JP2005161368A - Method for joining aluminum-based metal tube and ferrous metal tube and joining structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for joining an aluminum-based metal tube and a ferrous metal tube, which method is excellent in strength and airtightness and is high in reliability. <P>SOLUTION: A joining metal part 3 is manufactured by applying a burring machining to a two-layer metal clad plate consisting of stainless steel and aluminum-alloy, forming a cylindrical rising part, whose aluminum-alloy 3b in its inner peripheral face side is extended longer than stainless steel 3a in its outer peripheral face side, and cutting the root part of the rising part. Further, a stainless tube 1 and an aluminum-alloy tube 2, which are different metal tubes to each other, are separated to an outer peripheral face side 3a of the joining metal part 3 and to an inner peripheral face side 3b thereof respectively, and are inserted and fitted in such a way that the metals of similar material are brought into contact with each other. Thereafter, only the portions 9, 10, where these metals of similar material are in contact with each other, is joined by TIG welding. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a joining technique between an aluminum-based metal pipe and an iron-based metal pipe, and more particularly to a joining technique between an aluminum alloy pipe and a stainless steel vibration absorbing pipe used in a refrigerant circuit of an automobile air conditioner.

  In recent years, aluminum alloy pipes have been used for the refrigerant circuit pipes of automobile air conditioners for the purpose of reducing the weight of the vehicle body, but vibrations generated by a compressor or the like may resonate the pipes and cause noise. Therefore, in order to suppress the resonance of the pipe, conventionally, a composite hose made of rubber and resin has been used in the middle of the pipe.

By the way, HFC134a is frequently used as a refrigerant for air conditioners for automobiles in place of Freon, which is a depleting substance of the ozone layer. However, this HFC134a has an ozone depletion coefficient of zero, but has a high global warming potential and is becoming a cause of promotion of global warming. For this reason, it is being recommended to use a CO ₂ refrigerant, which is a natural refrigerant having a low global warming potential, as a substitute for HFC134a.

However, when CO ₂ refrigerant is used, the fluid temperature in the refrigerant circuit piping is 170 to 180 ° C. with respect to 120 to 140 ° C. of the HFC 134a refrigerant, and the pressure is 15 to 20 MPa with respect to 2 to 3 MPa of the HFC 134a refrigerant. .

For this reason, a conventional composite hose made of rubber and resin cannot withstand such a high temperature and high pressure specification, and a vibration absorbing tube having a stainless steel bellows has been proposed instead (for example, a patent) Reference 1). In addition, this stainless steel vibration absorption tube has a gas permeability that is far superior to a conventional composite hose made of rubber and resin because the tube wall is made of metal. There is no leakage. Therefore, this stainless steel vibration absorption tube is being used not only for CO ₂ refrigerant but also for the current HFC134a refrigerant and the like in order to bring the amount of leakage of the refrigerant to the outside air close to zero.

 However, there are the following problems when incorporating the vibration absorbing tube into the refrigerant circuit. That is, at present, only stainless steel can be used for the bellows portion of the vibration absorbing tube because of problems in workability, strength, corrosion resistance, and economy. On the other hand, if the refrigerant circuit piping is changed to stainless steel, equipment such as a compressor to which the piping is connected is made of an aluminum alloy, so that connection with these devices becomes difficult, and the weight of the vehicle body is reduced. Since it hinders and increases the cost, it is desirable to use the current aluminum alloy. Therefore, it is necessary to join a stainless steel vibration absorbing pipe and an aluminum alloy pipe. However, it is very difficult to obtain a reliable joint having high strength and high airtightness by simply mechanically fitting or screwing these metal pipes together. In addition, when an aluminum alloy and stainless steel are joined by welding or brazing, a brittle intermetallic compound is likely to be formed at the joint. In this case as well, a reliable joint having high strength and high airtightness is obtained. It is very difficult.

 As a method of joining the iron-based material and aluminum, after roughing the surface of the base material made of the iron-based material to form irregularities, an aluminum layer is temporarily formed, and this aluminum layer is pressed from the surface side. However, a method of forming a diffusion layer made of an Fe-Al intermetallic compound by high-frequency heating has been disclosed (see Patent Document 2).

However, this method is intended to improve the wear resistance and smoothness of the surface of the base material by forming a diffusion layer made of an intermetallic compound, and is reliable as long as an intermetallic compound is formed. A joint having a certain high strength and high airtightness cannot be obtained.
JP 2002-195474 A JP 7-310161 A

 This invention is made | formed in view of this condition, Comprising: It aims at providing the reliable joining method of the aluminum type metal tube and the iron type metal tube which was excellent in intensity | strength and airtightness.

  The invention according to claim 1 is a two-layer metal clad made of two dissimilar metals, an aluminum-based metal tube and an iron-based metal tube. It is a joining method of joining via a connection fitting formed from a plate, and the connection fitting is subjected to hole flange processing so that the inner peripheral surface side is the aluminum-based metal on the two-layer metal clad plate, A cylindrical upright portion having an open front end is formed, and at the front end portion, the cylindrical portion made of the aluminum-based metal is made longer than the cylindrical portion made of the iron-based metal, and then the root portion of the upright portion Is a cylindrical member obtained by cutting the steel metal tube on the outer peripheral surface side of the connection fitting, and after inserting the aluminum metal tube on the inner peripheral surface side of the connection fitting, Metals of the same kind of material An aluminum-based metal tube and an iron system that are joined while preventing or suppressing the formation of intermetallic compounds at the interface between the dissimilar metals constituting the connection fitting by joining only the contact portions by arc welding It is a joining method with a metal tube.

 According to a second aspect of the present invention, the welding heat source of the arc welding is fixed, and the connection fitting and the dissimilar metal pipe are integrally rotated at a predetermined rotation speed around the pipe axis. This is a joining method of an aluminum-based metal tube and an iron-based metal tube.

The invention according to claim 3 is the highest temperature at any position in the longitudinal direction of the connection fitting, at the position on the interface between the two types of dissimilar metals constituting the connection fitting during the arc welding. The temperature is set to 500 ° C. or lower, or the maximum temperature is set to be higher than 500 ° C. and lower than 650 ° C., and the relationship of log ₁₀ θ ≦ 42.92−0.258t + 0.00009603t ² is satisfied. This is a joining method of an aluminum-based metal tube and an iron-based metal tube.

  Invention of Claim 4 is a joining method of the aluminum-type metal pipe and iron-type metal pipe of any one of Claims 1-3 which makes said arc welding TIG welding.

  Invention of Claim 5 is a joining method of the aluminum type metal pipe and iron type metal pipe of Claim 4 which makes said TIG welding pulse TIG welding.

 Invention of Claim 6 makes joining of the site | part where the said iron-type metals contact TIG welding, and makes joining of the site | part where the said aluminum-type metals contact TIG brazing or MIG brazing. 4. The method for joining an aluminum-based metal tube and an iron-based metal tube according to any one of 3 above.

 The invention according to claim 7 is the aluminum system according to claim 6, wherein the melting point of the brazing material used in the TIG brazing or MIG brazing is 600 ° C. or less, and the activation start temperature of the flux is 500 ° C. or less. This is a method of joining a metal tube and an iron-based metal tube.

  Invention of Claim 8 makes the length of the said connection metal fitting 1.0 times or more of the internal diameter of the said connection metal fitting, The aluminum-type metal tube and iron system of any one of Claims 1-7. It is a joining method with a metal tube.

 The invention according to claim 9 is the invention according to any one of claims 1 to 8, wherein the fitting length of the aluminum-based metal tube fitted on the inner peripheral surface side of the connection fitting is equal to or longer than the length of the connection fitting. A joining method of the aluminum-based metal tube and the iron-based metal tube according to Item 1.

  The invention described in claim 10 is a joining structure of an aluminum-based metal tube and an iron-based metal tube obtained by the joining method according to any one of claims 1-9.

According to the present invention, since the double-layer metal clad plate is used as the material of the connection metal fitting, only the same kind of metal can be melt-joined by arc welding, and the interface between different metals is physically and firmly joined by the clad. Yes. Furthermore, the present invention limits the thermal effect of the fusion bonding to the interface between the different metals as much as possible, so that the formation of brittle intermetallic compounds at the interface can be suppressed. As a result, it has become possible to provide a highly reliable aluminum-based metal tube and iron-based metal tube and a bonded structure that are excellent in strength and airtightness. In addition, the provision of a highly reliable stainless steel pipe and aluminum alloy pipe with excellent strength and airtightness makes it possible to use a CO ₂ refrigerant in an automotive air conditioner. It has become possible to achieve both a reduction in load and a reduction in weight of the vehicle body.

 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

 FIG. 1 shows a joining structure joined by a joining method according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a stainless steel pipe as an iron metal pipe, reference numeral 2 denotes an aluminum alloy pipe as an aluminum metal pipe, and reference numeral 3 denotes a connection fitting.

(Forming connection fittings)
An example in which only burring processing is used as the hole flange processing for forming the connection fitting 3 will be described. The connection fitting 3 is formed as follows, for example. A double-layer metal clad plate made of stainless steel and an aluminum alloy (hereinafter also simply referred to as “clad plate”) is formed into a cut plate or slitter coil cut out to an appropriate size, and a pilot hole is previously formed in the cut plate or slitter coil. Then, burring is performed so that the inner peripheral surface side is made of an aluminum alloy, thereby forming a cylindrical rising portion having an open end. In this burring process, the aluminum alloy is more ductile than the stainless steel, so that the cylindrical portion 3b made of the aluminum alloy on the inner peripheral surface side is the cylindrical portion made of stainless steel on the outer peripheral surface side at the leading end of the rising portion. Extends longer than 3a. And the connection fitting 3 which is a cylindrical member can be formed by cut | disconnecting the root part of this raising part.

(Junction of connecting metal and dissimilar metal pipe)
Then, the stainless steel pipe 1 is inserted into the outer peripheral surface side 3 a of the connection fitting 3 from the base portion side (cut side), and the aluminum alloy tube 2 is inserted into the inner peripheral surface side 3 b of the connection fitting 3 with the tip end side ( The tube portion 3b is inserted from the side longer than the tube portion 3a. As a result, only the metals of the same kind are in contact with each other.

 After that, only the portions 9 and 10 that are the portions where the metals of the same kind are in contact with each other are joined by lap welding by TIG welding as arc welding. This eliminates the need to directly melt and bond dissimilar metals to each other, and also directly receives welding heat at the interface (hereinafter also referred to as “cladding interface”) 6 of two kinds of dissimilar metals constituting the connection fitting 3. Since there is no excessive temperature rise can be avoided. In addition, welding is performed after the dissimilar metal pipes 1 and 2 are inserted into the connection fitting 2, so that welding heat is dissipated to the outside air through the dissimilar metal pipes 1 and 2, and an excessive temperature rise at the cladding interface 6 occurs. Since it prevents more reliably, it becomes possible to join, preventing or suppressing the production | generation of an intermetallic compound.

 Here, if the connecting fitting 3 has the same length of the cylindrical portion 3a on the outer peripheral surface side and the cylindrical portion 3b on the inner peripheral surface side, lap welding can be employed to join the aluminum alloys together. First, it is necessary to join the end portion of the cylindrical portion 3b made of the aluminum alloy on the inner peripheral surface side and the aluminum alloy tube 2 by fillet welding. However, since there is a limit to constricting the arc, the clad interface 6 near the weld is also directly heated by the arc and excessively heated to produce an intermetallic compound. Although the present inventors are developing a joining technique that solves the above problems by using laser welding that excels in light condensing performance instead of arc welding, laser welding currently requires equipment costs. There is a problem that the joining cost becomes high due to its high cost, and development of joining technology by arc welding has been requested as a low cost joining technology.) In contrast, in the present invention, the cylindrical portion 3b on the inner peripheral surface side is on the outer peripheral surface side. Since it extends longer than the cylindrical portion 3a made of stainless steel, the end of the cylindrical portion 3b made of aluminum alloy on the inner peripheral surface side and the aluminum alloy tube 2 are joined by arc welding. Also, cladding interface 6 without being directly heated because apart from the welding unit, generation of the intermetallic compound is prevented or suppressed. In addition, it is desirable for the length which protrudes the cylinder part 3b from the cylinder part 3a to set it as 5 mm or more in consideration of the restriction | limiting of an arc.

 Joining by lap welding welds the entire circumference from the outer peripheral surface of the stainless steel pipe 1 at the position of reference numeral 9, and welds the entire circumference from the outer peripheral face of the cylindrical portion 3b at the position of reference numeral 10. For example, the welding heat source is fixed toward the position 9 or 10 and welded while integrally rotating at a predetermined rotational speed around the tube axis with the dissimilar metal tubes 1 and 2 being inserted into the connection fitting 3. It is desirable. As a result, the welding heat input is evenly distributed in the circumferential direction of the connection fitting 3, so that heat does not concentrate at a specific position in the circumferential direction of the cladding interface 6, and the rotational speed (ie, welding speed) is reduced. By adjusting, it can join, preventing or suppressing the production | generation of the intermetallic compound in the clad interface 6. FIG.

 At the time of joining by arc welding, the maximum temperature at the position on the interface (cladding interface) 6 between the two types of dissimilar metals constituting the joining fitting 3 and at any position in the longitudinal direction of the joining fitting 3 is 500 ° C. Or the maximum temperature is set to more than 500 ° C. and not more than 650 ° C., and the following formula (1) is satisfied.

log ₁₀ θ ≦ 42.92−0.258t + 0.00009603t ² Formula (1)
Here, t is an arbitrary temperature (° C.) higher than 500 ° C. and lower than or equal to 650 ° C., and θ is a holding time (s) of t ° C. or more at an arbitrary position of the cladding interface 6.

 As described above, the temperature and the holding time at the position on the clad interface 6 and at any position in the longitudinal direction of the joint fitting 3 are defined for the following reason.

 That is, FIG. 2 shows whether or not an intermetallic compound is generated at the clad interface 6 when the clad plate is held at a constant heating temperature for a predetermined time.

 (A) is a well-known document (written by Shojiro Oie, “Special Feature 1: Clad Material, Stainless Clad Aluminum Plate”, Metals, Agne Technology Center, July 1989, Vol. 59, No. 7, p. 25-29). From this figure, when the heating temperature is 500 ° C. or less, no intermetallic compound is formed regardless of the holding time. On the other hand, when the heating temperature exceeds 500 ° C., an intermetallic compound is generated after a certain holding time, and it is understood that the holding time at which the intermetallic compound starts to be generated decreases as the heating temperature increases. . The broken line in the figure shows the relationship between the heating temperature and the holding time at which an intermetallic compound begins to be generated at the cladding interface when the heating temperature exceeds 500 ° C.

 However, since the position of the broken line is considered to vary depending on the test conditions, and the detailed test conditions are not clearly described in the above-mentioned known literature, the inventors of the present invention are configured only from the data of the above-mentioned known literature. We thought it was insufficient to specify the requirements.

 Therefore, the inventors of the present application separately conducted a confirmation test on the relationship between the heating temperature and the holding time at which the intermetallic compound starts to form at the cladding interface at a heating temperature of over 500 ° C., and obtained the result of FIG. It was. In this confirmation test, a cut plate of a clad plate was inserted as a test piece in an inert gas atmosphere maintained at a predetermined temperature in a heating furnace, held for a certain period of time, and then removed, and the end face of the test piece (cut surface) ) Was micro-observed to determine the presence or absence of intermetallic compound formation at the cladding interface. For reference, FIG. 3 shows a comparison between (a) the case where no intermetallic compound is produced and (b) the case where an intermetallic compound is produced.

 The broken line in FIG. 2 (b) shows the relationship between the heating temperature and the holding time at which the intermetallic compound begins to be produced by this confirmation test. No intermetallic compound is produced or produced below this broken line. However, since the amount of generation is only a small amount and is only partially (discontinuously) formed on the cladding interface, it does not substantially affect the peel strength at the cladding interface.

 The region below this broken line is expressed by the following formula (1) '.

log ₁₀ θ ₁ ≦ 42.92−0.258t ₁ + 0.00009603t ₁ ² (1) ′
Here, t ₁ : heating temperature (° C.), θ ₁ : holding time (s).

  As described above, the temperature of the clad interface 6 of the connection fitting 3 also rises due to the heat generated by the fusion bonding between the dissimilar metal tubes 1 and 2 and the connection fitting 3, but the reached temperature (maximum temperature) does not exceed 500 ° C. No intermetallic compound is produced regardless of the retention time. Further, even when the temperature of the clad interface 6 exceeds 500 ° C., the holding time above the arbitrary temperature exceeding 500 ° C. and less than the ultimate temperature (maximum temperature) according to the ultimate temperature (maximum temperature) (1 ) ′ [That is, by limiting to satisfy the formula (1)], an intermetallic compound is not generated, or even if it is generated, the generated amount can be kept to a very small amount. The reason why the above formula (1) is satisfied at any position in the longitudinal direction of the connection fitting 3 on the cladding interface 6 is as follows. That is, if an intermetallic compound is not generated at any position in the longitudinal direction of the connection fitting 3, even if an intermetallic compound is generated at another position in the longitudinal direction, the clad plate constituting the connection fitting 3 This is because the peel strength and sealability (airtightness) can be maintained. The maximum temperature is set to 650 ° C. or lower because when the clad interface 6 is heated above 650 ° C., the aluminum alloy constituting the clad plate melts above its melting point and excessive intermetallic compounds are formed. This is because there is a high possibility that

 When TIG welding is used as arc welding, it is recommended to use pulse TIG welding. Thereby, it is possible to adjust the welding heat input with high accuracy by adjusting the intensity and frequency of the pulse, in particular by using together with the method of rotating the connecting fitting 3 and the dissimilar metal tubes 1 and 2 together. Therefore, it becomes easy to satisfy the above formula (1), and generation of an intermetallic compound at the cladding interface 6 can be more reliably prevented or suppressed.

 In the above embodiment, the same kind of metals are joined by lap welding. However, the present invention is not limited to this, and fillet welding may be used.

 In addition, for joining the portions 10 where the aluminum alloys are in contact with each other, TIG brazing or MIG brazing using a solution material (brazing material) in combination is employed in order to suppress the thermal effect on the aluminum alloy which is the material to be joined. Is also preferable. When TIG brazing or MIG brazing is adopted, joining is performed by fillet welding instead of lap welding. In addition, the brazing material has a melting point of 600 ° C. or lower, and further 590 ° C. so that the thermal effect on the aluminum alloy is minimized and an intermetallic compound is not generated at the clad interface or is kept in a very small amount even when generated. In particular, it is desirable to use a material having a temperature of 580 ° C. or lower, and a flux having an activation start temperature of 500 ° C. or lower, more preferably 480 ° C. or lower, particularly 460 ° C. or lower.

 In order to promote heat dissipation at the time of fusion bonding, the stainless steel tube 1 to be inserted into the outer peripheral surface side 3a of the connection fitting 3 is inserted as close as possible to the tip of the connection fitting 3 so that the contact area between the connection fitting 3 and the stainless steel tube 1 is increased. It is desirable to make it as large as possible to promote heat transfer.

 In addition, when the stainless steel pipe 1 and the aluminum alloy pipe 2 are inserted, the length of the connection fitting 3 is set so as to facilitate the work of fusion bonding by maintaining a sufficient contact area with each of the pipes 1 and 2. The inner diameter is preferably 1.0 times or more, more preferably 2.0 times or more. However, even if the connecting fitting 3 is excessively long, the heat dissipation effect is saturated, and on the contrary, the processing cost by hole flange processing increases, so that the inner diameter of the connecting fitting 3 is 4.0 times or less, and further 3.0 times or less. It is preferable to do this.

 Moreover, in order to further expand the heat radiation area, it is preferable that the fitting length of the aluminum alloy tube 2 fitted into the inner peripheral surface side 3 b of the connection fitting 3 is equal to or longer than the length of the connection fitting 3.

  In the above example, the double-layer metal clad plate constituting the connection fitting 3 is made of the same stainless steel and aluminum alloy as the materials of the dissimilar metal tubes 1 and 2, respectively. The same kind of material may be used. Here, the same kind of material as that of the dissimilar metal tube means that the base metal component is the same as that of the dissimilar metal tube, and does not form a brittle intermetallic compound even if it is melt-bonded to the dissimilar metal tube. It means something that is virtually unaffected. The metal component used as a base here is Fe in the case of stainless steel, and Al in the case of an aluminum alloy.

 Therefore, in the above example, the stainless steel constituting the clad plate may be made of a material (steel type) different from that of the stainless steel pipe 1 (for example, when the stainless steel pipe 1 is SUS304, the stainless steel of the clad plate is SUS430). Ordinary steel can be used instead of stainless steel, and can be appropriately selected in consideration of workability, weldability, strength, etc. by hole flange processing.

  In addition, the aluminum alloy constituting the clad plate may be made of a material different from that of the aluminum alloy tube 2 (for example, when the aluminum alloy tube 2 is A5052, the aluminum alloy of the clad plate is A1100). Pure aluminum can also be used, and can be appropriately selected in consideration of workability, weldability, strength, etc. by hole flange processing. From the viewpoint of facilitating the joining of the aluminum-based metals, it is desirable that the cylindrical portion 3b made of the aluminum-based metal be as long as possible than the cylindrical portion 3a made of the iron-based metal, and A1000 rich in ductility as an aluminum-based metal. It is recommended to use a system or pure aluminum. However, it should be noted that the use of these materials is limited due to their low material strength.

 The overall thickness of the clad plate is preferably thin so as not to make the joint portion excessively large. However, it is desirable to adjust appropriately in consideration of workability, weldability, strength, etc. by hole flange processing.

 Further, the ratio of the thicknesses of the dissimilar metals constituting the clad plate can be appropriately adjusted in consideration of workability, weldability, strength, etc. by hole flange processing. When the combination of different metal materials is a combination of an iron-based metal and an aluminum-based metal, the thickness of the iron-based metal constituting the double-layer metal clad plate is 15 to 15% of the total thickness of the double-layer metal clad plate. 35% is preferable. If it exceeds 35%, the proportion of aluminum-based metal with excellent workability is too small, and there is a possibility that the rising height of the raised portion (that is, the length of the connection fitting 3) cannot be sufficiently secured during hole flange machining. On the other hand, if it is less than 15%, the ratio of the iron-based metal is too small, and there is a possibility that the iron-based metal at the raised portion is thinned and cut during hole flange processing.

 The inner diameter of the connection fitting 3 can be easily inserted into the aluminum alloy tube 2, but is slightly larger than the outer diameter of the aluminum alloy tube 2 so that the gap does not open too much. In addition, when joining the inner peripheral surface of the connection metal fitting 3 and the aluminum alloy pipe 2 using a brazing material, a little more space is left so that the brazing material can be appropriately inserted. For example, when the outer diameter of the aluminum alloy tube 2 is 6.8 mm, the gap is preferably 0.1 to 0.15 mm.

 For burring, generally, a rising part is provided on the plate material and screwed there to use it as a stop screw, or a rising part is provided on the side wall of the main pipe and a branch pipe is brazed there to be used as a branch pipe It is used for the purpose of doing. For this reason, it is not necessary to make the rising height of the rising portion so high, and burring is usually performed at room temperature (cold). However, as described above, when it is necessary to make the length of the connection fitting 3 longer than 1.0 times the inner diameter of the connection fitting 3, depending on the material, it may be difficult to process in the cold. In this case, the clad plate may be preheated before burring.

 In the above embodiment, the case where only burring processing is used as the hole flange processing of the double-layer metal clad plate has been described, but the present invention is not limited to this, and a processing method combining deep drawing processing and burring processing is used. It is also preferable to use it. For example, after deep-drawing a double-layer metal clad plate, a pilot hole is opened at its tip, and then burring is performed to ensure the entire length of the connection fitting 3 and the tip of the connection fitting 3. The part can be finished into a required shape in which the cylindrical part 3b extends longer than the cylindrical part 3a. That is, in the burring process, the rising portion is formed by a single plastic deformation. Therefore, when the clad plate is made of a difficult-to-work material, the rising height of the rising portion is set to the required height (that is, the required height). In some cases, it is difficult to obtain the length of the connection fitting 3. On the other hand, when the raised part is formed by a combination of deep drawing and burring, plastic deformation can be applied little by little in deep drawing, which is difficult to process. However, it is possible to easily obtain a desired startup height (that is, the length of the connection fitting 3). Of course, in this processing method, the clad plate may be preheated before processing.

 When a clad plate made of different metals such as stainless steel and aluminum alloy is used, there is a concern that electrocorrosion may occur between different metals due to the presence of rainwater or the like. Therefore, if necessary, the end face of the clad plate where the interface of the dissimilar metal is exposed may be covered with, for example, resin.

  In the above example, only the combination of the stainless steel pipe and the aluminum alloy pipe has been described. However, the present invention is not limited to this combination of materials, and any combination of iron-based metal and aluminum-based metal can be used. Even applicable. For example, the ferrous metal may be plain steel in addition to the stainless steel of the above embodiment. The aluminum metal may be pure aluminum in addition to the aluminum alloy of the above embodiment.

It is a longitudinal cross-sectional view which shows the joining structure of the stainless steel pipe and aluminum alloy pipe which concern on embodiment. It is a graph which shows the presence or absence of the production | generation of the intermetallic compound in a clad interface when a clad board is hold | maintained for a predetermined time with a fixed heating temperature. When a clad board is hold | maintained for a predetermined time at fixed heating temperature, it is a partial side view which respectively shows the case where (a) the intermetallic compound was not produced | generated in the clad interface, (b) the case where the intermetallic compound was produced | generated.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Stainless steel pipe 2 ... Aluminum alloy pipe 3 ... Connection metal fitting 3a ... Outer peripheral surface side 3b ... Inner peripheral surface side 6 ... Cladding interface 9, 10 ... Joint part

Claims (10)

Two dissimilar metal tubes, an aluminum-based metal tube and an iron-based metal tube, are connected via a connecting metal fitting formed of a two-layer metal clad plate made of two kinds of dissimilar metals, an aluminum-based metal and an iron-based metal. Joining method,
The connection fitting forms a cylindrical upright portion with an open front end by subjecting the double-layer metal clad plate to hole flange processing so that the inner peripheral surface side is the aluminum-based metal. A cylindrical member obtained by cutting the base portion of the rising portion after making the cylindrical portion made of the aluminum-based metal longer than the cylindrical portion made of the iron-based metal in the portion,
After inserting the iron-based metal tube on the outer peripheral surface side of the connection fitting and inserting the aluminum-based metal tube on the inner peripheral surface side of the connection fitting, arc only the part where the same kind of metal contacts each other. A joining method of an aluminum-based metal tube and an iron-based metal tube, wherein the joining is performed by welding, while preventing or suppressing the formation of an intermetallic compound at the interface of the dissimilar metal constituting the connection fitting. .   2. The aluminum-based metal tube and the iron-based metal according to claim 1, wherein a welding heat source of the arc welding is fixed, and the connection fitting and the dissimilar metal tube are integrally rotated at a predetermined rotation speed around a tube axis. How to join the tube. At the time of the arc welding, the maximum temperature at any position in the longitudinal direction of the connection fitting, which is a position on the interface between the two types of dissimilar metals constituting the connection fitting, is 500 ° C. or less, or 3. The aluminum-based metal tube and the iron-based metal according to claim 1, wherein the maximum temperature is higher than 500 ° C. and lower than 650 ° C., and the relationship of log ₁₀ θ ≦ 42.92−0.258 t + 0.00009603 t ² is satisfied. How to join the tube.
Here, t is an arbitrary temperature (° C.) exceeding 500 ° C. and less than the maximum temperature, and θ is a holding time (s) of t ° C. or more at an arbitrary position of the interface.   The method for joining an aluminum-based metal tube and an iron-based metal tube according to any one of claims 1 to 3, wherein the arc welding is TIG welding.   The method for joining an aluminum-based metal tube and an iron-based metal tube according to claim 4, wherein the TIG welding is pulse TIG welding.   The joining of the site | part where the said iron-type metals contact is made into TIG welding, and joining of the site | part where the said aluminum-type metals contact is made into TIG brazing or MIG brazing. A joining method of an aluminum-based metal tube and an iron-based metal tube.   The melting point of the brazing material used in the TIG brazing or MIG brazing is 600 ° C. or less, and the flux activation start temperature is 500 ° C. or less. Joining method.   The method for joining an aluminum-based metal tube and an iron-based metal tube according to any one of claims 1 to 7, wherein a length of the connection fitting is 1.0 times or more of an inner diameter of the connection fitting.   The aluminum-based metal tube according to any one of claims 1 to 8, wherein an insertion length of the aluminum-based metal tube to be inserted into an inner peripheral surface side of the connection metal fitting is equal to or longer than a length of the connection metal fitting. Joining method of steel and ferrous metal pipe.   The joining structure of the aluminum-type metal tube obtained by the joining method of any one of Claims 1-9, and an iron-type metal tube.