Laser brazing method

Abstract

In a method of manufacturing a lap joint or a lap joint by brazing a steel sheet and an aluminum-based sheet, when brazing is performed by irradiating a preceding laser beam in front of a joining direction of a joining position (joining point) of the steel sheet and the aluminum-based sheet to preheat a joining predetermined position, supplying an aluminum-based filler wire after electric current heating to the joining position (joining point), and irradiating a following laser beam in back of the filler wire to melt the filler wire, the filler wire is fed in a manner inclined to the front or back of the joining direction within a range of 0° ≤ D ≤ 19° with respect to a line passing through the center of a bevel of the lap joint as a center line and perpendicular to the joining direction, or with respect to a line perpendicular to a lower sheet surface of the lap joint, thereby manufacturing the lap joint or the lap joint by the steel sheet and the aluminum-based sheet without bead appearance defects and having sufficient joint strength.

Description

TECHNICAL FIELD

[0001] The present application relates to a laser brazing method in which a laser beam is irradiated to a steel sheet and an aluminum-based sheet to perform brazing, and particularly relates to a laser brazing method in which an aluminum-based filler wire (brazing material) that is heated by electric current is fed to a joining portion of a steel sheet and an aluminum-based sheet, and a laser beam is irradiated to the brazing material to melt it, thereby producing a lap joint or a horn joint. BACKGROUND

[0002] In recent years, in order to lighten a vehicle body, an aluminum-based material is increasingly applied to a part of a vehicle body sheet. In the case where an aluminum-based material is used locally, it is necessary to join it to another member, such as a member made of a steel sheet. However, in the case where steel and an aluminum-based material are fusion joined, brittle intermetallic compounds of iron-aluminum are generated to cause a problem of a reduction in joining strength. Therefore, a so-called laser brazing method in which a filler material (brazing material) is supplied between steel and an aluminum-based material, and a laser beam is irradiated to the brazing material to heat and melt it to perform brazing has been proposed.

[0003] For example, in Patent Literature 1, a laser brazing method is disclosed in which, as a heat source for melting a brazing material, a laser beam capable of finely controlling input heat is used, the laser beam is irradiated to a processing point (joining point), and when a filler wire is supplied to the processing point, the penetration length of the molten wire into a workpiece (base material) is made to be a prescribed amount or more, and the wire supply amount is controlled so that a bulge or the like does not occur in an appearance portion, thereby ensuring joint strength.

[0004] In addition, in Patent Literature 2, a laser brazing method is disclosed in which an alloyed hot-dip galvanized steel sheet and an aluminum-based sheet are lap fillet joined by a pair of laser beams arranged in front and back in a joining direction, in which, before laser brazing, a preceding laser beam is irradiated to a joining portion of the galvanized steel sheet to remove a plated layer, and then a subsequent laser beam is irradiated to the portion from which the plated layer has been removed to melt a brazing material supplied to the portion, thereby obtaining a necessary and sufficient joining strength.

[0005] In addition, in Patent Literature 3, a laser beam joining method is disclosed in which, in a laser beam joining method of a steel sheet and an aluminum-based sheet, a preceding beam located on the front side of a processing point in a traveling direction and a subsequent beam located on the rear side of the traveling direction are used to preheat the preceding beam in such a manner that the input heat per unit area to the aluminum-based material portion is larger than the input heat per unit area to the steel sheet, and then the subsequent beam is irradiated to a brazing material to melt it, thereby suppressing appearance defects of a joining portion.

[0006] In addition, in Non-Patent Literature 1, a steel / aluminum dissimilar material joining technique is disclosed, in which a flux-cored wire (FCW) after being electrically heated is provided as a front, and two high-output semiconductor laser irradiation devices are provided behind the same, in which the irradiation area of the leading laser beam is formed into a rectangular spot for the purpose of stable melting and opening of the front end portion of the wire, and the irradiation area of the trailing laser beam is formed into a circular spot for the purpose of stable formation of a molten pool and stable melting of the wire, and the two spots are combined and irradiated as shown in FIG. 1. Figure 5 Thus, in this method, three types of steel sheets, a galvannealed (GA) steel sheet, a galvannealed (GI) steel sheet, and a cold-rolled steel sheet (CR) without a plated layer, and an A5052 Al alloy sheet are joined without defects at a construction speed of 9 m / min at a maximum at a laser output of 5 kW and at a construction speed of 6 m / min at a maximum at a laser output of 4 kW.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2003-225784

[0010] Patent Document 2: Japanese Patent Application Laid-Open (JP-A) No. 2007-075872

[0011] Patent Document 3: Japanese Patent Application Laid-Open (JP-A) No. 2013-146737

[0012] Non-Patent Documents

[0013] Non-Patent Document 1: Takano, Yamamoto, Sasaki, Oshida, Saki, Matsuda, "Study on High-Speed Construction of Steel / Aluminum Alloy Dissimilar Material Flared Joint by Hot Wire Laser Bead Welding Method - Development of Steel / Aluminum Alloy Dissimilar Material Joining Technology Using Hot Wire Laser Bead Welding Method (Report 6)" in Proceedings of the National Meeting of the Welding Society, No. 107 (2020-9), G-1-4 SUMMARY

[0014] PROBLEMS TO BE SOLVED BY THE INVENTION

[0015] However, in the laser brazing method disclosed in Patent Document 1, only one laser beam is used for joining. Therefore, in order to form a brazed bead with excellent appearance, a single laser beam is needed to melt the filler wire and further fuse the molten wire with the base material. However, the wettability of the molten filler wire with the base material is greatly affected by the heating state of the base material. Therefore, it is necessary to strictly adjust the irradiation position and focal position of the laser beam, especially in the case of high-speed joining, where it is difficult to achieve both a good joint appearance and the necessary joint strength.

[0016] Furthermore, the laser brazing method disclosed in Patent Document 2 involves using a preceding laser beam to remove the zinc plating layer from the steel plate, followed by a subsequent laser beam to melt the filler wire for brazing. However, this method requires the width of the plating layer removed by the preceding laser beam to be wider than the brazing width. However, if the laser beam is defocused to irradiate a large area, the energy of the irradiated laser beam needs to be increased, which presents a problem of difficulty in achieving high-speed bonding.

[0017] In addition, although the laser brazing method disclosed in Patent Document 3 can suppress poor weld appearance, since it only uses the subsequent laser beam to melt the filler wire, the wettability between the molten filler wire and the base material is insufficient and the filler wire cannot be supplied to a deeper position of the joint. Therefore, it is possible that the necessary wetting length cannot be fully ensured and high joint strength may not be obtained.

[0018] Furthermore, while the laser brazing method disclosed in Non-Patent Document 1 can achieve high-speed bonding, it also has limitations such as… Figure 5 As shown, in the structure where a laser beam is irradiated from above, the feed direction of the filler wire is restricted, and the feed angle θ of the filler wire becomes smaller. Therefore, in order to efficiently inject the filler wire metal into the material gap (butt joint), it is necessary to increase the energizing and heating temperature of the filler wire. Furthermore, in the structure where the material and the filler wire are overlapped and a laser beam is irradiated from above, since a portion of the laser's input heat is allocated to heating the filler wire, there is also the problem of needing a high-output laser to heat the filler wire to a sufficient temperature.

[0019] The present invention was developed in view of the above-mentioned problems existing in the prior art, and its purpose is to provide a laser brazing method that can produce a horn tube joint or lap joint with excellent joint strength made of steel plate and aluminum plate without causing poor weld appearance.

[0020] Technical solutions for solving the problem

[0021] The inventors repeatedly studied the joining method of the flare pipe joint disclosed in the above-described Non-Patent Literature 1 in order to solve the above-described problems. As a result, in the above-described method, in the case where the feeding angle Θ of the filler wire to the joining portion is small, it was considered that there is a limit in efficiently feeding the filler wire to the members of the flare pipe joint (the butting portion), and further studies were made on means for solving this problem. As a result, it was conceived that the feeding angle of the filler wire is made different from that of Non-Patent Literature 1, and is set to be substantially perpendicular to the joining direction. Thereby, the filler wire can be efficiently inserted to the butting portion, high-speed construction can be performed, and it is also expected that the restriction of the laser beam irradiation position can be relaxed. However, on the other hand, it was clarified that in the case where the feeding angle of the filler wire is increased and is set to be substantially perpendicular to the joining direction, the molten metal is spheroidized, the appearance of the bead is deteriorated, and depending on the case, it can become a joining defect.

[0022] Therefore, the inventors further repeatedly studied the conditions under which the joining portion can be stably formed without causing a joining defect even in the case where the filler wire is supplied substantially perpendicular to the joining portion. As a result, it was found that it is effective to supply the above-described filler wire at the flare pipe joint in a manner that is inclined to the front side or the rear side of the joining direction within a range of 0°≤D≤19° with respect to a line that is a center line passing through the center of the groove of the flare pipe joint and is perpendicular to the joining direction. Also, studies were made on a simple lap joint, and it was found that it is effective to supply in a manner that is inclined to the front side or the rear side of the joining direction within a range of 0°≤D≤19° with respect to a line that is perpendicular to the lower surface of the lap joint, and thereby the present application was completed.

[0023] The present application based on the above-described insight proposes a laser brazing joining method characterized in that, in a joining method of a flare pipe joint composed of a steel plate and an aluminum-based sheet, in the case where brazing is performed by preheating a joining predetermined position by irradiating a preceding laser beam to the front of the joining direction of the joining position (joining point) of the steel plate and the aluminum-based sheet, supplying an aluminum-based filler wire that is heated by electric current to the above-described joining position (joining point), and melting the filler wire by irradiating a following laser beam to the rear of the filler wire, the above-described filler wire is fed in a manner that is inclined to the front side or the rear side of the joining direction within a range of 0°≤D≤19° with respect to a line that is a center line passing through the center of the groove of the flare pipe joint and is perpendicular to the joining direction.

[0024] Further, the present application proposes a laser brazing joining method characterized in that, in a joining method of a lap joint composed of a steel sheet and an aluminum-based sheet, when brazing is performed by preheating a joining predetermined position by irradiating a preceding laser beam to a front of a joining direction of a joining position (joining point) of the steel sheet and the aluminum-based sheet, supplying an aluminum-based filler wire after electric resistance heating to the joining position (joining point), and melting the filler wire by irradiating a following laser beam to a rear of the filler wire, the filler wire is fed in a manner of being inclined to the front or rear of the joining direction with respect to a line perpendicular to a lower sheet surface of the lap joint within a range of 0°≤D≤19°.

[0025] The above laser brazing joining method of the present application is characterized in that, when a diameter of the filler wire is set as d, a distance L between a rear side end of an irradiation range of the preceding laser beam and a rear side end of the filler wire is set within a range satisfying the following (1) formula:

[0026] 0≤L≤4×d…(1).

[0027] Further, the above laser brazing joining method of the present application is characterized in that, when a sum of sheet thicknesses of the steel sheet and the aluminum-based sheet is set as T, a width W in a direction perpendicular to the joining direction of an irradiation range of the preceding laser beam is set within a range satisfying the following (2) formula:

[0028] 0.5×T≤W≤3×T…(2).

[0029] Further, the above laser brazing joining method of the present application is characterized in that the irradiation range of the preceding laser beam is rectangular, and a joining direction length A of the irradiation range of the laser beam is set within a range satisfying the following (3) formula in a relationship between the width W of the irradiation range and the joining direction length A:

[0030] W≤A≤10×W…(3).

[0031] Further, the above steel sheet to which the above laser brazing joining method of the present application is applied is characterized in that it is a flux-coated steel sheet.

[0032] Further, the above filler wire used in the above laser brazing joining method of the present application is characterized in that it is a flux-cored wire.

[0033] Further, the above preceding laser beam used in the above laser brazing joining method of the present application is characterized in that it is a solid laser.

[0034] Further, the above laser brazing joining method of the present application is characterized in that the steel sheet has a plated layer having zinc as a main component, and brazing is performed in a state where the plated layer is melted by the preceding laser beam.

[0035] Further, the laser brazing method of the present application is characterized in that, when a melting point of the filler wire is set to T m (K), the temperature T f (K) at which the filler wire is subjected to the electric current heating is in a range satisfying the following (4) formula:

[0036] 0.5 x T m ≤ T f ≤ T m … (4).

[0037] Further, the laser brazing method of the present application is characterized in that, when a diameter of the filler wire is set to d, a distance L B between the leading side end of the filler wire and the trailing side end of the irradiation range of the trailing laser beam is in a range satisfying the following (5) formula:

[0038] 0 ≤ L B ≤ 3 x d … (5).

[0039] Effects of the Invention

[0040] According to the present invention, when brazing a flared tube joint or lap joint of steel plate and aluminum plate using a laser beam, the joint position is irradiated with a laser beam from both directions before and after the joint direction. The predetermined joint position is preheated with the preceding laser beam at the required width, and then a heated filler wire is supplied to the joint position. Therefore, the filler wire supplied to the joint position can be melted without the subsequent laser beam directly irradiating the feed filler wire, thereby enabling high-speed brazing. Thus, in the present invention, the joint is formed by heating and melting the filler wire fed to the joint position using a laser beam from the rear. In addition, since the present invention appropriately adjusts the supply angle of the filler wire, it is possible to supply the filler wire deep into the mating portion of the flared tube joint or lap joint, thereby consistently obtaining a high-strength joint with excellent appearance. Furthermore, because the distance between the irradiation range of the preceding laser beam and the filler wire is within an appropriate range, the present invention can heat the predetermined joint position, which is ahead of the filler wire supply point, to an appropriate temperature, improving the wettability of the base metal surface and supplying the brazing filler metal deep into the gap of the mating portion. Therefore, a defect-free joint between the brazing filler metal and the base metal can be formed. Additionally, because the width of the irradiation range of the preceding laser beam in the direction perpendicular to the joint direction is within an appropriate range relative to the sum of the thicknesses of the steel plate and the aluminum plate, good wettability is ensured. Furthermore, because the present invention is formed into a rectangular shape where the length of the irradiation range in the joint direction is longer than the width of the irradiation range, rapid heating caused by the preceding laser beam can be suppressed, preventing the flux from peeling off the flux-coated base metal. This improves the wettability between the base metal and the molten brazing filler wire, resulting in a weld bead with excellent appearance and enabling high-speed jointing. Furthermore, when using flux-cored welding wire as the filler wire, this invention achieves a weld bead with excellent appearance without pre-coating the base material with flux, and enables high-speed bonding. Additionally, when using zinc-plated steel sheet as the base material, this invention uses a pre-applied laser beam to melt the plating before brazing, thus ensuring wettability between the base material and the molten welding wire without applying flux, resulting in a weld bead with excellent appearance and enabling high-speed bonding. Attached Figure Description

[0041] Figure 1 These are figures illustrating the laser brazing method of the present invention, (a) is a side view, and (b) is a top view.

[0042] Figure 2 This is a diagram illustrating the center line of the bevel of the horn tube connector.

[0043] Figure 3 This is a diagram illustrating the horn tube connector manufactured in the embodiment.

[0044] Figure 4is a view illustrating a position where a fracture occurs when a tensile test is performed on a lap joint.

[0045] Figure 5 is a view illustrating a laser brazing method of Non-Patent Literature 1, (a) is a side view, and (b) is a plan view.

[0046] Figure 6 is a view illustrating a lap joint produced in the example.

[0047] Figure 7 is a view illustrating a position where a fracture occurs when a tensile test is performed on a lap joint. DETAILED DESCRIPTION

[0048] The present application relates to a joining method of a flare pipe joint or a lap joint composed of a steel sheet and an aluminum-based sheet as dissimilar materials. Specifically, unlike the joining method of Non-Patent Literature 1 (refer to Figure 5 ), it is a joining technique in which, as shown in Figure 1 , a preceding laser beam is irradiated to the front of a joining direction of a joining position (joining point) of a steel sheet and an aluminum-based sheet to preheat a joining intended position, and an aluminum-based filler wire after current heating is supplied to the joining position (joining point), and a following laser beam is irradiated to the rear of the filler wire to melt and solidify the filler wire to perform brazing.

[0049] Furthermore, in the above-described joining method of the present application, it is most important that, in the case of a flare pipe joint, the above-described filler wire is fed at an inclination angle D of 0°≤D≤19° to the front or rear of the joining direction with respect to a line perpendicular to the joining direction and passing through the center of a groove of the flare pipe joint, and, in the case of a lap joint, the above-described filler wire is fed at an inclination angle D of 0°≤D≤19° to the front or rear of the joining direction with respect to a line perpendicular to a lower plate surface of the lap joint.

[0050] In the case of a flare pipe joint, the filler wire is fed at an inclination angle D of 0°≤D≤19° to the front or rear of the joining direction with respect to a line (a line V shown in Figure 1 ) perpendicular to the joining direction and passing through the center of a groove of the flare pipe joint, so that the filler wire can be efficiently inserted into the abutting portion, and the filler wire can be melted without directly irradiating the following laser beam to the filler wire, and thus high-speed brazing can be performed, and further a flare pipe joint having a good appearance and a high fracture strength can be stably obtained. In addition, the preferable inclination angle D is in the range of 0 to 15°.

[0051] Here, the center line C of the groove of the above-described flare pipe joint LIt is calculated in the following manner.

[0052] Figure 2 is a view showing a cross section of a joint before joining, (a) is a flare pipe joint in a case where there is no misalignment (no stagger of reference surface) between two base materials to be butted, (b) and (c) are flare pipe joints in a case where a step is provided between the base materials to be butted. In any case, a point where the base materials to be butted meet is set as X, a bending process end point of the proximal base material as viewed from X is set as Y, and a point of the distal base material which is the same distance from X as Y is set as Z, and a bisector of an angle formed by a line A passing through XY and a line B passing through XZ is set as a center line C passing through the center of the bevel L . In addition, in a case where there is a gap between the two base materials to be butted as in (d), a position where the two base materials are closest to each other is set as X, and the same manner is used to calculate.

[0053] In addition, in the case of a lap joint as well, the filler wire is fed in a manner inclined at an inclination angle D in the range of 0°≤D≤19° to the front side or the rear side of the joining direction with respect to a line V shown in FIG. 1 (a line perpendicular to the lower surface of the lap joint), whereby high-speed brazing can be performed, and furthermore, a lap joint having a good appearance and high breaking strength can be obtained. The preferable inclination angle D is in the range of 0-15° as in the case of the flare pipe joint. Figure 1

[0054] In addition, the laser brazing joining method of the present application is preferably such that, in addition to the irradiation position of the leading / lagging laser beams and the inclination angle D of the fed filler wire being limited to an appropriate range as described above, the distance L (refer to (b) of FIG. 1) between the lagging side end of the irradiation range of the leading laser beam and the lagging side end of the filler wire is in the range defined by the following (1) formula (including the case where the leading laser beam directly irradiates the filler wire), Figure 1

[0055] 0≤L≤4×d…(1).

[0056] Here, d in the above (1) formula is the diameter of the filler wire.

[0057] ​​By limiting the distance L between the rear side end of the irradiation range of the preceding laser beam and the rear side end of the filler wire to the range of the above (1), the joining predetermined position ahead of the supply point of the filler wire can be heated to an appropriate temperature, the wettability of the joint base material surface is improved, and thus stable fusion can be obtained. In addition, the irradiation range of the preceding laser beam can overlap the filler wire supply position, but as described above, by heating the joining predetermined position in a manner slightly separated forward, the heating effect based on heat conduction can be further improved, and the loss of the irradiation energy of the laser beam can be reduced. On the other hand, if the separation distance L is made too large, the above heating effect cannot be obtained. More preferably, L is in the range of 0.1 x d to 2 x d.

[0058] In addition, the laser brazing joining method of the present application is preferably such that, when the sum of the plate thicknesses of the steel plate and the aluminum-based plate material is T, the width W in the direction perpendicular to the joining direction of the above irradiation range of the preceding laser beam is in the range defined by the following (2):

[0059] 0.5 x T ≤ W ≤ 3 x T... (2).

[0060] W in the above (2) represents the heating width of the joint required in terms of ensuring the wettability of the brazing metal (brazing filler metal), and if it is too narrow, the wettability is insufficient, and on the contrary, if it is too wide, adverse effects such as heat loss due to energy dispersion, heat distortion, and the like can occur. More preferably, the irradiation width W is in the range of 0.7 x T to 2 x T. Further preferably, it is in the range of 1 x T to 2 x T.

[0061] In addition, the laser brazing joining method of the present application is preferably such that, on the basis of satisfying the above condition, further, the above irradiation range of the preceding laser beam is rectangular, and when the joining direction length of the irradiation range of the laser beam is A, the above A is in the range satisfying the following (3) in the relationship between the width W of the irradiation range:

[0062] W ≤ A ≤ 10 x W... (3)

[0063] The reason for limiting the joining direction length A of the irradiation range of the preceding laser beam to the above range is that, if the above A is smaller than the width W of the irradiation range, in the case of performing high-speed joining, particularly at 2 m / min or more, in such short-time heating by the irradiation of the laser beam, the heating in the plate thickness direction of the base material is insufficient, the temperature rise of the base material becomes insufficient due to the heat dissipation of the supplied filler wire, and deterioration of the bead appearance and reduction of the joint strength can occur. On the other hand, if A exceeds 10 times W, the heating range becomes too wide, and in addition to causing the evaporation of the plated layer of the base material metal other than the joint portion, a high-output laser is also required. More preferably, A is in the range of W to 5 x W, and further preferably, it is in the range of W to 4 x W.

[0064] Further, the filler wire used in the present application is preferably heated by electric current heating before being supplied to the joint, and the heating temperature T f (K) differs depending on the joining conditions, but when the melting point of the filler wire metal is set to T m (K), it is within the range satisfying the following (4) formula:

[0065] 0.5 x T m ≤ T f ≤ T m … (4).

[0066] This is because, if the electric current heating temperature T f of the filler wire is lower than 0.5 x T m , the filler wire is likely to have poor penetration, and on the other hand, if it exceeds T m , the filler wire is melted before being supplied due to excess input heat. More preferably, T f is within the range of 0.6 x T m ~ T m .

[0067] Further, the laser brazing joining method of the present application is preferably such that, when the diameter of the filler wire is set to d, the distance L B between the leading side end of the above-mentioned filler wire and the trailing side end of the irradiation range of the trailing laser beam (refer to (b) of Figure 1 ) is within the range satisfying the following (5) formula:

[0068] 0 ≤ L B ≤ 3 x d … (5)

[0069] This is because, in the case where the distance L B between the leading side end of the filler wire and the trailing side end of the irradiation range of the trailing laser beam is less than 0, or exceeds 3 x d, the bead shape becomes unstable. Further, by "less than 0", it means that the trailing side end of the irradiation range of the trailing laser beam is located on the joining direction side compared to the leading side end of the filler wire. More preferably, L B is within the range of 0.1 x d ~ 2 x d.

[0070] Further, the steel sheet constituting the flare pipe joint or the lap joint using the joining method of the present application is preferably joined on the basis of applying flux to the vicinity of the joint before brazing from the viewpoint of further improving the wettability with the brazing metal. Further, from the same viewpoint, it is effective that the filler wire used for the joining of the flare pipe joint or the lap joint of the present application uses flux cored wire (FCW). Further, the combination of the flux and the steel sheet or the filler wire can be appropriately selected from the viewpoint of ensuring wettability, and for example, solid wire coated with flux can also be used.

[0071] Further, the preceding laser beam used in the present application is preferably a solid laser, so that the shape of the heating region can be easily controlled. By using the profile control function of the solid laser, the side surface of the horn joint or the lap joint having different depths of the opening of the butt joint can be efficiently heated. Further, as the solid laser, there are a fiber laser using an optical fiber as an amplification medium, a semiconductor laser using a semiconductor as a medium, and the like, but from the viewpoint of securing wettability, the kind thereof is not particularly limited as long as the necessary output can be obtained.

[0072] Further, as the following laser beam, a solid laser is preferable from the viewpoint of the shape control of the heating region. The reason is that by using the profile control function of the solid laser, the shape of the weld bead can be controlled.

[0073] Further, in the case where a steel sheet having a plated layer mainly composed of zinc is used as the base material steel sheet constituting the horn joint or the lap joint, it is preferable to perform brazing in a state where the plated layer is melted by the preceding laser beam. This is because, like the flux, the molten plated layer has an effect of improving the wettability between the base material and the molten filler wire, and therefore by performing brazing in a state where the plated layer is melted, not only a weld bead having a good appearance can be stably obtained, but also a high-strength joint can be stably obtained even at a high speed.

[0074] The horn joint or the lap joint produced so as to satisfy the above conditions becomes a joint having a high strength and a good appearance, because the filler wire supplied is supplied to a deep portion of the butt joint of the base material, and the wettability of the molten filler metal with the base material (steel sheet, aluminum-based sheet material) is good.

[0075] Example 1

[0076] The following experiment was performed: a horn joint constituted by various steel sheets and an Al alloy different in the sheet thickness, the strength, and the kind of zinc-based plated layer shown in Table 1 was laser-brazed by a joining method of the present application shown in Table 2 and a joining method in which the filler wire precedes and the two laser beams follow the filler wire as described in Non-Patent Literature 1. Figure 1 Figure 5 The joining method of the present application shown in Table 2 and the joining method in which the filler wire precedes and the two laser beams follow the filler wire as described in Non-Patent Literature 1 were used to perform laser-brazing joining. Further, as the Al alloy, A5052 (Al-Mg alloy) having a sheet thickness of 1.2 mm was used. Further, as the filler wire of the brazing material, an Fe-Al laser brazing flux-cored wire (FCW) having a diameter of 1.2 mm was used.

[0077] As for the horn joint, a test piece raw material having a short side of 150 mm and a long side of 400 mm was cut out from the above-described material, and was bent at 90° along the long side at a position 20 mm from one end of the long side to be formed into an L shape, and the short sides of the L were made to face each other as shown in FIG. 1. Figure 2 ​After butting in a manner that the plate thickness center lines of the long sides of the L are aligned with each other as shown in (a), laser brazing is performed to form a joint portion of 300 mm in length.

[0078] At this time, the inclination angle D (angle with respect to a line V that is a center line through the center of the bevel of the flare pipe joint and is perpendicular to the joining direction) of the filler wire is six levels of 0°, 10°, 15°, 18°, 19°, and 20° in the method of the present application, and one level of 45° in the method of the related art. Further, as the laser used for the laser brazing, both the leading laser beam and the trailing laser beam are semiconductor lasers, and the output of the leading laser beam and the trailing laser beam is appropriately set in the range of 2 to 6 kW. Further, the irradiation range of the leading laser beam is a rectangle longer in the joining direction, and the length A in the joining direction is 3.2 times (constant) the width W in the direction at right angles to the joining direction. Further, the trailing laser beam is circular in the irradiation range in all conditions, and is irradiated in a manner that heats the position immediately behind the feeding position of the filler wire. Further, as the shielding gas, Ar gas is supplied at 20 L / min to the filler wire feeding portion, and at 40 L / min to the trailing laser beam irradiation portion. Further, as the filler wire, the current value is set to 275 A (fixed) and is fed at 17.5 m / min in a manner that the temperature of the filler wire becomes 0.5T m (K) becomes 0.5T m m . Further, as to the other joining conditions, they are summarized in Table 2.

[0079] [Table 1]

[0080]

[0081] The following evaluation tests were performed on the flare pipe joint obtained in the above-described manner.

[0082] [Appearance Evaluation]

[0083] The central portion 200 mm of the joint portion of 300 mm in length was visually inspected, and the case where there was no joining defect and a smooth bead was formed was evaluated as, the case where although there was no joining defect, unevenness or the like was observed in less than 20% of the bead length was evaluated as, the case where although there was no joining defect, unevenness or the like was confirmed in 20% or more and less than 50% of the bead length was evaluated as, and the case where there was a joining defect or unevenness or the like was confirmed in 50% or more of the bead length was evaluated as.

[0084] [Joint Strength]

[0085] From the flare pipe joint obtained in the above-described manner, as shown in Figure 3 ​​As shown, a T-shaped tensile test piece with a width of 50 mm was cut from the center of the joint along its length, and then subjected to tensile testing. Figure 3 A tensile test is conducted in the direction indicated by the middle arrow. The breaking strength is measured, and this breaking strength is divided by the joint length (50 mm) to determine the breaking strength per unit length of the joint. Furthermore, in evaluating the breaking strength, cases where the breaking strength per unit length of the joint is 120% or more of the yield strength per unit length of the steel plate in the joint direction are rated as ◎, cases where it is 100% or more but less than 120% are rated as ○, cases where it is 80% or more but less than 100% are rated as △, and cases where it is less than 80% are rated as ×.

[0086] <Fragment Location>

[0087] Observe the fracture surface after the above tensile test, such as Figure 4 As shown, fracture surfaces where the fracture surface is on the base material (Al alloy side) are classified as A. In fracture surfaces consisting only of the separation surface between the brazed metal and the base material, the separation surface on the Al alloy side is classified as B, and on the steel plate side as B'. In fracture surfaces consisting of both the fracture surface of the brazed metal and the separation surface between the brazed metal and the base material, the fracture surface on the Al alloy side is classified as C, and on the steel plate side as C'. Furthermore, even if the separation surface between the brazed metal and the base material is along the outer surface of the base material, and an alloy phase between the brazed metal and the base material is identified on the separation surface, it is still determined to be a fracture surface of the brazed metal.

[0088] [Table 2]

[0089]

[0090] The results of the above evaluations are recorded in Table 2. These results confirm that, for the horn tube joints joined under conditions suitable for this invention, even at high speeds, both the appearance and joint strength are excellent.

[0091] In addition, FCW was used as filler wire in the above experiment, but other experiments confirmed that the same results could be obtained even when using solid wire in steel plates with flux coating.

[0092] Example 2

[0093] The following experiments were conducted: Experiments were performed on various steel plates and Al alloy plates with different thicknesses, strengths, and zinc coating types as shown in Table 1. Figure 6 The lap joint shown uses Figure 1 The joining method of the present invention shown and as follows Figure 5The lap fillet joint was laser brazed using the joining method described in Non-Patent Literature 1, in which a filler wire is advanced and two laser beams follow the filler wire. As the Al alloy plate, A5052 (Al-Mg alloy) having a thickness of 1.2 mm was used. As the filler wire, Fe-Al laser brazing flux-cored wire (FCW) having a diameter of 1.2 mm was used.

[0094] For the lap fillet joint, a test piece raw material having a short side of 150 mm and a long side of 400 mm was cut out of the above-described material, and the test piece raw material was prepared. Figure 6

[0095] At this time, the inclination angle D (angle with respect to a line V perpendicular to the lower surface of the lap joint) of the filler wire was 0°, 10°, 15°, 18°, 19°, and 20° in the method of the present application, and was 45° in the method of the related art. In addition, as the laser used for the laser brazing, both the leading laser beam and the trailing laser beam were semiconductor lasers, and the output of the leading and trailing lasers was appropriately set in the range of 2 to 6 kW. In addition, the irradiation range of the leading laser beam was a rectangle longer in the joining direction, and the length A in the joining direction was 3.2 times (constant) the width W in the direction perpendicular to the joining direction. In addition, the trailing laser beam was a circle having an irradiation range of 2.5 mm in all conditions, and was irradiated in a manner of heating immediately behind the feeding position of the wire. In addition, as the shielding gas, Ar gas was supplied at 20 L / min to the wire feeding portion, and at 40 L / min to the trailing laser beam irradiation portion. In addition, as the filler wire, the current value was set to 275 A (fixed) and was electrically heated in a manner of being at a temperature of 0.5 T m m m In addition, as to the other joining conditions, they are summarized in Table 3.

[0096] [Table 3]

[0097]

[0098] The lap fillet joint obtained in the above-described manner was subjected to the following evaluation tests.

[0099] [Appearance Evaluation]

[0100] ​​​​Visually inspect the central 200mm portion of the 300mm long joint. A smooth weld bead without any joint defects is rated as ◎. A weld bead without joint defects but with unevenness or irregularities observed in less than 20% of the weld bead length is rated as ○. A weld bead without joint defects but with unevenness or irregularities observed in more than 20% but less than 50% of the weld bead length is rated as △. A weld bead with joint defects or with unevenness or irregularities observed in more than 50% of the weld bead length is rated as ×.

[0101] <Joint Strength>

[0102] The lap joint obtained in the above manner, such as Figure 6 As shown, a 50mm wide tensile test piece is cut from the center of the joint along its length, and then subjected to tensile testing. Figure 6 A tensile test is conducted in the direction indicated by the middle arrow. The breaking strength is measured, and this breaking strength is divided by the joint length (50 mm) to determine the breaking strength per unit length of the joint. Furthermore, in evaluating the breaking strength, cases where the breaking strength per unit length of the joint is 120% or more of the yield strength per unit length of the steel plate in the joint direction are rated as ◎, cases where it is 100% or more but less than 120% are rated as ○, cases where it is 80% or more but less than 100% are rated as △, and cases where it is less than 80% are rated as ×.

[0103] <Fragment Location>

[0104] Observe the fracture surface after the above tensile test, such as Figure 7 As shown, fracture surfaces where the fracture surface is on the base material (Al alloy side) are classified as A, fracture surfaces where the fracture surface is inside the brazed metal are classified as B, and fracture surfaces consisting of the separation surface between the brazed metal and the base material are classified as C if the separation surface is on the Al alloy side and C' if it is on the steel plate side. Furthermore, even if the separation surface between the brazed metal and the base material is along the outer surface of the base material, and an alloy phase between the brazed metal and the base material is identified on the separation surface, it is still considered a fracture surface of the brazed metal.

[0105] The results of the above evaluations are recorded in Table 3. These results confirm that, for lap joints joined under conditions suitable for this invention, even high-speed joining results in excellent appearance and joint strength.

[0106] In addition, FCW was used as filler wire in the above experiment, but other experiments confirmed that the same results could be obtained even when using solid wire in steel plates with flux coating.

[0107] Industrial availability

[0108] The technology of the present application is not limited to the brazing of dissimilar materials such as Al alloy plates and steel plates to each other, and can be widely applied, for example, to the technical field of additive manufacturing in which a filler wire is irradiated with laser light after being heated by electric current to melt and adhere to a prescribed position on the surface of a material. Specifically, the technology can be applied to a technique for increasing the thickness of a member by locally adhering molten metal to the member to increase the rigidity of the member, or a technique for sequentially stacking molten metal to obtain a three-dimensional solid model like a 3D printer.

[0109] Explanation of Reference Numerals

[0110] 1: Flared pipe joint

[0111] 2: Leading laser beam

[0112] 2': Range of leading laser beam irradiation

[0113] 3: Trailing laser beam

[0114] 3': Range of trailing laser beam irradiation

[0115] C L : Center line passing through the center of the bevel

[0116] V: Line perpendicular to the joining direction that is the center line passing through the center of the bevel of the flared pipe joint, or line perpendicular to the lower surface of the lap joint

[0117] D: Inclination angle of the filler wire

[0118] θ: Feed angle of the filler wire

[0119] A: Length of the range of leading laser beam irradiation in the joining direction

[0120] W: Width of the range of leading laser beam irradiation

[0121] L: Distance between the trailing side end of the range of leading laser beam irradiation and the trailing side end of the filler wire

[0122] L B : Distance between the trailing side end of the range of trailing laser beam irradiation and the leading side end of the filler wire

[0123] d: Diameter of the filler wire

[0124] St: Steel plate

[0125] Al: Al alloy plate

[0126] Br: Brazing portion

Claims

1. A laser brazing joining method characterized by, in a joining method of a lap joint composed of a steel sheet and an aluminum-based sheet, when brazing is performed by preheating a joining predetermined position by irradiating a preceding laser beam to a front side of a joining direction of a joining position of a steel sheet and an aluminum-based sheet, supplying an aluminum-based filler wire that is heated by electric current to the joining position, and melting the filler wire by irradiating a following laser beam to a rear side of the filler wire, the filler wire is fed in a manner that is inclined to the front side or the rear side of the joining direction within a range of 0°≤D≤19° with respect to a line that is a center line through a groove center of the lap joint and is perpendicular to the joining direction.

2. A laser brazing joining method characterized by, in a joining method of a lap joint composed of a steel sheet and an aluminum-based sheet, when brazing is performed by preheating a joining predetermined position by irradiating a preceding laser beam to a front side of a joining direction of a joining position of a steel sheet and an aluminum-based sheet, supplying an aluminum-based filler wire that is heated by electric current to the joining position, and melting the filler wire by irradiating a following laser beam to a rear side of the filler wire, the filler wire is fed in a manner that is inclined to the front side or the rear side of the joining direction within a range of 0°≤D≤19° with respect to a line that is perpendicular to a lower sheet surface of the lap joint.

3. The laser brazing joining method according to claim 1 or 2, characterized in that, when a diameter of the filler wire is d, a distance L between a rear side end of an irradiation range of the preceding laser beam and a rear side end of the filler wire is in a range that satisfies the following (1) formula: 0≤L≤4xd...(1).

4. The laser brazing joining method according to claim 1 or 2, characterized in that, when a sum of sheet thicknesses of the steel sheet and the aluminum-based sheet is T, a width W in a direction that is at right angles to the joining direction of an irradiation range of the preceding laser beam is in a range that satisfies the following (2) formula: 0.5XT≤W≤3XT...(2).

5. The laser brazing joining method according to claim 1 or 2, characterized in that, the irradiation range of the preceding laser beam is rectangular, and a joining direction length A of the irradiation range of the laser beam is in a range that satisfies the following (3) formula in a relationship between the width W of the irradiation range and the joining direction length A: W≤A≤10W...(3).

6. The laser brazing joining method according to claim 1 or 2, characterized in that, the steel sheet is a steel sheet that is coated with a flux.

7. The laser brazing joining method according to claim 1 or 2, characterized in that, the filler wire is a flux-cored wire.

8. The laser brazing joining method according to claim 1 or 2, characterized in that, the preceding laser beam is a solid laser.

9. The laser brazing joining method according to claim 1 or 2, characterized in that, the steel sheet has a plated layer that has zinc as a main component, and brazing is performed in a state where the plated layer is melted by the preceding laser beam.

10. The laser brazing joining method according to claim 1 or 2, characterized in that, When the melting point of the filler wire is set to T m (K), the temperature T f (K) at which the above filler wire is subjected to electric current heating is a range that satisfies the following (4) formula: 0.5 x T m ≤ T f ≤ T m …(4).

11. The laser brazing joining method according to claim 1 or 2, characterized in that, When the diameter of the filler wire is set to d, the distance L between the leading side end of the filler wire and the trailing side end of the irradiation range of the trailing laser beam is set to be within a range of 0.1d to 0.5d B to satisfy the range of the following (5) formula: 0 < L B ≤ 3 x d... (5).

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