Silver solder or brazing alloys, and their use

Abstract

The present invention relates to silver solder or brazing alloys and to their use in making soldered joints in various grades of silver, particularly silversmithing grades. They alloys are of the Ag-Cu-Zn family containing at least 55 wt % Ag and from 0.5 to 3 wt % Ge. Additional alloys are silver solders or brazing alloys of the Ag-Cu-Zn family containing more than 70 wt % Ag and from 0.5 to 3 wt % Ge. They can exhibit an advantageous combination of colour, flowability and corrosion resistance. A method is also provided of making a joint in Sterling silver which includes using a silver solder or brazing alloy of the Ag-Cu-Zn family containing 10-30 wt % Cu, 8-15 wt % Zn, from 0.5-3 wt % Ge, optionally 0.05-0.4 wt % Si, optionally 1-3 wt % Sn, optionally 1 ppm-0.3 wt % B, the balance being 55-77 wt %, Ag, said solder being a colour match for said Sterling silver.

Description

FIELD OF THE INVENTION [0001] The present invention relates to silver solder or brazing alloys and to their use in making soldered joints in various grades of silver, particularly silversmithing grades. Silver brazing alloys are also known in the silversmithing trade as silver solders or solders and these terms are used interchangeably herein. BACKGROUND TO THE INVENTION [0002] Various silver-based alloys of the silver-copper-zinc type are useful as solders (brazing materials). Brazing has been defined as a joining process in which a filler metal is used which has a melting point of above 450° C., but below that of the parent metal and which is distributed in the joint by capillary attraction. [0003] Silver, copper and zinc form a ternary eutectic with a silver content of 56% and melting at 665° C., see a ternary phase diagram which is given in FIG. 2 of Jacobson et al, Development of new silver-free brazing alloys for steel tubular assembly, supplement to the Welding Journal (spons...

AI Technical Summary

Benefits of technology

[0009] The above alloys can exhibit an advantageous combination of relatively low melting point, high flowability and good colour. In particular, such alloys may have a solidus temperature in the range of about 700 to about 750° C. and a liquidus temperature in the range of about 725° C. to about 780° C. They can be used for soldering or brazing jewellery metals including grades of silver such as Sterling. They are particularly advantageous for soldering Argentium silver.

[0010] Other preferred features of the invention will be apparent from the appended claims to which attention is directed. The alloys may contain 1.5-2.5 wt % Ge, especially 2.0-2.5 wt % Ge and more especially about 2.0 wt % Ge. Addition of Ge has been found to improve colour and reduce melting point as well as to increase corrosion resistance.

[0011] The Ag—Cu—Zn alloy typically contains 55-77 wt % Ag, 10-30 wt % Cu (preferably 56-75 wt %) and 8-15 wt % Zn. For flowability, it may further comprise 0.05-0.4 wt % Si especially about 0.1-0.2 wt % Si. Too large a proportion gives rise to brittleness. The alloy may further comprise 1-3 wt % Sn, especially about 2 wt % Sn which again reduces melting point and improves colour. It may further comprise an amount of boron of e.g. 1 ppm-0.3 wt % boron, and more typically 0.1-0.3 wt % of boron which reduces grain size and helps in rolling or drawing the composition.

Problems solved by technology

Too large a proportion gives rise to brittleness.

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