Preparation and application of low segregation sc containing aluminum intermediate alloy

Abstract

The application discloses a preparation method and application of a low-segregation scandium-containing aluminum intermediate alloy, and ingredients with weight ratio of aluminum, silicon and scandium fluoride equal to 10:(0.1-1.0):(0.4-1.0) are prepared; molten salt is added in the ingredients for heating reduction, the holding reduction temperature is 800-1200 DEG C, the holding time is 0.5-2h, slagging is carried out after the holding, and casting is carried out, so that the aluminum scandium silicon intermediate alloy with uniform composition, i.e. the low-segregation scandium-containing aluminum intermediate alloy, is obtained. The application realizes the homogenization of the scandium-containing aluminum intermediate alloy by alloying, i.e. the problem of local segregation of scandium in the scandium-containing aluminum intermediate alloy is solved by adding a small amount of silicon.

Description

TECHNICAL FIELD

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

[0002] Aluminum alloy has the advantages of low density, high specific strength, good electrical and thermal conductivity, and is widely used in the fields of automobiles, aerospace, ships and the like. Scandium is currently the best alloying element for grain refinement and recrystallization inhibition of aluminum alloy, and the addition of trace Sc element can effectively refine the grain structure of aluminum alloy, improve the mechanical properties of aluminum alloy, and improve the weldability of aluminum alloy.

[0003] In terms of market application, in addition to cast aluminum alloy, scandium-containing aluminum alloy is applied in the fields of aluminum alloy welding wire and additive manufacturing, and contains a certain content of Si, which has a broad market prospect. Among them, patents such as CN110257653A and CN106048272A propose a preparation method and application of Al-Si-Sc welding wire prepared from scandium-containing materials.

[0004] In the component design of scandium-containing high-strength aluminum-magnesium alloy in additive manufacturing, Wang Minbo pointed out that the addition of Si can refine the grain size while reducing the crack sensitivity factor, and the optimal composition is Al-8.0Mg-1.3Si-0.5Mn-0.5Sc-0.3Zr, [Component Design, Crack Resistance and Strengthening Mechanism of Scandium-Containing High-Strength Aluminum-Magnesium Alloy in Additive Manufacturing, Central South University, D, Wang Minbo, 2023].

[0005] Due to the large difference between the melting points of scandium and aluminum, scandium is generally added in the form of aluminum-scandium intermediate alloy during aluminum alloy smelting. However, due to the serious segregation of binary aluminum-scandium intermediate alloy, the scandium content on the upper and lower surfaces differs greatly, and the difference in some products reaches more than 1 times. As a trace alloying element, the use of scandium-containing aluminum intermediate alloy with serious scandium segregation will lead to difficulty in controlling the scandium content in the final aluminum alloy product, thereby poor product batch stability, which limits the application of scandium-containing aluminum alloy.

[0006] The current mature method for preparing scandium-containing aluminum intermediate alloy is the hot reduction method. Past research has focused on scandium yield, molten salt cost-effectiveness, and reduction rate. Patents such as CN105803235A, CN100546456C, and CN115896551A use the hot reduction method to prepare scandium-containing aluminum intermediate alloy, but there is little research on the segregation problem of scandium-containing aluminum alloy. In view of this problem, researchers have successively tried to reduce the casting temperature, increase the heat preservation stirring, and strengthen the mold cooling.

[0007] CN116904779A discloses a method for preparing homogenized aluminum-scandium master alloys. This method employs a two-step holding process with cooling and casting to achieve homogenization, specifically holding at 900–950℃ and 800–850℃ respectively, with a casting temperature of 750–800℃. Simultaneously, a circulating water system is used to rapidly cool the mold, preserving fine, dispersed Al3Sc particles and preventing Al3Sc phase growth and segregation. However, this method has a long production cycle, with each batch taking 2–4 hours, and requires rapid mold cooling, resulting in high mold manufacturing and operating costs.

[0008] In his research on the preparation and evaluation of aluminum-scandium master alloys, Li Zhi proposed using argon gas stirring to reduce scandium segregation. Argon gas stirring further reduced the difference in scandium content between the upper and lower parts of the ingot, indicating a significant improvement in the longitudinal segregation problem. Simultaneously, replacing the block mold with a large steel plate mold reduced the ingot height. Under optimal conditions, the difference in scandium content between the upper and lower parts was ultimately less than 20% [Li Zhi. Preparation and Evaluation of Aluminum-Scandium Master Alloys [D]. Qilu University of Technology, 2024]. However, this process increases the argon gas stirring process and reduces the ingot height to within 10 mm, increasing the preparation process and limiting it to the ingot height. While using molds with the same surface area, the output per furnace is reduced several times over. Summary of the Invention

[0009] In order to overcome the shortcomings of the prior art, the present invention aims to provide a method for preparing and applying a low-segregation scandium-containing aluminum master alloy. The homogenization of the scandium-containing aluminum master alloy is achieved by alloying, that is, by adding a small amount of silicon to solve the problem of local segregation of scandium in the scandium-containing aluminum master alloy.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A method for preparing a low-segregation scandium-containing aluminum master alloy involves mixing aluminum, silicon, and scandium fluoride in a weight ratio of 10:(0.1-1.0):(0.4-1.0); adding molten salt to the mixture and heating it for reduction at a temperature of 800-1200℃ for 0.5-2 hours; removing slag after the reduction is complete and casting the alloy to obtain a homogeneous aluminum-scandium-silicon master alloy, i.e., 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 molten salt added is 20-40% of the weight of aluminum.

[0013] In embodiments of the present invention, the weight ratio of alkali metal chloride to alkali metal fluoride is preferably (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 and reduction process is carried out at a heating rate of 7-10°C / min, and mechanical stirring or electromagnetic stirring is used during the heating and heat preservation process.

[0015] In an embodiment of the present invention, the low-segregation scandium-containing aluminum master alloy contains not only aluminum and scandium co-precipitated, but also aluminum, scandium and silicon co-precipitated products, which have a slender strip-like morphology.

[0016] The low-segregation scandium-containing aluminum master alloy prepared by the method 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 this invention can be used for aluminum alloy casting, scandium-containing aluminum alloy additive manufacturing, aluminum-silicon-scandium welding wire preparation, silicon-containing wrought aluminum alloy and other grade alloy preparation.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[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 co-deposition process effectively solves the problem of regional segregation in the solidification process of aluminum-scandium master alloy, where the Sc content is high in the first solidified region and low in the later solidified region.

[0020] 2. The addition of silicon can also reduce the oxygen content in the alloy, mainly because silicon has a stronger affinity for oxygen, forming SiO2 which enters the slag phase. Attached Figure Description

[0021] Figure 1 These are the morphology and energy dispersive spectroscopy (EDS) images of the scandium-containing aluminum master alloy prepared in Example 1 of this invention.

[0022] Figure 2 These are images showing the morphology and energy dispersive spectroscopy (EDS) spectrum of the scandium-containing aluminum master alloy prepared in the comparative example of this invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention are described in detail below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other implementation methods obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0024] This invention discloses a method for preparing a low-segregation scandium-containing aluminum master alloy. Aluminum, silicon, and scandium fluoride are mixed in a weight ratio of 10:(0.1–1.0):(0.4–1.0). Molten salt is then added to the mixture, and the mixture is heated in a furnace for reduction. The reduction temperature is maintained at 800–1200°C for 0.5–2 hours. After the reduction is completed, slag is removed, and the mixture is cast to obtain a homogeneous aluminum-scandium-silicon master alloy.

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

[0026] Meanwhile, when silicon is added, because silicon has a stronger affinity for oxygen, it is easier to form SiO2 and enter the slag phase. Therefore, this invention can also reduce the oxygen content of the alloy. Experiments have shown that the oxygen content in the product of this invention is less than 100 ppm.

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

[0028] The molten salt added in this invention consists of a mixture of alkali metal chlorides and alkali metal fluorides, and its addition amount is 20-40% of the weight of aluminum in the ingredients. The fluorides in the molten salt form a low-melting-point mixture with scandium fluoride, increasing the solubility of scandium fluoride and changing the reduction reaction from a "solid-liquid reaction" to a "liquid reaction," which is beneficial for scandium reduction. The chlorides in the molten salt act as a reaction solvent and covering agent, enriching the silicon- and aluminum-containing fluorides and oxides generated in the reaction into the solvent. Simultaneously, due to their low density, chlorides act as a covering agent to prevent oxidation of the alloy solution. Adding molten salt at less than 20% of the aluminum content will result in a viscous solution after adding scandium fluoride and poor covering effect. Adding molten salt at more than 40% of the aluminum content will lead to a decrease in scandium concentration, affecting the scandium yield, and increasing the amount of molten salt slag, thus increasing disposal costs.

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

[0030] Within this range, chlorides, as reaction solvents, provide a reaction environment with good fluidity and high slag solubility, while fluorides can form a low-melting-point mixture with scandium fluoride. An excessively high chloride ratio leads to a decrease in scandium concentration, reducing scandium reduction efficiency; conversely, an excessively low chloride ratio leads to an increase in fluoride content, decreased molten salt fluidity, and impaired mass transfer.

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

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

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

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

[0035] Comparative Example

[0036] 10 kg of metallic aluminum, 560 g of scandium fluoride, and molten salt were placed in a heating furnace along with 1.6 kg of potassium chloride and 600 g of sodium fluoride. Heating was initiated at a rate of 8 °C / min. Once the temperature reached 950 °C, it was held for 1.5 hours. The molten liquid was then poured into a ladle, and the top layer of slag was manually removed. The remaining aluminum alloy solution was poured into a flat mold and cooled to obtain a scandium-containing aluminum master alloy. Samples were taken from both the top and bottom of the alloy for scandium content analysis. The oxygen content was measured by mixing the top and bottom samples. The alloy was then cut along its thickness for electron scanning and energy dispersive spectroscopy analysis.

[0037] Example 1

[0038] 10 kg of metallic aluminum, 200 g of metallic silicon, and 560 g of scandium fluoride were placed in a heating furnace along with molten salt. Simultaneously, 1.6 kg of potassium chloride and 600 g of sodium fluoride were added. Heating was initiated at a rate of 8 °C / min. Once the temperature reached 950 °C, it was held for 1.5 hours. The molten liquid was then poured into a ladle, and the top layer of slag was manually removed. The remaining aluminum alloy solution was poured into a flat mold and cooled to obtain a scandium-containing aluminum master alloy. Samples were taken from both the top and bottom of the alloy for scandium and silicon content analysis. The oxygen content was measured by mixing the top and bottom samples. The alloy was then cut along its thickness for electron scanning and energy dispersive spectroscopy analysis.

[0039] Example 2

[0040] 10 kg of metallic aluminum, 250 g of metallic silicon, and 650 g of scandium fluoride were placed in a heating furnace along with molten salt. Simultaneously, 1.8 kg of potassium chloride, 400 g of sodium fluoride, and 100 g of lithium fluoride were added to a mixed salt solution. Heating was initiated at a rate of 10 °C / min. Once the temperature reached 1050 °C, it was held at that temperature for 1 hour. The molten liquid was then poured into a ladle, and the top layer of slag was manually removed. The remaining aluminum alloy solution was poured into a flat mold and cooled to obtain a scandium-containing aluminum master alloy. Samples from both the top and bottom of the alloy were taken separately for scandium and silicon content testing. The oxygen content of the mixed samples was then measured.

[0041] Example 3

[0042] 10 kg of metallic aluminum, 250 g of metallic silicon, and 650 g of scandium fluoride were placed in a heating furnace along with molten salt. Simultaneously, 2.5 kg of sodium chloride, 400 g of potassium fluoride, and 400 g of lithium fluoride mixed salt were added. Heating was initiated at a rate of 9 °C / min. Once the temperature reached 1150 °C, it was held for 1 hour. The molten liquid was then poured into a ladle, and the top layer of slag was manually removed. The remaining aluminum alloy solution was poured into a flat mold and cooled to obtain a scandium-containing aluminum master alloy. Samples from both the top and bottom of the alloy were taken separately for scandium and silicon content testing. The oxygen content of the mixed samples was then measured.

[0043] Depend on Figure 1 and Figure 2 As can be seen, in the comparative example, scandium precipitates in the matrix as Al3Sc, with an atomic ratio of Al to Sc close to 1:3, and the precipitated phases exhibit regular shapes such as squares, hexagons, and triangles. In Example 1, in addition to a portion precipitating as Al3Sc, the precipitated morphology is consistent with that of the comparative example, and there is also a portion of aluminum, scandium, and silicon co-deposition products, which have a slender strip-like morphology. This is also the main reason why scandium is more uniformly distributed on the upper and lower surfaces of the aluminum alloy.

[0044] The elemental content results of each embodiment 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 intermediate alloy

[0046]

[0047]

[0048] Based on the properties of the low-segregation scandium-containing aluminum master alloy obtained according to the present invention, it is expected to be applied to various fields such as aluminum alloy casting, scandium-containing aluminum alloy additive manufacturing, aluminum-silicon-scandium welding wire preparation, and silicon-containing wrought aluminum alloy preparation.

Claims

1. A method for preparing a low-segregation scandium-containing aluminum master alloy, characterized in that, Aluminum:silicon:scandium fluoride were mixed in a weight ratio of 10:(0.1~1.0):(0.4~1.0). Molten salt was added to the mixture and the mixture was heated and reduced at a temperature of 800~1200℃ for 0.5~2h. After the reduction was completed, the slag was removed and the mixture was cast to obtain a homogeneous aluminum-scandium-silicon master alloy, namely 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 chlorides and alkali metal fluorides, and the amount of molten salt added 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 the 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 in any proportion; the alkali metal fluoride is selected from lithium fluoride, sodium fluoride, potassium fluoride, or any mixture thereof in any proportion.

5. The method for preparing the low-segregation scandium-containing aluminum master alloy according to claim 1, characterized in that, The heating and reduction process involves a heating rate of 7–10 °C / min, with mechanical or electromagnetic stirring employed 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 co-precipitated products of aluminum, scandium and silicon, which have a slender strip-like morphology.

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-containing aluminum master alloy has an oxygen content of less than 100 ppm.

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

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