Device and method for preparing high-quality Al-5Ti-B aluminum alloy grain refiner by using Na3AlF6-CaF2 covering agent

Abstract

The invention discloses a device and method for preparing a high-quality Al-5Ti-B aluminum alloy grain refiner by using a Na3AlF6-CaF2 covering agent. The device comprises a medium-frequency induction furnace with a reaction crucible as a main body, air holes are formed in the side wall of the crucible, and a mechanical stirring paddle and a villiaumite feeding pipe are arranged at the top of the crucible. The method comprises the steps that industrial pure aluminum and mixed villiaumite K2TiF6 and KBF4 are subjected to sand blasting and equally divided into two parts, the industrial pure aluminum is heated and melted, a Na3AlF6-CaF2 covering agent is evenly spread on the surface of a melt, the mixed villiaumite is added into the melt in two times, Ar2 is introduced, stirring reaction is conducted, a by-product is poured out after reaction is finished, and the alloy melt is rolled into the Al-5Ti-B aluminum alloy grain refiner with the diameter being 9 mm. The Na3AlF6-CaF2 covering agent is used for inhibiting volatilization of villiaumite and isolating oxygen, the yield of the Ti element and the yield of the B element are increased, and inclusions generated by Al2O3 are reduced; by adding villiaumite and introducing Ar2 for stirring in batches, the uniformity of the alloy melt is improved. The aluminum alloy grain refiner prepared through the method is high in cleanliness, the Ti and B yield is high, second-phase particles are evenly distributed and good in shape, and the refining effect is remarkable.

Description

Technical Field

[0001] The present invention relates to the technical field of nonferrous metal smelting and manufacturing, and in particular to a device and method for preparing a high-quality Al-5Ti-B aluminum alloy grain refiner by using a Na3AlF6-CaF2 covering agent. Background Art

[0002] Aluminum alloys are widely used in construction, aerospace, machinery and electronics due to their excellent properties such as high specific strength, easy processing, corrosion resistance and light weight. They are important basic materials for current economic development and social construction. At present, China's demand for high-quality aluminum is increasing. In 2023, China's aluminum alloy output reached 14.587 million tons, a year-on-year increase of 17.8%. Fine, uniform equiaxed grains can improve the overall mechanical properties of aluminum alloys. A common industrial grain refinement method involves adding grain refiners during the aluminum alloy melt forming process. Aluminum-titanium-boron (Al-Ti-B) grain refiners are the most widely used aluminum alloy grain refiners due to their low production cost, high degree of automation, effective recycling of byproducts during the preparation process, and stable grain refinement results. They account for approximately 75% of the global market share.

[0003] The fluoride salt method for preparing Al-Ti-B aluminum alloy grain refiners is widely used in industrial production due to its low cost, simple process, and strong and stable product refinement. This method uses pure aluminum, K2TiF6, and KBF4 as raw materials. At high temperatures, the molten aluminum reacts fully with the fluoride salt, followed by casting and rolling to produce the refiner product. The Ti and B content, cleanliness, and morphology and distribution of the second-phase particles in the Al-Ti-B aluminum alloy grain refiner are important indicators of product quality.

[0004] The existing preparation method of Al-Ti-B aluminum alloy grain refiner has quality problems such as easy volatility of fluoride salt, low yield of Ti and B elements, high content of impurities such as Al2O3, uneven distribution of second phase particles and large differences in particle size and morphology. Summary of the Invention

[0005] In order to improve the quality of Al-5Ti-B aluminum alloy grain refiner, the present invention proposes a device and method for preparing high-quality Al-5Ti-B aluminum alloy grain refiner using Na3AlF6-CaF2 covering agent. The Al-5Ti-B aluminum alloy grain refiner prepared by the present invention has high Ti and B element yields, high cleanliness, uniform distribution of second-phase particles and good morphology, and significant refinement effect.

[0006] Specifically, the present invention proposes a device and method for preparing high-quality Al-5Ti-B aluminum alloy grain refiner using Na3AlF6-CaF2 covering agent. The device is a medium-frequency induction furnace, the main body of which is a reaction crucible, the side wall of the crucible is provided with air holes, and the top of the crucible is equipped with a mechanical stirring paddle and a fluoride salt feeding tube.

[0007] Furthermore, the medium frequency induction furnace also includes electrical control equipment, heating equipment, cooling equipment, etc.

[0008] Furthermore, the reaction crucible is a high-purity graphite crucible (purity ≥ 99.9%), the surface of which is coated with a SiC coating with a coating thickness of 20-50 μm.

[0009] Furthermore, the pores are arranged in two rows, 100 mm and 400 mm away from the bottom of the crucible respectively, with a pore diameter of 0.75-0.85 mm, a tangential deflection angle of 20±2°, and a circular distribution. The pores are embedded with an Al2O3 ceramic filter membrane with a pore diameter of 5 μm and a porosity of 40%.

[0010] Furthermore, the mechanical stirring paddle is a liftable mechanical stirring paddle, the blades are made of four-oblique blade SiC ceramics, the single blade size is 150×80×15 mm, and the blade inclination angle is 45°.

[0011] Furthermore, the fluoride salt feeding tube is a liftable fluoride salt feeding tube, with a total of 2, symmetrically distributed with the liftable mechanical stirring paddle as the center. The base material of the fluoride salt feeding tube is 316L stainless steel with a boron nitride coating with a coating thickness of 200-300 μm. The inner diameter of the fluoride salt feeding tube is 38±3 mm, the outer diameter is 42±2 mm, and the inner wall taper of the last 30 mm section is expanded by 5°.

[0012] The present invention also provides a device and method for preparing a high-quality Al-5Ti-B aluminum alloy grain refiner using a Na3AlF6-CaF2 covering agent, and the specific steps are as follows: Step (1), sandblasting industrial pure aluminum; Step (2), weighing pre-treated industrial pure aluminum, K2TiF6 and KBF4 according to mass fraction, uniformly mixing K2TiF6 and KBF4, and dividing the mixture into two equal parts of fluoride salt; Step (3), adding industrial pure aluminum into a reaction crucible, heating and melting, and scraping off the oxide slag on the surface of the aluminum melt; Step (4), using a stainless steel screen to evenly spread the covering agent on the surface of the aluminum melt; Step (5), inserting the fluoride salt feeding tube under the covering agent, adding the mixed fluoride salt for the first time, raising the fluoride salt feeding tube, starting mechanical stirring and introducing Ar gas; Step (6), suspend mechanical stirring and ventilation, insert the fluoride salt feeding tube under the covering agent, add the mixed fluoride salt for the second time, start mechanical stirring and introduce Ar gas, and pour out the by-product after the reaction is completed; Step (7), introducing the alloy melt into the connecting launder; In step (8), the alloy melt is introduced into the continuous casting and rolling mill through the connecting trough and rolled into an Al-5Ti-B aluminum alloy grain refiner with a diameter of 9 mm; and then the Al-5Ti-B aluminum alloy grain refiner wire coil is produced by an automatic wire coiling machine.

[0013] Furthermore, in step 1), the sandblasting is performed using white corundum abrasive with a particle size of 80-120 mesh, and the treatment time is 2-3 minutes. The industrial pure aluminum is melted within 4 hours after the sandblasting to avoid secondary oxidation.

[0014] Furthermore, in step 2), the particle size of K2TiF6 and KBF4 is 40-70 μm.

[0015] Furthermore, in step 3), the temperature of the aluminum melt is 700±10°C.

[0016] Furthermore, in step 4), the covering agent composition is 70 wt.% Na3AlF6-CaF2, the covering agent mass is about 5% of the mixed fluoride salt, and the covering thickness is 25±5 mm.

[0017] Furthermore, in step 5) and step 6), the insertion length of the fluoride salt feeding tube is 600±50 mm; Furthermore, in step 5), after adding the mixed fluoride salt, the fluoride salt feeding tube was raised and a mechanical stirring paddle was inserted. After the alloy melt was heated to 740±10°C at a rate of 5°C / min, mechanical stirring was started and Ar gas was introduced, and the reaction was continued for 15-20 minutes. The mechanical stirring was intermittent, running for 2 minutes and pausing for 30 seconds, and the stirring speed was 200 rpm. The Ar gas purge was continuous, with a purge flow rate of 12±2 L / min.

[0018] Furthermore, in step 6), after adding the mixed fluoride salt, the fluoride salt feeding tube was raised, and the alloy melt was heated to 800±10°C at a rate of 5°C / min. Mechanical stirring was then initiated and Ar gas was introduced, and the reaction was continued for 15-20 minutes. Mechanical stirring was intermittent, running for 2 minutes and pausing for 30 seconds, at a stirring speed of 200 rpm. Ar gas purge was continuous, with a purge flow rate of 12±2 L / min.

[0019] Furthermore, in step 7), the flow trough is provided with vortex pits for stirring and removing impurities, and there are 3-5 vortex pits evenly distributed in the flow trough; the flow trough is provided with a filter screen made of 20-30 ppi aluminum oxide, 8-10 mm thick, and a total of 3-5; Furthermore, in step 8), the alloy melt is first cast into a trapezoidal wire embryo by a casting machine, and then passed through a continuous rolling mill to be rolled into a box shape, an oval shape and a round shape in sequence.

[0020] Compared with the prior art, the present invention has the following advantages: The use of a Na3AlF6-CaF2 coating agent not only effectively inhibits the volatilization of fluoride salts and increases the yield of Ti and B elements, but also significantly reduces the reaction of molten aluminum with oxygen at high temperatures and the formation of Al2O3 inclusions. Furthermore, mechanical stirring and ventilation stirring improve the uniformity of the alloy melt and effectively optimize the size and distribution of second-phase particles. The Al-5Ti-B aluminum alloy grain refiner prepared by the present invention exhibits high Ti and B yields, high cleanliness, uniform distribution of second-phase particles with good morphology, and significant refinement effects, promising broad prospects for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of a device according to embodiment 1 of the present invention; Figure 2 This is the SEM morphology of the Al-5Ti-B aluminum alloy grain refiner prepared in Example 2 (250X); Figure 3 This is the SEM morphology of the Al-5Ti-B aluminum alloy grain refiner prepared in Example 2 (30kX); In the figure, 1. Fluoride salt feeding tube, 2. Mixed fluoride salt, 3. Graphite crucible, 4. SiC coating, 5. Pores, 6. Al2O3 ceramic filter membrane, 7. Aluminum melt, 8. Mechanical stirring paddle, 9. Na3AlF6-CaF2 covering agent. Specific implementation plan The following are preferred embodiments of the present invention, and the protection of the present invention is not limited to the following preferred embodiments. It should be noted that any modifications and improvements made on the basis of this invention are within the scope of protection of the present invention.

[0022] Example 1 This embodiment provides a device for preparing a high-quality Al-5Ti-B aluminum alloy grain refiner using a Na3AlF6-CaF2 covering agent. The device is a medium-frequency induction furnace. The medium-frequency induction furnace body is a reaction crucible 3. The side wall of the crucible 3 is provided with air holes 5. The top of the crucible 3 is equipped with a mechanical stirring paddle 8 and a fluoride salt feeding tube 1. The medium-frequency induction furnace also includes electrical control equipment, heating equipment, cooling equipment, etc. (not shown in the drawings).

[0023] The reaction crucible 3 is a high-purity graphite crucible (purity ≥ 99.9%), with a SiC coating 4 coated on the surface, and the coating thickness is 20-50 μm.

[0024] The pores 5 are arranged in two rows, 100 mm and 400 mm away from the bottom of the crucible 3 respectively. The pores 5 have a pore diameter of 0.75-0.85 mm, a tangential deflection angle of 20±2°, and are distributed in an annular shape. An Al2O3 ceramic filter membrane 6 with a pore diameter of 5 μm and a porosity of 40% is embedded in the pores 5.

[0025] The mechanical stirring paddle 8 is a liftable mechanical stirring paddle, and the blades are made of four-oblique blade SiC ceramics, with a single blade size of 150×80×15 mm and a blade inclination angle of 45°.

[0026] The fluoride salt feeding tube 1 is a liftable fluoride salt feeding tube, with a total of 2, symmetrically distributed with the liftable mechanical stirring paddle 8 as the center. The base material of the fluoride salt feeding tube 1 is 316L stainless steel with a boron nitride coating with a coating thickness of 200-300 μm. The inner diameter of the fluoride salt feeding tube is 38±3 mm, the outer diameter is 42±2 mm, and the inner wall taper of the last 30 mm section is expanded by 5°.

[0027] Example 2 This embodiment provides a method for preparing a high-quality Al-5Ti-B aluminum alloy grain refiner using a Na3AlF6-CaF2 covering agent, which is carried out using the apparatus of Example 1 and includes the following specific steps and parameters: (1) 1148.4 kg of sandblasted industrial pure aluminum was added to a medium frequency furnace and heated to 700 °C. The oxide slag on the surface of the aluminum melt was scraped off.

[0028] (2) Weigh 11.84 kg of 70 wt.% Na3AlF6-CaF2 and evenly spread the covering agent 9 on the surface of the aluminum melt 7 using a stainless steel mesh.

[0029] (3) 161.6 kg of K2TiF6 with a particle size of 40-70 μm and 75.2 kg of KBF4 with a particle size of 40-70 μm were weighed and mixed evenly to form a mixed fluoride salt 2.

[0030] (4) Fluoride salt was first added to the aluminum melt through the feeding tube. After the alloy melt was heated to 740±10℃ at a rate of 5℃ / min, mechanical stirring was started and Ar gas was introduced. The reaction was continued for 18 minutes. The mechanical stirring was intermittent, running for 2 minutes and pausing for 30 seconds, with a stirring speed of 200 rpm. The Ar gas purge was continuous, with a purge flow rate of 12 L / min.

[0031] (5) Fluoride salt was added to the aluminum melt for the second time through the fluoride feeding tube. After the alloy melt was heated to 800±10℃ at a rate of 5℃ / min, mechanical stirring was started and Ar gas was introduced. The reaction was continued for 18 minutes. The mechanical stirring was intermittent, running for 2 minutes and pausing for 30 seconds, and the stirring speed was 200 rpm. The Ar gas purge was continuous, with a purge flow rate of 12 L / min. After the reaction was completed, the by-products were poured out.

[0032] (6) The alloy melt is introduced into the connecting flow channel. The flow channel is equipped with vortex pits for stirring and removing impurities. There are 4 vortex pits evenly distributed in the flow channel. The flow channel is equipped with a filter screen. The filter screen is made of 20 ppi alumina and is 10 mm thick. There are 4 filters evenly distributed in the flow channel.

[0033] (7) The alloy melt from the trough is introduced into the continuous casting and rolling mill and rolled into an Al-5Ti-B aluminum alloy grain refiner with a diameter of 9 mm; then the Al-5Ti-B aluminum alloy grain refiner wire coil is produced by an automatic wire coiling machine.

[0034] The microstructure of the Al-5Ti-B aluminum alloy grain refiner prepared in this embodiment was analyzed, and the results are as follows: Figure 2 and Figure 3 The refiner contains no obvious oxide or salt inclusions, demonstrating high cleanliness. The refiner contains no particularly large (>100 μm) TiAl₃ particles, with the average TiAl₃ phase particle size less than 25 μm. The refiner also contains no particularly large (>2.0 μm) TiB₂ particles, with the average TiB₂ phase particle size being 0.66 μm. The composition of the Al-5Ti-B aluminum alloy grain refiner obtained by inductively coupled plasma optical emission spectrometry is shown in Table 1. The Ti content is 5.03%, the B content is 0.95%, the Si impurity content is 0.08%, and the Fe impurity content is 0.08%.

[0035]

[0036] The refinement performance experiment of the refiner refers to the "Evaluation Standard YS / T447.1-2011 for Aluminum Titanium Boron Alloy Wire". After the Al-5Ti-B aluminum alloy grain refiner prepared in Example 1 was used to refine industrial pure aluminum, the average grain size of the industrial pure aluminum was reduced to less than 150 μm.

[0037] Example 3 This embodiment provides a method for preparing a high-quality Al-5Ti-B aluminum alloy grain refiner using a Na3AlF6-CaF2 covering agent, which is carried out using the apparatus of Example 1 and includes the following specific steps and parameters: (1) 1244 kg of industrial pure aluminum after sandblasting was added into a medium frequency furnace and heated to 700 °C. The oxide slag on the surface of the aluminum melt was scraped off.

[0038] (2) Weigh 12.86 kg of 70 wt.% Na3AlF6-CaF2 and evenly spread the covering agent on the surface of the aluminum melt using a stainless steel screen.

[0039] (3) Weigh 175.1 kg of dried K2TiF6 with a particle size of 40-70 μm and 81.6 kg of dried KBF4 with a particle size of 40-70 μm and mix them evenly.

[0040] (4) Fluoride salt was first added to the aluminum melt through the feeding tube. After the alloy melt was heated to 740±10℃ at a rate of 5℃ / min, mechanical stirring was started and Ar gas was introduced. The reaction was continued for 18 minutes. The mechanical stirring was intermittent, running for 2 minutes and pausing for 30 seconds, with a stirring speed of 200 rpm. The Ar gas purge was continuous, with a purge flow rate of 12 L / min.

[0041] (5) Fluoride salt was added to the aluminum melt for the second time through the fluoride feeding tube. After the alloy melt was heated to 800±10℃ at a rate of 5℃ / min, mechanical stirring was started and Ar gas was introduced. The reaction was continued for 18 minutes. The mechanical stirring was intermittent, running for 2 minutes and pausing for 30 seconds, and the stirring speed was 200 rpm. The Ar gas purge was continuous, with a purge flow rate of 12 L / min. After the reaction was completed, the by-products were poured out.

[0042] (6) The alloy melt is introduced into the connecting flow channel. The flow channel is equipped with vortex pits for stirring and removing impurities. There are 4 vortex pits evenly distributed in the flow channel. The flow channel is equipped with a filter screen. The filter screen is made of 20 ppi alumina and is 10 mm thick. There are 4 filters evenly distributed in the flow channel.

[0043] (7) The alloy melt from the trough is introduced into the continuous casting and rolling mill and rolled into an Al-5Ti-B aluminum alloy grain refiner with a diameter of 9 mm; then the Al-5Ti-B aluminum alloy grain refiner wire coil is produced by an automatic wire coiling machine.

[0044] The refinement performance experiment of the Al-5Ti-B aluminum alloy grain refiner prepared in this embodiment was conducted with reference to the "Evaluation Standard YS / T447.1-2011 for Aluminum-Titanium-Boron Alloy Wire". After the Al-5Ti-B aluminum alloy grain refiner prepared in this embodiment 2 was used to refine industrial pure aluminum, the average grain size of the industrial pure aluminum was reduced to less than 150 μm.

[0045] Example 4 This embodiment provides a method for preparing a high-quality Al-5Ti-B aluminum alloy grain refiner using a Na3AlF6-CaF2 covering agent, which is carried out using the apparatus of Example 1 and includes the following specific steps and parameters: (1) Add 1435.6 g of industrial pure aluminum after sandblasting into a medium frequency furnace and heat it to 700 °C, and scrape off the oxide slag on the surface of the aluminum melt.

[0046] (2) Weigh 14.79 kg of 70 wt.% Na3AlF6-CaF2 and evenly spread the covering agent on the surface of the aluminum melt using a stainless steel screen.

[0047] (3) Weigh 201.9 kg of dried K2TiF6 with a particle size of 40-70 μm and 93.8 kg of dried KBF4 with a particle size of 40-70 μm and mix them evenly.

[0048] (4) Fluoride salt was first added to the aluminum melt through the feeding tube. After the alloy melt was heated to 740±10℃ at a rate of 5℃ / min, mechanical stirring was started and Ar gas was introduced. The reaction was continued for 18 minutes. The mechanical stirring was intermittent, running for 2 minutes and pausing for 30 seconds, with a stirring speed of 200 rpm. The Ar gas purge was continuous, with a purge flow rate of 12 L / min.

[0049] (5) Fluoride salt was added to the aluminum melt for the second time through the fluoride feeding tube. After the alloy melt was heated to 800±10℃ at a rate of 5℃ / min, mechanical stirring was started and Ar gas was introduced. The reaction was continued for 18 minutes. The mechanical stirring was intermittent, running for 2 minutes and pausing for 30 seconds, and the stirring speed was 200 rpm. The Ar gas purge was continuous, with a purge flow rate of 12 L / min. After the reaction was completed, the by-products were poured out.

[0050] (6) The alloy melt is introduced into the connecting flow channel. The flow channel is equipped with vortex pits for stirring and removing impurities. There are 4 vortex pits evenly distributed in the flow channel. The flow channel is equipped with a filter screen. The filter screen is made of 20 ppi alumina and is 10 mm thick. There are 4 filters evenly distributed in the flow channel.

[0051] (7) The alloy melt from the trough is introduced into the continuous casting and rolling mill and rolled into Al-5Ti-B aluminum alloy grain refiner wire with a diameter of 9 mm; then the Al-5Ti-B aluminum alloy grain refiner wire coil is produced by an automatic wire coiling machine.

[0052] The refinement performance experiment of the Al-5Ti-B aluminum alloy grain refiner prepared in this example was conducted with reference to the "Evaluation Standard YS / T447.1-2011 for Aluminum-Titanium-Boron Alloy Wire". After the Al-5Ti-B aluminum alloy grain refiner prepared in this example 3 was used to refine industrial pure aluminum, the average grain size of the industrial pure aluminum was reduced to less than 150 μm.

[0053] Example 5 This embodiment provides a method for preparing a high-quality Al-5Ti-B aluminum alloy grain refiner using a Na3AlF6-CaF2 covering agent, which is carried out using the apparatus of Example 1 and includes the following specific steps and parameters: (1) 1148.4 kg of sandblasted industrial pure aluminum was added to a medium frequency furnace and heated to 700 °C. The oxide slag on the surface of the aluminum melt was scraped off.

[0054] (2) Weigh 11.84 kg of 70 wt.% Na3AlF6-CaF2 and evenly spread the covering agent on the surface of the aluminum melt using a stainless steel screen.

[0055] (3) Weigh 161.6 kg of dried K2TiF6 with a particle size of 40-70 μm and 75.2 kg of dried KBF4 with a particle size of 40-70 μm and mix them evenly.

[0056] (4) Fluoride salt was first added to the aluminum melt through the fluoride feeding tube. After the alloy melt was heated to 740±10℃ at a rate of 5℃ / min, mechanical stirring was started and Ar gas was introduced. The reaction was continued for 15 minutes. The mechanical stirring was intermittent, running for 2 minutes and pausing for 30 seconds, with a stirring speed of 200 rpm. The Ar gas purge was continuous, with a purge flow rate of 12 L / min.

[0057] (5) Fluoride salt was added to the aluminum melt for the second time through the fluoride feeding tube. After the alloy melt was heated to 800±10℃ at a rate of 5℃ / min, mechanical stirring was started and Ar gas was introduced. The reaction was continued for 20 minutes. The mechanical stirring was intermittent, running for 2 minutes and pausing for 30 seconds, and the stirring speed was 200 rpm. The Ar gas purge was continuous, with a purge flow rate of 12 L / min. After the reaction was completed, the by-products were poured out.

[0058] (6) The alloy melt is introduced into the connecting flow channel. The flow channel is equipped with vortex pits for stirring and removing impurities. There are 4 vortex pits evenly distributed in the flow channel. The flow channel is equipped with a filter screen. The filter screen is made of 20 ppi alumina and is 10 mm thick. There are 4 filters evenly distributed in the flow channel.

[0059] (7) The alloy melt from the trough is introduced into the continuous casting and rolling mill and rolled into Al-5Ti-B aluminum alloy grain refiner wire with a diameter of 9 mm; then the Al-5Ti-B aluminum alloy grain refiner wire coil is produced by an automatic wire coiling machine.

[0060] The refinement performance experiment of the Al-5Ti-B aluminum alloy grain refiner prepared in this example was conducted with reference to the "Evaluation Standard for Aluminum-Titanium-Boron Alloy Wire YS / T447.1-2011". After the Al-5Ti-B aluminum alloy grain refiner prepared in this example 4 was used to refine industrial pure aluminum, the average grain size of the industrial pure aluminum was reduced to less than 150 μm.

[0061] Example 6 This embodiment provides a method for preparing a high-quality Al-5Ti-B aluminum alloy grain refiner using a Na3AlF6-CaF2 covering agent, which is carried out using the apparatus of Example 1 and includes the following specific steps and parameters: (1) 1148.4 kg of sandblasted industrial pure aluminum was added to a medium frequency furnace and heated to 700 °C. The oxide slag on the surface of the aluminum melt was scraped off.

[0062] (2) Weigh 11.84 kg of 70 wt.% Na3AlF6-CaF2 and evenly spread the covering agent on the surface of the aluminum melt using a stainless steel screen.

[0063] (3) Weigh 161.6 kg of dried K2TiF6 with a particle size of 40-70 μm and 75.2 kg of dried KBF4 with a particle size of 40-70 μm and mix them evenly.

[0064] (4) Fluoride salt was first added to the aluminum melt through the fluoride feeding tube. After the alloy melt was heated to 740±10℃ at a rate of 5℃ / min, mechanical stirring was started and Ar gas was introduced. The reaction was continued for 18 minutes. The mechanical stirring was intermittent, running for 2 minutes and pausing for 30 seconds, with a stirring speed of 250 rpm. The Ar gas purge was continuous, with a purge flow rate of 12 L / min.

[0065] (5) Fluoride salt was added to the aluminum melt for the second time through the fluoride feeding tube. After the alloy melt was heated to 800±10℃ at a rate of 5℃ / min, mechanical stirring was started and Ar gas was introduced. The reaction was continued for 18 minutes. The mechanical stirring was intermittent, running for 2 minutes and pausing for 30 seconds, and the stirring speed was 250 rpm. The Ar gas purge was continuous, with a purge flow rate of 12 L / min. After the reaction was completed, the by-products were poured out.

[0066] (6) The alloy melt is introduced into the connecting flow channel. The flow channel is equipped with vortex pits for stirring and removing impurities. There are 4 vortex pits evenly distributed in the flow channel. The flow channel is equipped with a filter screen. The filter screen is made of 20 ppi alumina and is 10 mm thick. There are 4 filters evenly distributed in the flow channel.

[0067] (7) The alloy melt from the trough is introduced into the continuous casting and rolling mill and rolled into an Al-5Ti-B aluminum alloy grain refiner with a diameter of 9 mm; then the Al-5Ti-B aluminum alloy grain refiner wire coil is produced by an automatic wire coiling machine.

[0068] The refinement performance experiment of the Al-5Ti-B aluminum alloy grain refiner prepared in this example was conducted with reference to the "Evaluation Standard for Aluminum-Titanium-Boron Alloy Wire YS / T447.1-2011". After the Al-5Ti-B aluminum alloy grain refiner prepared in this example 5 was used to refine industrial pure aluminum, the average grain size of the industrial pure aluminum was reduced to less than 150 μm.

Claims

1. A device for preparing high-quality Al-5Ti-B aluminum alloy grain refiner using Na3AlF6-CaF2 covering agent, characterized in that: The device is a medium frequency induction furnace, the main body of which is a reaction crucible, the side wall of the crucible is provided with air holes, and the top of the crucible is equipped with a mechanical stirring paddle and a fluoride salt feeding tube.

2. The device for preparing high-quality Al-5Ti-B aluminum alloy grain refiner using Na3AlF6-CaF2 covering agent according to claim 1, characterized in that: The reaction crucible is a high-purity graphite crucible with a purity of ≥99.9%, and the surface is coated with a SiC coating with a coating thickness of 20-50 μm.

3. The device for preparing high-quality Al-5Ti-B aluminum alloy grain refiner using Na3AlF6-CaF2 covering agent according to claim 1, characterized in that: The pores are arranged in two rows, 100 mm and 400 mm away from the bottom of the crucible respectively. The pore diameter is 0.70±0.05 mm, the inclination angle is 20±2° tangential deflection angle, the pores are distributed in a ring shape, and an Al2O3 ceramic filter membrane with a pore diameter of 5 μm and a porosity of 40% is embedded in the pores.

4. The device for preparing high-quality Al-5Ti-B aluminum alloy grain refiner using Na3AlF6-CaF2 covering agent according to claim 1, characterized in that: The mechanical stirring paddle is a liftable mechanical stirring paddle, the blades are made of four-oblique blade SiC ceramics, the size of a single blade is 150×80×15 mm, and the blade inclination angle is 45°.

5. The device for preparing high-quality Al-5Ti-B aluminum alloy grain refiner using Na3AlF6-CaF2 covering agent according to claim 1, characterized in that: The fluoride salt feeding tube is a liftable fluoride salt feeding tube, with a total of two, symmetrically distributed with the mechanical stirring paddle as the center. The base material of the fluoride salt feeding tube is 316L stainless steel with a boron nitride coating with a coating thickness of 200-300 μm. The inner diameter of the fluoride salt feeding tube is 38±3 mm, the outer diameter is 42±2 mm, and the inner wall taper of the last 30 mm section is expanded by 5°.

6. A method for preparing a high-quality Al-5Ti-B aluminum alloy grain refiner using a Na3AlF6-CaF2 covering agent, characterized in that: The preparation is carried out using the device according to claim 1, comprising the following steps: Step (1), sandblasting industrial pure aluminum; Step (2), weighing pre-treated industrial pure aluminum, K2TiF6 and KBF4 according to mass fraction, uniformly mixing K2TiF6 and KBF4, and dividing the mixture into two equal parts of mixed fluoride salt; Step (3), adding industrial pure aluminum into a reaction crucible, heating and melting, and scraping off the oxide slag on the surface of the aluminum melt; Step (4), using a stainless steel screen to evenly spread the covering agent on the surface of the aluminum melt; Step (5), inserting the fluoride salt feeding tube under the covering agent, adding the mixed fluoride salt for the first time, raising the fluoride salt feeding tube, starting mechanical stirring and introducing Ar gas; Step (6), suspend mechanical stirring and ventilation, insert the fluoride salt feeding tube under the covering agent, add the mixed fluoride salt for the second time, start mechanical stirring and introduce Ar gas, and pour out the by-product after the reaction is completed; Step (7), introducing the alloy melt into the connecting launder; In step (8), the alloy melt connected to the flow channel is introduced into a continuous casting and rolling mill, and rolled into an Al-5Ti-B aluminum alloy grain refiner with a diameter of 9 mm; and an Al-5Ti-B aluminum alloy grain refiner wire coil is produced by an automatic wire coiling machine.

7. The method for preparing a high-quality Al-5Ti-B aluminum alloy grain refiner using a Na3AlF6-CaF2 covering agent according to claim 6, wherein: In step 1), the sandblasting is performed using white corundum abrasive with a particle size of 80-120 mesh, the treatment time is 2-3 minutes, and the industrial pure aluminum is melted within 4 hours after the sandblasting.

8. The method for preparing a high-quality Al-5Ti-B aluminum alloy grain refiner using a Na3AlF6-CaF2 covering agent according to claim 6, wherein: In step 2), the particle size of K2TiF6 and KBF4 is 40-70 μm.

9. The method for preparing a high-quality Al-5Ti-B aluminum alloy grain refiner using a Na3AlF6-CaF2 covering agent according to claim 6, wherein: In step 3), the temperature of the aluminum melt is 700±10°C.

10. The method for preparing a high-quality Al-5Ti-B aluminum alloy grain refiner using a Na3AlF6-CaF2 covering agent according to claim 6, wherein: In step 4), the covering agent composition is 70 wt.% Na3AlF6-CaF2, the covering agent mass is about 5% of the mixed fluoride salt, and the covering thickness is 25±5 mm.

11. The method for preparing a high-quality Al-5Ti-B aluminum alloy grain refiner using a Na3AlF6-CaF2 covering agent according to claim 6, wherein: In step 5) and step 6), the insertion length of the fluoride salt feeding tube is 600±50 mm.

12. The method for preparing a high-quality Al-5Ti-B aluminum alloy grain refiner using a Na3AlF6-CaF2 covering agent according to claim 6, wherein: In step 5), after adding the mixed fluoride salt, raise the fluoride salt feeding tube and insert a mechanical stirring paddle. After the alloy melt is heated to 740±10°C at a rate of 5°C / min, mechanical stirring is started and Ar gas is introduced. The reaction is continued for 15-20 minutes. Mechanical stirring is intermittent, running for 2 minutes and pausing for 30 seconds, at a stirring speed of 200 rpm. Ar gas purge is continuous, with a purge flow rate of 12±2 L / min.

13. The method for preparing a high-quality Al-5Ti-B aluminum alloy grain refiner using a Na3AlF6-CaF2 covering agent according to claim 6, wherein: In step 6), after adding the mixed fluoride salt, the fluoride salt feeding tube was raised, and the alloy melt was heated to 800±10°C at a rate of 5°C / min. Mechanical stirring was then initiated and Ar gas was introduced. The reaction was continued for 15-20 minutes. Mechanical stirring was intermittent, running for 2 minutes and pausing for 30 seconds at a stirring speed of 200 rpm. Ar gas was continuously purged at a flow rate of 12±2 L / min.

14. The method for preparing a high-quality Al-5Ti-B aluminum alloy grain refiner using a Na3AlF6-CaF2 covering agent according to claim 6, wherein: In step 7), the connecting flow channel is provided with a vortex pit for stirring and removing impurities, and there are 3-5 vortex pits in total, which are evenly distributed in the connecting flow channel; the connecting flow channel is provided with a filter screen, and the filter screen is made of 20-30 ppi aluminum oxide, 8-10 mm thick, and there are 3-5 in total.

15. The method for preparing a high-quality Al-5Ti-B aluminum alloy grain refiner using a Na3AlF6-CaF2 covering agent according to claim 6, characterized in that: In step 8), the alloy melt is first cast into a trapezoidal wire embryo by a casting machine, and then passed through a continuous rolling mill to be rolled into a box shape, an oval shape and a round shape in sequence.

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