Preparation method of aluminum-scandium alloy target blank with high scandium content

Abstract

This invention belongs to the field of alloy target preparation technology and discloses a method for preparing a high scandium content aluminum-scandium alloy target billet, including the following steps: (1) Weighing metallic scandium and metallic aluminum according to the designed scandium and aluminum content in the aluminum-scandium alloy target billet, and mixing and melting metallic scandium and metallic aluminum to obtain an alloy melt; (2) Casting the alloy melt into a mold, and then cooling and shaping it to obtain a billet I; the cooling rate of the alloy melt in the mold is 50~100℃ / min; (3) After grinding, the billet I is melted again, and then cast into a mold, and cooled and shaped to obtain a billet II; the cooling rate is 3~12℃ / min; (4) Vacuum heat treatment of the billet II obtained in step (3). The high scandium content aluminum-scandium alloy target billet prepared by this invention has uniform aluminum-scandium particle grain size on the upper and lower surfaces, uniform target billet composition, high purity, and the finished product oxygen content can be controlled to be less than 200ppm and the target billet is not easy to crack.

Description

Technical Field

[0001] This invention belongs to the field of alloy target preparation technology, specifically relating to a method for preparing an aluminum-scandium alloy target blank with high scandium content. Background Technology

[0002] Scandium is an expensive rare earth metal. Currently, its main application is in alloy modification. Adding trace amounts of scandium to aluminum alloys can promote grain refinement and increase the recrystallization temperature by 250-280℃. It acts as a powerful grain refiner and effective recrystallization inhibitor, significantly impacting the alloy's structure and properties, greatly improving its strength, hardness, weldability, and corrosion resistance. Low-scandium aluminum-scandium alloys have wide applications in aerospace, shipbuilding, and some specialized industrial fields. High-scandium aluminum-scandium alloys are mainly used as sputtering targets in special fields, such as in the fabrication of micro-electromechanical systems (MEMS) integrating micro-sensors, actuators, signal processing and control circuits, interface circuits, communication, and power supplies. Patent document CN201610677045.1 discloses a high-scandium aluminum-scandium alloy and its preparation method, which involves mixing aluminum powder and scandium powder in a certain mass ratio, then thoroughly grinding and sintering to prepare the aluminum-scandium alloy. Patent document CN201910728801.2 discloses a high scandium content aluminum-scandium alloy target and its preparation method. The method involves melting metallic aluminum and metallic scandium into an alloy, ball milling the aluminum-scandium alloy, vacuum drying to obtain alloy powder, and then pre-pressing and vacuum sintering to obtain an aluminum-scandium alloy target blank. The obtained aluminum-scandium alloy target blank is then subjected to hot deformation processing to obtain the aluminum-scandium alloy target material. Patent document CN202010971649.3 discloses a method for preparing high scandium content aluminum-scandium alloys. This method involves melting metallic scandium and metallic aluminum, pouring the heat-preserved alloy liquid into a water-cooled copper mold, and using a mold circulating water cooling system to first cool the circulating water to 1–15°C. The cooled circulating water is then passed through the water-cooled copper mold to circulate and cool the alloy liquid. The alloy liquid solidifies within 3–8 seconds, yielding an aluminum-scandium alloy ingot with a scandium content of 5%–99%. Patent document CN202111160175.5 describes a method that uses Sc powder and Al3Sc powder (a second-phase compound) for mixing. Both Sc (1541℃) and Al3Sc (1320℃) have relatively high melting points, which can increase the powder sintering temperature to 1000~1300℃, thus improving the density of the AlSc target material. Furthermore, the direct addition of Al3Sc powder allows for a more uniform and dispersed distribution of the second phase. Patent document CN202010492396.1 describes a method where aluminum-scandium alloy melt is cast into a mold and cooled to obtain an aluminum-scandium alloy ingot. After atomization, aluminum-scandium alloy powder is obtained, which is then sintered to obtain an aluminum-scandium alloy target blank.The above-mentioned high-scandium-content aluminum-scandium alloy targets are prepared using powder metallurgy or water-cooled casting methods. Among them, aluminum-scandium alloy targets prepared by powder metallurgy have high oxygen content and low purity, which is not suitable for the needs of high-end BAW filters. Water-cooled casting after melting is not feasible because high-scandium aluminum-scandium targets (Sc content greater than 25 at%) are mainly composed of brittle phase particles such as Al2Sc, Al3Sc, and AlSc. The cooling rate cannot be accurately controlled during water-cooled casting, which can easily lead to cracking of the cast target blank and uneven grain size of aluminum-scandium particles along the thickness direction, affecting subsequent sputtering use. Moreover, cracking is also prone to occur during subsequent processing, which in turn increases the manufacturing cost of the target. Summary of the Invention

[0003] In view of the defects and shortcomings of the existing technology, the purpose of this invention is to provide a method for preparing an aluminum-scandium alloy target blank with uniform composition, uniform grains, low oxygen content, high purity, and low susceptibility to cracking.

[0004] To achieve the above objectives, the present invention provides the following specific technical solutions.

[0005] A method for preparing a high-scandium-content aluminum-scandium alloy target blank includes the following steps:

[0006] (1) Weigh out metallic scandium and metallic aluminum according to the scandium and aluminum content designed in the aluminum-scandium alloy target billet, and mix and melt the metallic scandium and metallic aluminum to obtain the alloy melt;

[0007] (2) The alloy melt is poured into the mold and then cooled to form a billet I; the cooling rate of the alloy melt in the mold is 50 ~ 100℃ / min;

[0008] (3) After grinding, the billet I is melted again, then cast into a mold and cooled to form billet II; the cooling rate is 3~12℃ / min;

[0009] (4) The blank II obtained by vacuum heat treatment step (3).

[0010] In a further preferred embodiment, the scandium content in the aluminum-scandium alloy target blank is designed to be 30-40 at.

[0011] In a further preferred embodiment, the melting temperature in step (1) is 1310℃~1345℃ and the time is 0.5-4h.

[0012] In a further preferred embodiment, the mold is one of a graphite mold, a water-cooled copper mold, or a carbon steel mold.

[0013] In a further preferred embodiment, the casting rate in step (2) is 0.3~0.5 kg / s.

[0014] In a further preferred embodiment, the melting temperature in step (3) is 1360℃~1435℃, and the melting time is 1~3h.

[0015] In a further preferred embodiment, the casting speed in step (3) is 0.3~0.5 kg / s.

[0016] In a further preferred embodiment, the vacuum heat treatment is performed at a temperature of 850~1050℃ for a duration of 2~4 hours.

[0017] In the preparation of high scandium content aluminum-scandium alloy targets, the present invention adopts a process of adding aluminum once and melting and casting twice to prepare high scandium content aluminum-scandium alloy target blanks. The preparation method is simple and easy to operate.

[0018] The aluminum-scandium alloy target blank prepared by this invention has uniform aluminum-scandium particle size on both the upper and lower surfaces, uniform target blank composition, high purity, and the oxygen content of the finished product can be controlled to be less than 200ppm. Furthermore, the internal stress is released by slow cooling combined with vacuum heat treatment to eliminate residual stress, and the resulting target blank is not prone to cracking. Attached Figure Description

[0019] Figure 1 This is a photograph of the finished product of Example 1.

[0020] Figure 2 The figures are metallographic images of the upper and lower surfaces of the finished product in Example 1, wherein Figure (a) is the metallographic image of the upper surface and Figure (b) is the metallographic image of the lower surface.

[0021] Figure 3 This is a photograph of the finished product from Example 2.

[0022] Figure 4 The figures are metallographic images of the upper and lower surfaces of the finished product in Example 2, wherein Figure (a) is the metallographic image of the upper surface and Figure (b) is the metallographic image of the lower surface. Detailed Implementation

[0023] The method for preparing aluminum-scandium alloy target blanks according to this invention belongs to the co-doping method. When preparing high-scandium-content aluminum-scandium alloy target blanks using the co-doping method, common problems encountered due to the high scandium content include: uneven distribution of components in the target blank, localized cracking, severe segregation, and coarse and uneven grain size. Although the uneven composition in the target blank can be improved by using a one-time casting method after alloy melting, problems such as coarse and uneven grain size and high oxygen content still exist.

[0024] The method for preparing a high scandium content aluminum-scandium alloy target blank provided by the present invention includes the following steps:

[0025] (1) Weigh out metallic scandium and metallic aluminum according to the scandium and aluminum content designed in the aluminum-scandium alloy target billet, and mix and melt the metallic scandium and metallic aluminum to obtain the alloy melt;

[0026] (2) The alloy melt is poured into the mold and then cooled to form a billet I; the cooling rate of the alloy melt in the mold is 50 ~ 100℃ / min;

[0027] (3) After grinding, the billet I is melted again, then cast into a mold and cooled to form billet II; the cooling rate is 3~12℃ / min;

[0028] (4) The blank II obtained by vacuum heat treatment step (3).

[0029] In a specific embodiment of the present invention, the scandium content in the high scandium content aluminum-scandium alloy is 30-40 at%. Here, at% is atomic percentage. The higher the scandium content, the more likely the scandium content will be uneven across different locations in the alloy during preparation, resulting in greater brittleness of the target material and a higher likelihood of cracking during casting, cooling, and subsequent processing.

[0030] This invention uses a two-stage melting-casting process to obtain alloy materials, controls the cooling rate of the alloy melt in the mold, and then performs vacuum heat treatment to obtain a high scandium content aluminum-scandium alloy target billet with uniform grain size, uniform target composition, high purity, low oxygen content, and resistance to cracking.

[0031] During the first melting-casting process, the cooling rate of the molten metal in the mold is controlled at 50~100℃ / min. A relatively high cooling rate is used in the first casting to obtain an alloy target billet free of impurity phases. This allows for good alloy melting and retention of the theoretical phases, while also allowing some surface oxide scale to float to the surface. After the first casting, the top and bottom surfaces of the target billet are ground before being fed into the crucible, which effectively removes the oxide scale.

[0032] After the first melting and casting, the phases of Al2Sc, Al3Sc, and AlSc were obtained by melting and alloying aluminum and scandium. There were no elemental aluminum or scandium phases. However, the uniformity of the cast target billet was not yet optimal at this time, and the target billet was more prone to cracking.

[0033] To further optimize the properties of the alloy material obtained after cooling following the first casting, this invention continues with a second melting and casting process, controlling the cooling rate of the molten metal in the mold to be 3~12℃ / min. Using a cooling rate within this range allows the internal stress of the target billet to be released during slow cooling, resulting in better shaping, better compositional uniformity, and less susceptibility to cracking.

[0034] Furthermore, in the two-stage melting-casting process, this invention can further employ a process where the temperature of the second melting is higher than that of the first melting. During the first melting process, aluminum and scandium melt and mix, but the resulting alloy material, obtained through rapid cooling during casting, still exhibits uneven internal distribution. By employing a second melting at a higher temperature, the aluminum and scandium in the alloy material can be more effectively and uniformly mixed, resulting in a more even distribution of aluminum and scandium. In a specific embodiment of this invention, the temperature for the first melting is selected as 1310℃~1345℃, and the temperature for the second melting is selected as 1360℃~1435℃.

[0035] The mold used for casting molten aluminum-scandium alloy can be one of a graphite mold, a water-cooled copper mold, or a carbon steel mold, all of which can meet the casting requirements. In a specific embodiment of the present invention, a graphite mold is selected.

[0036] To further ensure the uniformity of the temperature of the molten liquid inside the mold, in a specific embodiment of the present invention, the casting rate is 0.3~0.5 kg / s.

[0037] The prepared alloy material is further subjected to vacuum heat treatment to further release the residual stress in the cast target billet. In a specific embodiment of the present invention, the heat treatment temperature is 850~1050℃. Holding at this temperature for a period of time will relax the interior of the target billet, and after slow cooling, some of the stress can be removed.

[0038] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0039] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0040] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0041] All the raw materials used in the following examples and comparative examples, namely scandium metal particles and aluminum metal particles, are from the same batch.

[0042] Example 1

[0043] An aluminum-scandium alloy target blank with a scandium content of 30 at% was prepared.

[0044] Weigh 2.5 kg of scandium granules and place them in a crucible, and place 3.5 kg of aluminum granules in a feeder. Heat the scandium granules to 1568℃ until they are completely melted, then gradually add the aluminum granules. After the aluminum granules are completely melted, maintain the temperature of the alloy melt I at 1315±5℃ and smelt for 1 hour.

[0045] The molten alloy I was poured into a graphite mold with a diameter of 350 mm at a pouring speed of 0.3 kg / s, and the cooling rate of molten alloy I within the mold was controlled at 100℃ / min. After molten alloy I was completely cooled, the cooled material was obtained.

[0046] After the surface of the cooling material is cleaned, it is broken into pieces smaller than 3 cm and put back into the crucible. It is heated to 1420 °C until it is completely melted to obtain alloy melt II. The temperature of alloy melt II is maintained at 1430±5 °C for 2 hours.

[0047] The alloy molten liquid II was poured into a graphite mold with an inner diameter of 350 mm and an inner height of 7 mm at a pouring speed of 0.4 kg / s. The cooling rate of the alloy molten liquid II within the mold was controlled at 3 °C / min. After the alloy molten liquid II had completely cooled, the target blank was obtained.

[0048] The target blank was vacuum heat-treated at 850℃ for 3 hours and then ground into a finished product.

[0049] Figure 1 The image shows a photograph of the finished product from Example 1. As can be seen from the image, the target blank has a good appearance. Metallographic analysis of the finished product yielded results as shown in Figure 2. Figure 2 It can be seen that the grain size test results on the upper and lower surfaces of the target blank are relatively similar, with an average grain size of about 30 μm.

[0050] Comparative Example 1

[0051] The only difference between Comparative Example 1 and Example 1 is that the cooling rate of alloy solution I in the mold is 40°C / min.

[0052] Comparative Example 2

[0053] The only difference between Comparative Example 2 and Example 1 is that the cooling rate of alloy solution I in the mold is 110°C / min.

[0054] Comparative Example 3

[0055] The only difference between Comparative Example 3 and Example 1 is that the cooling rate of alloy solution II in the mold is 14°C / min.

[0056] Comparative Example 4

[0057] The only difference between Comparative Example 4 and Example 1 is that the cooling rate of alloy solution II in the mold is 2°C / min.

[0058] Example 2

[0059] An aluminum-scandium alloy target blank with a scandium content of 40 at% was prepared.

[0060] Weigh 3.034 kg of scandium particles and place them in a crucible, and place 2.677 kg of aluminum particles in a feeder. Heat the scandium particles to 1580℃ until they are completely melted, then gradually add the aluminum particles. After the aluminum particles are completely melted, maintain the temperature of the alloy melt I at 1340±5℃ and smelt for 2 hours.

[0061] The molten alloy I was poured into a graphite mold with a diameter of 350 mm at a pouring speed of 0.5 kg / s, and the cooling rate of molten alloy I within the mold was controlled at 50℃ / min. After molten alloy I was completely cooled, the cooled material was obtained.

[0062] After the cooled material is broken into pieces smaller than 3 cm, it is put back into the crucible and heated to 1370±10℃ to completely melt it, thus obtaining alloy melt II. The temperature of alloy melt II is maintained at 1370±10℃ for 2 hours.

[0063] The molten alloy II was poured into a graphite mold with an inner diameter of 360 mm and an inner height of 7 mm at a pouring speed of 0.5 kg / s. The cooling rate of the molten alloy II within the mold was controlled at 12 °C / min. After the molten alloy II had completely cooled, the target blank was obtained.

[0064] The target blank was vacuum heat-treated at 1050℃ for 4 hours and then ground into a finished product.

[0065] Figure 3 The image shows a finished product from Example 2. As can be seen from the image, the product has a good appearance and is free of cracks and oxidation points.

[0066] Metallographic analysis was performed on the finished product of Example 2, and the results are as follows: Figure 4 As shown in the figure, the grain size test results of the upper and lower surfaces of the target blank are relatively similar, with an average grain size of about 20 μm.

[0067] The surface quality of each finished product in Examples 1-2 and Comparative Examples 1-4 was observed, and the oxygen content of each finished product in Examples 1-2 and Comparative Examples 1-4 was tested using an oxygen-nitrogen analyzer. The average grain size of the upper and lower surfaces of each finished product in Examples 1-2 and Comparative Examples 1-4 was analyzed using a metallographic microscope. The results are shown in Table 1.

[0068] Table 1

[0069] Test Project Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Example 2 Is it cracked? no no no yes yes no Average grain size on the upper surface (μm) 28.18 27.25 29.61 24.31 35.21 25.44 Average grain size (μm) on the lower surface 37.16 43.16 37.16 57.16 40.36 20.56 Grain size difference between upper and lower surfaces (μm) 8.98 15.91 7.55 32.85 5.15 4.88 O content (ppm) 180 230 280 134 154 146

[0070] As can be clearly seen from Table 1, the method for preparing aluminum-scandium alloy target blanks with high scandium content through two melting-casting processes provided by the present invention is crucial for obtaining a target blank product that does not crack, has a small difference in grain size between the upper and lower surfaces, and has a low O content.

[0071] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-scandium-content aluminum-scandium alloy target blank, characterized in that, Includes the following steps: (1) Weigh metallic scandium and metallic aluminum according to the scandium and aluminum content designed in the aluminum-scandium alloy target billet, and mix and melt metallic scandium and metallic aluminum to obtain alloy melt; the scandium content designed in the aluminum-scandium alloy target billet is 30~40 at%; the melting temperature is 1310℃~1345℃; (2) The alloy melt is poured into the mold and then cooled to form a billet I; the cooling rate of the alloy melt in the mold is 50 ~ 100℃ / min; (3) After grinding, the billet I is melted again, then poured into the mold, cooled and shaped to obtain billet II; the cooling rate is 3~12℃ / min; the melting temperature is 1360℃~1435℃; (4) The blank II obtained by vacuum heat treatment step (3).

2. The method for preparing a high-scandium-content aluminum-scandium alloy target blank as described in claim 1, characterized in that, The mold is one of a graphite mold, a water-cooled copper mold, or a carbon steel mold.

3. The method for preparing a high-scandium-content aluminum-scandium alloy target blank as described in claim 1, characterized in that, The casting rate in steps (2) and (3) is 0.3~0.5 kg / s.

4. The method for preparing a high-scandium-content aluminum-scandium alloy target blank as described in claim 1, characterized in that, The vacuum heat treatment is performed at a temperature of 850~1050℃ for 2~4 hours.

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