JPS619997A - Flux for brazing aluminum and aluminum alloy material - Google Patents

Abstract

PURPOSE:To provide a flux for brazing Al and Al alloy material consisting of substance obtd. by crushing the melted and solidified substance of the mixture consisting of KF, AlF3 and PbF2 having the prescribed weight ratio. CONSTITUTION:A flux for brazing Al and Al alloy material is formed of what is obtd. by crushing the melted and solidified substance of the mixture consisting of 40-47% KF, 47-56% AlF3 and 0.1-10% PbF2 (each wt%) actually. Accordingly the operational temp. is lower and brazing is better than the conventional fluoride flux, and a good joining part equivalent to the brazing method of fluxless inert gas atmosphere and the soldering method in furnace of chloride flux is obtainable and yet a fluoride flux having insolubleness and non-hygroscopicity is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to the composition of a flux used for brazing aluminum (including aluminum alloys) materials.

Prior Art Flux brazing, which involves interposing an aluminum brazing alloy layer with a melting point lower than the melting point of the aluminum materials to be joined between the aluminum materials to be joined, generally uses chloride as the main component. fluxes are used in the atmosphere. These fluxes are water-soluble in nature, generally hygroscopic, and corrode aluminum, including aluminum braze alloys, in the presence of water. Therefore, such flux brazing residues must be removed by cleaning after the brazing process.

Vacuum brazing method and inert atmosphere brazing method are already known as fluxless brazing methods that perform brazing without using flux, but these methods require high vacuum or high purity inert gas as well as high-purity inert gas. Requires special aluminum material for bonding material or braze alloy. Furthermore, it is inferior to the flux brazing method in that it requires stricter precision in the clearance of the brazed part.

Also known are fluoride fluxes that leave a residue on the braze surface after brazing that is substantially insoluble in water, non-hygroscopic and non-corrosive to aluminum.

That is, British Patent No. 1,055,9T4 proposes a flux that is a mixture of AIF3 and KF. Furthermore, according to Japanese Patent Publication No. 58-27031, KAI is used as a flux that is non-hygroscopic before brazing and substantially water-insoluble after brazing.
A flux consisting of F4 and 3AIF5 has been proposed. This flux is obtained by pulverizing a solidified product after melting the mixture using KF and AI F3 as raw materials, and the solidified product contains KAI F4.
3AI F6 is generated. KF and A of raw material components
It is recommended that the ratio of IF3 be as close to the eutectic composition of both components as possible.

In this way, KF-AlF3 or
K3 AI Fs KAI F4 or 3AI
These fluoride fluxes, which are represented by the substantial chemical formula of F5 At F3 or KA, lF4, 1<3Δl F6-KAI F4 or KAI F4, or a combination thereof in the state after brazing, are different from conventional chloride-based fluxes. In addition to the advantages that it has, it also has the great advantage that it does not require cleaning after brazing because the residue is non-hygroscopic and non-corrosive to aluminum.

Further, these fluxes can be applied to brazing in any form, and are particularly suitable for torch brazing and furnace brazing.

However, these fluxes have the disadvantage that the operating temperature is slightly higher than that of chloride-based fluxes, making it difficult to obtain good joints.

The action mechanism of flux in brazing has not been fully elucidated;
In addition to covering the surface and destroying and removing the surface oxide film,
It is necessary to have the ability to improve the wettability of the base metal, to help the flow of the brazing alloy to the brazing surface, and to prevent re-oxidation by blocking contact with air. Therefore, it is significant in brazing to moderately lower the working temperature of flux.

Purpose The purpose of the present invention is to use a flux for brazing aluminum materials that has a lower operating temperature than conventional fluoride-based fluxes, thereby making it possible to use fluxless inert gas atmosphere brazing methods and chloride-based fluxes. The object of the present invention is to provide a fluoride-based flux that can form a good joint similar to the furnace brazing method and is substantially water-insoluble and non-hygroscopic.

Composition The present invention substantially consists of KF40-47 weight%, AlF34
This is a flux for brazing aluminum materials, which is obtained by crushing a molten solidified mixture of 7 to 56% by weight and 20.1 to 10% by weight of PbF.

The term "substantially" used here means that the fluoride used as a raw material does not necessarily have to be of high purity;
Impurities that are more mixed in than general commercially available fluoride are allowed, but KF, AI F3, Pb as pure substances
This is because only the weight ratio of the three substances in terms of F2 is important for the function of the flux of the present invention.

Substantial KF and Al in PbF2-free flux
Preferred values for the weight ratio of F3 are given in known literature (e.g. B
, Phlllips et al. J.

Amer, Ceram,, Soc, Vol, 49
(1966) 632 pages) KF-AIFB series 2
It can be easily understood from the original phase diagram, and as shown in this diagram, the eutectic composition is K F 45.8% by weight - AIF
The ratio is 354.2% by weight (KF55 mol% - Δ1F345 mol%) or around it.

The present invention further provides PbF20 for a mixture or molten mixture having substantially this weight ratio of 99.9 to 90% by weight.
．． When 1 to 103 Ii Ii% is added, the improvement is remarkable.

If the amount of PbF2 added is less than the specified lower limit, there will be no desired effect, and if it is added in a larger amount than the upper limit, the working temperature of the flux will rise, which is unfavorable for brazing.

Note that Pb dissociated above the working temperature has the effect of lowering the surface tension of the solder and improving the brazing properties.

Next, examples and effects thereof will be described.

Example 1 Using industrial KF and industrial At F3, taking into account the purity of each, substantially K F 45.8% by weight
- AIF354.2 mixed in a ratio of % by weight,
A flux prepared by melting this (the melting temperature was targeted at about 100°C above the eutectic temperature of 562°C) and a flux prepared by adding PbF2 to both components were substantially KF45.72.
Weight %-A I F 354.1 (1 weight %-PbF2
The action temperature of each of the PbFz-added flux prepared by mixing the mixture at a ratio of 0.18% by weight and melting the mixture was measured by the following method.

That is, both fluxes prepared in No. 11 were placed in a platinum crucible, heated and melted in an argon atmosphere, and then cooled at a cooling rate of 1°C.
Thermal analysis was carried out by the cooling method at 1/min, the liquidus temperature and solidus temperature were measured, and the working temperature was determined from these. The measurement results are shown in Table 1. As described above, the addition of PbF2 produced good results in lowering the solidus temperature, confirming a lowering of the operating temperature.

Table 1 Example 2 A brazing test was conducted in an inert atmosphere (in this atmosphere, brazing is not possible without flux) using the PbF2-added flux and the non-additive flux shown in Example 1. Fluxless inert atmosphere brazing was performed in the atmosphere. The bonding states of these were compared.

The figure shows a joint using a brazing test.

A 30 with B A 4045 aluminum alloy brazing filler metal clad on both sides on Δ3003 aluminum alloy.
A plating sheet made of 03 aluminum alloy was fixed at a joint angle θ, and after heating at 600°C x 3m1n, the fillet length was measured to determine the filling rate (L/LOX100).

The results are shown in Table 2. Comparing the filling ratios, the PbFz-added flux shows a higher value than additive-free flux brazing and flux brazing 1, indicating that excellent brazing parts can be obtained by using the flux of the present invention. I understand.

This result is due to the lowering of the working temperature of the flux of the present invention and the lowering of the surface tension of the solder due to Pb dissociated above the working temperature.

Table 2 Example 3 The water solubility of the PbF2-added flux and non-additive flux shown in Example 1 was measured, and these were compared with the water solubility of the main components of the chloride flux (literature values). . The results are shown in Table 3, and in the case of PbF2-added flux, it is comparable to that of non-additive flux,
The chloride content is extremely low.

Effects The flux for brazing aluminum materials of the present invention has a lower working temperature than conventional fluoride-based fluxes, and the surface tension of the solder decreases due to Pb dissociated above the working temperature. In addition to making the condition as good as that of 7-luxless inert gas atmosphere brazing method or chloride flux furnace brazing method, it also has non-hygroscopicity, which is a characteristic of fluoride flux.
It is substantially water-insoluble.

[Brief explanation of the drawing]

The figure is an explanatory diagram showing the configuration of the joint used in the brazing test. 1... A 3003 aluminum alloy, 2... Placing sheet,

Claims (1)

[Claims] (1) Substantially KF40-47% by weight, AlF_347
A flux for brazing aluminum and aluminum alloy materials, which is obtained by crushing a molten solidified mixture of ~56% by weight and PbF_20.1~10% by weight.