JPH0355235B2 - - 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. This flux is 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. Furthermore, compared to the flux brazing method, it is inferior in that it requires stricter precision in 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. 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 the mixture using KF and AlF ₃ as raw materials and powdering 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, in the state before brazing, KF-AlF ₃ or K ₃ -AlF ₆ -KAlF ₄ or K ₃ AlF ₆ -AlF ₃
or KAlF ₄ , K ₃ AlF ₆ − in the state 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 advantage of not requiring cleaning after brazing. These fluxes can also be applied in any form for brazing, 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 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 a good bond 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 comprises substantially 60 to 70% by weight of K ₃ AlF ₆ ,
This is a flux for brazing aluminum materials, which is made of a mixture consisting of 27 to 37% by weight of AlF ₃ and 0.1 to 10% by weight of KBF ₄ , or a product obtained by powdering 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, and generally a level of impurity that is mixed in with commercially available fluoride is acceptable, but only as a pure substance.
This is because only the weight ratio of the three substances in terms of K ₃ AlF ₆ , AlF ₃ and KBF ₄ is important for the flux function of the present invention. Substantial in KBF ₄ additive-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 KBF ₄ is added, the improvement is significant. 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 an amount exceeding the upper limit, the flux will evaporate rapidly and brazing will become difficult. Known fluoride fluxes remain mixed;
Alternatively, the fluxes of the present invention can be prepared by melting them after mixing and forming a solidified product into a powder frame, 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)
KBF ₄ was added to both components to obtain a flux of 64.28% by weight of K ₃ AlF ₆ - 30.43% by weight of AlF ₃ -.
KBF ₄ was mixed at a ratio of 5.29% by weight,
Regarding the KBF _4- 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 operating temperature was determined from this. The measurement results are shown in Table 1. By adding KBF ₄ in this manner, good results were obtained in which both the liquidus temperature and the solidus temperature were lowered, and a reduction 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. The results are shown in Table 2. Regarding the fillet appearance and cross-sectional shape, in the case of KBF ₄ -added flux, a similar color is obtained compared to fluxless brazing and non-additive flux brazing, and when comparing the fillet cross-sectional area, it is seen from the average value and dispersion. and
It can be seen that the most stable brazing can be obtained with the KBF ₄ -added flux.

[Table] Example 3 The solubility of the KBF ₄ -added flux shown in Example 1 and the non-additive flux in water 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 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, which improves the state of the joints by flux-less inert gas atmosphere brazing methods and chloride-based fluxes. It is as good as the flux furnace brazing method, and also has non-hygroscopicity and substantially water-insolubility, which are the characteristics of fluoride-based fluxes.

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 KBF ₄ ,
Or a flux for brazing aluminum and aluminum alloy materials, which is obtained by crushing a molten solidified product of the mixture.