JPH03204198A - Flux for brazing of aluminum member - Google Patents

Abstract

PURPOSE:To improve clearance packability by forming the flux of a compsn. contg. specific ratios of K2AlF5 or K2AlF5.H2O, KF, NaF into the flux and the balance KAlF4. CONSTITUTION:The flux is formed of the compsn. contg., by weight %, 5 to 95 K2AlF5 or K2AlF5.H2O and further <=5% in total of one or two kinds within the range of 0.5 to 5 KF and 0.5 to 5 NaF and the balance KAlF4. General soldering properties, such as flowability and wettability, are degraded even if the content of the K2AlF5 or K2AlF5.H2O is below 5% or exceeds 95%. The clearance packability is not improved if the ratios of both the KF and the NaF are below 0.5%. The m. p. of the flux increases and the brazing properties are degraded if the ratios thereof exceed 5%. The clearance packability is thus greatly improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a flux for brazing aluminum members made of aluminum and aluminum alloys, and particularly to a flux that significantly improves brazing properties in a non-oxidizing atmosphere. It is. In the following description, the terms aluminum and aluminum are used to include their alloys.

[Prior Art and Problems to be Solved by the Invention] Generally, aluminum heat exchangers, such as radiators and oil coolers for automobiles, condensers and evaporators for air conditioners, etc., are assembled by a brazing method.

In this brazing method, Al-5i or AA'-8i is applied to the surface of the aluminum member constituting the tube or fin in advance.
- Mg-based alloy brazing material is clad and heated to a temperature slightly higher than the melting temperature of the brazing material, that is, 590 to 620°C.

During this heating, in order to destroy the surface oxide film of the aluminum member and promote the fluidity and wettability of the brazing filler metal, a chloride-based flux may be used, or the aluminum member may be placed in a vacuum without using a flux. A method of brazing is used.

Conventionally, NaC was used as flux for brazing aluminum parts.
1. Chlorides such as KCl, LiC1, ZnCl2, and AI
A mixture of fluorides such as F, KF, NaF, and LiF in an appropriate composition was used. However, these fluxes must be removed with hot water or acid after brazing, and if the flux remains, chloride becomes an electrolyte due to its hygroscopic nature and corrodes the aluminum parts. Furthermore, flux removal always involves waste liquid treatment for pollution reasons, which causes high costs. Furthermore, in order to braze one heat exchanger, 100 to 400 g+ of flux must be used, which increases the cost. Furthermore, when brazing in a vacuum, the tendency of wax to flow into gaps, so-called capillary action, is not very good, and the equipment is expensive, and its maintenance and management is expensive. There is.

Recently, in order to improve the above-mentioned drawbacks, a flux consisting only of fluoride, such as AIFN, has been added to 53-55W1% (hereinafter referred to as W1%).
1% is abbreviated as %), and the remainder is a flux consisting of KF (see British Patent No. 1055914) or KAlF4.
A flux consisting of 5.6 to 99.9% and the remainder 3Ad F6 (see Japanese Patent Publication No. 58-27037) has been developed and has already been put into practical use.

In particular, since the KAI F4 Ki AJ F6 flux has a very high activity, it is effective in destroying the oxide film in a smaller amount than the chloride-based flux, and if brazing is performed in a non-oxidizing atmosphere, an even smaller amount is required. By the way, the amount of flux used per heat exchanger is 10 to 30 g, and even if the flux residue after brazing is left as is, it will not absorb moisture and will not corrode the aluminum, so the flux removal process is omitted. There are advantages that can be achieved.

However, this flux has the drawback of being difficult to manufacture and high cost. For example, Tokuko Sho 58-2703
In Publication No. 7, a mixed flux of KAA'F4 and 3AI F6 is produced by melting AlF3 and KF and then pulverizing them. Since the container is eroded, the material of the container is limited. Although the above publication uses a crucible made of graphite, the graphite crucible is porous and may leak outside during melting, which is not preferable. Additionally, ceramic crucibles made of alumina (AZ 2 (h), etc.) are not subject to much erosion, but are susceptible to external shocks and are
It may break after ~3 uses and is troublesome to handle. Furthermore, the melted and solidified flux is in the form of flakes, which requires a pulverization process to turn them into powder.

In order to solve this problem, a method of producing fluoride flux by chemical synthesis, which is inexpensive to produce, was proposed in JP-A-60-17.
It was developed in Publication No. 0596.

And the flux made in this way is very active,
It has an excellent effect on destroying the oxide film on aluminum, making it an excellent flux for brazing. However, since the wetting of the wax is very good, it has the disadvantage that wax is difficult to accumulate in the gaps. That is, as shown in Fig. 3, a praising sheet (1) is erected on one end of the base material (2) with a spacer rod (5) interposed therebetween, and this is connected to a thin wire (6).
When brazing the test sample fixed with
), wax tends to flow onto the surface (3) of the base material (2).

Such a phenomenon is a problem especially when the radiator tube and header are joined together when the clearance is large.

[Means to solve the problem]

In view of this, the present invention has conducted various studies with the aim of further improving the fluoride flux produced by the chemical synthesis described above. We have developed a flux for brazing aluminum parts that can significantly improve the gap-filling properties of the solder.

That is, the flux of the present invention is K2AIF or K2A
Contains 5 to 95% of IF 5 ・H2O, and further contains K
[Function] In the present invention, it is characterized by containing 5% or less of F in the range of 0.5 to 5% and NaF in the range of 0.5 to 5% in a total of 5% or less, with the balance consisting of KAlF4. K, AIF, or 2 AIF,・
The reason why H2O is limited to a range of 5 to 95% is that even if it is less than 5%, even if it exceeds 95%, general brazing properties such as fluidity and wettability will be significantly reduced.
5%, NaF within the range of 0.5 to 5%, and the reason why any one or both of them are limited to a total of 5% or less is that both KF and NaF are less than 0.5% to improve the gap filling property of the solder. If more than 5% is added, the melting point of the flux will rise and the brazing properties will be reduced, and when the flux is used dissolved in water, it will solidify in the aqueous solution and the flux will lose its effectiveness. This is because brazing becomes difficult.

In addition, K2AlF5 or K2AlF5・H2 in the present invention
O and KAIFa are HF solution, KF and AI (OH)
It can be easily obtained by chemically synthesizing K.3 by mixing appropriate amounts of K.
, AIF, one molecule of H2O remains as crystal water, and K2
Even if it becomes AIF, .H2O (stable in this state), exactly the same brazing properties as 2AIF can be obtained. Regarding its preparation, since both KF and NaF are easily available as commercial products, it can be prepared extremely easily by mixing KF and NaF into the above-mentioned flux made by chemical synthesis immediately before use. can.

〔Example〕

The present invention will be described in detail below with reference to Examples.

In the test sample shown in Figure 1, the plating sheet (11) was made of BA12PC (A3003) with a board thickness of 1.0 mm.
was used as the core material, and A 4343 was clad on both sides at a ratio of 10% each), and A 3003 with a plate thickness of 1 and θ threshold was used as the base material (2), and the flux of the present invention shown in Table 1 was used for comparison. Diagram showing flux and conventional flux (7)
The material was placed at a position of about 2 cm and heated to 605° C. for about 5 minutes in an electric furnace in a non-oxidizing atmosphere with nitrogen gas to perform brazing, and the gap filling property was evaluated. 5US304 with a diameter of 3 mm was used for the spacer rod (5), and although not shown in the figure, it was fixed using a thin 5US304 wire. The non-oxidizing atmosphere has a dew point of -40°C.

Oxygen concentration! It was 001 Um.

The gap filling property was evaluated based on the gap (
4) Measure the filling length and calculate the gap filling rate (%) using the formula below.
) was sought. The results are also listed in Table 1.

1 As is clear from Table 1, the flux N111 of the present invention
In brazing using ~9, the gap filling rate was 50 in all cases.
% or more, and other brazing properties were also good.

On the other hand, the comparative fluxes Nα10 to 15, which are outside the composition range of the flux of the present invention, either had a gap filling rate of 50% or less or were not brazingable. Moreover, the gap filling rate of the conventional fluxes Nα16 to Nα17 was 50% or less, and it is clear that the fluxes of the present invention are excellent in all cases.

As described above, the flux of the present invention can significantly improve brazing performance not only in a non-oxidizing atmosphere but also in torch brazing in the air. The flux of the present invention has an industrially significant effect on joints that must be completely filled with.

〔Effect of the invention〕

In this way, the flux of the present invention has 2 AI in KAlF4.
A trace amount of KF and N is added to the F5/H20 flux.
The addition of aF has the remarkable effect of significantly improving the property of accumulating solder in gaps, which is the most important property of brazing properties, that is, the gap filling property.

[Brief explanation of drawings]

Figure 1 is a side view of a test sample for measuring the gap filling properties in the example, Figure 2 is a side view of the test sample shown in Figure 1 after brazing, and Figure 3 is a side view of the test sample shown in Figure 1 after brazing to evaluate the gap filling properties. It is a perspective view showing an example of a test sample. (1) Placing sheet (2) Base material (3) Base material surface (4) Gap (5) Spacer rod (6) Thin wire for fixing (7) Flux Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] K_2AlF_5 or K_2AlF_5・H_2O to 5
Contains ~95 wt%, and further contains 0.5 to 5 wt% KF, N
A flux for brazing aluminum members, comprising a total of 5 wt% or less of one or two aF in the range of 0.5 to 5 wt%, and the remainder being KAlF_4.