Manufacturing method for dissimilar material joint structure and dissimilar material joint structure

Abstract

To provide a method for manufacturing a joint structure of dissimilar materials which dispenses with special adjustment of a welding condition, and can suppress occurrence of a blow hole.SOLUTION: A method for manufacturing a joint structure of dissimilar materials that joins an aluminum alloy plate 11 and a steel plate 21 includes steps of: low temperature thermal-spraying metal powder containing at least one selected from pure iron, carbon steel, stainless steel, nickel, nickel alloy, cobalt and cobalt alloy, onto at least a part of the surface of the aluminum alloy plate 11, and forming a low temperature thermal-sprayed film 12; superposing the aluminum alloy plate 11 and the steel plate 21 so that the low temperature thermal-sprayed film 12 and the steel plate 21 are opposite to each other; and performing laser welding from a side opposite to a surface opposite to the aluminum alloy plate 11 in the steel plate 21, where the metal powder is powdered from molten metal in a vacuum or inert gas atmosphere.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] In recent years, with the aim of reducing the weight of vehicle structures, there has been an increasing demand for dissimilar material joined structures in which lightweight aluminum or aluminum alloy material (hereinafter sometimes simply referred to as aluminum alloy material) is joined to steel material. There are various methods for joining dissimilar materials, for example, a method in which a cold spray coating (hereinafter sometimes referred to as a low-temperature thermal spray coating or CS (Cold Spray) coating) is formed in advance on the surface of an aluminum alloy material, and the steel and the coating are laser-welded.

[0003] However, with the above joining method, blowholes may occur in the weld metal due to gas in the CS coating, and these blowholes cause a decrease in joint strength.

[0004] Therefore, for example, Patent Document 1 proposes a manufacturing method capable of manufacturing a dissimilar metal welded structure with few blowholes and excellent joint strength. The manufacturing method of the dissimilar metal welded structure includes the steps of forming a low-temperature sprayed coating by low-temperature spraying a predetermined metal powder on at least a part of the surface of an aluminum alloy material, overlapping the aluminum alloy material and the steel material so that the low-temperature sprayed coating faces the steel material, and joining the aluminum alloy material and the steel material by laser welding from the steel material side. The joining step is performed under welding conditions that form molten parts in all of the steel material, the low-temperature sprayed coating, and the aluminum alloy material. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-30308 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the manufacturing method described in Patent Document 1, the joining process is performed under welding conditions that melt the aluminum alloy material as well, so it is necessary to appropriately control the conditions during laser welding, and the welding conditions for melting the base aluminum alloy material are limited. Furthermore, when the base aluminum alloy material is a material that contains many pores, such as a die-cast material, there is a concern that blowholes may occur due to melting a large amount of the aluminum alloy material. Therefore, there is a demand for the development of a manufacturing method for a dissimilar material welded structure that can suppress the occurrence of blowholes even when the allowable range of welding conditions is set wide.

[0007] The present invention has been made in consideration of the above problems, and aims to provide a method for manufacturing a dissimilar metal welded structure that does not require adjustment of special welding conditions and can suppress the occurrence of blowholes, and a dissimilar metal welded structure that is obtained by the welding method and has excellent joining strength. [Means for solving the problem]

[0008] The above object of the present invention is achieved by the following configuration (1) relating to a method for manufacturing a dissimilar material joint structure.

[0009] (1) A manufacturing method of a dissimilar material joint structure for joining a non-ferrous metal member and a steel material, comprising: forming a low-temperature sprayed coating on at least a portion of the surface of the non-ferrous metal member by low-temperature spraying a metal powder containing at least one selected from pure iron, carbon steel, stainless steel, nickel, a nickel alloy, cobalt, and a cobalt alloy; a step of overlapping the non-ferrous metal member and the steel material so that the low-temperature thermal spray coating and the steel material face each other; and performing laser welding on the steel material from the opposite side of the surface facing the non-ferrous metal member, A method for manufacturing a dissimilar material joint structure, wherein the metal powder is powdered from a molten metal in a vacuum or inert gas atmosphere.

[0010] Furthermore, preferred embodiments of the present invention relating to a method for manufacturing a dissimilar material bonded structure relate to the following configurations (2) and (3).

[0011] (2) The method for manufacturing a dissimilar material joint structure according to (1), characterized in that the metal powder is manufactured by one method selected from the group consisting of gas atomization, disk atomization, plasma atomization, and plasma rotating electrode method.

[0012] (3) The method for manufacturing a dissimilar material bonded structure according to (1) or (2), wherein the hydrogen content in the metal powder is 16 ppm or less.

[0013] The above object of the present invention can also be achieved by the following configuration (4) or (5) relating to a dissimilar material joined structure.

[0014] (4) A dissimilar material joint structure in which a non-ferrous metal member and a steel material are joined, a low-temperature thermal spray coating formed on at least a portion of a surface of the non-ferrous metal member, the low-temperature thermal spray coating being made of a metal powder containing at least one selected from pure iron, carbon steel, stainless steel, nickel, a nickel alloy, cobalt, and a cobalt alloy; The non-ferrous metal member and the steel material are overlapped so that the low-temperature thermal spray coating and the steel material face each other, a weld metal joining the steel material and the low-temperature thermal spray coating is formed on a surface of the steel material opposite to the non-ferrous metal member side, A dissimilar material bonded structure characterized in that the hydrogen content in the low-temperature sprayed coating is 16 ppm or less.

[0015] (5) A dissimilar material joint structure in which a non-ferrous metal member and a steel material are joined, a low-temperature thermal spray coating formed on at least a portion of a surface of the non-ferrous metal member, the low-temperature thermal spray coating being made of a metal powder containing at least one selected from pure iron, carbon steel, stainless steel, nickel, a nickel alloy, cobalt, and a cobalt alloy; The non-ferrous metal member and the steel material are overlapped so that the low-temperature thermal spray coating and the steel material face each other, a weld metal joining the steel material and the low-temperature thermal spray coating is formed on a surface of the steel material opposite to the non-ferrous metal member side, A dissimilar material welded structure, characterized in that the low-temperature sprayed coating is made of at least one type of powder selected from gas atomized powder, disk atomized powder, plasma atomized powder, and powder produced by a plasma rotating electrode method. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a manufacturing method of a dissimilar metal joint structure that does not require adjustment of special welding conditions and that can suppress the occurrence of blowholes. Also, according to the present invention, it is possible to provide a dissimilar metal joint structure that is obtained by the joining method and has excellent joining strength. [Brief explanation of the drawings]

[0017] [Figure 1A] FIG. 1A is a cross-sectional view showing a step of forming a low-temperature thermal spray coating in a manufacturing method for a dissimilar material joint structure according to an embodiment of the present invention. [Figure 1B] FIG. 1B is a cross-sectional view showing a dissimilar material joint structure manufactured by the manufacturing method for a dissimilar material joint structure according to the embodiment of the present invention. [Figure 2] FIG. 2 is a photograph showing gas atomized powder produced by gas atomization. [Figure 3] FIG. 3 is a photograph showing the water atomized powder produced by the water atomization method. [Figure 4] FIG. 4 is a diagram showing the joints of dissimilar material joint structures manufactured by the methods of the invention example and the comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of a dissimilar material joint structure and a manufacturing method thereof 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 implemented with any modifications within the scope of the gist of the present invention.

[0019] The present inventors have discovered that when joining dissimilar materials between a non-ferrous metal member and a steel material, the occurrence of blowholes can be suppressed by using a metal powder with a low hydrogen content, which is produced by a production method different from that used for conventional metal powders, as the material for forming the low-temperature sprayed coating.

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a dissimilar material joined structure and a dissimilar material joined structure according to embodiments of the present invention will be described in detail below with reference to the drawings.

[0021] [Method for manufacturing dissimilar material bonded structures] Fig. 1A is a cross-sectional view showing a step of forming a low-temperature thermal spray coating in a manufacturing method for a dissimilar material joint structure according to an embodiment of the present invention. Fig. 1B is a cross-sectional view showing a dissimilar material joint structure manufactured by the manufacturing method for a dissimilar material joint structure according to an embodiment of the present invention. First, the manufacturing method for a dissimilar material joint structure according to an embodiment of the present invention will be described with reference to Figs. 1A and 1B.

[0022] <Material preparation> In this embodiment, a non-ferrous metal member and a steel material are used as materials for manufacturing a dissimilar metal welded structure. As shown in Figures 1A and 1B, in this 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. The non-ferrous metal member refers to a member made of a non-ferrous metal, and can be a member made of one type selected from aluminum or an aluminum alloy, magnesium or a magnesium alloy, and titanium or a titanium alloy. The type of steel material is not particularly limited, and the contents of components other than iron can be designed to vary depending on the required performance of the structure.

[0023] <Process for forming low-temperature sprayed coating> First, as shown in FIG. 1A, a low-temperature sprayed coating 12 is formed by low-temperature spraying a metal powder (not shown) onto at least a portion of the surface of an aluminum alloy plate 11. The metal powder used for low-temperature spraying may be selected from those that are of the same quality as the steel plate 21 or that can form a low-temperature sprayed coating made of a material that is easily bonded to the steel plate 21. Specifically, a metal powder containing at least one selected from pure iron, carbon steel, stainless steel, nickel, nickel alloy, cobalt, and cobalt alloy is used. In this embodiment, the metal powder is powdered from a molten metal under vacuum or an inert gas atmosphere. The properties of such metal powders will be described in detail later.

[0024] <Process of overlapping aluminum alloy plate and steel plate> Next, as shown in FIG. 1B, the aluminum alloy plate 11 and the steel plate 21 are overlapped with each other so that the low-temperature sprayed coating 12 and the steel plate 21 face each other.

[0025] <Laser welding process> Thereafter, laser welding is performed on the region of the aluminum alloy plate 11 where the low-temperature sprayed coating 12 is formed, from the side of the steel plate 21 opposite to the surface facing the aluminum alloy plate 11. This forms a weld metal 23 that joins the steel plate 21 and the low-temperature sprayed coating 12, and a dissimilar metal welded structure can be manufactured.

[0026] When joining dissimilar materials such as an aluminum alloy plate 11 and a steel plate 21, a method is known in which a low-temperature sprayed coating 12 made of a material that is easily bonded to the steel plate 21 is formed on the surface of the aluminum alloy plate 11, and the low-temperature sprayed coating 12 and the steel plate 21 are joined by laser welding. However, a low-temperature sprayed coating formed on the surface of the aluminum alloy plate 11 by a general method is gasified by laser heat in the step of performing laser welding, and this gas penetrates into the weld metal, causing blowholes. In this embodiment, the formation of a specific low-temperature sprayed coating 12 can suppress the occurrence of blowholes in the subsequent laser welding process. The metal powder used in this embodiment and the low-temperature sprayed coating formed from this metal powder will be described in further detail, pointing out the differences from conventional metal powders and low-temperature sprayed coatings.

[0027] (metal powder) Generally, when forming a low-temperature thermal spray coating, a metal powder produced by water atomization (water-atomized powder) is used. The present inventors discovered that hydrogen in the low-temperature thermal spray coating is vaporized by the heat during laser welding, causing blowholes, and conducted various studies to find a method for reducing the hydrogen content in the low-temperature thermal spray coating. As a result, as described above, they discovered that it is effective to use a metal powder that has been powdered from a molten metal under a vacuum or inert gas atmosphere. Methods for producing such metal powder include gas atomization, disk atomization, plasma atomization, and plasma rotating electrode methods.

[0028] Gas atomization is a method in which a metal material containing the desired components for forming a low-temperature thermal spray coating is melted and then powdered by injecting an inert gas into the molten metal at high pressure. Disk atomization is a method in which the molten metal is brought into contact with a rotating disk and dispersed by centrifugal force to form a powder. Plasma atomization is a method in which plasma is sprayed onto a metal wire containing the desired components to melt the metal and then powder the molten metal. The plasma rotating electrode method is a method in which a metal material containing the desired components is rotated at high speed, irradiated with plasma to melt the metal material, and then the resulting molten metal is dispersed by centrifugal force to form a powder.

[0029] In this specification, metal powder produced by gas atomization is sometimes referred to as gas atomized powder, metal powder produced by disk atomization is sometimes referred to as disk atomized powder, metal powder produced by plasma atomization is sometimes referred to as plasma atomized powder, and metal powder produced by plasma rotating electrode process is sometimes referred to as PREP (Plasma Rotating Electrode Process) powder.

[0030] The gas atomized powder, disk atomized powder, plasma atomized powder, and PREP powder all melt and solidify in a vacuum or inert gas atmosphere, so the hydrogen content can be significantly reduced compared to water atomized powder. Therefore, a low-temperature sprayed coating 12 with a reduced hydrogen content can be formed by low-temperature spraying a metal powder produced by one method selected from gas atomization, disk atomization, plasma atomization, and plasma rotating electrode method onto the surface of an aluminum alloy plate 11.

[0031] In order to prevent blowholes from occurring in the weld metal 23 during laser welding, the hydrogen content in the metal powder used to form the low-temperature sprayed coating 12 is preferably 16 ppm or less, more preferably 14 ppm or less, even more preferably 12 ppm or less, and particularly preferably 10 ppm or less.

[0032] The appearances of the gas atomized powder, disk atomized powder, plasma atomized powder, and PREP powder produced by the above methods also differ from that of water atomized powder. Figure 2 is a photograph, substitute for a drawing, showing gas atomized powder produced by gas atomization, and Figure 3 is a photograph, substitute for a drawing, showing water atomized powder produced by water atomization. The gas atomized powder shown in Figure 2 and the water atomized powder shown in Figure 3 have the same components and average particle size.

[0033] As shown in Figure 2, gas atomized powder 1 is produced by cutting the molten metal with gas injection while pulverizing it, resulting in a slow cooling rate during the manufacturing process and a smooth, approximately spherical shape due to surface tension. Each gas atomized powder 1 is independent, with no fine particles adhering to its surface. Disk atomized powder, plasma atomized powder, and PREP powder also have similar shapes. In contrast, as shown in Figure 3, water atomized powder 2 is produced by injecting water into the molten metal at high pressure, and is rapidly cooled and solidified, resulting in a non-spherical shape and an uneven surface.

[0034] (low-temperature thermal spray coating) The low-temperature sprayed coating 12 formed by the method according to this embodiment uses metal powder produced by the above-mentioned specific method, and therefore has a lower hydrogen content than low-temperature sprayed coatings obtained using water-atomized powder. Therefore, in the process of laminating the aluminum alloy plate 11 and the steel plate 21 and then laser welding them from the top surface of the steel plate 21, even if the low-temperature sprayed coating 12 becomes hot due to laser heat, the amount of gas generated from the low-temperature sprayed coating 12 can be significantly reduced. As a result, the occurrence of blowholes in the resulting weld metal 23 can be suppressed.

[0035] In order to prevent blowholes from occurring in the weld metal 23 during laser welding, the hydrogen content in the low-temperature sprayed coating 12 is set to 16 ppm or less, similar to the hydrogen content of the metal powder, preferably 14 ppm or less, more preferably 12 ppm or less, and even more preferably 10 ppm or less.

[0036] The surface of the low-temperature sprayed coating 12 obtained by low-temperature spraying at least one powder selected from gas atomized powder, disk atomized powder, plasma atomized powder, and PREP powder retains the shape of the metal powder. That is, when the outermost surface of the low-temperature sprayed coating 12 is observed with an electron microscope or the like, characteristic spherical particles can be confirmed.

[0037] As described above in detail, the manufacturing method for a dissimilar metal welded structure according to this embodiment can form a low-temperature sprayed coating with a lower hydrogen content than conventional methods, and therefore can form a weld metal with reduced blowholes in the laser welding process. Note that the penetration depth of the weld metal formed by the manufacturing method according to this embodiment may or may not penetrate the low-temperature sprayed coating 12 and reach the aluminum alloy plate 11. Therefore, there is no need to strictly adjust the laser welding conditions to suppress the occurrence of blowholes, and the tolerance range of the manufacturing conditions can be increased.

[0038] Furthermore, when the aluminum alloy plate 11 (non-ferrous metal member) serving as the base material contains a large number of pores, the occurrence of blowholes can be further suppressed by designing the penetration depth of the weld metal so that it does not reach the aluminum alloy plate 11.

[0039] [Dissimilar materials joined structure] Next, the dissimilar material bonded structure according to this embodiment will be described below with reference to FIG. 1B. The dissimilar material bonded structure according to this embodiment can be manufactured by the manufacturing method for the dissimilar material bonded structure according to the embodiment described above. Therefore, the description of parts that overlap with the description of the manufacturing method described above will be omitted or simplified.

[0040] 1B , a dissimilar metal welded structure 10 is manufactured by joining an aluminum alloy plate 11 and a steel plate 21. Specifically, a low-temperature sprayed coating 12 is formed on a portion of the surface of the aluminum alloy plate 11, and the aluminum alloy plate 11 and the steel plate 21 are overlapped so that the low-temperature sprayed coating 12 faces the steel plate 21. A weld metal 23 is formed from the surface of the steel plate 21 opposite to the aluminum alloy plate 11 side, penetrating the steel plate 21 to reach the low-temperature sprayed coating 12, and joining the steel plate 21 and the low-temperature sprayed coating 12.

[0041] In this embodiment, the hydrogen content in the low-temperature sprayed coating 12 is 16 ppm or less. As described above, the low-temperature sprayed coating 12 preferably has a hydrogen content of 14 ppm or less, more preferably 12 ppm or less, and even more preferably 10 ppm or less. The hydrogen content in the low-temperature sprayed coating 12 of the dissimilar metal bonded structure 10 according to this embodiment may increase if another process, such as coating with paint, is performed after the dissimilar metal bonded structure 10 is manufactured. Therefore, the hydrogen content in the low-temperature sprayed coating 12 of the dissimilar metal bonded structure 10 according to this embodiment is a value measured within 90 days after manufacture, before the dissimilar metal bonded structure 10 is subjected to a process that would change the hydrogen content in the low-temperature sprayed coating 12.

[0042] In addition, in a dissimilar metal welded structure 10 according to another embodiment, the low-temperature sprayed coating 12 is made of at least one type of powder selected from gas atomized powder, disk atomized powder, plasma atomized powder, and PREP powder. The metal powder that is the material for the low-temperature sprayed coating 12 is as described above. Note that, after forming the low-temperature sprayed coating 12 using the above-mentioned predetermined metal powder and manufacturing the dissimilar metal welded structure 10, if the steel plate 21 is peeled off from the aluminum alloy plate 11, metal powder with a characteristic spherical shape can be confirmed on the surface of the low-temperature sprayed coating 12. [Example]

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

[0044] <Manufacturing of dissimilar material bonded structures> First, an aluminum alloy plate 11 and a steel plate 21 were prepared, and a low-temperature sprayed coating 12 was formed on a part of the surface of the aluminum alloy plate 11 by low-temperature spraying iron powder under the conditions shown below. Next, the steel plate was placed on top of the aluminum alloy plate so that the low-temperature sprayed coating 12 and the steel plate 21 faced each other. After that, laser welding was performed from above the steel plate under the conditions shown below, and the aluminum alloy plate 11 and the steel plate 21 were joined.

[0045] (Low temperature spray conditions) Equipment: High temperature and high pressure type Aluminum alloy plate material: 7204 aluminum alloy (plate thickness 3 mm) Metal powder: Gas atomized iron powder (average particle size 43 μm) or water atomized iron powder (average particle size 43 μm) Gas type: Nitrogen Gas pressure: 5MPa Gas temperature: 1000℃ Low temperature spray coating thickness: 2mm

[0046] (Laser welding conditions) Upper plate: 1470MPa class steel plate (plate thickness 1.4mm) Lower plate: Aluminum alloy plate with the above-mentioned low-temperature spray coating formed thereon Welding machine: Fiber laser (IPG photonics YLS-6000) Laser power: 2750W Welding speed: 4 (m / min) Spot diameter: 0.3 mm

[0047] <Evaluation method for dissimilar material joint structures> Cross-sectional photographs of the resulting joints were taken to observe blowholes in the weld metal. Using analysis software (Image J), ​​the blowhole rate was calculated according to the following formula: Blowhole rate (%) = total area of ​​blowholes x 100 / weld metal area The types of metal powder used and the calculated results of the blowhole rate are shown in Table 1 below, and the cross-sectional photograph taken is shown in FIG.

[0048] [Table 1]

[0049] As shown in Table 1 and Figure 4 above, in the invention examples, the low-temperature sprayed coating 12 was formed using gas atomized iron powder, so the hydrogen content in the low-temperature sprayed coating 12 was within the range specified by the present invention. Therefore, the rate of blowholes occurring in the weld metal 23 joining the low-temperature sprayed coating 12 and the steel plate 21 was significantly reduced, making it possible to obtain a sound weld metal, and as a result, a dissimilar metal welded structure with excellent joining strength was obtained.

[0050] On the other hand, in the comparative example, the low-temperature sprayed coating 12 was formed using water-atomized iron powder, and therefore the hydrogen content in the low-temperature sprayed coating 12 was high and outside the range specified in the present invention. As a result, blowholes 30 occurred in the weld metal 23, and it was not possible to obtain a dissimilar metal welded structure with excellent joining strength.

[0051] In both the inventive and comparative examples, there was a difference between the hydrogen content in the metal powder and the hydrogen content in the low-temperature sprayed coating, but theoretically, when a low-temperature sprayed coating is formed by low-temperature spraying of metal powder, the hydrogen content is thought to remain unchanged before and after low-temperature spraying, and therefore these differences are thought to be due to measurement errors. [Explanation of symbols]

[0052] 10 Dissimilar materials joined structure 11 Aluminum alloy plate 12 Low-temperature spray coating 21 Steel plate 23 Weld Metal 30 Blowhole

Claims

1. A manufacturing method of a dissimilar material joined structure for joining a non-ferrous metal member and a steel material, forming a low-temperature sprayed coating on at least a portion of the surface of the non-ferrous metal member by low-temperature spraying a metal powder containing at least one selected from pure iron, carbon steel, stainless steel, nickel, a nickel alloy, cobalt, and a cobalt alloy; a step of overlapping the non-ferrous metal member and the steel material so that the low-temperature sprayed coating and the steel material face each other; and performing laser welding from the opposite side of the surface of the steel material facing the non-ferrous metal member, The metal powder is powdered from a molten metal under vacuum or an inert gas atmosphere, A method for manufacturing a dissimilar material bonded structure, characterized in that the hydrogen content in the metal powder is 16 ppm or less.

2. 2. The method for manufacturing a dissimilar material joint structure according to claim 1, wherein the metal powder is manufactured by one method selected from the group consisting of gas atomization, disk atomization, plasma atomization, and plasma rotating electrode method.

3. A dissimilar material joined structure in which a non-ferrous metal member and a steel material are joined, a low-temperature thermal spray coating formed on at least a portion of a surface of the non-ferrous metal member, the low-temperature thermal spray coating being made of a metal powder containing at least one selected from pure iron, carbon steel, stainless steel, nickel, a nickel alloy, cobalt, and a cobalt alloy; The non-ferrous metal member and the steel material are overlapped so that the low-temperature sprayed coating and the steel material face each other, a weld metal joining the steel material and the low-temperature thermal spray coating is formed on a surface of the steel material opposite to the non-ferrous metal member side, A dissimilar material welded structure, characterized in that the hydrogen content in the low-temperature sprayed coating is 16 ppm or less.

4. The dissimilar material joining structure described in claim 3, characterized in that the low-temperature sprayed coating is made of at least one type of powder selected from gas atomized powder, disk atomized powder, plasma atomized powder and powder produced by the plasma rotating electrode method.

5. A dissimilar material joint structure as described in claim 3 or 4, wherein the penetration depth of the weld metal does not reach the non-ferrous metal component.

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