Aluminum alloy grain refining and strengthening method

Abstract

The invention relates to the technical field of material preparation, and discloses a method for refining and strengthening aluminum alloy grains, which comprises various synergistic effects of alloy smelting and component regulation, powder preparation and ball milling treatment, hot press molding and strengthening phase stabilization to realize metal strengthening. Through multiple synergistic effects of alloy smelting and component regulation, powder preparation and ball milling treatment, hot press molding and strengthening phase stabilization, accurate regulation of material grains is achieved, the grain size is stably controlled within the submicron range of 0.3-1 micron, and the submicron grains improve the toughness of the material by increasing grain boundary slippage channels; according to the invention, through precise component regulation and control and subsequent aging process optimization, the generated Al3 (Y, Zr) strengthening phase has extremely high high-temperature stability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of material preparation, and particularly relates to a method for grain refinement and strengthening of an aluminum alloy. BACKGROUND

[0002] In the field of material science and engineering, the macroscopic performance of a material depends on its microstructure, and the grain size and the characteristics of the strengthening phase are the core elements in the microstructure that determine the mechanical properties, physical properties and service stability of the material. As two classical material strengthening mechanisms, the synergistic effect of fine-grain strengthening and dispersion strengthening can significantly improve the strength, toughness and high-temperature stability of the material. Therefore, how to achieve ultra-fining of the grains and precise control of the high-stability strengthening phase has always been a core issue in material research and application.

[0003] In terms of strengthening phase control, an ideal strengthening phase should have the following characteristics: small size (nanoscale), uniform and dispersed distribution in the matrix, good interface bonding with the matrix, and high stability at high temperatures (not easy to coarsen). Traditional strengthening phase generation methods have many technical bottlenecks: direct addition of strengthening phase particles during casting can easily cause agglomeration due to density difference or surface energy effect, making it difficult to achieve uniform distribution, and can easily introduce interfacial impurities, reducing the strengthening effect; although aging treatment can achieve strengthening by precipitating intermetallic compounds, the traditional aging precipitated strengthening phase is prone to Ostwald ripening in high-temperature service environment, leading to an increase in the size and spacing of the strengthening phase, thereby reducing the strength of the material over time. For light alloys such as aluminum alloys and magnesium alloys widely used in the fields of aerospace, high-end equipment manufacturing, etc., the materials prepared by traditional methods are difficult to meet the comprehensive performance requirements of "high strength-high toughness-high temperature stability", for example, the tensile strength retention rate of traditional aluminum alloys is often less than 60% at temperatures above 200°C, which cannot meet the usage requirements of key components such as engine compartments and high-temperature structural parts.

[0004] In addition, existing material preparation techniques also have deficiencies in process stability and industrial adaptability. On the one hand, traditional process parameters are ambiguous, and the performance of different batches of materials fluctuates greatly, making it difficult to ensure product consistency; on the other hand, some high-performance material preparation techniques rely on high-end equipment or complex processes, resulting in high production costs and restricting their application in civilian high-end fields. Therefore, developing a material preparation method that can efficiently achieve submicron grain refinement, precise control of high-stability strengthening phase generation, and process stability and easy industrialization has important theoretical significance and practical value for breaking through the performance bottlenecks of traditional materials and expanding the application of light alloys in high-end fields. SUMMARY

[0005] The present application aims to overcome the problems in the prior art that it is difficult to stabilize and refine the material crystal grains to a submicron level, the high-temperature stability of the strengthening phase is insufficient, and the process controllability is poor, and provides a method for inducing grain refinement to a submicron level and promoting the formation of a high-stability strengthening phase, which realizes precise optimization of the microstructure of the material through multi-step synergistic control, and significantly improves the comprehensive performance of the material.

[0006] As conceived above, the technical solution adopted by the present application is: In a first aspect of the embodiment, a method for refining and strengthening aluminum alloy grains is provided, which includes multiple synergistic effects of alloy smelting and composition control, powder preparation and ball milling, hot pressing, and strengthening phase stabilization, to realize metal strengthening.

[0007] Preferably, the alloy smelting and composition control includes smelting the alloy using a vacuum induction melting device, and accurately calculating and adding alloy element additives according to the target alloy composition.

[0008] Preferably, the powder preparation and ball milling includes obtaining spherical alloy powder by gas atomization, and realizing preliminary grain refinement of the alloy powder through ball milling.

[0009] Preferably, the hot pressing includes loading the alloy powder after ball milling into a hot pressing mold to obtain a blank under heat and pressure.

[0010] Preferably, the strengthening phase stabilization includes any one of aging treatment and warm rolling treatment of the blank after hot pressing to obtain submicron grains.

[0011] In a second aspect of the embodiment, a strengthening method is provided, which includes the following steps: S1, raw materials and pretreatment The purity of the metal raw material is ≥99.99%, and the mass fractions of the main alloying elements are Fe ≤0.0015%, Si ≤0.0015%, Cu ≤0.0035%, Zn ≤0.0015%, Ti ≤0.002%, Y ≤0.005%, and Zr ≤0.005%, and the total content of the remaining unavoidable impurities is ≤0.002%; The pretreatment process includes chemical cleaning, ultrasonic cleaning, and drying treatment.

[0012] S2, smelting and composition control After the base metal raw material is added to the smelting furnace, the furnace is evacuated, heated to 50-120°C above the melting point of the base metal, and the base metal raw material is melted after being kept at temperature for 5-15 min; The alloying elements are added in the form of master alloy, the addition process lasts for 5-10 min to avoid excessive local concentration, and stirring is performed for 15-30 min after the addition is completed to promote composition homogenization, and sampling analysis is performed every 5-10 min during the process by a spark direct-reading spectrometer. S3, powder preparation and ball milling The alloy liquid temperature is kept at 30-80℃ above the melting point to ensure fluidity, and the atomizing medium is argon or nitrogen with purity≥99.999%. The spherical powder with an average particle size of 20-60μm is obtained by atomization through a nozzle; The spherical powder after atomization is ground in a ball mill tank with a ball-to-powder ratio of 50:1-120:1. The temperature is monitored in real time by an infrared thermometer during the ball milling process, and the temperature is automatically cooled to below 50℃ when it exceeds 80℃, until the internal grains are preliminarily refined to 50-200nm. S4, hot pressing and grain refinement The mold is preheated to 150-350℃ for 30-60min, and then the ground powder is loaded. The hot pressing temperature is 420℃. After hot pressing, the pressure is released and cooled. The temperature fluctuation during hot pressing is≤±3℃, and the pressure fluctuation is≤±1MPa. After hot pressing, the pressure is released and cooled to obtain a sub-micron billet with a density≥95% and a grain size of 0.3-1.0μm. S5, subsequent processing and strengthening phase stabilization First, the billet is surface treated to remove the oxidation layer and residual release agent, so that the surface roughness Ra is≤1.6μm. For age-hardening type alloys, heat to 160-200℃ in a resistance furnace for 5-12h. For plastic deformation strengthening type alloys, heat to 150-350℃ and perform plastic deformation processing with a deformation amount of 30%-80%.

[0013] In a third aspect of the embodiment, a high-stability aluminum alloy prepared by a strengthening method is provided.

[0014] Preferably, the mass fraction of aluminum in the aluminum alloy is 97.29-98.99%, and the remaining components include iron≤0.0015%, silicon≤0.0015%, copper≤0.0035%, zinc≤0.0015%, titanium≤0.002%, yttrium 0.5-1.2%, and zirconium 0.5-1.5%, as well as other unavoidable impurity elements.

[0015] Preferably, the yttrium and zirconium elements are added to the aluminum alloy through an aluminum-yttrium alloy containing 10% yttrium by mass and an aluminum-zirconium alloy containing 10% zirconium by mass.

[0016] Preferably, the aluminum alloy matrix uniformly distributes Al3(Y,Zr) strengthening phases with an average size of 0.3-1.0μm.

[0017] Preferably, the room temperature yield strength of the aluminum alloy is 480 MPa, the tensile strength is 580 MPa, and the elongation is 12%.

[0018] The beneficial effects of the present application are: 1、The present application realizes the precise control of material grain size by the synergistic effect of alloy smelting and composition control, powder preparation and ball milling, hot pressing and strengthening phase stabilization, and the grain size is stably controlled in the sub-micron range of 0.3-1 μm. The sub-micron grain size improves the toughness of the material by increasing the grain boundary slip channel, and the elongation is maintained at more than 5%, solving the problem of traditional high-strength materials being "strong but not tough". Moreover, the equipment is mature, and there is no need for special customization of high-end instruments, and the equipment investment cost is low.

[0019] 2、The present application generates Al3(Y,Zr) strengthening phase with extremely high high-temperature stability through precise composition control and subsequent aging process optimization. This high stability ensures that the material does not degrade in performance under high-temperature service environment, and the high-temperature tensile strength retention rate is ≥80% at 200-300℃. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a flowchart of the present application; DETAILED DESCRIPTION In order to make the technical means, creative features, purposes and effects of the present application easy to understand, the present application will be further described below in conjunction with specific embodiments.

[0021] As shown in Figure 1 , the present application includes alloy smelting and composition control, powder preparation and ball milling, hot pressing and strengthening phase stabilization, and realizes metal strengthening.

[0022] In this embodiment, the mass fraction of aluminum in the aluminum raw material is 99.98%, and the mass fraction of the remaining components includes ≤0.0015% iron, ≤0.0015% silicon, ≤0.0035% copper, ≤0.0015% zinc, ≤0.002% titanium, ≤0.005% yttrium and ≤0.005% zirconium, as well as other unavoidable impurity elements.

[0023] Aluminum ingot pretreatment: 10% hydrochloric acid solution is used as a chemical cleaning solution, and cleaning is carried out in a 30℃ constant temperature water bath for 15min, during which stirring is ensured to ensure uniform cleaning; then deionized water is used to rinse until the rinse water pH value is 7.0, and then it is transferred to an ultrasonic cleaning tank, and cleaned for 20min with 30kHz frequency and deionized water as the medium; after cleaning, it is placed in a drying oven at 120℃ and 3% relative humidity for 3h, and then sealed after cooling.

[0024] In this embodiment, the smelting equipment is a vacuum induction melting furnace, and the crucible is a high-density graphite crucible, which is preheated to 250°C and kept for 1 h before use. The pretreated aluminum raw material is added to the crucible, and the vacuum pump is started to vacuum to a vacuum degree of 5×10-5 Pa in the furnace. The temperature is raised to 950°C at a rate of 10°C / min, and the temperature is kept for 10 min to ensure that the aluminum ingot is completely melted.

[0025] In this embodiment, the intermediate alloy addition amount is calculated according to the target composition, and the Al-Y and Al-Zr intermediate alloys are slowly added to the melt. The addition process lasts for 8 min to avoid splashing of the melt. After the addition is completed, the electromagnetic stirring device is started, and the stirring time is set to 20 min to promote the homogenization of the composition. During the stirring, a small amount of alloy liquid is taken every 8 min with a sampling spoon, and the composition is analyzed by a spark direct-reading spectrometer after cooling. In this embodiment, the mass fraction of Y is 0.79% to 0.81%, and the Zr content is 0.99% to 1.01%, with a composition deviation of ±0.01%.

[0026] In this embodiment, the molten alloy after smelting is introduced into the gas atomization powder preparation device through a boron nitride flow guide pipe, and the alloy liquid temperature is kept at 750°C. The atomization medium is selected as argon gas with a purity of 99.999%, and the gas pressure is set to 0.8 MPa. The gas temperature is 1350°C, the gas nozzle and the alloy liquid flow angle are 45°, and the alloy liquid flow rate is controlled at 5 mL / s. The atomized powder is classified by a cyclone separator, and the powder with a particle size range of 30-60 μm is collected.

[0027] In this embodiment, the planetary ball mill is selected as the ball milling equipment, and the ball milling tank is made of hard alloy material. The alloy powder and the grinding balls are loaded into the ball milling tank at a ball-to-material ratio of 80:1. The ball milling tank is first evacuated to -0.098 MPa, and then filled with argon gas with a purity of 99.99% to 0.4 MPa. This operation is repeated 4 times to completely replace the air. The rotation speed of the ball mill is 400 r / min, and the intermittent ball milling is adopted with a total ball milling time of 40 h. During the ball milling process, the tank wall temperature is monitored in real time by an infrared temperature detector. When the temperature rises to 75°C, the water cooling device is automatically started, and the ball milling continues when the temperature drops to below 45°C. After 30 h of ball milling, 8% of new grinding balls are added to maintain the grinding efficiency. After the ball milling is completed, the sample is taken and observed by scanning electron microscopy. The powder particle morphology changes from spherical to irregular flaky, and the internal grain size is 80-150 nm by transmission electron microscopy analysis.

[0028] In this embodiment, the hot pressing mold is made of high-density graphite, and the inner wall of the mold is uniformly coated with 0.1 mm thick boron nitride release agent. The mold is preheated to 250°C and kept for 45 min. The alloy powder after ball milling is loaded into the mold, and the powder is uniformly filled by vibration. Then it is put into a vacuum hot pressing furnace.

[0029] In this embodiment, the hot-pressing process is vacuumized to a vacuum degree of 5*10-4 Pa in the furnace, heated to 420℃ at a heating rate of 8℃ / min, and after reaching the temperature, a pressure of 70 MPa is applied at a pressurizing rate of 10 MPa / min, and the temperature is kept constant and the pressure is kept constant for 1.2 h, and during the hot-pressing process, the temperature fluctuation is ≤±3℃, and the pressure fluctuation is ≤±1 MPa. After the heat preservation is completed, the temperature is cooled to 150℃ at a cooling rate of 10℃ / min, and a sub-micron blank with a density of ≥95% and a grain size of 0.3-1.0 μm is obtained.

[0030] In this embodiment, the blank is polished by sandpaper to remove the surface oxidation layer and the residual release agent, and the surface roughness Ra of the treated blank is 1.2 μm. The blank is placed in a box-type resistance furnace for aging treatment, and the heating rate is set to 8℃ / min, and the temperature is raised to 180℃ and kept constant for 8 h, and during this period, the temperature at different positions in the furnace is measured every 2.5 h, and the temperature difference is ≤±1℃; for the alloy that needs plastic processing, warm extrusion or warm rolling treatment is carried out, and the processing temperature is 150℃, and the deformation amount is 30%-80%, and the plastic processing temperature is adjusted according to the alloy, and temperature compensation control is increased: the warm extrusion temperature is 200℃, and the warm rolling temperature is 220℃; if the temperature exceeds the upper limit during the processing, the processing needs to be paused, and the temperature is naturally cooled to below 150℃ before the processing is resumed.

[0031] The aluminum alloy of this embodiment has a room temperature yield strength of 480 MPa, a tensile strength of 580 MPa, and an elongation of 12%; a high-temperature tensile strength of 500 MPa at 200℃, a retention rate of 86%; after being kept at 200℃ for 100 h, the tensile strength is 480 MPa, and the retention rate is 83%; and the Al3(Y, Zr) phase is dispersedly distributed in the form of spheres in the matrix, and the lattice mismatch degree with the matrix is ≤5%, and the interface is well combined, and after being kept at a temperature of 70% of the melting point (about 250℃ for the aluminum alloy) for 100 h, the strengthening phase coarsening rate is ≤10%.

[0032] From the common general knowledge, the present application can be realized by other embodiments without departing from the spirit or essential characteristics thereof. Therefore, the above disclosed embodiments are merely illustrative in all aspects and are not the only ones. All changes within the scope of the present application or within the equivalent scope of the present application are included in the present application.

Claims

1. A method of grain refinement and strengthening of an aluminum alloy, characterized by, The synergistic effect of alloy smelting and composition control, powder preparation and ball milling treatment, hot pressing forming and strengthening phase stabilization is realized to achieve metal strengthening.

2. A method of grain refinement and strengthening of an aluminum alloy according to claim 1, characterized in that, The alloy smelting and composition control comprises smelting the alloy by using a vacuum induction smelting device, and accurately calculating and adding alloy element additives according to the target alloy composition.

3. The method of grain refinement and strengthening of an aluminum alloy of claim 1, wherein, The powder preparation and ball milling treatment comprises obtaining spherical alloy powder by gas atomization, and preliminarily refining the grain size of the alloy powder by ball milling treatment.

4. The method of grain refinement and strengthening of an aluminum alloy of claim 1, wherein, The hot pressing forming comprises loading the alloy powder after ball milling into a hot pressing mold to obtain a blank.

5. The method of grain refinement and strengthening of an aluminum alloy of claim 1, wherein, The strengthening phase stabilization comprises aging treatment or warm rolling treatment of the blank after hot pressing forming to stabilize the Al3(Y, Zr) strengthening phase and avoid coarsening at high temperature.

6. The method of claims 1-5, wherein, The method comprises the following steps: S1, raw materials and pretreatment The purity of the metal raw material is greater than or equal to 99.99%, and the mass fraction of the main alloying elements is iron less than or equal to 0.0015%, silicon less than or equal to 0.0015%, copper less than or equal to 0.0035%, zinc less than or equal to 0.0015%, titanium less than or equal to 0.002%, yttrium less than or equal to 0.005%, and zirconium less than or equal to 0.005%, and the total content of the remaining unavoidable impurities is less than or equal to 0.002%; The pretreatment process comprises chemical cleaning, ultrasonic cleaning and drying treatment. S2, smelting and composition control After the base metal raw material is added to the smelting furnace, the furnace is evacuated, heated to 50-120℃ above the melting point of the base metal, and the base metal raw material is melted after being kept at temperature for 5-15min; The alloy element composition control is added in the form of intermediate alloy, and the adding process lasts for 5-10min to avoid local high concentration, and after the adding is completed, the stirring lasts for 15-30min to promote the composition homogenization, and the composition element ratio is analyzed every 5-10min during the process; S3, powder preparation and ball milling treatment The alloy liquid temperature is kept at 30-80℃ above the melting point to ensure the fluidity, the atomization medium is argon or nitrogen with a purity of greater than or equal to 99.999%, and the spherical powder with an average particle size of 20-60μm is obtained by nozzle atomization; The spherical powder after atomization and the grinding balls are ground in the ball mill tank at a ball-to-material ratio of 50:1-120:1, the temperature is monitored in real time by an infrared thermometer during the ball milling process, and the temperature is less than or equal to 80℃, when the temperature is too high, the temperature is automatically cooled to less than or equal to 50℃, and then the ball milling process is continued, until the internal grain size is preliminarily refined to 50-200nm; S4, hot pressing forming and grain refinement After the mold is preheated to 150-350℃ and kept at temperature for 30-60min, the ground powder is loaded into the mold, the hot pressing temperature is 420℃, and after the hot pressing is completed, the pressure is released and the mold is cooled to obtain a submicron blank with a density of greater than or equal to 95% and a grain size of 0.3-1.0μm; S5, subsequent treatment and strengthening phase stabilization First, the surface of the blank is treated to remove the oxidation layer and the residual release agent, so that the surface roughness Ra is less than or equal to 1.6μm; For the aging strengthening type alloy, the blank is heated to 160-200℃ in a resistance furnace and kept at temperature for 5-12h; For the plastic deformation strengthening type alloy, the blank is heated to 150-350℃ and subjected to plastic deformation processing with a deformation amount of 30%-80%.

7. A high-stability aluminum alloy prepared by the strengthening method according to any one of claims 1 to 6, characterized by The mass fraction of aluminum in the aluminum alloy is 97.29-98.99%, and the rest of the components include iron ≤0.0015%, silicon ≤0.0015%, copper ≤0.0035%, zinc ≤0.0015%, titanium ≤0.002%, yttrium 0.5-1.2%, zirconium 0.5-1.5%, and other inevitable impurity elements; In the aluminum alloy, the yttrium and zirconium elements are added to the aluminum alloy by smelting through an aluminum-yttrium alloy containing 10% yttrium by mass and an aluminum-zirconium alloy containing 10% zirconium by mass.

8. The high-stability aluminum alloy prepared according to the strengthening method of claim 7, characterized in that, The Al3(Y,Zr) strengthening phase is uniformly distributed in the aluminum alloy matrix, and the average size is 0.3-1.0 μm.

9. The high-stability aluminum alloy prepared according to the strengthening method of claim 7, characterized in that, The room temperature yield strength of the aluminum alloy is 480 MPa, the tensile strength is 580 MPa, and the elongation is 12%.

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