JPS6360097A - Production of flux for brazing of aluminum material and brazing method - Google Patents

Abstract

PURPOSE:To simplify production of a flux which obviates the generation of defective appearance of an Al material surface by controlling the drying temp. of a pasty material prepd. by adding water to a mixture is the range of the region near the eutectic point compsn. of AlF3 and KF to a specific temp. CONSTITUTION:The AlF3 and KF are uniformly mixed dry in the range of the eutectic point compsn. thereof of the compsn. near the same; thereafter, water is added thereto and the mixture is kneaded or the KF is preliminarily dissolved in the water and the AlF3 is added to the aq. soln. thereof and is kneaded. The pasty material obtd. in the above-mentioned manner is dried at the temp. above 450 deg.C and below the m.p., then the dried matter is pulverized. The flux prepd. to an aq. suspension exhibits the tendency to an increase in alkalinity and the detect arises in the surface appearance of the Al material after brazing, if the drying temp. at this time is below 450 deg.C. A cooled ingot is solidified to the hard matter by melting of the flux components and the pulverization in the next stage is difficult, if the drying temp. exceeds the m.p. of the above-mentioned mixture.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing a flux for brazing aluminum materials made of aluminum or an alloy thereof, and a method for brazing aluminum materials using the flux. More specifically, the present invention relates to a method for producing a non-corrosive fluoride flux using AQ F3 and KF as starting materials, and a brazing method using the same.

In this specification, "%" indicates a percentage by weight.

Conventional technology and its findings Conventionally, when manufacturing aluminum heat exchangers such as automobile radiators, car cooler evaporators, or condensers using brazing specifications, a chloride-based flux containing zinc chloride was used to heat the aluminum heat exchangers. A method of joining exchanger components by brazing is often used.

However, when using such a chloride-based flux, the flux used is essentially water-soluble and has strong hygroscopic properties, so it is necessary to quickly clean the flux residue after brazing. This requires removal, which increases equipment costs, complicates the process, and imposes a heavy workload. In addition, even if the above-mentioned cleaning is incomplete, or even if it is thoroughly cleaned, there is a risk that the aluminum parts will corrode relatively early due to residual flux components incorporated into the metal of the joint. was there.

On the other hand, as a brazing method that basically does not require flux cleaning as described above, for example, British Patent No. 105591
Aluminum fluoride (A
Brazing methods have already been proposed using fluoride-based fluxes, which are themselves non-corrosive, and consist of mixtures of potassium fluoride (KF) and potassium fluoride (KF). This known flux is 53-55% A12F3 and 47-45%
KF and KF are dry mixed and water is added to make a paste, or KF is made into an aqueous solution and AQFs is added to make a paste, and this paste is dried by heating at a temperature of 200°C or less. It is something that can be obtained by doing so.

However, when brazing an aluminum heat exchanger using this fluoride flux, for example, the flux is suspended in water and the suspension is After coating the heat exchanger by immersing it in it, it is dried and then heated to approximately 600°C in a non-oxidizing atmosphere such as an N2 gas atmosphere to perform brazing.The resulting brazed product is There were disadvantages in that the surface of the aluminum material had gray to white non-uniform stains, and the surface of the fillet portion also had a rough surface, resulting in a stained appearance. Therefore, in order to improve the appearance, it has become necessary to wash with an acid or alkaline etching solution after brazing. However, the use of fluoride-based flux has one important advantage in that it is non-corrosive and does not require flux cleaning after brazing, as described above. Requiring acid or alkaline cleaning after brazing to improve the surface negates the above advantages.

Other known examples of fluoride brazing flux include:
As shown in Japanese Patent Publication No. 58-27037, AQ
Fs and KF are used as starting materials and mixed uniformly in an appropriate ratio corresponding to a eutectic mixture.
It is known to heat it in advance to above its melting point to melt it, cool it, and then finely grind the resulting cooled mass.

This flux has a composition of KA as a complex compound.
It exhibits the state of a homogeneous mixture of QF4 and K3AΩF6, and is itself non-absorbent and stable. When this flux is used, even when the flux is made into an aqueous suspension and applied to an aluminum material for brazing, the phenomenon of deterioration of the appearance of the surface of the aluminum material as described above does not occur. Therefore, a fluoride flux made of this complex compound has high practical advantages.

However, there is a problem in that it takes time and effort to produce the flux itself, and in particular, since the cooled mass of the molten mixture of AQ F3 and KF is hard, it is difficult to crush it, which requires a lot of time and effort.

This invention was developed in view of the background of the prior art as described above.
The object of the present invention is to develop a brazing method that does not cause the above-mentioned appearance defects after brazing, while using a easily prepared fluoride flux made from S and KF as raw materials.

More specifically, the flux can be easily prepared, and even when the flux is applied in the form of an aqueous suspension and brazed, there will be no stains on the surface of the aluminum material. The purpose is to prevent appearance defects due to such occurrence.

Means for Solving the Problems For the above purpose, the present inventors used the above-mentioned KF and AgF.
We investigated the causes of problems when using a flux obtained by adding water to a mixture with No. 3 and drying it to form a paste. However, when the flux is suspended in water, the hydrogen ion concentration of the suspension is quite alkaline with a pH of around 10, and if this flux is directly applied to an aluminum material and brazed, after application, During discharge before brazing and during brazing, a high-pH flux suspension in water may react with aluminum to generate hydroxide on the surface of the aluminum material, or unevenly dissolve aluminum and generate smut. However, it was discovered that this caused the aforementioned problem of poor appearance.

The present invention has been made based on this clarification.

Therefore, in the flux manufacturing process, this invention
By controlling the drying temperature of a paste-like product made by adding water to a mixture of AgF3 and KF within a predetermined range, we can create a flux that is easy to manufacture and whose hydrogen ion concentration and pH do not exhibit strong alkalinity even when suspended in water. It was possible to complete it by finding the facts that can be obtained.

That is, one aspect of the present invention relates to a simple method for producing flux, in which AffF3 and KF are uniformly mixed within a range of their eutectic point composition or a composition in the vicinity thereof, and water is added to form a paste. The gist of the present invention is to provide a method for producing a flux for brazing aluminum materials, which comprises producing a paste, drying the paste at a temperature of 450° C. or more and below the melting point, and then pulverizing the dried product.

Another invention relates to a method for brazing aluminum materials using the flux obtained as described above, wherein the flux is suspended in water and the aqueous suspension is applied to the aluminum materials to be joined. The gist of the present invention is a brazing method for aluminum materials, which is dried and then heated to a predetermined temperature in a non-oxidizing atmosphere to melt and braze a joining brazing material.

In the present invention, it is preferable that the mixing ratio of AgF3 and KF used as starting materials for producing the flux be as close to the eutectic point composition as possible. Therefore, ideally the mixing ratio of A[F3 and KF is a relative ratio of 54.1%:45.9%, which provides the lowest melting point, but especially the eutectic point of AgF2. Even if the content exceeds the composition, the increase in the melting point is slight. The mixing ratio of AgF2 and KF as an allowable range is approximately 60-50% = 40-50%.

A paste may be prepared by uniformly dry-mixing fine powders of AgF2 and KF in advance, then adding the required amount of water and kneading, or by dissolving KF in water in advance. However, AgF2 may be added to this KF aqueous solution and kneaded.

In the subsequent step of drying the paste-like material, temperature control is important. That is, the lower limit of the drying temperature is at least 450°C.
above, and the upper limit is the melting temperature of the flux component (approximately 560
(°C) or less.

If the drying temperature is lower than 450°C, the pH tends to become strongly alkaline when made into an aqueous suspension, similar to the flux produced by the conventional method described above, resulting in defects in the surface appearance of the aluminum material after brazing. Therefore, the intended purpose of this invention cannot be achieved. On the other hand, the drying temperature is AgF
If the temperature exceeds the melting point of the mixture of No. 3 and KF, the cooling ring will become a hard solidified substance due to the melting of the flux components, making it difficult to grind in the next step. This increases the complexity and manufacturing difficulties. The most suitable drying temperature is approximately 470~
The temperature is about 500°C.

The dried product obtained above is a brittle solid. Therefore, it can be easily crushed by means such as stirring.

By this pulverization, the desired fluoride flux in a fine powder state is obtained. The particle size of this flux is preferably 200 μm or less, particularly 150 μm or less, so that it can be easily suspended uniformly in water.

When brazing aluminum materials, the flux obtained above is used by suspending it in water in the form of a slurry with a concentration of about 7 to 1096. The hydrogen ion concentration pH of this suspension is generally in the range of 7 to 8 when using the flux according to the present invention, and when applied to aluminum materials to be joined, it has almost no harmful effect on the surface of the aluminum materials. do not have. Although it is possible to apply a suspension of flux in water to aluminum materials by spraying or brushing, it is recommended to use the dipping method as a uniform application method suitable for mass production. .

The aluminum materials to be joined are dried after applying the above flux, and then heated in a non-oxidizing atmosphere such as an inert gas atmosphere using an aluminum alloy brazing filler metal whose melting point is lower than that of the aluminum materials. about 58 lower and higher than the melting point of the flux and brazing material.
By heating to 0 to 620°C, the brazing material is melted and a brazed joint is achieved. AQ-5i alloy with a St content of about 4.5 to 13.5% is normally used as the top filler filler metal, and from the viewpoint of workability, the filler metal is usually made of aluminum to be joined. It is used by cladding at least one of the materials.

Effects of the Invention The method for producing flux according to this invention is based on AQF3 and K.
Water is added to the mixture with F to form a paste, which is then dried at a temperature below the melting point of the above mixture and crushed into a brittle dry product. Compared to the case where flux is produced by pulverizing lumps, pulverization is particularly easy, and as a result, flux can be produced even more easily.

Moreover, when this flux is suspended in water, the hydrogen ion concentration of the aqueous suspension becomes neutral or close to pH 7 to 8, so it is difficult to use the flux in the form of an aqueous suspension. In the brazing method of the present invention, the surface of the aluminum material after brazing can be kept in a good appearance without stains, and the surface of the fillet can also be made smooth. Therefore, there is no need for cleaning with acid or alkali to improve the appearance after brazing, and the advantages of using non-corrosive fluoride flux can be enjoyed as is. Of course, the flux according to the present invention is non-hygroscopic in itself, and even when used as a suspension in water, it does not cause non-uniformity of the flux component composition, exhibits stable flux action, and has good properties. It can guarantee good brazing properties.

Example AQF3; 54.1% and KF, 45.9% are uniformly dry mixed, a small amount of water is added to this to make a paste, and this paste is then dried at a drying temperature of 10%.
Each rod was dried at a temperature ranging from 0 to 600° C. for 1 hour. Then, this dried material was pulverized to produce a fine powder flux.

Next, each of the fluxes obtained above was mixed with water to make an aqueous suspension with a concentration of 10%,
This was uniformly applied to the surface of an assembly of aluminum materials to be bonded for testing by a dipping method. The aluminum material assembly for this bonding test was A300 as shown in Figure 1.
A core material (2a) is attached to a first member (1) made of three alloys having a length Q of 70 mm, a width W of 25 mm, and a thickness of t -2 mm.
3003 alloy, and a second member (2) of the same size as above, which is clad on both sides with skin materials (2b) (21)) made of A4043 alloy at a cladding rate of 10%, is combined in a T-shape. Using. The assembly coated with the flux suspension was then dried and then heated in a N2 gas atmosphere at 610° C. for 10 minutes to perform brazing.

The appearance of the surface of the aluminum material after brazing was compared by visual inspection, and the hydrogen ion concentration and pH of the aqueous flux suspension used were measured and compared with the above appearance. The results were as follows: It was as shown in the table.

Note that the brazing condition was good no matter which flux was used.

[Left below] [Brief explanation of the drawing]

FIG. 1 is a perspective view showing an assembly of bonded test pieces used in an example of the present invention. (1)...first member, (2)...second member, (2b
)...Leather material. that's all

Claims (2)

[Claims] (1) AlF_3 and KF are mixed uniformly within their eutectic point composition or the composition region near it, water is added to make a paste, and the paste is heated to 450°C.
A method for producing a flux for brazing aluminum materials, which comprises drying at a temperature below the melting point and then pulverizing the dried product. (2) Mix AlF_3 and KF uniformly within the range of their eutectic point composition or the composition region near it, add water to make a paste, and heat the paste at a temperature of 450°C or higher and below the melting point. After drying, the dried material is crushed to make a flux, the obtained flux is then suspended in water, the aqueous suspension is applied to the aluminum materials to be joined, and after drying, A brazing method for aluminum materials that involves heating to a predetermined temperature in an oxidizing atmosphere to melt and braze the joining filler metal.