AU688773B2 - Silver alloy compositions - Google Patents

Description

PcT/AU 9 4 0 0 RECEIVED 2 1 JUL 1995 SILVER ALLOY COMPOSITIONS FIELD OF THE INVENTION This invention relates to silver alloy compositions.

This invention has particular reference to sterling silver alloy compositions of silver content of at least 92.5% for jewellery, flatware, coinage and other applications where a work hardening alloy is required and for illustrative purposes reference will be made to this application.

However, it is to be understood that this invention could be used to produce other types of silver alloys suitable for use as for example, electrical contacts or the like.

BACKGROUND OF THE INVENTION In general, silver as a material for the production of silver jewellery, certain coinage and the like is specified to be sterling silver comprising at least 925 parts per thousand by weight fine silver and is specified as ".925 silver". .925 silver accordingly typically comprises an alloy 92.5% by weight silver, generally alloyed with copper for hardness traces of other metals as additives or impurities.

Conventional silver alloys of the .925 type have several disadvantages in a manufacturing jewellery and other materials engineering contexts. Principal limitations include a characteristic firescale formation tendency attributable to oxidation of copper and other metals at the surface of cast or hot worked pieces. Additionally, traditional alloys have exhibited undesirable porosity in the recast metal and less than desirable grain size properties.

Several formulations have been proposed to overcome one or the other of the aforementioned disadvantages. United States Patent Nos. 5039479 and 4973446 disclose alloys of silver and master alloys for the production of such silver alloys having superior qualities over conventional alloys, and including, in addition to silver, controlled amounts of copper and zinc, together with tin, indium, boron and silicon.

The compositions exhibit reduced porosity, grain size and AMENDED SHEET

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fire scale production, and have acquired wide utilization in silver Jewellery production. It is presumed but not established that the addition of zinc to such compositions provides at least a degree of antioxidant properties to the compositicns when hot worked and improves colour, thus limiting the formation of principally copper oxide based fire scale, and reducing silver and copper oxide formation resulting in formation of pores in the cast or recast alloys. Silicon appears also to function as an antioxidant, thereby reducing firescale formation.

A disadvantage of the hereinbefore described firescale resisting alloys is that the alloys exhibit poor work hardening qualities thus not achieving the mechanical strength of traditional worked .925 silver goods.

DISCLOSURE OF THE INVENTION The present invention aims to provide silver alloy compositions which substantially alleviate at least one of the foregoing disadvantages. A further object of the present invention is to provide silver alloys having the desirable properties of reduced fire scale, reduced porosity and oxide formation and reduced grain size relative to traditional sterling silver alloys whilst providing improved work hardening performance over the current firescale resistant alloys. Other objects and advantages of this invention will hereinafter *"25 become apparent.

With the foregoing and other objects in view, this invention in one aspect resides broadly in firescale resistant, work hardenable jewellery silver alloy compositions consisting e of: 30 0.5 by weight copper; 0.02 7% by weight of a firescale resisting additive selected from one or a mixture of zinc and silicon, and 0.01 2.5% by weight germanium; 0.0 to 3.5% by weight of a grain refinement and/or surface tension reducing additive selected from one or a mixture of indium and boron; A ')J 7r- 0 2A 0.0 to 6% by weight tin, and the balance in silver.

The silver content of the alloy may be selected to be in the amounts commonly specified for grading silver. For e Seel RECEIVED 2 1 9J ;91 3 weight silver. Preferably, the alloy contains a proportion of silver required for the graded application to which the alloy is to be put, such as .925 silver, that is at least 92.5% by weight, for sterling silver applications and at least 90% by weight for coinage.

The copper content of the alloy may be selected according to the hardness required of the cast alloy. For example, for manufacturing jewellers .925 alloy, the copper content may advantageously be in the range of from about 2.0 to 3.0% by weight.

The zinc content of the alloy has a bearing on the colour of the alloy as well as functioning as a reducing agent for silver and copper oxides. Preferably, the amount of zinc used is selected to be between about 2.0 and 4.0% by weight.

The silicon content of the alloy is preferably adjusted relative to the proportion of zinc used to provide the desired firescale resistance whilst maintaining a suitable colour commensurate with the zinc content of the alloy, and may for example advantageously fall within the range of about 0.15 to 0.2% by weight.

The germanium content of the alloy has surprisingly resulted in alloys having work hardening characteristics of a kind with those exhibited by conventional .925 silver alloys, together with the firescale resistance of the hereinbefore described firescale resistant alloys. In general, it has been determined that amounts of germanium in the alloy of from about 0.04 to 2.0% by weight provide modified work hardening properties relative to alloys of the firescale resistant kind not including germanium. However, it is noted that the hardening performance is not linear with increasing germanium nor is the hardening linear with degree of work.

Preferably, the alloy also includes rheology modifying and other additives to aid in improving the castability and/or wetting performance of the molten alloy. For example, about 0.0 to 3.5% by weight of a modifying additive selected from one or a mixture of indium and boron may be advantageously AMENDED SHEET

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P /Au 9 4 0 RECEIVED 2 10A1995 4 added to the alloy to provide grain refinement and/or reduce surface tension, thereby providing greater wettability of the molten alloy. Where used, preferably the amount of boron utilized in the composition is from about 0 to 2% by weight boron and/or about 0 to 1.5% by weight indium. Other alloying elements may be added such as gold, tin or platinum.

Where tin is included in the composition, this may be advantageously used up to about 6% by weight, and is preferably utilized in an amount of from about 0.25 to 6%.

Accordingly, in a further aspect, this invention resides in silver alloy compositions including:- 81 99.409% by weight silver; 6% by weight copper; 0.05 5% by weight zinc; 0.02 2% by weight silicon; 0.001 2% by weight boron; 0.01 1.5% by weight indium, and 0.01 2.5% by weight germanium.

In a further aspect, this invention resides in silver alloy compositions including:- 99.159% by weight silver; 6% by weight copper; 0.05 5% by weight zinc; 0.02 2% by weight silicon; 0.001 2% by weight boron; 0.01 1.5% by weight indium; 0.01 2.5% by weight germanium, and 0.25 6.0% by weight tin.

Of course, it is of advantage to the manufacturing metallurgist to be able to alloy fine silver without having to individually measure components. Accordingly, it is preferred that the compositions of the present invention be formed by the addition of a master alloy to fine silver.

This also has the advantage that the master alloys are easier to transport than the made up alloys. Additionally, oxidizable components of the alloy are more stable to AMENDED SHEET lrn1«(* 1A I PCTAU 9 4 0 0 3 5 1 RECEIVED 2 1 JUL 1995 atmospheric oxidation when alloyed. Accordingly, in a further aspect this invention resides broadly in a method of producing firescale resistant, work hardenable silver alloy compositions and including the alloying of silver metal with a master alloy comprising, by weight: 52.5 99.85% by weight copper; 0.1 35% by weight of zinc or silicon or mixtures thereof, and 0.05 12.5% by weight germanium.

For production of the preferred modified alloys, there may be provided master alloys including additional alloying elements such as up to about 10% by weight boron, up to about by weight indium and/or up to about 30% by weight tin.

Accordingly, in a preferred aspect this invention resides in a method of producing firescale resistant, work hardenable silver alloy compositions including the alloying of silver metal with a master alloy comprising, by weight: 15.0 99.545% by weight copper; 0.25 25% by weight zinc; 0.1 10% by weight silicon; 0.005 10% by weight boron; 0.05 15% by weight indium, and 0.05 25% by weight germanium.

In a yet further aspect this invention resides in a method of producing firescale resistant, work hardenable silver alloy compositions including the alloying of silver metal with a master alloy comprising, by weight: 97.455% by weight copper; 0.25 25% by weight zinc; 0.1 10% by weight silicon; 0.005 10% by weight boron; 0.05 15% by weight indium; 0.05 25% by weight germanium, and 12.5% by weight tin.

In a yet further aspect this invention resides in a method of producing firescale resistant, work hardenable silver AMENDED SHEET 1 I L l r/Au 9 4 I 0 0 3 5 1 RECEIVED 2 1 JUL 1995 6 alloy compositions including the alloying of silver metal with a master alloy comprising, by weight: 97.455% by weight copper; 0.25 19.85% by weight zinc; 0.1 7.94% by weight silicon; 0.005 7.94% by weight boron; 0.05 11.92% by weight indium; 0.05 19.85% by weight germanium, and 30% by weight tin.

In order that this invention may be more readily understood and put into practical effect, reference will now be made to the following example which describes a preferred embodiment of the invention.

EXAMPLE 1 An Plloy consisting of the following constituents (by weight) and being in accordance with United States patent No.

5039479 was provided as a first control: silver 92.5% copper 3.29% zinc 3.75% indium 0.25% boron 0.01% silicon 0.2% This alloy is known as and will be referred to hereinafter as "UPM alloy". As a second control, a commercial sterling silver was used, comprising 92.5 by weight silver and the balance mainly copper.

Samples of the controls were cast and the hardness of each were measured as cast, at 50% and 75% work and annealed, according to the Vickers hardness VH scale. As used hereinafter the terms "50% work" and "75% work" mean subjecting a cast sample to cold rolling to 50% and 25% of its original thickness respectively.

Three alloys A to C in accordance with the present invention were prepared to the following compositions: AMENDED SHEET PCT/AU 9 4 0 03 5 1 RECEIVED 2 1 JUL 1995 7 ALLOY A ALLOY B ALLOY C Ag 92.5 92.5 92.5 Cu 2.35 3.25 Zn 2.82 3.75 3.14 Si 0.19 0.2 0.15 B 0.01 0.01 0.01 In 0.23 0.25 0.2 Ge 1.9 The three alloys were cast into samples as per the controls and were tested for Vickers Hardness as cast, at and 75% work and annealed. The hardness results for the controls and alloys A, B, and C are as follows: AMENDED SHEET

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PqVAU 94/0035 RECEIVED 2 1 M 99 8 ALLOY VH AS CAST VH 50% WORK VH @75% WORK VH ANNEALED STERLING 75.4 133 150 59 UPM 67 135 153 58.3 A 70.2 146 150 59.6 B 72.4 135 143 61.3 C 77.2 123 159 63.6 It can be seen that the alloy B having only 0.04% by weight Ge is harder than UPM and softer than sterling when cast, but that all three alloys are on par at 50% work.

Alloy B exhibited a softening relative to the controls at work and is hardest relative to the controls when annealed.

Alloy C, having 1.0% by weight Ge, exhibits an as-cast hardness on par with sterling, is softer than UPM or sterling at 50% work, but is markedly harder than these two alloys at work. Alloy A, having 1.9% by weight Ge, exhibits ascast hardness between that of UPM and sterling, is markedly harder than these two alloys at 50% work, but does not increase hardness as much as the controls upon further work to EXAMPLE 2 A firescale resistant, work hardening 925 silver alloy was prepared in accordance with the following formula, expressed as percentages by weight:- Zinc; 2.25 Indium 0.075 Tin 0.075 Germanium 0.125 Boron 0.003 Silicon 0.20 Copper 4.772 Silver 92.50 This alloy exhibited an as-cast Vickers hardness of approximately 15% greater than the firescale resistant alloy prepared without addition of germanium.

In use, alloys in accordance with the above embodiments and in accordance with the present invention may be selected by tailoring the germanium content of the alloys to provide AMENDED SHEET APF AU

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PCT/AT 9 4 0 0 5 RECEIVED 2 1 JUL 1995 the desired work hardening characteristics. The non-linear effect of use of germanium and the ability to vary other elements such as copper provides for production of a range of firescale resistant alloys of selected as-cast hareii!ss and work hardenability.

It will of course be realised that while the above has been given by way of illustrative example of this invention, all such and other modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this 1n as defined in the claims appended hereto.

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Claims (9)

1. Firescale resistant, work hardenable jewellery silver alloy compositions consisting of: 6% by weight copper; 0.02 7% by weight of a firescale resisting additive selected from one or a mixture of zinc and silicon, and 0.01 2.5% by weight germanium; 0.0 to 3.5% by weight of a grain refinement and/or surface tension reducing additive selected from one or a mixture of indium and boron; 0.0 to 6% by weight tin, and the balance in silver.

2. Firescale resistant, work hardenable jewellery silver alloy compositions in accordance with Claim 1, wherein silver is present to at least 92.5% by weight.

3. Firescale resistant, work hardenable jewellery silver alloy compositions in accordance with Claim 1, wherein the copper content is in the range of from 2.0 to 3.0% by weight.

4. Firescale resistant, work hardenable jewellery silver alloy compositions in accordance with Claim 1, wherein the zinc content is between 2.0 and 4.0% by weight. e 5. Firescale resistant, work hardenable jewellery silver alloy compositions in accordance with Claim 1, wherein the silicon content is in the range of 0.15 to 0.2% by weight.

6. Firescale resistant, work hardenable jewellery silver alloy compositions in accordance with Claim 1, wherein the germanium content is in the range of 0.04 to 2.0% by weight.

7. Firescale resistant, work hardenable jewellery silver alloy compositions in accordance with Claim 1, wherein said grain refinement and/or surface tension reducing additive comprises from 0.01 to 2% by weight boron and 0.01 to 1.5% by L- _g -~ILI weight indium.

8. Firescale resistant, work hardenable jewellery silver alloy compositions in accordance with Claim 1, wherein the tin is utilized in an amount of from 0.25 to 6% by weight.

9. Silver alloy compositions consisting of: 81 99.409% by weight silver; 6% by weight copper; 0.05 5% by weight zinc; 0.02 2% by weight silicon; 0.001 2% by weight boron; 0.01 1.5% by weight indium, and 0.01 2.5% by weight germanium. i 10. Silver alloy compositions consisting of:

99.159% by weight silver; 0.5 6% by weight copper; 0.05 5% by weight zinc; 0.02 2% by weight silicon; .0.001 2% by weight boron; 0.01 1.5% by weight indium; S0.01 2.5% by weight germanium, and 0.25 6.0% by weight tin. 11. A silver composition consisting of, by weight percent: Silver 92.5 Copper 2.35 Zinc 2.82 Silicon 0.19 Boron 0.01 Indium 0.23 Germanium 1.9 12. A silver composition consisting of, by weight percent: Silver 92.5 R Copper 3.25 I I I, Zinc Silicon Boron Indium Germanium 3.75 0.2 0.01 0.25 0.04 13. A silver composition Silver 92.5 Copper Zinc 3.14 Silicon 0.15 Boron 0.01 Indium 0.2 Germanium 14. A silver composition Zinc 2.25 Indium 0.075 Tin 0.075 Germanium 0.125 Boron 0.003 Silicon 0.20 Copper 4.772 Silver 92.50 consisting of, by weight percent: consisting of, by weight percent: S S S S S. SS S S S 5. S 5 S S 0 S 6@S 0 S 550 50 S S S. S. S 55 S. S .5.555 S SS 0* S 5 0 55 INTERNATIONAL PRELIMINARY EXAMINATION REPORT International application No. PCT/AU 94/00351 VIII Certain observations on the international application The following observations on the clarity of the claims, description, and drawings or on the question whether the claims arc fully supported by the description, are made: Claim 1 is indefinite and speculative as it is not explicitly stated that silver (and inevitable impurities) make up the balance of the alloy composition. See, for example, Mond Nickel (1948) 65 RPC 123, Form PCT/IPEA/409 (Box VIII) (January 1994) INTERNATIONAL SEARCH REPORT Internatninal apphlicoiltn No PCT/AU 94/00351 A. CLASSIFICATION OF SUBJECT MATTER Int. CI. 6 C22C 5/08, 5/06, 9/00, 9/04, 9/10, 30/06, 30/02, 1/03 According to International Patent Classification (IPC) or to both national classification and IPC B. FIELDS SEARCHED Minimum documentation searched (classification system followed by classification symbols) IPC as above Documentation searched other than minimum documentation to the extent tha: such documents are included in thf fields searched AU IPC as above Electronic data base consulted during the international search (name of data base, and where practicable, search terms used) C. DOCUMENTS CONSIDERED TO BE RELEVANT Category* Citation of document, with indication, where appropriate, of the relevant passages Relevant to Claim No. Derwent Abstract Accession No. 24286Y/14, Class L03, JP 52-023660 (TANAKA KIKINZOKU KK) 22 February 1977 (22.02,77) X Abstract 1-4,6-10,13 Derwent Abstract Accession No. 93-012634/02, Class P23, JP 04-339500 (CITIZEN WATCH CO LTD) 26 November 1992 (26.11.92) X Abstract 1,4,6-10,13 Derwent Abstract Accession No. 86-086006/13, Class V04, JP 61-034144 (TANAKA KIKINZOKU KK) 18 February 1986 (18.02.86) X Abstract 1-3,6,13 Further documents are listed See patent family annex. in the continuation of Box C. Special categories of cited documents later document published aftar the international filing date or priority date and not in conflict document defining the general state of the art which is with the application but cited to understand the not considered to be ofparticular relevance principle or theory underlying the invention earlier document but published on or after the document of particular relevance: the claimed international filing date invention cannot be considered novel or cannot be document which may throw doubts on priority claim(s) considered to involve an inventive step when the or which is cited to establish the publication date of document is taken alone another citation or other special reason (as specified) document of particular relevance; the claimed document referring to an oral disclosure, use, invention cannot be considered to involve an exhibition or other means inventive step when the document is combined document published prior to the international filing date with one or more other such documents, such but later than the priority date claimed comoination being obvious to a person skilled in the art document member of the same patent family Date of the actual completion of the international search Date of mailing of the international search report 8 September 1994 (08.09.94) 5 \Ca OP.>) Name and mailing address of the ISA/AU Authorized officer AUSTRALIAN INDUSTRIAL PROPERTY ORGANISATION PO BOX 200 WODEN ACT 2606 AUSTRALIA R. HOWE Facsimile No. 06 2853929 Telephone No. (06) 2832159 Form PCT/ISA/210 (continuation of first sheet (July 1992) copjne I II INTERNATIONAL SEARCH REPORT Intemational application No. PCT/AU 94/00351 C(Continuation). DOCUMENTS CONSIDERED TO BE RELEVANT Category* Citation of document, with indication, where appropriate of the relevant passages Relevant to Claim No. Patent Abstracts of Japan, M-192, page 156, JP 57-187195 (TOKURIKI HONTEN KK) 17 November 1982 (17.11.82) Abstract Patent Abstracts of Japan, C-83, page 148, JP 56-119747 (NIPPON DENSHIN DENWA KOSHA) 19 September 1981 (19.09.81) Abstract Patent Abstracts of Japan, C-357, page 94, JP 61-34147 (TANAKA KIKINZOKU (KOGYO KK) 18 February 1986 (18.02.86) Abstract Derwent Abstract Accession No. 92-320122/89, Class V04, JP 04-224645 (NIPPON MINING CO) 13 Aaugust 1992 (13.08.92) Abstract Derwent Abstract Accession No. 91-152508/21, Class M26, JP 03-087325 (NIPPON MINING KK) 12 April 1991 (12.04.91) Abstract Derwent Abstract Accession No. 91-262404/36, Class M26, JP 03-170646 (NIPPON MINING KK) 24 July 1991 (24.07.91) Abstract Derwent Abstract Accession No. 85-149928/25, Class M26, JP 60-082635 (NIPPON MINING KK) 10 May 1985 (10.05.85) Abstract EP,A1, 64181 (SIEMENS AG) 10 November 1981 (10.11.81) See claims 1-2 1,2,5,6,13 1-3,6,13 1,2,6,13 13-15 13,14 13,14 13,14 13 Form PCT/ISA/210 (continuation of second sheet)(July 1992) copjne -I Ir L INTERNATIONAL SE~ARCHI REPORT informnauti on patent family mcrn' international application No. PCT/AU 94100351 This Annex lists the known publication level patent family members relating to the patent documents cited in the above-mentioned international search report. The Australian Patent Office is in no way liable for these particulars which are merely given for the purpose of information. Patent Document Cited in Search Patent Family Member Report EP 64181 AT 11840 DE 3116680 ES 511703 Fl 820583 GR 75432 JP 57181348 NO 821339 PT 74797 ZA 8202858 END OF ANNEX Form PCT/ISA/210(patent family annex)(July 1992) copjne =mono