ES2227106T3 - GOLD ALLOYS AND MOTHER ALLOYS TO GET SUCH GOLD ALLOYS. - Google Patents

Abstract

Gold alloy comprising, by weight, at least Gold Au ≥ 51 %, Iridium Ir ≤ 0.1 %, Germanium Ge ≤ 2 % and Copper Cu ≤ 45 %. The alloy can also comprise, in percentage by weight, Silver Ag ≤ 34 %, nickel Ni ≤ 20 % and Zinc Zn ≤ 12 %. In some variations the gold alloy can further comprise no more than 4% of at least one of the elements of the group constituted by cobalt, manganese, tin and indium, and no more than 0.15% of at least one of the deoxidising elements of the group constituted by magnesium, silicon, boron and lithium. To the alloy can also be added at least one of the refining elements of the group constituted by ruthenium, rhenium and platinum in quantities not exceeding 0.4% by weight. The invention further relates to a master alloy for obtaining said gold alloy. <IMAGE>

Description

Gold alloys and mother alloys for get such gold alloys.

The present invention relates to alloys of gold and mother alloys to obtain such gold alloys, mainly for the manufacture of precious objects such as jewelry and goldsmith products, coins and medals.

One of the fundamental problems is that of obtain gold alloys that have good fluidity (it is say, a good ability to fill the mold) at the time of wash.

According to the procedures normally used At present, this is achieved by adding a little bit of silicon, which, in addition to giving a fluidizing effect to the Alloys, also has a deoxidizing effect.

During the period of the process in which the metal remains in a melted state, silicon tends to combine with the oxygen in the original materials and in the surrounding atmosphere.

This results in a protective ability of the silicon manifested during the production of granules by casting and during the process to produce the castings that includes the melting, overheating and filling of the Mold cavity made of refractory material.

However, the use of silicon in alloys of gold also gives rise to a considerable disadvantage constituted by the fact that these alloys exhibit, once solidified, a crystalline grain of relatively large size, consequently degradation of mechanical properties (especially in the case of 18-carat gold alloys), and a consequent fragility not desired of the same pieces.

Seen this problem, a method followed by sector operators to reduce grain size has been the to add an adequate amount of elements to the alloys such as iridium, ruthenium, cobalt, nickel and rhenium, which tend to refine the crystalline grain.

However, this solution is not lacking either Totally disadvantages.

First, silicon tends to combine with the commonly used refining elements giving rise to the formation of silicides that end up constituting agglomerates spheroidal inter-metallic compounds with high rigidity, causing imperfections known as hard points spots).

Such inclusions may appear on the surface of the finished part after the manufacturing process final, which involves the reworking of the piece, or its discard.

From documents EP 381.994 and JP 63,169,347 the addition of germanium to the gold alloys to improve its molding capacity and fluidity lowering the melting point.

In this situation the technical task that constitutes the basis of the present invention is to provide gold alloys and mother alloys to obtain such alloys of gold that overcomes the aforementioned disadvantages.

In particular the technical role of this invention is to provide gold alloys and alloys mothers to obtain such gold alloys that present a excellent fluidity in the melted state even without the addition of silicon.

The specific technical task and objectives mentioned are achieved substantially by gold alloys and mother alloys to obtain such gold alloys, as is described in the claims that follow.

An alternative element to silicon is germanium which, in the percentage of employment described herein invention, has very marked fluidization properties, superior to those of silicon: as described below, this characteristic is clearly demonstrated with experiments of comparative fusion between silicon-based alloys and alloys based on germanium, the latter described herein invention.

In addition, the bath of Germanium-based alloys exhibits an extremely clean and slag-free surface, characteristic due to the fact that germanium oxides that could be present on the surface of the bathroom disappear by sublimation at temperatures of approximately 710 ° C. With respect to silicon-based alloys, therefore, is reduced drastically the possibility of oxide particle inclusions in castings, with the consequent risk of fragility.

It has also been proven that Germanium concentrations that vary between 0.05% and 2% by weight have led to an increase in fluency considered greater than those provided by silicon in normal concentrations of use, if well exhibit an increase in grain size, as a result of said aggregate, which is decidedly smaller than that observed in the silicon alloys Therefore, in the case of alloys of germanium, with low or no silicon content, apart from obtaining the fluidizing effect, superior to that of silicon, is also improve the mechanical characteristics of the alloy, as you can See from the data illustrated below.

In addition, a remarkable effect of improvement of germanium over the ductility of the alloy obtained, superior to the effect of silicon.

Also interesting is the combined use of germanium and small amounts of silicon: this combination allows get "clean and bright" castings without causing the immediate degradation of mechanical properties as you can observe with the use of larger amounts of only silicon.

Therefore, the problem of the formation of hard, harmful points at the time of polishing the finished parts is also avoided, preventing the insertion into the alloy of refining elements (in order to bring the mechanical properties to the previous functional values) such as cobalt and nickel
quel.

The improvement effect of germanium on Mechanical properties can also be exhibited in alloys nickel-based white, as can be seen from the formulations described below.

Other features and advantages of this invention will become even more apparent from the detailed description of some preferred embodiments but not exclusive of gold alloys and mother alloys to obtain such gold alloys, and from the attached figures, in the which:

- Figure 1 shows, in graphic form, the effect of different elements and compounds on the size of the grain of a gold alloy;

- Figure 2 shows, in graphic form, the effect of the amount of silicon and germanium on the size of the gold alloy bead;

- Figure 3 shows, in graphic form, the effect of the elements and compounds of figure 1 on the maximum load bearable by the gold alloy obtained with the themselves;

- Figure 4 shows, in graphic form, the effect of the elements and compounds of figure 1 on the ductility properties (stretching due to traction) of the alloy.

The gold alloy of the present invention is defined in claim 1.

As previously noted, the fundamental characteristic of said alloy is to contain germanium as a fluidizing element, while not being able to contain silicon

To complete the alloy satisfying the better way special production requirements, also They can use other chemical elements.

Second, the alloy can also contain, in a proportion not exceeding 4% of the weight, at least one of the elements of the group consisting of cobalt, manganese, Tin and Indian.

To improve the qualities of the alloy, It is also possible to add one or more deoxidizing elements such as magnesium, silicon, boron and lithium, each of them in a proportion that does not exceed 0.15% of the weight.

Note that, even when silicon is added to the alloy, is added only in small quantities (in particular not exceeding 0.05% of the weight in 18-carat alloys, and not greater than 0.15% of the weight in 14 karat alloys) simply to ensure the protection of the alloy against formation of oxides, and not to improve its fluidity.

Due to particular productive demands in which requires a very small grain size, the alloy can also comprise refining elements such such as ruthenium, rhenium and platinum in an adequate amount and preferably not more than 0.4% of the weight.

For the production of precious objects, in addition, there are two preferential intervals for the amount of gold present in the alloy.

A preferred first interval is that associated with obtaining 18 karat gold, in which the amount of Gold present in the alloy is between 74% and 77% of the weight.

A second preferred interval is that associated with obtaining 14 karat gold, in which the amount of Gold present in the alloy is between 57% and 60% of the weight.

The mother alloys to obtain the alloys of gold set forth above are defined in claim 2.

Below are some examples of gold alloys that can be obtained with a composition according to The present invention.

Example A

14 carat yellow gold alloy whose Composition in terms of weight percentage is as follows:

Gold 58.5

with the mother alloy comprising (as percentage on the weight of the gold alloy):

Silver 8.0 Zinc 6.0

Iridium 0.01 Germanium 0.4

Copper, what is necessary to reach 100% (in this specific case, 27.09%).

Example B

18K yellow gold alloy whose Composition in terms of weight percentage is as follows:

Gold 75.0

with the mother alloy comprising (as percentage on the weight of the gold alloy):

Silver 15.0 Iridium 0.01 Germanium 0.2

Copper, what is necessary to reach 100% (in this specific case, 9.79%).

Example C

18K yellow gold alloy whose Composition in terms of weight percentage is as follows:

Gold 75.0

with the mother alloy comprising (as percentage on the weight of the gold alloy):

Silver 12.5 Zinc 0.5 Germanium 0.25 Silicon 0.04

Copper, what is necessary to reach 100% (in this specific case, 11.71%).

To obtain the three mentioned alloys of yellow gold described in examples A, B and C, a process Preferential includes the following stages:

- foundry in a controlled atmosphere or in a inert gas such as argon, of the elements in the respective dose, inside graphite or ceramic pots at a temperature between 880 and 940 ° C;

- subsequent heating at a temperature between 970 and 1,030 ° C before casting;

- pouring of the material into appropriate molds;

- mold cooling in air;

- subsequent cooling of the mold in water.

The present invention achieves important advantages.

First, the laboratory experiments conducted by the Applicant have shown that the use of germanium at concentrations of weight between 0.05% and 2%, it leads to an increase in the fluidity of the alloy in the melted state that it is even greater than that caused by the use of silicon in Normal concentrations of use.

Also, the increase in grain size consequently the use of germanium was less than that which takes place in traditional alloys containing silicon, as you can see in figures 1 and 2.

Figure 1 shows the variation of the dimensions of the crystalline alloy grain as a consequence of the addition, in it, of the indicated elements and compounds in the "x" coordinate. It is clear that the influence of Silicon (CuSi) on the increase in grain size is considerably greater than the influence of germanium (Ge).

Figure 2 shows the effect of concentration of silicon and germanium on the grain dimension of the alloy of gold. Also in this case, it is evident that a low concentration of silicon, in the graph of 0 to 300 ppm, carries a considerable increase in the size of the crystalline grain, even overcoming the increase in size caused by germanium aggregates in concentrations 10 times higher.

This has positive repercussions on the mechanical operation of the alloy, as can be seen in the Figure 3, which shows the variation (positive or negative) of the maximum load bearing (measured with a tensile test) by the alloy, as a result of the addition to the alloy of same amounts of different elements or compounds indicated in the "x" coordinate.

Figure 4 shows the percentage of variation of stretching the gold alloy undergoing a test of traction, depending on the aggregate, in equal quantities, of the elements and compounds, indicated in the "x" coordinate, to the alloy.

The use of germanium instead of silicon has also produced positive effects on the stretch percentage of the alloy as a result of the tensile test.

With respect to the combined use of germanium and silicon, to improve fluidity and reduce oxidation of the alloy respectively, very results were achieved encouraging.

The combined use of these two elements resulted in to deoxidized alloys that at the same time show a very good mechanical performance, generally better than that exhibited by alloys in which silicon is used as an element fluidizer, either as a deoxidant element.

Also, the alloys obtained according to the present invention (be it gold alloys or alloys mothers to get such gold alloys), thanks to the little crystalline grain size, usually may not require the use of Other elements of refining.

In any case, if necessary, the use of refining elements to obtain grain dimensions even smaller, silicide formation does not take place, thanks to the absence, or almost absence, of silicon.

It should also be noted that the present invention It is relatively easy to implement and also that the cost related to the implementation of the present invention follows being within the standards of the sector.

Claims (2)

1. Yellow gold alloy characterized by the fact that it comprises, in terms of weight, at least: Gold: in the range 74 \ leqAu \ leq77% or in the range 57? le60%; Iridium: 0 <Ir \ leq0.2%; Germanium: 0 <Ge \ leq2%; Silver: 0 <Ag \ leq34%; Zinc: 0 <Zn? 12%; Copper: Cu sufficient to reach 100%; and optionally one or more of the following elements: Silicon: 0 <Si? 0.15%; Lithium: 0 <Li? 0.15%; no more than 4% by weight of at least one of the elements of the group consisting of cobalt, tin and Indian; not more than 0.15% by weight of at least one of the elements of the group consisting of magnesium and boron; Y no more than 0.4% by weight of at least one of the elements of the group consisting of ruthenium, rhenium and platinum. 2. Mother alloy to obtain yellow gold alloys according to claim 1, characterized in that it comprises, by weight, at least: Iridium: 0 <Ir \ leq0.4%; Germanium: 0 <Ge \ leq4%; Silver: 0 <Ag ≤72%; Zinc: 0 <Zn? 25%; Copper: Cu sufficient to reach 100%; and optionally one or more of the following elements: Silicon: 0 <Si? 0.36%; Lithium: 0 <Li? 0.36%; no more than 8% of at least one of the elements of the group consisting of cobalt, tin and Indian; no more than 0.36% of at least one of the elements from the group consisting of magnesium and boron; Y no more than 0.96% by weight of at least one of the elements of the group consisting of ruthenium, rhenium and platinum.