JPH0645079B2 - Brazing flux and brazing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a brazing flux and a brazing method used for brazing a metal material such as aluminum or an aluminum alloy.

[Prior art and its problems]

Aluminum or aluminum alloy (hereinafter simply referred to as "aluminum") material has advantages such as light weight and good heat conductivity, and is used for various automobile parts and heat exchangers for automobiles such as radiators, condensers and evaporators. .

And, for example, most of heat exchangers are mainly assembled by brazing because it is necessary to join many minute parts, and this brazing means is, for example, vacuum brazing, inert gas atmosphere brazing or flux. There is brazing in the furnace using.

Among these brazing means, vacuum brazing does not use a flux, so there is some merits when the step of removing the residual flux is omitted, but it is expensive for the equipment and to prevent corrosion of the finished product. Most of the Zn in the sacrificial anode material (aluminum alloy material with 0.5 to 2 wt% Zn added) is evaporated and lost, resulting in insufficient corrosion resistance and other costly corrosion prevention. There are some drawbacks if you have to rely on means.

In addition, brazing in an inert gas atmosphere should be similar to that in the above case.
Although it will never evaporate, it must be cleaned with an alkali just before brazing to remove the surface oxide film of the aluminum material, and the inert gas used must have a low dew point of -60 ° C or less. However, there is a drawback that the process is complicated and the cost is high.

In addition, in the case of brazing in the furnace using the flux, there is no problem with evaporation of Zn and the brazing property is excellent considering the gap filling property, but the residual flux that promotes corrosion of the finished product Has to be removed, which results in a high cost.

[Disclosure of Invention]

The present inventor has no problem with evaporation of Zn in the sacrificial anode material, and has excellent brazing property, but using a flux which is considered to have a problem in terms of residual flux after brazing. In the course of research on the brazing means in the furnace of No. 1, it was found that it is extremely desirable if cyclodextrin, particularly preferably β cyclodextrin, is added to the flux.

That is, when a brazing flux containing cyclodextrin is applied to the surface of a metal member to be brazed, then this is fired, and then a predetermined brazed product is observed, the brazing property is good and It was also excellent in the later appearance.

The amount of cyclodextrin added is preferably about 1 to 20% by weight with respect to the amount of the flux, that is, if the ratio to the amount of the flux is less than 1%, the effect is weakened, and conversely 20%. This is because if the amount exceeds the above range, a large amount of carbon harmful to corrosion resistance remains in the brazing process.

Then, Furatsukusu for brazing containing cyclodextrin, for example _{KF-AlF 3, NaCl-KCl} -LiCl-AlF 3, NaCl-KCl-
ZnCl ₂ -LiF, was added in an amount of cyclodextrin of about 1 to 20 percent greater Furatsukusu of吸質property mainly containing chloride or hydrofluoric products such as _{NaCl-KCl-ZnCl 2 -SnCl 2} -LiF,
Then mix it thoroughly and then mix this mixture about 100 times.
It can be easily obtained by crushing into particles having a size of less than or equal to μm, preferably less than or equal to about 80 μm.

The particle size of the crushed flax is set to about 100 μm or less because the flax residue after brazing may not be removed if the particle size of the flux is too large.

The cyclodextrin-containing flux thus obtained is used, for example, as a flux component KF which is easily soluble in water.
Etc. are contained, for example, a suspension is prepared using ethyl alcohol or the like as a solvent, and the cyclodextrin-containing flux suspension is applied to the surface of the aluminum material by dipping, coating, spraying, or the like to contain cyclodextrin. The flux is adhered and kept in an atmospheric furnace at about 100 to 250 ° C. for about 5 to 60 minutes to dry and remove the solvent and the water present before the flux adjustment, and at the same time, the cyclodextrin is incinerated and removed. Brazing is performed under the brazing conditions of.

In addition, in the above-mentioned step, the firing condition is particularly about 100 to 250.
The reason why the temperature of ℃ is about 5 to 60 minutes is to satisfactorily incinerate cyclodextrin contained in the flux before brazing, that is, the temperature is 100 ℃.
If the time is less than 5 minutes and the time is less than 5 minutes, the removal by incineration may be insufficient.
This is because if the temperature is too high, exceeding 60 minutes, the surface oxidation of the metal material is promoted, which is not preferable.

The present invention has been achieved based on the above findings,
The present invention relates to a brazing flux containing about 1 to 20% by weight of cyclodextrin with respect to the flux, and a brazing flux containing about 1 to 20% by weight of cyclodextrin with respect to the flux. The present invention provides a brazing method, which comprises applying a brazing metal on the surface of a metal member to be brazed, followed by firing and brazing.

Further, according to the present invention, the flux residue lump that has occurred during brazing using the conventional flux is not recognized, and the appearance after brazing is improved.

It is assumed that this feature is based on the following reasons.

That is, KF, KCl, NaCl, Licl, Znc
The brazing flux such as l ₂ has hygroscopicity to some extent. Therefore, if it is left in a powder state, it absorbs water, it is difficult to maintain the powder state, it becomes a flux residue lump after brazing, which is difficult to remove,
It caused a deterioration in appearance.

However, when cyclodextrin is contained in an amount of about 1 to 20% by weight with respect to the flux, the flux can maintain a powder state in a good state, and there is no flux residue lump after brazing, which causes the conventional problems. It was resolved.

[Examples 1 to 4] For example, KF (46% by weight) -AlF ₃ which is hygroscopic and hardly pulverized.
A predetermined amount of β-cyclodextrin was added to the (54% by weight) flux, and the mixture was thoroughly mixed, and the mixture was crushed into particles of a predetermined size, and KF having β-cyclodextrin attached to the surface was mixed. -Get the AlF ₃ system flux.

Then, a β-cyclodextrin-adsorbed KF-AlF ₃ -based flux suspension is prepared using this β-cyclodextrin-adsorbed KF-AlF ₃ -based flux and ethyl alcohol. And, for example, 4045 on both sides of the core 3003 aluminum alloy plate
A brazing sheet having aluminum alloy brazing adhered thereto and a 3003 aluminum alloy plate are combined in a T shape, and the above suspension is uniformly applied to this T shape product. Then, after baking this in an atmospheric furnace, a predetermined brazing operation (holding for 5 minutes in an inert gas atmosphere at a brazing temperature of 600 ° C.) is performed.

[Example 5] As a flux, NaCl (26 wt%)-KC was used instead of KF-AlF _3.
1 (54 wt%)-ZnCl ₂ (12 wt%)-LiF (8 wt%)

[Comparative example]

A brazing operation is carried out in the same manner using the KF-AlF ₃ flax to which no β-cyclodextrin was added as used in Example 1.

〔Characteristic〕

The brazing properties of the products obtained in Examples 1 to 5 and the comparative example and the appearance after brazing are examined and the results are shown in the table.

In the evaluation of the brazeability test, a circle is marked when a sufficiently large fillet is formed without interruption, and a triangle is marked when a part of the brazing is bad and the brazing is not formed, and almost no fret is formed. The case is represented by a cross.

Claims (2)

[Claims] 1. A brazing flux comprising about 1 to 20% by weight of cyclodextrin with respect to the flux. 2. A brazing method comprising applying a brazing flux containing cyclodextrin in an amount of about 1 to 20% by weight based on the flux to the surface of a metal member to be brazed, followed by firing and brazing. Attaching method.