A method for preparing aluminum alloy dendrites

Abstract

The application provides a preparation method of aluminum alloy dendrite crystals, the dendrite crystals prepared by the application are more single, do not interfere with each other, are more independent, are more complete, and grow more freely compared with the dendrite crystals obtained by other methods, do not compete with each other due to the change of cooling mode and cooling gradient direction, do not produce defects such as grain boundaries, and only grow downward in a single dendrite crystal mode, so that the application hopes to obtain complete single aluminum alloy dendrite crystals by the preparation mode, and further research whether the dendrite crystals also exist element segregation and the smallest unit of the dendrite crystals, and further provide theoretical support for the research on the secondary unit of the aluminum alloy dendrite crystals. The application avoids the limitation of the traditional alloy material production process, produces complete single aluminum alloy dendrite crystals, and provides feasibility support for the research on the aluminum alloy dendrite crystals.

Description

Technical Field

[0001] This invention belongs to the field of materials science and technology, and specifically relates to a method for preparing aluminum alloy dendrites. Background Technology

[0002] In recent years, with the development of technology, parts produced by traditional solidification technology can no longer meet the requirements of harsh service conditions. There is an urgent need for new manufacturing technologies to produce higher-performance parts, especially those used in the rear sections of gas turbines and aero engines. These parts need to withstand temperatures exceeding 1000°C and centrifugal forces of 10000 rpm, which parts produced by traditional solidification processes cannot withstand for extended periods. Therefore, it is essential to improve the ultimate performance of materials. To improve the current situation, the invention of directional solidification technology and single-crystal blade fabrication technology is urgently needed. However, existing directional solidification and single-crystal technologies still have many shortcomings, including the inability to mass-produce, low yield rates, and excessively small parts. These problems mainly stem from insufficient theoretical understanding of the microscopic dendritic growth mechanism.

[0003] Therefore, countless scientists and scholars have tried to thoroughly understand the growth mechanism of dendrites and have hoped to prepare ideal dendritic structures through various methods, including laser cooling technology, electron beam melting pool solidification technology, directional solidification technology, single crystal technology and surface polishing technology. However, these methods cannot produce dendrites with a single dendritic structure; they are mostly aggregates of multiple dendrites. They cannot transform the microscale dendritic structure into the macroscale, let alone study and detect the growth law of a single dendrite. Most of the research is based on dendritic simulation and theoretical model research, and there is still very little research on the preparation of single dendrites.

[0004] Al-Si alloys are among the earliest materials studied for dendrite research. Some literature has shown that theoretical studies and models have been used to examine the influence of solidification parameters on microstructure characterization, mainly including the effects of primary dendrite spacing, secondary dendrite spacing, dendrite tip radius, temperature gradient, and dendrite growth rate. Some literature has also studied the effects of solidification process parameters and Si element content on dendrite spacing and hardness. However, no literature has been found on the preparation of Al-Si alloy dendrites using vapor phase solidification technology. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing aluminum alloy dendrites, revealing the growth law and morphology of aluminum alloy dendrites, and studying the morphological characteristics of aluminum alloy dendrites on a macroscopic scale.

[0006] A method for preparing aluminum alloy dendrites includes the following steps:

[0007] Step 1: Weigh 170g of raw material, whose chemical composition is Al-8.90Si-0.64P-0.57Pd-0.28Fe-0.24Ag-0.16Cd-0.10Mo-0.06Zn-0.05Ni-0.04Nb. Place it in a beaker and remove surface impurities and oil stains with acetone. Leave it in the beaker for 5 minutes, then pour out the acetone and rinse with deionized water to prevent the introduction of impurities and trace elements that could affect the final dendrite preparation. Place it back in the beaker, add an alcohol solution, and place it on an ultrasonic cleaner for 15 minutes. Pour it onto filter paper and let it air dry. After drying, weigh it again and take out 150g for the experiment.

[0008] Step 2: Before starting the experiment, check whether the heating device can be used normally, and check whether the gas and water circuits are normal. The heating device should have an error range of ±3℃ within the range of 900-1000℃, a heating rate of 5℃ / min, a cooling water pressure of 0.03MPa~0.05MPa, a cooling water temperature of 5℃~25℃, a gas pressure of 0.05MPa, and check whether the graphite dry pot is damaged. Check whether there are holes or cracks in the inner and outer dry pots. When loading raw materials, try to keep the molten liquid of the raw materials from overflowing into the inner dry pot and being contaminated by the outer dry pot.

[0009] Step 3: At the start of the experiment, ensure that Ar is introduced and air is purged, and purge the air multiple times. Introduce H2 to heat the aluminum granules in the crucible, and control the temperature at 200-300℃. After holding at this temperature for 30 minutes, raise the temperature of the high-temperature furnace. When the high-temperature furnace reaches the desired temperature, introduce HCl gas and control the temperature of the high-temperature furnace at 900-1000℃. Hold at this temperature for 3 hours. Then, turn off the heating device and shut off the introduction of H2 and HCl gas. Continue to slowly introduce Ar gas and slowly cool to room temperature.

[0010] Step 4: Use tweezers to handle the prepared dendrites as much as possible. Before extracting the dendrites for scanning electron microscopy (SEM) inspection, the surface needs to be cleaned and then dried naturally. The obtained dendrites are then placed in the digital microscope (OM) of the scanning electron microscope (SEM) for inspection. Due to their small size and easy bending, conductive tape is used to pick them up as much as possible during inspection.

[0011] Furthermore, in step 3, Ar gas is introduced to circulate and remove air, and the flow rates of H2 and HCl gas are controlled to be 0.1 MPa and 0.05 MPa, respectively.

[0012] The beneficial effects of this invention are as follows:

[0013] (1) The dendrites prepared by this invention are more uniform, do not interfere with each other, and are more independent. Compared with dendrites obtained by other methods, the dendrites obtained by this method are more complete and have a more free growth mode. They will not compete with each other for growth due to changes in cooling method and cooling gradient direction, and will not produce defects such as grain boundaries. They grow downwards in a single dendrite mode, which is not available in other growth methods. Other dendrite growth methods will more or less result in dendrites that cannot be observed from all directions due to the presence of solvent, and will also be unable to complete the observation of the entire three-dimensional direction due to the dendrite growth direction and the mutual occlusion of dendrites.

[0014] (2) The present invention aims to obtain complete single aluminum alloy dendrites through this preparation method, and then study whether dendrites also have dendritic element segregation, as well as the smallest constituent unit of dendrites, so as to provide theoretical support for the study of secondary units of aluminum alloy dendrites.

[0015] (3) This invention avoids the limitations of traditional alloy material production processes and produces complete and single aluminum alloy dendrites, providing feasibility support for the research of aluminum alloy dendrites. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the dendrite preparation apparatus of the present invention;

[0017] Figure 2 This is a photograph of the raw materials for preparing aluminum alloy dendrites according to the present invention.

[0018] Figure 3 Food illustrations for preparing dry pot mats using aluminum alloy dendrites according to the present invention;

[0019] Figure 4 This is a photograph of the residue remaining after the dendrite formation in the aluminum alloy according to the present invention.

[0020] Figure 5 This is an optical microscope image of the aluminum alloy dendrites of the present invention;

[0021] Figure 6(a) is a digital microscope image of the aluminum alloy dendrites of the present invention;

[0022] Figure 6(b) is a height cloud map of the aluminum alloy dendrite digital microscope of the present invention;

[0023] Figure 6(c) Outline diagram of the aluminum alloy dendrite digital microscope of the present invention;

[0024] Figure 7(a) is a morphology diagram of the middle position of the dendrites in this invention;

[0025] Figure 7(b) is a morphology diagram of the dendrite tip of the aluminum alloy of the present invention;

[0026] Figure 8 This is a surface scan of the aluminum alloy dendrites of the present invention;

[0027] Figure 9(a) is a scanned image (a) of the aluminum alloy dendrites of the present invention;

[0028] Figure 9(b) is a scanned image of the aluminum alloy dendrites of the present invention;

[0029] Figure 9(c) is a schematic diagram of the binary phase diagram of Al-Si alloy. Detailed Implementation

[0030] The present invention will now be further described with reference to the accompanying drawings.

[0031] A method for preparing aluminum alloy dendrites includes the following steps:

[0032] Step 1: Weigh 170g of raw material, whose chemical composition is Al-8.90Si-0.64P-0.57Pd-0.28Fe-0.24Ag-0.16Cd-0.10Mo-0.06Zn-0.05Ni-0.04Nb. Place it in a beaker and remove surface impurities and oil stains with acetone. Leave it in the beaker for 5 minutes, then pour out the acetone and rinse with deionized water to prevent the introduction of impurities and trace elements that could affect the final dendrite preparation. Place it back in the beaker, add an alcohol solution, and place it on an ultrasonic cleaner for 15 minutes. Pour it onto filter paper and let it air dry. After drying, weigh it again and take out 150g for the experiment.

[0033] Step 2: Before starting the experiment, check whether the heating device can be used normally, and check whether the gas and water circuits are normal. The heating device should have an error range of ±3℃ within the range of 900-1000℃, a heating rate of 5℃ / min, a cooling water pressure of 0.03MPa~0.05MPa, a cooling water temperature of 5℃~25℃, a gas pressure of 0.05MPa, and check whether the graphite dry pot is damaged. Check whether there are holes or cracks in the inner and outer dry pots. When loading raw materials, try to keep the molten liquid of the raw materials from overflowing into the inner dry pot and being contaminated by the outer dry pot.

[0034] Step 3: At the start of the experiment, ensure that Ar is introduced and air is purged, and purge the air multiple times. Introduce H2 to heat the aluminum granules in the crucible, and control the temperature at 200-300℃. After holding at this temperature for 30 minutes, raise the temperature of the high-temperature furnace. When the high-temperature furnace reaches the desired temperature, introduce HCl gas and control the temperature of the high-temperature furnace at 900-1000℃. Hold at this temperature for 3 hours. Then, turn off the heating device and shut off the introduction of H2 and HCl gas. Continue to slowly introduce Ar gas and slowly cool to room temperature.

[0035] Step 4: Use tweezers to handle the prepared dendrites as much as possible. Before extracting the dendrites for scanning electron microscopy (SEM) inspection, the surface needs to be cleaned and then dried naturally. The obtained dendrites are then placed in the digital microscope (OM) of the scanning electron microscope (SEM) for inspection. Due to their small size and easy bending, conductive tape is used to pick them up as much as possible during inspection.

[0036] In step 3, Ar gas is introduced to circulate and remove air, and the flow rates of H2 and HCl gas are controlled to be 0.1 MPa and 0.05 MPa, respectively.

[0037] This invention takes Al-Si alloy as the research object and establishes a method for preparing Al-Si alloy. The results show that this experiment can successfully prepare macroscopic Al-Si alloy dendrites.

[0038] The specific implementation plan involves releasing Al through a reduction reaction between aluminum halide and hydrogen at high temperatures. The specific design concept is as follows:

[0039] Step 1: Generation of vaporized aluminum compound AlCl x (This requires a large amount of AlCl3(g), a small amount of AlCl2(g), and AlCl(g)). The amount of HCl must be strictly controlled during this process, thereby controlling the amount of aluminum compounds (AlCl). x The amount of Ar and H2 generated should be carefully controlled, along with the initial reaction chamber temperature.

[0040] Step 2: With the aluminum compound AlCl x The formation of aluminum compounds AlCl x H2 is transported to a high-temperature furnace, where the temperature is typically controlled within the range of 900-1000℃, with a heating rate of 5℃ / min. The H2 flow rate is carefully controlled to far exceed the HCl gas flow rate to facilitate the high-temperature reduction of aluminum compounds (AlCl3). x The reaction produces elemental Al.

[0041] Step 3: Control the gas flow rate in the cooling well to prevent excessive gas flow from interfering with dendrite growth, while also facilitating the absorption of final exhaust gas.

[0042] Step 4: Throughout the entire process of preparing aluminum alloy dendrites, it is necessary to strictly control the influence of each process parameter on the aluminum alloy dendrites to prevent the growth of dendrites from being restricted or failing due to the incoordination of process parameters.

[0043] This invention prepares a macroscopic aluminum alloy dendrite, introducing the microscopic dendrite structure from the microscopic realm to the macroscopic realm, and prepares a single three-dimensional aluminum alloy dendrite without the obstruction of other dendrites. The prepared aluminum alloy dendrite can be characterized in both three-dimensional size and microscopic scale.

[0044] like Figure 2 As shown in the figure, the material selected for the current experiment comes from Al-Si alloy particles produced on a large industrial scale. Its main chemical element is Al-Si, while other elements such as P, Fe, and Ag are impurities. The addition of aluminum alloy particles in this experiment is also to prevent the introduction of a large number of impurities, facilitate cleaning, and prevent the gas passage from being blocked when the gas passes through.

[0045] like Figure 3 As shown in the figure, the graphite gasket is very brittle, but it is heat-resistant and can prevent contamination from the external dry pot during the smelting process.

[0046] like Figure 4 As shown in the figure, a large amount of aluminum alloy remained in the dry pot and solidified. The solidified aluminum alloy ingot still shows obvious dendrites.

[0047] As shown in Figure 6, the dendrites are very large, with a total length exceeding 1000 mm, and both secondary and tertiary dendrites are present. Figure 6(a) shows that the dendrites are distributed very randomly, exhibiting a trend of selective growth, which is due to the microscopic unevenness of elemental content in the dendrites.

[0048] Figure 7 shows numerous secondary and tertiary dendrites growing from the dendrite trunk, with inconsistent lengths. Figure 7(a) shows the morphology of the middle position of the dendrites, revealing chaotic dendrite growth with secondary and tertiary dendrites growing randomly in various directions. Figure 7(b) shows the morphology of the dendrite tips in the aluminum alloy, demonstrating highly regular dendrite growth. Testing revealed a close correlation between the growth of secondary dendrites and the elemental content on the dendrite trunk.

[0049] Figure 8 As can be seen from the figure, the distribution of alloying elements on the dendrites is very uneven. Al and Si elements are more abundant on the dendrites, while the distribution of other elements is very inconspicuous and appears sporadic. Further research found that the content of Si element has a significant impact on the growth of dendrites, and high Si concentration inhibits the growth of hexagonal dendrites.

[0050] As shown in Figure 9, the concentration of Si is relatively low at the secondary dendrite positions (points A, B, and D in Figure 9(a)) and relatively high at the secondary dendrite positions (point C in Figure 9(a) and point E in Figure 9(b)). Figure 9(c) shows that when the silicon content is below 12.6%, at the red dashed line position, dendrites with low Si concentration preferentially nucleate, pushing the high Si concentration solute towards the center of the dendrite spacing, forming a high concentration region in the middle of the dendrite, further inhibiting dendrite growth, and allowing the formed low Si concentration dendrites to continue to grow forward.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing aluminum alloy dendrites, characterized in that, Includes the following steps: Step 1: Weigh 170g of raw material, whose chemical composition is Al-8.90Si-0.64P-0.57Pd-0.28Fe-0.24Ag-0.16Cd-0.10Mo-0.06Zn-0.05Ni-0.04Nb. Place it in a beaker and remove surface impurities and oil stains with acetone. Place it in the beaker for 5 minutes, pour out the acetone, and rinse with deionized water to prevent the introduction of impurities and trace elements that may affect the final dendrite preparation. Place it back in the beaker, add alcohol solution, and place it on an ultrasonic cleaner for 15 minutes. After cleaning, pour it into filter paper and wait for it to dry naturally. After drying, weigh it again and take out 150g for the experiment. Step 2: Before the experiment begins, check whether the heating device can be used normally, and check whether the gas and water circuits are normal. The heating device should have an error range of ±3℃ within the range of 900-1000℃, a heating rate of 5℃ / min, a cooling water pressure of 0.03MPa~0.05MPa, a cooling water temperature of 5℃~25℃, a gas pressure of 0.05MPa, and check whether the graphite crucible is damaged. Check whether there are holes or cracks in the inner and outer crucibles. When loading raw materials, ensure that the molten liquid of the raw materials does not overflow from the inner crucible and is contaminated by the outer crucible. Step 3: At the beginning of the experiment, ensure that Ar is introduced and air is purged. Repeat the process of purging air multiple times. Introduce H2 to heat the aluminum particles in the crucible. Control the temperature at 200-300℃ and hold for 30 minutes. Then, raise the temperature of the high-temperature furnace. When the high-temperature furnace reaches the desired temperature, introduce HCl gas. Control the temperature of the high-temperature furnace at 900-1000℃ and hold for 3 hours. After that, turn off the heating device and shut off the introduction of H2 and HCl gas. Continue to slowly introduce Ar gas and slowly cool to room temperature. Step 4: The prepared dendrites are picked up with tweezers and extracted for scanning electron microscopy (SEM) inspection. Before inspection, the surface of the dendrites needs to be cleaned and then dried naturally. The obtained dendrites are then placed in the digital microscope (OM) of the scanning electron microscope (SEM) for inspection. Due to their small size and easy bending, conductive tape is used to pick them up during inspection. In step 3, Ar gas is introduced and circulated to remove air, and the pressures of H2 and HCl gases are controlled to be 0.1 MPa and 0.05 MPa, respectively.

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