JPH0450112B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a novel brazing flux, particularly for plates, pipes, and other components made of Al or Al alloy.
The present invention relates to a brazing flux suitable for joining electronic components. [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 if moisture is present, it may absorb moisture and corrode the base material. Therefore, in the case of chloride-based fluxes, there was a problem in that the residual flux had to be completely removed after brazing. As a conventional flux for improving these problems, a fluoride flux has been proposed as shown in US Pat. No. 3,951,328. This fluoride flux contains a mixture of K ₃ AlF ₆ and KAlF ₄ by mixing and dissolving KF and AlF ₃ . Therefore, in this flux, KF
-Even if the KF content is slightly increased beyond the eutectic point in the phase diagram of AlF ₃ , the melting point increases significantly. for example,
When KF is 50% by weight (AlF ₃ is 50% by weight), the melting point of the flux is 560-700°C. Therefore, in the range of 600 to 620° C. where brazing is normally performed, the flux becomes a semi-molten state, the activity of the flux decreases, the wetting and spreading properties deteriorate, and there is a risk that a partially soldered product may occur. Furthermore, this flux for Al and Al alloys has a problem in that it is not effective in improving corrosion resistance after brazing, and may cause defects in the corrosion resistance of brazed products. [Objective of the Invention] The object of the present invention is to have no hygroscopicity, excellent wettability, and a corrosion-resistant metal on the surface to be joined.
In particular, the object of the present invention is to provide a brazing flux that improves corrosion resistance by retaining Zn. [Summary of the invention] The present invention has KBF ₄ as a main component, and the KBF ₄ is _B
Contains at least one fluoride of Group _A , Group _B , Group _B metal, 20% by weight or less of fluoride of Group _B and Group _B metal, and 45% by weight of fluoride of Group _A and Group _B metal. The brazing flux contained below is as follows. An essential condition for a flux that can maintain corrosion resistance without removing the residual flux after brazing is that no hygroscopic components are present in the residual flux on the surface after brazing. Non-hygroscopic fluxes often contain fluoride components. In addition, chloride-based components are generally used to remove oxide films on Al and Al alloy members and increase wetting and spreading. However, since most of the chloride-based materials have hygroscopic properties, if the residual flux after brazing is not completely removed, corrosion resistance will be significantly reduced. Therefore, as a result of various studies in order to impart a suitable melting point, wettability and ability to form a sacrificial anodic film as a fluoride flux for Al and Al alloys, we found that KBF ₄ has an element that increases the wettability of wax. It has also been found that excellent brazing properties can be exhibited by adding these fluorides, an element that forms a sacrificial anodic film on the surface of the object to be brazed, and these fluorides alone or in combination. The present invention was made based on this knowledge, and it is possible to add fluoride to KBF ₄ to increase the wettability of the solder, or to add it to KBF ₄ to form a sacrificial anodic film on the surface of the object to be brazed. It is characterized by containing fluorides that form. Since KBF ₄ , the main component, itself has a melting point of about 530°C, it is conceivable that it can be used alone as a flux. Certainly high concentration
Wax wetting is obtained using KBF ₄ powder. However, in practical terms, such use is not possible, so it is necessary to reduce the flux concentration by adding a certain kind of additive element to make it usable. The results of various investigations are fluorides as shown above. Fluorides, which increase the wettability of wax, are in Group _B of the periodic table.
The fluorine compound, which is composed of at least one fluoride selected from the fluorides of each of Group _A , Group _B , and Group _B elements, and which forms the sacrificial anodic film on the surface of the brazing object is _B in the periodic table. It consists of at least one fluoride selected from the fluorides of each element of Group A and Group _A. The selected fluoride is preferably contained in an amount of 20% or less by weight to increase wettability, and preferably 45% or less by weight to form a sacrificial anode film. The goal will be achieved. For more information, see _B of the periodic table that increases wettability.
The family includes Cu, Ag and Au, the fluorides of which are CuF ₂ , AgF and AuF. Group _A includes Ca and Mg, and their fluorides include _CaF2 and _MgF2 . Group _B includes Zn and
Cd, and these fluorides include _ZnF2 and
There is CdF ₂ . Group _B includes Al and Ga, and their fluorides include AlF ₃ and GaF ₃ . In addition, _{the B} group that forms a sacrificial anodic film on the surface of the object to be brazed includes Zn and Cd, and fluorides of these include ZnF ₂ and CdF ₂ . Further _A
The family includes Ca and Mg, and their fluorides include CaF ₂ and MgF ₂ . Next, the effects of elements and fluorides that increase wettability, elements that form a sacrificial anode film and contribute to corrosion resistance, and fluorides on flux will be described. This is because it has been found that the fluoride that increases wettability is preferably added in a weight ratio of 20% or less to KBF ₄ , and that adding more than that does not improve wettability. An example of flux composition is 90% by weight.
_KBF4−10 % _CaF2 , 88% _KBF4−12 % _CuF2 and
A good example is 85% _KBF4-15 % _AlF3 . Considering the melting point of the brazing filler metal, these composition ranges are within the range at which an active reaction can occur at a temperature below that temperature. In addition, good wettability is exhibited even when a fluoride of ZnF ₂ .4H ₂ O is added to each flux. Next, as a flux additive that forms a sacrificial anodic film on the surface of the object to be brazed,
There is ZnF ₂ 4H ₂ O. add to flux
ZnF ₂ .4H ₂ O requires a predetermined Zn concentration and diffusion depth in order to form a sacrificial anodic film on the surface of Al, for example, and the amount added is preferably 45% or less by weight. If you braze with flux containing ZnF ₂ 4H ₂ O in this way, the surface of the brazed part will be
A sacrificial anodic film consisting of Zn is formed. Since Zn has a base potential with respect to Al, the film formed on the Al surface serves as a sacrificial anode for Al and has the role of preventing corrosion of Al. Therefore, we created fluxes with different ratios of KBF ₄ and ZnF ₂ 4H ₂ O, and investigated the wettability during brazing and the formation of sacrificial anodic films, and found that the amount of ZnF ₂ 4H ₂ O added was in terms of weight percent. It can be contained up to 45%. The lower limit is about 6%. This range of components is also suitable as the activation temperature of the flux. Even if a fluoride such as AlF ₃ is added in addition to the above-mentioned ZnF ₂ .4H ₂ O, the effect of forming a sacrificial anode film does not change. Fluxes containing such components are produced by conventional methods. For example, if two components, KBF ₄ -ZnF ₂ 4H ₂ O, which are blended to form a predetermined composition, or three components containing AlF ₃ are added to water,
There are methods such as making it into a creamy state while stirring and then drying it into a powder. Alternatively, a method can be adopted in which water is prepared so as to have the required flux concentration, the blended flux raw materials are added thereto, and the mixture is stirred to obtain a flux. The flux, which is made into a cream and then dried to create a powder, contains 80% KBF ₄ and
For 20% ZnF ₂ 4H ₂ O, in addition to KBF ₄ and ZnF ₂
Contains compounds such as KZnF ₃ , and contains compounded ingredients.
68% _KBF4 , 17% _ZnF2.4H2O and ₁₅ %
In the case of AlF ₃ , in addition to KBF ₄ , ZnF ₂ , AlF _{3 ,} KZnF ₃ ,
Contains compounds such as _KAlF4 . KF is not detected in these compounds, so even when stored as a flux, their hygroscopicity is extremely low and they are stable over long periods of time. A brazing method using the flux of the present invention includes, for example, blending the flux with an Al-Si based hard solder specified in JIS Z3263 on the surfaces of Al or Al alloy plates, pipes, and other structures to be joined. , above the melting point of both hard solder and flux, and Al or
A method is adopted in which the aluminum alloy material is heated to a temperature below the melting point of the material to be joined and brazed. Then, in order to obtain a reliable brazed joint, it is diluted as a 15-20% by weight aqueous solution, applied to the brazed surface in an inert atmosphere, and dried. Compounds such as KZnF ₃ , KAlF ₄ and ZnO were found on the surface of the object to be brazed after the flux was applied and brazed by X-ray diffraction. [Embodiment of the invention] A flux containing 80% KBF ₄ and 20% ZnF ₂ 4H ₂ O (invention No. 1) by weight and 70% KBF ₄
%, a flux (invention No. 2) containing 17% ZnF ₂ .4H ₂ O and 13% AlF ₃ was prepared. In addition, using a powder particle size of approximately 15 μm for each raw material,
Prepare approximately 0.6 parts of water per 1 part of the raw material, add ₄ weighed KBF to the water, and stir. It was then weighed
Add ZnF ₂ 4H ₂ O and make into a paste while stirring. Next, the water is evaporated in a constant temperature bath at approximately 100°C. The solidified flux was pulverized using a Raikai machine to create flux powder. The flux made as above was made to have a flux concentration (residual moisture) of about 15%, and the aluminum plate (A1050:
50□×1t) and 4343 brazing filler metal, which had been processed from φ2.4 to φ13, were immersed in an aqueous flux solution to adhere to it, and the wetting and spreading was tested. In the corrosion test, a brazing sheet (heart material: 3003, skin material: 4343) was placed at right angles to an A1050 board and immersed in an aqueous flux solution to adhere it. Both of the above wet spread and corrosion test pieces
It was heated at 615° C. for 10 seconds in an N ₂ inflow electric furnace. For comparison, wetting and corrosion _test specimens with the same shape as those used in the present invention were used. ₃ 45% component (comparative example 2), and KF 34%, AlF ₃ 46%, ZnF ₂ .
A flux containing 14% of 4H ₂ O and 6% of LiF (Comparative Example 3) was tested. In Comparative Examples 1 and 2, the fluxes were prepared by melting, cooling, solidifying, and then pulverizing. Comparative Example 3 was made into a cream, dried and ground in the same way as in the present invention, and both were used at a flux concentration of 15%. The results are shown in Table 1.

〔Effect of the invention〕

As described above, the brazing flux of the present invention has excellent wetting and spreading properties for brazing Al or Al alloy, and also
It has the remarkable effect of being able to suppress corrosion on the entire surface of Al or Al alloy, and eliminating cleaning work after brazing.

Claims (1)

[Claims] 1 KBF ₄ is the main component, and this KBF ₄ is _{a B} group, _A
Contains at least one fluoride of Group _B , Group _B , and Group _B metals, and contains 20% by weight or less of fluorides of Group B and Group _B metals, and 45% by weight or less of fluorides of Group _A and Group _B metals. A brazing flux characterized by: