JPH02220768A - Production of aluminum heat exchanger having excellent pitting corrosion resistance - Google Patents

Abstract

PURPOSE:To exhibit excellent pitting corrosion resistance over a long period of time by executing the formation of a coated layer of a specific thickness consisting of a synthetic resin binder of Zn powder and a Zn diffusion treatment at and for a specific temp. and time. CONSTITUTION:The Zn powder is applied on the surface of an Al or Al alloy tube material to 10 to 300mum thickness in the state of mixing the powder with the synthetic resin binder. The tube material is subjected to a heating treatment under the conditions of 400 to 600 deg.C and holding for 5 to 120 minutes in a nonoxidative atmosphere. The Zn is diffused deep into the surface layer of the tube material in this way and the Al heat exchange is provided with the excellent pitting corrosion resistance over a long period of time even in severe corrosive environment.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides an aluminum heat exchanger (hereinafter referred to as Al heat The present invention relates to a method for manufacturing an exchanger (referred to as an exchanger).

[Conventional technology]

Conventionally, Al7 heat exchangers such as automobile radiators, air conditioners/condensers, and evaporators have generally been made of (a) Al or AΩ materials such as JIS A 1050 materials, JIS A 1100 materials, JIS A 3003 materials, and JIS 3102 materials.
A tube material is formed by extrusion using an alloy, and the tube material is straight or bent into a meandering shape. (b) Same < 3003 material, 3102 material, 3202 material
A brazing sheet is constructed by cladding a core material made of A or Q alloy such as 6951 material with a brazing material made of A or 9-8i alloy such as 4343 material or 4045 material on one or both sides. (e) After applying fluoride-based flux or chloride-based flux mixed with water to this combination, (d) At a temperature of 580 to 610°C in the atmosphere. 3-20
Above (a), brazing heat treatment is performed under the condition of holding for a minute.
It is manufactured by the main steps of ~(d).

In addition, for the purpose of imparting pitting corrosion resistance to the Ag heat exchanger, a Zn layer is formed on the surface of the A, Q or Ag alloy tube material by thermal spraying or plating, and the brazing of this Zn layer is performed. It has also been proposed to electrochemically make the surface of the tube material less noble through diffusion during heat treatment, thereby making it fully corroded, thereby preventing the occurrence of pitting corrosion.

[Problem to be solved by the invention]

However, in the Zn diffusion-treated Ag heat exchanger manufactured by the above-mentioned conventional method, the A and Q heat exchangers are exposed to particularly severe corrosive environments due to insufficient diffusion of Zn to the tube surface. At present, it is impossible to avoid pitting corrosion from occurring relatively early when the steel is placed in a

[Means to solve the problem]

Therefore, from the above-mentioned viewpoint, the present inventors conducted research to promote Zn diffusion in Ag heat exchangers and thereby suppress the occurrence of pitting corrosion over a long period of time. In this process, instead of the Zn layer formed by conventional thermal spraying or plating on the surface of Ag or /47 alloy tube material, Zn powder, specifically Zn powder having an average particle size of 10 to 300, is added to the surface of the Ag or /47 alloy tube material. Specifically, it is mixed with an acrylic, epoxy, or vinyl chloride synthetic resin binder at a weight ratio of 1:9 to 9:1, and if necessary, a solvent such as water is added for 10 to 10 minutes. It is coated to a thickness of 300 mm and then coated with 40 mm in a non-oxidizing atmosphere.
When heat treatment is performed at a temperature of 0 to 600°C for 5 to 120 minutes, the synthetic resin binder decomposes during the heat treatment and becomes a strongly reducing gas, which decomposes Ag and Ag alloys. Since the surfaces of the tube material and Zn powder are significantly activated, the diffusion of Zn to the surface of the tube material progresses rapidly, and the Zn diffuses deep into the surface of the tube material.As a result, the Ap heat exchanger is exposed to harsh conditions. They found that it exhibits excellent pitting corrosion resistance over a long period of time even in corrosive environments.

Therefore, the present invention has been made based on the above findings, and includes an A, Q or Ag alloy tube material formed into an extruded straight tube shape or into a meandering shape by bending, with an Ag alloy core material on one or both sides. Corrugated Al consisting of a brazing sheet clad with NiheΩ-3L alloy brazing filler metal
When manufacturing an Ag heat exchanger through the main process of combining 7 alloy fin materials, applying flux mixed with water to this combination, and subjecting it to brazing heat treatment, the above A, l? Or, on the surface of A47 alloy pipe material, Zn powder mixed with a synthetic resin binder is applied for 10 to 30 minutes.
After coating with a thickness of 0uIn, 40μIn in a non-oxidizing atmosphere.
Zn was heated at a temperature of 0 to 600°C for 5 to 120 minutes.
This method is characterized by a method of manufacturing A and Q heat exchangers with excellent pitting corrosion resistance by performing a diffusion treatment.

Next, in the method of the present invention, the reason why the coating layer thickness of Zn powder and the Zn diffusion treatment conditions are limited as described above will be explained.

(a) Thickness of coated layer of Zn powder When the thickness is less than 10 mm, the relative amount of Zn powder is too small and Zn cannot be sufficiently diffused to the surface of the pipe material.On the other hand, when the thickness exceeds 300 layers, However, in consideration of economic efficiency, the thickness was reduced to 10 to 30 mm.
It was set as 0-.

(b) Zn diffusion treatment conditions This Zn diffusion treatment is possible only after the Zn powder is melted, and therefore it must be carried out at a temperature of 400°C or higher, which is higher than the melting temperature of Zn. If the temperature exceeds 600°C, the temperature will be close to the melting temperature of Ap and Al alloys, and the tube material will easily deform due to its own weight. Therefore, the temperature was set at 400 to BO0°C. Furthermore, if the holding time is less than 5 minutes, sufficient Zn diffusion will not take place, while if the holding time exceeds 120 minutes, Zn will be diffused into the pipe material too deep into the surface, resulting in a significant decrease in the strength of the pipe material. Therefore, the retention time is 5 to 12
It was set as 0 minutes.

〔Example〕

Next, the method of the present invention will be specifically explained using examples.

Each pipe material has a JIS standard composition shown in Table 1, and is formed by hot extrusion. Width: 30 m
A flat tube material with mX thickness: 5 mu A pipe material subjected to diffusion treatment and a serpentine shape (serpentine shape) obtained by bending this with a bending radius of 101111 are prepared separately and have a JIS standard composition shown in Table 1, and a core material. Thickness: 0.18 by cladding each side with 10% brazing filler metal.
M+W brazing sheets are assembled into a heat exchanger shape by combining them with corrugated fin materials, and a fluoride flux consisting of KAj7F and KAj)F6 mixed with water is applied to this assembly. After spray coating to a thickness, methods 1 to 10 of the present invention were carried out by performing brazing heat treatment under the conditions of holding at 600 ° C. for 5 minutes in a nitrogen atmosphere of 7 f 30 torr.
A J heat exchanger was manufactured.

For the purpose of comparison, conventional methods 1 to 1 were prepared under the same conditions except that a Zn layer was formed by ordinary thermal spraying or hot-dip plating instead of the above-mentioned Zn powder application and Zn diffusion treatment.
4 was carried out to manufacture an Ag heat exchanger.

Next, with respect to the various All-I heat exchangers obtained as a result, the Zn diffusion depth in the surface portion of the tube material, which is a structural member, was measured, and a CASS test was conducted to measure the time until pitting corrosion occurred. The results of these measurements are shown in Table 1.

〔Effect of the invention〕

From the results shown in Table 1, the depth of Zn diffusion in the surface portion of the tube material of the Ag heat exchanger manufactured by methods 1 to IO of the present invention is -stage deep, and as a result, the entire surface corrosion type occurs for a significantly long period of time. However, compared to conventional methods 1 to 4, the depth of Zn diffusion in the tube material in Ag heat exchangers manufactured by conventional methods 1 to 4 is relatively shallow. It is clear that pitting corrosion begins to occur in a short period of time.

As described above, according to the method of the present invention, Zn can be diffused deep into the surface of the pipe material by forming a coating layer of Zn powder with a synthetic resin binder and then performing a Zn diffusion treatment. This brings about industrially useful effects such as making it possible to manufacture Aj) heat exchangers that exhibit excellent pitting corrosion resistance over a long period of time.

Mitsubishi Aluminum Co., Ltd. 1 other person

Claims (1)

[Claims] (1) Corrugated processing consisting of a brazing sheet made by extruding a straight pipe or a meandering Al or Al alloy pipe material into a meandering shape by bending and cladding an Al-Si alloy brazing material on one or both sides of an Al alloy core material. In the method of manufacturing an aluminum heat exchanger by the main steps of combining Al alloy fin materials of 1 to 3, applying flux in a mixed state with water to this combination, and then subjecting it to brazing heat treatment, the above Al or Al alloy tube material Zn powder is mixed with a synthetic resin binder on the surface of the
After coating with a thickness of 5 to 12 m, it is heated to a temperature of 400 to 600 °C in a non-oxidizing atmosphere for 5 to 12 m.
A method for manufacturing an aluminum heat exchanger with excellent pitting corrosion resistance, characterized by carrying out Zn diffusion treatment under conditions of holding for 0 minutes.