JPH09323116A - Method for producing aluminum pipe material whose inner surface is coated with a zinc layer - Google Patents

Abstract

(57) An object of the present invention is to provide a method for manufacturing an aluminum pipe material having an inner surface coated with a Zn layer, which is excellent in corrosion resistance. SOLUTION: In a method for producing an aluminum pipe material in which an aluminum billet having a zinc layer sprayed on its inner surface is heated to a predetermined temperature to be hot extruded, and then cold drawn, the heating at the time of hot extrusion is carried out under an inert gas atmosphere. Do in [Effect] The Zn coating layer does not oxidize and is not cracked, so that an aluminum tube having an excellent corrosion resistance in which the entire inner surface is coated with the Zn layer can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an aluminum pipe material having an inner surface coated with a zinc layer, which is used for a refrigerant passage tube of a heat exchanger for an automobile.

[0002]

2. Description of the Related Art Conventionally, aluminum tubes have been used as refrigerant passage tubes for heat exchangers of automobile radiators. And this tube is required to be thin as a part of the weight reduction of the vehicle. However, aluminum generally has a problem that pitting corrosion easily occurs in a corrosive environment, and when the pitting corrosion penetrates the aluminum tube, the function as a refrigerant passage is lost. For this reason, the aluminum tube is coated with an electrochemically base Al-Zn alloy layer or Zn layer on the inner surface, and these coating layers are preferentially corroded to suppress the progress of pitting corrosion of the aluminum tube. Has been taken. By the way, for example, the production of an aluminum pipe material whose inner surface is coated with a Zn layer is
By forming a layered Al-Zn alloy or Zn on the inner surface of a cylindrical aluminum alloy billet, hot extruding this billet (tubular material), and repeatedly extruding and annealing this extruded raw tube to reduce the diameter and thickness. It is being appreciated. As a method for forming a layer of Zn or the like, there are a thermal spraying method, a chemical plating method, a clad (pressure welding) method, and the like, but the thermal spraying method has an advantage that it can be formed at low cost.

[0003]

However, when a billet having a Zn layer sprayed on its inner surface is hot extruded, there is a problem that the Zn coating layer is cracked and the corrosion resistance of the resulting tube is lowered. From this, the present inventors have
The cause of cracking in the Zn coating layer was investigated. as a result,
It was clarified that the Zn coating layer is oxidized by heating during hot extrusion, becomes brittle and cracks during extrusion, and further studies on a method for preventing oxidation of the Zn coating layer at low cost are completed to complete the present invention. I arrived. An object of the present invention is to provide a method for producing an aluminum pipe material having an inner surface coated with a Zn layer, which is excellent in corrosion resistance.

[0004]

According to the first aspect of the present invention,
In a method of manufacturing an aluminum pipe material in which an aluminum billet having a zinc layer sprayed on its inner surface is heated to a predetermined temperature and hot extruded, and then cold drawn, the heating at the time of hot extrusion is performed in an inert gas atmosphere. The method for producing an aluminum pipe material having an inner surface coated with a zinc layer.

According to a second aspect of the present invention, there is provided a method for producing an aluminum pipe material having an inner surface coated with a zinc layer, wherein the intermediate annealing is performed in an inert gas atmosphere during the drawing process. is there.

The invention according to claim 3 is characterized in that the heating at the time of hot extrusion is performed only in the aluminum pipe material coated with the zinc layer in an inert gas atmosphere, and the zinc layer is formed on the inner surface of the aluminum pipe material. It is a method for producing a coated aluminum pipe material.

The invention according to claim 4 is characterized in that the intermediate annealing carried out during the drawing process is carried out only in the aluminum pipe material coated with the zinc layer in an inert gas atmosphere, and the zinc is applied to the inner surface of the invention. It is a method for producing a layered aluminum pipe material.

[0008]

According to the first aspect of the present invention, since the heating during the hot extrusion of the aluminum pipe material having the Zn layer coated on the inner surface is performed in an inert gas atmosphere, the Zn coating layer is oxidized or embrittled. Without damp, it diffuses and adheres firmly to the inner surface of the aluminum pipe material. Therefore, the Zn coating layer is not cracked during hot extrusion or drawing. The effect of performing the heating at the time of hot extrusion in an inert gas atmosphere is particularly remarkable when pure Zn, which is easily oxidized, is sprayed.

According to the second aspect of the present invention, in addition to heating during hot extrusion, annealing during cold drawing is also performed in an inert gas atmosphere. The inner surface of the blank tube after extrusion of an aluminum tube material having a Zn layer sprayed on the inner surface generally has a high Zn concentration. Therefore, as in the present invention, if the annealing performed during the cold drawing is performed in an inert gas atmosphere to prevent the diffusion layer of Al and Zn from being oxidized, the cracking of the Zn coating layer becomes more difficult to occur. Even when the blank tube after hot extrusion is annealed before drawing, it is desirable to perform it in an inert gas atmosphere.

In the invention according to claim 3 or 4, since the inert gas atmosphere is provided only in the aluminum pipe material, the amount of the inert gas is smaller than that in the case where the entire furnace is provided with the inert gas atmosphere. Target. In addition, the inert gas atmosphere can be set in a short time. In order to replace the inside of the aluminum pipe material with an inert gas, an aluminum disc having a nozzle is fitted into the opening of the aluminum pipe material, and an inert gas is passed through the aluminum pipe material through the nozzle. The method is simple. When heat treatment is performed while flowing an inert gas, the degree of sealing with the aluminum plate does not need to be so high.

In the present invention, the Zn layer sprayed on the inner surface of the aluminum pipe material does not have to be a pure Zn layer, but Al-
Similar effects can be obtained even with Zn-based alloys such as Zn-based alloys. Nitrogen gas or argon gas, which is easily available, is suitable as the inert gas.

[0012]

EXAMPLES The present invention will be specifically described below with reference to examples. (Example 1) A cylindrical billet made of JIS-1050 alloy (outer diameter 20
A thermal spray gun was set inside (0 mm, inner diameter 60 mm) to spray Zn on the inner surface of the billet. The amount of thermal spray was 20 g / m ² . The billet (tubular material A) after thermal spraying is put in a furnace in a nitrogen gas atmosphere for 500
After heating to ℃, it was processed into a pipe material B having an outer diameter of 70 mm and a wall thickness of 6 mm by hot extrusion. This pipe material B was heated to 350 ° C. in a nitrogen gas atmosphere furnace and cooled. Next, this was repeatedly subjected to cold drawing and annealing in the atmosphere to manufacture a tube having an outer diameter of 10 mm and a wall thickness of 0.5 mm.

(Example 2) A tube was manufactured by the same method as in Example 1 except that the annealing during cold drawing of the pipe material B was performed in a nitrogen gas atmosphere.

(Example 3) In Example 1, the pipe material A,
The heating of B was carried out by fitting JIS-1050 alloy discs with nozzles attached to both open ends of the cylindrical billet, replacing the air in the pipe material with nitrogen gas through the nozzles, and then The heating was performed in a furnace in the air atmosphere. A tube was manufactured by the same method as in Example 1 except for the above.

Example 4 A tube was manufactured by the same method as in Example 3 except that the tube material B before cold drawing was not heated in Example 3.

(Comparative Example 1) In the same manner as in Example 1, except that the heating of the pipe A before hot extrusion and the heating of the pipe B before cold drawing were carried out in the atmosphere. The tube was manufactured.

The coating state of the Zn layer was observed for each of the obtained tubes. Further, this tube was cut into a length of 100 mm to prepare a sample, and this sample was immersed in a corrosive solution containing NaCl and Na ₂ SO ₄ for one month to test the corrosion resistance. The corrosion resistance was measured by splitting the sample after the test vertically, forming a flat plate, removing the corrosion product, and measuring the depth of pitting corrosion generated on the inner surface of the tube. The results are shown in Table 1.

[0018]

[Table 1] (Note) * Zn layer is entirely covered. × Zn layer is cracked and the tube is exposed.

As is clear from Table 1, the products of the present invention (N
Nos. 1 to 4) had a Zn layer coated on the entire surface, and the pitting depth after the immersion test was shallow, indicating excellent corrosion resistance. Especially in No. 2, since the annealing during the drawing process was also performed in an inert gas atmosphere, the diffusion layer was not oxidized at all and the pitting depth was the shallowest. No.
As for 3 and 4, since only the inside of the pipe material was replaced with nitrogen gas, the replacement of nitrogen gas was completed in a short time and the productivity was high, and the amount of nitrogen gas used was small. On the other hand, in No. 5 of the comparative example, the Zn layer was cracked because it was heated or annealed in the air, and the Al tube was partially exposed. Therefore, pitting corrosion occurred.

[0020]

As described above, in the present invention, the heat treatment or annealing of the aluminum pipe material having the Zn layer sprayed on the inner surface is performed in the inert gas atmosphere, so that the Zn coating layer is oxidized and hot extruded. Does not break at times. Therefore, it is possible to obtain an aluminum tube having an excellent corrosion resistance in which the entire inner surface is covered with a Zn layer. Further, by replacing only the inside of the pipe material with the inert gas, the amount of the inert gas used can be reduced, which is economical, and the replacement of the inert gas can be done in a short time, which is excellent in productivity. Therefore, a remarkable effect is industrially exhibited.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location F28F 19/06 F28F 19/06 B (72) Inventor Dokiko Takeyoshi 2 Marunouchi, Chiyoda-ku, Tokyo 6-1 Furukawa Electric Co., Ltd. (72) Inventor Akio Niikura 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (4)

[Claims] 1. A method for manufacturing an aluminum pipe material, comprising heating an aluminum billet having a zinc layer sprayed on its inner surface to a predetermined temperature to perform hot extrusion, and then performing cold drawing, wherein heating during the hot extrusion is performed with an inert gas. A method for producing an aluminum pipe material, the inner surface of which is coated with a zinc layer, which is performed in an atmosphere. 2. The method for producing an aluminum pipe material having an inner surface coated with a zinc layer according to claim 1, characterized in that the intermediate annealing performed during the drawing is performed in an inert gas atmosphere. 3. The production of an aluminum pipe material coated with a zinc layer on the inner surface according to claim 1, wherein heating during hot extrusion is performed only in the aluminum pipe material coated with the zinc layer in an inert gas atmosphere. Method. 4. The aluminum pipe material coated with a zinc layer on the inner surface according to claim 2, wherein the intermediate annealing performed during the drawing is performed only in the aluminum pipe material coated with the zinc layer in an inert gas atmosphere. Manufacturing method.