JPH0355236B2 - - 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, which involves interposing an aluminum brazing alloy layer with a melting point lower than the melting point of the aluminum materials to be joined between the aluminum materials to be joined, generally uses chloride as the main component. 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 special aluminum material for bonding. Furthermore, compared to the flux brazing method, it is inferior in that stricter precision is required for the clearance of the brazed portion, and the aluminum material that can be used is not a common one. 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. Further, according to Japanese Patent Publication No. 58-27037, a flux that is non-hygroscopic before brazing and substantially water-insoluble after brazing is
A flux consisting of KAlF ₄ and K ₃ AlF ₆ has been proposed. This flux is obtained by melting the mixture using 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 being generated. It is recommended that the ratio of the raw material components KF and AlF ₃ be as close to the eutectic composition of both components as possible. 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. These fluxes can also be applied to brazing in any form, and are particularly suitable for torch brazing or furnace brazing in the form of an aqueous slurry. 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 begins to melt, flux melts and covers the brazing surface, destroying and removing the surface oxide film, increasing the wettability of the base metal, and helping the brazing alloy flow to the brazing surface. Also, it is necessary to have the ability to prevent re-oxidation by blocking contact with air. 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 is an object of the present invention to provide a fluoride-based flux which can form good joints similar to the furnace brazing method using chloride-based fluxes, and which is non-hygroscopic and substantially water-insoluble. Structure The present invention is a method for brazing an aluminum material obtained by crushing a molten solidified product of a mixture substantially consisting of 40 to 70% KF, 47 to 56% by weight of AlF ₃ and 0.1 to 10% by weight of KBF ₄ . It is a flux for use. 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 KF, AlF ₃ and KBF ₄ is important for the function of the flux of the present invention. KBF ₄ Substantial KF in non-additive flux
Preferred values for the weight ratios _of
Vol. 49 (1966) page 623), it can be easily understood from the KF-AlF _3- system binary phase diagram, and as shown in this, the eutectic composition is
AlF ₃ 54.2% by weight (KF55 mol% - AlF ₃ 45 mol%)
Or the corresponding ratio before and after that. The present invention further provides for a mixture or a molten mixture having substantially this weight ratio of 99.9 to 90% by weight.
When 0.1 to 10% by weight of KBF ₄ is added, the improvement is remarkable. If the amount of KBF ₄ added is less than the specified lower limit, the desired effect will not be achieved, and if it is added in a larger amount than the upper limit, the evaporation of the flux will become intense and brazing will become difficult. Next, examples and effects thereof will be described. Example 1 Using industrial KF and industrial AlF ₃ and taking into account their respective purity, substantially KF45.8% by weight -
A flux prepared by mixing AlF ₃ at a ratio of 54.2% by weight and melting this (the melting temperature was set at approximately 100°C above the eutectic temperature of 562°C), and a flux prepared by mixing KBF ₄ in both components. Added to substantially KF43.38
The working temperature of each of the KBF _4- added flux prepared by mixing and melting the mixture in a ratio of weight% - AlF ₃ 51.33 weight% - KBF ₄ 5.29 weight% was measured by the following method. did. 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 carried out by the cooling method at a cooling rate of 1° C./min, the liquidus temperature and the solidus temperature were measured, and the working temperature was thereby determined. The measurement results are shown in Table 1.
As described above, by adding KBF ₄ , good results were obtained in which both the liquidus temperature and the solidus temperature were lowered, and a decrease in the operating temperature was confirmed.

[Table] Example 2 Brazing was performed in an inert atmosphere (fluxless brazing is not possible in this atmosphere) using the KBF ₄ -added flux and non-additive flux shown in Example 1, and in a standard inert atmosphere. Fluxless inert atmosphere brazing was performed in the atmosphere. The bonding states of these were compared and the results are shown in Table 2. In the case of KBF _4- added flux, the appearance and cross-sectional shape of the fillet are similar to those of fluxless brazing and non-additive flux brazing.
Comparing the fillet cross-sectional areas, it can be seen that the most stable brazing can be obtained with the KBF _4- added flux when looking at the average value and variation.

[Table] Example 3 The solubility in water of the KBF ₄ -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 chloride flux (literature values). I did it. The results are shown in Table 3, and in the case of the KBF _4- added flux, it is comparable to 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, so that the state of the joint can be improved by fluxless inert gas atmosphere brazing method or chloride-based flux. This makes it as good as the fluoride flux furnace brazing method, and also maintains the non-hygroscopicity and substantially water insolubility, which are the characteristics of fluoride fluxes.

Claims (1)

[Claims] 1. Brazing of aluminum and aluminum alloy materials, which is obtained by crushing a molten solidified mixture of 40-47% by weight of KF, 47-56% by weight of AlF ₃ and 0.1-10% by weight of KBF ₄ . Flux for use.