JPH1062095A - Zn coated aluminum tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Zn-coated aluminum tube which is excellent in pitting corrosion resistance and hardly peels off fins and is suitable for a heat exchanger or the like. In Zn coated aluminum tubes using A fin brazed, the a fin brazed are Zn coating amount V ₁ is 25g~35g per 1 m ² of the surface of the Zn coated aluminum tube, the other surface Zn coverage V ₂
Is ⁷ g to 25 g per 1 m ² , and V ₁ and V ₂
A relational expression of (V ₁ −V ₂ ) ≧ 5 g is established. [Effect] Since the Zn coating amount is defined separately for the surface to which the fin is brazed and the other surface, a sufficient sacrificial effect is provided, and the progress of pitting is delayed, so that the pitting resistance is improved. Excellent and hard to peel off fins.

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.
The high-temperature refrigerant that has absorbed heat is sent to the space on the other tank side through the inside, and the low-temperature refrigerant that has exchanged heat and radiated heat at the aluminum tube 11 and the fins 20 is circulated again. recent years,
To reduce the weight of each member of the automotive heat exchanger,
Aluminum is used, and the thickness is being reduced. However, aluminum is generally susceptible to pitting corrosion in a corrosive environment, and naturally there is a problem in that the function of the heat exchanger is lost when the pitting penetrates. For this reason, an aluminum tube is coated with a Zn layer,
A method has been adopted in which the layer is preferentially corroded. The fin is made of a material (sacrifice material) having a lower potential than the aluminum tube material, and the fin is preferentially corroded in addition to the Zn layer. The Zn-coated aluminum tube is formed by forming a composite plate obtained by cladding an aluminum plate and a Zn plate into a cylindrical shape and welding the ends of the cylindrical body by an electric resistance welding method, or by adding Zn to an aluminum tube (extruded multi-hole tube). It is manufactured by a method of thermal spraying. Wherein in the spraying method, it was uniformly coated with Zn around 15g per 1 m ² on the tube over the entire surface.

[0003]

However, the fin brazed aluminum tube sprayed with Zn is as follows.
There was a problem that the fins peeled off during use.
The present inventors have studied various countermeasures and found that peeling of the fins can be improved by coating a large amount of Zn on the surface to which the fins are brazed, and further research has been carried out to complete the present invention. It has arrived. An object of the present invention is to provide a Zn-coated aluminum tube which is excellent in pitting resistance and hardly peels off fins.

[0004]

SUMMARY OF THE INVENTION The present invention provides a method for brazing fins.
In the Zn-coated aluminum tube used by attaching,
Of the surface to which the fins of the Zn-coated aluminum tube are brazed
Zn coverage V₁Is 1m ^Two25g to 35g per
Zn coverage V on other surfaces_TwoIs 1m^Two7g to 25g per
And V₁And V_TwoBetween (V₁-V_Two) ≧ 5g
A Zn-coated aluminum tube characterized by satisfying a relational expression
It is.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described 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. A fin (brazing sheet) 20 is brazed to a flat portion 12 of an aluminum tube (flat multi-hole tube) 10 coated with Zn, and a Zn coating amount V ₁ of the flat portion 12 to which the fin 20 is brazed is 1 m. 25g-35 per ²
g, Zn coverage V _{2 on the} other surface (curved portion) 13 is 1 m ²
7 g to 25 g per unit, and (V ₁ -V ₂ ) is 5 g or more.

In the present invention, the reason why the Zn coating amount V ₁ on the surface of the Zn-coated aluminum tube to which the fins are brazed (the flat portion in FIG. 1) is defined as 25 g to 35 g per ₁ m ² is as follows.
If the weight is less than 25 g, the fins are liable to peel off. The cause of this easy peeling is that, at the time of brazing heating, the Zn in the fin brazed portion diffuses into the fillet portion (the deposited portion of the brazing where the tube and the fin come into contact), and the Z near the fillet portion is reduced.
This is because n is insufficient, and as a result, a large number of pits occur near the fillet portion of the tube. On the other hand, if the Zn coating amount exceeds 35 g, the potential of the tube becomes too low, and the progress of pitting is accelerated. In particular, at a location away from the fillet portion, the diffusion amount of Zn into the fillet portion is small, so that the effect of exceeding the upper limit is likely to occur.

The Z of the surface (curved portion) where the fin is not brazed
The reason for defining the n coating amount to be 7 g to 25 g per 1 m ² is as follows.
If the amount is less than 7 g, the sacrificial corrosion effect of the coated Zn cannot be sufficiently obtained, and if the amount exceeds 25 g, the potential of the tube becomes too low and the progress of pitting corrosion is accelerated. Where Zn
The reason why the upper limit of the coating amount is large on the surface where the fins are brazed and is small on the surface where the fins are not brazed is that diffusion of Zn into the fillet portion is expected on the surface where the fins are brazed.

In the present invention, the difference between the Zn coating amount V ₁ on the surface to which the fin is brazed and the Zn coating amount V ₂ on the other surface is specified to be 5 g or more because the difference in the coating amount is 5 g or more.
If it is less than g, the corrosion rate of the surface on which the fin is not brazed is
This is because the corrosion rate exceeds the corrosion rate of the surface on which the fins are brazed, and pitting corrosion occurs early on the surface on which the fins are not brazed.

In the present invention, JI is used for the aluminum tube.
S-1000 type aluminum or aluminum alloy with relatively low alloy concentration is mainly applied. The cross-sectional shape of the aluminum tube is arbitrary such as circular, elliptical, and flat. As the fin, a brazing sheet or the like in which a brazing material is combined on one surface of a core material is applied. As the Zn to be coated on the aluminum tube, a Zn alloy such as a Zn-Al alloy is mainly applied in addition to pure Zn.

In the present invention, a method for coating Zn on the surface on which the fins are to be brazed thickly and on the other surfaces thinly will be described with reference to FIGS. The method shown in FIG.
An aluminum tube 10 is placed between two opposed spraying guns 30,
This is a method of arranging and spraying such that the plane portion 12 is perpendicular to the spraying direction. The method shown in FIG. 2B is a method in which the thermal spraying gun is divided into a flat portion thermal spraying gun 31 and a curved portion thermal spraying gun 32 to perform thermal spraying. With this method, the amount of Zn coating on the plane portion 12 and the curved portion 13 can be controlled with high accuracy.

[0011]

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. This aluminum tube is coated with Zn by the thermal spraying method shown in FIG.
Was sprayed to produce a Zn-coated aluminum tube. The Zn coating amount of the flat part (fin brazing surface) and the curved part (fin brazing surface) of the aluminum tube was changed variously. The obtained Zn-coated aluminum tube was cut into a length of 60 mm, and fins 20 were brazed between the cut aluminum tubes 10 to assemble a mini core (see FIG. 3). As the fin 20, a corrugated brazing sheet in which a JIS-4045 alloy plate (brazing material) having a low potential was attached to a JIS-7072 alloy plate (core material) was used. Next, a CASS test was performed on the minicore. The CASS test was performed with NaCl and CuCl ₂ H
_The corrosion liquid containing ₂ O was sprayed 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. The state of peeling of the fin was also examined. Table 1 shows the results.

[0012]

[Table 1]

As is clear from Table 1, the examples of the present invention (No. 1)
In Nos. To 5), the fins did not peel off, and the pit depth was shallow in both the flat part and the curved part. On the other hand, in Comparative Example No. 6, since the Zn coverage in the plane portion was small, Zn near the fillet portion diffused into the fillet portion, so that the sacrificial corrosion effect of Zn was not obtained, and a large number of pitting corrosion near the fillet portion occurred. This caused the fins to peel off more places. In No. 7, the progress of pitting in the flat portion was accelerated due to the large amount of Zn coating in the flat portion, and deep pitting occurred in the flat portion. In Nos. 8 and 9, since the amount of Zn coating in the curved portion was large, the progress of pitting corrosion in the curved portion was accelerated, and deep pitting occurred in the curved portion. In No. 10, the sacrificial corrosion effect was not sufficient because the Zn coverage of the curved portion was small, and deep pitting occurred in the curved portion. In No. 11, the corrosion rate of the curved portion exceeded the corrosion rate of the flat portion because the difference in the amount of Zn deposition between the flat portion and the curved portion was less than 5 g / m ² , and deep pitting occurred in the curved portion.

The case where Zn is coated on the flat multi-hole tube has been described above. However, the present invention can be applied to an aluminum tube of another shape or a similar effect can be obtained by spraying a Zn alloy. It is.

[0015]

As described above, in the Zn-coated aluminum tube of the present invention, the Zn coating amount is specified separately for the surface on which the fins are to be brazed and the other surface, so that a sufficient sacrificial effect is obtained. The fins have a longer pitting corrosion resistance, and have excellent pitting corrosion resistance and are unlikely to peel off the fins. Therefore, when applied to an aluminum heat exchanger or the like, its reliability is improved, and an industrially significant effect is achieved.

[Brief description of 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.

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 perspective view of a CASS test mini-core.

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 Curved portion of aluminum tube (flat multi-hole tube) 20 Fin 30,31,32 Thermal spray gun 40 Header 50 Tank

Claims (1)

[Claims] 1. A Zn-coated aluminum tube used by brazing fins, wherein the Zn-coated amount V _{1 of the} surface of the Zn-coated aluminum tube to which the fins are brazed is 25 g to 35 g per ₁ m ² , Zn coverage V _{2 on the} surface
Is ⁷ g to 25 g per 1 m ² , and V ₁ and V ₂
A relational expression of (V ₁ −V ₂ ) ≧ 5 g is satisfied between the _two .