JPH0440112B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD This invention relates to a method for flux brazing aluminum and stainless steel. In this specification, the term aluminum is used to include aluminum alloys. BACKGROUND ART Conventionally, when joining aluminum materials and stainless steel materials by brazing, a chloride-based flux containing tin chloride has generally been used. Problems to be Solved by the Invention However, when using a chloride-based flux, the flux used is essentially water-soluble and has strong hygroscopicity, so the flux is removed immediately after brazing. It is necessary to wash and remove the residue, which increases equipment costs, complicates the process, and imposes a heavy workload. In addition, even if the above-mentioned cleaning is incomplete, or even if the cleaning is quite thorough, the aluminum or stainless steel material may corrode relatively early due to residual flux components incorporated into the metal of the joint. There was a fear that it would happen. The present invention was made in view of the above circumstances, and the purpose is to develop a flux that leaves a non-corrosive residue after brazing and can perform good and stable brazing. The present invention provides a brazing method using flux. Means for Solving the Problems For the above purpose, the present invention was completed as a result of the pursuit of a composition that can realize a good bonding state, focusing on using a non-corrosive fluoride-based flux. That's what I got. Therefore, this invention uses 0.05 to 15 wt% of tin fluoride.
It is characterized by using a fluoride-based flux containing aluminum, and after adhering the flux to at least one of an aluminum material and a stainless steel material, it is heated to a predetermined temperature in a non-oxidizing atmosphere to
The gist is a method for flux brazing aluminum and stainless steel, which involves melting and brazing a brazing filler metal made of a Si-based alloy. In the fluoride-based flux used in the present invention, tin fluoride is necessary to form a uniform fillet at the bonded portion to achieve a good and stable bonded state. However, the added content is 0.05wt%
If it is less than 15 wt%, the above effect will be poor, and if it exceeds 15 wt%, precipitates will be formed, making it impossible to obtain a uniform bonded state. The preferred content range of tin fluoride is 0.3 to 5.0 wt%. The fluoride-based flux _used in the present invention may contain tin fluoride within the above range, and other compositions are not limited _{. 4} ) and mixed with tin fluoride, a mixture of KAlF ₄ and KF, or a mixture of AlF ₃ and
Examples include those based on a mixture of KF and mixed with tin fluoride. Among these, it is particularly preferable to use the latter, that is, a flux based on a mixture of KAlF ₄ and KF. The reason is,
While this flux has properties equivalent to those of a flux made of a fluoroaluminum complex salt as a base and a mixture of tin fluoride in terms of non-corrosion of the residue, melting temperature range, etc., KAlF ₄ , This is because both KF and KF are easily available as commercial products, so they can be easily adjusted by simply mixing them. That is, in the production of a composition containing a fluoroaluminium complex salt, when it is actually produced and used industrially, generally AlF ₃ and KF are used as starting materials, and the starting materials are A method is adopted in which K ₃ AlF ₆ and KAlF ₄ are mixed in a dry state in an appropriate ratio corresponding to the eutectic composition region, this mixture is once melted, the molten mixture is further cooled and solidified, and then pulverized. Therefore, there are problems such as a large number of man-hours and troublesome preparation. Therefore, it is advantageous to use a KAlF ₄ -KF flux that is easy to prepare and does not have such problems. In this case, in the mixture of KAlF ₄ and KF to be mixed with tin fluoride, KAlF ₄
The ratio of KF and KF is preferably in the range of 80-99.8wt%:20-0.2wt%. By selecting this range, the melting point of the flux will be low and the flux will be able to work effectively during brazing heating.If KF is less than the allowable lower limit, the effect will be poor, and conversely if it exceeds the allowable upper limit. This is because, if too much is mixed, there is a risk that the complete melting temperature (liquidus temperature) will rise, making it impossible to perform good brazing. In addition, when a mixture of AlF ₃ and KF is used as a flux base, the mixture is prepared by mixing the two in a eutectic composition or a composition in the vicinity thereof, adding water to form a paste, and then drying and pulverizing the mixture. It is prepared. When performing brazing, the above-mentioned flux is used by suspending it in the form of a slurry in a liquid such as water, and this suspension is uniformly applied to at least one of the aluminum material or stainless steel material that is the joining member. Apply. In order to facilitate suspension and application in this liquid and improve brazing properties, the powder particle size of the flux component is approximately 74 μm.
It is best to use the following. Further, as the above-mentioned application method, spraying, brushing, etc. can be applied, and a dipping method can also be used as a uniform application method suitable for mass production. The aluminum and stainless steel materials used as bonding members are dried after being coated with the above flux, and then bonded in a non-oxidizing atmosphere such as an inert gas atmosphere using an aluminum alloy brazing filler metal whose melting point is lower than that of the bonding members. By heating to approximately 600-610° C. below the melting point of the component and above the melting point of the flux, the brazing material is melted and a brazed joint is achieved. The above brazing filler metal has a Si content of approximately 6.8~
Although an Al-Si alloy of about 13 wt% is used, the brazing filler metal may be constructed as a brazing sheet clad with an aluminum material. Effects of the Invention According to the implementation of the present invention as described above, an extremely good brazing joint between an aluminum material and a stainless steel material can be achieved. In other words, the flux used exhibits excellent flux effects such as destroying oxides on the surface of the joint and promoting wetting and spreading of the brazing material, and enables the formation of a uniform, stable, and sufficiently strong brazed joint with a fillet. possible. Moreover, since the flux used in this invention leaves a non-corrosive residue after brazing, there is no need to wash and remove the flux residue after brazing, unlike when using conventional chloride-based fluxes. While simplifying a series of brazing work steps, it is possible to provide brazed products made of aluminum and stainless steel that are completely bonded with even less risk of corrosion. EXAMPLES Next, in order to clarify the advantages of the present invention, some examples thereof will be shown in comparison with various comparative examples. As shown in Figure 1, an aluminum plate 1 with a thickness of 4 mm made of A1100 aluminum alloy is
When producing a heating plate for a water cooler by brazing a sheathed heater 2 with a diameter of 3 mm covered with a stainless steel pipe 2a made of SUS321 with a brazing filler metal 3 as shown in Fig. 2, the following table 1 is used. Fluxes with various compositions shown in sample Nos. 1 to 9 were prepared. The fluxes of samples Nos. 1 to 7 are based on a mixture of KAlF ₄ :KF at a ratio of 90:10 wt%, to which SnF ₂ is added. teeth
It is based on a K ₃ AlF ₆ :KAlF ₄ ratio of 18:82 wt%, to which SnF ₂ is added. In addition, samples No. 10 and 11 contained 54wt%
It is based on a fluoride flux consisting of a mixture of AlF ₃ and 46 wt% KF, to which SnF ₂ is added. Then add water to each of the above fluxes to make the concentration 15%.
2.4 in diameter at the joint between the aluminum plate of the heating plate and the sheathed heater.
mm of BA4047 brazing filler metal, and in this state each of the above suspensions was applied to the joint by brushing, and then
It was dried in a drying oven at 250°C. The powder particle size of the flux components was all 74 μm or less. Thereafter, each of the heating plates was heated at 635°C for 20 minutes using _N2 gas in a furnace whose dew point was adjusted to -50°C. Then, when the brazed state of each of the heating plates obtained above was examined, as shown in the table, in the case of samples Nos. 2 to 6, 8, and 9, in which the flux according to the present invention was used, A uniform fillet was formed and a sufficiently good brazed state was obtained. On the other hand, in sample No. 1 to which SnF ₂ was not added, the fillet was non-uniform and the bonding state was incomplete. Further, for sample No. 7 in which the added content of SnF ₂ exceeded 15 wt%, a uniform bonding state could not be obtained. In addition, a comparison with a conventional chloride-based flux containing tin chloride showed the following results. (Chloride-based flux) Water is added to fine powder of chloride-based flux having the composition shown in sample No. 12 in the table to make a suspension with a concentration of 50%, and it adheres to the joint between the aluminum plate and the sheathed heater. At least brazing was carried out in the atmosphere using a conventional method. After washing this brazed product with hot water, pickling, washing with water, and drying, a cast test based on JIS-H-8681 was conducted to examine its corrosion resistance. As a result, as shown in the right-hand column of the table, through-holes were formed in the aluminum plate and stainless steel pipe in about 600 hours. In contrast, the brazed product according to the present invention, which was subjected to the cast test without any cleaning after brazing,
It took more than 1000 hours for the formation of through holes, and it was clearly recognized that the material had excellent corrosion resistance.

【table】

[Table] Brazing condition: ○…Good ×…Poor

[Brief explanation of drawings]

FIG. 1 is a plan view of a heating plate for a water cooler used in an embodiment of the present invention, and FIG. 2 is an enlarged cross-sectional view taken along the line -- in FIG. 1. 1... Aluminum plate, 2... Sheathed heater, 2a... Stainless steel pipe, 3... Brazing metal.

Claims (1)

[Claims] 1. A fluoride-based flux containing 0.05 to 15 wt% of tin fluoride is used, and after the flux is attached to at least one of an aluminum material and a stainless steel material, the flux is placed in a non-oxidizing atmosphere. A flux brazing method for aluminum and stainless steel, in which aluminum and stainless steel are heated to a predetermined temperature to melt and braze a brazing filler metal made of an Al-Si alloy. 2 Flux contains KAlF ₄ and KF 80-99.8wt%:
A method for flux brazing aluminum and stainless steel according to claim 1, which is based on a mixture in a proportion of 20 to 0.2 wt%, and tin fluoride is mixed therein.