Method for manufacturing dissimilar material joined structure and dissimilar material joined structure

Abstract

To provide a method for manufacturing a joint structure of dissimilar materials which can suppress occurrence of a blow hole, in laser welding of a steel material having a galvanized film or an electrodeposition film formed, and a non-ferrous metal member having a low temperature thermal-sprayed film formed.SOLUTION: A method for manufacturing a joint structure of dissimilar materials includes steps of: forming a low temperature thermal-sprayed film 12 on the surface of an aluminum alloy plate 11; arranging the aluminum alloy plate 11 and a steel plate 21 so that the low temperature thermal-sprayed film 12 and an anticorrosive film 22 oppose each other; and laser welding a region provided with the low temperature spray-molded film 12 from the side of the steel plate 21, and forming weld metal 23 reaching the aluminum alloy plate 11. A distance between the surface of the low temperature thermal-sprayed film 12 in a region where the laser welding is performed and the surface of the anticorrosive film 22 is more than 0 mm and 0.4 mm or less, and a penetration depth by the laser welding is set to be a depth of 0.05 mm or more and 0.71 mm or less from the surface of the aluminum alloy plate 11.SELECTED DRAWING: Figure 2B

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a dissimilar material joined structure and a dissimilar material joined structure.

Background Art

[0002] Conventionally, when manufacturing a structure using steel materials, as a method for preventing corrosion of the structure, a method of applying zinc plating or electrodeposition coating to the surface of the steel material has been adopted. However, for example, when arc welding by overlapping zinc-plated steel sheets, when arc heat is applied to the overlapping surface of the steel sheets, zinc gasifies, and porosity defects such as blowholes, pits, and pinholes occur.

[0003] Therefore, Patent Document 1 discloses a method for manufacturing a joined product that can prevent the occurrence of joining defects and surely obtain a good joined portion. The method for manufacturing a joined product described in Patent Document 1 is a manufacturing method in which a first joining material and a second joining material subjected to specific processing are joined in a region where an appropriate joining distance is ensured.

[0004] Further, Patent Document 2 proposes a method for joining plated steel sheets in which a gap capable of surely discharging gas generated in a welded portion is provided to obtain a good joined structure without porosity defects. The joining method includes a step of forming a plurality of protruding portions on the overlapping surface of the first steel sheet with the second steel sheet, which are substantially perpendicular to the edge of the first steel sheet and arranged along the edge; a step of overlapping the first steel sheet and the second steel sheet so that the protruding portions protrude in a direction toward the overlapping surface with the second steel sheet; and a step of linearly arc-welding the edge of the first steel sheet. It comprises.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] By the way, in recent years, for the purpose of weight reduction of vehicle structures, there has been an increasing demand for dissimilar material joined structures in which a lightweight aluminum or aluminum alloy material (hereinafter sometimes simply referred to as an aluminum alloy material) is joined with a steel material. As methods for joining dissimilar materials, there are various methods. For example, a method of forming a cold spray coating (hereinafter sometimes referred to as a low-temperature sprayed coating or a CS (Cold Spray) coating) in advance on the surface of an aluminum alloy material and laser welding the steel and the coating can be mentioned.

[0007] However, the methods described in Patent Document 1 and Patent Document 2 above are both methods for welding steel materials, and no consideration has been given to welding methods that can suppress the generation of blowholes during welding of a steel material with a plating or electrodeposition coating and a non-ferrous metal member.

[0008] Specifically, according to the dissimilar material joining method as described above, blowholes may occur in the weld metal due to the gas in the CS coating. Further, when attempting to manufacture an automobile structure by joining dissimilar materials, in addition to preventing corrosion of the steel material itself, it is necessary to prevent galvanic corrosion between the steel material and the aluminum alloy material. Therefore, in order to prevent direct contact between the steel material and the aluminum alloy material, a method of forming a zinc-based plating film, an organic film, or the like on the surface of the steel material is frequently used. However, when such a film is formed on the surface of the steel material, similar to the case of manufacturing a structure of steel materials, the film vaporizes during welding and causes an increase in blowholes. And when the amount of blowholes generated during welding increases, the joining strength of the resulting structure decreases.

[0009] The present invention has been made in view of such problems, and when laser welding a steel material formed with a zinc-based plating film or an electrodeposited coating film and a non-ferrous metal member formed with a low-temperature sprayed film, it is possible to suppress the generation of blowholes. An object of the present invention is to provide a method for manufacturing a dissimilar material joined structure and a dissimilar material joined structure obtained by the joining method and having excellent joining strength.

Means for Solving the Problems

[0010] The above object of the present invention is achieved by the following configuration (1) relating to a method for manufacturing a dissimilar material joined structure.

[0011] (1) A method for manufacturing a dissimilar material joined structure, which joins a non-ferrous metal member and a steel material having a corrosion-resistant film formed of at least one of a zinc-based plating film and an electrodeposited coating film on at least a part of the surface, forming a low-temperature sprayed film by low-temperature spraying a metal powder containing at least one selected from pure iron, carbon steel, stainless steel, nickel, nickel alloy, cobalt, and cobalt alloy on at least a part of the surface of the non-ferrous metal member; arranging the non-ferrous metal member and the steel material so that the low-temperature sprayed film and the corrosion-resistant film face each other; performing laser welding from the opposite side of the surface of the steel material facing the non-ferrous metal member to the region of the non-ferrous metal member where the low-temperature sprayed film is formed to form a weld metal reaching the non-ferrous metal member, and in the arranging step, arranging the non-ferrous metal member and the steel material so that the distance between the surface of the low-temperature sprayed film and the surface of the corrosion-resistant film in the region where laser welding is performed is more than 0 mm and 0.4 mm or less; in the step of performing the laser welding, the penetration depth by the laser welding is set to a depth of 0.05 mm or more and 0.71 mm or less from the surface of the non-ferrous metal member, and is characterized by a method for manufacturing a dissimilar material joined structure.

[0012] Also, a preferred embodiment of the present invention related to a method for manufacturing a dissimilar material joined structure relates to the following configurations (2) to (4).

[0013] (2) In the step of arranging the non-ferrous metal member and the steel material, the distance between the surface of the low-temperature sprayed coating on the non-ferrous metal member and the surface of the corrosion-resistant coating on the steel material is more than 0 mm and 0.3 mm or less, In the step of performing the laser welding, the penetration depth by the laser welding is set to a depth of 0.05 mm or more and 0.32 mm or less from the surface of the non-ferrous metal member. The method for manufacturing a dissimilar material joined structure according to (1).

[0014] (3) The non-ferrous metal member is made of one selected from aluminum or an aluminum alloy, and titanium or a titanium alloy. The method for manufacturing a dissimilar material joined structure according to (1) or (2).

[0015] (4) The step of forming the low-temperature sprayed coating includes a step of forming the low-temperature sprayed coating including a thin film portion and a thick film portion provided at least partially around the thin film portion and having a film thickness thicker than that of the thin film portion, In the step of arranging the non-ferrous metal member and the steel material, by bringing the thick film portion of the low-temperature sprayed coating into contact with the corrosion-resistant coating on the steel material, the surface of the thin film portion of the low-temperature sprayed coating and the surface of the corrosion-resistant coating are separated at an interval of more than 0 mm and 0.3 mm or less, In the step of performing the laser welding, laser welding is performed from the opposite side of the surface of the steel material facing the non-ferrous metal member to the region where the thin film portion of the low-temperature sprayed coating is formed. The method for manufacturing a dissimilar material joined structure according to any one of (1) to (3).

[0016] Also, the above object of the present invention is achieved by the following configuration (5) related to a dissimilar material joined structure.

[0017] (5) A dissimilar material joining structure in which a non-ferrous metal member and a steel material having a corrosion-resistant film formed of at least one of a zinc-based plating film and an electrodeposited coating film on at least a part of its surface are joined together, On at least a part of the surface of the non-ferrous metal member, a low-temperature sprayed film made of a metal powder containing at least one selected from pure iron, carbon steel, stainless steel, nickel, nickel alloy, cobalt, and cobalt alloy is formed. The low-temperature sprayed film formed on the surface of the non-ferrous metal member and the corrosion-resistant film formed on the surface of the steel material are arranged so as to face each other. Weld metal is formed so as to penetrate at least the steel material, the corrosion-resistant film, and the low-temperature sprayed film in this order from the surface of the steel material on the side opposite to the non-ferrous metal member side and reach the non-ferrous metal member. At least around the weld metal, the low-temperature sprayed film and the corrosion-resistant film are separated in a range of more than 0 mm and 0.4 mm or less. A dissimilar material joining structure, characterized in that the weld metal reaches a depth of 0.05 mm or more and 0.71 mm or less from the surface of the non-ferrous metal member.

Advantages of the Invention

[0018] According to the present invention, it is possible to provide a method for manufacturing a dissimilar material joining structure that can suppress the generation of blow holes. Further, according to the present invention, it is possible to provide a dissimilar material joining structure having excellent joining strength.

Brief Description of the Drawings

[0019]

Figure 1A

Figure 1B

Figure 2A

Figure 2B

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments of the dissimilar material joining structure and its manufacturing method according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments described below, and can be arbitrarily modified and implemented without departing from the gist of the present invention.

[0021] The present inventor has conducted various studies on a method capable of suppressing the generation of blowholes even when a CS film or a corrosion-resistant film exists in a region where high heat is generated by welding when performing dissimilar material joining between a non-ferrous metal member and a steel material. As a result, it has been found that it is effective to appropriately control the distance and the penetration depth between the CS film formed on the non-ferrous metal member and the corrosion-resistant film formed on the steel material.

[0022] Hereinafter, a method for manufacturing a dissimilar material joined structure and the dissimilar material joined structure according to an embodiment of the present invention will be described in detail with reference to the drawings.

[0023] [Method for manufacturing a dissimilar material joined structure] FIG. 1A is a perspective view showing a step of forming a low-temperature sprayed coating film in a method for manufacturing a dissimilar material joined structure according to an embodiment of the present invention, and FIG. 1B is a cross-sectional view thereof. Further, FIG. 2A is a perspective view showing a step of performing laser welding in a method for manufacturing a dissimilar material joined structure according to an embodiment of the present invention, and FIG. 2B is a cross-sectional view thereof.

[0024] [Preparation of materials] In the present embodiment, as materials for manufacturing a dissimilar material joined structure, a non-ferrous metal member and a steel material are used. As shown in FIGS. 1A, 1B, 2A, and 2B, in the present embodiment, an aluminum alloy plate 11 is used as the non-ferrous metal member, and a steel plate 21 is used as the steel material. Note that the non-ferrous metal member represents a member made of a non-ferrous metal, and a member made of one selected from aluminum or an aluminum alloy, and titanium or a titanium alloy can be used. The type of the steel material is not particularly limited, and the content of components other than iron can be variously designed according to the required performance of the structure. However, in the steel plate 21 used in the present embodiment, a corrosion-resistant coating film 22 made of at least one of a zinc-based plating film and an electrodeposition coating film is formed on at least a part of the surface. Note that the zinc-based plating film refers to a plating film formed of zinc or a zinc alloy.

[0025] [Step of forming a low-temperature sprayed coating film] First, as shown in FIGS. 1A and 1B, a low-temperature sprayed coating 12 is formed on at least a part of the surface of the aluminum alloy plate 11. In the region where the low-temperature sprayed coating 12 is formed, in a later process, a steel plate 21 on which a corrosion-resistant coating 22 is formed is superposed, and laser welding is performed. In the present embodiment, the low-temperature sprayed coating 12 is assumed to have a thin film portion 13 and a thick film portion 14 thicker than the thin film portion 13, and the thick film portion 14 is formed on at least a part of the periphery of the thin film portion 13. The difference in thickness between the thick film portion 14 and the thin film portion 13 is set so that when the surface on which the low-temperature sprayed coating 12 is formed and the steel plate 21 are superposed, a void portion having a desired thickness is formed between the thin film portion 13 and the corrosion-resistant coating 22 on the surface of the steel plate 21.

[0026] As a method of forming the low-temperature sprayed coating 12 having the thin film portion 13 and the thick film portion 14, for example, metal powder is sprayed at a low temperature in a predetermined region to form a low-temperature sprayed coating having a thickness capable of being joined to the steel plate. Then, except for the region where the thin film portion 13 is formed, metal powder is continuously sprayed at a low temperature only on the region where the thick film portion 14 is formed. As a result, metal powder is laminated only on the region where the thick film portion 14 is desired to be formed, and the low-temperature sprayed coating 12 having the thin film portion 13 and the thick film portion 14 can be formed.

[0027] Note that as the metal powder used for low-temperature spraying, a metal powder that is of the same quality as the steel plate 21 or that forms a low-temperature sprayed coating made of a material that is easily joined to the steel plate 21 may be selected. Specifically, metal powder containing at least one selected from pure iron, carbon steel, stainless steel, nickel, nickel alloy, cobalt, and cobalt alloy is used.

[0028] <Step of arranging the aluminum alloy plate and the steel plate> Thereafter, as shown in FIGS. 2A and 2B, the aluminum alloy plate 11 and the steel plate 21 are arranged so that the low-temperature sprayed coating 12 and the corrosion-resistant coating 22 face each other. At this time, the thick film portion 14 of the low-temperature sprayed coating 12 is brought into contact with the corrosion-resistant coating 22 of the steel plate 21. As a result, a void portion 15 having a predetermined interval is formed between the surface of the thin film portion 13 of the low-temperature sprayed coating 12 and the surface of the corrosion-resistant coating 22. The interval of the void portion 15 will be described in detail later.

[0029] <Step of forming a weld metal (step of performing laser welding)> Thereafter, a laser beam 24 is irradiated from the opposite side of the surface of the steel plate 21 facing the aluminum alloy plate 11 to the region where the thin film portion 13 of the low-temperature sprayed coating 12 is formed on the aluminum alloy plate 11, and a weld metal 23 reaching the aluminum alloy plate 11 is formed.

[0030] When joining dissimilar materials such as the aluminum alloy plate 11 and the steel plate 21, a low-temperature sprayed coating 12 made of a material that is easily joined to the steel plate 21 is formed on the surface of the aluminum alloy plate 11, and a method of joining the low-temperature sprayed coating 12 and the steel plate 21 by laser welding is known. However, the corrosion-resistant coating 22 formed on the surface of the steel plate 21 and the low-temperature sprayed coating 12 formed on the surface of the aluminum alloy plate 11 are gasified by the laser heat, and this gas penetrates into the weld metal, generating blowholes. In the present embodiment, in the region where laser welding is performed, a gap portion 15 having a predetermined interval is formed between the surface of the low-temperature sprayed coating 12 and the surface of the corrosion-resistant coating 22. This gap portion 15 has the effect of discharging the gas generated from the corrosion-resistant coating 22 and the low-temperature sprayed coating 12 by the laser heat.

[0031] Further, the inventor has found that in order to completely discharge the gas generated from the low-temperature sprayed coating 12 or the like, it is effective to melt the aluminum alloy plate 11, which is the lower plate, during laser welding. When the molten aluminum alloy enters the molten pool, a density difference and a surface tension difference are generated, generating a flow of molten metal upward in the thickness direction of the aluminum alloy plate 11 and the steel plate 21. Thereby, the gas derived from the corrosion-resistant coating 22 and the low-temperature sprayed coating 12 that has entered the molten pool can be released to the outside of the molten pool. Thus, in the present embodiment, in the region where laser welding is performed, by controlling both the formation of the gap portion 15 and the penetration depth during laser welding, the generation of blowholes is suppressed. Hereinafter, the interval D1 of the gap portion 15 and the penetration depth D2 by laser welding will be described in more detail.

[0032] (Gap interval D1: greater than 0 mm and less than or equal to 0.4 mm) In order to discharge the gas generated from the corrosion-resistant film 22 and the low-temperature sprayed film 12, it is necessary to appropriately adjust the interval D1 of the gap portion 15, that is, the distance between the surface of the low-temperature sprayed film 12 and the surface of the corrosion-resistant film 22. When the interval D1 of the gap portion 15 is not formed at all (in the case of 0 mm), the generated gas cannot be discharged, and blowholes will occur. However, even if there is a slight interval D1 formed, the discharge of gas can be promoted. Therefore, the interval D1 of the gap portion 15 is preferably more than 0 mm, preferably 0.05 mm or more, and more preferably 0.1 mm or more.

[0033] On the other hand, if the interval D1 of the gap portion 15 is too large, the weld metal 23 will not be formed in the region of the gap portion 15, and welding will be impossible. When zinc-plated steel sheets are joined by laser welding, when the interval of the gap portion is 0.6 mm, the fact that welding cannot be performed in this gap portion is described, for example, in the Transactions of the Japan Society for Precision Engineering / Journal of the Japan Society for Precision Engineering, Vol84, No.5, 2018, p.405. Also, in order to form the weld metal in the region of the gap portion 15, if the laser output is increased, the hydrogen contained in the aluminum alloy plate 11 will vaporize, and blowholes will easily occur. Therefore, in order to obtain the weld metal 23 that can join the aluminum alloy plate 11 and the steel plate 21, the interval D1 of the gap portion 15 is preferably 0.4 mm or less, preferably 0.3 mm or less, and more preferably 0.2 mm or less.

[0034] (Penetration depth D2 by laser welding: 0.05 mm or more and 0.71 mm or less) By making the penetration depth D2 equal to or greater than a predetermined size, a flow of molten metal can be generated to discharge the gas generated from the corrosion-resistant film 22 and the low-temperature sprayed film 12. If the penetration depth D2 is less than 0.05 mm, it becomes difficult to generate a flow of molten metal, and blowholes may occur. Therefore, the penetration depth D2 by laser welding is preferably 0.05 mm or more, more preferably 0.09 mm or more, still more preferably 0.15 mm or more, and even more preferably 0.20 mm or more.

[0035] On the other hand, if the aluminum alloy plate 11 is melted too much, the hydrogen contained in the aluminum alloy plate 11 vaporizes, and gas is also generated from the aluminum alloy plate 11, making it easier for blowholes to occur. Therefore, from the viewpoint of suppressing the generation of blowholes, the penetration depth D2 is set to 0.71 mm or less. Note that if the penetration depth D2 is 0.32 mm or less, the formation of depressions (pits) on the surface of the weld metal 23 can be minimized. Therefore, from the viewpoint of suppressing the generation of pits, the penetration depth D2 is preferably 0.32 mm or less, and more preferably 0.25 mm or less.

[0036] Note that the numerical limitation ranges of the interval D1 of the void portion 15 and the penetration depth D2 are the same even when a non-ferrous metal member or titanium or a titanium alloy is used. The same also applies when pure iron, carbon steel, stainless steel, nickel, nickel alloy, cobalt, or cobalt alloy is used as the low-temperature sprayed film 12.

[0037] In the manufacturing method of the dissimilar material joining structure according to the above embodiment, the void portion 15 having a predetermined interval D1 is formed by forming the low-temperature sprayed film 12 having the thin film portion 13 and the thick film portion 14. However, the present invention is not limited to such a manufacturing method. For example, a low-temperature sprayed film 12 having a substantially uniform thickness may be formed, and a spacer or the like capable of forming the void portion 15 may be sandwiched and disposed between the low-temperature sprayed film 12 and the corrosion-resistant film 22 of the steel plate 21. The shape of the spacer or the like can be appropriately selected according to the region where laser welding is performed.

[0038] [Dissimilar Material Bonding Structure] Next, the dissimilar material bonding structure according to the present embodiment will be described below with reference to FIGS. 2A and 2B. The dissimilar material bonding structure according to the present embodiment can be manufactured by the method for manufacturing the dissimilar material bonding structure according to the above-described embodiment. Therefore, descriptions of parts overlapping with those in the above manufacturing method will be omitted or simplified.

[0039] As shown in FIGS. 2A and 2B, the dissimilar material bonding structure 10 is manufactured by bonding an aluminum alloy plate 11 and a steel plate 21 having a corrosion-resistant film 22 formed on its surface. Specifically, a low-temperature sprayed film 12 is formed on a part of the surface of the aluminum alloy plate 11, and the aluminum alloy plate 11 and the steel plate 21 are arranged such that the low-temperature sprayed film 12 and the corrosion-resistant film 22 face each other. In the present embodiment, the corrosion-resistant film 22 is formed on the entire surface of the steel plate 21. Therefore, the weld metal 23 is formed so as to penetrate the corrosion-resistant film 22, the steel plate 21, the corrosion-resistant film 22, and the low-temperature sprayed film 12 in this order from the surface of the steel plate 21 on the side opposite to the aluminum alloy plate 11 side and reach the aluminum alloy plate 11.

[0040] Note that around the weld metal 23, the low-temperature sprayed film 12 and the corrosion-resistant film 22 are separated in a range of more than 0 mm and 0.4 mm or less. Further, the weld metal 23 reaches a depth of 0.05 mm or more and 0.71 mm or less from the surface of the aluminum alloy plate 11.

[0041] In the dissimilar material joining structure 10 configured as described above, since the low-temperature sprayed coating 12 and the corrosion-resistant coating 22 are separated by a predetermined interval D1 and the void portion 15 is formed, the gas generated during manufacturing can be discharged to the outside through the void portion 15. Further, since the weld metal 23 has reached the aluminum alloy plate 11 and its penetration depth (penetration depth) is defined, the generated gas can flow upward, and it is also possible to prevent blowholes from occurring due to the gas in the aluminum alloy plate 11. Therefore, the dissimilar material joining structure 10 can have excellent joining strength.

[0042] In the present embodiment, the corrosion-resistant coating 22 is formed on the entire surface of the steel plate 21, but it is sufficient that the corrosion-resistant coating 22 is formed at least partially only in the necessary regions. Further, it is not limited to the corrosion-resistant coating, and other coatings may be formed. Therefore, it is sufficient that the weld metal 23 penetrates at least the steel plate 21, the corrosion-resistant coating 22, and the low-temperature sprayed coating 12 in this order and reaches the aluminum alloy plate 11.

Example

[0043] Hereinafter, the manufacturing method of the dissimilar material joining structure according to the present invention will be specifically described with reference to inventive examples and comparative examples.

[0044] <Manufacturing of dissimilar material joining structure> First, an aluminum alloy plate 11 and a steel plate 21 having a corrosion-resistant coating 22 formed on its surface were prepared, and a low-temperature sprayed coating was formed by low-temperature spraying iron powder on a part of the surface of the aluminum alloy plate 11 under the conditions shown below. Next, the steel plate was arranged on the aluminum alloy plate so that the low-temperature sprayed coating and the corrosion-resistant coating faced each other. At this time, for a part, a spacer having holes in the welding planned area was arranged between the aluminum alloy plate and the steel plate, and the interval of the void portion between the low-temperature sprayed coating of the aluminum alloy plate and the corrosion-resistant coating of the steel plate was adjusted in the welding planned area. Then, laser welding was performed on the welding planned area from above the steel plate under the conditions shown below, and the aluminum alloy plate and the steel plate were joined.

[0045] (Low-temperature spraying conditions) Equipment: High-temperature and high-pressure type Material of aluminum alloy plate: 7204-T6 aluminum alloy (plate thickness 3 mm) Metal powder: Water atomized iron powder (average particle size 40 μm) Gas type: Nitrogen Gas pressure: 5 MPa Gas temperature: 1000 °C Film thickness of low-temperature sprayed coating: 2 mm

[0046] (Laser welding conditions) Upper plate: Steel plate of 1470 MPa grade (plate thickness 1.4 mm), with corrosion-resistant coating by hot-dip galvanizing or cationic electrodeposition coating Lower plate: Aluminum alloy plate with the above low-temperature sprayed coating Welding machine: Fiber laser (YLS-6000 manufactured by IPG photonics) Laser output: 3250 - 4500 W Power density: 4.6 - 6.4×10 6 (W / cm 2 ) Welding speed: 4 (m / min) Spot diameter: 0.3 mm Interval D1 of voids: 0 - 0.4 mm

[0047] (Evaluation method for dissimilar material joined structure) Cross-sectional photographs were taken of the obtained joints, blowholes in the weld metal were observed, and the depth of pits was measured. Also, using analysis software (Image J), the blowhole rate was calculated by the following formula. Blowhole rate (%) = Total blowhole area × 100 / Weld metal area

[0048] (Evaluation criteria for dissimilar material joined structure) Those with a blowhole rate of less than 10% and a pit depth of less than 0.34 mm were rated as ◎ (excellent). Also, those with a blowhole rate of less than 10% and a pit depth of 0.34 mm or more and less than 0.68 mm were rated as 〇 (good). Furthermore, those with a blowhole rate of 10% or more or a pit depth of 0.68 mm or more were rated as △ (poor). Note that the criterion for judging that the pit depth is poor was set as 20% or more with respect to the total thickness of the steel plate and the thickness of the low-temperature sprayed coating. The types of corrosion-resistant coatings formed on the steel plate, the manufacturing conditions of each test material, and the evaluation results are shown in Table 1 below, and the photographed cross-sectional photographs are shown in FIGS. 3 to 6. Note that for the corrosion-resistant coating formed on the surface of the steel plate, since the film thickness was extremely small, it was difficult to confirm it with a cross-sectional photograph.

[0049]

Table 1

[0050] As shown in FIG. 3, for example, in Invention Example No. 1, the weld metal 23 that penetrated the steel plate 21, the corrosion-resistant coating (not shown), and the low-temperature sprayed coating 12 and reached the aluminum alloy plate 11 was formed. Also, since both the interval D1 and the penetration depth D2 of the gap between the corrosion-resistant coating of the steel plate 21 and the low-temperature sprayed coating 12 of the aluminum alloy plate 11 were controlled within an appropriate range, blowholes did not occur and a sound weld metal could be obtained.

[0051] Similarly, as shown in FIGS. 3 to 6 and Table 1, for Invention Examples No. 2 to 12 as well, since the interval D1 and penetration depth D2 of the void portions were controlled within the ranges defined in the present invention, the blowhole rate was low and deep pits were not formed. In particular, in Invention Examples No. 1 to 8 and 10, since the penetration depth D2 was 0.32 mm or less, it was possible to prevent the formation of pits 31 with a depth as shown in Invention Example No. 9, and as a comprehensive evaluation, it was rated ◎ (excellent). Therefore, according to the method for manufacturing a dissimilar material joined structure according to the present invention, a dissimilar material joined structure having high strength can be manufactured whether the corrosion-resistant coating is a hot-dip galvanized coating or a cationic electrodeposition coating.

[0052] In the above invention examples, examples of forming a corrosion-resistant coating by hot-dip galvanizing or cationic electrodeposition coating are given. However, it is presumed that the same effects can be obtained even when other zinc-based plating coatings or anionic electrodeposition coating films are formed.

[0053] On the other hand, as shown in FIG. 3, for example, in Comparative Example No. 1, large blowholes 30 communicating with the upper surface were generated in the weld metal 23. Further, as shown in FIG. 4, in Comparative Example No. 2, blowholes 30 were generated inside the weld metal 23, and the weld metal 23 had an appearance protruding from the upper surface of the steel plate 21. Similarly, as shown in FIGS. 3 to 6 and Table 1, for Comparative Examples No. 3 to 5 as well, since the interval D1 and penetration depth D2 of the void portion between the corrosion-resistant coating of the steel plate 21 and the low-temperature sprayed coating 12 of the aluminum alloy plate 11 deviated from the ranges defined in the present invention, blowholes were generated. Therefore, a dissimilar material joined structure having a desired joint strength could not be manufactured.

Explanation of Reference Numerals

[0054] 10 Dissimilar material joined structure 11 Aluminum alloy plate 12 Low-temperature sprayed coating 13 Thin film portion 14 Thick film portion 15 Void portion 21 Steel plate 22 Corrosion-resistant coating 23 Weld metal 30 Blowhole 31 Pit

Claims

1. A method for manufacturing a dissimilar material joined structure, which joins a non-ferrous metal member and a steel material having a corrosion-resistant film formed of at least one of a zinc-based plating film and an electrodeposition coating film on at least a part of its surface, comprising: forming a low-temperature sprayed film by low-temperature spraying a metal powder containing at least one selected from pure iron, carbon steel, stainless steel, nickel, nickel alloy, cobalt, and cobalt alloy on at least a part of the surface of the non-ferrous metal member; arranging the non-ferrous metal member and the steel material such that the low-temperature sprayed film and the corrosion-resistant film face each other; performing laser welding from the opposite side of the surface of the steel material facing the non-ferrous metal member to the region of the non-ferrous metal member where the low-temperature sprayed film is formed to form a weld metal reaching the non-ferrous metal member; and in the arranging step, arranging the non-ferrous metal member and the steel material such that the distance between the surface of the low-temperature sprayed film and the surface of the corrosion-resistant film in the region where laser welding is performed is more than 0 mm and 0.4 mm or less; in the step of performing laser welding, the penetration depth by the laser welding is set to a depth of 0.05 mm or more and 0.71 mm or less from the surface of the non-ferrous metal member. A method for manufacturing a dissimilar material joined structure, characterized by this.

2. In the step of arranging the non-ferrous metal member and the steel material, the distance between the surface of the low-temperature sprayed film on the non-ferrous metal member and the surface of the corrosion-resistant film on the steel material is set to more than 0 mm and 0.3 mm or less; In the step of performing laser welding, the penetration depth by the laser welding is set to a depth of 0.05 mm or more and 0.32 mm or less from the surface of the non-ferrous metal member. The method for manufacturing a dissimilar material joined structure according to claim 1, characterized by this.

3. The non-ferrous metal member is made of one selected from aluminum or an aluminum alloy, and titanium or a titanium alloy. The method for manufacturing a dissimilar material joined structure according to claim 1 or 2, characterized by this.

4. The step of forming the low-temperature sprayed film includes a step of forming the low-temperature sprayed film including a thin film portion and a thick film portion provided at least in part around the thin film portion and having a film thickness thicker than that of the thin film portion. In the step of arranging the non-ferrous metal member and the steel material, by bringing the thick film portion of the low-temperature sprayed coating into contact with the corrosion-resistant coating of the steel material, the surface of the thin film portion of the low-temperature sprayed coating and the surface of the corrosion-resistant coating are separated at an interval of more than 0 mm and 0.3 mm or less. In the step of performing the laser welding, the laser welding is performed from the opposite side of the surface of the steel material facing the non-ferrous metal member with respect to the region where the thin film portion of the low-temperature sprayed coating is formed. A method for manufacturing a dissimilar material joined structure according to claim 1 or 2.

5. A dissimilar material joined structure in which a non-ferrous metal member and a steel material having a corrosion-resistant coating formed of at least one of a zinc-based plating film and an electrodeposited coating film on at least a part of the surface are joined. On at least a part of the surface of the non-ferrous metal member, a low-temperature sprayed coating made of a metal powder containing at least one selected from pure iron, carbon steel, stainless steel, nickel, nickel alloy, cobalt, and cobalt alloy is formed. The low-temperature sprayed coating formed on the surface of the non-ferrous metal member and the corrosion-resistant coating formed on the surface of the steel material are arranged so as to face each other. Weld metal that reaches the non-ferrous metal member by penetrating at least the steel material, the corrosion-resistant coating, and the low-temperature sprayed coating in this order from the surface of the steel material on the side opposite to the non-ferrous metal member side is formed. At least around the weld metal, the low-temperature sprayed coating and the corrosion-resistant coating are separated in a range of more than 0 mm and 0.4 mm or less. A dissimilar material joined structure, characterized in that the weld metal reaches a depth of 0.05 mm or more and 0.71 mm or less from the surface of the non-ferrous metal member.

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