A method for preparing high-purity aluminum based on magnetron crystallization directional solidification

Abstract

The present invention discloses a method for preparing high-purity aluminum based on magnetron crystallization directional solidification, which belongs to the technical field of high-purity metal material preparation. A metal aluminum raw material is heated and melted in a vacuum environment to form an aluminum melt, and after a pulse magnetic field is applied to the aluminum melt, a downward drawing method is used for directional solidification. The obtained solidified body is cut off from the top and bottom parts, and the middle section is high-purity aluminum. The method is to apply a pulse magnetic field during the directional solidification of the aluminum melt, so that the aluminum melt generates strong convection, so that the impurity elements in the aluminum melt are quickly diffused and enriched at the top and bottom, which is conducive to the discharge of impurities and the improvement of aluminum purity. At the same time, the pulse magnetic field can also inhibit the growth of the initial aluminum crystal nucleus and refine the grains, which is conducive to the uniformity of the high-purity aluminum structure.

Description

Technical Field

[0001] The invention relates to a method for purifying aluminum, in particular to a method for preparing high-purity aluminum based on magnetron crystallization and directional solidification, belonging to the technical field of high-purity metal materials. Background Art

[0002] High-purity aluminum (generally refers to aluminum with a purity of 99.99% or higher) has been widely used in many fields due to its excellent physical and chemical properties. High-purity aluminum is often used in electronic components, connecting wires and cables due to its excellent conductivity and light weight. In the manufacturing process of integrated circuits and other microelectronic devices, high-purity aluminum is one of the important materials to ensure electrical performance and corrosion resistance. The light weight and high strength characteristics of high-purity aluminum make it an important structural material in aircraft and spacecraft, helping to reduce weight and increase load-bearing capacity. In engines and other high-temperature components, high-purity aluminum is used to manufacture heat exchangers and radiators.

[0003] At present, the main methods for preparing high-purity aluminum are three-layer liquid electrolysis and segregation. The three-layer liquid electrolysis method uses the density difference between refined aluminum, electrolyte and anode alloy to form a liquid layer. Under the action of direct current, an electrochemical reaction occurs in the melt, that is, the aluminum in the anode alloy is electrochemically dissolved, and high-purity aluminum is precipitated at the cathode. The three-layer liquid electrolysis method consumes a lot of energy and can only produce 4N-5N high-purity aluminum. The segregation method is based on the uneven distribution characteristics of the composition of the material during the phase change process. In solid or liquid aluminum, the solubility of different elements is usually different. When the temperature drops to a certain critical point, some impurity elements will be preferentially discharged into specific areas of the liquid phase or solid phase to form a phase with uneven composition. This phenomenon can be used to separate aluminum and impurities. The segregation method is divided into directional solidification and zone melting. The zone melting method can achieve very high purity, but the efficiency is low and the production cost is high. The directional solidification method can achieve a higher purity and high efficiency, which is suitable for large-scale production. It is the main research direction of the current high-purity aluminum purification technology. However, during directional solidification, the precipitated elements accumulate in the remaining liquid phase. Due to the limited diffusion rate of impurity elements in the melt, the concentration of impurities in the melt at the front of the liquid-solid interface increases significantly. When the conditions are stable, the solute concentration of the solid phase increases accordingly. As a result, the purification effect is poor, and the impurity element content of the aluminum ingot solidified later is high. In order to make the impurity concentration in the melt at the front of the liquid-solid interface relatively stable, the impurities in the melt must be evenly distributed. Traditional methods include mechanical stirring, electromagnetic stirring and ultrasonic stirring. Mechanical stirring has a poor effect and is easy to bring in impurities. There is no direct contact between electromagnetic stirring and aluminum melt, which avoids wear and aluminum liquid contamination that may occur in mechanical stirring, and reduces the risk of oxidation and gas absorption of the melt. Ultrasonic stirring Ultrasonic waves are very short in wavelength, easy to scatter, and have poor penetration ability, which will limit the size of the ingots that can be produced, and ultrasound has limited effect on the homogenization of the internal components of the melt. In addition, during directional solidification, due to the slow solidification rate, nucleation is suppressed, and the solid phase crystals mainly grow layer by layer along the temperature gradient direction through the incorporation of melt atoms into their crystal lattices. The ingot structure is characterized by coarse columnar crystals, that is, the grains are elongated along the solidification direction, and equiaxed crystal structure cannot be obtained. With the advancement of science and technology, the purity of aluminum in the fields of semiconductors, aerospace, etc. is getting higher and higher, and the existing directional solidification method can no longer meet the actual needs. Summary of the invention

[0004] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for preparing high-purity aluminum based on magnetron crystallization directional solidification. Compared with the existing directional solidification technology, this method applies a pulsed magnetic field to the aluminum melt during directional solidification, and utilizes the pulsed magnetic field to induce strong convection in the aluminum melt, so that the impurity elements in the aluminum melt can quickly diffuse and be enriched at the top and bottom, which is beneficial to the discharge of impurities and improves the purity of aluminum. At the same time, the pulsed magnetic field can also inhibit the growth of the initial aluminum crystal nucleus and refine the grains, which is beneficial to the uniformity of the high-purity aluminum structure.

[0005] In order to achieve the above technical objectives, the present invention provides a method for preparing high-purity aluminum based on magnetron crystallization directional solidification. The method is to heat and melt the metallic aluminum raw material in a vacuum environment to form an aluminum melt. After applying a pulsed magnetic field to the aluminum melt, a downward-drawing method is used for directional solidification. The obtained solidified body is cut off from the top and bottom ends, and the middle section is high-purity aluminum.

[0006] The key to the technical solution of the present invention is that during the directional solidification of the aluminum melt, an external pulsed magnetic field is applied to the aluminum melt, and the pulsed magnetic field is fully utilized to cause the aluminum melt to produce strong convection, so that the impurity elements in the aluminum melt can quickly diffuse and enrich at the top and bottom ends, which is beneficial to the discharge of impurities and improves the purity of aluminum. At the same time, the pulsed magnetic field can also inhibit the growth of the initial aluminum crystal nucleus and refine the grains, which is beneficial to the uniformity of the high-purity aluminum structure, and well solves the defect that it is difficult to obtain a uniform crystal phase structure during the directional solidification process.

[0007] As a preferred solution, the purity of the metal aluminum raw material is ≥ 4N grade. The present invention uses metal aluminum of 4N grade or above as raw material to obtain high-purity aluminum of higher purity, for example, 4N grade metal aluminum can obtain 5N or 6N grade metal aluminum.

[0008] As a preferred solution, the temperature of the aluminum melt is 670-700° C. Maintaining the temperature of the aluminum melt within an appropriate range is conducive to the diffusion of impurities.

[0009] As a preferred solution, the intensity of the pulsed magnetic field is ≥ 0.8T, and the frequency is 100-1000Hz. The greater the magnetic field intensity and frequency, the stronger the convection of the aluminum melt caused by the pulsed magnetic field, the faster the diffusion of impurity elements in the aluminum melt, and the better the purification effect after directional solidification. The intensity of the pulsed magnetic field is more preferably 1-2T, and the frequency is more preferably 200-500Hz.

[0010] As a preferred solution, the directional solidification speed is 10-40 cm / h. The directional solidification speed needs to be kept within an appropriate range. If the directional solidification speed is too fast, it will affect the diffusion of impurities, while if the directional solidification speed is too slow, it will affect production efficiency.

[0011] As a preferred solution, the thickness of the top and bottom portions of the solidified body cut off accounts for 5% to 10% of the thickness of the entire solidified body. As impurities are mainly concentrated at the top and bottom of the solidified body, the aluminum purity of the entire solidified body is greatly improved after the top and bottom portions are cut off.

[0012] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects: The method provided by the present invention is based on directional solidification technology. During directional solidification, a pulsed magnetic field is applied to the aluminum melt to generate strong convection in the aluminum melt, so that the impurity elements in the aluminum melt are quickly diffused and enriched at the top and bottom, which is conducive to the discharge of impurities to improve the purity of aluminum. At the same time, the pulsed magnetic field can also inhibit the growth of the initial aluminum crystal nucleus and refine the grains. In summary, the application of the pulsed magnetic field can improve the purity of aluminum, refine the grains, and improve the uniformity of the high-purity aluminum structure. DETAILED DESCRIPTION

[0013] The following specific examples are intended to further illustrate the present invention rather than to limit the scope of protection of the claims.

[0014] Example 1 1) Heat and melt the 4N raw aluminum in a vacuum environment, and control the melt temperature to 680°C; 2) Apply a pulsed magnetic field to the aluminum melt with an intensity of 1T and a frequency of 200Hz; 3) Directional solidification is carried out by downward drawing method at a speed of 40 cm / h; 4) After the aluminum melt is completely solidified, the ingot is taken out and part of the top and bottom ends are cut off (the thickness accounts for 7.5% of the total ingot thickness). The purity of 85% of the input material reaches 5N, and the ingot structure is uniform, completely equiaxed crystal, and the average grain size is about 140μm.

[0015] Example 2 1) Heat and melt 5N raw aluminum in a vacuum environment, and control the melt temperature to 690°C; 2) Apply a pulsed magnetic field to the aluminum melt with an intensity of 2T and a frequency of 500Hz; 3) Directional solidification is carried out by downward drawing method at a speed of 25 cm / h; 4) After the aluminum melt is completely solidified, the ingot is taken out and part of the top and bottom ends are cut off (the thickness accounts for 10% of the total ingot thickness). The purity of 80% of the input material reaches 6N, and the ingot structure is uniform, completely equiaxed crystal, and the average grain size is about 100μm.

[0016] Comparative Example 1 High purity aluminum was prepared by the method of Example 1, except that the pulse magnetic field strength was 0.7 T. As a result, only about 50% of the input material had a purity of 5N, and the average grain size was about 180 μm.

[0017] Comparative Example 2 High purity aluminum was prepared by the method of Example 1, except that the frequency of the pulsed magnetic field was 50 Hz. As a result, only about 40% of the input material had a purity of 5N, and the average grain size was about 200 μm.

[0018] Comparative Example 3 High purity aluminum was prepared by the method of Example 1, except that no pulse magnetic field was applied. As a result, only about 20% of the input material had a purity of 5N, and the ingot structure was characterized by coarse columnar crystals, and no equiaxed crystal structure was obtained.

[0019] For the convenience of the reader, the above description focuses on representative examples of all possible embodiments, which introduce the principles of the present invention and illustrate the best way to implement the present invention. This description does not attempt to exhaust all possible variations. There may also be other variations or changes that are not described.

Claims

1. A method for preparing high-purity aluminum based on magnetron crystallization directional solidification, characterized in that: The metallic aluminum raw material is heated and melted in a vacuum environment to form an aluminum melt. After a pulsed magnetic field is applied to the aluminum melt, a downward-drawing method is used for directionally solidifying. The top and bottom ends of the obtained solidified body are cut off, and the middle section is high-purity aluminum.

2. The method for preparing high-purity aluminum based on magnetron crystallization directional solidification according to claim 1, characterized in that: The purity of the metallic aluminum raw material is ≥4N grade.

3. The method for preparing high-purity aluminum based on magnetron crystallization directional solidification according to claim 1, characterized in that: The temperature of the aluminum melt is 670-700°C.

4. A method for preparing high-purity aluminum based on magnetron crystallization directional solidification according to claims 1 to 3, characterized in that: The intensity of the pulsed magnetic field is ≥0.8T, and the frequency is 100-1000Hz.

5. A method for preparing high-purity aluminum based on magnetron crystallization directional solidification according to claims 1 to 3, characterized in that: The speed of the directional solidification is 10-40 cm / h.

6. A method for preparing high-purity aluminum based on magnetron crystallization directional solidification according to claims 1 to 3, characterized in that: The thickness of the top and bottom parts of the solidified body cut off accounts for 5% to 10% of the thickness of the entire solidified body.