JPH052433B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a brazing flux and a brazing method using such a flux, and particularly to a flux and brazing method suitable for brazing aluminum, copper, iron, titanium, or alloys thereof. Regarding the method. The flux of the present invention has a function as a brazing material, and therefore can be brazed without using a brazing material. [Background of the Invention] Conventionally, chloride-based fluxes have been generally used for brazing Al or Al alloys. However, this chloride-based flux is highly hygroscopic and corrodes the base material by absorbing moisture. Therefore, with chloride-based fluxes, there was a problem in that the residual flux had to be completely removed after brazing. As a flux that has improved the problem of corrosion,
Fluoride-based fluxes have been proposed as shown in US Pat. No. 3,951,328. This fluoride flux is potassium fluoride.
KF and aluminum fluoride AlF ₃ are mixed and dissolved to contain a mixture of K ₃ AlF ₆ and KAlF ₄ . However, since this flux does not have the function of a brazing material, a separate brazing material is required for brazing. [Object of the invention] The object of the present invention is to have a function as a brazing material,
Therefore, it is an object of the present invention to provide a flux that can be brazed without using a brazing material and a brazing method using such a flux. [Summary of the Invention] The flux of the present invention contains tin fluoride and zinc fluoride in a ratio of 60 to 90% by weight of tin fluoride and 40 to 10% by weight of zinc fluoride. Apply such flux to the brazing surface of the base metal,
When heated to brazing temperature in an inert gas atmosphere,
Simultaneously with the flux action, the fluoride decomposes to produce metal precipitation, and the deposited metal can be used for brazing. The flux of the present invention is non-hygroscopic and therefore does not corrode the base material. Therefore, there is no problem even if the residual flux is not removed after brazing. The metal precipitated during brazing using the flux of the present invention is mainly tin, and the brazing material is substantially made of tin. However, when the flux is made up of only tin fluoride, the flux action is insufficient and the tin does not firmly adhere to the brazed portion, making it easy to peel off. Moreover, the temperature range in which it can be brazed is narrow, and it is necessary to heat it to over 500°C. By mixing tin fluoride and zinc fluoride,
The flux effect is enhanced and the amount of tin precipitated can be increased. The lower limit of brazing temperature is also approx.
The temperature reaches 400℃, which can be expanded by about 100℃. If the flux is composed only of zinc fluoride, zinc cannot be deposited as a metal, partly because the melting point of this fluoride is as high as about 872°C. When tin fluoride and zinc fluoride are mixed,
A small amount of zinc is also precipitated, and the precipitated zinc also acts as a brazing material. Note that the melting point of tin fluoride is about 250°C. In the flux of the present invention, the role of zinc fluoride is to promote the flux action and increase the amount of tin precipitated, so its amount should be smaller than that of tin fluoride. Specifically, the amount of tin fluoride is 60 to 90% by weight, and the remaining amount of zinc fluoride is 40 to 10% by weight.
If the amount of tin fluoride is less than 60% by weight, the amount of tin precipitated will be insufficient and it will be difficult to braze with only flux without using a brazing filler metal. If the amount of tin fluoride exceeds 90% by weight, the flux effect will be insufficient and tin will easily peel off from the brazed portion. An example of the flux of the present invention is composed only of tin fluoride and zinc fluoride. In addition to these components, cadmium fluoride, calcium fluoride, magnesium fluoride, copper fluoride, aluminum fluoride, lithium fluoride, potassium borofluoride, etc. can also be included. Cadmium fluoride, calcium fluoride, and magnesium fluoride also precipitate metal when heated to brazing temperatures, and the precipitated metal can serve as a brazing material. However, in this case, it is desirable that the amount of fluoride does not exceed 10% by weight of the total weight of the flux. Copper fluoride, aluminum fluoride, lithium fluoride, and potassium borofluoride all have a strong flux effect, so it is preferable to include them. Materials other than copper fluoride do not precipitate metal, and copper fluoride does not act as a brazing material although it precipitates metal. Therefore, it will not mix into the brazed parts and cause any adverse effects. Therefore, it can be contained in a large amount.
Specifically, the total amount of tin fluoride and zinc fluoride is 30 to 90.
% by weight, and the remaining 70 to 10% by weight is preferably composed of at least one of potassium fluoride, aluminum fluoride, lithium fluoride, potassium borofluoride, and copper fluoride. If the amount of the fluoride added to promote flux action is less than 10% by weight, the effect will be small, and if it is more than 70% by weight, sufficient solder cannot be supplied to the brazing location. It has been confirmed that when a flux promoting component such as potassium fluoride or aluminum fluoride is contained, if tin is used in the form of tin instead of as fluoride, it does not adhere well. Furthermore, it was confirmed that when zinc chloride is used instead of zinc fluoride, not only does it become necessary to remove residual flux, but also that zinc dissolves too much into the base material, causing deformation of the base material. An example of a brazing method using the flux of the present invention is shown below. (a) Mix the specified fluoride powder and add water to make a paste. This is heated to a temperature of about 100 to 120°C and dried. (b) Stir the powder well, then add water again to make a solution. (c) The solution is applied to the brazing surface of the base material, and then heated to evaporate water and dry. (d) Braze by heating to brazing temperature in an inert gas atmosphere. The step (a) above is performed to uniformly mix the flux raw materials. It is preferable that the fluoride powder is as small as possible, specifically 50 μm or less, especially
Particle sizes of 30 μm or less are preferred. When the flux raw material is mixed with water and then heated and dried, some of the fluoride reacts and hardens. Therefore, in step (b), it is crushed and made into powder again. Then, add water to form a solution. When applying a flux solution to the base material, the entire base material may be immersed in the solution. Flux attached to parts of the base material other than the brazing surface precipitates metal when heated to the brazing temperature, and this precipitate acts as a corrosion-resistant film. When a base material coated with the flux of the present invention is heated and brazed in the atmosphere, the wax does not adhere well to the base material and easily peels off. Brazing in an inert gas eliminates this problem. In the examples of the present invention, good results were obtained by brazing in a nitrogen atmosphere. A particularly preferred weight ratio of tin fluoride to zinc fluoride is 70-80% tin fluoride to 30-20% zinc fluoride. In addition, the flux that has undergone the step (a) above has the following properties:
_K3AlF6 , _K2LiAlF6 , _{KZnF3 , ZnF2} , _KF , _AlF3
and compounds such as _SnF2 . These compounds have extremely low hygroscopicity and are therefore stable for long periods even when stored as a flux. Furthermore, after brazing, the surface of the object to be brazed is marked with
Line diffraction studies revealed KZnF ₃ , KAlF ₄ , ZnO,
Compounds such as SnO and ZnSn were observed. A Zn-Sn alloy was also observed in the fillet. [Embodiments of the invention] Example 1 25% _SnF2 , 26% KF, 35% _AlF3 by weight
%, ZnF ₂ 4H ₂ O at 11%, LiF at 3% (No. 1 of the present invention), SnF ₂ at 70%,
Flux containing 30% ZnF ₂ 4H ₂ O (invention
No. 2) was created. When preparing the flux, each fluoride powder having a particle size of about 18 μm was used. First, water was prepared at a ratio of 0.6 to 1 part of the raw material fluoride, KF was added to this water, and then other fluorides were added little by little to form a paste while stirring. Next, the water is evaporated in a constant temperature bath at approximately 120°C. The solidified flux was pulverized using a pulverizer to create a flux powder. Water was again added to the flux thus prepared to obtain a solution having a flux concentration of approximately 20%, and two Al plates serving as the base material were immersed in this solution. One of the Al plates is a square with a side of 50 mm and a thickness of 1 mm, and the other one is a rectangle with a side length of 50 mm and a side length of 25 mm, and a thickness of 1 mm. It is. The Al plates taken out from the flux solution were combined into an inverted T-shape as shown in Figure 2, and the formation of fillets was examined. Further corrosion tests were conducted. In FIG. 2, reference numeral 1 indicates a square Al plate, 2 indicates a rectangular Al plate, and 3 indicates a flux. Brazing is done using an electric furnace while nitrogen is being introduced.
This was done by heating at 600°C for 3 seconds. For comparison, a test piece with the same shape as that used in the present invention was used, and the flux was expressed in weight%.
Components of KF 50%, AlF ₃ 50% (Comparative Example 1) and
KF34%, _AlF3 46%, _ZnF2・_4H2O14 % and LiF6
% (Comparative Example 2). In Comparative Example 1, the flux was prepared by melting, cooling, solidifying, and then pulverizing. Comparative Example 2 was made into a paste, dried and ground in the same way as in the present invention, and was used at a flux concentration of 20%. The corrosion test was conducted using the CASS test specified in JISH8681, which was operated continuously for 180 hours. Since brazing was not possible with the flux of the comparative example, a corrosion test was conducted on a sample of a 50 mm square, 1 mm thick Al plate coated with flux and heated at 600° C. for 30 seconds in N ₂ . The test results are shown in Table 1.

〔Effect of the invention〕

As described above, according to the brazing flux of the present invention, brazing can be performed without supplying solder.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing the relationship between the amount of tin and zinc precipitated from flux and heating temperature, and FIG. 2 is a perspective view showing the state in which flux is applied to the surface of a base material and the base materials are assembled. 1, 2...Base material, 3...Flux.

Claims (1)

[Scope of Claims] 1. Tin fluoride and zinc fluoride in a weight ratio of tin fluoride and zinc fluoride.
A brazing flux characterized by containing 60 to 90% by weight of zinc fluoride and 40 to 10% by weight of zinc fluoride. 2. The brazing flux according to claim 1, characterized in that it consists essentially only of the tin fluoride and the zinc fluoride. 3. Tin fluoride 60-90 to zinc fluoride 40-10 by weight
and contains a total of 30 to 90% by weight of both, and 70 to 10% by weight of at least one of potassium fluoride, aluminum fluoride, lithium fluoride, potassium borofluoride, and copper fluoride. Flux for brazing. 4 In claim 3, substantially the tin fluoride, the zinc fluoride, the potassium fluoride, the aluminum fluoride, the lithium fluoride, the potassium boron fluoride, and the copper fluoride A brazing flux characterized by comprising at least one flux. 5 A flux consisting of 60 to 90% by weight of tin fluoride and 40 to 10% by weight of zinc fluoride, and containing both of them in an amount of 80% or more of the total weight of the flux, is applied to the metal base material and the brazing surface, and placed in an inert gas atmosphere. A brazing method characterized by heating to brazing temperature inside. 6. The brazing method according to claim 5, characterized in that the inert gas atmosphere is a nitrogen atmosphere.