Brazing flux

Details Brazing flux Brazing flux

1986-08-22

1987-08-25

Rosenberg, Peter D.

Metal treatment

Compositions

Fluxing

228248, B23K 3536

Patent

active

046890920

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to a flux used in brazing an aluminum material, i.e. aluminum or an aluminum alloy.
2. Description of the Prior Art
When an aluminum material is brazed, it has been usual to employ as a brazing alloy a eutectic alloy of aluminum and silicon having a melting point which is somewhat lower than that of the aluminum material. In order to bond the brazing alloy to the aluminum material satisfactorily, it is necessary to remove all contaminants, such as an oxide film, from the surface of the aluminum material. A flux is used for that purpose. There has recently come to be used a non-corrosive flux composed of a KF-AlF.sub.3 complex. This substance melts at the eutectic point of KF-AlF.sub.3 and exhibits an excellent flux action. It is, however, at a temperature of 560.degree. C. or above that this flux begins to melt. It is, therefore, necessary to use a brazing alloy having a melting point which is several tens of degrees higher than 560.degree. C., and employ a correspondingly high brazing temperature. When a torch is used as a source of heat for brazing, a high temperature is difficult to control. Therefore, the use of the KF-AlF.sub.3 flux requires a high degree of skill and experience.
Anothe drawback of this flux is that it is not very effective as a flux for brazing an aluminum material containing magnesium.


SUMMARY OF THE INVENTION

It is, therefore, an object of this invention to provide a brazing flux which has a low melting point, and which is effective for brazing an aluminum material containing magnesium, too.
This object is attained by a flux which comprises at least one cesium fluoroaluminate complex and has an
fluoride (AlF.sub.3)/cesium fluoride (CsF) molar ratio aluminum of 67/33 to 26/74.
The flux of this invention melts at a temperature of about 450.degree. C. to remove any oxide film or other foreign matter from the surface of an aluminum material and promote the uniform flow and distribution of a brazing alloy. It enables the satisfactory brazing of even an aluminum material containing magnesium, as it does not form any substance that may hinder the flow of a brazing alloy. The flux remaining on the brazed material does not corrode it or the brazing alloy. Therefore, the brazed product need not be cleansed.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a phase diagram of the system CsF-AlF.sub.3 ;
FIG. 2 is a DTA curve obtained from a flux according to EXAMPLE 1;
FIG. 3 is an X-ray diffraction pattern of the flux according to EXAMPLE 1;
FIG. 4 is a perspective view of the materials brazed in EXAMPLE 1;
FIG. 5 is a DTA curve obtained from a flux according to EXAMPLE 2;
FIG. 6 is an X-ray diffraction pattern of the flux according to EXAMPLE 2;
FIG. 7 is a perspective view of the materials employed in EXAMPLE 2 to 4;
FIG. 8 is a DTA curve obtained from a flux according to EXAMPLE 3; and
FIG. 9 is an X-ray diffraction pattern of the flux according to EXAMPLE 3.


DETAILED DESCRIPTION OF THE INVENTION

The flux of this invention comprises at least one cesium fluoroaluminate complex composed of cesium (Cs), aluminum (Al) and fluorine (F). The complex is referred to as cesium fluoroaluminate in this invention, and includes a series of substances, such as Cs.sub.3 AlF.sub.6, CsAlF.sub.4 and Cs.sub.2 AlF.sub.5. H.sub.2 O. A lot of different complexes exist among those known as cesium fluoroaluminate. There also exist a lot of complexes of the same composition which differ from one another in sructure, depending on temperature.
FIG. 1 is a phase diagram of the system C.sub.2 F - AlF.sub.3 [Zeitschrift fuer Anorganische und Allgeneine Chemie, 81,357 (1913)]. As is obvious from FIG. 1, these complexes are very complicated in structure, and the phase diagram of any complexes containing more than 25 mol % of AlF.sub.3 is not clearly known.
The melting point of the flux according to this invention depends on the molar ratio of AlF.sub.3 /CsF. If the molar ratio of AlF.sub.3 /CsF is in the range of 67/33 to 26/74, the flux mel

REFERENCES:
patent: 3951328 (1976-04-01), Wallace
patent: 3971501 (1976-07-01), Cook
patent: 4131493 (1978-12-01), Gurevich
patent: 4475960 (1984-10-01), Yamawaki
patent: 4579605 (1986-04-01), Kawase
patent: 4619716 (1986-10-01), Suzuki

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