Master alloy for rose gold alloy and rose gold alloy

Abstract

100 18K rose gold alloy including: copper in a percentage by weight between 16% and 25%; silver in a percentage by weight between 0% and 9%; zinc in a percentage by weight between 0% and 1.5%; optionally silicon in a percentage by weight between 0.005% and 0.1 %; optionally indium in a weight percentage between 0.125 - 1.250% nano-sized ruthenium particles in a percentage by weight between 1 ppm and 100 ppm, with the rest of the composition up to 100% made up of unavoidable gold and impurities where the nano-sized ruthenium particles have an average size between 5 nm and 5000 nm, as measured by dynamic light scattering.

Description

[0001] MASTER ALLOY FOR ROSE GOLD ALLOY AND ROSE GOLD ALLOY

[0002] Field of invention

[0003] The present invention refers to the field of gold alloys for jewelry, and more specifically to an 18-carat rose gold alloy, and in particular to a rose gold master alloy and an 18-carat rose gold alloy.

[0004] State of the Art

[0005] 18K rose gold alloys are widely used in the jewelry industry for their attractive coloring and mechanical properties. These alloys typically contain gold, copper, and small amounts of other metals such as silver and zinc. The percentage of copper, usually between 20% and 25% by weight, gives the alloy its characteristic pinkish hue.

[0006] However, 18-carat rose gold alloys present some technical problems that limit their use in certain applications. One of the main challenges is susceptibility to "fire cracking," which is the formation of cracks or fissures when the alloy is subjected to uneven heating during processes such as welding or scaling. This phenomenon is particularly pronounced in thin sections of jewelry and can compromise its structural integrity.

[0007] Another technical challenge is to achieve a clean, oxidation-free surface after the casting processes. The addition of deoxidizing elements such as silicon can improve this, but it tends to interfere with grain refiners traditionally used to increase the mechanical strength of the alloy. This can lead to the formation of unwanted intermetallic compounds visible as hard spots on the surface of the jewelry after polishing.

[0008] It has been recognized that it would be advantageous to have an alloy that overcomes one or more of these problems.

[0009] Purpose of the invention

[0010] The purpose of the invention is to propose a master alloy to make an 18-carat rose gold alloy and an 18-carat rose gold alloy that would allow to overcome the drawbacks of the well-known solutions.

[0011] Another purpose of the invention is to propose a master alloy and an alloy that have a high resistance to fire cracking.Object of the invention

[0012] In a first aspect, an 18K 100 rose gold alloy is supplied. Alloy 100 includes: gold in a percentage by weight between 75% and 77%; copper in a percentage by weight between 16% and 25%; silver in a percentage by weight between 0% and 9%; zinc in a percentage by weight between 0% and 1.5%; nano-sized ruthenium particles in a percentage by weight between 1 ppm and 100 ppm, where the nano-sized ruthenium particles have an average size between 5 nm and 5000 nm as measured by X-ray diffraction, scanning electron microscopy, or dynamic light scattering. The use of nano-sized ruthenium particles as a grain refiner allows to obtain a finegrained structure that significantly improves the mechanical strength of the alloy and reduces the susceptibility to the phenomenon of fire cracking.

[0013] Nano-sized ruthenium particles can have an average size between 20 nm and 1000 nm.

[0014] This range of ruthenium particle sizes allows for optimal refinement of the crystalline grain, balancing the effectiveness of refinement with the ease of dispersion of the particles in the molten alloy.

[0015] The alloy can also include silicon in a percentage by weight between 0.005% and 0.1%.

[0016] The addition of silicon in this percentage improves the fluidity of the alloy during melting and contributes to deoxidation, without significantly interfering with the refining action of nanometric ruthenium.

[0017] In a specific composition, the percentage by weight of gold can be 75%, the percentage by weight of copper can be 23.2%, the percentage by weight of silver can be 1 %, the percentage by weight of zinc can be 0.75%, and the percentage by weight of silicon can be 0.04%.

[0018] This specific composition offers an optimal balance between mechanical properties, fire cracking resistance and the desired pinkish hue for jewelry applications.

[0019] The percentage by weight of nano-sized ruthenium particles can be 20 ppm.

[0020] This concentration of nanometer ruthenium has proven to be particularly effective in providing optimal grain refinement without causing problems with dispersion or formation of unwanted aggregates.

[0021] Brief description of the figuresThe present invention will now be described, by way of example and not limitation, according to some of its preferred forms of realization, and with the help of the attached figures, in which:

[0022] FIG. 1 illustrates several orthogonal views of jewelry elements.

[0023] FIG. 2 shows a perspective view of a tree structure assembled with the alloy according to the invention.

[0024] FIG. 3 presents a sequence of images of a fire cracking test on a ring.

[0025] FIG. 4a and FIG. 4b show microscopic views of material samples.

[0026] FIG. 5 presents a series of metallographic views of granular structures in gold alloy samples.

[0027] Detailed Description

[0028] The present invention concerns a new 18-carat rose gold alloy with an innovative composition. The alloy preferably comprises 75% gold, 23.2% copper, 1% silver, 0.75% zinc, 0.04% silicon and 20 parts per million ruthenium.

[0029] This composition was developed with the aim of obtaining an 18-carat rose gold alloy that offers better resistance to fire cracking, also known as "fire cracking", and exhibits excellent deoxidation and surface gloss after the investment casting process. An additional advantage of this alloy is the absence of hard spots on the surface of the metal after machining.

[0030] The presence of ruthenium in nanometric form, with average particle sizes between 5 and 5000 nanometers, is a key element in achieving the desired properties. Ruthenium acts as a refiner of the crystalline grain, helping to improve the mechanical characteristics and resistance to cracking of the alloy.

[0031] This new composition aims to overcome some limitations of conventional 18K rose gold alloys, offering a material more suitable for the production of high-quality jewelry, particularly for applications that require high mechanical strength and superior surface finish.

[0032] Alloy

[0033] The composition of the 18-carat rose gold alloy covered by this invention includes, and preferably consists of, the following elements:

[0034] gold (Au) between 75 and 77% by weight.

[0035] copper (Cu) between 16 and 25% by weight, and preferably between 17.5 and 24,and more preferably between 18.5 and 23.7, and more preferably between 19.5 and 23.5, and more preferably between 20.5 and 23.4, and more preferably between 21.5 and 23.3, and more preferably between 22.2 and 23.25, and more preferably equal to 23.2.

[0036] silver (Ag) between 0 and 9% by weight, and preferably between 0.2 and 7, and more preferably between 0.4 and 5, and more preferably between 0.6 and 3.5, and more preferably between 0.7 and 2.5, and more preferably between 0.8 and 1.8, and more preferably between 0.9 and 1.2, and more preferably equal to 1. zinc (Zn) between 0 and 1.5% by weight, and preferably between 0.2 and 1.3, and more preferably between 0.35 and 1.15, and more preferably between 0.45 and 1.0, and more preferably between 0.55 and 0.9, and more preferably between 0.6 and 0.85, and more preferably between 0.65 and 0.8, and more preferably equal to 0.75. silicon (Si) between 0.005 and 0.1% by weight, and preferably between 0.01 and 0.09, and more preferably between 0.02 and 0.08, and more preferably between 0.025 and 0.07, and more preferably between 0.03 and 0.06, and more preferably between 0.035 and 0.05, and more preferably between 0.038 and 0.045, and more preferably equal to 0.04

[0037] indium (In) between 0 and 1.5% by weight, and preferably between 0.2 and 1.3, and more preferably between 0.35 and 1.15, and more preferably between 0.45 and 1.0, and more preferably between 0.55 and 0.9, and more preferably between 0.6 and 0.8, and more preferably between 0.65 and 0.75, and more preferably equal to 0.7. ruthenium (Ru) between 1 and 100 ppm, and preferably between 5 and 70, and more preferably between 10 and 50, and more preferably between 14 and 40, and more preferably between 16 and 30, and more preferably between 18 and 25, and more preferably between 19 and 21 , and more preferably equal to 20 ppm.

[0038] Master alloy

[0039] The master alloy, from which the final alloy is obtained, may include, and preferably consist of, the following elements:

[0040] copper (Cu) between 64 and 99.5% by weight, and preferably between 68 and 98, and more preferably between 72 and 96, and more preferably between 76 and 94, and more preferably between 80 and 93.5, and more preferably between 84 and 93, and more preferably between 87 and 92.9, and more preferably between 89 and 92.8, and more preferably equal to 92.85.zinc (Zn) between 0 and 6% by weight, and preferably between 0.5 and 5, and more preferably between 1 and 4, and more preferably between 1.5 and 3.5, and more preferably between 2 and 3.2, and more preferably between 2.3 and 3.1 , and more preferably between 2.6 and 3.05, and more preferably between 2.8 and 3.02, and more preferably equal to 3.

[0041] silver (Ag) between 0 and 36% by weight, and preferably between 2 and 30, and more preferably between 2.5 and 24, and more preferably between 2.7 and 18, and more preferably between 2.8 and 12, and more preferably between 2.9 and 7, and more preferably between 2.95 and 5, and more preferably between 2.98 and 4.5, and more preferably equal to 4.

[0042] silicon (Si) between 0.02 and 0.4% by weight, and preferably between 0.04 and 0.35, and more preferably between 0.07 and 0.3, and more preferably between 0.1 and 0.26, and more preferably between 0.11 and 0.24, and more preferably between 0.12 and 0.22, and more preferably between 0.13 and 0.20, and more preferably equal to 0.14.

[0043] indium (In) between 0 and 6% by weight, and preferably between 0.5 and 5, and more preferably between 1 and 4, and more preferably between 1.5 and 3.5, and more preferably between 2 and 3.2, and more preferably between 2.3 and 3.1 , and more preferably between 2.6 and 3.05, and more preferably between 2.8 and 3.02, and more preferably equal to 3.

[0044] ruthenium (Ru) between 5 and 200 ppm, and preferably between 10 and 180, and more preferably between 20 and 150, and more preferably between 30 and 130, and more preferably between 50 and 120, and more preferably between 70 and 110, and more preferably between 85 and 105, and more preferably between 95 and 102, and more preferably equal to 80 ppm.

[0045] To obtain the final alloy from the parent alloy, the necessary amount of pure gold is added to reach the desired fineness of 18 carats (75% gold).

[0046] Each component plays a specific role in the alloy:

[0047] Gold gives the characteristic color and determines the title of the alloy.

[0048] Copper is the main alloying element and contributes to the red color. In addition, it improves mechanical properties such as hardness and strength.

[0049] Silver can be added in small amounts to lighten the color slightly and improve the workability of the alloy.

[0050] Zinc acts as a flux and improves the fluidity of the alloy during melting.Silicon performs an important flux function, improving surface quality and gloss after melting.

[0051] Indium can be added in small amounts to lighten the color and improve mechanical properties.

[0052] Ruthenium, in the form of nanoparticles with an average size between 5 and 5000 nm, acts as an effective refiner of crystalline grain. This helps to improve the mechanical strength and resistance to fire cracking of the alloy.

[0053] The combination of these elements in the indicated proportions results in an 18-carat rose gold alloy with excellent mechanical properties, crack resistance and surface quality after casting.

[0054] The use of nanometer ruthenium as a grain refiner in gold alloy represents a significant innovation in the composition of jewelry alloys. Nanometer ruthenium particles have an average size between 5 and 5000 nanometers. These nano-sized particles act as nucleation centers during the solidification of the alloy, promoting the formation of a fine-grained structure.

[0055] Fig. 6 shows a series of metallographic images illustrating the different microstructures obtained with various alloy compositions and refinement methods. In particular, images labeled as -I, L, M, and N show the effect of adding nanometer ruthenium with decreasing particle sizes.

[0056] Image C represents the microstructure obtained with standard ruthenium, while subsequent images show the effect of ruthenium particles of smaller and smaller sizes. A progressive reduction in the size of the crystalline grains can be observed from image C to images I, L, M and N.

[0057] The grain refinement effect achieved with nanometer ruthenium is due to the high number of nucleation sites provided by the finely dispersed particles in the molten alloy. During solidification, each ruthenium particle acts as a starting point for the growth of a new crystalline grain, thus limiting the growth of large grains.

[0058] The homogeneous distribution of nano-sized ruthenium particles in the alloy ensures uniform grain refinement throughout the material volume. This results in a more homogeneous microstructure and more uniform mechanical properties than alloys refined using traditional methods.

[0059] The use of nano-sized ruthenium particles also allows for effective grain refinement with lower refiner concentrations than conventional methods. This aspect is advantageous both from an economic point of view and to minimize potential sideeffects due to high concentrations of refining elements.

[0060] The fine-grained microstructure obtained from nano-sized ruthenium gives the gold alloy an optimal combination of mechanical strength and ductility. This combination of properties is particularly advantageous for the creation of jewelry with complex shapes and intricate details, such as those shown in Fig. 6.

[0061] The developed 18K rose gold alloy has improved mechanical and physical properties compared to traditional rose gold alloys.

[0062] The hardness of the alloy, measured on the Vickers scale, is between 170 HV and 300 HV. This hardness range is higher than conventional 18K rose gold alloys, which typically exhibit hardness values between 150 HV and 250 HV. The increase in hardness is attributable to the refinement of the crystalline grain obtained through the use of ruthenium nanoparticles as a refiner.

[0063] The tensile strength of the alloy was measured in a range of 450 MPa to 650 MPa. These values are higher than traditional rose gold alloys, which generally have a tensile strength of between 400 MPa and 550 MPa. The improvement in mechanical strength is related to the fine-grained structure of the alloy.

[0064] The density of the alloy was measured at 15.8 g / cm3, in line with the typical values of 18-carat gold alloys.

[0065] The coefficient of linear thermal expansion of the alloy was measured at 14.2 x 10-6K-1, slightly lower than traditional rose gold alloys that have values around 15.0 x 10-6K’1. This reduction can contribute to improved dimensional stability during thermal processes.

[0066] The melting temperature of the alloy is between 890°C and 920°C, in line with conventional 18K rose gold alloys. The cold and hot workability of the alloy is good, with the possibility of plastic deformation up to 70% without the need for intermediate annealing.

[0067] In summary, the developed 18-carat rose gold alloy exhibits superior mechanical properties in terms of hardness and tensile strength, while maintaining good machinability characteristics. These properties make the alloy particularly suitable for jewellery applications that require high mechanical performance and wear resistance.

[0068] The developed 18K rose gold alloy features significantly improved fire cracking resistance compared to standard commercial alloys. Fire cracking is a brittleness phenomenon that can occur during localized heating processes, such as solderingor resizing jewelry.

[0069] To evaluate the resistance to fire cracking, specific tests were conducted on different samples of jewelry made with the new alloy. The test consists of applying a localized flame to a small area of the sample for a set time, simulating welding conditions. Test results showed a reduction of more than 80% in the average number of cracks per piece compared to alloys refined with standard ruthenium. In addition, a 70% decrease in the number of damaged parts was observed.

[0070] This increased resistance to fire cracking is attributable to the refinement of the crystalline grain achieved by using ruthenium nanoparticles as an affineur. The finegrained structure increases the mechanical strength of the alloy and reduces the likelihood of crack formation and propagation during thermal processes.

[0071] Metallographic analysis of the samples confirmed a significantly reduced average grain size compared to standard alloys, with values ranging from 600 to 1000 pm depending on the process conditions.

[0072] The improved resistance to fire cracking results in greater machinability of the alloy and a reduction in production waste, making this composition particularly suitable for jewelry applications that require localized welding or heating processes.

[0073] A jewellery item 100 can be made in different shapes and styles using this innovative alloy. For example, a 100 jewelry item can be a bridge ring, wedding band, earring, or butterfly-shaped filigree decorative element. The superior resistance to fire cracking of this alloy makes it particularly suitable for making jewelry with complex shapes and intricate details.

[0074] The alloy allows for smooth and shiny surfaces after casting, without the presence of hard spots. This feature is beneficial for the production of high-quality jewelry, such as the illustrated jewelry item 100, which features uniform surfaces and well-defined details.

[0075] The alloy's increased mechanical strength makes it possible to make jewellery items 100 with thin and delicate sections, such as the filigree parts visible in the butterflyshaped decorative element of the jewellery item 100 shown. This property allows designers to create intricate and lightweight jewelry without compromising durability. The alloy is particularly suitable for investment casting processes with in-house stones, due to its excellent deoxidation after casting. This feature makes it possible to create jewellery items 100 with complex and detailed settings, while maintaining a high-quality surface finish.Superior resistance to fire cracking makes the alloy ideal for machining processes that require localized heating, such as welding and scaling. This property allows you to modify and repair jewellery items 100 with greater ease and safety, reducing the risk of damage during these operations.

[0076] In summary, the unique properties of this 18K rose gold alloy make it versatile and suitable for a wide range of applications in jewelry, from creating delicate and intricate pieces, to producing more robust and functional jewelry.

[0077] The 18-carat rose gold alloy described has a synergistic combination of elements that give optimal properties for jewelry applications. The interaction between the various components of the alloy helps to improve resistance to fire cracking and surface quality after casting.

[0078] Gold, as the main element, provides the precious basis of the alloy. Copper, present in a significant percentage, gives it its characteristic pink color and contributes to mechanical properties. Silver, in smaller quantities, helps to balance the color and improves workability. Zinc, in small amounts, acts as a flux and improves fluidity during melting.

[0079] A key element is ruthenium in nanometer form, which acts as a grain refiner. Ruthenium nanoparticles act as nucleation centers during solidification, promoting the formation of a fine-grained structure. This refined microstructure increases the mechanical strength of the alloy and reduces the tendency for cracking to form during thermal processes such as welding.

[0080] The interaction between nanometer ruthenium and silicon is particularly beneficial. Silicon, used as a flux, improves surface gloss after melting. In traditional alloys, silicon tends to form unwanted intermetallic compounds with conventional grain refiners. However, the use of nanometer ruthenium reduces this negative interaction, allowing both the flux effect of silicon and grain refinement to be maintained.

[0081] This synergy between the elements makes it possible to obtain an alloy with excellent characteristics for jewelry. The fine-grained structure gives greater resistance to fire cracking, reducing the risk of damage during subsequent processing such as welding and scaling. At the same time, the presence of silicon and the reduced formation of intermetallic compounds contribute to a smooth and shiny surface after melting.

[0082] The combination of these effects results in an alloy that is particularly suitable forhigh jewellery applications. The improved strength allows for complex and delicate designs, while the excellent surface quality reduces the need for re-machining, optimizing the production process. The alloy is particularly advantageous for techniques such as investment casting with in-situ stones and the creation of filigrees, where surface quality and mechanical strength are critical.

[0083] In summary, the synergistic interaction between the elements of the alloy, in particular the role of nanometric ruthenium, makes it possible to obtain a material that combines mechanical strength, workability and aesthetic quality, responding to the specific needs of the high-end jewellery sector.

[0084] The invention thus conceived and illustrated here is susceptible to numerous modifications and variations, all falling within the scope of the inventive concept. In addition, all the details can be replaced by other technically equivalent elements. Finally, the components used, as long as they are compatible with the specific use, as well as the dimensions, can be any according to the needs and the state of the art.

[0085] Where the characteristics and techniques mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and, consequently, those reference signs have no limiting effect on the interpretation of each element identified by way of example by those reference signs.

Claims

CLAIMS1. 18K rose gold alloy (100) comprising:copper in a percentage by weight between 16% and 25%;silver in a percentage by weight between 0% and 9%;zinc in a percentage by weight between 0% and 1.5%;optionally silicon in a percentage by weight between 0.005% and 0.1 %; optionally indium in a weight percentage between 0.125 - 1.250%nano-sized ruthenium particles in a percentage by weight between 1 ppm and 100 ppm,with the rest of the composition up to 100% made up of gold and unavoidable impuritieswhere the nano-sized ruthenium particles have an average size between 5 nm and 5000 nm, as measured by dynamic light scattering.

2. Alloy according to claim 1 , in which the nanometer ruthenium particles have an average size of between 20 nm and 1000 nm.

3. It alloys according to any of the above claims, in which the percentage by weight of gold is 75%, the percentage by weight of copper is 23.2%, the percentage by weight of silver is 1%, and the percentage by weight of zinc is 0.75%, the percentage of silicon is 0.04%.

4. Alloy according to claim 4, in which the percentage by weight of nano-sized ruthenium particles is 20 ppm.

5. Master alloy for the realization of an alloy according to one or more of the previous claims characterized by the fact of including the following elements:Zn 0-6%;Ag 2 - 30%;Yes 0.04 and 0.35%;Ru 5-200 ppm;Optionally In 0.5-5%with the rest of the composition up to 100% made up of unavoidable copper and impurities.

6. Parent alloy according to claim 5 characterized by the fact that nano-sized ruthenium particles have an average size between 5 nm and 5000 nm, as measured by dynamic light scattering.

7. Jewellery item (100) made of 18K rose gold alloy according to any of claims 1 to 4 or with a master alloy according to any of claims 5, 6.

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