ES2706474T3 - Cu-Ag alloy wires manufacturing process - Google Patents

Abstract

A method for manufacturing wires, including micro-wires, of Cu-Ag alloys, in particular of alloys with Cu- (3 ÷ 7.9)% Ag by weight, characterized in that the materials in the form of copper and silver with a high purity are melted at a temperature of 1083 ÷ 1300 ºC in a graphite crucible placed in a furnace and subsequently continuously cast at a temperature of 1083 ÷ 1300 ºC, in an inert gas atmosphere using a graphite mold, under conditions of primary cooling (cooling in mold) and secondary cooling (the solidified alloy after leaving the mold) and then the casting obtained in this way is subjected to a thermo-mechanical treatment during which the obtained casting is annealed in solution at a temperature of 600 ÷ 779.1 ºC for 0.5 ÷ 100 hours and then it cools sharply at a faster rate than the process of precipitating its constituents from the solid solution and then submits to additional two-stage heat treatment processes in which the first stage is maintenance at 150 ÷ 300 ºC for 0.1 ÷ 100 hours, followed by - in the second stage - maintenance at a temperature of 300 ÷ 500 ºC during 0.1 ÷ 20 hours and then slow cooling, followed by stretching in wires of the final cross section.

Description

DESCRIPTION

Cu-Ag alloy wires manufacturing process

The present invention relates to a method of manufacturing wires, including micro-wires, of Cu-Ag alloys, in particular of an alloy comprising Cu- (3-7.9)% Ag by weight. These alloys which are in the form of bars and which come from a casting and casting line are subjected to appropriately selected heat treatment sequences and are shaped into wires, presenting a set of excellent mechanical and electrical properties.

According to recent reports, Cu-Ag alloys can be used as conductors in power supply applications, in the automotive industry, in power supply and high-speed rail signaling systems, in medical accessories and as supply components for coils generating strong magnetic fields.

Up to now, the conductive alloys based on copper, which may also contain Nb, Be, Zn, Sn, Zr, Cr, etc. they have been applied in the analyzed fields of technology. However, these alloys, apart from their relatively high mechanical properties, are characterized by low electrical conductivity. Apart from their high mechanical properties, Cu-Ag alloys also show exceptionally high values of electrical conductivity. A number of global solutions focus on developing these properties by selecting an appropriate technology to obtain and process materials. Research in scientific centers and research institutes around the world is aimed at obtaining wires with excellent mechanical properties and, at the same time, the highest possible electrical conductivity. The production of ingots with various cross-sectional shapes and limited lengths and continuous casting and casting systems that ensure that a material with theoretically endless length can be obtained, are among the commonly known engineering solutions applied to obtain alloys.

An analysis of the global structures indicates that the alloys obtained with these processes are subsequently processed by the application of various technologies, in particular by plastic work, for example, laminar, forge, stretch, extrude, in addition heat treatment functions are applied in various Mechanical processing stages

A method for obtaining micro-wires of an alloy with the chemical composition of Cu- (2-14)% Ag by weight is known from a Japanese patent application JP 200-199042. The description provides a method of manufacturing microails with a diameter of 0.01 0.1 mm using eight treatment variants. The research findings presented in the patent description have focused on a material in the form of molded rods with a diameter of 8 mm and containing silver as a constituent of the alloy in the amount of 5 and 10% Ag in weight. The scheme for obtaining micro-wires according to the aforementioned description provides the execution of the following treatment sequences. The castings of the Cu-10% Ag alloy by weight were subjected to a reduction in diameter in the stretching process from 10 mm to 5 mm, at an adjusted reduction of 61%. Then, the deformed material was treated with heat at 450 ° C for 10 h, to subsequently apply overall reduction of either 94.2% or 99%. The diameter of the final wire was 1.2 mm and 0.5 mm, respectively. The wires with this history of thermo-mechanical treatment development reached mechanical and electrical properties at a high level of 1530 MPa and 76% of IACS (100% IACS = 58.0 MS / m). A separate treatment variant of molded bars with a slightly lower silver content than in the previous version (6% by weight of Ag) according to this solution, provided the application of the heat treatment carried out under the same conditions: 450 ° C / 10 h applied to the initial material, that is, the molded bar. Then, the overall reduction was adjusted to 98.4% (for a diameter of 1.0 mm), which finally allowed a tensile strength of 1320 MPa to be achieved. The electrical conductivity reached 78% of IACS. Apart from the treatment variants described above, the authors of this patent introduced an additional step of maintaining at 370 ° C / 15 h. Starting with a bar with a diameter of 8 mm when molding, the subsequent steps involved the overall reduction of 61% (to a diameter of 5 mm), a heat treatment (450 ° C / 10 h), again an overall reduction of 84% (to a diameter of 2 mm).

Then, one or two additional heat treatment steps were applied (370 ° C / 15 h). One of the variants assumed, after the overall reduction of 84%, a thermal treatment (370 ° C / 15 h) and an additional treatment with diameters of 0.05 0.03 mm (total reduction of 99.3 99.8 %). Said process allows a significant increase in mechanical properties within the range of 1420-1735 MPa and an increase in electrical conductivity to 60 65% of IACS. The second of the variants experienced, after the initial global reduction of 61%, a thermal treatment at 450 ° C / 10 h, the overall reduction of 84%, a thermal treatment at 370 ° C / 15 h, followed by the reduction overall of 97.8% at a diameter of 0.3 mm and a subsequent thermal treatment at 370 ° C / 60 h and the final overall reduction of 99.6% at a diameter of 0.02 mm. Said proceeding procedure allowed the wires to achieve the tensile strength of 1250 MPa and the electrical conductivity of 71% of IACS.

Another method for obtaining materials from a Cu-Ag alloy is presented in the description of international application No. WO 2007-046378. The input material was an ingot of Cu-Ag alloy with dimensions of 10x10x30 mm, obtained by melting in an electric Tamman furnace at a temperature of 1250 ° C.

^{Alloys of the Cu- (1 10)} % ^{Ag by weight, Cu- (2 6)} % ^{Ag by weight range were subjected to a} reduction in the stretching process. The heat treatment processes applied in the central phase of the reduction were carried out at temperatures of 400-500 ° C for a period of 1 to 50 hours in a vacuum or inert gas atmosphere to avoid oxidation of the surface of the material . The relationships presented in the description of the patent relate to alloys mainly in the range of Cu- (1 10)% Ag by weight. A Cu-Ag ingot with dimensions as mentioned above and a silver content of the first 1%, 2% and 3% Ag by weight was subjected to a heat treatment at 450 ° C / 20 h, and subsequently to a reduction global with a logarithmic measure of 0.6 (the true tension is the natural logarithm of the elongation coefficient in the stretching process of the wire, the elongation coefficient means a square of the ratio of the initial diameter of the wire and the final diameter of the wire).

Then the material of Cu-4% Ag by weight was subjected to maintenance at 450 ° C / 10 h and stretched with a tension of 0.6 on the logarithmic scale. As the silver content in the alloy increased, the time of the applied heat treatment decreased. An ingot of Cu-10% Ag by weight was subjected to maintenance at 450 ° C for 5 hours. Each alloy described, in the subsequent processing step, was subjected to a true voltage of 8 or 12. As a result of the investigation, wires with a voltage resistance of 1400 MPa and an electrical conductivity of 76.4% were obtained. IACS, as well as with a tensile strength of 1200 MPa and a conductivity of 81.7% of IACS. In the opinion of the author of this solution, the quotient of the resistance of the Cu-Ag alloys exceeding 10% by weight of Ag to the Ag content is disadvantageous, in this way the selected range of the alloys tested was between 1 and 10% Ag by weight.

In the description of the American application no. US 2008/0202648 A1, research discoveries of Cu-Ag alloys with the silver content within the range of 3.5% Ag by weight are presented. In this case, the initial material is an ingot with the maximum content of impurities of 10 ppm or less, obtained in the mold casting process. The metal during the casting is cooled to a cooling rate of 400-500 ° C / min. The product according to this solution is further processed for example by stretching, rolling, etc.

The heat treatment functions after the plastic treatment processes are carried out at 300 350 ° C for 10 20 h, 350 450 ° C for 5 10 h, or at temperatures of 450 550 ° C for 0.5 5 h in a inert gas atmosphere. After the maintenance processes, the program for obtaining Cu- (1 3.5%) Ag by weight products according to the present invention provides a stretch at a diameter of 0.05 mm or less. According to the description to which reference is made, the tensile strength of the final material is within the range of 800 1200 MPa, while the electrical conductivity is within the 84% range of IACS. This solution also assumes, at a certain stage of obtaining wires from the Cu- (1 3.5%) weight Ag alloy, an additional maintenance process at temperatures of 600 900 ° C for a very short time , that is, from 5 to 120 seconds.

A disadvantage shared by the solutions is the underutilization of a possibility to advantageously develop the microstructure of Cu-Ag alloys, and a related possibility of manufacturing wires with an even higher set of mechanical and electrical properties.

The multi-sequential thermomechanical treatment processes carried out at unfavorably selected temperature intervals, combined with a too extended heat treatment time, do not negatively influence the maximization of mechanical and electrical properties. In addition, the additional intermediate heat treatments (inherent to the generation of the full production cost), used at an inappropriate stage of wire production, do not fully translate into a high set of mechanical and electrical properties of the final product.

The object of the invention is to present a consistent, integrated process for the manufacture of wire components, including micro-wires, comprising the continuous processes of melting and casting of Cu-Ag alloy bars and a sequential thermal treatment combined with stretching, allowing that wires are obtained, including micro-wires, with a resistance to the voltage Rm within the range of 1100 1400 MPa and simultaneously an electrical conductivity within the 68 84% range of IACS.

Cu-Ag alloys have the possibility of mutual limited solubility in the solid state of silver in copper and copper in silver. The microstructure of the alloy consists of a matrix comprising mainly copper that contains a certain amount of silver without precipitating and precipitates rich in silver, which also contains a small amount of copper without precipitating. Using a thermo-mechanical multi-stage treatment of castings and appropriately selected temperature and time of the heat treatment (quenching and aging), many numerous fine silver precipitates can precipitate within the entire volume of the copper-supersaturated silver solution. The application of a significant plastic stress contributes to a substantial elongation of the precipitates formed as a result of the thermo-mechanical treatment of the alloy. The structure in a longitudinal section of the wires (micro-wires) consists of very numerous, thin, considerably elongated fibers that almost completely comprise silver with a small mixture of copper and the matrix comprising almost completely copper. The diameter of these fibers has nanometric dimensions. In the solution according to this invention, the materials in the form of copper and silver with a high chemical purity they are mixed at a temperature of 1083-1300 ° C in a graphite crucible placed in an oven and subsequently continuously cast at a temperature of 1083-1300 ° C, in an inert gas atmosphere using a graphite mold, under cooling conditions primary (in-mold cooling) and secondary cooling conditions (the solidified alloy after leaving the mold) and thus the cast obtained with this process is subjected to a thermo-mechanical treatment during which the obtained casting is annealed in a solution to a temperature of 600 779.1 ° C for 0.5 100 hours and subsequently quenched at a faster rate than the process of precipitating its constituents from the solid solution and then subjected to a two-step additional heat treatment processes in those that the first stage is maintenance at 150 300 ° C for 0.1 100 hours, followed by - in the second stage - maintenance at a temperature of 300 500 ° C last 0.1 to 20 hours and then slow cooling, followed by stretching in wires of the final cross section. Preferably, during the thermo-mechanical treatment, the obtained casting, after annealing in solution at a temperature of 600 779.1 ° C for 0.5 100 hours and then suddenly cooling and then extracting, with a tension measurement true of 0.1 1 and then subjected to the thermal treatment processes of two additional stages, followed by stretching in wires of the final cross section.

Preferably, when the material is deformed in the final cross section wires, at least one intermediate heat treatment is produced within 200 600 ° C for 0.150 hours, followed by slow cooling.

Preferably, during the deformation of the material in the final cross-sectional wires, at least one intermediate heat treatment at 600 900 ° C for 0.1 1000 seconds occurs, followed by abrupt cooling.

Preferably, the final cross-section wires are subjected to a heat treatment at a temperature of 50-300 ° C for 0.1 1000 hours.

Preferably, after annealing in solution, the melt is quenched with water.

Preferably after annealing in solution, the melt is quenched with oil.

Preferably after annealing in solution, the melt is quenched with liquid nitrogen. Preferably after annealing in solution, the melt is quenched with emulsion. Preferably, the graphite crucible is made of a highly pure graphite, in which the constituents of the alloy are placed under a layer of charcoal or graphite.

Preferably, the graphite crucible is placed in a protective atmosphere.

Preferably, the graphite mold is cooled with a system that is mounted therein, through which a cooling agent flows (the primary cooling system).

Preferably, the melt leaving the mold is further cooled by a cooling agent administered directly on the melt (the secondary cooling system).

Thanks to the application of the method according to the invention, the following technical and functional effects have been obtained, that is to say a possibility to form a set of excellent electrical and mechanical properties of the product, reduction of manufacturing costs thanks to the thermo treatments - appropriately selected mechanics, a possibility to select the optimal conditions of the thermo-mechanical treatment sequence to obtain the required mechanical and electrical properties, an advantageous weight ratio to the mechanical parameters of the products obtained.

The solution according to the invention is presented in the embodiment examples in Table 1, in which with an example of three Cu-Ag alloys with various silver contents within the range of the present invention, the procedure for obtain wires (including micro-wires), along with a list of mechanical and electrical properties in different stages of product manufacture.

Table 1

continuation

The process for obtaining micro-wires from Cu-Ag alloys is described with the following exemplary embodiments.

Example 1

The materials in the form of high purity 99.99% silver granules and OFE copper were melted at a temperature of 1200 ° C in a graphite crucible placed in an induction furnace. The continuous casting process was carried out at a temperature of 1200 ° C in an inert gas atmosphere. The continuous casting of the bars with a chemical composition of Cu-3% Ag by weight, using a graphite mold was carried out under conditions of primary cooling (cooling in mold) and secondary cooling (the solidified alloy left by the mold ). The round bars obtained as a result of the continuous casting process had a diameter of 9.5 mm and a tensile strength Rm = 190 MPa, and the electrical conductivity of 80% of IACS. The material was then subjected to thermo-mechanical treatment processes. The casting was annealed in solution at a temperature of 750 ° C for 20 hours and then cooled suddenly in oil to preserve the homogeneous structure of the material. The additional procedure included adjusting a tension in the stretching process, with the true tension measurement of 0.4. After this process, the bars showed the tensile strength of Rm = 230 MPa and the electrical conductivity of 94% of IACS. Next, a two-stage aging process was carried out to extract as much silver as possible from the homogenous solid solution of Cu-Ag. The primary aging (the first stage) was carried out at 300 ° C for 30 hours. The secondary aging (the second stage) was carried out at the temperature of 450 ° C for 10 hours. After the preliminary heat treatments completed, the alloy microstructure consisted of very numerous fine silver precipitates in the copper matrix. Next, the material was stretched on wires with a true tension of 2.7, followed by an intermediate heat treatment consisting of a maintenance at a temperature of 400 ° C for 2 hours. Next, the material was stretched on the wires of the final diameter. To enhance the electrical properties, the final diameter wires were subjected to a heat treatment at a temperature of 240 ° C for 2 hours. At the end, the wires with a diameter of 0.2 mm and a true voltage of 7.7 had a resistance to voltage Rm = 1100 MPa and an electrical conductivity of 82% of IACS. The final microstructure of the wire, as seen in its longitudinal section, showed very thin, elongated bands of silver and copper matrices, favorable to obtain a set of high mechanical properties and a high electrical conductivity of the product.

Example 2

^{The materials in the form of high purity 99.99} % ^{silver granules and OFE copper were melted at a temperature} of 1200 ° C in a graphite crucible placed in an induction furnace. The continuous casting process was carried out at a temperature of 1210 ° C in an inert gas atmosphere. The continuous casting of the bars with a chemical composition of Cu-5% Ag by weight, using a graphite mold was carried out under conditions of primary cooling (cooling in mold) and secondary cooling (of the solidified alloy after leaving mold). The round rods obtained as a result of the continuous casting process had a diameter of 9.5 mm and a tensile strength Rm = 210 MPa, and the electrical conductivity of 87% of IACS. In this way, the material obtained was subjected to the thermo-mechanical treatment process. The melt was annealed in solution at a temperature of 750 ° C for 10 hours and subsequently cooled in water to preserve the homogenous structure of the material. After this process, it was necessary to carry out an aging process in two stages, to extract as much silver as possible from the homogenous solid solution of Cu-Ag. The primary aging (the first stage) was carried out at 200 ° C for 20 hours. The secondary aging (the second stage) was carried out at a temperature of 450 ° C for 10 hours. After the preliminary heat treatments, the alloy microstructure consisted of very numerous fine silver precipitates in the copper matrix. Next, the material was stretched on the final diameter wires. To enhance the electrical properties, the final diameter wires were subjected to a heat treatment at a temperature of 180 ° C for 10 hours. Finally, the wires with a diameter of 0.37 mm and a true voltage of 6.5 had a resistance to voltage Rm = 1220 MPa and an electrical conductivity of 74% of IACS. The final microstructure of the wire, as seen in its longitudinal section, showed very thin, elongated bands of silver and copper matrices, favorable to obtain a set of high mechanical properties and a high electrical conductivity of the product.

Example 3

The materials in the form of high purity 99.99% silver granules and OFE copper were melted at a temperature of 1220 ° C in a graphite crucible placed in an induction furnace. The continuous casting process was carried out at a temperature of 1220 ° C in an inert gas atmosphere. The continuous casting of the bars with a chemical composition of Cu-7% Ag by weight, using a graphite mold was carried out under conditions of primary cooling (cooling in mold) and secondary cooling (of the solidified alloy after leaving mold). The round rods obtained as a result of the continuous casting process had a diameter of 9.5 mm and a tensile strength Rm = 240 MPa, and an electrical conductivity of 84% IACS. In this way, the material obtained was then subjected to thermo-mechanical treatment processes. The melt was annealed in solution at a temperature of 750 ° C for 20 hours and subsequently cooled in water to preserve the homogenous structure of the material. The additional procedure included adjusting a tension in the stretching process, with the true tension measurement of 0.4. After this process, the bars had a tensile strength of Rm = 260 MPa and an electrical conductivity of 83% of IACS. Next, a two-stage aging process was carried out, which was to extract as much silver as possible from the homogenous solid solution of Cu-Ag. The primary aging (the first stage) was carried out at 300 ° C for 20 hours. The secondary aging (the second stage) was carried out at the temperature of 450 ° C for 10 hours. After the preliminary heat treatments, the alloy microstructure consisted of very numerous fine silver precipitates in the copper matrix. Next, the material was stretched on the wires of the final diameter. To enhance the electrical properties, the final diameter wires were subjected to a heat treatment at a temperature of 150 ° C for 100 hours. Finally, the wires with a diameter of 0.2 mm and a true voltage of 7.7 had a resistance to voltage Rm = 1250 MPa and an electrical conductivity of 75% of IACS. The final microstructure of the wire, as seen in its longitudinal section, showed very thin, elongated bands of silver and copper matrices, favorable to obtain a set of high mechanical properties and a high electrical conductivity of the product.

The solution according to the invention is a previously unknown, consistent, integrated method of manufacturing finished rods as a result of the continuous casting and casting process of Cu-Ag alloys that carry a high chemical purity with an allowable oxygen content in the alloy of 3 ppm or less and other impurities up to a maximum of 20 ppm. The chemical composition and structure of the Cu-Ag alloy bars obtained based on the solution according to the invention are constant throughout the entire length of the cast. The final product in the form of wires (including micro-wires) is only obtained by stretching the continuous cast bars, using dies with a round or other profile.

Claims (13)

1. A method for manufacturing wires, including micro-wires, of Cu-Ag alloys, in particular of alloys with Cu- (3-7.9)% Ag by weight, characterized in that the materials in the form of copper and silver with a high chemical purity are melted at a temperature of 1083-1300 ° C in a graphite crucible placed in an oven and subsequently continuously cast at a temperature of 1083-1300 ° C, in an inert gas atmosphere using a graphite mold, in conditions of primary cooling (cooling in mold) and secondary cooling (the solidified alloy after leaving the mold) and then the casting obtained in this way is subjected to a thermomechanical treatment during which the obtained casting is annealed in solution to a temperature of 600 779.1 ° C for 0.5 100 hours and subsequently it cools sharply at a faster rate than the process of precipitating its constituents from the solid solution and then undergoes a few pr Additional two-stage heat treatment events in which the first stage is maintenance at 150-300 ° C for 0.1 100 hours, followed by - in the second stage - maintenance at a temperature of 300-500 ° C for 0.1 20 hours and then slow cooling, followed by stretching in wires of the final cross section. 2. A process according to claim 1, characterized in that during the thermomechanical treatment the obtained casting, after being annealed in solution at a temperature of 600 779.1 ° C for 0.5 100 hours and subsequently quenched at a high speed faster than the process of precipitation of its constituents from the solid solution, subsequently stretched, with a true tension measurement of 0.1 1 and then undergoes the additional two-stage heat treatment processes, followed by stretching in wires of the final cross section. A method according to claim 1, characterized in that during stretching of the material in wires of the final cross section, at least one intermediate heat treatment is produced within the range of 200 600 ° C for 0.1 50 hours, followed of slow cooling or of sudden cooling. 4. A method according to claim 1, characterized in that during stretching of the wire material of the final cross section, at least one intermediate heat treatment occurs within the range of 600 900 ° C for 0.1 1000 seconds, followed by of slow cooling or of sudden cooling. A method according to claim 2 or 1, characterized in that the wires of the final cross-section are subjected to a heat treatment at a temperature of 50-250 ° C for 0.1 1000 hours. 6. A process according to claim 2, characterized in that after annealing in solution the melt is quenched with water. 7. A process according to claim 2, characterized in that after annealing in solution the melt is quenched with oil, in particular with a process oil. 8. A process according to claim 2, characterized in that after annealing in solution the melt is quenched with liquid nitrogen. 9. A process according to claim 2, characterized in that after annealing in solution, the melt is quenched with emulsion, with the concentration of oil in water of between 3 and 25%. A process according to claim 1, characterized in that the graphite crucible is made of a highly pure graphite, in which the constituents of the alloy are placed under a layer of charcoal or graphite. 11. A process according to claim 1, characterized in that the graphite crucible is placed in a protective atmosphere. 12. A process according to claim 1, characterized in that the graphite mold is cooled with a system that is mounted therein, through which a cooling agent flows (the primary cooling system). 13. A process according to claim 1, characterized in that the casting left by the mold is further cooled by a cooling agent applied directly on the laundry (the secondary cooling system).