Heat-resistant oxygen-free copper material and preparation method and application thereof

Abstract

The invention provides a heat-resistant oxygen-free copper material and a preparation method and application thereof. Wherein alloy elements Mo, Ce, Yb, Ta and Sc are added into the oxygen-free copper; the preparation method comprises the steps that all the metal raw materials are prepared according to the design proportion and smelted to obtain alloy liquid, the alloy liquid is subjected to casting forming to obtain a cast ingot, then the cast ingot is subjected to homogenization treatment to obtain a homogenized blank, the homogenized blank is subjected to hot rolling treatment to obtain a rolled plate, and the rolled plate is subjected to thermomechanical treatment. The oxygen-free copper prepared by the invention has better heat resistance than common oxygen-free copper, and after high-temperature treatment at 1070 DEG C close to the melting point of the oxygen-free copper, the average grain size of a grain boundary containing sigma 3n (n = 1, 2, 3) is less than or equal to 65 [mu] m, and the average grain size of a grain boundary not containing sigma 3n (n = 1, 2, 3) is less than or equal to 150 [mu] m.

Description

Technical Field

[0001] The present invention belongs to the technical field of copper alloys, and particularly relates to a heat-resistant oxygen-free copper material, a preparation method thereof, and an application thereof. Background Art

[0002] Oxygen-free copper is pure copper that does not contain oxygen and any deoxidizer residues. However, in the actual production process, it is impossible to completely remove the oxygen content. Therefore, oxygen-free copper still contains very trace amounts of oxygen and other impurities. Generally, it is stipulated that the oxygen content should be below 0.003%, and the total impurity content should be below 0.05%. Compared with ordinary pure copper, it has good processing performance, welding performance, excellent electrical conductivity and thermal conductivity. Oxygen-free copper has a wide range of applications in the fields of electrical engineering, rail transit, and new energy, etc.

[0003] The application of oxygen-free copper in the field of electronics and electricity is the most extensive. Because oxygen-free copper is widely used in the semiconductor field, due to its excellent processing performance, outstanding conductivity and heat resistance, oxygen-free copper is often made into busbars, leads, lead frames, wires and cables, transformer coils, high-end audio equipment, high-precision electronic components, and vacuum electronic components, etc. IGBT (Insulated Gate Bipolar Transistor) insulated gate bipolar transistor is a common power semiconductor device. The core component DBC (Direct bonding copper) ceramic copper clad laminate in it is widely used in power module packaging because of its excellent thermal conductivity, electrical insulation, electrical conductivity, and welding performance, etc. It is the core material component of power module packaging. The DBC board is realized by directly bonding an oxygen-free copper strip to the ceramic surface under high temperature and high pressure to form a composite metal-ceramic substrate. The manufacturing process of the DBC board is as follows: First, the oxygen-free copper plate is attached to one side or both sides of the ceramic plate, and then at a high temperature of about 1070°C close to the melting point of copper and in an atmosphere containing a trace amount of oxygen, a eutectic melt thin layer of Cu+Cu 2 O is formed on the surface of the oxygen-free copper plate. After holding for a period of time, the eutectic melt fully infiltrates into the oxygen-free copper plate and the ceramic plate to form a firm bond between the two.

[0004] However, ordinary oxygen-free copper cannot maintain tissue stability at a high temperature of 1070°C, and the grains will grow rapidly, which will increase the surface roughness of the oxygen-free copper surface. This will increase the gap between the oxygen-free copper plate and the ceramic plate, resulting in a decrease in the bonding strength between the two plates and even bonding failure. It seriously restricts the development of high-end IGBT production and many related fields such as industry and new energy in our country. It is urgent to promote the localization of power semiconductor devices in our country. Therefore, it is of great significance to develop oxygen-free copper with better heat resistance. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the first object of the present invention is to provide a preparation method of a heat-resistant oxygen-free copper material.

[0006] The second object of the present invention is to provide a heat-resistant oxygen-free copper material prepared by the above preparation method. The oxygen-free copper provided by the present invention has both good mechanical properties and excellent electrical conductivity, and can maintain tissue stability at a high temperature of 1070 °C.

[0007] The third object of the present invention is to provide the application of the heat-resistant oxygen-free copper material prepared by the above preparation method.

[0008] In order to achieve the above objects, the present invention adopts the following technical solutions:

[0009] The present invention provides a preparation method of a heat-resistant oxygen-free copper material. Each metal raw material is weighed according to the designed proportion, melted to obtain an alloy liquid, the alloy liquid is cast into a ingot, and then the ingot is subjected to homogenization treatment to obtain a homogenized billet. The homogenized billet is subjected to hot rolling treatment to obtain a rolled plate, and the rolled plate is subjected to cyclic deformation heat treatment to obtain the product.

[0010] The hot rolling is carried out in a protective atmosphere, the temperature of the hot rolling is 700-900 °C, and the deformation amount is 50-70%.

[0011] The composition of the oxygen-free copper material is as follows: Mo 1-200 ppm, Ta 1-200 ppm, Ce 1-200 ppm, Yb 1-200 ppm, Sc 1-200 ppm, and the rest is Cu and unavoidable impurities.

[0012] In the preparation method of the present invention, after obtaining the ingot by melting, homogenization treatment is first carried out to make each component uniform, and then hot rolling treatment is carried out to eliminate casting defects, homogenize the grain structure, obtain a more uniform, dispersed and fine second-phase distribution. Finally, through cyclic deformation heat treatment, the grain boundary distribution is improved, more Σ3 grain boundaries are obtained, the Σ3 grain boundaries reach saturation, and more Σ3-Σ3-RHAGB triple grain boundary junctions are formed, interrupting the connectivity of the oxygen-free copper grain boundaries. At the same time, the cyclic deformation heat treatment process can also cause the second phase to undergo a dissolution-precipitation-dissolution-precipitation cycle, resulting in a more uniform distribution of the second phase.

[0013] In the present invention, a relatively low hot rolling temperature is adopted. The oxygen-free copper of the present invention has good processing performance and can still maintain good deformation ability at a relatively low temperature. For the deformation amount, a relatively high deformation amount is adopted, which is beneficial to the uniformity of the oxygen-free copper structure, refines the grains, and simultaneously eliminates most of the defects generated during casting. However, although the finer the grains of the oxygen-free copper structure obtained with a higher deformation amount, experiments have found that the initial grain size has nothing to do with the final grain size that the oxygen-free copper can maintain in a high-temperature environment. Adopting an excessive deformation amount to obtain overly fine grains will increase the grain boundary density in the oxygen-free copper and the stored energy at the grain boundaries will be too high, which will instead make it difficult to fully release the stored energy during the subsequent cyclic deformation heat treatment process. This stored energy will be fully released during the final grain growth process, resulting in a rapid increase in the grain size of the oxygen-free copper after the high-temperature process and a decrease in its heat resistance. By controlling the total deformation amount within the scope of the present invention, relatively fine grains can be obtained, and at the same time, lower stored energy can be obtained. During the cyclic deformation heat treatment process of the present invention, these stored energies can be released more thoroughly, thereby avoiding grain growth during subsequent high-temperature applications.

[0014] In the oxygen-free copper material provided by the present invention, the added Mo, Ta, Ce, Yb, and Sc can all form a variety of high-melting-point compounds with common impurities in the oxygen-free copper, so as to remove impurities and improve the mechanical properties and electrical properties; they can also cause the high-melting-point compounds to segregate at the grain boundaries of the oxygen-free copper, which can prevent the movement of the grain boundaries of the oxygen-free copper and effectively improve the heat resistance of the oxygen-free copper.

[0015] Among them, Mo and Ta are added as high-melting-point metals and can serve as heterogeneous nucleation sites to form a high-melting-point second phase in Cu, realizing the pinning of grain boundaries and hindering the movement of grain boundaries at high temperatures, thereby improving the heat resistance of oxygen-free copper; among them, the Mo element, as a high-melting-point element with high heat resistance itself, can reduce the grain boundary energy of ordinary random large-angle grain boundaries, hinder the movement of ordinary large-angle grain boundaries, obtain more special low-energy grain boundaries Σ3 grain boundaries, reduce the proportion of random large-angle grain boundaries, and form a Σ3-Σ3-RHAGB triple grain boundary junction. The formed Σ3-Σ3-RHAGB such a triple grain boundary can severely hinder the movement of random large-angle grain boundaries, thereby inhibiting the process of grain boundary movement and growth, and thus improving the heat resistance of oxygen-free copper. Ta also has a similar effect. Although Ta's ability to reduce the stacking fault energy of Cu is not as good as that of Mo, it has a higher melting point and a smaller solid solubility itself. In this regard, the two can achieve a complementary effect, and can form fine and uniform high-melting-point second phases in Cu, realizing the pinning of grain boundaries to improve the heat resistance of oxygen-free copper. At the same time, Ta can also remove Bi and H elements, while Mo can also form compounds with some impurities in oxygen-free copper such as MoS 2 and MoSi 2etc., further synergistically purify the matrix with rare earth elements, achieving a certain degree of second-phase strengthening while hindering grain boundary migration and grain growth.

[0016] As common rare earth elements, Ce, Yb, and Sc mainly aim to purify the matrix, refine grains, increase strength, improve conductivity, and enhance oxidation resistance. Among them, Ce is mainly used to remove S, Yb is mainly used to remove Pb, and Sc is mainly used to remove O and Bi. The synergistic use of the three can achieve a better purification effect. In addition, Ce and Yb can well improve the distribution of Mo and Ta in the copper matrix and can also form some dispersed second phases with Mo and Ta. Sc has a good effect on refining the grains of oxygen-free copper and can itself form dispersed second phases in the copper matrix. Therefore, under the synergy of the components and preparation methods of the present invention, the oxygen-free copper of the present invention has excellent heat resistance while maintaining excellent electrical and mechanical properties, enabling the oxygen-free copper of the present invention to remain stable at a high temperature of 1070 °C and can be applied to the preparation of DBC boards.

[0017] Of course, the addition amount of elements needs to be effectively controlled. When the addition amount of elements is too small, the grain refinement, purification of the copper matrix, and improvement of heat resistance will all be inhibited. Therefore, on the premise of ensuring electrical conductivity, the degree of alloying should be increased as much as possible. When the addition amount of elements > 200 ppm, the electrical conductivity of oxygen-free copper will rapidly decline, and at the same time, more low-melting-point second phases such as Cu 6 Ce and Cu 6 Yb, etc. will be formed, resulting in the heat resistance of oxygen-free copper not increasing but decreasing. Therefore, the addition amount of elements should not be too high.

[0018] In a preferred embodiment, electrolytic copper, pure Mo powder, pure Ta powder, Cu-25Ce master alloy, Cu-10Yb master alloy, and Cu-10Sc master alloy are taken as metal raw materials according to the designed ratio.

[0019] In the present invention, due to the active nature of the pure elements of Ce, Yb, and Sc, they are added in the form of master alloys, and the alloying elements will be more evenly distributed, avoiding burning loss. While Mo and Ta are added in the form of ultra-fine pure powders because Mo and Ta themselves have good high-temperature stability. Although the room-temperature solid solubility of Mo and Ta in Cu is extremely low, uniform precipitation can be achieved, but they can dissolve 1190 ppm and 88 ppm respectively at high temperatures. The added Mo and Ta can be completely dissolved during the melting process.

[0020] Further preferably, the particle sizes of the pure Mo powder and the pure Ta powder are both < 500 mesh; the particle sizes of the Cu-25Ce master alloy, the Cu-10Yb master alloy, and the Cu-10Sc master alloy are all < 5 mm. If the particle size of the intermediate element is too large, the element diffusion distance is poor and the uniformity is poor, and the melting time needs to be extended; if the particle size is too small, burning loss will occur before the covering agent and the refining agent play their roles.

[0021] In the preferred embodiment, the melting process is as follows: First, electrolytic copper, Mo, and Ta are heated to melting, kept standing and insulated for 5 - 20 min, preferably 5 - 10 min, and then the Cu-25Ce master alloy, the Cu-10Yb master alloy, and the Cu-10Sc master alloy are added successively while stirring. After melting, it is kept standing for another 5 - 10 min to remove the slag to obtain the alloy liquid. Melting in the above manner results in the most uniform final composition and can avoid burning loss, making the alloy liquid meet the designed composition. Since Mo and Ta are high melting point elements and are not prone to burning loss, they are put into the crucible together with electrolytic copper for melting. Ce, Yb, and Sc are easily burned elements, and the melting time needs to be minimized as much as possible to reduce burning loss. And controlling the holding time within the scope of the present invention can achieve sufficient element diffusion without causing excessive energy consumption and cost waste.

[0022] In the preferred embodiment, during melting, each metal raw material is placed in a graphite crucible and melted in an atmospheric melting furnace with a reducing gas introduced under the protection of a covering agent and a refining agent. In the actual operation process, the graphite crucible is a high-strength and high heat-resistant graphite crucible, and the material is an artificial crucible with an ash content ≤ 20 ppm.

[0023] Further preferably, the covering agent is selected from charcoal powder and / or graphite powder, and the covering thickness of the covering agent ≥ 10 cm.

[0024] The covering agent is a reducing medium. Through the covering of charcoal powder and graphite powder, a barrier layer is formed between the melt and the air medium to prevent oxidation, heat preservation, impurity removal, improve the fluidity of the melt, and at the same time reduce the burning loss of alloy elements. The thickness of the covering agent should be above 10 cm. If the thickness of the covering agent is too small, it cannot effectively keep heat, prevent oxidation and burning loss. Of course, in order to reduce costs and the difficulty of slag removal, it is not necessary to be too thick, and more than 10 cm is sufficient.

[0025] Even further preferably, the charcoal powder is calcined charcoal, with a particle size < 10 mm and a gray scale < 20 ppm. By calcining the charcoal powder, oxides, nitrides, moisture, etc. can be fully removed.

[0026] In the preferred embodiment, the refining agent is selected from at least one of sodium borate, sodium carbonate, calcium carbonate, calcium fluoride, and sodium fluoroaluminate, and the addition amount of the refining agent is 1 - 5% of the mass of the alloy liquid, preferably 3%.

[0027] In the present invention, since the added elements themselves have a good impurity removal function, adding a small amount of any one or several common refining agents can obtain oxygen-free copper with high quality and few impurities.

[0028] Preferably, the reducing gas is a mixed gas of CO and N 2 . CO is used because CO is safer than H 2 and CH 4 , and at the same time, it will not produce water to affect the oxygen-free copper ingot.

[0029] Preferably, the melting temperature is 1400 - 1500 °C.

[0030] Preferably, the casting and molding are carried out under a protective atmosphere, and the casting and molding temperature is 1200 - 1350 °C, preferably 1250 - 1300 °C.

[0031] In the present invention, the cooling method during casting and molding is water cooling, and the obtained ingot can be rod-shaped or block-shaped. In the present invention, the method of high-temperature heat preservation and low-temperature casting is adopted, so that a more uniform melt structure can be achieved, and a finer and more uniform initial grain structure can be obtained after casting. The casting temperature is selected to be higher than 1200 °C because too low a casting temperature will cause the melt to break off, resulting in obvious cold shut, slag inclusion and other defects; the casting temperature is lower than 1350 °C because too high a casting temperature is likely to cause casting defects, so the casting temperature should be as low as possible within a reasonable range.

[0032] Preferably, the homogenization treatment is carried out under a protective atmosphere, the homogenization treatment temperature is 700 - 900 °C, preferably 700 - 800 °C, and the homogenization treatment time is 1 - 4 h, preferably 2 h. In the present invention, since several elements such as Mo, Ce, Yb, and Sc will react with impurities in oxygen-free copper or with Cu to produce some low-melting-point compounds such as MoH 2 , Cu 5 Ce, Cu 5 Yb, etc., and since the melting point is less than 900 °C, the temperature is controlled below 900 °C to avoid overburning, and within the preferred range of 700 - 800 °C, the sufficiency of homogenization and the initial grain size can be ensured, and the increase of the initial grain size can be avoided.

[0033] Preferably, the hot rolling deformation is 50 - 60%.

[0034] Preferably, the cyclic thermomechanical treatment is carried out under a protective atmosphere. The process of the cyclic thermomechanical treatment is to perform cold rolling and annealing cyclically. The deformation amount of any cold rolling is 25 - 50%, preferably 25 - 30%. The temperature of any annealing is 300 - 500°C, preferably 350 - 450°C, more preferably 400 - 450°C. The annealing time is 5 - 180 min, preferably 10 - 20 min. Water cooling is carried out after any annealing.

[0035] In the present invention, through cyclic thermomechanical treatment, more Σ3 grain boundaries are obtained. When the Σ3 grain boundaries reach saturation, the connectivity of the grain boundaries of oxygen-free copper will gradually become worse. At the same time, a small amount of Σ9 and Σ27 grain boundaries obtained through grain boundary reactions can also reduce the connectivity of the grain boundaries. During the grain boundary migration process, a large number of Σ3-Σ3-RHAGB triple grain boundary junctions will be formed, interrupting the connectivity of the grain boundaries of oxygen-free copper and thus improving the heat resistance of oxygen-free copper. In the present invention, the temperature of 350 - 450°C is preferably selected during annealing to ensure the full precipitation of elements such as Ce and Sc with large solid solubility at high temperatures during the annealing process. If the temperature is too low, a supersaturated solid solution may be formed. If the temperature is too high, the movement of grain boundaries and dislocations will have sufficient driving force to break through the pinning of several elements such as Mo, Ta, Yb, and Sc, and partial recrystallization of grains will occur. At the same time, the change in the movement behavior of grain boundaries will make it difficult to obtain Σ3 grain boundaries and reduce the connectivity of grain boundaries. The appropriate deformation amount of 25 - 50% is to obtain a certain amount of distortion energy, so that during annealing, grain boundaries can migrate as much as possible to form more Σ3 grain boundaries instead of recrystallization, and it can also ensure that a large deformation amount is avoided to obtain a small initial grain size and excessive stored energy, thus avoiding the drastic growth of grains during high-temperature annealing.

[0036] In the present invention, water cooling is carried out after any annealing. Water cooling can reduce the oxidation behavior, inhibit the further growth of grains and the second phase, and improve the mechanical properties of oxygen-free copper.

[0037] More preferably, the number of times of cyclically performing cold rolling and annealing is 2 - 10 times, preferably 3 - 6 times.

[0038] In the present invention, the protective atmosphere used is pure N 2 or one of pure Ar gas.

[0039] Preferably, the oxygen-free copper material has the following composition: Mo 5 - 50 ppm, Ta 5 - 50 ppm, Ce 5 - 50 ppm, Yb 5 - 50 ppm, Sc 5 - 50 ppm, and the rest is Cu and unavoidable impurities.

[0040] The present invention also provides a heat-resistant oxygen-free copper material prepared by the above preparation method.

[0041] The present invention also provides an application of the heat-resistant oxygen-free copper material prepared by the above preparation method, and the oxygen-free copper material is applied to a DBC ceramic copper clad laminate.

[0042] Principle and Advantage

[0043] In the oxygen-free copper material provided by the present invention, the added Mo, Ta, Ce, Yb, and Sc can all form a variety of high-melting-point compounds with common impurities in oxygen-free copper, so as to remove impurities and improve mechanical properties and electrical properties; they can also cause the high-melting-point compounds to segregate at the grain boundaries of oxygen-free copper, which can prevent the movement of the grain boundaries of oxygen-free copper and effectively improve the heat resistance of oxygen-free copper.

[0044] Among them, Mo and Ta are added as high-melting-point metals and can serve as heterogeneous nucleation sites to form a high-melting-point second phase in Cu, realizing pinning of the grain boundaries and hindering grain boundary movement at high temperatures, thereby improving the heat resistance of oxygen-free copper; among them, the Mo element, as a high-melting-point element with high heat resistance itself, can reduce the grain boundary energy of ordinary random large-angle grain boundaries, hinder the movement of ordinary large-angle grain boundaries, obtain more special low-energy grain boundaries Σ3 grain boundaries, reduce the proportion of random large-angle grain boundaries, and form a Σ3-Σ3-RHAGB triple grain boundary junction. The formed Σ3-Σ3-RHAGB such a triple grain boundary can severely hinder the movement of random large-angle grain boundaries, thus playing a role in inhibiting the process of grain boundary movement and growth, and thus improving the heat resistance of oxygen-free copper. Ta also has a similar effect. Although Ta's ability to reduce the stacking fault energy of Cu is not as good as Mo, it itself has a higher melting point and a smaller solid solubility. In this regard, the two can achieve a complementary effect, and can form fine and uniform high-melting-point second phases in Cu, realizing pinning of the grain boundaries and thus improving the heat resistance of oxygen-free copper. At the same time, Ta can also remove Bi and H elements, and Mo can also form compounds with some impurities in oxygen-free copper such as MoS 2 and MoSi 2 etc., further synergistically purify the matrix with rare earth elements, realize a certain degree of second-phase strengthening while hindering grain boundary migration and grain growth.

[0045] Ce, Yb, and Sc, as common rare earth elements, mainly aim to purify the matrix, refine grains, improve strength, improve conductivity, and have antioxidant effects, etc.; among them, Ce is mainly used to remove S elements, Yb is mainly used to remove Pb elements, and Sc is mainly used to remove O and Bi elements. The three used in combination can achieve a better purification effect. In addition, Ce and Yb can well improve the distribution of Mo and Ta in the copper matrix, and can also form some dispersed second phases with Mo and Ta. Sc has a good effect on refining the grains of oxygen-free copper, and it can also form dispersed second phases in the copper matrix itself.

[0046] In the preparation method of the present invention, after obtaining an ingot through melting, homogenization treatment is first carried out to make each component uniform, and then hot rolling treatment is carried out to eliminate casting defects, homogenize the grain structure, obtain a more uniform, dispersed and fine distribution of the second phase. Finally, through thermomechanical treatment, the grain boundary distribution is improved, more Σ3 grain boundaries are obtained, the Σ3 grain boundaries reach saturation, a Σ3-Σ3-RHAGB triple grain boundary junction is formed, the connectivity of the grain boundaries of oxygen-free copper is interrupted. At the same time, the cyclic thermomechanical treatment process can also cause the second phase to undergo a dissolution-precipitation-dissolution-precipitation cycle, resulting in a more uniform distribution of the second phase.

[0047] Through the synergy of the composition and preparation method of the present invention, the provided oxygen-free copper has a hardness ≥ 61 HV, a conductivity ≥ 99% IACS. At a high temperature of 1070 °C for 20 min, the grain size is significantly smaller than that of ordinary oxygen-free copper treated generally. The average grain size of the grains containing Σ3 n grain boundaries ≤ 65 μm, and the average grain size of the grains without Σ3 n grain boundaries ≤ 150 μm. While maintaining excellent electrical and mechanical properties, it has excellent heat resistance, enabling the oxygen-free copper of the present invention to remain stable at a high temperature of 1070 °C and can be used for the preparation of DBC boards.

[0048] During the preparation process of the present invention, atmospheric melting is adopted, and the whole process is simple, reducing time and economic costs, which is conducive to large-scale production. Brief Description of the Drawings

[0049] Figure 1 is the inverse pole figure image of the oxygen-free copper sample 1. Figure 1 The oxygen-free copper shown has a significantly uniform and fine grain structure, and the Σ3 n grain boundaries distributed therein are often straighter and penetrate the entire grain, showing excellent heat resistance.

[0050] Figure 2 is the inverse pole figure image of the oxygen-free copper sample 2. Figure 2 The oxygen-free copper shown also has a uniform and fine grain structure, and the Σ3 n grain boundaries distributed therein are straight, showing more through-type and grain boundary angle types, demonstrating good heat resistance.

[0051] Figure 3 is the inverse pole figure image of the oxygen-free copper sample 3. Figure 3 The oxygen-free copper shown also has a uniform and fine grain structure, and the Σ3 n grain boundaries distributed therein are straight, showing more through-type and grain boundary angle types, demonstrating good heat resistance.

[0052] Figure 4It is the IPF inverse pole figure image of the oxygen-free copper sample 4. Figure 4 The shown oxygen-free copper also has a uniform and fine grain structure, and the Σ3 n grain boundaries are distributed straight, showing more through-type and grain boundary angle types, demonstrating good heat resistance.

[0053] Figure 5 It is the IPF inverse pole figure image of the oxygen-free copper sample 5. Figure 5 The shown oxygen-free copper has good grain structure uniformity, but the grain size is significantly coarser than Figures 1-4 the oxygen-free copper sample shown in n it, and many straight Σ3

[0054] Figure 6 It is the IPF inverse pole figure image of the oxygen-free copper sample 6. Figure 6 Some obvious grain structure inhomogeneities appear in the shown oxygen-free copper, and the Σ3 n grain boundaries are often finer, showing an interrupted type, and the grain size is relatively large.

[0055] Figure 7 It is the IPF inverse pole figure image of the oxygen-free copper sample 7. Figure 7 The shown oxygen-free copper has a relatively uniform grain structure, and the Σ3 n grain boundaries are relatively straight, and the grain size is coarser than Figures 1-4 .

[0056] Figure 8 It is the IPF inverse pole figure image of the oxygen-free copper sample 8. Figure 8 The shown grain size is significantly coarser than Figures 1-4 the oxygen-free copper in

[0057] Figure 9 It is the IPF inverse pole figure image of the oxygen-free copper sample 9. Figure 9 The grain size in Figure 8 is similar to n and obvious secondary recrystallization also occurs, and the Σ3 Specific implementation mode

[0058] The following are specific implementation cases of the present invention, and the technical solutions of the present invention are further described in combination with the embodiments, but the present invention is not limited to these embodiments.

[0059] Embodiment 1

[0060] This example provides an oxygen-free copper and its preparation method, and the specific steps are as follows:

[0061] (1) According to the total alloy amount of 25 ppm of Mo element, 25 ppm of Ta element, 25 ppm of Ce element, 25 ppm of Yb element and 25 ppm of Sc element, high-purity Mo powder, high-purity Ta powder, Cu-25Ce master alloy, Cu-10Yb master alloy, Cu-10Sc master alloy and high-purity electrolytic copper are taken for batching.

[0062] (2) Melting: First, electrolytic copper, Ta and Mo, 3% refining agent and 10 cm covering agent are sequentially added into a graphite crucible, and heated to 1400 °C and held for 10 min under a composite reducing gas atmosphere of CO and N 2 Then, while stirring, Cu-25Ce master alloy, Cu-10Yb master alloy and Cu-10Sc master alloy are sequentially added. After melting, it is left standing for 10 min, and then cooled to 1250 °C for casting to obtain an ingot;

[0063] (3) Under a protective atmosphere, the ingot obtained in step S2 is subjected to homogenization treatment at a treatment temperature of 700 °C for a treatment time of 2 h.

[0064] (4) Under a protective atmosphere, the homogenized blank obtained in step S3 is hot-rolled at 700 °C, and the hot-rolling deformation amount is 50%.

[0065] (5) Under a protective atmosphere, the rolled plate obtained in step S4 is subjected to thermomechanical treatment, which consists of 4 cycles of cold rolling - annealing. The deformation amount of any cold rolling treatment is 26%, the annealing temperature is 400 °C, the annealing time is 10 min, and water cooling treatment is carried out after any annealing to obtain oxygen-free copper sample 1.

[0066] The IPF image of oxygen-free copper sample 1 after high-temperature annealing at 1070 °C for 20 min is as Figure 1 shown. It can be seen from the figure that the oxygen-free copper has a significantly uniform and fine grain structure, and the Σ3 n grain boundaries distributed therein are often straighter and penetrate the entire grain, and the heat resistance is excellent.

[0067] Example 2

[0068] This example provides a method for preparing oxygen-free copper to improve the heat resistance of oxygen-free copper. The specific steps are different from those of Example 1 in that:

[0069] (1) The deformation amount of each pass in the thermomechanical treatment in step S5 is 50%.

[0070] Oxygen-free copper sample 2 is obtained.

[0071] The IPF image of oxygen-free copper sample 2 after high-temperature annealing at 1070 °C for 20 min is as Figure 2As shown. Oxygen-free copper also has a uniform and fine grain structure, with Σ3 distributed therein n The grain boundaries are straight, showing more through-type and grain boundary angle types, demonstrating good heat resistance.

[0072] Example 3

[0073] This example provides a method for preparing oxygen-free copper to improve its heat resistance. The specific steps are different from those of Example 1 in that:

[0074] (1) In step S5, the annealing temperature of the thermomechanical treatment is 300 °C, and the annealing time is 20 min.

[0075] Oxygen-free copper sample 3 is obtained.

[0076] The IPF image of oxygen-free copper sample 3 after high-temperature annealing at 1070 °C for 20 min is as Figure 3 shown. Oxygen-free copper also has a uniform and fine grain structure, with Σ3 distributed therein n The grain boundaries are straight, showing more through-type and grain boundary angle types, demonstrating good heat resistance.

[0077] Example 4

[0078] This example provides a method for preparing oxygen-free copper to improve its heat resistance. The specific steps are different from those of Example 1 in that:

[0079] (1) In step S5, the cold deformation amount of the thermomechanical treatment is 50%.

[0080] (2) In step S5, the annealing temperature of the thermomechanical treatment is 300 °C, and the annealing time is 20 min.

[0081] Oxygen-free copper sample 4 is obtained.

[0082] The IPF image of oxygen-free copper sample 4 after high-temperature annealing at 1070 °C for 20 min is as Figure 4 shown. Oxygen-free copper also has a uniform and fine grain structure, with Σ3 distributed therein n The grain boundaries are straight, showing more through-type and grain boundary angle types, demonstrating good heat resistance.

[0083] Comparative Example 1

[0084] This example provides a method for preparing oxygen-free copper to improve its heat resistance. The specific steps are different from those of Example 1 in that:

[0085] (1) In step S4, the hot rolling temperature is 700 °C, and the hot rolling deformation amount is 90%.

[0086] Oxygen-free copper sample 5 is obtained.

[0087] The IPF image of the oxygen-free copper sample 5 after high-temperature annealing at 1070°C for 20 min is as follows Figure 5 shown. The oxygen-free copper has good grain structure uniformity, but the grain size is significantly coarser than that of the oxygen-free copper sample shown in Figures 1-4 , and many straight Σ3 n grain boundaries are also obtained.

[0088] Comparative Example 2

[0089] This example provides a method for preparing oxygen-free copper to improve its heat resistance. The specific steps are different from those of Example 1 in that:

[0090] (1) In step S4, the hot rolling temperature is 700°C and the hot rolling deformation is 90%.

[0091] (2) In step S5, the first cold rolling deformation is 80%, the annealing temperature is 300°C, and the holding time is 120 min; except for the first shape-changing heat treatment, the cold deformation is 50% and the number of cycles is 2.

[0092] (3) In step S5, the annealing temperature for the shape-changing heat treatment except the first one is 500°C and the annealing time is 5 min.

[0093] The oxygen-free copper sample 6 is obtained.

[0094] The IPF image of the oxygen-free copper sample 6 after high-temperature annealing at 1070°C for 20 min is as follows Figure 6 shown. Figure 6 Some obvious grain structure non-uniformities appear in the oxygen-free copper shown, and the Σ3 n grain boundaries are often finer, showing an interrupted type, and the grain size is relatively large.

[0095] Comparative Example 3

[0096] This example provides a method for preparing oxygen-free copper to improve its heat resistance. The specific steps are different from those of Example 1 in that:

[0097] (1) In step S1, according to the total alloy amount of 25 ppm of Ce element, 25 ppm of Yb element, and 25 ppm of Sc element, Cu-25Ce master alloy, Cu-10Yb master alloy, Cu-10Sc master alloy and high-purity electrolytic copper are used for batching.

[0098] (2) In step S4, the hot rolling temperature is 700°C and the hot rolling deformation is 90%.

[0099] (3) In step S5, the first cold rolling deformation is 80%, the annealing temperature is 300°C, and the holding time is 120 min; except for the first shape-changing heat treatment, the cold deformation is 50% and the number of cycles is 2.

[0100] (4) In step S5, except for the first shape change heat treatment, the annealing temperature is 350 °C and the annealing time is 120 min.

[0101] An oxygen-free copper sample 7 is obtained.

[0102] The IPF image of the oxygen-free copper sample 7 after high-temperature annealing at 1070 °C for 20 min is as Figure 7 shown. Figure 7 The shown oxygen-free copper grain structure is relatively uniform, and the Σ3 n grain boundary is relatively straight, and the grain size is coarser than Figures 1-4 .

[0103] Comparative Example 4

[0104] This example provides a method for preparing oxygen-free copper to improve the heat resistance of oxygen-free copper. The specific steps are different from those of Example 1 in that:

[0105] (1) In step S1, only high-purity electrolytic copper is taken for melting.

[0106] (2) In step S4, the hot rolling temperature is 700 °C and the hot rolling deformation amount is 90%.

[0107] (3) In step S5, the first cold rolling deformation amount is 80%, the annealing temperature is 300 °C, and the heat preservation time is 120 min; except for the first shape change heat treatment, the cold deformation amount is 50% and the number of cycles is 2 times.

[0108] (4) In step S5, except for the first shape change heat treatment, the annealing temperature is 300 °C and the annealing time is 120 min.

[0109] An oxygen-free copper sample 8 is obtained.

[0110] The IPF image of the oxygen-free copper sample 8 after high-temperature annealing at 1070 °C for 20 min is as Figure 8 shown. Figure 8 The shown grain size is significantly coarser than that of the oxygen-free copper in Figures 1-4 . The grains grow violently, and at the same time, secondary recrystallization occurs, and the organizational structure is uneven.

[0111] Comparative Example 5

[0112] This example provides a method for preparing oxygen-free copper to improve the heat resistance of oxygen-free copper. The specific steps are different from those of Example 1 in that:

[0113] (1) In step S1, only high-purity electrolytic copper is taken for melting.

[0114] (2) In step S4, the hot rolling temperature is 700 °C and the hot rolling deformation amount is 90%.

[0115] (3) Step S5 only performs cold rolling deformation heat treatment once, with a cold rolling deformation amount of 80%, a heat treatment temperature of 350 °C, and an annealing time of 120 min, without subsequent treatment.

[0116] An oxygen-free copper sample 9 is obtained.

[0117] The IPF image of the oxygen-free copper sample 9 after high-temperature annealing at 1070 °C for 20 min is as Figure 9 shown. Figure 9 The grain size is similar to Figure 8 and obvious secondary recrystallization also occurs. The Σ3 n grain boundary growth is not straight enough, and the microstructure is uneven.

[0118] Test example

[0119] In this example, the heat resistance, hardness, electrical conductivity, and grain microstructure morphology of the obtained oxygen-free copper samples in Examples 1-4 and Comparative Examples 1-5 were tested;

[0120] The test method for the hardness of the oxygen-free copper sample refers to the national standard document "Vickers hardness test for metallic materials - Part 1: Test method" numbered GB / T 4340.1-2009.

[0121] The test method for the electrical conductivity of the oxygen-free copper sample refers to the national standard document "Method for measuring resistivity of metallic materials" numbered GB / T 351-2019.

[0122] Heat resistance test of the oxygen-free copper sample:

[0123] The oxygen-free copper samples 1-9 were placed under vacuum conditions, with specific atmosphere conditions of O content less than 10 ppm and H 2 O content less than 10 ppm. The high-temperature annealing conditions were: high temperature of 1070 °C for 20 min. The metallographic structure diagram and IPF image of Electron Backscattering Diffraction (EBSD) of the oxygen-free copper samples before and after annealing were obtained. The metallographic tissue images were observed, the proportion of special grain boundaries of oxygen-free copper was compared, and parameters such as the grain size and grain size of oxygen-free copper were measured as shown in Table 1 to determine whether the high-temperature holding treatment had an impact on the oxygen-free copper samples. That is, whether the oxygen-free copper samples obtained by the present invention have higher heat resistance.

[0124]

[0125] Combined with the test parameters of Examples 1-4 and Comparative Examples 1-5, the IPF diagrams of the oxygen-free copper samples, and the data results shown in Table 1, it can be seen that:

[0126] (1) The oxygen-free copper prepared by the experimental method according to the present invention (Examples 1-4) has excellent electrical conductivity and sufficient strength. Before high-temperature annealing at 1070 °C, the average grain size of the grains containing Σ3 n grain boundaries is 16-26 μm, and the average grain size of the grains without Σ3 n grain boundaries reaches 54-63 μm. After high-temperature annealing at 1070 °C, the average grain size of the grains containing Σ3 n grain boundaries can be as fine as 64 μm at the thinnest, with only a 253% increase. The average grain size of the grains without Σ3 n grain boundaries can be as fine as 148 μm at the thinnest, with only a 237% increase. For Comparative Example 5, which is ordinary oxygen-free copper without special treatment, the average grain size of the grains containing Σ3 n grain boundaries is 158 μm, with a 3762% increase, and the average grain size of the grains without Σ3 n grain boundaries is 331 μm, with a 4534% increase. It can be seen that the heat resistance of the oxygen-free copper prepared by the experimental method of the present invention has been significantly improved. It can also be seen from the IPF diagram that a large number of low-energy Σ3 n grain boundary structures are obtained in the oxygen-free copper of Examples 1-4. The grain boundary network of ordinary large-angle grain boundaries is damaged, and the grain boundary migration behavior is restricted by the Σ3 n grain boundaries, so the heat resistance is significantly improved.

[0127] (2) Through cross-comparison of Examples 1-4, it is found that compared with a large deformation amount, a smaller deformation amount will result in lower energy storage. During rapid annealing, the energy storage of a small deformation amount can be released more completely, while the energy storage of a large deformation amount cannot be completely released. This energy storage is finally released under high-temperature annealing at 1070 °C, causing the grains to grow violently. The higher the annealing temperature before high-temperature annealing, the more completely the energy storage in the grains is released, and the more difficult it is for the grains to grow during high-temperature annealing.

[0128] (3) Through comparison of Example 1 and Comparative Examples 1-2, it is found that neither the hot-rolling nor the cold-rolling deformation amount should be too large, as it is not conducive to the release of the grain boundary energy of oxygen-free copper. The initial grain size has nothing to do with the final grain size of oxygen-free copper. However, overly fine grains will lead to an increase in the grain boundary density in oxygen-free copper. Although the hot-rolling and the first cold-rolling deformation amounts are large and the initial grain size is finer, the grain boundary energy storage increases, which will instead lead to a decrease in the heat resistance of oxygen-free copper. Therefore, it is very important to control the deformation amount of hot and cold deformation. At the same time, too short a heat treatment time will also limit the release of the distortion energy storage of oxygen-free copper and the formation of Σ3 n grain boundaries by grain boundary migration, affecting the heat resistance of oxygen-free copper; while too long a heat treatment time will cause an increase in the initial grain size of oxygen-free copper, resulting in a larger final grain size.

[0129] (4) By comparing Examples 1-4 with Comparative Examples 1, 3-4, it can be seen that when only Ce, Yb, and Sc are added, the electrical conductivity of oxygen-free copper is somewhat improved, but the grain size has grown to a large extent. This indicates that only purifying the matrix will result in a matrix that is too pure and lacks sufficient second phases and impurities to pin the grain boundaries of oxygen-free copper, which instead reduces the heat resistance of oxygen-free copper. The addition of Mo and Ta plays an indispensable role in improving the heat resistance of oxygen-free copper. Comparative Example 3 shows that Ce, Yb, and Sc have a purifying effect on the oxygen-free copper matrix, which improves the overall electrical conductivity. Comparing with Comparative Example 1, although Comparative Example 3 does not contain Σ3 n the grain size of the grain boundaries is similar to that of Comparative Example 1, but it contains Σ3 n the grain size of the grain boundaries is significantly coarser than that of Comparative Example 1. This shows that through the synergistic effect of Mo, Ta, Ce, Yb, and Sc, the grain boundary network structure of oxygen-free copper is greatly improved, and the grain boundary network is segmented more obviously by Σ3 n grain boundaries, resulting in better mechanical and electrical properties.

[0130] Finally, Examples 1-4 obtained by combining the above advantages have excellent heat resistance. Among them, Example 1 obtained a hardness of 61.2 HV, a conductivity of 99.5% IACS, and at 1070 °C for 20 min, the average grain size of the grain boundaries containing Σ3 n is 64 μm, and the average grain size of the grain boundaries without Σ3 n is 148 μm, obtaining an oxygen-free copper sample with a significant improvement in heat resistance.

[0131] The present invention has been described in detail above in conjunction with the embodiments. However, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the scope of knowledge possessed by those of ordinary skill in the art.

Claims

1. A method for preparing a heat-resistant oxygen-free copper material, characterized in that: The metal raw materials are mixed according to the designed proportion, smelted to obtain alloy liquid, the alloy liquid is cast to obtain an ingot, the ingot is homogenized to obtain a homogenized billet, the homogenized billet is hot-rolled to obtain a rolled plate, and the rolled plate is subjected to cyclic deformation heat treatment to obtain the rolled plate; The hot rolling is carried out in a protective atmosphere, the hot rolling temperature is 700-900°C, and the deformation amount is 50-70%; The oxygen-free copper material has the following components: Mo 1-200ppm, Ta 1-200ppm, Ce 1-200ppm, Yb 1-200ppm, Sc 1-200ppm, and the rest is Cu and inevitable impurities.

2. The method for preparing a heat-resistant oxygen-free copper material according to claim 1, characterized in that: Electrolytic copper, pure Mo powder, pure Ta powder, Cu-25Ce master alloy, Cu-10Yb master alloy and Cu-10Sc master alloy are prepared as metal raw materials according to the designed proportion; The particle sizes of the pure Mo powder and the pure Ta powder are all less than 500 meshes; the particle sizes of the Cu-25Ce master alloy, the Cu-10Yb master alloy, and the Cu-10Sc master alloy are all less than 5 mm.

3. The method for preparing a heat-resistant oxygen-free copper material according to claim 1, characterized in that: The smelting process is as follows: firstly, electrolytic copper, Mo and Ta are heated to melt, and then kept at a temperature for 5 to 20 minutes, and then Cu-25Ce master alloy, Cu-10Yb master alloy and Cu-10Sc master alloy are added in sequence while stirring, and after melting, the alloy is kept at a temperature for 5 to 10 minutes to remove the slag and obtain the alloy liquid; During the smelting, each metal raw material is placed in a graphite crucible, and smelted in an atmospheric smelting furnace into which a reducing gas is introduced, under the protection of a covering agent and a refining agent; The covering agent is selected from charcoal powder and / or graphite powder, and the covering thickness of the covering agent is ≥10cm; The charcoal powder is calcined charcoal with a particle size of less than 10 mm and a gray level of less than 20 ppm; The refining agent is selected from at least one of sodium borate, sodium carbonate, calcium carbonate, calcium fluoride and sodium fluoroaluminate, and the amount of the refining agent added is 1-5% of the mass of the alloy liquid; The reducing gas is a mixed gas of CO and N2; The smelting temperature is 1400-1500°C.

4. The method for preparing a heat-resistant oxygen-free copper material according to claim 1, characterized in that: The casting is carried out under a protective atmosphere at a temperature of 1200-1350°C.

5. The method for preparing a heat-resistant oxygen-free copper material according to claim 1, characterized in that: The homogenization treatment is carried out under a protective atmosphere, the temperature of the homogenization treatment is 700-900° C., and the time of the homogenization treatment is 1-4 hours.

6. The method for preparing a heat-resistant oxygen-free copper material according to claim 1, characterized in that: The deformation amount of the hot rolling is 50-60%.

7. The method for preparing a heat-resistant oxygen-free copper material according to claim 1, characterized in that: The cyclic deformation heat treatment is carried out under a protective atmosphere, and the process of the cyclic deformation heat treatment is cyclic cold rolling and annealing; the deformation amount of any cold rolling is 25-50%, the temperature of any annealing is 300-500°C, and the annealing time is 5-180min; water cooling is performed after any annealing; The number of cold rolling and annealing in the cycle is 2-10 times.

8. The method for preparing a heat-resistant oxygen-free copper material according to claim 1, characterized in that: The oxygen-free copper material has the following components: Mo 5-50ppm, Ta 5-50ppm, Ce 5-50ppm, Yb 5-50ppm, Sc 5-50ppm, and the rest is Cu and unavoidable impurities.

9. The heat-resistant oxygen-free copper material prepared by the preparation method according to any one of claims 1 to 8.

10. Application of the heat-resistant oxygen-free copper material prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The oxygen-free copper material is applied to DBC ceramic copper-clad laminates.

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