JP7123674B2 - Dissimilar material joined structure manufacturing method and dissimilar material joined structure - Google Patents

Description

The present invention relates to a method for manufacturing a dissimilar metal joined structure and a dissimilar metal joined structure.

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 Even the aluminum or aluminum alloy material is melted, and there is a possibility that the bonding strength is lowered.

The present invention has been made in view of the above-mentioned problems, and in joining dissimilar materials of aluminum or aluminum alloy material and steel material, welding by one-sided welding from the steel material side is possible and a good welded joint is obtained. It is an object of the present invention to provide a method for manufacturing a dissimilar-materials-bonded structure and a dissimilar-materials-bonded structure.

A method for manufacturing a dissimilar metal joined structure according to the present invention has the following configuration (1).
(1) Low-temperature thermal spray coating by low-temperature thermal spraying of at least one metal powder selected from pure iron, carbon steel, nickel, nickel alloys, cobalt, and cobalt alloys on at least part of the surface of 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;
a step of joining the low-temperature spray coating and the steel material by laser welding from the steel material side;
A method for manufacturing a dissimilar metal joined structure, comprising:

A preferred embodiment of the method for manufacturing a dissimilar metal joined structure according to the present invention has the following configurations (2) to (5).
(2) The method for manufacturing a dissimilar metal joined structure according to (1) above, wherein the laser welding melts only the low-temperature thermal spray coating and the steel material.
(3) The method for manufacturing a dissimilar metal joined structure according to (1) or (2) above, wherein the low-temperature spray coating has a thickness of 0.3 mm or more.
(4) The method for manufacturing a dissimilar metal joined structure according to any one of (1) to (3) above, wherein the steel material has a tensile strength of 590 MPa or more.
(5) The method for manufacturing a dissimilar metal joined structure according to any one of (1) to (4) above, wherein the aluminum or aluminum alloy material is an extruded material with a closed cross section.

Further, a dissimilar metal joined structure according to the present invention has the following configuration (6).
(6) an aluminum or aluminum alloy material;
a low-temperature thermal spray coating formed on at least a portion of the surface of the aluminum or aluminum alloy material;
a steel material superimposed on the low-temperature spray coating;
a weld metal formed by welding the low-temperature spray coating and the steel material,
A dissimilar metal joining structure, wherein the low-temperature thermal spray coating contains at least one metal selected from pure iron, carbon steel, nickel, nickel alloys, cobalt, and cobalt alloys.

Further, a preferred embodiment of the dissimilar metal joined structure according to the present invention comprises the following configurations (7) to (10).
(7) The dissimilar metal joining structure according to (6) above, wherein the weld metal is formed by melting only the low-temperature thermal spray coating and the steel material.
(8) The dissimilar metal joined structure according to (6) or (7) above, wherein the low-temperature thermal spray coating has a thickness of 0.3 mm or more.
(9) The dissimilar metal joined structure according to any one of (6) to (8) above, wherein the steel material has a tensile strength of 590 MPa or more.
(10) The dissimilar metal joined structure according to any one of (6) to (9) above, wherein the aluminum or aluminum alloy material is an extruded material with a closed cross section.

According to the present invention, in dissimilar metal joining of aluminum or aluminum alloy material and steel material, welding by one-sided welding from the steel material side is possible and a good joint can be obtained. and a dissimilar metal joint structure can be provided.

FIG. 1 is a cross-sectional view schematically showing a dissimilar metal joined structure according to an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to the embodiments described below, and can be arbitrarily modified without departing from the gist 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 sprayed 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 sprayed coating and the steel are separated by a laser beam from the steel side. It has been found that a good joint can be obtained by joining by welding.

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 for the dissimilar-materials-joined structure obtained by subsequent laser welding with the steel material.

Therefore, it is considered important to appropriately select the components of the metal powder used for low-temperature thermal spraying and the type of steel material in order to obtain a good welded joint.

As described above, in the method for manufacturing a dissimilar metal joined structure 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, 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.

FIG. 1 is a cross-sectional view schematically showing a dissimilar metal joined structure according to an embodiment of the present invention. As shown in FIG. 1, a dissimilar metal joined structure 10 according to this embodiment has a low-temperature thermal spray coating 1 formed on at least part of the surface of an aluminum or aluminum alloy material 2 . Further, the aluminum or aluminum alloy material 2 and the steel material 3 are superimposed so that the low temperature thermal spray coating 1 and the steel material 3 face each other. Further, the low temperature thermal spray coating 1 and the steel material 3 are laser welded by the laser beam L irradiated from the steel material 3 side, and the weld metal (weld bead) 4 is formed by melting the low temperature thermal spray coating 1 and the steel material 3. .

The low temperature thermal spray coating 1 contains at least one metal selected from pure iron, carbon 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 firmly joined by an anchor effect.

Next, based on FIG. 1, the manufacturing method of the dissimilar metal joined structure according to the present embodiment will be specifically described.
First, the low-temperature thermal spray coating 1 is formed on at least part of the surface of the aluminum or aluminum alloy material 2 by the cold spray method. 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. This method can be carried out by appropriately selecting the type of gas used, pressure, temperature, particle size of metal powder, and the like.
As a method for forming a thermal spray coating, other than the cold spray method, other thermal spraying methods such as plasma thermal spraying and arc thermal spraying are conceivable. It is not preferable because it may cause 2 to dissolve.

After that, the steel material 3 is placed on the obtained low-temperature thermal spray coating 1, and laser welding is performed from the opposite side of the steel material 3 to the side facing the aluminum or aluminum alloy material 2, thereby joining the low-temperature thermal spray coating 1 and the steel material 3 together. It can be melted to form the weld metal 4 and the dissimilar metal joined structure 10 can be manufactured.

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 even the aluminum or aluminum alloy material 2 may melt and the joint strength may decrease. However, when laser welding is used, the heat effect on the aluminum or aluminum alloy material 2 can be minimized, and the melting of the aluminum or aluminum alloy material 2 can be suppressed, thereby preventing a decrease in joint strength. , a good bonded joint can be obtained.

In order to further minimize the thermal influence on the aluminum or aluminum alloy material 2, it is preferable to select appropriate welding conditions so that only the low-temperature thermal spray coating 1 and the steel material 3 are melted. As the laser welding conditions, the heat source, power, welding speed, diameter of the welded portion, the distance between the low-temperature spray coating 1 and the steel material 3, and the like can be appropriately selected.

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, 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. 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. Therefore, the metal powder used for cold spraying is 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 is oxidized, it may adversely affect laser weldability, so it is preferable to use nitrogen or helium as the gas species.

<Temperature of working gas>
As described above, when the temperature of the gas used in cold spraying is high, there is a risk of melting the aluminum or aluminum alloy material 2 serving as the base material of the low-temperature thermal spray coating 1 . Therefore, the temperature of the working gas is preferably lower than the melting point of the metal powder used for cold spray.

<Thickness of low-temperature thermal spray coating>
If the thickness of the low-temperature spray coating 1 formed by cold spraying is less than 0.3 mm, even if the welding conditions are appropriately selected such that only the low-temperature spray coating 1 and the steel material 3 are melted, the influence of the variation in the laser beam L As a result, it may be difficult to melt only the low-temperature sprayed coating 1 and the steel material 3, resulting in low robustness.
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 necessary. Therefore, the film thickness of the low-temperature thermal spray coating 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 spray coating 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 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, even closed cross-section extruded materials that are frequently used in the field of automobiles can be used without problems. can.

<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 method for joining dissimilar metals between steel and aluminum, to a steel plate having a tensile strength of 590 MPa or more. Therefore, the present invention is particularly effective for high-strength steel sheets having a tensile strength of 590 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.

<Example>
First, a metal coating (low-temperature thermal spray coating) was formed on the surface of an aluminum alloy plate having a thickness of 3 mm using 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 dissimilar metal joint structure was manufactured by laser welding a metal film and a steel plate by the method. The laser irradiation was controlled by a galvanometer scanner, and welding was performed in a circular shape as shown in FIG.

The test materials, cold spray conditions, and welding conditions are shown below.
[Test material]
Aluminum alloy plate: 7N01
Steel plate: hot stamping material (22MnB steel, tensile strength 1500 MPa class)
[Cold spray conditions]
Gas type: Nitrogen Gas pressure: 4 MPa
Gas temperature: 750-1100°C
Particle size of metal powder: 10 to 50 μm
[Laser welding conditions]
Heat source: Fiber laser Output: 2.5-3.5 kW
Speed: 4m/min
Beam condensing diameter: φ0.6mm
Laser scanning trajectory: Circular Weld diameter (circle diameter): Aim for φ6 mm Shield gas: None Gap (plate gap): 0 to 0.3 mm

<Comparative example>
An aluminum alloy plate and a steel plate having a thickness of 1.4 mm were superimposed on the surface of the aluminum alloy plate having a thickness of 3 mm without forming a metal coating (low-temperature thermal spray coating) using cold spray. Subsequently, the aluminum alloy plate and the steel plate were laser-welded by irradiating the laser from the surface of the steel plate opposite to the surface in contact with the aluminum alloy plate to manufacture a dissimilar metal joined structure. As in the example, the laser irradiation was controlled by a galvanometer scanner, and welding was performed in a circular shape. Also, the laser welding conditions were the same as in the example.

After that, regarding the obtained dissimilar metal joined structure, the cross-sectional macroscopic observation was performed on the joint to investigate the state of penetration and welding defects.
As the evaluation criteria for penetration and welding defects, a weld metal was formed only between the steel material and the metal film, and the aluminum alloy plate was not melted. Among the cases where the weld metal reached the aluminum alloy plate and the aluminum alloy plate melted, △ (evaluation: acceptable) was given when the steel material and aluminum were joined, and × (evaluation: unacceptable) was given when the steel material and aluminum were not joined. did.

Table 1 below shows the material of the metal powder used in the cold spray, the film thickness of the formed metal film, the laser welding conditions (output, gap), and the evaluation results (state of penetration and welding defects).

As shown in Table 1 above, test no. 1 to 5 are manufactured by forming a metal film on the surface of an aluminum or aluminum alloy plate and laser-welding the metal film and a steel material to manufacture a dissimilar metal joined structure. Good bonded joints were obtained within the scope of the present invention.
In particular, test no. In 1 to 4, since the film thickness of the metal film is within the preferred range of the present invention, only the metal film and the steel plate can be laser-welded without the molten portion reaching the aluminum or aluminum alloy plate, which is more excellent. A quality weld could be obtained.
In addition, test No. in which the evaluation of penetration and welding defects was ○. As a result of a strength test, No. 3 had a tensile shear strength of 8.7 kN and a cross tensile strength of 5 kN, confirming that good joint strength was obtained. In the strength test, tensile shear strength and cross tensile strength were measured according to JIS Z3136 and JIS Z3137. The test speed of the tensile test was set to 10 mm/min for both.

On the other hand, Test No. which is a comparative example. In No. 6, no joining was observed between the steel material and the aluminum after welding, making it unsuitable for use.

As described in detail above, according to the present invention, it is possible to provide a dissimilar-materials-joined structure that allows welding by one-sided welding from the steel material side and that can obtain a good welded joint.

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

Claims (10)

A low-temperature spray coating is formed by low-temperature spraying at least one metal powder selected from pure iron, carbon steel, nickel, nickel alloys, cobalt, and cobalt alloys on at least part of the surface of an aluminum or aluminum alloy material. process and
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 low-temperature spray coating and the steel material by laser welding from the steel material side;
A method for manufacturing a dissimilar metal joined structure, comprising: 2. The method of manufacturing a dissimilar metal joined structure according to claim 1, wherein said laser welding melts only said low temperature thermal spray coating and said steel material. 3. The method for manufacturing a dissimilar metal joined structure according to claim 1, wherein the film thickness of said low-temperature thermal spray coating is 0.3 mm or more. The method for manufacturing a dissimilar metal joined structure according to any one of claims 1 to 3, wherein the steel material has a tensile strength of 590 MPa or more. The method for manufacturing a dissimilar metal joined structure according to any one of claims 1 to 4, wherein the aluminum or aluminum alloy material is an extruded material with a closed cross section. an aluminum or aluminum alloy material;
a low-temperature thermal spray coating formed on at least a portion of the surface of the aluminum or aluminum alloy material;
a steel material superimposed on the low-temperature spray coating;
a weld metal formed by welding the low-temperature spray coating and the steel material,
A dissimilar metal joining structure, wherein the low-temperature thermal spray coating contains at least one metal selected from nickel , nickel alloys, cobalt, and cobalt alloys. 7. The dissimilar metal joining structure according to claim 6, wherein said weld metal is formed by melting only said low-temperature thermal spray coating and said steel material. 8. The dissimilar metal joint structure according to claim 6, wherein the film thickness of said low-temperature spray coating is 0.3 mm or more. The dissimilar metal joined structure according to any one of claims 6 to 8, wherein the steel material has a tensile strength of 590 MPa or more. The dissimilar metal joined structure according to any one of claims 6 to 9, wherein said aluminum or aluminum alloy material is an extruded material with a closed cross section.

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