High performance alloy wire and method of making same

Abstract

This invention discloses a high-performance alloy wire and its preparation method, relating to the field of alloy manufacturing technology. The method involves a first continuous drawing of a silver-based alloy rod followed by intermediate annealing to adjust the distribution of grain boundary precipitates while preserving non-recrystallized deformation regions. A second continuous drawing process further refines these non-recrystallized deformation regions, forming subgrains. Subsequent annealing and cooling are then performed to distribute precipitates more extensively at the subgrain boundaries, controlling the formation state of grain boundary precipitates and recrystallized regions. During continuous preparation, process control is achieved through annealing temperature, wire speed, heating zone length, protective atmosphere, and cooling conditions. Sampling tests confirm the formed microstructure. The resulting alloy wire exhibits good strength, plasticity, and microstructure uniformity, improving the stability and consistency of continuous fine drawing, arc forming, and solder bonding.

Description

Technical Field

[0001] This invention relates to the field of alloy manufacturing technology, specifically to a high-performance alloy wire and its preparation method. Background Technology

[0002] Silver-based alloy wires have good conductivity, ductility and bonding adaptability, and are widely used in lead connections in electronic devices. Their performance depends not only on the alloy composition, but also on the grain boundary state, subgrain structure and recrystallization structure formed during drawing and heat treatment.

[0003] Existing silver-based alloy wires are usually produced by melting, drawing and annealing to obtain the required wire diameter and mechanical properties. However, during the annealing process, alloying elements may continuously precipitate along high-angle grain boundaries. If the annealing temperature is further increased or the heating time is extended, it will also promote the expansion and interconnection of recrystallization regions, resulting in the simultaneous occurrence of local embrittlement of grain boundaries and local softening of the microstructure, which affects the uniformity of the microstructure and properties of the alloy wire.

[0004] The above problems are mainly caused by the difficulty in controlling the precipitation location of alloying elements and the continuous expansion of recrystallization regions. Continuous grain boundary precipitation will form intergranular crack channels, and interconnected recrystallization regions will reduce local load-bearing capacity, thereby causing ultrafine drawing wire breakage, decreased tensile strength, elongation fluctuation and dispersion of bonding properties. Summary of the Invention

[0005] The present invention aims to solve the problems of difficulty in controlling the precipitation location of alloying elements during the drawing and annealing process of silver-based alloy wires, easy formation of continuous precipitation along grain boundaries, and continuous expansion and interconnection of recrystallization regions, which affect the uniformity of alloy wire structure, continuous fine drawing stability and bonding performance.

[0006] A method for preparing a high-performance alloy wire includes the following steps: S1. The silver-based alloy rod with a diameter of 9.5 mm to 10.5 mm formed by casting is subjected to the first continuous drawing to produce an alloy wire with a diameter of 0.9 mm to 1.1 mm. The entry line speed of the first pass is 10 mm / s to 20 mm / s, and the single-pass section reduction rate of each pass is 11.5% to 12.5%. No annealing is performed between each pass. S2. The alloy wire is passed through an intermediate annealing zone with an effective heating length of 650mm to 750mm in an argon atmosphere at 475°C to 485°C and at a wire speed of 60m / min to 70m / min. After leaving the intermediate annealing zone, it immediately enters the argon protective cooling section. S3. The alloy wire after intermediate annealing is continuously drawn a second time to produce alloy wire with a diameter of 25μm to 35μm. The entry line speed of the first pass is 10mm / s to 20mm / s. The single-pass section reduction rate of each pass is 7.5% to 8.5%. No annealing is performed between each pass. S4. The alloy wire is passed through a finished product annealing zone with an effective heating length of 650mm to 750mm in an argon atmosphere at 450°C to 460°C and at a wire speed of 60m / min to 70m / min. After leaving the finished product annealing zone, it is immediately cooled under argon protection. The wire is then continuously wound up after the surface temperature of the alloy wire is not higher than 50°C to obtain a high-performance alloy wire.

[0007] The silver-based alloy rod comprises, by weight percentage, 2.5% to 4.5% copper, 2.5% to 4.5% aluminum, 0.5% to 1% palladium, 0.1% to 0.3% platinum, 1% to 1.5% zinc, 100 ppm to 400 ppm rare earth elements, with the balance being silver and unavoidable impurities; The rare earth element is composed of neodymium and europium, and the mass ratio of neodymium to europium is 1:0.1 to 1:0.4.

[0008] Both the first and second wire drawing processes employ a continuous multi-pass drawing method. The linear velocity at the subsequent traction position is increased step by step according to the change in the cross-sectional area of ​​the alloy wire in the preceding and following passes, so that the volumetric flow rate of the alloy wire per unit time remains consistent between adjacent passes.

[0009] Intermediate annealing is performed under stable furnace temperature of 475℃ to 485℃, wire speed of 60m / min to 70m / min, and effective heating length of 650mm to 750mm. Alloy wire is introduced after argon purity is not less than 99.99% and oxygen content in the device is not higher than 50ppm.

[0010] During the second wire drawing process, continuous lubrication is used and the wire drawing die and lubricant are circulated and cooled. No annealing treatment is performed between adjacent passes.

[0011] The finished product annealing adopts a stable furnace temperature of 450℃ to 460℃, a wire speed of 60m / min to 70m / min, and an effective heating length of 650mm to 750mm. The alloy wire is immediately cooled under argon protection after leaving the effective heating area.

[0012] The electron backscatter diffraction and transmission electron microscopes in this invention are used for process calibration, microstructure confirmation and post-production sampling verification during the research and development stage. They are not used as judgment conditions for real-time feedback control or start / stop of processes during continuous production. Continuous production is carried out according to the calibrated furnace temperature, wire speed, effective heating length, atmosphere, drawing and cooling parameters.

[0013] The present invention also provides a high-performance alloy wire, which is composed of a silver-based multi-element alloy and has a microstructure in which the subgrain boundary precipitates are more extensive than the grain boundaries and the recrystallization regions are separated from each other.

[0014] The high-performance alloy wire comprises, by mass percentage, 2.5% to 4.5% copper, 2.5% to 4.5% aluminum, 0.5% to 1% palladium, 0.1% to 0.3% platinum, 1% to 1.5% zinc, 100 ppm to 400 ppm rare earth elements, with the balance being silver and unavoidable impurities. The rare earth elements are composed of neodymium and europium, with the mass ratio of neodymium to europium being 1:0.1 to 1:0.4.

[0015] The high-performance alloy wire has a diameter of 25 μm to 35 μm. Subgrains are formed within the high-performance alloy wire. The coverage of subgrain boundary precipitates is higher than that of grain boundary precipitates, and the ratio of the two is not less than 2.5. The recrystallized regions are separated from each other, and an unrecrystallized deformed region containing the subgrains is retained between adjacent recrystallized regions.

[0016] In a specific embodiment, the alloy is prepared using a specific composition within the range of the alloy composition, and sampling tests are performed on the subgrain size, subgrain boundary precipitate coverage, grain boundary precipitate coverage, recrystallization region area ratio, and minimum boundary spacing between adjacent recrystallization regions.

[0017] The high-performance alloy wire is suitable for continuous wire laying, electrical discharge balling, first solder joint bonding, arc forming and second solder joint bonding processes in integrated circuit packaging.

[0018] This invention provides a high-performance alloy wire and its preparation method, which has the following beneficial effects: By limiting the actual control quantities of continuous production to the number of drawing passes, single-pass section reduction rate, furnace temperature, wire speed, effective heating length, protective atmosphere, and cooling conditions, and by using microstructure parameters for process calibration and sampling verification, the preparation process can be stably executed under continuous high-speed production conditions. At the same time, the microstructure characteristics of preferential distribution of subgrain boundary precipitates and separation of recrystallization regions are maintained, thereby improving the continuous fine drawing, arc forming, and bonding stability of alloy wires. Attached Figure Description

[0019] Figure 1 This is a schematic diagram illustrating the microstructure evolution during the preparation process of a high-performance alloy wire. Figure 2 This is an EBSD orientation diagram after the first wire drawing process; Figure 3 This is an EBSD image of the near-surface region after intermediate annealing; Figure 4 This is an EBSD plot of the central region after intermediate annealing; Figure 5TEM image of grain boundary precipitates after intermediate annealing; Figure 6 TEM image of subgrain after the second wire drawing process; Figure 7 This is a microstructure diagram of the subcrystalline structure after the second wire drawing process. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] Example 1

[0022] This embodiment uses fine-pitch wire bonding between chip pads and lead frames in integrated circuit packaging as an application scenario. In this scenario, the alloy wire needs to sequentially complete continuous wire feeding, EDM balling, first solder joint bonding, arc forming, and second solder joint bonding. It must withstand continuous stretching, bending, and localized heat generated by EDM balling while maintaining a small diameter. Therefore, in addition to possessing sufficient tensile strength, the alloy wire also needs to maintain appropriate plasticity and a relatively uniform internal structure along its length. This prevents wire breakage, arc height fluctuations, or solder joint tension dispersion during the fine drawing, feeding, arc forming, and solder joint formation processes due to continuous distribution of grain boundary precipitates, localized excessive recrystallization, or uneven distribution of the hardness of the microstructure.

[0023] The alloy rod referred to in this application is a silver-based alloy rod with silver as the matrix. The alloy rod used in Example 1 includes, by mass percentage, 3.5% copper, 3.5% aluminum, 0.75% palladium, 0.20% platinum, 1.30% zinc, 200ppm neodymium, and 50ppm europium, with the balance being silver and unavoidable impurities. No alloying elements are intentionally added or removed during the subsequent wire drawing and annealing processes.

[0024] In this application, electron backscatter diffraction, transmission electron microscopy, and focused ion beam sample preparation are all used for process calibration, microstructure confirmation, and post-production sampling verification during the R&D phase. During continuous production, the coverage of grain boundary precipitates, the area ratio of non-recrystallized deformation regions, subgrain size, length of continuous precipitate segments, area ratio of recrystallized regions, or boundary spacing are not used as online feedback control quantities. Furthermore, offline microscopic inspection is not required for each roll before release. After process calibration is completed, continuous operation is performed according to the determined drawing passes, single-pass section shrinkage rate, furnace temperature, wire speed, effective heating length, protective atmosphere, and cooling conditions.

[0025] This embodiment provides a method for preparing high-performance alloy wire. Please refer to [link / reference]. Figures 1 to 7 This includes the following steps.

[0026] To facilitate the identification and statistical analysis of the organizational state in this embodiment, interfaces with an orientation difference of not less than 15° between adjacent grains are identified as grain boundaries, and interfaces located inside grains with an orientation difference of not less than 2° and less than 15° between adjacent regions are identified as subgrain boundaries.

[0027] Grain boundary precipitate coverage refers to the ratio of the sum of the projected lengths of the precipitates along the grain boundary direction to the total length of the observed grain boundary; subgrain boundary precipitate coverage refers to the ratio of the sum of the projected lengths of the precipitates along the subgrain boundary direction to the total length of the observed subgrain boundary.

[0028] The non-recrystallized deformation region refers to the region that still retains the orientation characteristics of the drawing direction, has an orientation gradient and substructure within the grain, and has not yet been transformed into recrystallized grains with uniform internal orientation. The subgrain equivalent size is characterized by the average equivalent circle diameter of the subgrain. The average equivalent circle diameter of the subgrain refers to the diameter obtained by converting the area of ​​a single subgrain on the observation section into an equal-area circle, and taking the average value of the equivalent circle diameters of the subgrains within the corresponding observation area. The edge spacing between adjacent recrystallized regions refers to the shortest straight-line distance between the boundaries of two adjacent and non-connected recrystallized regions, also known as the minimum boundary spacing between adjacent recrystallized regions.

[0029] In this embodiment, the first and second wire drawing speeds refer to the entry linear speed of the first pass in the corresponding wire drawing stage. During multiple consecutive wire drawing passes, each pass is equipped with a traction wheel or drum. The linear speed at the next traction position is increased synchronously according to the change in the cross-sectional area of ​​the alloy wire in the preceding and following passes, so that the volumetric flow rate of the alloy wire per unit time in adjacent passes remains consistent. Furthermore, the traction tension is controlled to prevent the alloy wire from becoming loose or over-tight between adjacent passes. Therefore, the 15 mm / s mentioned in the first and second wire drawing passes refers to the entry linear speed of the first pass, and not the same linear speed is used at the die in each pass.

[0030] S1, First continuous wire drawing S1. The silver-based alloy rod with a diameter of 10mm formed by casting is continuously drawn into an alloy wire with a diameter of 1mm through 36 passes. The entry line speed of the first pass is set to 15mm / s, and the single-pass section reduction rate of each pass is set to 12.01%. No annealing treatment is performed between each pass.

[0031] According to the target composition of 3.5% copper, 3.5% aluminum, 0.75% palladium, 0.20% platinum, 1.30% zinc, 200 ppm neodymium, and 50 ppm europium, silver, copper, aluminum, palladium, platinum, and zinc were weighed out, and a silver-based master alloy containing neodymium and europium was also weighed out, so that the mass ratio of neodymium to europium was 1:0.25. The weighed raw materials were placed in a vacuum melting device and heated to 1350°C under vacuum protection to completely melt and mix the raw materials evenly. After the melt state stabilized, continuous casting was carried out at a casting speed of 30 mm / s to obtain an alloy rod with a diameter of 10 mm. After the obtained alloy rod was cooled to room temperature, its surface was cleaned to remove oil, metal particles, and oxides attached to the surface, and the surface of the alloy rod was checked for folds, cracks, obvious pits, and other defects that would affect continuous wire drawing.

[0032] After melting and casting, neodymium and europium exist in one or more of the following states: solid solution atoms, rare earth-containing second phases, or interfacial segregation. During subsequent annealing, they hinder the migration of grain boundaries and subgrain boundaries to preserve the subgrain structure and limit the continued expansion of the recrystallization region. Their specific state of existence is not limited to a certain fixed compound.

[0033] A 10mm diameter alloy rod is installed at the feed end of a continuous multi-pass wire drawing machine and passes through 36 wire drawing dies sequentially. The wire drawing speed for the first pass is set to 15mm / s, and the single-pass section reduction rate for each pass is set to 12.01%. During the wire drawing process, alloy wire drawing lubricant is used to continuously lubricate the alloy rod and the wire drawing dies, and the wire feed direction for each pass is kept consistent with the center of the die hole.

[0034] In this embodiment, the first wire drawing pass is set to 36 passes because, under the condition that the cross-sectional reduction rate of a 10mm diameter alloy rod is 12.01% per pass, the theoretical diameter after 35 wire drawing passes is approximately 1.066mm, which has not yet reached the target diameter of 1mm. The theoretical diameter after 36 wire drawing passes is approximately 0.9995mm, which corresponds to the target diameter of 1mm. Increasing the number of passes to 37 would reduce the theoretical diameter to approximately 0.938mm. Therefore, 36 passes are used to complete the first wire drawing process from a diameter of 10mm to a diameter of 1mm.

[0035] During the first wire drawing process, the exit traction speed of each pass is adjusted according to the ratio of the cross-sectional area of ​​the alloy wire in the previous pass to the cross-sectional area of ​​the alloy wire in the current pass. Under the condition that the section shrinkage rate of a single pass is 12.01%, the speed is increased step by step. After completing 36 wire drawing passes, the exit speed of the last pass is about 1.50 m / s.

[0036] After the alloy rod passes through 36 drawing dies, it forms an alloy wire with a nominal diameter of 1 mm. Based on a single-pass section reduction rate of 12.01%, the theoretical diameter of a 10 mm diameter alloy rod after 36 drawing passes is 0.9995 mm, which corresponds to the nominal diameter of 1 mm. Therefore, no separate diameter adjustment drawing step is required.

[0037] The 12.01% single-pass section reduction rate was determined by reversing the target of 1mm diameter after 36 passes of wire drawing of an alloy rod with a diameter of 10mm. Under the condition that the same section reduction rate is used in each pass, the calculated single-pass section reduction rate is about 12.0077%, which is determined to be 12.01% after rounding to two decimal places.

[0038] No annealing is performed during the first wire drawing process. The deformed structure formed in the previous pass is directly transferred to the next pass without heat treatment, allowing plastic deformation to accumulate continuously between passes. During the wire drawing process, the die cooling and lubricant circulation are controlled to avoid scratches on the alloy wire surface and abnormal local deformation caused by die temperature rise or lubrication failure.

[0039] After the first wire drawing, samples were taken from the front, middle, and rear sections of the alloy wire. A longitudinal observation section was prepared along the axial direction of the sample, and after mounting, grinding, polishing, and ion thinning, electron backscatter diffraction was performed. At least 10 independent observation areas were selected at each sampling location. Unrecrystallized deformation areas were identified based on grain orientation expansion values ​​and pull-out orientation gradients, and the proportion of their sum to the total area of ​​the observation areas was calculated.

[0040] Statistical results show that the area of ​​the non-recrystallized deformation region after the first wire drawing is 85%. This microstructure indicates that 36 consecutive wire drawing passes have formed a sufficiently deformed structure inside the alloy wire, providing a microstructure basis for retaining the non-recrystallized deformation region after subsequent intermediate annealing and for the formation of subgrains during the second wire drawing.

[0041] S2, Intermediate Annealing S2. The alloy wire with a diameter of 1mm after the first continuous drawing is passed through an intermediate annealing zone with an effective heating length of 700mm at a speed of 65m / min in an argon atmosphere at 480℃. After leaving the intermediate annealing zone, it immediately enters the argon protective cooling section.

[0042] The intermediate annealing temperature mentioned in this embodiment refers to the stable furnace temperature of the effective heating area of ​​the continuous annealing device. First, the furnace temperature of the effective heating area is set to 480℃ and stabilized for 30 minutes. Then, calibrated temperature measuring elements are used to detect the inlet, middle and outlet positions of the effective heating area along the wire routing direction. When the deviation of the measured temperature at each position from 480℃ is no more than 2℃, argon gas with a purity of 99.999% is continuously introduced to replace the air in the device. After the oxygen content in the device is no higher than 50ppm, the alloy wire is introduced.

[0043] The alloy wire with a diameter of 1 mm after the first drawing is continuously passed through the annealing device along the center of the effective heating zone. The wire speed is set to 65 m / min and the effective heating length is set to 700 mm. The effective heating time referred to in this embodiment is the theoretical dwell time required for the alloy wire to pass through the effective heating zone at the set wire speed. It is calculated as 0.646 s by dividing the effective heating length by the wire speed. The stable furnace temperature of 480℃ and the theoretical dwell time of 0.646 s are used together as the process control conditions for intermediate annealing.

[0044] For the radial heat transfer timescale of 0.646s short-time continuous annealing, a conservative calculation was performed based on the radial transient heat conduction of cylindrical wire during process calibration. To avoid overestimating the thermal conductivity of the silver-based alloy, a thermal conductivity of 50 W / (m·K) and a density of 1.0 × 10⁻⁶ were used. 4 With a specific heat capacity of 250 J / (kg·K) and a thermal diffusivity of 2.0 × 10⁻⁻⁻⁶, calculated using α = k / (ρc), the thermal diffusivity is given as 250 J / (kg·K). 5 m² / s, where α is the thermal diffusivity in m² / s, k is the thermal conductivity in W / (m·K), ρ is the material density in kg / m³, and c is the specific heat capacity in J / (kg·K); then, the radial characteristic thermal diffusion time r² / α is calculated using an alloy wire with a diameter of 1 mm and a radius of 0.5 mm, where r is the radius of the alloy wire in m, and r² / α is the radial characteristic thermal diffusion time obtained by using the radius of the alloy wire as the radial heat transfer characteristic length, used to characterize the time scale corresponding to the diffusion of heat from the surface of the alloy wire to the core. The radial characteristic thermal diffusion time r² / α is 0.0125s. Based on the effective heating length and wire speed, the time for the alloy wire to pass through the effective heating area is calculated to be 0.646s. The time to pass through the effective heating area is approximately 51.7 times the radial characteristic thermal diffusion time, indicating that the radial temperature difference between the core and the surface can rapidly decay within the time scale of passing through the effective heating area. This calculation is used to determine the core-to-surface heat transfer time scale, and the 480℃ furnace temperature is not equated with the instantaneous actual temperature of the wire. The effectiveness of the intermediate annealing process is verified by the microstructure obtained from the sampling after annealing.

[0045] The alloy wire passes through the effective heating zone once at a constant wire speed, without stopping or repeating intermediate annealing within the effective heating zone. After leaving the effective heating zone, the alloy wire immediately enters the argon-protected cooling section, where room temperature argon is continuously purged and cooled along the wire direction. The surface temperature of the alloy wire is detected by an online non-contact temperature measuring device located at the outlet of the cooling section. Once the surface temperature is no higher than 50°C, the wire is continuously wound up.

[0046] After intermediate annealing, samples were taken from the front, middle, and rear sections of the alloy wire. The area ratio of the non-recrystallized deformation region was detected by electron backscatter diffraction. Based on the grain boundary positions obtained by electron backscatter diffraction, transmission electron microscope (TEM) samples were prepared at the corresponding positions using focused ion beam (FIB) microscopy. The precipitates at the grain boundaries were observed using TEM microscopy.

[0047] At each sampling location, select no fewer than 10 grain boundaries for statistical analysis. Measure the projected length of the precipitates along the grain boundary direction. Divide the sum of the projected lengths of each precipitate by the total length of the observed grain boundaries to obtain the grain boundary precipitate coverage.

[0048] The test results show that the grain boundary precipitate coverage rate after intermediate annealing is 25%, and the area of ​​the non-recrystallized deformation region accounts for 60%.

[0049] Therefore, under the fixed intermediate annealing conditions of 480℃, 65m / min and 700mm, the non-recrystallized deformation area, which accounts for 85% of the area after the first wire drawing, undergoes limited recovery and local recrystallization. After annealing, sampling and testing showed that the non-recrystallized deformation area accounts for 60% of the area, and the grain boundary precipitate coverage is 25%.

[0050] The aforementioned grain boundary precipitate coverage and non-recrystallized deformation area ratio are used to verify the stage microstructure formed under fixed intermediate annealing conditions of 480℃, 65m / min and 700mm. They do not participate in the real-time feedback of the running production line, nor are they used as release trigger conditions before each roll is transferred to the second drawing process. After the process calibration is completed, the corresponding batch is transferred to the second drawing process according to the predetermined process sequence, and offline sampling verification is carried out according to the specified batches.

[0051] S3, Second Continuous Drawing S3. The alloy wire with a diameter of 1mm after intermediate annealing and cooling is drawn into an alloy wire with a diameter of 30μm through 84 continuous wire drawing passes. The entry line speed of the first pass is set to 15mm / s, and the single-pass section reduction rate of each pass is set to 8.01%. No annealing treatment is performed between each pass.

[0052] The 1mm diameter alloy wire, after intermediate annealing and cooling to room temperature, is installed at the wire feeding end of a continuous multi-pass fine drawing machine and passes through 84 fine drawing dies in sequence.

[0053] The drawing speed for the second drawing was set to 15 mm / s, and the single-pass section reduction rate for each pass was set to 8.01%. No annealing was performed between adjacent drawing passes. After the alloy wire completed the previous drawing pass, it directly entered the next pass, allowing the non-recrystallized deformation area retained after intermediate annealing to continue to undergo continuous plastic deformation.

[0054] During the second wire drawing process, the exit traction speed of each pass is adjusted according to the ratio of the cross-sectional area of ​​the alloy wire in the previous pass to the cross-sectional area of ​​the alloy wire in the current pass. Under the condition that the section shrinkage rate of a single pass is 8.01%, the speed is increased step by step. After completing 84 wire drawing passes, the exit speed of the final pass is approximately 16.67 m / s.

[0055] The 36 passes and 12.01% single-pass shrinkage rate of the first wire drawing, and the 84 passes and 8.01% single-pass shrinkage rate of the second wire drawing, were all determined based on the initial diameter, target diameter, and equal shrinkage rate conditions of the corresponding stages. In the first wire drawing, the diameter was reduced from 10 mm to 1 mm, and the single-pass shrinkage rate calculated in reverse was approximately 12.0077%. In the second wire drawing, the diameter was reduced from 1 mm to 30 μm, and the single-pass shrinkage rate calculated in reverse was approximately 8.0099%. These were determined to be 12.01% and 8.01% respectively after rounding to two decimal places. At the same time, a smaller single-pass shrinkage rate was used in the second wire drawing to reduce the risk of wire breakage caused by the continuous reduction of wire diameter and the accumulation of work hardening.

[0056] Continuous lubrication is used during the second wire drawing process, and the die and lubricant are circulated and cooled to avoid local recovery, surface damage, or wire diameter fluctuations caused by die temperature rise during the fine-diameter wire drawing stage. A stable drawing speed and take-up tension are maintained in each pass, and no independent heat treatment is added between passes.

[0057] An alloy wire with a diameter of 1 mm is drawn into an alloy wire with a diameter of 30 μm after 84 drawing passes. Based on 84 passes and a single pass section reduction rate of 8.01%, the theoretical diameter after all passes is 29.999 μm, which matches the target diameter of 30 μm.

[0058] The single-pass reduction of area used in the second wire drawing is less than that used in the first wire drawing, in order to reduce the risk of local stress concentration and wire breakage caused by excessive deformation in a single pass during the thin-diameter wire drawing process. Annealing is not performed between adjacent passes, so that the non-recrystallized deformation area retained after intermediate annealing is further subdivided under continuous deformation and subgrain boundaries are formed within the original grains.

[0059] After the second wire drawing was completed, samples were taken from the front, middle, and rear sections of the alloy wire. Electron backscatter diffraction was performed on the longitudinal cross-section of the samples, and the results were verified using transmission electron microscopy.

[0060] Subgrains are identified as regions located within the original grain and surrounded by subgrain boundaries with an orientation difference of not less than 2° and less than 15°. The area of ​​each subgrain on the observation section is measured, and the equivalent circle diameter of the subgrain is calculated using the following formula: The diameter of the subcrystalline equivalent circle is twice the square root of the ratio of the subcrystalline area to pi.

[0061] At least 100 subgrains were sampled at each sampling location, and the average equivalent circle diameter of all subgrains was calculated. The test results show that the average equivalent circle diameter of the subgrains formed after the second wire drawing is 0.20 μm.

[0062] The electron backscattering diffraction orientation pattern also indicates that the subgrains are formed in the non-recrystallized deformation region retained after intermediate annealing, rather than in the equiaxed grains that have already undergone recrystallization.

[0063] Thus, S3 not only draws the alloy wire from 1mm to an alloy wire with a diameter of 30μm, but also utilizes the non-recrystallized deformation region retained in S2 to form subgrains with an average equivalent circle diameter of 0.20μm and corresponding subgrain boundaries, thereby providing an interface basis for the precipitates to form a high degree of coverage at the subgrain boundaries during the annealing process of the finished product.

[0064] S4, Finished product annealing and cooling, winding up S4. The alloy wire with a diameter of 30μm after the second drawing is passed through the finished product annealing zone with an effective heating length of 700mm at 455℃ in an argon atmosphere and at a wire speed of 65m / min.

[0065] The alloy wire with a diameter of 30μm after the second drawing is continuously introduced into an argon-protected continuous annealing device. The finished product annealing temperature mentioned in this embodiment refers to the stable furnace temperature of the effective heating area of ​​the continuous annealing device. First, the furnace temperature of the effective heating area is set to 455℃ and stabilized for 30 minutes. Then, calibrated temperature measuring elements are used to detect the entrance, middle and exit positions of the effective heating area along the wire direction. When the deviation of the measured temperature at each position from 455℃ is not greater than 2℃, the finished product annealing begins.

[0066] Argon gas with a purity of 99.999% is introduced into the continuous annealing apparatus to replace the interior of the apparatus; when the oxygen content in the apparatus is not higher than 50 ppm, the alloy wire is introduced.

[0067] The alloy wire is continuously passed through the center of the effective heating area. The wire speed is set to 65m / min and the effective heating length is set to 700mm. The theoretical residence time of the alloy wire in the effective heating area is calculated by dividing the effective heating length by the wire speed. The stable furnace temperature of 455℃ and the theoretical residence time of 0.646s are used together as the process control conditions for the annealing of the finished product.

[0068] Calculations were performed using the same conservative thermophysical parameters as intermediate annealing. For an alloy wire with a diameter of 30 μm and a radius of 15 μm, the radial characteristic thermal diffusion time r² / α is approximately 1.13 × 10⁻⁻⁻⁶. 5 s, where r is the radius of the alloy wire and α is the thermal diffusivity; based on the effective heating length and wire speed during the finished product annealing process, the time for the alloy wire to pass through the effective heating region is calculated to be 0.646s, which is approximately 5.7 × 10⁻⁶ times the radial characteristic thermal diffusivity time. 4 Therefore, the radial heat transfer time scale from the surface to the core inside the 30μm alloy wire is much smaller than the time scale of its passage through the effective heating area; this calculation is used to determine the radial heat transfer time scale during the annealing process of the finished product, and is not used to indicate that the alloy wire instantaneously reaches the furnace temperature. The distribution of precipitates and recrystallization structure after the finished product is still confirmed by offline sampling and testing.

[0069] The alloy wire passes through the effective heating zone only once, without stopping or repeating the finished product annealing within the effective heating zone. After leaving the effective heating zone, the alloy wire immediately enters the argon-protected cooling section, so that the distribution of subgrains, precipitates, and recrystallization zones formed during the finished product annealing are preserved during the continuous cooling process.

[0070] The finished product annealing temperature is 455℃, lower than the intermediate annealing temperature of 480℃. This is because the diameter of the alloy wire after the second drawing has decreased to 30μm, and both the heating and cooling rates are higher than those of an intermediate-annealed wire with a diameter of 1mm. Furthermore, subgrains with an average equivalent circular diameter of 0.20μm have already formed inside the alloy wire. Using a short continuous annealing process at 455℃ for 0.646s allows for adjustment of the precipitate distribution at subgrain boundaries and grain boundaries while preserving some of the subgrain structure.

[0071] It should be noted that although both intermediate annealing and finished annealing adopt the treatment method of short-time continuous passage through the annealing zone, the treatment objects and the effects on microstructure formation are different. Intermediate annealing is applied to 1mm alloy wire after the first drawing to adjust the deformed microstructure and grain boundary precipitation state after the first drawing. Finished annealing is applied to 30μm alloy wire after the second drawing to further adjust the distribution of precipitates and the degree of recrystallization on the basis of the already formed subgrain microstructure. Continuous production is carried out according to fixed process conditions of 480℃, 65m / min, 700mm and 455℃, 65m / min, 700mm, respectively.

[0072] After the finished product is annealed, samples are taken from the front, middle, and rear sections of the alloy wire. Electron backscatter diffraction is used to identify the locations of grain boundaries and subgrain boundaries. Then, transmission electron microscopy samples are prepared at the corresponding locations using focused ion beam, and the positional relationship between the precipitates and the subgrain boundaries or grain boundaries is confirmed using transmission electron microscopy.

[0073] At each sampling location, no fewer than 10 subgrain boundaries and 10 grain boundaries were selected for statistical analysis. The subgrain boundary precipitate coverage was calculated as the ratio of the sum of the projected lengths of the precipitates along the subgrain boundary direction to the total length of the observed subgrain boundaries; the grain boundary precipitate coverage was calculated as the ratio of the sum of the projected lengths of the precipitates along the grain boundary direction to the total length of the observed grain boundaries.

[0074] The test results show that the coverage of subgrain boundary precipitates after annealing is 52%, and the coverage of grain boundary precipitates is 14%, with a ratio of: 52% ÷ 14% = 3.71.

[0075] Further measurements were taken of the continuous precipitate segments at subgrain boundaries and grain boundaries. At each sampling location, no fewer than 50 continuous precipitate segments and their corresponding non-precipitate intervals were counted.

[0076] Further analysis of the continuous precipitate segments revealed that the length of a single continuous precipitate segment on the subgrain boundary ranged from 0.04 μm to 0.12 μm, with an average length of 0.08 μm. The interval between adjacent non-precipitate segments ranged from 0.05 μm to 0.16 μm, with an average interval of 0.10 μm. On the grain boundary, the length of a single continuous precipitate segment ranged from 0.08 μm to 0.19 μm, with an average length of 0.15 μm. The interval between adjacent non-precipitate segments ranged from 0.06 μm to 0.12 μm, with an average interval of 0.08 μm.

[0077] The above length and interval data were obtained based on all continuous precipitate segments counted at each sampling location. At each sampling location, no fewer than 50 continuous precipitate segments and corresponding non-precipitate intervals were counted. The length of a continuous precipitate segment was determined by the projected length of a single continuous precipitate distribution area along the corresponding grain boundary or subgrain boundary direction. The non-precipitate interval was determined by the shortest interface length between the edges of two adjacent continuous precipitate segments on the same grain boundary or subgrain boundary.

[0078] The above test results show that the coverage of precipitates at subgrain boundaries is significantly higher than that at grain boundaries. However, the precipitates at subgrain boundaries are still distributed in the form of continuous segments that are spaced apart from each other, and no completely continuous precipitate layer is formed. Similarly, no precipitate-free intervals are retained at grain boundaries, and no precipitate channels that extend continuously along the grain boundaries are formed.

[0079] The above sampling results show that the microstructure formed by fixed intermediate annealing and second wire drawing can provide a subgrain boundary basis for finished product annealing. After finished product annealing, the coverage rate of subgrain boundary precipitates was measured to be 52% and the coverage rate of grain boundary precipitates was 14%. The precipitates were more distributed in the subgrain boundaries inside the grains, while ordinary grain boundaries still retained precipitate-free intervals.

[0080] Cooling after annealing and obtaining the finished product The alloy wire that has completed the finished annealing is immediately put into the argon-protected cooling section, and the surface temperature of the alloy wire is detected at the outlet of the cooling section. After the surface temperature is not higher than 50°C, the wire is continuously wound up to obtain a high-performance alloy wire with a diameter of 30μm.

[0081] After the finished product is annealed, the alloy wire directly enters the argon-protected cooling section for continuous cooling and winding, eliminating the need for a step to determine the annealing endpoint based on real-time microstructure detection.

[0082] In this embodiment, an alloy wire with a diameter of 30 μm is annealed in one continuous process at an annealing temperature of 455℃, a wire speed of 65 m / min, and an effective heating length of 700 mm. The alloy wire is heated in the effective heating area for 0.646 s and then leaves the effective heating area and immediately enters the argon-protected cooling section without repeated annealing.

[0083] In the early process calibration stage, offline sampling and testing of fixed annealing parameter combinations confirmed that the combination of 455℃, 65m / min and 700mm could form the corresponding precipitate distribution and recrystallization structure. Therefore, the continuous preparation process was directly operated according to this set of fixed parameters. The structure test was used for calibration confirmation and subsequent sampling verification, and did not participate in the real-time feedback of the production line.

[0084] After the finished product is annealed, electron backscatter diffraction is used to detect the recrystallization area. The recrystallization area is identified as the area with uniform internal orientation, internal orientation extension value of grains not greater than 1° and no longer with obvious pull-out orientation gradient. The area ratio of the recrystallization area is obtained by dividing the sum of the areas of the identified recrystallization areas by the total area of ​​the corresponding observation area.

[0085] At least 10 observation areas were selected in the front, middle and rear sections of the alloy wire for statistical analysis, and the area ratio of the recrystallized region was found to be 18%.

[0086] Adjacent but unconnected recrystallized regions were identified in the same electron backscatter diffraction orientation pattern. The shortest straight-line distance between the boundaries of two adjacent recrystallized regions was measured and used as the minimum boundary spacing between adjacent recrystallized regions. The test results showed that the minimum boundary spacing between adjacent recrystallized regions was 0.8 μm.

[0087] The maximum intercept of a single recrystallization region was measured along the radial direction of the alloy wire. The maximum intercept of a single recrystallization region along the radial direction of the alloy wire was 8 μm, which is 26.67% of the diameter of the alloy wire with a diameter of 30 μm.

[0088] There is no direct connection between adjacent recrystallization regions. Instead, there is a non-recrystallized deformation region containing subgrains with an average equivalent circle diameter of 0.20 μm. Precipitates are distributed on the subgrain boundaries in the non-recrystallized deformation region, thereby keeping the adjacent recrystallization regions separated from each other.

[0089] After the finished product is collected, offline microstructure analysis is performed on the samples from the front, middle and rear sections. The recrystallization area ratio is 18% and the minimum boundary distance between adjacent recrystallization areas is 0.8 μm. These values ​​are used to characterize the final microstructure formed under fixed annealing conditions and are not used as online control quantities to determine when to stop annealing during continuous production.

[0090] After the finished product is annealed, the alloy wire is continuously purged and cooled with room temperature argon gas. The surface temperature of the alloy wire is detected by an online non-contact temperature measuring device set at the outlet of the cooling section. After the surface temperature is not higher than 50°C, the wire is continuously wound up according to the set winding tension to obtain a high-performance alloy wire with a diameter of 30μm.

[0091] The Examples 1 and Comparative Examples used in Tables 1 to 3 were all actually prepared according to the corresponding preparation conditions. Each group was subjected to tissue testing and performance testing according to the same sampling location, number of samples and testing methods. The tissue parameters listed in Tables 1 to 3 were obtained by offline sampling after the corresponding process was completed and were not involved in the real-time control of continuous production. The tensile strength, elongation and bonding performance were taken as the arithmetic mean of the test results of the corresponding number of samples.

[0092] To verify whether the preparation method described in Example 1 can synergistically improve the high-performance alloy wire in terms of breaking force, elongation, continuous fine drawing stability, arc forming consistency and weld connection performance, comparative experiments were conducted with Comparative Examples 1 to 3 compared with Example 1.

[0093] Example 1 and Comparative Examples 1 to 3 all selected alloy rods with the same casting batch, a diameter of 10 mm and the same alloy composition as raw materials. Five rolls of samples were set up in each group. The same continuous multi-pass wire drawing equipment, wire drawing die, lubricant, die cooling conditions and take-up tension were used in each group.

[0094] The first drawing of each group involved 36 consecutive drawing passes at a speed of 15 mm / s. The single-pass section shrinkage rate of each pass was 12.01%. Alloy rods with a diameter of 10 mm were drawn into alloy wires with a nominal diameter of 1 mm. No annealing was performed during the first drawing process.

[0095] Each group's second drawing process involved 84 consecutive drawing passes at a speed of 15 mm / s. The single-pass section shrinkage rate for each pass was 8.01%. No annealing was performed between adjacent passes. Alloy wires with a diameter of 1 mm were drawn into alloy wires with a diameter of 30 μm.

[0096] The 15 mm / s mentioned in each group refers to the entry linear velocity of the first pass in the corresponding wire drawing stage. The traction linear velocity of each subsequent pass is increased step by step according to the same single-pass cross-sectional shrinkage rate and the change relationship of the cross-sectional area of ​​the alloy wire, thereby ensuring that Example 1 and each comparative example use the same wire drawing speed to control the diameter.

[0097] All annealing was carried out under argon gas with a purity of 99.999%. After annealing, the wires or alloy wires were immediately placed in the argon-protected cooling zone and continuously wound up using the same winding tension. The sampling locations, tensile test conditions, EDM balling conditions, bonding parameters, and testing methods were all the same for each group.

[0098] Example 1 was prepared according to the aforementioned specific implementation method. After the first wire drawing, intermediate annealing was carried out under fixed conditions of 480°C, 65m / min and 700mm. After the second wire drawing, finished product annealing was carried out under fixed conditions of 455°C, 65m / min and 700mm. After the alloy wire left the finished product annealing area, it immediately entered the argon protective cooling section and was continuously wound up.

[0099] The difference between Comparative Example 1 and Example 1 is that intermediate annealing is omitted. After obtaining an alloy wire with a diameter of 1 mm by the first wire drawing, the distribution of grain boundary precipitates and the non-recrystallized deformation area formed by the first wire drawing are not adjusted in the intermediate stage. Instead, the second wire drawing and finished product annealing are carried out directly under the same conditions as in Example 1.

[0100] The difference between Comparative Example 2 and Example 1 is that the intermediate annealing degree is increased. Comparative Example 2 uses an intermediate annealing temperature of 500°C, a wire speed of 55 m / min, and an effective heating length of 800 mm. The effective heating time is 0.873 s, which makes the amount of non-recrystallized deformation area retained after intermediate annealing lower than that in Example 1. Its first drawing, second drawing, and finished product annealing conditions are the same as those in Example 1.

[0101] The conditions for the first wire drawing, intermediate annealing, and second wire drawing of Comparative Example 3 were the same as those of Example 1. The difference was that the degree of annealing of the finished product was increased. Comparative Example 3 used a finished product annealing temperature of 470°C, a wire speed of 55 m / min, and an effective heating length of 800 mm. The effective heating time was 0.873 s, which made the subgrain boundaries disappear further and the recrystallization region continue to expand during the finished product annealing process.

[0102] In Comparative Example 3, the annealing temperature, wire speed, and effective heating length of the finished product were adjusted simultaneously to achieve a higher degree of annealing than in Example 1 through the combined change of the three parameters. The comparison results are used to illustrate the changes in microstructure and properties caused by the excessive combined effect of the finished product annealing, and are not used to distinguish the independent effects of any single parameter.

[0103] Fifty finished alloy wires were randomly selected from each group for tensile testing. The gauge length of the specimen was 100 mm and the tensile speed was 10 mm / min. The number of wire breaks was counted according to the continuous preparation length of 100 km for each group. 200 sets of wire bonding tests were completed using the same parameters for electric spark balling, first solder joint bonding, arc forming and second solder joint bonding. The arc height, first solder joint tension and second solder joint tension were recorded.

[0104] The comprehensive performance test results of Example 1 and Comparative Examples 1 to 3 are shown in Table 1.

[0105] Table 1: Effects of different preparation methods on the comprehensive application performance of high-performance alloy wires; Finished alloy wire diameter / μm 30 30 30 30 Tensile strength / gf 17.1 17.9 14.2 14.6 Elongation / % 13.2 7.8 14.5 13.9 Number of consecutive wire breakages per 100km⁻¹ 0.6 3.4 2.3 1.9 Curve height variation coefficient / % 2.9 6.8 7.3 6.5 Average tensile force at the first weld point / gf 8 6.7 6.9 7.1 Average tensile force at the second weld point / gf 6.3 5.3 5.5 5.7 As can be seen from Table 1, Example 1 does not simply achieve the highest breaking force or the highest elongation, but rather achieves a good overall balance among breaking force, elongation, continuous fabrication stability, arc forming consistency, and weld joint connection performance.

[0106] In Comparative Example 1, after the intermediate annealing was eliminated, the high-density deformed structure, grain boundary precipitate distribution, and residual deformation state formed in the first wire drawing were directly entered into the second wire drawing without intermediate adjustment. The resulting alloy wire had a breaking force of 17.9 gf, which was slightly higher than 17.1 gf in Example 1, but the elongation was only 7.8%, which was significantly lower than 13.2% in Example 1. The number of consecutive wire breaks reached 3.4 times / 100km, the coefficient of variation of arc height reached 6.8%, and the average tensile force of the first and second weld points were 6.7 gf and 5.3 gf, respectively.

[0107] The results indicate that while eliminating intermediate annealing can retain a high degree of deformation strengthening, it fails to establish an intermediate microstructure suitable for the formation of uniform subgrains during the second wire drawing. This reduces the plasticity of the alloy wire and the consistency of deformation at different locations, thereby increasing the breakage of fine-diameter wires and fluctuations in arc forming.

[0108] After increasing the intermediate annealing degree in Comparative Example 2, the elongation of the resulting alloy wire reached 14.5%, but the breaking force decreased to 14.2 gf. The number of consecutive wire breaks reached 2.3 times / 100km, the coefficient of variation of arc height reached 7.3%, and the average tensile force of the first weld point and the average tensile force of the second weld point were 6.9 gf and 5.5 gf, respectively, both lower than those in Example 1.

[0109] The results indicate that excessive intermediate annealing will eliminate too much of the non-recrystallized deformation area formed during the first wire drawing. Although the second wire drawing can still draw the alloy wire to 30 μm, it lacks sufficient and properly formed deformation areas to form uniform subgrains. This results in the finished alloy wire exhibiting high plasticity but insufficient internal load-bearing capacity, and producing a large arc height dispersion.

[0110] After improving the annealing degree of the finished product in Comparative Example 3, the resulting alloy wire had a breaking force of 14.6 gf, an elongation of 13.9%, a continuous breakage rate of 1.9 times / 100km, a curve height variation coefficient of 6.5%, and average tensile forces of the first and second weld points of 7.1 gf and 5.7 gf, respectively.

[0111] The results indicate that under the annealing conditions of higher finished product annealing temperature, lower wire speed and longer effective heating length used in Comparative Example 3, some subgrain boundaries formed by the second wire drawing disappear, reducing the distribution advantage of precipitates at the subgrain boundaries and causing the recrystallized regions to continue to grow and approach each other, resulting in local softening, reducing tensile strength, arc forming consistency and solder joint connection performance.

[0112] The alloy wire obtained in Example 1 has a breaking strength of 17.1 gf and an elongation of 13.2%, which avoids the high strength and low plasticity problem of Comparative Example 1, as well as the problem of increased plasticity but significantly decreased breaking strength in Comparative Examples 2 and 3.

[0113] In Example 1, the number of wire breaks during continuous preparation was only 0.6 times / 100km, which was 82.35%, 73.91%, and 68.42% lower than that of Comparative Examples 1, 2, and 3, respectively. The coefficient of variation of the arc height was 2.9%, which was significantly lower than that of the comparative examples, indicating that the arc forming state of the alloy wire along the length direction was more consistent.

[0114] In Example 1, the average tensile force of the first and second solder joints reached 8.0 gf and 6.3 gf respectively, both higher than those of the comparative examples. This indicates that the alloy wire obtained in Example 1 can maintain a relatively stable connection state during continuous wire feeding, electrical discharge balling, first solder joint bonding, arc forming, and second solder joint bonding.

[0115] Among them, the number of wire breaks during continuous preparation: starting from the second wire drawing, the total number of wire breaks that occurred during the period from the finished product annealing, cooling and continuous winding end is counted, and is calculated based on 100km of alloy wire produced continuously.

[0116] Curve height variation coefficient: Under the same bonding span, balling parameters and bonding parameters, 200 sets of wire bonding were completed. The vertical distance between the highest point of the arc between the first and second solder joints of each set and the reference plane was measured. The result was calculated by dividing the standard deviation of the arc height by its average value and multiplying by 100%.

[0117] Average tensile force of the first solder joint: Perform a tensile test on the bonded specimen, record the maximum load when the first solder joint detaches or the alloy wire near the first solder joint breaks, and take the average value of the test results of 200 sets of specimens.

[0118] Average tensile force of the second solder joint: Perform a tensile test on the bonded specimen, record the maximum load when the second solder joint detaches or the alloy wire near the second solder joint breaks, and take the average value of the test results of 200 sets of specimens.

[0119] In the above tests, the breaking force and elongation were tested according to GB / T 10573-2020 "Tension Test Method for Non-ferrous Metal Wires"; the average tensile force of the first solder joint and the average tensile force of the second solder joint were tested according to GB / T 4937.22-2018 "Mechanical and Climatic Test Methods for Semiconductor Devices - Part 22: Bond Strength", and the same bonding parameters, sample quantity and tensile test conditions were maintained among the test groups; the number of consecutive wire breaks and the coefficient of variation of arc height were used to evaluate the wire breakage situation and the consistency of arc forming after bonding of the alloy wire in this application during the continuous preparation process, and were measured according to the aforementioned unified statistical method. The same equipment, the same production and bonding conditions and the same statistical caliber were used in each test group to ensure the comparability of the test results between different test groups.

[0120] Therefore, Table 1 is used to demonstrate the final comprehensive effect achieved by the complete preparation method of Example 1. Intermediate annealing, second wire drawing, finished product annealing and subsequent cooling and wire winding are continuously connected by fixed process parameters, and the microstructure formation results are verified by offline microstructure detection, so that the strength, plasticity, continuous fine drawing stability and bonding performance of alloy wire are synergistically improved.

[0121] To verify the distinguishing technical feature in Example 1, namely, "while adjusting the distribution of grain boundary precipitates through intermediate annealing, the non-recrystallized deformation region is retained, and the retained non-recrystallized deformation region is used to form subgrains in the second wire drawing process," Comparative Examples 1 and 2 were set up to compare with Example 1.

[0122] Example 1, Comparative Example 1, and Comparative Example 2 all used alloy rods from the same casting batch, with the same alloy composition and a diameter of 10 mm. The first wire drawing of the three groups all used 36 continuous wire drawing passes, with a wire drawing speed of 15 mm / s. The single-pass section reduction rate of each pass was 12.01%, resulting in alloy wires with a nominal diameter of 1 mm. No annealing treatment was performed during the first wire drawing process.

[0123] All three groups of second-stage wire drawing used 84 consecutive drawing passes at a drawing speed of 15 mm / s. The single-pass section reduction rate of each pass was 8.01%. No annealing treatment was performed between adjacent passes, and an alloy wire with a diameter of 30 μm was finally obtained.

[0124] The three groups used the same wire drawing equipment, molds, lubrication methods, mold cooling conditions, take-up tension, sampling locations, and microstructure testing methods. The only difference between the three groups was the intermediate processing state between the first and second wire drawing.

[0125] Example 1 uses an intermediate annealing temperature of 480℃, a line speed of 65m / min, and an effective heating length of 700mm. The effective heating time is 0.646s. This treatment adjusts the grain boundary precipitate coverage to 25% while retaining 60% of the non-recrystallized deformation area.

[0126] Comparative Example 1 eliminated intermediate annealing. The alloy wire after the first drawing was not heat-treated, and the distribution of grain boundary precipitates and the non-recrystallized deformation area were not adjusted. It directly entered the second drawing stage.

[0127] Comparative Example 2 improved the intermediate annealing degree by using an intermediate annealing temperature of 500℃, a wire speed of 55m / min, and an effective heating length of 800mm, with an effective heating time of 0.873s, which caused a greater degree of recovery and recrystallization in the non-recrystallized deformation area formed during the first wire drawing.

[0128] After completing the corresponding intermediate processing, all three groups underwent a second drawing process under the same 84-pass drawing conditions. The tissue state and continuous fine drawing results of Example 1, Comparative Example 1, and Comparative Example 2 before and after the second drawing are shown in Table 2.

[0129] Among them, Example 1, Comparative Example 1 and Comparative Example 2 used in Table 2 are from the same batch of samples as the test groups with corresponding names in Table 1. Based on the comprehensive performance test in Table 1, Table 2 separately statistically analyzes the stage microstructure parameters and second wire drawing stability of each group after intermediate annealing and after the second wire drawing, in order to verify the relationship between the microstructure state after intermediate annealing and the formation of subgrains.

[0130] Table 2: Effect of microstructure after intermediate annealing on subgrain formation and continuous fine-graining stability; Effective heating time of intermediate annealing / s 0.646 0 0.873 Grain boundary precipitate coverage before second wire drawing / % 25 41 38 Percentage of non-recrystallized deformed area before the second drawing / % 60 92 30 Second drawing terminal diameter / μm 30 30 30 Average equivalent circle diameter of subgrain after second wire drawing / μm 0.2 0.11 0.31 Subgrain size variation coefficient / % 15 34.5 30.8 Number of wire breaks during the second drawing stage per 100km⁻¹ 0.4 2.9 1.8 The subgrain size variation coefficient is calculated by dividing the standard deviation of the subgrain equivalent circle diameter measured at each sampling location by the average value and then multiplying by 100%. It is used to characterize the uniformity of the subgrain size distribution. The number of wire breaks in the second drawing stage only counts the number of wire breaks that occur when an alloy wire with a diameter of 1 mm is drawn into an alloy wire with a diameter of 30 μm through 84 drawing passes, and is converted according to the continuous production length of 100 km of alloy wire.

[0131] As shown in Table 2, after intermediate annealing in Example 1, the grain boundary precipitate coverage rate before the second wire drawing was 25%, and the area of ​​the non-recrystallized deformation region accounted for 60%. This microstructure not only adjusted the distribution of grain boundary precipitates and high-density deformation microstructure formed in the first wire drawing, but also did not completely eliminate the non-recrystallized deformation region that could be further subdivided during the second wire drawing process.

[0132] After completing 84 passes of the second wire drawing in Example 1, the average equivalent circle diameter of the subgrains formed was 0.20 μm, the subgrain size variation coefficient was 15.0%, and the number of wire breaks in the second wire drawing stage was 0.4 times / 100km. These results indicate that the non-recrystallized deformation region, which accounts for 60% of the area, can be further subdivided during continuous fine drawing and form subgrains of appropriate size and relatively uniform distribution, so that the deformation load state at different locations tends to be consistent, thereby reducing the wire breakage frequency in the second wire drawing stage.

[0133] After the intermediate annealing was removed in Comparative Example 1, the area of ​​the non-recrystallized deformation region before the second wire drawing reached 92%, and the grain boundary precipitate coverage reached 41%. The average equivalent circle diameter of the subgrains formed after the second wire drawing in this group was 0.11 μm, which was smaller than 0.20 μm in Example 1, but the subgrain size variation coefficient reached 34.5%, and the number of wire breaks during the second wire drawing stage increased to 2.9 times / 100km.

[0134] The results indicate that a smaller average equivalent circle diameter of subgrains does not necessarily mean that the microstructure is more suitable for continuous fine drawing. After the intermediate annealing is eliminated, the high-density deformed microstructure, residual stress, and grain boundary precipitation state formed in the first drawing are directly introduced into the second drawing without adjustment. There are significant differences in the degree of deformation and microstructure refinement in different regions. Some regions form subgrains that are too small and dense, while other regions form subgrains that are too large due to differences in local stress and temperature rise. This results in uneven distribution of subgrain size, which in turn increases the possibility of local stress concentration and wire breakage.

[0135] After increasing the intermediate annealing degree in Comparative Example 2, the area ratio of the non-recrystallized deformation region decreased to 30%, and the deformation region that could be further subdivided during the second wire drawing process was insufficient. The average equivalent circle diameter of the subgrains after the second wire drawing in this group increased to 0.31 μm, the subgrain size variation coefficient reached 30.8%, and the number of wire breaks in the second wire drawing stage was 1.8 times / 100km.

[0136] The effective heating time for intermediate annealing is calculated by dividing the effective heating length by the wire speed, using the time required for the alloy wire to pass through the effective heating length of the annealing zone.

[0137] The grain boundary precipitate coverage before the second wire drawing: First, the grain boundary position is determined by electron backscatter diffraction, and then the precipitates on the grain boundary are observed by transmission electron microscopy. The sum of the projected lengths of the precipitates along the grain boundary direction is divided by the total observed length of the corresponding grain boundary and multiplied by 100% to obtain the result.

[0138] The percentage of the area of ​​the non-recrystallized deformation region before the second wire drawing: The region that still maintains the drawing orientation gradient, has obvious orientation changes within the crystal, and has not formed uniformly equiaxed grains is identified by electron backscatter diffraction orientation pattern. The sum of the areas of the regions is divided by the total area of ​​the observed region and multiplied by 100%.

[0139] Average equivalent circle diameter of subgrains after the second wire drawing: Interfaces with an orientation difference of not less than 2° and less than 15° are identified as subgrain boundaries, and the regions enclosed by subgrain boundaries are identified as subgrains. The area of ​​a single subgrain is measured and converted into the diameter of an equal-area circle. The average value of the equivalent circle diameters of not less than 100 subgrains is taken.

[0140] Subgrain size variation coefficient: The standard deviation of the measured subgrain equivalent circle diameter is divided by the average value and multiplied by 100% to characterize the uniformity of the subgrain size distribution.

[0141] Number of wire breaks during the second drawing stage: Only the number of wire breaks that occurred during the process of forming a 30μm diameter alloy wire from an alloy wire with a diameter of 1mm through 84 second drawing stages is counted, and the number is calculated based on 100km of alloy wire produced continuously.

[0142] The results indicate that excessive intermediate annealing can eliminate too much of the non-recrystallized deformation area formed during the first wire drawing, resulting in the inability of the second wire drawing to form appropriately sized and uniformly distributed subgrains within a sufficiently large deformation area. Although intermediate annealing can reduce some residual deformation, the remaining non-recrystallized deformation area is insufficiently distributed and discontinuous, making it difficult to stably withstand plastic deformation during 84 consecutive wire drawing passes. Therefore, its subgrain size uniformity and second wire drawing stability are still lower than those of Example 1.

[0143] In Example 1, the number of wire breaks during the second drawing stage was 0.4 times / 100km, which was lower than that of Comparative Example 1 (2.9 times / 100km) and Comparative Example 2 (1.8 times / 100km), representing reductions of 86.21% and 77.78%, respectively. This result further illustrates that neither insufficient intermediate annealing nor excessive intermediate annealing can provide a suitable initial microstructure for the second drawing stage.

[0144] Therefore, the distinguishing technical features verified in Table 2 are not simply about setting up one intermediate annealing, nor are they about simply pursuing a higher or lower area ratio of the non-recrystallized deformation region. Instead, they involve simultaneously forming two interrelated stages through intermediate annealing: adjusting the grain boundary precipitate coverage to 25% and retaining a 60% area ratio of the non-recrystallized deformation region. Then, the retained non-recrystallized deformation region is used to form subgrains with an average equivalent circle diameter of 0.20 μm and a size variation coefficient of 15.0% through a second wire drawing process. This creates a sequential relationship between the microstructure after intermediate annealing and the process of forming subgrains through the second wire drawing process, and improves the stability of the continuous fine drawing process.

[0145] To verify the effect of the annealing conditions for fixing the finished product after the second drawing on the distribution of precipitates, recrystallization structure and arc forming stability, Comparative Examples 3 and 4 were set up to compare with Example 1.

[0146] Example 1, Comparative Example 3, and Comparative Example 4 all used alloy rods from the same casting batch, with the same alloy composition and a diameter of 10 mm. The first wire drawing of all three groups used 36 passes, a wire drawing speed of 15 mm / s, and a single-pass area reduction rate of 12.01%. The intermediate annealing was carried out at 480℃, 65 m / min, and 700 mm. The second wire drawing used 84 passes, a wire drawing speed of 15 mm / s, and a single-pass area reduction rate of 8.01%.

[0147] After the second drawing was completed, all three groups obtained alloy wires with a diameter of 30 μm and an average subgrain equivalent circle diameter of 0.20 μm. Therefore, Example 1, Comparative Example 3 and Comparative Example 4 had the same wire diameter and subgrain structure before entering the finished product annealing.

[0148] The three groups had the same argon protection conditions, cooling methods, wire tension, sampling locations, microstructure testing methods, and arc forming test conditions. The only difference between the three groups was the degree of heating during the annealing of the finished product.

[0149] Example 1 uses a finished product annealing temperature of 455℃, a wire speed of 65m / min, and an effective heating length of 700mm. The theoretical dwell time is 0.646s. The alloy wire is cooled immediately after completing one continuous annealing. After annealing, sampling tests show that the subgrain boundary precipitate coverage rate is 52%, the grain boundary precipitate coverage rate is 14%, and the recrystallization area ratio is 18%. Adjacent recrystallization areas remain separated.

[0150] Comparative Example 3 improved the degree of annealing of the finished product by using an annealing temperature of 470℃, a line speed of 55m / min, and an effective heating length of 800mm, with an effective heating time of 0.873s. This caused some subgrain boundaries to disappear during the recovery and recrystallization process, and allowed the recrystallized regions to continue to expand and approach each other.

[0151] Comparative Example 4 reduced the degree of annealing of the finished product, using a finished product annealing temperature of 440℃, a line speed of 75m / min, and an effective heating length of 550mm, with an effective heating time of 0.440s. As a result, the formation and distribution adjustment of precipitates at the subgrain boundaries and the formation of recrystallization regions were not fully completed.

[0152] The precipitate distribution, recrystallization region status, and arc forming test results of Examples 1, Comparative Examples 3, and Comparative Examples 4 are shown in Table 3.

[0153] Among them, Example 1 and Comparative Example 3 used in Table 3 are from the same batch of samples as the test groups with corresponding names in Table 1; Comparative Example 4 is an additional group of finished products with insufficient annealing under the same raw materials, first drawing, intermediate annealing and second drawing conditions, used to verify the effect of the degree of finished product annealing on the final microstructure together with Example 1 and Comparative Example 3.

[0154] Table 3: Effect of the degree of annealing on the distribution of precipitates and the state of recrystallization zones; Effective heating time for finished product annealing / s 0.646 0.873 0.44 Subgrain boundary precipitate coverage / % 52 39 34 Grain boundary precipitate coverage / % 14 25 17 The ratio of subgrain boundary precipitate coverage to grain boundary precipitate coverage 3.71 1.56 2 Recrystallization area percentage / % 18 34 8 Minimum boundary spacing between adjacent recrystallization regions / μm 0.8 0.15 1.6 Curve height variation coefficient / % 2.9 6.5 5.8 As shown in Table 3, after short-time annealing of the finished product in Example 1 (0.646s), the coverage of subgrain boundary precipitates was 52%, and the coverage of grain boundary precipitates was 14%, with a ratio of 3.71. This indicates that the distribution of precipitates at subgrain boundaries was significantly higher than that at ordinary grain boundaries.

[0155] Meanwhile, in Example 1, the recrystallized region area accounted for 18%, and the minimum boundary distance between adjacent recrystallized regions was 0.80 μm, indicating that a recrystallized region capable of undertaking local plastic deformation was formed in the alloy wire. However, the adjacent recrystallized regions were not connected to each other, and a non-recrystallized deformation region containing subgrains was still retained between them.

[0156] In Comparative Example 3, after increasing the degree of annealing of the finished product, the coverage of subgrain boundary precipitates decreased to 39%, the coverage of grain boundary precipitates increased to 25%, the ratio of the two decreased to 1.56, the area ratio of recrystallization region increased to 34%, the minimum boundary spacing between adjacent recrystallization regions decreased to 0.15 μm, and the coefficient of variation of arc height increased to 6.5%.

[0157] The results indicate that when the degree of annealing of the finished product is too high, some subgrain boundaries will disappear during the recovery and recrystallization process, reducing the number of interfaces that can support precipitates at the subgrain boundaries; the recrystallized regions continue to grow and approach each other, easily forming local continuous softened regions, which leads to an increase in the dispersion of the arc-shaped state.

[0158] After reducing the degree of annealing of the finished product in Comparative Example 4, the coverage of subgrain boundary precipitates was only 34%, and the coverage of grain boundary precipitates was 17%, with a ratio of 2.00. The subgrain boundary preferential precipitation state present in Example 1 was not formed.

[0159] In Comparative Example 4, the recrystallized region accounted for only 8% of the total area, and the minimum boundary distance between adjacent recrystallized regions was 1.60 μm. Although the recrystallized regions maintained a large distance from each other, the formation of recrystallized regions capable of withstanding local plastic deformation was insufficient, making it easy for the alloy wire to produce large differences in elastic recovery during the arc forming process, with the arc height variation coefficient reaching 5.8%.

[0160] The subgrain boundary precipitate coverage is obtained by determining the subgrain boundary position through electron backscatter diffraction, observing the precipitates on the subgrain boundary using a transmission electron microscope, dividing the sum of the projected lengths of the precipitates along the subgrain boundary direction by the total observed length of the corresponding subgrain boundary, and multiplying by 100%.

[0161] Grain boundary precipitate coverage: The location of the grain boundary is determined by electron backscatter diffraction, and the precipitates on the grain boundary are observed by transmission electron microscopy. The sum of the projected lengths of the precipitates along the grain boundary direction is divided by the total observed length of the corresponding grain boundary and multiplied by 100% to obtain the coverage.

[0162] The ratio of subgrain boundary precipitate coverage to grain boundary precipitate coverage is obtained by dividing the subgrain boundary precipitate coverage measured in the same experimental group by the grain boundary precipitate coverage, and the result is rounded to two decimal places.

[0163] Recrystallization region area percentage: Identify equiaxed regions with uniform internal orientation and no longer maintaining a significant pull-out orientation gradient by electron backscatter diffraction orientation pattern. Divide the sum of the areas of the identified recrystallization regions by the total area of ​​the observed region and multiply by 100% to obtain the percentage.

[0164] Minimum boundary spacing between adjacent recrystallization regions: Select two adjacent and unconnected recrystallization regions in the same electron backscatter diffraction orientation pattern and measure the shortest straight-line distance between their boundaries.

[0165] Curve height variation coefficient: Using the same measurement method as in Table 1, 200 sets of bonded arc heights were measured under the same bonding span and bonding parameters. The standard deviation of the arc height was divided by the average value and multiplied by 100% to calculate the coefficient.

[0166] Therefore, Table 3 does not simply verify the selection of a certain annealing temperature or heating time for a finished product, but rather the simultaneous formation of two sets of related states through the same finished product annealing: on the one hand, the coverage of subgrain boundary precipitates is significantly higher than that of grain boundary precipitates; on the other hand, the recrystallization region is formed to an appropriate extent, but is still separated from each other by the non-recrystallized deformation region containing subgrains.

[0167] In this embodiment, after the first wire drawing, sampling inspection revealed that the area of ​​the non-recrystallized deformation region accounted for 85%. After fixing the intermediate annealing, sampling inspection revealed that the grain boundary precipitate coverage was 25% and the area of ​​the non-recrystallized deformation region accounted for 60%. After the second wire drawing, sampling inspection revealed that the average equivalent circle diameter of the subgrain was 0.20 μm. After fixing the finished product annealing, sampling inspection revealed that the subgrain boundary precipitate coverage was 52%, the grain boundary precipitate coverage was 14%, the ratio of the two was 3.71, the recrystallized region area accounted for 18%, and the minimum boundary distance between adjacent recrystallized regions was 0.8 μm. The above microstructure parameters are used to verify the microstructure results formed under fixed process conditions. Continuous production itself is performed according to the wire drawing, annealing, cooling, and take-up parameters.

[0168] Further analysis of the microstructure of offline samples from the front, middle, and rear sections of the finished alloy wire from Example 1 revealed that the maximum intercept of a single recrystallized region along the radial direction of the alloy wire was 8 μm, accounting for 26.67% of the diameter of the 30 μm alloy wire. The length of a single continuous precipitate segment on the subgrain boundary along the subgrain boundary direction was 0.04 μm to 0.12 μm, and the interval without precipitates between adjacent continuous precipitate segments was 0.05 μm to 0.16 μm. The length of a single continuous precipitate segment on the grain boundary along the grain boundary direction was 0.08 μm to 0.19 μm, and the interval without precipitates between adjacent continuous precipitate segments was 0.06 μm to 0.12 μm. All of the above microstructure parameters were obtained through offline sampling after the finished wire was collected and are only used to illustrate the final product microstructure formed under fixed process conditions, and are not used as online feedback control parameters in continuous production processes.

[0169] Example 2

[0170] This embodiment is used to verify whether the representative parameter combination of the side with lower thermal effect within the preparation process range can complete the microstructure adjustment under a larger intermediate wire diameter and a shorter theoretical residence time, while retaining the specific composition of the alloy composition range side. The high-performance alloy wire includes, by mass percentage, 2.5% copper, 4.5% aluminum, 0.9% palladium, 0.3% platinum, 1.1% zinc, 330 ppm rare earth elements, with the balance being silver and unavoidable impurities, wherein the mass ratio of neodymium to europium is 1:0.1.

[0171] A silver-based alloy rod with a diameter of 10.5 mm was prepared by vacuum melting and continuous casting according to Example 1. The silver-based alloy rod was subjected to 37 continuous wire drawing passes. The entry linear velocity of the first pass was set to 20 mm / s, and the single-pass section reduction rate of each pass was set to 11.5%. No annealing was performed between each pass. The theoretical diameter after 37 wire drawing passes was 1.096 mm.

[0172] The alloy wire after the first drawing is introduced into an argon-protected continuous annealing device. The intermediate annealing temperature is set to 475℃, the wire speed is set to 70m / min, the effective heating length is set to 650mm, the argon purity is 99.999%, and the oxygen content in the device is not higher than 50ppm. The theoretical residence time of the alloy wire in the effective heating zone is 0.557s. After leaving the effective heating zone, it immediately enters the argon-protected cooling section.

[0173] Radial heat transfer timescale calculations were performed using the conservative thermophysical parameters adopted in Example 1. With a diameter of 1.096 mm and a radius of 0.548 mm for the alloy wire, the radial characteristic thermal diffusion time is approximately 0.0150 s. 0.557 s is approximately 37.1 times the radial characteristic thermal diffusion time. This calculation is used to illustrate that the relatively short theoretical residence time is still significantly greater than the radial thermal diffusion timescale inside the alloy wire, and the furnace temperature of 475 °C is not equated with the instantaneous actual temperature of the alloy wire core.

[0174] To ensure consistent detection aperture at different sampling locations, the alloy wire radius R is used as a reference on the longitudinal section of the alloy wire. A strip-shaped area no more than 0.1R from the outer surface is designated as the near-surface area, and a strip-shaped area no more than 0.1R from the central axis is designated as the central area. The observation areas for the front, middle, and rear sections are selected according to the same relative positions.

[0175] After intermediate annealing, samples were taken from the front, middle, and rear sections of the alloy wire. Electron backscatter diffraction and transmission electron microscopy were performed on the near-surface and central regions at each sampling location. The coverage of grain boundary precipitates and the proportion of non-recrystallized deformation area in the near-surface and central regions were statistically analyzed. In this embodiment, the ability to detect adjusted grain boundary precipitate distribution in both the near-surface and central regions while still retaining non-recrystallized deformation areas was used as the microstructure criterion for the simultaneous action of 0.557s short-time intermediate annealing on the near-surface and central regions of the alloy wire.

[0176] The alloy wire, after intermediate annealing and cooling, was subjected to 89 consecutive second-stage wire drawing. The entry speed of the first stage was set to 20 mm / s, and the single-stage section reduction rate of each stage was set to 7.5%. No annealing was performed between stages. The theoretical diameter after 89 stages of wire drawing was 34.13 μm. After the second wire drawing, the average equivalent circle diameter of the subgrains and the subgrain size variation coefficient were determined according to the same sampling and statistical methods as in Example 1 to confirm that the non-recrystallized deformation area retained after intermediate annealing could continue to be refined and form subgrains during the continuous fine drawing process.

[0177] The alloy wire after the second drawing is annealed in an argon atmosphere. The annealing temperature is set to 450℃, the wire speed is set to 70m / min, the effective heating length is set to 650mm, and the theoretical dwell time of the alloy wire in the effective heating area is 0.557s. After leaving the effective heating area, it is immediately cooled under argon protection, and the wire is continuously wound up after the surface temperature of the alloy wire is not higher than 50℃.

[0178] After the finished product is collected, offline microstructure analysis is performed on the front, middle and rear samples. The coverage of subgrain boundary precipitates, the ratio of the two, the area ratio of recrystallized regions and the minimum boundary distance between adjacent recrystallized regions are statistically analyzed using the same method as in Example 1. Among them, the subgrain boundary precipitate coverage is higher than the grain boundary precipitate coverage and the ratio of the two is not less than 2.5. The adjacent recrystallized regions are kept separate from each other and there is a non-recrystallized deformation region containing subgrains between the adjacent recrystallized regions. This is used as the basis for determining the formation of the target finished product microstructure under the representative working condition of lower thermal effect.

[0179] The obtained high-performance alloy wire was subjected to the same tensile and bonding performance tests as in Example 1. The breaking force was 22.4 gf, the elongation was 12.4%, and the coefficient of variation of the arc height was 3.4%. The results were compared with those in Example 1 and the test results listed in Tables 1 to 3 using the same test aperture. This was used to evaluate the microstructure formation and comprehensive application performance under the representative boundary conditions of lower thermal effects consisting of 475℃, 70m / min, and 650mm, as well as the corresponding wire drawing parameters.

[0180] Example 3

[0181] This embodiment is used to verify whether the representative parameter combination on the side with higher thermal effect within the preparation process range will cause the non-recrystallized deformation area to disappear excessively or the recrystallized areas to become interconnected. At the same time, the specific composition on the other side of the alloy composition range is retained. The high-performance alloy wire includes, by mass percentage, 4.5% copper, 2.5% aluminum, 0.5% palladium, 0.1% platinum, 1.5% zinc, 140 ppm rare earth elements, and the balance being silver and unavoidable impurities. The mass ratio of neodymium to europium is 1:0.4.

[0182] A silver-based alloy rod with a diameter of 9.5 mm was prepared by vacuum melting and continuous casting according to Example 1. The silver-based alloy rod was subjected to 35 consecutive first-pass wire drawing. The entry linear velocity of the first pass was set to 10 mm / s, and the single-pass section reduction rate of each pass was set to 12.5%. No annealing was performed between each pass. The theoretical diameter after 35 passes of wire drawing was 0.918 mm.

[0183] The alloy wire after the first drawing is introduced into an argon-protected continuous annealing device. The intermediate annealing temperature is set to 485℃, the wire speed is set to 60m / min, the effective heating length is set to 750mm, the argon purity is 99.999%, and the oxygen content in the device is not higher than 50ppm. The theoretical residence time of the alloy wire in the effective heating zone is 0.750s. After leaving the effective heating zone, it immediately enters the argon-protected cooling section.

[0184] Radial heat transfer timescale calculations were performed using the conservative thermophysical parameters adopted in Example 1. With a radius of 0.459 mm for an alloy wire with a diameter of 0.918 mm, the radial characteristic thermal diffusion time was approximately 0.0105 s. 0.750 s is approximately 71.4 times the radial characteristic thermal diffusion timescale. This calculation is used to demonstrate that the representative upper boundary conditions have a sufficient radial thermal diffusion timescale. At the same time, the microstructure of the near-surface region and the central region after annealing was examined to determine whether it had entered an over-recovery or over-recrystallization state.

[0185] After intermediate annealing, samples were taken from the front, middle, and rear sections of the alloy wire according to the sampling locations defined in Example 2 for the near-surface and central regions. Electron backscatter diffraction and transmission electron microscopy were performed on the near-surface and central regions at each sampling location, and the coverage of grain boundary precipitates and the proportion of non-recrystallized deformation area were statistically analyzed. In this example, the central region still retains non-recrystallized deformation areas that can participate in the second wire drawing refinement, and no large-scale interconnection of recrystallized areas appears in the near-surface and central regions, which is used as the stage microstructure criterion for not over-annealing under the relatively high thermal conditions of 485℃, 60m / min, and 750mm.

[0186] The alloy wire, after intermediate annealing and cooling, was subjected to 81 passes of continuous second-stage wire drawing. The entry speed of the first pass was set to 10 mm / s, and the single-pass section reduction rate of each pass was set to 8.5%. No annealing was performed between passes. The theoretical diameter after 81 passes of wire drawing was 25.14 μm. After the second wire drawing, the average equivalent circle diameter of the subgrains and the subgrain size variation coefficient were determined according to the same sampling and statistical methods as in Example 1 to confirm that the non-recrystallized deformation region retained under higher thermal boundary conditions could still form subgrains during the second continuous wire drawing process.

[0187] The alloy wire after the second drawing is annealed in an argon atmosphere. The annealing temperature is set to 460℃, the wire speed is set to 60m / min, the effective heating length is set to 750mm, the theoretical dwell time of the alloy wire in the effective heating area is 0.750s, and it is immediately cooled under argon protection after leaving the effective heating area. The wire is then continuously wound up after the surface temperature of the alloy wire is not higher than 50℃.

[0188] After the finished product is collected, offline microstructure analysis is performed on the front, middle and rear samples. The coverage of subgrain boundary precipitates, the ratio of the two, the area ratio of recrystallized regions and the minimum boundary distance between adjacent recrystallized regions are statistically analyzed using the same method as in Example 1. Among them, the subgrain boundary precipitate coverage is higher than the grain boundary precipitate coverage, the ratio of the two is not less than 2.5, the recrystallized regions remain separated from each other, and there are unrecrystallized deformation regions containing subgrains between adjacent recrystallized regions. This is used as the basis for judging whether the high heat treatment condition has not entered the over-annealing state of the finished product and formed the target finished product microstructure.

[0189] The obtained high-performance alloy wire was subjected to the same tensile and bonding performance tests as in Example 1. The breaking force was 11.8 gf, the elongation was 13.7%, and the coefficient of variation of the arc height was 3.6%. The test results were compared with those of Example 1 and Comparative Example 3 using the same test aperture to evaluate whether the target microstructure and corresponding comprehensive application performance could still be maintained under the representative boundary conditions of higher thermal effects consisting of 485℃, 60m / min and 750mm and the corresponding wire drawing parameters.

[0190] Example 4

[0191] This embodiment is used to verify the ability of fixed process parameters to repeatedly form the target microstructure in continuous industrial production. It adopts the same alloy composition and core process conditions as in Example 1, and utilizes the production arrangement of 5 rolls of samples per group in the comprehensive performance test of Example 1. During the production process, electron backscatter diffraction and transmission electron microscopy results are not used as conditions for starting or stopping the process, adjusting parameters, or releasing roll by roll.

[0192] All five samples were subjected to 36 continuous first-pass wire drawing using a 10mm diameter silver-based alloy rod. The entry linear velocity for the first pass was 15mm / s, and the single-pass section reduction rate was 12.01%. The intermediate annealing was performed at 480℃, 65m / min, and 700mm. The second wire drawing was performed with 84 continuous passes, an entry linear velocity of 15mm / s for the first pass, and a single-pass section reduction rate of 8.01%. The final annealing was performed at 455℃, 65m / min, and 700mm. All samples were immediately cooled under argon protection after the corresponding annealing was completed.

[0193] During continuous preparation, five rolls of samples were completed according to predetermined process parameters. The production of the next roll was not started until the microstructure test results of any roll were obtained. According to the statistical method in Example 1, the number of wire breaks during continuous preparation of the sample was 0.6 times / 100km, the coefficient of variation of arc height was 2.9%, the average tensile force of the first weld point was 8.0gf, and the average tensile force of the second weld point was 6.3gf.

[0194] After production, samples were taken from the front, middle, and rear sections of the finished product from five rolls of samples, forming a total of 15 sampling locations. The samples were then subjected to tissue analysis according to the offline testing method specified in Example 1. Simultaneously, after intermediate annealing and the second wire drawing, stage sampling was conducted using the same front, middle, and rear sampling principles. All sampling results were summarized and statistically analyzed. The summarized statistical value for grain boundary precipitate coverage after intermediate annealing was 25%, the summarized statistical value for the area of ​​the non-recrystallized deformation region was 60%, the summarized statistical value for the average equivalent circle diameter of subgrains after the second wire drawing was 0.20 μm, and the summarized statistical value for the subgrain size variation coefficient was 15.0%. The summarized statistical values ​​for subgrain boundary precipitate coverage after finished product annealing were 52%, grain boundary precipitate coverage was 14%, the ratio of the two was 3.71, the summarized statistical value for the area of ​​the recrystallized region was 18%, and the summarized statistical value for the minimum boundary distance between adjacent recrystallized regions was 0.8 μm.

[0195] All the above-mentioned tissue tests were carried out in the offline sampling stage after the corresponding process was completed. The test results were used to evaluate the stage tissue and finished product tissue formed by the pre-set drawing and annealing parameters under the condition of continuous production of 5 rolls, and were not fed back to the production process in operation. The summarized statistical values ​​were used to characterize the overall tissue state of continuous production of multiple rolls. The original test values ​​of each roll and each sampling position should be saved in the R&D test record so that the differences between rolls and positional differences can be verified when needed.

[0196] Examples 2 and 3 respectively use representative parameter combinations with low and high thermal effects within the process range, and combine them with the specific composition on both sides of the alloy composition range to verify the microstructure and final properties after intermediate annealing, second wire drawing and finished product annealing. Example 4 uses the central process parameters of Example 1 to prepare multiple rolls continuously, in order to verify the ability of fixed process parameters to continuously reproduce the target microstructure without using electron backscatter diffraction and online feedback of transmission electron microscopy.

[0197] Through the aforementioned continuous wire drawing and continuous annealing process range, high-performance alloy wires can be continuously prepared without relying on online microstructure detection feedback, and offline sampling microstructure detection can be used to verify the correspondence between process conditions and subgrain, precipitate distribution and recrystallization structure.

[0198] Although embodiments of the present invention have been shown and described, those skilled in the art can make corresponding changes or substitutions without departing from the inventive concept. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing a high-performance alloy wire, characterized in that, Includes the following steps: S1. The silver-based alloy rod with a diameter of 9.5 mm to 10.5 mm formed by casting is subjected to continuous drawing for the first time to produce alloy wire with a diameter of 0.9 mm to 1.1 mm, thereby obtaining alloy wire with a drawing deformation structure. S2. The alloy wire is subjected to intermediate annealing in an argon atmosphere at an annealing temperature of 475°C to 485°C, a wire speed of 60m / min to 70m / min, and an effective heating length of 650mm to 750mm. The deformed structure formed during the first continuous wire drawing is restored by retaining the non-recrystallized deformed area, which accounts for 50% to 70% of the area and has a grain boundary precipitate coverage of 20% to 30%. S3. The alloy wire after intermediate annealing is continuously drawn a second time to produce an alloy wire with a diameter of 25μm to 35μm. The non-recrystallization deformation area is continuously deformed to form subgrains in the non-recrystallization deformation area. The average equivalent circle diameter of the subgrains is 0.15μm to 0.25μm. S4. The alloy wire is annealed in an argon atmosphere at a temperature of 450°C to 460°C, a wire speed of 60m / min to 70m / min, and an effective heating length of 650mm to 750mm to complete the annealing process and obtain a high-performance alloy wire.

2. The method for preparing a high-performance alloy wire according to claim 1, characterized in that, Before the intermediate annealing, the temperatures at the inlet, middle, and outlet of the effective heating area are detected; When the deviation between the measured temperature at each location and the set target temperature is no greater than 2°C, argon gas with a purity of no less than 99.99% is continuously introduced, and the alloy wire is introduced after the oxygen content in the device is no higher than 50ppm. The theoretical residence time of the alloy wire through the effective heating area is 0.55s to 0.75s.

3. The method for preparing a high-performance alloy wire according to claim 1, characterized in that, During the second continuous wire drawing process, each pass is set with a corresponding traction position, and the linear velocity of the traction position of the next pass is set according to the relationship between the cross-sectional area of ​​the alloy wire in the previous pass and the current pass. During the second continuous drawing process, the single-pass section shrinkage rate of each pass is 7.5% to 8.5%.

4. The method for preparing a high-performance alloy wire according to claim 1, characterized in that, Before the finished product is annealed, the temperatures at the inlet, middle, and outlet of the effective heating zone are detected. When the deviation between the measured temperature at each location and the set target temperature is no greater than 2°C, argon gas with a purity of no less than 99.99% is continuously introduced, and the alloy wire is introduced after the oxygen content in the device is no higher than 50ppm. The theoretical residence time of the alloy wire through the effective heating area is 0.55s to 0.75s.

5. The method for preparing a high-performance alloy wire according to claim 1, characterized in that, The second continuous wire drawing process includes 84 continuous wire drawing processes. During the second continuous wire drawing process, a lubricant is used for lubrication, and the wire drawing die and the lubricant are circulated and cooled.

6. The method for preparing a high-performance alloy wire according to claim 1, characterized in that, The finished annealed alloy wire is cooled in an argon-protected cooling section, and continuous winding is performed after the surface temperature of the alloy wire drops to no higher than 50°C.

7. A high-performance alloy wire, characterized in that, The high-performance alloy wire is manufactured by the preparation method of a high-performance alloy wire according to any one of claims 1-6. The diameter of the high-performance alloy wire is 25 μm to 35 μm. Subgrains are formed within the high-performance alloy wire. The coverage of subgrain boundary precipitates is higher than that of grain boundary precipitates, and the ratio of the coverage of subgrain boundary precipitates to that of grain boundary precipitates is not less than 2.

5. The recrystallized regions are separated from each other, and an unrecrystallized deformed region containing the subgrains is retained between adjacent recrystallized regions.

8. The high-performance alloy wire according to claim 7, characterized in that, The high-performance alloy wire comprises, by mass percentage, 2.5% to 4.5% copper, 2.5% to 4.5% aluminum, 0.5% to 1% palladium, 0.1% to 0.3% platinum, 1% to 1.5% zinc, and 100 ppm to 400 ppm rare earth elements, with the balance being silver and unavoidable impurities; the rare earth elements are composed of neodymium and europium, with the mass ratio of neodymium to europium being 1:0.1 to 1:0.4.

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