JPH0148117B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to the composition of flux used for brazing aluminum (including aluminum alloys) materials. Prior Art Flux brazing, in which a layer of aluminum brazing alloy having a melting point lower than that of the aluminum materials to be joined is interposed between the aluminum materials to be joined, is generally performed using flux brazing which mainly contains chloride. fluxes are used in the atmosphere. These fluxes are water-soluble in nature, generally hygroscopic, and corrode aluminum, including aluminum braze alloys, in the presence of water. Therefore, such flux brazing residues must be removed by cleaning after the brazing process. Vacuum brazing and inert atmosphere brazing are already known as fluxless brazing methods that perform brazing without using flux. Requires a special aluminum material for the filler or brazing alloy. Furthermore, it is inferior to the flux brazing method in that it requires greater precision in the clearance of the brazed portion. In addition, after brazing, it is virtually insoluble in water,
Fluoride fluxes are also known that leave a residue on the braze surface that is non-hygroscopic and non-corrosive to aluminum. That is, according to British Patent No. 1055914,
A flux containing a mixture of AlF ₃ and KF has been proposed. Furthermore, Japanese Patent Publication No. 58-27037 proposed a flux consisting of KAlF ₄ and K ₃ AlF ₆ as a flux that is non-hygroscopic before brazing and substantially water-insoluble after brazing. ing. This flux is obtained by melting a mixture of KF and AlF ₃ as raw materials and pulverizing the solidified product, and the solidified product contains KAlF ₄ and
K ₃ AlF ₆ is generated. Raw material components KF and AlF ₃
It is recommended that the ratio be as close to the eutectic composition of both components as possible. In this way, KF-AlF ₃ or K ₃ AlF ₆ - KAlF ₄ or K ₃ AlF ₆ - AlF ₃ or KAlF ₄ before brazing, and K ₃ AlF ₆ - after brazing.
These fluoride fluxes, which have the substantial chemical formula KAlF ₄ or KAlF ₄ , or combinations thereof, have the advantages of conventional chloride-based fluxes, as well as the fact that the residue is non-hygroscopic and non-corrosive to aluminum. It has the great advantage of not requiring cleaning after brazing. Furthermore, these fluxes can be applied to brazing in any form, and are particularly suitable for torch brazing and furnace brazing. However, these fluxes have the disadvantage that the operating temperature is slightly higher than that of chloride-based fluxes, making it difficult to obtain good joints. The action mechanism of flux in brazing has not been fully elucidated, but as a flux,
Generally, before the brazing alloy starts melting, the flux melts and covers the brazing surface, destroys and removes the surface oxide film, and improves the wettability of the base material.
What is needed is something that helps the flow of the braze alloy to the brazing surface, and also has the ability to block contact with air and prevent re-oxidation. Therefore, it is significant in brazing to moderately lower the working temperature of flux. Purpose An object of the present invention is to use a flux for brazing aluminum materials, which has a lower operating temperature than conventional fluoride fluxes, and thereby enables a fluxless inert gas atmosphere brazing method.
It can form good joints similar to the furnace brazing method using chloride flux, and is substantially water-insoluble and non-hygroscopic.
The purpose of the present invention is to provide a fluoride flux. Composition The present invention substantially comprises 60 to 70% by weight of K ₃ AlF ₆ ,
A flux for brazing aluminum and aluminum alloy materials, which is made of a mixture of 27 to 37% by weight of AlF ₃ and 0.1 to 10% by weight of PbF ₂ , or a product obtained by crushing a molten solidified product of the mixture. The term ``substantially'' used here means that the fluoride used as a raw material does not necessarily have to be of high purity; it is acceptable to have impurities that are more mixed in than ordinary commercially available fluoride, but only as a pure substance. of
This is because only the weight ratio of the three substances in terms of K ₃ AlF ₆ , AlF ₃ , and PbF ₂ is important for the function of the flux of the present invention. Substantial in _PbF2- free flux
Preferred values for the weight ratio of K ₃ AlF ₆ and AlF ₃ are known from known literature (e.g. B. Phillips et al. J. Amer. Ceram. Soc.
It can be easily understood from the KF-AlF ₃ system binary phase diagram of Vol. 49 (1966, page 632), and as shown in this, the eutectic composition is
AlF ₃ 54.2% by weight (KF55 mol% - AlF ₃ 45 mol%)
Or, it is a ratio corresponding to before or after that. The present invention further provides for a mixture or molten mixture having substantially this weight ratio of 99.9 to 90% by weight.
When 0.1 to 10% by weight of PbF ₂ is added, the improvement is significant. If the amount of PbF ₂ added is less than the specified lower limit,
It does not have the desired effect, and if added in excess of the upper limit, the working temperature of the flux will rise, which is unfavorable for brazing. Incidentally, Pb dissociated above the working temperature has the effect of lowering the surface tension of the solder and improving the brazing properties. Known fluoride fluxes remain mixed;
Alternatively, it can be prepared by mixing, melting, and pulverizing the solidified product, but the flux of the present invention can similarly be prepared by various methods. Next, examples and effects thereof will be described. Example 1 Using technical grade K ₃ AlF ₆ and technical grade AlF ₃ and taking into account the purity of each, substantially K ₃ AlF ₆ 67.87
% by weight - AlF ₃ 32.13% by weight and melted (melting temperature is 562℃ of eutectic temperature)
The flux was prepared by adding PbF ₂ to both components (with a target temperature of about 100°C or above), and the flux was substantially K ₃ AlF ₆ 67.75% by weight - AlF ₃ 32.07% by weight.
PbF ₂ was mixed at a ratio of 0.18% by weight,
Regarding the PbF ₂ -added flux prepared by melting this, the respective operating temperatures were measured by the following method. That is, a certain amount of both of the prepared fluxes was placed in a platinum crucible, heated and melted in an argon atmosphere, and then
Thermal analysis was performed by a cooling method at a cooling rate of 1° C./min, the liquidus temperature and solidus temperature were measured, and the working temperature was determined from these. The measurement results are shown in Table 1. As described above, by adding PbF ₂ , good results were obtained in which the solidus temperature was lowered, and a lowering of the operating temperature was confirmed.

[Table] Example 2 A brazing test was conducted in an inert atmosphere (fluxless brazing is not possible in this atmosphere) using the PbF _2- added flux and the non-additive flux shown in Example 1. Fluxless inert atmosphere brazing in an active atmosphere was performed. The bonding states of these were compared. The figure shows the joint used in the brazing test. A3003 with BA4045 aluminum alloy filler metal clad on both sides on A3003 aluminum alloy
Brazing sheet 2 made of aluminum alloy
is fixed at the joint angle θ, and after heating at 600°C for 3 minutes, the fillet length L is measured and the filling rate (L/Lo x
100). The results are shown in Table 2. Comparing the filling rate
In the case of PbF ₂ -added flux, the value is higher than that of additive-free flux brazing and flux brazing, indicating that excellent brazed parts can be obtained by using the flux of the present invention. This result is due to the lowering of the working temperature of the flux of the present invention and the lowering of the surface tension of the solder due to Pb dissociated above the working temperature.

[Table] Example 3 The solubility in water of the PbF _2- added flux and non-additive flux shown in Example 1 was measured, and these were compared with the water solubility of the main components of the chloride flux (literature values). I did it. The results are shown in Table 3, and in the case of the PbF ₂ -added flux k, it is comparable to that of the non-additive flux, and the chloride component is extremely low.

【table】

[Table] Effects The flux for brazing aluminum materials of the present invention has a lower operating temperature than conventional fluoride-based fluxes, and has the ability to dissociate above the operating temperature.
By lowering the surface tension of the solder with Pb, the condition of the joint becomes as good as that of fluxless inert gas atmosphere brazing method or chloride flux furnace brazing method, and it also improves the properties of fluoride flux. However, it is non-hygroscopic and substantially water-insoluble.

[Brief explanation of drawings]

The figure is an explanatory diagram showing the configuration of the joint used in the brazing test. 1...A3003 aluminum alloy, 2...brazing sheet.

Claims (1)

[Claims] 1 Substantially K ₃ AlF ₆ 60-70% by weight, AlF ₃ 27-37
% by weight and a mixture consisting of 0.1-10% by weight of _PbF2 ,
Or a flux for brazing aluminum and aluminum alloy materials, which is obtained by crushing a molten solidified product of the mixture.