JPH0445577B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method of manufacturing an aluminum flat tube for use in a heat exchanger, in which Zn is diffused on the surface of the aluminum flat tube. [Prior Art] An aluminum heat exchanger core has flat tubes and fins as its main components, and is assembled into a vehicle, etc.
It is used in harsh environments. If the flat tube in such a core is corroded and leaks, it will be a fatal defect. For this purpose, clad tubes whose surfaces are coated with Zn have traditionally been used, and this is extremely effective in preventing pitting corrosion and crevice corrosion of aluminum flat tubes. When brazing, the brazing process may be hindered by the Zn layer covering the surface of the flat tube, or
If the Zn content is excessive, there are drawbacks such as the Zn content melting and flowing down during heating during brazing, making the work difficult. The present inventors, instead of providing the above Zn coating layer,
An attempt was made to obtain a heat exchanger free of the above drawbacks by using an extruded aluminum flat tube with a Zn diffusion layer formed on the surface as the core for the heat exchanger. However, obtaining a flat extruded aluminum tube with a uniform Zn permeation layer on its surface requires an extremely large number of steps, and it is difficult to obtain a uniform permeation layer. In other words, conventional methods for forming a Zn permeation layer on the surface of an aluminum material include coating the surface of the aluminum material with Zn by, for example, immersing the aluminum material in a molten Zn bath, and then applying another heating process. A method is known in which the Zn adhering to the aluminum surface is infiltrated into the surface of the aluminum material by heating and holding it in a furnace for a long time, but this method requires a lot of effort and time for the infiltration treatment. Not only is it necessary, but it is also difficult to adjust the thickness of the resulting permeation layer.
Furthermore, when a flat tube in the air is selected as the material to be treated as in the present invention, only the outer surface of the tube is
There were problems such as difficulty in forming a Zn permeation layer. [Problems to be Solved by the Invention] As a result of various studies, the inventors focused on the fact that the surface of aluminum flat tubes immediately after extrusion has no oxide film and is extremely active. When injecting molten Zn onto the surface of extruded aluminum material using a Zn wire near the extrusion port during molding,
It has been found that the molten Zn particles are sprayed onto the heated active surface of the extruded tubing, spread evenly over the active surface, and easily diffuse into the active surface to form a diffused and permeable layer. The present invention has been made based on the above findings. [Means for Solving the Problems] That is, the present invention provides hot or warm extrusion molding of aluminum flat tubes for heat exchangers at a location where the temperature of the aluminum flat tube near the extrusion exit of a molding machine is at least 400°C or higher, After spraying Zn on the surface of the extruded flat tube using the Zn wire spraying method,
By naturally cooling the flat tube,
This is a method for producing an aluminum flat tube cladding material for a heat exchanger, which is characterized by forming a Zn diffusion permeation layer. The method of the present invention will be explained in more detail below. Fig. 1 is a side view illustrating an embodiment of the method of the present invention, Fig. 2 is a front view from the extruded material advancing direction showing an example of the arrangement of thermal spray guns, and Fig. 3 is an enlarged sectional view of the extruded flat tube. , is. The aluminum or aluminum alloy extruded tube material 2 that has been hot or warm extruded by the extruder 1 is conveyed out by the conveyance rollers 3.
Thermal spraying of Zn is performed by a thermal spraying gun 4 arranged between the groups so as to spray perpendicularly to the surface of the extruded material. A plurality of thermal spray guns 4 may be appropriately arranged depending on the shape of the extruded material. Thermal spraying uses a Zn wire, and the tip of the wire is continuously sent into an oxygen-acetylene flame, for example, directed toward the object to be thermally sprayed. This is done by so-called wire thermal spraying. Thermal spraying of high-temperature Zn droplets on the material to be thermally sprayed is as follows:
The temperature of the hot or warm rolled aluminum extruded flat tube near the extrusion exit of the forming machine is at least Zn
It is desirable to carry out the process in a place where the melting temperature of the metal is kept at about 400℃ or higher. If the temperature of the flat tube at the spraying location is too low, subsequent diffusion will be difficult to take place, and excessive Zn will remain on the surface of the object to be thermally sprayed, which is undesirable. The sprayed Zn droplets are violently sprayed onto the surface to be thermally sprayed immediately after extrusion, and spread over the activated surface of the surface to be thermally sprayed immediately after extrusion, and most of them easily diffuse into the surface to be thermally sprayed and become A diffusion layer is formed within the sprayed surface. It is desirable to avoid rapidly cooling the flat tube immediately after extrusion, which is the material to be thermally sprayed with Zn droplets, immediately after thermal spraying. If a Zn-sprayed material is artificially quenched immediately after spraying, the Zn droplets sprayed onto the surface of the material will be prevented from diffusing into the surface of the material being sprayed, resulting in a sufficiently thick layer of diffusion. It becomes difficult to form a permeable layer. Therefore, it is desirable that the Zn-sprayed material be cooled at a slow rate comparable to natural cooling in the air. As described above, the present invention provides Zn on the surface of the extruded flat tube in the vicinity of the extrusion port during hot or warm extrusion molding of the aluminum flat tube.
This method directly forms a well-balanced Zn diffusion layer on an extruded flat tube by thermally spraying Zn droplets using a wire rod, but the thickness of the diffusion layer in the present invention cannot be adjusted. , extrusion speed of flat tube in extruder and Zn supplied to thermal spray gun
This can be easily done by appropriately adjusting the feeding speed of the wire rod. In addition, in the method of the present invention, instead of the thermal spraying method using Zn wire, a so-called powder spraying method using known Zn powder is used to apply Zn powder to the surface of the flat tube immediately after extrusion, as in the present invention. If spraying is used, it is difficult to obtain a flat tube with a sufficiently uniform diffusion and permeation layer formed thereon as in the present invention by only an extrusion molding process. This means that when using the powder spraying method, even if Zn powder is sprayed onto a hot molded product extruded from an extruder,
The Zn powder is simply fused to the surface of the compact and coats it, and even when the Zn powder is sprayed onto the surface of the compact using, for example, an oxygen-acetylene flame, the amount of powder supplied is It is difficult to keep the temperature constant, and with heating for such a short period of time, not all of the sprayed Zn powder on the surface of the compact is necessarily liquefied, and in that case, only the surface of the Zn powder is liquefied. It is fused to the surface of the molded body in a molten state, and most of it only covers the flat tube, and only a part of it diffuses into the surface of the flat tube. Therefore, when the powder method is used, it is difficult to obtain a flat tube material with a sufficient Zn diffusion layer formed through the extrusion process, and the Zn coating layer obtained by extrusion is difficult to obtain. Further, in a heating furnace, the extruded material having
It is necessary to go through a process of diffusing and permeating Zn into the extruded surface through long-term heat treatment. [Example] Next, examples of the present invention are listed. Example 1 As shown in Figures 1 and 2, four automatic thermal spraying machines were installed near the die end of the extruder, and aluminum material A1050 with the composition shown in Table 1 was continuously cast with a pillar diameter of 148 mm x length of 500 mm. Using a flat tube with a cross-sectional shape shown in Fig. 3, which has four channels with a width of 26 mm and a height of 5 mm, a tube thickness of 0.8 mm, and a partition wall thickness of 1.0 mm, the extrusion speed is approximately
Hot extrusion molding was carried out at a rate of 15 m/min, and during extrusion, Zn wire was applied to the surface of the extruded material at a rate of approximately 20 g/m ² at a location where the surface temperature was 550°C under the thermal spraying conditions shown in Table 2. , Zn was continuously sprayed. The obtained extruded flat tube is naturally cooled,
An aluminum flat tube with a Zn diffusion layer was obtained.

【table】

[Table] The extruded flat tube formed in this manner is combined with a corrugated fin formed from a brazing sheet whose core material is coated with brazing material on both sides, and brazed under the conditions shown in Table 3 below. A laminated brazed product was created using this method.

[Table] As a result of measuring the obtained brazed product, it was found that the surface layer of the extruded flat tube had a Zn concentration of 2 to 3% by weight and a Zn diffusion layer with a depth of 70 to 150 μm, with a concentration distribution as shown in Figure 4. Its formation was confirmed by an X-ray microanalyzer. This brazed item is JIS H
As a result of conducting the CASS test for 720 hours as specified in 8661, all the corrosion that occurred was in the form of face corrosion.
No pitting corrosion was observed, indicating that a uniformly adhered Zn diffusion layer was formed. Example 2 Under the same conditions as in Example 1, an aluminum material A1050 continuous casting pillar was extruded into a flat tube. During extrusion molding, the surface temperature of the extruded product is about 450℃,
Using Zn wire with a diameter of 1.6 mm, arc spraying method (two
A Zn coating layer of about 10 g/m ² is applied to the surface of the molded body using a method in which Zn wires are brought together at their tips, and a current is applied to melt the tips while blowing molten droplets onto the sprayed surface using compressed air. In addition to forming
It was allowed to cool naturally without using a cooling fan. As a result of measuring the Zn concentration distribution of this sample using an X-ray microanalyzer on a cross section of the surface layer, it was confirmed that a diffusion layer of 10 to 20 μm was formed in the thickness direction, indicating that the Zn diffusion layer was evenly formed during extrusion. Rukoto has been shown. [Effects of the Invention] As described above, the method of the present invention makes it possible to easily and reliably form a uniform diffusion layer of Zn with an arbitrary thickness on the surface of the molded material at the same time when extruding a flat tube. This invention has the excellent effect of being able to.

[Brief explanation of the drawing]

FIG. 1 is a side view of an embodiment of the method of the invention;
The figure is a front view from the extruded material advancing direction showing an example of the arrangement of thermal spray guns, and Figure 3 is an enlarged cross-sectional view of the extruded flat tube.
FIG. 4 is a drawing showing the state of Zn diffusion into the surface layer of the aluminum material. 1... Extruder, 2... Extruded material, 3... Conveyance roller, 4... Thermal spray gun.

Claims (1)

[Claims] 1. In hot or warm extrusion molding of aluminum flat tubes for heat exchangers, in areas where the temperature of the aluminum flat tube near the extrusion exit of the molding machine is at least 400°C or higher, Zn wire is thermally sprayed onto the surface of the extruded flat tube. A method for producing an aluminum flat tube cladding material for a heat exchanger, characterized in that a Zn diffusion permeation layer is formed on the surface of the flat tube by naturally cooling the flat tube after thermally spraying Zn.