JPH0216200B2 - - 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 fluxes, but also have a non-hygroscopic residue and non-corrosion to aluminum. Therefore, it has the great advantage of not requiring cleaning after brazing. Also,
These fluxes can be used in any form of brazing, 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 brazing material melts and covers the brazing surface, destroying and removing the surface oxide film, increasing the wettability of the base metal, and allowing the brazing alloy to flow to the brazing surface. There is a need for something that has the ability to help 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 possible to form a good joint similar to the furnace brazing method using chloride-based flux, and it is also possible to improve the corrosion resistance of the joint, and it is substantially water-insoluble and non-hygroscopic. The purpose of the present invention is to provide a fluoride flux. Composition In order to achieve the above object, the present invention adds ZnF ₂ to the composition of conventional fluoride-based flux, thereby lowering the working temperature of additive-free flux, and also lowering the working temperature during brazing. Corrosion resistance has also been improved by forming an Al--Zn alloy on the surface of the aluminum alloy through reaction. That is, the present invention substantially comprises 60-70% by weight of K ₃ AlF ₆ , 27-37% by weight of AlF ₃ and 0.1-5% by weight of ZnF ₂ .
(However, this flux does not contain 5% by weight) or a product obtained by crushing a molten solidified product of the mixture, for brazing aluminum materials. 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 ZnF ₂ is important for the function of the flux of the present invention. Substantial in _ZnF2- 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.
ZnF ₂ 0.1 to 5% by weight (excluding 5% by weight)
The improvement is remarkable when . Addition of ZnF ₂ lowers the operating temperature of flux, and Zn generated from ZnF ₂ diffuses into Al-
Since it forms a Zn alloy and its potential is less noble than that of ordinary aluminum alloys, it also significantly improves the corrosion resistance of brazed parts due to the sacrificial anode effect. If the amount of ZnF 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, brazing properties will deteriorate. 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 , taking into account their respective purity, substantially
A flux prepared by mixing the mixture in a ratio of 67.87% by weight of K ₃ AlF ₆ - 32.13% by weight of AlF ₃ and melting the mixture (the melting temperature was set at approximately 100°C above the eutectic temperature of 562°C). , ZnF ₂ is also added to both components, resulting in substantially K ₃ AlF ₆ 67.77% by weight − AlF ₃ 32.08
wt% - ZnF ₂ 0.15 wt%, and
K ₃ AlF ₆ 64.90% by weight − AlF ₃ 30.72% by weight,
The working temperature of each of the ZnF ₂ -added flux prepared by mixing and melting the ZnF ₂ at a ratio of 4.38% by weight was 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 ZnF ₂ , 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 A brazing test was conducted in an inert atmosphere (fluxless brazing is not possible in this atmosphere) using the ZnF ₂ (0.15% by weight) added flux and non-additive flux shown in Example 1. Fluxless inert atmosphere brazing was performed in a suitable inert atmosphere. The bonding states of these were compared. The figure shows a joint using a brazing test. BA4045 aluminum alloy filler metal is clad on both sides of A3003 aluminum alloy 1.
The brazing sheet 2 made of A3003 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×100) was calculated. The results are shown in Table 2. Comparing the filling rate
In the case of ZnF 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.

[Table] Example 3 The brazing samples using the ZnF ₂ (0.15% by weight) added flux and the non-additive flux shown in Example 1 were subjected to a dry-wet alternating test (pH 3, 40°C 30°C).
% NaCl water for 30 minutes, then dried in air at 50°C for 30 minutes) for one month, and the corrosion resistance was compared. As shown in Table 3, when ZnF ₂ -added flux is used, the pitting corrosion resistance is significantly improved.

[Table] Example 4 The solubility in water of the ZnF ₂ (0.15% by weight) added flux and the non-additive flux shown in Example 2 was measured, and the solubility of the main components of these and the chloride flux in water (literature value) was measured. ). The results are shown in Table 4, and in the case of the ZnF ₂ -added flux, it is comparable to the non-additive flux, and is extremely low compared to the chloride component.

【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. By adding ZnF ₂ , an Al-Zn alloy is formed by diffusion on the aluminum alloy surface, and its sacrificial anode effect improves the brazing properties of the brazed parts. Improves corrosion resistance. Furthermore, it possesses non-hygroscopicity and substantial water solubility, which are characteristics of fluoride fluxes.

[Brief explanation of drawings]

The figure is an explanatory drawing 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
Weight% and ZnF ₂ 0.1 to 5% by weight (however, 5% by weight
Flux for brazing aluminum materials, which is obtained by crushing a molten solidified mixture consisting of (excluding)