An aerospace intermediate alloy and a method of making the same

Abstract

The application provides an aerospace intermediate alloy and a preparation method thereof, and belongs to the technical field of metallurgy, and comprises the following steps: step S1, industrial pure aluminum is melted, and then first Al-10Ti alloy is added in batches, temperature is raised, and stirring is carried out, so that Ti-rich aluminum melt is obtained; step S2, Al-5C alloy which is crushed, dried and cooled by argon is added into the Ti-rich aluminum melt in batches, and temperature is kept and stirring is carried out, so that a mixed melt is obtained; step S3, second Al-10Ti alloy and industrial pure aluminum are alternately added, temperature is lowered, and stirring is carried out, so that Al-Ti-C alloy melt is obtained; step S4, rotary degassing and standing slag removal are carried out; and step S5, thin blank pouring, heat preservation and hot rolling are carried out, so that the aerospace intermediate alloy is obtained. The application can improve the grain refinement effect and heat preservation stability of the obtained intermediate alloy on Zr-containing aerospace aluminum alloy.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, specifically to an aerospace intermediate alloy and its preparation method. Background Technology

[0002] High-strength aluminum alloys in the 2xxx and 7xxx series for aerospace applications have high requirements for as-cast microstructure uniformity, grain size, and subsequent hot working stability. This is typically achieved by adding grain-refining master alloys to improve the solidification structure. Some high-strength aluminum alloys contain Zr, and the refining effect of TiB2 particles in traditional Al-Ti-B master alloys is easily affected in Zr-containing aluminum melts. Furthermore, the refining effect may further decrease with prolonged holding time after addition. In contrast, Al-Ti-C master alloys with TiC... x As a heterogeneous nucleation phase, particles contain little or no boron and have good application potential in Zr-containing aluminum alloys.

[0003] Patent application CN108425028A discloses a method for preparing an Al-Ti-C master alloy without the Al3Ti phase. The method involves ball milling Al powder, C powder, and Ti powder to form a preform, pressing the preform into molten pure aluminum for reaction, and then remelting it after casting. While this method can produce an Al-Ti-C master alloy, it requires numerous process steps, including powder mixing, preform pressing, and remelting, and demands high precision in controlling powder dispersion and reaction consistency.

[0004] Patent application CN106480331A discloses an Al-Ti-C master alloy and its preparation method, using carbon nanotubes as the carbon source and potassium fluorotitanate as the titanium source, reacting with molten aluminum at 1150-1250℃. This method is beneficial for carbon source dispersion, but the reaction temperature is relatively high, which can easily increase melt oxidation, gas absorption, burn-off, and energy consumption control pressure during industrial smelting.

[0005] In the preparation of existing Al-Ti-C master alloys, the carbon component tends to agglomerate locally or exhibit uneven Ti-C reaction after entering the aluminum melt. Increasing the temperature or extending the holding time to promote the reaction can further increase the possibility of the already formed second phase continuing to grow or agglomerate. Therefore, there remains a difficult problem in balancing the stable introduction of carbon components, the sufficiency of the Ti-C reaction, and the control of the second phase microstructure.

[0006] Therefore, there is a need to provide an aerospace intermediate alloy and its preparation method to solve the problems existing in the prior art. Summary of the Invention

[0007] In view of this, the present invention provides an aerospace intermediate alloy and its preparation method. By coordinating and controlling the addition process of Ti source and carbon source as well as the subsequent refining, casting and hot working processes, the grain refinement effect and thermal stability of the intermediate alloy are improved.

[0008] To achieve the above objectives, the present invention provides a method for preparing an aerospace intermediate alloy, comprising the following steps: Step S1: Heat and melt industrial pure aluminum, add the first Al-10Ti alloy in batches after preheating, heat and stir to obtain Ti-enriched aluminum melt; Step S2: After crushing and drying the Al-5C alloy and cooling it in a dry argon atmosphere, add the Ti-enriched aluminum melt in batches. After the addition is completed, keep it warm and stir to obtain a mixed melt. Step S3: After preheating the second Al-10Ti alloy and industrial pure aluminum, add them to the mixed melt in batches alternately. After complete melting, cool down and stir to obtain Al-Ti-C alloy melt. Step S4: After cooling the Al-Ti-C alloy melt, argon gas is introduced for rotary degassing, and the melt is allowed to stand and slag is removed to obtain a refined alloy melt. Step S5: After cooling the refined alloy melt, pour it into a preheated metal mold, cool and demold it, then heat-hold and hot-roll it to obtain an aerospace intermediate alloy.

[0009] This invention introduces the Ti source in two stages. First, a first Al-10Ti alloy is added to industrial pure aluminum to form a Ti-enriched aluminum melt, allowing the subsequently added Al-5C alloy to melt, disperse, and react in the pre-Ti-containing melt environment. After the Al-5C alloy completes the corresponding high-temperature holding and stirring process, a second Al-10Ti alloy and industrial pure aluminum are added, allowing the remaining Ti component to enter the melt after the aforementioned high-temperature reaction stage. Compared to adding all Ti sources to the melt before the Al-5C alloy, this staged addition method ensures sufficient contact between the Al-5C alloy and the Ti-containing melt while shortening the time required for the later-added Ti component to undergo the initial high-temperature treatment. The added materials are then uniformly melted into the system by cooling and stirring. The melt is then purified by argon rotation degassing and static settling to remove slag. The solidification and plastic deformation processes are regulated by controlled casting, heat preservation and hot rolling. This allows for continuous process control of melting, reaction, purification, solidification and hot working processes, which is beneficial to improving the quality stability of the obtained Al-Ti-C master alloy and provides a process basis for its stable grain refinement effect.

[0010] In this invention, Al-10Ti alloy refers to an aluminum-titanium master alloy with Al as the matrix and Ti mass fraction of 10%; Al-5C alloy refers to an aluminum-carbon master alloy with Al as the matrix and C mass fraction of 5%.

[0011] The "first Al-10Ti alloy" and "second Al-10Ti alloy" described in this invention are used to distinguish different addition stages of the Al-10Ti alloy during the preparation process. The first Al-10Ti alloy is the Al-10Ti alloy used to prepare Ti-enriched aluminum melt before the addition of Al-5C alloy, and the second Al-10Ti alloy is the Al-10Ti alloy added again after the Al-5C alloy has been heated and stirred. The first Al-10Ti alloy and the second Al-10Ti alloy have the same chemical composition, and their main difference lies in the addition sequence and amount.

[0012] Preferably, in step S1, the Ti-enriched aluminum melt comprises the following components in parts by weight: 35-38 parts of industrial pure aluminum and 28-32 parts of the first Al-10Ti alloy; the heating and stirring temperature is 1020-1040℃, the stirring speed is 200-240 r / min, and the stirring time is 3-5 min.

[0013] The amounts of industrial pure aluminum and the first Al-10Ti alloy were controlled at 35-38 parts and 28-32 parts, respectively, to ensure that the aluminum melt before the addition of the Al-5C alloy contained a certain amount of Ti component, providing conditions for the subsequent dispersion and contact reaction of the Al-5C alloy in the Ti-containing melt. After the first Al-10Ti alloy was added, the melt temperature was controlled at 1020-1040℃ to ensure that the added Al-10Ti alloy was fully melted and to maintain good flow and mass transfer conditions in the melt. Combined with a stirring speed of 200-240 r / min and a stirring time of 3-5 min, the internal temperature and Ti component distribution of the melt tended to be uniform. If the temperature was too low or the stirring time was insufficient, it would not be conducive to the rapid melting of the Al-10Ti alloy and the formation of a uniform Ti-enriched aluminum melt; if the temperature was too high or the high-temperature residence time was too long, it would increase the possibility of melt oxidation, gas absorption, and burn-off.

[0014] Preferably, in step S2, the Al-5C alloy is 1.8-2.2 parts by weight and the particle size of the Al-5C alloy is 3-8 mm; the drying temperature is 230-270℃ and the drying time is 1.5-2.5 h; the Al-5C alloy is added in 5 batches, with an interval of 30-60 s between each addition, and the total feeding time is 3-5 min.

[0015] The carbon in the Al-5C alloy is pre-existing in the aluminum-based support, which helps improve the interfacial contact state when the carbon component enters the aluminum melt. Adding the carbon in stages reduces the instantaneous enrichment and floating aggregation of localized carbon components, allowing newly added particles to continuously contact the Ti-enriched melt, thereby improving the uniformity of the Ti-C reaction.

[0016] Preferably, in step S2, the temperature for heat preservation and stirring is 1015-1035℃, the speed is 200-240 r / min, and the time is 10-15 min.

[0017] Preferably, in step S3, the preheating temperature is 200-240℃ and the time is 1-2h; the cooling and stirring temperature is 840-860℃, the speed is 160-220r / min, and the time is 5-8min; the weight percentage of the second Al-10Ti alloy is 18-22 parts; and the weight percentage of industrial pure aluminum is 11-15 parts.

[0018] Preferably, in step S4, the temperature for rotary degassing is 770-790℃, the argon flow rate is 6-10L / min, the time is 6-8min, and the settling time is 3-5min.

[0019] Preferably, in step S5, the pouring temperature is 750-770℃; the preheating temperature of the metal mold is 180-220℃; and the effective thickness of the cast billet is 20-40mm.

[0020] Using 750-770℃ for pouring and controlling the preheating temperature of the metal mold and the effective thickness of the billet helps to shorten the heat transfer distance and high-temperature residence time during solidification while stabilizing the filling process, thus providing conditions for obtaining a more uniform solidification structure.

[0021] Preferably, in step S5, the heat preservation temperature is 390-420℃ and the time is 1-2 hours.

[0022] Preferably, in step S5, the initial rolling temperature of hot rolling is 380-410℃, the total reduction rate is 50%-65%, and the single-pass reduction rate is 10%-15%.

[0023] Controlling the initial rolling temperature, total reduction rate, and single-pass reduction rate of hot rolling allows the billet to undergo sufficient plastic deformation while maintaining its thermoplasticity. This is beneficial for improving the internal microstructure of the billet and thus enhancing the uniformity of the resulting master alloy.

[0024] To achieve the above objectives, the present invention also provides an aerospace intermediate alloy prepared by the above-described method for preparing aerospace intermediate alloys.

[0025] The aerospace intermediate alloy prepared by the above method exhibits controlled processes including the addition of Ti and carbon sources, the high-temperature reaction of the melt, the melt purification process, and subsequent solidification and hot working. According to the grain refinement performance test results described later, the intermediate alloy obtained in this invention, after being added to a Zr-containing aerospace aluminum alloy melt, achieves a smaller average grain size, and the increase in grain size is relatively small after extending the holding time, indicating that it has good grain refinement effect and thermal stability.

[0026] The above-described technical solution of the present invention has at least the following beneficial effects: 1. The present invention adopts a phased addition of Ti source. First, a Ti-enriched aluminum melt is formed by using the first Al-10Ti alloy, then an Al-5C alloy is added for mixing and reaction, and then a second Al-10Ti alloy is added. This allows some Ti components to enter the melt before the addition of Al-5C and some Ti components to enter the melt after this reaction stage. This is beneficial to take into account both the contact reaction between Al-5C and the Ti-containing melt and the high-temperature treatment process of the later added Ti components.

[0027] 2. By controlling the particle size, drying and cooling the Al-5C alloy in a dry argon atmosphere, and adding it in stages, this invention can reduce the possibility of adsorbed water on the surface of the Al-5C alloy being carried into the melt and reduce local aggregation caused by a single concentrated addition. This allows the Al-5C alloy to obtain more uniform contact and mixing conditions in the Ti-enriched aluminum melt, which is beneficial to improving the consistency of the Ti-C reaction process.

[0028] 3. This invention purifies the melt by cooling and stirring, argon rotation degassing, and static slag removal. Combined with thinner billet casting, heat preservation, and controlled hot rolling, the purity of the melt and the subsequent solidification and deformation processes are continuously controlled. This helps to reduce the inclusion content and improve the uniformity of the billet structure, thereby improving the grain refinement effect and heat preservation stability of the obtained intermediate alloy. Attached Figure Description

[0029] Figure 1 This is a scanning electron microscope image of the aerospace intermediate alloy prepared in Example 3 of the present invention. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments.

[0031] Example 1 Add 35 kg of industrial pure aluminum to the smelting furnace and heat until completely melted; preheat 28 kg of the first Al-10Ti alloy at 220℃ for 2 hours, and add it to the molten aluminum in 3 batches. Add the next batch after each batch has basically melted. After all the batches have been added, raise the temperature of the melt to 1020℃ and stir at 200 r / min for 3 minutes to obtain Ti-enriched aluminum melt.

[0032] Weigh 1.8 kg of Al-5C alloy, crush it to a particle size of 3 mm, dry it at 230℃ for 1.5 h, then cool it to room temperature in a dry argon atmosphere, and add it to the Ti-enriched aluminum melt in 5 portions, with an interval of 30 s between each addition, and control the total feeding time to 3 min. After the feeding is completed, keep it at 1015℃ and stir it at 200 r / min for 10 min to obtain a mixed melt.

[0033] Weigh 18 kg of the second Al-10Ti alloy and 11 kg of industrial pure aluminum, preheat both at 200℃ for 1 hour, and add them to the mixed melt in 5 batches, with a total feeding time of 6 minutes. After the added materials have completely melted, cool down to 840℃ and stir at 160 r / min for 5 minutes to obtain the Al-Ti-C alloy melt.

[0034] The Al-Ti-C alloy melt was cooled to 770℃ and subjected to rotary degassing treatment with argon gas. The argon gas flow rate was 6 L / min, the rotor speed was 220 r / min, and the treatment time was 6 min. After the gas supply was stopped, the melt was allowed to stand for 3 min to remove surface slag. Samples were taken for testing, and the final composition of the resulting melt was in the range of Ti 4.8-5.2 wt.%, C 0.08-0.12 wt.%, Fe≤0.10 wt.%, Si≤0.08 wt.%, and B≤0.003 wt.%, thus obtaining a refined alloy melt.

[0035] The refined alloy melt was cooled to 750°C and poured into a metal mold preheated to 180°C. The effective thickness of the cast billet was controlled to be 20 mm. After cooling to room temperature, the billet was demolded and held at 390°C for 1 hour. Then, it was hot rolled with an initial rolling temperature of 380°C and a final rolling temperature of 300°C. The total reduction rate was 50%, and the single-pass reduction rate was 10%, resulting in an aerospace intermediate alloy.

[0036] Example 2 38 kg of industrial pure aluminum was added to a smelting furnace and heated until completely melted. 32 kg of the first Al-10Ti alloy was preheated at 220°C for 2 hours and added to the molten aluminum in 3 batches. Each batch was added after it was basically melted. After all the batches were added, the melt was heated to 1040°C and stirred at 240 r / min for 5 minutes to obtain Ti-enriched aluminum melt.

[0037] Weigh 2.2 kg of Al-5C alloy, crush it to 8 mm particle size, dry it at 270 °C for 2.5 h, then cool it to room temperature in a dry argon atmosphere, and add it to the Ti-enriched aluminum melt in 5 portions, with an interval of 60 s between each addition, and control the total feeding time to 5 min. After the feeding is completed, keep it at 1035 °C and stir it at 240 r / min for 15 min to obtain a mixed melt.

[0038] Weigh 22 kg of the second Al-10Ti alloy and 15 kg of industrial pure aluminum, preheat both at 240℃ for 2 hours, and add them to the mixed melt in 5 batches, with a total feeding time of 10 minutes. After the added materials have completely melted, cool down to 860℃ and stir at 220 r / min for 8 minutes to obtain the Al-Ti-C alloy melt.

[0039] The Al-Ti-C alloy melt was cooled to 790℃ and subjected to rotary degassing treatment with argon gas. The argon gas flow rate was 10 L / min, the rotor speed was 280 r / min, and the treatment time was 8 min. After the gas supply was stopped, the melt was allowed to stand for 5 min to remove surface slag. Samples were taken for testing. The final composition of the resulting melt was in the range of Ti 4.8-5.2 wt.%, C 0.08-0.12 wt.%, Fe≤0.10 wt.%, Si≤0.08 wt.%, and B≤0.003 wt.%, thus obtaining a refined alloy melt.

[0040] The refined alloy melt was cooled to 770°C and poured into a metal mold preheated to 220°C. The effective thickness of the cast billet was controlled to be 40 mm. After cooling to room temperature, the billet was demolded and held at 420°C for 2 hours. Then, it was hot rolled with an initial rolling temperature of 410°C and a final rolling temperature of 330°C. The total reduction rate was 65%, and the single-pass reduction rate was 15%, resulting in an intermediate alloy for aerospace applications.

[0041] Example 3 36.5 kg of industrial pure aluminum was added to a smelting furnace and heated until completely melted. 30 kg of the first Al-10Ti alloy was preheated at 220℃ for 2 hours and added to the molten aluminum in 3 batches. Each batch was added after it was basically melted. After all the batches were added, the melt was heated to 1030℃ and stirred at 220 r / min for 4 minutes to obtain Ti-enriched aluminum melt.

[0042] Weigh 2.0 kg of Al-5C alloy, crush it to a particle size of 5 mm, dry it at 250 °C for 2 h, then cool it to room temperature in a dry argon atmosphere, and add it to the Ti-enriched aluminum melt in 5 portions, with an interval of 45 s between each addition, and control the total feeding time to 4 min. After the feeding is completed, keep it at 1025 °C and stir it at 220 r / min for 12 min to obtain a mixed melt.

[0043] Weigh 20 kg of the second Al-10Ti alloy and 13 kg of industrial pure aluminum, preheat both at 220℃ for 1.5 h, and add them to the mixed melt in 5 batches alternately, with a total feeding time of 8 min; after the added materials have completely melted, cool down to 850℃ and stir at 190 r / min for 6.5 min to obtain the Al-Ti-C alloy melt.

[0044] The Al-Ti-C alloy melt was cooled to 780℃ and subjected to rotary degassing treatment with argon gas. The argon gas flow rate was 8 L / min, the rotor speed was 250 r / min, and the treatment time was 7 min. After the gas supply was stopped, the melt was allowed to stand for 4 min to remove surface slag. Samples were taken for testing, and the final composition of the resulting melt was in the range of Ti 4.8-5.2 wt.%, C 0.08-0.12 wt.%, Fe≤0.10 wt.%, Si≤0.08 wt.%, and B≤0.003 wt.%, thus obtaining a refined alloy melt.

[0045] The refined alloy melt was cooled to 760°C and poured into a metal mold preheated to 200°C. The effective thickness of the cast billet was controlled to be 30 mm. After cooling to room temperature, the billet was demolded and held at 405°C for 1.5 hours. Then, it was hot rolled with an initial rolling temperature of 395°C and a final rolling temperature of 315°C. The total reduction rate was 58%, and the single-pass reduction rate was 12%, resulting in an aerospace intermediate alloy.

[0046] Example 4 Add 35 kg of industrial pure aluminum to a smelting furnace and heat until completely melted; preheat 32 kg of the first Al-10Ti alloy at 220℃ for 2 hours and add it to the molten aluminum in 3 batches. Add the next batch after each batch has basically melted. After all the batches have been added, raise the temperature of the melt to 1040℃ and stir at 200 r / min for 5 minutes to obtain Ti-enriched aluminum melt.

[0047] Weigh 2.2 kg of Al-5C alloy, crush it to a particle size of 3 mm, dry it at 270℃ for 1.5 h, then cool it to room temperature in a dry argon atmosphere, and add it to the Ti-enriched aluminum melt in 5 portions, with an interval of 60 s between each addition, and control the total feeding time to 3 min. After the feeding is completed, keep it at 1035℃ and stir it at 200 r / min for 15 min to obtain a mixed melt.

[0048] Weigh 18 kg of the second Al-10Ti alloy and 15 kg of industrial pure aluminum, preheat both at 200℃ for 2 hours, and add them to the mixed melt in 5 batches, with a total feeding time of 6 minutes. After the added materials have completely melted, cool down to 860℃ and stir at 160 r / min for 8 minutes to obtain the Al-Ti-C alloy melt.

[0049] The Al-Ti-C alloy melt was cooled to 770℃ and subjected to rotary degassing treatment with argon gas. The argon gas flow rate was 10 L / min, the rotor speed was 220 r / min, and the treatment time was 8 min. After the gas supply was stopped, the melt was allowed to stand for 3 min to remove surface slag. Samples were taken for testing. The final composition of the resulting melt was in the range of Ti 4.8-5.2 wt.%, C 0.08-0.12 wt.%, Fe≤0.10 wt.%, Si≤0.08 wt.%, and B≤0.003 wt.%, thus obtaining a refined alloy melt.

[0050] The refined alloy melt was cooled to 770°C and poured into a metal mold preheated to 180°C. The effective thickness of the cast billet was controlled to be 40 mm. After cooling to room temperature, the billet was demolded and held at 390°C for 2 hours. Then, it was hot rolled with an initial rolling temperature of 385°C and a final rolling temperature of 305°C. The total reduction rate was 55%, and the single-pass reduction rate was 11%, resulting in an aerospace intermediate alloy.

[0051] Example 5 38 kg of industrial pure aluminum was added to a smelting furnace and heated until completely melted. 28 kg of the first Al-10Ti alloy was preheated at 220°C for 2 hours and added to the molten aluminum in 3 batches. Each batch was added after it was basically melted. After all the batches were added, the melt was heated to 1020°C and stirred at 240 r / min for 3 minutes to obtain Ti-enriched aluminum melt.

[0052] Weigh 1.8 kg of Al-5C alloy, crush it to 8 mm particle size, dry it at 230℃ for 2.5 h, then cool it to room temperature in a dry argon atmosphere, and add it to the Ti-enriched aluminum melt in 5 portions, with an interval of 30 s between each addition, and control the total feeding time to 5 min. After the feeding is completed, keep it at 1015℃ and stir it at 240 r / min for 10 min to obtain a mixed melt.

[0053] Weigh 22 kg of the second Al-10Ti alloy and 11 kg of industrial pure aluminum, preheat both at 240℃ for 1 hour, and add them to the mixed melt in 5 batches, with a total feeding time of 10 minutes. After the added materials have completely melted, cool down to 840℃ and stir at 220 r / min for 5 minutes to obtain the Al-Ti-C alloy melt.

[0054] The Al-Ti-C alloy melt was cooled to 790℃ and subjected to rotary degassing treatment with argon gas. The argon gas flow rate was 6 L / min, the rotor speed was 280 r / min, and the treatment time was 6 min. After the gas supply was stopped, the melt was allowed to stand for 5 min to remove surface slag. Samples were taken for testing, and the final composition of the resulting melt was in the range of Ti 4.8-5.2 wt.%, C 0.08-0.12 wt.%, Fe≤0.10 wt.%, Si≤0.08 wt.%, and B≤0.003 wt.%, thus obtaining a refined alloy melt.

[0055] The refined alloy melt was cooled to 750°C and poured into a metal mold preheated to 220°C. The effective thickness of the cast billet was controlled to be 20 mm. After cooling to room temperature, the billet was demolded and held at 420°C for 1 hour. Then, it was hot rolled with an initial rolling temperature of 405°C and a final rolling temperature of 325°C. The total reduction rate was 62%, and the single-pass reduction rate was 14%, resulting in an aerospace intermediate alloy.

[0056] Example 6 37 kg of industrial pure aluminum was added to a smelting furnace and heated until completely melted. 31 kg of the first Al-10Ti alloy was preheated at 220°C for 2 hours and added to the molten aluminum in 3 batches. Each batch was added after it was basically melted. After all the batches were added, the melt was heated to 1035°C and stirred at 230 r / min for 4.5 min to obtain Ti-enriched aluminum melt.

[0057] Weigh 2.1 kg of Al-5C alloy, crush it to a particle size of 6 mm, dry it at 260℃ for 2.2 h, then cool it to room temperature in a dry argon atmosphere, and add it to the Ti-enriched aluminum melt in 5 portions, with an interval of 50 s between each addition, and control the total feeding time to 4.5 min. After the feeding is completed, keep it at 1030℃ and stir it at 230 r / min for 14 min to obtain a mixed melt.

[0058] Weigh 21 kg of the second Al-10Ti alloy and 14 kg of industrial pure aluminum, preheat both at 230℃ for 1.8 h, and add them to the mixed melt in 5 batches, with a total feeding time of 9 min. After the added materials have completely melted, cool down to 855℃ and stir at 210 r / min for 7 min to obtain the Al-Ti-C alloy melt.

[0059] The Al-Ti-C alloy melt was cooled to 785℃ and subjected to rotary degassing treatment with argon gas. The argon gas flow rate was 9 L / min, the rotor speed was 270 r / min, and the treatment time was 7.5 min. After the gas supply was stopped, the melt was allowed to stand for 4.5 min to remove surface slag. Samples were taken for testing, and the final composition of the resulting melt was in the range of Ti 4.8-5.2 wt.%, C 0.08-0.12 wt.%, Fe≤0.10 wt.%, Si≤0.08 wt.%, and B≤0.003 wt.%, thus obtaining a refined alloy melt.

[0060] The refined alloy melt was cooled to 765°C and poured into a metal mold preheated to 210°C. The effective thickness of the cast billet was controlled to be 35 mm. After cooling to room temperature, the billet was demolded and held at 415°C for 1.8 hours. Then, it was hot rolled with an initial rolling temperature of 400°C and a final rolling temperature of 320°C. The total reduction rate was 60%, and the single-pass reduction rate was 13%, resulting in an aerospace intermediate alloy.

[0061] The present invention also includes comparative examples and related experiments.

[0062] Comparative Example 1 The only difference between Comparative Example 1 and Example 3 is that the first Al-10Ti alloy and the second Al-10Ti alloy are not added in stages, but are combined into 50kg of Al-10Ti alloy and added to industrial pure aluminum in 3 batches; the second Al-10Ti alloy is not added in step S3, and the other composition and preparation method are the same as in Example 3, so as to prepare an aerospace intermediate alloy.

[0063] Comparative Example 2 The difference between Comparative Example 2 and Example 3 is that the Al-5C alloy is no longer added in 5 separate additions, but is added continuously to the Ti-enriched aluminum melt in one go within 4 minutes. The other composition and preparation method are the same as in Example 3, and an intermediate alloy for aerospace applications is prepared.

[0064] Comparative Example 3 The difference between Comparative Example 3 and Example 3 is that after the Al-5C alloy was crushed to 5mm, it was not dried at 250℃ and cooled in a dry argon atmosphere. Instead, it was placed in air at room temperature and then added to the Ti-enriched aluminum melt in 5 batches as in Example 3. The other composition and preparation method were the same as in Example 3, and an aerospace intermediate alloy was prepared.

[0065] Comparative Example 4 The difference between Comparative Example 4 and Example 3 is that the refined alloy melt was still poured into a metal mold preheated to 200°C at 760°C, but the effective thickness of the billet was controlled to be 80 mm. After cooling to room temperature, it was held at 405°C for 1.5 h as in Example 3, and hot rolled using the same hot rolling parameters. Other components and preparation methods were the same as in Example 3, and an aerospace intermediate alloy was prepared.

[0066] Comparative Example 5 The difference between Comparative Example 5 and Example 3 is that the refined alloy melt was poured into a preheated metal mold at 200°C as in Example 3, and the effective thickness of the cast billet was controlled to be 30 mm. After cooling to room temperature and demolding, it was not subjected to 405°C heat preservation and subsequent hot rolling. The other components and the aforementioned preparation method were the same as in Example 3, and it was an aerospace intermediate alloy.

[0067] Performance testing The aerospace intermediate alloys prepared in Examples 1-6 and Comparative Examples 1-5 were subjected to performance testing.

[0068] 1. Grain Refinement Effect Test: A batch of Zr-containing 7xxx series aerospace aluminum alloy base melt was taken, and intermediate alloys obtained in Examples 1-6 and Comparative Examples 1-5 were added at 730℃ to increase the added Ti mass fraction in the melt to 0.02 wt.%. After stirring evenly, the melt was held at this temperature for 10 min and 60 min respectively, and then cast using the same metal mold. After grinding, polishing, and etching, the average equiaxed grain size was statistically analyzed using the cross-section method. The 10-minute average grain size characterized the immediate refinement effect, and the 60-minute average grain size and the grain size growth rate at 60 min relative to 10 min characterized the holding stability.

[0069] 2. Cleanliness characterization: After filtering the intermediate alloy melt, samples were prepared, and the number of inclusions larger than 20 μm per unit area was determined by metallographic statistical method to characterize the cleanliness after rotary degassing, static slag removal and raw material pretreatment.

[0070] The test results are summarized in Table 1.

[0071] Table 1

[0072] Depend on Figure 1 It can be seen that the intermediate alloy prepared in Example 3 did not show large-area continuous agglomeration regions, and the overall structure was relatively uniform.

[0073] As shown in Table 1, Comparative Example 1 combined the first Al-10Ti alloy and the second Al-10Ti alloy, both of which were added during the preparation of Ti-enriched aluminum melt, allowing all Ti components to undergo the high-temperature reaction stage after the addition of the Al-5C alloy. The average grain size of Comparative Example 1 at 10 min was 132 μm, and the average grain size at 60 min was 168 μm, both significantly higher than the 96 μm and 107 μm of Example 3, and the grain size growth rate increased from 11.5% in Example 3 to 27.3%. This indicates that adding the Ti source in stages, with some Ti components entering the melt before the addition of the Al-5C alloy and others added after its reaction, is beneficial for coordinating the contact reaction process between the Al-5C alloy and the Ti-containing melt, as well as the high-temperature treatment process of the later-added Ti components. This improves the immediate grain refinement effect of the resulting intermediate alloy and reduces the refinement decay after long-term holding.

[0074] The number of inclusions per unit area in Comparative Example 2 increased only slightly compared to Example 3, but its 10-minute average grain size increased from 96 μm in Example 3 to 126 μm, and its 60-minute average grain size increased from 107 μm to 151 μm, with the grain size growth rate increasing from 11.5% to 19.8%. This indicates that the phased addition method can avoid the carbon component from concentrating into the Ti-enriched aluminum melt in a short time, which is beneficial to improving the contact and mixing uniformity between the Al-5C alloy and the melt, thereby improving the grain refinement effect and thermal stability of the obtained intermediate alloy.

[0075] In Comparative Example 3, the number of inclusions per unit area increased from 3.9 in Example 3 to 9.8, while the average grain size over 10 minutes increased from 96 μm to 116 μm, and the average grain size over 60 minutes increased from 107 μm to 136 μm. This indicates that drying the Al-5C alloy and cooling it in a dry argon atmosphere can reduce water adsorption on the raw material surface and secondary moisture absorption during the cooling process. This helps to reduce the possibility of moisture being introduced into the melt, causing gas absorption, oxidation, and inclusions, thereby maintaining the cleanliness of the melt and ensuring that the resulting intermediate alloy maintains good grain refinement properties.

[0076] The number of inclusions in Comparative Example 4 was basically similar to that in Example 3, but its 10-minute average grain size increased from 96 μm in Example 3 to 119 μm, and its 60-minute average grain size increased from 107 μm to 143 μm, with the grain size growth rate increasing from 11.5% to 20.2%. This indicates that controlling the effective thickness of the cast billet within the range of 20-40 mm is beneficial to improving the grain refinement effect and thermal stability of the obtained intermediate alloy.

[0077] The number of inclusions in Comparative Example 5 was basically similar to that in Example 3, but its 10-minute average grain size increased from 96 μm in Example 3 to 127 μm, and its 60-minute average grain size increased from 107 μm to 154 μm, with the grain size growth rate increasing from 11.5% to 21.3%. This indicates that, under basically the same melting and refining conditions, the combination of reheating and controlled hot rolling is beneficial to improving the grain refinement effect of the obtained master alloy and reducing the refinement decay after long-term holding.

Claims

1. A method for preparing an aerospace-grade master alloy, characterized in that, Includes the following steps: Step S1: Heat and melt industrial pure aluminum, add the first Al-10Ti alloy in batches after preheating, heat and stir to obtain Ti-enriched aluminum melt; Step S2: After crushing and drying the Al-5C alloy and cooling it in a dry argon atmosphere, add the Ti-enriched aluminum melt in batches. After the addition is completed, keep it warm and stir to obtain a mixed melt. Step S3: After preheating the second Al-10Ti alloy and industrial pure aluminum, add them to the mixed melt in batches alternately. After complete melting, cool down and stir to obtain Al-Ti-C alloy melt. Step S4: After cooling the Al-Ti-C alloy melt, argon gas is introduced for rotary degassing, and the melt is allowed to stand and slag is removed to obtain a refined alloy melt. Step S5: After cooling the refined alloy melt, pour it into a preheated metal mold, cool and demold it, then heat-hold and hot-roll it to obtain an aerospace intermediate alloy.

2. The method for preparing an aerospace intermediate alloy according to claim 1, characterized in that, In step S1, the Ti-enriched aluminum melt comprises the following components in parts by weight: 35-38 parts of industrial pure aluminum and 28-32 parts of the first Al-10Ti alloy; the temperature for heating and stirring is 1020-1040℃, the speed is 200-240 r / min, and the time is 3-5 min.

3. The method for preparing an aerospace intermediate alloy according to claim 1, characterized in that, In step S2, the Al-5C alloy is 1.8-2.2 parts by weight and the particle size of the Al-5C alloy is 3-8 mm; the drying temperature is 230-270℃ and the time is 1.5-2.5 h; the Al-5C alloy is added in 5 batches, with an interval of 30-60 s between each addition, and the total feeding time is 3-5 min.

4. The method for preparing an aerospace intermediate alloy according to claim 1, characterized in that, In step S2, the temperature for heat preservation and stirring is 1015-1035℃, the speed is 200-240 r / min, and the time is 10-15 min.

5. The method for preparing an aerospace intermediate alloy according to claim 1, characterized in that, In step S3, the preheating temperature is 200-240℃ and the time is 1-2h; the cooling and stirring temperature is 840-860℃, the speed is 160-220r / min, and the time is 5-8min; the weight percentage of the second Al-10Ti alloy is 18-22 parts; and the weight percentage of industrial pure aluminum is 11-15 parts.

6. The method for preparing an aerospace intermediate alloy according to claim 1, characterized in that, In step S4, the temperature for rotary degassing is 770-790℃, the argon flow rate is 6-10L / min, the time is 6-8min, and the settling time is 3-5min.

7. The method for preparing an aerospace intermediate alloy according to claim 1, characterized in that, In step S5, the pouring temperature is 750-770℃; the preheating temperature of the metal mold is 180-220℃; and the effective thickness of the cast billet is 20-40mm.

8. The method for preparing an aerospace intermediate alloy according to claim 1, characterized in that, In step S5, the heat preservation temperature is 390-420℃, and the time is 1-2 hours.

9. The method for preparing an aerospace intermediate alloy according to claim 1, characterized in that, In step S5, the initial rolling temperature of hot rolling is 380-410℃, the total reduction rate is 50%-65%, and the single-pass reduction rate is 10%-15%.

10. An aerospace intermediate alloy, characterized in that, It is prepared by the preparation method of an aerospace intermediate alloy as described in any one of claims 1-9.

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