JPH0571360B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a brazing aid used in flux brazing aluminum or aluminum alloy. [Prior art and its problems] Recently, aluminum or aluminum alloys are
Due to its light weight and good thermal conductivity, it is used in various automobile parts and automobile heat exchangers such as radiators, condensers, and evaporators. Most of these parts are assembled by brazing, which is suitable for joining many small parts, and the brazing methods include vacuum brazing, furnace brazing using flux, Alternatively, there is brazing in an inert gas atmosphere, etc. By the way, various types of automotive equipment are required to have durability, and corrosion resistance is especially important for heat exchangers. Conventionally, surface treatments for corrosion prevention such as plating or painting, and chloride-based fluxes have been used. Although a method has been adopted in which a small amount of ZnCl ₂ is added to form a film on the surface of the aluminum material after brazing that has a sacrificial anode effect due to a Zn diffusion layer, in the former case, contact and impact during use have been adopted. If the surface layer is destroyed by this, corrosion progresses, and in the latter case, it is not easy to remove chlorides such as ZnCl ² and NaCl, KCl, etc. that are present in the remaining flux. Moreover, the equipment for removing these chlorides is also large-scale and requires a long time, resulting in high costs. In addition, when a brazing method using flux is adopted, it is proposed to use a flux mainly composed of fluoride, which is less likely to cause corrosion even if there is flux remaining after brazing, instead of containing chloride as the main component. (Japanese Patent Publication No. 58-27037), but even if this proposed brazing method is implemented, it still has the disadvantage that its corrosion resistance is not sufficient under severe conditions. It is also possible to prevent corrosion by providing a sacrificial anode effect to the surface by vapor depositing Zn on the surface of the aluminum material before or after brazing or by depositing Zn by plating. The equipment cost and operation cost are high, and the cost is high. [Disclosure of the Invention] When brazing aluminum materials such as aluminum or aluminum alloy using a flux, the present inventor discovered that the flux is a powder flux mainly composed of fluorides, and that Zn
- It has been found that if Al alloy powder is used in combination, the corrosion resistance of the product after brazing is significantly improved. In particular, as Zn-Al alloy powder, about 3~
It is a Zn alloy consisting of 30% Al and unavoidable impurities,
The average particle size is selected to be approximately 1 to 200 μm, more preferably approximately 10 to 150 μm, and added in an amount of approximately 1 to 8 parts by weight per 30 parts by weight of the fluoride-based flux. It was found that this method had a significantly superior effect. In other words, if the Al content in the Zn alloy powder added to a flux mainly composed of fluoride is too low (less than 3%), the Zn or Zn alloy powder may melt and diffuse and be distributed on the surface of the aluminum material. The corrosion resistance of the aluminum material tends to be uneven, and the effect of improving the corrosion resistance of the target aluminum material is small.
Also, depending on the heating conditions during brazing, the aluminum material may be locally eroded by Zn or Zn alloy, and conversely, if the Al content is too high, exceeding 30%, This is because the melting point of the Zn alloy powder becomes high, which is not favorable for the melting and flow of the Zn alloy powder. Therefore, the Al content of the Zn-Al alloy added to the powder flux mainly composed of fluoride is about 3. A content of ~30 Wt% was highly desirable. In addition, if the average particle size of the Zn-Al alloy powder is too small (less than 1 μm), the surface area will be large relative to the amount added, and it will be oxidized during heating for brazing, resulting in loss. If the average particle size becomes too large, exceeding 200 μm, Zn-Al alloy powder and fluoride will form the main component. As a result, it becomes difficult to form a uniform sacrificial anodic oxide layer on the surface of the aluminum material. Particle size is approximately 1~
A diameter of 200 .mu.m, more preferably between about 10 and 150 .mu.m, was highly desirable. In addition, if the amount of Zn-Al alloy powder added to the flux mainly composed of fluoride is too small (less than 1:30), it will be difficult to form a uniform sacrificial anodic oxide layer on the surface of the aluminum material; If the number exceeds 30, the ratio of flux mainly composed of fluoride decreases and its function as a flux tends to be insufficient, and on the other hand, the ratio of flux acting on Zn-Al alloy powder decreases. Therefore, it is extremely desirable that the amount of Zn-Al alloy powder added to the flux mainly composed of fluoride is 1 to 8:30. be. For example, 30 parts by weight of a flux powder mainly composed of fluorides such as KF or AlF ₃ and about 3 to 30 parts by weight
Zn alloy powder containing % by weight of Al (average particle size of approx. 1~
200 μm) and 1 to 8 parts by weight, a liquid such as alcohol is added thereto, and the mixture is stirred and dispersed by mechanical means to form a flux suspension having a solute concentration of approximately 5 to 20%. This flux suspension is then interposed on the surface of the aluminum material to be brazed, but if the wettability between the flux suspension and the aluminum material is insufficient,
The surface of the aluminum material is pretreated with a degreasing liquid, etc., and then immersed in a flux suspension, or the flux suspension is applied with a brush or spray, and the solvent is evaporated to remove the brazing property. Dry to improve. Then, by heating this aluminum material to a predetermined brazing temperature in an inert gas such as nitrogen or argon gas and performing brazing, a brazed assembly that is highly corrosive can be easily obtained. Incidentally, it is sufficient that the brazing material is supplied in advance as a skin material of a plating sheet pasted on a part or all of the surface of the aluminum material, or in the form of a soldering material such as a wire. In the present invention, an Al-Si alloy such as JIS BA4045 is used as the brazing material.
The brazed parts are more durable than when Zn-based brazing filler metals are used. [Example] Using the composition shown in Table 1, JISA3003
JIS at a ratio of 10% on both sides of the board and JISA3003 board
A T-shaped joint formed from a brazing sheet laminated with BA4045 (Al-Si brazing material) was brazed in Ar gas. The brazing performance evaluated from the appearance of brazing with focus on fillet formation and the maximum pitting depth after 720 hours of CASS are as shown in Table 1.

[Comparative example 1]

In the above example, brazing was performed in the same manner using a flux of KAKF ₄ -K ₃ AlF ⁶ to which no Zn-Al alloy powder was added, and the brazing properties and maximum pitting depth after 720 hours of CASS were evaluated. If you look into it,
Although the brazing properties were good as in the previous example, the maximum pitting depth was as large as 0.55 mm, and the corrosion resistance was poor. [Comparative Example 2] Brazing was performed by a vacuum brazing method that does not use any flux (the brazing sheet was JIS BA 8PC), and the brazing properties and maximum pitting depth after 720 hours of CASS were examined. Although the corrosion resistance was good, the maximum pitting depth was as much as 1 mm, and the corrosion resistance was poor.

Claims (1)

[Claims] 1. A brazing aid used together with an Al-Si brazing material during flux brazing. This brazing aid does not contain chloride and contains a flux mainly composed of fluoride and about 3 to 30% Al. Contains 30% by weight
Zn-Al alloy powder, wherein the Zn-Al alloy powder is in a proportion of about 1 to 8 parts by weight relative to 30 parts by weight of the flux.