WO2013183560A1

WO2013183560A1 - Method for joining metal members

Info

Publication number: WO2013183560A1
Application number: PCT/JP2013/065200
Authority: WO
Inventors: 真司小山
Original assignee: 国立大学法人群馬大学
Priority date: 2012-06-05
Filing date: 2013-05-31
Publication date: 2013-12-12
Also published as: JPWO2013183560A1; JP6132316B2

Abstract

Metal members are joined through a method which comprises: a step wherein the surface of a first metal member that is formed of aluminum is immersed in an alkali solution or exposed to a vapor that contains an alkali; a subsequent step wherein the surface of the first metal member is boiled in an organic acid solution or exposed to a vapor that contains an organic acid; and a subsequent step wherein the surface of a second metal member is abutted to the surface of the first metal member and heat and pressure are applied thereto, thereby joining the first metal member and the second metal member with each other.

Description

Method of joining metal members

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

Currently, aluminum, or aluminum and steel are heated to 580 to 620 ° C. and joined by brazing.

In the joining by brazing, the joining itself is extremely strong, but it is necessary to remove the oxide film that is a joining inhibiting factor.
Therefore, a flux containing halogen is used for removing the oxide film, and bonding defects such as corrosion after bonding due to the residue of the flux and formation of an unbonded portion (void) due to vaporization of the flux have occurred.
Further, since the bonding pressure has to be increased in order to mechanically destroy the oxide film, there is a problem that the deformation amount at the time of bonding increases.

In order to solve these problems, a solid phase bonding method is known as a method for bonding at a low temperature.
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.

Further, for example, it has been proposed to perform solid-phase bonding after treating a 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, the present invention provides a method for joining metals at a low temperature and in a solid phase.

The method for joining metal members of the present invention is a method for joining a plurality of metal members, wherein the surface of the first metal member made of aluminum is immersed in an alkaline solution or exposed to vapor containing alkali. A step of boiling the surface of the first metal member in an organic acid solution, or exposing the surface of the first metal member to a vapor containing an organic acid, and then a second metal on the surface of the first metal member. A process of joining the first metal member and the second metal member by butting the surfaces of the members, heating and pressurizing them.

In the joining method of the metal member of this invention, a 2nd metal member consists of the same material as a 1st metal member, and a 2nd metal member is also immersed in an alkaline solution like a 1st metal member. Alternatively, after performing the step of exposing to vapor containing alkali, the surface is boiled in an organic acid solution, or the step of exposing to vapor containing organic acid is performed, and then the first metal member and It is also possible to perform the process of joining.
In the method for joining metal members of the present invention, the second metal member can be made of a material different from that of the first metal member.
In the method for joining metal members of the present invention, the organic acid may be one or more selected from formic acid, citric acid, and stearic acid.

According to the metal member joining method of the present invention described above, the surface of the first metal member made of aluminum is formed on the surface of aluminum by being immersed in an alkali solution or exposed to vapor containing alkali. The formed oxide film can be effectively removed or replaced with a hydroxide.
Thereafter, the surface of the first metal member is boiled in an organic acid solution or exposed to vapor containing an organic acid, whereby the hydroxide substituted from the oxide film is replaced with the organic acid salt. .
Thereafter, the surface of the second metal member is abutted against the surface of the first metal member, and the oxide film is removed by heating and pressurizing to join the first metal member and the second metal member. Alternatively, since heating and pressurization are performed in a state where the organic acid salt is substituted, the organic acid salt is decomposed by a thermal decomposition reaction, so that the atomic plane of the first metal member is exposed and the bonding strength is increased. It can be increased.
And since high joint strength is obtained, it becomes possible to obtain sufficiently high joint strength at a temperature lower than before.

According to the above-described present invention, it is possible to obtain a sufficient bonding strength at a bonding temperature lower than that of the prior art.
As a result, it is possible to lower the bonding temperature, simplify the structure of the bonding apparatus, reduce the energy required for heating, and reduce the deformation amount during bonding.

It is a flowchart of the procedure of the joining method of the metal of embodiment of this invention. 2 is a perspective view of a pure aluminum sample used in Experiment 1. FIG. 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 / aluminum joining). A to C are SEM photographs of the bonding interface of a sample that has not been subjected to alkali treatment or organic acid treatment. A to C are SEM photographs of the bonding interface of a sample that has not been subjected to alkali treatment or organic acid treatment. It is an EDX analysis result of the inclusion which exhibited the white of FIG. A to C are SEM photographs of the bonding interface of a sample subjected to an organic acid treatment after an alkali treatment. It is the result of the FT-IR analysis of the sample surface which performed the organic acid process after the alkali process. It is a perspective view of the sample of the aluminum alloy and stainless steel (SUS) used in Experiment 2. It is a figure which shows the method of the tension test in Experiment 2. FIG. It is a figure which shows the result of the tension test of Experiment 2 (aluminum alloy / SUS joining). It is a figure which shows the result of the tension test of Experiment 2 (aluminum alloy / SUS joining). It is a perspective view of the sample of pure aluminum and pure copper used in Experiment 3. It is a figure which shows the result of the tension test of Experiment 3 (aluminum / copper joint). It is a SEM photograph of each fracture surface after a tensile test of each sample of Experiment 3, and a photograph showing the distribution of copper on the fracture surface on the aluminum side. It is a figure which shows the SEM photograph in the joint interface vicinity of the sample of Experiment 3, and distribution of aluminum and copper.

Hereinafter, the best mode for carrying out the invention (hereinafter referred to as an embodiment) will be described.
The description will be given in the following order.
1. 1. Outline of the present invention Embodiment 3 FIG. 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 step of immersing the surface of the first metal member made of aluminum in an alkali solution or exposing the surface of the first metal member to vapor containing alkali, and then the surface of the first metal member with an organic acid. The step of boiling in a solution or exposing to a vapor containing an organic acid, and then bringing the surface of the second metal member into contact with the surface of the first metal member, heating and pressurizing, Joining the metal member and the second metal member.

In the present invention, as the material of the first metal member made of aluminum, for example, an aluminum pure metal or an aluminum alloy can be used. In this case, the oxide film on the surface of aluminum can be removed by dipping in an aqueous alkali solution or by exposing to an alkali-containing vapor.
In the present invention, a metal member made of various metal materials can be used for the second metal member. For example, copper, stainless steel (SUS), or the like can be used for the second metal member.

Further, the first metal member and the second metal member to be joined may be the same material or different materials.
When the first metal member and the second metal member are made of the same material, the surface treatment (alkali treatment + organic acid treatment) is applied to the second metal member as well as the first metal member. It is desirable to do.
Even when the second metal member is made of a material different from that of the first metal member, the same treatment as the first metal member (alkali treatment + organic acid treatment) is performed on the second metal member. Also good.

In the present invention, various alkalis can be used for the alkali solution or the vapor containing the alkali.
For example, sodium hydroxide and sodium carbonate can be used. And the aqueous solution of these alkalis and the water vapor | steam containing an alkali can be used.
When the surface of the metal member is immersed in an alkaline aqueous solution, the alkaline aqueous solution is more preferably boiled. By boiling the alkaline aqueous solution, the oxide film on the surface of the metal member can be efficiently removed.

In the present invention, various organic acids can be used as the organic acid.
For example, at least one selected from formic acid, citric acid, and stearic acid can be used.

In the present invention, the surface of the first metal member made of aluminum is oxidized by immersing the surface of the first metal member in an alkaline solution or exposing the surface of the first metal member to a vapor containing alkali, and including a surface contamination layer formed on the surface of the metal member. The material film is removed or replaced with hydroxide, and aluminum is replaced with aluminum hydroxide.
Since the surface contamination layer becomes a bondability inhibiting factor, the presence of the surface contamination layer reduces the bonding strength. Moreover, in the process of joining a metal member by heating and pressurizing, a hydroxide undergoes a thermal decomposition reaction to expose an atomic plane of metal atoms.
Therefore, the bonding strength can be increased by effectively removing the surface contamination layer or replacing it with a hydroxide.
Thus, since high joint strength can be obtained, it becomes possible to obtain high joint strength at a temperature lower than before.

In addition, since aluminum hydroxide undergoes a thermal decomposition reaction in the step of joining the metal members by heating and pressurizing and the atomic plane of aluminum is exposed, the second metal member (aluminum or other metal) and the metal are exposed. A high bonding strength can be obtained by increasing the metallic contact area between the materials.

Furthermore, in the present invention, after the surface of the first metal member is immersed in an alkali solution or exposed to vapor containing alkali, the surface is further boiled in an organic acid solution, or vapor containing an organic acid. Exposure to aluminum replaces aluminum hydroxide with an organic acid salt of aluminum. When formic acid is used as the organic acid, it is replaced with aluminum formate.
Therefore, the bonding strength can be increased by replacing the surface contamination layer with an organic acid salt.
Thus, since high joint strength can be obtained, it becomes possible to obtain high joint strength at a temperature lower than before.
Moreover, it becomes possible to obtain a high bonding strength from a lower temperature as compared with the case of only the treatment using alkali.

In addition, an aluminum organic acid salt, such as aluminum formate, causes a thermal decomposition reaction in the step of joining metal members by heating and pressurizing, similar to aluminum hydroxide, and the atomic plane of aluminum is exposed. By increasing the metallic contact area between the two metal members (aluminum or other metal) and the metal material, a high bonding strength can be obtained.

As described above, according to the present invention, a sufficiently high bonding strength can be obtained at a temperature lower than that 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, it is possible to obtain a sufficiently high bonding strength even if the pressure at the time of 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. By improving the positional accuracy of the joining, it becomes possible to maintain a high positional accuracy, and it becomes possible to join metal members having complicated shapes that were difficult to weld.
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.

<2. Embodiment>
FIG. 1 shows a flowchart of the procedure of the metal bonding method according to the embodiment of the present invention.
As shown in FIG. 1, first, in step S <b> 11, the surface of the metal member to be joined (first metal member made of aluminum) is immersed in an alkali solution or exposed to vapor containing alkali.
Thereby, the surface contamination layer (for example, chemical adsorption layer such as an oxide film) formed on the surface of the metal member can be effectively removed or replaced with a hydroxide.

As the metal member (first metal member) made of aluminum, aluminum or an aluminum alloy can be used.
Sodium hydroxide, sodium carbonate, and various alkalis can be used for the alkali solution or the vapor containing the alkali. Water can be used as the solvent of the solution. It is also possible to use other various polar solvents.

In addition, after the process of step S11, before progressing to the next step, you may perform the process of wash | cleaning the surface of a metal member (1st metal member), and the process of drying.

Next, in step S12, the surface of the metal member (first metal member) is boiled in an organic acid solution or exposed to vapor containing an organic acid.
Thereby, the hydroxide substituted from the surface contamination layer is further substituted with an organic acid salt.

As the organic acid, formic acid, citric acid, stearic acid, and other organic acids can be used. As the solvent, water or various polar solvents can be used.

In addition, after the process of step S12, before proceeding to the next step, the surface of the metal member (first metal member) may be cleaned or dried.

Next, in step S13, the surfaces of the two metal members (the first metal member and the second metal member) are brought into contact with each other and joined by heating and pressing.
As a result, since the surface contamination layer is removed or replaced with the organic acid salt, heating and pressurization are performed, so that the organic acid salt is decomposed by a thermal decomposition reaction, so that the metal of the first metal member The atomic plane of the atoms is exposed, and the bonding strength can be increased. Since a high bonding strength can be obtained, it is possible to obtain a high bonding strength at a lower temperature and lower deformation than in the past.
That is, it is possible to lower the heating temperature and the applied pressure during bonding as compared to the conventional bonding method in which the steps S11 and S12 are not performed.

For the second metal member, the same material as the first metal member or a material different from the first metal member can be used.
When the second metal member is made of the same material as the first metal member, it is desirable to perform the steps S11 and S12 on the second metal member.
Even when the second metal member is made of a material different from that of the first metal member, the second metal member may be processed in the same manner as in the steps S11 and S12.

In the present embodiment, an oxide film (aluminum oxide) is easily formed as a surface contamination layer in aluminum or an aluminum alloy used as the first metal member.
In the process of step S11, by using an aqueous solution or water vapor containing sodium hydroxide or sodium carbonate, the oxide film (aluminum oxide) which is a surface contamination layer is removed or replaced with hydroxide, and aluminum Is replaced by aluminum hydroxide.
When immersed in an aqueous solution, the aqueous solution is more preferably boiled. By boiling the aqueous solution, the oxide film can be efficiently removed.
Moreover, you may perform the process of wash | cleaning with alcohol etc. and the process of drying the surface of a metal member after that as needed.

In the step S12, for example, formic acid, citric acid, or stearic acid can be used as the organic acid.
By using these organic acids, the aluminum hydroxide substituted from the surface contamination layer is replaced with an organic acid aluminum salt (aluminum formate, aluminum citrate, aluminum stearate) which is an organic acid salt.
Moreover, you may perform the process of wash | cleaning with alcohol etc. and the process of drying the surface of a metal member after that as needed.

In the process of step S13, as the second metal member to be joined to the first metal member, in addition to the same type of material (aluminum or aluminum alloy), different materials such as copper and stainless steel (SUS) are also used. It is possible to use.
In step S13, since the organic acid aluminum in which the oxide film is replaced is thermally decomposed, the atomic plane of aluminum is exposed, so that the bonding strength with the second metal member can be increased. As a result, it is possible to obtain a high bonding strength at a lower temperature than in the past.
From the same viewpoint as the temperature, it is possible to obtain a sufficiently high bonding strength even if the pressure at the time of bonding is lowered. As a result, joining at a low pressure is possible, and the amount of deformation at the time of joining can be reduced, and high positional accuracy can be maintained.
In addition, since the bonding can be performed at a low temperature and a low pressure, energy efficiency can be improved.

Note that if the step S11 is omitted and only the steps S12 and S13 are performed on the first metal member using aluminum or an aluminum alloy, a sufficient bonding strength improvement effect cannot be obtained.
This is presumably because the oxide film of aluminum is not replaced with an organic acid alone or is not easily replaced.
Once the oxide film is replaced with aluminum hydroxide, it can be easily replaced with organic acid aluminum.

According to the above-described embodiment, the surface of the metal member is obtained by immersing the surface of the metal member to be joined (first metal member made of aluminum) in an alkaline solution or exposing the surface to vapor containing alkali. The surface contamination layer (for example, a chemisorption layer such as an oxide film) formed in (1) can be effectively removed or replaced with a hydroxide.
Then, the surface of the metal member (first metal member made of aluminum) is boiled in an organic acid solution, or exposed to a vapor containing an organic acid, thereby replacing the hydroxide substituted from the surface contamination layer. An organic acid salt can be substituted.
Furthermore, the surface contamination layer was removed or replaced with an organic acid salt by joining the surfaces of the two metal members (first metal member and second metal member) with each other but heated and pressurized. In this state, since heating and pressurization are performed, the organic acid salt is decomposed by causing a thermal decomposition reaction, so that the atomic planes of the metal atoms of the first metal member are exposed and the bonding strength can be increased.
As a result, a high bonding strength can be obtained, so that a high bonding strength can be obtained at a low temperature. Compared to the conventional case in which a treatment process using an alkali and a treatment process using an organic acid are not performed, The heating temperature can be lowered. That is, bonding in a solid state can be performed at a low temperature.
And even if the pressure at the time of joining is lowered, it becomes possible to obtain a sufficiently high joining strength, and joining in a solid phase state is possible at a low pressure, thereby reducing the deformation amount at the time of joining. Therefore, the bonding position accuracy can be improved. By improving the positional accuracy of the joining, it becomes possible to maintain a high positional accuracy, and it becomes possible to join metal members having complicated shapes that were difficult to weld.
In addition, since the bonding can be performed at a low temperature and a low pressure, energy efficiency can be improved. For example, it becomes possible to reduce power consumption, fuel for heating, time required for joining, and the like.

<3. Example>
Next, the metal members were actually joined according to the present invention, and the characteristics were examined.

(Experiment 1) Aluminum / aluminum bonding As shown in the perspective view of FIG. 2, two columnar pure aluminums having a diameter of 20 mm and a height of 15 mm were prepared as two metal members to be bonded.
Then, the joining surfaces of the two pure aluminums were mechanically polished up to number 800 with emery paper.
The chemical composition of the pure aluminum used is as shown in Table 1 below.

(Alkaline treatment only)
Two pure aluminums were boiled in an aqueous sodium hydroxide solution for 30 seconds and then washed with methanol for 10 seconds.
Thereafter, in a vacuum furnace, the joining time was set to 30 minutes, and two pieces of pure aluminum were joined by heating and pressurizing.
And the joining pressure to set was changed into 3MPa and 6MPa, joining temperature was changed, and each joined metallic member, and produced the coupling.

(Alkali treatment and organic acid treatment)
Two pure aluminums were boiled in an aqueous sodium hydroxide solution for 30 seconds and then washed with methanol for 10 seconds.
Further, the pure aluminum joint surface was boiled in formic acid for 60 seconds and then washed with distilled water for 10 seconds.
Thereafter, in a vacuum furnace, the joining time was set to 30 minutes, and two pieces of pure aluminum were joined by heating and pressurizing.
And the joining pressure to set was 6 Mpa, joining temperature was changed, and each metal member was joined, and the joint was produced.

(No processing)
As a comparative control, a sample in which neither alkali treatment nor organic acid treatment was performed was prepared.
Two pieces of pure aluminum were joined as they were (as they were polished) in a vacuum furnace by setting the joining time to 30 minutes and heating and pressurizing them.
And the joining pressure to set was changed into 3MPa and 6MPa, joining temperature was changed, and each joined metallic member, and produced the coupling.

(Organic acid treatment only)
Moreover, the sample which performed only the organic acid process was produced as a comparison control.
In formic acid, each joining surface of two pure aluminums was boiled for 60 seconds and then washed with distilled water for 10 seconds.
Thereafter, in a vacuum furnace, the joining time was set to 30 minutes, and two pieces of pure aluminum were joined by heating and pressurizing.
And the joining pressure to set was 6 Mpa, joining temperature was changed, and each metal member was joined, and the joint was produced.

(Tensile test)
Further, the joint obtained by joining two pure aluminums is processed to produce a test piece that is processed so that the diameter in the vicinity of the joining surface becomes small as shown in a side view in FIG. did.
A tensile test was performed on the test piece by hooking a jig for a tensile test to a portion with a reduced diameter.
As the tensile tester, 5567 manufactured by INSTRON was used.
Note that samples with very large deformation at the time of joining and samples that could not be joined correctly were excluded from the tensile test because they could not be measured.
The results of the tensile test for each sample are summarized in FIG.

In the case of no treatment, the joining temperature could be increased up to 590 ° C. at a joining pressure of 3 MPa and up to 540 ° C. at a joining pressure of 6 MPa, and the tensile strength increased as the joining temperature was increased. However, when the joining temperature is further increased, deformation at the time of joining increases, and a predetermined test piece cannot be produced. And the tensile strength did not reach the 0.2% proof stress (30 MPa) of aluminum.

When the treatment was performed with an aqueous sodium hydroxide solution, it was possible to join at a bonding pressure of 6 MPa at a temperature 100 ° C. or more lower than that without treatment. The joining temperature for obtaining the joining strength reaching the 0.2% proof stress (30 MPa) of aluminum was about 555 ° C. at a joining pressure of 3 MPa and about 450 ° C. at a joining pressure of 6 MPa.
And since there is a correlation between the bonding temperature and the amount of deformation at the time of bonding, the deformation can be suppressed from 40% or more without treatment to about 10%.

Further, when the treatment with formic acid is carried out following the treatment with the aqueous sodium hydroxide solution, a higher connection strength can be obtained from a lower temperature than in the case of only the modification treatment with the aqueous sodium hydroxide solution. FIG. 4 shows that the same connection strength can be obtained at a temperature as low as 20 to 30 ° C. at a bonding pressure of 6 MPa.

In addition, when it joined only by processing with formic acid, joining strength was weak, and the junction part broke in the middle of producing the test piece shown in FIG. Therefore, in FIG. 4, the tensile strength is set to zero. That is, although it was possible to join in the range of 440 to 480 ° C., sufficient joining strength was not obtained.

Here, the structure in the vicinity of the bonding interface after the bonding step was observed with a SEM (scanning electron microscope) in a sample that was not subjected to alkali treatment or organic acid treatment (no treatment).
SEM photographs of the bonding interface when the bonding pressure is 3 MPa and the bonding temperature of 590 ° C. are shown in FIGS. 5A to 5C, and SEM photographs of the bonding interface when the bonding pressure is 6 MPa and the bonding temperature is 540 ° C. are shown in FIGS. Show. 5 and 6, FIG. A shows a photograph of the central portion, FIG. B shows a photograph of an intermediate portion between the central portion and the end portion, and FIG. C shows a photograph of the end portion.

As shown in FIGS. 5A to 5C, when the bonding pressure was 3 MPa and the bonding temperature was 590 ° C., white inclusions were observed in the vicinity of the bonding interface regardless of the observation position.
As shown in FIGS. 6A to 6C, white inclusions were observed in the vicinity of the bonding interface when the bonding pressure was 6 MPa and the bonding temperature was 540 ° C.

Further, qualitative analysis was performed by EDX on the white inclusion in FIG. The results of this EDX analysis are shown in FIG.
From FIG. 7, Al and O are detected strongly. From this, it was suggested that the white inclusions observed in the vicinity of the bonding interface were aluminum oxides. And since this white inclusion was present in the joint surface, it is considered that the self-diffusion of aluminum was inhibited and the joint strength was low.

Next, in the sample subjected to the organic acid treatment after the alkali treatment (composite modification treatment), the structure in the vicinity of the joining interface after the joining step was observed with a SEM (scanning electron microscope).
8A to 8C show SEM photographs of the bonding interface when the bonding pressure is 6 MPa and the bonding temperature is 440 ° C. 8A shows a photograph of the central portion, FIG. 8B shows a photograph of an intermediate portion between the central portion and the end portion, and FIG. 8C shows a photograph of the end portion.

As shown in FIGS. 8A to 8C, when the joining pressure is 6 MPa and the joining temperature is 440 ° C., the joining lines are discontinuous, and aluminum is in close contact with each other in some regions.
Here, compared with the sample without treatment, the white inclusions observed in the vicinity of the bonding interface were not recognized in the sample subjected to the composite modification treatment. This is presumably because the processed layer and the processed layer including the oxide film formed on the bonding surface of aluminum were modified and removed by the alkali treatment. As a result, as the aluminum is plastically deformed due to the increase in the bonding temperature, the area where the aluminum is in close contact with each other increased. Therefore, in the result of FIG. 4, it is estimated that the bonding strength increased with the increase in the bonding temperature regardless of the bonding pressure. The

Next, an aluminum surface was analyzed by FT-IR for a sample that had been subjected to alkali treatment and organic acid treatment under the same conditions as in Experiment 1. As a comparative control, a sample that was not subjected to the modification treatment immediately after polishing was similarly analyzed.
The analysis result of FT-IR is shown in FIG.

As shown in FIG. 9, in the sample subjected to complex modification ^treatment, 1740 cm ^-1, 1640 cm -1, it is caused a peak at 1400 cm ^-1.
Among, 1740 cm ^-1 and 1400 cm ^-1 vicinity, respectively, a carboxy group, are known to be the peak of the ether bond. Further, it is known that the vicinity of 1640 cm ⁻¹ is a bicarbonate peak. Therefore, when the combined reforming treatment using sodium hydroxide and formic acid was performed, these peaks tended to increase as compared with the case where no reforming was performed. It was suggested that aluminum formate was formed on the surface. This is supported by the fact that the basic salt Al (OH) (HCOO) ₂ .H ₂ O is obtained when Al (OH) ₃ is dissolved in 90% or more of heated formic acid. Yes.

Here, aluminum formate, which is an aluminum formate, undergoes a dehydration reaction in the temperature range near 100 ° C. and releases H ₂ O, and then thermally decomposes into Al ₂ O ₃ in the temperature range near 300 ° C. Has been.
Therefore, under the conditions of this experiment, since the bonding temperature is set to 300 ° C. or higher, first, a dehydration reaction occurs in the temperature range near 100 ° C., and a part of the surface of the aluminum substrate is exposed. It is considered that further exposure of the base surface of aluminum was caused by the thermal decomposition of aluminum formate into Al ₂ O ₃ in the temperature range.
By these reactions, it is presumed that the reduction of the proportion of the oxide film existing on the bonding surface of aluminum, that is, the destruction of the oxide film, occurred, and the self-diffusion of aluminum atoms proceeded in the initial stage of bonding.
As a result, it is considered that the bonding strength increased from a lower temperature, and sufficient strength was obtained at a lower temperature compared to the case where the modification treatment was not performed.

From the above results, in joining aluminum to each other, by performing a combined modification treatment of alkali treatment and organic acid treatment on aluminum, the joining strength is improved, and the temperature is lower than when no treatment is performed. It can also be seen that joining is possible with a low deformation amount.

(Experiment 2) Aluminum alloy / SUS bonding As shown in the perspective view of FIG. 10, a cylindrical high silicon aluminum alloy having a diameter of 22 mm and a height of 20 mm, and a diameter of 10 mm and a high as two metal members to be bonded. A cylindrical SUS304 stainless steel having a length of 15 mm was prepared.
The chemical composition of the used SUS304 stainless steel is shown in Table 2, and the chemical composition of the high silicon aluminum alloy used is shown in Table 3.

(Alkaline treatment only)
The joint surface of the aluminum alloy was boiled in an aqueous sodium hydroxide solution for 20 seconds and then ultrasonically cleaned in acetone.
Thereafter, the aluminum alloy and SUS304 stainless steel were joined in a vacuum furnace by heating and pressurizing with a joining time of 15 minutes and a joining pressure of 6 MPa.
And joining temperature was changed and metal member was joined, respectively, and the joint was produced.

(Alkali treatment and organic acid treatment)
The joint surface of the aluminum alloy was boiled in an aqueous sodium hydroxide solution for 20 seconds and then ultrasonically cleaned in acetone.
Subsequently, the joint surface of the aluminum alloy was boiled in formic acid for 3 minutes.
Thereafter, the aluminum alloy and SUS304 stainless steel were joined in a vacuum furnace by heating and pressurizing with a joining time of 15 minutes and a joining pressure of 6 MPa.
And joining temperature was changed and metal member was joined, respectively, and the joint was produced.

(No processing)
As a comparative control, a sample in which neither alkali treatment nor organic acid treatment was performed was prepared.
In a vacuum furnace, the aluminum alloy and SUS304 stainless steel were joined by heating and pressurizing with a joining time of 15 minutes and a joining pressure of 6 MPa.
And joining temperature was changed and metal member was joined, respectively, and the joint was produced.

(Tensile test)
Furthermore, the joint obtained by joining the aluminum alloy and SUS304 stainless steel was used, and the joint was used as it was as a test piece without performing the process of reducing the diameter near the joint surface as in Experiment 1.
As shown in FIG. 11, with respect to this test piece, a jig for tensile test is hooked on the end surface on the aluminum alloy side having a large diameter, and the outside of SUS304 stainless steel is sandwiched by the jig, and an arrow in the figure indicates A tensile test was performed by applying stress in the direction shown.
As the tensile tester, 5567 manufactured by INSTRON was used.
The result of the tensile test of each sample is shown in FIG.

Further, under the conditions of no treatment and alkali treatment + organic acid treatment as described above, the joint pressure was set to 12 MPa, and the other conditions were made in the same manner to produce a joint, and this joint was used as a test piece. A test was conducted.
FIG. 13 shows the result of the tensile test of each sample in which the joining pressure is set to 12 MPa.

As can be seen from FIGS. 12 and 13, the tensile strength is 510 ° C. when the joining pressure is 6 MPa and 480 ° C. when the joining pressure is 12 MPa, and the tensile strength sufficiently exceeds the 0.2% proof stress (30 MPa) of aluminum. Connection strength that can be achieved is obtained, and joining is possible at a lower temperature and with a lower amount of deformation than when no treatment is performed.
From FIG. 12, it can be seen that the effect is reduced by treatment with sodium hydroxide alone without surface modification with formic acid.

From the above results, even in the joining of aluminum alloy and stainless steel (SUS), the joint strength is improved and the treatment is not performed by subjecting the aluminum alloy to a combined modification treatment of an alkali treatment and an organic acid treatment. It can be seen that joining is possible at a lower temperature and a lower deformation amount than in the case.

(Experiment 3) Pure Aluminum / Pure Copper Joining As two metal members to be joined, as shown in a perspective view in FIG. 14, a columnar pure aluminum having a diameter of 20 mm and a height of 15 mm, and a diameter of 10 mm and a height. 15 mm columnar pure copper was prepared.
The purity of the used pure aluminum and pure copper is 99.9%.

(Alkaline treatment only)
The bonded surface of pure aluminum was boiled in an aqueous sodium hydroxide solution for 20 seconds and then washed with methanol for 10 seconds.
Then, pure aluminum and pure copper were joined by heating and pressurizing in a vacuum furnace with a joining time of 15 minutes and a joining pressure set to 12 MPa.
And joining temperature was changed and metal member was joined, respectively, and the joint was produced.

(Alkali treatment and organic acid treatment)
The bonded surface of pure aluminum was boiled in an aqueous sodium hydroxide solution for 20 seconds and then washed with methanol for 10 seconds.
Subsequently, the joining surface of pure aluminum was boiled in formic acid for 60 seconds.
Then, pure aluminum and pure copper were joined by heating and pressurizing in a vacuum furnace with a joining time of 15 minutes and a joining pressure set to 12 MPa.
And joining temperature was changed and metal member was joined, respectively, and the joint was produced.

(No processing)
As a comparative control, a sample in which neither alkali treatment nor organic acid treatment was performed was prepared.
In a vacuum furnace, pure aluminum and pure copper were joined by setting the joining time to 15 minutes, setting the joining pressure to 12 MPa, and heating and pressurizing.
And joining temperature was changed and metal member was joined, respectively, and the joint was produced.

(Tensile test)
Furthermore, using the joint obtained by joining pure aluminum and pure copper, the processing for reducing the diameter near the joint surface as in Experiment 1 was not performed, and the joint was directly used as a test piece as in Experiment 2. It was.
In the same manner as in Experiment 2 shown in FIG. 11, a tensile test jig was hooked on the end surface on the pure aluminum side having a large diameter, and the outside of pure copper was sandwiched between the test pieces with the jig. A tensile test was performed by applying stress in the direction indicated by the arrow.
As the tensile tester, 5567 manufactured by INSTRON was used.
The result of the tensile test of each sample is shown in FIG.

As can be seen from FIG. 15, a joint strength comparable to the 0.2% proof stress of aluminum is obtained at a joining temperature of 773 K (500 ° C.), and the joining can be performed at a lower temperature and with a lower deformation amount than when no treatment is performed. It becomes possible.
FIG. 15 shows that the effect is reduced by treatment with only sodium hydroxide without surface modification with formic acid.

From the above results, even in the joining of pure aluminum and pure copper, the joint strength is improved by performing combined modification treatment of alkali treatment and organic acid treatment on pure aluminum, compared with the case where no treatment is performed. Thus, it can be seen that the joining is possible at a lower temperature and a lower deformation amount.

Here, for each sample, the copper-side fracture surface and the aluminum-side fracture surface after the tensile test when the bonding temperature was 773 K (500 ° C.) were observed with an SEM (scanning electron microscope). Further, surface analysis of the fracture surface on the aluminum side was performed by EDX (energy dispersive X-ray analysis).
The SEM photograph of each fracture surface and the copper distribution on the fracture surface on the aluminum side are shown in FIG.
As shown in FIG. 16, by performing alkali treatment or composite modification treatment (alkali treatment and organic acid treatment), it is more likely that each metal adheres more significantly to the fracture surface than when no treatment is performed. Thus, the ratio of the copper element detected from the fracture surface on the pure aluminum side also increases.

For each sample, the structure in the vicinity of the bonding interface after the bonding step when the bonding temperature was 773 K (500 ° C.) was observed with a SEM (scanning electron microscope). Further, line analysis in the vicinity of the bonding interface was performed by EDX (energy dispersive X-ray analysis).
FIG. 17 shows the SEM photograph near the bonding interface and the distribution of aluminum and copper.
As shown in FIG. 17, by performing alkali treatment or composite modification treatment (alkali treatment and organic acid treatment), a layered structure is uniformly formed as compared to the case where no treatment is performed. This is presumed that by performing alkali treatment or composite modification treatment (alkali treatment and organic acid treatment), the atomic planes of pure aluminum and pure copper were brought into close contact, and the reaction between the metals proceeded uniformly.

The present invention is not limited to the above-described embodiments and examples, 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 makes it possible to join metal members at low temperatures and low deformation amounts, and has industrial applicability.

Claims

A method of joining a plurality of metal members,
Immersing the surface of the first metal member made of aluminum in an alkali solution or exposing it to vapor containing alkali;
Then, boiling the surface of the first metal member in an organic acid solution, or exposing to a vapor containing an organic acid,
Thereafter, the surface of the first metal member is brought into contact with the surface of the second metal member, and heated and pressurized to join the first metal member and the second metal member. Member joining method.
The second metal member is made of the same material as the first metal member,
Similarly to the first metal member, the second metal member is immersed in an alkali solution or exposed to a vapor containing alkali, and then the surface is boiled in an organic acid solution. Or the process of exposing to the vapor | steam containing an organic acid is performed, and the process of joining with a said 1st metal member is performed after that. The joining method of the metal member of Claim 1.
The metal member joining method according to claim 1, wherein the second metal member is made of a material different from that of the first metal member.
The method for joining metal members according to claim 1, wherein the organic acid is at least one selected from formic acid, citric acid, and stearic acid.