A high-strength nickel-chromium-silicon reinforced copper alloy and its preparation method

Abstract

This invention relates to the field of alloy technology, specifically to a high-strength nickel-chromium-silicon reinforced copper alloy and its preparation method. The alloy uses copper as a matrix, with added nickel, silicon, and chromium. By optimizing the two-form, two-time addition method of chromium (adding chromium flakes first, followed by copper foil-coated chromium powder), combined with heat treatment processes such as short-time pre-aging, deep cryogenic shock, low-temperature micro-deformation, and two-stage final aging, the microstructure uniformity of thick-section products is significantly improved. The resulting alloy possesses high tensile strength, high hardness, and good electrical conductivity, making it suitable for high-end applications such as injection molds, effectively solving the problems of insufficient hardenability and large performance fluctuations in traditional alloys.

Description

Technical Field

[0001] This invention relates to the field of alloy technology, and in particular to a high-strength nickel-chromium-silicon reinforced copper alloy and its preparation method. Background Technology

[0002] Copper alloys, as important structural materials, have wide applications in mold manufacturing, especially in injection molds and die-casting molds. These applications require materials to simultaneously possess high strength, high hardness, good wear resistance, and high electrical conductivity to meet precision molding, long service life, and safety standards. Traditional high-strength copper alloys, such as UNS C18000, show fluctuations in strength / hardness depending on the state (for example, some sources state a tensile strength on the order of approximately 586 MPa). However, under thick-section conditions, they still face bottlenecks such as inconsistencies in microstructure and properties caused by the cooling gradient during heat treatment, and the challenge of further improving strength and wear resistance.

[0003] Furthermore, nickel-chromium-silicon reinforced copper alloy systems such as AA944, developed to enhance strength, achieve precipitation strengthening through the formation of precipitates from nickel and silicon, thus improving mechanical properties to some extent. However, during the manufacturing process of thick-section products, this system reveals a series of inherent defects: in the quenching stage after solution treatment, the significant gradient in cooling rate between the center and the surface of the cross-section leads to insufficient hardenability, resulting in lower retention of supersaturated solid solution in the central region, while the surface layer may generate internal stress due to excessively rapid cooling. This uneven cooling causes differences in microstructure, such as low nucleation density and coarsening of precipitates in the central region, while precipitation is too rapid and unevenly distributed on the surface.

[0004] The direct consequence of organizational variations is fluctuation in mechanical and physical properties, making it difficult for thick-section products to consistently achieve the target performance range in mass production. Performance fluctuations not only affect mold reliability but can also lead to premature failure or dimensional instability. This uncertainty becomes a technical obstacle, especially in fields with extremely high safety and lifespan requirements, such as medical and food-grade injection molds. Furthermore, thermal stress concentration during quenching easily induces cracking, further limiting the yield and application range of thick-section products.

[0005] Existing technologies, while attempting to improve performance by adjusting alloy composition or optimizing heat treatment parameters, primarily focus on single-element content or conventional timing adjustments, failing to fundamentally address the challenge of controlling chromium's role in smelting and precipitation. As a key element, chromium's addition method, dissolution behavior, and role in subsequent heat treatment directly affect hardenability and microstructure uniformity. Improper chromium addition can easily lead to macroscopic segregation, oxide inclusions, or uncontrolled precipitate distribution, exacerbating performance fluctuations. Therefore, a deep-modification strategy for controlling chromium is urgently needed to overcome the bottleneck in balancing strength, hardness, conductivity, and stability in thick-section copper alloys. Summary of the Invention

[0006] In view of this, the purpose of this invention is to propose a high-strength nickel-chromium-silicon strengthened copper alloy and its preparation method, in order to address the inconsistency in microstructure / properties and cracking tendency caused by the cooling gradient of thick section heat treatment in Ni-Si precipitation strengthened copper alloy system, and to improve the synchronization of composition and precipitated phase in the thickness direction without significantly sacrificing conductivity, thereby stably obtaining high strength and high hardness and reducing cracking risk.

[0007] To achieve the above objectives, the present invention provides a method for preparing a high-strength nickel-chromium-silicon reinforced copper alloy, comprising the following steps:

[0008] (1) Smelting and casting: After melting copper, nickel and silicon are added, and chromium is added; wherein, the chromium is added in two forms and in two sequences, the first form being chromium flakes and the second form being chromium powder; the first sequence is to add the chromium flakes to the high-temperature melt and keep it at a high temperature to dissolve it; the second sequence is to add a chromium powder package covered with copper foil to the melt after slag removal, degassing and temperature stabilization, so that the chromium powder is released in the melt; then the melt is cast into an ingot;

[0009] (2) The ingot is hot-processed to obtain a billet, then solution-treated and quenched, followed by short-term pre-aging. The temperature of the short-term pre-aging is 495~505℃ and the holding time is 10~20min. After pre-aging, it is water-cooled.

[0010] (3) Then, pre-cooling, short-time liquid nitrogen impact, low-temperature micro-deformation and water temperature equalization treatment are performed in sequence, wherein the pre-cooling temperature is -75~-80℃ and the pre-cooling time is 15~25min; the immersion time of the short-time liquid nitrogen impact is 30~50s; the transfer time from the short-time liquid nitrogen impact to the start of low-temperature micro-deformation is 30~90s; the thickness reduction rate of the low-temperature micro-deformation is 5%~12%; the water temperature equalization is to keep warm in deionized water at 20~30℃ for 60~180s;

[0011] (4) Then perform final aging, which is a two-stage aging process. The first stage aging temperature is 420~480℃ and the time is 30~90min. The second stage aging temperature is 350~410℃ and the time is 60~180min.

[0012] Furthermore, based on 100 parts by mass of copper, nickel comprises 4.8 to 5.3 parts by mass, silicon comprises 1.1 to 1.3 parts by mass, and chromium comprises 0.40 to 0.52 parts by mass; the copper foil used to coat the chromium powder accounts for 0.05% to 0.06% of the total mass of copper; and the chromium sheet accounts for 82% to 85% of the total mass of chromium.

[0013] Preferably, the silicon is silicon powder with an average particle size of 20-35 μm; the chromium powder has an average particle size of 120-180 μm.

[0014] Preferably, the temperature at which the chromium sheet is added in step (1) is 1240~1260℃, and the heat preservation time of the chromium sheet is 30~50min.

[0015] Preferably, in step (1), the chromium powder bag is added after the melt is degassed, slag is removed and the temperature is stabilized, and the chromium powder bag is added after the melt temperature is stabilized at 1230~1280℃; when adding, the chromium powder bag is pressed into the melt surface by a pressure head 30~80mm below the surface of the melt.

[0016] Preferably, the chromium powder package is covered with copper foil; the thickness of the copper foil is 0.1~0.5mm; the cut size of the copper foil is 60mm×60mm~100mm×100mm; the area of ​​the chromium powder is 30mm×30mm~50mm×50mm; the number of folds along the four sides is 2~4 times; and the diameter of the vent hole is 0.5~2.0mm.

[0017] Preferably, step (1) is carried out using inert gas protection during melting, wherein the inert gas is argon or helium, and the flow rate of the protective gas is 5~15L / min.

[0018] Preferably, in step (2), the solution treatment temperature is 950~1000℃ and the holding time is 90~150min; the quenching is a staged quenching, first entering the polymer water-based quenching liquid and then transferring to deionized water for further quenching, wherein the polymer water-based quenching liquid has a mass fraction of 12%~18%, a liquid temperature of 25~35℃, a first stage quenching time of 60~180s, a time interval of 5~20s between stages of deionized water, and a second stage deionized water quenching temperature of 20~30℃ and a quenching time of 120~240s.

[0019] Preferably, the low-temperature micro-deformation in step (3) is rolling, molding or roll pressing; the holding time for water temperature equalization is 90~150s; and after step (3) and before step (4), a mild micro-deformation peak elimination step is also included, which is to first heat to 60~100℃ and hold for 5~20min, and then perform mild micro-deformation with a reduction rate of 1%~3%.

[0020] Furthermore, the present invention also provides a high-strength nickel-chromium-silicon reinforced copper alloy, which is obtained by the above-mentioned preparation method of the high-strength nickel-chromium-silicon reinforced copper alloy.

[0021] The beneficial effects of this invention are:

[0022] This invention significantly improves the microstructure uniformity and overall performance of thick-section copper alloys by optimizing the chromium addition method and heat treatment process. During the smelting stage, a phased and sequential chromium introduction strategy is employed. First, chromium flakes are dissolved at high temperatures to establish the matrix composition background. Then, chromium powder is coated with copper foil to achieve delayed release, forming microscopic chromium enrichment sites. This design promotes the uniformity of the melt's macroscopic composition and provides a controllable nucleation basis for subsequent precipitation, effectively reducing the risk of macroscopic segregation and inclusions. It also suppresses compositional fluctuations in the thick section direction, laying the foundation for microstructure consistency.

[0023] In the heat treatment chain, the short-term pre-aging step induces preferential nucleation of chromium silicides, altering the traditional sequence of direct nickel silicide precipitation and resulting in earlier and more uniform nucleation of the precipitated phases. The chromium silicide nuclei formed during pre-aging serve as templates for subsequent nickel silicide precipitation, promoting simultaneous nucleation and growth of the strengthening phase in the thickness direction, thereby reducing the performance gradient between the center and the surface. This mechanism improves the efficiency of precipitation strengthening, enabling the alloy to maintain high strength while avoiding the decrease in toughness caused by localized coarse precipitation.

[0024] The introduction of cryogenic shock and low-temperature micro-deformation processes further enhances the dislocation density and defect distribution uniformity. The pre-cooling step reduces the risk of thermal shock, while short-term liquid nitrogen shock introduces high-density dislocations into the alloy. Low-temperature micro-deformation then ensures the uniform distribution of these dislocations, providing ample nucleation sites for the dispersed precipitation of strengthening phases during the final aging stage. This coupling effect promotes refined nickel silicide precipitation, strengthens grain boundary and phase boundary stability, thereby improving the alloy's strength, toughness, and resistance to stress cracking.

[0025] Overall, this invention achieves a high degree of consistency between microstructure and properties in thick-section products through controlled chromium addition, pre-aging precipitation sequence rearrangement, and synergistic cryogenic deformation. The alloy exhibits excellent strength-hardness matching and conductivity stability, making it particularly suitable for applications sensitive to comprehensive performance, such as injection molds. Optimization of the process chain reduces the risk of quenching cracks, improves production reliability, and makes it easier to achieve performance targets for high-strength, high-conductivity copper alloys in mass applications. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. 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.

[0027] This invention provides a method for preparing a high-strength nickel-chromium-silicon reinforced copper alloy, comprising:

[0028] (1) By adding chromium in two forms and two time sequences, the macroscopic composition of the melt can be made uniform and the microscopic chromium enrichment sites can be controlled without increasing the total chromium content or introducing other alloying elements.

[0029] (2) Based on the above-mentioned chromium enrichment sites, a short-term pre-aging of about 500°C is set to allow chromium silicides to nucleate preferentially, thereby changing the subsequent precipitation sequence and improving the uniformity of the microstructure in the thick section direction;

[0030] (3) The process of pre-cooling (about -78°C), short-term liquid nitrogen impact, low-temperature micro-deformation, and water temperature equalization is embedded between pre-aging and final aging. While suppressing the risk of thermal shock cracks and stress concentration, high-density dislocations are introduced to further promote the dispersion precipitation of strengthening phases and reduce the performance fluctuation of the center / surface.

[0031] In the high-strength nickel-chromium-silicon reinforced copper alloy provided by this invention, the alloying elements preferably include copper, nickel, silicon, and chromium, with copper as the balance. More preferably, nickel and silicon are used to form nickel silicide precipitates to provide the main precipitation strengthening, and chromium is used to control the hardenability, precipitation uniformity, and stress cracking resistance in the solution-quench-aging chain of thick sections. This material system is optimized to address the problems of center / surface microstructure differences and performance fluctuations that easily occur in thick-section products during the solution-quench-aging process, and can be used in high-strength and high-hardness mold applications (such as injection molds).

[0032] In the preparation method provided by the present invention, the raw materials preferably include: copper granules, nickel granules, silicon powder, chromium flakes, chromium powder, and copper foil for coating the chromium powder. The preferred ratio of the amounts of copper granules, nickel granules, silicon powder, chromium flakes, chromium powder, and copper foil is such that the nickel, silicon, and total chromium content in the alloy is within a range that balances strength and conductivity; more preferably, based on 100 parts by weight of copper (including copper granules and copper foil included in the copper matrix), the preferred amounts of nickel are about 4.8 to 5.3 parts by weight, silicon are about 1.1 to 1.3 parts by weight, and total chromium are about 0.40 to 0.52 parts by weight.

[0033] Preferably, the copper foil accounts for 0.03% to 0.1% of the total mass of copper, more preferably 0.05% to 0.06%.

[0034] Preferably, the chromium sheet accounts for 80% to 90% of the total mass of chromium, more preferably 82% to 85%.

[0035] In the preparation method provided by the present invention, the average particle size of the silicon powder is preferably 10~50μm, more preferably 20~35μm, and specifically can be 20μm, 25μm, 30μm or 35μm.

[0036] In the preparation method provided by the present invention, the average particle size of the chromium powder is preferably 80~200μm, more preferably 120~180μm, and specifically can be 120μm, 155μm, 180μm or 200μm.

[0037] In the preparation method provided by the present invention, chromium element is added in "two forms and two time sequences": the first form is chromium sheet, and the second form is chromium powder; the first time sequence is that the chromium sheet is pre-solubilized in the high-temperature melt, and the second time sequence is that the chromium powder is released in the later stage in the form of a package and forms micro-regional chromium enrichment sites.

[0038] In the "two-form, two-time" addition method provided by the present invention, the addition temperature of the chromium sheet is preferably 1230~1280℃, more preferably 1240~1260℃, and specifically 1240℃, 1250℃ or 1260℃; the heat preservation time of the chromium sheet is preferably 20~60min, more preferably 30~50min, and specifically 30min, 40min or 50min.

[0039] In the package provided by the present invention, the package preferably uses copper foil as the coating material, and more preferably high-purity copper foil; this choice allows the package to melt quickly in the melt and be incorporated into the copper matrix, thereby avoiding the introduction of new element sources other than copper.

[0040] In the preparation of the material package provided by the present invention, the thickness of the copper foil is preferably 0.1~0.5mm, more preferably 0.2~0.4mm, and specifically can be 0.2mm, 0.3mm or 0.4mm; the cutting size of the copper foil is preferably 60mm×60mm~100mm×100mm, more preferably 75mm×75mm~85mm×85mm; the area of ​​the chromium powder is preferably 30mm×30mm~50mm×50mm, more preferably 35mm×35mm~45mm×45mm; the number of folds along the four sides is preferably 2~4 times, more preferably 3 times; the diameter of the vent hole is preferably 0.5~2.0mm, more preferably 0.8~1.5mm, and specifically can be 0.8mm, 1.0mm or 1.5mm.

[0041] The aforementioned structural parameters of the chromium pack affect the spatial isolation and delayed release window of the chromium powder during charging: the number of folds and the reliability of the seal affect the direct contact rate between the chromium powder and the melt, thus affecting the risk of chromium powder oxidation, floating, and inclusion; the size of the vent hole affects the risk of gas expansion and release and splashing at the moment of furnace entry; the spread area and the size of the copper foil together affect the spreading / melting behavior of the pack in the melt, thus affecting the scale and dispersion of the chromium enrichment micro-regions. This can reduce macroscopic segregation, reduce crack initiation caused by coarse second phases, and demonstrate the improved crack resistance brought about by the spatial concept.

[0042] In the smelting steps provided by this invention, the chromium powder package is preferably added after melt degassing, slag removal, and temperature stabilization. More preferably, the package is added after the melt temperature is stabilized at 1230~1280℃, and then pressed into the melt surface by a pressure head 30~80mm (more preferably 40~60mm) to achieve submerged delayed release. This addition site and timing affect the effective entry and dissolution path of the chromium powder, thereby affecting the number, size, and spatial distribution of chromium-enriched micro-regions. In conjunction with pre-solubilization of chromium flakes, it can achieve both macroscopic uniformity and microscopic controllability without increasing the total chromium content, providing usable reaction sites for subsequent pre-aging.

[0043] In the smelting process provided by this invention, inert gas protection is preferably used; the inert gas is preferably argon or helium, more preferably argon. The flow rate of the protective gas is preferably 5~15 L / min, more preferably 8~12 L / min.

[0044] In the smelting process provided by the present invention, copper is preferably melted to 1150~1200°C first, then nickel is added in batches and stirred and kept at the temperature; then silicon is added in batches and kept at 1210~1250°C; then chromium sheets are added and kept at 1230~1280°C; after the holding period, slag is preferably removed and gas is degassed; finally, after the temperature stabilizes, chromium powder is added and kept at the temperature for a short time, stirred and then poured.

[0045] In the casting process provided by the present invention, the mold is preferably preheated to 200~350°C, more preferably 230~280°C, specifically 230°C, 250°C or 280°C.

[0046] In the hot forging provided by this invention, the forging heating temperature is preferably 820~880℃, more preferably 840~860℃; the holding time is preferably 30~90min, more preferably 50~70min; multi-fire forging is adopted, and the billet is reheated in the furnace when the surface temperature is lower than 650~720℃ (more preferably 680~710℃). This forging temperature window affects the degree of dendrite and segregation fragmentation, grain refinement, and pore closure in the cast state, thereby affecting the consistency of the microstructure in the center / surface of the thick section and the uniformity of the subsequent solution treatment.

[0047] The forging pretreatment provided by this invention preferably includes solution treatment, staged quenching, low-temperature holding (stress relief / stabilization), and short-term pre-aging:

[0048] The solution treatment temperature is preferably 950~1000℃, more preferably 960~980℃, specifically 960℃, 970℃, or 980℃; the holding time is preferably 90~150min, more preferably 110~130min. This solution treatment process affects the degree of solid solution of nickel, silicon, and chromium in the copper matrix and the degree of initial second phase dissolution, thereby affecting the uniformity of the supersaturated solid solution after quenching and its subsequent precipitation strengthening potential.

[0049] The preferred method for staged quenching is to first quench in a polymer-based water-based quenching solution, followed by quenching in deionized water. The polymer-based water-based quenching solution is preferably a polyalkylene glycol-based water-based quenching agent, but polyethylene glycol or polypropylene glycol-based water-based quenching agents can also be used. Its mass fraction is preferably 12%–18%, more preferably 14%–16%, specifically 14%, 15%, or 16%. The liquid temperature is preferably 25–35°C, more preferably 28–32°C, specifically 28°C, 30°C, or 32°C. The first stage quenching time is preferably 60–180 s, more preferably 100–140 s; the time interval between quenching in deionized water is preferably 5–20 s, more preferably 8–12 s; the second stage deionized water quenching temperature is preferably 20–30°C, and the time is preferably 120–240 s.

[0050] This staged quenching strategy reduces the peak thermal stress and quenching crack risk of thick sections by using a cooling curve that is slow at the beginning and fast at the end, while maintaining sufficient supersaturation; thereby improving the consistency of the solid solution state in the center and the surface, providing an equal driving force for subsequent aging precipitation.

[0051] The preferred low-temperature holding temperature is 220~280℃, more preferably 240~260℃; the preferred holding time is 60~180min, more preferably 90~150min. This step mainly affects the release of residual stress and dimensional stability, thereby reducing stress concentration and cracking tendency during subsequent cryogenic deformation.

[0052] The short-term pre-aging temperature is preferably 480~520℃, more preferably 495~505℃, specifically 490℃, 500℃, or 510℃; the holding time is preferably 5~30min, more preferably 10~20min, specifically 10min, 15min, or 20min; rapid water cooling is preferred after pre-aging. This pre-aging is used to induce preferential nucleation of chromium silicides and adjust the precipitation from "direct nickel silicide precipitation" to "chromium silicide nucleation first, followed by dense nickel silicide precipitation", thereby making the subsequent strengthening phase more uniform in the thickness direction and reducing performance fluctuations.

[0053] In the preparation method provided by this invention, the process flow of pre-cooling, short-time liquid nitrogen impact, low-temperature micro-deformation, and water homogenization is preferably set after short-time pre-aging and before final aging. This timing arrangement allows the chromium silicide nucleation embryos and chromium enrichment sites formed during pre-aging to be fully amplified in the subsequent dislocation introduction stage, thereby obtaining a higher density and more uniform distribution of precipitated strengthening phases in the final aging stage.

[0054] In the precooling provided by this invention, the precooling bath is preferably prepared using an organic solvent and solid carbon dioxide; the organic solvent is preferably anhydrous ethanol, isopropanol, or acetone, more preferably anhydrous ethanol; the bath temperature is preferably -60~-90℃, more preferably -75~-80℃, specifically -70℃, -78℃, or -80℃; the precooling time is preferably 10~30 min, more preferably 15~25 min. This precooling step affects the overall temperature field and thermal gradient of the workpiece, thereby affecting the peak value of the subsequent liquid nitrogen impact thermal stress; by precooling first, the probability of surface thermal cracking and stress cracking caused by direct liquid nitrogen impact can be significantly reduced.

[0055] In the liquid nitrogen shock provided by this invention, the liquid nitrogen immersion time is preferably 20-60s, more preferably 30-50s, and specifically can be 30s, 40s, or 50s. This time affects the transient temperature drop and dislocation initiation conditions; if it is too short, the dislocation density will be insufficient, and if it is too long, it may increase the risk of thermal shock. Therefore, it needs to be set in conjunction with the precooling and temperature equalization steps.

[0056] In the low-temperature micro-deformation provided by this invention, the deformation method is preferably rolling, die pressing, or roll pressing, with rolling being more preferred; the thickness reduction rate is preferably 5%~12%, more preferably 7%~9%, specifically 6%, 8%, or 10%; the transfer time from liquid nitrogen impact to the start of deformation is preferably 30~90s, more preferably 45~75s. This parameter directly affects the dislocation density and distribution uniformity, thereby affecting the nucleation rate and dispersion degree of the final aged precipitate; at the same time, the superposition of low-temperature deformation and chromium enrichment sites can make the nucleation of the strengthening phase in the thickness direction more synchronous and reduce the center / surface difference.

[0057] In the water temperature equalization process provided by this invention, it is preferable to immerse the object in deionized water at 20-30°C for 60-180 seconds immediately after deformation, more preferably for 90-150 seconds. This temperature equalization step suppresses thermal shock cracks and stress concentration by rapidly passivating the temperature difference and reducing residual thermal stress.

[0058] In the mild micro-deformation peak reduction method provided by this invention, it is preferable to first heat to 60~100℃ and hold for 5~20 min, more preferably to hold at 75~85℃ for 8~12 min; then perform mild micro-deformation with a reduction rate of 1%~3%, more preferably 1.5%~2.5%. This step is used to control the dislocation density introduced by cryogenic deformation in a peak-reduction homogenization manner, reduce local stress concentration points, and thus reduce the risk of stress cracking during the final aging process and improve performance stability.

[0059] In the final aging process provided by this invention, a two-stage aging process is preferably adopted: the first stage aging temperature is preferably 420~480℃ and the time is preferably 30~90min; the second stage aging temperature is preferably 350~410℃ and the time is preferably 60~180min. This two-stage aging process promotes nucleation and growth first, and then refinement and homogenization, making the distribution of the strengthening phase more dispersed and the thickness direction more consistent, thereby ensuring conductivity while stably obtaining high strength and high hardness comprehensive properties.

[0060] In the preparation method provided by this invention, the following auxiliary processes that do not change the nature of the alloy system may also be selected:

[0061] Surface cleaning / decontamination: To meet the cleanliness and corrosion resistance requirements of medical and food-grade molds, ultrasonic cleaning with deionized water can be used after heat treatment. Organic acids (such as citric acid) or chelating agents (such as ethylenediaminetetraacetic acid) can be used for light cleaning, followed by thorough rinsing and drying. These substances are only used as surface treatment aids and do not penetrate the internal structure of the alloy.

[0062] Alternative degassing methods: In addition to bottom blowing argon, conventional methods such as vacuum degassing or rotary degassing can also be used to reduce the gas content and inclusions in the melt.

[0063] This invention integrates a process flow that combines chromium morphology / timing control, pre-aging precipitation sequence rearrangement, and deep cryogenic / deformation / isotropic coupling. Under thick cross-section conditions, this process can significantly improve the consistency of the microstructure and properties of the center and surface layers, reduce the tendency of stress cracking, and make it easier to stably achieve high strength and high conductivity in mass production.

[0064] For clarity, the following detailed description is provided in conjunction with embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0065] Example 1:

[0066] The raw materials used in this embodiment are as follows: copper granules with a purity of 99.99%; copper foil with a purity of 99.99% and a size of 120mm×100mm×0.3mm; nickel granules with a purity of 99.99%; silicon powder with an average particle size of 25μm and a purity of 99.5%; chromium sheets with a purity of 99.995% and a size of 10mm×8mm×0.8mm; chromium powder with a purity of 99.8% and an average particle size of 155μm; and polyalkylene glycol-based water-based quenching agent AQUA-QUENCH 251 from Quaker Houghton.

[0067] Ingredients and pretreatment: Weigh 18136g of copper granules, 920g of nickel granules, 220g of silicon powder, 70g of chromium sheet, 14g of chromium powder, and 10g of copper foil; place the 18136g of copper granules, 920g of nickel granules, 220g of silicon powder, 70g of chromium sheet, 14g of chromium powder, and 10g of copper foil in a 120℃ oven for 30 minutes to remove adsorbed moisture, and then store them in a dry environment for later use.

[0068] Preparation of chromium powder package: Take 10g of copper foil and cut it into 80mm×80mm single pieces. Spread 14g of chromium powder evenly in the center area of ​​the copper foil (spreading area 40mm×40mm). Fold it three times along the four sides to form a bag-shaped package. Spot weld it at the seal and leave a 1mm diameter vent hole to prevent gas expansion and splashing when it enters the furnace. Keep the 24g package at 120℃ for 10min before use.

[0069] Water-based quenching fluid: Add 170 kg of deionized water to the quenching tank and stir to form a vortex. Then add 30 kg of polyalkylene glycol-type water-based quenching agent concentrate and mix for 10 min to obtain 200 kg of quenching fluid with a mass fraction of 15%. Stabilize the liquid temperature at 30℃ for later use.

[0070] Melting: 300L of argon gas (flow rate 10L / min) was introduced into an induction melting furnace as a furnace protection gas. 18136g of copper granules were added to a graphite crucible and heated to 1180℃ to melt. Then, 920g of nickel granules were added in three batches, stirring for 3 minutes and holding for 5 minutes after each addition with a graphite stirring rod. Next, 220g of silicon powder was added in two batches, stirring for 2 minutes after each addition and holding at 1230℃ for 10 minutes. Finally, 70g of chromium sheet was added at 1250℃ and held for 4 minutes. 0 min, while stirring for 1 min every 10 min; after the holding time is completed, remove the slag and degas the melt by bubbling a small amount of argon gas from the bottom of the crucible for 5 min; after adjusting the melt temperature to 1250℃ and stabilizing for 2 min, add a 24g chromium powder bag, press it into the melt surface 50mm using a graphite indenter and hold for 2 min, then stir for 60s; then pour the melt into a preheated graphite mold at 250℃ under argon protection, let it stand to solidify, and then demold to obtain an ingot;

[0071] Hot forging: The ingot is placed at 850℃ and held for 60 minutes before hot forging. The thickness is forged from 150mm to 80mm using a multi-fire forging method. When the surface temperature of the billet is below 700℃, it is returned to the furnace and held at 850℃ for 20 minutes before forging continues. After forging, it is air-cooled to room temperature and the surface is machined to remove oxide scale and shrinkage cavities, resulting in a forged billet with a thickness of 80mm.

[0072] Pretreatment of forging billets: The forging billets are placed in a box-type resistance furnace and heated to 970℃. After the furnace temperature reaches 970℃, the temperature is held for 120 minutes. Then, within 60 seconds after being taken out of the furnace, they are immersed in 200kg of quenching liquid for 120 seconds. Then, within 10 seconds, they are transferred to 800kg of deionized water at 25℃ for 180 seconds. After that, they are removed and air-cooled to room temperature. Then, they are placed at 250℃ and held for 120 minutes. After that, they are removed from the furnace and air-cooled to room temperature. Then, the temperature is raised to 500℃ and held for 15 minutes. Then, they are immediately immersed in 200kg of deionized water at 25℃ for 60 seconds. After that, they are removed and air-cooled to dry. The pretreated forging billets are obtained.

[0073] Transient cryogenic shock and low-temperature micro-deformation: Preparation of cryogenic precooling bath: Add 40 kg of anhydrous ethanol to a container, then add 100 kg of dry ice in batches and stir to stabilize the bath temperature at -78℃; immerse the pretreated forging billet completely in the precooling bath for 20 min, then immediately immerse it in 40 kg of liquid nitrogen for 40 s to form transient cryogenic shock, and then transfer it to the rolling equipment within 60 s for low-temperature micro-deformation, controlling the thickness reduction rate to 8%; after deformation, immediately immerse the workpiece in 800 kg of deionized water at 25℃ for 120 s, then remove it and air-cool it to dry, obtaining a high-density dislocation forging billet;

[0074] Mild micro-deformation peak elimination and final aging: After heating the high-density dislocation forging billet to 80℃ and holding it for 10 min, it was subjected to mild micro-deformation with a reduction rate of 2%. Then, it was heated to 450℃ and held for 60 min, followed by air cooling to room temperature. Finally, it was heated to 380℃ and held for 120 min, followed by air cooling to room temperature, to obtain a high-strength nickel-chromium-silicon reinforced copper alloy.

[0075] Example 2:

[0076] The difference from Example 1 is as follows: In the batching and pretreatment steps, 18134g of copper granules, 920g of nickel granules, 220g of silicon powder, 60g of chromium sheet, 24g of chromium powder, and 12g of copper foil are weighed; in the preparation step of the chromium powder package, 12g of copper foil is cut into 85mm×85mm single pieces, and 24g of chromium powder is evenly spread in the central area of ​​the copper foil (spreading area 45mm×45mm), and folded three times along the four sides to form a bag-shaped package, which is then spot-welded at the seal and a 1mm diameter vent hole is reserved; in the smelting step, 36g of chromium powder package is added; the remaining conditions are the same as in Example 1.

[0077] Example 3:

[0078] The difference from Example 1 is as follows: In the batching and pretreatment steps, 18138g of copper granules, 920g of nickel granules, 220g of silicon powder, 75g of chromium sheet, 9g of chromium powder, and 8g of copper foil are weighed; in the preparation step of the chromium powder package, 8g of copper foil is cut into 75mm×75mm single pieces, and 9g of chromium powder is evenly spread in the center area of ​​the copper foil (spreading area 35mm×35mm), and folded three times along the four sides to form a bag-shaped package, and spot welded to fix it at the seal and leaving a 1mm diameter vent hole; in the smelting step, 17g of chromium powder package is added; the remaining conditions are the same as in Example 1.

[0079] Example 4:

[0080] The difference from Example 1 is that in the batching and pretreatment steps, 18150g of copper granules, 920g of nickel granules, 220g of silicon powder, 56g of chromium sheet, 14g of chromium powder, and 10g of copper foil are weighed; in the smelting step, the amount of chromium sheet added is 56g; the other conditions are the same as in Example 1.

[0081] Example 5

[0082] The difference from Example 1 is as follows: In the batching and pretreatment steps, 18118g of copper granules, 920g of nickel granules, 220g of silicon powder, 80g of chromium sheet, 20g of chromium powder, and 12g of copper foil are weighed; in the preparation step of the chromium powder package, 20g of chromium powder is wrapped with 12g of copper foil to form a 32g package; in the smelting step, 32g of chromium powder package is added; the remaining conditions are the same as in Example 1.

[0083] Example 6:

[0084] The difference from Example 1 is that the pretreatment step of the forging billet is changed from heating to 500°C and holding for 15 minutes to heating to 490°C and holding for 25 minutes, and the subsequent immersion in 200 kg of deionized water at 25°C for 60 seconds is changed to immersion in 200 kg of deionized water at 25°C for 90 seconds; the other conditions are the same as in Example 1.

[0085] Comparative Example 1:

[0086] The difference from Example 1 is that the operation of adding copper foil containing chromium powder at 1180°C is cancelled in Example 1. Instead, 84g of chromium sheet is added at 1250°C and pressed into the melt and held for 3 minutes. At the same time, only 10g of copper foil is added at 1180°C and pressed into the melt and held for 2 minutes. The other conditions are the same as in Example 1.

[0087] Comparative Example 2

[0088] The difference from Example 1 is that the operation of wrapping 14g of chromium powder with 10g of copper foil and sealing it to form a material bag before adding it to the melt is replaced by preheating 14g of chromium powder at 200°C for ten minutes and then directly adding it to the melt at 1180°C. The powder is then pressed into the melt by a graphite press head for 50mm and held at that temperature for 2 minutes. At the same time, 10g of copper foil is added to the melt separately and pressed into the melt by 50mm and held at that temperature for 2 minutes. The other conditions are the same as in Example 1.

[0089] Comparative Example 3

[0090] The difference from Example 1 is that the short-term pre-aging treatment of heating to 500°C and holding for 15 minutes followed by water cooling for 60 seconds is omitted in Example 1. Instead, the transient deep cryogenic shock and low-temperature micro-deformation treatment is directly carried out after completing the stabilization treatment at 250°C and air cooling to room temperature. The other conditions are the same as in Example 1.

[0091] Comparative Example 4

[0092] The difference from Example 1 is that the transient deep cryogenic shock and low temperature micro-deformation treatment in Example 1 are replaced by directly subjecting the pretreated forging billet to mild micro-deformation peak elimination and final aging; the other conditions are the same as in Example 1.

[0093] Performance testing:

[0094] Sample preparation: Alloy plates were prepared according to the processes of the examples and comparative examples. 0.3 mm was removed from the top and bottom surfaces of each plate by machining. Then, using the thickness direction of the plate as the sampling reference, a surface sample was taken 10 mm from the top surface, and a center sample was taken half the thickness from the top surface. The length direction of all mechanical and physical property test specimens was consistent with the main deformation direction of the hot forging of the plate. For each test item, three parallel specimens were prepared at the same sampling location, and the arithmetic mean was taken. After all tests were completed, the results were filled into Table 1.

[0095] Chemical composition consistency and determination of oxygen and hydrogen content: Nickel and chromium were determined by inductively coupled plasma mass spectrometry according to GB / T 5121.28-2021. Silicon content was determined according to GB / T 5121.23-2008. Oxygen and hydrogen content were determined by inert gas melting-infrared absorption / thermal conductivity method according to GB / T5121.8-2024. Metal shavings were drilled from the surface and center of each plate. The difference between the surface and center was used as an indicator of the synchronicity of the composition of the thick section. Oxygen and hydrogen content were used as sensitive indicators of the cleanliness of smelting and chromium addition.

[0096] Room temperature tensile properties and thickness direction consistency: Room temperature tensile test was conducted according to GB / T 228.1-2021; rectangular tensile specimens were prepared from the surface and center respectively, with a gauge length of 50 mm, a parallel section width of 12.5 mm, a specimen thickness of 6 mm, a corner radius of 12.5 mm on both sides of the specimen, and a surface roughness of 0.8 μm; the tensile strength and elongation after fracture were recorded respectively, and the difference between the surface and center of the same plate was calculated as the thickness direction consistency index.

[0097] Brinell hardness and thickness direction hardness fluctuation: Brinell hardness test was performed according to GB / T 231.1-2018; the sample surface at each sampling location was polished to the same texture as 1200 grit sandpaper, a cemented carbide ball indenter with a diameter of 2.5 mm was used, the test force was set to 1837 N, and the holding time was set to 15 s; 10 points were measured at each sampling location, the center distance between adjacent indentations was not less than three times the indentation diameter, the arithmetic mean was calculated, and the difference between the average value of the surface layer and the average value of the center was used as the hardness synchronization index of the thick section.

[0098] Conductivity and thickness-direction conductivity consistency: The conductivity of copper and copper alloys was determined by eddy current method according to GB / T 32791—2016; an eddy current conductivity meter was used, the detection frequency was set to 60kHz, and two metrologically traceable standard blocks were used to calibrate the instrument at two points. The sample thickness was not less than 0.3mm and the surface roughness was not greater than 0.8μm; 10 tests were conducted at each sampling location, and the readings were recorded and the average value was calculated. The conductivity was expressed as a percentage of the international standard for annealed copper; the surface-to-center difference was used to evaluate the synchronicity of the conductivity of the thick section.

[0099] Table 1 Performance Test Results

[0100]

[0101] As can be seen from the data in Table 1 of the embodiments, the high-strength nickel-chromium-silicon reinforced copper alloy prepared by the present invention exhibits good consistency between composition and performance in the thickness direction. The fluctuations in nickel, silicon, chromium, oxygen, and hydrogen content in the surface and center layers are relatively small, indicating that argon-protected melting combined with stepwise feeding can effectively reduce the risk of gas inclusions and macroscopic segregation. In terms of mechanical properties, each embodiment achieves high tensile strength and Brinell hardness while maintaining moderate electrical conductivity. Furthermore, different embodiments show a pattern where strength-conductivity is adjustable with changes in chromium content and aging path: increasing chromium content and strengthening phase nucleation density is beneficial for improving load-bearing capacity and wear resistance, while moderately reducing chromium content or optimizing pre-aging parameters is more conducive to maintaining electrical conductivity and toughness. Based on the preparation steps, it is speculated that the reason is that chromium forms a fine nucleation core in the early stage in the form of chromium silicide, which then induces nickel silicide to precipitate uniformly around it; at the same time, the high-density deformation defects introduced by low-temperature micro-deformation further promote the refinement and homogenization of the precipitated phase, so that it can still take into account strength, hardness and conductivity under thick cross-section conditions, and is suitable for applications that are sensitive to comprehensive performance, such as injection molds, die casting molds and resistance welding electrodes.

[0102] As can be seen from the data in Table 1 for Example 1 and Comparative Examples 1 and 2, when chromium is added only as a single chromium sheet or when chromium powder is added directly without copper foil coating, the tensile strength, Brinell hardness, and electrical conductivity in the thickness direction fluctuate more, and the oxygen and hydrogen contents are more likely to increase. This is because the chromium sheet is prone to incomplete local dissolution under short-term heat treatment, leading to macroscopic segregation. Meanwhile, the exposed chromium powder has a large specific surface area and is easily oxidized and floats, forming inclusions, thus reducing the proportion of effective chromium participating in precipitation strengthening. Therefore, establishing the matrix composition with chromium sheets and using copper foil to coat the chromium powder achieves spatial isolation and delayed release, balancing dissolution efficiency and micro-dispersion, producing a significant synergistic effect. This significantly improves the synchronicity of thick sections, demonstrating a 1+1 greater than 2 effect.

[0103] As can be seen from the data in Example 1 and Comparative Example 3 in Table 1, the improvement in tensile strength and Brinell hardness is weakened after the short-term pre-aging is removed, while the electrical conductivity and its thickness direction consistency are also affected. It is speculated that this is because the pre-aging stage facilitates the formation of fine and stable chromium silicide nuclei, which then induces nickel silicides to precipitate at a higher density and more uniformly during subsequent staged aging. Without this stage, the precipitation process relies more on spontaneous nucleation during subsequent aging, easily leading to localized coarse precipitation and uneven distribution, thus weakening the dual effect of strengthening and purifying solid solution atoms. Therefore, there is a temporal synergy between pre-aging and subsequent aging, which can achieve a more stable combination of strength and conductivity without sacrificing toughness.

[0104] As can be seen from the data in Example 1 and Comparative Example 4 in Table 1, omitting the pre-cooling and low-temperature micro-deformation steps makes it difficult to simultaneously improve the tensile strength and Brinell hardness of the alloy, and the electrical conductivity also shows a limited improvement trend. This may be because low-temperature micro-deformation can introduce a high density of deformation defects in thick-section materials. These defects provide heterogeneous nucleation sites for precipitates and promote element diffusion, thereby driving the refinement of nickel silicides and accelerating the precipitation of solid solution atoms during subsequent aging. When there are insufficient nucleation sites, the precipitated strengthening phase is more likely to grow and is unevenly distributed, making it difficult to achieve both strengthening and conductivity recovery. Therefore, the coupling of low-temperature micro-deformation and graded aging has a significant synergistic effect and is key to achieving a balance between strength and conductivity in thick sections.

[0105] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing a high-strength nickel-chromium-silicon reinforced copper alloy, characterized in that, Includes the following steps: (1) Smelting and casting: After melting copper, nickel and silicon are added, and chromium is added; wherein, the chromium is added in two forms and in two sequences, the first form being chromium flakes and the second form being chromium powder; the first sequence is to add the chromium flakes to the high-temperature melt and keep it at a high temperature to dissolve it; the second sequence is to add a chromium powder package covered with copper foil to the melt after slag removal, degassing and temperature stabilization, so that the chromium powder is released in the melt; then the melt is cast into an ingot; (2) The ingot is hot-processed to obtain a billet, then solution-treated and quenched, followed by short-term pre-aging. The temperature of the short-term pre-aging is 495~505℃ and the holding time is 10~20min. After pre-aging, it is water-cooled. (3) Then, pre-cooling, short-time liquid nitrogen impact, low-temperature micro-deformation and water temperature equalization treatment are performed in sequence, wherein the pre-cooling temperature is -75~-80℃ and the pre-cooling time is 15~25min; the immersion time of the short-time liquid nitrogen impact is 30~50s; the transfer time from the short-time liquid nitrogen impact to the start of low-temperature micro-deformation is 30~90s; the thickness reduction rate of the low-temperature micro-deformation is 5%~12%; the water temperature equalization is to keep warm in deionized water at 20~30℃ for 60~180s; (4) Then perform final aging, which is a two-stage aging process. The first stage aging temperature is 420~480℃ and the time is 30~90min. The second stage aging temperature is 350~410℃ and the time is 60~180min. Based on 100 parts by mass of copper, nickel comprises 4.8 to 5.3 parts by mass, silicon comprises 1.1 to 1.3 parts by mass, and chromium comprises 0.40 to 0.52 parts by mass; the copper foil used to coat the chromium powder accounts for 0.05% to 0.06% of the total mass of copper; and the chromium sheet accounts for 82% to 85% of the total mass of chromium.

2. The method for preparing high-strength nickel-chromium-silicon reinforced copper alloy according to claim 1, characterized in that, The silicon is silicon powder, and the average particle size of the silicon powder is 20~35μm; the average particle size of the chromium powder is 120~180μm.

3. The method for preparing high-strength nickel-chromium-silicon reinforced copper alloy according to claim 1, characterized in that, In step (1), the temperature at which the chromium sheet is added is 1240~1260℃, and the heat preservation time of the chromium sheet is 30~50min.

4. The method for preparing high-strength nickel-chromium-silicon reinforced copper alloy according to claim 1, characterized in that, In step (1), the chromium powder bag is added after the melt is degassed, slag is removed and the temperature is stabilized, and the chromium powder bag is added after the melt temperature is stabilized at 1230~1280℃; when adding, the chromium powder bag is pressed into the melt surface by a pressure head 30~80mm below the surface of the melt.

5. The method for preparing high-strength nickel-chromium-silicon reinforced copper alloy according to claim 1, characterized in that, The chromium powder package is covered with copper foil; the thickness of the copper foil is 0.1~0.5mm; the cut size of the copper foil is 60mm×60mm~100mm×100mm; the area of ​​the chromium powder is 30mm×30mm~50mm×50mm; the number of folds along the four sides is 2~4 times; and the diameter of the vent hole is 0.5~2.0mm.

6. The method for preparing high-strength nickel-chromium-silicon reinforced copper alloy according to claim 1, characterized in that, The step (1) involves melting under inert gas protection. The inert gas is argon or helium, and the flow rate of the protective gas is 5~15L / min.

7. The method for preparing high-strength nickel-chromium-silicon reinforced copper alloy according to claim 1, characterized in that, In step (2), the solution treatment temperature is 950~1000℃ and the holding time is 90~150min; the quenching is a staged quenching, first entering the polymer water-based quenching liquid and then transferring to deionized water for further quenching, wherein the polymer water-based quenching liquid has a mass fraction of 12%~18%, a liquid temperature of 25~35℃, a first stage quenching time of 60~180s, a time interval of 5~20s between stages of deionized water, and a second stage deionized water quenching temperature of 20~30℃ and a quenching time of 120~240s.

8. The method for preparing high-strength nickel-chromium-silicon reinforced copper alloy according to claim 1, characterized in that, The low-temperature micro-deformation in step (3) is rolling, molding or roll pressing; the holding time for water temperature equalization is 90~150s; and after step (3) and before step (4), there is also a mild micro-deformation peak elimination step, which is to first heat to 60~100℃ and hold for 5~20min, and then perform mild micro-deformation with a reduction rate of 1%~3%.

9. A high-strength nickel-chromium-silicon reinforced copper alloy, characterized in that, It is obtained by the preparation method of the high-strength nickel-chromium-silicon reinforced copper alloy according to any one of claims 1-8.

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