Aluminum-scandium alloy, its preparation method and application

Abstract

This invention discloses an aluminum-scandium alloy, its preparation method, and its applications, belonging to the field of rare earth alloy sputtering target technology. The invention uses metallic aluminum particles and metallic scandium particles as raw materials. A high vacuum is created, and inert gas is introduced for multiple arc melting processes to obtain a homogeneous aluminum-scandium alloy melt. After cooling, an aluminum-scandium alloy ingot is obtained. The ingot prepared by arc melting is then subjected to induction heating to completely melt the alloy, obtaining an alloy melt. This alloy melt is guided by an argon pressure difference and injected into a mold. After natural cooling, a primary alloy is formed. The primary alloy is then homogenized and annealed under vacuum conditions to eliminate residual internal stress, yielding the aluminum-scandium alloy. The aluminum-scandium alloy prepared using this invention has low oxygen content, high density, fine grains, uniform microstructure, and good processing performance.

Description

Technical Field

[0001] This invention relates to the field of rare earth alloy sputtering target technology, specifically to an aluminum-scandium alloy and its preparation method and application. Background Technology

[0002] With the rapid development of 5G communication technology, the trend towards high performance, high stability, and high frequency has placed higher demands on piezoelectric thin films used in microelectromechanical systems (MEMS) and next-generation RF filters. High-purity aluminum scandium alloy targets are important raw materials for preparing aluminum scandium nitride piezoelectric thin films. Sc-doped AlN piezoelectric thin films possess high SAW wave velocity, high thermal stability, and high thermal conductivity, exhibiting superior piezoelectric performance compared to AlN thin films, and are even compatible with CMOS processes.

[0003] Scandium aluminum nitride is an ideal material for fabricating piezoelectric microelectromechanical systems (MEMS) and NEMS devices, possessing high acoustic velocity and high power. The addition of the rare-earth element scandium will solve the challenges of low piezoelectric coefficient and low electromechanical coupling coefficient in aluminum nitride piezoelectric films, achieving integrated low insertion loss, high bandwidth, high integration, and high operating frequency. This will lead to significant progress in surface acoustic waves, thin-film bulk acoustic resonators, piezoelectric ultrasonic transducers, power electronic devices, micro-energy systems, and high electron mobility field-effect transistors, providing technical support for 5G communication and the Internet of Things (IoT).

[0004] Common methods for producing aluminum-scandium alloys include doping, molten salt electrolysis, thermal reduction, and powder sintering. Patent CN111455327A discloses a method for preparing a high-scandium-content aluminum-scandium alloy target. This method involves selecting metallic aluminum and metallic scandium as raw materials, melting the scandium, then adding metallic aluminum to the scandium in multiple batches for smelting, ball milling the resulting aluminum-scandium alloy, vacuum drying to obtain alloy powder, pre-pressing the powder, and vacuum sintering. Patent CN113981386A discloses a process for preparing a high-scandium-content aluminum-scandium alloy target, involving the mixing and sintering of scandium powder and Al3Sc powder.

[0005] Although the above-mentioned method of preparing aluminum-scandium alloy by powder can greatly reduce problems such as porosity inside the alloy, the powder has a certain risk factor and the gas absorption phenomenon of alloy powder will cause the obtained aluminum-scandium alloy target to contain a variety of impurities, making it difficult to densify the target and reducing its purity. Summary of the Invention

[0006] This invention provides an aluminum-scandium alloy, its preparation method, and its application, effectively solving the technical problems of existing aluminum-scandium alloys using powder raw materials, which poses a hazard, and the alloy target material prepared due to impurities, insufficient purity, and non-dense structure caused by the gas absorption phenomenon of alloy powder. At the same time, it constructs an aluminum-scandium alloy with uniform microstructure and chemical composition, high relative density, excellent processing performance, and small grain size.

[0007] This invention provides a method for preparing an aluminum-scandium alloy, comprising the following steps:

[0008] Scandium metal particles and aluminum metal particles are subjected to multiple vacuum arc melting processes at 1300℃~1500℃ in an inert gas environment to alloy them and obtain aluminum-scandium alloy ingots.

[0009] The aluminum-scandium alloy ingot is melted using vacuum induction heating to obtain an alloy melt. The alloy melt is then spray-cast and cooled to solidify, resulting in a primary alloy. The primary alloy is then annealed under vacuum conditions at 200°C to 800°C to eliminate residual internal stress, thus obtaining the aluminum-scandium alloy.

[0010] In a preferred embodiment, the aluminum-scandium alloy contains 10% to 50% scandium and 50% to 90% aluminum, totaling 100%.

[0011] In a preferred embodiment, the vacuum arc melting is performed using a programmed current control method. First, the current is programmed to increase for arc melting and alloying, then the current is programmed to decrease to obtain an aluminum-scandium alloy ingot. Specifically, the programmed current control method is as follows:

[0012] Current ramp-up program: Starting from 0A, ramp up to 90A to 180A in increments of 10A to 20A and hold for 1 to 3 minutes.

[0013] Current reduction program: From 90A to 180A, reduce the current by decreasing it in increments of 10A to 15A and holding it for 1 to 2 minutes, until it reaches 50A to 90A; reduce the current by decreasing it in increments of 6A to 10A and holding it for 2 to 3 minutes, until it reaches 50A; then reduce the current by decreasing it in increments of 5A to 8A and holding it for 2 to 3 minutes, until it reaches 0A.

[0014] In a preferred embodiment, the multiple vacuum arc melting is performed 4 to 8 times, and the time for each vacuum arc melting is 60 to 80 minutes.

[0015] In a preferred embodiment, the vacuum induction heating is performed using a vacuum induction melting furnace, the induction heating power supply is a 35KW IGBT high-frequency power supply, the preheating current of the vacuum induction melting furnace is 1A to 10A, the duration is 1min to 2min, and the melting heating current is 5A to 30A, the duration is 2min to 3min.

[0016] In a preferred embodiment, the spray casting is performed using an argon pressure differential of 0.0025 MPa to 0.02 MPa.

[0017] In a preferred embodiment, the vacuum condition is 1×10⁻⁶. -3 pa~5×10 -3 pa.

[0018] In a preferred embodiment, the annealing process takes 8 to 24 hours.

[0019] The second objective of this invention is to provide an aluminum-scandium alloy prepared by the above-described preparation method.

[0020] The third objective of this invention is to provide an application of the above-mentioned aluminum-scandium alloy in the preparation of aluminum-scandium nitride piezoelectric thin films or as a sputtering target for thin-film bulk acoustic resonators or bulk acoustic devices.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] This invention uses aluminum and scandium particles as raw materials, employing a high vacuum and inert gas to perform multiple arc melting processes to obtain a homogeneous aluminum-scandium alloy molten liquid. After cooling, an aluminum-scandium alloy ingot is obtained. Multiple arc melting processes ensure the uniform distribution of elements in the alloy, homogenizing the concentration of different elements within the molten metal. These processes also reduce macroscopic and microscopic defects in the material, such as porosity, inclusions, and segregation, which affect the material's mechanical properties and corrosion resistance. Reducing these defects through multiple melting processes results in a more uniform microstructure. Arc melting in a vacuum or protective atmosphere reduces metal oxidation and contamination, thereby improving material purity, which is particularly important for alloys requiring high purity. During arc melting, the high temperature of the molten alloy removes some impurities and gases, further enhancing the material's purity and performance. An aluminum-scandium alloy ingot prepared by arc melting is completely melted by induction heating to obtain an alloy molten liquid. Argon gas is injected into the molten alloy and allowed to cool naturally to form a primary alloy. This primary alloy is then homogenized and annealed under vacuum to obtain the aluminum-scandium alloy. The annealing process eliminates residual internal stress in the primary alloy and removes thermal and mechanical stresses generated during casting and cooling. Furthermore, the heating and slow cooling during annealing promote grain recrystallization, resulting in finer grain sizes, a more uniform microstructure, reduced microscopic defects, and improved strength and toughness. The aluminum-scandium alloy prepared using this invention has low oxygen content, high density, fine grains, uniform microstructure, and good processing performance. Attached Figure Description

[0023] Figure 1 The microstructure characteristics of the aluminum-scandium alloy prepared in Example 1 of this invention are typical.

[0024] Figure 2 The microstructure characteristics of the aluminum-scandium alloy prepared in Example 2 of this invention are typical.

[0025] Figure 3 The image shows an elemental scanning electron microscope (SEM) image of the aluminum-scandium alloy prepared in Example 1 of this invention.

[0026] Figure 4 This is an elemental scanning electron microscope image of the aluminum-scandium alloy prepared in Comparative Example 1 of this invention. Detailed Implementation

[0027] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention will be further described below with reference to specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the invention. Unless otherwise specified, the following test methods and detection methods are conventional methods; unless otherwise specified, the reagents and raw materials are commercially available.

[0028] The technical solution of the present invention will be described in detail below.

[0029] This invention first provides a method for preparing an aluminum-scandium alloy, comprising the following steps:

[0030] Scandium and aluminum particles are subjected to multiple vacuum arc melting processes at 1300℃~1500℃ in an inert gas atmosphere to alloy them, thereby obtaining an aluminum-scandium alloy ingot.

[0031] The aluminum-scandium alloy ingot is melted using vacuum induction heating to obtain an alloy melt. The alloy melt is then spray-cast and cooled to solidify, resulting in a primary alloy. The primary alloy is then annealed under vacuum conditions at 200°C to 800°C to eliminate residual internal stress, thus obtaining the aluminum-scandium alloy.

[0032] In a preferred embodiment, the aluminum-scandium alloy contains 10%–50% scandium and 50%–90% aluminum, totaling 100%. For the aluminum-scandium alloy target, the aluminum-nitrogen-scandium thin film manufactured by reactive sputtering deposition exhibits excellent piezoelectric properties; as the scandium content increases, the piezoelectric constant and electromechanical coupling coefficient increase linearly. In summary, within a certain range, the higher the scandium content, the higher the performance of the thin film manufactured using the aluminum-scandium alloy target.

[0033] In a preferred embodiment, the vacuum arc melting is performed using a programmed current control method, wherein the programmed current control method specifically includes:

[0034] Current ramp-up program: Starting from 0A, ramp up to 90A to 180A in increments of 10A to 20A and hold for 1 to 3 minutes.

[0035] Current reduction program: From 90A to 180A, reduce the current by decreasing it in increments of 10A to 15A and holding it for 1 to 2 minutes, until it reaches 50A to 90A; reduce the current by decreasing it in increments of 6A to 10A and holding it for 2 to 3 minutes, until it reaches 50A; then reduce the current by decreasing it in increments of 5A to 8A and holding it for 2 to 3 minutes, until it reaches 0A.

[0036] For the programmed current control process described above, programmed current increase ensures the uniformity of the alloy composition. Directly increasing the current to a very high level may lead to localized overheating, resulting in uneven melting and segregation. By gradually increasing the current, the melting process can be better controlled, allowing scandium and aluminum to mix thoroughly and form a homogeneous alloy structure. Scandium is highly reactive, and its melting point is much higher than aluminum; directly melting it with high current may cause scandium burn-off. Programmed current increase reduces scandium oxidation and volatilization, thereby improving scandium yield, which is particularly important for the expensive scandium metal. Rapid current increase may cause thermal stress within the melting furnace, potentially damaging the furnace lining or causing internal cracks in the alloy. Programmed current increase reduces this risk, ensuring the safety and stability of the melting process. Increasing the current by 5A or 25A each time may lead to inaccurate temperature control during melting, affecting the alloy's microstructure and properties. Smaller current increases may not be sufficient to maintain uniform melting and mixing, while larger increases may lead to localized overheating and burn-off. Therefore, selecting an appropriate current rise rate is crucial for ensuring alloy quality. The current reduction process is equally important; it needs to be matched with the current rise process to ensure uniformity during solidification and reduce thermal stress. Reducing the current too quickly may lead to cracks or uneven microstructures within the alloy, while reducing it too slowly may prolong the melting cycle and increase production costs.

[0037] In a preferred embodiment, the multiple vacuum arc melting processes are performed 4 to 8 times, with each melting session lasting 60 to 80 minutes. If the number of melting processes is too few, less than 4 times, the purity and uniformity of the alloy will be insufficient. Because each melting process during vacuum arc melting removes gases and non-metallic inclusions from the alloy, and reduces oxides and other impurities, too few melting processes may not be sufficient to completely purify the alloy, affecting its final properties. Increasing the number of melting processes will increase production costs and time.

[0038] In a preferred embodiment, the vacuum induction heating is performed using a vacuum induction melting furnace, the induction heating power supply is a 35KW IGBT high-frequency power supply, the preheating current of the vacuum induction melting furnace is 1A to 10A, the duration is 1min to 2min, and the melting heating current is 5A to 30A, the duration is 2min to 3min.

[0039] It should be noted that the preheating current is 1A to 10A, and the duration is 1 to 2 minutes. The preheating stage is to allow the furnace charge to gradually adapt to the heating environment, avoiding breakage of the furnace charge or crucible due to excessive temperature difference. The lower preheating current allows for slow heating and reduces thermal stress. Appropriate preheating time helps remove moisture and volatile impurities from the surface of the furnace charge, preventing excessive gas generation during high-temperature melting.

[0040] The heating current for melting is 5A to 30A, with a duration of 2 to 3 minutes. A higher current is needed during the melting stage to rapidly melt the charge. The choice of current depends on the properties of the charge and the capacity of the furnace. An appropriate current ensures complete melting of the charge while preventing overheating that could lead to metal oxidation or volatilization. The duration ensures complete melting of the charge and a uniform temperature in the molten pool. Too short a time may result in incomplete melting, while too long a time may cause overheating and metal burn-off.

[0041] If the heating current is too low or the duration is too short, the charge may not melt sufficiently, affecting the uniformity and purity of the alloy. If the heating current is too high or the duration is too long, it may cause excessive oxidation and burning of the metal, and may even damage the furnace lining or cause charge splashing.

[0042] To ensure the smooth and uniform flow of the prepared alloy molten metal into the mold for spray casting, an argon gas pressure differential of 0.0025 MPa to 0.02 MPa is used during the spray casting process. Too small a pressure differential will prevent the alloy molten metal from being completely sprayed into the lower mold, while too large a pressure differential will result in the alloy molten metal sprayed into the lower mold containing air pockets.

[0043] It should be noted that the vacuum condition is 1×10⁻⁶. -3 pa~5×10 -3 pa.

[0044] In a preferred embodiment, the annealing treatment time is 8 to 24 hours. Annealing at 200°C for less than 8 hours will result in insufficient annealing, failing to completely eliminate internal stress and improve the microstructure. Annealing temperatures below 200°C may be even less effective in eliminating internal stress, potentially failing to significantly improve the material's mechanical properties, and may even generate new stresses due to prolonged low-temperature heating. If treatment at 800°C for more than 24 hours, it will cause overheating, leading to excessive grain growth and reducing the material's strength and toughness. Furthermore, prolonged high-temperature heating may cause surface oxidation or carbonization, affecting the material's surface quality. If treatment at temperatures above 800°C for 24 hours, the annealing temperature may cause overheating, resulting in coarse grains and affecting the material's mechanical properties. Additionally, prolonged heating at high temperatures may cause oxidation, decarburization, or other chemical reactions, affecting the material's purity and performance.

[0045] The technical effects of the present invention will be described below through specific embodiments and comparative examples.

[0046] Example 1

[0047] A method for preparing an aluminum-scandium alloy includes the following steps:

[0048] Aluminum with a purity of 99.999% and scandium with a purity of 99.99% were selected as raw materials.

[0049] The prepared aluminum-scandium raw materials were sequentially placed into the copper crucible. The furnace chamber cover of the electric arc melting furnace was slowly rotated until it reached the top of the chamber. The cover was then slowly closed using the hydraulic control device. The mechanical pump was turned on, and the pre-evacuation valve was rotated until the pressure gauge reading reached -0.1 MPa. The pre-evacuation valve was then closed, and inert gas was introduced. Once the reading reached -0.05 MPa, the pre-evacuation valve was reopened. This process was repeated three times. The composite vacuum gauge was then turned on. Once the resistance unit reading reached 8 Pa, the pre-evacuation valve was closed, the fore-stage valve was opened, and then the high-vacuum gate valve was opened. The molecular pump was then turned on. The process continued until the resistance unit reading reached 3 × 10⁻⁶ Pa. -3 pa, close the composite vacuum gauge, close the high vacuum gate valve, stop the molecular pump, close the fore-stage valve, and when the molecular pump reading is 0, close the mechanical pump, introduce argon gas, and prepare for electric arc melting.

[0050] Adjust the position of the tungsten electrode and the molten material, placing the tungsten electrode 3mm above the molten material. Turn on the power of the argon arc welding machine and start arc ignition and melting. Increase the current at a rate of 20A, each time for 2 minutes. When the current reaches 130A, keep the arc on one side of the alloy melt for 5 minutes to ensure that the molten metal is fully alloyed.

[0051] After the molten metal is alloyed, the present invention uses the method of controlling the rate of current decrease to control the speed of temperature change. The current starts from 130A and decreases by 15A at a time, maintaining for 1 minute at a time, until it drops to 85A; when it drops from 85A, it decreases by 10A at a time, maintaining for 2 minutes at a time, until it drops to 45A; when it drops from 45A, it decreases by 5A at a time, maintaining for 2 minutes at a time, until it drops to 20A, maintaining for 20A at 2 minutes, and then extinguishing the flame.

[0052] After the high-temperature aluminum-scandium alloy melt cools into an alloy ingot, the vacuum chamber is pre-evacuated to remove gaseous impurities. Then, air is introduced into the chamber, and the cooled aluminum-scandium alloy ingot is removed.

[0053] The aluminum-scandium alloy ingot is further placed into a specially made quartz tube inside the high-vacuum chamber. The chamber door is closed, the mechanical pump is started, and the pre-evacuation valve is slowly opened. Once the chamber pressure gauge reaches -0.1 MPa, the gas distribution pipeline is cleaned 1-3 times. After cleaning the gas distribution pipeline, the fore-stage valve is opened, and the composite vacuum gauge is activated. Once the vacuum level is ≤8 Pa, the pre-evacuation valve is closed, the high-vacuum gate valve is opened, and the molecular pump is started. Once the vacuum level is ≤5 × 10⁻⁶ Pa, the pre-evacuation valve is closed, the high-vacuum gate valve is opened, and the molecular pump is started. -3 Pa, shut off the molecular pump, shut off the fore-stage valve, shut off the mechanical pump, and introduce argon gas into the chamber to -0.05 MPa.

[0054] After gas mixing is complete, turn on the power to the vacuum induction melting machine. Adjust the current knob to 1A-5A to initiate the preheating stage of the alloy, which is maintained for 1-2 minutes. After preheating, adjust the current knob to 5A-15A to initiate the melting stage of the alloy, which is maintained for 2-3 minutes. Once the alloy is completely melted, turn on the jet switch to inject argon gas at 0.0025MPa-0.02MPa into the quartz tube. Use the injection system to precisely control the injection of argon gas, ensuring the molten alloy is smoothly injected into the mold. After cooling, a primary alloy is obtained. The aluminum-scandium alloy ingot is then annealed at 470℃ under vacuum for 12 hours to obtain an aluminum-scandium alloy with an atomic content of 13 at.%.

[0055] Example 2

[0056] A method for preparing an aluminum-scandium alloy includes the following steps:

[0057] Aluminum with a purity of 99.999% and scandium with a purity of 99.99% were selected as raw materials.

[0058] The prepared aluminum-scandium raw materials were sequentially placed into the copper crucible. The furnace chamber cover of the electric arc melting furnace was slowly rotated until it reached the top of the chamber. The cover was then slowly closed using the hydraulic control device. The mechanical pump was turned on, and the pre-evacuation valve was rotated until the pressure gauge reading reached -0.1 MPa. The pre-evacuation valve was then closed, and inert gas was introduced. Once the reading reached -0.05 MPa, the pre-evacuation valve was reopened. This process was repeated three times. The composite vacuum gauge was then turned on. Once the resistance unit reading reached 8 Pa, the pre-evacuation valve was closed, the fore-stage valve was opened, and then the high-vacuum gate valve was opened. The molecular pump was then turned on. The process continued until the resistance unit reading reached 3 × 10⁻⁶ Pa. -3 pa, close the composite vacuum gauge, close the high vacuum gate valve, stop the molecular pump, close the fore-stage valve, and when the molecular pump reading is 0, close the mechanical pump, introduce argon gas, and prepare for electric arc melting.

[0059] Adjust the position of the tungsten electrode and the molten material, placing the tungsten electrode 3mm above the molten material. Turn on the power of the argon arc welding machine and start arc ignition and melting. Increase the current at a rate of 20A, each time for 2 minutes. When the current reaches 180A, the arc stays on one side of the alloy melt for 5 minutes to ensure that the metal melt is fully alloyed.

[0060] After the molten metal is alloyed, the present invention adopts the method of controlling the rate of current decrease to control the speed of temperature change. The current starts from 180A and decreases by 15A at a time, maintaining for 1 minute at a time, until it drops to 75A; when it drops from 75A, it decreases by 10A at a time, maintaining for 2 minutes at a time, until it drops to 45A; when it drops from 45A, it decreases by 5A at a time, maintaining for 2 minutes at a time, until it drops to 20A, maintaining for 20A at 2 minutes, and then extinguishing the flame.

[0061] After the high-temperature aluminum-scandium alloy melt cools into an alloy ingot, the vacuum chamber is pre-evacuated to remove gaseous impurities. Then, air is introduced into the chamber, and the cooled aluminum-scandium alloy ingot is removed.

[0062] The aluminum-scandium alloy ingot is further placed into a specially made quartz tube inside the high-vacuum chamber. The chamber door is closed, the mechanical pump is started, and the pre-evacuation valve is slowly opened. Once the chamber pressure gauge reaches -0.1 MPa, the gas distribution pipeline is cleaned 1-3 times. After cleaning the gas distribution pipeline, the fore-stage valve is opened, and the composite vacuum gauge is activated. Once the vacuum level is ≤8 Pa, the pre-evacuation valve is closed, the high-vacuum gate valve is opened, and the molecular pump is started. Once the vacuum level is ≤5 × 10⁻⁶ Pa, the pre-evacuation valve is closed, the high-vacuum gate valve is opened, and the molecular pump is started. -3 Pa, shut off the molecular pump, shut off the fore-stage valve, shut off the mechanical pump, and introduce argon gas into the chamber to -0.05 MPa.

[0063] After gas mixing is complete, turn on the power to the vacuum induction melting machine. Adjust the current knob to 5A-10A to initiate the preheating stage of the alloy, which should be maintained for 1-2 minutes. After preheating, adjust the current knob to 10A-30A to initiate the melting stage of the alloy, which should be maintained for 2-3 minutes. Once the alloy is completely melted, turn on the jet switch and inject argon gas at 0.0025MPa-0.02MPa into the quartz tube. Use the injection system to precisely control the injection of argon gas, ensuring the molten alloy is smoothly injected into the mold. After cooling, a primary alloy is obtained. The aluminum-scandium alloy ingot is then annealed at 650℃ under vacuum for 10 hours to obtain an aluminum-scandium alloy with an atomic content of 30 at.%.

[0064] Example 3

[0065] A method for preparing an aluminum-scandium alloy includes the following steps:

[0066] Aluminum with a purity of 99.999% and scandium with a purity of 99.99% were selected as raw materials.

[0067] The prepared aluminum-scandium raw materials were sequentially placed into the copper crucible. The furnace chamber cover of the electric arc melting furnace was slowly rotated until it reached the top of the chamber. The cover was then slowly closed using the hydraulic control device. The mechanical pump was turned on, and the pre-evacuation valve was rotated until the pressure gauge reading reached -0.1 MPa. The pre-evacuation valve was then closed, and inert gas was introduced. Once the reading reached -0.05 MPa, the pre-evacuation valve was reopened. This process was repeated three times. The composite vacuum gauge was then turned on. Once the resistance unit reading reached 8 Pa, the pre-evacuation valve was closed, the fore-stage valve was opened, and then the high-vacuum gate valve was opened. The molecular pump was then turned on. The process continued until the resistance unit reading reached 3 × 10⁻⁶ Pa. -3 pa, close the composite vacuum gauge, close the high vacuum gate valve, stop the molecular pump, close the fore-stage valve, and when the molecular pump reading is 0, close the mechanical pump, introduce argon gas, and prepare for electric arc melting.

[0068] Adjust the position of the tungsten electrode and the molten material, placing the tungsten electrode 3mm above the molten material. Turn on the power of the argon arc welding machine and start arc ignition and melting. Increase the current at a rate of 20A, each time for 2 minutes. When the current reaches 160A, keep the arc on one side of the alloy melt for 5 minutes to ensure that the metal melt is fully alloyed.

[0069] After the molten metal alloys, the present invention uses the method of controlling the rate of current decrease to control the speed of temperature change. The current starts from 160A and decreases by 15A at a time, maintaining for 1 minute at a time, until it drops to 85A; when it drops from 85A, it decreases by 10A at a time, maintaining for 2 minutes at a time, until it drops to 45A; when it drops from 45A, it decreases by 5A at a time, maintaining for 2 minutes at a time, until it drops to 20A, maintaining for 20A at 2 minutes, and then extinguishing the flame.

[0070] After the high-temperature aluminum-scandium alloy melt cools into an alloy ingot, the vacuum chamber is pre-evacuated to remove gaseous impurities. Then, air is introduced into the chamber, and the cooled aluminum-scandium alloy ingot is removed.

[0071] The aluminum-scandium alloy ingot is further placed into a specially made quartz tube inside the high-vacuum chamber. The chamber door is closed, the mechanical pump is started, and the pre-evacuation valve is slowly opened. Once the chamber pressure gauge reaches -0.1 MPa, the gas distribution pipeline is cleaned 1-3 times. After cleaning the gas distribution pipeline, the fore-stage valve is opened, and the composite vacuum gauge is activated. Once the vacuum level is ≤8 Pa, the pre-evacuation valve is closed, the high-vacuum gate valve is opened, and the molecular pump is started. Once the vacuum level is ≤5 × 10⁻⁶ Pa, the pre-evacuation valve is closed, the high-vacuum gate valve is opened, and the molecular pump is started. -3 Pa, shut off the molecular pump, shut off the fore-stage valve, shut off the mechanical pump, and introduce argon gas into the chamber to -0.05 MPa.

[0072] After gas mixing is complete, turn on the power to the vacuum induction melting machine. Adjust the current knob to 3A-7A to initiate the preheating stage of the alloy, which should be maintained for 1-2 minutes. After preheating, adjust the current knob to 7A-20A to initiate the melting stage of the alloy, which should be maintained for 2-3 minutes. Once the alloy is completely melted, turn on the jet switch to inject argon gas at 0.0025MPa-0.02MPa into the quartz tube. Use the injection system to precisely control the injection of argon gas, ensuring the molten alloy is smoothly injected into the mold. After cooling, a primary alloy is obtained. The primary alloy is then annealed at 550℃ under vacuum for 12 hours to obtain an aluminum-scandium alloy with a scandium atomic content of 50 at.%.

[0073] To further illustrate the technical effects of the present invention, a comparative example is also provided, as follows:

[0074] Comparative Example 1

[0075] A method for preparing an aluminum-scandium alloy includes the following steps:

[0076] Aluminum with a purity of 99.999% and scandium with a purity of 99.99% were selected as raw materials.

[0077] The prepared aluminum-scandium raw materials are sequentially placed into the copper crucible. The furnace cover of the electric arc melting furnace is slowly rotated until it reaches the top of the furnace body. The cover is then slowly closed using the hydraulic control device. The mechanical pump is turned on, and the pre-evacuation valve is rotated until the pressure gauge reading reaches -0.1 MPa. The pre-evacuation valve is then closed, and inert gas is introduced. When the reading reaches -0.05 MPa, the pre-evacuation valve is reopened. This step is repeated three times. The composite vacuum gauge is turned on, and when the resistance unit reading reaches 8 Pa, the pre-evacuation valve is closed, the fore-stage valve is opened, and then the high-vacuum gate valve is opened. The molecular pump is then turned on. When the resistance unit reading reaches 3 × 10⁻³ Pa, the composite vacuum gauge is turned off, the high-vacuum gate valve is closed, the molecular pump is stopped, and the fore-stage valve is closed. When the molecular pump reading reaches 0, the mechanical pump is turned off, and argon gas is introduced to prepare for electric arc melting.

[0078] Adjust the position of the tungsten electrode and the molten material, placing the tungsten electrode 3mm above the molten material. Turn on the power of the argon arc welding machine and start arc ignition and melting. Increase the current at a rate of 20A, each time for 2 minutes. When the current reaches 130A, keep the arc on one side of the alloy melt for 5 minutes to ensure that the metal melt is fully alloyed.

[0079] After the molten metal is alloyed, the present invention uses the method of controlling the rate of current decrease to control the speed of temperature change. The current starts from 130A and decreases by 15A at a time, maintaining for 1 minute at a time, until it drops to 85A; when it drops from 85A, it decreases by 10A at a time, maintaining for 2 minutes at a time, until it drops to 45A; when it drops from 45A, it decreases by 5A at a time, maintaining for 2 minutes at a time, until it drops to 20A, maintaining for 20A at 2 minutes, and then extinguishing the flame.

[0080] After the high-temperature aluminum-scandium alloy melt cools into an alloy ingot, the vacuum chamber is pre-evacuated to remove gaseous impurities. Then, air is introduced into the chamber, and the cooled aluminum-scandium alloy is taken out, in which the atomic content of metallic scandium is 13 at.%.

[0081] The properties of the aluminum-scandium alloys prepared in the above embodiments and comparative examples were tested, and the results are as follows:

[0082] Figure 1 , Figure 2 The typical microstructure characteristics of the aluminum-scandium alloys prepared in Examples 1 and 2 are shown respectively. Figure 3 , Figure 4The images show elemental scanning electron microscope (SEM) images of the aluminum-scandium alloys prepared in Example 1 and Comparative Example 1 of this invention, respectively. By observing the typical microstructure characteristics of the aluminum-scandium alloy prepared in this invention and through comparative analysis, it can be seen that the aluminum-scandium alloy prepared in this invention has a fine microstructure, uniform chemical composition, and no significant defects. Comparative Example 1 adjusted the preparation process, reducing the induction melting and sputtering steps. It can be seen that this affected the size of the alloy phase and the distribution of elements; the alloy phase became larger, and the uniformity of the Al and Sc element distribution decreased. Ultimately, this adversely affects the sputtering rate and uniformity of the target material, leading to a decline in the quality and performance of the thin film.

[0083] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing an aluminum-scandium alloy, characterized in that, Includes the following steps: Scandium metal particles and aluminum metal particles are subjected to multiple vacuum arc melting processes at 1300℃~1500℃ in an inert gas environment to alloy them and obtain aluminum-scandium alloy ingots. The aluminum-scandium alloy ingot is melted using vacuum induction heating to obtain an alloy melt. The alloy melt is then sprayed using argon pressure difference and cooled to solidify, resulting in a primary alloy. The primary alloy is then annealed under vacuum conditions at 200℃~800℃ to eliminate residual internal stress, thus obtaining the aluminum-scandium alloy. The vacuum arc melting is performed using a programmed current control method. First, the current is programmed to increase for arc melting and alloying, then the current is programmed to decrease to obtain an aluminum-scandium alloy ingot. Specifically, the programmed current control is as follows: Current ramp-up program: Starting from 0A, ramp up to 90A to 180A in increments of 10A to 20A and hold for 1 to 3 minutes. Current reduction program: From 90A to 180A, reduce the current by decreasing it in increments of 10A to 15A and holding it for 1 to 2 minutes, until it reaches 50A to 90A; reduce the current by decreasing it in increments of 6A to 10A and holding it for 2 to 3 minutes, until it reaches 50A; then reduce the current by decreasing it in increments of 5A to 8A and holding it for 2 to 3 minutes, until it reaches 0A. The spray casting is carried out using an argon gas pressure difference, which is 0.0025 MPa to 0.02 MPa. The multiple vacuum arc melting processes are 4 to 8 times, and the time for each vacuum arc melting process is 60 to 80 minutes. The annealing process takes 8 to 24 hours.

2. The preparation method according to claim 1, characterized in that, In the aluminum-scandium alloy, the atomic content of metallic scandium is 10% to 50%, and the atomic content of metallic aluminum is 50% to 90%, totaling 100%.

3. The preparation method according to claim 1, characterized in that, The vacuum induction heating is carried out in a vacuum induction melting furnace. The preheating current of the vacuum induction melting furnace is 1A to 10A and the duration is 1min to 2min. The melting heating current is 5A to 30A and the duration is 2min to 3min.

4. The preparation method according to claim 1, characterized in that, The vacuum condition is 1×10⁻⁶. -3 pa~5×10 - 3 pa.

5. An aluminum-scandium alloy prepared by the preparation method according to any one of claims 1 to 4.

6. The application of the aluminum-scandium alloy of claim 5 in the preparation of aluminum-scandium nitride piezoelectric thin films.

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