JP7231586B2 - Method for manufacturing dissimilar material joined structure - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Law Posting date: August 8, 2019 Website address: https://www. j stage. jst. go. jp/article/jwstaikai/2019f/0/2019f_206/_pdf/-char/ja

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

Further, with the aim of further reducing the weight of the vehicle body, there is an increasing demand for a dissimilar metal joint material in which a lightweight aluminum or aluminum alloy material and a steel material are joined together. As a method of joining dissimilar metals, there is generally a method of joining with nails or screws. There is a problem that the resulting bonding material becomes heavy by the weight.

On the other hand, when aluminum or aluminum alloy material and steel material are directly welded 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 or aluminum alloy materials and steel materials.

As a method for joining dissimilar metals by welding, 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 forming a first base material made of this film and aluminum or an aluminum alloy. A joining method is disclosed in which two substrates are opposed to each other and welded.

JP 2013-188780 A

By the way, when the aluminum or aluminum alloy material is an extruded material with a closed cross section, welding by one-sided welding from the high-strength steel material side is required. Inert Gas (MIG) welding, MIG (Metal Inert Gas) welding, and plasma welding, which use high heat-affected arc welding. For this reason, when a metal film that can be welded with steel is formed on the surface of an aluminum or aluminum alloy material by cold spray, and this film is welded to high-strength steel, the large amount of heat generated during arc welding causes The adhesion strength of the metal coating to the high-strength steel is greatly reduced, and the joint strength may be reduced.

Laser welding is conceivable as welding capable of suppressing the amount of heat input during welding to such an extent that the aluminum or aluminum alloy material does not melt, but the joining method of Patent Document 1 does not mention laser welding. Also, when welding metal thermal spray coatings, there is a disadvantage that large blowholes tend to occur in the weld metal due to residual gas contained in the coating during thermal spraying. If a large amount remains, there are problems such as a decrease in joint strength, but the joining method of Patent Document 1 does not describe the problem of blow holes. Therefore, there has been a demand for the development of a method for manufacturing a dissimilar metal joined structure that allows one-sided construction from the high-strength steel material side and has excellent joint strength.

The present invention has been made in view of the above-mentioned problems, and in the dissimilar material joining of aluminum or aluminum alloy material and steel material, welding by one-sided welding from the steel material side is possible, there are few blowholes, and the joint An object of the present invention is to provide a method for manufacturing a dissimilar metal joined structure excellent in strength and a dissimilar metal joined structure.

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) 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 aluminum or aluminum alloy material a step of forming a low-temperature thermal spray coating;
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;
joining the aluminum or aluminum alloy material and the steel material by laser welding from the steel material side;
A method for manufacturing a dissimilar metal joined structure, wherein the joining step is performed under welding conditions in which a melted portion is formed in any of the steel material, the low-temperature thermal spray coating, and the aluminum or aluminum alloy material.

In addition, a preferred embodiment of the present invention relating to a method for manufacturing a dissimilar metal joined structure relates to the following (2).
(2) According to (1), the bonding step is performed by at least two laser irradiations, and the heat input in the second and subsequent laser irradiations is equal to or less than the heat input in the first laser irradiation. A method for manufacturing a dissimilar metal joined structure.

Further, the above object of the present invention is achieved by the following configuration (3) relating to a dissimilar metal joined structure.
(3) an aluminum or aluminum alloy material;
At least one metal powder selected from pure iron, carbon steel, stainless steel, nickel, nickel alloys, cobalt and cobalt alloys formed on at least part of the surface of the aluminum or aluminum alloy material is low-temperature sprayed. a low-temperature thermal spray coating,
a steel material superimposed on the low-temperature spray coating;
a weld metal in which a molten portion is formed in any of the steel material, the low temperature thermal spray coating, and the aluminum or aluminum alloy material;
A dissimilar metal joint structure comprising:

Further, the above object of the present invention is achieved by the following configuration (4) relating to a method for manufacturing a dissimilar-materials-joined structure.
(4) 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 aluminum or aluminum alloy material a step of forming a low-temperature thermal spray coating;
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;
joining the aluminum or aluminum alloy material and the steel material by laser welding from the steel material side;
The bonding step is performed by laser irradiation at least twice under conditions where the low-temperature thermal spray coating is partially penetrated, and the heat input in the second and subsequent laser irradiations is equivalent to the heat input in the first laser irradiation. The method for manufacturing a dissimilar metal joined structure is as follows.

In the method for manufacturing a dissimilar metal joined structure according to the present invention, at least part of the surface of the aluminum or aluminum alloy material 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 one type of metal powder; a step of superimposing an aluminum or aluminum alloy material and a steel material so that the low-temperature sprayed coating and the steel material face each other; and joining the aluminum or aluminum alloy material and the steel material by laser welding, and in the joining process, a molten portion is formed in any of the steel material, the low temperature thermal spray coating, and the aluminum or aluminum alloy material. Since the welding is performed under the following welding conditions, it is possible to weld from one side from the steel material side, and a dissimilar metal joined structure with less blowholes and excellent joint strength can be obtained.

Further, in another method for manufacturing a dissimilar metal joined structure according to the present invention, the joining step is performed by laser irradiation at least twice under conditions in which the low-temperature thermal spray coating is partially penetrated. Since the amount of heat input is equal to or less than the amount of heat input in the first laser irradiation, the occurrence of blowholes is greatly suppressed, and a dissimilar metal joined structure having excellent joint strength can be obtained.

FIG. 1 is a perspective view of a dissimilar-material joined structure according to a first embodiment of the present invention formed by laser welding. FIG. 2 is an enlarged cross-sectional view of the dissimilar metal joined structure of Example 1 formed by the manufacturing method of the dissimilar metal joined structure of the first embodiment. FIG. 3 is an enlarged sectional view of a dissimilar metal joined structure of Example 2 formed by the manufacturing method of the dissimilar metal joined structure of the first embodiment. FIG. 4 is a perspective view of forming a dissimilar metal joined structure according to a second embodiment of the present invention by laser welding. FIG. 5 is an enlarged sectional view of a dissimilar metal joined structure of Example 3 formed by the manufacturing method of the dissimilar metal joined structure of the second embodiment. FIG. 6 is an enlarged cross-sectional view of a dissimilar metal joined structure of a comparative example formed by a conventional manufacturing method.

Each embodiment of the present invention will be described in detail below. The present invention is not limited to the embodiments described below, and can be arbitrarily modified without departing from the scope of the present invention.

The inventors of the present invention have made intensive studies in order to obtain a joining method capable of obtaining a good joined joint even when welding is performed from the steel material side by one-sided welding in dissimilar metal joining of aluminum or aluminum alloy material and steel material. piled up. As a result, a low-temperature spray coating is formed by low-temperature spraying metal powder that can be welded with the steel on at least a part of the surface of the aluminum or aluminum alloy material, and the low-temperature spray coating and the steel are laser-welded from the steel side. It was found that a good bonded joint can be obtained by bonding by

Specifically, when a metal coating (low-temperature spray coating) is formed on the surface of an aluminum or aluminum alloy plate by spraying a predetermined metal powder at a high speed by a low-temperature spray method (cold spray method), aluminum or aluminum alloy Since a high-strength mechanical bond can be obtained between the plate and the metal film, it was found that a good welded joint can be obtained even in the dissimilar-materials-joined structure obtained by subsequent laser welding with steel materials.

Furthermore, laser welding conditions are an important factor in suppressing blowholes that occur in the molten part in laser welding between steel materials and low-temperature thermal spray coatings formed on aluminum or aluminum alloy plates. It has been found that by properly managing, a welded joint having a high joint strength with less occurrence of blowholes can be obtained.

(First embodiment)
In the method for manufacturing a dissimilar metal joined body according to the present embodiment, at least part of the surface of an aluminum or aluminum alloy material 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 one kind of metal powder; a step of superimposing an aluminum or aluminum alloy material and a steel material so that the low-temperature sprayed coating and the steel material face each other; and a low-temperature sprayed coating. and joining the steel material by laser welding from the steel material side.

As shown in FIG. 1, in a dissimilar metal joined structure 10 according to this embodiment, a low-temperature thermal spray coating 1 is formed on at least part of the surface of an aluminum or aluminum alloy material 2 . Next, the aluminum or aluminum alloy material 2 and the steel material 3 are overlaid so that the low temperature thermal spray coating 1 and the steel material 3 face each other. Furthermore, the laser beam L irradiated from the steel material 3 side is applied to the steel material 3, the low-temperature thermal spray coating 1, and the aluminum or aluminum alloy material 2 under welding conditions in which a molten portion is formed through the low-temperature thermal spray coating 1. A steel material 3 and an aluminum or aluminum alloy material 2 are laser-welded, and a weld metal (weld bead) 4 is formed by melting the steel material 3, the low-temperature thermal spray coating 1, and the aluminum or aluminum alloy material 2.

The low temperature thermal spray 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 or aluminum alloy material 2 to which the metal powder is sprayed at high speed by low-temperature thermal spraying has fine unevenness due to the large amount of metal powder, so that the low-temperature spray coating 1 and the steel material 3 are mechanically and firmly joined by an anchor effect.

A cold spray method is suitable as a method for forming the low-temperature thermal spray coating 1 by injecting metal powder at a low temperature and at a high speed. The cold spray method is a method of forming the low-temperature thermal spray coating 1 by spraying gas and metal powder onto an object at a speed higher than the speed of sound. In this method, since the working gas has a relatively low temperature (for example, 900° C. or less, which is the melting point of iron particles or less), metal powder with a relatively high melting point such as iron and aluminum or aluminum alloy material may melt together. However, metal powder having a relatively high melting point, such as iron, bites into the aluminum or aluminum alloy material 2 due to its velocity energy, resulting in a macroscopic mechanical fastening state.

Therefore, intermetallic compounds are less likely to be generated and brittle phases are less likely to be generated, so that as a result, a strong low-temperature thermal spray coating (iron-based coating in this embodiment) 1 is formed on a part of the aluminum or aluminum alloy material 2. be done. 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.

As a method for forming the low temperature thermal spray coating 1, other than the cold spray method, other thermal spraying methods such as plasma thermal spraying and arc thermal spraying are conceivable. 2000° C. or higher), both the particles and the aluminum base material exceed their melting points and become liquid, and intermetallic compounds are formed by chemical reactions, and only brittle coatings can be formed.

After that, the steel material 3 is placed on the obtained low-temperature thermal spray coating 1, and the steel material 3, the low-temperature thermal spray coating 1, and the aluminum or aluminum alloy material 2 are arranged from the opposite side of the steel material 3 to the side facing the aluminum or aluminum alloy material 2. In any of the above, the weld metal 4 is formed by laser welding under the welding conditions under which a molten portion is formed, and the dissimilar metal joined structure 10 is manufactured.

As shown in FIG. 2 (corresponding to Example 1 to be described later) and FIG. When performing laser welding, welding is performed under conditions in which part of the aluminum or aluminum alloy material 2 is melted together with the steel material 3 and the low temperature thermal spray coating 1, thereby welding the steel material 3, the low temperature thermal spray coating 1, and the aluminum or aluminum alloy material 2. A metal (weld bead) 4 is formed and welded.

If the heat input becomes excessively large, the aluminum or aluminum alloy material 2 is melted too much and the bead becomes unstable, and cracks are likely to occur in the welded portion. Therefore, it is preferable to suppress the amount of heat input as much as possible. Welding is preferably performed under heat input conditions such that the amount of aluminum contained in the weld metal 4 is preferably 5% or less, more preferably 1% or less.

By controlling the amount of heat input so that the aluminum or aluminum alloy material 2 is partially melted, the occurrence of blowholes 5 can be greatly suppressed, and the joint strength of the dissimilar metal joint structure 10 is improved. It is considered that this is because the strength improvement due to the disappearance of the blowholes 5 is greater than the strength reduction due to the partial melting of the aluminum or aluminum alloy material 2 .

Here, laser welding is a welding method with a low heat input and a small thermal effect compared to other welding methods such as arc welding. When arc welding is used, the heat generated during welding tends to reach the aluminum or aluminum alloy material 2, so the adhesion strength of the metal film to the high-strength steel is greatly reduced, and the joint strength may be reduced. There is However, when laser welding is used, the heat effect on the aluminum or aluminum alloy material 2 can be minimized, and the decrease in the adhesion strength of the metal coating to the high-strength steel can be suppressed, so the decrease in bonding strength can be prevented. can be prevented and a good bonded joint can be obtained.

Next, in the manufacturing method according to the present embodiment, the low temperature thermal spray coating 1, the metal powder used as the material thereof, the aluminum or 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 low-temperature spray coating 1 and the steel material 3 by laser welding, the material of the low-temperature spray coating 1 can be welded with the steel material 3 with a desired bonding strength, and the properties of the weld metal 4 are improved. The choice of metal material is important.

In this embodiment, stainless steel (SUS) can be suitably selected because it can easily weld a good joint to the steel material 3 .
In particular, among various stainless steels, ferritic stainless steel, austenitic stainless steel, and duplex stainless steel of ferritic and austenitic series are more excellent in corrosion resistance than martensitic stainless steel, so they are exposed to corrosive environments. Suitable as a material for automobiles. Therefore, as the metal powder used for cold spraying, powder made of at least one metal selected from ferritic stainless steel, austenitic stainless steel, and duplex stainless steel of ferritic and austenitic series is preferably used. .

On the other hand, if 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 base material is diluted when the steel material 3 is a high-strength steel plate or a hot stamp material. All or part of the weld metal 4 undergoes martensite transformation, and the hardness becomes too high, which may reduce the joint strength (joint strength) or cause cracks. In such a case, the metal powder used for cold spray is preferably a 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 low-temperature thermal spray coating 1 is not particularly limited, but when the gas pressure of the cold spray is set to a low pressure condition of 1 MPa or less, it is preferably 20 μm or less, for example, 10 μm or less. is more preferable.
On the other hand, when the gas pressure is set to a high pressure condition of 1 MPa to 5 MPa, it is preferably 50 μm or less, more preferably 30 μm or less.
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 low temperature thermal spray 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 low-temperature thermal spray coating becomes higher, and an improvement in joint strength can be expected.

<Temperature of working gas>
As described above, when the temperature of the gas used in cold spraying is high, the metal powder melts and undergoes a chemical reaction with the aluminum or aluminum alloy material 2 serving as the base material of the low-temperature thermal spray coating 1 to generate an intermetallic compound. There is a risk of Therefore, the temperature of the working gas is preferably lower than the melting point of the metal powder used for cold spray. For obtaining the dissimilar metal joined body according to the present embodiment, it is preferable to set the temperature to room temperature (20° C.) to 1200° C., for example.

<Film thickness>
If the thickness of the low-temperature spray coating 1 formed by cold spraying is less than 0.3 mm, welding that melts only the low-temperature spray coating 1 and the steel material 3 is required (for example, the welding method of the second embodiment described later etc.), it may be difficult to melt only the low-temperature thermal spray coating 1 and the steel material 3 due to the influence of the variation in the laser beam L, so the robustness is lowered.

Therefore, by setting the film thickness of the low-temperature thermal spray coating 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 required. Therefore, the film thickness of the low-temperature thermal spray coating 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 low-temperature thermal spray coating 1 exceeds 3 mm, the film-forming time becomes long, which may increase the manufacturing cost. Therefore, the film thickness of the low-temperature thermal spray coating 1 is preferably 3 mm or less, more preferably 2 mm or less.

<Aluminum or aluminum alloy material>
The aluminum or aluminum alloy material 2 is also not particularly limited, but when it is applied to members used in automobiles, etc., from the viewpoint of strength, it is possible to use aluminum alloy materials such as 2000 series, 5000 series, 6000 series and 7000 series. preferable. In addition, in this embodiment, since laser welding is used that allows welding by one-sided welding from the steel material 3 side, not only plate materials but also extruded materials, cast materials, and forged materials that are frequently used in the field of automobiles and the like can be used. can be used without problems.

<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 for high-strength steel sheets having a tensile strength of 980 MPa or more.

(Second embodiment)
A method for manufacturing a dissimilar metal joined body according to the second embodiment will be described. The method for manufacturing a joined body of dissimilar metals according to this embodiment differs from the method for manufacturing a joined body of dissimilar metals according to the first embodiment in the joining step. Others are the same as the manufacturing method of the dissimilar metal joined body of the first embodiment, so the different parts will be explained.

As shown in FIGS. 4 and 5 (corresponding to Example 3, which will be described later), the joining process of this embodiment is performed by laser irradiation at least twice under the condition that the low-temperature spray coating 1 is partially penetrated. Specifically, a weld metal 4 is formed by partially melting the steel material 3 and the low-temperature thermal spray coating 1 to manufacture the dissimilar metal joint structure 10 . Note that two arrows in FIG. 4 schematically indicate that the laser welding from the steel material 3 side is performed twice at almost the same position.

In this case, the amount of heat input in the second and subsequent laser irradiations should preferably be equal to or less than the amount of heat input in the first laser irradiation. If the amount of heat input in the second and subsequent laser irradiations is larger than the amount of heat input in the first time, blow holes 5 are generated from the newly melted low-temperature thermal spray coating 1, which is not preferable.

As a result, even if the blow hole 5 is generated by the first laser irradiation, the second and subsequent laser irradiations whose heat input is equal to or less than that of the first laser irradiation cause the blow holes 5 generated by the first laser irradiation to be reduced. Hole 5 can be eliminated. As a result, the number of blowholes 5 is reduced and the bonding strength is improved.
Although laser irradiation may be performed three times or more, burn-through is likely to occur and the tact time becomes longer.

Note that FIG. 5 shows a case where no molten portion is formed in any of the steel material 3, the low-temperature thermal spray coating 1, and the aluminum or aluminum alloy material 2 in the first laser irradiation. As shown in the form, the steel material 3, the low-temperature spray coating 1, and the aluminum or aluminum alloy material 2 are welded together with the steel material 3 and the low-temperature spray coating 1 under conditions in which part of the aluminum or aluminum alloy material 2 melts. After the weld metal (weld bead) 4 is formed and welded, the second and subsequent laser irradiation may be performed.
That is, by combining the welding conditions of the first embodiment and the second embodiment, it is possible to more reliably reduce the number of blowholes and improve the joint strength.

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.

<Example>
First, on the surface of an aluminum alloy plate having a thickness of 3 mm, a metal coating (low-temperature thermal spray coating) having a thickness of 2 mm was formed using a cold spray.
After that, 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 produce a dissimilar-metal joint structure. The laser irradiation was controlled by a galvanometer scanner, and linear welding was performed once in Examples 1 and 2 (see FIGS. 2 and 3) and twice in Example 3 (see FIG. 5).

The test materials, cold spray conditions and welding conditions are shown below.
[Test material]
Aluminum alloy plate: A7N01-T6 material Steel plate: Hot stamped material (22MnB steel, tensile strength 1500 MPa class)
[Cold spray conditions]
Gas type: Nitrogen Gas pressure: 5 MPa
Gas temperature: 1000°C
Metal powder: Iron powder Average particle size of metal powder: 40 μm
[Laser welding conditions]
Heat source: fiber laser Welding speed: 4 m/min (4 m/min for both laser irradiations in Example 3)
Beam condensing diameter: φ0.6mm
Weld length: 18.8 mm
Shield gas: None Output: Example 1: 5 kW (one irradiation)
Example 2: 6 kW (one irradiation)
Example 3: 4 kW + 3 kW (twice irradiation)

<Comparative example>
On the surface of an aluminum alloy plate with a thickness of 3 mm, a metal film (low-temperature thermal spray coating) with a thickness of 2 mm was formed using cold spray, and then the aluminum alloy plate with a thickness of 1.4 mm was formed through the metal film. A dissimilar metal joint structure was manufactured by superimposing the steel sheets and laser-welding the steel sheets and the metal film by irradiating the laser from the surface of the steel sheets opposite to the surface in contact with the aluminum alloy plate. It should be noted that laser irradiation was controlled by a galvanometer scanner and welded in a straight line as in the example.
The laser welding conditions were the same as in the example, but the output was 4 kW and the irradiation was performed once (see FIG. 6).

<Evaluation>
After that, in both the example and the comparative example, the joint strength of the dissimilar metal joined structures obtained was measured, and cross-sectional macroscopic observation was performed on the joints to examine the penetration and the blowhole rate.
Regarding the joint strength, the tensile shear strength (kN) was measured with reference to the test method described in JIS Z3136 and JIS Z3137. The test speed of the tensile test was set to 10 mm/min for both.
Regarding the penetration, by cross-sectional macroscopic observation, the evaluation "II" was given when it was confirmed that the aluminum alloy plate was melted, and the evaluation "I" was given when it was not confirmed that the aluminum alloy plate was melted.
The blowhole rate (%) was calculated as a ratio of the area of the blowholes 5 to the area of the weld metal (molten metal) 4 in the cross-sectional macrophotograph, rounded off to the nearest whole number.

2 is a cross-sectional view of the dissimilar metal joined structure of Example 1, FIG. 3 is a cross-sectional view of the dissimilar metal joined structure of Example 2, and FIG. 5 is a dissimilar metal joined structure of Example 3. , and FIG. 6 is a cross-sectional view of a dissimilar metal joined structure of a comparative example.

Laser welding conditions (number of laser irradiation times, first and second laser outputs) and evaluation results (penetration of aluminum alloy plate, blowhole rate (%) and tensile shear strength (kN) are shown in Table 1 below. "-" in the "second output (kW)" column of Table 1 indicates that the second laser irradiation was not performed.

As shown in Table 1 above, in Examples 1, 2 and 3, since the welding conditions satisfied the conditions of the present invention, good welds with few blowholes were obtained. Also, the tensile shear strength was increased. On the other hand, in the comparative example, as shown in FIG. 6, many blowholes were generated and the tensile shear strength was low.

As described in detail above, according to the present invention, it is possible to obtain a dissimilar metal joined structure having a high joint strength and capable of welding with few blowholes by one-sided welding from the steel material side.

It should be noted that the present invention is not limited to the above-described embodiments and examples, and can be modified, improved, etc. as appropriate. For example, in each embodiment, the output is changed to control the amount of heat input, but the amount of heat input may be controlled by changing the welding speed or the beam focus position.

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 or aluminum alloy material. a step of forming a low-temperature thermal spray coating;
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;
joining the aluminum or aluminum alloy material and the steel material by laser welding from the steel material side;
A method for manufacturing a dissimilar metal joined structure, wherein the joining step is performed under welding conditions in which a melted portion is formed in any of the steel material, the low-temperature thermal spray coating, and the aluminum or aluminum alloy material.
According to this configuration, welding by one-sided welding from the steel material side is possible, blowholes are reduced, and joint strength is improved.

(2) According to (1), the bonding step is performed by at least two laser irradiations, and the heat input in the second and subsequent laser irradiations is equal to or less than the heat input in the first laser irradiation. A method for manufacturing a dissimilar metal joined structure.
According to this configuration, the number of blowholes can be reduced more reliably, and the joint strength can be improved.

(3) an aluminum or aluminum alloy material;
At least one metal powder selected from pure iron, carbon steel, stainless steel, nickel, nickel alloys, cobalt and cobalt alloys formed on at least part of the surface of the aluminum or aluminum alloy material is low-temperature sprayed. a low-temperature thermal spray coating,
a steel material superimposed on the low-temperature spray coating;
a weld metal in which a molten portion is formed in any of the steel material, the low temperature thermal spray coating, and the aluminum or aluminum alloy material;
A dissimilar metal joint structure comprising:
According to this configuration, a dissimilar metal joined structure having excellent joint strength with few blowholes can be obtained by welding by one-sided welding from the steel material side.

(4) 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 aluminum or aluminum alloy material a step of forming a low-temperature thermal spray coating;
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;
joining the aluminum or aluminum alloy material and the steel material by laser welding from the steel material side;
The bonding step is performed by laser irradiation at least twice under conditions where the low-temperature thermal spray coating is partially penetrated, and the heat input in the second and subsequent laser irradiations is equivalent to the heat input in the first laser irradiation. The method for manufacturing a dissimilar metal joined structure is as follows.
According to this configuration, the amount of heat input in the second and subsequent laser irradiations is equal to or less than the amount of heat input in the first laser irradiation, so that the occurrence of blowholes is greatly suppressed and the bonding strength is improved.

1 low-temperature thermal spray coating 2 aluminum or aluminum alloy material 3 steel material 4 weld metal 10 dissimilar metal joint structure L laser beam (laser irradiation)

Claims (3)

A low-temperature spray coating obtained 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 a portion of the surface of an aluminum or aluminum alloy material. forming a
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;
joining the aluminum or aluminum alloy material and the steel material by laser welding from the steel material side;
A method for manufacturing a dissimilar metal joined structure, wherein the joining step is performed under welding conditions in which a melted portion is formed in any of the steel material, the low-temperature thermal spray coating, and the aluminum or aluminum alloy material. 2. The joining of dissimilar materials according to claim 1, wherein the joining step is performed by laser irradiation at least twice, and the heat input in the second and subsequent laser irradiations is equal to or less than the heat input in the first laser irradiation. A method of manufacturing a structure. A low-temperature spray coating obtained 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 a portion of the surface of an aluminum or aluminum alloy material. forming a
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;
joining the aluminum or aluminum alloy material and the steel material by laser welding from the steel material side;
The bonding step is performed by laser irradiation at least twice under conditions where the low-temperature thermal spray coating is partially penetrated, and the heat input in the second and subsequent laser irradiations is equivalent to the heat input in the first laser irradiation. The method for manufacturing a dissimilar metal joined structure is as follows.

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