High-strength and high-thermal-conductivity aluminum alloy material and preparation method thereof

Abstract

The invention discloses a high-strength and high-thermal-conductivity aluminum alloy material and a preparation method thereof, relates to the technical field of aluminum alloys and preparation thereof, and solves the problem of inherent contradiction between strength and thermal conductivity. Comprising Si, Mg, Fe, Cu, Mn, Ti, Zr, Cr, B, mischmetal and the balance aluminum and inevitable impurities, and the total amount of the impurities is smaller than or equal to 0.10%. Wherein Ti and B are added in the form of an Al-5Ti-1B intermediate alloy; the mixed rare earth is added in the form of an aluminum-rare earth intermediate alloy. On the premise of keeping excellent casting flowability, the high-strength and high-heat-conductivity liquid-cooled component has high strength and high heat conductivity, so that the high-strength and high-heat-conductivity liquid-cooled component can perfectly adapt to a precise forming process of a complex thin-wall liquid-cooled component, and the precise size, the uniform wall thickness, the smooth surface and the excellent mechanical property and heat dissipation performance of the formed component are guaranteed; and the heat dissipation requirements of a 5G / 6G base station liquid cooling plate complex thin-wall component on high power, long service life and high reliability are met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aluminum alloy and its preparation, and relates to a high-strength and high-thermal-conductivity aluminum alloy material and a preparation method thereof. BACKGROUND

[0002] With the large-scale commercialization of 5G mobile communication technology and the rapid development of 6G mobile communication technology, mobile communication base stations are developing towards ultra-high density, ultra-high speed and ultra-large capacity. This significantly increases the power consumption of base stations, especially the core chips and power amplifiers of base stations, which generate a large amount of heat during operation. If the heat cannot be dissipated in time and efficiently, it will lead to high chip junction temperature, performance degradation, signal distortion, and even equipment failure, which seriously restricts the stability, reliability and service life of the communication system. To solve this problem, the direct liquid cooling technology using liquid cooling plates for forced convection heat dissipation has become the mainstream solution for 5G / 6G base station cooling due to its high efficiency, silence and precise temperature control. The core of the liquid cooling plate is an aluminum alloy component with complex flow channels and thin walls.

[0003] Currently, such complex thin-walled liquid cooling plate components are mainly manufactured by processes such as die casting or extrusion molding. In order to balance good casting fluidity and formability, cast aluminum alloys or extruded aluminum alloys are commonly selected in the industry. However, there are still the following problems in actual large-scale production and application: (1) The inherent performance contradiction of the material makes it difficult to balance heat dissipation and strength: although the existing cast aluminum alloy has excellent casting performance, its thermal conductivity coefficient is generally low, which cannot meet the instantaneous heat dissipation demand of future higher power chips; while high-strength extruded aluminum alloy has excellent mechanical properties, but its casting fluidity is poor and cannot be used for die casting of complex thin-walled structures; this inherent contradiction between material strength and thermal conductivity performance makes the existing liquid cooling plate material have a "seesaw" effect in mechanical properties and heat dissipation performance, which cannot meet the dual harsh requirements of structural bearing and efficient heat dissipation of base station components; (2) The existing material process has poor adaptability, resulting in large forming defects of the component: when die casting a complex thin-walled structure, the traditional aluminum alloy melt has insufficient fluidity and a wide solidification interval, which easily leads to incomplete filling, uneven wall thickness, large size deviation and poor surface quality, directly affecting the uniformity of component heat dissipation, chip assembly precision and service life, etc. (3) The comprehensive performance of the component is difficult to meet the high demand: due to the serious casting defects in the component, the actual mechanical properties (such as yield strength and elongation) of the component are significantly reduced, which makes it have the risk of failure in harsh environments such as vibration and impact; at the same time, these defects act as phonon scattering centers, which seriously hinder the conduction of heat, resulting in that the actual measured thermal conductivity of the component is much lower than the theoretical value of the material, which cannot meet the fundamental demand of high-reliability and efficient heat dissipation for high-power base stations.

[0004] Therefore, there is an urgent need in the art to develop a new type of aluminum alloy material and its supporting preparation method. SUMMARY

[0005] In view of the above problems, the present application provides a high-strength and high-thermal-conductivity aluminum alloy material and a preparation method thereof, which can be used for 5G / 6G base station liquid cooling plates, and fundamentally solves the inherent contradiction between strength and thermal conductivity. The high-strength and high-thermal-conductivity aluminum alloy material can have high strength and high thermal conductivity while maintaining excellent casting fluidity, thereby perfectly adapting to the precise forming process of complex thin-walled liquid cooling components, ensuring that the formed components have accurate dimensions, uniform wall thickness, smooth surface, and excellent mechanical properties and heat dissipation performance, and meeting the heat dissipation requirements of high power, long service life, and high reliability of complex thin-walled components of 5G / 6G base station liquid cooling plates. The specific technical solutions are as follows: A high-strength and high-thermal-conductivity aluminum alloy material, by weight percentage, the chemical composition comprises: Si: 0.4% to 0.7%; Mg: 0.7% to 1.1%; Fe: 0.06% to 0.12%; Cu: 0.02% to 0.05%; Mn: 0.03% to 0.06%; Ti: 0.02% to 0.05%; Zr: 0.08% to 0.15%; Cr: 0.05% to 0.12%; B: 0.004% to 0.01%; Mixed rare earth: 0.10% to 0.30%; The rest is aluminum and unavoidable impurities, and the content of a single impurity is ≤0.03%, and the total amount of impurities is ≤0.10%; Among them, Ti and B are added in the form of Al-5Ti-1B intermediate alloy; The mixed rare earth is added in the form of aluminum-rare earth intermediate alloy, i.e. in the form of Al-10RE, and RE represents La and Ce mixed rare earth. The mixed rare earth is a mixture of rare earth elements Ce and La, and the mass ratio of Ce to La is (1.5-2):1.

[0006] Preferably, the aluminum is an aluminum ingot with a purity of ≥99.8%.

[0007] Preferably, the high-strength and high-thermal-conductivity aluminum alloy material has a tensile strength of ≥335 MPa, a yield strength of ≥306 MPa, an elongation of ≥10.5%, and a thermal conductivity of ≥215 W / (m·K).

[0008] Preferably, a preparation method of the high-strength and high-thermal-conductivity aluminum alloy material described above comprises the following steps: (1) Melting, refining and purifying: according to the above-mentioned component proportion, Si, Mg, Fe, Cu, Mn, Zr, Cr, aluminum are put into a heat accumulating type gas melting furnace with permanent magnet stirring function to melt into liquid at 740-760 ℃, then preheated aluminum-rare earth intermediate alloy at 300-400 ℃ is added, electromagnetic stirring is adopted, and argon is sprayed and refined by rotation, then it is placed and slagged to obtain alloy liquid; (2) Grain refinement casting: the alloy liquid of step (1) is treated by on-line degassing and grain refinement through a flow channel with ceramic filter plate, then semi-continuous casting is carried out to obtain a rough cast bar; (3) Multi-stage homogenization treatment: the cast bar of step (2) is subjected to multi-stage homogenization treatment; First stage: heating to 480-520 ℃ at 10-15 ℃ / min, and keeping for 3-5 h to dissolve low melting point eutectic phase; Second stage: continue to heat to 560-580 ℃ at 5-8 ℃ / min, and keep for 8-12 h to fully dissolve the soluble strengthening phase and promote Fe phase spheroidization; Third stage: control cooling to 200-250 ℃ at a rate of 30-50 ℃ / min, and air cooling after discharging to obtain a homogenized cast bar; (4) Gradient heating and isothermal extrusion: the homogenized cast bar of step (3) is subjected to surface peeling, then gradient heating is carried out: first keeping at 430-460 ℃ for 2-4 h, then rapidly heating to 470-500 ℃ and keeping for 0.5-1 h, and then isothermal extrusion to obtain a profile; (5) Off-line solution quenching: the profile extruded in step (4) is immediately subjected to off-line solution quenching, the solution temperature is 430-450 ℃, and the heating and keeping time is 200-250 min; the quenching method is: the water temperature is ≤30 ℃ at the beginning of quenching, the profile is immersed in the water tank, and the circulating water is started to ensure that the water temperature is ≤45 ℃ at the end of quenching; the transfer time of the profile from the extrusion cylinder to complete immersion in water is ≤30 s, the immersion time of the profile in water is ≥20 min, and the profile is straightened to obtain a straightened profile; (6) Multi-stage overaging treatment: the straightened profile of step (5) is subjected to multi-stage overaging treatment: First stage aging: keeping at 185-200 ℃ for 2-3 h; Second stage aging: keeping at 220-240 ℃ for 1-2 h; Third stage aging: keeping at 170-190 ℃ for 1-2 h to obtain the high-strength high-thermal-conductivity aluminum alloy material.

[0009] Preferably, in step (1), the flow rate of the argon is 10-20 L / min, and the purity is ≥99.9%; the refining time is 25-40 min; and the standing time is 25-35 min.

[0010] Preferably, in step (2), the on-line degassing is performed by blowing argon with a flow rate of 10-20 L / min, a pressure of 0.20-0.45 MPa, and a purity of ≥99.9%; the grain refinement treatment is performed by on-line adding Al-5Ti-1B intermediate alloy grain refiner into the alloy liquid in the flow tank at a speed of 1-3 m / min; the semi-continuous casting speed is 60-90 mm / min, and the cooling water intensity is 0.8-1.2 m 3 / h.

[0011] Preferably, in step (3), after the second stage of heat preservation is completed, the temperature is first cooled to 400-450 ℃ at a rate of 80-100 ℃ / h, and then the third stage of homogenization treatment is performed by controlling the cooling operation.

[0012] Preferably, in step (4), the isothermal extrusion is performed by preheating the mold to 420-450 ℃, and extruding under the conditions of an extrusion cylinder temperature of 400-430 ℃, an extrusion speed of 4-8 m / min, and an extrusion specific pressure of 25-40 MPa.

[0013] Preferably, in step (5), the straightening is performed by using a multi-roller tension straightening machine to straighten the extruded profile, and the straightening tension is 10%-20% of the yield strength of the material.

[0014] Preferably, in step (6), the total aging time of the multi-stage overaging treatment is not more than 6 h, and the second aging temperature is at least 20 ℃ higher than the first aging temperature.

[0015] Preferably, in step (1), the intensity of the electromagnetic stirring is 20-40 mT, the stirring mode is intermittent, the stirring time is 5 min, the stopping time is 2 min, and the total stirring time is 20-30 min.

[0016] The present application at least achieves the following beneficial effects: 1. The present application forms highly dispersed, thermally stable Al3Zr and CrAl7 nanoscale precipitates in the aluminum matrix by introducing Zr and Cr micro-alloying elements, which can effectively pin grain boundaries and dislocations, producing a strong strengthening effect, while their small size and uniform distribution reduce scattering effects on electron and phonon transport; combined with Sr element modification treatment of eutectic silicon, the adverse effects of coarse silicon phase on plasticity and thermal conductivity are eliminated; further grain refinement by rare earth elements, improvement of precipitate type, size and distribution, make the strength, plasticity and thermal conductivity of aluminum alloy reach a balance, finally obtain high strength, high impact resistance, high corrosion resistance and lightweight aluminum alloy, so that the strength and thermal conductivity of the component can meet the use requirements of 5G / 6G base station liquid cooling plate for high strength, high heat dissipation performance and high precision. The inherent contradiction between strength and thermal conductivity is fundamentally solved, which can have high strength and high thermal conductivity under the premise of maintaining excellent casting fluidity, so as to perfectly adapt to the precise forming process of complex thin-walled liquid cooling components, ensure the size accuracy, uniform wall thickness, smooth surface of the formed component, as well as excellent mechanical properties and heat dissipation performance, meet the harsh heat dissipation requirements of high power, long life and high reliability of 5G / 6G base station liquid cooling plate complex thin-walled components.

[0017] 2. The rare earth elements of the present application can significantly refine the as-cast structure of aluminum alloy, reduce the interdendritic arm spacing of α-Al, and make the shape of eutectic silicon and other phases more rounded and uniform. Moreover, the rare earth elements can effectively inhibit grain growth, making the grain structure of the aluminum alloy more fine and uniform. Smaller grains result in more grain boundaries, which can effectively hinder dislocation movement, thereby improving the strength of the aluminum alloy. Secondly, rare earth elements can react with hydrogen and oxygen to purify the melt and reduce pinhole defects in the casting. Rare earth elements can also interact with impurity elements such as iron (Fe) to change the morphology and distribution of harmful phases such as iron-rich phases, reducing their hindrance to the transport of free electrons and phonons. Fine-grained grains also help the transport of electrons and phonons, thereby improving the thermal conductivity of the aluminum alloy. In addition, trace amounts of rare earth atoms may dissolve into the aluminum matrix, producing solid solution strengthening, or form rare earth-containing dispersed precipitates, producing precipitation strengthening, thereby improving the strength of the aluminum alloy.

[0018] 3. The multi-stage homogenization process of this invention, through precisely controlled heating, holding, and cooling steps, completely eliminates dendritic segregation and micro-compositional inhomogeneity in the ingot, providing a billet with uniform structure and low internal stress for subsequent hot working, thus improving the material's structural uniformity and thermal stability. Gradient heating avoids the problem of uneven deformation caused by excessive differences in flow stress between the surface and the core during extrusion, while isothermal extrusion suppresses defects such as surface cracks and pitting caused by temperature fluctuations, ensuring the stability of component dimensions. Therefore, gradient heating and isothermal extrusion ensure the forming accuracy and surface quality of complex thin-walled components. Through controllable offline solution quenching, it is ensured that the soluble strengthening phases (such as Mg2Si) formed in the ingot during homogenization and extrusion processes can be fully and thoroughly dissolved into the aluminum matrix to form a supersaturated solid solution, optimizing the stress and dimensional accuracy of the aluminum alloy material, and preparing it for subsequent multi-stage over-aging treatment to obtain high-strength, high-thermal-conductivity aluminum alloys. Detailed Implementation

[0019] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in the present invention are commercially available or can be prepared by existing methods.

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] The Al-5Ti-1B master alloy used in this invention is a commercially available product, which can be an Al-5Ti-1B master alloy product prepared by the methods of patent CN104278176B (a method for preparing a high-quality Al-5Ti-1B master alloy) or patent CN107034374B (a method for preparing Al-5Ti-1B master alloy by fluoride salt reaction).

[0022] The aluminum-rare earth master alloy used in this invention is a commercially available product, which can be a high-purity aluminum-rare earth master alloy product prepared by the method of patent CN112391545B (a method for preparing a high-purity aluminum-rare earth master alloy).

[0023] Example 1 A high-strength and high-thermal-conductivity aluminum alloy material, in terms of percentage by weight, has the following chemical composition: Si: 0.4%; Mg: 0.7%; Fe: 0.06%; Cu: 0.02%; Mn: 0.06%; Ti: 0.05%; Zr: 0.15%; Cr: 0.12%; B: 0.01%; mixed rare earth: 0.30%; the rest is aluminum and unavoidable impurities, and the content of each impurity is ≤0.03%, and the total content of impurities is ≤0.10%; wherein, Ti and B are added in the form of Al-5Ti-1B intermediate alloy; the mixed rare earth is added in the form of aluminum-rare earth intermediate alloy, i.e. in the form of Al-10RE, RE representing La and Ce mixed rare earth; the mixed rare earth is a mixture of rare earth elements Ce and La, and the mass ratio of Ce to La is 1.5:1. The aluminum is an aluminum ingot with a purity of ≥99.8%. The high-strength and high-thermal-conductivity aluminum alloy material has a tensile strength of ≥335 MPa, a yield strength of ≥306 MPa, an elongation of ≥10.5%, and a thermal conductivity of ≥215 W / (m·K).

[0024] A preparation method of the high-strength and high-thermal-conductivity aluminum alloy material, comprising the following steps: (1) Melting, refining and purifying: according to the above composition ratio, Si, Mg, Fe, Cu, Mn, Zr, Cr, aluminum are fed into a heat accumulating gas melting aluminum furnace with permanent magnet stirring function to melt into liquid at 740℃, then aluminum-rare earth intermediate alloy preheated to 300℃ is added, intermittent stirring for 5 min, stopping for 2 min, 20 mT electromagnetic stirring for 20 min, and argon gas with a purity of ≥99.9% is used for refining and degassing for 25 min, followed by standing for 25 min and slagging to obtain alloy liquid; (2) Grain refinement casting: the alloy liquid of step (1) is poured through a flow channel equipped with a ceramic filter plate for online degassing and grain refinement treatment, the online degassing is performed by spraying argon gas with a purity of ≥99.9% at a flow rate of 10 L / min and a pressure of 0.20 MPa, the grain refinement treatment is performed by adding Al-5Ti-1B intermediate alloy grain refinement agent into the alloy liquid in the flow channel at a speed of 1 m / min, then semi-continuous casting is performed at a speed of 60 mm / min and a 0.8 m 3 / h cooling water intensity, to obtain a rough cast rod; (3) multi-stage homogenization treatment: the casting rod of step (2) is subjected to multi-stage homogenization treatment; first stage: heating to 480℃ at 10℃ / min, and keeping for 3h to dissolve low-melting-point eutectic phase; second stage: continuing to heat to 560℃ at 5℃ / min, and keeping for 8h to fully solid-solution soluble strengthening phase and promote Fe phase spheroidization; third stage: after the second stage keeping ends, first cooling to 400℃ at a rate of 80℃ / h, and then controlling cooling to 200℃ at a rate of 30℃ / min, and taking out and air cooling to obtain a homogenized casting rod; (4) gradient heating and isothermal extrusion: the homogenized casting rod of step (3) is subjected to surface peeling, and then gradient heating: first keeping at 430℃ for 2h, and then rapidly heating to 470℃ and keeping for 0.5h, preheating the mold to 420℃, and performing isothermal extrusion under the conditions of extrusion cylinder temperature 400℃, extrusion speed 4m / min, and extrusion specific pressure 25MPa to obtain a profile; (5) offline solution quenching: the profile extruded in step (4) is immediately subjected to offline solution quenching, the solution method is: solution temperature is 430℃, and the total heating and keeping time is 200min; the quenching method is: the water temperature at the beginning of quenching is ≤30℃, the profile is immersed in the water tank during the immersion process, and circulating water is started to ensure that the water temperature at the end of quenching is ≤45℃; wherein the transfer time of the profile from the extrusion cylinder to complete immersion in water is ≤30s, the immersion time of the profile in water is ≥20min, a multi-roll tension straightening machine is used to straighten the extruded profile, and the straightening tension is 10% of the yield strength of the material to obtain a straightened profile; (6) multi-stage overaging treatment: the straightened profile of step (5) is subjected to multi-stage overaging treatment: first aging: keeping at 185℃ for 3h; second aging: keeping at 220℃ for 2h; third aging: keeping at 190℃ for 1h to obtain the high-strength high-thermal-conductivity aluminum alloy material.

[0025] Example 2 A high-strength high-thermal-conductivity aluminum alloy material, the chemical composition includes, by weight percentage: Si: 0.7%; Mg: 1.1%; Fe: 0.12%; Cu: 0.05%; Mn: 0.03%; Ti: 0.02%; Zr: 0.08%; Cr: 0.05%; B: 0.004%; mixed rare earth: 0.10%; the rest is aluminum and inevitable impurities, and the content of each impurity is ≤0.03%, and the total content of impurities is ≤0.10%; wherein, Ti and B are added in the form of Al-5Ti-1B intermediate alloy; the mixed rare earth is added in the form of aluminum-rare earth intermediate alloy, i.e. in the form of Al-10RE, RE representing La and Ce mixed rare earth; the mixed rare earth is a mixture of rare earth elements Ce and La, and the mass ratio of Ce to La is 2:1. The aluminum is an aluminum ingot with purity ≥99.8%. The high-strength high-thermal-conductivity aluminum alloy material has a tensile strength ≥335 MPa, a yield strength ≥306 MPa, an elongation ≥10.5%, and a thermal conductivity ≥215 W / (m·K).

[0026] A preparation method of the high-strength high-thermal-conductivity aluminum alloy material, comprising the following steps: (1) Melting, refining and purifying: according to the above component ratio, Si, Mg, Fe, Cu, Mn, Zr, Cr, and aluminum are fed into a heat accumulating type gas melting aluminum furnace with permanent magnet stirring function to be melted into liquid at 760℃, then aluminum-rare earth intermediate alloy preheated to 400℃ is added, intermittent stirring for 5 min, stopping for 2 min, 40 mT electromagnetic stirring for 30 min, and argon gas with purity ≥99.9% is used for refining and degassing for 40 min, followed by standing for 35 min, slagging, to obtain alloy liquid; (2) Grain refinement casting: the alloy liquid of step (1) is cast through a flow channel equipped with a ceramic filter plate for online degassing and grain refinement treatment, the online degassing is performed by spraying argon gas with purity ≥99.9% at a flow rate of 20 L / min and a pressure of 0.45 MPa, the grain refinement treatment is performed by adding Al-5Ti-1B intermediate alloy grain refinement agent into the alloy liquid in the flow channel at a speed of 3 m / min, then semi-continuous casting is performed at a speed of 90 mm / min and a 1.2 m 3 / h cooling water intensity, to obtain a rough casting rod; (3) Multi-stage homogenization treatment: the casting rod of step (2) is subjected to multi-stage homogenization treatment; first stage: heating to 520℃ at a rate of 15℃ / min, and holding for 5h to dissolve low melting point eutectic phase; second stage: continuing to heat to 580℃ at a rate of 8℃ / min, and holding for 12h to fully dissolve soluble strengthening phase and promote Fe phase spheroidization; third stage: after the second stage holding ends, first cooling to 450℃ at a rate of 100℃ / h, then controlled cooling to 250℃ at a rate of 50℃ / min, discharging and air cooling, to obtain a homogenized casting rod; (4) Gradient heating and isothermal extrusion: the homogenized bar of step (3) is subjected to surface peeling, and then gradient heating: first, heat preservation at 460℃ for 4h, then rapid heating to 500℃ and heat preservation for 1h, then isothermal extrusion under the conditions of preheating the mold to 450℃, the extrusion cylinder temperature to 430℃, the extrusion speed to 8m / min, and the extrusion specific pressure to 40MPa, to obtain a profile; (5) Off-line solution quenching: the profile extruded in step (4) is immediately subjected to off-line solution quenching, the solution method is: the solution temperature is 450℃, and the heating and heat preservation time is 250min in total; the quenching method is: the water temperature at the beginning of quenching is ≤30℃, the profile is immersed in the water tank during the water circulation to ensure that the water temperature at the end of quenching is ≤45℃; wherein the transfer time of the profile from the extrusion cylinder to complete immersion in water is ≤30s, the immersion time of the profile in water is ≥20min, a multi-roll tension straightening machine is used to straighten the extruded profile, and the straightening tension is 20% of the yield strength of the material, to obtain a straightened profile. (6) Multi-stage overaging treatment: the straightened profile of step (5) is subjected to multi-stage overaging treatment: first aging: heat preservation at 200℃ for 2h; second aging: heat preservation at 240℃ for 1h; third aging: heat preservation at 170℃ for 2h, to obtain the high-strength high-thermal-conductivity aluminum alloy material.

[0027] Example 3 A high-strength high-thermal-conductivity aluminum alloy material, by weight percentage, the chemical composition includes: Si: 0.5%; Mg: 0.8%; Fe: 0.08%; Cu: 0.03%; Mn: 0.04%; Ti: 0.03%; Zr: 0.09%; Cr: 0.06%; B: 0.006%; mixed rare earth: 0.15%; the rest is aluminum and unavoidable impurities, and the content of each impurity is ≤0.03%, and the total amount of impurities is ≤0.10%; wherein, Ti and B are added in the form of Al-5Ti-1B intermediate alloy; the mixed rare earth is added in the form of aluminum-rare earth intermediate alloy, that is, in the form of Al-10RE, RE represents La and Ce mixed rare earth; the mixed rare earth is a mixture of rare earth elements Ce and La, and the mass ratio of Ce to La is 1.6:1. The aluminum is an aluminum ingot with a purity of ≥99.8%. The high-strength high-thermal-conductivity aluminum alloy material has a tensile strength of ≥335MPa, a yield strength of ≥306MPa, an elongation of ≥10.5%, and a thermal conductivity of ≥215W / (m·K).

[0028] A preparation method of the high-strength high-thermal-conductivity aluminum alloy material, comprising the following steps: (1) Melting, refining and purifying: according to the above-mentioned component proportion, Si, Mg, Fe, Cu, Mn, Zr, Cr, aluminum are put into a heat accumulating gas melting furnace with permanent magnet stirring function to melt into liquid at 745℃, then preheated aluminum-rare earth intermediate alloy at 330℃ is added, intermittent stirring for 5min, stop for 2min, 25mT electromagnetic stirring for 22min, argon gas with purity ≥99.9% is used for refining for 30min, then standing for 27min, slagging, to obtain alloy liquid; (2) Grain refinement casting: the alloy liquid of step (1) is cast through a flow channel with ceramic filter plate for online degassing and grain refinement treatment, online degassing is argon gas with purity ≥99.9% with flow rate of 13L / min and pressure of 0.25MPa, grain refinement treatment is adding Al-5Ti-1B intermediate alloy grain refiner into the alloy liquid in the flow channel at a speed of 1.5m / min, then semi-continuous casting at a speed of 70mm / min and 0.9m 3 / h cooling water intensity, to obtain rough cast bar; (3) Multi-stage homogenization treatment: the cast bar of step (2) is subjected to multi-stage homogenization treatment; first stage: heating to 490℃ at a rate of 11℃ / min, holding for 3.5h, to dissolve low melting point eutectic phase; second stage: continue heating to 565℃ at a rate of 6℃ / min, holding for 9h, to fully dissolve soluble strengthening phase and promote Fe phase spheroidization; third stage: after the second stage holding ends, first cooling to 410℃ at a rate of 85℃ / h, then controlled cooling to 210℃ at a rate of 35℃ / min, furnace cooling, to obtain homogenized cast bar; (4) Gradient heating and isothermal extrusion: the homogenized cast bar of step (3) is subjected to surface peeling, then gradient heating: first holding at 440℃ for 2.5h, rapidly heating to 480℃ and holding for 0.6h, then isothermal extrusion under the conditions of preheating the mold to 430℃, extrusion cylinder temperature 410℃, extrusion speed 5m / min, extrusion specific pressure 30MPa, to obtain profile; (5) Offline solution quenching: the extruded profile of step (4) is immediately subjected to offline solution quenching, solution method: solution temperature is 435℃, heating and holding time is 210min; quenching method: water temperature ≤30℃ at the beginning of quenching, the profile is immersed in the water tank, circulating water is started to ensure that the water temperature ≤45℃ at the end of quenching; the transfer time of the profile from the extrusion cylinder to complete immersion in water is ≤30s, the immersion time of the profile in water is ≥20min, the extruded profile is straightened by a multi-roll tension straightening machine, the straightening tension is 12% of the yield strength of the material, to obtain straightened profile; (6) multi-stage overaging treatment: the straightened profiled material of step (5) is subjected to multi-stage overaging treatment: first-stage aging: 190℃ for 2.8h; second-stage aging: 225℃ for 1.2h; third-stage aging: 175℃ for 2h, to obtain the high-strength high-thermal-conductivity aluminum alloy material.

[0029] Example 4 A high-strength high-thermal-conductivity aluminum alloy material, in terms of percentage by weight, has the following chemical composition: Si: 0.6%; Mg: 1.0%; Fe: 0.11%; Cu: 0.04%; Mn: 0.05%; Ti: 0.04%; Zr: 0.13%; Cr: 0.11%; B: 0.008%; mixed rare earth: 0.25%; the rest being aluminum and unavoidable impurities, with the content of each impurity ≤0.03% and the total content of impurities ≤0.10%; wherein, Ti and B are added in the form of Al-5Ti-1B intermediate alloy; the mixed rare earth is added in the form of aluminum-rare earth intermediate alloy, i.e. in the form of Al-10RE, with RE representing La and Ce mixed rare earth; the mixed rare earth is a mixture of rare earth elements Ce and La, with the mass ratio of Ce to La = 1.9:1. The aluminum is an aluminum ingot with purity ≥99.8%. The high-strength high-thermal-conductivity aluminum alloy material has a tensile strength ≥335MPa, a yield strength ≥306MPa, an elongation ≥10.5%, and a thermal conductivity ≥215W / (m·K).

[0030] A method for preparing the above high-strength high-thermal-conductivity aluminum alloy material, comprising the following steps: (1) melting, refining and purifying: ingredients are prepared according to the above composition ratio, Si, Mg, Fe, Cu, Mn, Zr, Cr, and aluminum are put into a heat storage type gas aluminum melting furnace with permanent magnet stirring function to be melted into liquid at 755℃, then aluminum-rare earth intermediate alloy preheated to 380℃ is added, intermittent stirring for 5min, stopping for 2min, electromagnetic stirring for 28min at an intensity of 35mT, and argon gas with purity ≥99.9% is used for refining for 35min at a rotary spraying flow of 18L / min to remove gas and impurities, followed by standing for 33min and slagging to obtain alloy liquid; (2) grain refinement casting: the alloy liquid of step (1) is cast through a flow channel equipped with a ceramic filter plate for online degassing and grain refinement treatment, online degassing is performed by spraying argon gas with purity ≥99.9% at a flow rate of 18L / min and a pressure of 0.40MPa, grain refinement treatment is performed by adding Al-5Ti-1B intermediate alloy grain refinement agent into the alloy liquid in the flow channel at a speed of 2.5m / min, followed by semi-continuous casting at a speed of 80mm / min and a cooling water intensity of 1.1m 3 / h to obtain a rough cast rod; (3) multi-stage homogenization treatment: the casting rod of step (2) is subjected to multi-stage homogenization treatment; first stage: heating to 510℃ at 14℃ / min, and keeping for 4.5h to dissolve low-melting-point eutectic phase; second stage: continuing to heat to 575℃ at 7℃ / min, and keeping for 11h to fully solid-solution soluble strengthening phase and promote Fe phase spheroidization; third stage: after the second stage keeping ends, first cooling to 440℃ at a rate of 95℃ / h, and then controlling cooling to 240℃ at a rate of 45℃ / min, and taking out and air cooling to obtain a homogenized casting rod; (4) gradient heating and isothermal extrusion: the homogenized casting rod of step (3) is subjected to surface peeling, and then gradient heating: first keeping at 450℃ for 3.5h, rapidly heating to 490℃ and keeping for 0.9h, and then isothermal extrusion under the conditions of preheating the mold to 440℃, extrusion cylinder temperature 420℃, extrusion speed 7m / min, and extrusion specific pressure 35MPa to obtain a profile; (5) offline solution quenching: the profile extruded in step (4) is immediately subjected to offline solution quenching, the solution method is: solution temperature is 445℃, and the total heating and keeping time is 240min; the quenching method is: water temperature ≤30℃ at the beginning of quenching, the profile is immersed in the water tank, and circulating water is started to ensure that the water temperature ≤45℃ at the end of quenching; wherein the transfer time from the extrusion cylinder to completely immerse in water is ≤30s, the immersion time of the profile in water is ≥20min, a multi-roll tension straightening machine is used to straighten the extruded profile, and the straightening tension is 18% of the yield strength of the material to obtain a straightened profile; (6) multi-stage over-aging treatment: the straightened profile of step (5) is subjected to multi-stage over-aging treatment: first aging: keeping at 195℃ for 2.3h; second aging: keeping at 235℃ for 2h; third aging: keeping at 185℃ for 1.7h to obtain the high-strength high-thermal-conductivity aluminum alloy material.

[0031] Example 5 The high-strength and high-thermal-conductivity aluminum alloy material comprises the following chemical components in percentage by weight: Si: 0.55%; Mg: 0.9%; Fe: 0.09%; Cu: 0.035%; Mn: 0.045%; Ti: 0.035%; Zr: 0.12%; Cr: 0.09%; B: 0.007%; mixed rare earth: 0.20%; the rest is aluminum and inevitable impurities, and the content of each impurity is less than or equal to 0.03%, and the total content of impurities is less than or equal to 0.10%; wherein, Ti and B are added in the form of Al-5Ti-1B intermediate alloy; the mixed rare earth is added in the form of aluminum-rare earth intermediate alloy, i.e. in the form of Al-10RE, RE representing La and Ce mixed rare earth; the mixed rare earth is a mixture of rare earth elements Ce and La, and the mass ratio of Ce to La is 1.7:1. The aluminum is an aluminum ingot with a purity of greater than or equal to 99.8%. The high-strength and high-thermal-conductivity aluminum alloy material has a tensile strength of greater than or equal to 335 MPa, a yield strength of greater than or equal to 306 MPa, an elongation of greater than or equal to 10.5%, and a thermal conductivity of greater than or equal to 215 W / (m·K).

[0032] The preparation method of the high-strength and high-thermal-conductivity aluminum alloy material comprises the following steps: (1) Melting, refining and purifying: ingredients are prepared according to the above composition ratio, Si, Mg, Fe, Cu, Mn, Zr, Cr, and aluminum are put into a heat accumulating gas melting furnace with permanent magnet stirring function to melt into liquid at 750℃, then aluminum-rare earth intermediate alloy preheated to 350℃ is added, intermittent stirring for 5 min, stopping for 2 min, electromagnetic stirring for 25 min with intensity of 30 mT, refining for 33 min by spraying argon with purity of greater than or equal to 99.9% at a flow rate of 15 L / min to remove gas and impurities, then standing for 30 min, skimming the slag to obtain alloy liquid; (2) Grain refinement casting: the alloy liquid of step (1) is cast through a flow channel equipped with a ceramic filter plate for online degassing and grain refinement treatment, online degassing is carried out by spraying argon with purity of greater than or equal to 99.9% at a flow rate of 15 L / min and a pressure of 0.35 MPa, grain refinement treatment is carried out by adding Al-5Ti-1B intermediate alloy grain refinement agent into the alloy liquid in the flow channel at a speed of 2 m / min, then semi-continuous casting is carried out at a speed of 75 mm / min and a cooling water intensity of 1.0 m 3 / h to obtain a rough casting rod; (3) Multi-stage homogenization treatment: the casting rod of step (2) is subjected to multi-stage homogenization treatment; first stage: heating to 500℃ at a rate of 13℃ / min and keeping for 4 h to dissolve low-melting-point eutectic phase; second stage: continuing to heat to 570℃ at a rate of 6.5℃ / min and keeping for 10 h to fully dissolve soluble strengthening phase and promote Fe phase spheroidization; third stage: after the second stage of keeping, first cooling to 430℃ at a rate of 90℃ / h, then controlled cooling to 230℃ at a rate of 40℃ / min, discharging and air cooling to obtain a homogenized casting rod. (4) Gradient heating and isothermal extrusion: the homogenized ingot of step (3) is subjected to surface peeling, and then gradient heating is performed: first, it is kept at 445℃ for 3h, then it is rapidly heated to 485℃ and kept for 0.75h, and then isothermal extrusion is performed under the conditions of preheating the mold to 435℃, the temperature of the extrusion cylinder being 415℃, the extrusion speed being 6m / min, and the extrusion specific pressure being 32MPa, to obtain a profile; (5) Off-line solution quenching: the profile extruded in step (4) is immediately subjected to off-line solution quenching, the solution method being: the solution temperature is 440℃, and the heating and holding time is 230min in total; the quenching method being: the water temperature at the beginning of quenching is ≤30℃, and the profile is immersed in the water tank during the process of immersion, and circulating water is started to ensure that the water temperature at the end of quenching is ≤45℃; wherein the transfer time of the profile from the extrusion cylinder to complete immersion in water is ≤30s, and the immersion time of the profile in water is ≥20min, a multi-roll tension straightening machine is used to straighten the extruded profile, and the straightening tension is 15% of the yield strength of the material, to obtain a straightened profile; (6) Multi-stage overaging treatment: the straightened profile of step (5) is subjected to multi-stage overaging treatment: first aging: at 195℃ for 2.5h; second aging: at 230℃ for 1.5h; third aging: at 180℃ for 1.5h, to obtain the high-strength high-thermal-conductivity aluminum alloy material.

[0033] Comparative Example 1 The difference between this example and Example 5 is that the mass ratio of Ce to La in the mixed rare earths = 1.2:1, and other conditions are unchanged.

[0034] Comparative Example 2 The difference between this example and Example 5 is that the mass ratio of Ce to La in the mixed rare earths = 2.5:1, and other conditions are unchanged.

[0035] Comparative Example 3 The difference between this example and Example 5 is that the mixed rare earths are not added in the form of aluminum-rare earth intermediate alloy, but are directly added in the form of mixed rare earths, and other conditions are unchanged.

[0036] Comparative Example 4 The difference between this example and Example 5 is that Ti and B are not added in the form of Al-5Ti-1B intermediate alloy, but are directly added in their own form during preparation, and other conditions are unchanged.

[0037] Comparative Example 5 The difference between this example and Example 5 is that Ti and B are added in the form of Al-2Ti-1B intermediate alloy, and other conditions are unchanged.

[0038] Comparative Example 6 The difference between the present comparative example and Example 5 is that, in the preparation process, after the end of the second stage of heat preservation in step (3), the controlled cooling is directly performed at a rate of 40℃ / min to 230℃ without the operation of "first cooling to 430℃ at a rate of 90℃ / h", and other conditions remain unchanged.

[0039] Comparative Example 7 The difference between the present comparative example and Example 5 is that, in the preparation process, a single-stage homogenization treatment is adopted in step (3): the cast bar is heated to 550℃ at a rate of 20℃ / min, and then slowly cooled to 200℃ at a cooling rate of 100℃ / h, and then air-cooled to room temperature, and other conditions remain unchanged.

[0040] Comparative Example 8 The difference between the present comparative example and Example 5 is that, in the preparation process, gradient heating is not adopted in step (4), but is directly heated to 500℃ and kept for 5h, and other conditions remain unchanged.

[0041] Comparative Example 9 The difference between the present comparative example and Example 5 is that, in the preparation process, offline solution quenching is not adopted in step (5), but online quenching is adopted, specifically: the solution temperature is 550℃, the holding time is 250min, and then immediately cooled by cooling water, and the cooling rate is not less than 50℃ / s, and other conditions remain unchanged.

[0042] Comparative Example 10 The difference between the present comparative example and Example 5 is that, in the preparation process, a single-stage aging treatment is adopted in step (6), specifically: the straightened profile is aged at 220℃ for 6h, and other conditions remain unchanged.

[0043] Comparative Example 11 The difference between the present comparative example and Example 5 is that, in the preparation process, the total aging time in step (6) is 7h, specifically: the first-stage aging is kept at 200℃ for 3h; the second-stage aging is kept at 230℃ for 2h; and the third-stage aging is kept at 170℃ for 2h, and other conditions remain unchanged.

[0044] The aluminum alloy materials prepared by the methods of Examples 1-5 and Comparative Examples 1-11 are subjected to performance testing, and the tensile strength (MPa), yield strength (MPa), elongation (%) and thermal conductivity coefficient (W / m·K) of the aluminum alloy materials prepared by each method are tested, and the test results are shown in Table 1.

[0045] Table 1 From the experimental data of Table 1, compared with Example 5, from the experimental results of Comparative Example 1, Comparative Example 2 and Comparative Example 3, it can be seen that the mixed rare earth addition form and the mass ratio of Ce to La in the mixed rare earth have an influence on the performance of the aluminum alloy material. From Comparative Examples 1 and 2, it can be seen that the Ce / La ratio is unbalanced, the rare earth modification effect is slightly poor, resulting in a slight decrease in the plasticity and thermal conductivity of the product; the direct addition of rare earth in Comparative Example 3 leads to serious burning loss, uneven composition, and significant deterioration of strengthening effect and microstructure uniformity; the ratio and addition form of the present application are more conducive to improving the strength, thermal conductivity and other comprehensive performance of the aluminum alloy material.

[0046] From the experimental data of Comparative Example 4 and Comparative Example 5, it can be seen that the addition of Ti and B in the form of Al-5Ti-1B intermediate alloy is conducive to improving the strength, thermal conductivity and other comprehensive performance of the aluminum alloy material. Direct addition of Ti and B cannot effectively dissolve and disperse, resulting in a small number of effective heterogeneous nucleation cores in the melt, uneven aggregation and dispersion of the refiner, and inability to refine the grains, resulting in coarse grains and segregation in the cast ingot, leading to a decrease in the strength, plasticity and toughness (i.e. elongation) of the product. The addition of Ti, B and Al-5Ti-1B intermediate alloy according to the component ratio of the present application is conducive to realizing ultra-fine grain and uniform microstructure, thereby improving the strength and plasticity of the product.

[0047] Comparative Example 6 and Comparative Example 7 show that single-stage homogenization results in insufficient microstructure uniformity, leading to a decrease in the performance of the aluminum alloy. Multi-stage treatment and precise controlled cooling are conducive to obtaining ideal microstructure. Comparative Example 8 shows that non-gradient heating leads to a large temperature difference between the center and the surface of the cast rod, uneven extrusion flow stress, and poor uniformity of the product microstructure and performance. It can be seen that the gradient heating of the present application ensures uniform heat penetration of the extrusion billet, thereby realizing stable forming and high dimensional accuracy.

[0048] Comparative Example 9 (online quenching) shows that online quenching cools too quickly, resulting in high residual stress, slightly higher strength, but damaged plasticity, thermal conductivity and dimensional stability, leading to a decrease in the elongation and thermal conductivity of the product. It can be seen that the high residual stress state of online quenching cannot meet the requirements of liquid cooling plate for heat dissipation efficiency and dimensional stability.

[0049] Comparative Example 10 (single-stage aging) and Comparative Example 11 (three-stage aging but aging time exceeding 6h) show that the aging method affects the strength, thermal conductivity, plasticity and other properties of the product. Single-stage aging or aging time exceeding 6h cannot precisely control the precipitation phase, resulting in a decrease in the strength and thermal conductivity of the product.

[0050] The formula and preparation method can obtain high-strength and high-thermal-conductivity aluminum alloy, multi-stage homogenization treatment completely eliminates dendritic segregation and micro-component unevenness of the ingot through precisely controlled heating, holding and cooling processes, provides a uniform structure and low internal stress blank for subsequent hot working, and improves the uniformity and thermal stability of the material; gradient heating avoids the problem of uneven deformation caused by too large flow stress difference between the surface and the core during extrusion, and isothermal extrusion suppresses surface cracks, pitting and other defects caused by temperature fluctuations, ensuring the stability of the component size, so gradient heating and isothermal extrusion ensure the forming precision and surface quality of the complex thin-walled component; through controllable offline solid solution quenching, it is ensured that the soluble strengthening phase (such as Mg2Si) formed in the ingot during homogenization treatment and extrusion can be fully and completely dissolved into the aluminum matrix to form a supersaturated solid solution, and the stress and size precision of the aluminum alloy material are optimized, and the high-strength and high-thermal-conductivity aluminum alloy is prepared for subsequent multi-stage overaging treatment.

[0051] The foregoing description of specific exemplary embodiments of the application is intended to be illustrative only and is not intended to limit the application to the precise forms disclosed. Many modifications and variations are possible in light of the above teachings without departing from the spirit or essential characteristics of the present application. The exemplary embodiments were chosen and described in order to explain the principles of the application and its practical application to achieve the high-strength and high-thermal-conductivity aluminum alloy material, and to enable others skilled in the art to implement and utilize the application in various embodiments and with various modifications as are suited to the particular use contemplated. The scope of the application is to be defined by the claims and their equivalents.

Claims

1. A high-strength, high-thermal-conductivity aluminum alloy material, characterized in that, The chemical composition, by weight percentage, includes: Si: 0.4%~0.7%; Mg: 0.7%–1.1%; Fe: 0.06%~0.12%; Cu: 0.02%~0.05%; Mn: 0.03%~0.06%; Ti: 0.02%~0.05%; Zr：0.08%～0.15%； Cr：0.05%～0.12%； B：0.004%～0.01%； Mixed rare earth elements: 0.10%–0.30%; The remainder consists of aluminum and unavoidable impurities, with individual impurities comprising ≤0.03% and total impurities comprising ≤0.10%. Ti and B are added in the form of Al-5Ti-1B master alloy; The mixed rare earth is added in the form of an aluminum-rare earth intermediate alloy, that is, in the form of Al-10RE, where RE represents a mixed rare earth of La and Ce; the mixed rare earth is a mixture of rare earth elements Ce and La, and the mass ratio of Ce to La is (1.5~2):

1.

2. The high-strength, high-thermal-conductivity aluminum alloy material according to claim 1, characterized in that, The aluminum is an aluminum ingot with a purity of ≥99.8%.

3. The high-strength, high-thermal-conductivity aluminum alloy material according to claim 1, characterized in that, The high-strength, high-thermal-conductivity aluminum alloy material has a tensile strength ≥335MPa, a yield strength ≥306MPa, an elongation ≥10.5%, and a thermal conductivity ≥215W / (m·K).

4. A method for preparing a high-strength, high-thermal-conductivity aluminum alloy material as described in any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Smelting, refining and purification: According to the composition ratio of claim 1, Si, Mg, Fe, Cu, Mn, Zr, Cr and aluminum are fed into a regenerative gas-fired aluminum melting furnace with permanent magnet stirring function and smelted into liquid at 740-760°C. Then, aluminum-rare earth intermediate alloy preheated to 300-400°C is added, and the mixture is stirred electromagnetically. Refining and degassing are carried out by rotary argon gas blowing. After that, the mixture is allowed to stand and the slag is removed to obtain the alloy liquid. (2) Grain refinement casting: The alloy liquid from step (1) is subjected to online degassing and grain refinement treatment, and then semi-continuous casting is carried out to obtain a rough casting rod; (3) Multi-stage homogenization treatment: The casting rod from step (2) is subjected to multi-stage homogenization treatment; First stage: Increase the temperature to 480-520℃ at a rate of 10-15℃ / min, and hold for 3-5 hours; Second stage: Continue to increase the temperature to 560-580℃ at a rate of 5-8℃ / min, and hold for 8-12 hours; The third stage: Cooling is controlled at a rate of 30-50℃ / min to 200-250℃, then air-cooled after removal from the furnace to obtain a homogenized casting rod; (4) Gradient heating and isothermal extrusion: The homogenized casting rod from step (3) is peeled off, and then gradient heating is performed: first, it is kept at 430-460℃ for 2-4 hours, then the temperature is rapidly increased to 470-500℃ and kept for 0.5-1 hours, and then isothermal extrusion is performed to obtain the profile. (5) Offline solution quenching: The profile extruded in step (4) is immediately subjected to offline solution quenching. The solution method is: the solution temperature is 430-450℃, and the heating and holding time is 200-250min. The quenching method is: the water temperature at the beginning of quenching is ≤30℃, and the circulating water is turned on during the immersion process of the profile in the water tank to ensure that the water temperature at the end of quenching is ≤45℃. The transfer time from the extrusion cylinder to the complete immersion in water is ≤30s, and the immersion time of the profile in water is ≥20min. The profile is straightened to obtain a straightened profile. (6) Multi-stage over-aging treatment: The straightened profile from step (5) is subjected to multi-stage over-aging treatment: Level 1 aging: Keep warm at 185-200℃ for 2-3 hours; Secondary aging: Keep warm at 220-240℃ for 1-2 hours; Level 3 aging: The high-strength, high-thermal-conductivity aluminum alloy material is obtained by holding at 170–190℃ for 1–2 hours.

5. The preparation method according to claim 3, characterized in that, In step (2), the online degassing is performed by blowing argon gas with a purity ≥99.9% at a flow rate of 10–20 L / min and a pressure of 0.20–0.45 MPa; the grain refinement treatment involves adding Al-5Ti-1B intermediate alloy grain refiner online to the alloy liquid in the flow channel at a speed of 1–3 m / min; the semi-continuous casting speed is 60–90 mm / min, and the cooling water intensity is 0.8–1.2 m / min. 3 / h.

6. The preparation method according to claim 3, characterized in that, In step (3), after the second stage of heat preservation is completed, the temperature is first cooled to 400-450℃ at a rate of 80-100℃ / h, and then the third stage of homogenization treatment is carried out by controlled cooling.

7. The preparation method according to claim 3, characterized in that, In step (4), the isothermal extrusion is carried out by preheating the mold to 420-450°C, and under the conditions of extrusion cylinder temperature of 400-430°C, extrusion speed of 4-8 m / min, and extrusion specific pressure of 25-40 MPa.

8. The preparation method according to claim 3, characterized in that, In step (5), the straightening is performed by using a multi-roll tension straightener to straighten the extruded profile, with the straightening tension being 10% to 20% of the material's yield strength.

9. The preparation method according to claim 3, characterized in that, In step (6), the total aging time of the multi-stage over-aging process does not exceed 6 hours, and the aging temperature of the second stage is at least 20°C higher than that of the first stage.

10. The preparation method according to claim 3, characterized in that, In step (1), the flow rate of the argon gas is 10-20 L / min and the purity is ≥99.9%; the refining time is 25-40 min; the settling time is 25-35 min; the intensity of the electromagnetic stirring is 20-40 mT, the stirring method is intermittent, stirring for 5 min and stopping for 2 min, and the total stirring time is 20-30 min.

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