Preparation method of ultra-fine grain ODS-Cu composite material for synergistically improving mechanical-electrical conductivity

Abstract

The invention provides a preparation method of an ultra-fine grain ODS-Cu composite material for synergistically improving mechanical-electrical conductivity, and relates to the technical field of copper-based composite materials and preparation. The method comprises the following steps: preparing superfine ODS-Cu powder containing 0.5-1.5 wt% of Al2O3 by adopting an in-situ endogenous oxidation-reduction method, carrying out cold isostatic pressing, sintering under a hydrogen protection atmosphere, carrying out hot extrusion and annealing to obtain a densified ODS-Cu formed blank, and drawing or rolling to obtain an intermediate plate; carrying out low-temperature annealing on the intermediate plate and then transferring the intermediate plate into liquid nitrogen until the core temperature of the plate is less than or equal to-150 DEG C; and the obtained plate is subjected to multi-pass cold rolling treatment, and the composite material is obtained. Compared with similar copper-based dispersion strengthening or severe plastic deformation routes in the prior art, the tensile strength and the yield strength can be improved by more than 10%, the ductility can be improved by more than 50%, the electric conductivity is higher than 75% IACS, and the softening temperature is higher than 900 DEG C.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of copper-based composite materials and preparation, in particular to a preparation method of ultra-fine grain ODS-Cu composite material with synergistically improved mechanical and electrical properties. BACKGROUND

[0002] Oxide dispersion strengthened copper-based composite material (ODS-Cu) has excellent electrical and thermal conductivity and high strength, and has been widely used in many high-tech fields such as ultra-large scale integrated circuit lead frame, high pulse magnetic field conductor, high power microwave tube, overhead conductor for high-speed rail transit, resistance welding electrode and electromagnetic track. It is difficult to simultaneously achieve high strength, high electrical conductivity, good elongation and high softening temperature in engineering. The existing technology introduces nanometer oxide dispersion strengthening to refine the grain and improve the high temperature stability, but this path inevitably increases the grain boundary and dislocation density, resulting in a decrease in electrical conductivity and elongation, so it is difficult to achieve synergistic optimization between strength, electrical conductivity, elongation and softening temperature.

[0003] From the mechanism, improving strength often depends on dislocation strengthening, fine-grain strengthening and Orowan bypassing strengthening mechanism, accompanied by an increase in dislocation density and an increase in the proportion of high-angle grain boundaries, which intensifies electron scattering and damages electrical conductivity. For example, Chinese patent CN115921850A discloses a preparation method of high-strength and high-conductivity aluminum oxide dispersion strengthened copper, which improves the strength by constructing a multi-scale non-uniform grain structure (coexistence of nanocrystalline, ultra-fine grain and coarse grain), but the organization distribution is uneven, which easily leads to unbalanced performance distribution, and the process is complicated and inefficient.

[0004] On the contrary, simply pursuing electrical conductivity often requires reducing solid solution content and defect density, which weakens dislocation and fine-grain strengthening, resulting in insufficient strength. Chinese patent CN102660696A introduces rare earth oxides into the copper matrix to improve electrical conductivity, but the common problem is that the strength improvement is limited, and strict control of oxidation / reduction during rolling increases the process complexity and cost pressure.

[0005] Although SPD (such as ECAP / HPT) can significantly refine grains and increase strength, a large number of dislocations and high-angle grain boundaries introduced at the same time will lead to excessive accumulation of defects, making it difficult for the material to maintain uniform deformation, enhancing electron scattering of the current, and causing a significant decrease in electrical conductivity. More importantly, in this state, heat treatment or service heat exposure is more likely to occur, and recovery and recrystallization are more likely to occur, which can increase the electrical conductivity and elongation, but due to the reduction of dislocations and interfaces, the strength and softening temperature will decrease to varying degrees. Chinese patent CN102108451A reports that after multiple passes of ECAP and subsequent cold working, the strength of the alloy increases and the electrical conductivity decreases to about 35% IACS, and can only be restored by high-temperature annealing; However, subsequent heat treatment triggers recovery / recrystallization, which reduces the strength by about 9%.

[0006] Therefore, the existing technology has the following problems: increasing strength at the expense of electrical conductivity and elongation by using high dislocation density or high-angle grain boundaries; restoring electrical conductivity and elongation through heat treatment, resulting in a decrease in strength and high-temperature softening resistance; and relying on SPD for strength improvement, which is equipment-specific and size-limited, making it difficult to scale. Therefore, there is an urgent need to develop an ODS-Cu synergistic control process implemented in conventional rolling mills and common heat treatment equipment to achieve excellent matching of strength, electrical conductivity, elongation, and softening temperature. SUMMARY

[0007] To solve the technical problem of the existing technology that strength, electrical conductivity, elongation, and softening temperature cannot be synergistically optimized, the present application proposes a method for preparing an ultra-fine-grained ODS-Cu composite material that synergistically improves mechanical and electrical properties. The technical solution is as follows:

[0008] A method for preparing an ultra-fine-grained ODS-Cu composite material that synergistically improves mechanical and electrical properties, the method comprising the following steps:

[0009] S1, in-situ internal oxidation-reduction method for preparing powder and densification: an ultra-fine ODS-Cu powder containing 0.5-1.5wt% Al2O3 is prepared by an in-situ internal oxidation-reduction method, and after cold isostatic pressing, sintering is carried out in a hydrogen atmosphere, followed by hot extrusion and annealing, to obtain a densified ODS-Cu forming blank;

[0010] S2, large deformation pre-processing: the ODS-Cu forming blank obtained in S1 is drawn or rolled to obtain an intermediate plate;

[0011] S3, low-temperature annealing: the intermediate plate obtained in S2 is subjected to low-temperature annealing, and after the annealing is completed, the plate is transferred to liquid nitrogen until the core temperature of the plate is ≤-150℃;

[0012] S4, liquid nitrogen rolling: using a conventional rolling mill to cold roll the plate obtained in S3 under cryogenic conditions, to obtain an ultra-fine grain ODS-Cu composite plate with synergistically improved mechanical and electrical properties.

[0013] Optionally, the pressing pressure of the cold isostatic pressing in S1 is 100-600 MPa, and the pressure holding time is 30-300 s; the sintering temperature is 900-1050 DEG C, and the holding time is 0.5-5 h; the sintering method is vacuum sintering or atmosphere protection sintering, and the atmosphere protection sintering is connected with one or more of dry hydrogen, nitrogen and argon; the density of the sintered blank is greater than 8.7 g / cm 3 , and the density reaches more than 99.3%.

[0014] Optionally, the preheating temperature of the hot extrusion in S1 is 700-950 DEG C, and the extrusion ratio is 9:1-25:1; the annealing temperature is 500-600 DEG C, and the duration is 1-2 h.

[0015] Optionally, in S2, the cumulative equivalent true strain is greater than or equal to 2.3 (or the cumulative deformation is greater than or equal to 90.00%) by drawing or rolling, the single pass reduction rate is 3-10%, and the pass deformation amount is constant or increasing. The purpose of drawing or rolling is to refine the structure and introduce high-density dislocations to improve the strength and density of the alloy.

[0016] Optionally, the low-temperature annealing temperature of S3 is 150-350 DEG C, and the holding time is 10-120 min. The purpose of low-temperature annealing is to maintain the grain size while reducing the defect density, restoring the electrical conductivity and elongation. After annealing, the plate is quickly transferred into liquid nitrogen within 1 min. After this step, the electrical conductivity and elongation are improved, and the average grain size is still less than 0.3 microns.

[0017] Optionally, the liquid nitrogen rolling of S4 is carried out at a temperature of less than or equal to -150 DEG C, preferably -196 DEG C, the natural nitrogen recovery time between passes is controlled to be 1-2 min or the surface temperature is not higher than -150 DEG C; the single pass reduction rate is 3-10%, the pass deformation amount is constant or increasing, and the cumulative equivalent true strain in the liquid nitrogen stage is greater than or equal to 4.0 (or the cumulative deformation is greater than or equal to 98.18%). After rolling, straightening and edge trimming are carried out.

[0018] Optionally, the cumulative equivalent true strain of the plate obtained after S1-S4 is greater than or equal to 6.0 (or the cumulative deformation is greater than or equal to 99.75%).

[0019] Optionally, compared with the prior art adopting the same copper-based dispersion strengthening or severe plastic deformation route, the application realizes the synergistic performance of strength-conductivity-ductility-softening resistance by introducing a nanoscale dispersion phase into the copper alloy and adopting a staged regulation process, while improving the mechanical strength and stably maintaining the elongation at more than 10% and considering the higher electrical conductivity. Under the same test conditions, the material prepared by the method of the application can simultaneously satisfy the tensile strength and yield strength increased by more than 10%, the elongation increased by more than 50%, the electrical conductivity higher than 75% IACS, and the softening temperature higher than 900 DEG C.

[0020] The application further provides the ultrafine-grain ODS-Cu composite material with synergistically improved mechanical and electrical properties, which contains 0.5-1.5 wt% of Al2O3 and the balance of Cu and inevitable impurities in terms of mass percentage. The microstructure of the composite material is ultrafine grains with an average grain size of less than 0.3 microns, and has a multi-level barrier structure composed of a nanoscale Al2O3 dispersion phase and subgrains / twins.

[0021] Optionally, the microstructure of the ultrafine-grain ODS-Cu composite material with synergistically improved mechanical and electrical properties is an Al2O3 dispersion phase with a volume fraction of 1.13-3.34 vol% and an average size of 13-35 nm, which is uniformly distributed in the Cu matrix.

[0022] Optionally, the density of the ultrafine-grain ODS-Cu composite material with synergistically improved mechanical and electrical properties is 8.73-8.89 g / cm 3 , and the relative density is 99.3-99.9%.

[0023] The technical principle of the application is as follows:

[0024] The step S1 of the application takes a Cu-Al ultrafine alloy powder as a precursor, and uses an in-situ endogenous oxidation-reduction method to prepare an ultrafine ODS-Cu powder with an Al2O3 dispersion phase size of less than 20 nm, and the powder particle size is controlled in the range of an average particle size D 50 ≤ 50 microns, so as to improve the initial density and sintering activity, and lay a foundation for subsequent grain continuous refinement and interface structure stability; then the above-mentioned powder is used to prepare an ultrafine-grain ODS-Cu forming blank and densify the blank by sintering, extrusion and other processes; if the extrusion ratio is less than 9:1 or the extrusion temperature is too low, the blank porosity is insufficient, the particles / impurities are banded, the large deformation pre-processability of S2 is reduced, and edge cracks are induced, so that the elongation is damaged; if the temperature is too high or the holding time is too long, the blank grain is coarsened, the Zener pinning is weakened, and the softening temperature and uniform elongation in the later stage of S4 are affected.

[0025] Step S2 is a large deformation pre-processing of the ODS-Cu shaped rod / plate blank of S1, which refines the structure and introduces high-density dislocations, improves the strength and density of the alloy, and provides the necessary structure stability and performance basis for subsequent deformation; the cumulative equivalent true strain η≥2.3 (≈cumulative reduction≥90%); the single pass reduction rate is 3-10%, preferably constant or increasing. If η<2.0 or single pass<3%, the billet is not refined enough, and the CTB formation is less in S4; if the single pass is >10% or η is too large, the billet is prone to edge cracking / warping, interlayer instability (plate), and high energy storage, which leads to recrystallization in S3, resulting in a decrease in elongation and softening temperature.

[0026] Step S3 is low-temperature annealing, which can effectively eliminate defects such as dislocations and vacancies in the ODS-Cu rod / plate blank while maintaining ultra-fine grains and high strength, and retain beneficial interfaces (subgrain boundaries, particle-matrix boundaries), while maintaining high strength, the electrical conductivity and elongation are restored, and the grain size is maintained at an ultra-fine level of <0.3 μm; T<150℃ or t<10min, then the billet defects are not eliminated enough, and the energy storage is uneven; T>350℃ or t>120min, then the billet is prone to recovery or recrystallization in S4, and the grain grows. After low-temperature annealing, immerse in liquid nitrogen quickly, which can selectively eliminate vacancies / dislocations and homogenize the energy storage without coarsening the grains. If the pre-annealing is left in the air or slowly cooled, recovery / dislocation rearrangement will occur, which will destroy the initial state of "low defects but fine grains" established in the previous step.

[0027] Step S4 is multi-pass rolling under liquid nitrogen conditions (≤-150℃, preferably -196℃), with a single pass reduction rate of 3-10%, constant or increasing reduction rate, and a 1-2 min inter-pass temperature. The cumulative equivalent true strain η≥4.0 in the liquid nitrogen stage; the cumulative equivalent true strain η≥6.0 (or the equivalent total deformation amount≥99.75%) in the whole process. This process suppresses dynamic recovery and recrystallization, and the dislocation slip is limited, which is more prone to decomposition into partial dislocations for sliding, thereby promoting the formation of nanotwins. The CTB / subgrain boundaries formed together with the Al2O3 nanodispersion phase provide strong dislocation obstacles and Zener pinning, which on the one hand improves the strength and maintains a high work hardening rate, delays necking, and significantly improves the uniform elongation; on the other hand, the scattering of electrons by CTB is weaker than that by high-angle grain boundaries, which is conducive to maintaining a high level of electrical conductivity. At the same time, the low-mobility interface limits grain boundary migration and delays recrystallization, making the material softening temperature≥900℃. If η (liquid nitrogen stage) <4.0 or the inter-pass temperature is too long (>2min or the surface temperature>-120℃), the number of CTBs is insufficient and the recovery is significant; if the single pass reduction rate is >10%, the risk of deep cryogenic brittle cracking / edge cracking increases, which will weaken the overall performance of the composite material. Finally, an ODS-Cu plate with ultra-fine grains (average grain size <0.3 μm), high strength, high conductivity, high elongation, and high softening temperature is obtained.

[0028] Compared with the prior art, the technical scheme has at least the following beneficial effects:

[0029] The application provides a preparation method of an ultrafine-grain ODS-Cu composite material with synergistically improved mechanical and conductive properties, which can realize synchronous improvement of strength and elongation rate without significantly sacrificing the conductivity and high-temperature softening resistance compared with the same kind of copper-based dispersion strengthening or severe plastic deformation route in the prior art, and can realize more than 10% increase of tensile strength and yield strength, more than 50% increase of elongation rate, more than 75% IACS of conductivity and more than 900 DEG C of softening temperature. Specifically, the tensile strength is greater than or equal to 700 MPa, the yield strength is greater than or equal to 650 MPa, the total elongation is greater than or equal to 10%, the conductivity is greater than or equal to 75% IACS and the softening temperature is greater than or equal to 900 DEG C.

[0030] The process of the application can generate a large number of high-density subgrain / coherent twin boundaries, and the Al2O3 dispersion phase provides Zener pinning to the grain boundary, together constructing a low-mobility interface. On the basis of reducing defect energy storage, the grain boundary growth and recrystallization are effectively inhibited, so that the softening temperature can be stabilized at a level of greater than or equal to 900 DEG C.

[0031] The preparation method of the application can rely on conventional extrusion / rolling mills and common heat treatment equipment, and does not need special SPD equipment such as ECAP / HPT; the key parameters (pass reduction rate, preannealing temperature / time, liquid nitrogen stage cumulative deformation) are continuously adjustable, have a wide window, are easy to record, and have high process repeatability and stability.

[0032] In summary, the method of the application can prepare an ultrafine-grain ODS-Cu composite material plate with synergistically improved mechanical and conductive properties through endogenous oxidation-reduction, CIP / sintering, extrusion / predeformation, low-temperature annealing and liquid nitrogen rolling; the whole process relies on conventional equipment, the parameters are easy to control and implement, the energy consumption and cost are low, and the method is suitable for large-scale manufacturing and engineering promotion. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without any creative effort.

[0034] Figure 1 is a process flow chart of the preparation method of the ultrafine-grain ODS-Cu composite material with synergistically improved mechanical and conductive properties in the embodiment of the application;

[0035] Figure 2is a microstructure chart and grain size distribution chart of the copper-based composite material with 1.13wt% Al2O3 prepared in Example 1 of the present application;

[0036] Figure 3 is a transmission electron microscope chart of the copper-based composite material with 1.13wt% Al2O3 prepared in Example 1 of the present application;

[0037] Figure 4 is a mechanical property chart of the copper-based composite material with 1.13wt% Al2O3 prepared in Example 1 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0038] To make the technical problems, technical solutions and advantages to be solved by the present application more clear, the following will be described in detail in combination with the drawings and specific embodiments. To ensure the comparability of various performance indicators, unless otherwise specified, the parameters of the examples are obtained according to the following methods / standards:

[0039] (1) Chemical composition (Al2O3 content, wt%)

[0040] The Al content in the master alloy Cu-Al alloy is quantified by ICP-OES / ICP-MS, and after sufficient oxidation and reduction, the Al2O3 mass fraction is converted according to the stoichiometric amount.

[0041] (2) Dispersion phase size

[0042] Transmission electron microscope (TEM / HAADF-STEM) image statistics, single sample not less than 10 fields of view, ≥500 particles; the size distribution is represented by the equivalent circle diameter.

[0043] (3) Grain / subgrain size

[0044] Electron backscatter diffraction (EBSD) statistics, step ≤50nm, using equivalent circle diameter for representation; high-angle grain boundary threshold value 15°, Σ3 twin grain boundary is determined according to 60° / <111>.

[0045] (4) Density and compactness

[0046] Archimedes method is used to measure the apparent density (GB / T 5163 / ISO 3369 / ASTM B962 equivalent standard); the theoretical density is calculated according to the component addition:

[0047]

[0048] Wherein, ρ Cu =8.96g / cm 3 , ρ Al2O3 =3.95g / cm 3 ), compactness = measured density / theoretical density × 100%.

[0049] (5) Electrical conductivity

[0050] DC four-probe method to measure resistivity ρ; convert electrical conductivity according to IACS = 100 x (1.7241 μΩ·cm) / ρ. Test after deoxidation and polishing; n ≥ 3 for each group.

[0051] (6) Mechanical properties (UTS, YS, EL)

[0052] Room temperature tensile, follow standard GB / T 228.1-2021, constant strain rate, sample in rolling direction; standard dumbbell sample, consistent gauge length; n ≥ 3, report average ± standard deviation.

[0053] (7) Softening temperature definition and determination

[0054] Softening temperature is defined as the lowest temperature at which the hardness (or 0.2% yield strength) decreases to 80% of the pre-treatment value.

[0055] (8) Product of strength and elongation (PSE)

[0056] Defined as PSE = UTS (MPa) x total elongation (%), expressed in GPa·%; used to characterize the strength-plasticity synergy level.

[0057] Figure 1 is a process flow chart of a preparation method of a super-fine-grained ODS-Cu composite material for synergistically improving mechanical and electrical properties according to an embodiment of the present application; comprising the following steps: preparation of super-fined ODS-Cu powder by internal oxidation reduction method → cold isostatic pressing / sintering / hot extrusion → large deformation (drawing or cold rolling) → low temperature pre-annealing (150-350℃, 10-120min) → quickly transferred to liquid nitrogen immersion → deep cold rolling (interpass temperature 1-2min) → obtain ODS-Cu plate with strong and matched conductivity and good ductility.

[0058] Example 1

[0059] A super-fine-grained ODS-Cu composite material for synergistically improving mechanical and electrical properties, containing 1.13wt% Al2O3 and the balance Cu and unavoidable impurities in terms of mass percentage. Its microstructure is super-fine-grained with an average grain size of 0.26μm, and has a multi-level barrier structure composed of nanoscale Al2O3 dispersed phase and sub-grains / twin crystals.

[0060] The preparation method of the super-fine-grained ODS-Cu composite material for synergistically improving mechanical and electrical properties comprises the following steps:

[0061] S1, in-situ internal oxidation-reduction method for preparing powder and densification: the oxide content of 1.13wt% of the ultra-fine ODS-Cu powder with an average particle size of 40μm is prepared by the internal oxidation-reduction method, and the ultra-fine ODS-Cu powder is cold isostatic pressed at 300MPa for 5min, and then high-temperature sintering is carried out at 1000℃ for 2h under a hydrogen protection atmosphere, so that the density of the sintered compact is 99.40%, and the density of the sintered compact is 8.78g / cm 3 ;

[0062] Then hot extrusion is carried out at 950℃ with an extrusion ratio of 25:1 to obtain an initial rod blank, and annealing is carried out at 600℃ for 2h to eliminate processing stress;

[0063] S2, large deformation pre-processing: the ODS-Cu forming blank of S1 is subjected to large deformation drawing treatment for pre-strengthening, and the cumulative equivalent true strain is 4.36 (deformation amount is 98.72%), and the ODS-Cu rod blank is obtained;

[0064] S3, low-temperature annealing: the ODS-Cu intermediate rod blank obtained in S2 is subjected to low-temperature annealing at 200℃ for 1h;

[0065] S4, liquid nitrogen rolling: under deep cooling conditions (≤-150℃, preferably -196℃), multi-pass cold rolling treatment is carried out by using a conventional rolling mill, and the single-pass reduction rate is 5%, and a constant deformation amount strategy is adopted, and the cumulative equivalent true strain in the liquid nitrogen stage is 2.30 (or the cumulative deformation amount is 90%), and the nitrogen is returned for 2min between passes to maintain low temperature. After rolling, straightening and edge trimming are carried out, and the ultra-fine grain ODS-Cu composite plate with synergistically improved mechanical and electrical properties is obtained.

[0066] Figure 2 is a microstructure diagram and grain size distribution diagram of the copper-based composite material prepared in Example 1 of the present application 1.13wt% Al2O3; wherein the left diagram is a microstructure diagram, and the right diagram is a grain size distribution diagram; the statistical results show that the average grain size d̄=0.26μm, which meets the ultra-fine grain requirement of the present application "average grain size <0.3μm".

[0067] Figure 3 is a transmission electron microscope diagram of the copper-based composite material prepared in Example 1 of the present application 1.13wt% Al2O3; the black arrow mark in the diagram is Al2O3 dispersed phase particles, which show that the particles are nanoscale and are distributed in the intracrystalline and subcrystalline / twin crystal boundary; the area circled by the dashed line is a coherent twin lamella and a subcell, and the distribution of the twin lamella and the subcrystalline boundary can be seen. Figure 2 It can be known in combination that the composite material contains uniformly dispersed Al2O3 dispersed phase, and the average grain size is less than 0.3μm.

[0068] The microstructure of the ultra-fine grain ODS-Cu composite material prepared in the embodiment has a copper grain with a volume fraction of 97.47% and an Al2O3 dispersion phase with a volume fraction of 2.53% uniformly distributed in the copper grain, the average grain size of the copper grain is 0.26 μm, and the average size of the Al2O3 dispersion phase is 18 nm.

[0069] The cumulative total strain of the ultra-fine grain ODS-Cu composite material prepared in the embodiment is 6.57 (or cumulative deformation 99.88%), the density is 8.83 g / cm 3 , the relative density is 99.93%, the hardness is HRB94, the tensile strength is 772 MPa, the yield strength is 684 MPa, the electrical conductivity is 75.6% IACS, the softening temperature is 930°C, the elongation is 10.3%, and the strength-plasticity product is 7.95 GPa%.

[0070] Embodiment 2

[0071] An ultra-fine grain ODS-Cu composite material with improved mechanical and electrical properties, the composite material contains 0.66 wt% of Al2O3 and the balance of Cu and unavoidable impurities in terms of mass percentage. The microstructure of the composite material is an ultra-fine grain structure with an average grain size of 0.29 μm, and has a multi-level barrier structure composed of a nanoscale Al2O3 dispersion phase and subgrains / twins.

[0072] The preparation method of the ultra-fine grain ODS-Cu composite material includes the following steps:

[0073] S1, in-situ internal oxidation-reduction method for preparing powder and densification: an ultra-fine ODS-Cu powder with an average particle size of 42 μm and an oxide content of 0.66 wt% is prepared by an internal oxidation-reduction method, the ultra-fine ODS-Cu powder is cold isostatic pressed at 300 MPa for 5 min, and then high-temperature sintering is carried out at 1000°C for 2 h under a hydrogen protection atmosphere, so that the sintered compact has a relative density of 99.54% and a density of 8.85 g / cm 3 ;

[0074] Then hot extrusion is carried out at 950°C with an extrusion ratio of 25:1 to obtain an initial rod blank, and annealing is carried out at 600°C for 2 h to eliminate processing stress;

[0075] S2, large deformation pre-processing: the ODS-Cu forming blank of S1 is pre-strengthened by large deformation drawing treatment with an equivalent true strain of 1.64 (deformation of 80.65%), and then a 6mm×12mm plate blank is obtained by variable cross-section drawing; the cumulative equivalent true strain of the process is 2.16 (cumulative deformation of 88.50%);

[0076] S3, low temperature annealing: the ODS-Cu intermediate rod blank obtained in S2 is subjected to low temperature annealing at 200℃ for 2h;

[0077] S4, liquid nitrogen rolling: under cryogenic conditions (≤-150℃, preferably -196℃), multi-pass cold rolling treatment is carried out using a conventional rolling mill, with a single pass reduction rate of 5%, a constant deformation amount strategy is adopted, and the cumulative equivalent true strain in the liquid nitrogen stage is 4.09 (or the cumulative deformation amount is 98.33%), and the nitrogen is returned for 2min between passes to maintain low temperature. After rolling, straightening and edge trimming are carried out to obtain an ultra-fine-grained ODS-Cu composite material plate with synergistically improved mechanical and electrical properties.

[0078] The microstructure of the ultra-fine-grained ODS-Cu composite material with synergistically improved mechanical and electrical properties prepared in this embodiment is 98.52% by volume of copper grains and 1.48% by volume of Al2O3 dispersed phase uniformly distributed inside the copper grains, the average grain size of the copper grains is 0.29μm, and the average size of the Al2O3 dispersed phase is 25nm.

[0079] The cumulative total strain of the ultra-fine-grained ODS-Cu composite material with synergistically improved mechanical and electrical properties prepared in this embodiment is 6.25 (or the cumulative deformation amount is 99.81%), the density is 8.87g / cm 3 , the relative density is 99.77%, the tensile strength is 700MPa, the yield strength is 651MPa, the electrical conductivity is 80.5%IACS, the softening temperature is 900℃, the elongation is 10.1%, and the strength-plasticity product is 7.07GPa·%.

[0080] Example 3

[0081] An ultra-fine-grained ODS-Cu composite material with synergistically improved mechanical and electrical properties, the composite material contains 0.85wt% of Al2O3 by mass percentage, and the balance is Cu and unavoidable impurities. The microstructure of the composite material is an ultra-fine-grained structure with an average grain size of 0.28μm, and has a multi-level barrier structure composed of nanoscale Al2O3 dispersed phase and subgrains / twin crystals.

[0082] The preparation method of the ultra-fine-grained ODS-Cu composite material with synergistically improved mechanical and electrical properties comprises the following steps:

[0083] S1, in-situ internal oxidation-reduction method for preparing powder and densification: an oxide content of 0.85wt% of the average particle size of 41 μm of ultra-fine ODS-Cu powder is prepared by internal oxidation-reduction method, and the ultra-fine ODS-Cu powder is cold isostatic pressed at 300 MPa for 5 min, and then high-temperature sintering is carried out at 1000°C for 2h under hydrogen protection atmosphere, to obtain a sintered compact with a density of 8.82 g / cm 3 ;

[0084] Then hot extrusion is carried out at 950°C with an extrusion ratio of 25:1 to obtain an initial rod blank, and annealing is carried out at 600°C for 2h to eliminate processing stress;

[0085] S2, large deformation pre-processing: the ODS-Cu forming blank of S1 is pre-strengthened by large deformation drawing treatment with an equivalent true strain of 4.38 (deformation of 98.75%), to obtain an ODS-Cu rod blank;

[0086] S3, low-temperature annealing: the ODS-Cu intermediate rod blank obtained in S2 is annealed at 200°C for 1h;

[0087] S4, liquid nitrogen rolling: under deep cooling conditions (≤-150°C, preferably -196°C), multi-pass cold rolling treatment is carried out by using a conventional rolling mill with a single pass reduction rate of 3-10%, and a pass deformation increment strategy is adopted, and the cumulative equivalent true strain in the liquid nitrogen stage is 2.20 (or the cumulative deformation is 89.0%), and the nitrogen is returned for 2min between passes to maintain low temperature. After rolling, straightening and edge trimming are carried out to obtain an ultra-fine grain ODS-Cu composite material plate with synergistically improved mechanical and electrical properties.

[0088] The microstructure of the ultra-fine grain ODS-Cu composite material prepared in this embodiment is 98.09% by volume fraction of copper grains and 1.91% by volume fraction of Al2O3 dispersed phase uniformly distributed inside the copper grains, the average grain size of the copper grains is 0.28 μm, and the average size of the Al2O3 dispersed phase is 27 nm.

[0089] The cumulative total strain of the ultra-fine grain ODS-Cu composite material prepared in this embodiment is 6.57 (or the cumulative deformation is 99.86%), the density is 8.82 g / cm 3 , the density is 99.51%, the tensile strength is 715 MPa, the yield strength is 651 MPa, the electrical conductivity is 79.6% IACS, the softening temperature is 925°C, the elongation is 10.1%, and the strength-plastic product is 7.15 GPa·%.

[0090] Example 4

[0091] An ultrafine-grained ODS-Cu composite material for synergistically improving mechanical and electrical conductivity properties, wherein the composite material contains 0.92 wt% Al2O3, with the balance being Cu and unavoidable impurities. Its microstructure is an ultrafine-grained structure with an average grain size of 0.25 μm, and it possesses a multi-level barrier structure composed of nanoscale Al2O3 dispersed phases and subgrains / twins.

[0092] The preparation method of the ultrafine-grained ODS-Cu composite material with synergistic improvement of mechanical and electrical conductivity includes the following steps:

[0093] S1. In-situ endogenous oxidation-reduction method for powder preparation and densification: Ultrafine ODS-Cu powder with an oxide content of 0.92 wt% and an average particle size of 45 μm was prepared using an endogenous oxidation-reduction method. The ultrafine ODS-Cu powder was subjected to cold isostatic pressing at 300 MPa for 5 min, followed by high-temperature sintering at 1000℃ for 2 h under a hydrogen protective atmosphere. The sintered blank had a density of 99.91% and a density of 8.85 g / cm³. 3 ;

[0094] Subsequently, hot extrusion was carried out at 950℃ with an extrusion ratio of 25:1 to obtain the initial slab, which was then annealed at 600℃ for 2 hours to eliminate processing stress.

[0095] S2. Large deformation pre-processing: The extruded sheet is pre-strengthened by plate drawing treatment, and the cumulative equivalent true strain is 4.36 (deformation amount 98.72%) to obtain ODS-Cu slab.

[0096] S3, Low-temperature annealing: The ODS-Cu intermediate slab obtained in S2 is annealed at 200℃ and held for 1 hour.

[0097] S4. Liquid Nitrogen Rolling: Under cryogenic conditions (≤-150℃, preferably -196℃), multi-pass cold rolling is performed using a conventional rolling mill. The single-pass reduction rate is 5%, and a constant deformation strategy is adopted. The cumulative equivalent true strain in the liquid nitrogen stage is 2.30 (or the cumulative deformation is 90%). Nitrogen is returned for 2 minutes between passes to maintain the low temperature. After rolling, straightening and edge trimming are performed to obtain an ultrafine-grained ODS-Cu composite material sheet with synergistically improved mechanical and electrical properties.

[0098] The microstructure of the ultrafine-grained ODS-Cu composite material with synergistic improvement of mechanical and electrical properties prepared in this embodiment consists of copper grains with a volume fraction of 97.94% and Al2O3 dispersed phase with a volume fraction of 2.06% uniformly distributed inside the copper grains. The average grain size of the copper grains is 0.25 μm, and the average size of the Al2O3 dispersed phase is 23 nm.

[0099] The cumulative total strain of the ultra-fine grain ODS-Cu composite prepared in the embodiment is 6.57 (or cumulative deformation 99.86%), the density is 8.85 g / cm 3 , the compactness is 99.91%, the tensile strength is 743 MPa, the yield strength is 651 MPa, the conductivity is 77.5% IACS, the softening temperature is 920°C, the elongation is 10.5%, and the strength-plasticity product is 7.07 GPa%.

[0100] Comparative Example 1

[0101] In step S2, the large deformation pre-processing amount is reduced from 98.72% to 80%. The other steps are the same as in Example 1.

[0102] Through performance testing, the cumulative total strain of the ultra-fine grain slab prepared in the comparative example is 3.82, the tensile strength is 650 MPa, the yield strength is 608 MPa, the elongation is 12.5%, the softening temperature is 930°C, the conductivity is 84.5% IACS, and the strength-plasticity product is 8.13 GPa%. It is shown that reducing the pre-processing deformation amount results in insufficient cumulative equivalent true strain of the material, and the copper matrix grains are not fully refined (the average grain size is 0.45 μm). The grain boundary density and dislocation density are significantly reduced, weakening the effects of grain refinement and dislocation strengthening, resulting in a significant decrease in strength and hardness.

[0103] Figure 4 is a mechanical property diagram of the copper-based composite material with 1.13wt% Al2O3 prepared in Example 1 and Comparative Example 1 of the present application, wherein the blue solid line represents the "room temperature rolling sample" and the red dashed line represents the "low temperature pre-annealing + liquid nitrogen rolling sample". The representative values are listed in the table: the UTS of the room temperature rolling sample is 680±6 MPa, the EC is 74.9±0.3% IACS, and the EL is 6.6±0.71%; the UTS of the process sample is 756±7 MPa, the EC is 75.6±0.3% IACS, and the EL is 10.5±0.09%, showing synchronous improvement in strength and elongation and maintaining conductivity.

[0104] Comparative Example 2

[0105] In step S3, the low temperature annealing is cancelled and the liquid nitrogen rolling of S4 is directly entered. The other steps are the same as in Example 1.

[0106] Through performance testing, the tensile strength is 733 MPa, the yield strength is 620 MPa, the elongation is 7.6%, the softening temperature is 930°C, the conductivity is 70.1% IACS, and the strength-plasticity product is 5.57 GPa%. It is shown that the material does not use low temperature annealing for defect cleaning, the material provides strength with high dislocation density, the conductivity is significantly reduced, the elongation is deteriorated, and it does not have the synergistic advantages of strength-conductivity-elongation-softening temperature.

[0107] Comparative Example 3

[0108] In step S3, the low-temperature annealing temperature before liquid nitrogen deformation was increased from 200℃ to the high-temperature annealing temperature 800℃. The other steps were the same as in Example 3.

[0109] After performance testing, the tensile strength was 603MPa, the yield strength was 547MPa, the elongation was 14.2%, the softening temperature was 900℃, the electrical conductivity was 80.9%IACS, and the strength-plasticity product was 8.56GPa·%. It was shown that too high a heat treatment temperature (800℃) would cause the matrix to recover / recrystallize and lead to grain growth (the average grain size increased to 0.46μm), destroying the ultra-fine grain structure. At the same time, the reduction of defect density would weaken the pinning effect of the aluminum oxide dispersion phase on dislocations and grain boundaries, leading to a decrease in material strength; the reduction in electron scattering and the recovery of uniform deformation ability would cause the electrical conductivity and elongation to increase slightly, but the overall performance would be poor.

[0110] Comparative Example 4

[0111] In step S4, the liquid nitrogen rolling was replaced by room temperature rolling. The other steps were the same as in Example 4.

[0112] After performance testing, the tensile strength was 662MPa, the yield strength was 578MPa, the elongation was 8.9%, the softening temperature was 930℃, the electrical conductivity was 74.7%IACS, and the strength-plasticity product was 5.89GPa·%. It was shown that replacing deep cryogenic rolling with room temperature rolling would significantly weaken the synergistic improvement of strength and elongation. The mechanism lies in the fact that dynamic recovery is more likely to occur at room temperature, and it is difficult to obtain high dislocation storage and nanotwin boundaries under deep cryogenic conditions, thus leading to a simultaneous decrease in strength and uniform elongation.

[0113] Comparative Example 5

[0114] On the premise of keeping step S1 (powdering-densification-extrusion-annealing) consistent, the subsequent deformation steps of Example 1 were replaced by the following sequence in this comparative example:

[0115] S1, powdering-densification-extrusion-annealing (same as in Example 1) was followed by pre-strengthening of the extruded rod by large deformation drawing (deformation amount 94%) to obtain an ODS-Cu rod blank; the size of the ODS-Cu rod blank was φ14mm×450mm;

[0116] S2, ODS-Cu plate blank preparation: the ODS-Cu rod blank of S1 was subjected to rolling deformation with a rolling reduction of 85.9% to obtain an ODS-Cu plate blank; the size of the ODS-Cu plate blank was approximately 850mm×30mm×7mm, which was cut into 4 segments for standby use;

[0117] S3, slab surface pretreatment: the ODS-Cu slab of S2 is subjected to surface mechanical polishing and chemical cleaning to obtain a surface-cleaned ODS-Cu slab; the oxides, grease and other impurities attached to the surface of the surface-cleaned ODS-Cu slab are completely removed, and the surface roughness is 0.8 μm;

[0118] S4, cold stacking: the surface-cleaned ODS-Cu slab of S3 is stacked in four layers to form a group slab with an initial thickness of 28 mm, and a conventional double-roller mill is used for multi-pass cold rolling to improve the surface flatness of the material, eliminate interlayer gaps as much as possible, and achieve preliminary interlayer bonding to prevent oxidation diffusion during heat treatment; when the target plate size is 300 mm x 70 mm x 12 mm, the total cold stacking reduction rate is 57.3%, the single-pass reduction rate is controlled at 10%, and the cold stacking pass is 6 passes to obtain an ODS-Cu cold stacking plate.

[0119] S5, warm stacking: the ODS-Cu cold stacking plate of S4 is heated and kept warm, and then subjected to multi-pass warm stacking using a conventional double-roller mill; the rolling process is controlled by increasing the reduction rate of each pass and controlling the deformation amount of each pass within 15% at most; the warm stacking temperature is 500°C, the warm stacking time is 0.5 h, and when the target plate size is 400 mm x 85 mm x 1 mm, the total warm stacking reduction rate is 91.7% and the warm stacking pass is 6-8 passes; after rolling, air cooling, straightening and edge trimming, a high-strength high-conductivity ultra-fine-grained ODS-Cu-based composite plate is obtained.

[0120] Performance testing shows that the tensile strength is 752 MPa, the yield strength is 665 MPa, the elongation is 5.74%, the softening temperature is 950°C, the electrical conductivity is 76.4% IACS, and the strength-plasticity product is 4.32 GPa·%. It is shown that under the condition of consistent chemical composition and lower total strain (Example 1: η≈6.57), the present application still obtains higher strength (772 MPa) and significantly higher elongation (10.3%, increased by about 79% compared with the comparative example). The electrical conductivity is basically the same (75.6% IACS), and the softening temperature is still in the range of ≥900°C. The comprehensive index shows that the strength-elongation synergy of the present application is significantly better than that of the comparative example. The mechanism lies in the introduction of the mechanism of "low-temperature annealing (defect cleaning, no grain coarsening) + liquid nitrogen rolling (inhibition of recovery, promotion of nano-twin formation)", which constructs a multi-level barrier of CTB / subgrain boundary and Al2O3 dispersion phase, providing a stable source of work hardening and maintaining a relatively weak electron scattering, thereby realizing the synchronous improvement of strength and elongation without significantly sacrificing electrical conductivity and softening resistance.

[0121] The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing an ultrafine-grained ODS-Cu composite material with synergistically improved mechanical and electrical conductivity properties, characterized in that, The method includes the following steps: S1. In-situ endogenous oxidation-reduction method for powder preparation and densification: Ultrafine ODS-Cu powder containing 0.5-1.5wt%Al2O3 is prepared by in-situ endogenous oxidation-reduction method. After cold isostatic pressing, it is sintered under hydrogen protective atmosphere, followed by hot extrusion and annealing to obtain densified ODS-Cu preform. S2, Large Deformation Pre-processing: The ODS-Cu forming billet obtained in S1 is drawn or rolled to obtain an intermediate plate; S3, Low-temperature annealing: The intermediate board obtained in S2 is subjected to low-temperature annealing. After annealing, the board is transferred into liquid nitrogen until the core temperature of the board is ≤-150℃. S4. Liquid nitrogen rolling: The plate obtained in S3 is subjected to multiple cold rolling processes under deep cryogenic conditions using a conventional rolling mill to obtain an ultrafine-grained ODS-Cu composite material plate with synergistically improved mechanical and electrical properties.

2. The preparation method of the ultrafine-grained ODS-Cu composite material with synergistically improved mechanical and electrical properties according to claim 1, characterized in that, The pressing pressure of S1 medium-cooled isostatic pressing is 100-600 MPa, and the holding time is 30-300 s; the sintering temperature is 900-1050℃, and the holding time is 0.5-5 h; the sintering method is vacuum sintering or atmosphere-protected sintering, with atmosphere-protected sintering using one or more of dry hydrogen, nitrogen, and argon; the density of the sintered blank is greater than 8.7 g / cm³. 3 The density reaches over 99.3%.

3. The method for preparing the ultrafine-grained ODS-Cu composite material with synergistically improved mechanical and electrical conductivity properties according to claim 2, characterized in that, The preheating temperature for hot extrusion in S1 is 700-950℃, and the extrusion ratio is 9:1-25:1; the annealing temperature is 500-600℃, and the duration is 1-2 hours.

4. The method for preparing the ultrafine-grained ODS-Cu composite material with synergistically improved mechanical and electrical conductivity properties according to claim 1, characterized in that, In S2, the cumulative equivalent true strain is ≥2.3 by drawing or rolling, the single-pass reduction rate is 3-10%, and a constant or incremental deformation strategy is adopted for each pass.

5. The method for preparing the ultrafine-grained ODS-Cu composite material with synergistically improved mechanical and electrical conductivity properties according to claim 1, characterized in that, The low-temperature annealing temperature of S3 is 150-350℃, and the holding time is 10-120 minutes. After annealing, the board is quickly transferred into liquid nitrogen within ≤1 minute.

6. The method for preparing the ultrafine-grained ODS-Cu composite material with synergistically improved mechanical and electrical conductivity properties according to claim 1, characterized in that, S4 liquid nitrogen rolling is carried out at a temperature of ≤-150℃, preferably -196℃. Natural nitrogen return between passes is controlled within 1-2 minutes or the surface temperature is limited to not exceeding -150℃. The single-pass reduction rate is 3-10%, and a strategy of constant or incremental deformation per pass is adopted. The cumulative equivalent true strain in the liquid nitrogen stage is ≥4.

0.

7. The method for preparing the ultrafine-grained ODS-Cu composite material with synergistically improved mechanical and electrical conductivity properties according to any one of claims 1 to 6, characterized in that, The cumulative equivalent true strain of the plate obtained through S1-S4 is ≥6.

0.

8. The ultrafine-grained ODS-Cu composite material with synergistically improved mechanical and electrical conductivity properties prepared by the method according to any one of claims 1 to 7, characterized in that, The composite material contains 0.5-1.5 wt% Al2O3 by mass, with the balance being Cu and unavoidable impurities; its microstructure consists of ultrafine crystals with an average grain size of <0.3 μm, and has a multi-level barrier structure composed of nanoscale Al2O3 dispersed phases and sub-crystals / twins.

9. The material according to claim 8, characterized in that, The microstructure of the ultrafine-grained ODS-Cu composite material that synergistically enhances mechanical and electrical properties is a dispersed phase of Al2O3 with a volume fraction of 1.13-3.34 vol% and an average size of 13-35 nm, which is uniformly distributed in the Cu matrix.

10. The material according to claim 8, characterized in that, The density of the ultrafine-grained ODS-Cu composite material that synergistically enhances mechanical and electrical conductivity is 8.73-8.89 g / cm³. 3 The density is 99.3-99.9%.

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