Dissimilar metal laser welding method and dissimilar metal joint

Abstract

To improve a bond strength.SOLUTION: A method for performing lap welding of a first member comprising a first metal and a second member comprising a second metal different from the first metal by laser, includes (a) radiating laser from the first component side, (b) intermittently radiating while moving laser, (c) making a laser radiation direction inclined with respect to a lap direction of the first component and the second component, (d) when viewed in the lap direction from the first component side, making a laser radiation direction at a first irradiation point a first radiation direction, and a laser radiation direction at a second irradiation point separated from the first irradiation point a second radiation direction different from the first radiation direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for laser welding dissimilar metals and a joint. [Background technology]

[0002] Laser welding dissimilar metals is more difficult than laser welding the same kind of metals. For example, welding an iron member with a non-ferrous metal member such as an aluminum alloy is difficult from the viewpoint of ensuring weld strength. When an iron member and an aluminum alloy member are overlapped and laser welded, an intermetallic compound is formed in the bead. This intermetallic compound is brittle, making it difficult to ensure joint strength. In response to this, Patent Documents 1 to 3 listed below propose various methods, such as forming a wedge-shaped bead, but these are not sufficient. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-136489 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-125829 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-4619 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to improve the bonding strength when bonding dissimilar metals together. [Means for solving the problem]

[0005] The laser welding method for dissimilar metals according to the present invention is a method for lap-welding a first member made of a first metal and a second member made of a second metal different from the first metal using a laser, and has the following configuration. (a) Irradiating the laser from the first member side; (b) Intermittent irradiation while moving the laser. (c) The laser irradiation direction is set to a direction inclined with respect to the overlapping direction of the first member and the second member. (d) When viewed from the first component side in the overlapping direction, the laser irradiation direction at the first irradiation point is a first irradiation direction, and the laser irradiation direction at the second irradiation point away from the first irradiation point is a second irradiation direction different from the first irradiation direction.

[0006] According to this method, the laser is irradiated from the first member side, so the bead extends from the first member side toward the second member side. Since the laser is irradiated intermittently while moving, the bead is spot-shaped, and the beads are formed intermittently at intervals along the laser movement path. Furthermore, since the laser irradiation direction is inclined with respect to the overlapping direction of the first and second members (hereinafter simply referred to as the overlapping direction), the bead extends from the first member side toward the second member side in a direction inclined with respect to the overlapping direction. The first irradiation direction of the first irradiation point and the second irradiation direction of the second irradiation point are different from each other. Therefore, the extending direction of the bead extending obliquely from the first member side toward the second member side is different between the first irradiation point and the second irradiation point. That is, if the extension direction of the first bead formed at the first irradiation point is defined as the first extension direction and the extension direction of the second bead formed at the second irradiation point is defined as the second extension direction, the first extension direction and the second extension direction are different from each other. Therefore, even if the second member attempts to separate from the first member in a direction along the first extension direction, the second bead extending in the second extension direction prevents the separation in the first extension direction. Also, even if the second member attempts to separate from the first member in a direction along the second extension direction, the first bead extending in the first extension direction prevents the separation in the second extension direction. In this way, the cooperation of the first bead extending in the first extension direction and the second bead extending in the second extension direction effectively prevents the first member and the second member from separating from each other, resulting in high joining strength.

[0007] In particular, it is preferable that the laser irradiation directions of adjacent irradiation points are different from each other. That is, by forming the first irradiation point and the second irradiation point adjacent to each other and the first bead extending in the first extension direction and the second bead extending in the second extension direction adjacent to each other, the first member and the second member are more effectively prevented from separating from each other, and the joining strength is further improved.

[0008] Furthermore, it is preferable to change the laser irradiation directions of adjacent irradiation points so that they are not aligned in a straight line when viewed from the first member side in the overlapping direction. When the laser irradiation directions of adjacent irradiation points are aligned in a straight line, the laser irradiation directions of adjacent irradiation points are aligned in a 0-degree direction and a 180-degree direction when viewed from the first member side in the overlapping direction. That is, when viewed from the first member side in the overlapping direction as shown in Figure 5, there are two combinations: one in which the laser irradiation direction at one irradiation point faces the other irradiation point and the laser irradiation direction at the other irradiation point faces the one irradiation point, as in the combination shown in part C of Figure 5; and one in which the laser irradiation direction at one irradiation point faces the 180-degree opposite side from the other irradiation point and the laser irradiation direction at the other irradiation point faces the 180-degree opposite side from the one irradiation point, as in the combination shown in part D of Figure 5. In either case, if the laser irradiation directions of adjacent irradiation points are aligned in a straight line, the extension directions of the beads formed at the adjacent irradiation points will be aligned in a straight line when viewed from the first member side, which may cause cracks to occur on that line. Therefore, it is preferable to set the irradiation direction so that the extension directions of the beads formed at adjacent irradiation points are not aligned in a straight line when viewed from the first member side.

[0009] Furthermore, it is preferable that the melting point of the first metal is higher than that of the second metal. Since the laser is irradiated from the first member side, which has a relatively higher melting point, it is possible to reliably melt the first member and easily extend the bead to the second member.

[0010] Furthermore, the dissimilar metal joined body according to the present invention is a dissimilar metal joined body in which a first member made of a first metal and a second member made of a second metal different from the first metal are lap-welded, and has the following configuration. (e) The bead extends from the first member side toward the second member side. (f) Spot-like beads are formed intermittently at intervals. (g) The bead extends from the first member side toward the second member side in a direction inclined with respect to the overlapping direction of the first member and the second member. (h) When viewed in the overlapping direction from the first member side, it has a first bead whose extension direction from the first member side to the second member side is a first extension direction, and a second bead whose extension direction from the first member side to the second member side is a second extension direction different from the first extension direction.

[0011] According to this configuration, even if the second member attempts to separate from the first member in a direction along the first extension direction, the second bead extending in the second extension direction prevents the separation in the direction along the first extension direction. Also, even if the second member attempts to separate from the first member in a direction along the second extension direction, the first bead extending in the first extension direction prevents the separation in the direction along the second extension direction. In this way, cooperation between the first bead extending in the first extension direction and the second bead extending in the second extension direction effectively prevents the first member and the second member from separating from each other, resulting in high joining strength. [Effects of the Invention]

[0012] As described above, the first beads extending in the first stretching direction and the second beads extending in the second stretching direction cooperate to improve the bonding strength. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a plan view of a main part of a bonded body according to an embodiment of the present invention, viewed from the first member side in the overlapping direction. [Figure 2] Enlarged view of the main part of Figure 1. [Figure 3] (a) is a cross-sectional view taken along line AA in Figure 2, and (b) is a cross-sectional view taken along line BB in Figure 2. [Figure 4] 10(a) and 10(b) are plan views of a bonded body according to another embodiment of the present invention, viewed from the first member side in the overlapping direction. [Figure 5] FIG. 10 is a plan view of a joined body according to another embodiment of the present invention, viewed from the first member side in the overlapping direction. [Figure 6] 10(a) and 10(b) are plan views of a bonded body according to another embodiment of the present invention, viewed from the first member side in the overlapping direction. [Figure 7] FIG. 10 is a plan view of a joined body according to another embodiment of the present invention, viewed from the first member side in the overlapping direction. [Figure 8] FIG. 10 is a plan view of a joined body according to another embodiment of the present invention, viewed from the first member side in the overlapping direction. [Figure 9] FIG. 10 is a plan view of a joined body according to another embodiment of the present invention, viewed from the first member side in the overlapping direction. [Figure 10] FIG. 10 is a plan view of a joined body according to another embodiment of the present invention, viewed from the first member side in the overlapping direction. DETAILED DESCRIPTION OF THE INVENTION

[0014] A laser welding method and a joined body according to one embodiment of the present invention will be described below with reference to the drawings. The joined body is made of metal. The joined body is formed by joining two metal members. That is, the joined body includes a first member 1 and a second member 2, both of which are made of metal. The joined body is formed by overlapping the first member 1 and the second member 2 and joining them together at predetermined locations to form an integrated body.

[0015] Specifically, the first member 1 and the second member 2 are made of different metals. Therefore, the bonded body is a bonded body of dissimilar metals. The first member 1 is made of a first metal. The second member 2 is made of a second metal different from the first metal. The first metal has a first melting point. The second metal has a second melting point. The first melting point is higher than the second melting point. The types of metals for the first member 1 and the second member 2 may vary. Typically, the first member 1 is steel, and the second member 2 is an aluminum alloy. The first member 1 and the second member 2 may each have a variety of forms. For example, the first member 1 may be a plate material, and the second member 2 may be a cast material such as a die-cast material.

[0016] The first member 1 and the second member 2 are welded by a laser. That is, the joining method is laser welding. As shown in FIG. 3, the laser 3 is irradiated from the first member 1 side. In this embodiment, the thickness T1 of the first member 1 is thinner than the thickness T2 of the second member 2. By irradiating the first member 1 with the laser 3, the first member 1, which has a higher melting point, melts first, followed by the second member 2, which has a lower melting point. Then, a bead 4 (weld bead) is formed. In the drawing, the bead 4 is indicated by a number of dots.

[0017] A laser 3 (torch) is moved along the joint. The movement path 10 of the laser 3 is arbitrary and may be linear. In this embodiment, as shown by the two-dot chain line in Figures 1 and 2, in a plan view of the joined body seen from the first member 1 side in the overlapping direction X, the movement path 10 of the laser 3 is a waveform (sine curve) that has a predetermined amplitude 11 and vibrates left and right with respect to a predetermined direction. Note that the amplitude 11 and wavelength 12 of the waveform are arbitrary. In a plan view, the movement path 10 connects the centers of the base ends 4a of the beads 4.

[0018] The laser 3 is not irradiated continuously but intermittently. That is, the laser 3 is irradiated intermittently while moving along a predetermined movement path 10. Therefore, the beads 4 are not formed in a continuous line along the movement path 10 of the laser 3, but are formed in spots at intervals along the movement path 10 of the laser 3, as shown in FIGS. 1 and 2. The beads 4 are formed in a dashed line along the movement path 10. The interval between adjacent beads 4 may be constant or may vary. In this embodiment, the interval between adjacent beads 4 is constant. The irradiation points of the laser 3 are provided at regular intervals along the movement path 10 of the laser 3, and the beads 4 are formed at regular intervals along the movement path 10 of the laser 3.

[0019] The bead 4 has a wedge shape. The bead 4 has a base end 4a on the first member 1 side and a tip end 4b on the second member 2 side, and is tapered toward the tip end 4b. In the drawings, the shape of the bead 4 is simplified and shown as a cone. The bead 4 passes through the joining surface 5 between the first member 1 and the second member 2 and reaches the second member 2, but does not penetrate the second member 2. Therefore, the bead 4 is a non-penetrating bead. The bead 4 preferably extends into the second member 2 to a depth approximately equal to the thickness T1 of the first member 1. In other words, the extension depth D of the bead 4 into the second member 2 (depth in the overlap direction X) is preferably equal to or greater than the thickness T1 of the first member 1. The extension depth D is the depth in the overlap direction X, and is the dimension in the overlap direction X from the joining surface 5 to the tip end 4b of the bead 4.

[0020] The laser 3 is not irradiated perpendicularly to the first member 1 but is irradiated obliquely. That is, the irradiation direction 3a of the laser 3 is inclined with respect to the overlapping direction X. In FIG. 3, the inclination angle θ of the irradiation direction 3a of the laser 3 with respect to the overlapping direction X is indicated in a cross-sectional view. As shown in FIGS. 1 and 2, the irradiation direction 3a of the laser 3 is not constant in a plan view but changes along the movement path 10 of the laser 3. The change may take various forms. Preferably, the irradiation directions 3a of the laser 3 at adjacent irradiation points P in a plan view are different from each other. In a plan view, the first irradiation direction 3a of the laser 3 at a first irradiation point P is different from the second irradiation direction 3a of the laser 3 at a second irradiation point P adjacent to the first irradiation point P. In FIG. 2, the irradiation direction 3a of the laser 3 at each irradiation point P in a plan view is indicated by a dashed arrow. The irradiation direction 3a of the laser 3 in a plan view is a direction from the center of the bead 4 on the surface of the first member 1 (the center of the base end 4a of the bead 4) toward the tip end 4b of the bead 4. The bead 4 extends from the first member 1 side to the second member 2 side along the irradiation direction 3a of the laser 3, and therefore the irradiation direction 3a of the laser 3 is the extension direction of the bead 4.

[0021] The degree of change from the first irradiation direction 3a of the first irradiation point P to the second irradiation direction 3a of the second irradiation point P is arbitrary, but in this embodiment, the directions are opposite left and right with respect to the movement path 10 of the laser 3 for each group. That is, there is a first group 21 in which the irradiation direction 3a of the laser 3 (extension direction of the bead 4) faces a first left-right direction with respect to the traveling direction of the laser 3 in a plan view, and a second group 22 in which the irradiation direction 3a of the laser 3 faces a second left-right direction that is opposite to the first left-right direction with respect to the traveling direction of the laser 3. The first group 21 is made up of a plurality of irradiation points P. That is, the first group 21 is made up of a plurality of beads 4. The second group 22 is similarly made up of a plurality of irradiation points P and a plurality of beads 4.

[0022] The first group 21 and the second group 22 alternate. The number of irradiation points P and beads 4 in the first group 21 is arbitrary, and the number of irradiation points P and beads 4 in the second group 22 is also arbitrary. However, in this embodiment, the number of irradiation points P and beads 4 in the first group 21 and the number of irradiation points P and beads 4 in the second group 22 are the same, for example, three each. Furthermore, in this embodiment, at each irradiation point P, the irradiation direction 3a of the laser 3 is inclined at an angle close to a right angle with respect to the movement path 10 of the laser 3 in a plan view. Therefore, in a plan view, the irradiation direction 3a of the laser 3 at each irradiation point P does not follow the movement path 10 of the laser 3, and the irradiation directions 3a of the laser 3 of adjacent irradiation points P are not aligned in a straight line. In this embodiment, the irradiation direction 3a of the laser 3 is approximately perpendicular to the movement path 10 of the laser 3 in a planar view, but it does not have to be approximately perpendicular, and even in that case, it is preferable that the direction be inclined at a predetermined angle to the movement path 10 of the laser 3 in a planar view.

[0023] When switching from the first group 21 to the second group 22, and when switching from the second group 22 to the first group 21, the irradiation direction 3a of the laser 3 and the extension direction of the bead 4 at adjacent irradiation points P are reversed by 180 degrees in plan view. Furthermore, within each group, the irradiation direction 3a of the laser 3 in plan view also changes sequentially. Within the first group 21, the irradiation direction 3a of the laser 3 in plan view gradually changes along the movement path 10 of the laser 3, and similarly changes within the second group 22.

[0024] As described above, in this embodiment, the laser 3 is irradiated from the first member 1 side. This ensures that the first member 1, which has a high melting point, can be reliably melted, and the bead 4 can easily extend to the second member 2. Furthermore, because the laser 3 movement path 10 is not linear but wavy, the welded portion can be made wide according to the predetermined amplitude 11, making it easy to increase the joining strength. Furthermore, by intermittently irradiating the laser 3, spot-shaped beads 4 are formed, and the extension direction of the beads 4 in a plan view is sequentially changed along the laser 3 movement path 10. Therefore, when the first member 1 and the second member 2 attempt to separate from each other, the multiple beads 4 with different extension directions cooperate to prevent the separation. This results in high joining strength. In particular, because adjacent beads 4 have different extension directions, the adjacent beads 4 cooperate to prevent the members from separating, further increasing the joining strength. Furthermore, since the extension direction of the bead 4 relative to the moving path 10 is reversed left and right for each group, i.e., the first group 21 and the second group 22, it is easier to control the angle of the torch compared to when the extension direction is reversed left and right for each bead 4.

[0025] However, as shown in FIG. 4, the extension direction of the beads 4 relative to the moving path 10 (the irradiation direction 3a of the laser 3) may be reversed left and right for each bead 4, without forming a group. In the bonded structure shown in FIG. 4, the extension direction of the beads 4 alternately reverses left and right along the moving path 10. In FIG. 4(a), the moving path 10 is zigzag rather than linear, while in FIG. 4(b), it is linear. When the moving path 10 is linear, the base ends 4a of the beads 4 are formed in a linear row with intervals between them. Furthermore, the extension direction of the beads 4 is not perpendicular to the moving path 10, but has an inclination angle of less than 90 degrees. The extension direction of all the beads 4 faces forward or backward relative to the moving direction of the laser 3. Therefore, the inclination angle of the torch can be easily controlled.

[0026] The extension directions of adjacent beads 4 may be aligned in a straight line in a plan view. For example, in FIG. 5, the movement path 10 is linear, and the extension direction of the beads 4 is aligned along the movement path 10. In part C of FIG. 5, the tip ends 4b of adjacent beads 4 face each other. In part D of FIG. 5, the tip ends 4b of adjacent beads 4 face opposite each other. In a plan view, the extension direction of the beads 4 is not inclined with respect to the movement path 10 but is aligned along the movement path 10.

[0027] 6(a), the movement path 10 may be formed in a zigzag shape, and the extension direction of the bead 4 may be alternately reversed by 180 degrees to the left and right of the movement path 10. As shown in FIG. 6(b), the movement path 10 may be linear instead of zigzag.

[0028] Furthermore, the beads 4 may be formed radially. For example, as shown in FIG. 7, radial array groups 30 each having a plurality of beads 4 arranged radially may be arranged at intervals along a predetermined direction. In this case, the movement path 10 of the laser 3 in the radial array group 30 is circular, and irradiation points P are located at predetermined angles on each circle. A plurality of such radial array groups 30 are arranged at intervals along a predetermined direction. In this embodiment, the radial array group 30 is composed of four beads 4, but the number is arbitrary. The four beads 4 are arranged in a cross shape on the same circle. That is, the beads 4 are arranged at 90-degree intervals, and are located at 0-degree, 90-degree, 180-degree, and 270-degree positions, respectively. In the radial array group 30, the extension direction of each bead 4 is not toward the center of the cross direction but toward the outside. That is, the extension direction of all the beads 4 faces radially outward, and in a plan view, the base end 4a of the bead 4 is located radially inward, and the tip end 4b of the bead 4 is located radially outward.

[0029] 8, multiple types, for example, two types of radiating array groups 30 may be provided. The two types of radiating array groups 30 may be arranged alternately. For example, first radiating array groups 31 arranged in a cross shape at the 0-degree position, the 90-degree position, the 180-degree position, and the 270-degree position, and second radiating array groups 32 arranged in a cross shape at the 45-degree position, the 135-degree position, the 225-degree position, and the 315-degree position may be provided, and the first radiating array groups 31 and the second radiating array groups 32 may be arranged alternately at regular intervals in a row in a predetermined direction.

[0030] The number of beads 4 in the radial array group 30 may vary. For example, as shown in Fig. 9, a total of eight beads 4 may be arranged on the same circle at 45-degree intervals. Furthermore, instead of all of the beads 4 in the radial array group 30 extending radially outward in plan view as shown in Figs. 7 to 9, some beads 4 may extend radially outward and some may extend radially inward. For example, as shown in Fig. 10, beads 4 extending radially outward and some may extend radially inward may be arranged alternately in the circumferential direction. Furthermore, instead of all of the irradiation points P being arranged on the same circle, four irradiation points P may be arranged on each of a first circle and a second circle having different diameters. [Explanation of symbols]

[0031] 1 First member 2 Second member 3 Laser 3a Irradiation direction 4 beads 4a Proximal end 4b Tip 5 Joint surface 10. Travel Route 11 Amplitude 12 wavelengths 21 Group 1 22 Group 2 30 Radial Array Group 31 Radial Array Group 1 32 Second Radial Array Group X overlapping direction T1 Thickness of first part T2 Thickness of the second part D. Depth of progression P Irradiation point

Claims

1. A method for laser welding dissimilar metals by lap welding a first member made of a first metal and a second member made of a second metal different from the first metal, the method comprising the following configuration. (a) irradiating the laser from the first member side; (b) intermittent irradiation while moving the laser; (c) the laser irradiation direction is set to a direction inclined with respect to the overlapping direction of the first member and the second member; (d) When viewed from the first member side in the overlapping direction, the laser irradiation direction at the first irradiation point is a first irradiation direction, and the laser irradiation direction at the second irradiation point away from the first irradiation point is a second irradiation direction different from the first irradiation direction.

2. 2. The laser welding method for dissimilar metals according to claim 1, wherein the laser irradiation directions of adjacent irradiation points are different from each other.

3. 3. The laser welding method for dissimilar metals according to claim 2, wherein the laser irradiation directions of adjacent irradiation points are changed so that the laser irradiation directions of adjacent irradiation points are not aligned in a straight line when viewed in the overlapping direction from the first member side.

4. 4. The method for laser welding dissimilar metals according to claim 1, wherein the melting point of the first metal is higher than the melting point of the second metal.

5. A dissimilar metal joined body in which a first member made of a first metal and a second member made of a second metal different from the first metal are lap-welded, the dissimilar metal joined body having the following configuration. (e) the bead extends from the first member side toward the second member side; (f) Spot-like beads are formed intermittently at intervals. (g) the bead extends from the first member side toward the second member side in a direction inclined with respect to the overlapping direction of the first member and the second member; (h) When viewed in the overlapping direction from the first member side, the extension direction from the first member side to the second member side is a first extension direction, and the extension direction from the first member side to the second member side is a second extension direction different from the first extension direction.

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