A method for preparing a magnesium-based in-situ refining agent and synthesizing refining magnesium alloys

Abstract

This invention provides a method for preparing a magnesium-based in-situ grain refiner. The method utilizes an Al-Mg3N2-Mg reaction system and a hot-pressing sintering process to obtain the magnesium-based in-situ grain refiner AlN / Mg. The in-situ synthesis method effectively controls the size and content of the AlN particles generated in the refiner, enabling the AlN particles to reach nanoscale size and preventing agglomeration. Simultaneously, the interface between the AlN / Mg and the matrix is ​​clean and uncontaminated, exhibiting good interfacial bonding. When the magnesium-based in-situ grain refiner AlN / Mg is used to synthesize refined magnesium alloys, the AlN particles show good compatibility with the magnesium alloy matrix and can act as heterogeneous nucleation sites for α-Mg, increasing the grain nucleation rate. Simultaneously, it inhibits dendrite growth, improving the size and distribution of the second phase and significantly refining the matrix microstructure.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy technology, specifically relating to a method for preparing a magnesium-based in-situ refining agent and synthesizing a refining magnesium alloy. Background Technology

[0002] Magnesium alloys possess excellent properties such as low density, high thermal conductivity, and high specific strength and specific stiffness, making them highly valuable and promising for applications in the automotive, aerospace, and defense industries. However, their low strength and poor plasticity limit their large-scale application. For example, in alloys such as Mg-Al-Ca, Mg-Al-La, and Mg-Al-Ce, the second phase is distributed in a network along the grain boundaries, and is mostly in the form of lamellar, rod-shaped, and acicular eutectic phases. These coarse eutectic phases are prone to breakage, leading to a decrease in alloy performance.

[0003] Adding ceramic grain refiners to magnesium alloys can refine grains, improve the morphology and distribution of the second phase, thereby enhancing the mechanical properties of the alloy and better meeting industrial requirements for high strength and lightweight materials. Currently, common grain refiners such as TiC and TiB2 are mostly used for aluminum alloys, while research on grain refiners suitable for magnesium alloys is limited. AlN ceramic particles have low density, low coefficient of thermal expansion, and good interfacial bonding strength with the magnesium matrix, making them a promising magnesium-based grain refiner for further research and development. However, traditional external addition methods can lead to interfacial contamination between the particles and the matrix material, uneven distribution of reinforcing particles, and poor microstructure improvement. Therefore, exploring the in-situ synthesis of nanoscale magnesium-based grain refiners is of great significance for further improving the wettability between reinforcing particles and the magnesium alloy matrix, and obtaining magnesium alloy materials with better microstructure and higher mechanical properties. Summary of the Invention

[0004] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a method for preparing a magnesium-based in-situ grain refiner. This method uses an Al-Mg3N2-Mg reaction system and a hot-pressing sintering process to prepare the magnesium-based in-situ grain refiner AlN / Mg. This process can effectively control the content and size of the generated AlN particles, resulting in AlN particles with nanometer-sized particles in the obtained magnesium-based in-situ grain refiner. The magnesium-based in-situ grain refiner of this invention can serve as an effective grain refiner for magnesium alloy matrices. During the synthesis of magnesium alloys, it improves the matrix structure and the size and distribution of the second phase by providing a heterogeneous nucleation substrate and inhibiting dendrite growth.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing a magnesium-based in-situ refining agent, wherein the mass percentage of each component in the magnesium-based in-situ refining agent is: AlN 20-50 wt.%, with the balance being Mg; the preparation method of the magnesium-based in-situ refining agent is as follows:

[0006] Under argon protection, Al powder, Mg3N2 powder and Mg powder are ball-milled and mixed evenly to obtain Al-Mg3N2-Mg mixed powder; the Al-Mg3N2-Mg mixed powder is pre-pressed and then hot-pressed and sintered into a blank to obtain magnesium-based in-situ refining agent AlN / Mg.

[0007] Preferably, the purity of the Al powder is 99.9 wt.%, and the powder size is 1–3 μm;

[0008] The Mg powder has a purity of 99.9 wt.% and a powder size of 1–3 μm;

[0009] The purity of the Mg3N2 powder is 99.9 wt.%, and the powder size is 1-2 μm.

[0010] Preferably, the mass ratio of Al powder, Mg3N2 powder and Mg powder in the 20wt.% AlN / Mg magnesium-based in-situ refining agent is 13.16wt.%: 24.63wt.%: 62.21wt.%;

[0011] The mass ratio of Al powder, Mg3N2 powder and Mg powder in the 30wt.% AlN / Mg magnesium-based in-situ refining agent is 19.75wt.%: 36.94wt.%: 43.31wt.%;

[0012] The mass ratio of Al powder, Mg3N2 powder and Mg powder in the 40wt.% AlN / Mg magnesium-based in-situ refining agent is 26.32wt.%: 49.26wt.%: 24.42wt.%;

[0013] The mass ratio of Al powder, Mg3N2 powder and Mg powder in the 50wt.% AlN / Mg magnesium-based in-situ refining agent is 32.91wt.%: 61.57wt.%: 5.52wt.%.

[0014] Preferably, the ball milling speed is 80-110 r / min, the ball milling time is 4-7 h, and the ball-to-material ratio is 10:1.

[0015] Preferably, the pre-compression operation has a pre-compression pressure of 4t and a time of 1-2min; the hot-pressing sintering has a heating rate of 100℃ / min, a pressure of 0.2-0.4t during heating, a sintering temperature of 1000℃, and a holding time of 2min.

[0016] The present invention also provides an application of the magnesium-based in-situ refining agent prepared by the above method, wherein the magnesium-based in-situ refining agent is used to synthesize refining magnesium alloys.

[0017] A method for synthesizing a fine-refining magnesium alloy, which involves adding a magnesium-based in-situ refining agent during the melting process of the magnesium alloy and then casting it, specifically including the following steps:

[0018] Pure magnesium was placed in a resistance melting furnace and heated to 1023K until it was completely melted. Then, pure aluminum and Mg-Ca / La / Ce / Nd-Mn master alloy were added in sequence. After complete melting, magnesium-based in-situ refining agent AlN / Mg was added to the alloy melt and stirred continuously. Finally, the alloy liquid was slag-removed and cast into a metal mold. After solidification, an as-cast sample of AlN particle-refined magnesium alloy was obtained.

[0019] Preferably, the purity of the pure magnesium is 99.8%, the purity of the pure aluminum is 99.9%, and the Mg-Ca / La / Ce / Nd-Mn master alloy includes Mg-30wt.%Ca master alloy, Mg-30wt.%La master alloy, Mg-30wt.%Ce master alloy, Mg-30wt.%Nd master alloy, and Mg-5wt.%Mn master alloy.

[0020] Preferably, the amount of the magnesium-based in-situ refining agent AlN / Mg is: AlN particles account for 0.1 to 1.0% of the mass of the magnesium alloy refined by AlN particles.

[0021] The particle size range of the AlN particles refined magnesium alloy synthesized in this invention is 5–25 μm, wherein the size of the AlN particles is 50–500 nm.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. This invention provides a method for preparing a magnesium-based in-situ refining agent. The method uses an Al-Mg3N2-Mg reaction system and a hot-pressing sintering process to obtain the magnesium-based in-situ refining agent AlN / Mg. The in-situ synthesis method can effectively control the size and content of AlN particles generated in the refining agent, so that the size of AlN particles can reach the nanoscale and the particles are not prone to agglomeration. At the same time, the interface with the matrix is ​​clean and free from pollution, and the interface bonding is good.

[0024] 2. Adding the magnesium-based in-situ grain refiner AlN / Mg to the magnesium alloy has several advantages. First, the lattice mismatch between AlN particles and the magnesium matrix is ​​relatively small, thus providing a heterogeneous nucleation substrate for the α-Mg phase during solidification, significantly increasing the grain nucleation rate and refining the grains. Second, AlN distributed at the solid-liquid interface front can effectively inhibit the growth of α-Mg dendrites, reducing dendrite size while promoting a uniform distribution of the eutectic phase. Furthermore, the refinement of the matrix structure also makes the distribution of the main solute elements more uniform, thereby affecting the size of the second phase and making it smaller.

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0026] Figure 1 This is a metallographic image of the as-cast microstructure of the AlN-refined Mg-9Al-4Ca magnesium alloy prepared in Example 1 of this invention.

[0027] Figure 2 This is a metallographic image of the as-cast microstructure of the AlN-refined Mg-4Al-4La magnesium alloy prepared in Example 2 of this invention.

[0028] Figure 3 This is a scanning electron microscope image of the as-cast microstructure of the AlN-refined Mg-4Al-4Ce magnesium alloy prepared in Example 3 of this invention.

[0029] Figure 4 This is a metallographic image of the as-cast microstructure of the AlN-refined Mg-4Al-4Nd-0.3Mn magnesium alloy prepared in Example 4 of this invention.

[0030] Figure 5 This is a metallographic image of the as-cast microstructure of the unrefined Mg-9Al-4Ca magnesium alloy of Comparative Example 1 of this invention.

[0031] Figure 6 This is a metallographic image of the as-cast microstructure of the unrefined Mg-4Al-4La magnesium alloy of Comparative Example 2 of this invention.

[0032] Figure 7 This is a scanning electron microscope image of the as-cast microstructure of the unrefined Mg-4Al-4Ce magnesium alloy of Comparative Example 3 of this invention.

[0033] Figure 8 This is a metallographic image of the as-cast microstructure of the unrefined Mg-4Al-4Nd-0.3Mn magnesium alloy of Comparative Example 4 of this invention. Detailed Implementation

[0034] Example 1

[0035] This example describes the preparation of a 20wt.% AlN / Mg magnesium-based in-situ refining agent and the synthesis of AlN particles to refine Mg-9Al-4Ca magnesium alloy.

[0036] S1, Preparation of magnesium-based in-situ refining agent

[0037] S101. First, weigh Al powder, Mg3N2 powder, and Mg powder at a mass ratio of 13.16:24.63:62.21. The purity of Al powder is 99.9 wt.%, and the powder size is 1-3 μm; the purity of Mg powder is 99.9 wt.%, and the powder size is 1-3 μm; the purity of Mg3N2 powder is 99.9 wt.%, and the powder size is 1-2 μm.

[0038] S102. The weighed raw materials are ball-milled and mixed using a planetary ball mill. After the powder is placed in the ball mill jar, the jar is evacuated and argon protective gas is introduced into it. Then the mixing ball mill is run at a ball milling speed of 80 r / min for 4 hours and the ball-to-material ratio is 10:1 to obtain a uniformly mixed Al-Mg3N2-Mg powder.

[0039] S103. Weigh 40g of Al-Mg3N2-Mg mixed powder and perform pre-pressing operation. The pre-pressing pressure is 4t and the time is 1-2min. Then, perform hot pressing sintering at 1000℃ to form a blank. During the hot pressing sintering process, the instrument heating rate is 100℃ / min, the pressure during heating is 0.2-0.4t, and the holding time is 2min. Finally, an AlN / Mg refining agent with a content of 20wt.% is obtained.

[0040] S2, Synthetic Refined Magnesium Alloy

[0041] S201, weigh 75g of 20wt.% AlN / Mg refining agent, 2260g of pure magnesium, 270g of pure aluminum, and 500g of Mg-30wt.% Ca master alloy, wherein the purity of pure magnesium is 99.8% and the purity of pure aluminum is 99.9%.

[0042] S202. Place pure magnesium in a crucible and place it in a resistance melting furnace. Heat the furnace to 1023K and wait for it to melt completely. Then, add pure aluminum and Mg-30wt.%Ca master alloy in sequence. After it melts completely, add 20wt.%AlN / Mg refiner to the alloy melt and stir continuously. Finally, after slag removal, pour the alloy liquid into a metal mold. After solidification, the as-cast sample of AlN-refined Mg-9Al-4Ca magnesium alloy is obtained.

[0043] Figure 1 The image shows the as-cast microstructure of the AlN-refined Mg-9Al-4Ca magnesium alloy prepared in Example 1.

[0044] Example 2

[0045] This example describes the preparation of a 30wt.% AlN / Mg magnesium-based in-situ refining agent and the synthesis of AlN particles to refine Mg-4Al-4La magnesium alloy.

[0046] S1, Preparation of magnesium-based in-situ refining agent

[0047] S101. First, weigh Al powder, Mg3N2 powder, and Mg powder at a mass ratio of 19.75:36.94:43.31. The purity of Al powder is 99.9 wt.%, and the powder size is 1-3 μm; the purity of Mg powder is 99.9 wt.%, and the powder size is 1-3 μm; the purity of Mg3N2 powder is 99.9 wt.%, and the powder size is 1-2 μm.

[0048] S102. The weighed raw materials are ball-milled and mixed using a planetary ball mill. After the powder is placed in the ball mill jar, the jar is evacuated and argon protective gas is introduced into it. Then the mixing ball mill is run at a ball milling speed of 90 r / min for 5 hours and the ball-to-material ratio is 10:1 to obtain a uniformly mixed Al-Mg3N2-Mg powder.

[0049] S103. Weigh 40g of Al-Mg3N2-Mg mixed powder and perform a pre-pressing operation. The pre-pressing pressure is 4t and the time is 1-2min. Then, perform hot pressing and sintering at 1000℃ to form a blank. During the hot pressing and sintering process, the instrument heating rate is 100℃ / min, the pressure during heating is 0.2-0.4t, and the holding time is 2min. Finally, an AlN / Mg refining agent with a content of 30wt.% is obtained.

[0050] S2, Synthetic Refined Magnesium Alloy

[0051] S201, weigh 50g of 30wt.% AlN / Mg refining agent, 2410g of pure magnesium, 120g of pure aluminum, and 500g of Mg-30wt.% La master alloy, wherein the purity of pure magnesium is 99.8% and the purity of pure aluminum is 99.9%.

[0052] S202. Place pure magnesium in a crucible and place it in a resistance melting furnace. Heat the furnace to 1023K and wait for it to melt completely. Then, add pure aluminum and Mg-30wt.%La master alloy in sequence. After it melts completely, add 30wt.%AlN / Mg refiner to the alloy melt and stir continuously. Finally, after slag removal, pour the alloy liquid into a metal mold. After solidification, the as-cast sample of AlN-refined Mg-4Al-4La magnesium alloy is obtained.

[0053] Figure 2 Metallographic image of the as-cast microstructure of the AlN-refined Mg-4Al-4La magnesium alloy prepared in Example 2.

[0054] Example 3

[0055] This example describes the preparation and synthesis of 40wt.% AlN / Mg magnesium-based in-situ refining agent and AlN particle refining of Mg-4Al-4Ce magnesium alloy.

[0056] S1, Preparation of magnesium-based in-situ refining agent

[0057] S101. First, weigh Al powder, Mg3N2 powder, and Mg powder at a mass ratio of 26.32:49.26:24.42. The purity of Al powder is 99.9 wt.%, and the powder size is 1-3 μm; the purity of Mg powder is 99.9 wt.%, and the powder size is 1-3 μm; the purity of Mg3N2 powder is 99.9 wt.%, and the powder size is 1-2 μm.

[0058] S102. The weighed raw materials are ball-milled and mixed using a planetary ball mill. After the powder is placed in the ball mill jar, the jar is evacuated and argon protective gas is introduced into it. Then the mixing ball mill is run at a ball milling speed of 100 r / min for 6 hours and the ball-to-material ratio is 10:1 to obtain a uniformly mixed Al-Mg3N2-Mg powder.

[0059] S103. Weigh 40g of Al-Mg3N2-Mg mixed powder and perform a pre-pressing operation. The pre-pressing pressure is 4t and the time is 1-2min. Then, perform hot pressing and sintering at 1000℃ to form a blank. During the hot pressing and sintering process, the instrument heating rate is 100℃ / min, the pressure during heating is 0.2-0.4t, and the holding time is 2min. Finally, an AlN / Mg refining agent with a content of 40wt.% is obtained.

[0060] S2, Synthetic Refined Magnesium Alloy

[0061] S201, weigh 37.5g of 40wt.% AlN / Mg refining agent, 2410g of pure magnesium, 120g of pure aluminum, and 500g of Mg-30wt.% Ce master alloy, wherein the purity of pure magnesium is 99.8% and the purity of pure aluminum is 99.9%.

[0062] S202. Place pure magnesium in a crucible and place it in a resistance melting furnace. Heat the furnace to 1023K and wait for it to melt completely. Then, add pure aluminum and Mg-30wt.%Ce master alloy in sequence. After it melts completely, add 40wt.%AlN / Mg refiner to the alloy melt and stir continuously. Finally, after slag removal, pour the alloy liquid into a metal mold. After solidification, the as-cast sample of AlN-refined Mg-4Al-4Ce magnesium alloy is obtained.

[0063] Figure 3 The image shows the as-cast microstructure of the AlN-refined Mg-4Al-4Ce magnesium alloy prepared in Example 3.

[0064] Example 4

[0065] This example describes the preparation and synthesis of AlN particle refinement of Mg-4Al-4Nd-0.3Mn magnesium alloy using a 50wt.% AlN / Mg magnesium-based in-situ refining agent.

[0066] S1, Preparation of magnesium-based in-situ refining agent

[0067] S101. First, weigh Al powder, Mg3N2 powder, and Mg powder at a mass ratio of 32.91:61.57:5.52. The purity of Al powder is 99.9 wt.%, and the powder size is 1-3 μm; the purity of Mg powder is 99.9 wt.%, and the powder size is 1-3 μm; the purity of Mg3N2 powder is 99.9 wt.%, and the powder size is 1-2 μm.

[0068] S102. The weighed raw materials are ball-milled and mixed using a planetary ball mill. After the powder is placed in the ball mill jar, the jar is evacuated and argon protective gas is introduced into it. Then the mixing ball mill is run at a ball milling speed of 110 r / min for 7 hours and the ball-to-material ratio is 10:1 to obtain a uniformly mixed Al-Mg3N2-Mg powder.

[0069] S103. Weigh 40g of Al-Mg3N2-Mg mixed powder and perform a pre-pressing operation. The pre-pressing pressure is 4t and the time is 1-2min. Then, perform hot pressing and sintering at 1000℃ to form a blank. During the hot pressing and sintering process, the instrument heating rate is 100℃ / min, the pressure during heating is 0.2-0.4t, and the holding time is 2min. Finally, an AlN / Mg refining agent with a content of 50wt.% is obtained.

[0070] S2, Synthetic Refined Magnesium Alloy

[0071] S201, weigh 30g of 50wt.% AlN / Mg refining agent, 2173g of pure magnesium, 120g of pure aluminum, 500g of Mg-30wt.% Nd master alloy, and 240g of Mg-5wt.% Mn master alloy, wherein the purity of pure magnesium is 99.8% and the purity of pure aluminum is 99.9%;

[0072] S202. Place pure magnesium in a crucible and place it in a resistance melting furnace. Heat the furnace to 1023K and allow it to melt completely. Then, add pure aluminum, Mg-30wt.%Nd master alloy, and Mg-5wt.%Mn master alloy in sequence. After complete melting, add 50wt.%AlN / Mg refining agent to the alloy melt and stir continuously. Finally, after slag removal, pour the alloy liquid into a metal mold. After solidification, a cast sample of AlN-refined Mg-4Al-4Nd-0.3Mn magnesium alloy is obtained.

[0073] Figure 4The image shows the as-cast microstructure of the AlN-refined Mg-4Al-4Nd-0.3Mn magnesium alloy prepared in Example 4.

[0074] Comparative Example 1

[0075] Preparation of unrefined Mg-9Al-4Ca magnesium alloy:

[0076] S1. Weigh 2260g of pure magnesium, 270g of pure aluminum, and 500g of Mg-30wt.%Ca master alloy, wherein the purity of pure magnesium is 99.8% and the purity of pure aluminum is 99.9%.

[0077] S2. Place pure magnesium in a crucible and place it in a resistance melting furnace. Heat the furnace to 1023K and wait for it to melt completely. Then, add pure aluminum and Mg-30wt.%Ca master alloy in sequence. After the alloy melt is completely melted, keep the alloy liquid at a temperature for 30 minutes. Finally, remove the slag from the alloy liquid and pour it into a metal mold. After solidification, you will get the as-cast sample of unrefined Mg-9Al-4Ca magnesium alloy.

[0078] Figure 5 The image shows the as-cast microstructure of the unrefined Mg-9Al-4Ca magnesium alloy in Comparative Example 1.

[0079] Figure 1 and Figure 5 The results indicate that the addition of AlN significantly refined the grains of the Mg-9Al-4Ca magnesium alloy, with a marked reduction in dendrite spacing and a finer microstructure. Simultaneously, the addition of the particle refiner also significantly optimized the size and morphology of the second phase, refining the lamellar eutectic microstructure from 10–30 μm to 5–20 μm.

[0080] Comparative Example 2

[0081] Preparation of unrefined Mg-4Al-4La magnesium alloy:

[0082] S1. Weigh 2410g of pure magnesium, 120g of pure aluminum, and 500g of Mg-30wt.%La master alloy, wherein the purity of pure magnesium is 99.8% and the purity of pure aluminum is 99.9%.

[0083] S2. Place pure magnesium in a crucible and place it in a resistance melting furnace. Heat the furnace to 1023K and wait for it to melt completely. Then, add pure aluminum and Mg-30wt.%La master alloy in sequence. After the alloy melt is completely melted, keep the alloy liquid at a temperature for 30 minutes. Finally, remove the slag from the alloy liquid and pour it into a metal mold. After solidification, you will get the as-cast sample of unrefined Mg-4Al-4La magnesium alloy.

[0084] Figure 6The image shows the as-cast microstructure of the unrefined Mg-4Al-4La magnesium alloy in Comparative Example 2.

[0085] Figure 2 and Figure 6 Without the addition of AlN to refine the grains, the acicular and granular second phases in the Mg-4Al-4La alloy exhibit a network structure distributed at the grain boundaries, with uneven distribution of the acicular phase and significant enrichment at the grain boundaries. After adding AlN, the alloy microstructure is significantly improved, with a marked refinement of the matrix grains. Simultaneously, the acicular second phase is broken up, its size is reduced to 10–20 μm, and its distribution uniformity in the matrix is ​​also significantly optimized.

[0086] Comparative Example 3

[0087] Preparation of unrefined Mg-4Al-4Ce magnesium alloy:

[0088] S1. Weigh 2410g of pure magnesium, 120g of pure aluminum, and 500g of Mg-30wt.%Ce master alloy, wherein the purity of pure magnesium is 99.8% and the purity of pure aluminum is 99.9%.

[0089] S2. Place pure magnesium in a crucible and place it in a resistance melting furnace. Heat the furnace to 1023K and wait for it to melt completely. Then, add pure aluminum and Mg-30wt.%Ce master alloy in sequence. After the alloy melt is completely melted, keep the alloy liquid at a temperature for 30 minutes. Finally, remove the slag from the alloy liquid and pour it into a metal mold. After solidification, you will get the as-cast sample of unrefined Mg-4Al-4Ce magnesium alloy.

[0090] Figure 7 The image shows the as-cast microstructure of the unrefined Mg-4Al-4Ce magnesium alloy in Comparative Example 3.

[0091] Figure 3 and Figure 7 This indicates that the Mg-4Al-4Ce alloy contains acicular phases and granular second phases of 20–40 μm in size distributed along the grain boundaries, with the acicular phases often clustered in a fan shape. Adding 40 wt.% AlN / Mg refining agent to the alloy significantly refines the grain size of the Mg-4Al-4Ce matrix alloy and reduces the dendrite spacing. Simultaneously, the acicular phases are broken up, and the clustering phenomenon is improved, while the granular phase increases.

[0092] Comparative Example 4

[0093] Preparation of unrefined Mg-4Al-4Nd-0.3Mn magnesium alloy:

[0094] S1. Weigh 2173g of pure magnesium, 120g of pure aluminum, 500g of Mg-30wt.%Nd master alloy, and 240g of Mg-5wt.%Mn master alloy, wherein the purity of pure magnesium is 99.8% and the purity of pure aluminum is 99.9%.

[0095] S2. Place pure magnesium in a crucible and place it in a resistance melting furnace. Heat the furnace to 1023K and allow it to melt completely. Then, add pure aluminum, Mg-30wt.%Nd master alloy, and Mg-5wt.%Mn master alloy in sequence. After they are completely melted, keep the alloy liquid at a constant temperature for 30 minutes. Finally, remove the slag from the alloy liquid and pour it into a metal mold. After solidification, you will get an as-cast sample of unrefined Mg-4Al-4Nd-0.3Mn magnesium alloy.

[0096] Figure 8 The image shows the as-cast microstructure of the unrefined Mg-4Al-4Nd-0.3Mn magnesium alloy in Comparative Example 4.

[0097] Figure 4 and Figure 8 The results show that the second phase in the Mg-4Al-4Nd-0.3Mn magnesium alloy mainly consists of small polygonal particles with sizes of approximately 200–800 nm and a large number of acicular phases with widths of approximately 100 nm and lengths of approximately 1–20 μm distributed at the grain boundaries. After adding the AlN / Mg refining agent, a significant optimization of the second phase distribution was observed, and the clustering of acicular phases at the grain boundaries was greatly reduced. Furthermore, the size of the second phase was reduced to 1–10 μm.

[0098] Table 1 shows the α-Mg dendrite and second phase size statistics in the magnesium alloys prepared in Examples 1-4 and Comparative Examples 1-4.

[0099] Table 1. Size of α-Mg dendrites and second phase in magnesium alloys

[0100] Example 1 10～20 1～15 Example 2 8～25 1～20 Example 3 15～25 2～20 Example 4 5～15 1～8 Comparative Example 1 20～25 2～40 Comparative Example 2 10～45 2～30 Comparative Example 3 20～40 5～45 Comparative Example 4 8～20 2～10

[0101] In this invention, the size and content of AlN particles generated in the magnesium-based in-situ refining agent AlN / Mg can be effectively controlled through in-situ synthesis. In-situ 20–50 wt.% AlN / Mg refining agent was successfully prepared using an Al-Mg3N2-Mg reaction system. The introduction of the magnesium-based in-situ refining agent AlN / Mg into magnesium alloys specifically includes: adding 20 wt.% AlN / Mg refining agent to Mg-Al-Ca alloys, adding 30 wt.% AlN / Mg refining agent to Mg-Al-La alloys, adding 40 wt.% AlN / Mg refining agent to Mg-Al-Ce alloys, and adding 50 wt.% AlN / Mg refining agent to Mg-Al-Nd-Mn alloys. The synthesized AlN particles refine the magnesium alloy particle size in the range of 5–25 μm, and the AlN particle size is 50–500 nm.

[0102] Data from Examples 1-4 and Comparative Examples 1-4 show that the introduction of magnesium-based in-situ nano-refining agent AlN / Mg into the Mg-Al-Ca / La / Ce / Nd-Mn alloy effectively improves the distribution of the microstructure, making the microstructure denser and reducing the clustering phenomenon of the second phase. Simultaneously, it significantly refines the size of the grains and the second phase, and reduces the dendrite spacing. This is because introducing nano-AlN particles as a refining agent into the magnesium alloy avoids problems such as AlN particle surface contamination, poor dispersion uniformity, and poor wettability, ensuring a clean and continuous interface and good lattice matching between the refined AlN particles and the α-Mg matrix, effectively strengthening the magnesium alloy. Furthermore, the good compatibility of AlN particles with the magnesium alloy matrix allows them to act as heterogeneous nucleation sites for α-Mg, increasing the grain nucleation rate. Additionally, the excellent high-temperature thermal stability of the particles hinders dendrite growth during alloy solidification, improving the size and distribution of the second phase and significantly refining the matrix microstructure.

[0103] Therefore, the addition of magnesium-based in-situ grain refiners AlN / Mg can effectively refine the matrix structure and second phase distribution of magnesium alloys. Grain refinement is beneficial to both the strength and plasticity of magnesium alloys, and is of great significance for expanding the application of magnesium alloys.

[0104] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for synthesizing refined magnesium alloys, characterized in that, Includes the following steps: S1. Preparation of magnesium-based in-situ refining agent Weigh out raw materials Al powder, Mg3N2 powder and Mg powder, wherein the purity of Al powder is 99.9 wt.% and the powder size is 1~3 μm, the purity of Mg powder is 99.9 wt.% and the powder size is 1~3 μm, and the purity of Mg3N2 powder is 99.9 wt.% and the powder size is 1~2 μm; Under argon protection, Al powder, Mg3N2 powder, and Mg powder are ball-milled and mixed uniformly at a speed of 80-110 r / min for 4-7 h with a ball-to-powder ratio of 10:1 to obtain Al-Mg3N2-Mg mixed powder. The Al-Mg3N2-Mg mixed powder is then pre-pressed at a pressure of 4 t for 1-2 min, followed by hot pressing and sintering into a blank at a heating rate of 100 °C / min, a pressure of 0.2-0.4 t, a sintering temperature of 1000 °C, and a holding time of 2 min to obtain a magnesium-based in-situ refining agent, AlN / Mg. The mass percentage of each component in the magnesium-based in-situ refining agent is: AlN 20-40 wt.%, with the balance being Mg. S2, Synthetic Refined Magnesium Alloy Pure magnesium was placed in a resistance melting furnace and heated to 1023K to be completely melted. Then, pure aluminum and Mg-Ca / La / Ce master alloy were added in sequence. After complete melting, magnesium-based in-situ refining agent AlN / Mg was added to the alloy melt and stirred continuously. Finally, the alloy liquid was slag-removed and cast into a metal mold. After solidification, an as-cast sample of AlN particle-refined magnesium alloy was obtained. The size of the AlN particles is 50~500nm, and the particle size range of the refined magnesium alloy by the AlN particles is 5~25μm; The amount of the magnesium-based in-situ refining agent AlN / Mg is: AlN particles account for 0.1~1.0% of the mass of the magnesium alloy refined by AlN particles.

2. The method according to claim 1, characterized in that, When preparing a 20 wt.% AlN / Mg magnesium-based in-situ refining agent in S1, the mass ratio of Al powder, Mg3N2 powder, and Mg powder was 13.16 wt.% : 24.63 wt.% : 62.21 wt.%; When preparing a 30 wt.% AlN / Mg magnesium-based in-situ refining agent, the mass ratio of Al powder, Mg3N2 powder, and Mg powder was 19.75 wt.% : 36.94 wt.% : 43.31 wt.%; When preparing 40wt.% AlN / Mg magnesium-based in-situ refining agent, the mass ratio of Al powder, Mg3N2 powder and Mg powder is 26.32wt.%: 49.26wt.%: 24.42wt.%.

3. The method according to claim 1, characterized in that, The purity of the pure magnesium in S2 is 99.8%, the purity of the pure aluminum is 99.9%, and the Mg-Ca / La / Ce master alloy is Mg-30wt.%Ca master alloy, Mg-30wt.%La master alloy, or Mg-30wt.%Ce master alloy.

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