Method for manufacturing a dissimilar material joint structure

Abstract

Provided is a method for manufacturing a dissimilar material joint structure, which can suppress the occurrence of cracks in a HAZ in the joining of an aluminum or aluminum alloy material and a steel material. A method for manufacturing a dissimilar material joint structure in which a steel material (13) and an aluminum alloy material (11) having a cold spray coating film (12) containing a metal powder capable of being joined to the steel material (13) on at least a part of a surface are joined, includes: a step of superimposing the aluminum alloy material (11) and the steel material (13) in such a manner that the cold spray coating film (12) opposes the steel material (13); and a step of irradiating a laser beam (14) from the side of the steel material (13), the region in which the laser beam (14) is irradiated including: a first region (W1) in which at least the steel material (13) and the cold spray coating film (12) are melted; and a second region (W2) in which the steel material (13) and the cold spray coating film (12) are not melted in a peripheral portion of the first region (W1).

Description

TECHNICAL FIELD

[0001] The present application relates to a manufacturing method of a dissimilar material joint structure, and is a method of laser welding an aluminum or aluminum alloy material and a steel material on which a cold sprayed film is formed on a surface.

[0002] Also, hereinafter, an aluminum or aluminum alloy material will sometimes be collectively referred to as an "aluminum alloy material". BACKGROUND

[0003] In recent years, in order to achieve vehicle body weight reduction and collision safety enhancement aimed at reducing CO2 emissions, high tensile strength steel sheets (HTSS) are applied to vehicle body frames and the like.

[0004] In addition, in order to further reduce the weight of the vehicle body, the demand for dissimilar metal joint materials that join lightweight aluminum alloy materials and steel materials is increasing. As a method of joining dissimilar metals, there are generally methods of joining using nails or bolts and the like, but there are problems in that the cost of the nails or bolts is relatively high, which leads to an increase in the manufacturing cost of the joint material, and the resulting joint material becomes heavy, that is, the weight of the nails or bolts increases.

[0005] On the other hand, if an aluminum alloy material and a steel material are directly welded by a general method, a brittle intermetallic compound is formed at the joint interface, and good strength cannot be obtained. Therefore, in the joining of an aluminum alloy material and a steel material, a welding technique capable of obtaining high strength is required.

[0006] As a method of joining dissimilar metals by welding, Patent Literature 1 discloses a joining method in which at least one kind of metal powder selected from pure iron, carbon steel, nickel, nickel alloy, cobalt, and cobalt alloy is cold sprayed to at least a part of the surface of an aluminum alloy material, the resulting cold sprayed film is overlapped with a steel material so as to oppose the aluminum alloy material and the steel material, and laser welding is performed from the side of the steel material.

[0007] PRIOR ART DOCUMENTS

[0008] PATENT LITERATURE

[0009] Patent Literature 1: Japanese Patent Application Laid-Open No. 2020-11276 SUMMARY

[0010] PROBLEMS TO BE SOLVED BY THE INVENTION

[0011] However, when the penetration formed by laser welding reaches the aluminum alloy material, particularly in the heat affected zone (HAZ) of the cold sprayed film, there is a problem in that cracks are easily generated.

[0012] The present application has been made in view of the foregoing problems, and aims to provide a manufacturing method of a dissimilar material joined structure, which can suppress the occurrence of a crack in a HAZ in the joining of dissimilar materials of an aluminum or aluminum alloy material and a steel material.

[0013] Means for solving the problem

[0014] The manufacturing method of a dissimilar material joined structure of the present application is constituted by the following (1).

[0015] (1) A manufacturing method of a dissimilar material joined structure, which is a manufacturing method of a dissimilar material joined structure in which a steel material and an aluminum or aluminum alloy material having a cold spray coating film containing a metal powder capable of being joined to the steel material on at least a part of a surface are joined, wherein

[0016] has the following steps:

[0017] a step of overlapping the aluminum or aluminum alloy material and the steel material in such a manner that the cold spray coating film opposes the steel material;

[0018] a step of irradiating a laser beam from the side of the steel material,

[0019] the region in which the laser beam is irradiated includes a first region in which at least the steel material and the cold spray coating film are melted, and a second region in which the steel material and the cold spray coating film are not melted in a peripheral portion of the first region.

[0020] Further, the preferred embodiment of the manufacturing method of a dissimilar material joined structure of the present application is constituted by the following (2) to (8).

[0021] (2) The manufacturing method of a dissimilar material joined structure according to (1), wherein the second region includes a heat-affected portion of the steel material and the cold spray coating film.

[0022] (3) The manufacturing method of a dissimilar material joined structure according to (1), wherein the first region is a region in which the steel material, the cold spray coating film, and the aluminum or aluminum alloy material are melted by irradiation of a part of the laser beam, and the second region is a region in which the steel material, the cold spray coating film, and the aluminum or aluminum alloy material are not melted.

[0023] (4) The manufacturing method of a dissimilar material joined structure according to (3), wherein the second region includes a heat-affected portion of the steel material, the cold spray coating film, and the aluminum or aluminum alloy material.

[0024] (5) The manufacturing method of the dissimilar-material joined structure according to any one of (1) to (4), wherein the intensity distribution of the laser beam has a first peak having the highest light intensity in the first region and at least one second peak in the form of a ring centered on the first peak in the second region.

[0025] (6) The manufacturing method of the dissimilar-material joined structure according to any one of (1) to (4), wherein the intensity of the laser beam is the highest in the first region and gradually decreases away from the first region in the second region.

[0026] (7) The manufacturing method of the dissimilar-material joined structure according to any one of (1) to (6), wherein the metal powder contains at least one selected from the group consisting of pure iron, carbon steel, stainless steel, nickel, nickel alloy, cobalt, and cobalt alloy.

[0027] (8) The manufacturing method of the dissimilar-material joined structure according to any one of (1) to (7), wherein the laser beam is obtainable by selecting one from the group consisting of a ring mode using a diffractive optical element, a double fiber, or a conical condenser lens, defocusing, and focusing.

[0028] Effects of Invention

[0029] According to the present application, it is possible to provide a manufacturing method of a dissimilar-material joined structure, which can suppress the occurrence of cracks in the HAZ in the joining of dissimilar materials of an aluminum alloy material and a steel material. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1A is a schematic cross-sectional view for explaining the manufacturing method of the dissimilar-material joined structure of the first embodiment of the present application, and is a view showing a step of irradiating a laser beam.

[0031] Figure 1B is a schematic cross-sectional view for explaining the manufacturing method of the dissimilar-material joined structure of the first embodiment of the present application, and is a view showing the manufactured dissimilar-material joined structure.

[0032] Figure 2 is a view schematically showing the intensity distribution of the laser beam of the first embodiment when the vertical axis is the light intensity and the horizontal axis is the distance from the center of the light beam.

[0033] Figure 3 is a view schematically showing the temperature distribution of the cold sprayed film of the first embodiment when the vertical axis is the temperature and the horizontal axis is the distance from the center of the light beam.

[0034] Figure 4A is a schematic cross-sectional view for explaining the manufacturing method of the dissimilar-material joined structure of the first embodiment of the present application, and is a view showing a step of irradiating a laser beam.

[0035] Figure 4B is a schematic cross-sectional view for explaining a manufacturing method of a conventional dissimilar material joining structure, and is a view showing a manufactured dissimilar material joining structure.

[0036] Figure 5 is a view schematically showing an intensity distribution of a laser beam of the conventional manufacturing method when a longitudinal axis is a beam intensity and a lateral axis is a distance from a beam center.

[0037] Figure 6 is a view schematically showing a temperature distribution of a cold sprayed film of the conventional manufacturing method when a longitudinal axis is a temperature and a lateral axis is a distance from a beam center.

[0038] Figure 7 is a view schematically showing an intensity distribution of a laser beam of the second embodiment when a longitudinal axis is a beam intensity and a lateral axis is a distance from a beam center.

[0039] Figure 8 is a view schematically showing an intensity distribution of a laser beam of the third embodiment when a longitudinal axis is a beam intensity and a lateral axis is a distance from a beam center.

[0040] Figure 9 is a view schematically showing an intensity distribution of a laser beam of the fourth embodiment when a longitudinal axis is a beam intensity and a lateral axis is a distance from a beam center. DETAILED DESCRIPTION

[0041] Hereinafter, embodiments of the present application are explained in detail. Also, the present application is not limited by the following explained embodiments, and the embodiments can be arbitrarily changed without departing from the gist of the present application.

[0042] The present inventors have repeatedly and diligently studied in order to obtain a method capable of suppressing cracks occurring in a HAZ in joining of dissimilar materials of an aluminum alloy material and a steel material. As a result, it has been found that it is effective to irradiate a laser beam at a temperature at which the steel material and the cold sprayed film do not melt until a peripheral portion of a molten region of the steel material and the cold sprayed film in order to suppress rapid heating or rapid cooling of the HAZ.

[0043] That is, the manufacturing method of the dissimilar-material joined structure of the present embodiment is a manufacturing method of a dissimilar-material joined structure in which a steel material and an aluminum or aluminum alloy material having a cold spray film containing a metal powder capable of being joined to the steel material on at least a part of a surface are joined, and includes a step of superimposing the aluminum or aluminum alloy material and the steel material in a manner that the cold spray film opposes the steel material, and a step of irradiating a laser beam from the side of the steel material. In addition, the region in which the laser beam is irradiated includes a first region in which at least the steel material and the cold spray film are melted, and a second region in which the steel material and the cold spray film are not melted in a peripheral portion of the first region.

[0044] Hereinafter, the manufacturing method of the dissimilar-material joined structure of the embodiment of the present application will be described in detail.

[0045] (First Embodiment)

[0046] Figure 1A and Figure 1B are schematic cross-sectional views for explaining the manufacturing method of the dissimilar-material joined structure of the first embodiment of the present application. As shown in Figure 1A , a cold spray film 12 is formed on at least a part of a surface of an aluminum alloy material 11 by a cold spray method in which, for example, a metal powder containing pure iron is sprayed. The cold spray method is a method in which a gas and a metal powder are sprayed at a speed of sound or higher toward an object to form the cold spray film 12. This method can be implemented by appropriately selecting the kind of gas, the pressure, the temperature, the particle diameter of the metal powder, and the like.

[0047] Thereafter, the aluminum alloy material 11 and a steel material 13 are superimposed in a manner that the cold spray film 12 opposes the steel material 13, a laser beam 14 is irradiated from the side of the steel material 13, and a molten portion 15 is formed.

[0048] Thereafter, as shown in Figure 1B , the irradiation of the laser beam 14 is stopped, and cooling is performed, whereby a welded metal 17 extending from the steel material 13 to the cold spray film 12 is formed, and a dissimilar-material joined structure 10 in which the aluminum alloy material 11 and the steel material 13 are joined is manufactured.

[0049] In the present embodiment, for example, a central beam 14a that forms the molten portion 15 and a ring-shaped beam 14b that supplies desired heat to a peripheral portion of the molten portion 15 are generated by a ring mode that utilizes two optical fibers, and the laser beam 14 is constituted by the central beam 14a and the ring-shaped beam 14b. Also, the ring mode is a mechanism that can obtain two coaxial laser beams (the central beam 14a and the ring-shaped beam 14b) at the same time, and can individually control the intensities of these beams.

[0050] The intensity of the laser beam 14 at the condensing point and the temperature of the cold sprayed film 12 when the laser beam 14 is irradiated from the steel material 13 side will be described below.

[0051] Figure 2 is a graph schematically showing the intensity distribution of the laser beam of the first embodiment when the vertical axis is the beam intensity and the horizontal axis is the distance from the beam center. Further, Figure 3 is a graph schematically showing the temperature distribution of the cold sprayed film of the first embodiment when the vertical axis is the temperature and the horizontal axis is the distance from the beam center.

[0052] As shown in Figure 2 , in the first region Wl irradiated by the central beam 14a, the first peak Pl having the highest beam intensity is generated, and in the peripheral portion of the first peak Pl, i.e., the second region W2 irradiated by the annular beam, the second peak P2 in the form of a ring centered on the first peak Pl is generated.

[0053] Further, when the intensity distribution of the laser beam is the profile shown in Figure 2 , the cold sprayed film 12 has the temperature distribution shown in Figure 3 . That is, the first region Wl irradiated by the central beam 14a has a temperature of the melting point T or more of the cold sprayed film 12, and the second region W2 irradiated by the annular beam 14b has a temperature of not more than the melting point T of the cold sprayed film 12.

[0054] Further, when the melting points of the steel material 13 and the cold sprayed film 12 are different from each other, the central beam 14a controls the conditions of the laser welding in such a manner that the steel material 13 and the cold sprayed film 12 are melted, and the annular beam 14b controls the conditions of the laser welding in such a manner that neither the steel material 13 nor the cold sprayed film 12 is melted.

[0055] According to the manufacturing method of the first embodiment described above, since the cold sprayed film 12 is formed on the surface of the aluminum alloy material 11 by the cold spraying method, the surface of the aluminum alloy material 11 is formed with fine irregularities by a large amount of metal powder. Therefore, the cold sprayed film 12 and the aluminum alloy material 11 are mechanically firmly joined by the asperity bonding effect.

[0056] Further, the cold sprayed film 12 formed of metal powder such as pure iron which can be joined to the steel material can be easily joined to the steel material 13 by the laser welding, and thus the dissimilar material joined structure 10 of the aluminum alloy material 11 and the steel material 13 can be manufactured.

[0057] Further, the second region W2 irradiated by the annular light beam 14b includes at least a portion of the HAZ 16 of the steel material 13 and the thermal spray coating film 12, and the temperature thereof is increased in a range where neither the steel material 13 nor the thermal spray coating film 12 is melted. As for the irradiation conditions of the annular light beam 14b, they are different depending on the kind of the thermal spray coating film 12, and are not particularly limited as long as the conditions are such that neither the steel material 13 nor the thermal spray coating film 12 is melted, but it is preferable to adjust them in such a manner that the temperature gradient is made small from the molten portion 15 of the thermal spray coating film 12 via the HAZ 16 to the steel material 13 and the thermal spray coating film 12 around the HAZ 16. Thus, the occurrence of cracks in the HAZ 16 can be suppressed.

[0058] Further, in the above-described first embodiment, an example in which the annular second peak P2 in the second region W2 is one is illustrated, but the temperature of the second region W2 can be controlled in such a manner that the rapid heating or rapid cooling of the HAZ 16 is suppressed as long as the temperature is such that neither the steel material 13 nor the thermal spray coating film 12 is melted, and the annular peak can be plural.

[0059] Further, as described above, as the laser welding conditions for controlling the temperature of the first and second regions and the irradiation range of the laser light, a heat source, an output power, a welding speed, and the diameter of a welding portion, and the like can be appropriately selected.

[0060] (Manufacturing method of conventional dissimilar material joined structure)

[0061] For comparison, an example in which only a laser beam that melts the steel material and the thermal spray coating film is irradiated is described.

[0062] Figure 4A and Figure 4B is a schematic cross-sectional view for explaining a manufacturing method of a conventional dissimilar material joined structure. Further, Figure 5 is a graph that schematically represents the intensity distribution of a laser beam in the conventional manufacturing method when the vertical axis is the beam intensity and the horizontal axis is the distance from the center of the beam. Figure 6 is a graph that schematically represents the temperature distribution of a thermal spray coating film in the conventional manufacturing method when the vertical axis is the temperature and the horizontal axis is the distance from the center of the beam.

[0063] Further, in Figure 4A and Figure 4B , the same symbols are attached to the same or equivalent parts as those of the above-described first embodiment, and the description thereof is omitted or simplified.

[0064] As Figure 4AAs shown, the aluminum alloy material 11 and the steel material 13 are arranged so that the cold sprayed film 12 of the aluminum alloy material 11 opposes the steel material 13, and the laser beam 24 is irradiated from the side of the steel material 13 to form a molten portion 25. At this time, a HAZ 26 is generated around the molten portion 25.

[0065] Thereafter, as shown, the irradiation of the laser beam 24 is stopped and cooling is performed, thereby forming a weld metal 27 extending from the steel material 13 to the cold sprayed film 12, and manufacturing the dissimilar material joined structure 20 in which the aluminum alloy material 11 and the steel material 13 are joined. Figure 4B

[0066] As shown, in the conventional manufacturing method of the dissimilar material joined structure 20, a peak P3 is generated only in the region W3 irradiated by the laser beam 24, and the peripheral portion thereof is not irradiated by the laser beam 24 and does not have a peak. Therefore, as shown, the molten portion 25 is formed in the region W3 so as to reach the melting point T or more of the cold sprayed film 12, but heat is not supplied to other regions and the temperature does not rise. Figure 5 Figure 6

[0067] In the above-described conventional manufacturing method of the dissimilar material joined structure 20, the molten portion 25 formed by the irradiation of the laser beam 24 is extremely high in temperature, higher than the melting temperatures of the steel material 13 and the cold sprayed film 12. Moreover, in the HAZ 26, a large temperature difference occurs between the molten portion 25 and other portions, and the rapid heating or rapid cooling causes a strain to occur, and thus a crack 28 occurs.

[0068] In contrast, in the first embodiment, as described above, the laser beam 14 also irradiates the second region W2, and as shown, a HAZ 16 wider than the HAZ 26 generated by the conventional manufacturing method can be generated. Figure 1A Therefore, in the first embodiment, compared with the conventional manufacturing method, the temperature gradient of the HAZ 16 can be reduced, and thus the occurrence of a crack can be suppressed.

[0069] (Second Embodiment)

[0070] Next, the manufacturing method of the dissimilar material joined structure of the second embodiment will be described. Also, the manufacturing processes of the second to fourth embodiments described below are the same as those of the above-described first embodiment, and thus the manufacturing processes will be described with reference to FIGS. 1 to 5 of the first embodiment. Figure 1A Figure 1B Thus, the manufacturing processes are omitted, and only the irradiation method of the laser beam will be specifically described.

[0071] Figure 7 is a graph schematically showing the intensity distribution of the laser beam of the second embodiment when the vertical axis is the beam intensity and the horizontal axis is the distance from the center of the beam. ​​​​

[0072] In the second embodiment, as in the first embodiment, a ring mode laser using a double fiber is used, for example. Specifically, in the first region Wl irradiated by the central beam 14a, a peak P4 having the highest beam intensity is generated, and the intensity of the central beam 14a and the like are controlled in such a manner that the temperature of the steel material 13 and the cold sprayed coating film 12 exceeds the temperature at which they are melted. In addition, in the second region W2 irradiated by the annular beam 14b, the intensity of the annular beam 14b and the like are controlled in such a manner that the temperature of the steel material 13 and the cold sprayed coating film 12 does not exceed the temperature at which they are melted. Further, unlike the first embodiment, in the second region W2, a peak is not generated, but a portion having a certain intensity regardless of the distance from the center of the beam and a portion in which the intensity decreases as the distance from the center of the beam increases are generated. That is, in the second region W2, the beam intensity gradually decreases as the distance from the first region Wl increases.

[0073] In the manufacturing method of the second embodiment described above, the second region W2, including at least a portion of the HAZ 16 of the steel material 13 and the cold sprayed coating film 12, is heated in a range in which neither the steel material 13 nor the cold sprayed coating film 12 is melted. Therefore, the HAZ 16 is wide, and the temperature gradient from the melted portion 15 to the steel material 13 and the cold sprayed coating film 12 around the HAZ 16 is small, so that the occurrence of cracks caused by rapid heating or rapid cooling can be suppressed.

[0074] (Third Embodiment)

[0075] Figure 8 is a graph schematically showing the intensity distribution of the laser beam of the third embodiment when the vertical axis represents the beam intensity and the horizontal axis represents the distance from the center of the beam.

[0076] In the third embodiment, as in the second embodiment, a ring mode laser using a double fiber is used, for example, and in the first region Wl irradiated by the central beam 14a, a peak P5 having the highest beam intensity is generated. In addition, in the first region Wl, the intensity of the central beam 14a and the like are controlled in such a manner that the temperature of the steel material 13 and the cold sprayed coating film 12 exceeds the temperature at which they are melted, and in the second region W2, the intensity of the annular beam 14b and the like are controlled in such a manner that the temperature of the steel material 13 and the cold sprayed coating film 12 does not exceed the temperature at which they are melted. Further, the peak intensity of the second region W2 gradually decreases as the distance from the center of the beam increases, as in the second embodiment, and differs from the second embodiment in that the peak intensity decreases in a more stepped manner.

[0077] In the manufacturing method of the third embodiment described above, the second region W2, including at least a part of the HAZ 16 of the steel material 13 and the cold sprayed film 12, is raised in temperature within a range in which neither the steel material 13 nor the cold sprayed film 12 is melted. Therefore, the HAZ 16 is wide, and from the molten portion 15 via the HAZ 16 to the steel material 13 and the cold sprayed film 12 in the periphery thereof, the temperature gradient is small, and thus generation of cracks due to rapid heating or rapid cooling can be suppressed.

[0078] Further, in the first to third embodiments described above, although a ring mode using a double fiber is used, in addition thereto, a ring mode using a diffractive optical element (DOE), or a conical condenser lens, or the like can be used to generate the central light beam 14a and the annular light beam 14b.

[0079] (Fourth Embodiment)

[0080] Figure 9 is a graph schematically showing an intensity distribution of the laser beam of the fourth embodiment when the vertical axis is the light beam intensity and the horizontal axis is the distance from the center of the light beam.

[0081] The fourth embodiment uses, for example, a laser beam 14 formed by defocusing. Specifically, the laser beam 14 is focused on the side of the welding head (not shown) with respect to the surface of the steel material 13 to be welded, and the intensity distribution of the laser beam 14 is controlled to be wide as shown in the graph of FIG. 8. Figure 5 The intensity distribution of the laser beam 14 is controlled to be wide as shown in the graph of FIG. 8. Further, in the fourth embodiment using the laser beam 14 formed by defocusing, a peak P6 having the highest light beam intensity is generated in the first region Wl, and in the second region W2, the light beam intensity gradually decreases as it moves away from the first region Wl. In addition, the intensity and the like of the laser beam 14 are controlled in such a manner that in the first region Wl, the temperature becomes higher than the temperature at which the steel material 13 and the cold sprayed film 12 are melted, and in the second region W2, the temperature becomes lower than the temperature at which the steel material 13 and the cold sprayed film 12 are melted.

[0082] In the manufacturing method of the fourth embodiment described above, the second region W2, also including at least a part of the HAZ 16 of the steel material 13 and the cold sprayed film 12, is raised in temperature within a range in which neither the steel material 13 nor the cold sprayed film 12 is melted. Therefore, the HAZ 16 is wide, and from the molten portion 15 via the HAZ 16 to the steel material 13 and the cold sprayed film 12 in the periphery thereof, the temperature gradient is small, and thus generation of cracks due to rapid heating or rapid cooling can be suppressed.

[0083] In the above-described fourth embodiment, defocusing is used in order to make the light beam intensity a broad intensity distribution, but focusing on the aluminum alloy material 11 side with respect to the surface of the steel material 13 can also be used. Also, the degree of focus offset is not particularly limited, but regardless of whether the focus is on the welding head side or the steel material 13 side, the distance LI from the surface of the steel material 13 to the focus is preferably 1 to 5% with respect to the distance L2 from the welding head to the surface of the steel material 13.

[0084] In addition, in the above-described first to fourth embodiments, as shown in Figs. 1 to 4, the irradiation conditions of the laser beam 14 are controlled in such a way that the molten portion 15 does not reach the aluminum alloy material 11, but the irradiation conditions of the laser beam 14 can also be controlled in such a way that the molten portion 15 reaches the aluminum alloy material 11. Figure 1A and Figure 1B In this case, the irradiation conditions of the laser beam 14 are preferably set in such a way that the second region W2 includes the steel material 13 and the cold sprayed film 12, and also includes a heat affected portion of the aluminum alloy material 11.

[0085] Also, when laser welding is performed in such a way that deep penetration is achieved, that is, when the laser is irradiated in such a way that the molten portion 15 reaches the aluminum alloy material 11, cracks in the HAZ occur significantly, so the present application is more preferable.

[0086] Next, the aluminum or aluminum alloy material, the metal powder as the material of the cold sprayed film, and the steel material in the manufacturing method of the dissimilar material joined structure of the present application will be described in detail.

[0087] <ALUMINUM OR ALUMINUM ALLOY MATERIAL>

[0088] The aluminum or aluminum alloy material is not particularly limited, but when applied to a member used in a vehicle or the like, an aluminum alloy material of the 2000 series, 5000 series, 6000 series, and 7000 series, or the like is preferably used from the viewpoint of strength. Also, in the present embodiment, since laser welding that can be performed by one-sided construction from the steel material side is used, even a closed cross-section extruded material that is used in large quantities in the field of vehicles or the like can be used without any problems.

[0089] <METAL POWDER>

[0090] In the present application, since the steel material and the cold sprayed film are joined by laser welding, a metal powder that can be joined to the steel material is used as the material of the cold sprayed film. As such a metal powder, for example, a metal powder of at least one kind selected from the group consisting of pure iron, carbon steel, stainless steel, nickel, nickel alloy, cobalt, and cobalt alloy can be selected.

[0091] Further, in the present application, the so-called pure iron indicates an industrial iron that can be easily obtained, and has a purity of 99.9 mass% or more. In addition, the so-called carbon steel indicates an iron steel material that contains iron and carbon as main components, and contains silicon, manganese, impurities such as phosphorus, sulfur, copper, and the like in small amounts. Further, as the nickel alloy, an alloy that contains Ni as a main component, and appropriately contains Mo, Fe, Co, Cr, Mn, and the like can be used, and is commonly called Inconel alloy, Incoloy alloy, and Hastelloy alloy.

[0092] <Particle diameter and shape of metal powder>

[0093] The particle diameter of the metal powder as a material of the cold sprayed film is not particularly limited, but in the case of a low pressure condition in which the gas pressure of the cold spraying is 1 MPa or less, it is, for example, preferably 20 μm or less, and more preferably 10 μm or less.

[0094] On the other hand, in the case of a high pressure condition in which the gas pressure is 1 MPa to 5 MPa, it is, for example, preferably 100 μm or less, and more preferably 50 μm or less.

[0095] The particle shape of the metal powder is not particularly limited, but from the viewpoint of fluidity, a spherical shape is preferable.

[0096] <Kind of working gas>

[0097] The gas used in the cold spraying is not particularly limited, and generally, air, nitrogen, helium, or a mixed gas thereof can be used. On the other hand, if the cold sprayed film is oxidized, it can adversely affect the laser weldability, and therefore, as the kind of gas, nitrogen or helium is preferably used.

[0098] <Steel material>

[0099] As the steel material, there is no particular limitation as long as it is a member composed of a metal generally called steel. However, in recent years, as a steel material used for a vehicle body frame and the like of an automobile, a high-tension steel material (high-tensile strength material) and the like are often used for the purpose of lightening the vehicle body and strengthening the collision safety. The mechanical joining method, which is a method of joining dissimilar materials of steel and aluminum, is difficult to apply to a steel material having a tensile strength of 590 MPa or more. Therefore, the present application is particularly effective in a high-tension steel material having a tensile strength of 590 MPa or more.

[0100] Further, for example, in Japanese Patent Application Publication No. 2013-95974, as a method for forming a densified layer of a sprayed film, a method is disclosed in which a preceding laser beam is caused to irradiate a surface of a sprayed film while scanning, and a following laser beam is caused to re-irradiate an irradiated region scanned by the preceding laser beam while scanning. Further, in Japanese Patent Application Publication No. 2008-266724, as a surface treatment method of a sprayed film, a method is disclosed in which fusion densification is performed with a laser having a wavelength of 9 μm or more.

[0101] These methods are all techniques in which a laser is directly irradiated to a surface of a sprayed film to modify the surface of the sprayed film, and there is no mention of a method in which an aluminum alloy material and a steel material are overlapped in a manner in which the cold-sprayed film faces the steel material, and a dissimilar material joined structure is manufactured by laser welding from the steel material side, as shown in the present application. Further, there is no mention of a crack in a heat-affected portion at the time of laser irradiation, which is a problem of the present application.

[0102] The above describes various embodiments with reference to the drawings, but the present application is of course not limited to such examples. As is apparent to those skilled in the art, various modifications or corrections can be conceived within the scope of the patent claims, and these are of course understood to be within the scope of the technical range of the present application. Further, the respective components of the above embodiments can also be arbitrarily combined within the scope of the object of the present application.

[0103] Further, the present application is based on Japanese Patent Application (Tokugan 2020-117997) filed on July 8, 2020, the content of which is incorporated herein by reference.

[0104] Explanation of Symbols

[0105] 10, 20 dissimilar material joined structure

[0106] 11 aluminum alloy material

[0107] 12 cold-sprayed film

[0108] 13 steel material

[0109] 14, 24 laser beam

[0110] 14a central light beam

[0111] 14b annular light beam

[0112] 15, 25 molten portion

[0113] 16, 26 HAZ

[0114] 17, 27 weld metal

[0115] 28 crack

[0116] P1 first peak

[0117] P2 second peak

[0118] T melting point of cold sprayed coating

[0119] W1 first region

[0120] W2 second region

Claims

1. A method for manufacturing a dissimilar material joined structure, characterized by, A manufacturing method of a dissimilar material joint structure in which a steel material and an aluminum or aluminum alloy material having a cold spray coating film including a metal powder capable of being joined to the steel material on at least a part of a surface thereof are joined, includes the steps of: overlapping the aluminum or aluminum alloy material and the steel material in a manner that the cold spray coating film opposes the steel material; irradiating a laser beam from the steel material side, the region irradiated with the laser beam includes a first region in which at least the steel material and the cold spray coating film are melted, and a second region in which the steel material and the cold spray coating film are not melted at a peripheral portion of the first region, the second region includes at least a part of a HAZ of the steel material and the cold spray coating film, conditions of laser welding are controlled in a manner that the first region is at a temperature higher than a melting point of the cold spray coating film, and the second region is at a temperature not higher than the melting point of the cold spray coating film, and laser irradiation conditions for the second region are adjusted in a manner that a temperature gradient is made smaller from a molten portion of the cold spray coating film through the HAZ to the steel material and the cold spray coating film at a periphery thereof.

2. The manufacturing method of a dissimilar-material joined structure according to claim 1, wherein the second region includes a heat-affected portion of the steel material and the cold spray coating film.

3. The manufacturing method of a dissimilar-material joined structure according to claim 1, wherein the first region is a region irradiated with a part of the laser beam to melt the steel material, the cold spray coating film, and the aluminum or aluminum alloy material, and the second region is a region not to melt the steel material, the cold spray coating film, and the aluminum or aluminum alloy material.

4. The manufacturing method of a dissimilar-material joined structure according to claim 3, wherein the second region includes a heat-affected portion of the steel material, the cold spray coating film, and the aluminum or aluminum alloy material.

5. The manufacturing method of the dissimilar-material joined structure according to any one of claims 1 to 4, wherein an intensity distribution of the laser beam has a first peak having a highest beam intensity in the first region, and at least one second peak having a ring shape centered on the first peak in the second region.

6. The manufacturing method of a dissimilar-material joined structure according to any one of claims 1 to 4, wherein an intensity of the laser beam is highest in the first region, and gradually decreases as it is farther from the first region in the second region.

7. The method of manufacturing a dissimilar-material joined structure according to any one of claims 1 to 4, wherein the metal powder contains at least one selected from pure iron, carbon steel, stainless steel, nickel, nickel alloy, cobalt, and cobalt alloy.

8. The method of manufacturing a dissimilar-material joined structure according to any one of claims 1 to 4, wherein the laser beam can be obtained by one selected from a ring mode using a diffractive optical element, a double optical fiber, or a conical condenser lens, defocusing, and focusing.

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