Medium-temperature honeysuckle filament solder and preparation method thereof

Abstract

The invention discloses a medium-temperature silver flower wire solder and a preparation method thereof, the medium-temperature silver flower wire solder comprises 17-19.5% of copper, 0.01-2% of zinc, 0.01-1.4% of indium, 0.01-0.5% of germanium, 0.01-0.4% of tin, 0.01-0.3% 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 welding flux, silver, copper, zinc, indium, germanium, tin, rare earth and the like serve as main alloy elements, the component proportion of the main alloy elements is optimized and adjusted, the alloy formula is optimized, and the medium-temperature-grade silver welding flux which is excellent in comprehensive performance and can well meet the welding requirement of the silver wire jewelry is prepared.

Description

Technical Field

[0001] This invention relates to the field of jewelry solder technology, and in particular to a medium-temperature silver wire solder 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 silver 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 process called "assembly." After assembly, they must be fixed by welding. However, for complex designs, some parts are difficult to weld after assembly (colloquially known as "not resistant to heat"), and the blank is easily melted when the heat is increased.

[0004] Filigree work requires welding to form the jewelry, involving numerous and widely distributed welding points that need to be worked on multiple times. Therefore, the solder used is crucial. There are various types of filigree solder, categorized by melting point into high-temperature, medium-temperature, and low-temperature solders. During production, the appropriate solder is selected based on the different parts of the jewelry and the specific manufacturing process, and the solder is then prepared into powder form.

[0005] Filigree work demands high welding skills, especially in the precise control of flux properties, flux dosage, and welding temperature. Problems include poor flux properties leading to poor weldability, easy oxidation and impurity formation, unsuitable flux melting point, low weld strength, poor flux corrosion resistance, and difficulty in electroplating the welded area. Too little flux results in areas without weld or weak welds; too much flux creates unsightly weld scars, increasing subsequent cleaning work. An excessively strong welding flame can melt the delicate filigree into gold beads, ruining the entire work; too little flame makes it difficult to weld.

[0006] Because filigree jewelry has a delicate and intricate structure, it needs to be made into several parts, which are then assembled together, either as a whole or in stages. Therefore, after the initial welding and shaping, the next step is intermediate welding. Since intermediate welding is done on the basis of the previous welding, the solder used has special requirements. Welding temperature control must be ensured to avoid affecting the safety of the previous welding; otherwise, the welded parts will remelt and disintegrate. At the same time, sufficient space must be left for subsequent welding operations. Especially when multi-stage welding is required, the solder gradation in the intermediate stages must be appropriately controlled to prepare a suitable medium-temperature solder.

[0007] Over a long period of time, traditional silver filigree craftsmanship has developed unique formulas and preparation techniques. Modern silver filigree production has basically continued these practices. Medium-temperature silver filigree solder mainly includes old flux, yellow flux, red flux, and new flux. In terms of medium-temperature solder, yellow flux or red flux with a silver content of 60-70% is generally used. Their melting point is generally between 670-780℃, which can meet the welding requirements of intermediate stages. However, yellow (red) flux medium-temperature solder has the following main problems: (1) The purity of medium-temperature solder is low, only 60-70%. The purity of silver filigree products must meet the silver content requirements of pure silver. Although the silver material used in the frame and wire of filigree jewelry can 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) A certain amount of Cd is often added to the medium-temperature welding flux formulation. Some solders contain 15-20% Cd. Cd can lower the melting point of the solder alloy, improve fluidity, and increase welding strength and plasticity. 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 vapors of Cd metal and oxides are 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. (3) Bletilla striata is used as a binder in the production of wire in order to fix the wire 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. (4) The copper content of the old flux is very high. It is easy to oxidize during the welding process, which affects the welding performance. In particular, the corrosion resistance of the welded part is poor, which makes the product prone to discoloration during production and use. (5) Medium-temperature solder for filigree jewelry is mainly used in the form of solder powder. The traditional method of making solder powder is to first melt and cast the solder into an ingot, and then grind it into powder using a steel abrasive. This results in problems such as uneven powder particle size, poor flux flowability, and the presence of iron impurities.

[0008] Therefore, traditional silver filigree hot-temperature solders 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℃, but the color of this solder is too low. 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 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, its melting point is too high to meet the needs of medium-temperature welding, and it is mainly designed for vacuum welding of hermetically sealed components, not for welding jewelry under atmospheric conditions. Patent 201611147938.1 discloses a method for preparing solder powder for silver filigree jewelry. It uses 100g of pure silver, 38g of copper solder, and 6g of brass to prepare the solder. It is essentially a xanthate solder with a melting point of about 680℃, a silver content of only 56%, and a high copper content. Furthermore, the silver solder is ground into powder using steel tools, inevitably introducing iron impurities into the solder powder. When used for medium-temperature welding of filigree jewelry, this results in problems such as affecting the color, easy high-temperature oxidation, and poor corrosion resistance. Summary of the Invention

[0009] To overcome the shortcomings of existing technologies, one of the objectives of this invention is to provide a medium-temperature silver filigree solder to solve the aforementioned problems of traditional technologies. Addressing the technical challenge that existing silver solders cannot adequately meet the medium-temperature welding requirements in the production of silver filigree jewelry, this invention optimizes the alloy formula to prepare a medium-temperature silver solder with excellent comprehensive performance, perfectly meeting the welding requirements of intermediate processes in silver filigree jewelry making. This solder has a purity of no less than 80%, a liquidus temperature no higher than 830℃, and a solidus temperature no lower than 750℃. This ensures a sufficient distance between the melting point of the initial high-temperature solder and the base material, while also allowing sufficient space for the preparation of low-temperature solders for subsequent welding. The crystallization interval of this solder does not exceed 60℃, and the brazing rate for pure silver welds reaches over 91%, exhibiting excellent fluidity and brazing rate. The solder has excellent ductility, making it suitable for making solder sheets. It also has excellent casting properties, making it suitable for making solder powder, and is easy to use. The alloying elements selected for this solder are environmentally friendly, containing no toxic or harmful elements and producing no toxic side effects. The solder has excellent resistance to sweat corrosion.

[0010] The second objective of this invention is to provide a method for preparing the above-mentioned medium-temperature silver wire solder.

[0011] One of the objectives of this invention is achieved through the following technical solution:

[0012] A medium-temperature silver wire solder comprises the following components by weight percentage:

[0013] 17–19.5% copper, 0.01–2% zinc, 0.01–1.4% indium, 0.01–0.5% germanium, 0.01–0.4% tin, 0.01–0.3% rare earth elements, the remainder being silver, and unavoidable impurity elements, of which rare earth elements are one or more of cerium, yttrium, lanthanum, neodymium, and gadolinium.

[0014] 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, tin is pure tin 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.

[0015] In this invention, considering the unique characteristics of filigree jewelry welding, the following aspects were emphasized when developing the medium-temperature solder for silver filigree jewelry welding:

[0016] (1) Filigree jewelry has a complex and delicate structure, which needs to be broken down into several parts and manufactured and assembled by process. Therefore, it requires multiple welding processes. Subsequent welding is carried out on the basis of the previous welding. Therefore, the previous welding is the basis for subsequent welding and processing. The solder used in different welding sequences must have an appropriate melting temperature range.

[0017] (2) The melting point and melting temperature range of medium-temperature solder should be reasonably controlled so that it is not only a certain distance away from the melting point of the substrate itself and the high-temperature solder, but also has a high enough melting point to withstand the heating during subsequent welding, so as to leave enough process operation space for welding operation, so as not to bring the risk of burning during welding due to the close melting points of the two, and to ensure the safety of the welded workpiece and the operability of the welding process.

[0018] (3) The silver content of the solder should be as high as possible to reduce its impact on the color of the substrate. The solder should be formulated through the synergistic effect of multi-element alloying to achieve an optimized match of welding performance, physical properties, chemical properties and mechanical properties.

[0019] (4) The solder should have good wettability, gap filling and bonding rate to the substrate. Alloying can make the solder have good wettability and gap filling 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 substrate, or formation of brittle compounds. Therefore, the selection of alloying elements and the amount added should be beneficial to wettability without increasing corrosion of the substrate.

[0020] (5) The solder has little color difference from the pure silver substrate, and the passivation effect of the alloying elements gives it excellent corrosion resistance and anti-discoloration properties.

[0021] (6) The alloying elements used in the solder must be green and environmentally friendly, do not produce toxic side effects, be inexpensive, and not contain precious elements.

[0022] Based on the above considerations, this invention uses silver, copper, zinc, indium, germanium, tin, and rare earth elements as the main alloying elements. By optimizing and adjusting their component ratios and alloy formulations, a medium-temperature silver solder with excellent comprehensive performance, capable of meeting the welding requirements of silver filigree jewelry, is prepared. Copper alloys have good compatibility with silver, which is beneficial for improving the mechanical properties of the alloy; its content is controlled at 17-19.5%. Zinc alloys have good compatibility with silver and is a green additive element. Zinc can effectively lower the melting point, but excessive content can easily cause oxidation slag; its content is controlled between 0.01-2%. Indium helps lower the melting point and vapor pressure of the solder and improves wettability; it is a green additive element, and its content is controlled between 0.01-1.4%, preferably 0.2-1.4%. Germanium can form a eutectic with silver, lowering the melting point of the alloy and improving flow properties. Germanium can also improve the solder's oxidation resistance and resistance to sulfide discoloration; its content is controlled between 0.01-0.5%. Tin, characterized by its low melting point, high boiling point, and low vapor pressure, is a green additive element. Tin can improve the electrochemical corrosion resistance of silver solder; its content should be controlled at 0.01–0.4%. Rare earth elements can refine the grain structure of silver solder, improve its strength properties and resistance to aging softening, and enhance its resistance to discoloration. One or more rare earth elements such as cerium, lanthanum, yttrium, gadolinium, and neodymium can be used, with their content controlled at 0.01–0.3%.

[0023] Furthermore, the total content of the unavoidable impurity elements does not exceed 0.1%.

[0024] Furthermore, the silver content is not less than 80%. Silver is the base element of solder. To ensure the color and basic welding performance after soldering, controlling its content to not less than 80% can effectively reduce the impact of solder on the color of the entire product.

[0025] Furthermore, the indium content is 0.2% to 1.4%.

[0026] Furthermore, the medium-temperature silver wire solder has a purity of not less than 80%, a liquidus temperature not higher than 830℃, and a solidus temperature not lower than 750℃. This creates a sufficient distance between the melting points of the substrate and the high-temperature solder, while also allowing ample space for the preparation of subsequent solder materials. Moreover, the solder's melting temperature range does not exceed 65℃, exhibiting good fluidity.

[0027] Furthermore, the crystallization interval of the medium-temperature silver wire solder does not exceed 60°C, and the brazing rate of pure silver welds reaches over 91%, exhibiting excellent fluidity and brazing rate.

[0028] Furthermore, the medium-temperature silver wire solder exhibits a wetting angle of no more than 31° on pure silver surfaces, demonstrating excellent wetting properties. Within a weld seam of 0.05–0.08 mm, the solder's brazing rate reaches over 91%.

[0029] Furthermore, the medium-temperature silver wire solder is in the form of sheet solder or powder solder. Depending on the application requirements, solder in either of these two shapes can be manufactured.

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

[0031] A method for preparing a medium-temperature silver wire solder, wherein the medium-temperature silver wire solder is a thin sheet solder, and the preparation of the thin sheet solder includes the following steps:

[0032] 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.

[0033] S2: Roll the ingot into sheets, with a single processing rate controlled at 12-16%. 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.

[0034] S3: Bury the thin sheet in charcoal powder, heat to 450-480℃, anneal, clean and then put it into boiling alum water to remove the oxide film on the surface.

[0035] S4: After cleaning and drying the thin film obtained in step S3, cut it into square thin films of 10-20mm.

[0036] Furthermore, in step S1, the preparation steps for fabricating the continuously cast slab using the vacuum traction continuous casting process are as follows:

[0037] First, pure silver and pure 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.

[0038] The second objective of this invention is also achieved by the following technical solution:

[0039] A method for preparing a medium-temperature silver wire solder, wherein the medium-temperature silver wire solder is a powdered solder, and the preparation of the powdered solder includes the following steps:

[0040] S1: Prepare the ingredients according to the proportions, pre-melt them using induction melting process, and obtain the ingot;

[0041] S2: Using a vacuum atomization powder making equipment, the ingot obtained in step S1 is remelted and welding powder is produced.

[0042] Furthermore, in step S1, the pre-melting step using induction melting process is as follows: first, pure silver and pure 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.

[0043] In step S2, the specific steps are as follows: the temperature of the molten metal is controlled at 1060-1110℃, 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.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] 1. The medium-temperature silver wire solder of the present invention uses silver, copper, zinc, indium, germanium, tin, rare earth and other main alloying elements. By optimizing and adjusting the composition ratio and the alloy formula, a medium-temperature silver solder with excellent comprehensive performance can be prepared, which can well meet the welding requirements of silver wire jewelry.

[0046] 2. The solder of the present invention has the following properties:

[0047] (1) Solder color

[0048] The silver content of this medium-temperature solder is no less than 80%, which can effectively reduce the impact of the solder on the color of the entire product.

[0049] (2) Flow properties

[0050] The medium-temperature solder for this filigree jewelry has a liquidus temperature not exceeding 820℃ and a solidus temperature not lower than 760℃, which is sufficiently far from the melting point of the substrate and high-temperature solder, and also leaves enough room for the preparation of subsequent solders. In addition, the melting temperature range of the solder does not exceed 65℃, and it has good fluidity.

[0051] (3) Color and corrosion resistance

[0052] The solder of this invention is a slightly grayish-silver-white color, which is close to the color of pure silver and is significantly superior to the color of traditional solders. After being soaked in artificial sweat for 8 hours, its color change is basically the same as that of pure silver, which is significantly better than that of traditional solders.

[0053] (4) Welding performance

[0054] The solder of this invention exhibits excellent wetting properties with a wetting angle of no more than 31° on a pure silver surface. Within a weld seam of 0.05–0.08 mm, the solder's brazing rate reaches over 91%.

[0055] (5) Processing and manufacturing performance

[0056] The solder of this invention has good cold deformation processing performance and can be rolled into thin sheets with a thickness of 0.1 to 0.2 mm. In addition, it can be made into solder powder of 300 to 350 mesh using a vacuum atomization powder preparation process. Detailed Implementation

[0057] 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.

[0058] Example 1

[0059] A thin-film solder includes the following steps:

[0060] 1. Solder composition

[0061] The chemical composition of this solder is designed as follows by mass percentage: 18.8% copper, 0.52% zinc, 0.18% indium, 0.06% germanium, 0.04% tin, 0.01% yttrium, 0.01% lanthanum, with the remainder being silver, and unavoidable impurities.

[0062] 2. Solder preparation

[0063] 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-pass processing rate controlled at 13-15%. When the total processing rate reaches 60-75%, intermediate annealing is performed, followed by continued rolling until a sheet with a thickness of 0.13 mm is obtained. The sheet is then buried in charcoal powder and annealed at 450-480℃. After cleaning, it is immersed in boiling alum water to remove the oxide film on the surface. The sheet is then cleaned, dried, and cut into 15 mm square sheets for later use.

[0064] 3. The solder's properties were tested and are as follows:

[0065] (1) Solder color

[0066] The silver content of this medium-temperature solder is no less than 80%, which can effectively reduce the impact of the solder on the color of the entire product.

[0067] (2) Flow properties

[0068] In this embodiment, the medium-temperature solder has a liquidus temperature of 815°C and a solidus temperature of 770°C, which is sufficiently far from the melting points of the substrate and the high-temperature solder. This also leaves enough room for the preparation of solder for subsequent welding. Furthermore, the melting temperature range of the solder does not exceed 50°C, and it has excellent fluidity.

[0069] (3) Color and corrosion resistance

[0070] This medium-temperature solder has a slightly grayish-yellowish-white appearance, while traditional fluxes exhibit a more pronounced dark reddish-yellow color. Therefore, this solder is significantly superior in appearance to traditional fluxes, with a smaller color contrast compared to pure silver. After soaking in artificial sweat for 8 hours, the color difference was approximately 4.2, demonstrating that this solder has good resistance to sweat corrosion.

[0071] (4) Welding performance

[0072] The solder exhibits a wetting angle of 28° on pure silver surfaces, demonstrating excellent wetting properties. Within a 0.05mm weld seam, the solder achieves a brazing rate of 92%, demonstrating excellent seam-filling performance.

[0073] (5) Processing and manufacturing performance

[0074] This solder has excellent cold deformation processing performance, and when combined with intermediate annealing, it can be rolled into a sheet with a thickness of 0.15mm.

[0075] Example 2

[0076] A thin-film solder includes the following steps:

[0077] 1. Solder composition

[0078] The chemical composition of this solder is designed as follows by mass percentage: 19% copper, 0.4% zinc, 0.4% indium, 0.05% germanium, 0.1% tin, 0.01% cerium, with the remainder being silver, and unavoidable impurities.

[0079] 2. Solder preparation

[0080] 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-pass processing rate controlled at 13-15%. When the total processing rate reaches 60-75%, intermediate annealing is performed, followed by continued rolling until a sheet with a thickness of 0.13 mm is obtained. The sheet is then buried in charcoal powder and annealed at 450-480℃. After cleaning, it is immersed in boiling alum water to remove the oxide film on the surface. The sheet is then cleaned, dried, and cut into 15 mm square sheets for later use.

[0081] 3. The solder's properties were tested and are as follows:

[0082] (1) Solder color

[0083] The silver content of this medium-temperature solder is no less than 80%, which can effectively reduce the impact of the solder on the color of the entire product.

[0084] (2) Flow properties

[0085] In this embodiment, the medium-temperature solder has a liquidus temperature of 815°C and a solidus temperature of 766°C, which is sufficiently far from the melting points of the substrate and the high-temperature solder. This also leaves enough room for the preparation of solder for subsequent welding. Furthermore, the melting temperature range of the solder does not exceed 50°C, and it has excellent fluidity.

[0086] (3) Color and corrosion resistance

[0087] This medium-temperature solder has a slightly warm, yellowish-silver-white color, while traditional fluxes are a more pronounced dark reddish-yellow. Therefore, this solder is significantly superior in appearance to traditional fluxes, and its color contrast with pure silver is smaller. After soaking in artificial sweat for 8 hours, the color difference is approximately 4.0, demonstrating that this solder has good resistance to sweat corrosion.

[0088] (4) Welding performance

[0089] This solder exhibits a wetting angle of 28° on pure silver surfaces, demonstrating excellent wetting properties. Within a weld seam of 0.05–0.06 mm, the solder achieves a brazing rate of 92%, demonstrating excellent seam-filling performance.

[0090] (5) Processing and manufacturing performance

[0091] This solder has good cold deformation processing properties and can be rolled into a thin sheet with a thickness of 0.11 mm.

[0092] Example 3

[0093] A soldering powder, comprising the following steps:

[0094] 1. Solder composition

[0095] The chemical composition of this solder is designed as follows by mass percentage: 17% copper, 1.5% zinc, 0.5% indium, 0.05% germanium, 0.2% tin, 0.02% gadolinium, 0.01% neodymium, with the remainder being silver, and unavoidable impurities.

[0096] 2. Solder preparation

[0097] 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 1090–1100℃. High-purity nitrogen (99.999%) is used at a pressure of 2.9–3.3 MPa, and the nozzle employs a tightly coupled, confined annular 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.

[0098] 3. The solder's properties were tested and are as follows:

[0099] (1) Solder color

[0100] The silver content of this medium-temperature solder is no less than 80%, which can effectively reduce the impact of the solder on the color of the entire product.

[0101] (2) Flow properties

[0102] In this embodiment, the medium-temperature solder has a liquidus temperature of 812°C and a solidus temperature of 752°C, which is sufficiently far from the melting points of the substrate and the high-temperature solder. This also leaves enough room for the preparation of subsequent solders. Furthermore, the melting temperature range of the solder does not exceed 60°C, and it has excellent fluidity.

[0103] (3) Color and corrosion resistance

[0104] The medium-temperature solder exhibits a slightly warm silvery-white color, significantly superior to that of traditional solders. After immersion in artificial sweat for 8 hours, the color difference was approximately 4.2, demonstrating the solder's good resistance to sweat corrosion.

[0105] (4) Welding performance

[0106] This solder exhibits a wetting angle of 27° on pure silver surfaces, demonstrating excellent wetting properties. Within a weld seam of 0.05–0.06 mm, the solder achieves a brazing rate of 93%, demonstrating excellent seam-filling performance.

[0107] (5) Processing and manufacturing performance

[0108] This solder has good cold deformation processing properties and can be rolled into thin sheets of 0.15 mm thickness.

[0109] The following is a comparative example, as follows:

[0110] Comparative Example 1 (Traditional Welding Flux)

[0111] The medium-temperature solder is prepared using traditional xanthate from the filigree process, and its composition is: 66% Ag-18% Cu-13% Zn-3% Cd.

[0112] Testing revealed the following performance characteristics of the traditional solder in Comparative Example 1: Its silver content is only 66%, significantly lower than that of the medium-temperature solder in this invention, which is detrimental to the control of silver content in wire-flanged products. The solder's color is a slightly yellowish, dark silver-white, showing a clear contrast to pure silver. After soaking in sweat for 8 hours, the color difference reached 8.2, indicating significant discoloration. The brazing rate within a 0.05–0.06 mm weld seam is 90–93%, but its main contributor is Cd, a highly toxic element. Therefore, the traditional solder is significantly inferior to the medium-temperature solder of this invention in terms of color, resistance to sweat corrosion, and environmental friendliness.

[0113] Comparative Example 2

[0114] The chemical composition of a thin-film solder is: 11% copper, 2% zinc, 0.2% indium, 0.03% tin, 1% germanium, 0.05% cerium, with the remainder being silver, and unavoidable impurities.

[0115] The preparation was carried out according to the steps in Example 1, and will not be repeated here.

[0116] Testing revealed that the solder had a silver content exceeding 80%, a liquidus temperature of approximately 844°C, a crystallization interval of approximately 129°C, and relatively poor fluidity. The wetting angle between the solder and the pure silver substrate was 36°, and the brazing rate within the weld was only about 80%. Furthermore, the solder's low solidus temperature severely limited the operational space for low-temperature soldering. The solder's color was significantly more reddish-yellow than pure silver, and the weld exhibited inconsistent color gradations. After soaking in artificial sweat with a pH of 6.5 for 8 hours, the surface showed a slight discoloration, appearing darker yellow or light brown. Therefore, the welding effect of this comparative example as a medium-temperature solder was significantly inferior to that of Examples 1 or 2 of this invention.

[0117] Comparative Example 3

[0118] The chemical composition of a solder powder is: 17% copper, 1.8% zinc, 0.3% indium, 0.3% tin, 0.4% germanium, 0.2% cerium, with the remainder being silver, and unavoidable impurities.

[0119] The preparation was carried out according to the steps in Example 3, and will not be repeated here.

[0120] Testing revealed that the solder had a silver content of 80%, a liquidus temperature of 825°C, a solidus temperature of 740°C, a crystallization interval of 85°C, and relatively poor fluidity. The wetting angle between the solder and the pure silver substrate was 44°, and the brazing rate within the weld was only about 80%. After soaking in artificial sweat with a pH of 6.5 for 8 hours, the solder surface turned a dark yellow or light brown, showing a noticeable discoloration. This solder was prone to edge cracking during rolling. Therefore, the welding effect of this comparative example as a medium-temperature solder was significantly inferior to that of Example 3.

[0121] 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 medium-temperature silver wire solder, characterized in that, The components include the following mass percentages: 17–19.5% copper, 0.01–2% zinc, 0.01–1.4% indium, 0.01–0.5% germanium, 0.01–0.4% tin, 0.01–0.3% rare earth elements, 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 medium-temperature silver wire solder according to claim 1, characterized in that, The silver content is not less than 80%.

3. The medium-temperature silver wire solder according to claim 1, characterized in that, The indium content is 0.2% to 1.4%.

4. The medium-temperature silver wire solder according to claim 1, characterized in that, The medium-temperature silver wire solder has a purity of not less than 80%, a liquidus temperature of not more than 830°C, and a solidus temperature of not less than 750°C.

5. The medium-temperature silver wire solder according to claim 4, characterized in that, The crystallization interval of the medium-temperature silver wire solder does not exceed 60°C.

6. The medium-temperature silver wire solder according to claim 4, characterized in that, The medium-temperature silver wire solder has a wetting angle of no more than 31° on a pure silver surface.

7. A method for preparing a medium-temperature silver wire solder as described in any one of claims 1-6, wherein the medium-temperature silver wire solder is a sheet-like solder, characterized in that... The preparation of the sheet-like 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 12-16%. 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 450-480℃, 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 medium-temperature silver wire solder 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, pure silver and pure copper are melted under a protective atmosphere. Then, the remaining materials are added in a secondary feeding process. After they are completely melted and stirred evenly, they are poured into ingots.

9. A method for preparing a medium-temperature silver wire solder as described in any one of claims 1-6, wherein the medium-temperature silver wire solder is a powdered solder, characterized in that... The preparation of the powdered 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 medium-temperature silver wire solder according to claim 9, characterized in that, In step S1, the pre-melting step using induction melting process is as follows: first, pure silver and pure 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. In step S2, the specific steps are as follows: the temperature of the molten metal is controlled at 1060-1110℃, 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.