JPH0318496A - Vapor brazing method of al or al alloy - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance and quality of members by brazing the members to be brazed in a nonoxidative atmosphere where the vapor generated from a mixture composed of the fluorides having the m.p. lower than the m.p. of a potassium fluoroaluminate complex and contg. the above- mentioned material as its essential component exists. CONSTITUTION:A tube material 3 consisting of a pure Al system is bent zigzag. Corrugated fins 4 consisting of a brazing sheet formed by using an Al-Mn-Zn alloy as a core material and cladding both surfaces thereof with facing materials of an Al-Si-Zn alloy are inserted between the zigzag tube materials. Further, connectors 5 consisting of an Al-Zn-Mg material are mounted thereto to assemble a condenser of a serpent type. The joint parts of the corrugated tins 4 and the connectors 5 are previously joined by a TIG welding. The mixture composed of KAlF-CsF is placed in an electric furnace for brazing and the assembly is inserted therein and is brazed while the assembly is heated at and for a prescribed temp. and time. A heat exchanger having the good surface treatability in a post treatment, such as chromate treatment, and the excellent 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, which improves the performance of brazed parts and reduces manufacturing costs, for example in the manufacture of heat exchangers for automobiles. This makes it cheaper.

[Conventional technology]

Normally, when brazing Al or Al alloy, the Al or Al alloy members to be joined are fixed together through a brazing filler metal whose melting point is lower than that of the brazing filler metal (A), which is lower than the melting point 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.An Al-Si alloy is generally used as the brazing material, and its shape can be plate-like or linear. Alternatively, it is used in the form of a powdered brazing material, or a laminated material (hereinafter referred to as a plating sheet) in which a core material made of Al or an Al alloy is coated with the brazing material.

As conventional brazing methods, flags brazing method that uses flux to remove the oxide film on the surface of the parts to be brazed and vacuum brazing method that does not use flux are usually used.

Examples of the above-mentioned flux brazing method include a furnace brazing method in which an assembly to be joined is immersed in molten chloride-based flux and heated for brazing. However, since this chloride-based flux is corrosive to Al, it must be completely removed by cleaning after brazing, making the manufacturing process very complicated.

According to the vacuum brazing method, in which the assemblies to be joined are placed in a vacuum and then heated for brazing, there is no need for cleaning as a post-process, and the surface of the parts after brazing is also good. However, there are problems such as the need for high vacuum and material limitations.

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

As described in Japanese Patent Publication No. 58-27037, this method uses KAlF4 and K2AlF. which are non-hygroscopic and non-corrosive to Al as fluxes. using a mixture of
This is suspended in water and applied to the surfaces of the assemblies to be joined for brazing. One of its features is that it uses non-corrosive flux, so no post-treatment is required to remove the flux. .

[Problems to be Solved by the Invention] However, the method described in Japanese Patent Publication No. 58-27037 necessarily requires a coating and drying process for adhering the flux to the surface of the assembly. Many flags fall off from the assembly while the assembly is being transported to the next process, resulting in a low yield of effectively used flux. In addition, since 7 lux residue remains unevenly on the surface of the joined parts after brazing, the surface becomes dirty compared to the conventional vacuum brazing method, and the commercial value is inferior. There were drawbacks such as the treatment, black coating, etc. becoming non-uniform and the effects not being fully exhibited.

Furthermore, since this 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 and the corrosion prevention effect cannot be obtained sufficiently. There is.

Furthermore, when brazing Mg-containing Al alloy members in a furnace using the above-mentioned fluoride-based flux, the brazing properties are inferior to conventional ones, so in order to obtain industrially stable brazing properties, brazing is The Mg content in the Al alloy that is the member is 0.6
It must be less than wtX (hereinafter, X is simply abbreviated as %).

Furthermore, with an Al alloy member containing more Mg than this, brazing becomes difficult even if the amount of flux applied is increased. The cause of this is that the Mg in the Al alloy and the flux react during the brazing heat, and as a result, the composition of the flux changes and its effectiveness as a flux is lost.
This is because M+r 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 wax. It is.

The fact that Al alloy members with a high Mg content 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 a vapor phase brazing method for Al or Al alloy that does not require the process of directly applying flux to the assemblies to be joined.
In the method of brazing L or Al alloys through a brazing material, the parts to be brazed are generated from a fluoride mixture whose main component is potassium fluoroaluminate complex, which has a lower melting point than potassium fluoroaluminate complex. Specially required for brazing in a non-oxidizing atmosphere where steam is present. It is a sign.

[Effect]

By placing the assembly as the members to be joined in a non-oxidizing atmosphere in which the vapor generated from the fluoride mixture containing potassium fluoroaluminate complex as the main component exists, this vapor can be removed in a very small amount. It adheres uniformly to the assembly and destroys the AD oxide film on its surface, promoting wetting of the wax, resulting in the wax flowing uniformly and forming a uniform fillet at the joint of the assembly. have

Furthermore, this vapor combines with moisture and oxygen in the atmosphere to make the atmosphere more non-oxidizing. It has the effect of preventing oxidation of the material surface.

In addition, as the potassium fluoroaluminate complex vapor that can be used in the brazing method of the present invention, the specific chemical formula is K
A Q F 4, K! A Q F s and K. A
lF. The general formula K. AlF. , s, and their mixture KAl7Fn+KtA (J
Fs, KAlF4+K. AlF. ．． KtAlF,+K
．． A(7F■KAlF4+K,-+AlF.+x and K t A O F n +K., AllJF..l
, etc., and further includes KAlFi+KzAlFs
- Vapors generated from mixtures such as Hto are also included. In addition, solid KF, which is the usual raw material for the above compounds,
The steam generated by mixing and heating and melting A(!F3) may also be used.

Note that the vapor of the potassium fluoroaluminate complex is generated when the vapor-generating material is heated and melted.

Therefore, by melting this generating material, potassium fluoroaluminate complex, at a lower temperature to generate steam, it covers the assembly to be joined at a lower temperature, preventing surface oxidation and improving brazing properties. can be improved.

A fluoride mixture containing a potassium fluoroaluminate complex as a main component that can lower the melting temperature of the potassium fluoroaluminate complex is, for example, 95XK AlF.
．． -5XK B F 4+ 95! %K Al7F
．． -5XZnFz. 84%KAlF, -12%KF-4
1iF, 95XKAlF4, 5XCSF, etc., and other fluoroaluminate acids. A fluoride mixture containing a potassium fluoroaluminate complex as a main component that can lower the melting temperature of the ium complex is effective.

In order to generate such steam, the above-mentioned 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.

Additionally, the presence of vapors of such potassium fluoroaluminate complexes in a non-oxidizing atmosphere allows the assembly to be completely covered with vapors, thus requiring less vapor density and reducing flux consumption. . Note that as the non-oxidizing atmosphere, for example, nitrogen, argon, carbon monoxide, or any other atmosphere can be used.

Further, in order to carry out the present invention, it is preferable to use a furnace with a high degree of airtightness, but even if a furnace with a degree of airtightness is inferior, the assemblies to be joined are placed in a container made of stainless steel or the like together with the steam generated and brazed. It can be easily brazed by heating.

Furthermore, according to the present invention, even Al-Mg alloys containing more than 0.6% Mg can be brazed. This is because the vapor of the potassium fluoroaluminate complex is extremely small and adheres uniformly to the assembly. For this reason, the reaction between the vapor of the potassium fluoroaluminate complex, which acts as a 7-lux, and the Mg in the material is extremely small, so that the effect of the vapor as a flag is not inhibited, and the vapor in the Mg-containing material is In this case, Msr diffuses into the surface layer and there is no difference in Mg concentration within the material.
Furthermore, since the amount of brax that penetrates into the surface layer of the material is small, the flow of the wax is not obstructed.

By using the vapor of potassium fluoroaluminate complex in this way, it is possible to braze without directly applying black to the assembly. For heat exchangers that also have joints inside the assembly, such as the Dron cup type evaporator shown in Figure 1 or the parallel flow type condenser shown in Figure 2, internal brazing is not required. Generally difficult. Therefore, in such cases, apply fluorocarbons to the joints inside the assembly in advance. A fluoride-based flux such as potassium fluoroaluminate complex is applied and dried, and the joints outside the assembly are brazed in a non-oxidizing atmosphere in the presence of vapor of potassium fluoroaluminate complex without applying flux. The method is valid.

In addition, partial application of fluoride-based flux such as potassium fluoroaluminate complex is not limited to the inside of the assembly, but can also be applied to the outside of the assembly. If brazing is difficult, a fluoride flag such as potassium fluoroaluminate complex may be applied directly to the part.

〔Example〕

Next, examples of the present invention will be described.

Example 1> As shown in Fig. 3, JIS A3003 (A(>-Cu
O. 05 ~0. 20X-Mn l. 0 to 1.
5%) St6.8 to 8.2 on one side of the A O alloy core material
One edge of a rolled plate (1) with a thickness of 1mlI1 made of a plating sheet of JIS BA12PC clad with a JIS A4343 Al alloy brazing material containing JIS Al050 (Al99.5X or above or G;
! A Q-0. Both plate materials +
1) Assemble the inverted T joint test pieces in which (2) are brought into contact so that they are perpendicular to each other, and perform brazing under the conditions shown below.
The brazing situation was investigated.

That is, 400 g of each of the fluoride mixtures shown in Table 1 was weighed out per lm' of internal volume of the brazing furnace, and placed in the brazing furnace, and in each case, the inside of the furnace was kept at a dew point of -40°C. The atmosphere was replaced with a nitrogen gas atmosphere with an oxygen concentration of 100 ppm, and the inside of the furnace was further maintained at 610°C. Then, the inverted T joint test piece shown in Figure 3 using the Al alloy plate shown in Table 1 was inserted into this furnace after being degreased with an organic solvent, and this assembly was
Brazing was carried out by heating at lO<0>C for 5 minutes. As shown in Table 1, the temperature at which these fluoride mixtures start melting is below 570°C, and K A Q F a
It can be seen that it is lower than the melting point of 571°C alone.

After the above brazing, the inverted T-joint joint was taken out of the furnace and the flow factor (cross-sectional area of the fillet/cross-sectional area of the brazing sheet brazing metal layer) was measured, and the results are shown in Table 1. I checked the brazing situation. Furthermore, the surface of the brazed part was observed, and those parts that were clean were marked with a circle, and those that were dirty with a lot of residue were marked with an x mark, and these parts were also listed in Table 1.

In addition, as a conventional method, the above-mentioned rolled plate (1) and the Al alloy plate (2) shown in Table 1 are assembled into an inverted T-joint test piece as shown in Fig. 3, and after degreasing, this assembly is coated with KA ( !F4 was applied and dried, and then this assembly was inserted into an electric furnace which was replaced with a nitrogen gas atmosphere with a dew point of -40°C and an oxygen concentration of 100 ppm as described above, and the inside of the furnace was further maintained at 610°C. This was heated at 610° C. for 5 minutes to perform brazing, and the brazing situation was similarly investigated and the results are also listed in Table 1.

As is clear from Table 1, the present invention method No. l-No.
8 and KAlF. Comparative method No. 1 that generated steam alone.
No. 9 and No. 10 both had good brazing properties, could be well brazed even with Mg-containing materials, and had a beautiful surface appearance. And the present invention method No. 1~NO.
According to Comparative Method No. 8. 9, No. It can be seen that the flow factor is larger than that of No. 10, and the brazing properties are better.

In contrast, conventional method No. Although the brazing properties of conventional method No. Brazing was not possible with 12.

<Example 2> As shown in Fig. 4, a JIS A1050 tube material (3) hot-extruded into a tubular shape by a conventional method is bent into a meandering shape, and Al-IXMn is inserted between the meandering tube material (3). {% Z
N alloy is used as the core material, and A(?-10%Sl-
Thickness 0.1% Zn alloy skin material cladding. 16mo+
Corrugated fin (4) consisting of a brazing sheet of
In between, further i. :A(2-4.3%Zn-1.3XM
A serpentine type capacitor was assembled by attaching the g-alloy color connector (5). Note that the joint between the corrugated fin (4) and the connector (5) was previously joined by TIG welding using a JIS A1070 (Al99.70X or higher) welding rod.

This assembly was then degreased with an organic solvent and then 95XKAl
Weighed 400 g of a mixture of Fs-5% CsF per 11 internal volumes of the brazing furnace and placed it in the brazing electric furnace, which was purged with a nitrogen gas atmosphere with a dew point of 40°C and an oxygen concentration of 100pplll, and was maintained at 610°C. This assembly was inserted into the above-mentioned furnace, and the assembly was heated at 610° C. for 5 minutes to perform brazing.

After the brazing, the 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 2. After that, chromate treatment is carried out by a conventional method.
A black coating was applied, and the adhesion properties of these films are also listed in Table 2 as chromate properties and paintability. In addition, in order to evaluate the corrosion resistance of the capacitor after this coating, JIS H868
A CASS test was carried out for 500 hours based on 1, to examine the presence or absence of through pitting corrosion, and the results are also listed in Table 2.

Furthermore, for comparison, the characteristics of the serpentine type capacitor assembly shown in FIG. 4, which was brazed using the conventional method shown below, were investigated.

That is, after this assembly was degreased with an organic solvent, a KAlF4 suspension with a concentration of 10% was applied and dried at 200° C. for 10 minutes. Then the dew point was -40℃. Oxygen concentration 100p
This assembly was inserted into an electric furnace purged with a nitrogen gas atmosphere of pm 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 in the above invention example, and the brazed capacitor was subjected to the same evaluation tests as above, and the results are shown in Table 2.

As is clear from Table 2, the surface of the capacitor after brazing by the method of the present invention was clean and the brazing condition was also good. Furthermore, the chromate property and paintability were also good, and the corrosion resistance was also good.

On the other hand, in the case of a capacitor manufactured by the conventional method, the flux residue is thick and non-uniformly adhered to the entire surface of the capacitor, which is unfavorable in terms of appearance. Although the brazing condition was good, the chromate treatment and painting after brazing were uneven, and with regard to corrosion resistance, through-pitting corrosion occurred at the bent portion (6) of the pipe material (3) in FIG. 4.

〔Effect of the invention〕

As described above, according to the present invention, compared to the conventional brazing method, the manufacturing process of heat exchangers for automobiles, etc. can be shortened, resulting in lower manufacturing costs, and the surface of the parts after brazing is clean. It has good surface treatment properties in post-treatments such as chromate treatment, has improved 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.

[Brief explanation of the drawing]

Fig. 1 is a side view showing an example of a Dron cup type evaporator, Fig. 2 is a side view showing an example of a parallel flow type condenser, Fig. 3 is a perspective view showing an inverted T-joint test piece, Fig. 4 5 is a perspective view showing an example of a serpentine type condenser which is a heat exchanger for an air conditioner, and FIG. 5 is an enlarged side view showing the fin portion of FIG. 4. l... Rolled plate 2 - Al alloy plate 3 - Tube material 4 - Corrugated fin 5 - Connector 6 - Bending portion Fig. 1 Fig. 4 Fig. 2 Fig. 5

Claims (1)

[Claims] (1) In the method of brazing Al or Al alloy through a brazing material, the parts to be brazed are made of a fluoride mixture whose main component is a potassium fluoroaluminate complex, which has a lower melting point than the potassium fluoroaluminate complex. 1. A vapor phase brazing method for Al or Al alloy, characterized by brazing in a non-oxidizing atmosphere in the presence of steam generated from.