JP2023008279A - Method for manufacturing joint structure of dissimilar materials - Google Patents

Abstract

To suppress the generation of blow holes in weld metal, when welding a steel material and a CS film formed on a surface of an aluminum alloy material or the like, in manufacturing a joint structure of dissimilar materials such as an aluminum alloy material and a steel material.SOLUTION: A method for manufacturing a joint structure of dissimilar materials includes the steps of: forming a low-temperature sprayed coating 1 by low-temperature spraying at least one kind of metal powder selected from pure iron, carbon steel, stainless steel, nickel, a nickel alloy, cobalt, and a cobalt alloy, on at least one part of a surface of an aluminum material or an aluminum alloy material 2; subjecting the low-temperature sprayed coating 1 to heating at 200-600°C; superimposing the aluminum material or the aluminum alloy material 2 and the steel material 3 so that the low-temperature sprayed coating 1 and the steel material 3 are opposed to each other; and joining the aluminum material or the aluminum alloy material 2 to the steel material 3 according to welding from a steel material 3 side.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a dissimilar metal joined structure, and more particularly to a method for manufacturing a dissimilar metal joined structure for joining an aluminum material or an aluminum alloy material and a steel material.

BACKGROUND ART In recent years, high tensile strength steel (HTSS) has been applied to automobile body frames and the like in order to reduce vehicle body weight and enhance collision safety for the purpose of reducing CO ₂ emissions.

In addition, for the purpose of further reducing the weight of the vehicle body, there is a growing demand for dissimilar metal joint materials that are made by joining lightweight aluminum materials or aluminum alloy materials (hereinafter also referred to as "aluminum alloy materials, etc.") and steel materials. . As a method of joining dissimilar metals, there is generally a method of joining with nails or screws. There is a problem that the weight of the bonding material obtained becomes heavy.

On the other hand, when an aluminum alloy material or the like is directly welded to a steel material by a general method, a fragile intermetallic compound is formed at the joint interface, and good strength cannot be obtained. Therefore, there is a demand for a welding technique capable of obtaining high strength in joining aluminum alloy materials and steel materials.

As a method for joining an aluminum alloy material or the like and a steel material, Patent Document 1 discloses forming an aluminum or aluminum alloy film on the surface of a first base material made of steel by a cold spray method, and bonding the film to the aluminum or aluminum alloy. A technique of facing and welding a second base material made of is disclosed.
In addition, as a method for forming a low-temperature thermal spray coating member, Patent Document 2 discloses that particles of a thermal spray material are sprayed onto the surface of a substrate to be treated, while the temperature is kept at a low temperature of 300 ° C. or less, and the flight speed is 500 m / s. A low-temperature sprayed coating is formed by colliding with the above high-speed low-temperature spraying, and after forming the low-temperature sprayed coating, solution treatment is performed at 1000 to 1200 ° C. for 1 to 10 hours. A technique of performing aging treatment at 1° C. for 1 to 30 hours is disclosed.

JP 2013-188780 A JP-A-2002-309364

By the way, dissimilar metal joining (dissimilar metal joining) is performed by forming a low-temperature thermal spray (cold spray) coating (hereinafter also referred to as "CS coating") on the surface of an aluminum alloy material or the like in advance and welding the steel material and the CS coating. In some cases, there is a drawback that large blowholes tend to occur in the weld metal due to residual gas contained in the CS coating during low-temperature thermal spraying. If many large blowholes remain in the weld metal, there are problems such as a decrease in joint strength, but Patent Document 1 does not mention the blowhole problem at all.
Further, the technique described in Patent Document 2 is a method for forming a desired compound in the CS film by a predetermined heat treatment, and does not mention the gas contained in the CS film at all. There is no mention of a technique for superimposing on the CS coating and welding from the steel plate side, or blowholes that occur during welding of the steel plate and the CS coating.

The present invention has been made in view of the above-mentioned problems, and in manufacturing a dissimilar metal joint structure of an aluminum alloy material or the like and a steel material, welding a CS coating formed on the surface of the steel material and the aluminum alloy material or the like. The object is to suppress the occurrence of blowholes in the weld metal in some cases.

Therefore, the above object of the present invention is achieved by the following configuration [1] relating to a method for manufacturing a dissimilar metal joined structure.

[1] By low-temperature spraying at least one metal powder selected from pure iron, carbon steel, stainless steel, nickel, nickel alloys, cobalt, and cobalt alloys onto at least part of the surface of an aluminum or aluminum alloy material. a step of forming a low-temperature thermal spray coating;
A step of heat-treating the low-temperature spray coating at 200 to 600 ° C.;
a step of superimposing the aluminum or aluminum alloy material and the steel material so that the low-temperature spray coating and the steel material face each other;
a step of joining the aluminum or aluminum alloy material and the steel material by welding from the steel material side;
A method for manufacturing a dissimilar metal joined structure, comprising:

Further, preferred embodiments of the present invention relating to a method for manufacturing a dissimilar-material joined structure relate to the following [2] to [4].

[2] The method for manufacturing a dissimilar metal joined structure according to [1], wherein the heat treatment time of the low-temperature thermal spray coating is 5 minutes or longer.
[3] The method for manufacturing a dissimilar metal joined structure according to [1] or [2], wherein the welding is laser welding.
[4] The method for manufacturing a dissimilar metal joined structure according to any one of [1] to [3], wherein the step of forming the low-temperature thermal spray coating is performed using a working gas pressure of 3 MPa or less.

According to the present invention, in manufacturing a dissimilar metal joint structure of an aluminum alloy material or the like and a steel material, the CS film formed on the surface of the aluminum alloy material or the like is heat-treated at 200 to 600° C. to obtain the steel material. Since the gas contained in the CS coating can be effectively released prior to the welding of the CS coating with the CS coating, the blowholes generated during welding can be suppressed.

FIG. 1 is a diagram showing a part of a process for forming a dissimilar metal joined structure according to an embodiment of the present invention by laser welding. 2A is an enlarged cross-sectional view (photograph substituting for a drawing) of a dissimilar metal joined structure formed under the conditions of Comparative Example 1. FIG. 2B is an enlarged cross-sectional view (photograph substituting for a drawing) of a dissimilar metal joined structure formed under the conditions of Example 1. FIG. FIG. 3A is a graph showing the results of thermal desorption gas analysis (TDS analysis) performed on a cold spray sample (Example 1) in which a low-temperature thermal spray coating was formed on the surface of an aluminum alloy material. FIG. 3B is a graph showing the results of thermal desorption gas analysis (TDS analysis) performed on only the aluminum alloy material.

An embodiment of a method for manufacturing a dissimilar metal joined structure according to the present invention will be described in detail below with reference to the drawings. The present invention is not limited to the following embodiments, and can be arbitrarily modified without departing from the gist of the present invention.

In joining dissimilar materials such as an aluminum alloy material and a steel material, the present inventors have applied a low-temperature thermal spraying method (cold spray method) to at least a part of the surface of the aluminum alloy material, etc. to spray metal powder that can be welded with the steel material. A dissimilar metal joint structure with few blowholes can be obtained by forming a CS film, heat-treating the CS film at 200 to 600° C., and then joining an aluminum alloy material or the like with a steel material. I found out that it can be done.

More specifically, the blowholes are considered to be formed when the gas contained in the CS coating is involved in the molten portion formed when the steel material and the CS coating are welded together. For this reason, the present inventors have found that if a CS film formed on the surface of an aluminum alloy material is heat-treated at 200 to 600 ° C., it will be included in the CS film prior to welding between the steel material and the CS film. It has been found that blowholes generated during welding can be effectively suppressed because gas can be released.

In the method for manufacturing a dissimilar metal joined structure according to the present embodiment, at least a portion of the surface of an aluminum alloy material or the like is coated with at least one selected from pure iron, carbon steel, stainless steel, nickel, nickel alloys, cobalt, and cobalt alloys. A step of forming a low-temperature sprayed coating by low-temperature spraying a seed metal powder, a step of heat-treating the low-temperature sprayed coating at 200 to 600 ° C., and an aluminum alloy so that the low-temperature sprayed coating faces the steel material. and a step of joining the aluminum alloy material and the steel material by welding from the steel material side.

FIG. 1 is a perspective view showing a part of a process for forming a dissimilar metal joined structure according to this embodiment by laser welding. As shown in FIG. 1, in manufacturing a dissimilar metal joined structure 10 according to the present embodiment, a CS film 1 is first formed on at least part of the surface of an aluminum alloy material 2 or the like. Then, the CS film 1 formed on the surface of the aluminum alloy material 2 or the like is heat-treated at 200 to 600.degree. Then, the aluminum alloy material 2 and the steel material 3 are overlapped so that the heat-treated CS coating 1 and the steel material 3 face each other. Furthermore, the steel material 3 and the CS coating 1 are laser-welded by a laser beam L emitted from the steel material 3 side, preferably under welding conditions such as an aluminum alloy material 2 that does not melt, and the steel material 3 and the CS coating 1 melt to melt the weld metal ( Weld bead) 4 is formed.
In this embodiment, laser welding is used as a method for welding the steel material 3 and the CS coating 1, but the method is not limited to this, and arc welding may be used as described later.

The CS coating 1 contains at least one metal selected from pure iron, carbon steel, stainless steel, nickel, nickel alloys, cobalt and cobalt alloys. Although not shown, the surface of the aluminum alloy material 2 to which the metal powder is sprayed at high speed by low-temperature thermal spraying has fine irregularities formed by a large amount of metal powder. 2 are mechanically and firmly joined by an anchor effect.

A cold spray method is suitable as a method for forming the CS film 1 by injecting metal powder at a low temperature and at a high speed. The cold spray method is a method of forming the CS film 1 by spraying gas and metal powder onto an object at a speed higher than the speed of sound. In this method, the working gas is relatively low temperature, for example, 900 ° C. or less, which is the melting point of iron particles or less. are not melted together, and metal powder having a relatively high melting point, such as iron, bites into the aluminum alloy material 2 or the like due to its velocity energy, resulting in a macroscopic mechanical fastening state.

Therefore, an intermetallic compound is less likely to form and a brittle phase is less likely to be formed, and as a result, a strong CS film 1 is formed on a portion of the surface of the aluminum alloy material 2 or the like. As will be described later, the type of gas used in the cold spray method, the pressure, the temperature, the particle size of the metal powder, etc. can be appropriately selected.

After that, the obtained CS film 1 is heat-treated at 200 to 600.degree. Here, when dissimilar materials are joined by forming a CS coating 1 on an aluminum alloy material 2 or the like in advance and welding the steel material 3 and the CS coating 1, the remaining gas contained in the CS coating 1 during low-temperature thermal spraying Due to this, large blowholes tend to occur in the weld metal 4 . If many large blowholes remain in the weld metal 4, there is a problem such as a reduction in joint strength. However, according to the manufacturing method of the dissimilar metal joined structure of the present embodiment, the CS coating 1 formed on the surface of the aluminum alloy material 2 or the like is heat-treated at 200 to 600° C., thereby separating the steel material 3 and the CS coating. Since the gas contained in the CS coating 1 can be released prior to welding with the CS coating 1, blowholes generated during welding can be effectively suppressed.

If the heat treatment temperature for the CS coating 1 is less than 200° C., the gas contained in the CS coating 1 cannot be released effectively, and there is a possibility that blowholes generated during welding cannot be suppressed. Therefore, the heat treatment temperature for the CS film 1 is set to 200° C. or higher, preferably 300° C. or higher, more preferably 350° C. or higher, and most preferably 400° C. or higher.

If the heat treatment temperature for the CS coating 1 exceeds 600° C., the aluminum alloy material 2, which is the base material of the CS coating 1, is solutionized, and the joint strength may be extremely reduced. In addition, intermetallic compounds are likely to be formed at the interface between the CS film 1 and the aluminum alloy material 2, etc., which may impair the strength of the joint after welding. Therefore, the heat treatment temperature for the CS film 1 is set to 600° C. or lower, preferably 550° C. or lower, more preferably 500° C. or lower, and most preferably 450° C. or lower.

The lower limit of the heat treatment time for the CS film 1 is not particularly limited, but in order to more effectively release the gas contained in the CS film 1, it is preferably 5 minutes or more, more preferably 30 minutes. or more, and most preferably 60 minutes or more. The upper limit of the heat treatment time is also not particularly limited, but is preferably 1440 minutes or less because the effect of releasing the gas contained in the CS film 1 gradually saturates.

Subsequently, a steel material 3 is placed on the heat-treated CS coating 1, and the steel material 3 is welded from the side opposite to the side facing the aluminum alloy material 2, preferably under welding conditions in which the aluminum alloy material 2 does not melt, A weld metal 4 is formed by laser welding, and a dissimilar metal joined structure 10 with less occurrence of blowholes is manufactured.

In this embodiment, the welding of the steel material 3 and the CS coating 1 can also be performed by arc welding, but laser welding has a lower heat input and a smaller heat effect than other welding methods such as arc welding. It is preferable because it is a law. When arc welding is used, the heat generated during welding tends to reach the aluminum alloy material 2, etc., so the adhesion strength of the CS coating 1 to the aluminum alloy material 2, etc. may decrease, and the bonding strength may decrease. There is However, when laser welding is used, the thermal effect on the aluminum alloy material 2 can be minimized, and the decrease in adhesion strength of the CS coating 1 to the aluminum alloy material 2 can be effectively suppressed. It is possible to prevent a decrease in joint strength and obtain a better dissimilar metal joint structure 10 .

Next, in the manufacturing method of the dissimilar metal joined structure 10 according to the present embodiment, the CS film 1, the metal powder as its material, the aluminum alloy material 2, and the steel material 3 will be described in detail below.

<Metal type of metal powder: at least one selected from pure iron, carbon steel, stainless steel, nickel, nickel alloy, cobalt and cobalt alloy>
In order to join the steel material 3 and the CS coating 1 by, for example, laser welding, a metal material that can be welded with the steel material 3 with a desired bonding strength and has good characteristics of the weld metal 4 is used as the material of the CS coating 1. It is important to choose

If, for example, stainless steel (SUS) to which a large amount of quenching elements such as Cr and Ni is added is used as the metal powder, the weld metal that has undergone the base material dilution will All or part of 4 undergoes martensite transformation, and the hardness becomes too high, which may lead to a decrease in joint strength (joint strength) or the occurrence of cracks. In such a case, the metal powder used in the cold spray method is preferably powder containing at least one metal selected from pure iron, carbon steel, nickel, nickel alloys, cobalt and cobalt alloys.

In the present specification, pure iron refers to iron that is readily available for industrial use and has a purity of 99.9% by mass or more. Carbon steel is a steel material containing iron and carbon as main components and containing silicon, manganese, and trace amounts of impurities phosphorus, sulfur, and copper. As the nickel alloy, alloys commonly known as Inconel alloys, Incoloy alloys, and Hastelloy alloys, in which Ni is the main component and appropriate amounts of Mo, Fe, Co, Cr, Mn, etc. are added can be used.

<Particle size and shape of metal powder>
The particle size of the metal powder that is the material of the CS coating 1 is not particularly limited, but when the gas pressure of the cold spray is a high pressure condition of 1 MPa to 5 MPa, it is preferably 100 μm or less, and 50 μm or less. is more preferable.
Although the particle shape of the metal powder is not particularly limited, it is preferably spherical from the viewpoint of fluidity.

<Type of working gas>
The gas used in cold spraying is not particularly limited, but generally air, nitrogen, helium, or a mixed gas thereof is used. On the other hand, if the CS coating 1 is oxidized, it may adversely affect weldability, so it is preferable to use nitrogen or helium as the gas species. When helium is used as the gas species, the adhesion strength of the CS film 1 is further increased, and an improvement in joint strength can be expected.

<Temperature of working gas>
If the temperature of the gas used in the cold spray is high, the metal powder may melt and chemically react with the aluminum alloy material 2 serving as the base material of the CS coating 1 to form an intermetallic compound. Therefore, the temperature of the working gas is preferably lower than the melting point of the metal powder used for cold spray. In addition, in order to obtain the dissimilar metal joined structure 10 according to the present embodiment, it is preferable to set the temperature to room temperature (20° C.) to 1200° C., for example.

<Pressure of working gas>
When the pressure of the gas used in the cold spray is high, there is a possibility that the consumption of the gas increases and the deformation of the aluminum alloy material 2, which is the base material of the CS coating 1, is likely to occur. Therefore, from the viewpoint of cost reduction by reducing gas consumption or suppression of deformation of the aluminum alloy material 2, the pressure of the working gas is preferably 10 MPa or less, more preferably 7 MPa or less, and 5 MPa or less. is more preferable, and 3 MPa or less is most preferable.

<Film thickness>
If the thickness of the CS coating 1 formed by cold spraying is less than 0.3 mm, and welding that melts only the CS coating 1 and the steel material 3 is required, the influence of variations in the laser beam L may cause the CS coating 1 and Since it may be difficult to melt only the steel material 3, the robustness is lowered.

Therefore, by setting the film thickness of the CS film 1 to 0.3 mm or more, it is possible to flexibly cope with the variations in the laser beam L, so that strict condition setting is not necessary. Therefore, the thickness of the CS film 1 is preferably 0.3 mm or more, more preferably 0.6 mm or more.

On the other hand, when the film thickness of the CS film 1 exceeds 3 mm, the film formation time becomes long, which may increase the manufacturing cost. Therefore, the thickness of the CS coating 1 is preferably 3 mm or less, more preferably 2 mm or less.

<Aluminum alloy material (aluminum material or aluminum alloy material)>
The aluminum alloy material 2 is also not particularly limited, but when applied to a member used in an automobile or the like, from the viewpoint of strength, 2000 series, 5000 series, 6000 series, and 7000 series, etc. are preferred to aluminum materials that are pure aluminum. It is preferable to use an aluminum alloy material. In addition to plate materials, extruded materials, cast materials, and forged materials that are frequently used in the field of automobiles and the like can also be used without any problem.

<Steel material>
The steel material 3 is not particularly limited as long as it is a member made of a metal generally called steel. However, in recent years, high-strength steel materials (high-tensile steel materials) and the like are frequently used as steel sheets used for automobile body frames and the like for the purpose of reducing the weight of automobile bodies and enhancing collision safety. It is difficult to apply the mechanical joining method, which is widely used as a steel-aluminum dissimilar metal joining method, to a steel plate having a tensile strength of 980 MPa or more. Therefore, the present invention is particularly effective in high-strength steel sheets having a tensile strength of 980 MPa or more, preferably 1470 MPa or more.

EXAMPLES The present invention will be described in detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these.

<Examples 1 to 3>
A metal coating (low-temperature thermal spray coating) made of iron or nickel was formed on the surface of an aluminum alloy plate (7N01) having a thickness of 3 mm using cold spray. The thickness of the iron coating was set to 2 mm, and the thickness of the nickel coating was set to 1.5 mm. Then, a heat treatment sample was prepared by subjecting a cold spray sample in which a low-temperature thermal spray coating was formed on the surface of an aluminum alloy plate to heat treatment under the predetermined conditions shown in Table 1. Subsequently, a steel plate having a thickness of 1.4 mm is placed so as to overlap with the aluminum alloy plate through the obtained metal film, and laser irradiation is performed from the surface of the steel plate opposite to the surface in contact with the metal film. A steel plate and an aluminum alloy plate were laser-welded to manufacture the dissimilar metal joined structures of Examples 1 to 3.

The test materials, cold spray conditions, heat treatment conditions and welding conditions are shown below.

[Test material]
Steel plate (upper plate): Tensile strength 1470 MPa class steel plate (plate thickness 1.4 mm)
Aluminum alloy plate (lower plate): A7N01-T6 material (thickness 3 mm)

[Cold spray conditions]
Apparatus: High temperature and high pressure type Gas type: Nitrogen Metal powder: Iron powder or nickel powder Average particle size of metal powder: 40 μm (iron powder and nickel powder)
Gas pressure: 3 MPa (iron powder), 5 MPa (nickel powder)
Gas temperature: 1000°C
Film thickness: 2 mm (iron film), 1.5 mm (nickel film)

[Heat treatment conditions for cold spray samples]
Heat treatment equipment: muffle furnace Atmosphere: atmospheric heat treatment temperature: 180°C, 350°C, or 450°C (details are listed in the table)
Heat treatment time: either 5 minutes or 60 minutes (details are listed in the table)

[Laser welding conditions]
Welder: Fiber laser (manufactured by IPGphotonics, device name: YLG-6000)
Welding speed: 4m/min
Beam condensing diameter (spot diameter): φ0.6 mm
Laser output: either 4.5 kw or 4.9 kw (details are listed in the table)
Welding shape: Circle (φ12mm)

<Comparative Examples 1 to 3>
A metal film (CS film) made of iron or nickel was formed on the surface of an aluminum alloy plate (7N01) having a thickness of 3 mm using cold spray. The thickness of the iron coating was set to 2 mm, and the thickness of the nickel coating was set to 1.5 mm. In Comparative Examples 1 and 2, non-heat-treated samples were prepared by not heat-treating the cold-sprayed samples in which the low-temperature spray coating was formed on the surface of the aluminum alloy plate. In Comparative Example 3, a heat-treated sample was prepared by subjecting a cold-sprayed sample in which a low-temperature thermal spray coating was formed on the surface of an aluminum alloy plate to heat treatment under the predetermined conditions shown in Table 1. Subsequently, a steel plate having a thickness of 1.4 mm is placed so as to overlap with the aluminum alloy plate through the obtained metal film, and laser irradiation is performed from the surface of the steel plate opposite to the surface in contact with the metal film. A steel plate and an aluminum alloy plate were laser-welded to manufacture dissimilar metal joint structures of Comparative Examples 1 to 3.
The test material, cold spray conditions, heat treatment conditions, and welding conditions are the same as in Examples 1 to 3, and are omitted.

<Evaluation>
After that, cross-sectional macroscopic observation was performed on the dissimilar metal joined structures (welded joints) obtained in both the examples and the comparative examples, and the blowhole rate was examined.
The blowhole ratio (%) is defined as the ratio of the total area of the blowholes 5 to the area of the weld metal 4 in the cross-sectional macrophotograph, calculated from the cross-sectional photograph using analysis software (image J), and rounded to the nearest whole number. .
The blowhole rate was evaluated as ⊚ (excellent) when it was less than 10%, ◯ (good) when it was 10% or more and less than 20%, and Δ (bad) when it was 20% or more.

Representative examples of cross-sectional macro photographs of the weld metal 4 are shown in FIGS. 2A and 2B. 2A is an enlarged cross-sectional view of the vicinity of the crater portion of the dissimilar metal bonded structure formed under the conditions of Comparative Example 1, and FIG. 2B is the vicinity of the crater portion of the dissimilar metal bonded structure formed under the conditions of Example 1. It is an expanded sectional view.

Table 1 summarizes the coating material, heat treatment conditions, laser output, blowhole rate and evaluation results in Examples 1 to 3 and Comparative Examples 1 to 3.

As shown in the results of Table 1, in Comparative Examples 1 and 2 in which the low-temperature spray coating was not heat-treated, and in Comparative Example 3 in which the heat treatment temperature was less than 200 ° C., the blowhole rate was 20% or more. A good weld metal 4 was not obtained. In addition, as shown in FIG. 2A, in the dissimilar metal joined structure 10 formed under the conditions of Comparative Example 1, it can be seen that large blowholes 5 are formed in the weld metal 4 .

On the other hand, in Examples 1 to 3 in which the heat treatment temperature was 350° C. or 450° C., the blowhole rate was less than 20%, and a good weld metal 4 with few blowholes was obtained. As shown in FIG. 2B, in the dissimilar metal joined structure 10 formed under the conditions of Example 1, although the blowhole 5 is formed in the weld metal 4, the size of the blowhole 5 is kept small. I understand.
Moreover, when Example 2 and Example 3 were compared, it was found that Example 3, in which the heat treatment time was longer, had a significantly lower blowhole rate.

Subsequently, the cold spray sample (iron film) prepared in Example 1 and the aluminum alloy plate: A7N01-T6 material (thickness 3 mm) were subjected to thermal desorption gas analysis (TDS; Thermal Desorption Spectroscopy analysis). did

A graph of the TDS analysis results of the cold spray sample (Al alloy + low temperature thermal spray coating) is shown in FIG. .

As shown in the results of FIG. 3A, when the heat treatment temperature is 200° C. or higher, the mass-to-charge ratio M/z= ₂ (corresponding to H2), M/z=28 (corresponding to CO, _N2 ), and M/ It can be seen that a large amount of gas with z=44 (corresponding to CO ₂ ) is released. In particular, each peak was confirmed at a heat treatment temperature of around 300°C. Therefore, it was shown that the heat treatment temperature for the CS film should be 200° C. or higher.

On the other hand, as shown in the results of FIG. 3A, it is understood that the higher the heat treatment temperature, the more gas is released. Aluminum alloy materials, etc., which are used as materials, are solutionized, and there is a risk that the joint strength will be extremely reduced, and intermetallic compounds will be easily formed at the interface between the CS coating and aluminum alloy materials, etc., and the joint strength after welding will be impaired. Because of this possibility, it is necessary to limit the heat treatment temperature for the CS coating to 600°C or less.

As shown in the results of FIG. 3B, in the case of only the aluminum alloy plate used as the base material of the cold spray sample, the heat treatment temperature is 200° C., as is clear from the graphs of the mass-to-charge ratio M/z. It can also be seen from the above that the amount of gas released is small. That is, it was confirmed that most of the gas causing blowholes was contained in the CS film 1 .

As described in detail above, according to the present invention, in manufacturing a dissimilar-materials-joined structure of an aluminum alloy material or the like and a steel material, when welding the steel material and the CS coating formed on the surface of the aluminum alloy material or the like, It is possible to suppress the occurrence of blowholes in the weld metal.

It should be noted that the present invention is not limited to the above-described embodiments, and can be modified, improved, etc. as appropriate. For example, the heat treatment method is not particularly limited, and an electric furnace, a muffle furnace, or the like can be used. The atmosphere during the heat treatment is not particularly limited, either, and air, nitrogen, argon atmosphere, or the like may be appropriately selected according to the application. Furthermore, a method of directly heat-treating only the film, for example, heat-treating with a burner, laser, or the like can also be applied.

As described above, this specification discloses the following matters.

(1) Low-temperature thermal spraying of at least one metal powder selected from pure iron, carbon steel, stainless steel, nickel, nickel alloys, cobalt, and cobalt alloys onto at least part of the surface of an aluminum material or aluminum alloy material. A step of forming a low-temperature spray coating by
A step of heat-treating the low-temperature spray coating at 200 to 600 ° C.;
a step of superimposing the aluminum material or aluminum alloy material and the steel material so that the low-temperature spray coating and the steel material face each other;
a step of joining the aluminum material or aluminum alloy material and the steel material by welding from the steel material side;
A method for manufacturing a dissimilar metal joined structure, comprising:
According to this configuration, in manufacturing a dissimilar metal joint structure of an aluminum alloy material or the like and a steel material, the CS film formed on the surface of the aluminum alloy material or the like is heat-treated at 200 to 600° C. to obtain the steel material. Since the gas contained in the CS coating can be effectively released prior to the welding of the CS coating with the CS coating, the blowholes generated during welding can be suppressed.

(2) The method for manufacturing a dissimilar metal joined structure according to (1), wherein the heat treatment time of the low-temperature thermal spray coating is 5 minutes or longer.
According to this configuration, the gas contained in the CS coating can be released more effectively, and the occurrence of blowholes during welding can be further suppressed.

(3) The method for manufacturing a dissimilar metal joined structure according to (1) or (2), wherein the welding is laser welding.
According to this configuration, it is possible to minimize the thermal effect on the aluminum alloy material and the like, effectively suppress the deterioration of the adhesion strength of the CS coating to the aluminum alloy material and the like, and prevent the deterioration of the bonding strength, A better dissimilar metal joined structure can be obtained.

(4) The method for manufacturing a dissimilar metal joined structure according to any one of (1) to (3), wherein the step of forming the low-temperature thermal spray coating is performed using a working gas pressure of 3 MPa or less.
According to this configuration, it is possible to reduce costs by reducing gas consumption or to suppress deformation of the aluminum alloy material or the like.

1 CS film 2 Aluminum alloy material, etc. 3 Steel material 4 Weld metal 5 Blowhole 10 Dissimilar metal joint structure L Laser beam (laser irradiation)

Claims (4)

Low-temperature spraying by low-temperature spraying at least one metal powder selected from pure iron, carbon steel, stainless steel, nickel, nickel alloys, cobalt and cobalt alloys onto at least part of the surface of an aluminum material or an aluminum alloy material. a step of forming a coating;
A step of heat-treating the low-temperature spray coating at 200 to 600 ° C.;
a step of superimposing the aluminum material or aluminum alloy material and the steel material so that the low-temperature spray coating and the steel material face each other;
a step of joining the aluminum material or aluminum alloy material and the steel material by welding from the steel material side;
A method for manufacturing a dissimilar metal joined structure, comprising: 2. The method for manufacturing a dissimilar metal joint structure according to claim 1, wherein the heat treatment time of said low-temperature thermal spray coating is 5 minutes or more. 3. The method for manufacturing a dissimilar metal joined structure according to claim 1, wherein said welding is laser welding. The method for manufacturing a dissimilar metal joined structure according to any one of claims 1 to 3, wherein in the step of forming the low-temperature thermal spray coating, the working gas pressure is 3 MPa or less.

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