Alloys or metallic compositions – Copper base
Patent
1982-04-16
1983-11-22
Rutledge, L. Dewayne
Alloys or metallic compositions
Copper base
420470, 420473, 420485, 420487, 420489, 420490, C22C 900
Patent
active
044168535
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an inexpensive Cu-Ag base alloy brazing filler material that has a relative low silver content and low vapor pressure, and yet achieves satisfactory brazing.
BACKGROUND ART
The technique of vacuum brazing is used to fabricate electron tubes and vacuum tubes. If a brazing filler material having high vapor pressure is exposed to the vacuum brazing atmosphere, the vapor fouls the area to be brazed as well as the inner wall of the vacuum furnace. The brazed part is also exposed to high temperatures during the service of the tubes, and the filler material is evaporated to give a vapor that not only reduces the degree of vacuum in the tubes but also fouls their interior. For these reasons, an alloy having low vapor pressure is used as the brazing filler material. Typical filler materials having low vapor pressure include an Ag-Cu alloy filler material (silver brazing filler metal BAg-8 of JIS Z 3261) consisting of 27-29% Cu with the balance being Ag and incidental impurities and an Ag-Cu-Sn alloy brazing material consisting of 59-61% Ag, 9.5-10.5% Sn, with the balance being CU and incidental impurities (all percents used herein are by weight). One example of each type is listed in Table 26.1 on page 297 of "Brazing Manual" published by Kogaku Tosho Shuppan, October 1980 which is a translation of "Brazing Manual", 3rd ed., edited by American Welding Society, 1976. But the silver content of these conventional Cu-Ag base alloy filler materials is so high that with the rapid increase and considerable fluctuation in the price of silver in recent years, economic considerations put rigid limits on expanding the applications of these filler materials. At the same time, it has been desired to improve the brazability, especially wetting property, of the conventional Ag-Cu alloy filler materials. Attempts have been made to reduce the silver content, but this results in reduced wettability and increased brazing temperatures, which in turn impair the brazability of the filler materials. Multi-component alloy filler materials with improved brazing properties have been proposed, but they raise new problems with respect to workability and vapor pressure. Hence, no low-Ag, brazing filler metal is commercially available that has good properties, workability and low vapor pressure.
DISCLOSURE OF THE INVENTION:
Therefore, the present invention made studies to produce a brazing filler material that has a relatively low silver content, low vapor pressure and satisfactory workability, and also achieves good brazability. As a result, they successfully obtained an alloy that meets all of these requirements. The filler alloy material according to the present invention comprises 5 to 35% of Ag, 2.5 to 13% of Si, with the balance being Cu and incidental impurities. The inventors have found that this Cu-Ag base alloy has a significantly lower Ag content than the conventional Ag-Cu base alloys and yet, without decreasing the wetting property and workability, it has a lower vapor pressure and melting point than the conventional products.
If further reduction in the melting point and improved wettability are desired when, for example, the brazing filler material must flow into a very small brazing area, 1 to 10% of Sn or In or both can be added to the alloy having the above indicated basic composition. The additional element increases the wetting property of the alloy and lowers its melting point, with the result that the brazing properties of the alloy are improved.
If a stronger brazed area is desired, adding 1 to 10% of at least one element selected from among Fe, Ni and Co to the basic compostion is effective.
Further improvement in the wetting property is obtained by addition of a small amount of B or Li, and the physical and mechanical properties of the filler alloy are not changed greatly if the amount of B or Li added is very small. So, if improved wetting property is particularly needed, 0.001 to 0.8% of B or Li or both may be added to the basic composition. The experiment conduc
REFERENCES:
patent: 3693246 (1972-09-01), Novikov et al.
patent: 3977869 (1976-08-01), Steine et al.
Kishida Kunio
Morikawa Masaki
Tanaka Chuji
Yoshida Hideaki
Mitsubishi Kinzoku Kabushiki Kaisha
Rutledge L. Dewayne
Yee Debbie
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