High-temperature welding flux for honeysuckle silk jewelry and preparation method of high-temperature welding flux

Abstract

The invention discloses a high-temperature solder for honeysuckle silk jewelry and a preparation method thereof, the solder comprises 0-2% of copper, 2.0-5.0% of zinc, 0.3-5.0% of indium, 0-0.5% of germanium, 0.01-0.1% of rare earth and the balance silver and inevitable impurity elements, and the rare earth is one or more of cerium, yttrium, lanthanum, neodymium and gadolinium. According to the high-temperature solder for the honeysuckle silk jewelry, the copper, the zinc, the indium, the germanium, the rare earth, the silver and the like serve as main alloy elements, and the high-temperature silver solder which is excellent in comprehensive performance and capable of well meeting the welding requirement of the honeysuckle silk jewelry is prepared by optimizing and adjusting the component proportion of the main alloy elements and optimizing the alloy formula.

Description

Technical Field

[0001] This invention relates to the field of jewelry solder technology, and in particular to a high-temperature solder for silver filigree jewelry and its preparation method. Background Technology

[0002] Filigree craft originated from the gold and silver inlay technique of the Spring and Autumn and Warring States periods. It is a long-standing traditional Chinese handicraft, primarily used for the production of royal ornaments. The basic process of filigree involves drawing gold, silver, and other materials into wires of different specifications. Then, through several of the eight major techniques—pinching, filling, piling, stacking, weaving, stitching, assembling, and welding—the wires are shaped and processed into blanks of various shapes, structures, and patterns. Finally, the blanks undergo surface treatment to enhance their quality and color. Filigree craft reached a high level of artistry in the mid-to-late Ming Dynasty, particularly excelling in weaving and piling techniques, and often employing kingfisher feather inlay to achieve a magnificent and resplendent effect. Filigree is a traditional gold and silver filigree craft with the most iconic Chinese elements, and was listed as a national intangible cultural heritage in June 2008.

[0003] In making filigree jewelry, silver bars are first rolled into thin rods, then drawn into fine wires. Two or more strands of wire are then twisted together to create various patterns. Tweezers or pliers are used to shape the wires into various designs, which are then filled or stacked within a specified pattern to form different shapes. Solder powder is sifted evenly through a small sieve, and the patterns are then welded together. Filigree jewelry is often composed of several filigree components, which need to be assembled into a whole through a series of sew-making techniques. After assembly, these components are then fixed together by welding.

[0004] Filigree work requires welding to form the product, involving numerous and widely distributed welding points that need to be worked on multiple times. Therefore, the solder used is crucial. Solder used for frame or large edge forming must withstand multiple welding operations in subsequent filigree, filler, and stacking processes, thus requiring a high melting point. However, due to the delicate nature of filigree products and the numerous welding points, excellent solderability is also essential. Furthermore, with the increasing emphasis on green manufacturing and green products, the production and use of filigree products must be environmentally and human-friendly.

[0005] The preparation of high-temperature solder for existing silver filigree continues the traditional filigree process, commonly known as "old flux," which is used for shaping high-temperature solder. Old flux is also known as 80% silver, with the remainder mainly being brass or copper. The melting point of old flux using brass is 810℃, and the melting point of old flux using copper is 850℃. Old flux has good fire resistance and is often used for welding in the first process of making the base. However, the current old flux solder has the following main problems: (1) The flux has a low purity, with the old flux having a purity of only 80%. The purity of silver filigree products must meet the silver content requirement of pure silver. Although the silver material used in the frame and wire of filigree jewelry can generally reach 99.9%, a large amount of flux is used in filigree production. If the purity of the flux is too low, the product purity will not meet the standard. (2) The flux formula contains a high amount of copper. Since high-temperature solder requires a high temperature, it is prone to oxidation, which affects the welding performance, causes the weld to turn black and form oxide inclusions, and the corrosion resistance of the welded part is poor, which makes the product prone to discoloration during production and use. (3) Traditional fluxes often need to add a certain amount of Cd to lower the melting point of the alloy, improve fluidity, and increase welding strength and plasticity; however, copper is prone to causing the weld to oxidize and discolor. During the solder melting process, a considerable amount of arsenic trioxide is added for stirring to improve the wettability and flowability of the flux. Since the vapor of Cd metal and oxide is highly toxic, and arsenic trioxide is commonly known as arsenic, it is a highly toxic substance and is harmful to human health during alloy melting and welding. (4) In the production of wire inlay, Bletilla striata is used as a binder to fix the wire inlay to the mold, and then the flux is sieved for welding. However, the current old flux has poor tolerance to Bletilla striata and is prone to forming slag, which affects the welding effect. (5) In the first welding of filigree jewelry, some situations are suitable for using welding sheets, while others are suitable for using welding powder. However, when making welding powder from traditional old-fashioned solder, the ingot is first cast and then filed into powder with a steel file. This process is inefficient and inevitably introduces impurities such as iron filings into the solder, affecting its welding performance and physicochemical properties.

[0006] Therefore, traditional high-temperature solders for silver filigree jewelry have certain problems in terms of color retention, welding performance, environmental safety, and resistance to discoloration, and cannot adequately meet the current needs of filigree jewelry production. Although many silver solders have been developed for industrial applications in recent years, they were not specifically developed for the filigree jewelry process and are unsuitable for welding filigree jewelry. For example, patent 201210281681.4 discloses a silver solder and its preparation method, with a chemical composition of 23-60% Ag, 38-75% Cu, and 0.01-2% P, and a melting point of approximately 780℃. However, this solder fails to meet the requirements for filigree jewelry in terms of both color and melting point. Patent 201611247738.3 discloses a silver-based solder without a separator and its preparation method. This solder does not contain the harmful element cadmium and its chemical composition is 39-41% Ag, 29.5-31.5% Zn, 1.3-1.7% Ni, 0.1-0.2% In, 2.5-3.5% Sn, 0.05-0.1% Co, 0.01-0.02% graphene, with Cu as the balance. It exhibits good spreadability and plasticity when welding stainless steel, but its color and melting point distribution are not suitable for welding filigree jewelry. Patent 02106267.6 discloses an Ag solder for welding and a brazing method using it. This solder has a chemical composition of 1-10% Sn, 2.5-10% Cu, <6% Mn, 0.1-2.5% Ni, with the balance being Ag. This solder can improve welding strength by adding Ni and Mn, with a melting temperature range of 800-900℃ and a silver content of up to 96%. However, this solder is mainly for vacuum welding of hermetically sealed components and cannot meet the welding requirements of jewelry under atmospheric conditions. Patent 201611147938.1 discloses a solder powder formulation method for silver filigree jewelry. It uses 100g of pure silver, 38g of copper solder rod, and 6g of brass to prepare the solder powder, which has a melting point of 680℃. However, the silver content is only 56%, and there is no melting point gradation, which cannot meet the needs of graded welding of filigree jewelry. Moreover, the traditional mechanical grinding process is used in the preparation of the solder powder. During the grinding process, powder debris from the grinding tools inevitably gets mixed into the solder powder, causing solder powder defects. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, one of the objectives of this invention is to provide a high-temperature solder for silver filigree jewelry. Addressing the problem that existing silver solders cannot adequately meet the requirements for high-temperature soldering of silver filigree jewelry, this invention optimizes the alloy formula to achieve a maximum melting temperature not exceeding 910°C, a crystallization interval not exceeding 50°C, a solder purity of over 93%, excellent welding and oxidation resistance, a color close to pure silver, and the ability to meet the preparation process and mechanical property requirements of different solder morphologies.

[0008] The second objective of this invention is to provide a method for preparing the above-mentioned high-temperature solder for silver filigree jewelry.

[0009] One of the objectives of this invention is achieved through the following technical solution:

[0010] A high-temperature solder for silver filigree jewelry comprises the following components by weight percentage:

[0011] The composition is: copper 0-2% (inclusive), zinc 2.0-5.0%, indium 0.3-5.0%, germanium 0-0.5% (inclusive), rare earth elements 0.01-0.1%, with the remainder being silver and unavoidable impurity elements, wherein the rare earth elements are one or more of cerium, yttrium, lanthanum, neodymium, and gadolinium.

[0012] Among the above materials, silver is pure silver with a content of 99.95 wt% or higher, copper is pure copper with a content of 99.95 wt% or higher, zinc is pure zinc with a content of 99.95 wt% or higher, indium is pure indium with a content of 99.95 wt% or higher, germanium is pure germanium with a content of 99.95 wt% or higher, cerium is pure cerium with a content of 99.95 wt% or higher, yttrium is pure yttrium with a content of 99.95 wt% or higher, lanthanum is pure lanthanum with a content of 99.95 wt% or higher, neodymium is pure neodymium with a content of 99.95 wt% or higher, and gadolinium is pure gadolinium with a content of 99.95 wt% or higher.

[0013] In this invention, the following approach was followed during the development of high-temperature solder for silver filigree jewelry production to address the existing problems: (1) The melting point and melting temperature range of the high-temperature solder were reasonably controlled so that it was both a certain distance from the melting point of the substrate itself and had a sufficiently high melting point to withstand the heating during repeated welding. This provided sufficient process operation space for the welding operation and prevented the risk of burning during welding due to the close melting points of the two materials, thus ensuring the safety of the welded workpiece and the operability of the welding process. (2) The silver content of the solder was maintained above 93%, meeting the standard pure silver purity requirements. The solder was formulated through the synergistic effect of multi-element alloying to achieve an optimized match of welding performance, physical properties, chemical properties, and mechanical properties. (3) The solder had good wettability, gap filling properties, and brazing rate on the substrate. Alloying can make the solder have good wettability and filling properties to the base material, but excessive alloying will cause complex interface reactions, which will lead to changes in the flow point temperature, corrosion of the base material, or formation of brittle compounds. Therefore, the selection of alloying elements and the amount added should be conducive to wettability without increasing corrosion of the base material. (4) Control the copper content in the content to reduce the tendency of oxidation and discoloration. The color difference with pure silver base material is small, and the passivation effect of alloying elements makes it have excellent corrosion resistance and anti-discoloration properties. (5) The first batch of welding is the main load-bearing factor of the wire product. The high-temperature grade solder has high strength and excellent ductility, and the welded joint can resist impact and vibration. (6) The alloying elements selected for the solder must be green and environmentally friendly, do not produce toxic side effects, be inexpensive, and not contain precious elements.

[0014] Based on the above considerations, this invention uses zinc, indium, germanium, rare earth elements, etc. as the main alloying elements, and by optimizing and adjusting their composition ratios and by optimizing the alloy formula, prepares a high-temperature silver solder with excellent comprehensive performance that can well meet the welding requirements of silver filigree jewelry.

[0015] Furthermore, the total content of the unavoidable impurity elements does not exceed 0.1%.

[0016] Furthermore, the silver content is not less than 93%.

[0017] Furthermore, the copper content does not exceed 2%.

[0018] Furthermore, the liquidus temperature of the high-temperature solder is 890℃~910℃, and the melting temperature range is less than 50℃.

[0019] Furthermore, the color index of the high-temperature solder is: L* value of 91.5 to 94.0, a* value of -0.5 to 0.1, and b* value of 3.5 to 4.5, which makes it a slight color difference that is perceptible to the naked eye compared to pure silver.

[0020] Furthermore, after the high-temperature solder melts on the pure silver surface, the wetting angle is 22°–28°. Generally, a wetting angle less than 30° indicates good wetting; the smaller the contact angle, the better the wettability. Therefore, this solder exhibits excellent wettability on pure silver. When the weld gap is between 0.04 and 0.06 mm, the solder bonding rate reaches over 94%, demonstrating excellent performance. The solder has a low copper content, significantly reducing oxidation and discoloration during high-temperature welding.

[0021] Furthermore, the high-temperature solder is either a sheet-like high-temperature solder or a powdered high-temperature solder. Solder of either of these shapes can be manufactured according to the application requirements.

[0022] The second objective of this invention is achieved by the following technical solution:

[0023] A method for preparing a high-temperature solder for silver filigree jewelry, wherein the high-temperature solder is a thin sheet-like high-temperature solder, and the preparation of the thin sheet-like high-temperature solder includes the following steps:

[0024] S1: The ingredients are proportioned and the continuous casting slab is made using a vacuum traction continuous casting process to obtain the ingot. A graphite plug rod is set in the vacuum melting chamber, and a temperature measuring thermocouple is set inside the graphite plug rod.

[0025] S2: Roll the ingot into sheets, with a single processing rate controlled at 14-16%. When the total processing rate reaches 60-75%, perform intermediate annealing and continue rolling until a thin sheet with a thickness of 0.1-0.2 mm is rolled.

[0026] S3: Bury the thin sheet in charcoal powder, heat to 480-500℃, anneal, clean and then put it into boiling alum water to remove the oxide film on the surface.

[0027] S4: After cleaning and drying the thin film obtained in step S3, cut it into square thin films of 10-20mm.

[0028] Furthermore, in step S1, the preparation steps for fabricating the continuously cast slab using the vacuum traction continuous casting process are as follows:

[0029] First, silver and copper are melted under a protective atmosphere (nitrogen). Then, the remaining materials are added in a two-stage process. After they are completely melted and stirred evenly, they are poured into ingots.

[0030] The second objective of this invention is also achieved by the following technical solution:

[0031] A method for preparing a high-temperature solder for silver filigree jewelry, wherein the high-temperature solder is a powdered high-temperature solder, and the preparation of the powdered high-temperature solder includes the following steps:

[0032] S1: Prepare the ingredients according to the proportions, pre-melt them using induction melting process, and obtain the ingot;

[0033] S2: Using a vacuum atomization powder making equipment, the ingot obtained in step S1 is remelted and welding powder is produced.

[0034] The above-mentioned welding powder has a sphericity of over 80% and an oxygen content of less than 220 ppm.

[0035] Furthermore, in step S1, the pre-melting step using induction melting process is as follows: first, silver and copper are melted under a protective atmosphere, and then the remaining materials are added in a secondary feeding manner. After complete melting and uniform stirring, the mixture is poured into an ingot.

[0036] In step S2, the specific steps are as follows: the temperature of the molten metal is controlled at 1190-1210℃, high-purity nitrogen with a purity of 99.999% is used, the nitrogen pressure is 2.9-3.3MPa, the nozzle adopts a tightly coupled confined ring structure, under the high-speed jet and cooling of nitrogen, the molten metal is dispersed into fine liquid mist and quickly solidified into powder, the powder falls into the collection bucket in the conical cylinder, and does not come into contact with air throughout the process.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] 1. The high-temperature solder for silver filigree jewelry of the present invention uses copper, zinc, indium, germanium, rare earth, silver and other main alloying elements. By optimizing and adjusting the composition ratio and the alloy formula, a high-temperature silver solder with excellent comprehensive performance can be prepared, which can well meet the welding requirements of silver filigree jewelry.

[0039] 2. Physical properties of solder

[0040] The liquidus temperature of the high-temperature solder used in silver filigree jewelry is 890℃~910℃, and the melting temperature range is less than 50℃. The color index of the solder is L* value of 91.5~94.0, a* value of -0.5~0.1, and b* value of 3.5~4.5. Compared with pure silver, the color deviation is only slightly noticeable to the naked eye.

[0041] 3. Brazing performance of the solder

[0042] After melting on a pure silver surface, the solder exhibits a wetting angle of 22°–28°. Generally, a wetting angle less than 30° indicates good wetting; the smaller the contact angle, the better the wetting. Therefore, this solder demonstrates excellent wettability on pure silver. When the weld gap is between 0.05 and 0.06 mm, the solder bonding rate reaches over 94%, demonstrating excellent performance. The solder has a low copper content, significantly reducing oxidation and discoloration during high-temperature soldering.

[0043] 4. Machining properties of solder

[0044] The solder has excellent cold working properties and, combined with intermediate annealing, can be rolled into thin sheets of 0.1–0.2 mm.

[0045] The produced solder powder has a sphericity of over 80% and an oxygen content of less than 220 ppm.

[0046] 5. Corrosion resistance of solder

[0047] After immersing in artificial sweat for 8 hours, the solder surface darkens or yellows slightly, with a color difference of 3.0–4.0, indicating mild corrosion discoloration. No pitting or intergranular corrosion is observed, making it suitable for complex structures like filigree jewelry. Pure silver exhibits a corrosion color difference of approximately 1.8–2.3 under the same conditions, while traditional solders show a difference of 6.8–8.8. Therefore, the corrosion resistance of this solder in sweat is very close to that of pure silver and significantly superior to traditional solders. Detailed Implementation

[0048] The present invention will now be further described in conjunction with specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0049] Example 1

[0050] A square-shaped thin sheet, comprising the following steps:

[0051] 1. Solder composition

[0052] High-temperature solder for filigree jewelry welding uses copper, zinc, indium, and rare earth elements as the main alloying elements. Its chemical composition, by mass percentage, is as follows: copper 0.39%, zinc 2.6%, indium 4%, cerium 0.01%, with the remainder being silver and unavoidable impurities. The purity of the solder is not less than 93%.

[0053] 2. Solder preparation

[0054] The raw materials are proportioned according to the above ratio, with necessary losses added, and continuously cast slabs are produced using a vacuum traction continuous casting process. A graphite stopper rod is installed in the vacuum melting chamber, and a thermocouple is installed inside the graphite stopper rod. Pure silver and pure copper are first melted under a protective atmosphere, and then the remaining materials are added in a two-stage feeding process. After complete melting and uniform stirring, the mixture is poured into ingots. The ingots are rolled into sheets, with a single processing rate controlled at about 14-15%. When the total processing rate reaches 65%-70%, intermediate annealing is performed, followed by continued rolling until a sheet with a thickness of 0.15 mm is formed. The sheet is then buried in charcoal powder, heated to 490℃ for annealing, cleaned, and immersed in boiling alum water to remove the oxide film on the surface. After cleaning and drying, the sheet is cut into 15 mm square sheets for later use.

[0055] 3. The solder's properties were tested and are as follows:

[0056] (1) Physical properties of solder

[0057] The liquidus temperature of the high-temperature solder used in silver filigree jewelry is 902℃, and the melting temperature range is 46℃. The color index of the solder is L* value of 92.3, a* value of -0.35, and b* value of 3.94. Compared with pure silver, the color deviation is within the range of minor color difference that can be perceived by the naked eye.

[0058] (2) Brazing performance of the solder

[0059] After melting on a pure silver surface, the solder exhibits a wetting angle of 22°, demonstrating excellent wettability. When the weld gap is 0.05–0.08 mm, the solder bonding rate reaches 96%, showing outstanding performance.

[0060] (3) Solder processing performance

[0061] Cast-rolled solder has excellent cold working properties and, combined with intermediate annealing, can be rolled into thin sheets of 0.15 mm.

[0062] (4) Corrosion resistance of solder

[0063] After being soaked in artificial sweat for 8 hours, the surface color of the solder darkened or yellowed slightly, with a color difference of 3.9, which is considered a slight corrosion discoloration. There was no pitting or intergranular corrosion, making it suitable for welding complex structures such as filigree jewelry.

[0064] Example 2

[0065] A soldering powder, comprising the following steps:

[0066] 1. Solder composition

[0067] High-temperature solder for filigree jewelry welding uses copper, zinc, indium, germanium, and rare earth elements as the main alloying elements. Its chemical composition, by mass percentage, is as follows: copper 0.2%, zinc 4%, indium 1.6%, germanium 0.2%, cerium 0.01%, yttrium 0.02%, with the remainder being silver and unavoidable impurities. The purity of the solder is not less than 93%.

[0068] 2. Solder preparation

[0069] The materials are prepared according to the above proportions, with necessary losses added. Induction melting is used for pre-melting, first melting pure silver and pure copper under a protective atmosphere, then adding the remaining materials in a secondary feeding process. After complete melting and uniform stirring, the mixture is poured into ingots. Vacuum atomization powder-making equipment is used for remelting and preparing welding powder. The temperature of the molten metal is controlled at 1190℃. High-purity nitrogen (99.999%) is used at a pressure of 2.9–3.0 MPa, and the nozzle employs a tightly coupled, confined circular structure. Under the high-speed jet and cooling effect of nitrogen, the molten metal disperses into fine liquid mist and rapidly solidifies into powder. The powder falls into a collection bin within a conical cylinder, without contact with air throughout the process.

[0070] 3. The solder's properties were tested and are as follows:

[0071] (1) Physical properties of solder

[0072] The liquidus temperature of the high-temperature solder used in silver filigree jewelry is 900℃, and the melting temperature range is 49℃. The color index of the solder is L* value of 91.7, a* value of -0.29, and b* value of 4.8. Compared with pure silver, the color deviation is only slightly noticeable to the naked eye.

[0073] (2) Brazing performance of the solder

[0074] After melting on a pure silver surface, the solder exhibits a wetting angle of 25°, demonstrating excellent wettability. When the weld gap is between 0.06 and 0.08 mm, the solder bonding rate reaches 95%, showing outstanding performance.

[0075] (3) Powder properties of solder

[0076] The produced solder powder has a sphericity of over 85% and an oxygen content of less than 190 ppm.

[0077] (4) Corrosion resistance of solder

[0078] After being soaked in artificial sweat for 8 hours, the surface color of the solder darkened or yellowed slightly, with a color difference of 3.6, which is considered a slight corrosion discoloration. There was no pitting or intergranular corrosion, making it suitable for welding complex structures such as filigree jewelry.

[0079] Example 3

[0080] A square-shaped thin sheet, comprising the following steps:

[0081] 1. Solder composition

[0082] High-temperature solder for filigree jewelry welding uses copper, zinc, indium, germanium, and rare earth elements as the main alloying elements. Its chemical composition, by mass percentage, is as follows: copper 0.5%, zinc 4%, indium 0.3%, germanium 0.2%, gadolinium 0.01%, with the remainder being silver and unavoidable impurities. The purity of the solder is not less than 93%.

[0083] 2. Solder preparation

[0084] The raw materials are proportioned according to the above ratio, with necessary losses added, and continuously cast slabs are produced using a vacuum traction continuous casting process. A graphite stopper rod is installed in the vacuum melting chamber, and a thermocouple is installed inside the graphite stopper rod. Pure silver and pure copper are first melted under a protective atmosphere, and then the remaining materials are added in a two-stage feeding process. After complete melting and uniform stirring, the mixture is poured into ingots. The ingots are rolled into sheets, with a single processing rate controlled at about 14-16%. When the total processing rate reaches 60%-64%, intermediate annealing is performed, followed by continued rolling until a sheet with a thickness of 0.12 mm is obtained. The sheet is then buried in charcoal powder, heated to 500℃ for annealing, cleaned, and immersed in boiling alum water to remove the oxide film on the surface. After cleaning and drying, the sheet is cut into 15 mm square sheets for later use.

[0085] 3. The solder's properties were tested and are as follows:

[0086] (1) Physical properties of solder

[0087] The liquidus temperature of the high-temperature solder used in silver filigree jewelry is 905℃, and the melting temperature range is 46℃. The color index of the solder is L* value of 92.6, a* value of -0.29, and b* value of 4.2. Compared with pure silver, the color deviation is minimal and perceptible to the naked eye.

[0088] (2) Brazing performance of the solder

[0089] After melting on a pure silver surface, the solder exhibits a wetting angle of 28°, demonstrating excellent wettability. When the weld gap is 0.05–0.07 mm, the solder bonding rate reaches 94%, which is also excellent.

[0090] (3) Solder processing performance

[0091] The solder has excellent cold working properties and, combined with intermediate annealing, can be rolled into a thin sheet of 0.12 mm.

[0092] (4) Corrosion resistance of solder

[0093] After being soaked in artificial sweat for 8 hours, the surface color of the solder darkened or yellowed slightly, with a color difference of 3.3, which is considered a slight corrosion discoloration. There was no pitting or intergranular corrosion, making it suitable for welding complex structures such as filigree jewelry.

[0094] The following is a comparative example (compared to Example 1), as follows:

[0095] Comparative Example 1 (copper content greater than 2%)

[0096] A square-shaped thin sheet, comprising the following steps:

[0097] 1. Solder composition

[0098] High-temperature solder for filigree jewelry welding uses copper, zinc, indium, and rare earth elements as the main alloying elements. Its chemical composition, by mass percentage, is as follows: copper 4.2%, zinc 2%, indium 0.6%, cerium 0.01%, with the remainder being silver and unavoidable impurities. The purity of the solder is not less than 93%.

[0099] 2. Solder preparation

[0100] The raw materials are proportioned according to the above ratio, with necessary losses added, and continuously cast slabs are produced using a vacuum traction continuous casting process. A graphite stopper rod is installed in the vacuum melting chamber, and a thermocouple is installed inside the graphite stopper rod. Pure silver and pure copper are first melted under a protective atmosphere, and then the remaining materials are added in a two-stage feeding process. After complete melting and uniform stirring, the mixture is poured into ingots. The ingots are rolled into sheets, with a single processing rate controlled at about 14-16%. When the total processing rate reaches 60-70%, intermediate annealing is performed, followed by continued rolling until a sheet with a thickness of 0.15 mm is formed. The sheet is then buried in charcoal powder, heated to 490℃ for annealing, cleaned, and immersed in boiling alum water to remove the oxide film on the surface. After cleaning and drying, the sheet is cut into 15 mm square sheets for later use.

[0101] 3. The solder's properties were tested and are as follows:

[0102] (1) Physical properties of solder

[0103] The liquidus temperature of the high-temperature solder used in silver filigree jewelry is 900℃, and the melting temperature range is 89℃. The color index of the solder is L* value of 91.2, a* value of 0.12, and b* value of 4.7, which is darker, redder, and more yellow than pure silver.

[0104] (2) Brazing performance of the solder

[0105] After the solder melts on the pure silver surface, the wetting angle is 34°, indicating weak wettability. When the weld gap is 0.05–0.07 mm, the solder bonding rate reaches 84%, and there is a risk of slag inclusion and incomplete welding in the weld.

[0106] (3) Solder processing performance

[0107] The cold working performance of the solder is slightly worse than that of Example 1. Combined with intermediate annealing, it is rolled into a thin sheet of about 0.15 mm in multiple passes, and there is a risk of cracks appearing at the edges.

[0108] (4) Corrosion resistance of solder

[0109] The solder, after being immersed in artificial sweat for 8 hours, showed varying surface tones, ranging from darker to yellow, with a color difference of 4.80. Therefore, the overall performance of the comparative example is significantly worse than that of the embodiment.

[0110] Comparative Example 2 (Increased Zinc)

[0111] A square-shaped thin sheet, comprising the following steps:

[0112] 1. Solder composition

[0113] High-temperature solder for filigree jewelry welding uses copper, zinc, indium, and rare earth elements as the main alloying elements. Its chemical composition, by mass percentage, is as follows: copper 0.05%, zinc 5.2%, indium 0.3%, germanium 0.3%, cerium 0.09%, with the remainder being silver and unavoidable impurities. The purity of the solder is not less than 93%.

[0114] 2. Solder preparation

[0115] The raw materials are proportioned according to the above ratio, with necessary losses added, and continuously cast slabs are produced using a vacuum traction continuous casting process. A graphite stopper rod is installed in the vacuum melting chamber, and a thermocouple is installed inside the graphite stopper rod. Pure silver and pure copper are first melted under a protective atmosphere, and then the remaining materials are added in a two-stage feeding process. After complete melting and uniform stirring, the mixture is poured into ingots. The ingots are rolled into sheets, with a single processing rate controlled at about 12-15%. When the total processing rate reaches 60-70%, intermediate annealing is performed, followed by continued rolling until a sheet with a thickness of 0.2 mm is formed. The sheet is then buried in charcoal powder, heated to 480℃ for annealing, cleaned, and immersed in boiling alum water to remove the oxide film on the surface. After cleaning and drying, the sheet is cut into 15 mm square sheets for later use.

[0116] 3. The solder's properties were tested and are as follows:

[0117] (1) Physical properties of solder

[0118] The liquidus temperature of the high-temperature solder used in silver filigree jewelry is 891℃, and the melting temperature range is 66℃. The color index of the solder is L* value of 91.4, a* value of -0.15, and b* value of 4.6, which is darker, yellower, and redder than pure silver.

[0119] (2) Brazing performance of the solder

[0120] After the solder melts on the pure silver surface, the wetting angle is 38°. When the weld gap is 0.05–0.08 mm, the solder bonding rate is approximately 84%.

[0121] (3) Solder processing performance

[0122] Cold rolling of solder, combined with intermediate annealing, can produce sheets as thin as 0.2 mm, but there is a risk of cracks appearing at the edges.

[0123] (4) Corrosion resistance of solder

[0124] After the solder was soaked in artificial sweat for 8 hours, the surface color turned grayish-yellow, with a color difference of 5.5.

[0125] Comparative Example 3 (Increased Indium Content)

[0126] A square-shaped thin sheet, comprising the following steps:

[0127] 1. Solder composition

[0128] High-temperature solder for filigree jewelry welding uses copper, zinc, indium, and rare earth elements as the main alloying elements. Its chemical composition, by mass percentage, is as follows: copper 0.6%, zinc 0.6%, indium 5.5%, cerium 0.15%, with the remainder being silver and unavoidable impurities. The purity of the solder is not less than 93%.

[0129] 2. Solder preparation

[0130] The raw materials are proportioned according to the above ratio, with necessary losses added, and continuously cast slabs are produced using a vacuum traction continuous casting process. A graphite stopper rod is installed in the vacuum melting chamber, and a thermocouple is installed inside the graphite stopper rod. Pure silver and pure copper are first melted under a protective atmosphere, and then the remaining materials are added in a two-stage feeding process. After complete melting and uniform stirring, the mixture is poured into ingots. The ingots are rolled into sheets, with a single processing rate controlled at about 10-14%. When the total processing rate reaches 50-60%, intermediate annealing is performed, followed by continued rolling until a sheet with a thickness of 0.22 mm is obtained. The sheet is then buried in charcoal powder, heated to 470℃ for annealing, cleaned, and immersed in boiling alum water to remove the oxide film on the surface. After cleaning and drying, the sheet is cut into 15 mm square sheets for later use.

[0131] 3. The solder's properties were tested and are as follows:

[0132] (1) Physical properties of solder

[0133] The liquidus temperature of the high-temperature solder used in silver filigree jewelry is 919℃, and the melting temperature range is 44℃. The high liquidus temperature reduces the working space for soldering. The solder's color index is L* value of 90.9, a* value of -0.17, and b* value of 5.5, which is lower in brightness and more yellowish than pure silver.

[0134] (2) Brazing performance of the solder

[0135] After the solder melts on the pure silver surface, the wetting angle is 36°. When the weld gap is 0.05–0.07 mm, the solder bonding rate is approximately 86%.

[0136] (3) Solder processing performance

[0137] The solder can be cold-rolled and then annealed to form a 0.22mm thin sheet. However, cracks are more likely to appear at the edges during processing.

[0138] (4) Corrosion resistance of solder

[0139] When the solder is soaked in artificial sweat for 8 hours, the surface color changes to brownish-yellow, with a color difference of 4.1.

[0140] Comparative Example 4 (Traditional Old Drug)

[0141] The comparative solder was prepared using a traditional old-fashioned formula for high-temperature welding of silver wire. Its composition was 10% copper, 6% zinc, 4% cadmium, and the remainder silver. The purity of this content was only 80%, far lower than the purity of over 93% in this application, and it contained a large amount of the toxic element cadmium.

[0142] The solder of Comparative Example 4 was tested under the same conditions, and its performance is as follows:

[0143] (1) Physical properties of solder

[0144] The liquidus temperature of traditional old-fashioned solder is 802℃, and the crystallization interval is 67℃. The color index of the solder is L* value of 90.2, a* value of 0.9, and b* value of 5.8. Its color has a large contrast with pure silver, and it appears noticeably darker, redder, and yellower.

[0145] (2) Brazing performance of the solder

[0146] When traditional solder melts on a pure silver surface, the wetting angle is 25–27°. When the weld gap is 0.05–0.07 mm, the solder bonding rate is approximately 92–94%.

[0147] (3) Solder processing performance

[0148] Cold rolling of solder has a strong work hardening effect. Combined with intermediate annealing, it can be rolled into a 0.15mm thin sheet. Edge cracks and oxidation discoloration streaks are prone to occur during the rolling process.

[0149] (4) Corrosion resistance of solder

[0150] When the solder is soaked in artificial sweat for 8 hours, the surface color changes to brownish-yellow and the edges become darker, with a color difference of 8.2.

[0151] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A high-temperature solder for silver filigree jewelry, characterized in that, The components include the following mass percentages: The composition is: copper 0-2%, zinc 2.0-5.0%, indium 0.3-5.0%, germanium 0-0.5%, rare earth elements 0.01-0.1%, with the remainder being silver and unavoidable impurity elements, of which rare earth elements are one or more of cerium, yttrium, lanthanum, neodymium, and gadolinium.

2. The high-temperature solder for silver filigree jewelry according to claim 1, characterized in that, The silver content is not less than 93%.

3. The high-temperature solder for silver filigree jewelry according to claim 1, characterized in that, The liquidus temperature of the high-temperature solder is 890℃~910℃, and the melting temperature range is less than 50℃.

4. The high-temperature solder for silver filigree jewelry according to claim 1, characterized in that, The color index of the high-temperature solder is: L* value is 91.5~94.0, a* value is -0.5~0.1, and b* value is 3.5~4.

5.

5. The high-temperature solder for silver filigree jewelry according to claim 1, characterized in that, The high-temperature solder has a wetting angle of 22° to 28° after melting on the pure silver surface.

6. The high-temperature solder for silver filigree jewelry according to claim 1, characterized in that, The high-temperature solder is either a sheet-like high-temperature solder or a powdered high-temperature solder.

7. A method for preparing a high-temperature solder for silver filigree jewelry as described in any one of claims 1-6, characterized in that, The high-temperature solder is a thin-film high-temperature solder, and the preparation of the thin-film high-temperature solder includes the following steps: S1: The ingredients are proportioned and the continuous casting slab is made using a vacuum traction continuous casting process to obtain the ingot. A graphite plug rod is set in the vacuum melting chamber, and a temperature measuring thermocouple is set inside the graphite plug rod. S2: Roll the ingot into sheets, with a single processing rate controlled at 14-16%. When the total processing rate reaches 60-75%, perform intermediate annealing and continue rolling until a thin sheet with a thickness of 0.1-0.2 mm is rolled. S3: Bury the thin sheet in charcoal powder, heat to 480-500℃, anneal, clean and then put it into boiling alum water to remove the oxide film on the surface. S4: After cleaning and drying the thin film obtained in step S3, cut it into square thin films of 10-20mm.

8. The method for preparing high-temperature solder for silver filigree jewelry according to claim 7, characterized in that, In step S1, the preparation steps for fabricating continuously cast slabs using vacuum traction continuous casting process are as follows: First, silver and copper are smelted under a protective atmosphere. Then, the remaining materials are added in a two-stage process. After they are completely melted and stirred evenly, they are poured into ingots.

9. A method for preparing a high-temperature solder for silver filigree jewelry as described in any one of claims 1-6, characterized in that, The high-temperature solder is a powdered high-temperature solder, and the preparation of the powdered high-temperature solder includes the following steps: S1: Prepare the ingredients according to the proportions, pre-melt them using induction melting process, and obtain the ingot; S2: Using a vacuum atomization powder making equipment, the ingot obtained in step S1 is remelted and welding powder is produced.

10. The method for preparing the high-temperature solder for silver filigree jewelry according to claim 7, characterized in that, In step S1, the pre-melting step using induction melting process is as follows: first, silver and copper are melted under a protective atmosphere, and then the remaining materials are added in a two-stage feeding manner. After complete melting and uniform stirring, the mixture is poured into an ingot. In step S2, the specific steps are as follows: the temperature of the molten metal is controlled at 1190-1210℃, high-purity nitrogen with a purity of 99.999% is used, the nitrogen pressure is 2.9-3.3MPa, the nozzle adopts a tightly coupled confined ring structure, under the high-speed jet and cooling of nitrogen, the molten metal is dispersed into fine liquid mist and quickly solidified into powder, the powder falls into the collection bucket in the conical cylinder, and does not come into contact with air throughout the process.