JPH08257743A - Method for joining aluminum or its alloy and different metal - Google Patents

Abstract

PURPOSE: To reduce a joining cost by suppressing the formation of intermetallic compds., enhancing the reliability of joint parts and decreasing the man-hours in pretreatment stages before brazing in brazing of an aluminum metal and different metal. CONSTITUTION: The joint surface of the different metal 2 is coated with nitride or carbide of a rock salt type structure. The aluminum metal 1 and the different metal 2 are joined by aluminum brazing 3 via this coating layer 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining aluminum or its alloy and dissimilar metals represented by steel by brazing. In the present specification, aluminum or its alloy is generically referred to as an aluminum-based metal.

[0002]

2. Description of the Related Art In a composite structure of aluminum-based metal and steel such as a heat exchanger, it is considered that joining different metals is not easy. This is because normal welding cannot be adopted because a brittle intermetallic compound is generated at the joint interface due to melting of the joint surface and a sound joint cannot be obtained. Therefore, solid-state joining methods such as HIP and pressure welding are generally used, and as the liquid-phase joining method, a brazing method using an insert material has been studied. However, the solid-phase bonding method cannot avoid the cost problem and the limitation of the application range due to the shape.
It can be said that a brazing method using an insert material together is industrially preferable.

For example, the following is known as a brazing method of aluminum-based metal and steel using an insert material together. Al on the joining surface of steel, especially stainless steel
Vacuum brazing after coating with Al-Si, Ag or Sn (Japanese Patent Laid-Open No. 60-133971). A method of coating the joint surface of steel, particularly stainless steel with Ti and performing vacuum brazing (Japanese Patent Laid-Open No. 2-6368).
No. 1), ceramic on the joining surface of steel, specifically Al
_{A method in which 2} O ₃ is coated, Al is further coated, and brazing is performed (Japanese Patent Publication No. 61-21747).

[0004]

The first method and the second method basically coat non-ferrous metal on the joining surface of steel, but completely suppress the formation of intermetallic compounds at the joining interface. Is difficult. On the other hand, the third method of coating the joining surface of steel with ceramics is extremely effective in suppressing the formation of intermetallic compounds. However, since it is necessary to further overcoat Al on the ceramic layer, the number of man-hours for pretreatment until brazing is large, and the pretreatment is complicated, which reduces the ease of brazing. There is.

The object of the present invention is not only to obtain a sound joint by suppressing the formation of intermetallic compounds at the joint interface, but also to reduce the number of pretreatment steps required for brazing to achieve high performance and high performance. It is to provide a joining method by efficient brazing.

[0006]

A ceramic coating is extremely effective as a means for suppressing the formation of intermetallic compounds, which is a problem in brazing aluminum-based metals and dissimilar metals. However, Al ₂ O ₃ which has been conventionally proposed as the ceramic has a further A
1 needs to be overcoated. The reason is considered to be as follows.

The surface of Al is covered with a strong oxide film, and the behavior of the oxide film is greatly related to the bonding. Therefore, in general brazing of Al, flux brazing or brazing containing Mg is used for the purpose of removing the oxide film. However, these flux and Mg is, Al ₂
In brazing joining of O ₃ and Al, it becomes a factor that hinders the interfacial reaction and makes the joining difficult. Therefore, when the ceramic is Al ₂ O ₃ , A is added to the ceramic layer.
1 overcoating is required.

The inventors of the present invention have conducted various experimental studies to find a ceramic that does not require overcoating with Al. As a result, they have found that a nitride or carbide having a rock-salt type structure meets the requirements, and the present invention It came to completion.

The joining method of the present invention is a method of joining aluminum or its alloy and a dissimilar metal, wherein a coating layer made of a nitride or a carbide having a rock salt type structure is formed on the joint surface of the dissimilar metals and the coating is performed. 6 through layers
Aluminum or its alloy and dissimilar metals are joined by a brazing material containing aluminum as a main component that can be joined at 20 ° C or lower.

[0010]

[Function] The rock salt type structure is also called a salt type structure or a sodium chloride type structure, and is a kind of crystal structure belonging to the cubic system. TiC, which is a typical carbide and nitride of this structure,
TiN is a coating material that is widely used for decoration of tableware and watches, for corrosion resistance, or for wear resistance of tools and the like, and its film forming technology has been established, so it is technically easy. Therefore it is cheap.

Moreover, the carbide and nitride of this structure are Al
Unlike pure ceramics such as ₂ O ₃ , it is a compound that has both properties of ceramics and metals, so it is one of the important factors that determines whether or not brazing of ceramics and metals Excellent wettability. Therefore, it is not necessary to overcoat the coating layer with Al. In addition, the brazing can effectively suppress the formation of intermetallic compounds at the bonding interface.

As the rock salt type nitride, specifically, M
N (M: rare earth element, Ti, Zr, Hf, V, Nb, T
a, Cr, U, etc.). Further, as the carbide of the structure, specifically, MC (M: Ti, Zr,
Hf, V, Nb, Ta, Mo, W etc.).

The thickness of the coating layer is 2 to 6 μm
Is desirable. If the thickness is less than 2 μm, a porous portion is formed depending on the coating method, and diffusion of the brazing from that portion to the dissimilar metal side occurs to generate an intermetallic compound. 6 μm
If it exceeds, peeling or reduction in strength occurs due to the difference in thermal expansion coefficient. In addition, as a coating method, PVD
A method (ion plating method or the like) or a CVD method (plasma CVD method, laser CVD or the like) is desirable. This is because it is suitable as a method for coating a predetermined film thickness and has been technically established as a method for coating the above-mentioned nitride and carbide.

In the brazing process, as a brazing material, 6
A material whose main component is aluminum that can be bonded at 20 ° C. or lower is used. The brazing temperature of the brazing material is 62
The reason why the temperature is 0 ° C. or lower is to prevent the base metal from melting on the aluminum side during brazing, and the main component being aluminum is that an intermetallic compound is formed at the interface between the coating layer and the aluminum-based metal. This is to prevent this. As such a brazing material, for example, Al
-Si based wax or brazing sheet may be mentioned. Also, the brazing load is preferably 0.2 MPa or less in order to secure the brazing material necessary for joining at the interface, and the brazing temperature must be lower than 640 ° C, which is the melting temperature of the base metal on the aluminum side. Is.

The aluminum-based metal as the base material is basically brazable, and specifically, in addition to pure aluminum, Al-Mn-based, Al-Mg-based, Al-Mg-
An aluminum alloy such as a Si-based material can be used. Examples of the dissimilar metals include various steels such as carbon steel, stainless steel, heat resistant steel, spring steel, tool steel, cast iron, and cast steel, as well as various alloy steels, high alloys, and non-ferrous metals other than aluminum-based metals. it can.

[0016]

Examples of the present invention will be described below. As shown in FIG. 1, a 20 mm square block of aluminum-based metal 1 made of 3003 alloy and a 20 mm square block of SUS3
When joining the steel 2 made of 04, a coating layer 4 made of TiN and having a thickness of about 2 μm was formed on the joining surface of the steel 2 by using an ion plating method. Then, a 4045 alloy brazing filler metal 3 having a thickness of about 100 μm is sandwiched, and the degree of vacuum is 5 × 1.
Bonding was performed by vacuum brazing under the conditions of 0 ^-5 Torr or less, a pressure of 0.002 MPa, a temperature of 600 ° C, and a time of 60 minutes. A small piece was cut out from the obtained joined body and a tensile test was performed. As a result, fracture of the base material occurred at a strength of 100 MPa.

Also, using the same steel 2 and braze 3, the 3003 alloy as the aluminum-based metal 1 was changed to 1050 pure aluminum, the vacuum degree was 10 ⁻⁶ to 10 ⁻⁷ Torr, the pressure was 0.002 MPa, and the temperature was 620 ° C. Vacuum brazing was performed for 60 minutes, and a tensile test was conducted in the same manner. As a result, fracture of the base metal occurred at a strength of 70 MPa.

[0018]

As described above, since the method of joining aluminum or its alloy and the dissimilar metal of the present invention uses brazing, there is little limitation in the range of application depending on the shape, and the degree of freedom of the product shape can be expanded. Moreover, since it is possible to perform inexpensive bonding, it is possible to reduce the product price.
Secondly, despite the use of brazing, the formation of intermetallic compounds at the joint interface can be suppressed, so that the reliability of the joint can be improved. Thirdly, since it is not necessary to overcoat the coating layer with Al, the number of man-hours required for pretreatment up to brazing is small, and from this point also the bonding cost can be reduced. Therefore, the present invention has an industrially significant effect that a highly reliable composite structure can be provided at a lower cost than before.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a joint structure according to the method of the present invention.

[Explanation of symbols]

 1 Aluminum-based metal 2 Steel (dissimilar metal) 3 Wax 4 Coating layer

Claims (1)

[Claims] 1. A method for joining aluminum or its alloy and a dissimilar metal, comprising forming a coating layer made of a nitride or a carbide having a rock salt type structure on the joint surface of the dissimilar metals, and interposing the coating layer therebetween. A method of joining aluminum or an alloy thereof and a dissimilar metal, which comprises joining aluminum or an alloy thereof and a dissimilar metal with a brazing material containing aluminum as a main component which can be joined at 620 ° C. or lower.