Metal foil welding method

Abstract

To strongly join thin metal foils while making those end faces abutted on each other.SOLUTION: A metal foil welding method laser welds a first metal foil and a second metal foil having different compositions while making those end faces abutted on each other, wherein thicknesses of the first metal foil and the second metal foil are 0.1 mm or more and 0.5 mm or less, and the method welds the metal foils along the end faces while repeatedly scanning an irradiation position of a laser beam in a direction crossing the abutted end faces.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for butt welding metal foils made of different materials. [Background technology]

[0002] Joints of dissimilar metals have been used in a wide range of fields, including electronic components, transportation machinery, and general industrial equipment. For example, lithium-ion batteries installed in hybrid vehicles often have an aluminum positive electrode and a non-aluminum negative electrode, such as copper, iron, or nickel. Therefore, there is a great demand for technology to join dissimilar metals, such as aluminum and copper or aluminum and iron.

[0003] Patent Document 1 discloses a method of forming peaks and valleys at the ends of a first metal plate (Cu plate) having a thickness of 3 mm and a second metal plate (Al plate) having the same thickness, overlapping and pressing down so that the peaks of the first metal plate and the valleys of the second metal plate 2 engage with each other, and joining them. Patent Document 2 discloses a method of butting the end faces of an aluminum member and a copper member having a thickness of 1.0 mm against each other and laser welding them. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2008-6496 A [Patent Document 2] JP 2011-5499 A Summary of the Invention [Problem to be solved by the invention]

[0005] The joining method described in the cited document 1 can be applied when the metal foil is thick, about 3 mm, but when the foil is thin, it is difficult to form peaks and valleys and join the foil. On the other hand, if a laser is used as in the cited document 2, it is more likely that thin metal foils can be joined, but as shown in Table 1 of the cited document 2, the shear strength ratio (the ratio to the shear strength when aluminum members are joined together) is low, and the foil is prone to breakage with even a small stress. For this reason, it has been difficult to apply this technology to thinner metal foils. In view of the above, an object of the present invention is to firmly bond thin metal foils by butting their ends together. [Means for solving the problem]

[0006] The present invention is a method for laser welding by butting the end faces of a first metal foil and a second metal foil together, wherein the thicknesses of the first metal foil and the second metal foil are 0.1 mm or more and 0.5 mm or less, and the method comprises welding along the end faces while repeatedly scanning the irradiation position of a laser beam in a direction that intersects with the butted end faces.

[0007] It is also preferable that the laser beam is subjected to wobbling scanning. It is also preferable that the first metal foil is made of aluminum or an aluminum alloy, and the second metal foil is made of copper or a copper alloy. Effect of the Invention

[0008] According to the present invention, a technique can be provided for firmly joining the ends of thin metal foils by butting them together. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic diagram illustrating an example of a laser beam irradiated onto an interface between metal foils. [Diagram 2] FIG. 13 is an enlarged schematic diagram showing a trajectory when a circle is drawn with a laser beam. [Diagram 3] FIG. 3 is an enlarged view of a portion of the trajectory of the laser beam depicted in FIG. 2. [Figure 4] FIG. 1 is a schematic diagram illustrating an example of a laser welding machine for welding metal foils. [Diagram 5] 1 is a microscope photograph after laser welding in Example 1. [Figure 6] 4 is a micrograph of the surface and cross section after laser welding in Example 1. [Figure 7] 4 shows the results of measuring the fracture stress after laser welding in Examples 2 to 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0011] The present embodiment is a method for welding metal foils in which a first metal foil and a second metal foil having different compositions are butted together at their end faces and laser-welded, in which welding is performed along the end faces while repeatedly scanning the irradiation position of a laser beam in a direction intersecting the butted end faces. Such a welding method can also be said to be a method for manufacturing a joint of a first metal foil and a second metal foil.

[0012] In this disclosure, dissimilar metals refer to metals that have different main elements, i.e., different most abundant elements. For example, in the case of stainless steel and brass, the main metal of stainless steel is iron (Fe) and the main metal of brass is copper (Cu), so these two are dissimilar metals. On the other hand, in the case of stainless steel and general structural rolled steel, the main metal of both is iron (Fe), so they are the same metal.

[0013] The material of the first metal foil and the second metal foil is, for example, copper (Cu), aluminum (Al), iron (Fe), nickel (Ni), or an alloy mainly composed of these. The state where the end faces are butted together means a state where the end face (side face) of the first metal foil and the end face of the second metal foil are in contact with each other, that is, a state where the edges of the juxtaposed foils are in contact with each other.

[0014] (Laser scanning) Figure 1 is a schematic diagram of an example of a laser beam being irradiated onto the butted interface of metal foils. The first metal foil F1 and the second metal foil F2 are placed on a stage (not shown) with their end faces butted together, and the stage is moved in the direction of the white arrow in the figure (from top to bottom on the paper) while the laser beam is swung so as to draw a specific shape on the butted interface C. In this way, the laser beam is scanned along a trajectory T, joining the first metal foil F1 and the second metal foil F2.

[0015] The specified shape is a circle in the case of Figure 1(a) and a straight line in the case of (b). If the stage is fed while tracing a circle or a straight line, it can trace a spiral (also called a volute or trochoid) trajectory as shown in Figure 1(a) or a wave-shaped trajectory (also called a triangular wave or sine wave, zigzag, W-shaped or Z-shaped) trajectory as shown in Figure 1(b). When scanning in a spiral shape, it can be traced clockwise as shown in the figure, or counterclockwise. When scanning in a wave-shaped shape, it is preferable to round the corners (the turning points of the scan) to prevent overheating.

[0016] Generally, scanning that draws a spiral trajectory as shown in FIG. 1(a) is called wobbling scanning, and scanning that draws a waveform trajectory as shown in FIG. 1(b) is called weaving scanning. In this embodiment, it is preferable to perform wobbling scanning of the laser beam. In weaving scanning, there is a possibility that overheating occurs due to acceleration and deceleration at turning points of the waveform (points where the scanning direction is switched), but in wobbling scanning, there are no turning points and there is little acceleration and deceleration, so more uniform joining is possible. An embodiment of wobbling scanning will be described below.

[0017] The butt interface C may be located within the width W of the path along the traveling direction of the laser beam. In the configuration shown in Fig. 1, the butt interface c is located in the center of the width W of the path, but it does not necessarily have to be located in the center of the width W. In the cited document 1, the melting ratio of the two metals is adjusted by irradiating the laser light toward the metal with the lower melting point, but this embodiment does not require such an adjustment.

[0018] Here, we will explain the scanning of the laser beam in the "direction intersecting the butted end faces" in this embodiment. Figure 2 is an enlarged schematic diagram of the trajectory when a circle is drawn with the laser beam. (a) is an example when the center of the circle drawn by the laser beam is shifted from the butted interface, and (b) is an example when the circle drawn by the laser beam is small.

[0019] In Fig. 2(a), when a laser beam with a beam diameter 11 traces a path T with a width W, the metal in the area through which the laser beam passes and the surrounding area that is thermally affected melts to form a molten pool, which solidifies to form a bead. The inner circumference 12 and outer circumference 13 of the bead at this time are shown in the figure. Scanning the laser beam "in a direction intersecting the butted end faces" means that in this figure, the butted interface C of the metal foils is inside the inner circumference 12 of the bead. In other words, the entire laser beam with a specified diameter moves back and forth between the first metal foil and the second metal foil across the butted end faces, that is, the laser beam moves to a position where it does not overlap the end faces on either the first metal foil side or the second metal foil side, and then moves toward the area of ​​the metal foil on the opposite side.

[0020] In Fig. 2(b), the bead inner circumference 12 is close to the butt interface C, so if the bead width W becomes smaller than this, the laser beam will not be able to intersect the butt interface C. Therefore, in order to scan the "laser beam irradiation position in a direction intersecting the butted end faces", it is necessary to enlarge the trajectory T at least to the extent that the bead inner circumference does not come into contact with the butt interface C.

[0021] In this embodiment, it is preferable to irradiate the laser beam to a position adjacent to the bead before the temperature of the molten base material drops due to irradiation with the laser beam, so as to form a bead by partially overlapping the earlier molten pool and the later molten pool.

[0022] Figure 3 is an enlarged view of a portion of the trajectory of the laser beam depicted in Figure 2. It shows the bead width B, the bead inner circumference 121 and bead outer circumference of the bead obtained in the first pass, and the bead inner circumference and bead outer circumference 132 of the bead obtained in the second pass after moving by the feed pitch P.

[0023] In this diagram, it is preferable for the feed pitch P to be smaller than the bead width B. This allows the bead of the first round to overlap the bead of the second round, ensuring that the butt interface C is welded without any omissions. It is also preferable for the second round to be scanned before the temperature of the base material, which was raised by the first round, drops. This improves thermal efficiency, as the bead of the second round can be formed by receiving the heat from the bead of the first round.

[0024] As described above, by performing wobbling scanning with the laser beam, it is possible to increase the joining strength. Although the reason for this has not been fully elucidated, it is assumed that this is because the intermetallic compound formed by the passage of the butt interface C on the first round and the intermetallic compound formed by the passage of the butt interface C on the second round are less likely to be continuously connected in the direction of the butt interface C, making it less likely for cracks to occur along the butt interface C.

[0025] (Laser welding machine) An example of a schematic diagram of a laser welding machine for welding metal foils is shown in Fig. 4. The laser welding machine is composed of a fiber laser 20, a galvanometer scanner 30, and a stage 40. The fiber laser 20 excites a laser with a laser oscillator 21, and irradiates the laser from the tip of a laser head 23 via an optical fiber cable 22.

[0026] The galvanometer scanner 30 is composed of a collimator lens 31, two pairs of galvanometer mirrors 32a and 32b, and an fθ lens 33. The laser emitted from the laser head 23 is collimated by the collimator lens 31, reflected by the galvanometer mirrors 32a and 32b, and passed through the fθ lens 33 to be focused and then irradiated onto the target object. The galvanometer mirrors 32a and 32b can be swung around the rotation axes of the galvanometer scan motors 320a and 320b in the directions indicated by the black arrows in the figure. By controlling the swing width and swing speed, it is possible to draw a trajectory of the above-mentioned predetermined shape.

[0027] The stage 40 can be moved in the direction of the white arrow in the drawing. That is, the first metal foil F1 and the second metal foil F2 are arranged so that the butted interface between them is parallel to the stage moving direction.

[0028] The laser welder in this embodiment is not limited to the above configuration. The laser welder is not limited to a fiber laser, and various lasers such as a CO2 laser, a YAG laser, a semiconductor laser, a disk laser, and a fiber laser can be used.

[0029] (Metal foil) In this embodiment, the first metal foil is preferably aluminum or an aluminum alloy, and the second metal foil is preferably copper or a copper alloy. In addition, in this embodiment, the thickness of the first metal foil and the second metal foil is preferably 0.1 mm or more and 0.5 mm or less. The configuration of this embodiment is suitable for welding such thin metal foils. Furthermore, the welding conditions of the laser beam in this embodiment are preferably an output of 200 W or more and 300 W or less, a rotation diameter of the laser beam of 0.5 mm or more and 1.5 mm or less, a scanning speed of 35 mm / s or more and 90 mm / s or less, and a stage feed speed of 3.5 mm / s or more and 9.0 mm / s or less.

[0030] (Evaluation items) When laser welding the ends of metal foils together, it is necessary to evaluate the joining performance and the subsequent use. In this embodiment, the evaluation of defects using a microscope and the breaking strength of a tensile test are used as indicators, and in the following examples, the feasibility of joining is judged based on these results. EXAMPLES

[0031] Example 1 The ends of aluminum foil (A1050) and copper foil (C1020, oxygen-free copper) were butted together and laser welded. The foil thickness was 0.2 mm. The laser used was a fiber laser (IPG Photonics, YLR-150-1500-QCW, wavelength 1064 nm), and the stage was scanned (wobbling scan) while rotating. The focal length of the fθ lens was 254 mm, the irradiation conditions were CW mode, the output was 250 W (100%), the rotation diameter was 1 mm, the scanning speed was 50, 75 mm / s, and the stage feed speed was 5.0, 7.5 mm / s.

[0032] After laser welding, the top surface of the welded foils, including the joint surface, was observed with a microscope (Keyence, VHX900). The results are shown in Figure 5. The left photo is copper and the right is aluminum, with a bead formed in the center. From these photos a, b, c, and d, it was confirmed that a good bead was formed under all conditions, and a joint in which copper and aluminum were joined was obtained.

[0033] Next, the surface and cross section were polished with a microscope (KEYENCE, VHX900), and the cross section was observed. The results are shown in Figure 6. Figure 6(a) is a top view of the joint surface as seen from above, as shown in (c). The dark gray part on the left side of the page is copper, and the light gray part on the right side is aluminum. In the welded part in the center, a molten layer with a swirling shape was confirmed, where the copper and aluminum phases were mixed in a complex manner (irregularly mixed).

[0034] Figure 6(b) shows an enlarged view of the cross section obtained by cutting this molten layer (cross section seen from the direction shown in Figure 6(c)). The black areas visible at the top and bottom are the resin that was used to fill the resin for cross section polishing, and the grey area in the center is the metal foil, with copper on the left, the molten layer in the center, and aluminum on the right. The copper and aluminum phases were stirred as described above, but they also appeared to be separated. The width of the molten layer was greater than the thickness of the aluminum, which was the first metal foil, and the copper, which was the second metal foil. No defects were observed in either the top view or the cross section.

[0035] (Examples 2 to 5) The conditions for Examples 2 to 5 and Comparative Examples 2 to 5 are shown in Table 1. [Table 1]

[0036] The foils of the materials and thicknesses shown in Table 1 were prepared, and the same laser as in Example 1 was used to join the pieces at a stage feed rate of 5.0 mm / s and a scanning rate of 50 mm / s. The obtained test pieces were cut to a width of 5 mm, and a tensile test was performed using a tensile tester (Aiko Engineering, MODEL-1018). In the comparative example, the same metal foils and laser welding machine as in each example were used, but the laser beam was scanned linearly once along the butt surfaces instead of wobbling.

[0037] The results are shown in FIG. 7. The cross marks indicate fracture at the bead, and the circles indicate fracture at the HAZ (heat affected zone). The vertical axis on the left indicates fracture stress (MPa). The fracture stress of each example was clearly higher than that of each comparative example, more than twice as high. Specifically, in the case of aluminum foil and copper foil, Comparative Examples 2 to 4 were all 30 MPa or less, whereas Examples 2 to 4 were 60 MPa or more. In addition, in the case of Al foil and SUS foil, Comparative Example 5 was all 10 MPa or less, whereas Example 5 was 40 MPa or more. That is, welding with high joint strength was achieved in all of the examples.

[0038] The vertical axis on the right side shows the percentage (%) of the stress at which the aluminum foil veneer broke, assuming that the tensile strength of the aluminum foil veneer is 70 MPa. If the breaking stress of the bonded sample is higher than a certain percentage of the tensile strength of the aluminum foil veneer, it can be said that the bond is superior. The certain percentage can be, for example, 50% or more. As can be seen from FIG. 7, in the case of bonding between aluminum foil and copper foil (Examples 2 to 4), the ratio was 85% or more and 145% or less, and in the case of bonding between aluminum foil and stainless steel foil (Example 5), the ratio was 65% or more and 100% or less.

[0039] Furthermore, in Examples 2 to 4, there were several samples in which the breaking stress relative to the tensile strength of the aluminum foil alone exceeded 100%. All of these broke at the HAZ. This means that there was no brittle intermetallic compound inside the bead, and it can be said that good bonding was performed.

[0040] From the above, according to this embodiment, the interface between the two base materials forms an irregularly swirling molten layer, and it was shown that it can be joined without defects. Furthermore, it was shown that it is possible to obtain a joint strength more than twice as high as that of the conventional method of scanning the laser in a straight line. Furthermore, in multiple joint samples of aluminum foil and copper foil, a breaking stress higher than the tensile strength of the aluminum foil single sheet was shown. It is presumed that this is because it was possible to suppress the continuous generation of intermetallic compounds formed during laser welding.

[0041] Although the embodiments of the invention have been described above, the present invention is not limited to the above-described embodiments. [Explanation of symbols]

[0042] 11: Laser beam diameter 12: Bead inner circumference 121: Inner circumference of bead on the first turn 13: Bead circumference 132: Bead circumference on the second lap 20: Fiber laser 21: Laser oscillator 22: Fiber optic cable 23: Fiber connector 30: Galvano scanner 31: Collimator lens 32: Galvano mirror 320: Galvano scanning motor 33: fθ lens 40: Stage B: Bead width C: Butt interface F1, F2: Metal foil P: Feed pitch during scanning T: Laser beam trajectory W: Width of the laser beam trajectory

Claims

1. A metal foil welding method in which a first metal foil and a second metal foil having different compositions are butted together at their end faces and laser-welded, comprising the steps of: The thickness of the first metal foil and the second metal foil is 0.1 mm or more and 0.5 mm or less, A method for welding metal foils, comprising the steps of: repeatedly scanning a laser beam irradiation position in a direction intersecting the butted end faces while welding along the end faces.

2. 2. The method for welding metal foils according to claim 1, wherein the laser beam is subjected to wobbling scanning.

3. 3. The method for welding metal foils according to claim 1, wherein the first metal foil is made of aluminum or an aluminum alloy, and the second metal foil is made of copper or a copper alloy.

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