Joined body, laser machining method and laser machining device

Abstract

This laser machining method is for joining a first member containing a first metal and a second member containing second metal which is different from the first metal. The laser machining method includes: a first step for forming, by scanning a first laser beam, a joined section where the first metal and the second metal are melted; and a second step for agitating a metallic structure in the vicinity of the joined section by scanning a second laser beam rearward of the scanning direction of the first laser beam, the second laser beam having a greater beam diameter and lower power density than the first laser beam.

Description

Joint, laser processing method and laser processing device

[0001] The present invention relates to a joined body produced by laser welding overlapping strip materials of different metals, and to a laser processing method and laser processing device for the same.

[0002] In recent years, there has been an increasing demand in the industrial world for lap welding of dissimilar metal materials. Major examples include joining iron and aluminum, iron and copper, and copper and aluminum, which are done from the perspective of reducing the weight of the joined components and improving the electrical and thermal conductivity of the materials. However, welding these components presents challenges specific to dissimilar metal welding methods, such as the following, and is generally considered difficult to weld.

[0003] An example of a conventional joining of dissimilar metal materials is the laser welding of iron and copper, for example, in the case of welding a battery can and tab (see, for example, Patent Document 1). FIG. 12 is a schematic cross-sectional view showing the cross-sectional structure of the conventional joining and penetration shape of dissimilar metal materials described in Patent Document 1. FIG. 12 shows a can 26 made of iron and a negative electrode tab 27 made of copper. FIG. 12 also shows a fusion zone 28, in which the penetration depth reaches from the iron side to the copper side when the can and negative electrode tab are laser welded. Furthermore, FIG. 12 shows a remelted zone 29 formed when, after forming the fusion zone 28, the concentration of Ni plating present on the surface is adjusted by irradiating only the surface portion of the can with a laser once more.

[0004] Patent Application No. 2019-539062

[0005] When welding dissimilar metal materials by irradiating a laser, for example, in the case of the combination of iron and copper as described above, the laser is irradiated from the iron or copper side to melt and join them. In this case, due to differences in material properties such as melting points and thermal conductivities between iron and copper, there is a problem that solidification cracks occur near the joint due to segregation of copper in the weld.

[0006] The present invention is intended to solve the above-mentioned conventional problems, and has an object to provide a joining method that suppresses welding defects when welding dissimilar metal materials together.

[0007] The joined body according to the present disclosure includes a first workpiece made of a first metal, a second workpiece made of a second metal different from the first metal, and a joint joining the first workpiece and the second workpiece, the joint including a first joint located on the side of the first workpiece and a second joint located on the side of the second workpiece, and the concentration of the metal contained in the first joint differs from the concentration of the metal contained in the second joint.

[0008] The laser processing method according to the present disclosure is a laser processing method for joining a first member including a first metal and a second member including a second metal different from the first metal, and includes a first step of forming a joint by melting the first metal and the second metal by scanning a first laser beam, and a second step of agitating the metal structure in the vicinity of the joint by scanning a second laser beam having a larger beam diameter and a lower power density than the first laser beam behind the scanning direction of the first laser beam.

[0009] The laser processing apparatus according to the present disclosure includes an irradiation optical system that irradiates a workpiece with a first laser beam in front and a second laser beam in rear along a scanning direction, and a scanning system that scans the workpiece along the scanning direction while irradiating the first laser beam and the second laser beam onto the workpiece.

[0010] As described above, the joined body, laser processing method, and laser processing apparatus according to the present disclosure enable the composition of the joined body obtained after laser welding of dissimilar metal materials to be controlled, thereby avoiding solidification cracking caused by segregation of the dissimilar metal materials in the molten part of the joined body or the formation of intermetallic compounds that may reduce the joining strength of the joined body, thereby achieving good joining of dissimilar metal materials.

[0011] 1 is a schematic perspective view showing a configuration of an optical system using a two-dimensional diffractive optical element as a laser oscillator and a branching optical system in a laser processing apparatus according to a first embodiment. FIG. 2 is a schematic perspective view showing a configuration of an optical system using a laser oscillator and a branching optical system in a laser processing apparatus according to a first modification of the first embodiment. FIG. 3 is a schematic perspective view showing a configuration of an optical system using a three-dimensional diffractive optical element as a laser oscillator and a branching optical system in a laser processing apparatus according to a second modification of the first embodiment. FIG. 4 is a schematic cross-sectional view showing, in time series order, (a), (b), and (c) the state of a cross section of a molten part when a first laser beam and a second laser beam are scanned sequentially in the laser processing method according to the first embodiment. FIG. 5 is a plan view showing laser diameters and inter-beam distances of the first laser beam and the second laser beam irradiated onto a workpiece in the laser processing method according to the first embodiment. FIG. 6 is a schematic view showing, in (a) to (c), the proportion of Cu elements in a cross section after laser beam scanning, divided by the number of laser scans, in a simulation of laser welding of overlapping members of Fe and Cu in the laser processing method according to the first embodiment. Fig. 1 is a schematic diagram showing in time series how dissimilar metals are mixed and stirred near the joining interface of workpieces P1 and P2 in the laser processing method according to embodiment 1. Fig. 2 is a schematic cross-sectional view showing a cross-sectional structure when a multi-branched laser is scanned multiple times in the embodiment. Fig. 3 is an equilibrium diagram between Fe and Cu. Fig. 4 is an equilibrium diagram between Fe and Al. Fig. 4 is an equilibrium diagram between Al and Cu. Fig. 5 is a schematic cross-sectional view showing the cross-sectional structure of a molten zone by lap laser welding of conventional dissimilar metals.

[0012] (Background to the present disclosure) First, we considered the factors that cause solidification cracking during the joining of dissimilar metal materials. The factors that cause solidification cracking can be explained by the elemental composition ratios based on the equilibrium phase diagram as follows: (1) The composition of the joint between dissimilar metals, iron and copper, forms a good solid solution when the copper concentration is within 15 atomic % of region 23 in the Fe-Cu equilibrium phase diagram shown in FIG. 10 . However, in the region where the copper concentration relative to iron is 15 atomic % or more, a solubility gap occurs, making two-phase separation more likely. Furthermore, such solid solution phases with two or more mixed compositions become unstable as the temperature decreases, causing fluctuations in the mixed composition and accelerating two-phase separation, a phenomenon known as spinodal decomposition. It has been reported that copper segregates within the molten metal upon complete solidification, and solidification cracking occurs due to differences in mechanical properties between iron and copper. (2) Regarding the dissimilar metal bonding between iron and aluminum, in the region 24 of the equilibrium phase diagram shown in FIG. 10, the aluminum-rich intermetallic compound Fe is formed in the region where the aluminum concentration relative to the iron is 65 atomic % or more and 75 atomic % or less. ２ Al ５ and FeAl ２ , FeAl ３ It has been reported that in dissimilar metal bonding between aluminum and copper, when the concentration of Al relative to Cu is 30 atomic % or more and 80 atomic % or less, CuAl and CuAl ２ It has been reported that these defects are formed near the interface of the joint, reducing the joint strength and becoming the starting point for cracks.

[0013] From the respective equilibrium diagrams, it can be seen that these are all welding defects that occur when laser irradiation causes dissimilar metals to fall within a specific range of mixing ratios when components are melted and welded. In other words, welding dissimilar metal materials together presents unique challenges, such as poor solidification cracking and the formation of intermetallic compounds that reduce strength and can become the starting point for cracks.

[0014] The inventors noticed that the above-mentioned defects frequently occur near the joint between the metals on the laser irradiated side during laser welding of dissimilar metal materials, and after extensive research to resolve the above-mentioned defects, they discovered that when overlapping members made of dissimilar metal materials are scanned and welded using a branched laser, the mixed region of the dissimilar metals near the joint expands and the overall concentration of each metal decreases, leading to the present invention.

[0015] The present invention relates to laser welding of overlapping dissimilar metal members, which are two plate-shaped members made of either iron, copper, or aluminum. The laser welding method of the present invention is characterized in that the overlapping members are joined by irradiating and scanning the first laser beam from the front side in the scanning direction and the second laser beam from the rear side in the scanning direction, followed by irradiating and scanning the second laser beam from the rear side. This allows the metal structure near the joint formed by irradiating the first laser beam to be agitated by irradiating the second laser beam, thereby reducing the concentration of the dissimilar metal materials mixed during joining of the members, thereby producing a joint that prevents solidification cracking and the formation of intermetallic compounds.

[0016] The following describes aspects of the present disclosure.

[0017] The bonded body according to the first aspect is a bonded body in which a first workpiece made of a first metal and a second workpiece made of a second metal different from the first metal are bonded together by a bonding portion, the bonding portion including a first bonding portion located on the side of the first workpiece and a second bonding portion located on the side of the second workpiece, and the first bonding portion and the second bonding portion have different concentrations of metals contained therein.

[0018] In the joined body of the second aspect, in the above-mentioned first aspect, the first joint may have a thickness greater than that of the second joint when viewed in a cross-sectional view perpendicular to the overlapping direction of the first workpiece material and the second workpiece material.

[0019] A joined body according to a third aspect is the joined body according to the first or second aspect, wherein the first workpiece and the second workpiece may be made of any of iron, copper, and aluminum.

[0020] A joined body according to a fourth aspect may be the third aspect, wherein when the first workpiece is made of iron and the second workpiece is made of copper, the concentration of copper in the first joint may be 15 atomic % or less.

[0021] A joined body according to a fifth aspect may be the third aspect, wherein when the first workpiece is made of copper and the second workpiece is made of iron, the concentration of iron in the first joint may be 20 atomic % or less.

[0022] The joined body according to the sixth aspect may be the third aspect, wherein when the first workpiece is made of iron and the second workpiece is made of aluminum, the concentration of aluminum in the first joint may be 65 atomic % or less.

[0023] A joined body according to a seventh aspect may be the same as that of the third aspect, except that when the first workpiece is made of aluminum and the second workpiece is made of iron, the concentration of iron in the first joint may be 24 atomic % or less.

[0024] The joined body according to the eighth aspect may be the third aspect, wherein when the first workpiece is made of copper and the second workpiece is made of iron, the concentration of iron in the first joint may be 15 atomic % or less.

[0025] A joined body according to a ninth aspect may be the third aspect, wherein when the first workpiece is made of iron and the second workpiece is made of aluminum, the concentration of aluminum in the first joint may be 65 atomic % or less.

[0026] A tenth aspect of the joined body is the third aspect, wherein when the first workpiece is made of copper and the second workpiece is made of aluminum, the iron concentration in the first joint may be 20 atomic % or less.

[0027] The bonded body according to the eleventh aspect may be the same as the third aspect, except that when the first workpiece is made of aluminum and the second workpiece is made of copper, the concentration of copper in the first bonded portion may be 30 atomic % or less.

[0028] A laser processing method according to a twelfth aspect is a laser processing method for joining a first member containing a first metal and a second member containing a second metal different from the first metal, and includes a first step of forming a joint by melting the first metal and the second metal by scanning a first laser beam, and a second step of agitating the metal structure in the vicinity of the joint by scanning a second laser beam having a larger beam diameter and a lower power density than the first laser beam backward in the scanning direction of the first laser beam.

[0029] A laser processing method according to a thirteenth aspect is the twelfth aspect, wherein the beam diameter of the second laser light is between two and three times the beam diameter of the first laser light.

[0030] A laser processing method according to a fourteenth aspect is the twelfth or thirteenth aspect, wherein the first laser light and the second laser light are branched from a single laser light into a plurality of beams in the scanning direction, and the inter-beam distance between adjacent laser lights among the plurality of beams is at least twice the beam diameter of the laser light in the front of the adjacent laser light in the scanning direction, and may be at most twice the beam diameter of the laser light in the rear of the adjacent laser light in the scanning direction.

[0031] A laser processing method according to a fifteenth aspect is the laser processing method according to the fourteenth aspect, wherein the second laser light is a beam from an output source that is branched into a plurality of beams by an optical system.

[0032] A laser processing method according to a sixteenth aspect is the laser processing method according to the fourteenth aspect, wherein the second laser light is a beam from an output source that is split into a plurality of beams by a diffraction grating.

[0033] A laser processing method according to a seventeenth aspect is any one of the twelfth to sixteenth aspects, wherein the second laser light may have a wavelength of 266 nm to 11 μm.

[0034] The laser processing apparatus according to the eighteenth aspect includes an irradiation optical system that irradiates a workpiece with a first laser beam in front and a second laser beam in the rear along a scanning direction, and a scanning system that scans the workpiece along the scanning direction while irradiating the first laser beam and the second laser beam onto the workpiece.

[0035] The laser processing apparatus according to a 19th aspect may be the 18th aspect, wherein the irradiation optical system includes a laser oscillator that emits a single laser beam, and a branching optical system that branches the single laser beam emitted from the laser oscillator into a first laser beam and a second laser beam and irradiates the workpiece along the scanning direction.

[0036] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the following embodiments. Furthermore, appropriate modifications are possible within the scope of the effects of the present disclosure. Furthermore, combinations with other embodiments are also possible.

[0037] The dissimilar metal welding method according to the present disclosure can be applied to lap welding of a combination of metal plate materials commonly used in industry, such as iron, copper, and aluminum.

[0038] First Embodiment <Laser Processing Apparatus> The configuration of a laser processing apparatus according to a first embodiment will be described.

[0039] FIG. 1 is a schematic perspective view showing the configuration of a laser oscillator 7 and an optical system using a two-dimensional diffractive optical element 9a as a branching optical system in a laser processing apparatus 30 according to the first embodiment.

[0040] The laser processing apparatus 30 includes irradiation optical systems 7, 8, 9a, 10a that irradiate workpieces P1, P2 with a first laser beam B5 in the front direction and a second laser beam B6 in the rear direction along the scanning direction 3, and a scanning system (not shown) that scans the workpieces P1, P2 along the scanning direction 3 while irradiating them with the first laser beam B5 and the second laser beam B6. The irradiation optical system includes a laser oscillator 7 that emits a single laser beam B4, and branching optical systems 8, 9a, 10a that branch the single laser beam B4 into the first laser beam B5 and the second laser beam B6 and irradiate the workpieces P1, P2 along the scanning direction 3.

[0041] <Workpiece> The first metal that is the material of workpiece P1 is iron, and has a thickness of 0.3 mm, a laser absorptance of 40% at a wavelength λ of 1070 nm, and a melting point of 1700 K. The second metal that is the material of workpiece P2 is copper, and has a thickness of 0.1 mm, a laser absorptance of 5% at a wavelength λ of 1070 nm, and a melting point of 1300 K. During laser processing, workpiece P1 and workpiece P2 are overlapped and fixed together, and a fixing member is not shown.

[0042] <Irradiation Optical System> The laser oscillator 7 is a continuous wave single mode fiber laser with a wavelength of 1070 nm. The laser light B4 is a substantially parallel light beam emitted by the laser oscillator 7.

[0043] The folding mirror 8 reflects 90% or more of light with a wavelength of 1070 nm. The two-dimensional diffractive optical element 9a transmits 90% or more of light with a wavelength of 1070 nm. Parallel light incident on the two-dimensional diffractive optical element 9a can be transmitted through a lens to form branched beams at the focal position of the lens. The number of branched beams, branching interval, and intensity ratio can be set arbitrarily by changing the pattern of the two-dimensional diffractive optical element 9a. The compatible wavelength of the f-θ lens 10 is 1070 nm, the focal length is 255 mm, and the scanning range is 200 mm x 200 mm. The folding mirror 8, the two-dimensional diffractive optical element 9a, and the f-θ lens 10 correspond to a branching optical system.

[0044] <Operation of Two-Dimensional Diffractive Optical Element> Next, the operation of the two-dimensional diffractive optical element 9a will be described.

[0045] The laser beam B4 emitted from the laser oscillator 7 is bent by a folding mirror 8 at an angle of 45° relative to the vertical direction toward the scanning direction 3, and is then branched into a first laser beam B5 and a second laser beam B6 by passing through a two-dimensional diffractive optical element 9a and an f-θ lens 10a. The focal position of the first laser beam B5, which is irradiated at an angle of 45° relative to the vertical direction toward the scanning direction 3, is set to be the surface of the workpiece P1. Therefore, due to the inclination of the irradiation angle, the irradiation diameter of the second laser beam B6 on the workpiece P1 is larger than that of the first laser beam B5 on the workpiece P1.

[0046] <Scanning System> A scanning system (not shown) irradiates the workpieces P1 and P2 with the first laser beam B5 and the second laser beam B6 while scanning them along the scanning direction 3. The scanning system may be any system that moves the irradiation optical system and the workpieces relative to each other. For example, the scanning system may be any system that moves at least a part of the irradiation optical system along the scanning direction 3. Alternatively, the workpieces P1 and P2 may be moved in the opposite direction to the scanning direction 3 relative to the irradiation optical system. Furthermore, the scanning direction 3 is not limited to a linear direction and may be a curved direction, for example, an arc. Furthermore, the scanning system may be any commonly used driving unit.

[0047] It should be noted that irradiation and scanning with the first and second laser beams B5 and B6 are performed simultaneously, and therefore, for convenience, the term "irradiation" may be omitted when referring to "scanning" except when describing scanning and irradiation separately.

[0048] (Modification 1) FIG. 2 is a schematic perspective view showing a configuration using a laser oscillator 7 and branching optical systems 8, 11, 10a, and 10b in a laser processing apparatus 30a according to Modification 1 of the first embodiment.

[0049] Similar to the configuration using the two-dimensional diffractive optical element shown in FIG. 1 , laser beam B4 is emitted from laser oscillator 7 and split into two beams at the same ratio by half mirror 11. These split first and second laser beams B5 and B6 are focused onto workpiece P1 by two f-θ lenses. In this case, the f-θ lens 10a that focuses first laser beam B5, which is located forward in the scanning direction 3, and the f-θ lens 10b that focuses second laser beam B6, which is located rearward, have the same focal length. Therefore, if the beam diameters are to be different, the beam diameter of second laser beam B6 can be made larger than the beam diameter of first laser beam B5 by shifting the lens positions in the height direction. Furthermore, the focal length of f-θ lens 10b that focuses second laser beam B6 may be different from that of the f-θ lens that focuses first laser beam B5.

[0050] 3 is a schematic perspective view showing the configuration of an optical system that uses a laser oscillator 7 and a three-dimensional diffractive optical element 9b as a branching optical system in a laser processing apparatus 30b according to a second modification of embodiment 1. Unlike the two-dimensional diffractive optical element 9a, the three-dimensional diffractive optical element 9b does not determine the focal diameter on the focal plane after light passes through a lens, but rather can change the focal direction of branched beams in the optical axis direction.

[0051] This eliminates restrictions on the configuration of the device, such as interference between f-θ lens 10a and f-θ lens 10b in the configuration shown in Fig. 2. Furthermore, by setting the angle of reflection of the laser by reflection mirror 8 to 90° incidence, which is generally used in laser processing, and without adjusting the mirror angle to 45°, it is possible to set the beam diameters of first laser beam B5 and second laser beam B6 to any desired diameters and to set inter-beam distance L15 to any desired inter-beam distance.

[0052] The wavelength of the laser light emitted from the laser oscillator 7 shown in FIGS. 1 to 3 of the present disclosure may be in the range of 266 nm to 11 μm, which is a wavelength range that allows laser welding.

[0053] Although the mirror angle is set to 45° in FIG. 2, other angles may be used as long as a difference in focal diameter between the first laser beam B5 and the second laser beam B6 can be created.

[0054] Figure 4 is a schematic cross-sectional view showing the cross-sectional state of the molten part in time series in the order of (a), (b), and (c) when the first laser light B5 and the second laser light B6 are scanned sequentially on the overlapping workpiece P1 and workpiece P2 in the laser processing method of embodiment 1.

[0055] The first molten zone 12a is a portion melted by the incidence of the first laser beam B5. The second molten zone 12b is a portion melted by the second laser beam B6 branched off from the first laser beam B5. The inter-beam distance L15 is the distance between the centers of the first laser beam B5 and the second laser beam B6 branched off from the rear.

[0056] The molten zone formed in the laser processing method according to the first embodiment will be described in chronological order with reference to Figure 4. (1) As shown in Figure 4(a), a first laser beam B5 is incident on the joint between dissimilar metal materials, workpiece P1 and workpiece P2, and scanned in the scanning direction 3. The workpiece P1 and workpiece P2 are melted to form a first molten zone 12a. (2) As shown in Figure 4(b), a second laser beam B6 branched off from the first laser beam B5 is scanned to form a second molten zone 12b that melts into the workpiece P1 up to the vicinity of the joint.

[0057] At this time, the penetration depth of the second fusion zone 12b needs to be such that it does not penetrate the workpiece P1 and does not reach the workpiece P2, and an ideal stirring effect can be obtained by penetrating to a depth of 80% to 95% of the thickness of the workpiece P1. (3) As shown in Figure 4(c), the first laser beam B5 and the second laser beam B6 are scanned in the scanning direction 3, and both the first laser beam B5 and the second laser beam B6 are scanned in a manner that they run through to the ends of the workpieces P1 and P2, thereby obtaining a joined body.

[0058] In this case, the following relationship exists: the penetration depth of the first molten zone 12a≦the thickness of the workpiece P1≦the penetration depth of the second molten zone 12b≦the thickness of the workpiece P1+the thickness of the workpiece P2. As described above, the joined body shown in FIG. 4(c) includes a workpiece P1 (an example of a first workpiece), a workpiece P2 (an example of a second workpiece), a first molten zone 12a (an example of a first joining zone), and a second molten zone 12b (an example of a second joining zone). Here, the first molten zone 12a and the second molten zone 12b are an example of a joining zone that joins the workpiece P1 and the workpiece P2.

[0059] Figure 5 is a plan view showing the beam diameters D13, D14 and inter-beam distance L15 of the first laser light B5 and the second laser light B6 irradiated onto the workpiece P1 in the laser processing method according to embodiment 1.

[0060] The beam diameter of the first laser beam B5 in the forward direction in the scanning direction 3 is D13, and the beam diameter of the second laser beam B6 branched backward is D14. The inter-beam distance between the first laser beam B5 and the second laser beam B6 is L15.

[0061] The first laser beam B5 and the second laser beam B6 irradiated onto the surface of the workpiece P1 are scanned at the same speed in the scanning direction 3 with a beam distance L15 between them. The focused diameter of the second laser beam B6 branched backward at the processing point is larger than that of the first laser beam B5. If the beam diameter D14 is small, the volume of the stirred molten pool will be small and insufficient stirring will occur. Conversely, if the beam diameter D14 is too large, a large keyhole will be formed where the first laser beam B5 and the second laser beam B6 are integrated, preventing the desired stirring effect. Therefore, in order to control the composition of the molten zone and achieve sufficient stirring, it is desirable that the beam diameter D14 be between two and three times the beam diameter D13.

[0062] Furthermore, if the inter-beam distance L15 is too small, the first laser beam B5 and the second laser beam B6 will be integrated to form a large keyhole, and the desired stirring effect will not be obtained. Furthermore, if the inter-beam distance L15 is too large, solidification of the first molten zone 12a melted by the first laser beam B5 will proceed, and convection will not be promoted in the area scanned by the second laser beam B6, resulting in a failure to obtain a sufficient stirring effect. Therefore, a sufficient stirring effect can be obtained by setting the inter-beam distance L15 to a distance between two times the beam diameter D13 and two times the beam diameter D14.

[0063] 6A to 6C are schematic diagrams showing the proportion of Cu elements in a cross section after laser beam scanning, divided by the number of laser scans, in a simulation of laser welding of overlapping members of Fe and Cu in the laser processing method according to embodiment 1.

[0064] 6A is a schematic diagram showing the model before laser irradiation. The thick rectangular member at the top of the model represents the Fe workpiece P1, and the thin rectangular member at the bottom of the model represents the Cu workpiece P2.

[0065] 6(b) is a schematic diagram showing the concentration of Cu in a cross section after the workpieces P1 and P2 are joined by scanning only the first laser beam B5. In a typical lap welding using a single laser beam, the Cu concentration exceeds 15 atomic % inside the workpiece P1 made of Fe, and there are many regions such as regions 16a and 17a where solidification cracking occurs.

[0066] 6C is a cross-sectional view showing the state where the second laser beam B6 branched backward after the first laser beam B5 is scanned. As a result of the agitation of the vicinity of the weld with the second laser beam B6, the Cu concentration in regions 16b and 17b, which are the same as regions 16a and 17a in FIG. 6B, where the Cu concentration exceeded 15 atomic %, was significantly reduced to 10 atomic % or less, at which solidification cracking did not occur.

[0067] Figure 7 is a schematic diagram showing, in chronological order (a), (b), and (c), the mixing and stirring of dissimilar metals near the joining interface between the workpiece P1 and the workpiece P2 when the workpiece P1 and the workpiece P2 are superimposed and scanned with the first laser light B5 and the second laser light B6 in the laser processing method of embodiment 1.

[0068] The explanation will be given in chronological order.

[0069] 7A, a first laser beam B5 is irradiated onto the overlapping dissimilar metal materials of the workpiece P1 and the workpiece P2, and a region m18 of a mixed layer of dissimilar metals of the workpiece P1 and the workpiece P2 is formed above the joint between the workpiece P1 and the workpiece P2. In this mixed layer region m18 of dissimilar metals, there are locations where the proportion of the metals that make up the workpiece P2 is several tens of atomic percent or more, as in the above-mentioned FIG. 6B.

[0070] 7(b) shows the state when the second laser beam B6 branched off from the first laser beam B5 is irradiated, penetrates into the vicinity of the interface between the workpieces P1 and P2, and is scanned. The second laser beam B6 has a diameter two to three times larger than the diameter of the first laser beam B5 used for joining, and scanning this beam promotes convection, stirring the metal elements constituting the workpiece P2 in the region m18 over a wide area within the workpiece P1. The second laser beam B6 is scanned along the scanning direction 3.

[0071] c) As shown in (c) of Figure 7, the metal elements that make up the workpiece P2 are stirred over a wide range including region m18, and a region m19 of a heterogeneous metal mixed layer is formed in which the proportion of metal elements that make up the workpiece P2 is reduced compared to region m18.

[0072] In (c) of Figure 7, the first laser beam B5 joins the overlapping workpieces P1 and P2, and the second laser beam B6 branched off to the rear reaches the ends of the workpieces P1 and P2, completely filling in the area m18 of the mixed layer of different metals, forming an area m19 up to the end of the member.

[0073] (Regarding Welding Defects) As described in the problem section, for example, when welding a workpiece P1 made of Fe to a workpiece P2 made of Cu, solidification cracking occurs as a defect in the dissimilar metal joint. Furthermore, when welding other metals such as Fe and Al, or Cu and Al, the formation of intermetallic compounds reduces the joint strength. The dominant factor is thought to be the influence of the atomic ratio of dissimilar metal materials contained in regions m18 and m19 of the dissimilar metal mixed layer near the joint being within a specific range when the workpiece P1 and the workpiece P2 are joined. In the laser processing method according to the present disclosure, the ratios of the structures in regions m18 and m19 are controlled as follows, with the aim of suppressing solidification cracking and suppressing the formation of an intermetallic compound layer.

[0074] When the method of the present disclosure is used and the workpiece P1 is Fe and the workpiece P2 is Cu, the proportion of Cu in region m19 is controlled to 15 atomic % or less so as not to fall within the proportion of region 23 in the equilibrium diagram shown in Fig. 9. On the other hand, when the workpiece P1 is Cu and the workpiece P2 is Fe, by setting the proportion of Cu in region m19 to 90 atomic % or more, solidification cracking does not occur and a good solid solution is formed.

[0075] (Suppression of formation of intermetallic compound layer) (1) When the combination of workpiece P1 and workpiece P2 is Al and Cu, the overlapping members are welded by laser scanning, and the regions m18 and m19 of the mixed layer of dissimilar metals near the joint become a mixed layer of Al and Cu. According to the Al-Cu equilibrium phase diagram of Figure 11, when the ratio of Cu in the mixed layer of dissimilar metals m18 and m19 of Al and Cu is in the range of 52.5 atomic % to 90 atomic %, the intermetallic compound CuAl ２(2) When the combination of the workpiece P1 and the workpiece P2 is Fe and Al, M1 in the vicinity of the welded joint is similarly a mixed layer of Fe and Al. When the Al ratio is in the region 24 of the Fe-Al equilibrium diagram in Figure 10, which is between 65 atomic % and 67 atomic %, FeAl ２ , 71 atomic % to 73 atomic % is Fe ２ Al ５ , 76 atomic % FeAl ３ Aluminum-rich intermetallic compounds such as

[0076] These intermetallic compounds have harder and more brittle mechanical properties than the simple substances Cu, Al, and Fe, and therefore when a load is applied, they are more likely to become the starting point for cracks, which causes a decrease in the strength of the welded joint.

[0077] By using the method of the present disclosure, the mixed region m18 is stirred over a wider range with a second laser beam B6 branched from the first laser beam B5 used for joining, and a region of a mixed layer of different metals such as a region m19 in which the mixed ratio of Al, Cu, Fe, and Al is reduced is created, thereby making it possible to suppress the formation of an intermetallic compound layer.

[0078] Furthermore, the workpiece P1 and workpiece P2 on the laser irradiation side in this disclosure shown in Figures 1 and onwards are plate materials made primarily of iron, copper, and aluminum, and the effect is achieved even if they are plated with a few microns of Ni or the like.

[0079] (Regarding multi-branch irradiation) In the present invention, the second laser beam B6 is scanned from behind the first laser beam B5 for welding in order to stir the molten zone, but there are cases where this single stirring does not sufficiently stir the mixed portion of the dissimilar metals in the molten zone. In such cases, as shown in Figure 8, the molten zone that has been stirred once may be re-stirred by scanning with a third laser beam B20 that is further branched from behind.

[0080] 8A is a schematic cross-sectional view showing a third molten portion 22 after further stirring by three beam scanning including a third laser beam B20 branched further rearward from the rearward branched second laser beam B6 in a region m18 of the different metal mixed layer formed by scanning with the second laser beam B6. The third molten portion 22 is formed by stirring the second molten portion 12b once stirred by the second laser beam B6 again by the third laser beam B20.

[0081] At this time, the third fusion zone 22 melts to a depth that is 80% to 95% of the melting depth of the second fusion zone 12b, thereby achieving the effect of stirring a wide range.

[0082] FIG. 8B shows the simulation results when the molten part that has been stirred once is stirred again by a third laser beam that is scanned from behind, as described above.

[0083] The simulation results in Figure 8(b) confirm that the Cu concentration in the entire heterogeneous metal mixed region after two stirring scans is lower than the Cu concentration in the entire heterogeneous metal mixed region after one stirring scan in the embodiment shown in Figure 6(c), and it can be seen that a good joint is formed.

[0084] (Regarding an embodiment of three-branch stirring scanning) The focused diameter (beam diameter D20) of the third laser beam B20 branched backward at the processing point diameter is preferably larger than those of the first laser beam B5 and the second laser beam B6. Moreover, in order to obtain a stirring effect over a wide range while controlling the composition of the molten zone based on the results of a simulation, the beam diameter D20 is preferably two to three times the diameter of the beam diameter D14 of the second laser beam B6.

[0085] Regarding the inter-beam distance L21, a simulation also showed that if the inter-beam distance L21 is too small, the second laser beam B6 and the third laser beam B20 become one and form a large keyhole, and the desired stirring effect cannot be obtained. Furthermore, if the inter-beam distance L21 is too large, convection in the area scanned by the third laser beam B20 is not promoted, and a sufficient stirring effect cannot be obtained. Therefore, a sufficient stirring effect can be obtained by setting the inter-beam distance L21 to a distance approximately the same as the inter-beam distance L15.

[0086] It should be noted that the present disclosure includes appropriate combinations of any of the various embodiments and / or examples described above, and can achieve the effects of each embodiment and / or example.

[0087] According to the laser processing method and laser processing apparatus disclosed herein, overlapping members are joined by irradiating and scanning a first laser beam from the front, followed by irradiating and scanning a second laser beam from the rear. This agitates the metal structure near the joint by irradiating the second laser beam, reducing the concentration of the dissimilar metal materials in the joint, thereby creating a joint that prevents solidification cracking and the formation of intermetallic compounds. Therefore, this method is useful for joining dissimilar metal materials.

[0088] 3 Scanning direction 7 Laser oscillator 8 Folding mirror 9a, 9b Two-dimensional diffractive optical element 10, 10a f-θ lens 11 Half mirror 12a First fusion zone 12b Second fusion zone 22 Third fusion zone 23 Region 24 Region 25 Region 26 Can 27 Negative electrode tab 28 Fusion zone 29 Re-melted portion 30, 30a, 30b Laser processing device P1 Workpiece P2 Workpiece B4 Laser beam B5 First laser beam B6 Second laser beam B20 Third laser beam D13 Beam diameter D14 Beam diameter D20 Beam diameter

Claims

1. a first workpiece made of a first metal; a second workpiece made of a second metal different from the first metal; a joining portion that joins the first workpiece and the second workpiece; Equipped with The joint portion includes a first joint portion located on a side of the first workpiece and a second joint portion located on a side of the second workpiece, The concentration of the metal contained in the first joint is different from the concentration of the metal contained in the second joint. zygote.

2. In a cross-sectional view in a direction perpendicular to a direction in which the first workpiece and the second workpiece are overlapped, the first joint portion has a thickness greater than that of the second joint portion. The joint body according to claim 1 .

3. Each of the first workpiece and the second workpiece is made of any one of iron, copper, and aluminum. The bonded body according to claim 1 or 2.

4. the first workpiece is made of iron, the second workpiece is made of copper; The copper concentration in the first bonding portion is 15 atomic % or less. The joint body according to claim 3.

5. The first workpiece is made of copper, the second workpiece is made of iron; The concentration of iron in the first joint is 20 atomic % or less. The joint body according to claim 3.

6. the first workpiece is made of iron, the second workpiece is made of aluminum; The aluminum concentration in the first bonding portion is 65 atomic % or less. The joint body according to claim 3.

7. the first workpiece is made of aluminum, the second workpiece is made of iron; The iron concentration in the first joint is 24 atomic % or less. The joint body according to claim 3.

8. The first workpiece is made of copper, the second workpiece is made of iron; The iron concentration in the first joint is 15 atomic % or less. The joint body according to claim 3.

9. the first workpiece is made of iron, the second workpiece is made of aluminum; The aluminum concentration in the first bonding portion is 65 atomic % or less. The joint body according to claim 3.

10. The first workpiece is made of copper, the second workpiece is made of aluminum; The concentration of iron in the first joint is 20 atomic % or less. The joint body according to claim 3.

11. the first workpiece is made of aluminum, the second workpiece is made of copper; The copper concentration in the first bonding portion is 30 atomic % or less. The joint body according to claim 3.

12. A laser processing method for joining a first member including a first metal and a second member including a second metal different from the first metal, comprising: a first step of forming a joint by melting the first metal and the second metal by scanning a first laser light; a second step of scanning a second laser beam having a larger beam diameter and a lower power density than the first laser beam backward in the scanning direction of the first laser beam to stir the metal structure in the vicinity of the weld; 、 A laser processing method comprising:

13. a beam diameter of the second laser beam is two or more and three or less times the beam diameter of the first laser beam; The laser processing method according to claim 12.

14. the first laser beam and the second laser beam are branched into a plurality of beams in a scanning direction from a single laser beam, The distance between adjacent laser beams among the plurality of split beams is The beam diameter of the adjacent laser beams is more than twice the beam diameter of the laser beam at the front in the scanning direction, and is less than twice the beam diameter of the adjacent laser beams at the rear in the scanning direction. The laser processing method according to claim 12.

15. The second laser light is a beam from an output source which is split into a plurality of beams by an optical system. The laser processing method according to claim 14.

16. The second laser light is a beam from an output source, which is split into a plurality of beams by a diffraction grating. The laser processing method according to claim 14.

17. The laser processing method according to any one of claims 12 to 16, wherein the second laser light has a wavelength of 266 nm to 11 µm.

18. an irradiation optical system that irradiates a workpiece with a first laser beam in a forward direction and a second laser beam in a backward direction along a scanning direction; a scanning system that scans the workpiece along a scanning direction while irradiating the workpiece with the first laser light and the second laser light; A laser processing device comprising:

19. The irradiation optical system includes: A laser oscillator that emits a single laser beam; 19. The laser processing apparatus according to claim 18, further comprising: a branching optical system that branches a single laser beam emitted from the laser oscillator into a first laser beam and a second laser beam and irradiates the first laser beam and the second laser beam onto a workpiece along a scanning direction.