WO2016134787A1

WO2016134787A1 - Silver alloy composition

Info

Publication number: WO2016134787A1
Application number: PCT/EP2015/054157
Authority: WO
Inventors: Udo Rabe
Original assignee: Ögussa Österreichische Gold- Und Silber-Scheideanstalt Ges.M.B.H.
Priority date: 2015-02-27
Filing date: 2015-02-27
Publication date: 2016-09-01

Abstract

The invention relates to a silver alloy composition having improved tarnish resistance and casting quality, which silver alloy composition contains 92.5-96.0 wt% Ag, preferably 93.5-94 wt% Ag, 2.27-4.96 wt% Cu, preferably 2.50-4.40 wt% Cu, 0.19-0.24 wt% Ge, preferably 0.19-0.23 wt% Ge, 0.04-0.05 wt% Si, preferably 0.04 wt% Si, 1.20-1.50 wt% Zn, preferably 1.30-1.50 wt% Zn, 0.13-0.16 wt% Sn, preferably 0.14-0.15 wt% Sn, 0.06-0.08 wt% In, preferably 0.07-0.08 wt% In, 0.0020-0.0040 wt% B, 0.0-0.08 wt% Ga, and P as the remainder. Because of the properties of the alloy, the alloy is suitable especially for producing jewelry and large goods.

Description

Silver alloy composition

The invention relates to a silver alloy composition and its use for the production of jewelry and carcass.

Usually, silver is used as a material for making jewelry and others

Silver articles defined as sterling silver containing at least 925 parts per thousand parts by weight of fine silver. Sterling silver typically comprises an alloy of 92.5 weight percent silver, the silver being usually alloyed with copper as well as traces of other metals and elements as additives for hardness and other desirable properties.

Conventional silver alloys have several weaknesses associated with the production of jewelry and in other material engineering contexts. Major drawbacks include the typical tendency for classic blackening, the so-called "tarnish", which is due to the formation of AgS, and most known silver alloys have undesirable porosity in the remelted state as well as undesirable grain size characteristics

Processing conventional alloys, i. When casting in molds, it also often leads to the formation of voids, so cavities in the solidification of the cast parts, when the volume contraction associated with the cooling can not be compensated by inflowing melt.

Numerous formulations have been proposed in the prior art in order to overcome the disadvantages mentioned. Thus, US Pat. No. 5,039,479 and US Pat. No. 4,973,466 disclose silver alloys and master alloys for producing such silver alloys which have better properties than the conventional alloys and contain, in addition to silver, controlled amounts of copper and zinc together with tin, indium, boron and silicon.

These compositions show reduced porosity, grain size and

Oxidation tendency. It is believed that the addition of zinc this

In the casting process, compositions impart antioxidant properties and reduce the formation of silver and copper oxide which results in pore formation in the cast or remelted alloys. A disadvantage of these known compositions, however, is that the

Alloys have poor cold curing properties and thus do not reach the mechanical strength and hardness of conventional sterling silverware.

DE 4213897 proposes an Ag-Cu alloy containing 0.5-3 wt. Germanium. This alloy has improved hardness, ductility, and tensile strength, and less quickly becomes dull or black than classic Ag-Cu alloys due to the appearance of preferential sulfurization of germanium over silver.

GB 2 355 990 and GB 2 414 739 teach Ag-Cu-Ge alloys containing as additives for example Sn, Sb, Si, Ni, In or also Ir and Fe. This extra

Alloy components to improve the tarnish protection while reducing the Ge content and the processability of the alloy.

WO 95/14112 discloses a silver alloy containing 89-95% by weight of Ag, 0.5-6% by weight of Cu, 0.05-5% by weight of Zn, 0.02-2% by weight. Si, 0.001-2% by weight B, 0.01-1.5% by weight In, 0.01-2.5% by weight of Ge and 0.25-6% by weight of Sn, which are a increased tarnish resistance and a reduced porosity and grain size with improved cold forming properties.

According to EP 2 453 028 B, the use of an Ag-Cu-Ge alloy for

Precision casting provided either 93.5 wt .-% Ag, 1.1 wt .-% Ge, 700 ppm Si, 3-60 ppm B, with the balance Cu, or 96 wt .-% Ag, 0.65 wt % Zn, 0.7 wt% Ge, 700 ppm Si, 3-60 ppm B, with the remainder Cu, and having a spotless silver appearance and reduced or eliminated shrinkage porosity.

US 2010/0239454 discloses an Ag-Cu-Ge alloy which consists of more than 93.5% by weight to 95.5% by weight of Ag, from 0.5 to 3% by weight of Ge, 1 -40 ppm of B, optionally 0.5% by weight of Zn, Cd and Sn, optionally 0.1-1% by weight of Si and the remainder, besides impurities, copper, wherein the weight ratio of Cu to Ge of 4: 1 to 3: 1. The alloy is against the emergence of porosity and brittleness, the emergence of

Cracking defects during investment casting, the formation of fractures or shattering during annealing and quenching, and the formation of cracks and "sagging" when heated by bonding and welding annealing resistant.

The object of the invention is to provide a silver alloy composition

to provide a high tarnish resistance, a high casting density and a high Has fine grain and is characterized at the same time by an easy to perform and effective thermal curability.

This object is achieved according to the invention by a silver alloy composition which:

92.5-96.0% by weight of Ag, preferably 93.5-94% by weight of Ag,

2.27-4.96 wt.% Cu, preferably 2.50-4.40 wt.% Cu,

0.19-0.24% by weight of Ge, preferably 0.19-0.23% by weight of Ge,

0.04-0.05 wt% Si, preferably 0.04 wt% Si,

1.20-1.50% by weight Zn, preferably 1.30-1.50% by weight Zn,

0.13-0.16% by weight of Sn, preferably 0.14-0.15% by weight of Sn,

0.06-0.08 wt% In, preferably 0.07-0.08 wt% In,

0.0020-0.0040% by weight B,

0.0-0.08 wt.% Ga, and

P as rest, contains.

It has been found that the silver alloy composition according to the invention in comparison to the conventional and known tarnish-optimized Ag alloys has a smaller amount of pores and voids and thus a denser cast structure, thus having a significantly better castability or casting quality.

This is accompanied by a high degree of fine granularity of the alloy, which leads to a particularly good ductility and polishability, which would be essential in particular for the production of jewelry and body.

Furthermore, the fiction, contemporary silver alloy composition has a significantly improved tarnish resistance to sulfur-containing media, as the black color is delayed and starts at the same load duration to a lesser extent than in alloys of the prior art.

In addition, the silver alloy composition according to the invention is characterized by an advantageous thermal curability, which allows with simple means a hardness increase of up to 200% of the initial hardness (eg Vickers hardness HV2 = 60-65). Thus, for example, by means of annealing (dark red heat: approx. 600 - 620 ° C) and subsequent heat treatment in a conventional oven, a hardness increase to about HV2 110-120 can be achieved. By increasing the initial hardness can be For example, the surface wear of silver jewelry, such as rings, brooches, etc., significantly reduce.

Preferably, the Sn content in the fiction, contemporary

Silver alloy composition 0.15 wt.

Preferably, the In content is in the fiction, contemporary

Silver alloy composition 0.07 wt.

The B content in the silver alloy composition of the present invention is preferably 0.0030 wt%.

The P content in the fiction, silver alloy composition is preferably 0.0070 wt .-%.

In a preferred embodiment, the silver alloy composition contains 94.00 wt% Ag, 3.93 wt% Cu, 0.23 wt% Ge, 0.04 wt% Si, 1.50 wt% Zn , 0.15 wt% Sn, 0.07 wt% In, 0.07 wt% Ga, 0.0020 wt% B and P as the balance.

In another aspect, the invention relates to the use of the above

described silver alloy composition for the production of jewelery, especially in investment casting, and carcass. For these products, the silver alloy composition of the invention is particularly advantageously suitable.

The invention is explained in more detail below with reference to examples and the drawing.

Examples

The silver alloys containing the composition according to the invention are produced by a melt-metallurgical process in which individual components and partially pre-alloyed components (CuB, CuSi, CuZn) are melted, preferably by means of inductive low-frequency heating. The melting takes place under extensive exclusion of air, by protective gases such as nitrogen or argon a protective

Atmosphere is generated, which prevents the partial oxidation and / or depletion of the base alloy components. Preferably, the molten alloy is then continuously cast, wherein the melt or the solidified strand is withdrawn via a water-cooled mold as a round or square profile.

The further processing depends on the intended use of the alloy. In the sheet metal or wire production, the processing is carried out by conventional cold forming such as rolling or wire drawing with appropriate annealing steps, by which the material is transferred after previous work hardening by microstructural relaxation or recrystallization in a soft, well deformable state.

The thus processed silver alloy according to the invention is suitable for use as a classic jewelry alloy for the production of Pretiosen by pressing, pressing or casting and also for the production of carcasses, such as vessels, plates, tableware and the like.

For use as a casting alloy, the alloy is made into granules by rolling and cutting into small sections of sheet (e.g., 10x10x2mm) or by a granulation process. In the granulation process, the alloy melt or the melt stream in a liquid medium, preferably water with surface-active additives, out, the formation of the granules or balls is supported by an additional stirring by means of agitator or water jet.

The sheet sections or granules thus produced can then be processed by casting in lost form (investment casting) to jewelry blanks, which are then brought into their final form by grinding, sanding, polishing, bending, soldering, grabbing stones, etc.

Table 1 shows embodiments of the invention

Silver alloy composition prepared by the method described above.

Table 1 (all data in parts by weight)

Variant Ag Cu Ge Si Zn Sn In Ga El.

1 92.5 4.96 0.19 0.05 1.5 0.15 0.07 0.07 *)

2 93.5 4.53 0.19 0.05 1.5 0.15 0.07 - *)

3 93.5 4.46 0.19 0.05 1.5 0.15 0.07 0.07 *) 4 94.0 4.03 0.19 0.05 1.5 0.15 0.07 - *)

5 94.0 3.96 0.19 0.05 1.5 0.15 0.07 0.07 *)

6 96.0 2.34 0.19 0.04 1.2 0.15 0.07 - *)

7 96.0 2.27 0.19 0.04 1.2 0.15 0.07 0.07 *)

*) B = 0.0030, P = 0.0070

Table 2 shows alloy compositions of conventional silver alloys (variants 4 and 5) and alloys according to EP 2 453 028 A (variants 1-3).

Table 2 (all data in parts by weight)

*) B = 10 ppm (0.001 wt%) and P = 30 ppm (0.003 wt%)

In comparison to the silver alloy composition according to the invention, the alloy according to variant 4 has a lower tarnish resistance as well as a higher porosity and poorer casting quality.

The alloy according to variant 5, in contrast to the Invention according to

Silver alloy composition a coarse-grained texture and a worse

Cast quality on. In addition, no thermal curability was found.

With regard to variants 1 and 2, studies on the tarnish resistance were made

carried out (described below), which show that the fiction, contemporary

Silver alloy composition has an improved protection against these alloys.

Start-up test:

The test specimens used were rectangular plates of 45 × 15 × 2 mm of the following silver alloys: a) 925 silver ("sterling silver")

b) 940 Alpine V6 Plus (preferred embodiment of the alloy according to the invention) c) 960 argentium (according to EP 2 453 028 A)

d) fine silver

The specimens are positioned on a stainless steel net placed on a beaker (3000 ml). The experiment is carried out in a digestive system with the suction switched on. The test solution (in a beaker) consists of 1.40 ml of ammonium sulfide and 400 ml of dist. Water together.

All specimens were removed before storage (5 days and 20.5 hours) with ASTM 2400 sandpaper. In addition, these were cleaned before and after storage in the ultrasound and with alcohol and dry-rubbed with a cotton cloth.

The tarnish protection is lowest at 960 argentium (alloy c) and in fine silver after 40 minutes. As in Fig. 1 (Fig la): Figure of the top of the test specimen Fig. Lb:

Illustration of the underside of the specimens) shows, the inventive

Composition 940 Alpine-V6 Plus (alloy b) after 150 minutes the best tarnish protection on (arrangement of the specimens from left to right: a-b-c-d).

Cast structure:

For the test, test casting trees of 940 Alpine V6 Plus and 960 argentium were cast at a casting temperature of 1020 ° C and a cuvette temperature of 550 ° C. Subsequently, a grinding was made per trial to assess the casting quality and the structure.

As shown in Figure 2, the alloy 940 Alpine-V6 Plus (Figure 2a) according to the invention also has a fine-grained, i.e., 960 argentium (Figure 2b). low-pore structure on.

As shown in FIGS. 3 and 4, the structure of the alloy according to the invention in the

1) and is sealed both along the ring rail and in the sprue area (FIG. 4). On the other hand, shrinkage cavities (FIG. 5) and a higher porosity can be recognized in the case of 960 argentium in the interior of the frame (FIG. 6). Aushärtungstest:

To investigate the hardenability was the fiction, contemporary

Alloy composition 940 Alpine V6 Plus subjected to various heat treatments. The parameters of the heating as well as the resulting Vickers hardness (HVl) plus hardness increase in relation to the initial hardness are listed in Table 3.

Table 3

As the test results show, the hardness of the alloy can be significantly increased by simple means.

Claims

claims:

1. Silver alloy composition containing:

92.5-96.0% by weight of Ag, preferably 93.5-94% by weight of Ag,

2.27-4.96 wt.% Cu, preferably 2.50-4.40 wt.% Cu,

0.19-0.24% by weight of Ge, preferably 0.19-0.23% by weight of Ge,

0.04-0.05 wt% Si, preferably 0.04 wt% Si,

1.20-1.50% by weight Zn, preferably 1.30-1.50% by weight Zn,

0.13-0.16% by weight of Sn, preferably 0.14-0.15% by weight of Sn,

0.06-0.08 wt% In, preferably 0.07-0.08 wt% In,

0.0020-0.0040% by weight B,

0.0-0.08 wt.% Ga, and

P as rest.

2. Silver alloy composition according to claim 1, characterized in that the Sn content is 0.15 wt .-%.

3. Silver alloy composition according to claim 1 or 2, characterized in that the In content is 0.07 wt .-%.

4. Silver alloy composition according to one of claims 1 to 3, characterized in that the B content is 0.0030 wt .-%.

5. Silver alloy composition according to one of claims 1 to 4, characterized in that the P content is 0.0070 wt .-%.

6. silver alloy composition according to one of claims 1 to 3, characterized in that they 94.00 wt .-% Ag, 3.93 wt .-% Cu, 0.23 wt .-% Ge, 0.04 wt% Si, 1.50 wt% Zn, 0.15 wt% Sn, 0.07 wt% In, 0.07 wt% Ga, 0.0020 wt% B and P as the balance.

7. Use of a silver alloy composition according to one of claims 1 to 6 for the production of jewelery, in particular in investment casting, and body goods.