Aluminum-scandium master alloy and method for preparing the same

Abstract

The application discloses an aluminum-scandium intermediate alloy and a preparation method thereof, and belongs to the technical field of new materials. The application selects Na3ScF6 / K3ScF6 as raw materials, NaCl and KCl as a molten salt reaction system, does not add fluoride, obtains uniformly mixed powders by mechanical stirring, and adopts an aluminothermic reduction method combined with a protective gas refining stirring process, so that fine Al3Sc particles can be uniformly dispersed in Al liquid, and the application is a low-cost and short-process Al-Sc intermediate alloy preparation method. In the whole thermal reduction process, the molten salt is added in stages, the problem that the molten salt system changes in the thermal reduction reaction process due to volatilization of the molten salt can be effectively improved, the stability of the molten salt system is further improved, the uncontrollable problem of the thermal reduction reaction caused by the instability of the molten salt system is avoided, and the conversion rate of Sc is provided.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology, specifically relating to an aluminum-scandium master alloy and its preparation method. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Aluminum (Al) alloys are widely used in aerospace, transportation, and shipbuilding due to their low density, high specific strength, ease of processing, corrosion resistance, and excellent electrical and thermal conductivity. With the rapid development of modern industry, higher demands are being placed on the comprehensive performance of aluminum alloys. Scandium (Sc), a typical rare earth element, is an excellent modifier for aluminum and aluminum alloys. The addition of trace amounts of Sc can significantly improve the strength, structural stability, corrosion resistance, and weldability of aluminum alloys. Low-scandium-content aluminum-scandium (Al-Sc) master alloys (typically with a Sc mass percentage below 2%) are mainly used for modifying aluminum alloys, improving their strength, toughness, weldability, and corrosion resistance. Modified aluminum alloys can be used as structural materials in aerospace, marine, and other specialized industries. The alloying rate of common Al-Sc master alloys is approximately 2 wt.% or less. Because Sc has low solid solubility in the Al matrix, it generally exists in the form of Al3Sc particles. However, its density differs significantly from that of Al, which can easily lead to compositional segregation in Al-Sc master alloys with higher alloying rates, thus affecting the quality of the master alloy.

[0004] Currently, methods for preparing aluminum-scandium master alloys include the co-doping method, molten salt electrolysis, and aluminothermic reduction method. The co-doping method, also known as the direct fusion method, involves directly fusing elemental Sc with Al at high temperatures to prepare the aluminum-scandium master alloy. Due to the significant difference in melting points between Sc and Al, this method requires high preparation temperatures, resulting in high alloy loss and low recovery rates. Furthermore, the generated Al3Sc intermetallic compound particles are large and unevenly distributed, affecting alloy quality. The molten salt electrolysis method often uses a scandium oxide-fluoride system, requiring high purity raw materials. Common metal ions such as Fe can precipitate at the cathode during electrolysis, affecting alloy purity. Additionally, the molten salt electrolysis method is energy-intensive, causes environmental pollution, and the electrolytic cells are prone to corrosion, resulting in short lifespans and reduced production efficiency. Metallothermic reduction typically uses scandium fluoride, scandium chloride, or scandium oxide as raw materials, fluorides, NaCl, KCl, etc., as molten salt systems, and metallic aluminum as a reducing agent to prepare Al-Sc master alloys. However, the conversion rate of Sc is not high, generally between 70% and 80%, resulting in the preparation of low-Sc-content aluminum-scandium master alloys (usually with a Sc mass percentage of less than 2%). Furthermore, ScCl3 is hygroscopic, posing numerous inconveniences in storage and transportation; Sc2O3 exhibits a low degree of reaction with Al, leading to a low Sc recovery rate; and ScF3 is relatively expensive, increasing the production cost.

[0005] Currently, there is an urgent need for a new, low-cost method for preparing aluminum-scandium master alloys to increase the scandium content in these alloys. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide an aluminum-scandium master alloy and its preparation method. The preparation method of the present invention enables fine Al3Sc particles to be uniformly dispersed in Al liquid, and is a low-cost, short-process Al-Sc master alloy preparation method.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] In a first aspect, the present invention provides a method for preparing an aluminum-scandium master alloy, comprising the following steps:

[0009] S1. Using Na3ScF6 or K3ScF6 as a scandium source, mix with chloride molten salt and dry to obtain a mixed salt;

[0010] S2. The mixed salt is added to the aluminum liquid in batches to carry out the aluminothermic reduction reaction and obtain an aluminum alloy solution containing scandium;

[0011] S3. A protective gas is passed through the aluminum alloy solution containing scandium and stirred to obtain an aluminum-scandium intermediate alloy solution, which is then cast into a mold and cooled to obtain an aluminum-scandium intermediate alloy.

[0012] Preferably, the chloride molten salt is sodium chloride and potassium chloride, and the mass ratio of sodium chloride to potassium chloride is 1:1.

[0013] Preferably, the mass ratio of scandium source to chloride molten salt is 1:2 to 10.

[0014] Preferably, the mass ratio of the mixed salt to the molten aluminum is 1:1 to 5.

[0015] Preferably, the reaction conditions for the aluminothermic reduction reaction are: reaction temperature 700-850℃, reaction time 20-60min.

[0016] Preferably, the number of batches is 2 to 5, and the interval between each batch is 5 to 20 minutes.

[0017] Preferably, the protective gas is one or more of argon and nitrogen.

[0018] Preferably, the protective gas is introduced at a rate of 5 to 20 L / min and for a duration of 5 to 10 min.

[0019] Preferably, the casting temperature is 680-750℃, and the mold is one of graphite mold, steel mold, and copper mold.

[0020] In a second aspect, the present invention provides an aluminum-scandium master alloy, which is prepared by the above-described method for preparing aluminum-scandium master alloy, wherein the scandium content in the aluminum-scandium master alloy is 1-3 wt.%, and the second phase particles are uniformly distributed in the aluminum matrix without the presence of pores or impurities.

[0021] The beneficial effects of this invention are as follows:

[0022] This invention discloses a method for preparing an aluminum-scandium master alloy, comprising the following steps: S1. Using Na3ScF6 or K3ScF6 as a scandium source, mixing it with a chloride molten salt and drying it to obtain a mixed salt; S2. Adding the mixed salt to molten aluminum in batches to carry out an aluminothermic reduction reaction to obtain an aluminum alloy solution containing scandium; S3. Passing a protective gas through the aluminum alloy solution containing scandium and stirring it to obtain an aluminum-scandium master alloy solution, casting it into a mold, and cooling it to obtain the aluminum-scandium master alloy. This invention uses Na3ScF6 / K3ScF6 as raw material, NaCl and KCl as the molten salt system for the reaction, without adding fluorides, using mechanical stirring to obtain a uniformly mixed powder, and employing an aluminothermic reduction method combined with a protective gas refining and stirring process to prepare an Al-(1-3wt.%)Sc master alloy with uniformly distributed Al3Sc particles, which is an environmentally friendly preparation method. Adding molten salt in stages throughout the thermal reduction process effectively mitigates the problem of molten salt system alteration caused by volatilization during the thermal reduction reaction, further enhancing the stability of the molten salt system and avoiding uncontrollable thermal reduction reactions due to its instability, thus increasing the conversion rate of Sc. Inert gas stirring serves two purposes: firstly, it purifies the melt and removes hydrogen; secondly, the rising bubbles prevent Al3Sc particles from depositing and accumulating at the bottom of the molten aluminum, thus reducing the temperature of the Al-Sc alloy and enabling rapid cooling of the Al-Sc intermediate alloy after casting. Simultaneously, during the aluminothermic reduction process, Na3ScF6 or K3ScF6 reacts with Al to form Na3AlF6 or K3AlF6, effectively removing the oxide film on the surface of the molten aluminum, ensuring sufficient contact between the molten salt system and the molten aluminum, promoting the aluminothermic reaction, and further increasing the conversion rate of Sc.

[0023] The preparation method of this invention is simple, convenient to operate, highly practical, and easy to promote. The aluminum-scandium master alloy obtained by this invention has a high scandium conversion rate, and the second-phase particles are uniformly distributed in the aluminum matrix without the presence of pores or impurities. When added as a master alloy to the aluminum alloy casting process, the alloy ratio can be accurately adjusted with a small amount of addition, making the operation convenient and highly practical. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0025] Figure 1 The microstructure of the Al-Sc master alloy prepared in Example 1;

[0026] Figure 2 SEM image of the Al-Sc master alloy prepared in Example 1;

[0027] Figure 3 XRD analysis of the Al-Sc master alloy prepared in Example 1. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] A typical embodiment of the present invention provides a method for preparing an aluminum-scandium master alloy, comprising the following steps:

[0030] S1. Using Na3ScF6 or K3ScF6 as a scandium source, mix with chloride molten salt and dry to obtain a mixed salt;

[0031] S2. The mixed salt is added to the aluminum liquid in batches to carry out the aluminothermic reduction reaction and obtain an aluminum alloy solution containing scandium;

[0032] S3. A protective gas is passed through the aluminum alloy solution containing scandium and stirred to obtain an aluminum-scandium intermediate alloy solution, which is then cast into a mold and cooled to obtain an aluminum-scandium intermediate alloy.

[0033] The preparation method of this invention uses Na3ScF6 or K3ScF6 as raw materials and NaCl and KCl as molten salt system. It obtains uniformly mixed powder by mechanical stirring, and adds molten salt in stages. Combined with protective gas refining and stirring process, it can achieve uniform dispersion of fine Al3Sc particles in Al liquid. It is a low-cost and short-process Al-Sc master alloy preparation method.

[0034] In some embodiments of the present invention, the scandium source and the chloride molten salt can be mixed by stirring. Further, a mechanical stirrer can be used for stirring at a speed of 800–3000 r / min for a time of 5–30 min. In some embodiments, the stirring speed can specifically be 800 r / min, 900 r / min, 1000 r / min, 1350 r / min, 1500 r / min, 1850 r / min, 2000 r / min, 2500 r / min, or 3000 r / min. In some embodiments, the stirring time can specifically be 5 min, 7 min, 9 min, 10 min, 18 min, 20 min, 21 min, 23 min, 27 min, or 30 min.

[0035] Excessive moisture content can cause hydrolysis or side reactions in some components of the mixed salt, resulting in toxicity to the molten salt system. Therefore, the scandium source and chloride molten salt need to be dried. Dehydration can be carried out in a drying oven to obtain a dry and uniformly mixed salt.

[0036] In some embodiments of the present invention, the drying conditions are drying at 80–200°C for 1–2 hours. In some embodiments, the drying temperature may be 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 170°C, or 200°C. In some embodiments, the drying time may be 1 hour, 1.2 hours, 1.5 hours, 1.7 hours, 1.8 hours, 1.9 hours, or 2.0 hours.

[0037] In some embodiments of the present invention, the chloride molten salt is sodium chloride and potassium chloride, and the mass ratio of sodium chloride to potassium chloride is 1:1.

[0038] In some embodiments of the present invention, the mass ratio of scandium source to chloride molten salt is 1:2 to 10. In some embodiments, the mass ratio of scandium source to chloride molten salt may be specifically 1:2, 1:4, 1:8, or 1:10, etc. In some embodiments, the chloride molten salt is sodium chloride and potassium chloride in a mass ratio of 1:1, and the mass ratio of scandium source, sodium chloride, and potassium chloride is 1:1 to 5:1 to 5.

[0039] In some embodiments of the present invention, the mass ratio of the mixed salt to the molten aluminum is 1:1 to 5. In certain embodiments, the mass ratio of the mixed salt to the molten aluminum is 1:1, 1:3, or 1:5, etc.

[0040] Adding the mixed salt after the aluminum ingot has melted reduces the melting time and improves preparation efficiency. The reaction vessel is an alumina or magnesium oxide crucible. Na3ScF6 or K3ScF6 reacts with Al to form Na3AlF6 or K3AlF6, which effectively removes the oxide film on the surface of the molten aluminum, ensuring sufficient contact between the molten salt system and the molten aluminum and promoting the aluminothermic reaction. The NaCl or KCl molten salt system lowers the melting point of Na3ScF6 or K3ScF6, achieving liquid-liquid bonding between Na3ScF6 or K3ScF6 and the molten aluminum, thus promoting the reduction reaction.

[0041] In some embodiments of the present invention, the reaction conditions for the aluminothermic reduction reaction are: a reaction temperature of 700–850°C and a reaction time of 20–60 min. In some embodiments, the reaction temperature may specifically be 700°C, 710°C, 750°C, 800°C, or 850°C, etc. In some embodiments, the reaction time may specifically be 20 min, 25 min, 27 min, 30 min, 40 min, 50 min, 57 min, or 60 min, etc.

[0042] In some embodiments of the present invention, the number of batches is 2 to 5, and the interval between each batch is 5 to 20 minutes. In some embodiments, the number of batches may specifically be 2, 3, 4, or 5, etc. In some embodiments, the interval between each batch may specifically be 5 minutes, 10 minutes, 15 minutes, or 20 minutes, etc.

[0043] Adding the mixed salt in batches can prevent the molten salt from volatilizing due to high temperature, thus keeping the reaction environment of the aluminum liquid and scandium-containing compounds stable and promoting the aluminothermic reduction reaction.

[0044] In some embodiments of the present invention, the protective gas is one or more of argon and nitrogen.

[0045] Inert gases, such as nitrogen or argon, can be used to remove impurities and stir the solution. Impurities such as alumina adhere to the surface of the bubbles and float to the surface of the alloy solution, forming slag. Hydrogen in the solution is absorbed by the bubbles and removed. At the same time, the stirring effect of the rising bubbles prevents Al3Sc particles from depositing and accumulating at the bottom of the aluminum liquid, thus reducing the temperature of the Al-Sc alloy liquid.

[0046] In some embodiments of the present invention, the introduction rate of the protective gas is 5–20 L / min, and the introduction time is 5–10 min. In some embodiments, the introduction rate may specifically be 5 L / min, 10 L / min, 15 L / min, or 20 L / min, etc. In some embodiments, the introduction time may specifically be 5 min, 7 min, 8 min, or 10 min. Introducing the protective gas can achieve the effects of impurity removal and cooling, so that the impurities in the aluminum liquid are less than 0.1% (this percentage is the hydrogen content in milliliters (mL) of 100g of aluminum liquid), that is, the hydrogen content in 100g of aluminum is less than 0.1mL, and the temperature of the Al-Sc alloy liquid is 680-750℃.

[0047] In some embodiments of the present invention, the casting temperature is 680-750°C, and the mold is one of graphite mold, steel mold, or copper mold. In some embodiments, the casting temperature may specifically be 680°C, 690°C, 700°C, 710°C, 720°C, 740°C, or 750°C, etc.

[0048] Another typical embodiment of the present invention provides an aluminum-scandium master alloy, prepared using the above-described method. The scandium content in the aluminum-scandium master alloy is 1-3 wt.%, and the second-phase particles are uniformly distributed in the aluminum matrix without porosity or impurities. The aluminum-scandium master alloy provided by the present invention, when added as a master alloy to the aluminum alloy casting process, allows for accurate adjustment of the alloy ratio with a relatively small amount added, making it convenient to operate and highly practical.

[0049] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0050] Example 1

[0051] S1. Mix 15.5g Na3ScF6 with 41g NaCl and 41g KCl in a mechanical stirrer at 3000r / min for 30min, and then dehydrate in a 200℃ drying oven for 1h.

[0052] S2. Add the mixed salt obtained in step S1 to the molten aluminum at a mass ratio of 1:1 with aluminum, and keep it at 850℃ for 60 minutes to obtain an aluminum alloy solution containing Sc element. Add 27g of mixed salt for the first time.

[0053] S3. After the initially added mixed molten salt has melted, add the remaining mixed salt in four batches during the subsequent heat preservation process, with an interval of 10 minutes between each batch.

[0054] S4. Argon gas is introduced into the aluminum alloy liquid obtained in step S3 at a rate of 15 L / min for 10 min to remove gas and impurities. The temperature of the Al-Sc alloy melt after treatment is 750℃.

[0055] S5. The Al-Sc alloy melt obtained in step S4 is poured into a copper mold and air-cooled to obtain an Al-3wt.%Sc master alloy with uniform Al3Sc particle distribution and a thickness of 30mm, free of pores and impurities, with a Sc yield of 98.4%.

[0056] Metallographic observation of the intermediate alloy obtained in Example 1, such as Figure 1 As shown, the second phase particles are fine and uniformly distributed in the aluminum matrix, without the presence of pores or impurities, thus achieving the objective of this invention.

[0057] The EDS results of the aluminum-scandium master alloy prepared in Example 1 are shown in Table 1.

[0058] Table 1

[0059]

[0060] Example 2

[0061] S1. Mix 16g K3ScF6 with 30g NaCl and 30g KCl in a mechanical stirrer at 2000r / min for 20min, and then dehydrate in a 150℃ drying oven for 1.5h.

[0062] S2. The mixed salt obtained in step S1 is added to the aluminum liquid at a mass ratio of 1:1.3 with aluminum, and kept at 800℃ for 40 minutes to obtain an aluminum alloy solution containing Sc element. 26g of mixed salt is added for the first time.

[0063] S3. After the initially added mixed salt has melted, add the remaining mixed salt in three batches during the subsequent heat preservation process, with an interval of 10 minutes.

[0064] S4. The aluminum alloy liquid obtained in step S3 is subjected to degassing and impurity removal by introducing nitrogen gas at a rate of 10 L / min for 8 min. The temperature of the Al-Sc alloy melt after treatment is 720℃.

[0065] S5. The Al-Sc alloy melt obtained in step S4 is poured into a steel mold and air-cooled to obtain an Al-2.5wt.%Sc master alloy with uniform Al3Sc particle distribution and a thickness of 25mm, free of pores and impurities, with a Sc yield of 98.9%.

[0066] Example 3

[0067] S1. Mix 5.1Na3ScF6 with 20gNaCl and 20gKCl in a mechanical stirrer at 800r / min for 10min, and then dehydrate in an 80℃ drying oven for 1h.

[0068] S2. Add the mixed salt obtained in step S1 into the aluminum liquid at a mass ratio of 1:2.2 with aluminum, and keep it at 750℃ for 30 minutes to obtain an aluminum alloy solution containing Sc element. Add 25g of mixed salt for the first time.

[0069] S3. After the initially added mixed salt has melted, the remaining molten salt is added in two batches during the subsequent heat preservation process, with an interval of 8 minutes.

[0070] S4. Argon gas is introduced into the aluminum alloy liquid obtained in step S3 at a rate of 5 L / min for 5 min to remove gas and impurities. The temperature of the Al-Sc alloy melt after treatment is 700℃.

[0071] S5. The Al-Sc alloy melt obtained in step S4 is poured into a graphite mold and air-cooled to obtain an Al-1wt.%Sc master alloy with uniform Al3Sc particle distribution and a thickness of 20mm, free of pores and impurities, with a Sc yield of 98.3%.

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an aluminum-scandium master alloy, characterized in that, Includes the following steps: S1. Using Na3ScF6 or K3ScF6 as a scandium source, mix with chloride molten salt and dry to obtain a mixed salt; S2. The mixed salt is added to the aluminum liquid in batches to carry out the aluminothermic reduction reaction and obtain an aluminum alloy solution containing scandium; S3. A protective gas is passed through an aluminum alloy solution containing scandium and stirred to obtain an aluminum-scandium intermediate alloy solution, which is then poured into a mold and cooled to obtain an aluminum-scandium intermediate alloy. The protective gas is introduced at a rate of 5-15 L / min for a duration of 5-10 min.

2. The method for preparing the aluminum-scandium master alloy as described in claim 1, characterized in that, The chloride molten salt is composed of sodium chloride and potassium chloride, with a mass ratio of sodium chloride to potassium chloride of 1:

1.

3. The method for preparing the aluminum-scandium master alloy as described in claim 1 or 2, characterized in that, The mass ratio of scandium source to chloride molten salt is 1:2~10.

4. The method for preparing the aluminum-scandium master alloy as described in claim 1, characterized in that, The mass ratio of the mixed salt to the molten aluminum is 1:1~5.

5. The method for preparing the aluminum-scandium master alloy as described in claim 1, characterized in that, The reaction conditions for the aluminothermic reduction reaction are: reaction temperature 700~850℃, reaction time 20~60 min.

6. The method for preparing the aluminum-scandium master alloy as described in claim 1, characterized in that, The number of batches is 2 to 5, with an interval of 5 to 20 minutes between each batch.

7. The method for preparing the aluminum-scandium master alloy as described in claim 1, characterized in that, The protective gas is one or both of argon and nitrogen.

8. The method for preparing the aluminum-scandium master alloy as described in claim 1, characterized in that, The casting temperature is 680-750℃, and the mold is one of graphite mold, steel mold, or copper mold.

9. An aluminum-scandium master alloy, characterized in that, The aluminum-scandium master alloy is prepared by any one of the preparation methods of claims 1-8, wherein the scandium content in the aluminum-scandium master alloy is 1-3 wt.%, the second phase particles are uniformly distributed in the aluminum matrix, and there are no pores or impurities present.

Images