Method for preparing 5N high-purity aluminum

Abstract

The invention belongs to the technical field of aluminum purification, and discloses a method for preparing 5N high-purity aluminum. The method comprises the following steps: 1) melting a 4N5 high-purity aluminum raw material, and removing impurity elements of which the equilibrium partition coefficient is greater than 1 to obtain a high-purity aluminum melt; (2) Fe and Si elements are added into the high-purity aluminum melt, and segregation liquid is prepared; 3) performing fractional crystallization treatment on the segregation liquid; and (4) the aluminum ingot is taken out, the end, with many impurities, of the aluminum ingot is removed, and the 5N high-purity aluminum is obtained through re-melting ingot forming. According to the method, the added Fe and Si impurity elements are effectively removed, and the impurity elements which are difficult to remove through a segregation method are not introduced. According to the method, the segregation rate of Fe and Si impurity elements exceeds 90%, the removal rate of the Fe and Si impurity elements ranges from 70% to 90%, and the 5N high-purity aluminum is obtained. The method is simple and easy to implement and low in production cost.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum purification, and in particular to a method for preparing 5N high-purity aluminum. Background Art

[0002] High-purity aluminum generally refers to pure aluminum materials with an aluminum purity greater than 99.95%. It is mainly used in the fields of wire manufacturing, capacitor electrode foil, sputtering target, semiconductor devices, optoelectronic storage media, computer storage hard disks, etc. Its application field is closely related to purity. The industry generally refers to high-purity aluminum alloys with a purity greater than 99.95% as 3N5, and high-purity aluminum with an aluminum content of ≥99.999% as 5N high-purity aluminum, which is mainly used in advanced manufacturing fields represented by semiconductor devices. The manufacturing process of 5N high-purity aluminum is complex and the production cost is high.

[0003] According to the basic principle, the current production of high-purity aluminum mainly includes three-layer liquid and segregation methods. The three-layer liquid production efficiency is high, but the energy consumption is high, and a large amount of hazardous waste containing fluorine will be generated. It can only produce 4N grade high-purity aluminum. The segregation method has the advantages of relatively low energy consumption, no pollutant emissions, and can obtain higher purity. The main principle of the segregation method is that the equilibrium composition of the solid phase and the liquid phase will change with the decrease of temperature during the solidification of the melt, and the redistribution of the solute elements will produce enrichment or depletion at the interface front, which will show uneven solute distribution on a macro scale. The main processes of the current segregation method are: step-by-step crystallization, directional solidification, and zone melting. Among them, the step-by-step crystallization method can be produced continuously and has high efficiency. It is the main method for producing high-purity aluminum, especially high-purity aluminum above 5N grade.

[0004] The fractional crystallization method in the segregation method is a common method for purifying high-purity aluminum. Its basic principle is: put the aluminum melt into a crucible, and a cooling device is placed on the side wall of the crucible to cool the local area. The aluminum liquid will solidify and crystallize in the lower temperature area to form aluminum primary crystals, and then the aluminum primary crystals are scraped from the side wall to the bottom by a tamping device. The aluminum crystals at the bottom gather to form large crystals, and then high-purity aluminum is obtained by solid-liquid separation. The impurity elements with equilibrium distribution coefficient K < 1 in aluminum can be effectively removed by the fractional crystallization method, and the smaller the K value, the easier it is to remove the impurity elements, but the impurity elements with K > 1 in aluminum cannot be removed by the fractional crystallization method.

[0005] Chinese invention patent application CN 118256736A discloses a purification device and a process for preparing 5N high-purity aluminum based on a fractional crystallization method, in which aluminum liquid is cooled in a longitudinally movable purification container to crystallize on the inner wall. When the solid aluminum is scraped off, the bottom of the purification container gradually moves downward as the amount of aluminum increases until it is completely separated from the container. However, the process is difficult to operate, the technology is complex, and high-precision equipment and mechanical structures are required. In addition, the purification efficiency is relatively low, which is not conducive to large-scale batch production of 5N high-purity aluminum.

[0006] In the process of preparing high-purity aluminum by segregation-based fractional crystallization, the outer cooling zone of the segregation furnace wall crystallizes due to air blowing for temperature reduction, and then the high-purity aluminum crystals are scraped off to the bottom of the segregation furnace by a ramming plate. The ramming plate is supported by a ramrod and moves up and down repeatedly to finally achieve the production of high-purity aluminum. During the movement of the ramming plate, it is necessary to overcome the resistance brought by the melt viscosity and can induce torque generation. The higher the melt viscosity, the greater the movement speed, and the greater the resistance and torque generated. When the resistance and torque are too large, it is easy to cause damage to the ramming plate and even break at the support point between the ramrod and the ramming plate, seriously affecting production efficiency and manufacturing cost.

[0007] How to reduce the viscosity of high-purity aluminum melt and ensure efficient segregation is crucial for the production of higher purity (5N and above). Moreover, in the production of higher purity high-purity aluminum, the efficient removal of Fe / Si impurities is very important. Although the segregation coefficients of Fe and Si during the solidification of Al melt are 0.023 and 0.1 respectively, both are elements that can be efficiently removed based on segregation; however, how to efficiently remove impurities while reducing the viscosity of aluminum melt to achieve efficient segregation is one of the problems that people urgently need to solve. Summary of the Invention

[0008] In order to overcome the shortcomings and deficiencies of the prior art, the purpose of the present invention is to provide a method for preparing 5N high-purity aluminum. The method of the present invention is simple, has high purification efficiency, realizes the preparation of 5N high-purity aluminum, and the method of the present invention can effectively produce 5N high-purity aluminum on a large scale.

[0009] To achieve the above purpose, the present invention adopts the following technical solutions:

[0010] A method for preparing 5N high-purity aluminum, comprising the following steps:

[0011] 1) Melting the 4N5 high-purity aluminum raw material, removing impurity elements with an equilibrium distribution coefficient greater than 1, and obtaining a high-purity aluminum melt;

[0012] 2) Adding Fe and Si elements to the high-purity aluminum melt to prepare a segregation liquid;

[0013] 3) Performing fractional crystallization treatment on the segregation liquid;

[0014] 4) Taking out the aluminum ingot, removing the end with more impurities of the aluminum ingot, and remelting it into an ingot to obtain 5N high-purity aluminum.

[0015] Removing the impurity elements with an equilibrium distribution coefficient greater than 1 in step 1) means adding an Al-B master alloy to the melt, mixing well, and keeping it static for heat preservation.

[0016] The addition amount of B is calculated based on the content of impurity elements with an equilibrium distribution coefficient greater than 1 in the high-purity aluminum raw material; B completely reacts with impurity elements (such as Cr, V, Ti) with an equilibrium distribution coefficient greater than 1 in the high-purity aluminum raw material to form precipitates (such as CrB2, TiB2, VB2, ZrB2 precipitates), which are deposited at the bottom of the melt, and the addition amount of B is determined by calculation.

[0017] The mixing is to stir and mix evenly, and the stirring time is 5 - 10 min; the standing and heat preservation time is 2 - 60 min.

[0018] After removing the impurity elements with an equilibrium distribution coefficient greater than 1 in step 1), refining and slag removal are carried out. The refining and slag removal is to add a refining agent and a slagging agent, mix evenly and then stand and heat preserve to remove the floating slag and bottom precipitates on the surface of the melt. The commercial grades of the refining agent and the slag removal agent are YT-J-1 and YT-D-4 respectively, and they are proportioned by mass ratio of 1:1, and then mixed evenly, and the total addition amount is 1% of the weight of the melt. The refining and slag removal is a conventional operation.

[0019] The melting temperature in step 1) is 720 - 800 °C.

[0020] The addition of Fe and Si elements in step 2) means adding Al-Fe master alloy and Al-Si master alloy, mixing evenly, and standing and heat preserving.

[0021] The Al-Fe master alloy is Al-20wt% Fe, and the Al-Si master alloy is Al-20wt% Si.

[0022] The mixing is to stir and mix evenly, and the stirring time is 5 - 10 min; the standing and heat preservation time is 2 - 60 min.

[0023] The prepared segregation liquid is used to detect the viscosity of the melt by a high-temperature melt viscosity detection device.

[0024] The addition amounts of Fe element and Si element in step 2) meet the following conditions: after adding Fe element and Si element to the 4N5 high-purity aluminum raw material, the total Fe content is 20 - 200 ppm, preferably 30 - 120 ppm; the total Si content is 20 - 200 ppm, preferably 30 - 120 ppm; and the mass content ratio of Fe / Si is (0.2 - 6):1, preferably (0.4 - 4):1, more preferably (0.5 - 4):1, and more preferably (1.5 - 3.5):1.

[0025] The stepwise crystallization treatment described in step 3) means maintaining the temperature of the segregation liquid at 665 - 670 °C, and then cooling the segregation liquid placed in the device through a cooling device provided on the side wall of the device. The primary aluminum crystals precipitate from the segregation liquid in contact with the side wall. While scraping off the primary aluminum crystals, the segregation liquid is stirred, and this is repeated. The primary aluminum crystals aggregate and grow to complete the stepwise crystallization.

[0026] Scrape off the primary aluminum crystals and compress them. Specifically, scrape off the primary aluminum crystals and press them to the bottom of the cavity filled with the segregation liquid in the device.

[0027] When scraping off the primary aluminum crystals and stirring the segregation liquid at the same time, the aggregation and growth of the primary aluminum crystals mean that the primary aluminum crystals are scraped off and compacted by the up - and - down movement of the crystal scraping device. And the crystal scraping device is provided with holes or gaps. While the primary aluminum crystals are scraped off and compressed, the aluminum melt passes through the holes or gaps. Through such back - and - forth movement, the primary aluminum crystals aggregate and grow.

[0028] The crystal scraping device is a ram disk ram rod or an annular plunger. The ram disk ram rod includes a ram disk and a ram rod provided on the ram disk. The ram disk and the ram rod are provided with holes, and the ram disk ram rod moves up and down.

[0029] The speed of the up - and - down movement of the crystal scraping device is 5 - 10 times / min.

[0030] The cooling means introducing a cooling gas for cooling. The introduction speed of the cooling gas is 10 - 50 m 3 / h.

[0031] For removing the end of the aluminum ingot with more impurities in step 4), the composition of the aluminum ingot can be detected by an instrument, and the part with more impurities can be removed, or 1 / 5 - 1 / 10 of the later - crystallized aluminum ingot can be removed.

[0032] The melting temperature for remelting into an ingot is 700 - 780 °C.

[0033] For the 5N high - purity aluminum of the present invention, the key impurities and their contents (by mass):

[0034] Fe < 2.5 ppm

[0035] Si < 2.5 ppm

[0036] Al > 99.999%

[0037] The balance is other impurities, including Cu < 1.0 ppm, Zn < 0.9 ppm, Ti < 1.0 ppm, V < 1.0 ppm, B < 1.0 ppm; among the remaining other impurities, there are Mn, Mg, Cr, Ni, Ga, Zr, Pb, etc., and the content of each single impurity < 0.5 ppm;

[0038] The total content of other impurities < 10 ppm.

[0039] Principle of the present invention:

[0040] Principle of melt viscosity reduction: The influence of iron atoms and silicon atoms on the viscosity of aluminum melt is relatively complex. When the addition amounts of Fe and Si are small, the addition of iron and silicon elements will reduce the viscosity of aluminum melt. The atomic radius of iron (about 126 ppm) and the atomic radius of silicon (about 118 pm) are smaller than that of aluminum atoms. The addition of Fe and Si elements will cause changes in the atomic structure of the melt, enabling a certain "lubricating" effect in the aluminum melt, making the relative sliding between aluminum atoms easier, and macroscopically manifested as a reduction in melt viscosity. From the perspective of the interatomic interaction energy, there is a certain interatomic interaction energy between aluminum atoms in the aluminum melt. When iron and silicon elements are added, new chemical bonds can be formed between them and aluminum atoms. The new Fe-Al bonds and Si-Al bonds are different from the Al-Al bonds, which will change the energy state of the entire melt system. These new chemical bonds make the binding between atoms relatively weak, making the relative movement between atoms easier, thus reducing the viscosity of the melt. At the same time, the presence of Fe atoms and Si atoms disrupts the orderly arrangement of aluminum atoms, making the structure of the melt relatively loose. During the liquid flow process, this change in structure reduces the internal friction of the melt, so the viscosity of the melt decreases.

[0041] Principle of segregation: The essence of the segregation method is the phenomenon of solute redistribution of solute atoms in the solid phase and liquid phase during the solidification of metals. Through the segregation method, impurity elements with an equilibrium distribution coefficient less than 1 in aluminum can be effectively removed. For example, the equilibrium distribution coefficients of Fe and Si are 0.023 and 0.10 respectively in aluminum, and the impurity elements with a smaller equilibrium distribution coefficient in aluminum are easier to remove.

[0042] Process characteristics: The 5N high-purity aluminum in the present invention is based on 4N5 high-purity aluminum, and further reduces the Fe / Si impurities therein to meet the 5N purity requirement. The present invention proposes a "reverse" path, adding Fe / Si impurities to 4N5 to reduce the viscosity, and then achieving efficient removal based on segregation. Without introducing other impurities, Fe / Si impurities are introduced into the aluminum melt. During fractional crystallization, the temperature at the bottom of the device is slightly higher than the melting point of aluminum, and cooling gas is passed through the sidewall cooling pipes. Using the segregation effect, high-purity aluminum primary crystals are precipitated on the sidewall. Through the up-and-down movement of the ram rod of the ram plate, the aluminum primary crystals are scraped off to the bottom of the device and compacted, squeezing out the aluminum melt rich in impurities between the crystals. The holes on the ram rod of the ram plate facilitate the passage of the aluminum melt. In the initial stage of fractional crystallization, the ram rod of the ram plate can effectively scrape off the primary crystals. As the aluminum primary crystals accumulate, although the viscosity of the melt increases, the stroke of the ram rod of the ram plate decreases and the resistance decreases, ensuring the smooth progress of segregation. By repeating the operation, the aluminum primary crystals aggregate into larger and purer aluminum crystals, realizing the purification of aluminum. Continuous fractional crystallization can continuously remove Fe and Si impurities, reducing the content of Fe / Si impurities in the final aluminum ingot to less than 2.5 ppm. This method is applicable to the purification of aluminum by fractional crystallization. Compared with the traditional segregation method, it has low cost, simple addition, does not introduce new impurities, and is conducive to large-scale production of 5N high-purity aluminum.

[0043] Compared with the existing methods, the present invention has the following outstanding advantages and beneficial effects:

[0044] (1) Based on a reverse research idea, the present invention pre-adds Fe / Si to high-purity aluminum to reduce the melt viscosity, which is more conducive to the smooth progress of the fractional crystallization method. The process is relatively simple and the cost is relatively low.

[0045] (2) The present invention can achieve efficient removal of key impurity elements (Fe and Si) in high-purity aluminum, and the removal rates of Fe and Si impurity elements are both close to 90%.

[0046] (3) The reduction range of the melt viscosity after adding Fe / Si is between 30% and 50%, and the segregation rate of adding Fe / Si elements can reach more than 90%, ensuring that the content of key impurity elements in the product meets the regulations.

[0047] (4) The preparation process of the present invention is relatively simple, without applying other coarse purification materials, without using complex equipment, with low cost and energy consumption, and is applicable to batch production and large-scale manufacturing of 5N ultra-high-purity aluminum for the semiconductor industry. Description of the Drawings

[0048] Figure 1 It is the main view sectional structure schematic diagram of the fractional crystallization furnace used in the present invention; 1 - furnace cover, 2 - ram rod, 3 - ram plate, 4 - hole, 5 - aluminum melt, 6 - cooling gas pipe, 7 - solid aluminum, 8 - cooling part, 9 - aluminum primary crystal, 10 - heating coil, 11 - furnace shell;

[0049] Figure 2 It is a diagram showing the fracture at the connection between the rammer and the ram disk due to excessive melt viscosity during the step crystallization process;

[0050] Figure 3 It is the change in melt viscosity of high-purity aluminum at 680 °C and 670 °C in Comparative Examples 1-5 and Examples 1-5;

[0051] Figure 4 It is the segregation rate of Fe and Si impurities in the high-purity aluminum samples prepared in Comparative Example 3, Comparative Example 5, and Examples 1-5;

[0052] Figure 5 It is the removal rate of Fe and Si impurity elements in the high-purity aluminum samples prepared in Comparative Example 3, Comparative Example 5, and Examples 1-5. Detailed implementation mode

[0053] The present invention will be described in detail below with reference to specific embodiments, but the implementation modes of the present invention are not limited thereto. Taking 4N5 high-purity aluminum raw material as an example, the process flow and implementation effects are described based on the comparative examples and examples. The segregation rate is the removal degree of Fe / Si impurity elements before and after step crystallization, and the removal rate is the removal degree of the content of Fe / Si impurity elements after step crystallization compared with the content of Fe / Si in the 4N5 raw material.

[0054] In the embodiment of the present invention, a cross-sectional view of the device (step crystallization furnace) used in step crystallization is as Figure 1 shown, including a furnace body with a cavity, a rammer 2, a ram disk 3, a furnace lid 1, and a furnace shell 11. A heating coil 10 is provided on the outer side of the furnace body, and a cooling device is provided on one side wall of the furnace body. One end of the rammer 2 is arranged on the ram disk 3, and the other end of the rammer 2 passes through a pore on the furnace lid 1. The ram disk 3 moves up and down with the rammer 2; the furnace body and the heating coil 10 are arranged inside the furnace shell 11, the upper part of the furnace body is open and covered by the furnace lid 1; the cooling device includes a cooling gas pipe 6, and the cooling gas pipe passes through the furnace shell. There are holes 4 on the ram disk and the rammer.

[0055] In the furnace body of the present invention, there is an aluminum melt 5. The present invention transports cooling gas through the cooling gas pipe 6 to the side wall 8 (i.e., the cooling part) of the furnace body to cool the melt in the furnace body. High-purity aluminum primary crystals 9 precipitate at the side wall. Next, the small aluminum primary crystals are scraped to the bottom of the furnace body (such as a crucible) and compacted through the up-and-down movement of the ram disk and the rammer. The compaction action can also squeeze out the aluminum melt rich in impurity elements between the crystals. The holes 4 on the ram disk and the rammer can allow the aluminum melt to pass through. Repeating this process makes the aluminum primary crystals at the bottom gradually aggregate and grow into larger and purer aluminum crystals 7, achieving the purpose of aluminum purification.

[0056] Figure 2 It is a diagram showing the fracture at the connection between the rammer and the ram disk due to excessive melt viscosity during the step crystallization process.

[0057] Comparative Example 1: 4N5 high-purity aluminum

[0058] The raw material used in this comparative example is 4N5 high-purity aluminum (mass content, Fe 10 ppm, Si 8 ppm, Cu 12 ppm, Mn 0.5 ppm, Mg 2.0 ppm, Cr 0.3 ppm, Ni 1.0 ppm, Zn 2.0 ppm, Ga 3.0 ppm, V 0.1 ppm, B 1.7 ppm, Ti 0.3 ppm, Zr 0.1 ppm, Pb 1.4 ppm, Al 99.9957%, the same throughout the text). The specific steps and process parameters are as follows:

[0059] (1) Preparation of high-purity aluminum: Select 4N5 high-purity aluminum raw materials and weigh the required weight to prepare two portions of high-purity aluminum, one for detecting the viscosity of the high-purity aluminum melt and the other for subsequent fractional crystallization treatment.

[0060] (2) Melt pretreatment: Put the high-purity aluminum raw materials into a pretreatment furnace to melt at a melting temperature of 720 °C. After melting, calculate according to the impurity content in the raw materials and add Al-B master alloy for impurity removal (the amount of B added is determined by calculating to completely react with Cr, V, and Ti in the high-purity aluminum raw materials to form precipitates of CrB2, TiB2, VB2, and ZrB2). After electromagnetic stirring and uniform mixing, let it stand and heat to obtain a segregated liquid.

[0061] (3) Viscosity detection: Put the high-purity aluminum used for melt viscosity detection into a crucible inside an ultra-high-temperature rheometer, set the temperature to one hour above the melting point of the Al melt for heating. After melting, introduce argon gas at a gas flow rate of 260 mL / min, and then measure the rotational speed of 0.1 revolutions per second, and detect the melt viscosity at 680 °C and 670 °C respectively.

[0062] (4) Fractional crystallization treatment: Transfer the segregated liquid obtained in step (2) into a segregation furnace for fractional crystallization treatment. Keep the aluminum melt at a temperature of 670 °C, introduce cooling gas (the temperature of the cooling gas is at room temperature) into the cooling pipes on the side wall of the segregation furnace, and the gas flow rate is 20 m 3 / h. High-purity aluminum primary crystals precipitate on the side wall of the segregation furnace. Next, through the up-and-down movement of the ram rod (the movement speed is 5 times / min), scrape the fine aluminum primary crystals to the bottom of the crucible and compact them. The compaction action can also squeeze out the aluminum melt rich in impurity elements between the crystals. The holes on the ram rod allow the aluminum melt to pass through. Repeat this process so that the aluminum primary crystals at the bottom gradually aggregate and grow into larger and purer aluminum crystals, achieving the purpose of aluminum purification (the aluminum crystals crystallize from the bottom upwards, and the time is about 12 h).

[0063] (5) Remelting into ingots: After the fractional crystallization is completed, the concentrated liquid inside the crucible is poured out. After the pouring of the concentrated liquid is completed, the head of the aluminum ingot is cut off (the crystallization process crystallizes gradually from the bottom to the top of the fractional crystallization furnace. The first part to crystallize at the bottom has a higher purity, and the last part to crystallize is the top, that is, the head, and 1 / 5 - 1 / 10 of the aluminum ingot needs to be cut off, or the components of each part of the aluminum ingot are detected by an instrument, and the part with more impurities is cut off). Next, the remaining aluminum ingot is remelted and then subjected to electromagnetic stirring to make the composition uniform, and then cast into an ingot to obtain high-purity aluminum.

[0064] The melt viscosities of the 4N5 high-purity aluminum melt detected in step (3) at 680 °C and 670 °C are 20.2 [Pa·s] and 22.3 [Pa·s] respectively. By performing the steps in Comparative Example 1, it is found that in the early stage of the fractional crystallization treatment in step (4), due to the too high melt viscosity, the resistance during the up-and-down movement of the ram rod of the ram is large, resulting in the fracture of the ram rod of the ram and the failure of the fractional crystallization process. The connection between the ram and the ram rod breaks, as Figure 2 shown.

[0065] Component detection: Detect the components of the high-purity aluminum obtained in step (5).

[0066] The content of Al in the components of the high-purity aluminum obtained in the detection furnace is 99.9957%, the content of Fe impurity element is 10.0 ppm, and the content of Si impurity element is 8.0 ppm. The Fe and Si impurity elements are not removed, and the prepared high-purity aluminum cannot meet the component requirements of 5N high-purity aluminum.

[0067] Comparative Example 2: 4N5 high-purity aluminum + Fe (mass content is 40 ppm)

[0068] In this comparative example, 4N5 high-purity aluminum and Al-20Fe master alloy are used as raw materials for batching, and the composition of 4N5 high-purity aluminum is the same as that in Comparative Example 1. By calculation, the mass content of Fe element in high-purity aluminum (that is, the mixed system of 4N5 high-purity aluminum and Al-20Fe master alloy) is controlled to be 40 ppm. The specific steps and process parameters:

[0069] (1) Preparation of high-purity aluminum: According to the mass contents of Fe and Si elements in high-purity aluminum being 40 ppm and 8.0 ppm respectively, calculate and weigh the required 4N5 high-purity aluminum and Al-20Fe master alloy for high-purity aluminum, and prepare two samples according to the requirements, one for melt viscosity detection and the other for subsequent fractional crystallization treatment.

[0070] (2) Melt pretreatment: Put high-purity aluminum raw materials into a pretreatment furnace for melting. The melting temperature is 740 °C. After melting, calculate according to the impurity content in the raw materials and add Al-B master alloy for impurity removal (the amount of B added is determined by calculating to completely react with Cr, V, and Ti in the high-purity aluminum raw materials to form precipitates of CrB2, TiB2, VB2, and ZrB2). Then refine and remove slag. Next, add Al-20Fe master alloy to the high-purity aluminum melt, stir evenly by electromagnetic stirring and then keep it warm statically, so that the mass content of Fe element in the melt is 40 ppm to obtain a segregation liquid.

[0071] (3) Viscosity detection: Conduct a viscosity test on the melt prepared in step (2).

[0072] (4) Stepwise crystallization treatment: Transfer the segregation liquid obtained in step (2) into a segregation furnace for stepwise crystallization treatment. Keep the aluminum melt at a temperature of 669 °C, and introduce a cooling gas into the cooling pipes on the side wall of the segregation furnace. The gas inlet speed is 30 m 3 / h. High-purity aluminum primary crystals precipitate on the side wall of the segregation furnace. Next, scrape the fine aluminum primary crystals to the bottom of the crucible and compact them through the up-and-down movement of the ramming plate rammer (the movement speed is 6 times / min). The compaction action can also squeeze out the aluminum melt rich in impurity elements between the crystals. The holes on the ramming plate rammer can allow the aluminum melt to pass through. Repeat this process so that the aluminum primary crystals at the bottom gradually aggregate and grow into larger and purer aluminum crystals, achieving the purpose of aluminum purification.

[0073] (5) Remelting and ingot casting: Pour out the concentrated liquid inside the crucible after completing stepwise crystallization. After pouring out the concentrated liquid, cut off the head of the aluminum ingot (it is necessary to cut off 1 / 5 - 1 / 10 of the aluminum ingot, or detect the components of each part of the aluminum ingot by an instrument and cut off the part with more impurities). Next, remelt the remaining aluminum ingot and use electromagnetic stirring to make the composition uniform, and then cast it into an ingot to obtain high-purity aluminum.

[0074] Composition detection: Use an instrument to detect the composition of the high-purity aluminum obtained in step (5).

[0075] The melt viscosities of the high-purity aluminum melt detected in step (3) at 680 °C and 670 °C are 15.1 [Pa·s] and 18.1 [Pa·s] respectively, which are lower than the melt viscosity of 4N5 high-purity aluminum in Comparative Example 1. By performing the steps in Comparative Example 2, it is found that in the early stage of the stepwise crystallization treatment in step (4), due to the too high melt viscosity, the resistance during the up-and-down movement of the ramming plate rammer is large, resulting in the fracture of the ramming plate rammer and the failure of the stepwise crystallization process.

[0076] The Al content in the high-purity aluminum obtained from the detection furnace is 99.9931%, the content of Fe impurity element is 38 ppm, the content of Si impurity element is 7.8 ppm, and the segregation rates of Fe and Si impurity elements are 5.0% and 2.5% respectively. The prepared high-purity aluminum cannot meet the composition requirements of 5N high-purity aluminum.

[0077] Comparative Example 3: 4N5 high-purity aluminum + Fe (mass content is 80 ppm)

[0078] In this comparative example, 4N5 high-purity aluminum and Al-20Fe master alloy are used as raw materials for batching. The composition of 4N5 high-purity aluminum is the same as that in Comparative Example 1. By calculation, the mass content of the final Fe element in the high-purity aluminum (i.e., the mixed system of 4N5 high-purity aluminum and Al-20Fe master alloy) is controlled to be 80 ppm. The specific steps and processes are as follows:

[0079] (1) Preparation of high-purity aluminum: According to the mass contents of Fe and Si elements in the high-purity aluminum being 80 ppm and 8.0 ppm respectively, calculate and weigh the required 4N5 high-purity aluminum and Al-20Fe master alloy for high-purity aluminum, and prepare two samples according to the requirements. One is used for melt viscosity detection, and the other is used for subsequent fractional crystallization treatment.

[0080] (2) Melt pretreatment: Put the high-purity aluminum raw materials into the pretreatment furnace for melting. The melting temperature is 760 °C. After melting, calculate according to the impurity content in the raw materials and add Al-B master alloy for impurity removal. Refine and remove slag. Next, add Al-20Fe master alloy to the high-purity aluminum melt, stir evenly by electromagnetic stirring and then keep it warm statically to make the mass content of Fe element in the melt be 80 ppm, and obtain the segregation liquid.

[0081] (3) Viscosity detection: Conduct viscosity testing on the melt prepared in step (2). The testing method is the same as that in Comparative Example 1.

[0082] (4) Fractional crystallization treatment: Transfer the segregation liquid obtained in step (2) into the segregation furnace for fractional crystallization treatment. Keep the aluminum melt at a temperature of 667 °C, and introduce cooling gas into the cooling pipes on the side wall of the segregation furnace. The gas introduction speed is 35 m 3 / h. High-purity aluminum primary crystals precipitate on the side wall of the segregation furnace. Next, scrape the fine aluminum primary crystals to the bottom of the crucible and compact them through the up-and-down movement (movement speed is 7 times / min) of the ram rod of the ram. The compaction action can also squeeze out the aluminum melt rich in impurity elements between the crystals. The holes on the ram rod of the ram can allow the aluminum melt to pass through. Repeat this process to gradually aggregate and grow the aluminum primary crystals at the bottom into larger and purer aluminum crystals, which can achieve the purpose of aluminum purification.

[0083] (5) Remelting into ingots: The specific operation process is exactly the same as that in Comparative Example 1.

[0084] The melt viscosities of the high-purity aluminum melt detected in Comparative Example 3 at 680 °C and 670 °C were 13.2 [Pa·s] and 15.6 [Pa·s] respectively, which were lower than those of the 4N5 high-purity aluminum in Comparative Example 1 and Comparative Example 2. By performing the steps in Comparative Example 3, it was found that the fractional crystallization process of step (4) could be successfully completed. Finally, the content of Al in the obtained high-purity aluminum was 99.9980%, the content of Fe impurity element was 3.0 ppm, the content of Si impurity element was 3.5 ppm, and the segregation rates of Fe and Si impurity elements were 96.3% and 56.3% respectively. Compared with Comparative Example 1, the removal rates of Fe and Si impurity elements were 70.0% and 56.3% respectively, and the prepared high-purity aluminum could not meet the compositional requirements of 5N high-purity aluminum.

[0085] Comparative Example 4: 4N5 high-purity aluminum + Si (mass content is 40 ppm)

[0086] In this comparative example, 4N5 high-purity aluminum and Al-20Si master alloy were used as raw materials for batching, and the composition of 4N5 high-purity aluminum was the same as that in Comparative Example 1. By calculation, the mass content of Si element in the final high-purity aluminum (i.e., the mixed system of 4N5 high-purity aluminum and Al-20Si master alloy) was controlled to be 40 ppm. The specific steps and processes are as follows:

[0087] (1) Preparation of high-purity aluminum: According to the mass contents of Fe and Si elements in high-purity aluminum being 10 ppm and 40 ppm respectively, the required 4N5 high-purity aluminum and Al-20Si master alloy for high-purity aluminum were calculated and weighed respectively, and two samples were prepared according to the requirements, one for melt viscosity detection and the other for subsequent fractional crystallization treatment.

[0088] (2) Melt pretreatment: The high-purity aluminum raw materials were put into a pretreatment furnace for melting, the melting temperature was 740 °C, and after melting, according to the impurity content in the raw materials, Al-B master alloy was added for impurity removal. Refining and slag removal. Next, Al-20Si master alloy was added to the high-purity aluminum melt, and after electromagnetic stirring and uniform mixing, it was left standing for heat preservation, so that the mass content of Si element in the melt was 40 ppm, and a segregated liquid was obtained.

[0089] (3) Viscosity detection: The viscosity of the melt prepared in step (2) was tested, and the test method was the same as that in Comparative Example 1.

[0090] (4) Fractional crystallization treatment: The segregated liquid obtained in step (2) was transferred to a segregation furnace for fractional crystallization treatment. The aluminum melt was maintained at a temperature of 669 °C, and cooling gas was introduced into the cooling pipes on the side wall of the segregation furnace, and the gas introduction speed was 30 m 3 / h, high-purity aluminum primary crystals precipitate on the side wall of the segregation furnace. Next, through the up-and-down movement of the ramming plate rammer (the movement speed is 6 times / min), the fine aluminum primary crystals are scraped to the bottom of the crucible and compacted. The compaction action can also squeeze out the aluminum melt rich in impurity elements between the crystals. The holes on the ramming plate rammer allow the aluminum melt to pass through. Repeating this process makes the aluminum primary crystals at the bottom gradually aggregate and grow into larger and purer aluminum crystals, achieving the purpose of aluminum purification.

[0091] (5) Remelting and ingot casting: The specific operation process is exactly the same as that of Comparative Example 1.

[0092] The melt viscosities of the high-purity aluminum melt detected in Comparative Example 4 at 680 °C and 670 °C are 14.4 [Pa·s] and 16.3 [Pa·s] respectively, which are lower than the melt viscosity of 4N5 high-purity aluminum in Comparative Example 1. By performing the steps in Comparative Example 4, it is found that in the early stage of the fractional crystallization treatment in step (4), due to the too high melt viscosity, the resistance during the up-and-down movement of the ramming plate rammer is large, resulting in the fracture of the ramming plate rammer and the failure of the fractional crystallization process. Using an instrument to detect the composition of the high-purity aluminum obtained in step (5), the Al content in the high-purity aluminum obtained in the detection furnace is 99.9931%, the content of Fe impurity element is 9.6 ppm, the content of Si impurity element is 37 ppm, and the segregation rates of Fe and Si impurity elements are 4.0% and 7.5% respectively. The prepared high-purity aluminum cannot meet the composition requirements of 5N high-purity aluminum.

[0093] Comparative Example 5: 4N5 high-purity aluminum + Si (mass content is 80 ppm)

[0094] In this comparative example, 4N5 high-purity aluminum and Al-20Si master alloy are used as raw materials for batching. The composition of 4N5 high-purity aluminum is the same as that of Comparative Example 1. By calculation, the mass content of Si element in the high-purity aluminum (i.e., the mixed system of 4N5 high-purity aluminum and Al-20Si master alloy) is controlled to be 80 ppm. The specific steps and processes are as follows:

[0095] (1) Preparation of high-purity aluminum: According to the mass contents of Fe and Si elements in high-purity aluminum being 10 ppm and 80 ppm respectively, calculate and weigh the required 4N5 high-purity aluminum and Al-20Si master alloy for high-purity aluminum, and prepare two samples according to the requirements, one for melt viscosity detection and the other for subsequent fractional crystallization treatment.

[0096] (2) Melt pretreatment: Put the high-purity aluminum raw materials into a pretreatment furnace for melting at a melting temperature of 750 °C. After melting, calculate according to the impurity content in the raw materials and add Al-B master alloy for impurity removal. Refine and remove slag. Next, add Al-20Si master alloy to the high-purity aluminum melt, stir evenly by electromagnetic stirring and then keep it static for heat preservation to make the mass content of Si element in the melt be 80 ppm, obtaining a segregation liquid.

[0097] (3) Viscosity detection: The melt prepared in step (2) is subjected to viscosity testing, and the testing method is the same as that of Comparative Example 1.

[0098] (4) Stepwise crystallization treatment: The segregated liquid obtained in step (2) is transferred into a segregation furnace for stepwise crystallization treatment. The aluminum melt is maintained at a temperature of 668 °C, and cooling gas is introduced into the cooling pipes on the side wall of the segregation furnace. The gas introduction speed is 35 m 3 / h. High-purity primary aluminum crystals precipitate on the side wall of the segregation furnace. Next, the small primary aluminum crystals are scraped to the bottom of the crucible and compacted by the up-and-down movement of the ramming disc rod (the movement speed is 7 times / min). The compaction action can also squeeze out the aluminum melt rich in impurity elements between the crystals. The holes on the ramming disc rod allow the aluminum melt to pass through. Repeating this process makes the primary aluminum crystals at the bottom gradually aggregate and grow into larger and purer aluminum crystals, achieving the purpose of aluminum purification.

[0099] (5) Remelting into ingots: The specific operation process is exactly the same as that of Comparative Example 1.

[0100] The melt viscosities of the high-purity aluminum melt detected in Comparative Example 5 at 680 °C and 670 °C are 12.1 [Pa·s] and 14.3 [Pa·s] respectively, which are lower than the melt viscosity of 4N5 high-purity aluminum in Comparative Example 1. By performing the steps in Comparative Example 5, it is found that the step (4) stepwise crystallization process can be successfully completed. Finally, the Al content in the obtained high-purity aluminum is 99.9982%, the Fe impurity element content is 2.7 ppm, the Si impurity element content is 3.0 ppm, and the segregation rates of Fe and Si impurity elements are 73.0% and 96.3% respectively. Compared with Comparative Example 1, the removal rates of Fe and Si impurity elements are 73.0% and 62.5% respectively, and the prepared high-purity aluminum cannot meet the component requirements of 5N high-purity aluminum.

[0101] To further illustrate the implementation effects of the present invention, the present invention will be described below in conjunction with embodiments.

[0102] It should be noted that the raw materials used in the embodiments are all 4N5 high-purity aluminum, and the components are the same as those of the comparative examples. The significant difference between all the embodiments and the comparative examples is that Fe and Si are added simultaneously, and the addition amounts of Fe and Si and their Fe / Si mass ratios are different in different embodiments.

[0103] Example 1: 4N5 high-purity aluminum + Fe (mass content is 40 ppm) + Si (mass content is 40 ppm)

[0104] In this embodiment, 4N5 high-purity aluminum, Al-20Fe master alloy, and Al-20Si master alloy are used as raw materials for batching, and the composition of 4N5 high-purity aluminum is the same as that in Comparative Example 1. By calculation, the mass contents of Fe and Si elements in the high-purity aluminum (i.e., the mixed system of 4N5 high-purity aluminum, Al-20Fe master alloy, and Al-20Si master alloy) are both controlled to be 40 ppm. The specific steps and process parameters are as follows:

[0105] (1) Preparation of high-purity aluminum: According to the mass contents of Fe and Si elements in the high-purity aluminum being both 40 ppm, calculate and weigh the required 4N5 high-purity aluminum, Al-20Fe master alloy, and Al-20Si master alloy for the target high-purity aluminum respectively, and prepare two samples according to the requirements, one for melt viscosity detection and the other for the next segregation purification experiment.

[0106] (2) Melt pretreatment: Put the high-purity aluminum raw materials into a pretreatment furnace for melting. The melting temperature is 760 °C. After melting, calculate according to the impurity content in the raw materials and add Al-B master alloy for impurity removal (the amount of B added is determined by calculating to completely react with Cr, V, and Ti in the high-purity aluminum raw materials to form precipitates of CrB2, TiB2, VB2, and ZrB2). Refine and remove slag. Next, add a certain amount of Al-20Fe master alloy and Al-20Si master alloy to the high-purity aluminum melt, stir evenly by electromagnetic stirring and then keep it warm statically, so that the mass contents of Fe and Si elements in the melt are both 40 ppm to obtain a segregation liquid.

[0107] (3) Viscosity detection: Conduct viscosity tests on the melt prepared in step (2), and the test method is the same as that in Comparative Example 1.

[0108] (4) Stepwise crystallization treatment: Transfer the segregation liquid obtained in step (2) into a segregation furnace for stepwise crystallization treatment. Keep the aluminum melt at a temperature of 668 °C, and introduce cooling gas into the cooling pipes on the side wall of the segregation furnace. The gas introduction speed is 30 m 3 / h. High-purity aluminum primary crystals precipitate on the side wall of the segregation furnace. Next, scrape the fine aluminum primary crystals to the bottom of the crucible and compact them through the up-and-down movement of the ram rod of the rammer (the movement speed is 6 times / min). The compaction action can also squeeze out the aluminum melt rich in impurity elements between the crystals. The holes on the ram rod of the rammer can allow the aluminum melt to pass through. Repeat this process so that the aluminum primary crystals at the bottom gradually aggregate and grow into larger and purer aluminum crystals, which can achieve the purpose of aluminum purification.

[0109] (5) Remelting into ingots: The specific operation process is exactly the same as that in Comparative Example 1.

[0110] The melt viscosities of the high-purity aluminum melt detected in step (3) at 680 °C and 670 °C are 13.3 [Pa·s] and 15.2 [Pa·s] respectively, which are lower than those of the 4N5 high-purity aluminum in Comparative Example 1. By carrying out the steps in Example 1, it is found that the fractional crystallization process in step (4) can be successfully completed. Finally, the content of Al in the obtained high-purity aluminum is 99.9990%, the content of Fe impurity element is 2.4 ppm, the content of Si impurity element is 2.4 ppm, and the segregation rates of Fe and Si impurity elements are 94.0% and 94.0% respectively. Compared with Comparative Example 1, the removal rates of Fe and Si impurity elements are 76.0% and 70.0% respectively. The contents of other impurity elements all meet the composition requirements of 5N high-purity aluminum. Therefore, 5N high-purity aluminum is successfully prepared.

[0111] Example 2: 4N5 high-purity aluminum + Fe (mass content is 40 ppm) + Si (mass content is 80 ppm)

[0112] In this example, 4N5 high-purity aluminum, Al-20Fe master alloy, and Al-20Si master alloy are used as raw materials for batching, and the composition of 4N5 high-purity aluminum is the same as that in Comparative Example 1. By calculation, the mass contents of Fe and Si elements in the final high-purity aluminum are controlled to be 40 ppm and 80 ppm respectively. The specific steps and process parameters are as follows:

[0113] (1) Preparation of high-purity aluminum: According to the mass contents of Fe and Si elements in high-purity aluminum being 40 ppm and 80 ppm respectively, calculate and weigh the required 4N5 high-purity aluminum, Al-20Fe master alloy, and Al-20Si master alloy for high-purity aluminum, and prepare two samples according to the requirements, one for melt viscosity detection and the other for the next segregation purification experiment.

[0114] (2) Melt pretreatment: Put the high-purity aluminum raw materials into a pretreatment furnace for melting, the melting temperature is 770 °C. After melting, calculate according to the impurity content in the raw materials and add Al-B master alloy for impurity removal. Refine and remove slag. Next, add Al-20Fe master alloy and Al-20Si master alloy to the high-purity aluminum melt, stir evenly by electromagnetic stirring and then keep it warm statically, so that the mass contents of Fe and Si elements in the melt are 40 ppm and 80 ppm respectively, and obtain the segregation liquid.

[0115] (3) Viscosity detection: Conduct viscosity tests on the melt prepared in step (2), and the test method is the same as that in Comparative Example 1.

[0116] (4) Fractional crystallization treatment: Transfer the segregation liquid obtained in step (2) into a segregation furnace for fractional crystallization treatment, keep the aluminum melt at a temperature of 667 °C, and introduce cooling gas into the cooling pipes on the side wall of the segregation furnace, and the gas introduction speed is 30 m 3 / h, high-purity aluminum primary crystals precipitate on the side wall of the segregation furnace. Next, through the up-and-down movement of the ramming plate rammer (the movement speed is 6 times / min), the fine aluminum primary crystals are scraped to the bottom of the crucible and compacted. The compaction action can also squeeze out the aluminum melt rich in impurity elements between the crystals. The holes on the ramming plate rammer allow the aluminum melt to pass through. Repeating this process makes the aluminum primary crystals at the bottom gradually aggregate and grow into larger and purer aluminum crystals, achieving the purpose of aluminum purification.

[0117] (5) Remelting into ingots: The specific operation process is exactly the same as that of Comparative Example 1.

[0118] The melt viscosities of the high-purity aluminum melt detected in Example 2 at 680 °C and 670 °C are 11.5 [Pa·s] and 13.2 [Pa·s] respectively, which are lower than the melt viscosity of 4N5 high-purity aluminum in Comparative Example 1. By carrying out the steps of Example 2, it is found that the fractional crystallization process of step (4) can be successfully completed. Finally, the content of Al in the high-purity aluminum obtained is 99.9990%, the content of Fe impurity element is 2.3 ppm, the content of Si impurity element is 2.4 ppm, and the segregation rates of Fe and Si impurity elements are 94.3% and 97.0% respectively. Compared with Comparative Example 1, the removal rates of Fe and Si impurity elements are 77.0% and 70.0% respectively. The contents of other impurity elements all meet the composition requirements of 5N high-purity aluminum. Therefore, 5N high-purity aluminum is successfully prepared.

[0119] Example 3: 4N5 high-purity aluminum + Fe (mass content is 80 ppm) + Si (mass content is 40 ppm)

[0120] In this example, 4N5 high-purity aluminum, Al-20Fe master alloy, and Al-20Si master alloy are used as raw materials for batching, and the composition of 4N5 high-purity aluminum is the same as that of Comparative Example 1. By calculation, the mass contents of Fe and Si elements in the final high-purity aluminum (i.e., the mixed system of 4N5 high-purity aluminum, Al-20Fe master alloy, and Al-20Si master alloy) are controlled to be 80 ppm and 40 ppm respectively. The specific steps and process parameters are as follows:

[0121] (1) Preparation of high-purity aluminum: According to the mass contents of Fe and Si elements in high-purity aluminum being 80 ppm and 40 ppm respectively, calculate and weigh the required 4N5 high-purity aluminum, Al-20Fe master alloy, and Al-20Si master alloy for the target high-purity aluminum, and prepare two samples according to the requirements, one for melt viscosity detection and the other for the next segregation purification experiment.

[0122] (2) Melt pretreatment: Put the high-purity aluminum raw materials into a pretreatment furnace for melting. The melting temperature is 780 °C. After melting, calculate according to the impurity content in the raw materials and add a certain amount of Al-B master alloy for impurity removal. Refine and remove slag. Next, add a certain amount of Al-20Fe master alloy and Al-20Si master alloy to the high-purity aluminum melt. After electromagnetic stirring and uniform mixing, keep it warm for 30 min to make the mass contents of Fe and Si elements in the melt be 80 ppm and 40 ppm respectively, obtaining a segregation liquid.

[0123] (3) Viscosity detection: Conduct a viscosity test on the melt prepared in step (2). The test method is the same as that in Comparative Example 1.

[0124] (4) Stepwise crystallization treatment: Transfer the segregation liquid obtained in step (2) into a segregation furnace for stepwise crystallization treatment. Keep the aluminum melt at a temperature of 666 °C, and introduce a cooling gas into the cooling pipes on the side wall of the segregation furnace. The gas flow rate is 40 m 3 / h. High-purity aluminum primary crystals precipitate on the side wall of the segregation furnace. Next, through the up-and-down movement of the ramming plate rammer (the movement speed is 8 times / min), scrape the fine aluminum primary crystals to the bottom of the crucible and compact them. The compaction action can also squeeze out the aluminum melt rich in impurity elements between the crystals. The holes on the ramming plate rammer can allow the aluminum melt to pass through. Repeat this process to gradually grow the aluminum primary crystals at the bottom into larger and purer aluminum crystals, achieving the purpose of aluminum purification.

[0125] (5) Remelting and ingot casting: The specific operation process is exactly the same as that in Comparative Example 1.

[0126] The melt viscosities of the high-purity aluminum melt detected in Example 3 at 680 °C and 670 °C are 11.9 [Pa·s] and 14.0 [Pa·s] respectively, which are lower than the melt viscosity of 4N5 high-purity aluminum in Comparative Example 1. Through the steps in Example 3, it is found that the step (4) stepwise crystallization process can be successfully completed. Finally, the Al content in the obtained high-purity aluminum is 99.9993%, the content of Fe impurity element is 1.0 ppm, the content of Si impurity element is 1.2 ppm, and the segregation rates of Fe and Si impurity elements are 98.8% and 97.0% respectively. Compared with Comparative Example 1, the removal rates of Fe and Si impurity elements are 90.0% and 85.0% respectively. The contents of other impurity elements all meet the requirements of the composition of 5N high-purity aluminum. Therefore, 5N high-purity aluminum is successfully prepared.

[0127] Example 4: 4N5 high-purity aluminum + Fe (mass content is 80 ppm) + Si (mass content is 80 ppm)

[0128] In this embodiment, 4N5 high-purity aluminum, Al-20Fe master alloy, and Al-20Si master alloy are used as raw materials for batching, and the composition of 4N5 high-purity aluminum is the same as that in Comparative Example 1. By calculation, the mass contents of Fe and Si elements in the target high-purity aluminum (i.e., the mixed system of 4N5 high-purity aluminum, Al-20Fe master alloy, and Al-20Si master alloy) are controlled to be 80 ppm. The specific steps and process parameters are as follows:

[0129] (1) Preparation of high-purity aluminum: According to the mass contents of Fe and Si elements in the target high-purity aluminum being 80 ppm respectively, weigh the required 4N5 high-purity aluminum, Al-20Fe master alloy, and Al-20Si master alloy for the target high-purity aluminum, and prepare two samples according to the requirements. One is used for melt viscosity detection, and the other is used for the next segregation purification experiment.

[0130] (2) Melt pretreatment: Put the high-purity aluminum raw materials into a pretreatment furnace for melting. The melting temperature is 790 °C. After melting, calculate according to the impurity content in the raw materials and add Al-B master alloy for impurity removal. Refine and remove slag. Next, add a certain amount of Al-20Fe master alloy and Al-20Si master alloy to the high-purity aluminum melt, stir evenly by electromagnetic stirring and then keep it standing for heat preservation (the standing heat preservation time is 30 min) to make the mass contents of Fe and Si elements in the melt both 80 ppm, obtaining a segregation liquid.

[0131] (3) Viscosity detection: Conduct viscosity testing on the melt prepared in step (2), and the testing method is the same as that in Comparative Example 1.

[0132] (4) Stepwise crystallization treatment: Transfer the segregation liquid obtained in step (2) into a segregation furnace for stepwise crystallization treatment. Keep the aluminum melt at a temperature of 665 °C, and introduce cooling gas into the cooling pipes on the side wall of the segregation furnace. The gas introduction speed is 30 m 3 / h. High-purity aluminum primary crystals precipitate on the side wall of the segregation furnace. Next, scrape the fine aluminum primary crystals to the bottom of the crucible and compact them through the up-and-down movement of the ram rod (the movement speed is 7 times / min). The compaction action can also squeeze out the aluminum melt rich in impurity elements between the crystals. The holes on the ram rod allow the aluminum melt to pass through. Repeat this process to gradually grow the aluminum primary crystals at the bottom into larger and purer aluminum crystals, achieving the purpose of aluminum purification.

[0133] (5) Remelting into ingots: The specific operation process is exactly the same as that in Comparative Example 1.

[0134] The melt viscosities of the high-purity aluminum melt detected in Example 4 at 680 °C and 670 °C were 9.8 [Pa·s] and 12.1 [Pa·s], respectively, which were lower than those of the 4N5 high-purity aluminum in Comparative Example 1. By performing the steps in Example 4, it was found that the fractional crystallization process of step (4) could be successfully completed. Finally, the content of Al in the high-purity aluminum obtained was 99.9990%, the content of Fe impurity element was 2.0 ppm, the content of Si impurity element was 2.3 ppm, and the segregation rates of Fe and Si impurity elements were 97.5% and 97.1%, respectively. Compared with Comparative Example 1, the removal rates of Fe and Si impurity elements were 80.0% and 71.3%, respectively. The contents of other impurity elements all met the composition requirements of 5N high-purity aluminum. Therefore, 5N high-purity aluminum was successfully prepared.

[0135] Example 5: 4N5 high-purity aluminum + Fe (mass content is 90 ppm) + Si (mass content is 30 ppm)

[0136] In this example, 4N5 high-purity aluminum, Al-20Fe master alloy, and Al-20Si master alloy were used as raw materials for batching, and the composition of 4N5 high-purity aluminum was the same as that in Comparative Example 1. By calculation, the mass contents of Fe and Si elements in the target high-purity aluminum were controlled to be 90 ppm and 30 ppm, respectively. The specific steps and process parameters are as follows:

[0137] (1) Preparation of high-purity aluminum: According to the mass contents of Fe and Si elements in the target high-purity aluminum being 90 ppm and 30 ppm respectively, the amounts of 4N5 high-purity aluminum, Al-20Fe master alloy, and Al-20Si master alloy required for high-purity aluminum were calculated and weighed respectively. Two samples were prepared according to the requirements, one for melt viscosity detection and the other for the next segregation purification experiment.

[0138] (2) Melt pretreatment: The high-purity aluminum raw materials were put into a pretreatment furnace for melting at a melting temperature of 800 °C. After melting, according to the impurity content in the raw materials, Al-B master alloy was added for impurity removal. The melt was refined and slag was removed. Next, Al-20Fe master alloy and Al-20Si master alloy were added to the high-purity aluminum melt. After electromagnetic stirring and uniform mixing, the melt was kept standing and insulated (the standing and insulation time was 30 min) to make the mass contents of Fe and Si elements in the melt be 90 ppm and 30 ppm respectively, obtaining a segregation liquid.

[0139] (3) Viscosity detection: The melt prepared in step (2) was tested for viscosity, and the test method was the same as that in Comparative Example 1.

[0140] (4) Fractional crystallization treatment: The segregation liquid obtained in step (2) was transferred to a segregation furnace for fractional crystallization treatment. The aluminum melt was maintained at a temperature of 665 °C, and cooling gas was introduced into the cooling pipes on the side wall of the segregation furnace, and the gas introduction speed was 50 m 3 / h, high-purity aluminum primary crystals precipitate on the side wall of the segregation furnace. Next, through the up-and-down movement of the ramming plate rammer (the movement speed is 10 times / min), the fine aluminum primary crystals are scraped to the bottom of the crucible and compacted. The compaction action can also squeeze out the aluminum melt rich in impurity elements between the crystals. The holes on the ramming plate rammer allow the aluminum melt to pass through. Repeating this process makes the aluminum primary crystals at the bottom gradually aggregate and grow into larger and purer aluminum crystals, achieving the purpose of aluminum purification.

[0141] (5) Remelting into ingots: The specific operation process is exactly the same as that of Comparative Example 1.

[0142] The melt viscosities of the high-purity aluminum melt detected in Example 5 at 680 °C and 670 °C are 12.0 [Pa·s] and 14.2 [Pa·s] respectively, which are lower than the melt viscosity of 4N5 high-purity aluminum in Comparative Example 1. By performing the steps in Example 5, it is found that the fractional crystallization process of step (4) can be successfully completed. Finally, the content of Al in the obtained high-purity aluminum is 99.9993%, the content of Fe impurity element is 0.9 ppm, the content of Si impurity element is 1.0 ppm, and the removal rates of Fe and Si impurity elements are 99.0% and 96.7% respectively. Compared with Comparative Example 1, the removal rates of Fe and Si impurity elements are 91.0% and 87.5% respectively. The contents of other impurity elements all meet the composition requirements of 5N high-purity aluminum, so 5N high-purity aluminum is successfully prepared.

[0143] To better compare and illustrate the differences in the processes and effects of each comparative example and example, the melt viscosity data are respectively summarized in Table 1, and the element content data are summarized in Table 2.

[0144] The reasons for the failure of the experiments in Comparative Example 1, Comparative Example 2, and Comparative Example 4 are that the melt viscosity did not decrease to a level that allows the fractional crystallization process to proceed smoothly, and the resistance encountered by the ramming plate rammer during the up-and-down movement is too large, so the experiment cannot be successfully completed; Comparative Example 3 and Comparative Example 5 prove that although adding a large amount of Fe element alone and adding a large amount of Si element alone can reduce the melt viscosity to a level that allows the fractional crystallization process to proceed smoothly, the prepared high-purity aluminum cannot meet the composition requirements of 5N high-purity aluminum. All the examples of the present invention reduce the melt viscosity by adding Fe and Si elements before the fractional crystallization method, and remove the excessive Fe and Si impurity elements through the fractional crystallization method. This process can effectively purify high-purity aluminum, promote the smooth progress of the fractional crystallization process, and will not introduce other impurity elements additionally, and 5N high-purity aluminum has been successfully prepared. In particular, the effects of Example 3 and Example 5 are the best, and the optimal Fe / Si ratio added before the fractional crystallization process is 2 - 3.

[0145] Table 1 Melt viscosities of high-purity aluminum in comparative examples and examples at 680 °C and 670 °C

[0146]

[0147] Table 2 Content of high-purity aluminum element in comparative examples and examples (unit: ppm)

[0148]

[0149] Figure 3 Changes in melt viscosity of high-purity aluminum at 680 °C and 670 °C in Comparative Examples 1-5 and Examples 1-5

[0150] Figure 4 Segregation rates of Fe and Si impurities in high-purity aluminum samples prepared in Comparative Example 3, Comparative Example 5, and Examples 1-5

[0151] Figure 5 Removal rates of Fe and Si impurity elements in high-purity aluminum samples prepared in Comparative Example 3, Comparative Example 5, and Examples 1-5

[0152] The implementation manners of the present invention are not limited by the described examples. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement manners and are all included in the protection scope of the present invention.

Claims

1. A method for preparing 5N high purity aluminum, characterized in that: The following steps are involved: 1) Melting 4N5 high-purity aluminum raw material, removing impurity elements with a balanced distribution coefficient greater than 1, and obtaining a high-purity aluminum melt; 2) adding Fe and Si elements to high purity aluminum melt to prepare a segregation solution; 3) performing a fractional crystallization treatment on the segregated liquid; 4) Take out the aluminum ingot, remove the end of the aluminum ingot with more impurities, and remelt it into an ingot to obtain 5N high-purity aluminum; In step 2), the amounts of Fe and Si added satisfy the following conditions: after the Fe and Si are added to the 4N5 high-purity aluminum raw material, the total Fe content is 20 to 200 ppm, the total Si content is 20 to 200 ppm, and the Fe / Si mass content ratio is (0.2 to 6):

1.

2. The method for preparing 5N high purity aluminum according to claim 1, characterized in that: In step 2), the addition amount of Fe element and Si element meets the following conditions: Fe / Si mass content ratio is (0.4-4):1; The fractional crystallization treatment in step 3) refers to maintaining the temperature of the segregation liquid at 665-670°C, and then cooling the segregation liquid in the device by a cooling device arranged on the side wall of the device, so that primary aluminum crystals precipitate from the segregation liquid in contact with the side wall, and stirring the segregation liquid while scraping off the primary aluminum crystals. This process is repeated, and the primary aluminum crystals aggregate and grow, thereby completing the fractional crystallization.

3. The method for preparing 5N high purity aluminum according to claim 2, characterized in that: In step 2), the addition amount of Fe element and Si element meets the following conditions: Fe / Si mass content ratio is (0.5-4):1; The scraping of the primary aluminum crystals while stirring the segregation liquid, and the aggregation and growth of the primary aluminum crystals means that the primary aluminum crystals are scraped off and compacted by the up-and-down movement of the scraping device, and the scraping device is provided with holes or gaps, and the primary aluminum crystals are scraped off and compressed while the aluminum melt passes through the holes or gaps, and the back-and-forth movement causes the primary aluminum crystals to aggregate and grow; The cooling refers to cooling by introducing cooling gas.

4. The method for preparing 5N high purity aluminum according to claim 3, characterized in that: The Fe / Si mass content ratio is (1.5-3.5):1; The scraping device moves up and down at a speed of 5 to 10 times / min; The cooling gas introduction speed is 10~50m 3 / h.

5. The method for preparing 5N high purity aluminum according to claim 1, characterized in that: In step 2), the amounts of Fe and Si added satisfy the following conditions: after the Fe and Si elements are added to the 4N5 high-purity aluminum raw material, the total Fe content is 30 to 120 ppm, and the total Si content is 30 to 120 ppm.

6. The method for preparing 5N high purity aluminum according to claim 1, characterized in that: In step 1), removing the impurity elements with a balanced distribution coefficient greater than 1 refers to adding Al-B master alloy to the melt, mixing, and standing to keep warm; The amount of B added is calculated based on the content of impurity elements with a balanced distribution coefficient greater than 1 in the high-purity aluminum raw material.

7. The method for preparing 5N high purity aluminum according to claim 1, characterized in that: After removing the impurity elements with equilibrium distribution coefficient greater than 1 in step 1), refining and slag removal; The melting temperature in step 1) is 720-800°C.

8. The method for preparing 5N high purity aluminum according to claim 1, characterized in that: The adding of Fe and Si elements in step 2) refers to adding Al-Fe master alloy and Al-Si master alloy, mixing them evenly, and standing them to keep warm.

9. The method for preparing 5N high purity aluminum according to claim 8, characterized in that: Al-Fe master alloy is Al-20wt%Fe, Al-Si master alloy is Al-20wt%Si; The static insulation time is 2 to 60 minutes.

10. The method for preparing 5N high purity aluminum according to claim 1, characterized in that: In step 4), the end of the aluminum ingot with more impurities is removed by an instrument to detect the composition of the aluminum ingot, and the part with more impurities is removed or 1 / 5 to 1 / 10 of the aluminum ingot crystallized later is removed; The melting temperature of the remelting ingot is 700-780°C.

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