addition, when the processing temperature of the first heat treatment is higher than the above range or when the processing time is longer than the above range, a part of the aluminum alloy may be dissolved, and the cost of performing the first heat treatment is high. It becomes large and disadvantageous economically.

"Cooling process"
The cooling step is a step in which the aluminum alloy that has become high temperature by the first heat treatment is brought to room temperature after the first heat treatment and before the second heat treatment.
The Zr compound deposited in the aluminum alloy improves the lubricity at the time of high-speed extrusion of the contact part between the mold of the extrusion device and the extruded alloy for the heat exchanger, and suppresses the occurrence of pick-up and also wears the mold. To improve. The size of the precipitate (site) made of the Zr compound is larger as the temperature in the homogenization treatment is higher, and is smaller as the temperature is lower. The number of the precipitate made of the Zr compound is higher in the temperature in the homogenization treatment. The lower the temperature, the higher the temperature. Therefore, by forming a large number of small-sized precipitates serving as nuclei of the precipitates made of the Zr compound in the cooling step, Zr around the small precipitates formed in the cooling step in the second heat treatment. The precipitation of the compound can be promoted, and a large number of large precipitates can be formed.

  In the cooling step, the aluminum alloy after the first heat treatment is preferably cooled at a cooling rate of 20 ° C./min to 100 ° C./min, more preferably 40 ° C./min to 60 ° C./min. Even if the cooling rate is less than 20 ° C./min, the effect of forming the nuclei of precipitates composed of Zr compounds by performing the cooling step is not changed, and the time required for the cooling step is not preferable. On the other hand, if the cooling rate exceeds 100 ° C./min, there is a possibility that the nucleus of the precipitate made of the Zr compound is not sufficiently formed even if the cooling step is performed.

"Second heat treatment"
In the second heat treatment, the aluminum alloy after the first heat treatment is subjected to a temperature in the range of 450 ° C. to 520 ° C., more preferably in the range of 480 ° C. to 510 ° C. for more than 2 hours to 18 hours, more preferably 3 hours to 10 hours. Hold for hours.
By performing the second heat treatment, Si, Cu, Mn, and Zr once dissolved by the first heat treatment are combined with the precipitates (sites) formed in the cooling step, so that the mold for the extrusion apparatus and the heat exchanger are used. Lubricity at the time of high-speed extrusion of the contact portion with the extruded alloy can be improved, generation of pick-up can be suppressed, and wear of the mold can be improved.

  When the treatment temperature of the second heat treatment is lower than the above range or the treatment time is shorter than the above range, there is a possibility that the precipitates of the AlFeSi stable phase and the AlFeSi (Cu) stable phase cannot be sufficiently precipitated, There is a possibility that precipitates cannot be sufficiently diffused in the aluminum alloy. Further, when the treatment temperature of the second heat treatment is higher than the above range, the diffusion of elements in the aluminum alloy becomes active, and the elements in the aluminum alloy diffuse to precipitate AlFeSi stable phase and AlFeSi (Cu) stable phase. Even if the treatment time is longer than the above range, the effect obtained is not changed, and it is economically disadvantageous.

  In addition, it does not specifically limit about the heating method in the said homogenization process, the structure of a heating furnace, etc. Moreover, the extruded alloy for heat exchangers is obtained by extruding the aluminum alloy after the step of homogenizing. In the extrusion here, the extrusion shape is not particularly limited, and the extrusion shape is selected according to the shape of the heat exchanger and the like. Further, the extrusion method (method) is not particularly limited, and a conventional method can be appropriately employed according to the extrusion shape and the like.

Such an extruded alloy for a heat exchanger is used as a material for a heat exchanger, and is used, for example, as an extruded flat multi-hole tube for a heat exchanger for circulating a heat medium. Moreover, although the use place of a heat exchanger is not specifically limited, It is suitable for the heat exchanger for motor vehicles. Further, as a heat exchanger for automobiles, specifically, it can be suitably used for applications such as condensers, evaporators and intercoolers.
Moreover, when using such an extruded flat multi-hole tube for a heat exchanger as a component for a heat exchanger, it is assembled with other members (for example, fins and header pipes) and usually joined by brazing. In the present invention, the conditions such as the atmosphere, the heating temperature, and the time for brazing are not particularly limited, and the brazing method is not particularly limited.

  Such an extruded flat multi-hole tube for a heat exchanger is a good one having no pickup on the surface even when manufactured by high-speed extrusion. In addition, when such an extruded flat multi-hole tube for heat exchanger has high strength, and the extruded flat multi-hole tube for heat exchanger is thinned and reduced in cross-sectional area by high-speed extrusion, Even so, the dimensional accuracy of the extruded shape is sufficiently high.

  In the above-described embodiment, the first heat treatment, the cooling step, and the second heat treatment are sequentially performed in the step of homogenizing the aluminum alloy. However, only the first heat treatment and the second heat treatment may be performed. Even in this case, it is possible to manufacture a multi-hole tube having sufficient strength and corrosion resistance and having no pickup on the surface when the multi-hole tube is manufactured by high speed extrusion. In addition, when the cooling process is not performed, it is not necessary to reheat from normal temperature to a predetermined temperature for the second heat treatment, so that energy required for manufacturing can be reduced as compared with the case where the cooling process is performed. Further, when the cooling process is not performed, the manufacturing process can be reduced as compared with the case where the cooling process is performed, so that the manufacturing efficiency can be improved.

In the above-described embodiment, the cooling step is performed in the step of homogenizing the aluminum alloy. However, the following intermediate step may be performed instead of the cooling step.
"Intermediate process"
In the intermediate step, after the first heat treatment and before the second heat treatment, the temperature of the aluminum alloy that has been increased to a high temperature of 560 ° C. or higher by the first heat treatment is 380 ° C. to 440 ° C., more preferably 400 ° C. to 420 ° C. And holding for 10 minutes to 4 hours.
By performing an intermediate step performed at a lower temperature than the first heat treatment and the second heat treatment, a large number of precipitates having a small size as a nucleus of the precipitate made of the Zr compound can be formed. , The precipitation of the Zr compound with the small precipitate formed in the intermediate step as the axis can be promoted, and a large number of large precipitates can be formed.
In addition, even if the holding time exceeding 4 hours of the said range is provided, the effect obtained will not change, but rather it becomes economically disadvantageous.

[Brazing composition]
A brazing composition in which a Zn-containing flux, Si powder, and a binder are mixed is applied to the outer surface of the extruded alloy material thus obtained.
The Zn-containing flux preferably contains at least one Zn compound such as ZnF ₂ , ZnCl ₂ , KZnF ₃ , for example.
The coating amount of the Zn-containing flux is preferably in the range of 5 to ²⁰ g / m2. When the coating amount is less than 5 g / m ² , the formation of the Zn diffusion layer is insufficient and the anticorrosion effect cannot be sufficiently obtained, and when the coating amount exceeds 20 g / m ² , it is not preferable. Since excess Zn concentrates on the fillet portion, which is a joint portion with the component, and the corrosion rate increases at the joint portion, it is not preferable.
Further, in addition to the Zn-containing flux, a Zn-free flux can be contained. For example, fluorides such as LiF, KF, CaF ₂ , AlF ₃ , and SiF _4, and KAlF ₄ and KAlF that are complex compounds of the fluorides. ₃ etc. are mentioned.

The application amount of Si powder is preferably in the range of 1 to 5 g / m ² . If the coating amount is less than 1 g / m ² , the amount of brazing material is insufficient and sufficient brazing strength cannot be obtained, and furthermore, the diffusion of Zn becomes insufficient. On the other hand, if the coating amount exceeds 5 g / m ² , the Si concentration on the surface of the extruded flat multi-hole pipe for heat exchanger becomes high and the corrosion rate is increased, which is not preferable.
A slurry-like brazing material composition was prepared using the above-described Si powder and Zn-containing flux using an acrylic binder and an alcohol solvent.

  By applying a brazing composition in which a Zn-containing flux, Si powder, and a binder are mixed, the brazing composition forms a molten brazing during brazing and promotes uniform Zn diffusion and distribution. Eliminates uniformity caused by occasion Further, when Zn diffuses into the Al substrate, the sacrificial anode effect is exhibited. On the other hand, Si is dissolved in the matrix by diffusion, and the sacrificial anode effect due to Zn is hindered. Therefore, in the present invention, it is anticipated that Si will diffuse in the stage before brazing, and by generating nuclei that form an AlFeSi phase, at the time of brazing, the nuclei and the diffused Si are combined to form an AlFeSi phase. This suppresses the solid solution of Si in the matrix, makes the sacrificial anode effect due to Zn more effective, and improves the corrosion resistance and brazing function.

[Heat exchanger]
A heat exchanger can be constituted by brazing a header pipe or fin for heat exchanger to the extruded flat multi-hole pipe for heat exchanger.
That is, this heat exchanger is configured by joining the extruded flat multi-hole pipe for heat exchanger according to the present invention, the header pipe for heat exchanger, and the fins. That is, similar to the heat exchanger described in the related art, a pair of left and right tubes called a heat exchanger header pipe and the heat exchanger header pipe are provided in parallel with a space therebetween. It is comprised with the several tube and the fin provided between tubes. The internal space of each tube communicates with the internal space of the header pipe for heat exchanger, and the medium is circulated between the internal space of the header pipe for heat exchanger and the internal space of each tube so that heat can be exchanged efficiently through the fins. It has become.

"Example 1 to Example 27, Comparative Example 1 to Comparative Example 10"
Examples of the present invention and comparative examples will be described below.
Billets formed by casting aluminum alloys containing the components shown in Table 1 were produced. The billet was homogenized as shown in Table 2. And the extruded flat multi-hole pipe 11 for heat exchangers of the cross-sectional shape which has the some hole 4 for medium passages shown in FIG. 1 was obtained by extruding the billet after a homogenization process on the conditions shown below.

    The extruded flat multi-hole tube 11 for heat exchanger thus obtained was subjected to rolling to adjust the external shape under predetermined conditions, and the casting crack, surface roughness, and AlFeSi stable phase area ratio were measured.

"Casting crack"
The measurement of the casting crack was performed by a bipolar determination using USM25J manufactured by Clautramer. The evaluation method is that the casting crack is ◯ means that there was no crack that would cause a defect in the extrusion of the next process in the billet, and that the casting crack was x means that the next process in the billet. This means that there was a crack that would cause a defect in the extrusion.

"Tube surface roughness"
The tube surface roughness tends to worsen as the mold wear progresses, leading to unevenness when flux or SBL is applied. Further, the brazing of the header is guided to the concave / convex groove during brazing and flows onto the tube, erosion occurs, and a through hole is easily generated in the tube.
Therefore, as a measurement of the tube surface roughness, the value of R _max in the tube width direction was measured, and it was determined that it was not preferable that the value of R _max was 15 μm or more.

As a method for measuring the AlFeSi stable phase area ratio, Fe and Si atom concentrations were measured by EDX (Energy Dispersive X-ray Spectroscopy) for all particles present in a measurement visual field having a measurement area of 1 mm ² . The criterion for determining the AlFeSi stable phase was that the ratio of the atomic concentration of Fe and Si (= Fe atomic concentration / Si atomic concentration) was less than 3.5. And the AlFeSi stable phase total area ratio (%) was computed by the following formula | equation (1).
AlFeSi stable phase total area ratio (%) = AlFeSi stable phase total area ÷ measured area × 100 (1)

Subsequently, a brazing composition in which a Zn-containing flux, Si powder, and a binder were mixed was applied to the outer surface of the extruded flat multi-hole tube 11 for heat exchanger to provide the coating layer 2. The Zn-containing flux and the amount of Si powder applied are shown in Table 1, and an acrylic resin was used as the binder.
Further, after brazing and heating at 600 ° C. for 3 minutes, the strength of the extruded flat multi-hole tube 11 for heat exchanger is measured by a method of pulling the extruded flat multi-hole tube 11 for heat exchanger in the longitudinal direction with a tensile tester. did.

Further, a core in which these extruded flat multi-hole tubes 11 for heat exchangers are combined with fins 6 having double-sided wax as shown in FIG. 2 is produced, and SWAAT (Sea Water Acidic Acid Test, artificial seawater spray test) Evaluation was performed. The test method was performed in accordance with ASTM (G85-85) standard by performing (1) and (2) for two cycles under the following conditions.
(1) Artificial seawater (pH = 3) Spray: 50 ° C., 0.5 hours (2) Wet: 50 ° C., 1.5 hours The results are shown in Tables 3 to 5.

From Tables 3 and 4, in Examples 1 to 27, the area ratio (%) of the AlFeSi stable phase is 0.1% or more and less than 0.5%, and the strength after brazing is 65 (MPa) or more. Sufficient strength was obtained, the casting crack was evaluated as “good”, and the surface roughness (R _max ) was less than 15 μm.
Furthermore, in SWAAT evaluation, the SWAAT penetration days exceeded 30 days, and it was confirmed that the corrosion resistance was improved.

On the other hand, in Comparative Example 1, since the amount of each element added was too small, the purity of aluminum was relatively high, so the strength after brazing was as low as less than 60 MPa, and the strength was insufficient. It was.
In Comparative Example 2 and Comparative Example 3, since the amount of each element added is too large, Comparative Example 2 has a high strength after brazing, but the evaluation of casting cracks is x, and Comparative Example 3 has a strength after brazing. Although the evaluation of casting crack was good, the surface roughness exceeded 15 μm.
Further, in Comparative Example 4, since the amount of Zr and Ti added was too large, the casting crack was evaluated as x and the surface roughness exceeded 15 μm.

  Moreover, in the homogenization process, after the first heat treatment, the cooling step was performed at 200 ° C., and in Comparative Examples 5 to 7 where the second heat treatment was not performed, the total area ratio of the AlFeSi stable phase was less than 0.1%. there were.

Further, in Comparative Example 8, since the Zn-free layer using KAIF ₄ as the flux was used, the SWAAT penetration days were less than 20 days.
In Comparative Example 9 and Comparative Example 10, since the Si powder was not applied, the SWAAT penetration days decreased to less than 30 days compared to Example 5.

FIG. 1 is a perspective view showing an example of an extruded flat multi-hole tube for a heat exchanger according to the present invention. FIG. 2 is a perspective view showing an example of a heat exchanger.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Tube, 2 ... Coating layer, 3 ... Extrusion tube, 4 ... Hole for medium passages, 5 ... Header pipe, 6 ... Fin, 11 ... Extrusion for heat exchanger Flat multi-hole tube.

Claims (3)

In a composition consisting of Si: 0.01 to 0.30%, Fe: 0.01 to 0.30%, Cu: 0.05 to 0.40%, and Mn: 0.05 to 0.30% in mass%. Ti: 0.05-0.25%, or Zr: 0.05-0.25%, or Zr: 0.05-0.25% and Ti: 0.05-0.25% And the total of Zr and Ti is 0.3% or less, the balance is made of an aluminum alloy consisting of Al and inevitable impurities, and particles having a particle area of 1.0 μm ² or more dispersed in the matrix Among them, the area ratio occupied by the AlFeSi stable phase was 0.1% or more and less than 0.5%, and a brazing composition in which a Zn-containing flux, Si powder, and a binder were mixed was applied to the outer surface. Extruded flat multi-hole tube for heat exchangers characterized by _{2. The} extruded flat multi-hole tube for a heat exchanger according to claim 1, wherein the Zn flux layer is composed of one or more of ZnF ₂ , ZnCl ₂ , and KZnF ₃ .   A heat exchanger comprising the extruded flat multi-hole tube for a heat exchanger according to any one of claims 1 and 2.

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