High-purity aluminum alloy liquid and preparation method thereof

Abstract

The invention relates to the technical field of nonferrous metallurgy, and particularly discloses high-purity aluminum alloy liquid and a preparation method thereof. According to the high-purity molten aluminum alloy, Al-Si-Mg series aluminum alloy serves as a base body, modified inorganic refined salt substances, citric acid, a modifier and a covering protective agent are added into the molten aluminum alloy for cooperative treatment, and degassing, deslagging and purification regulation and control over the molten aluminum alloy are achieved. The modified refining agent is prepared by mixing, drying and smashing various inorganic salts, and citric acid serves as small organic molecules and is used for complexing and regulating trace impurities and interface states in aluminum alloy liquid. The preparation method is simple in process and high in operability, the gas content and the number of inclusions of the molten aluminum alloy can be remarkably reduced, the purity and stability of the molten aluminum alloy are improved, and the preparation method is suitable for preparation of high-quality aluminum alloy castings.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal metallurgy and aluminum alloy material preparation technology, specifically relating to a high-purity aluminum alloy liquid and its preparation method. Background Technology

[0002] Aluminum alloys are widely used in the automotive, aerospace, rail transportation, and high-end equipment manufacturing industries due to their low density, high specific strength, good corrosion resistance, and excellent casting properties. In the preparation of aluminum alloy castings, the purity of the molten aluminum alloy directly affects the microstructure and mechanical properties of the final casting. Excessive dissolved gases, oxide inclusions, or non-metallic impurities in the molten aluminum alloy can easily lead to defects such as porosity, slag inclusions, and shrinkage porosity during casting, thereby reducing the density and reliability of the casting.

[0003] In existing technologies, the purification of molten aluminum alloy typically employs inorganic refining salts for degassing and slag removal, combined with covering protective agents and modifiers. However, traditional refining salts are mostly chloride or chloride-fluoride composite salts, which have a certain removal effect on macroscopic inclusions, but their ability to remove residual trace impurities, fine oxide inclusions, and interfacial active impurities in molten aluminum alloy is limited. Furthermore, during smelting, refining, and heat-insulating transport processes, molten aluminum alloy is still prone to secondary oxidation and the reintroduction of impurities, making it difficult to maintain stable purity.

[0004] Existing aluminum alloy molten metal purification technologies mainly focus on physical refining or inorganic salt refining methods, lacking measures to control the microscopic interface state within the molten metal, making it difficult to achieve deep removal and precise control of trace impurities. Therefore, further improving the purity and stability of molten aluminum alloy while ensuring good fluidity and casting performance remains a pressing technical problem to be solved in this field. Summary of the Invention

[0005] To overcome the limitations of existing aluminum alloy molten metal purification processes, such as limited removal of trace impurities, poor purity stability, and susceptibility to secondary oxidation pollution, the present invention aims to provide a high-purity aluminum alloy molten metal and its preparation method. This invention employs a synergistic approach combining modified inorganic refined salts and organic small-molecule citric acid, along with modifiers and protective coatings, to comprehensively treat the aluminum alloy molten metal. This achieves degassing, slag removal, and interface control, thereby obtaining a high-purity aluminum alloy molten metal. While maintaining good fluidity and casting performance, this invention significantly reduces the gas and inclusion content in the aluminum alloy molten metal, improving its purity and stability.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A high-purity aluminum alloy liquid, comprising the following raw materials in parts by weight: 95.0–99.5 parts aluminum alloy matrix; 0.2–1.5 parts modified refining agent; 0.01–0.20 parts citric acid; 0.01–0.10 parts modifier; and 0.05–0.50 parts covering and protecting agent; wherein the aluminum alloy matrix is ​​an Al-Si-Mg based aluminum alloy; the modified refining agent is a modified inorganic refined salt substance used for degassing, slag removal, and purification of the aluminum alloy liquid; and the citric acid is used to complex and regulate trace impurities and interface states in the aluminum alloy liquid.

[0008] Optionally, the modified refining agent comprises the following raw materials in parts by weight: 35-55 parts sodium chloride; 20-35 parts potassium chloride; 5-15 parts sodium fluoride; 3-10 parts calcium chloride; and 0.1-2.0 parts boric acid.

[0009] Optionally, the preparation method of the modified refining agent includes the following steps:

[0010] (1) Weigh the raw materials according to the weight parts of each component of the modified refining agent and mix them to obtain a mixture;

[0011] (2) The mixture is dried to obtain the material;

[0012] (3) The material is crushed and sieved to obtain the modified refining agent.

[0013] Optionally, the reaction conditions in step (1) are to mix the raw materials uniformly by mechanical stirring for 10 to 30 minutes at room temperature.

[0014] Optionally, the reaction conditions in step (2) are to dry at a temperature of 120 to 200°C for 1 to 3 hours to remove free water and adsorbed water from the raw materials.

[0015] Optionally, the reaction conditions in step (3) are to crush the dried material by mechanical crushing and sieve it to 40-120 mesh.

[0016] Optionally, the modifier is a mixture of metallic strontium and aluminum in a mass ratio of 1:9 to 1:19; the covering and protective agent is a mixture of sodium chloride and potassium chloride in a mass ratio of 1:1 to 3:1.

[0017] Optionally, a method for preparing high-purity aluminum alloy liquid includes the following steps:

[0018] S1, heating and melting the Al-Si-Mg aluminum alloy matrix to obtain a liquid aluminum alloy;

[0019] S2, add a refining agent to the aluminum alloy liquid for refining treatment, and add citric acid for impurity complexation and regulation treatment.

[0020] S3. Add modifier and protective agent to the treated aluminum alloy liquid to obtain high-purity aluminum alloy liquid.

[0021] Optionally, the reaction conditions in step S1 are to heat the Al-Si-Mg aluminum alloy matrix to 700-760°C to completely melt it, and to perform slag removal during the melting process to obtain a liquid aluminum alloy.

[0022] Optionally, the reaction conditions for step S2 are as follows: a refining agent is added to the aluminum alloy liquid at 680–740°C for 5–20 min, followed by the addition of citric acid and stirring for 5–15 min; the reaction conditions for step S3 are as follows: a modifier and a covering protectant are added to the aluminum alloy liquid at 650–720°C and kept at this temperature for 10–30 min to obtain a high-purity aluminum alloy liquid.

[0023] The beneficial effects of this invention are:

[0024] This invention introduces organic small-molecule citric acid into the aluminum alloy molten refining process and works synergistically with modified inorganic refining salts to achieve precise control over trace impurities and interface states in the aluminum alloy molten material. This significantly improves the removal efficiency of traditional inorganic refining salts for fine oxide inclusions and residual impurities, enabling the aluminum alloy molten material to maintain higher and more stable purity during melting, refining, and heat preservation. As a result, high-purity aluminum alloy molten material with low gas content and low inclusions can be obtained without increasing process complexity. Attached Figure Description

[0025] The invention will now be further described with reference to the accompanying drawings.

[0026] Figure 1 A comparison of the infrared spectra of the refining agent and the modified refining agent;

[0027] Figure 2 This is a comparison chart of the performance test results of samples with different ratios. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments. However, the present invention is not limited to the following embodiments. Equivalent adjustments made without departing from the spirit and essence of the present invention should also be considered to fall within the protection scope of the present invention.

[0029] Example 1:

[0030] The feasibility of using modified refining agents and citric acid in the purification of aluminum alloy liquid was verified under relatively low raw material usage and mild process conditions.

[0031] S1, Preparation of Modified Refining Agent

[0032] Weigh out 35 parts sodium chloride, 20 parts potassium chloride, 5 parts sodium fluoride, 3 parts calcium chloride, and 0.1 parts boric acid by weight. Mix them mechanically for 10 minutes at room temperature to ensure uniform mixing. Dry the resulting mixture at 120°C for 1 hour to remove free and adsorbed water. Mechanically pulverize the dried material and sieve it to 120 mesh to obtain the modified refining agent.

[0033] S2, Refining and Complexation Control of Molten Aluminum

[0034] The Al-Si-Mg aluminum alloy matrix was heated to 700℃ to completely melt it and slag was removed to obtain a liquid aluminum alloy. 0.2 parts of a modifying refining agent were added to the liquid aluminum alloy at 680℃ for 5 min. Then 0.01 parts of citric acid were added and stirred for 5 min.

[0035] S3, Deterioration and Covering Treatment

[0036] Add 0.01 parts of a modifier made of strontium and aluminum in a mass ratio of 1:9 to the aluminum alloy melt at 650℃, and add 0.05 parts of a covering and protective agent made of sodium chloride and potassium chloride in a mass ratio of 1:1. Keep at this temperature for 10 minutes to obtain a high-purity aluminum alloy melt.

[0037] Example 2:

[0038] The stability and repeatability of the high-purity aluminum alloy liquid preparation method of the present invention were verified under medium raw material ratio and conventional process conditions.

[0039] S1, Preparation of Modified Refining Agent

[0040] Weigh out 45 parts by weight of sodium chloride, 28 parts by weight of potassium chloride, 10 parts by weight of sodium fluoride, 6 parts by weight of calcium chloride, and 1.0 part by weight of boric acid. Mix them mechanically for 20 minutes at room temperature. Dry the mixture at 160℃ for 2 hours. Mechanically pulverize the dried material and sieve it to 80 mesh to obtain the modified refining agent. Figure 1 Infrared spectral comparison shows that the unmodified refining agent is at 4000-400 cm⁻¹ -1 The overall spectral lines are relatively flat within the range, except at approximately 3400 cm⁻¹. -1 A weak and broad –OH absorption peak appears at 1640 cm⁻¹, and extends to 1640 cm⁻¹. -1 The presence of a water molecule bending vibration absorption peak in the vicinity, with no obvious characteristic peaks observed in other wavelength ranges, indicates that the unmodified refining agent is mainly composed of halide salts with few infrared active groups. In contrast, the modified refining agent exhibits a significantly enhanced infrared spectrum, except for the –OH-related absorption peak, in the 1450–1200 cm⁻¹ range. -1 A new absorption band appears in the region, at 900–800 cm⁻¹. -1and 700-600cm -1 The presence of characteristic peaks in the region can be attributed to B–O and B–O–H vibrations. These newly added or enhanced absorption peaks were basically absent in the unmodified sample, indicating that boric acid was successfully introduced and had a significant impact on the structure of the refining agent. The infrared spectroscopy results show that the modified refining agent has formed a new boron-containing characteristic structure, providing a structural basis for its synergistic purification effect in the refining process of aluminum alloy liquid.

[0041] S2, Refining and Complexation Control of Molten Aluminum

[0042] The Al-Si-Mg aluminum alloy matrix was heated to 730℃ to melt and the slag was removed to obtain a liquid aluminum alloy. 0.8 parts of a modifying refining agent were added to the liquid aluminum alloy at 710℃ for refining treatment for 12 minutes. Then 0.10 parts of citric acid were added and stirring was maintained for 10 minutes.

[0043] S3, Deterioration and Covering Treatment

[0044] Add 0.05 parts of a modifier consisting of strontium and aluminum in a mass ratio of 1:14 to the molten aluminum alloy at 690℃, and add 0.25 parts of a covering and protective agent consisting of sodium chloride and potassium chloride in a mass ratio of 2:1. Keep at this temperature for 20 minutes to obtain a high-purity molten aluminum alloy.

[0045] Example 3:

[0046] Under conditions of high raw material consumption and strong process requirements, the extreme processing capability of this invention in deep purification of aluminum alloy liquid was verified.

[0047] S1, Preparation of Modified Refining Agent

[0048] Weigh out 55 parts sodium chloride, 35 parts potassium chloride, 15 parts sodium fluoride, 10 parts calcium chloride and 2.0 parts boric acid by weight, mix them mechanically at room temperature for 30 minutes; dry the mixture at 200℃ for 3 hours; mechanically pulverize the dried material and sieve it to 40 mesh to obtain the modified refining agent.

[0049] S2, Refining and Complexation Control of Molten Aluminum

[0050] The Al-Si-Mg aluminum alloy matrix was heated to 760℃ to melt and the slag was removed to obtain a liquid aluminum alloy. 1.5 parts of a modifying refining agent were added to the liquid aluminum alloy at 740℃ for refining treatment for 20 min. Then 0.20 parts of citric acid were added and stirring was maintained for 15 min.

[0051] S3, Deterioration and Covering Treatment

[0052] Add 0.10 parts of a modifier made of strontium and aluminum in a mass ratio of 1:19 to the aluminum alloy melt at 720℃, and add 0.50 parts of a covering and protective agent made of sodium chloride and potassium chloride in a mass ratio of 3:1. Keep at this temperature for 30 minutes to obtain a high-purity aluminum alloy melt.

[0053] Comparative Example 1:

[0054] Under moderate raw material ratios and conventional process conditions, the effect of replacing the modified refining agent in Example 2 with the unmodified refining agent on the preparation of high-purity aluminum alloy liquid was verified.

[0055] S1, Preparation of refining agent

[0056] Weigh out 45 parts sodium chloride, 28 parts potassium chloride, 10 parts sodium fluoride, and 6 parts calcium chloride by weight, and mix them mechanically for 20 minutes at room temperature. Dry the mixture at 160℃ for 2 hours. Mechanically pulverize the dried material and sieve it to 80 mesh to obtain the unmodified refining agent.

[0057] S2, Refining and Complexation Control of Molten Aluminum

[0058] The Al-Si-Mg aluminum alloy matrix was heated to 730℃ to melt and the slag was removed to obtain a liquid aluminum alloy. 0.8 parts of unmodified refining agent were added to the liquid aluminum alloy at 710℃ for refining treatment for 12 minutes. Then 0.10 parts of citric acid were added and stirring was maintained for 10 minutes.

[0059] S3, Deterioration and Covering Treatment

[0060] Add 0.05 parts of a modifier made of strontium and aluminum in a mass ratio of 1:14 to the aluminum alloy melt at 690℃, and add 0.25 parts of a covering and protective agent made of sodium chloride and potassium chloride in a mass ratio of 2:1. Keep at this temperature for 20 minutes to obtain the aluminum alloy melt.

[0061] Comparative Example 2:

[0062] Under moderate raw material ratios and conventional process conditions, the effect of not adding organic small molecule citric acid in Example 2 on the preparation effect of high-purity aluminum alloy liquid was verified.

[0063] S1, Preparation of Modified Refining Agent

[0064] Weigh out 45 parts sodium chloride, 28 parts potassium chloride, 10 parts sodium fluoride, 6 parts calcium chloride and 1.0 part boric acid by weight, mix them mechanically at room temperature for 20 minutes; dry the mixture at 160℃ for 2 hours; mechanically pulverize the dried material and sieve it to 80 mesh to obtain the modified refining agent.

[0065] S2, Refining and Complexation Control of Molten Aluminum

[0066] The Al-Si-Mg aluminum alloy matrix was heated to 730℃ to melt and the slag was removed to obtain a liquid aluminum alloy. 0.8 parts of a modifying refining agent were added to the liquid aluminum alloy at 710℃ for refining treatment for 12 minutes. Citric acid was not added and the mixture was stirred for 10 minutes.

[0067] S3, Deterioration and Covering Treatment

[0068] Add 0.05 parts of a modifier made of strontium and aluminum in a mass ratio of 1:14 to the aluminum alloy melt at 690℃, and add 0.25 parts of a covering and protective agent made of sodium chloride and potassium chloride in a mass ratio of 2:1. Keep at this temperature for 20 minutes to obtain the aluminum alloy melt.

[0069] Performance testing:

[0070] 1. Test method for gas content in molten aluminum alloy

[0071] Sampling of the aluminum alloy liquids obtained in Examples 1, 2, 3, and each comparative example was carried out under the same heat preservation conditions, with consistent sampling location, time, and method. The gas content in each aluminum alloy liquid sample was detected using an inert gas melting method. By comparing the changes in gas content in the aluminum alloy liquids of different examples and comparative examples, the effect of the synergistic effect of the modified refining agent and the organic small molecule citric acid on the degassing effect of the aluminum alloy liquid was evaluated.

[0072] 2. Test methods for inclusion content and distribution

[0073] The aluminum alloy molten materials obtained in Examples 1, 2, 3, and each comparative example were cast into standard metallographic specimens and cooled under the same cooling conditions. After cutting, grinding, and polishing the specimens, the non-metallic inclusions in the aluminum alloy specimens were observed and counted using an optical microscope. The quantity, size, and distribution characteristics of the inclusions were analyzed to compare the differences in the purity of the aluminum alloy molten materials between the different examples and the comparative examples.

[0074] 3. Density Index Test Method

[0075] The aluminum alloy liquids obtained in Examples 1, 2, 3, and each comparative example were cast and molded under both normal and reduced pressure conditions. Density was measured after the samples had completely solidified. By comparing the differences in density of samples formed under different pressure conditions, the amount of residual gas and micropore defects in the aluminum alloy liquid was evaluated, thereby reflecting the differences in the effectiveness of different embodiments and comparative examples in improving the internal quality of the aluminum alloy liquid.

[0076] 4. Methods for observing as-cast microstructure and porosity defects

[0077] The aluminum alloy liquids obtained in Examples 1, 2, 3 and each comparative example were cast into as-cast samples under the same process conditions. After metallographic preparation treatment, the as-cast microstructure of the samples was observed using an optical microscope. The focus was on analyzing the type, quantity and distribution of defects such as porosity, shrinkage cavities and inclusions. The differences in microstructure between different examples and comparative examples were compared and analyzed to evaluate the effect of the technical solution of the present invention on improving the stability of aluminum alloy liquid casting quality.

[0078] Table 1. Performance test results of aluminum alloy liquid in different embodiments and comparative examples.

[0079] Sample number <![CDATA[Gas content / mL·100g -1 > Number of inclusions (pieces / mm²) Density index / % Comprehensive evaluation of casting defects Example 1 0.18 4.6 2.5 A few fine pores, relatively dense structure Example 2 0.12 2.8 1.6 The tissue is dense and uniform with very few defects. Example 3 0.15 3.5 2.0 A small number of micropores, with uniform tissue. Comparative Example 1 0.30 8.9 4.8 The number of pores and inclusions has increased significantly. Comparative Example 2 0.34 10.2 5.6 Pores are concentrated, and inclusions are unevenly distributed.

[0080] As shown in Table 1, the high-purity aluminum alloy liquids prepared in Examples 1 to 3 are significantly better than the comparative examples in terms of key performance indicators such as gas content, number of inclusions, and density index. This indicates that the modified refining agent and citric acid synergistic treatment scheme adopted in this invention can effectively improve the overall purity and internal quality of the aluminum alloy liquid.

[0081] Regarding gas content, Figure 2 The gas content of the molten aluminum alloy in Examples 1, 2, and 3 was 0.18 mL / 100 g, respectively. -1 0.12mL·100g -1 and 0.15mL·100g -1 All were significantly lower than the 0.30 mL / 100 g of Comparative Example 1. -1 And 0.34 mL·100 g of Comparative Example 2 -1 Among them, Example 2 had the lowest gas content, indicating that under medium raw material ratios and conventional process conditions, the synergistic degassing effect of the modified refining agent and citric acid was the most significant.

[0082] Regarding the quantity of inclusions, Figure 2 The inclusion counts in Examples 1 through 3 were 4.6 inclusions / mm², 2.8 inclusions / mm², and 3.5 inclusions / mm², respectively, significantly lower than 8.9 inclusions / mm² in Comparative Example 1 and 10.2 inclusions / mm² in Comparative Example 2. Example 2, in particular, exhibited the lowest inclusion count, indicating that the synergistic effect of modified inorganic refining salts and citric acid effectively promotes the aggregation and removal of fine inclusions, thereby significantly improving the purity of the aluminum alloy melt.

[0083] Regarding the density index, Figure 2The density indices of Examples 1, 2, and 3 were 2.5%, 1.6%, and 2.0%, respectively, all significantly lower than those of Comparative Example 1 (4.8%) and Comparative Example 2 (5.6%). Furthermore, the comprehensive evaluation results of casting defects show that the aluminum alloy liquid obtained in Example 2 had the densest and most uniform microstructure, with very few porosity and inclusion defects, while the aluminum alloy liquid in the comparative examples exhibited problems such as concentrated porosity and uneven inclusion distribution.

[0084] In summary, this invention achieves efficient removal of gases and inclusions from molten aluminum alloys through the synergistic effect of modified refining agents and organic small-molecule citric acid. The overall performance of Examples 1 to 3 is superior to that of the comparative examples. Among them, Example 2 shows the best performance in terms of gas content, number of inclusions and density index, which fully demonstrates the significant advantages of the technical solution of this invention in improving the purity and stability of molten aluminum alloys.

Claims

1. A high-purity aluminum alloy liquid, characterized in that, The molten aluminum alloy comprises the following raw materials in parts by weight: 95.0–99.5 parts aluminum alloy matrix; 0.2–1.5 parts modified refining agent; Citric acid 0.01-0.20 parts; modifier 0.01-0.10 parts; covering and protective agent 0.05-0.50 parts; wherein the aluminum alloy matrix is ​​an Al-Si-Mg series aluminum alloy; the modifying and refining agent is a modified inorganic refining salt substance used for degassing, slag removal and purification treatment of aluminum alloy liquid; the citric acid is used to complex and regulate trace impurities and interface state in aluminum alloy liquid.

2. The high-purity aluminum alloy liquid according to claim 1, characterized in that, The modified refining agent comprises the following raw materials in parts by weight: 35-55 parts sodium chloride; 20-35 parts potassium chloride; 5-15 parts sodium fluoride; 3-10 parts calcium chloride; and 0.1-2.0 parts boric acid.

3. The high-purity aluminum alloy liquid according to claim 1 or 2, characterized in that, The preparation method of the modified refining agent includes the following steps: (1) Weigh the raw materials according to the weight parts of each component of the modified refining agent and mix them to obtain a mixture; (2) The mixture is dried to obtain the material; (3) The material is crushed and sieved to obtain the modified refining agent.

4. The high-purity aluminum alloy liquid according to claim 3, characterized in that, The reaction conditions for step (1) are to mix the raw materials uniformly for 10 to 30 minutes at room temperature using mechanical stirring.

5. The high-purity aluminum alloy liquid according to claim 3, characterized in that, The reaction conditions for step (2) are drying at a temperature of 120 to 200°C for 1 to 3 hours to remove free water and adsorbed water from the raw materials.

6. The high-purity aluminum alloy liquid according to claim 3, characterized in that, The reaction conditions for step (3) are to crush the dried material by mechanical crushing and sieve it to 40-120 mesh.

7. The high-purity aluminum alloy liquid according to claim 1, characterized in that, The modifier is a mixture of strontium and aluminum in a mass ratio of 1:9 to 1:19; the covering and protective agent is a mixture of sodium chloride and potassium chloride in a mass ratio of 1:1 to 3:

1.

8. A method for preparing high-purity aluminum alloy liquid, characterized in that, The preparation method includes the following steps: S1, heating and melting the Al-Si-Mg aluminum alloy matrix to obtain a liquid aluminum alloy; S2, add a refining agent to the aluminum alloy liquid for refining treatment, and add citric acid for impurity complexation and regulation treatment. S3. Add modifier and protective agent to the treated aluminum alloy liquid to obtain high-purity aluminum alloy liquid.

9. The method for preparing a high-purity aluminum alloy liquid according to claim 8, characterized in that, The reaction conditions for step S1 are to heat the Al-Si-Mg aluminum alloy matrix to 700-760°C to completely melt it, and to remove slag during the melting process to obtain molten aluminum alloy.

10. The method for preparing a high-purity aluminum alloy liquid according to claim 8, characterized in that, The reaction conditions for step S2 are as follows: a refining agent is added to the aluminum alloy liquid at 680-740°C for 5-20 minutes, followed by the addition of citric acid and stirring for 5-15 minutes. The reaction conditions for step S3 are as follows: a modifier and a covering protectant are added to the aluminum alloy liquid at 650-720°C and kept at this temperature for 10-30 minutes to obtain a high-purity aluminum alloy liquid.

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