Preparation and application of low-segregation intermediate alloy containing scandium and aluminum

Abstract

The invention discloses a preparation method and application of a low-segregation scandium-containing aluminum intermediate alloy. The preparation method comprises the following steps: proportioning aluminum, silicon and scandium fluoride according to the weight ratio of 10: (0.1-1.0): (0.4-1.0); the method comprises the steps that molten salt is added into ingredients for temperature rise and heating reduction, the heat preservation reduction temperature ranges from 800 DEG C to 1200 DEG C, the heat preservation time ranges from 0.5 h to 2 h, slagging-off and casting are conducted after heat preservation is completed, and the aluminum-scandium-silicon intermediate alloy, namely the low-segregation scandium-containing aluminum intermediate alloy, with uniform components is obtained. The scandium-containing aluminum intermediate alloy is homogenized in an alloying mode, that is, a small amount of silicon is added to solve the problem of local segregation of the scandium element of the scandium-containing aluminum intermediate alloy.

Description

Technical Field

[0001] The invention belongs to the technical field of alloy preparation, and particularly relates to the preparation and application of a low-segregation scandium-containing aluminum master alloy. Background Art

[0002] Aluminum alloys have the advantages of low density, high specific strength, good electrical and thermal conductivity, etc., and are widely used in the fields of automobiles, aerospace, ships, etc. Scandium is the alloying element that has the best grain refinement and recrystallization inhibition effect on aluminum alloys discovered so far. The addition of trace Sc elements can effectively refine the grain structure of aluminum alloys, improve the mechanical properties of aluminum alloys, and improve the weldability of aluminum alloys.

[0003] In terms of market application, in addition to cast aluminum alloys, aluminum alloys containing scandium used in aluminum alloy welding wires, additive manufacturing and other fields all contain a certain amount of Si, and have broad market prospects. Among them, patents such as CN110257653A and CN106048272A have proposed methods for preparing Al-Si-Sc welding wires using scandium-containing materials and their applications.

[0004] Wang Minbu pointed out in the composition design of high-strength aluminum-magnesium alloy containing scandium for additive manufacturing that the addition of Si can reduce the crack sensitivity factor while refining the grain size. The optimal composition is Al-8.0Mg-1.3Si-0.5Mn-0.5Sc-0.3Zr, [Composition design of high-strength aluminum-magnesium alloy containing scandium for additive manufacturing and its crack prevention and strengthening mechanism, Central South University, D, Wang Minbu, 2023].

[0005] Due to the large difference in the melting points of scandium and aluminum, scandium is generally added to aluminum alloys by means of aluminum-scandium master alloys during aluminum alloy smelting. However, due to the severe segregation of binary aluminum-scandium master alloys, the scandium content difference between the upper and lower surfaces is large, and the difference in some products is more than 1 times. As a trace alloying element, the use of aluminum master alloys containing scandium with severe scandium segregation will make it difficult to control the scandium content in the final aluminum alloy product, resulting in poor batch stability of the product, which limits the application of aluminum alloys containing scandium.

[0006] At present, the more mature method for preparing scandium-containing aluminum master alloy is thermal reduction method. Past research has focused on the yield of scandium, the cost-effectiveness of molten salt, the reduction rate, etc. Patents CN105803235A, CN100546456C, CN115896551A, etc. use thermal reduction method to prepare scandium-containing aluminum master alloy, but there are few studies on the segregation of scandium-containing aluminum alloy. To address this problem, some researchers have tried to reduce the casting temperature, increase heat preservation and stirring, and strengthen mold cooling.

[0007] Among them, CN116904779A discloses a method for preparing a homogenized aluminum-scandium master alloy, which uses a two-step heat preservation method to cool down the casting to achieve homogenization, that is, the heat preservation is at 900-950℃ and 800-850℃ respectively, and the casting temperature is 750-800℃. At the same time, the mold is rapidly cooled by circulating water to retain the fine dispersed Al3Sc particles and prevent the Al3Sc phase from growing and causing segregation. However, this method has a long production cycle, and the production time of each furnace reaches 2-4h, and the mold needs to be rapidly cooled, and the mold manufacturing cost and use cost are high.

[0008] In the study of the preparation and evaluation of aluminum-scandium master alloy, Li Zhi proposed to increase argon stirring to reduce the segregation of scandium. By using argon stirring, the difference in scandium content between the upper and lower parts of the ingot was further reduced, indicating that the problem of longitudinal segregation of the ingot was well alleviated. At the same time, a large steel plate mold was used to replace the block mold to reduce the ingot height. Under the optimal conditions, the difference in scandium content between the upper and lower parts was finally achieved to be less than 20%. [Li Zhi. Preparation and Evaluation of Aluminum-scandium Master Alloy [D]. Qilu University of Technology, 2024.] However, this process adds an argon stirring process, reduces the ingot height to within 10 mm, increases the preparation process and is limited by the ingot height. The mold with the same plane but the furnace output is doubled. Summary of the invention

[0009] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a preparation and application of a low-segregation scandium-containing aluminum master alloy, and to achieve homogenization of the scandium-containing aluminum master alloy by alloying, that is, adding a small amount of silicon to solve the problem of local segregation of the scandium element in the scandium-containing aluminum master alloy.

[0010] In order to achieve the above object, the technical solution adopted by the present invention is:

[0011] A method for preparing a low-segregation scandium-containing aluminum master alloy comprises the following steps: preparing aluminum: silicon: scandium fluoride in a weight ratio of 10: (0.1-1.0): (0.4-1.0); adding molten salt to the prepared ingredients for heating and reduction, wherein the reduction temperature is 800-1200°C for a holding time of 0.5-2h, and after the holding is completed, slag is removed and cast to obtain an aluminum-scandium-silicon master alloy with uniform composition, namely, a low-segregation scandium-containing aluminum master alloy.

[0012] In an embodiment of the present invention, the molten salt is a mixture of alkali metal chloride and alkali metal fluoride, and the amount of the molten salt added is 20-40% of the weight of the aluminum.

[0013] In an embodiment of the present invention, the weight ratio of alkali metal chloride to alkali metal fluoride can preferably be (3-4):1, wherein the alkali metal chloride can be selected from potassium chloride, sodium chloride or any mixture thereof; the alkali metal fluoride can be selected from lithium fluoride, sodium fluoride, potassium fluoride or any mixture thereof.

[0014] In an embodiment of the present invention, the heating reduction is carried out at a heating rate of 7 to 10° C. / min, and mechanical stirring or electromagnetic stirring is used during the heating and heat preservation process.

[0015] In the embodiment of the present invention, in the low-segregation scandium-containing aluminum master alloy, in addition to the co-precipitation of aluminum and scandium, there are also aluminum, scandium and silicon eutectoid products, and the morphology is long and thin strips.

[0016] The low-segregation scandium-containing aluminum master alloy prepared by the method for preparing the low-segregation scandium-containing aluminum master alloy of the present invention has a scandium content deviation of less than 10%, and further, an oxygen content of less than 100 ppm.

[0017] The scandium-containing aluminum master alloy obtained by the present invention can be used for aluminum alloy casting, scandium-containing aluminum alloy additive manufacturing, aluminum silicon scandium welding wire preparation, silicon-containing deformed aluminum alloy and other alloy preparations.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The segregation of aluminum-scandium master alloy is mainly caused by the precipitation of Al3Sc during the solidification process. After adding silicon, due to the large latent heat of crystallization and good fluidity of the aluminum-silicon phase, the aluminum-scandium-silicon eutectoid process effectively solves the regional segregation problem of high Sc content in the first solidified area and low Sc content in the later solidified area during the solidification process of the aluminum-scandium master alloy.

[0020] 2. The addition of silicon can also reduce the oxygen content in the alloy. The main reason is that silicon has a stronger ability to combine with oxygen, forming SiO2 and entering the slag phase. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the morphology and energy spectrum image of the scandium-containing aluminum master alloy prepared in Example 1 of the present invention.

[0022] Figure 2 The figure shows the morphology and energy spectrum of the scandium-containing aluminum master alloy prepared in the comparative example of the present invention. DETAILED DESCRIPTION

[0023] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention is described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0024] The present invention is a method for preparing a low-segregation scandium-containing aluminum master alloy, wherein aluminum, silicon and scandium fluoride are prepared in a weight ratio of 10: (0.1-1.0): (0.4-1.0). Molten salt is then added to the prepared ingredients and placed in a heating furnace for heating and reduction, wherein the insulation reduction temperature is 800-1200°C and the insulation time is 0.5-2h. After the insulation is completed, slag is removed and cast to obtain an aluminum-scandium-silicon master alloy with uniform composition.

[0025] The present invention adds a small amount of silicon into the ingredients, and the aluminum-silicon phase combined with aluminum has the characteristics of good fluidity and large crystallization latent heat. Therefore, the phenomenon that the Sc content in the first solidification area is high and the Sc content in the later solidification area is low during the solidification process of the aluminum-scandium master alloy can be avoided. The deviation of the scandium content in the product is less than 10%, which proves that the present invention has obtained a low-segregation scandium-containing aluminum master alloy.

[0026] At the same time, after adding silicon, due to the stronger ability of silicon to combine with oxygen, SiO2 is easily formed and enters the slag phase. Therefore, the present invention can also reduce the oxygen content of the alloy. Experiments have shown that the oxygen content in the product of the present invention is less than 100ppm.

[0027] Further preferably, in order to increase the application scenarios of the intermediate alloy, the weight ratio of aluminum, silicon and scandium fluoride is preferably 10: (0.1-0.3): (0.5-0.7).

[0028] The molten salt added to the ingredients of the present invention is composed of a mixture of alkali metal chloride and alkali metal fluoride, and the addition amount is 20-40% of the weight of aluminum in the ingredients. The fluoride in the molten salt forms a low melting point mixture with scandium fluoride, which increases the solubility of scandium fluoride, so that the reduction reaction changes from "solid-liquid reaction" to "liquid reaction", which is beneficial to the reduction of scandium; the chloride in the molten salt acts as a reaction solvent and a covering agent, enriching the silicon- and aluminum-containing fluorides and oxides generated by the reaction into the solvent, and at the same time, the chloride acts as a covering agent to avoid oxidation of the alloy solution due to its low density. If the amount of molten salt added is less than 20% of the aluminum content, the solution will become viscous after adding scandium fluoride, and the covering effect will be poor. If the amount of molten salt added is higher than 40% of the aluminum content, the concentration of scandium will decrease, affecting the yield of scandium, and the amount of molten salt slag will increase, increasing the disposal cost.

[0029] Furthermore, the weight ratio of alkali metal chloride to alkali metal fluoride in the molten salt is (3-4):1,

[0030] In this range, chloride as a reaction solvent can provide a reaction environment with good fluidity and high slag solubility, and fluoride can form a low melting point mixture with scandium fluoride. Too high a chloride ratio will lead to a decrease in the concentration of scandium and reduce the reduction efficiency of scandium; too low a chloride ratio will lead to an increase in the fluoride content, a decrease in the fluidity of the molten salt, and affect the mass transfer of materials.

[0031] For example, the alkali metal chloride may be selected from potassium chloride, sodium chloride or any mixture thereof; the alkali metal fluoride may be selected from lithium fluoride, sodium fluoride, potassium fluoride or any mixture thereof.

[0032] Furthermore, in the heating reduction of the present invention, the heating rate is 7-10°C / min, and mechanical stirring or electromagnetic stirring is used during the heating and heat preservation process.

[0033] Furthermore, in the slag removal and casting process, after the insulation is completed, the upper slag liquid is clear and transparent. After mechanical or manual slag removal, the alloy solution is poured into a cast iron mold. In order to obtain better alloy uniformity, the ingot height does not exceed 40 mm.

[0034] The following are several specific embodiments of the present invention.

[0035] Comparative Example

[0036] Put 10kg of aluminum, 560g of scandium fluoride and molten salt into a heating furnace, and put in 1.6kg of potassium chloride and 600g of sodium fluoride at the same time, and start heating at a heating rate of 8℃ / min. When the temperature reaches 950℃, keep it warm for 1.5h, pour the molten metal into a ladle, manually scrape off the upper slag liquid, pour the remaining aluminum alloy solution into a flat mold, and cool it to obtain a scandium-containing aluminum intermediate alloy. Take samples from the upper and lower parts of the alloy for scandium content detection, mix the upper and lower samples to measure the oxygen content, and cut the alloy along the thickness direction for electronic scanning and energy spectrum analysis.

[0037] Example 1

[0038] Put 10kg of aluminum, 200g of silicon, 560g of scandium fluoride and molten salt into a heating furnace, and put in 1.6kg of potassium chloride and 600g of sodium fluoride at the same time. Start heating at a rate of 8℃ / min. When the temperature reaches 950℃, keep it warm for 1.5h, pour the molten metal into a ladle, manually scrape off the upper slag liquid, pour the remaining aluminum alloy solution into a flat mold, and cool it to obtain a scandium-containing aluminum intermediate alloy. Take samples from the upper and lower parts of the alloy for scandium and silicon content testing, mix the upper and lower samples to measure oxygen content, and cut the alloy along the thickness direction for electronic scanning and energy spectrum analysis.

[0039] Example 2

[0040] Put 10kg of aluminum, 250g of silicon, 650g of scandium fluoride and molten salt into a heating furnace, and put in 1.8kg of potassium chloride, 400g of sodium fluoride, and 100g of lithium fluoride mixed salt at the same time, start heating, and the heating rate is 10℃ / min. When the temperature reaches 1050℃, keep it warm for 1h, pour the molten liquid into the ladle, manually scrape off the upper slag liquid, pour the remaining aluminum alloy solution into the flat mold, and cool it to obtain the scandium-containing aluminum intermediate alloy. Take samples from the upper and lower parts of the alloy and send them for scandium and silicon content detection, and mix the upper and lower samples to measure the oxygen content.

[0041] Example 3

[0042] Put 10kg of aluminum, 250g of silicon, 650g of scandium fluoride and molten salt into a heating furnace, and put in 2.5kg of sodium chloride, 400g of potassium fluoride, and 400g of lithium fluoride mixed salt at the same time, start heating, and the heating rate is 9℃ / min. When the temperature reaches 1150℃, keep it warm for 1h, pour the molten liquid into the ladle, manually scrape off the upper slag liquid, pour the remaining aluminum alloy solution into the flat mold, and cool it to obtain the scandium-containing aluminum intermediate alloy. Take samples from the upper and lower parts of the alloy and send them for scandium and silicon content detection, and mix the upper and lower samples to measure the oxygen content.

[0043] Depend on Figure 1 and Figure 2 It can be seen that in the comparative example, aluminum-scandium precipitates in the matrix in the form of Al3Sc, the atomic ratio of Al to Sc is close to 1:3, and the precipitated phase morphology is regular shapes such as squares, hexagons, triangles, etc. In Example 1, in addition to a part of scandium precipitating in the form of Al3Sc, the precipitation morphology is consistent with the comparative example, and there is also a part of aluminum, scandium, and silicon eutectic products, which are in the form of thin and long strips. This is also the main reason why scandium is more evenly distributed on the upper and lower surfaces of the aluminum alloy.

[0044] The element content results of various embodiments of the present invention are shown in Table 1. Table 1 shows that the addition of silicon can significantly improve the regional segregation of scandium, and at the same time, the oxygen content in the alloy is also reduced to a certain extent.

[0045] Table 1 Composition of master alloy

[0046]

[0047]

[0048] According to the properties of the low-segregation scandium-containing aluminum master alloy obtained in the present invention, it is expected to be applied to aluminum alloy casting, scandium-containing aluminum alloy additive manufacturing, aluminum-silicon-scandium welding wire preparation, silicon-containing deformed aluminum alloy preparation and other aspects.

Claims

1. A method for preparing a low-segregation scandium-aluminum master alloy, characterized in that: The weight ratio of aluminum: silicon: scandium fluoride is equal to 10: (0.1-1.0): (0.4-1.0) and the ingredients are prepared; molten salt is added to the ingredients for heating and reduction, the insulation reduction temperature is 800-1200°C, the insulation time is 0.5-2h, and after the insulation is completed, the slag is removed and cast to obtain an aluminum-scandium-silicon master alloy with uniform composition, that is, a low-segregation scandium-containing aluminum master alloy.

2. The method for preparing the low-segregation scandium-containing aluminum master alloy according to claim 1, characterized in that: The molten salt is a mixture of alkali metal chloride and alkali metal fluoride, and the added amount of the molten salt is 20-40% of the weight of aluminum.

3. The method for preparing the low-segregation scandium-containing aluminum master alloy according to claim 2, characterized in that: The weight ratio of the alkali metal chloride to the alkali metal fluoride is (3-4):

1.

4. The method for preparing a low-segregation scandium-containing aluminum master alloy according to claim 2 or 3, characterized in that: The alkali metal chloride is selected from potassium chloride, sodium chloride or any mixture thereof; the alkali metal fluoride is selected from lithium fluoride, sodium fluoride, potassium fluoride or any mixture thereof.

5. The method for preparing the low-segregation scandium-containing aluminum master alloy according to claim 1, characterized in that: The heating reduction process has a heating rate of 7 to 10° C. / min, and mechanical stirring or electromagnetic stirring is used during the heating and heat preservation process.

6. The method for preparing the low-segregation scandium-containing aluminum master alloy according to claim 1, characterized in that: In the low-segregation scandium-containing aluminum master alloy, in addition to the co-precipitation of aluminum and scandium, there are also aluminum, scandium and silicon eutectoid products, which are in the shape of long and thin strips.

7. A low-segregation scandium-containing aluminum master alloy prepared by the preparation method of the low-segregation scandium-containing aluminum master alloy according to claim 1.

8. The low-segregation scandium-containing aluminum master alloy according to claim 7, characterized in that: The low-segregation scandium-containing aluminum master alloy has a scandium content deviation of less than 10%.

9. The method for preparing the low-segregation scandium-containing aluminum master alloy according to claim 1, characterized in that: The scandium-aluminum master alloy has an oxygen content of less than 100 ppm.

10. The low-segregation scandium-containing aluminum master alloy prepared by the preparation method of the low-segregation scandium-containing aluminum master alloy according to claim 1 is used in aluminum alloy casting, scandium-containing aluminum alloy additive manufacturing, aluminum-silicon-scandium welding wire preparation, and silicon-containing deformed aluminum alloy preparation.

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