JP7637944B2 - Joining Method - Google Patents

Description

This disclosure relates to a joining method. In particular, this disclosure relates to a joining method using an insert material.

Various methods for joining materials, particularly metal materials, have been considered. One of the joining methods involves placing an insert material between the parts to be joined and joining the parts together.

For example, Patent Document 1 discloses a method for joining aluminum alloy members using one or more metal or alloy powders selected from silicon, magnesium, zinc, and aluminum as an insert material (brazing material). Patent Document 1 also discloses that joining must be performed in an inert gas atmosphere or in a vacuum to avoid or suppress oxidation of the joint during joining.

Patent Document 2 discloses a brazing sheet (sheet for soldering) for joining aluminum alloy members in an inert gas atmosphere or in a vacuum. Patent Document 2 also discloses that by including magnesium in the brazing sheet, it is possible to avoid or suppress the oxide film on the brazing sheet surface from interfering with joining.

Patent Document 3 discloses that when joining aluminum alloy members using an insert material (brazing material), reoxidation of the joining surface is avoided or suppressed by switching from vacuum evacuation to the introduction of an inert gas at a specified timing.

JP 2015-44208 A JP 2018-35386 A JP 2019-155453 A

In the joining methods of Patent Documents 1 to 3, in order to obtain a practically sufficient joining strength when joining metal materials, it was necessary to supply an inert gas throughout the entire joining process, or throughout most of the joining process. Therefore, despite the fact that inert gas is expensive, a large amount of inert gas was used during joining. For this reason, the inventors have found a problem in that there is a demand for a method of joining metal materials that can obtain a practically sufficient joining strength while reducing the amount of inert gas used as much as possible.

This disclosure has been made to solve the above problems. In other words, the purpose of this disclosure is to provide a method for joining materials that can obtain sufficient joining strength for practical use while minimizing the amount of inert gas used.

The present inventors have conducted extensive research to achieve the above object and have completed the bonding method of the present disclosure. The bonding method of the present disclosure includes the following aspects.
<1> A method for joining a first member and a second member, comprising the steps of:
disposing an insert material between the first member and the second member; and applying a load to the insert material through at least one of the first member and the second member while supplying an inert gas, heating the first member, the insert material, and the second member, and joining the first member and the second member by forming a liquid phase of the insert material;
Including,
The insert material has a lower melting point than the first member and the second member, and after the insert material forms a liquid phase, the supply amount of the inert gas is reduced.
Joining method.
<2> The joining method described in <1>, wherein the insert material is composed of a metal or alloy that undergoes a eutectic reaction with the first member and the second member, and the amount of the inert gas supplied is reduced after the insert material forms a liquid phase by the eutectic reaction.
<3> The joining method described in <1> or <2>, in which the liquid phase formation of the insert material is detected by a change in the reaction force of the load applied to the insert material or a change in the thickness of the insert material.
<4> The joining method according to any one of <1> to <3>, wherein at least one of the first member and the second member is made of an aluminum alloy.
<5> The joining method described in <4>, wherein the insert material is made of metallic zinc or a zinc alloy.
<6> The joining method described in <5>, in which a formate coating is formed in advance on one or both sides of the insert material.

According to the present disclosure, it is possible to provide a method for joining metal materials that provides sufficient joining strength for practical use while minimizing the amount of inert gas used by supplying inert gas until the insert material forms a liquid phase and then reducing the amount of inert gas supplied.

FIG. 1 is a schematic cross-sectional view showing one embodiment of the bonding method of the present disclosure. FIG. 2 shows the changes over time in bonding pressure and bonding temperature during bonding of the samples of the example and comparative examples 1 and 2. FIG. 3 is a graph showing the bonding strength of the samples of Example 1 and Comparative Examples 1 and 2.

Below, aspects of the bonding method of the present disclosure are described in detail. Note that the following aspects do not limit the bonding method of the present disclosure.

Without being bound by theory, we will explain why the diffusion bonding disclosed herein can achieve sufficient bonding strength for practical use while minimizing the amount of inert gas used.

When the joining surfaces of the first and second members and the insert material are oxidized by oxygen in the joining atmosphere, the high melting point oxide film reduces the wettability of the molten liquid of the insert material. Then, a part of the molten liquid of the insert material is discharged to the outside of the joint without interdiffusing with the joining surfaces of the first and second members, and the oxide film remains in the joint. When a load is applied to the joint of the joint thus obtained, brittle fracture occurs in the oxide film. As a result, the joint strength decreases. Therefore, an inert gas is supplied to the joining surfaces of the first and second members and the insert material until the insert material melts and forms a liquid phase. Then, after the insert material forms a liquid phase, the joining surfaces are covered with the liquid phase, making it difficult for oxygen in the joining atmosphere to come into contact with the joining surfaces. Therefore, after the insert material forms a liquid phase, the amount of inert gas supplied can be reduced.

The constituent elements of the joining method disclosed herein, which were perfected based on the findings and other information discussed thus far, are described below.

<Joining method>
The bonding method of the present disclosure includes an insert material placement step and a bonding step. The bonding method of the present disclosure may also include a formate coating step as an option. Each step will be described below with reference to the drawings. Figure 1 is a schematic cross-sectional view showing one embodiment of the bonding method of the present disclosure.

<Insert material placement process>
1, an insert member 20 is disposed between a first member 11 and a second member 12. The first member 11 and the second member 12 are members to be joined.

There are no particular limitations on the combination of the first member 11 and the second member 12 with the insert material 20, as long as the insert material 20 has a lower melting point than the first member 11 and the second member 12, and the first member 11 and the second member 12 can be joined using the insert material 20. The first member 11 and the second member 12 may be made of the same material or different materials.

Typically, the first member 11 and the second member 12 are made of a metallic material, and the insert material 20 is made of a metallic material that can be alloyed with the first member 11 and the second member. Unless otherwise specified, in this specification, "metallic material" means a metal or an alloy. "Metal" means an unalloyed simple metal, and "alloy" means a composition containing two or more elements that are alloyed with each other. "Consists of" means that a material other than the material in question may be contained, and the content of the material in question may be, for example, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more by mass.

The joining method of the present disclosure is particularly useful when the first member 11, the second member 12, and the insert material 20 are metal materials that are easily oxidized and whose oxide films tend to adversely affect the joining. Examples of such metal materials include aluminum metal and aluminum alloys.

The purity of metallic aluminum may be, by mass %, 90% or more, 95% or more, 97% or more, 98% or more, or 99% or more, or may be 100%. For example, metallic aluminum with a purity of 90% or more can be said to contain 90% or more aluminum, with the remainder being unavoidable impurities. The same applies when the purity is 95% or more, 97% or more, 98% or more, or 99% or more. In this specification, "unavoidable impurities" refers to impurities contained in raw materials or impurities mixed in during the manufacturing process, which cannot be avoided, or which would result in a significant increase in manufacturing costs if avoided. Impurities mixed in during the manufacturing process include substances that are included to the extent that they do not affect the bonding strength, etc., for manufacturing reasons.

There is no particular restriction on the type of aluminum alloy as long as there is no particular difficulty in joining. In the joining method of the present disclosure, it is preferable that the insert material 20 is made of an alloy that undergoes a eutectic reaction with the first member 11 and the second member 12. From this perspective, the first member 11 and the second member 12 may more typically be made of an aluminum alloy containing silicon. Such an aluminum alloy is easily oxidized during joining, and is also preferable from the viewpoint of the usefulness of the oxidation suppression effect of the joining method of the present disclosure. Examples of such aluminum alloys include aluminum alloys for wrought materials and aluminum alloys for casting that contain silicon. Unless otherwise specified, in this specification, aluminum alloys for wrought materials include aluminum alloys for forging, and aluminum alloys for casting include aluminum alloys for die casting.

In the wrought aluminum alloys and cast aluminum alloys containing silicon, the silicon content may be, for example, 0.1% or more, 0.5% or more, 0.7% or more, 1.0% or more, 1.5% or more, 2.0% or more, 4.0% or more, 6.0% or more, or 8.0% or more by mass, and may be 24.0% or less, 22.0% or less, 20.0% or less, 18.0% or less, 16.0% or less, 14.0% or less, 12.0% or less, or 10.0% or less. In addition to silicon, both the wrought aluminum alloys and cast aluminum alloys may contain, for example, copper, magnesium, zinc, iron, manganese, nickel, titanium, lead, tin, and chromium, depending on the application, in order to improve age hardenability, corrosion resistance, heat resistance, and/or wear resistance. The total content of those elements other than silicon may be, for example, in mass%, 0.05% or more, 0.1% or more, 0.5% or more, 1.0% or more, 3.0% or more, or 5.0% or more, and may be 15.0% or less, 13.0% or less, 10.0% or less, or 7.0% or less. The remainder may be aluminum and unavoidable impurities.

Examples of aluminum alloys for wrought materials include alloys containing, by mass%, 0.01-5.0% copper, 0.1-1.5% silicon, 0.01-3.0% magnesium, and 0-2.0% zinc, iron, manganese, nickel, titanium, lead, tin, and chromium in total, with the remainder being aluminum and unavoidable impurities. In particular, aluminum alloys for wrought materials may be, for example, the 1000 series, 2000 series, 3000 series, 4000 series, 6000 series, or 7000 series of the Japanese Industrial Standards, and in particular the 4000 series, 6000 series, or 7000 series.

Examples of aluminum alloys for casting include alloys containing, by mass%, 0.10-5.0% copper, 4.0-24.0% silicon, 0.1-2.0% magnesium, and 0-5.0% zinc, iron, manganese, nickel, titanium, lead, tin, and chromium in total, with the remainder being aluminum and unavoidable impurities. In particular, aluminum alloys for casting may be, for example, AC2A, AC2B, AC2C, AC3A, AC4B, AC4C, AC4CH, AC4D, AC8A, AC8B, AC8C, AC9A, or AC9B, etc., according to the Japanese Industrial Standards.

In particular, AC2C may contain, for example, by mass, 0.5-1.1% copper, 6.5-7.5% silicon, 0.2-0.4% magnesium, 0-0.1% zinc, 0-0.1% manganese, 0-0.1% nickel, and 0-0.1% tin, with the remainder being aluminum and unavoidable impurities. In this specification, unless otherwise specified, 0% means that the component does not need to be contained.

The aluminum alloy for casting may be an alloy for die casting, for example an alloy containing, by mass%, 0.10-5.0% copper, 5.0-20.0% silicon, 0-2.0% magnesium, 0-5.0% zinc, iron, manganese, nickel, titanium, lead, tin, and chromium in total, with the balance being aluminum and unavoidable impurities. In particular, the aluminum alloy for die casting may be, for example, ADC3, ADC10, ADC10Z, ADC12, ADC12Z, or ADC14, etc., as specified by the Japanese Industrial Standards, and in particular, ADC10, ADC12, and ADC14, etc.

In particular, ADC12 may contain, for example, by mass, 1.5-3.5% copper, 9.6-12.0% silicon, 0-0.3% magnesium, 0-0.3% zinc, 0-0.5% magnesium, 0-0.5% nickel, and 0-0.3% tin, with the remainder being aluminum and unavoidable impurities.

As described above, the insert material 20 is not particularly limited as long as it is a material that has a lower melting point than the first member 11 and the second member 12. As the insert material 20, a well-known material that can be used in brazing, liquid phase diffusion bonding, etc. can be used. Such an insert material 20 is preferably composed of a metal or alloy that undergoes a eutectic reaction with the first member 11 and the second member 12. This generally gives the insert material 20 a lower melting point. As a result, at the time of bonding, the bonded portion of the first member 11 and the second member 12 is surrounded by the liquid phase of the insert material 20 at a lower temperature, improving the effect of inhibiting oxidation of the bonded portion.

When the first member 11 and the second member 12 are made of metallic aluminum or an aluminum alloy, the insert material 20 as described above may be made of metallic zinc or a zinc alloy, for example.

When the insert material 20 is made of metallic zinc, the purity of the metallic zinc may be, in mass %, 90% or more, 95% or more, 97% or more, 98% or more, or 99% or more, or may be 100%. For example, metallic zinc with a purity of 90% or more can be said to contain 90% or more of zinc, with the remainder being unavoidable impurities. The same applies when the purity is 95% or more, 97% or more, 98% or more, or 99% or more.

The insert material 20 may be made of a zinc alloy. A zinc alloy means a composition containing, in addition to zinc, an element that alloys with zinc. The content of such alloying elements may be, in mass%, 0.1% or more, 0.5% or more, 1% or more, or 3% or more, and may be 15% or less, 10% or less, 7% or less, or 5% or less. When multiple alloying elements are contained, the total content is the total content. Examples of such alloying elements include copper, aluminum, titanium, lead, tin, cadmium, and iron. It can be said that such a zinc alloy contains, in mass%, 0.1 to 15% of the alloying elements, with the remainder being zinc and unavoidable impurities.

The thickness of the insert material 20 may be appropriately determined taking into consideration the joining conditions, etc., so that substances originating from the insert material 20 do not remain in the joint after joining and adversely affect the joint strength. The thickness of the insert material 20 may be 0.2 mm or more, 0.4 mm or more, or 0.6 mm, and may be 1.6 mm or less, 1.4 mm or less, 1.2 mm or less, 1.0 mm or less, or 0.8 mm or less.

<Joining process>
As shown in FIG. 1, from a state in which the insert material 20 is disposed between the first member 11 and the second member 12, a load is applied to the insert material 20 through at least one of the first member 11 and the second member 12. At that time, the first member 11, the second member 12, and the insert material 20 are heated to form a liquid phase of the insert material 20, thereby bonding the first member 11 and the second member 12. At that time, an inert gas is supplied to the place where the insert material 20 is disposed and its vicinity until the insert material 20 forms a liquid phase. Then, after the insert material 20 forms a liquid phase, the supply amount of the inert gas is reduced. This makes it possible to reduce the supply amount of the inert gas required for bonding the first member 11 and the second member 12 while suppressing oxidation of the bonding portion. The load direction is a direction in which the thickness of the insert material 20 is compressed, and is the same as the direction in which the insert material 20 is sandwiched between the first member 11 and the second member 12.

As described above, in the joining method disclosed herein, the inert gas is supplied until the insert material 20 forms a liquid phase, and the amount of inert gas supplied is reduced after the insert material 20 forms a liquid phase. When the insert material 20 is composed of a metal or alloy that undergoes a eutectic reaction with the first member 11 and the second member 12, the amount of inert gas supplied can be reduced after the insert material 20 forms a liquid phase through a eutectic reaction.

The supply amount of the inert gas may be appropriately determined in consideration of the ease of oxidation of the first member 11 and the second member 12, the joining temperature, and the type of inert gas, so as to suppress oxidation of the joint portion of the first member 11 and the second member 12 during joining, particularly before the insert material 20 forms a liquid phase. The supply amount of the inert gas may be, for example, 0.001 to 1.000 m ³ /min under standard conditions until the insert material 20 forms a liquid phase. After the insert material 20 forms a liquid phase, the supply amount of the inert gas may be, for example, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less, or may be 0%, based on the amount before the insert material 20 forms a liquid phase. "After the insert material 20 forms a liquid phase, the supply amount of the inert gas is set to 0% based on the amount before the insert material 20 forms a liquid phase" means that the supply of the inert gas is completely shut off.

A well-known device can be used for the joining. For example, the first member 11, the second member 12, and the insert material 20 are stored in a chamber, and the first member 11 and the second member 12 are joined together. Typically, a vacuum pump and an inert gas supply source are connected to the chamber, and the chamber is depressurized with the vacuum pump, and then the inert gas is supplied. When supplying the inert gas, the operation of the vacuum pump is typically stopped, and the piping connecting the vacuum pump is left open.

The type of inert gas may be appropriately determined in consideration of the susceptibility of the first member 11 and the second member 12 to oxidation, the joining temperature, the supply amount of the inert gas, and the like, so as to suppress oxidation of the joint between the first member 11 and the second member 12. Typical examples of the inert gas include rare gases such as helium gas, neon gas, argon gas, and krypton gas, nitrogen gas, and carbon dioxide gas. A mixed gas of a combination of these may also be used. The inert gas may also be a mixed gas in which a reducing gas is added to the aforementioned gases. The reducing gas is typically hydrogen gas.

There are no particular limitations on the method of detecting the formation of the liquid phase of the insert material 20, so long as it can be detected reliably, and it may be, for example, visual detection or detection using an imaging device. Alternatively, it may be detected by, for example, the following methods, but is not limited to these.

As described above, during joining, a load is applied in a direction that compresses the thickness of the insert material 20 through at least one of the first member 11 and the second member 12. To do this, for example, a hydraulic cylinder or the like is connected to at least one of the first member 11 and the second member 12 to apply a load to the insert material 20. When a load is applied to the insert material 20, the first member 11 and the second member 12 receive a reaction force of the same magnitude as the load. When the insert material 20 melts and forms a liquid phase, the reaction force decreases. The formation of the liquid phase of the insert material may be detected by detecting a change (decrease) in this reaction force. Examples of methods for measuring the reaction force include a method in which a load cell or the like is placed between the first member 11 and/or the second member 12 and the hydraulic cylinder.

Alternatively, when at least a portion of the insert material 20 melts and forms a liquid phase, at least a portion of the molten insert material 20 is discharged from the space between the first member 11 and the second member 12. As a result, the thickness of the insert material 20 changes. The formation of the liquid phase of the insert material may be detected by detecting this change in thickness. Examples of methods for measuring the change in thickness of the insert material 20 include a method of measuring the stroke of a hydraulic cylinder.

The joining temperature may be appropriately determined depending on the type of the first member 11 and the second member 12 and the insert material 20. Typically, the joining temperature is equal to or higher than the melting point of the insert material 20 and equal to or lower than the melting point of the first member 11 and the second member 12, and preferably equal to or lower than the solution temperature of the joint. When the first member 11 and the second member 12 are made of an aluminum alloy, particularly an aluminum alloy for casting, and the insert material is made of metallic zinc or a zinc alloy, the joining temperature may be equal to or higher than 380°C, which is the eutectic temperature of aluminum and zinc, and equal to or lower than the solution temperature of the joint. Specifically, the joining temperature may be, for example, 380°C or higher, 400°C or higher, or 450°C or higher, and may be 660°C or lower, 650°C or lower, 600°C or lower, 550°C or lower, or 500°C or lower.

The load applied to the insert material can be controlled by the joining pressure. The joining pressure may be appropriately determined so as to be equal to or greater than the pressure at which the insert material 20 does not shift position when sandwiched between the first member 11 and the second member 12, and equal to or less than the pressure at which the joint does not deform significantly. The joining pressure may typically be 1 MPa or more, 2 MPa or more, 3 MPa or more, or 4 MPa or more, and may be 25 MPa or less, 20 MPa or less, 15 MPa or less, 10 MPa or less, or 5 MPa or less.

The joining time may be appropriately determined so that the insert material 20 is discharged to the outer periphery of the joint by forming a liquid phase with the first member 11 and the second member 12 through a eutectic reaction, or by melting when the insert material 20 reaches its melting point, and does not remain in the joint. In addition, when the first member 11 and the second member 12 are made of an alloy and at least a part of the alloy elements are in solid solution, the joining time may be appropriately determined taking into consideration the time for solution formation. The joining time may be, for example, 10 minutes or more, 30 minutes or more, 60 minutes or more, 90 minutes or more, 120 minutes or more, or 150 minutes or more, and may be 300 minutes or less, 270 minutes or less, 240 minutes or less, 210 minutes or less, or 180 minutes or less.

<Formate Coating Step>
When the first member 11 and the second member 12 are made of metal aluminum or an aluminum alloy, and the insert material 20 is made of metal zinc or a zinc alloy, a formate coating may be formed in advance on one or both sides of the insert material. The formate coating can remove the oxide film on the joining surface, and can also prevent or suppress reoxidation of the joining surface. As a result, the joining strength can be improved. Without being bound by theory, it is believed that this is because the formate coating is thermally decomposed during joining to remove the oxide film on the joining surfaces of the first member 11 and the second member 12.

One method for forming the formate coating is, for example, to immerse the foil or plate material for the insert material 20 in boiling formic acid for 1 to 5 minutes and then rinse with water.

In addition to what has been described so far, the joining method disclosed herein can be modified in various ways within the scope of the claims.

The bonding method of the present disclosure will be explained in more detail below with reference to examples and comparative examples. Note that the bonding method of the present disclosure is not limited to the conditions used in the following examples.

<Preparation of joint specimen>
The joint specimens were prepared as follows.

Example
As shown in FIG. 1, an insert material 20 was placed between a first member 11 and a second member 12, and the first member 11 and the second member 12 were joined to obtain a joint sample of the example.

The first member 11 and the second member 12 were both made of a Japanese Industrial Standard AC2C-F cast aluminum alloy, which contained, by mass%, 0.5-1.1% copper, 6.5-7.5% silicon, 0.2-0.4% magnesium, less than 0.1% zinc, less than 0.1% manganese, less than 0.1% nickel, and less than 0.1% tin, with the remainder being aluminum and unavoidable impurities. The joining surfaces of the first member 11 and the second member 12 (the surfaces that come into contact with the insert material 20) were roughened using #1200 abrasive paper before joining.

The insert material 20 was a zinc alloy foil with a thickness of 0.4 mm. The zinc alloy foil contained, by mass%, 0.30% copper, 0.002% aluminum, 0.02% titanium, less than 0.02% lead, less than 0.01% cadmium, and less than 0.01% iron, with the remainder being zinc and unavoidable impurities.

A formate coating was formed in advance on both sides of the insert material 20. The formate coating was formed by immersing the zinc alloy foil in boiling formic acid for 2 minutes.

The liquid phase diffusion bonding conditions were as follows.
Bonding temperature: 500° C.
Bonding pressure: 5 MPa
Bonding time: 180 minutes Supply gas: nitrogen Supply amount: 0.005 m ³ /min

Then, when the insert material 20 formed a liquid phase, the supply of nitrogen gas was stopped. The formation of the liquid phase was detected by the reaction force of the load (joining pressure) applied to the insert material. Figure 2 shows the change over time in the joining pressure and joining temperature during joining. The joining pressure is the reaction force (pressure) measured by a load cell attached to a hydraulic cylinder connected to the first member 11.

Comparative Example 1
A joint sample of Comparative Example 1 was obtained in the same manner as in Example, except that nitrogen gas was continuously supplied from the start of joining to the end of joining.

Comparative Example 2
A joint sample of Comparative Example 2 was obtained in the same manner as in Example, except that joining was carried out in the air without supplying nitrogen gas.

"evaluation"
A tensile test was performed on each of the joint samples to measure the joint strength (fracture strength). The tensile direction was approximately opposite to the compression direction of the insert material 20. The tensile speed was 10 mm/min. In addition, the fracture surface of each of the joint samples after the tensile test was observed using a scanning electron microscope, and surface analysis of oxygen was performed using EDX.

The results of the measurement of the bonding strength are shown in Figure 3. From Figure 3, it was confirmed that the bonding strength of the sample of the embodiment is lower than that of the sample of Comparative Example 1, in which nitrogen gas was continuously supplied from the start of bonding to the end of bonding, but that the sample of the embodiment has a bonding strength sufficient for practical use. In contrast, it was confirmed that the bonding strength of the sample of Comparative Example 2, which was bonded in the air without supplying nitrogen gas, was significantly lower. From these facts, it was confirmed that a bonding strength sufficient for practical use can be obtained even if the supply of nitrogen gas is stopped when the liquid phase of the insert material is formed, as in the embodiment. In addition, as a result of the surface analysis of the fracture surface after the tensile test, it was confirmed that the amount of oxygen in the sample of the embodiment is smaller than that of the sample of Comparative Example 2, and that oxidation of the joint was suppressed during the preparation of the sample of the embodiment.

These results confirm the effectiveness of the joining method disclosed herein.

11 First member 12 Second member 20 Insert material

Claims (5)

A method for joining a first member and a second member, comprising the steps of:
disposing an insert material between the first member and the second member; and applying a load to the insert material through at least one of the first member and the second member while supplying an inert gas, heating the first member, the insert material, and the second member, and joining the first member and the second member by forming a liquid phase of the insert material;
Including,
The insert material has a lower melting point than the first member and the second member,
After the insert material forms a liquid phase, the supply amount of the inert gas is reduced, and the liquid phase formation of the insert material is detected based on a change in a reaction force of a load applied to the insert material or a change in a thickness of the insert material.
Joining method. The joining method according to claim 1, wherein the insert material is made of a metal or alloy that undergoes a eutectic reaction with the first member and the second member, and the amount of the inert gas supplied is reduced after the insert material forms a liquid phase through the eutectic reaction. The joining method according to claim 1 or 2, wherein at least one of the first member and the second member is made of an aluminum alloy. The joining method according to claim 3, wherein the insert material is made of metallic zinc or a zinc alloy. The joining method according to claim 4, in which a formate coating is formed in advance on one or both sides of the insert material.

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