Methods to improve the agglomeration of micron-sized AlN particles in magnesium rare earth-based composites

Abstract

This invention discloses a method for improving the agglomeration of micron-sized AlN particles in magnesium rare earth-based composite materials, comprising the following steps: 1) preparation of AlN / Al composite powder; 2) adding AlN / Al composite powder to the semi-solid temperature range of the magnesium rare earth-based alloy, and dispersing it uniformly by mechanical stirring to obtain a magnesium rare earth-based composite material melt; 3) heating the magnesium rare earth-based composite material melt, holding it at that temperature, and then water-cooling it to obtain the magnesium rare earth-based composite material. This method, by changing the form of Al element addition, using Al powder instead of Al ingots and using the Al powder to prepare the composite powder to achieve pre-dispersion of AlN particles, combined with mechanical stirring, not only effectively reduces the agglomeration of AlN particles but also effectively improves the sedimentation problem of micron-sized AlN particles, increasing the uniform distribution of AlN particles in the vertical direction of the magnesium rare earth-based alloy, making it suitable for subsequent extrusion processes, and providing a guarantee for the subsequent deformation of the composite material. This is a technical means suitable for commercial application.

Description

Technical Field

[0001] This invention belongs to the field of metal matrix composite technology, specifically relating to a method for improving the agglomeration of micron-sized AlN particles in magnesium rare earth matrix composites. Background Technology

[0002] To meet the demands for high strength and heat resistance in magnesium alloys, adding refractive elements (REs) has become a primary method for improving alloy strength and heat resistance. Researchers have developed GW-based alloys, such as Mg-10Gd-3Y-1Zn-0.4Zr, which combine high strength and heat resistance. However, the high price of REs limits the development of magnesium alloys due to their production costs. Therefore, to further enhance the mechanical properties of GW-based alloys, in addition to adding REs, the addition of inexpensive and high-performance ceramic particles such as SiC, TiB2, and AlN to prepare magnesium-based composite materials has become an important option for developing high-strength, heat-resistant magnesium alloys. Among these, AlN, with its low density and crystal structure and lattice parameters similar to Mg, has become a highly promising reinforcing phase.

[0003] Currently, the commercially viable method for preparing composite materials is stirred casting. However, the biggest challenge of this method lies in achieving uniform dispersion of particles in the matrix. Due to the poor wettability of AlN particles with the Mg matrix, large particle agglomerations easily form during stirred casting, thus limiting the performance enhancement effect of AlN on the alloy. Patent CN114277277A discloses an AlN-Al particle-reinforced magnesium-aluminum rare earth matrix composite material and its preparation method. By adding Al / AlN nanopowder and combining mechanical stirring with ultrasonic stirring, nano-sized AlN is successfully introduced into the alloy. However, this method is relatively complex, and the nano-sized particles are prone to sedimentation during ultrasonication and prolonged settling, and the particle dispersion cannot be well guaranteed. Micron-sized AlN particles have gained wider application due to their reasonable price. However, micron-sized AlN particles not only have the problem of agglomeration, but also have the problem of more easily settling than nano-sized AlN. Therefore, in order to effectively improve the mechanical properties of magnesium alloys by micron-sized AlN particles, it is necessary to find a simple and low-cost method to improve the particle agglomeration problem in the preparation process of composite materials, and provide technical support for the development of magnesium-based composite materials. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the main objective of this invention is to provide a method for improving the agglomeration of micron-sized AlN particles in magnesium rare earth-based composite materials, aiming to solve the problems that existing micron-sized AlN particles easily form large particle agglomerates during stirred casting and easily settle to the bottom of the melt.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for improving the agglomeration of micron-sized AlN particles in magnesium rare earth-based composites includes the following steps:

[0007] 1) Preparation of AlN / Al composite powder: In a glove box protected by pure argon, micron-sized AlN particles and Al powder were mixed and ball-milled in a ball mill. After ball milling, the ball-milled mixture was wrapped with aluminum foil to obtain AlN / Al composite powder.

[0008] 2) Melting and casting of magnesium rare earth-based composite materials: Add the AlN / Al composite powder obtained in step 1) to the semi-solid temperature range of magnesium rare earth-based alloy, and disperse it evenly by mechanical stirring to obtain magnesium rare earth-based composite material melt.

[0009] 3) Heat the magnesium rare earth-based composite material melt from step 2), keep it at the temperature and let it stand, then cool it with water to obtain the magnesium rare earth-based composite material.

[0010] In some specific embodiments, the mass ratio of Al powder to AlN particles in step 1) is (3-1):(1-3), and the particle size of the Al powder and AlN particles is 5-10 μm.

[0011] In some specific embodiments, the mass percentage content of each component in the magnesium rare earth-based composite material is: 97-99.9% magnesium rare earth-based alloy and 0.1-3% AlN particles.

[0012] In some specific implementations, the ball milling conditions in step 1) are: ball-to-material ratio of (10-20):1, rotation speed of 80-120 rpm, and running time of 240-360 min.

[0013] In some specific embodiments, the Al element in the magnesium rare earth-based composite material is added in the form of Al powder.

[0014] In some specific embodiments, the preparation process of the magnesium rare earth-based composite melt in step 3) is as follows:

[0015] 31) In a protective atmosphere with a CO2:SF6 volume ratio of 99:1, a crucible containing pure Mg ingots is placed in an electric resistance furnace and heated to 720-740°C until it is completely melted to obtain molten magnesium.

[0016] 32) Add the Mg-RE master alloy and pure Zn particles to the magnesium melt in sequence, and let it stand at 720-740℃ for 10-20 minutes until the alloy is completely melted. Scrape off the slag on the surface of the melt to obtain the Mg-RE-Zn alloy melt.

[0017] 33) Cool the Mg-RE-Zn alloy melt to the semi-solid temperature range, add Al / AlN composite powder to the Mg-RE-Zn alloy melt to obtain AlN / Mg-RE-Zn-Al composite melt; mechanically stir to disperse the AlN particles in the Mg-RE-Zn-Al alloy melt to obtain magnesium rare earth-based composite melt.

[0018] Furthermore, in step 33), the temperature of the Mg-RE-Zn-Al alloy melt is 605-630℃, the mechanical stirring speed is 100-500rpm, and the stirring time is 5-10min.

[0019] In some specific embodiments, the Al / AlN composite powder, pure Mg ingot, Mg-RE master alloy and pure Zn particles are preheated at a temperature of 150-200°C.

[0020] In some specific embodiments, in step 4), the holding temperature of the magnesium rare earth-based composite melt is 640-650℃, and the standing time is 2-5 minutes.

[0021] Compared with the prior art, the present invention has at least the following advantages:

[0022] 1) The method for improving the agglomeration of micron-sized AlN particles in magnesium rare earth-based composite materials provided by the present invention involves uniformly mixing Al powder and AlN particles through mechanical ball milling to obtain Al / AlN composite powder. This allows harder AlN ceramic particles to uniformly adhere to softer Al powder, thereby achieving pre-dispersion of AlN particles before alloy melting and reducing the tendency of particle agglomeration. At the same time, the Al and AlN composite ball milling can significantly reduce the exposed surface of AlN particles, reduce the adsorption of surface gases and impurities, thereby improving the wettability between AlN and the melt and further reducing the formation of agglomerates. Furthermore, since Al has a melting point lower than the melt temperature, while AlN has a melting point much higher than 740°C and does not melt into the matrix, when Al / AlN composite powder is added to the magnesium rare earth alloy melt, the Al powder will melt preferentially, and then the AlN ceramic particles attached to the Al powder will be slowly released in situ into the melt, and further dispersed under the action of external mechanical stirring, thereby achieving the purpose of uniform dispersion. Compared with directly adding AlN particles, the pre-dispersion effect of Al / AlN composite powder in this application can significantly improve the dispersibility of AlN particles in the composite material, thereby effectively improving the problem of AlN particle agglomeration in magnesium rare earth-based composite materials and reducing the impact of particle agglomeration on the mechanical properties of the composite material.

[0023] 2) In this invention, Al powder is added to the alloy instead of Al ingots, and the Al powder and AlN particles are mechanically ball-milled to pre-disperse the AlN particles on the Al powder, thereby changing the dispersibility of the AlN particles. That is, this application changes the form of aluminum addition and adds Al powder and AlN particles to the Mg-RE-Zn alloy after pre-forming a composite powder, which greatly improves the dispersibility of AlN particles in the magnesium-rare earth-based alloy without changing the composition of the magnesium-rare earth-based composite material, and greatly increases the filling amount of AlN particles in the magnesium-rare earth-based alloy.

[0024] 3) The method provided by this invention is simple. By changing the form of Al element addition and preparing it into a composite powder, and then combining ball milling and mechanical stirring, it not only effectively reduces the agglomeration of AlN particles, but also effectively improves the problem of sedimentation of micron-sized AlN particles, and improves the uniform distribution of AlN particles in the vertical direction of magnesium rare earth-based alloy. That is, it effectively increases the ingot height of magnesium rare earth-based composite material, making it suitable for subsequent extrusion processes, and providing a guarantee for the subsequent deformation of composite material. It is a technical means suitable for commercial application. Attached Figure Description

[0025] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below.

[0026] Figure 1 The process flow diagrams for preparing magnesium-based composite materials by adding Al / AlN composite powder in Examples 1, 2, and 3 of this invention are provided.

[0027] Figure 2 Metallographic image of the as-cast GWZ+0.8Al / 1AlN composite material prepared in Example 1 of this invention, taken at a height of 60 mm;

[0028] Figure 3 Metallographic image of the as-cast GWZ+0.8Al / 2AlN composite material prepared in Example 2 of this invention, taken at a height of 60 mm;

[0029] Figure 4 Metallographic image of the as-cast GWZ+0.8Al / 3AlN composite material prepared in Example 3 of this invention, taken at a height of 60 mm;

[0030] Figure 5 The process flow diagrams for preparing magnesium-based composite materials by adding AlN particles alone in Comparative Examples 1, 2, and 3 provided by the present invention are shown below.

[0031] Figure 6Metallographic image of the as-cast GWZA+1%AlN composite material prepared in Comparative Example 1 provided by the present invention, taken at a height of 60 mm.

[0032] Figure 7 Metallographic image of the as-cast GWZA+2%AlN composite material prepared in Comparative Example 2 provided by the present invention, taken at a height of 60 mm.

[0033] Figure 8 Metallographic image of the as-cast GWZA+3%AlN composite material prepared in Comparative Example 3 provided by the present invention, taken at a height of 60 mm.

[0034] Figure 9 SEM images of the Al / AlN composite powders in Examples 1, 2, and 3 provided by this invention;

[0035] Figure 10 Metallographic images of the as-cast GWZA+AlN composite material prepared in Comparative Example 4 of this invention, taken from samples at different heights. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are merely descriptive and not limiting, and should not be construed as limiting the scope of protection of the present invention.

[0037] When a quantity, concentration, or other value or parameter is described as a range, preferred range, or preferred upper and lower limits, it should be understood that it is equivalent to specifically disclosing any range by combining any pair of upper or preferred values ​​with any lower or preferred values, regardless of whether the range is specifically disclosed. Unless otherwise stated, the numerical range values ​​listed herein include the endpoints of the range and all integers and fractions within that range.

[0038] Unless otherwise stated, all percentages, parts, ratios, etc. in this document are by weight.

[0039] The materials, methods, and embodiments described herein are exemplary and should not be construed as limiting unless otherwise stated.

[0040] In the following examples and comparative examples, the pure magnesium ingots, pure aluminum ingots, pure zinc granules, magnesium-gadolinium master alloy and magnesium-yttrium master alloy, Al powder and AlN particles used were commercially available products. The purity of the pure magnesium ingots, pure aluminum ingots, magnesium-gadolinium master alloy and magnesium-yttrium master alloy was ≥99.95%; the purity of the pure zinc granules was ≥99.99%; the purity of the selected Al powder was ≥99.95%; and the average size of the selected AlN particles was 5-10 μm.

[0041] In the magnesium-gadolinium and magnesium-yttrium master alloys used, gadolinium and yttrium each account for 25-35% of the total alloy mass;

[0042] The metallurgical microscope used was an OLYMPUS PMG3.

[0043] The scanning electron microscope used was a Tescan Vega 3LMH.

[0044] In the following comparative examples and embodiments, this application uses Mg-10Gd-3Y-1Zn-0.8Al (hereinafter referred to as GWZA) and Mg-10Gd-3Y-1Zn (hereinafter referred to as GWZ) as examples to illustrate the preparation method of magnesium rare earth-based composite materials and the method of improving AlN particle agglomeration provided in this application.

[0045] Example 1

[0046] In this embodiment, 0.8% Al powder and 1% AlN particles were uniformly mixed using a mechanical ball milling method to obtain a 0.8Al / 1.0AlN composite powder; subsequently, according to... Figure 1 The process shown prepared the as-cast GWZ+0.8Al / 1.0AlN composite material, specifically including the following steps:

[0047] Based on the designed alloy composition (by mass percentage, the GWZ matrix alloy comprises Gd: 10%, Y: 3%, Zn: 1%, with the balance being Mg) and the burn-off rate, calculate the mass of pure Mg ingots, Mg-30wt.%Gd, Mg-30wt.%Y, pure Zn granules, Al powder, and AlN granules required for smelting.

[0048] 0.8% Al powder and 1% AlN particles were uniformly mixed by mechanical ball milling to obtain 0.8Al / 1.0AlN composite powder; the particle size of Al powder and AlN particles was 5-10μm; the ball-to-powder ratio of the ball mill was 10:1, the rotation speed was 100rpm, and the running time was 300min.

[0049] The aforementioned pure Mg ingots, Mg-30wt.%Gd, and Mg-30wt.%Y alloy raw materials were polished to remove the surface oxide layer, and then batched according to the calculated mass. Finally, they were preheated to 200°C.

[0050] After the high-temperature resistance furnace has been preheated for a period of time, pure Mg ingots are placed in the crucible and clamped into the furnace, and the high temperature of 740℃ is set and 99% CO2 + 1% SF6 protective gas is introduced.

[0051] After the pure Mg ingot is melted, the slag is removed with a slag skimmer, and the corresponding proportions of Mg-30wt.%Gd and Mg-30wt.%Y are placed into the crucible; after the alloy is completely melted, the slag is removed with a slag skimmer, and the corresponding proportions of pure Zn granules are added.

[0052] After the alloy is completely melted, set the resistance furnace temperature to 630℃. When the alloy enters the semi-solid temperature zone, add 0.8Al / 1.0AlN composite powder wrapped in aluminum foil and mechanically stir for 5 minutes at a stirring speed of 300 rpm until the melt forms a conical vortex.

[0053] After mechanical stirring, the temperature was raised to 650℃ and kept at that temperature for 3 minutes; finally, it was cooled to room temperature with water to obtain the as-cast GWZ+0.8Al / 1.0AlN composite material.

[0054] The metallographic microstructure of the as-cast GWZ+0.8Al / 1.0AlN composite material prepared in this embodiment is as follows: Figure 2 As shown, from Figure 2 It can be seen that the added AlN particles are relatively uniformly dispersed, and no obvious agglomeration phenomenon was observed. Compared with Comparative Example 1, it can be clearly found that the particle dispersion of the composite material prepared by adding 0.8Al / 1.0AlN composite powder is better than that of adding 1% AlN particles alone.

[0055] Example 2

[0056] In this embodiment, 0.8% Al powder and 2% AlN particles were uniformly mixed using a mechanical ball milling method to obtain a 0.8Al / 2.0AlN composite powder; subsequently, according to... Figure 5 The process shown prepared the as-cast GWZ+0.8Al / 2.0AlN composite material, specifically including the following steps:

[0057] Based on the designed alloy composition (by mass percentage, the GWZ matrix alloy comprises Gd: 10%, Y: 3%, Zn: 1%, with the balance being Mg) and the burn-off rate, calculate the mass of pure Mg ingots, Mg-30wt.%Gd, Mg-30wt.%Y, pure Zn granules, Al powder, and AlN granules required for smelting.

[0058] 0.8% Al powder and 2% AlN particles were uniformly mixed by mechanical ball milling to obtain 0.8Al / 2.0AlN composite powder; the particle size of Al powder and AlN particles was 5-10μm; the ball-to-material ratio of the ball mill was 10:1, the rotation speed was 100rpm, and the running time was 300min.

[0059] The aforementioned pure Mg ingots, Mg-30wt.%Gd, and Mg-30wt.%Y alloy raw materials were polished to remove the surface oxide layer, and then batched according to the calculated mass. Finally, they were preheated to 200°C.

[0060] After the high-temperature resistance furnace has been preheated for a period of time, pure Mg ingots are placed in the crucible and clamped into the furnace, and the high temperature of 740℃ is set and 99% CO2 + 1% SF6 protective gas is introduced.

[0061] After the pure Mg ingot is melted, the slag is removed with a slag skimmer, and the corresponding proportions of Mg-30wt.%Gd and Mg-30wt.%Y are placed into the crucible; after the alloy is completely melted, the slag is removed with a slag skimmer, and the corresponding proportions of pure Zn granules are added.

[0062] After the alloy is completely melted, set the resistance furnace temperature to 630℃. Once the alloy enters the semi-solid temperature zone, add 0.8Al / 2.0AlN composite powder wrapped in aluminum foil and mechanically stir for 5 minutes at a stirring speed of 300 rpm until the melt forms a conical vortex.

[0063] After mechanical stirring, the temperature was raised to 650℃ and kept at that temperature for 3 minutes; finally, it was cooled to room temperature with water to obtain the as-cast GWZ+0.8Al / 2.0AlN composite material.

[0064] The metallographic microstructure of the as-cast GWZ+0.8Al / 2.0AlN composite material prepared in this embodiment is as follows: Figure 3 As shown, from Figure 3 It can be seen that with the increase of AlN content, the added AlN particles are more uniformly dispersed, and no obvious agglomeration phenomenon was observed. Compared with Comparative Example 2, it is obvious that the particle dispersion of the composite material prepared by adding 0.8Al / 2.0AlN composite powder is better than that of adding 2% AlN particles alone.

[0065] Example 3

[0066] In this embodiment, 0.8% Al powder and 3% AlN particles were uniformly mixed using a mechanical ball milling method to obtain a 0.8Al / 3.0AlN composite powder; subsequently, according to... Figure 5 The process shown prepared the as-cast GWZ+0.8Al / 3.0AlN composite material, specifically including the following steps:

[0067] Based on the designed alloy composition (by mass percentage, the GWZ matrix alloy comprises Gd: 10%, Y: 3%, Zn: 1%, with the balance being Mg) and the burn-off rate, calculate the mass of pure Mg ingots, Mg-30wt.%Gd, Mg-30wt.%Y, pure Zn granules, Al powder, and AlN granules required for smelting.

[0068] 0.8% Al powder and 3% AlN particles were uniformly mixed by mechanical ball milling to obtain 0.8Al / 3.0AlN composite powder; the particle size of Al powder and AlN particles was 5-10μm; the ball-to-powder ratio of the ball mill was 10:1, the rotation speed was 100rpm, and the running time was 300min.

[0069] The aforementioned pure Mg ingots, Mg-30wt.%Gd, and Mg-30wt.%Y alloy raw materials were polished to remove the surface oxide layer, and then batched according to the calculated mass. Finally, they were preheated to 200°C.

[0070] After the high-temperature resistance furnace has been preheated for a period of time, pure Mg ingots are placed in the crucible and clamped into the furnace, and the high temperature of 740℃ is set and 99% CO2 + 1% SF6 protective gas is introduced.

[0071] After the pure Mg ingot is melted, the slag is removed with a slag skimmer, and the corresponding proportions of Mg-30wt.%Gd and Mg-30wt.%Y are placed into the crucible; after the alloy is completely melted, the slag is removed with a slag skimmer, and the corresponding proportions of pure Zn granules are added.

[0072] After the alloy is completely melted, set the resistance furnace temperature to 630℃. Once the alloy enters the semi-solid temperature zone, add 0.8Al / 3.0AlN composite powder wrapped in aluminum foil and mechanically stir for 5 minutes at a stirring speed of 300 rpm until the melt forms a conical vortex.

[0073] After mechanical stirring, the temperature was raised to 650℃ and kept at that temperature for 3 minutes; finally, it was cooled to room temperature with water to obtain the as-cast GWZ+0.8Al / 3.0AlN composite material.

[0074] The metallographic microstructure of the as-cast GWZA+0.8Al / 3.0AlN composite material prepared in this embodiment is as follows: Figure 4 As shown, from Figure 4 It can be seen that with the increase of AlN content, the added AlN particles are also very uniformly dispersed, and no obvious agglomeration phenomenon was observed. Compared with Comparative Example 3, it is obvious that the particle dispersion of the composite material prepared by adding 0.8Al / 3.0AlN composite powder is better than that of adding 3% AlN particles alone.

[0075] Comparative Example 1

[0076] The preparation method of GWZA+AlN composite material by adding AlN alone in this invention is as follows: Figure 5 As shown, according to Figure 5 The process shown prepared a cast GWZA+1%AlN composite material, specifically including the following steps:

[0077] Based on the designed alloy composition (by mass percentage, the GWZA matrix alloy comprises Gd: 10%, Y: 3%, Zn: 1%, Al: 0.8%, with the balance being Mg) and the burn-off rate, calculate the mass of pure Mg ingots, Mg-30wt.%Gd, Mg-30wt.%Y, pure Al ingots, pure Zn particles, and AlN particles required for smelting;

[0078] The alloy raw materials of the aforementioned pure Mg ingot, Mg-30wt.%Gd, Mg-30wt.%Y and pure Al ingot are polished to remove the surface oxide layer, and then the materials are batched according to the calculated mass and preheated to 200℃.

[0079] After the high-temperature resistance furnace has been preheated for a period of time, pure Mg ingots are placed in the crucible and clamped into the furnace, and the high temperature of 740℃ is set and 99% CO2 + 1% SF6 protective gas is introduced.

[0080] After the pure Mg ingot is melted, the slag is removed with a slag skimmer, and the corresponding proportions of Mg-30wt.%Gd and Mg-30wt.%Y are placed into the crucible; after the alloy is completely melted, the slag is removed with a slag skimmer, and the corresponding proportions of pure Al ingot and pure Zn granules are added.

[0081] After the alloy is completely melted, set the resistance furnace temperature to 630℃. When the alloy enters the semi-solid temperature zone, add 1% AlN particles wrapped in aluminum foil and mechanically stir for 5 minutes at a stirring speed of 300 rpm until the melt forms a conical vortex.

[0082] After mechanical stirring, the temperature was raised to 650℃ and kept at that temperature for 3 minutes; finally, it was cooled to room temperature with water to obtain the as-cast GWZA+1%AlN composite material.

[0083] The metallographic microstructure of the as-cast GWZA+1%AlN composite material prepared in this comparative example is as follows: Figure 6 As shown, from Figure 6 It can be seen that the added AlN particles are not evenly dispersed and exhibit obvious agglomeration.

[0084] Comparative Example 2

[0085] This comparative example is based on Figure 5 The process shown prepared a cast GWZA+2%AlN composite material.

[0086] Based on the designed alloy composition (by mass percentage, the GWZA matrix alloy comprises Gd: 10%, Y: 3%, Zn: 1%, Al: 0.8%, with the balance being Mg) and the burn-off rate, calculate the mass of pure Mg ingots, Mg-30wt.%Gd, Mg-30wt.%Y, pure Al ingots, pure Zn particles, and AlN particles required for smelting;

[0087] The alloy raw materials of the aforementioned pure Mg ingot, Mg-30wt.%Gd, Mg-30wt.%Y and pure Al ingot are polished to remove the surface oxide layer, and then the materials are batched according to the calculated mass and preheated to 200℃.

[0088] After the high-temperature resistance furnace has been preheated for a period of time, pure Mg ingots are placed in the crucible and clamped into the furnace, and the high temperature of 740℃ is set and 99% CO2 + 1% SF6 protective gas is introduced.

[0089] After the pure Mg ingot is melted, the slag is removed with a slag skimmer, and the corresponding proportions of Mg-30wt.%Gd and Mg-30wt.%Y are placed into the crucible; after the alloy is completely melted, the slag is removed with a slag skimmer, and the corresponding proportions of pure Al ingot and pure Zn granules are added.

[0090] After the alloy is completely melted, set the resistance furnace temperature to 630℃. Once the alloy enters the semi-solid temperature zone, add 2% AlN particles wrapped in aluminum foil and mechanically stir for 5 minutes at a stirring speed of 300 rpm until the melt forms a conical vortex.

[0091] After mechanical stirring, the temperature was raised to 650℃ and kept at that temperature for 3 minutes; finally, it was cooled to room temperature with water to obtain the as-cast GWZA+2%AlN composite material.

[0092] The metallographic microstructure of the as-cast GWZA+2%AlN composite material prepared in this comparative example is as follows: Figure 7 As shown, from Figure 7 It can be seen that as the AlN particle content increases, the particle dispersion becomes more uneven and the agglomeration phenomenon becomes more serious.

[0093] Comparative Example 3

[0094] This comparative example is based on Figure 5 The process shown prepared a cast GWZA+3%AlN composite material.

[0095] Based on the designed alloy composition (by mass percentage, the GWZA matrix alloy comprises Gd: 10%, Y: 3%, Zn: 1%, Al: 0.8%, with the balance being Mg) and the burn-off rate, calculate the mass of pure Mg ingots, Mg-30wt.%Gd, Mg-30wt.%Y, pure Al ingots, pure Zn particles, and AlN particles required for smelting;

[0096] The alloy raw materials of the aforementioned pure Mg ingot, Mg-30wt.%Gd, Mg-30wt.%Y and pure Al ingot are polished to remove the surface oxide layer, and then the materials are batched according to the calculated mass and preheated to 200℃.

[0097] After the high-temperature resistance furnace has been preheated for a period of time, pure Mg ingots are placed in the crucible and clamped into the furnace, and the high temperature of 740℃ is set and 99% CO2 + 1% SF6 protective gas is introduced.

[0098] After the pure Mg ingot is melted, the slag is removed with a slag skimmer, and the corresponding proportions of Mg-30wt.%Gd and Mg-30wt.%Y are placed into the crucible; after the alloy is completely melted, the slag is removed with a slag skimmer, and the corresponding proportions of pure Al ingot and pure Zn granules are added.

[0099] After the alloy is completely melted, set the resistance furnace temperature to 630℃. Once the alloy enters the semi-solid temperature zone, add 3% AlN particles wrapped in aluminum foil and mechanically stir for 5 minutes at a stirring speed of 300 rpm until the melt forms a conical vortex.

[0100] After mechanical stirring, the temperature was raised to 650℃ and kept at that temperature for 3 minutes; finally, it was cooled to room temperature with water to obtain the as-cast GWZA+3%AlN composite material.

[0101] The metallographic microstructure of the as-cast GWZA+3%AlN composite material prepared in this comparative example is as follows: Figure 8 As shown, from Figure 8 It can be seen that as the AlN particle content further increases, the particle dispersion becomes more uneven, and the agglomeration phenomenon is also very obvious.

[0102] The results of comparisons 1, 2, and 3 show that adding AlN particles alone and mechanically stirring cannot effectively disperse particle agglomeration in magnesium-based composites. Furthermore, as the AlN particle content increases, the particle dispersion becomes more uneven, and the particle agglomeration problem becomes more severe. Therefore, it cannot improve the mechanical properties of magnesium rare earth-based composites.

[0103] Comparative Example 4

[0104] The AlN / Mg-RE-Zn-Al composite material provided in this comparative example has the same composition and proportion as Comparative Examples 1, 2, and 3, and its process steps are also basically the same. The difference lies in that after mechanical stirring, the melt is heated to 670℃ and then subjected to 20kHz ultrasound with a power of 150-300W for 7 minutes for stirring and dispersion. The effective ingot height of the 1% AlN / Mg-RE-Zn-Al and 2% AlN / Mg-RE-Zn-Al composite materials prepared by this process is only about 25mm. This indicates that when using ultrasonic stirring, prolonged ultrasonication and settling will lead to severe sedimentation of micron-sized AlN particles, which is not only complex in process and wasteful of energy and alloy materials, but also difficult to use for subsequent extrusion deformation. In contrast, the method proposed in this application does not require ultrasonic dispersion, and the micron-sized AlN particles do not settle significantly. The effective ingot height of the prepared magnesium rare earth-based composite material is 60mm. That is, this method is not only simple and energy-saving, but also ensures that raw materials are not wasted. The magnesium rare earth-based composite material with the effective ingot height is also suitable for extrusion processing.

[0105] The comparison results of Examples 1, 2, and 3 with Comparative Examples 1, 2, and 3 show that: adding AlN particles alone for mechanical stirring cannot effectively disperse particle agglomeration in magnesium-based composite materials; and with the increase of AlN content, the particle dispersion becomes more uneven, and the particle agglomeration problem becomes more serious, with limited AlN particle addition. However, after ball milling Al powder and AlN particles, adding the Al / AlN composite powder to the alloy for mechanical stirring can effectively improve the original particle agglomeration and sedimentation problems. Furthermore, with the increase of AlN content, AlN particles do not exhibit significant aggregation but remain uniformly dispersed around the grain boundaries of the alloy. This indicates that the method of ball milling Al powder and AlN particles and then adding them to the melt for mechanical stirring is an effective technique for improving AlN particle agglomeration and sedimentation in magnesium rare earth-based composite materials.

[0106] This is mainly because, when Al powder and AlN particles are mixed into a composite powder using mechanical ball milling, the harder AlN particles can be uniformly adhered to the softer Al powder, such as... Figure 9 As shown, this allows for the pre-dispersion of AlN particles before alloy melting, reducing the tendency for particle agglomeration. Furthermore, since Al's melting point is lower than the melt temperature, while AlN's melting point is much higher than 740℃ and it does not melt into the matrix, when Al / AlN composite powder is added to the magnesium rare earth alloy melt, the Al powder melts preferentially. Then, the AlN ceramic particles attached to the Al powder are slowly released in situ into the melt and further dispersed under the action of external mechanical stirring, achieving uniform dispersion. And from... Figure 9It can be seen that AlN adhering to Al powder significantly reduces the exposed surface area of ​​AlN particles, decreases the adsorption of surface gases and impurities, thereby improving the wettability between AlN and the melt and further reducing the formation of agglomerates. Compared with the direct addition of AlN particles, the pre-dispersion effect of Al / AlN composite powder can significantly improve the dispersibility of AlN particles in the composite material, thus effectively improving the problem of AlN particle agglomeration and sedimentation in magnesium rare earth-based composite materials, and reducing the impact of particle agglomeration and sedimentation on the mechanical properties of the composite material.

[0107] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for improving the agglomeration of micron-sized AlN particles in a magnesium-rare earth based composite, characterized in that, It comprises the following steps: 1) Preparation of AlN / Al composite powder: In a glove box under pure argon protection, micron-sized Al powder and AlN particles are mixed and ball milled in a ball mill. After ball milling, the mixed material after ball milling is wrapped with aluminum foil to obtain AlN / Al composite powder; 2) Melting and casting of magnesium-rare earth-based composite material: The AlN / Al composite powder obtained in step 1) is added to the semi-solid temperature zone of the magnesium-rare earth-based alloy, and is uniformly dispersed by mechanical stirring without ultrasonic dispersion, to obtain a magnesium-rare earth-based composite material melt; 3) The magnesium-rare earth-based composite material melt in step 2) is heated, and after heat preservation and standing, it is water-cooled to obtain a magnesium-rare earth-based composite material; the mass ratio of the Al powder to the AlN particles in step 1) is (3-1):(1-3), and the particle size of the Al powder and the AlN particles is 5-10 μm; the Al element in the magnesium-rare earth-based composite material is added in the form of Al powder; and the mass percentage content of each component in the magnesium-rare earth-based composite material is: 97-99.9% of the magnesium-rare earth-based alloy and 0.1-3% of the AlN particles.

2. The method of improving the agglomeration of micron-sized AIN particles in a magnesium-rare earth based composite of claim 1, wherein, The ball milling conditions in step 1) are: the ball-to-material ratio is (10-20):1, the rotation speed is 80-120 rpm, and the running time is 240-360 min.

3. The method of improving the agglomeration of micron-sized AIN particles in a magnesium-rare earth based composite of claim 2, wherein, In step 3), the preparation process of the magnesium-rare earth-based composite melt is: 31) In a protective atmosphere of CO2:SF6 with a volume ratio of 99:1, a crucible containing a pure Mg ingot is placed in a resistance furnace, heated to 720-740 ℃, and kept until the magnesium melt is completely melted; 32) The Mg-RE intermediate alloy and pure Zn particles are sequentially added to the magnesium melt, and the alloy is completely melted at 720-740 ℃ for 10-20 min. The surface dross of the melt is removed to obtain a Mg-RE-Zn alloy melt; 33) The Mg-RE-Zn alloy melt is cooled to the semi-solid temperature zone, the Al / AlN composite powder is added to the Mg-RE-Zn alloy melt to obtain an AlN / Mg-RE-Zn-Al composite melt; the AlN particles in the Mg-RE-Zn-Al alloy melt are dispersed by mechanical stirring to obtain a magnesium-rare earth-based composite melt.

4. The method of improving the agglomeration of micron-sized AIN particles in a magnesium-rare earth based composite of claim 3, wherein, In step 33), the temperature of the Mg-RE-Zn-Al alloy melt is 605-630 ℃, the mechanical stirring speed is 100-500 rpm, and the stirring time is 5-10 min.

5. The method of improving the agglomeration of micron-sized AIN particles in a magnesium-rare earth based composite of claim 1, wherein, It also includes preheating the Al / AlN composite powder, the pure Mg ingot, the Mg-RE intermediate alloy, and the pure Zn particles, and the preheating temperature is 150-200 ℃.

6. The method of improving the agglomeration of micron-sized AIN particles in a magnesium-rare earth based composite of claim 5, wherein, In step 4), the heat preservation temperature of the magnesium-rare earth-based composite melt is 640-650 ℃, and the standing time is 2-5 min.

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