Laser welding method for dissimilar metals 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

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[0001] The present invention relates to a method for laser welding different metals and a joined body.

Background Art

[0002] Laser welding of different metals is more difficult than laser welding of the same metals. For example, welding an iron member and a non-ferrous metal member such as an aluminum alloy is difficult from the viewpoint of ensuring welding strength. When an iron member and an aluminum alloy member are overlapped and laser welded, intermetallic compounds are formed in the bead. Since these intermetallic compounds are brittle, it is difficult to ensure joint strength. In contrast, in Patent Documents 1 to 3 below, various proposals have been made, such as making the shape of the bead wedge-shaped, but they are not sufficient.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to improve joint strength when joining different metals.

Means for Solving the Problems

[0005] The laser welding method for different metals according to the present invention is a method for overlapping and welding a first member made of a first metal and a second member made of a second metal different from the first metal by a laser, and includes the following configuration. (a) A laser is irradiated from the first member side, (b) Intermittent irradiation while moving the laser, (c) The direction of laser irradiation is inclined with respect to the direction in which the first and second members are superimposed. (d) When viewed from the first member side in the overlapping direction, the laser irradiation direction at the first irradiation point is the first irradiation direction, and the laser irradiation direction at the second irradiation point, which is far from the first irradiation point, is the second irradiation direction, which is different from the first irradiation direction.

[0006] In this method, since the laser is irradiated from the first member side, the bead extends from the first member side toward the second member side. Because the laser is moved and irradiated intermittently, the bead becomes spot-like, and the bead is formed intermittently with gaps along the laser's path. Furthermore, since the direction of laser irradiation 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. Moreover, the first irradiation direction at the first irradiation point and the second irradiation direction at the second irradiation point are different from each other. Therefore, the direction of extension of the bead, which extends inclined from the first member side toward the second member side, will differ between the first and second irradiation points. In other words, if we define the extension direction of the first bead formed at the first irradiation point as the first extension direction, and the extension direction of the second bead formed at the second irradiation point as the second extension direction, then the first extension direction and the second extension direction are different from each other. Therefore, even if the second member were to attempt to separate from the first member in a direction along the first extension direction, the second bead extending in the second extension direction would prevent separation in that direction. Similarly, even if the second member were to attempt to separate from the first member in a direction along the second extension direction, the first bead extending in the first extension direction would prevent separation in that direction. In this way, the 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 and second members from separating from each other, resulting in high joint strength.

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

[0008] Furthermore, it is preferable to change the laser irradiation directions of adjacent irradiation points so that when viewed from the first member side in the overlapping direction, the laser irradiation directions of adjacent irradiation points do not align in a straight line. The case in which the laser irradiation directions of adjacent irradiation points align in a straight line is when the laser irradiation directions of adjacent irradiation points are at 0 degrees and 180 degrees respectively when viewed from the first member side in the overlapping direction. That is, as shown in Figure 5, when viewed from the first member side in the overlapping direction, there are cases where, as in the combination of section C in Figure 5, the laser irradiation direction of one irradiation point faces the other irradiation point and the laser irradiation direction of the other irradiation point faces the one irradiation point, and cases where, as in the combination of section D in Figure 5, the laser irradiation direction of one irradiation point faces 180 degrees opposite to the other irradiation point and the laser irradiation direction of the other irradiation point faces 180 degrees opposite to the one irradiation point. 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 adjacent irradiation points will be aligned in a straight line when viewed from the first member, and there is a possibility that cracks will occur along 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.

[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, the first member can be reliably melted, and the bead can be easily extended to the second member.

[0010] Furthermore, the dissimilar metal joint according to the present invention is a dissimilar metal joint 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 overlapped and 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 and second members. (h) When viewed from the first member side in the overlapping direction, it has a first bead whose extension direction from the first member side to the second member side is the 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] With this configuration, even if the second member were to attempt to separate from the first member in the direction along the first extension direction, the second bead extending in the second extension direction would prevent separation in that direction. Similarly, even if the second member were to attempt to separate from the first member in the direction along the second extension direction, the first bead extending in the first extension direction would prevent separation in that 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 and second members from separating from each other, resulting in high joint strength. [Effects of the Invention]

[0012] As described above, the joint strength can be improved by the cooperation of the first bead extending in the first stretching direction and the second bead extending in the second stretching direction. [Brief explanation of the drawing]

[0013] [Figure 1] A plan view of the main part of the joined body in one embodiment of the present invention as viewed in the superposition direction from the first member side. [Figure 2] An enlarged view of the main part of FIG. 1. [Figure 3] (a) is a cross-sectional view taken along the line A-A of FIG. 2, and (b) is a cross-sectional view taken along the line B-B of FIG. 2. [Figure 4] (a) and (b) are plan views of the joined body in another embodiment of the present invention as viewed in the superposition direction from the first member side. [Figure 5] A plan view of the joined body in another embodiment of the present invention as viewed in the superposition direction from the first member side. [Figure 6] (a) and (b) are plan views of the joined body in another embodiment of the present invention as viewed in the superposition direction from the first member side. [Figure 7] A plan view of the joined body in another embodiment of the present invention as viewed in the superposition direction from the first member side. [Figure 8] A plan view of the joined body in another embodiment of the present invention as viewed in the superposition direction from the first member side. [Figure 9] A plan view of the joined body in another embodiment of the present invention as viewed in the superposition direction from the first member side. [Figure 10] A plan view of the joined body in another embodiment of the present invention as viewed in the superposition direction from the first member side.

Mode for Carrying Out the Invention

[0014] Hereinafter, a laser welding method and a joined body according to an embodiment of the present invention will be described 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 made of metal. The joined body is formed by overlapping the first member 1 and the second member 2 and joining them at a predetermined location to integrate them.

[0015] In detail, the first member 1 and the second member 2 are made of different metals. Therefore, the joint is a joint 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 used for the first member 1 and the second member 2 can vary. Typically, the first member 1 is steel and the second member 2 is an aluminum alloy. The forms of the first member 1 and the second member 2 can vary. For example, the first member 1 may be a plate 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 together by laser. That is, the joining method is laser welding. As shown in Figure 3, the laser 3 is irradiated from the side of the first member 1. In this embodiment, the thickness T1 of the first member 1 is thinner than the thickness T2 of the second member 2. When the laser 3 is irradiated onto the first member 1, 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 figure, the bead 4 is shown with numerous dots.

[0017] The laser 3 (torch) is moved along the joint. The movement path 10 of the laser 3 is arbitrary and may be a straight line. In this embodiment, as shown by the dashed line in Figures 1 and 2, in a plan view of the joint viewed 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 vibrates left and right in a predetermined direction with a predetermined amplitude 11. 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 bead 4.

[0018] Laser 3 is not continuously irradiated but intermittently. That is, laser 3 is intermittently irradiated while moving along a predetermined movement path 10. Therefore, the beads 4 are not formed in a continuous linear shape along the movement path 10 of laser 3, but rather in a spot-like shape with intervals between them along the movement path 10 of laser 3, as shown in Figures 1 and 2. The beads 4 are formed in a dashed line shape 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 laser 3 are provided at regular intervals along the movement path 10 of laser 3, and the beads 4 are formed at regular intervals along the movement path 10 of laser 3.

[0019] The shape of the bead 4 is wedge-shaped. 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 towards the tip end 4b. In the drawing, the shape of the bead 4 is simplified and shown as a cone. The bead 4 passes through the joint 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 non-penetrating. It is preferable that the bead 4 advances into the second member 2 to a depth approximately the same as the thickness T1 of the first member 1. That is, it is preferable that the advancement depth D of the bead 4 into the second member 2 (depth in the overlapping direction X) is greater than or equal to the thickness T1 of the first member 1. The advancement depth D is the depth in the overlapping direction X, and is the dimension in the overlapping direction X from the joint surface 5 to the tip end 4b of the bead 4.

[0020] Laser 3 is irradiated obliquely to the first member 1, rather than perpendicularly. That is, the irradiation direction 3a of laser 3 is inclined with respect to the superposition direction X. In Figure 3, the angle of inclination of the irradiation direction 3a of laser 3 with respect to the superposition direction X is shown as θ in a cross-sectional view. As shown in Figures 1 and 2, the irradiation direction 3a of laser 3 is not constant in a plan view, but changes along the movement path 10 of laser 3. The manner of this change can vary. Preferably, the irradiation directions 3a of laser 3 in a plan view of adjacent irradiation points P are different from each other. In a plan view, the first irradiation direction 3a of laser 3 at the first irradiation point P is different from the second irradiation direction 3a of laser 3 at the second irradiation point P adjacent to the first irradiation point P. In Figure 2, the irradiation direction 3a of laser 3 at each irradiation point P in a plan view is shown by dashed arrows. In a plan view, the irradiation direction 3a of the laser 3 is the direction from the center of the bead 4 on the surface of the first member 1 (the center at the base end 4a of the bead 4) toward the tip end 4b of the bead 4. Furthermore, the bead 4 extends from the first member 1 side toward 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 direction of extension 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, for each group, the direction is opposite to the left and right with respect to the movement path 10 of the laser 3. That is, there is a first group 21 in which the irradiation direction 3a of the laser 3 (the extension direction of the bead 4) is oriented in the first left-right direction in a plan view with respect to the direction of travel of the laser 3, and a second group 22 in which the irradiation direction 3a of the laser 3 is oriented in the second left-right direction, which is the opposite direction to the first left-right direction with respect to the direction of travel of the laser 3. The first group 21 consists of multiple irradiation points P. That is, the first group 21 consists of multiple beads 4. Similarly, the second group 22 consists of multiple irradiation points P and multiple beads 4.

[0022] The first group 21 and the second group 22 are arranged alternately. 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 equal, for example, three each. In addition, in this embodiment, at each irradiation point P, the irradiation direction 3a of the laser 3 is inclined at an angle close to perpendicular to the laser 3's movement path 10 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 laser 3's movement path 10, and the irradiation directions 3a of adjacent irradiation points P are not aligned in a straight line. In this embodiment, the irradiation direction 3a of the laser 3 is substantially perpendicular to the movement path 10 of the laser 3 in a plan view, but it does not have to be substantially perpendicular. Even in that case, it is preferable that the direction is inclined at a predetermined angle with respect to the movement path 10 of the laser 3 in a plan view.

[0023] When switching from group 1 21 to group 22, and when switching from group 22 to group 1 21, the irradiation direction 3a of the laser 3 and the extension direction of the bead 4 of adjacent irradiation points P are reversed by 180 degrees in a plan view. Furthermore, within each group, the irradiation direction 3a of the laser 3 in a plan view changes sequentially. Within group 1 21, the irradiation direction 3a of the laser 3 in a plan view gradually changes along the laser 3's movement path 10, and the same change occurs within group 22.

[0024] As described above, in this embodiment, the laser 3 is irradiated from the first member 1 side. Therefore, the first member 1, which has a high melting point, can be reliably melted, and the bead 4 can be easily extended to the second member 2. In addition, since the movement path 10 of the laser 3 is wave-shaped rather than linear, the welded portion can be made wider according to a predetermined amplitude 11, making it easy to increase the joint strength. Furthermore, by intermittently irradiating with the laser 3 to form spot-shaped beads 4, and by sequentially changing the extension direction of the beads 4 in a plan view along the movement path 10 of the laser 3, when the first member 1 and the second member 2 try to separate from each other, multiple beads 4 with different extension directions cooperate to prevent separation. Therefore, high joint strength can be obtained. In particular, since the extension directions are different for adjacent beads 4, adjacent beads 4 can cooperate to prevent the members from separating, further increasing the joint strength. Furthermore, since the extension direction of the bead 4 relative to the movement path 10 is reversed left to right for each group, such as the first group 21 and the second group 22, the angle control of the torch becomes easier compared to the case where the extension direction is reversed left to right on a bead 4-by-bead basis.

[0025] However, as shown in Figure 4, instead of forming a group, the stretching direction of the bead 4 relative to the movement path 10 (the irradiation direction 3a of the laser 3) may be reversed left to right for each bead 4 unit. In the joint shown in Figure 4, the stretching direction of the bead 4 is alternately reversed left to right along the movement path 10. In Figure 4(a), the movement path 10 is not linear but zigzag, and in Figure 4(b), it is linear. When the movement path 10 is linear, the base ends 4a of the bead 4 are formed in a straight line with spacing between them. Also, the stretching direction of the bead 4 is not perpendicular to the movement path 10, but has an inclination angle of less than 90 degrees. The stretching direction of all the beads 4 is oriented either forward or backward in the direction of movement of the laser 3. Therefore, the inclination angle of the torch can be easily controlled.

[0026] Furthermore, the extension directions of adjacent beads 4 may be aligned in a straight line in a plan view. For example, in Figure 5, the movement path 10 is straight, and the extension direction of the beads 4 follows the movement path 10. In section C of Figure 5, the tips 4b of adjacent beads 4 face each other. In section D of Figure 5, the tips 4b of adjacent beads 4 face opposite directions. In a plan view, the extension direction of the beads 4 is not inclined with respect to the movement path 10 and follows the movement path 10.

[0027] Alternatively, as shown in Figure 6(a), the movement path 10 may be formed in a zigzag shape, while 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 Figure 6(b), the movement path 10 may be straight instead of zigzag.

[0028] Furthermore, the beads 4 may be formed radially. For example, as shown in Figure 7, a group of radial arrays 30, each consisting of multiple beads 4 arranged radially, may be arranged at intervals along a predetermined direction. In this case, the laser 3's movement path 10 in the group of radial arrays 30 is circular, and irradiation points P are located on each circle at predetermined angles. Multiple such groups of radial arrays 30 are provided at intervals along a predetermined direction. In this embodiment, the group of radial arrays 30 consists 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 provided at 90-degree intervals, located at 0-degree, 90-degree, 180-degree, and 270-degree positions, respectively. In the group of radial arrays 30, the extension direction of each bead 4 is outward, not towards the center of the cross shape. In other words, the extension direction of the bead 4 is entirely 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] Furthermore, as shown in Figure 8, there may be multiple types, for example, two types of radial array groups 30. The two types of radial array groups 30 may be arranged alternately. For example, there may be a first radial array group 31 arranged in a cross shape at 0 degrees, 90 degrees, 180 degrees, and 270 degrees, and a second radial array group 32 arranged in a cross shape at 45 degrees, 135 degrees, 225 degrees, and 315 degrees, with the first radial array group 31 and the second radial array group 32 arranged alternately at regular intervals in a predetermined direction.

[0030] The number of beads 4 in the radial array group 30 can vary; for example, a total of eight beads may be arranged on the same circle at 45-degree intervals, as shown in Figure 9. Furthermore, the extension direction of the beads 4 in the radial array group 30 does not have to be aligned to the radially outward direction in a plan view, as shown in Figures 7 to 9; instead, a mixture of beads oriented radially outward and those oriented radially inward may be used. For example, beads 4 with extension directions radially outward and those oriented radially inward may be arranged alternately in the circumferential direction, as shown in Figure 10. Also, not all irradiation points P are arranged on the same circle; for example, four irradiation points P may be arranged on a first circle and a second circle with different diameters. [Explanation of Symbols]

[0031] 1. First member 2. Second Member 3 lasers 3a Irradiation direction 4 Beads 4a Proximal end 4b Tip 5 Joint surface 10 Travel Path 11 Amplitude 12 wavelengths 21 Group 1 22 Group 2 30 radial arrays 31. First radial array group 32 Second radial array group X overlapping direction T1 Thickness of the first member T2 Thickness of the second member D Depth of progression P Irradiation Point

Claims

1. A laser welding method for dissimilar metals, comprising the following configuration, for overlapping and welding a first member made of a first metal and a second member made of a second metal different from the first metal at a joint having a predetermined length in a predetermined direction using a laser. (a) A laser is irradiated from the first member side, (b) To prevent the beads from overlapping, the laser is intermittently irradiated along a waveform, zigzag, or linear path from one end to the other in the predetermined direction of the joining area. (c) The direction of laser irradiation is inclined with respect to the direction in which the first and second members are superimposed. (d) When viewed from the first member side in the overlapping direction, the laser irradiation direction is alternately reversed left to right for each group consisting of multiple irradiation points.

2. A laser welding method for dissimilar metals, comprising the following configuration, for overlapping and welding a first member made of a first metal and a second member made of a second metal different from the first metal at a joint having a predetermined length in a predetermined direction using a laser. (a) A laser is irradiated from the first member side, (b) To prevent the beads from overlapping, the laser is intermittently irradiated along a waveform, zigzag, or linear path from one end to the other in the predetermined direction of the joining area. (c) The direction of laser irradiation is inclined with respect to the direction in which the first and second members are superimposed. (d) When viewed from the first member side in the overlapping direction, the laser irradiation direction is alternately reversed left and right for each irradiation point.

3. A laser welding method for dissimilar metals, comprising the following configuration, for overlapping and welding a first member made of a first metal and a second member made of a second metal different from the first metal at a joint having a predetermined length in a predetermined direction using a laser. (a) A laser is irradiated from the first member side, (b) To prevent the beads from overlapping, the laser is intermittently irradiated while moving along a linear path from one end to the other in the predetermined direction of the joining area. (c) The direction of laser irradiation is inclined with respect to the direction in which the first and second members are superimposed. (d) When viewed from the first member side in the overlapping direction, the laser irradiation direction is set to be in the direction along the movement path and alternately in the opposite direction at each irradiation point.

4. A dissimilar metal joint 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 overlapped and welded at a joint having a predetermined length in a predetermined direction, the dissimilar metal joint having the following configuration. (e) The bead extends from the first member side toward the second member side. (f) Spot-shaped beads are formed intermittently at intervals along a wavy, zigzag, or linear movement path from one end to the other in the predetermined direction of the joint, so that the beads do not overlap. (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 from the first member side in the overlapping direction, the extension direction of the beads alternates between left and right for each group of beads.

5. A dissimilar metal joint 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 overlapped and welded at a joint having a predetermined length in a predetermined direction, the dissimilar metal joint having the following configuration. (e) The bead extends from the first member side toward the second member side. (f) Spot-shaped beads are formed intermittently at intervals along a wavy, zigzag, or linear movement path from one end to the other in the predetermined direction of the joint, so that the beads do not overlap. (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 from the first member side in the overlapping direction, the stretching direction of the bead alternates between left and right for each bead.

6. A dissimilar metal joint 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 overlapped and welded at a joint having a predetermined length in a predetermined direction, the dissimilar metal joint having the following configuration. (e) The bead extends from the first member side toward the second member side. (f) Spot-shaped beads are formed intermittently at intervals along a linear movement path from one end to the other in the predetermined direction of the joint, so that the beads do not overlap. (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 from the first member side in the overlapping direction, the extension direction of the bead is in the direction along the movement path and alternately in the opposite direction for each bead.

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