JPH11254127A - Method for brazing copper and aluminum - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of brazing Cu and Al to obtain a member having both the lightweight property of Al and the excellent heat conductivity and electric conductivity of Cu. SOLUTION: In a method of brazing Cu 1 and Al 2, the composite coating of Al 8 is applied on a base material of Cu 1 with Ni 5 as an intermediate material and Al 8 as a skin, and the brazing is achieved using an Al-Si brazing filler metal 6 with Al as joining surfaces with each other. At least one kind among Fe, Co, Ta, Mo, Nb, W, Ti, Zr, Hf and an alloy thereof can be used in place of Ni 5 for the intermediate material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the brazing of Cu and Al to obtain a member having both the light weight and excellent thermal properties of Al, the excellent thermal conductivity, electric conductivity, solderability and the like of Cu. About the method.

[0002]

2. Description of the Related Art Soldering of Cu and Al,
The brazing method has been used for a long time, but as a conventional example, 1) soldering using Sn-Pb, Sn-Zn solder or the like. 2) High melting point solder of Zn-5% Al (MP: 382)
℃) and solder with flux. 3) Soldering by fluxless method such as a friction method or an ultrasonic method using the Zn-Al solder. 4) Using an Al-Si brazing material or an Ag-Al brazing material, brazing with a fluoride or a flux composed of a fluoride and a chloride. 5) Using an Al-Si brazing material or an Ag-Al brazing material,
Fluxless brazing in vacuum etc. There are several ways and so on. However, there are still many problems and their practical use is refused. For example, in the case of Conventional Example 1 described above, the bonding strength is low,
In addition, poor corrosion resistance is a major bottleneck. In the cases 2) and 3), there is no problem in joining Al, but in the case of Cu-Al heterogeneous joining, Cu
A compound layer of -Zn is generated, and the bonding portion becomes brittle, which is not suitable for practical use. In the cases of 4) and 5), Al has very good brazing properties, excellent strength and corrosion resistance, and has already been put to practical use in various brazings including heat exchangers. However, in the case of joining Cu and Al, Cu-
An Al compound CuAl ₂ (θ phase) is generated, and the bonding strength is low, and a practically usable strength cannot be expected. Cu and Al
Produces a eutectic (548 ° C.) having a low melting point, and because of the remarkable diffusion of Cu and Al, defects such as easy melting and penetration of the base material occur. Therefore, even at present, the problem of Cu-Al bonding has not been solved yet, and the present situation is that practical application is hampered. Therefore, the main feature of the present invention is a brazing method for obtaining a high bonding strength that can be put to practical use in a brazing method of Cu and Al.

[0002]

As shown in FIG. 2A, when Cu and Al are overlaid and heated in a non-oxidizing atmosphere as shown in FIG. 2A, the contact portion between Cu and Al starts melting at 548 ° C. This is because a eutectic is generated by the diffusion phenomenon, and the eutectic composition is Al-33% Cu. At the same time, diffusion and melting of the molten metal into the base material are accelerated, and after solidification, the eutectic and the Cu side are eroded as shown in FIG. 2B, and an intermetallic compound CuAl ₂ (θ phase) is generated at the interface at the same time as the Al side. Also significant erosion takes place. This has been a major factor that hinders brazing of Cu and Al. Therefore, in the present invention, a structure that avoids a direct reaction between Cu and Al based on the fact that a low melting point eutectic of Cu-Al is not formed, and that a harmful compound of Cu and Al is not formed at the joint. We invented and devised a method and solved it. First, as a means for avoiding a direct reaction between Cu and Al, Ni was used as an intermediate material on the Cu side, and the Cu was coated by a cladding method. FIG. 3A is a schematic diagram showing the case where Cu is Ni
To avoid direct contact with Al. FIG. 3B shows a cross section obtained by brazing the above sample using Al-12% Si, and the above-described problem of FIG. 2 was cleared.
It was found that a compound phase of NiAl ₃ was formed at the interface on the i side, which was brittle, and that the joining strength was not significantly improved.

In the present invention, the problem was solved by further coating pure Ni on the Ni coating layer.
The coating method at this time was performed by a cladding method. FIG. 1A shows an example of the structure of the coating layer in which a Ni coating layer is provided on a Cu base material, and an Al coating layer is further provided thereon. As a result, the bonding surface is completely in surface contact between Al and not Al and Cu. FIG. 1B is a cross-section of the case where they are joined with an Al-12% Si brazing material.
The base metals Al are brazed with Al-12% Si. The brazing temperature at this time is desirably 640 ° C. or less at which the Al skin coating layer is not dissolved. Thereby, a compound of Cu-Al which has conventionally been a problem,
The formation of the Ni-Al compound was completely prevented, and high bonding strength was obtained.

[0004]

The effect of the composite coating of Ni and Al on the Cu side is Ni
Is an intermediate material for avoiding a direct contact reaction between Cu and Al.
-It has the effect of changing to the same type of bonding of Al
The brazing method using the Al-Si brazing material for the brazing material eliminates any problem.

[0005]

Example 1 99.9% for base material of 3 mmt plate of oxygen-free copper
Of Ni and 99.99% of Al were subjected to composite coating on one surface by hot and cold rolling methods. In the sample shape used in this experiment, the overall plate thickness was 1.0 mmt, the thickness of the intermediate material Ni to Cu was 20 μm, and the Al as the skin material was 1
It was 00 μm.

FIG. 1A Next, the same sample was actually brazed with pure Al. The test piece was prepared by laminating a coated Cu plate A having a width of 10 mm, a length of 50 mm, and a thickness of 1.0 mmt on a pure Al plate B by about 4 mm, and then placing an Al-12% Si brazing material thereon, and applying a nitrogen gas at 600 ° C. It was heated in an atmosphere and brazed.

FIG. 1B: The flux used at this time was AlF ₃ -KF-
The LiF-based or _AlF 3 -KF-NaF system consisting fluoride is mainly formed. Next, the strength of the test piece prepared by the above method was measured by a tensile tester.
It was found that the base material of the 1-plate B was broken, and the joining strength was very high. In addition to the Al-Si binary system as a brazing material, Cu, Zn, Ag, Ni, Sn, I
The same effect can be obtained by using a brazing material containing a small amount of n, Bi, or the like.

[0006]

Example 2 Next, the effect when the thickness of Al of the skin material coated with Cu was set to 5 μm was examined. (Other conditions are based on Example 1.)
It was broken at 5 kgf (corresponding to 2.3 kgf / mm ² ), and the broken portion was the joint. As a result of conducting microscopic observation of the fracture surface and examining it in detail, Al of the skin material was diffused and eroded by the Al-12% Si brazing material and completely disappeared, and thus bonding with Ni of the intermediate material was performed. As a result, a compound of NiAl ₃ is generated at the interface,
It was found that destruction was also performed in this alloy layer. Therefore, in the present invention, it is important not to dissolve Al of the skin material, and the skin thickness is preferably 50 μm or more. Although the Al skin material is made of pure Al in Examples 1 and 2,
An Al alloy such as Al-Mn has a similar effect.

[0007]

Example 3 Next, a test was performed by changing the intermediate material for avoiding a direct reaction between Cu and Al from Ni of Examples 1 and 2 to Fe. (Other conditions are in accordance with Example 1.) As a result, the reaction between Cu and Al does not occur even in Fe,
An effect similar to that of Ni was observed. Similar effects can be obtained by using Co, Ta, Mo, Nb, W, Ti, Zr, Hf and their alloys, Ni-based alloys, Fe-based alloys, etc. in addition to Ni and Fe. Although the present invention is applied to the coating of the intermediate material and the skin material by the cladding method, a similar effect can be obtained by a well-known coating method such as a dipping method, electroplating, chemical plating, vapor deposition, and spraying method, in addition to the cladding method.

[0008]

Embodiment 4 In the present invention, a flux is required in each case, and a conventional chloride-fluoride flux can be used. However, it is necessary to wash with water and remove flux residues after brazing. According to the fluoride flux used in the above, there is no fear of corrosion even without cleaning.

[0009]

[Effect] In the brazing method of Cu and Al, Cu
Side, Ni, Al or Cu side, Ni, Al, Al-Si
Is changed from a dissimilar joint form of Cu and Al to a joint form of the same kind of Al by coating a composite or multilayer. As a result, the conventional Al brazing technique can be applied as it is, and the connection of Cu-Al pipes and the manufacture of a heat exchanger, which have been impossible until now, can be realized.

[Brief description of the drawings]

FIG. 1 is a side view showing an embodiment of the present invention.

FIG. 2: Side view showing a conventional example

FIG. 3 is a side view showing another conventional example.

[Description of Signs] Cu base material Ni layer (intermediate material) Al base material Al-Si brazing material Al-Cu eutectic NiAl ₃ intermetallic compound CuAl ₂ intermetallic compound Al layer (skin material)

Claims (5)

[Claims] In a method of brazing Cu or a Cu alloy and Al or an Al alloy, an N.sub.
i or Ni alloy, a composite coating of Al or Al alloy as a skin material is applied, the joining surfaces are made to be Al, Al-Si
A brazing method using a brazing filler metal. 2. The brazing method according to claim 1, wherein the brazing is performed without eroding Al of the skin material. 3. The method according to claim 1, wherein the intermediate material is Fe, Co, T instead of Ni.
3. The method according to claim 1, wherein at least one of a, Mo, Nb, W, Ti, Zr, Hf and an alloy thereof is used.
The brazing method described in 1. 4. A brazing method according to claim 1, wherein said composite coated surface is further coated with an Al-Si-based brazing material as a skin material, and brazing is performed using said brazing material. 5. The brazing method according to claim 1, wherein brazing is performed using a chloride-based, fluoride-based or mixed flux thereof.