JP6288632B2 - Method for joining metal members - Google Patents

Description

  The present invention relates to a metal member joining method for joining a plurality of metal members.

Conventionally, for example, aluminum, or aluminum and steel were heated to 580 to 620 ° C. and joined by brazing.
In joining by brazing, since the brazing material is melted and joined (580 to 620 ° C.), there is a problem in positioning accuracy, and the application range is also limited. In addition, flux containing fluoride is used for brazing, and the problem of corrosion due to flux residue and flux is harmful to the human body, and therefore, elimination is desired. Furthermore, an intermetallic compound (brittle property) is formed between the brazing material and the aluminum base material, and there is a problem that the joint portion becomes brittle.

As other joining methods for metal members, laser welding, friction stir welding, and spot welding are also performed.
In joining by these welding, the vicinity of a welding part softens with welding heat, and a microcrack generate | occur | produces. Also, corrosion is a problem due to the clearance of the joint.
Furthermore, when the member to join is aluminum, since heat conductivity is high, big electric power (heat input) is required.

As another method for joining metal members, a solid phase joining method is known.
The solid phase bonding method is a method of bonding by heating and pressurizing without melting a base material and without causing significant deformation in a solid phase state. It has the characteristics that the damage to the member due to heat is reduced, the spread of wetting due to not being melted, and the precision assembly and joining are possible.

  When a metal material (especially aluminum) is exposed to the atmosphere, it forms a strong natural oxide film that is a bonding inhibiting factor. In order to obtain a joint having high strength, it is necessary to increase the joining pressure and joining temperature to mechanically destroy the oxide film, and there is a problem that the amount of deformation during joining naturally increases.

  Therefore, for example, it has been proposed to perform solid-phase bonding after treating the copper bonding surface with an oxide film removing solution made of an organic acid (see, for example, Patent Document 1).

JP 2006-334652 A

  However, when aluminum or the like is used for solid phase bonding only by treating the surface with an organic acid, sufficient bonding strength cannot be obtained.

  In order to solve the above-described problems, in the present invention, a joining method for metal members that can be joined at a relatively low temperature, can suppress deformation during joining, and can join metals in a solid state. Is to provide.

The method for joining metal members of the present invention is a method for joining a plurality of metal members, but the first metal member and the second metal member are abutted, heated and pressurized, and the first metal member and the first metal member are joined together. A step of joining the first metal member and the second metal member by passing an electric current between the first metal member and the second metal member , and heating and pressurizing the first metal member and the second metal member; In the step of joining the first metal member and the second metal member with current flowing between them, the temperature is controlled by a heater.

In the method for joining metal members according to the first aspect of the present invention , the first metal member is aluminum, the second metal member is copper, and current is supplied from the second metal member to the first metal member. It is configured to flow in the direction .
In the method for joining metal members according to the second aspect of the present invention , the first metal member is aluminum, the second metal member is stainless steel, and the current is transferred from the first metal member to the second metal member. It is set to flow in the direction .

According to the joining method of the metal members of the first and second inventions described above, the joining strength can be increased by heating and pressurizing and passing a current between the first metal member and the second metal member. Can be increased.
And since high joining strength is obtained, it becomes possible to obtain high joining strength at a joining temperature lower than before.

According to the present invention described above, a high bonding strength can be obtained at a bonding temperature lower than that of the prior art.
This makes it possible to lower the bonding temperature, reduce the energy required for heating, and reduce the amount of deformation during bonding.

2 is a perspective view of a sample used in Experiment 1. FIG. It is a schematic block diagram of the joining apparatus used in each experiment. 3 is a side view of a test piece for a tensile test used in Experiment 1. FIG. It is a figure which shows the result of the tension test of Experiment 1 (aluminum / copper joint). It is a figure which shows the relationship between the joining temperature of the result of the tension test of Experiment 1, and joining deformation amount. It is a figure which shows the result of the analysis of the SEM photograph of the fracture surface of the sample after a tension test, and copper. It is a figure which shows the result of the SEM photograph and elemental analysis of the joining interface of the sample after a tension test. 6 is a perspective view of a sample used in Experiment 2. FIG. 6 is a side view of a test piece for a tensile test used in Experiment 2. FIG. It is a figure which shows the result of the tension test of Experiment 2 (aluminum / stainless steel joining). 6 is a perspective view of a sample used in Experiment 3. FIG. 5 is a side view of a test piece for a tensile test used in Experiment 3. FIG. It is a figure which shows the result of the tension test of Experiment 3 (aluminum / aluminum alloy joining). AC is a figure which shows the sample used in Experiment 4, and the test piece of a tension test. It is a figure which shows the result of the tension test of Experiment 4 (copper / copper joint).

Hereinafter, modes for carrying out the invention (hereinafter referred to as “embodiments”) will be described.
The description will be given in the following order.
1. 1. Outline of the present invention Example

<1. Summary of the present invention>
First, an outline of the present invention will be described.
The method for joining metal members of the present invention is a method for joining a plurality of metal members made of the same material or different materials.
In the present invention, the first metal member and the second metal member are brought into contact with each other, heated and pressurized, and a current is passed between the first metal member and the second metal member. A step of joining the metal member and the second metal member;

  In the present invention, as the materials of the first metal member and the second metal member, metal members made of various metal materials can be used. For example, aluminum, aluminum alloy, copper, stainless steel (SUS), etc. can be used.

  The first metal member and the second metal member to be joined may be the same material or different materials.

Further, when the first metal member and the second metal member are made of different materials, depending on the combination of the materials of the respective metal members, depending on the direction in which the current flows, The amount of current at which the maximum bonding strength is obtained is different.
For example, when the first metal member is aluminum and the second metal member is copper, when a current is passed in the direction from copper to aluminum (electrons are passed in the direction from aluminum to copper), the direction is reversed. The maximum bonding strength can be obtained as compared with the case where an electric current is passed through. In addition, the amount of current at which the maximum bonding strength can be obtained is smaller than when a current is passed in the opposite direction.
For example, when the first metal member is aluminum and the second metal member is stainless steel, when an electric current is passed in the direction from aluminum to stainless steel (electrons are passed in the direction from stainless steel to aluminum), The maximum joint strength can be obtained as compared with the case where the current is passed in the opposite direction. In addition, the amount of current at which the maximum bonding strength can be obtained is greater than when a current is passed in the opposite direction.

In the present invention, when joining metal members, heating and pressurization are performed, and a current is passed through the metal members to be joined. Therefore, the diffusion of the elements of each metal member is promoted by the current.
Thereby, when each metal member is a different kind of material, a reaction layer is generated near the joint surface, and when each metal member is the same kind of material, atoms near the joint surface are bonded. Further, in the initial stage of the joining process, only the vicinity of the joining interface is plastically deformed by Joule heat, thereby completing the adhesion of the joining interface.
Accordingly, the bonding strength can be increased.
Thus, since high joint strength can be obtained, it becomes possible to obtain high joint strength at a temperature lower than before.

As described above, according to the present invention, a sufficiently high bonding strength can be obtained at a lower temperature than in the prior art, so that bonding in a solid state can be performed at a low temperature.
From the same viewpoint as the temperature, a sufficiently high bonding strength can be obtained even if the pressure during bonding is lowered.
Thereby, bonding in a solid phase can be performed at a low pressure, and the amount of deformation at the time of bonding can be reduced, so that the positional accuracy of bonding can be improved. And since the positional accuracy of joining improves, it can maintain high positional accuracy, Therefore The joining of the metal member of the complicated shape which was difficult by welding is also attained.
Further, since bonding can be performed at a low temperature and a low pressure, the structure of the bonding apparatus can be simplified, energy required for heating can be reduced, and energy efficiency can be improved. For example, it becomes possible to reduce power consumption, fuel for heating, time required for joining, and the like.

  In addition, when using a material that easily forms an oxide film such as aluminum as the metal member, for example, alkali treatment or organic acid treatment is performed in order to remove the oxide film formed on the surface. Therefore, bonding may be performed.

<2. Example>
Next, the metal members were actually joined according to the present invention, and the characteristics were examined.

(Experiment 1) Aluminum / copper joint As two metal members to be joined, as shown in a perspective view in FIG. 1, cylindrical aluminum having a diameter of 20 mm and a height of 15 mm, and a diameter of 10 mm and a height of 15 mm. Columnar copper was prepared. The purity of aluminum was 99.9%, and the purity of copper was 99.99%.

FIG. 2 shows a schematic configuration diagram of the joining apparatus used in the experiment.
The bonding apparatus 1 shown in FIG. 2 is configured by disposing a pressurizing unit 2 that pressurizes a test piece in a vacuum chamber 11 and providing a heater 13 around the vacuum chamber 11.
A vacuum pump 12 is connected to the vacuum chamber 11. A nitrogen gas supply pipe 18 connected to the nitrogen gas supply unit 14 is inserted into the vacuum chamber 11. Thereby, after evacuating the inside of the vacuum chamber 11, nitrogen gas can be supplied and the inside of the vacuum chamber 11 can be made into nitrogen atmosphere.
A test piece (in this case, aluminum 21 and copper 22) is installed in the space inside the pressurizing unit 2, and the ceramic plate 4 is disposed in contact with the upper and lower sides of the test pieces 21 and 22, respectively. A ceramic plate 4 is placed on the substrate 3. A constant pressure adjusted by a pressure adjusting unit (not shown) is applied to the test pieces 21 and 22 through the substrate 3 and the ceramic plate 4.
The heater 13 is connected to the power supply unit 15. Further, a thermocouple 20 is connected to the substrate 3 in the pressurizing unit 2 from the control unit 16 connected to the power supply unit 15. Thereby, the temperature of the board | substrate 3 is measured with the thermocouple 20, and the measurement result is fed back. And the electric power supplied from the electric power supply part 15 to the heater 13 by the control part 16 is controlled, and the temperature in the vacuum chamber 11 is controlled.
A wiring 19 is connected from the DC power source 17 to the test piece (aluminum 21 and copper 22) in the pressurizing unit 2. As a result, current can flow through the aluminum 21 and the copper 22. 2 shows a state in which the positive electrode of the DC power source 17 is connected to the copper 22 and the negative electrode is connected to the aluminum 21. In this joining apparatus 1, the negative electrode is connected to the copper 22 contrary to FIG. It is also possible to connect and connect the positive electrode to the aluminum 21.

As shown in FIG. 2, when the positive electrode of the DC power source 17 is connected to the copper 22 and the negative electrode is connected to the aluminum 21, the current flows from the copper 22 to the aluminum 21, and the electron current flows from the aluminum 21 to the copper 22. Flowing.
In contrast to FIG. 2, when the positive electrode of the DC power supply 17 is connected to the aluminum 21 and the negative electrode is connected to the copper 22, the current flows from the aluminum 21 to the copper 22, and the electron flow flows from the copper 22 to the aluminum 21. .

In the joining apparatus 1 shown in FIG. 2, the joining pressure is set to 12 MPa, the joining temperature is set to 460 ° C., the joining time is set to 15 minutes, and the aluminum 21 and the copper 22 are joined by heating and pressurizing, thereby connecting the joint. Produced.
Furthermore, the joining pressure was set to 12 MPa, the joining time was set to 15 minutes, the current value, the direction of current, and the joining temperature were changed, and the metal members were joined to produce a joint.
In addition, for comparison, a joint that was joined without electric assistance (current 0) was also produced.
Furthermore, as a modified example, a joint was produced in which the oxide film at the aluminum bonding interface was replaced with a metal salt, and then joined by electric assistance.

(Tensile test)
A tensile test was performed using a joint obtained by joining aluminum and copper as a test piece.
As shown in FIG. 3, a tensile test jig is hooked on the end surface on the aluminum side with a large diameter, the outside of the copper is sandwiched between the jigs, stress is applied in the direction indicated by the arrow in the figure, and the tensile test is performed. went.
As the tensile tester, 5567 manufactured by INSTRON was used.
The joint pressure was constant at 12 MPa, and the tensile test was performed on each joint, which was joined by changing the current value, the direction of current, and the joining temperature, to obtain the interface strength of the joint.

  As a result of the tensile test of Experiment 1, FIG. 4 shows changes in the interface strength when the bonding pressure is fixed at 12 MPa and the bonding temperature is fixed at 460 ° C., and the current value and the direction of the current are changed. The arrows “Cu → Al” and “Al → Cu” in the legend of FIG. 4 indicate the direction of the electron flow. When the negative electrode of the DC power source 17 shown in FIG. → Cu ”.

As can be seen from FIG. 4, in order to obtain a high interface strength, it is necessary to appropriately select the current value and the direction of the current.
In addition, when Al and Cu are to be joined, as indicated by the mark ● in FIG. 4, the electron flow is directed from Al to Cu, that is, the current is directed from Cu to Al, and 10 A (about 0.8 V). It can be seen that the highest interface strength can be obtained by flowing.
When the current is passed in the direction from Cu to Al, the peak interface strength is higher than that in the case where the current is passed in the direction from Al to Cu, and the peak interface strength is obtained. The amount of current that is generated is reduced.

As described above, the cause of the phenomenon in which the peak interface strength differs depending on the direction of the current is considered as follows.
When electrons are moved from the Cu side to the Al side (in the case of □ in FIG. 4), the repulsive force between the oxygen ions on the Cu side and the electrons works, and the oxygen ions move to the Al side. A large amount of Al ₂ O ₃ is generated at the bonding interface, and the change to a state in which the reaction between Al / Cu hardly occurs is considered to be a cause of the low interface strength.
When electrons are moved from the Al side to the Cu side (in the case of the mark ● in FIG. 4), oxygen ions of Al ₂ O ₃ generated on the Al side in the initial stage of bonding are separated by repulsive force with the electrons. Since it moves to the Cu side and the bonding temperature is 250 ° C. or higher, the fact that Al and Cu easily react with each other due to the reducing action of copper oxide with CO is considered to be a cause of the increased interface strength.

In addition, when electrons are moved from the Al side to the Cu side (in the case of the ● mark in FIG. 4), when the current amount is increased, the current amount (10 A) at which the peak interface strength can be obtained. The cause of the phenomenon that the interface strength decreases when the interface strength increases and the current amount is further increased is considered as follows.
As a result of the reduction of the aluminum oxide by the electric current and the movement of oxygen ions to the Cu bonding surface, the reaction between Al and Cu is more likely to occur, which is considered to increase the interface strength. Further, it is considered that when the amount of current is further increased, electrons are vigorously moved to the Cu side, thereby suppressing the diffusion of Cu to the Al side.

  Next, FIG. 5 shows the results when the junction temperature was changed while fixing the current direction and current amount conditions, in which the highest interface strength was obtained in FIG. FIG. 5 shows the relationship between the bonding temperature, the interface strength, and the amount of deformation of joint (“height before bonding−height after bonding” in the pressure direction of Al). There was almost no change in the amount of joint deformation regardless of the presence or absence of electric assist. In addition, in FIG. 5, the measurement result of the joint joined without performing electrical assist, which is a comparative control, and the modified example, the oxide film was replaced with a metal salt, and then joined with electrical assist. The joint measurement results are also shown.

From FIG. 5, it was recognized that the interface strength tended to increase as the bonding temperature increased regardless of the presence or absence of electrical assist.
However, it can be seen that by performing electrical assist, the interface strength increases from a lower temperature and a low deformation amount, and it is possible to obtain a connection portion having an interface strength approximately three times that in the case where electrical assist is not performed. Furthermore, it was found that the interface strength is further increased by performing electric assist after replacing the oxide film at the bonding interface with a metal salt.

The fracture surface of the sample after the tensile test was observed with an SEM (scanning electron microscope). The analysis of copper on the fracture surface on the aluminum side was also conducted.
The SEM photograph of the bonding interface obtained by observation and the copper distribution at the bonding interface on the aluminum side obtained by analysis are shown in FIG. FIG. 6 shows the case where the electric assist was not performed on the upper stage, the case where the electric assist was performed on the lower stage, and the results of the samples when the bonding temperatures are 500 ° C. and 520 ° C., respectively.

From FIG. 6, when electric assist was performed, the mutual elements were detected from the entire fracture surface, but when electric assist was not performed, only a part of the deposit was observed.
Therefore, it is suggested that the high interfacial strength was exhibited when the electric assist was performed because reaction diffusion due to the mutual atoms between the joint surfaces occurred more remarkably.

  Next, observation and elemental analysis were performed using SEM on the bonding interface of the same connection portion as the bonding conditions shown in FIG. The result is shown in FIG. FIG. 7 shows a case where electric assist is not performed on the upper stage, and a case where electric assist is performed on the lower stage. Further, the case where the bonding temperature is 500 ° C. is shown on the left side, and the case where the bonding temperature is 520 ° C. is shown on the right side. And about these four conditions, the line analysis result of the quantity of Al and Cu of the position corresponding to a SEM photograph is shown.

From FIG. 7, when the electric assist was performed, a remarkable reaction layer was observed at the interface, but when the electric assist was not performed, only a slight reaction region was observed.
Therefore, it was suggested that the high interfacial strength was exhibited when the electric assist was performed because the reaction and diffusion by the mutual atoms between the bonding surfaces was promoted by the electric assist.

(Experiment 2) Aluminum / stainless steel (SUS304) joining As two metal members to be joined, as shown in a perspective view in FIG. 8, columnar aluminum having a diameter of 20 mm and a height of 15 mm, and a diameter of 10 mm and a high height. A cylindrical SUS304 stainless steel rope having a length of 15 mm was prepared. The purity of aluminum was 99.9%.
Table 1 shows the chemical composition of the SUS304 stainless steel used.

In the joining apparatus 1 shown in FIG. 2, the joining pressure is set to 6 MPa, the joining temperature is set to 460 ° C., the joining time is set to 15 minutes, the current value and the direction of the current are changed, and aluminum and stainless steel are joined respectively. Thus, a joint was produced.
In addition, for comparison, a joint that was joined without electric assistance (current 0) was also produced.

(Tensile test)
A tensile test was performed using a joint obtained by joining aluminum and stainless steel as a test piece.
As shown in FIG. 9, a tensile test jig is hooked on the end surface of the thick aluminum side, the outside of the stainless steel is sandwiched between the jigs, stress is applied in the direction indicated by the arrow in the figure, and the tensile test is performed. went.
As the tensile tester, 5567 manufactured by INSTRON was used.
Tensile tests were performed on the respective joints that were joined with the joining pressure, joining temperature, and joining time being constant, and the current value and the direction of the current were changed, and the interface strength of the joint was obtained.

  As a result of the tensile test of Experiment 2, FIG. 10 shows changes in the interface strength when the amount of current and the direction of current are changed. Note that FIG. 10 also shows the measurement results of the joint joined without performing the electric assist, which is a comparative control. In addition, the arrows of “Al → SUS304” and “SUS304 → Al” in the legend of FIG. 10 indicate the direction of electron flow, as in FIG.

As can be seen from FIG. 10, in order to obtain a high interface strength, it is necessary to appropriately select the current value and the direction of the current.
In addition, when Al and SUS304 are to be joined, the highest interfacial strength is obtained by flowing an electron flow from SUS304 to Al, that is, a current from Al to SUS304 in a direction of 20 A (about 1.6 V). It can be seen that It should be noted that when current flows in the direction from Al to SUS304, the amount of current that provides peak interfacial strength is larger than when current flows in the direction from SUS304 to Al.

Experiment 2 shows that the joining method by electric assist is applicable also to joining of Al and stainless steel.
Therefore, it was shown that the joining method by electric assist is applicable to various metals.

(Experiment 3) Aluminum / aluminum alloy joining As shown in the perspective view of FIG. 11, as two metal members to be joined, cylindrical aluminum having a diameter of 20 mm and a height of 15 mm, and a diameter of 10 mm and a height of 15 mm. A cylindrical aluminum alloy was prepared. The purity of aluminum was 99.9%.
Table 2 shows the chemical composition of the aluminum alloy used.

In the joining apparatus 1 shown in FIG. 2, the joining pressure is set to 6 MPa, the joining temperature is set to 460 ° C., the joining time is set to 15 minutes, the current value and the direction of current are changed, and aluminum and aluminum alloy are joined respectively. Thus, a joint was produced.
In addition, for comparison, a joint that was joined without electric assistance (current 0) was also produced.

(Tensile test)
A tensile test was performed using a joint obtained by joining aluminum and an aluminum alloy as a test piece.
As shown in FIG. 12, a tensile test jig is hooked on the end surface on the aluminum side having a large diameter, the outside of the aluminum alloy is sandwiched between the jigs, and a stress is applied in the direction indicated by the arrow in the figure to test the tensile test. Went.
As the tensile tester, 5567 manufactured by INSTRON was used.
Tensile tests were performed on the joints that were joined with the joining pressure and joining temperature being constant and the current value and direction of the current were changed, and the interface strength of the joint was obtained.

  As a result of the tensile test of Experiment 3, the change in the interface strength when the current value and the direction of the current are changed is shown in FIG. Note that FIG. 13 also shows the measurement results of the joint joined without performing the electric assist, which is a comparative control. In addition, the arrows of “Al → Al alloy” and “Al alloy → Al” in the legend of FIG. 13 indicate the direction of electron flow, as in FIG.

As shown in FIG. 13, it is understood that the direction of the current needs to be appropriately selected in order to obtain a high interface strength.
In addition, when Al and an Al alloy are to be joined, it can be seen that the interface strength can be increased by causing electrons to flow from Al to the direction of the Al alloy (□ in FIG. 13) and increasing the amount of current.

From Experiment 3, it can be seen that the joining method using electric assist is also applicable to joining of Al and an Al alloy.
Therefore, it was shown that the joining method by electric assist is applicable to various metals.

(Experiment 4) Copper / copper joint As two metal members to be joined, as shown in FIG. 14A, the diameter is 1.2 mm, and the lower end is bent at a curvature radius R = 8.5 mm, and the height is 60 mm. A wire (copper wire) 31 and a copper plate 32 having a length and width of 15 mm and a thickness of 5 mm were prepared.
As shown in FIG. 14B, a load is applied to the copper wire 31 and the copper plate 32 in the direction indicated by the arrow by a pressing jig 34 having a tip 33 on the side of a round bar having a diameter of 5 mm. A current was passed between and heated, and the copper wire 31 and the copper plate 32 were joined to produce a test piece.
14B, the bonding load by the pressing jig 34 is set to 588 N, the bonding temperature is set to 300 ° C., the bonding time is set to 15 minutes, the current value is changed, and the copper wire 31 and the copper plate 32 are bonded to each other. A test piece was prepared.
In addition, for comparison, a joint that was joined without electric assistance (current 0) was also produced.

(Tensile test)
A tensile test was performed using a test piece obtained by joining the copper wire 31 and the copper plate 32.
As shown in FIG. 14C, a tensile test jig was hooked on the copper plate 32, the copper wire side 31 was sandwiched between the jigs, and pulled upward as indicated by an arrow in the figure to perform a tensile test.
A tensile test was performed on each of the test pieces that were joined with the joining pressure, the joining temperature, and the direction of the current being constant and the current value was changed, to obtain the interface strength.

  As a result of the tensile test of Experiment 4, the relationship between the current value and the interface strength is shown in FIG. Note that FIG. 15 also shows the measurement results of the joint joined without performing the electric assist, which is a comparative control.

FIG. 15 shows that it is necessary to appropriately select the current value in order to obtain a high interface strength.
In addition, when joining Cu and Cu, it can be seen that the interface strength can be maximized by applying a current of 10 A (about 0.8 V).
Therefore, it was shown that the joining method by electric assist can be applied even between the same kind of metals.

  The present invention is not limited to the above-described embodiments, and various other configurations can be taken without departing from the gist of the present invention.

  As described above, the method for joining metal members according to the present invention enables joining of metal members at a low temperature and a low deformation amount, and has industrial applicability.

DESCRIPTION OF SYMBOLS 1 Joining device, 2 Pressurization part, 3 Substrate, 4 Ceramic board, 11 Vacuum chamber, 12 Vacuum pump, 13 Heater, 14 Nitrogen gas supply part, 15 Power supply part, 16 Control part, 17 DC power supply, 18 Nitrogen gas supply Tube, 19 Wiring, 20 Thermocouple, 21 Aluminum, 22 Copper, 31 Copper wire (copper wire), 32 Copper plate, 34 Pressing jig

Claims (2)

A method of joining a plurality of metal members,
The first metal member and the second metal member are brought into contact with each other, heated and pressurized, and an electric current is passed between the first metal member and the second metal member so that the first metal member and the second metal member are in contact with each other. Having a step of joining metal members,
In the process of heating and pressurizing and joining the first metal member and the second metal member by passing a current between the first metal member and the second metal member, the temperature is controlled by the heater. ,
The metal member joining method, wherein the first metal member is aluminum, the second metal member is copper, and the current flows in a direction from the second metal member to the first metal member. A method of joining a plurality of metal members,
The first metal member and the second metal member are brought into contact with each other, heated and pressurized, and an electric current is passed between the first metal member and the second metal member so that the first metal member and the second metal member are in contact with each other. Having a step of joining metal members,
In the process of heating and pressurizing and joining the first metal member and the second metal member by passing a current between the first metal member and the second metal member, the temperature is controlled by the heater. ,
The method for joining metal members, wherein the first metal member is aluminum, the second metal member is stainless steel, and the current flows in a direction from the first metal member to the second metal member.