JPH09217996A - Aluminum tube with zinc coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum tube capable of preventing a peeling off of fins and having an excellent pitting corrosion resistance. SOLUTION: A zinc coated aluminum tube 10 has a zinc coating amounting to less than 7g/m<2> at portions where fins 20 are brazed and not less than 7g/m<2> and not more than 25g/m<2> at remaining portions other than the brazed portions 20. In this manner, since the portions of the aluminum tube 10 where the fins 20 are brazed are provided with a small amount of zinc coating, brazing filler metal becomes a base material as a result of diffusion of a large amount of zinc and corrodes preferentially so that a peeling off of the fins 20 can be prevented. Namely, a small amount of zinc coating is compensated by the preferential corrosion effect of the fins. Since the remaining portions of the aluminum tube 10 where fins are not brazed have a large amount of zinc coating, pitting corrosion does not occur on these portions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Zn-coated aluminum tube used by brazing fins suitable for a heat exchanger for automobiles and the like.

[0002]

2. Description of the Related Art As shown in FIG. 4, for example, a heat exchanger of a radiator for an automobile is a thin fin formed in a corrugated shape between a plurality of aluminum tubes (flat multi-hole tubes) 11.
20 are integrally formed, and both ends of the aluminum tube 11 are respectively opened to spaces formed by the header 40 and the tank 50.
A high-temperature refrigerant is sent through the inside to the space on the other tank side, and the refrigerant having a low temperature due to heat exchange between the aluminum tubes 11 and the fins 20 is circulated again. In recent years, aluminum has been used for each member of the heat exchanger for automobiles in order to reduce the weight, and the thickness has been reduced. However, aluminum is generally susceptible to pitting corrosion in a corrosive environment, and if the pitting corrosion penetrates, the function of the heat exchanger is lost. Therefore, the Zn layer is coated on the aluminum tube,
A method of preferentially corroding the n-layer is adopted. Further, a material (sacrificial material) whose electric potential is lower than that of the aluminum tube material is used for the fin so that the fin is preferentially corroded in addition to the Zn layer. The Zn-coated aluminum tube is manufactured by a method in which an aluminum plate and a clad plate of a Zn plate are electrosewn into the tube, or a method in which Zn is sprayed on the aluminum tube.

[0003]

However, the aluminum tube in which the fins are brazed to the Zn-coated aluminum tube has a problem that the fins peel off during use.
The present inventors investigated the cause of the peeling of the fins, and when the Zn coating amount was large, a large amount of Zn diffused into the brazing material during brazing, and the potential of the brazing material became base, and the brazing material took precedence. It has been found that it is due to corrosion. Then, they found that the fin can be prevented from peeling off by reducing the coating amount of Zn, and further research was conducted to complete the present invention. An object of the present invention is to provide a Zn-coated aluminum tube in which fins do not peel off and which is excellent in pitting corrosion resistance.

[0004]

SUMMARY OF THE INVENTION The present invention provides a method for brazing fins.
In the Zn-coated aluminum tube used by attaching,
Zn at the brazing point of the fin of the Zn-coated aluminum tube
Coverage is 7g / m^TwoLess than the fin brazing point
Zn coating amount at the location is 7 g / m^TwoAbove, 25g / m ^TwoBelow
It is a Zn-coated aluminum tube characterized by the above.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a place where the Zn coating amount of an aluminum tube is less than 7 g / m ² is a place where a preferential corrosion effect by a brazed fin is exerted. In the present invention, the Zn coating amount at the fin brazing location is 7 g /
The reason for limiting to less than m ² is that the Zn coating amount is 7 g / m 2.
^When it is ² or more, Zn is diffused in a large amount into the brazing filler metal of the fin when the fin is brazed, the brazing filler metal becomes base, and as a result, the brazing filler metal is preferentially corroded and the fin is peeled off. If the Zn coating amount at the location where the fins are brazed is less than 3 g / m ² , local pitting corrosion will occur, so 3 g / m ² or more is desirable. Also the Zn coverage of locations other than locations brazing the fins 7 g / m ² or more, the reason for limiting to 25 g / m ² or less, is less than 7 g / m ² pitting progresses, greater than 25 g / m ² This is because the pitting corrosion prevention effect is saturated, and Zn in this portion diffuses to the brazing portion of the fin and causes the fin to peel off. In addition, at the brazing point of the fin, Z
The reason why pitting corrosion does not proceed even when the coating amount of n is less than 7 g / m ² is that the preferential corrosion effect of the fin is added to the brazing portion of the fin.

In the present invention, JI is used for the aluminum tube.
S-1000 series aluminum, or aluminum alloy having a relatively low alloy concentration is applied. The cross-sectional shape of the aluminum tube is arbitrary such as circular, elliptical, and flat. For the fins, a brazing sheet in which a brazing material is compounded on one side of a core material, a brazing sheet in which a brazing material is compounded on one side of a core material, or a sacrificial material is compounded on the other surface is applied. For Zn coated on the aluminum tube, in addition to pure Zn, any Zn-containing alloy such as Al-Zn alloy is applied.

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a perspective view showing an example of a state in which fins are brazed to a Zn-coated aluminum tube of the present invention. Zn
Flat part of aluminum tube (flat multi-hole tube) 10 coated with
A fin (brazing sheet) 20 is brazed to the fin 12, the flat portion 12 brazed with the fin 20 has a Zn coating amount of less than 7 g / m ² , and the bent portion 13 to which the fin 20 is not joined
Zn coating amount is 7 g / m ² or more.

A method of coating Zn on the bent portion of the aluminum tube thickly and on the flat portion thereof thinly will be described below with reference to FIGS. The method shown in FIG. 2A is a method of spraying by arranging the aluminum tube 10 between two facing spray guns 30 so that the plane portion 12 thereof is parallel to the spray direction. In the method shown in FIG. 2B, there is a method of arranging the flat surface portion 12 so as to be oblique to the thermal spraying direction and performing thermal spraying. With these methods, a plurality of aluminum tubes 10 can be simultaneously sprayed with Zn, and high productivity can be obtained. The method shown in FIG. 2C is a method of individually controlling the spray amount by dividing the spray gun 31 that sprays onto the flat surface portion 12 of the aluminum tube 10 and the spray gun 32 that sprays onto the curved portion 13. With this method, the amount of Zn coating on the plane portion 12 and the curved portion 13 can be controlled with high accuracy.

[0009]

Next, the present invention will be described in detail with reference to examples.
Extruded JIS-1100 alloy, thickness 2mm, width 15mm, thickness
A 0.4mm aluminum tube (flat multi-hole tube) was manufactured. Zn was applied to this aluminum tube by the thermal spraying method shown in FIG.
Was sprayed to produce a Zn-coated aluminum tube. The coating amount of Zn on the flat surface portion and the curved portion of the aluminum tube was variously changed. The obtained Zn-coated aluminum tube was cut into a length of 60 mm, and fins 20 were brazed between two sheets of this aluminum tube 10 to assemble a mini-core, as shown in FIG. For the fins 20, JIS-40, which has a base of JIS-7072 alloy plate (core material)
A corrugated brazing sheet in which 45 alloy plates (brazing material) were laminated was used. Next, about this mini core, N
A CASS test was conducted by spraying a corrosive liquid containing aCl and CuCl ₂ .H ₂ O for 720 hours. After the test was completed, corrosion products attached to the surface of the minicore were removed, and then the depth of pitting generated in the aluminum tube was measured. Also, the presence or absence of peeling of the fin was examined. The results are shown in Table 1.

[0010]

[Table 1]

As is clear from Table 1, the products of the present invention (N
In o.1 to 5), the fin did not peel off, and the depth of pitting was shallow in both the flat and curved portions. In contrast,
In Comparative Example No. 6, fins were peeled off at many places. This is because the Zn layer in the flat portion was thick, and during brazing, a large amount of Zn diffused into the brazing filler metal of the fin, the brazing filler metal became base, and preferential corrosion occurred. In No. 7, since the amount of Zn in the bent portion was small, deep pitting occurred in the bent portion. No. 8 had a large amount of Zn coating in the curved portion, and Zn in the curved portion diffused to the flat surface portion, so the fin was partially peeled off.

Although the flat multi-hole tube has been described above, the present invention can be applied to aluminum tubes having other shapes to obtain the same effect.

[0013]

As described above, the Zn-coated aluminum tube of the present invention does not peel off the fins and is excellent in pitting corrosion resistance. Is improved, and a remarkable effect is industrially achieved.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a state in which fins are brazed to a Zn-coated aluminum tube of the present invention.

FIG. 2 is an explanatory view showing an embodiment of a Zn coating method when manufacturing a Zn-coated aluminum tube of the present invention.

FIG. 3 is a vertical sectional view of a mini core used in an example.

FIG. 4 is a partial cross-sectional perspective view showing an embodiment of a radiator.

[Explanation of symbols]

 10,11 …… Aluminum tube (flat multi-hole tube) 12 ………… Flat part of aluminum tube (flat multi-hole tube) 13 ………… Bent part of aluminum tube (flat multi-hole tube) 20 ………… Fins 30,31,32… Spray gun 40 ………… Header 50 ………… Tank

Claims (1)

[Claims] 1. A Zn-coated aluminum tube used for brazing fins, wherein the Zn-coated aluminum tube has a Zn coating amount of less than 7 g / m ^{2 at} the brazed portion of the fin,
Zn coating amount of the part other than the brazing part of the fin is 7 g /
Zn characterized in that it is not less than m ^{2 and not} more than 25 g / m ^2.
Coated aluminum tube.