Method for joining aluminum material and copper material, and method for producing joints

Abstract

To realize stable mechanical joining strength and electrical joining performance in a method for joining an aluminum material and a copper material.SOLUTION: Used is a material on which a tin plating layer is formed on the surface of at least one of joining regions of an aluminum material 10 and a copper material 20. First, in a mechanical clinching step, the aluminum material and the copper material are clinched by a concave die and a convex die to obtain mechanical joining strength. Next, in a resistance-welding process using a pair of electrodes 3, 4, the tin-plated layer is melted, and an interface 9 is filled with a molten 40A of tin, thereby supplementing the electrical junction property.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for joining an aluminum material and a copper material, and a method for manufacturing a joined joint. [Background technology]

[0002] Resistance welding (e.g., resistance spot welding) is a known method for joining dissimilar metals, aluminum and copper. Resistance welding generally results in the formation of hard, brittle intermetallic compounds at the joint interface, making it difficult to obtain a high-strength welded joint. Therefore, in order to increase the strength of the welded joint, it is desirable to control the thickness of the intermetallic compound layer at the joint interface to be as thin as possible. However, because the condition of the resistance welding electrode and the surface condition of the joined materials change with each shot, controlling the thickness of the intermetallic compound layer is itself difficult.

[0003] For example, Patent Document 1 discloses an example of joining an aluminum material and a copper material by resistance welding. In this method, first, the copper material and the aluminum material are sandwiched between two electrodes for resistance welding, and current is passed through while applying a primary pressure to heat the contact area between the two metal materials, raising the temperature of the contact area to a range above the eutectic temperature of the two metal materials but below their melting points (eutectic temperature to +50°C). Then, when a eutectic reaction occurs at the contact area and a molten liquid phase begins to form at the contact area, current is stopped and the two metal materials are subjected to a secondary pressure greater than the primary pressure. This secondary pressure creates a state where almost no molten liquid phase exists at the contact area between the two metal materials, resulting in a diffusion bond between the two metals. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-140049 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the above method requires that the contact point (joining area) between the aluminum and copper materials be heated to a temperature above the eutectic point of aluminum and copper (approximately 550°C) but below the melting point of aluminum. This makes heating extremely difficult to control, and there is a concern that the electrode and aluminum may weld together as the temperature of the aluminum material increases. Furthermore, even if the same joining conditions are set, the strength can vary significantly depending on the surface condition of the electrode and material, resulting in unstable performance of the joined joint.

[0006] The present invention has been made in view of the above circumstances, and its object is to realize stable mechanical joint strength and electrical joint performance in a method for joining aluminum materials and copper materials. Another object of the present invention is to provide a method for manufacturing a joint having stable mechanical joint strength and electrical joint performance. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the method for joining aluminum materials and copper materials according to the present invention has the following features. A method for joining an aluminum material and a copper material, comprising: a mechanical clinching process in which the aluminum material and the copper material, each having a tin-plated layer formed on a surface of at least one of the joining regions of the aluminum material and the copper material, are overlapped with each other in a range including the joining region, and the overlapped portion is sandwiched between a concave mold and a convex mold and pressurized to crimp the joining region; a resistance welding process in which the joining region crimped in the mechanical clinching process is sandwiched between electrodes for resistance welding and current is passed through to melt at least a portion of the tin plating layer; having A method for joining aluminum and copper materials.

[0008] Furthermore, the method for manufacturing a bonded joint according to the present invention is characterized as follows. A method for manufacturing a bonded joint using the above-mentioned method for joining an aluminum material and a copper material. [Effects of the Invention]

[0009] According to the present invention, stable mechanical bonding strength and electrical bonding performance can be achieved.

[0010] The present invention has been briefly described above. The details of the present invention will become clearer by reading the following detailed description of the invention (hereinafter referred to as "embodiments") with reference to the accompanying drawings. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view showing a mechanical clinching step in a joining method according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing a resistance welding step in the joining method according to the embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view showing a welded joint produced using the welding method according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Specific embodiments of the present invention will be described below with reference to the accompanying drawings. Fig. 1 is a cross-sectional view showing a mechanical clinching step in a joining method according to an embodiment, Fig. 2 is a cross-sectional view showing a resistance welding step, and Fig. 3 is a cross-sectional view showing a joined joint produced using the joining method according to an embodiment of the present invention.

[0013] In the joining method of the embodiment, a copper material 20 whose surface has been previously plated with tin is used. Therefore, a plating process is performed before the actual joining process to form a tin plating layer 40 with a thickness of about 1 μm. The tin plating layer 40 does not necessarily have to be formed on the entire surface of the copper material 20, as long as it is formed on at least the surface of the joining region (contact portion) with the aluminum material 10. Furthermore, the tin plating may be applied to the surface of at least one of the joining regions of the aluminum material 10 and the copper material 20. In other words, the tin plating may be applied to the aluminum material 10 side rather than the copper material 20 side, or may be applied to both the copper material 20 and the aluminum material 10.

[0014] The joining method of the embodiment includes two steps: a mechanical clinching step and a resistance welding step performed after the mechanical clinching step, and by joining an aluminum material 10 and a copper material 20 using this joining method, a joined joint 5 shown in Fig. 3 is obtained. In this embodiment, the aluminum material 10 and the copper material 20 are formed into a plate shape.

[0015] First, in the mechanical clinching process, the copper material 20 on which the tin plating layer 40 is formed and the aluminum material 10 are overlapped in a range including the joining region. Then, as shown in Fig. 1, the overlapped portion is sandwiched between a concave mold 1 and a convex mold 2 and pressure is applied, thereby plastically deforming the joining region between the aluminum material and the copper material, and crimping is performed to obtain mechanical joining strength.

[0016] Specifically, a flat portion of an aluminum material 10 and a flat portion of a copper material 20 are overlapped, and the overlapped portion is placed on a lower die (concave die) 1. In the illustrated example, the aluminum material 10 is placed on the concave die 1 with its bottom side facing down. In this state, a punch 2, which is an upper die, is pressed downward relative to the concave die 1. By doing so, the joining region 8 of both the flat portions of the aluminum material 10 and the copper material 20 is plastically deformed by the concave die 1 and the convex die 2 into a recess 11 that is wider at the bottom than the entrance, and a protrusion 21 that is pressed into the recess 11 and conforms to the inner surface of the recess 11. Then, due to the plastic deformation of the materials 10 and 20 into the recess 11 and the protrusion 21, the aluminum material 10 and the copper material 20 are crimped so as to generate an engaging force in the planar and perpendicular directions of the interface 9 between the flat portions. In this embodiment, the description will be given using the up-down direction in Figures 1 to 3, but the actual arrangement is not limited to the example shown in the figures, and for example, the concave mold 1 and the convex mold 2 may be arranged upside down or side by side in the left-right direction.

[0017] In the resistance welding process, as shown in FIG. 2 , the flat-plate overlapping portion of the aluminum material 10 and the copper material 20 in the joining region 8, which have been crimped in the mechanical clinching process, is sandwiched between a pair of upper and lower electrodes 3 and 4 for resistance welding. In this state, the pair of electrodes 3 and 4 applies pressure to the flat-plate overlapping portion in a direction perpendicular to the joined interface 9 of the flat-plate overlapping portion, while current is passed between the electrodes 3 and 4. By passing current between the electrodes 3 and 4, the joining region 8 is heated to a temperature lower than the eutectic temperature of aluminum and copper (approximately 550°C) and higher than the melting temperature of tin (232°C), thereby melting at least a portion of the tin plating layer 40. Molten tin 40A, which is at least a portion of the molten tin plating layer 40 solidified, is present at the interface of the joining region 8 between the aluminum material 10 and the copper material 20, thereby strengthening the electrical bond between the aluminum material 10 and the copper material 20. Specifically, in the resistance welding process, current is passed between the electrodes 3 and 4 to heat the joining region 8 to a temperature in the range of 232°C to 400°C, thereby melting at least a portion of the tin-plated layer 40. By keeping the temperature of the joining region 8 at 400°C or less, only the tin-plated layer 40 melts, without melting the aluminum. This reduces welding between the electrodes 3 and 4 and the aluminum material 10, resulting in excellent maintainability. The melting points of aluminum and copper are 660°C and 1085°C, respectively.

[0018] As described above, the joining method of this embodiment can provide a joined joint having stable mechanical joint strength and electrical joint performance by performing the mechanical clinching process and the resistance welding process. That is, mechanical clinching, which is a mechanical joining, can provide stable mechanical joint strength, but because it only forms a conductive path by physical contact between the materials, the electrical characteristics are unstable. To compensate for this, the tin-plated layer 40 at the interface 9 is melted in the subsequent resistance welding process, and the molten tin 40A fills the gap at the interface 9 and chemically bonds it, thereby stabilizing the electrical characteristics of the joined joint between the aluminum material 10 and the copper material 20.

[0019] Furthermore, the heating temperature range during resistance welding can be controlled to 232°C (the melting point of tin) to 400°C (a temperature lower than the eutectic temperature of aluminum and copper, approximately 550°C), at which point only the tin plating layer 40 melts, making it easy to control heating at low temperatures and over a wide temperature range. Furthermore, since resistance welding is performed at a lower temperature than in conventional technology, which required heating at or above the eutectic temperature of aluminum and copper (548°C), there is less welding between the electrode and the aluminum material, and maintenance is easier.

[0020] The copper material 20 described above includes pure copper and copper alloys. The aluminum material 10 includes pure aluminum and aluminum alloys. In the above embodiment, the copper material 20 is placed on top of the aluminum material 10, and the concave mold 1 is placed below the aluminum material 10, and the convex mold 2 is relatively pressed downward to displace it. However, the mechanical clinching process may be performed with the aluminum material 10 placed on top of the copper material 20. In the resistance welding process, the aluminum material 10 and the copper material 20 are placed on top of each other.

[0021] Here, the features of the method for joining an aluminum material and a copper material and the method for manufacturing a joint according to the above-described embodiment of the present invention will be briefly summarized and listed below in [1] to [7]. [1] A method for joining an aluminum material (10) and a copper material (20), comprising: a mechanical clinching step of overlapping the aluminum material and the copper material, each having a tin-plated layer (40) formed on the surface of at least one of the joining regions (8) of the aluminum material and the copper material, in a range including the joining region, and clamping the overlapped portion between a concave mold (1) and a convex mold (2) and applying pressure to the joining region, thereby crimping the joining region; a resistance welding step of clamping the joining region crimped in the mechanical clinching step between electrodes (3, 4) for resistance welding and passing current through them to melt at least a portion of the tin plating layer; having A method for joining aluminum and copper materials.

[0022] According to the joining method [1] above, stable mechanical joint strength and electrical joint performance can be achieved by performing the mechanical clinching process and the resistance welding process. That is, mechanical clinching, which is a mechanical joining, can achieve stable mechanical joint strength, but since it only forms a conductive path by physically contacting the materials, the electrical characteristics are unstable. To compensate for this, the tin plating layer 40 at the interface 9 is melted in the subsequent resistance welding process, which fills the gap at the interface 9 and forms a chemical bond, thereby stabilizing the electrical characteristics in the joining region between the aluminum material 10 and the copper material 20.

[0023] [2] In the mechanical clinching step, A flat plate overlapping portion, which is the overlapping portion of the flat plate portion of the aluminum material and the flat plate portion of the copper material, is placed between the concave mold (1) and the convex mold, and the convex mold (2) is relatively pressed and displaced toward the concave mold, thereby plastically deforming the joining region (8) of both the flat plate portions of the aluminum material and the copper material between the concave mold and the convex mold into a concave portion (11) having a shape wider than the entrance, and a convex portion (21) that is pressed into the concave portion and takes a shape that follows the inner surface of the concave portion. The method for joining an aluminum material and a copper material according to [1] above.

[0024] According to the joining method [2] above, the mechanical joining strength can be ensured by the mechanical clinching process for the overlapping portion of the flat plates.

[0025] [3] In the resistance welding step, The flat plate overlapping portion of the joining region crimped in the mechanical clinching process is sandwiched between a pair of electrodes (3, 4) for resistance welding, and current is passed between the electrodes while the pair of electrodes pressurize the flat plate overlapping portion from a direction perpendicular to the joined interface (9) of the flat plate overlapping portion, thereby melting at least a portion of the tin plating layer interposed at the interface of the joining region. The method for joining an aluminum material and a copper material according to [2] above.

[0026] According to the joining method [3] above, high electrical joining performance can be ensured by the resistance welding process for the mechanically joined overlapping flat plates.

[0027] [4] before the mechanical clinching step, a plating process step of forming the tin plating layer on the surface of at least one of the joining regions (8) of the aluminum material and the copper material, The method for joining an aluminum material and a copper material according to any one of [1] to [3] above.

[0028] According to the joining method [4] above, a tin plating layer can be formed on the surface of the joining region between the aluminum material and the copper material by the plating process.

[0029] [5] In the resistance welding step, By passing a current between the electrodes, the joining region is heated to a temperature lower than the eutectic temperature of aluminum and copper and higher than the melting temperature of tin, thereby melting at least a portion of the tin plating layer. The method for joining an aluminum material and a copper material according to any one of [1] to [4] above.

[0030] According to the joining method [5] above, by simply controlling the joining region within a wide temperature range of relatively low temperatures, it is possible to melt only the tin plating layer 40 without melting the aluminum material 10. Therefore, there is little welding between the electrode and the aluminum material, and maintenance is easy.

[0031] [6] In the resistance welding process, By passing a current between the electrodes, the joining region is heated to a temperature in the range of 232°C or higher and 400°C or lower, thereby melting at least a portion of the tin plating layer. The method for joining an aluminum material and a copper material according to any one of [1] to [5] above.

[0032] According to the joining method [6] above, the joining region only needs to be controlled to 232°C (the melting point of tin) to 400°C (a temperature lower than the eutectic point of aluminum and copper, approximately 550°C), so by simply controlling the temperature within a relatively low, wide range, it is possible to melt only the tin plating layer 40 without melting the aluminum material 10. Therefore, there is little welding between the electrode and the aluminum material, and maintenance is easy.

[0033] [7] A method for manufacturing a joint (5) using the method for joining an aluminum material and a copper material described in any one of [1] to [6] above.

[0034] According to the manufacturing method of the bonded joint described above in [7], stable mechanical joint strength and electrical joint performance can be achieved by performing the mechanical clinching process and the resistance welding process. That is, mechanical clinching, which is a mechanical joint, can achieve stable mechanical joint strength, but since it only forms a conductive path by physically contacting the materials, the electrical characteristics are unstable. To compensate for this, the tin-plated layer 40 at the interface 9 is melted in the subsequent resistance welding process, which fills the gap at the interface 9 and forms a chemical bond, thereby stabilizing the electrical characteristics of the bonded joint 5 between the aluminum material 10 and the copper material 20. [Explanation of symbols]

[0035] 1 Concave 2 Convex 8 Joint area 9 Interface 10. Aluminum material 11 Recess 20 Copper material 21 Convex part 40 Tin plating layer 40A molten tin

Claims

1. A method for joining an aluminum material and a copper material, comprising: a mechanical clinching process in which the aluminum material and the copper material, each having a tin-plated layer formed on a surface of at least one of the joining regions of the aluminum material and the copper material, are overlapped with each other in a range including the joining region, and the overlapped portion is sandwiched between a concave mold and a convex mold and pressurized to crimp the joining region; a resistance welding process in which the joining region crimped in the mechanical clinching process is sandwiched between electrodes for resistance welding and current is passed through to melt at least a portion of the tin plating layer; having A method for joining aluminum and copper materials.

2. In the mechanical clinching step, A flat plate overlapping portion, which is a portion where the flat plate portion of the aluminum material and the flat plate portion of the copper material are overlapped, is placed between the concave mold and the convex mold, and the convex mold is relatively pressed and displaced toward the concave mold, thereby plastically deforming the joining region of both the flat plate portions of the aluminum material and the copper material between the concave mold and the convex mold into a concave portion that is wider inward than its inlet, and a convex portion that is pressed into the concave portion and takes a shape that follows the inner surface of the concave portion.

2. The method for joining an aluminum material and a copper material according to claim 1.

3. In the resistance welding step, The flat plate overlapping portion of the joining region crimped in the mechanical clinching process is sandwiched between a pair of electrodes for resistance welding, and the pair of electrodes pressurize the flat plate overlapping portion from a direction perpendicular to the joined interface of the flat plate overlapping portion while passing current between the electrodes, thereby melting at least a portion of the tin plating layer interposed at the interface of the joining region.

3. The method for joining an aluminum material and a copper material according to claim 2.

4. Before the mechanical clinching step, a plating process step of forming the tin plating layer on a surface of at least one of the joining regions of the aluminum material and the copper material, 2. The method for joining an aluminum material and a copper material according to claim 1.

5. In the resistance welding step, By passing a current between the electrodes, the joining region is heated to a temperature lower than the eutectic temperature of aluminum and copper and higher than the melting temperature of tin, thereby melting at least a portion of the tin plating layer.

2. The method for joining an aluminum material and a copper material according to claim 1.

6. In the resistance welding step, The joining region is heated to a temperature in the range of 232°C or higher and 400°C or lower by passing a current between the electrodes, thereby melting at least a portion of the tin plating layer.

2. The method for joining an aluminum material and a copper material according to claim 1.

7. A method for manufacturing a welded joint using the method for joining an aluminum material and a copper material according to any one of claims 1 to 6.

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