JPH0390275A - Vapor brazing method for al or al alloy - Google Patents

Abstract

PURPOSE:To shorten the production process of the heat exchanger for automobiles, etc., by brazing Al members in a nonoxidative atmosphere where the vapor of a chloride or fluoride flux exists under a specific partial pressure. CONSTITUTION:Corrugated fins 2 consisting of a brazing sheet formed by using Al or Al alloy as a core material and cladding the facing materials consisting of an Al-Si-Zn alloy on both surfaces are inserted between zigzag tube materials 1 consisting of Al or Al alloy to assemble a condenser. This condenser is inserted together with a prescribed amt. of KAlF4 into a vessel and is brazed by heating. The two materials 1, 2 are, thereupon, brazed in the nonoxidative atmosphere where the vapor of the chloride or bromide flux exists under >=0.05mmHg and <1.7mmHg partial pressure. The improved quality, such as improved corrosion resistance, is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for brazing Al or Al alloy. For example, in the manufacture of automobile heat exchangers, the performance of the brazed members is This improves the performance and reduces the manufacturing cost.

[Conventional technology]

Normally, in brazing Al or Al alloy, the Al or Al alloy members to be joined are fixed together via a brazing filler metal whose melting point is lower than that of Ag, etc., and the melting point is higher than that of the brazing filler metal. This is done by heating to a temperature lower than the melting point of the Al or Al alloy members to be joined. Generally, Al-3i alloy is used as the brazing material, and its shape is a plate.

It is used as a laminated material (hereinafter referred to as a plating sheet) in which a wire or powdered brazing material or a core material made of Al or an Al alloy is coated with this brazing material.

As conventional brazing methods, flux brazing, which uses flux to remove the oxide film on the surface of the parts to be brazed, and vacuum brazing, which does not use flux, are commonly used. The above-mentioned flux brazing properties include furnace brazing properties, in which the assembly to be joined is immersed in molten chloride-based flux and heated for brazing. However, this chloride-based flux is corrosive to Al, so it must be completely removed by cleaning after brazing.
The manufacturing process is extremely complicated. On the other hand, vacuum brazing, in which the assembly to be joined is placed in a vacuum and subjected to brazing heat, does not require cleaning as a post-process, and the surface of the parts after brazing is also good. There are problems such as the need for high vacuum and material limitations.

Furthermore, recently, a method of brazing in a furnace using a fluoride flux has been widely used as a method of brazing to solve the above-mentioned problems.

As described in Japanese Patent Publication No. 58-27037, this method uses a mixture of KAJFa and Ks At Fb, which is non-hygroscopic and non-corrosive to Al, as a flux, and suspends it in water. It is applied to the surfaces of the assemblies to be joined and brazed, and its feature is that since it uses non-corrosive flux, no post-treatment to remove the flux is required.

[Problem to be solved by the invention]

However, the method described in Japanese Patent Publication No. 58-27037 necessarily requires coating and drying steps to adhere the flux to the surface of the assembly. Many items fall off from the assembly during transport, and therefore the flux that can be used effectively is reduced. In addition, flux residue remains unevenly on the surface of the joined parts after brazing, so the surface becomes dirty compared to conventional vacuum brazing, and the commercial value is inferior. There were drawbacks such as chromate treatment, black coating treatment, etc. becoming non-uniform and the effects not being fully exhibited.

Furthermore, since flux residue is non-conductive, for example, when adopting a corrosion prevention method that protects the pipe body with sacrificial fins in a heat exchanger, the flow of anticorrosion current is obstructed, making it impossible to obtain a sufficient corrosion protection effect. There are cases. Furthermore, when brazing in a furnace using Mg-containing 1-alloy fluoride flux, the brazing properties are inferior to conventional ones, so in order to obtain industrially stable brazing properties, it is necessary to The content must be less than 1,391% (hereinafter wt% is simply abbreviated as %).

If the Al alloy contains more Mg than this, brazing becomes difficult even if the amount of flux applied is increased.

The cause of this is that Mg in the Al alloy reacts with the flux during brazing heat, and as a result, the composition of the flux changes and its effectiveness as a flux is lost.
This is because the Mg in the Al alloy diffuses into the surface layer, increasing the Mg concentration in the surface layer, and phenomena such as flux entering the surface layer of the Al alloy occur, inhibiting the flow of the solder. It is. In this way, A with a high Mg content
The fact that l-alloy cannot be used as a material for heat exchangers has been a major obstacle in terms of durability and weight reduction of heat exchangers.

[Means to solve the problem]

In view of this, as a result of various studies, the present invention has developed vapor phase brazing properties that do not require the process of directly applying flux to the assemblies to be joined. In the method of attaching Al or Al
The vapor of chloride or fluoride flux is applied to the alloy member at a partial pressure of 0. [15mm 1g or more, 7mm
It is characterized by brazing in a non-oxidizing atmosphere containing less than Hg.

[For production]

By placing the assembly as the members to be bonded in a non-oxidizing atmosphere where chloride-based or fluoride-based flux vapor is present, this vapor adheres uniformly to the assembly in a very small amount. Since it destroys the Al oxide film on the surface, it promotes wetting of the solder, and has the characteristic that the solder flows in a uniform manner and forms a uniform fillet at the joints of the assembly. Furthermore, this vapor combines with moisture and oxygen in the atmosphere to make it less oxidizing than the atmosphere, which has the effect of preventing oxidation of the material surface.

The flux that can be used here is a chloride-based or fluoride-based compound that can destroy the Al oxide film, and a compound or a single substance containing a metal complex that can form the above-mentioned compound after evaporation. Specifically, the vapors include zinc chloride, tin chloride, etc., and fluoroaluminate metal complex vapors. Furthermore, KAlF
4+ also includes vapors generated from mixtures such as 2 Al F5◆H,O. To generate such steam, the above mixture etc. may be placed in advance in the furnace where brazing will be carried out, and when the temperature of the furnace is raised, it may be evaporated at the same time, or this steam may be It is also possible to generate nitrogen gas outside and supply it into the furnace using nitrogen gas or the like as a carrier.

Furthermore, the presence of such flux vapor in a non-oxidizing atmosphere allows the assembly to be completely covered with vapor, thereby requiring less vapor density and reducing flux consumption. However, in open type furnaces where flux vapor tends to scatter, the original function of the flux is insufficient.

Therefore, as a result of intensive studies on the amount of flux vapor required in the present invention, we found that in order to achieve good brazing, it is preferably 0. It has been found that it is desirable to ensure a partial pressure of O5 mmHg or more.

According to the present invention, Al-
Even Mg-based alloys can be brazed. This is because the amount of flux vapor is very small and it evenly adheres to the assembly. For this reason, the reaction between the vapor that acts as a flux and the Mg in the material is extremely small, so the effect of the vapor as a flux is not inhibited, and the Mg surface layer inside the Mg-containing material is diffused. This is because no difference in Mg concentration occurs within the material, and the amount of flux components that penetrate into the surface layer of the material is small, so the flow of the wax is not inhibited. On the other hand, when the flux partial pressure becomes high concentration such as 1.7 mmHg or more, the amount of flux that adheres to the surface of the molded product increases, the corrosion resistance deteriorates, and the surface appearance of the brazed surface deteriorates. In order to carry out the present invention, it is desirable to use a furnace with a high degree of airtightness, but even in a furnace with a degree of airtightness, the assemblies to be joined can be placed in a container made of stainless steel or the like together with the steam generated to heat the brazing. Then, a flux atmosphere of a predetermined concentration can be easily formed and brazing can be performed. As the non-oxidizing atmosphere, for example, a nitrogen atmosphere, an argon-carbon oxide atmosphere, or a vacuum state can be used.

〔Example〕

The present invention will be described below with reference to Examples.

Example 1 As shown in Fig. 1, a tube material (1) made of 115Al050 (CAI 99.5% or more) which was hot-extruded into a tubular shape by a conventional method was bent into a serpentine shape, and between the serpentine tube material (1) Corrugated fin (2) consisting of a plating sheet with a thickness of 0.16 mm, with A/-1%Mn-1%Zn alloy as the core material and Al-10%5i-1%Zn alloy skin material clad on both sides. sandwiched between Al-4%Zn-1%M
A connector (3) made of g-alloy was attached, and a wire rod made of ll5A4047 (Al-11 to 13% Si) with a wire diameter of 1.6 mon was wound around this joint to assemble a serpentine type capacitor. This assembly was degreased with an organic solvent and inserted into a stainless steel narrow-mouthed container having an internal volume of 1 cubic meter together with a predetermined amount of KAlF4. Thereafter, the inside of the container was replaced with nitrogen gas, the tray was inserted into an electric furnace maintained at 610°C, and the assembly was heated at 610°C for 5 minutes to perform brazing. The flux concentration in the gas discharged from the container during this brazing process was analyzed. At this time, KAlF4 melts and evaporates while being heated up to the brazing temperature after being inserted into the furnace, and its concentration increases, so that it covers the assembly as an atmosphere during brazing.

The re-brazed capacitor was taken out of the furnace and the appearance of the surface was observed, and the brazing condition was examined. The results are shown in Table 1. After that, chromate treatment is carried out by the usual method.
A black coating was applied, and the adhesion properties are also listed in Table 1 as chromate property and paintability. In order to evaluate the corrosion resistance of the capacitor after coating, a CASS test based on 115H8681 was conducted for 500 hours to check for the presence or absence of through pitting corrosion, and the results are also listed in Table 1.

For comparison, the characteristics of the capacitor assembly shown in FIG. 1, brazed using a conventional method, were investigated.

That is, after degreasing the assembly shown in Fig. 1 with an organic solvent, a 10% concentration KAlF4 suspension was applied, and the mixture was heated at 200°C for 1 hour.
Drying was performed for 0 minutes. Thereafter, this assembly was inserted into an electric furnace purged with a nitrogen gas atmosphere and maintained at 610°C, and brazed by heating at 610°C for 5 minutes. The subsequent steps were carried out in the same manner as above, and the brazed capacitor was subjected to the same evaluation tests as above, and the results are shown in Table 1.

As is clear from Table 1, the surface of the capacitor after brazing according to the present invention is clean, and the brazing conditions are also good: the fin part, which is the joint between the fin and the tube material, and the connector part, which is the joint part between the connector and the pipe material. He was excellent in both departments. Furthermore, the chromate property and paintability were also good, and the corrosion resistance was also good.

On the other hand, in the capacitor manufactured by the conventional method, flux residue is thickly and non-uniformly adhered to the entire surface of the capacitor, which is unfavorable in terms of appearance. Also, the brazing condition was good on the fin part, but some parts of the connector could not be brazed. Furthermore, the chrome-4 treatment and painting after brazing were uneven, and with regard to corrosion resistance, through-pitting corrosion occurred particularly at bent portions of the pipe material.

[Effects of the invention] As described above, according to the present invention, the manufacturing process for heat exchangers for automobiles, etc., can be shortened compared to conventional brazing properties, resulting in lower manufacturing costs, and the surface after brazing is Because it is clean, it has good surface treatment properties in post-treatments such as chromate treatment, improves quality such as excellent corrosion resistance, and has remarkable industrial effects such as being able to braze alloys containing a large amount of Mg. It is something.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an example of a condenser that is a heat exchanger for an air conditioner, and FIG. 2 is an enlarged side view showing a joint between a tube and a fin. 1... Tube material 2... Fin 3... Connector

Claims (1)

[Claims] (1) In a method of brazing Al or Al alloy through a brazing material, the vapor of chloride or fluoride flux is applied to the Al or Al alloy member at a partial pressure of 0.05 mmH.
A vapor phase brazing method for Al or Al alloy, characterized in that brazing is carried out in a non-oxidizing atmosphere where the pressure is greater than or equal to 1.7 mmHg.