CN112672841A

CN112672841A - Joint body of copper pipe and aluminum pipe and joining method thereof

Info

Publication number: CN112672841A
Application number: CN201980059160.4A
Authority: CN
Inventors: 芝栄一
Original assignee: Aocun Metal Co ltd
Current assignee: Aocun Metal Co ltd; Okumura Metals Co Ltd
Priority date: 2018-09-14
Filing date: 2019-08-28
Publication date: 2021-04-16
Also published as: JP2020044538A; WO2020054425A1; JP6928804B2

Abstract

The conjugant (1) is a conjugant of a copper pipe (5) and an aluminum pipe (3). A tapered portion (7) which is reduced in diameter as it approaches the tip is provided at the end of the copper pipe (5) joined to the aluminum pipe (3). The tapered portion (7) of the copper pipe (5) is inserted into the aluminum pipe (3), and the inner surface of the aluminum pipe (3) is in contact with the outer surface of the tapered portion (7) of the copper pipe (5). In a cross-sectional view of the joint body (1) in the longitudinal direction, the inner surface of the aluminum pipe (3) and the outer surface of the copper pipe (5) are in contact obliquely with respect to the longitudinal direction of the joint body (1). The outer surface of the aluminum pipe (3) is formed substantially parallel to the longitudinal direction of the joint body (1). In addition, a eutectic layer (9) is formed around the entire circumference of the inner surface of the aluminum pipe (3) and the outer surface of the copper pipe (5). That is, the aluminum pipe (3) and the copper pipe (5) are joined by the eutectic layer (9).

Description

Joint body of copper pipe and aluminum pipe and joining method thereof

Technical Field

The present invention relates to a joined body obtained by joining a copper pipe and an aluminum pipe, and a joining method thereof.

Background

Conventionally, copper pipes have been used as piping materials for air conditioners, but in recent years, aluminum pipes have been increasingly used in place of copper pipes from the viewpoint of reduction in material cost or weight. In particular, aluminization of heat exchangers is being widely carried out. Thus, in the case where the copper pipe and the aluminum pipe are mixedly present, it is necessary to connect the copper pipe and the aluminum pipe.

There are several methods of connecting copper pipes and aluminum pipes, and eutectic bonding is currently one of the methods widely used in mass production (for example, non-patent document 1). Eutectic bonding is one type of diffusion bonding, characterized in that the bonding surface is temporarily liquefied. The method is to embed a copper pipe with the front end subjected to pipe reducing processing into an aluminum pipe, and heat the copper pipe while forcibly pressing the copper pipe into the aluminum pipe for jointing.

Since a eutectic point (548 ℃) exists in a binary state diagram of copper and aluminum, when the copper pipe and the aluminum pipe are brought into contact and heated, atoms are mixed with each other at the contact surface by diffusion, and the vicinity of the contact surface melts when the temperature reaches the eutectic point. Eutectic bonding is a method of bonding a copper pipe and an aluminum pipe in a short time by utilizing this point (non-patent document 2).

Documents of the prior art

Non-patent document

Non-patent document 1: light metal welding Vol.42(2004), No.9, pp429-434 of "joining of dissimilar metal pipes" in superficial field you Yilang

Non-patent document 2: lidamong, Beigang shan Zhi and Shenwei "light metal Vol.38(1988), No.9, pp558-578

Patent document

Patent document 1: japanese laid-open patent publication No. 11-33747

Patent document 2: japanese patent laid-open publication No. 2011-140049

Disclosure of Invention

Problems to be solved by the invention

However, as a conventional eutectic bonding technique, it has been studied mainly to obtain higher bonding quality by optimizing the taper shape of the tip of the copper pipe, the insertion condition of the copper pipe into the aluminum alloy pipe, the heating condition, and the like.

For example, patent document 1 discloses the following eutectic bonding method in detail: the heating tip is machined into a tapered copper tube, which is pressed into an aluminum tube at a specified speed. In patent document 1, a copper pipe having an outer diameter slightly larger than the inner diameter of an aluminum pipe is used. The tip of a copper pipe is processed at a taper angle of 1 to 8 degrees, and the copper pipe is heated to a temperature of not less than the eutectic point (548 ℃) of copper-aluminum and not more than the melting point of the aluminum pipe by a high-frequency heating coil. In this state, the copper pipe is pressed into the aluminum pipe at a speed of 10 mm/sec or more, and then the pipe is cooled by introducing compressed air, thereby joining the two.

For example, in the example of patent document 1, as a practical specific joining example, an outer diameter is used

0.6mm wall thickness of deoxidized copper pipe and same outer diameter

Aluminium tube (99.3% Al) with a wall thickness of 0.6 mm. The copper pipe was heated for 10 seconds to a temperature of 750 ℃ and then the heating rate was decreased to a temperature of 560 ℃ and then the copper pipe was pressed into the aluminum pipe at a rate of 50 mm/sec, and then the copper pipe and the aluminum pipe were joined together by cooling with compressed air. However, in such a method, only initial heating takes 10 seconds, and the method cannot be directly applied to mass production from the viewpoint of productivity.

In contrast, patent document 2 proposes a method for mass production in which a current is passed through electrodes to a copper material and an aluminum material, as in resistance welding, to thereby rapidly heat the materials. In addition, in order to improve the quality of eutectic bonding, additional secondary pressurization is proposed. If a eutectic reaction occurs at the interface where the copper material and the aluminum material are pressed against each other, a liquid phase is generated at the interface, and as a result, displacement may occur on the pressing surface.

However, in both of the methods of patent documents 1 and 2, the connecting portion of the aluminum pipe expands at the time of joining, and the outer diameter becomes large. Among them, one of the important factors for obtaining high-quality eutectic bonding is high contact pressure of the copper pipe and the aluminum pipe. When the connection portion of the aluminum pipe expands due to the insertion of the copper pipe, the pressure generated at the contact surface between the copper pipe and the aluminum pipe is reduced, and therefore, there is a risk that the quality of the bonding layer is reduced, the bonding strength is reduced, and the like. In addition, when the aluminum pipe is expanded, there is a risk that problems such as a reduction in strength of the joint and an abnormal appearance occur due to an abnormal shape such as eccentricity of the pipe at the joint. Therefore, the aluminum pipe is not desired to be a joint which seems to be expanded at first sight.

Further, patent documents 1 and 2 each show detailed numerical values of the shape of the copper pipe and the conditions at the time of joining, but do not consider the situation that is required to be met in the actual production, such as whether eutectic bonding is possible or not under the proposed method and conditions, in the case where the thickness of the pipe changes due to, for example, design changes, material dimensional variations, or the like.

The present invention has been made in view of the above problems, and an object thereof is to provide a joint body of a copper pipe and an aluminum pipe excellent in manufacturability and high in reliability, and a joining method thereof.

Means for solving the problems

In order to achieve the above object, a first invention is a copper pipe and aluminum pipe joint, wherein the joint is composed of a copper pipe and an aluminum pipe, an inner surface of the aluminum pipe and an outer surface of the copper pipe are in contact obliquely with respect to a longitudinal direction of the joint in a cross-sectional view in the longitudinal direction, the outer surface of the aluminum pipe is substantially parallel to the longitudinal direction, and a eutectic layer is formed on the inner surface of the aluminum pipe and the outer surface of the copper pipe.

Preferably, a tapered portion that decreases in diameter toward the front end is provided at an end portion of the copper pipe that is engaged with the aluminum pipe, and an inner surface of the aluminum pipe is in contact with an outer surface of the tapered portion of the copper pipe.

In a cross section perpendicular to the longitudinal direction of the joined body, the sectional area of the raw pipe portion of the copper pipe is preferably smaller than the sectional area of the raw pipe portion of the aluminum pipe.

In a cross section perpendicular to the longitudinal direction of the joined body, a cross-sectional area ratio of a raw pipe portion of the copper pipe to a cross-sectional area of a raw pipe portion of the aluminum pipe is preferably 0.53 to 0.85.

According to the first invention, the contact portion between the outer surface of the copper pipe and the inner surface of the aluminum pipe is joined obliquely with respect to the longitudinal direction, but the outer diameter of the copper pipe and the aluminum pipe does not increase because the outer surface of the aluminum pipe is substantially linear. Therefore, the pressure generated at the contact surface between the copper pipe and the aluminum pipe can be increased, and the high-quality joint can be obtained because the shape abnormality such as the eccentricity of the pipe at the joint is less likely to occur.

Further, by providing a tapered portion, which is reduced in diameter as it goes toward the tip, at the end of the copper pipe joined to the aluminum pipe, the aluminum pipe can be easily inserted and joined.

Further, by making the sectional area of the raw pipe portion of the copper pipe smaller than the sectional area of the raw pipe portion of the aluminum pipe in the section perpendicular to the longitudinal direction of the joined body, when heating is simultaneously performed under the same conditions, the temperature difference between the copper pipe and the aluminum pipe in the joined portion can be reduced, and joining can be performed with higher quality.

In particular, if the ratio of the cross-sectional area of the tubular blank portion of the copper pipe to the cross-sectional area of the tubular blank portion of the aluminum pipe is 0.53 to 0.85, the joining can be performed more reliably and with high quality. For example, if heating is performed without considering the cross-sectional area, the temperature of the copper pipe is hardly higher than that of the aluminum pipe, and therefore heating to the eutectic temperature is not sufficient, and there is a risk of poor bonding. Further, if the copper pipe is sufficiently heated, the temperature of the aluminum pipe becomes excessively high, and there is a problem that the aluminum pipe is partially melted. In contrast, by appropriately setting the cross-sectional area, the temperatures of the two can be made substantially equal, and high-quality joining can be performed.

A second aspect of the present invention is a method of joining a copper pipe and an aluminum pipe, wherein the copper pipe has a tapered portion that decreases in diameter as it approaches a tip at one end, the tapered portion of the copper pipe is inserted into an end of the aluminum pipe, and the copper pipe and the aluminum pipe are directly heated by applying current, so that a eutectic layer is formed at a joint portion between an outer surface of the copper pipe and an inner surface of the aluminum pipe, and the copper pipe and the aluminum pipe are joined together.

In a cross section perpendicular to the longitudinal direction, a cross-sectional area ratio of a tube blank portion of the copper tube to a cross-sectional area of a tube blank portion of the aluminum tube is preferably 0.53 to 0.85.

According to the second aspect of the present invention, the copper pipe and the aluminum pipe can be directly connected to each other by heating them in a short time.

In this case, when the ratio of the cross-sectional area of the raw pipe portion of the copper pipe to the cross-sectional area of the raw pipe portion of the aluminum pipe is 0.53 to 0.85, the copper pipe and the aluminum pipe can be joined with high quality as described above.

Effects of the invention

According to the present invention, a joint body of a copper pipe and an aluminum pipe excellent in manufacturability and high in reliability and a joining method thereof can be provided.

Drawings

Fig. 1A is a view showing the joined body 1.

Fig. 1B is an enlarged view of a portion a of fig. 1A.

Fig. 2A is a diagram showing a production process of the joined body 1.

Fig. 2B is a diagram showing a production process of the joined body 1.

Fig. 3A is a diagram illustrating a bending test method of the joined body 1.

Fig. 3B is a diagram illustrating a bending test method of the joined body 1.

Fig. 4 is a diagram illustrating a hydraulic airtightness testing method for the joined body 1.

Detailed Description

Embodiments of the present invention will be described below with reference to the drawings. Fig. 1A is a cross-sectional view of the joined body 1 in the longitudinal direction, and fig. 1B is an enlarged view of a portion a of fig. 1A. The joint 1 is a joint of a copper pipe 5 and an aluminum pipe 3. The copper pipe 5 is a pipe made of copper or a copper alloy, and the aluminum pipe 3 is a pipe made of aluminum or an aluminum alloy.

A tapered portion 7, which is reduced in diameter as it approaches the tip, is provided at the end of the copper pipe 5 joined to the aluminum pipe 3. The tapered portion 7 of the copper pipe 5 is inserted into the aluminum pipe 3, and the inner surface of the aluminum pipe 3 is in contact with the outer surface of the tapered portion 7 of the copper pipe 5.

In a sectional view of the joint body 1 in the longitudinal direction, the inner surface of the aluminum pipe 3 and the outer surface of the copper pipe 5 are in contact obliquely with respect to the longitudinal direction of the joint body 1 (line B of fig. 1A). The outer surface of the aluminum pipe 3 is formed substantially parallel to the longitudinal direction of the joint body 1 (line B in fig. 1A). The outer surface of the aluminum pipe 3 is substantially parallel to the longitudinal direction, which means that the outer diameter of the joint portion is increased by 5% or less with respect to the outer diameter of the aluminum pipe 3.

In addition, as shown in FIG. 1B, a eutectic layer 9 is formed on the entire circumference around the inner surface of the aluminum pipe 3 and the outer surface of the copper pipe 5. That is, the aluminum pipe 3 and the copper pipe 5 are joined through the eutectic layer 9.

Next, a method of joining the copper pipe 5 and the aluminum pipe 3 will be described. First, as shown in fig. 2A, the aluminum pipe 3 and the copper pipe 5 are opposed to each other. The aluminum pipe 3 is disposed on an electrode not shown. For example, the aluminum pipe 3 can be restrained from the outer surface by sandwiching the aluminum pipe 3 with a pair of electrodes having grooves corresponding to the outer diameter of the aluminum pipe 3.

As described above, the copper pipe 5 has the tapered portion 7 whose diameter decreases toward the distal end at the end portion facing the aluminum pipe 3. The taper angle (θ in the drawing) of the tapered portion 7 is preferably 3 degrees to 9 degrees.

Next, as shown in fig. 2B, the tapered portion 7 of the copper tube 5 is inserted into the end of the aluminum tube 3 held by the electrode, and the power source 11 is connected to the copper tube 5 and the aluminum tube 3 and directly energized, thereby performing heating. The power supply 11 can rapidly raise the temperature of the copper pipe 5 and the aluminum pipe 3 to the vicinity of the eutectic point by, for example, flowing a large current of several thousand a for about 1 second. As a result, the eutectic layer 9 can be formed and bonded at the bonding portion between the outer surface of the copper pipe 5 and the inner surface of the aluminum pipe 3. At this time, the aluminum pipe 3 is restrained from the outer surface and thus is not expanded in diameter.

In the present embodiment, the sectional area of the raw tube portion of the copper tube 5 is preferably smaller than the sectional area of the raw tube portion of the aluminum tube 3 in the cross section perpendicular to the longitudinal direction of the joined body 1. Here, the cross-sectional area of the blank pipe portion means the cross-sectional area of the pipe body at a portion which is not a tapered portion and is not affected by the change in the cross-sectional area at the time of joining, and is substantially equal to the cross-sectional area of each pipe body (blank pipe) before joining.

The reason why the sectional areas of the copper pipe 5 and the aluminum pipe 3 are different from each other is as follows. In the eutectic bonding, the temperature of the contact portion between the copper pipe 5 and the aluminum pipe 3 becomes equal to or higher than the eutectic point, and a reaction occurs. The inventors have noted that in eutectic bonding of the copper pipe 5 and the aluminum pipe 3, material temperatures of both are very important, and have found that appropriately setting the material temperature at the time of eutectic bonding is important to obtain a higher quality bonded portion.

Here, when the copper pipe 5 and the aluminum pipe 3 are heated under the same conditions at the same time, the temperatures of the copper pipe 5 and the aluminum pipe 3 change according to the heat capacities of both. That is, if the heat capacity is large, the temperature is hard to rise, and if the heat capacity is small, the temperature is easy to rise.

Further, the front ends of the copper pipe 5 and the aluminum pipe 3 are brought into contact to form a series circuit, and when a current flows, joule heat generated in the pipes is a main heat generation source. The amount of joule heating per unit length is determined by the resistivity of the material. The degree of the temperature change caused by the heat is determined by the specific heat capacity of the material. Although such physical parameters are inherent to the material, when the cross-sectional area is changed, the heat capacity and the heat generation amount per unit length are also changed, and therefore, the temperature difference between the two pipes due to the physical parameters can be compensated for by adjusting the cross-sectional area. That is, the inventors found that since the sectional areas of the copper pipe 5 and the aluminum pipe 3 are adjustable, by appropriately setting the sectional areas of the copper pipe 5 and the aluminum pipe 3, both can be made to be at an appropriate temperature.

For example, if the cross-sectional area increases by 1%, the heat capacity per unit length of the tube increases by 1%, but the resistance value per unit length of the tube decreases by 1%, and as a result, the amount of heat generation decreases by 1%, and therefore the temperature increase per unit length of the tube decreases by about 2%. As a result of calculating the temperature on the assumption of the thermal model, it was found that the temperature difference caused by the physical parameters of the copper pipe 5 and the aluminum pipe 3 can be compensated by making the sectional area of the copper pipe 5 smaller than the sectional area of the aluminum pipe 3 by a predetermined amount.

That is, by appropriately setting the ratio of the cross-sectional areas of the copper pipe 5 and the aluminum pipe 3, the temperature increase rates of the both can be made substantially the same in a temperature range from zero degrees to about 600 degrees above the eutectic point (about 550 degrees celsius), and therefore, when the copper pipe 5 and the aluminum pipe 3 are heated simultaneously from the same temperature, the temperatures of both reach the same temperature at the same time. In this way, when joining the copper pipe 5 and the aluminum pipe 3, by appropriately setting the ratio of the cross-sectional areas of the two, the temperatures of the two can be simultaneously heated to the eutectic point, and thereby the eutectic joining quality can be improved.

The inventors further verified the appropriate cross-sectional area ratio, and found that it is particularly preferable that the cross-sectional area ratio of the raw pipe portion of the copper pipe 5 to the cross-sectional area of the raw pipe portion of the aluminum pipe 3 in the cross section perpendicular to the longitudinal direction is 0.53 to 0.85.

Further, as a method for measuring the cross-sectional area, the outer diameter and the wall thickness of a portion of the raw pipe which is not subjected to the end finishing and is not affected by the end finishing are measured in two directions orthogonal to the longitudinal direction, and the cross-sectional area is calculated from the average value of the measured values of the diameter and the wall thickness.

In the vicinity of the joint portion of the joined body 1, there is a possibility that the cross-sectional area of each pipe body changes from before joining due to heating or the like at the time of joining, but the cross-sectional area before and after joining hardly changes as long as it is a position sufficiently apart from the joint portion of the joined body 1. Therefore, as shown in fig. 2A, the cross-sectional area of the raw tube portion of the copper tube 5 is the cross-sectional area of the copper tube 5 at a position spaced apart from the end 3L of the copper tube 5 when the length of the tapered portion 7 is L. Similarly, the sectional area of the blank portion of the aluminum pipe 3 means the sectional area of the aluminum pipe 3 at a position distant from the end 3L of the aluminum pipe 3.

In practice, the cross-sectional area of each pipe body to be considered in eutectic bonding is the joint portion between the two, and therefore the cross-sectional area of the copper pipe 5 is the cross-sectional area of the tapered portion 7. In the tapered portion 7, since the sectional area differs depending on the location, accurate calculation of the sectional area of the copper pipe 5 is complicated. However, if the taper angle is about 3 to 9 degrees, a large difference does not occur even if the cross-sectional area measured at the raw pipe portion is used. Therefore, in the present embodiment, for the sake of simplicity, a preferable range of the cross-sectional area ratio is determined by using the cross-sectional area measured at the raw pipe portion.

By so doing, it is possible to more reliably form the high-quality eutectic layer 9 over the entire circumference around the inner surface of the aluminum pipe 3 and the outer surface of the copper pipe 5. In which the eutectic layer 9 may be formed not completely annularly in a cross section perpendicular to the axial direction of the joined body 1. For example, the eutectic layer 9 may also be formed while being bent in the tube axial direction. That is, the eutectic layer 9 may also be a three-dimensional closed curve undulating in the circumferential direction and the axial direction on the tapered surface.

When the joint body 1 is used as, for example, a pipe of an air conditioner, the pressure applied to the inside of the pipe during the air conditioner operation is usually at most about 4.2 MPa. If the eutectic layer 9 is effectively present on the bonding portion, the withstand voltage against such pressure can be sufficiently ensured. On the other hand, if there is a defective portion in the junction portion, such as when the eutectic layer 9 is not sufficiently formed, the above-described withstand voltage performance cannot be obtained.

Further, the presence of the eutectic layer 9 at the leak portion can also be checked by performing image analysis using SEM or the like, line analysis of composition change in the thickness direction of the bonding surface, or the like. Further, empirically, in the region of the eutectic layer 9, the result of the composition analysis was that copper was in the range of 30% to 60% (copper concentration on the copper side was high, and the copper concentration gradually decreased from the copper side to the aluminum side as a tendency). If the eutectic layer 9 is removed, the copper concentration or the aluminum concentration changes rapidly, and therefore, the presence or absence of the eutectic layer 9 can be determined.

As described above, in the present embodiment, by appropriately setting the ratio of the cross-sectional areas of the copper pipe 5 and the aluminum pipe 3, both can be heated efficiently, and eutectic bonding can be performed.

Further, since overheating of one of the copper pipe 5 and the aluminum pipe 3 can be suppressed, deformation of the copper pipe 5, fusion of the aluminum pipe 3, and the like at the time of joining can be suppressed, and high joining strength can be obtained.

Examples

As the air-conditioning piping, a pipe having a normal outside diameter is used

The copper pipe and the aluminum pipe were subjected to eutectic bonding, and differences in the bonding quality with respect to the sectional area ratio were evaluated. The wall thickness of the copper pipe is 0.4mm, 0.5mm, 0.6mm, 0.8mm and 1.0mm, and the wall thickness of the aluminum pipe isIs 1.0mm and 1.2 mm. The combination of copper and aluminum tubes is shown in table 1.

TABLE 1

As shown in Table 1, Nos. 1 to 5 show the cases where the thickness of the aluminum pipe was set to be the same as 1mm, and the thickness of the copper pipe was changed from 0.4mm to 1 mm. No.5 and No.6 show the case where the thickness of the copper pipe was 1mm and the thickness of the aluminum pipe was 1.0mm and 1.2mm, respectively. The results of eutectic bonding for the combinations in table 1 are shown in table 2.

TABLE 2

The eutectic bonding quality was evaluated by a hydraulic pressure airtight test, a peeling test, and appearance. The hydraulic pressure airtight test is performed in consideration of the pressure resistance of the air conditioning pipe. First, as shown in fig. 3A, the joint body 1 is vertically fixed to the fixing jig 13. Next, as shown in fig. 3B, the left and right are bent by θ 1 in the vertical direction by 5 degrees, and the process returns to the vertical direction by one round trip, and is repeated three times.

Thereafter, as shown in fig. 4, one end of the joined body 1 was sealed by the sealing portion 15, the other end was connected to the pump 17, and a water pressure of 4.2MPa was applied from the water tank 19 to the joined body 1 by the pump 17 to investigate leakage. If there is no leak, the joined body 1 is returned to the fixing jig 13 so that the bending angle is 10 degrees, and after three bending loads are applied, an air tightness test under the same water pressure is performed. In table 2, the leakage was not found and is denoted as "good", and the leakage was found and is denoted as "bad".

The peeling test was carried out by peeling the aluminum pipe of the joint from the copper pipe using a tool, and measuring the axial length of the peeling trace of the aluminum pipe remaining on the joint surface of the copper pipe. When the bonding was weak, the aluminum tube was once peeled from the interface with the copper tube as a whole, and no aluminum was found to remain. On the other hand, if the joint is strong, the aluminum pipe cannot be peeled off from the copper pipe, and if the aluminum pipe is forcibly peeled off, the aluminum pipe is broken and remains. In this case, the length of the peeling trace included the length of the remaining aluminum pipe. As described above, the length of the copper pipe relative to the peeling trace of the aluminum pipe was measured in the peeling test to evaluate the bonding strength.

Further, since the length of the peeling trace slightly varies in the circumferential direction of the copper pipe, the length of the shortest peeling trace is defined as the bonding length of the bonded body as viewed from the entire circumference. An experiment was performed under the same conditions with n being 3, and the evaluation of each condition was performed using the average length of the peeling traces. The average value of the bonding length was "bad", the average value of the bonding length was "average" when the peeling mark was observed but the average bonding length was less than 5mm, and the average bonding length was "good" when the average bonding length was 5mm or more.

In addition, in terms of appearance, immediately after eutectic bonding, melting, flaw, hole, fracture, expansion, deformation, and the like of the aluminum pipe were visually examined for the vicinity of the bonded portion. In table 2, "good" indicates no particular abnormality, and "bad" indicates an abnormality having an influence on the bonding strength and the air-tightness test, and "average" indicates that the abnormality has no significant influence on the quality, although some deformation or the like is observed.

In table 2, as a comprehensive evaluation, "good" is evaluated for all items, "good" is evaluated for some items, and "bad" is evaluated for some items.

From the results, the cross-sectional area ratio was 0.53 to 0.85 (nos. 2 to 4 and 5), and in either case, the airtightness test was evaluated as "good" and the bonding strength was evaluated as "average" to "good". The joint length increased with the increase of the cross-sectional area ratios of 0.53, 0.63, and 0.82 (nos. 2 to 4), but the joint length decreased slightly with the cross-sectional area ratio of 0.85(No.6) compared with the cross-sectional area ratio of 0.82(No. 4).

On the other hand, when the cross-sectional area ratio was 0.43(No.1), the airtightness test was evaluated as "bad", and it was examined that no eutectic layer was formed at the eutectic bonding portion. In addition, when the cross-sectional area ratio was 0.43(No.1), the cross-sectional area of the copper pipe was too small, so that the copper pipe was overheated and insufficient in rigidity, and the copper pipe was deformed, and the appearance was evaluated as "bad".

In addition, when the cross-sectional area ratio is 1.0(No.5), the joint length is reduced as compared with that when the cross-sectional area ratio is 0.82(No. 4). Further, the reduction of the joining length at the time of temperature decrease is large as compared with the case where the cross-sectional area ratio is 0.82(No.4) or 0.85(No.6), and there is a tendency that it is not suitable for mass production requiring stability.

When the cross-sectional area ratio was 1.0(No.5), a part of aluminum was melted. The copper pipe of No.6 had a wall thickness of 1.0mm which was the same as that of No.5, but the joining length was increased to approach No.4 as compared with No.5 having a wall thickness of the copper pipe by increasing the wall thickness of the aluminum pipe to 1.2mm to reduce the cross-sectional area ratio. In addition, no melting of the aluminum tube was found.

As a result, the eutectic bonding of the combination of the copper pipe and the aluminum pipe having the cross-sectional area ratio of 0.43 to 1.0 is performed, and as a result, the eutectic bonding of particularly high quality can be performed within the range of the cross-sectional area ratio of 0.53 to 0.85.

The embodiments of the present invention have been described above with reference to the drawings, but the technical scope of the present invention is not limited to the above embodiments. Various modifications and alterations can be made by those skilled in the art within the scope of the technical idea described in the claims, and it should be understood that these also naturally fall within the technical scope of the present invention.

Description of reference numerals:

1: bonded body

3: aluminum pipe

5: copper pipe

7: tapered portion

9: eutectic layer

11: power supply

13: fixing clamp

15: sealing part

17: pump and method of operating the same

19: water tank

Claims

1. A joint body of a copper pipe and an aluminum pipe, characterized in that,

the joint body is composed of a copper pipe and an aluminum pipe,

in a sectional view in a longitudinal direction of the joint body, an inner surface of the aluminum pipe and an outer surface of the copper pipe are in contact obliquely with respect to the longitudinal direction, the outer surface of the aluminum pipe is substantially parallel with respect to the longitudinal direction,

eutectic layers are formed on the inner surface of the aluminum pipe and the outer surface of the copper pipe.

2. The joint body of a copper pipe and an aluminum pipe as recited in claim 1,

a tapered portion which is reduced in diameter as it approaches the front end is provided at an end portion of the copper pipe which is joined to the aluminum pipe,

the inner surface of the aluminum tube is in contact with the outer surface of the tapered portion of the copper tube.

3. The joint body of copper and aluminum tubes as recited in claim 1 or 2,

in a cross section perpendicular to the longitudinal direction of the joined body, the sectional area of the tube blank portion of the copper pipe is smaller than the sectional area of the tube blank portion of the aluminum pipe.

4. A joint body of a copper pipe and an aluminum pipe as recited in claim 3,

and a cross-sectional area ratio of the raw pipe portion of the copper pipe to the raw pipe portion of the aluminum pipe in a cross section perpendicular to the longitudinal direction of the joined body is 0.53 to 0.85.

5. A method of joining a copper pipe and an aluminum pipe, characterized in that,

the copper pipe has a tapered portion which is tapered toward the tip at one end,

inserting the tapered portion of the copper tube into the end portion of the aluminum tube, and directly electrifying the copper tube and the aluminum tube for heating,

a eutectic layer is formed and bonded on a bonding portion of an outer surface of the copper pipe and an inner surface of the aluminum pipe.

6. The joining method of a copper pipe and an aluminum pipe according to claim 5, wherein,

and a cross-sectional area ratio of the tube blank portion of the copper tube to the tube blank portion of the aluminum tube in a cross section perpendicular to the longitudinal direction is 0.53 to 0.85.