Ceramic particle premix enhanced magnesium matrix composite semi-solid die casting method and system

Abstract

The application belongs to the technical field of non-ferrous composite material preparation and application, and more particularly relates to a semi-solid die casting method and system of ceramic particle premixed reinforced magnesium-based composite material. The application adds a preparation step of pre-prepared composite particles in front of the inlet of a semi-solid hydraulic casting slurry machine. The pre-prepared composite particles are obtained by heating, melting, premixing and cooling and crushing of interface-optimized ceramic particles and magnesium-based alloy particles. The ceramic particles are interface-optimized and further premixed with the magnesium-based alloy through a specific premixing process. The two cooperate to prepare the pre-prepared composite particles, which form a high-quality metallurgical bonding interface under controllable conditions. The pre-prepared composite particles are used as the feedstock of the semi-solid die casting process, which completely changes the raw material basis of the semi-solid die casting and ensures the uniformity and excellent interface of the final composite material product, thereby significantly improving the mechanical properties of the composite material.

Description

Technical Field

[0001] This invention belongs to the field of preparation and application technology of non-ferrous metal composite materials, and more specifically, relates to a semi-solid die-casting method and system for magnesium-based composite materials premixed with ceramic particles for reinforcement. Background Technology

[0002] Semi-solid metal forming technology offers numerous unique advantages over traditional forming methods, such as near-net-shape forming, long mold life, low energy consumption, and heat treatment capability, earning it the reputation as one of the most promising metal processing technologies of the 21st century. Based on different processing methods, semi-solid forming technologies are broadly classified into rheological forming and thixotropic forming. Thixotropic forming technology offers easy quality control and has been applied industrially; however, it requires secondary heating of the semi-solid blank, resulting in a long process flow and high costs. Rheological forming directly shapes the semi-solid slurry, resulting in a shorter process flow, lower costs, and significant development potential, making it a current research hotspot.

[0003] The preparation technology of semi-solid metal slurry is a key technology in semi-solid metal rheological forming. Semi-solid metal slurry preparation methods are mainly divided into stirring methods and non-stirring methods. Stirring methods typically employ mechanical or electromagnetic stirring to break up dendrites in the melt through vigorous agitation, obtaining a semi-solid slurry. While these methods can produce semi-solid slurries, they often result in oxide inclusions, which can easily cause defects in the product during subsequent slurry molding. Non-stirring methods include near-liquidline casting, inclined plate casting, and chemical refining methods. The semi-solid slurries produced by these methods are of low quality and difficult to prepare on a large scale.

[0004] Traditional semi-solid die casting using a stirring method employs a screw mixer. The screw shears heated, shaving-like or granular alloy material into a molten slurry containing solid components, which is then stored at the front end of the die casting machine's barrel. During the injection process, a hydraulic cylinder pushes the entire screw forward, extruding molten metal into the mold for shaping.

[0005] In the traditional stirring-method semi-solid die casting process for preparing particle-reinforced magnesium matrix composites, reinforcing phase particles and alloy matrix phase particles are fed separately or simultaneously through a hopper and heated to prepare a semi-solid slurry. However, due to the significant density difference between the ceramic reinforcing particles and the magnesium-based alloy, their intrinsic wettability is poor. This results in uneven mixing and weak interfacial interactions when using the traditional stirring-method semi-solid die casting process to prepare particle-reinforced magnesium matrix composites, ultimately leading to poor and unstable mechanical properties of the composite material.

[0006] Although some existing technologies have improved the stirring process in the preparation of semi-solid slurries, such as CN101875105A which discloses a method and apparatus for preparing semi-solid slurries by bubble stirring, this method proposes a process for preparing semi-solid slurries by adding mechanical vibration to a rotating graphite rod, and designs and manufactures a set of semi-solid slurry preparation apparatus for this purpose. However, the mixing intensity generated by the airflow disturbance and the mechanical vibration system of the graphite rod in the above design scheme is insufficient, and it has a significant disadvantage in terms of material uniformity compared with traditional screw stirring. This is mainly reflected in the low mixing efficiency caused by insufficient shear force. Similarly, it is difficult to solve the problem of uneven mixing and weak interfacial bonding between ceramic reinforcing particles and magnesium alloys in direct co-feed semi-solid die casting during the melting process of semi-solid metal slurries due to density difference and poor intrinsic wettability. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a semi-solid die-casting method for magnesium-based composite materials reinforced by ceramic particles based on the synergistic reinforcement of pre-fabricated composite particles and interfaces. This method aims to solve the technical problem of uneven mixing and weak interfacial bonding caused by the density difference and intrinsic wettability of nano-ceramic particles and matrix melt during the preparation of magnesium-based composite materials in semi-solid die-casting, which leads to poor overall performance of the prepared composite materials.

[0008] To achieve the above objectives, in a first aspect, the present invention provides a semi-solid die-casting method for magnesium-based composite materials premixed with ceramic particles, comprising the following steps:

[0009] (1) Obtaining interface-optimized ceramic particles; the interface-optimized ceramic particles are aluminum-coated ceramic particles or ceramic particles with an oxide layer on the surface; wherein the ceramic particles with an oxide layer on the surface are oxide ceramic particles, or are prepared by the following method: heating and pre-oxidizing non-oxide ceramic particles to form an oxide layer on their surface to obtain ceramic particles with an oxide layer on the surface.

[0010] (2) The magnesium-based alloy particles and the interface-optimized ceramic particles are heated together to melt the magnesium-based alloy and obtain a mixed melt; an inert gas is introduced into the mixed melt and the mixed melt is stirred to obtain a uniformly mixed melt; and when the interface-optimized ceramic particles are aluminum-coated ceramic particles, the magnesium-based alloy contains metallic aluminum.

[0011] (3) Cool the uniformly mixed melt to obtain a solid intermediate alloy, and crush the solid intermediate alloy to obtain pre-made composite particles;

[0012] (4) The pre-made composite particles are die-cast using a semi-solid die-casting process to obtain a magnesium-based composite material reinforced with ceramic particles.

[0013] Preferably, in step (1) when preparing ceramic particles with an oxide layer on the surface, the non-oxide ceramic particles are first heated and pre-oxidized at a temperature above 800°C to form an oxide layer on their surface.

[0014] More preferably, the pre-oxidation temperature in step (1) is 800-950℃, and the pre-oxidation time is 1-3 h.

[0015] Preferably, in step (2), the magnesium-based alloy particles and the ceramic particles with optimized interface from step (1) are heated together at a temperature of 650-700°C to melt the magnesium-based alloy and obtain a mixed melt.

[0016] Preferably, the stirring in step (2) is gas stirring and / or ultrasonic stirring.

[0017] Preferably, the cooling rate in step (3) is 1-50℃ / s, cooling to a temperature of 100-200℃, and then crushing.

[0018] Preferably, the particle size of the pre-made composite particles in step (3) is 2-20 mm.

[0019] Preferably, the solid fraction of the semi-solid slurry prepared in step (4) during the semi-solid die casting process is controlled at 5-40%.

[0020] According to another aspect of the present invention, a magnesium-based composite material reinforced with ceramic particles is provided, obtained by the preparation method described above.

[0021] According to another aspect of the present invention, a preparation system for the ceramic particle-reinforced magnesium-based composite material is provided, comprising a premixing device and a semi-solid die-casting device.

[0022] The premixing device is used to achieve heating, premixing, cooling, and crushing of magnesium-based alloy particles and interface-optimized ceramic particles. It includes a heating premixing unit, a cooling unit, and a crushing unit. The heating premixing unit includes a heating furnace, a slurry container placed inside the heating furnace, a graphite ultrasonic probe inserted below the liquid surface of the slurry container, a temperature sensor, and a temperature controller. The graphite ultrasonic probe is hollow and has a perforated design, used to introduce inert gas into the slurry container to perform gas stirring and / or ultrasonic stirring of the melt inside the slurry container, thereby obtaining a uniformly mixed melt. The temperature sensor is used to detect the temperature inside the heating furnace, and the temperature controller is used to control the temperature of the heating furnace. The cooling unit is connected to the slurry container and is used to cool the uniformly mixed melt to obtain a solid intermediate alloy. The crushing unit is connected to the cooling unit and is used to crush the solid intermediate alloy to obtain pre-formed composite particles.

[0023] The semi-solid die-casting device is used to die-cast the pre-made composite particles using a semi-solid die-casting process, thereby producing a magnesium-based composite material reinforced with ceramic particles.

[0024] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art:

[0025] (1) The semi-solid die casting method for magnesium-based alloy composite materials proposed in this invention adds a pre-prepared composite particle preparation step before the feed inlet of the semi-solid hydraulic casting slurry machine. The pre-prepared composite particles are obtained by heating, melting, pre-mixing, cooling, and crushing interface-optimized ceramic particles with magnesium-based alloy particles. The interface-optimized ceramic particles are ceramic particles with an oxide layer on the surface or aluminum-coated ceramic particles. The ceramic particles are pre-mixed with magnesium-based alloy through a specific pre-mixing process after interface optimization treatment. The two work together to prepare the pre-prepared composite particles, which solves the technical problems of density difference, poor wettability, and weak interface bonding between magnesium-based alloy particles and reinforcing phase particles in the traditional semi-solid die casting process in advance. Under controllable conditions, a high-quality metallurgical bonding interface is formed. Using the pre-prepared composite particles as feed for the semi-solid die casting process completely changes the raw material basis of semi-solid die casting, ensuring the uniformity and excellent interface of the final composite material product, thereby significantly improving the mechanical properties of the composite material.

[0026] (2) In this invention, when ceramic particles with an oxide layer on their surface are used as ceramic particles for interface optimization, a dense oxide layer is first formed on the surface of the ceramic particles through pre-oxidation, which makes it easier to effectively wet the magnesium-based alloy. Moreover, the formation of the oxide layer can also avoid excessive reaction between the ceramic particles and the molten magnesium alloy. This invention reduces the agglomeration phenomenon in the subsequent slurry preparation process through the pre-formed interface bonding, laying a good foundation for obtaining a semi-solid slurry with a uniform structure. This improvement not only retains the process advantages of traditional semi-solid die casting, but also improves the comprehensive performance of the composite material through the uniform distribution of the reinforcing phase.

[0027] (3) In the process of preparing intermediate alloys of ceramic particles and magnesium alloys, the present invention innovatively adopts a synchronous coupling process of gas stirring and ultrasonic stirring. Compared with the coupling method of gas stirring and mechanical stirring in the prior art, this process has significant advantages: First, the two stirring methods based on different physical mechanisms have better compatibility. The macroscopic flow field generated by gas stirring and the high-frequency micro-flow field formed by ultrasonic stirring have less mutual interference, which is conducive to maintaining a stable mixing environment of the melt. Second, the two processes have a significant positive synergistic effect. The ultrasonic cavitation effect achieves micro-stirring by generating micron-sized bubbles and their collapse process, while the inert gas continuously introduced by gas stirring not only forms macroscopic convection, but also provides sufficient gas source supply for ultrasonic cavitation. The synergistic effect of the two enhances the bubble growth-collapse dynamics process, and the final mixing effect shows a synergistic enhancement characteristic of 1+1>2, making the component mixing more uniform.

[0028] (4) Compared with the limitations of traditional graphite head mechanical stirring, the present invention uses a combined stirring method of gas stirring and ultrasonic stirring in the premixing process for preparing intermediate alloys. This not only improves the mixing efficiency but also avoids the melt contamination problem that may be caused by mechanical stirring, providing a reliable process guarantee for the preparation of high-performance magnesium-based composite materials. The present invention can also further reduce the speed of mechanical stirring during semi-solid die casting by premixing, thus reducing contamination.

[0029] (5) This invention innovatively employs a partially cooled warm crushing process in the preparation of intermediate alloy premix. When the intermediate alloy is cooled to a suitable temperature with a certain residual heat in the cooling chamber, it can be transferred to the crushing process, instead of having to be cooled to room temperature before crushing as in the traditional process. This warm crushing method makes full use of the plastic deformation capacity of the material at higher temperatures, which not only significantly reduces crushing energy consumption, but also more effectively controls the size and morphology of the intermediate alloy particles (metals become softer at high temperatures and are more prone to plastic deformation rather than brittle fracture, while at room temperature, metals may be more brittle and easily break into smaller particles. The size of warm crushed particles is larger than that of room temperature crushed particles. The smaller relative area of ​​large-sized intermediate alloy particles in contact with air can reduce oxidation and avoid particle cracks, etc.). At the same time, the appropriate residual temperature helps to reduce the internal stress generated during the crushing process, avoid defects such as microcracks in the particles, and provide intermediate alloy raw materials with uniform size and stable quality for subsequent pulping processes, thus improving the overall efficiency and controllability of the process.

[0030] (6) This invention breaks through the traditional semi-solid die casting process. First, pre-made composite particles are prepared and then pre-mixed with magnesium-based alloy. The pre-mixed composite particles with high-quality metallurgical bonding interface are fed into the semi-solid die casting device as raw materials for semi-solid die casting production. Compared with the traditional process without pre-mixing, pre-mixing before semi-solid die casting can shorten the mixing time of semi-solid slurry and reduce the risk of oxidation inclusion caused by air exposure. It can also further improve the mechanical properties of the final composite material. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of the ceramic particle and magnesium alloy premixing device for preparing intermediate alloy raw materials involved in some embodiments of the present invention.

[0032] Figure 2 This is a schematic diagram of a semi-solid die-casting machine structure in which the injection part and the slurry preparation part are integrated, according to some embodiments of the present invention.

[0033] Figure 3 These are the test results of the mechanical properties of cast magnesium alloy materials prepared in different embodiments and comparative examples of the present invention;

[0034] Figure 4 This is a flowchart of a semi-solid die-casting method for magnesium-based composite materials premixed with ceramic particles, as described in some embodiments of the present invention.

[0035] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0036] 1-Heating furnace; 2-Paddle container; 3-Graphite ultrasonic probe; 4-Ultrasonic stirring and gas stirring controller; 5-Temperature sensor; 6-Temperature controller; 7-Valve; 8-Cooler; 9-Crushing motor; 10-Crusher; 11-Hydraulic injection unit; 12-Screw rotation unit; 13-Screw; 14-Feeding hopper; 15-Heater; 16-Nozzle. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0038] This invention provides a semi-solid die-casting preparation method for magnesium-based composite materials premixed with ceramic particles, comprising the following steps:

[0039] (1) Obtaining interface-optimized ceramic particles; the interface-optimized ceramic particles are aluminum-coated ceramic particles or ceramic particles with an oxide layer on the surface; wherein the ceramic particles with an oxide layer on the surface are oxide ceramic particles, or are prepared by the following method: heating and pre-oxidizing non-oxide ceramic particles to form an oxide layer on their surface, thereby obtaining ceramic particles with an oxide layer on their surface. That is, first heating and pre-oxidizing non-oxide ceramic particles to form an oxide layer on their surface, thereby obtaining ceramic particles with an oxide layer on their surface; when the ceramic particles are oxide ceramic particles, their surface itself has an oxide layer, and the above heating and oxidation step is omitted;

[0040] (2) The magnesium-based alloy particles and the ceramic particles with optimized surface interface from step (1) are heated together to melt the magnesium-based alloy and obtain a mixed melt. An inert gas is introduced into the mixed melt and the mixed melt is stirred to obtain a uniformly mixed melt. In order to avoid the introduction of impurity elements, when the ceramic particles with optimized interface are aluminum-coated ceramic particles, the magnesium-based alloy contains metallic aluminum. When the ceramic particles with optimized interface are ceramic particles with an oxide layer on the surface, this restriction does not apply.

[0041] (3) Cool the uniformly mixed melt to obtain a solid intermediate alloy, and crush the solid intermediate alloy to obtain pre-made composite particles;

[0042] (4) The prefabricated composite particles described in step (3) are die-cast using a semi-solid die-casting process to obtain a magnesium-based composite material reinforced with ceramic particles.

[0043] The ceramic particles used as the reinforcing phase in this invention can be of commonly used types of ceramic particles in the prior art. In some embodiments, the ceramic particles are one or more of micron- or nano-sized Al2O3 ceramic particles, SiC ceramic particles, B2C ceramic particles, Si3C4 ceramic particles, and TiB2 ceramic particles; the interface-optimized ceramic particles account for 0.1-40% of the magnesium-based alloy mass. The magnesium-based alloy described in this invention can be various magnesium-based alloys, including but not limited to AZ series magnesium alloys, AM series magnesium alloys, etc.

[0044] In some embodiments, when preparing ceramic particles with an oxide layer on the surface in step (1), the non-oxide ceramic particles are first heated and pre-oxidized at a temperature above 900°C to form an oxide layer on their surface.

[0045] In a preferred embodiment, step (1) involves heating the non-oxide ceramic particles at 800℃-950℃ for pre-oxidation to form an oxide layer on their surface. The pre-oxidation time in step (1) is 1-3 hours.

[0046] In step (1), the heating furnace is first raised to 900℃ or higher, and ceramic particles that need to be pre-oxidized are added, such as SiC ceramic particles, B4C ceramic particles, Si3N4 ceramic particles, etc. (Al2O3 ceramic particles are oxides themselves, so this step can be omitted). The purpose of pre-oxidation is to form a dense oxide layer on the surface of the ceramic particles. For example, after pre-oxidation, SiC particles and Si3N4 particles form a dense SiO2 layer on their surface, and after pre-oxidation, B4C ceramic particles form a dense B2O3 layer on their surface. This reduces the excessive reaction between the ceramic particles and the molten magnesium alloy in the premixing process and the subsequent semi-solid die-casting process. The pre-oxidation reaction of the ceramic particles is as follows:

[0047]

[0048]

[0049]

[0050] Oxides, such as the SiO2 layer, act as a diffusion barrier, preventing direct contact between Mg and SiC and inhibiting the formation of harmful phases such as Mg2Si. Furthermore, the untreated SiC surface exhibits magnesium-phobic properties, making it difficult for liquid magnesium to effectively wet the particles, resulting in interfacial porosity and weak bonding. In contrast, SiO2's chemical properties are closer to oxide ceramics (such as Al2O3), and its wettability with molten magnesium is superior to SiC, promoting tight interfacial adhesion and reducing porosity. After pre-oxidation for 1-3 hours, the furnace is cooled to the melting temperature of the magnesium-based alloy, and the magnesium-based alloy is added for melting.

[0051] In other embodiments, the interface-optimized ceramic particles are aluminum-coated ceramic particles. The aluminum-coated ceramic particles can be prepared using molten aluminum impregnation, physical vapor deposition, mechanical ball milling, or thermal spraying; the thickness of the aluminum coating can be 0.1-100 μm. Molten aluminum impregnation involves immersing ceramic particles in molten aluminum, achieving coating through capillary action or external force. Physical vapor deposition involves evaporating or sputtering aluminum onto the ceramic surface in a vacuum environment. Mechanical ball milling involves pressing aluminum powder onto the ceramic surface via cold welding during high-energy ball milling. For example, in some embodiments, a mechanical ball milling coating method is used. Ceramic particles and aluminum powder are mixed in a ball mill jar at a mass ratio of 1.5-2:1, with a ball-to-particle ratio of 10:1-20:1. The milling speed is 200-500 rpm, and the milling time is 2-5 hours. This process is carried out under an inert atmosphere (such as Ar) to prevent oxidation. Alternatively, an aluminum-coated ceramic particle can be prepared using a thermal spraying method, where molten aluminum wire or powder is sprayed at high speed onto a stream of ceramic particles.

[0052] In a preferred embodiment, the thickness of the aluminum coating layer on the surface of the aluminum-coated ceramic particles is controlled to be 0.5-50 μm to obtain better wetting and interfacial bonding effects. When the aluminum-coated ceramic particles are premixed with Mg-Al alloys (such as AZ91), due to the compatibility of the Al coating layer with the Al matrix composition, and the formation of a continuous solid solution between the Al coating layer and the Al matrix, heterogeneous interfaces can be avoided, thereby improving the wettability of the ceramic particles and facilitating their diffusion.

[0053] In some embodiments, step (2) involves heating the magnesium-based alloy particles together with the ceramic particles with optimized interface from step (1) at a temperature of 650-700°C to melt the magnesium-based alloy and obtain a mixed melt. This ensures the fluidity of the melt during premixing while avoiding overheating that could lead to severe oxidation of magnesium, dissolution or reaction of the ceramic, or excessive energy consumption.

[0054] In some embodiments, the stirring in step (2) is gas stirring and / or ultrasonic stirring. More preferably, both gas and ultrasonic stirring are used.

[0055] In some embodiments, the cooling rate in step (3) is 1-50°C / s, cooling to a temperature of 100-200°C, and then crushing. The particle size of the granular intermediate alloy raw material in step (3) is 2-20 mm.

[0056] When crushing solid master alloys, this invention allows for the selection of a suitable crusher based on the size of the solid master alloy and the required crushing force. By appropriately setting the crusher parameters, large pieces of alloy material can be pulverized into uniform small pieces. The motor power of the crusher can be selected from 15KW to 110KW, and the crushed material can be controlled to obtain granular metal pieces with a diameter or side length of 2-20mm.

[0057] This invention first optimizes the interface of ceramic particles, then heats and melts the optimized ceramic particles with a magnesium-based alloy, premixes, cools, and warm-crushes them to obtain granular intermediate alloy raw materials, referred to as pre-formed composite particles. These pre-formed composite particles, possessing a high-quality metallurgical bonding interface, are then used as raw materials for semi-solid die casting. Existing semi-solid die casting processes and equipment are used to prepare ceramic particle-reinforced magnesium-based composite materials. In some embodiments, the solid fraction of the semi-solid slurry prepared during the semi-solid die casting process in step (4) is controlled at 5-40%.

[0058] Since the present invention premixes interface-optimized ceramic particles and magnesium-based alloys to form an intermediate alloy, the two have already undergone good mixing and dispersion during the premixing process. Therefore, the mixing time of the slurry during the semi-solid die casting process can be appropriately shortened, and the same good dispersion effect of the reinforcing phase can be achieved. In a preferred embodiment, the stirring time of the semi-solid slurry during the semi-solid die casting process in step (4) of the present invention is 5-8 minutes.

[0059] This invention also provides a system for preparing a ceramic particle-reinforced magnesium-based composite material, including a premixing device and a semi-solid die-casting device; the premixing device is used to achieve heating premixing, cooling, and crushing of magnesium-based alloy particles and interface-optimized ceramic particles, such as... Figure 1 As shown, it includes a heating premixing unit, a cooling unit, and a crushing unit. The heating premixing unit includes a heating furnace 1, a slurry container 2 placed inside the heating furnace 1, a graphite ultrasonic probe 3 inserted below the liquid surface in the slurry container 2, a temperature sensor 5, and a temperature controller 6. The graphite ultrasonic probe 3 is hollow and has a through-hole design, used to introduce inert gas into the slurry container 2 to perform gas stirring and / or ultrasonic stirring of the melt in the slurry container 2, thereby obtaining a uniformly mixed melt. The temperature sensor 5 is used to detect the temperature inside the heating furnace 1, and the temperature controller 6 is used to control the temperature of the heating furnace 1. The cooling unit is connected to the slurry container 2 and is used to cool the uniformly mixed melt to obtain a solid master alloy. The crushing unit is connected to the cooling unit and is used to crush the solid master alloy to obtain granular master alloy raw materials, i.e., pre-formed composite particles. The semi-solid die-casting device is used to die-cast the pre-formed composite particles using a semi-solid die-casting process, thereby obtaining a ceramic particle-reinforced magnesium-based composite material.

[0060] In some embodiments, such as Figure 2 As shown, the semi-solid die-casting device includes a hydraulic injection unit 11, a screw rotation unit 12, a screw 13, a feeding hopper 14, a heater 15, and a nozzle 16. During operation, the pre-formed composite particles prepared by the magnesium-based alloy and ceramic particle premixing device are fed through the feeding hopper 14. After feeding, the pre-formed composite particles undergo semi-solid melting under the heating action of the heater 15. At the same time, the screw rotation unit 12 drives the screw 13 to rotate at a set speed (preferably within the range of 100-150 rpm) to agitate the molten material and prepare a semi-solid metal slurry. Under the action of the hydraulic injection unit 11, the semi-solid metal slurry propels the entire screw 13 forward to spray the semi-solid metal slurry from the nozzle 16 into the mold for molding.

[0061] This invention prepares pre-composite particles with a high-quality metallurgical interface by premixing magnesium-based alloys and ceramic particles. These pre-composite particles can then be semi-solid die-cast using conventional semi-solid die-casting equipment. For example, a method such as... Figure 2The illustrated semi-solid die casting machine integrates the injection and slurry preparation sections. Other semi-solid die casting devices can also be used, such as semi-solid die casting machines with separate injection and slurry preparation sections. In some embodiments, during the semi-solid die casting of intermediate alloy particles, a composite stirring process combining mechanical stirring with electromagnetic stirring is employed in the slurry preparation stage. By utilizing the non-contact characteristics of electromagnetic stirring, the uniformity of the slurry is ensured while reducing the mechanical stirring speed of the screw.

[0062] Traditional semi-solid die casting processes feed ceramic particles and magnesium-based alloy particles simultaneously from the hopper. Due to the significant density difference between the ceramic particles and the molten / semi-solid magnesium alloy, they are prone to stratification during flow. Furthermore, the inherent poor wettability of the ceramic particles and magnesium alloy makes it difficult for the particles to be effectively encapsulated and dispersed by the melt, leading to agglomeration. In addition, the direct mixing and die casting of these two raw materials lacks sufficient shear force or time to overcome the density difference and wettability barriers to achieve uniform mixing during the brief residence time in the die casting machine barrel or injection chamber. Uneven mixing of ceramic particles and magnesium-based alloy directly results in a large gradient in the distribution of ceramic particles in the composite material, severe local agglomeration, and weak interfacial bonding. This is not merely a matter of mixing "uniformity," but also an interfacial problem and a source of stress concentration, ultimately leading to key mechanical properties of the resulting composite material, such as strength, toughness, and fatigue performance, being significantly lower than theoretical expectations or failing to consistently meet the standards.

[0063] This invention discloses a semi-solid die-casting preparation method for ceramic particle-reinforced magnesium matrix composites, belonging to the field of non-ferrous metal composite material processing technology. The method first obtains interface-optimized ceramic particles, then premixes these particles with magnesium-based alloy particles to prepare pre-fabricated composite particles with a high-quality metallurgical bonding interface. These pre-fabricated composite particles are then used as raw materials for semi-solid die-casting to prepare the composite material. During the premixing process, the heating temperature is carefully controlled to ensure the fluidity of the melt while avoiding overheating that could lead to severe magnesium oxidation, ceramic dissolution or reaction, or excessive energy consumption. (This temperature control objective differs from that of existing direct die-casting techniques, where temperature control is primarily aimed at forming a semi-solid slurry.) Combined with specific stirring and cooling / crushing processes during premixing, the various steps work synergistically to ultimately produce a metallurgical bonding interface quality significantly superior to that obtained in existing direct die-casting composites. This solves the problems of poor wettability, uneven dispersion, and material contamination associated with traditional semi-solid die-casting.

[0064] The core innovations of this invention include: 1) adding a pre-mixing process for interface-optimized ceramic particles and magnesium alloy before feeding into the pulper; 2) preparing high-quality metallurgical interface pre-fabricated composite particles through a simultaneous coupling process of gas stirring and ultrasonic stirring, significantly improving the uniformity of the reinforcing phase distribution; and 3) employing warm crushing technology, crushing the intermediate alloy before it is completely cooled, reducing energy consumption and avoiding microcracks. Compared with existing technologies, this invention achieves efficient dispersion and interfacial bonding of ceramic particles through a multi-stage synergistic process, reducing melt oxidation and impurity introduction. It also features a short process flow, low energy consumption, and excellent finished product performance, making it suitable for the large-scale production of high-performance magnesium-based composite materials.

[0065] Unlike existing die-casting processes where ceramic particles and magnesium alloy particles form a weak bonding interface during brief contact in the die-casting machine, this invention achieves full contact and favorable interfacial interaction / reaction between the molten magnesium alloy and ceramic particles under optimized wetting conditions (through surface oxidation or Al coating) during the premixing stage. This results in a high-quality metallurgical bonding interface between the ceramic particles and the magnesium matrix within the premixed particles after cooling. Thus, the die-casting machine feeds not a physical mixture, but pre-formed composite particles with a uniform internal structure and good interfacial bonding. This fundamentally solves the segregation problem and poor initial wettability caused by the density difference between ceramic particles and magnesium alloy. During semi-solid remelting / stirring, the prepared pre-formed composite particles, due to the elimination of segregation caused by density difference, can be considered a homogeneous mixed solution after melting. In contrast, the unmixed original mixture, after melting, causes stratification / precipitation due to density mismatch, resulting in a two-phase separation structure in the slurry, and requires additional energy to break up agglomerates. Therefore, this invention significantly improves the fluidity of the melt during semi-solid remelting / stirring by preparing pre-formed composite particles.

[0066] The embodiments of the present invention are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally in accordance with conventional conditions.

[0067] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0068] The process parameters in the following examples, unless otherwise specified, are generally performed under conventional conditions.

[0069] Example 1

[0070] Nanoscale SiC particles (10-200 nm in size) with surface oxidation are used as reinforcing particles, and AZ91D is used as the magnesium-based alloy. The process involves... Figure 1 Magnesium-based alloy and ceramic particle premixing device and Figure 2 The magnesium-based composite material of this embodiment is prepared using a semi-solid die-casting apparatus, wherein: the surface-oxidized SiC accounts for 10% of the total mass of the final magnesium-based composite material.

[0071] like Figure 1 As shown, the magnesium-based alloy and ceramic particle premixing device includes a heating premixing unit, a cooling unit, and a crushing unit. The heating premixing unit includes a heating furnace 1, a paddle container 2 placed inside the heating furnace 1, a graphite ultrasonic probe 3 inserted below the liquid surface of the paddle container 2, an ultrasonic stirring and gas stirring controller 4, a temperature sensor 5, a temperature controller 6, and a valve 7. The graphite ultrasonic probe 3 is hollow and has a through-hole design, used to introduce inert gas into the paddle container 2 to perform gas stirring and ultrasonic stirring of the liquid in the paddle container 2. The ultrasonic stirring and gas stirring controller 4 is connected to the graphite ultrasonic probe 3. The temperature sensor 5 (i.e., a thermocouple) is inserted into the furnace chamber from the side of the furnace body to test the internal temperature of the heating furnace 1. The temperature controller 6 is used to control the temperature of the heating furnace 1. The heating furnace 1 is a resistance heating furnace. The cooling unit is connected to the slurry container 2 via valve 7, which is used to pass the premixed melt in the slurry container 2 into the cooler 8 in the cooling unit. The crushing unit includes a crushing motor 9 and a crusher 10; the crushing motor 9 drives the crusher 10. The solid master alloy cooled by the cooler 8 is crushed by the crushing motor 9 and the crusher 10 to obtain the granular master alloy raw material.

[0072] Figure 2 The semi-solid die-casting apparatus shown includes a hydraulic injection unit 11, a screw rotation unit 12, a screw 13, a hopper 14, a heater 15, and a nozzle 16. The granular intermediate alloy raw material, i.e., the pre-formed composite particles, prepared by the magnesium-based alloy and ceramic particle premixing device, is fed through the hopper 14. Under the heating action of the heater 15, the granular intermediate alloy raw material is melted. At the same time, the screw rotation unit 12 drives the screw 13 to rotate to perform strong agitation to prepare a semi-solid metal slurry. Under the action of the hydraulic injection unit 11, the semi-solid metal slurry propels the entire screw 13 forward to spray the semi-solid metal slurry from the nozzle 16 into the mold for molding.

[0073] The preparation method flowchart is shown below. Figure 4 Specifically:

[0074] Step 1: Place the slurry container 2 in the furnace chamber of the heating furnace 1, and heat the slurry container 2 to the pre-oxidation temperature of 900℃. Add nano-sized SiC particles to the slurry container for pre-oxidation for 2 hours. After pre-oxidation, set the heating furnace temperature to the AZ91D melting temperature of 680℃. Add AZ91D magnesium-based alloy metal particles to the slurry container 2.

[0075] Step two: Inside the slurry container 2, high-energy ultrasonic vibration and gas agitation are applied to the molten metal through direct contact. The graphite ultrasonic probe is lowered to 10 mm below the molten metal surface, and ultrasonic vibration is activated while high-purity argon gas is simultaneously introduced for bubble agitation for 30 minutes. The ultrasonic frequency is adjusted to 20 kHz, and the ultrasonic vibration volumetric power is 30 W / cm³. The vibration volumetric power is the ratio of the ultrasonic vibration power to the volume of the vibrated melt, resulting in a premixed melt.

[0076] Step 3: The premixed melt is fed into the cooling chamber through a valve to cool into a solid intermediate alloy; the temperature of the cooling chamber is adjusted so that the cooling rate of the melt is 1-50℃ / s, and the cooling is stopped when the alloy cools to 100℃-200℃.

[0077] Step 4: The obtained solid intermediate alloy is fed into a crusher to obtain small pieces of intermediate alloy raw material after crushing; the motor power of the crusher is selected to be 30KW, and the crushing is controlled to obtain granular metal pieces with a diameter or side length of 2-20mm.

[0078] Step 5: Add small pieces of intermediate alloy raw material, i.e., pre-made composite particles. Figure 2Semi-solid die casting is performed in the feed hopper of the semi-solid die casting machine shown. The granular intermediate alloy raw material blocks, i.e., pre-made composite particles, prepared by the premixing device are fed through the feeding hopper 14. Under the heating action of the heater 15, the melt temperature is controlled at the target value of 580±10°C, so that the granular intermediate alloy raw material melts to its solid-liquid phase temperature range. At the same time, the screw rotation unit 12 drives the screw 13 to rotate at a set speed of 120 rpm, applying a strong shearing and stirring action to the alloy in the semi-molten state. The stirring time is 5.5±0.5 min, and the solid fraction is controlled at 30%. After the semi-solid metal slurry is prepared, the hydraulic injection unit 11 is activated, applying a set propulsion pressure of 90 MPa ± 5 MPa to drive the entire screw 13 forward rapidly as a plunger. This propels the semi-solid metal slurry through the nozzle 16 at high speed and into the pre-closed die-casting mold cavity. The injection speed is controlled by adjusting the flow rate of the hydraulic system to ensure that the mold cavity is filled in a very short time (<0.5 seconds). A holding pressure of 35 MPa ± 2 MPa is applied for a holding time of 3-10 seconds to compensate for solidification shrinkage and ensure the density of the casting. The slurry rapidly fills the mold and solidifies under pressure, ultimately obtaining a near-net-shape magnesium-based composite die-casting part.

[0079] Comparative Example 1

[0080] The rest is the same as in Example 1, except that ceramic particles are not introduced; instead, ceramic particles are used directly. Figure 2 The semi-solid die-casting apparatus shown is used to prepare AZ91D material.

[0081] Comparative Example 2

[0082] The rest is the same as in Example 1, except that ceramic particles are introduced, but no premixing is performed; they are used directly. Figure 2 The semi-solid die-casting apparatus shown adds ceramic particles (SiC particles) and AZ91D magnesium-based alloy particles from the feed hopper 14 to prepare a ceramic particle-reinforced magnesium-based composite material according to the same semi-solid die-casting method as in Example 1, and the stirring time of the semi-solid metal slurry is 10 ± 0.5 min.

[0083] Comparative Example 3

[0084] The other steps are the same as in Example 1, except that in step one, the SiC ceramic particles are not pre-oxidized and are directly pre-mixed with the magnesium alloy. Step one specifically involves:

[0085] Step 1: Place the slurry container 2 in the furnace chamber of the heating furnace 1, add nano-sized SiC particles to the slurry container, set the heating furnace temperature to the AZ91D melting temperature of 680℃, and add AZ91D magnesium-based alloy metal particles to the slurry container 2.

[0086] Example 2

[0087] The rest is the same as in Example 1, except that the ceramic particles used for interface optimization in this example are aluminum-coated SiC ceramic particles, and the aluminum-coated SiC accounts for 10% of the total mass of the final magnesium-based composite material. Other steps are the same as in Example 1. Step one specifically involves:

[0088] Step 1: Prepare aluminum-coated SiC ceramic particles using ball milling. Nano-SiC particles (10-200 nm in size) and aluminum powder are mixed in a ball mill jar at a mass ratio of 1.8:1 (ball-to-particle ratio 15:1). Argon gas is introduced into the ball mill jar, and dry milling is performed at 400 r / min for 2.5 h to obtain aluminum-coated SiC ceramic particles with a particle size of 0.1-2.5 mm and an aluminum coating thickness of 30-50 μm. Place the slurry container 2 in the furnace chamber of furnace 1, add the prepared aluminum-coated SiC particles into the slurry container, and then set the furnace temperature to the AZ91D melting temperature of 680℃. Add AZ91D magnesium-based alloy metal particles into the slurry container 2.

[0089] The mechanical properties of the magnesium alloy materials prepared in Examples 1, 2, 1, 2 and 3 were tested, and the test results are shown in Table 1.

[0090] Table 1. Test results of mechanical properties of cast magnesium alloy materials prepared in different embodiments and comparative examples.

[0091]

[0092] As shown in Table 1 and Figure 3 As shown, in Comparative Example 2, the introduction of ceramic particles as a reinforcing phase resulted in a significant improvement in the mechanical properties of the magnesium alloy material compared to Comparative Example 1, which did not introduce ceramic particles. Comparative Example 3, based on Comparative Example 2, added a premixing step, but it was only a simple premix without interface optimization of the ceramic particles. Compared to Comparative Example 2, the mechanical properties were improved, but the improvement was small (tensile strength, yield strength, and elongation increased by 4.7%, 2.9%, and 5.6%, respectively). In Examples 1 and 2, ceramic particles were first pre-oxidized and then aluminum-coated before premixing to prepare pre-formed composite particles, which were used as feed material for a semi-solid die-casting device. The resulting composite materials showed a significant improvement in mechanical properties compared to the comparative examples. Specifically, the tensile strength, yield strength, and elongation of Example 1 increased by 12.5%, 12.2%, and 38% compared to Comparative Example 2, respectively; while the tensile strength, yield strength, and elongation of Example 2 increased by 17.2%, 17.6%, and 52.8% compared to Comparative Example 2, respectively.

[0093] Comparative Example 4

[0094] The rest is the same as in Example 1, except that the graphite ultrasonic probe only turns on ultrasonic vibration, and the vibration frequency, power and time are the same as in Example 1.

[0095] Comparative Example 5

[0096] The rest is the same as in Example 1, except that the graphite ultrasonic probe only turns on gas stirring, and the stirring time is the same as in Example 1.

[0097] Table 2. Effects of different stirring methods on the mechanical properties of the prepared magnesium-based composite materials.

[0098]

[0099] As shown in Table 2 (where "×" indicates that this stirring method was not used, and "√" indicates that the corresponding stirring method was used), the simultaneous use of ultrasonic stirring and gas stirring during premixing significantly improves the mechanical properties of the resulting composite material compared to using only one stirring method. The likely reasons are: the macroscopic flow field generated by gas stirring and the high-frequency microflow field formed by ultrasonic stirring have less mutual interference, which is beneficial for maintaining a stable mixing environment for the melt; the ultrasonic cavitation effect achieves micro-stirring through the generation of micron-sized bubbles and their collapse process, while the inert gas continuously introduced by gas stirring not only forms macroscopic convection but also provides sufficient gas supply for ultrasonic cavitation, resulting in a significant positive synergistic effect between the two stirring methods. The final mixing effect exhibits a synergistic enhancement characteristic of 1+1>2, making the component mixing more uniform, and thus the mechanical properties of the resulting composite material also show a synergistic enhancement effect of 1+1>2.

[0100] Example 3

[0101] Magnesium-based composite materials were prepared using micron-sized Al2O3 ceramic particles as reinforcing particles and AM60 as a magnesium-based alloy, wherein Al2O3 accounted for 12% of the total mass of the final magnesium-based composite material.

[0102] The specific preparation method is as follows:

[0103] Step 1: Place the slurry container in the furnace chamber and heat it to the preset AM60 melting temperature of 680℃. Add the metal particles and micron-sized Al2O3 ceramic particles to the slurry container.

[0104] Step two involves applying high-energy ultrasonic vibration and gas agitation to the molten metal inside the slurry container using a graphite ultrasonic probe through direct contact. The graphite ultrasonic probe is lowered to 10 mm below the molten metal surface, and ultrasonic vibration is activated while simultaneously introducing high-purity argon gas for bubble agitation for 25-30 minutes. The ultrasonic frequency is adjusted to 20 kHz, and the ultrasonic vibration volumetric power is 30 W / cm³, where the ultrasonic vibration volumetric power is the ratio of the ultrasonic vibration power to the volume of the vibrated melt.

[0105] Step 3: The mixed molten metal is flowed into the cooling chamber through a valve to cool into a solid intermediate alloy; the temperature of the cooling chamber is adjusted so that the cooling rate of the melt is 1-50℃ / s, and the cooling is stopped when the alloy cools to 100℃-200℃.

[0106] Step 4: The obtained solid intermediate alloy is fed into a crusher to obtain small pieces of intermediate alloy raw material after crushing; the motor power of the crusher is selected to be 30KW, and the crushing is controlled to obtain granular metal pieces with a diameter or side length of 2-20mm.

[0107] Step 5: Add small pieces of intermediate alloy raw material. Figure 2 Semi-solid die casting is performed in the feed hopper of the semi-solid die casting machine shown. The granular intermediate alloy raw material pieces prepared by the premixing device are fed through the feeding hopper 14. Under the heating action of the heater 15, the melt temperature is controlled at the target value of 580 ± 10°C, so that the granular intermediate alloy raw material melts to its solid-liquid phase temperature range. At the same time, the screw rotation unit 12 drives the screw 13 to rotate at a set speed of 120 rpm, applying a strong shearing and stirring action to the alloy in the semi-molten state. The stirring time is 5.5 ± 0.5 min, and the solid fraction is controlled at 25%. After the semi-solid metal slurry is prepared, the hydraulic injection unit 11 is activated, applying a set propulsion pressure of 90 MPa ± 5 MPa to drive the entire screw 13 forward rapidly as a plunger. This propels the semi-solid metal slurry through the nozzle 16 at high speed and into the pre-closed die-casting mold cavity. The injection speed is controlled by adjusting the flow rate of the hydraulic system to ensure that the mold cavity is filled in a very short time (<0.5 seconds). A holding pressure of 35 MPa ± 2 MPa is applied for a holding time of 3-10 seconds to compensate for solidification shrinkage and ensure the density of the casting. The slurry rapidly fills the mold and solidifies under pressure, ultimately obtaining a near-net-shape magnesium-based composite die-casting part.

[0108] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A semi-solid die-casting method for magnesium-based composite materials premixed with ceramic particles, characterized in that, Includes the following steps: (1) Obtaining interface-optimized ceramic particles; the interface-optimized ceramic particles are aluminum-coated ceramic particles or ceramic particles with an oxide layer on the surface; wherein the ceramic particles with an oxide layer on the surface are oxide ceramic particles, or are prepared by the following method: heating and pre-oxidizing non-oxide ceramic particles to form an oxide layer on their surface to obtain ceramic particles with an oxide layer on the surface. (2) The magnesium-based alloy particles and the interface-optimized ceramic particles are heated together to melt the magnesium-based alloy and obtain a mixed melt; an inert gas is introduced into the mixed melt and the mixed melt is stirred to obtain a uniformly mixed melt; the stirring is gas stirring and ultrasonic stirring; and when the interface-optimized ceramic particles are aluminum-coated ceramic particles, the magnesium-based alloy contains metallic aluminum. (3) Cool the uniformly mixed melt to obtain a solid intermediate alloy, and crush the solid intermediate alloy to obtain pre-made composite particles; the cooling rate is 1-50℃ / s, and the temperature is cooled to 100-200℃, and then crushed. (4) The pre-made composite particles are die-cast using a semi-solid die-casting process to obtain a magnesium-based composite material reinforced with ceramic particles.

2. The method of claim 1, wherein, The ceramic particles in step (1) are one or more of the following: micron-sized or nano-sized Al2O3 ceramic particles, SiC ceramic particles, B2C ceramic particles, Si3C4 ceramic particles, and TiB2 ceramic particles; and / or, In step (2), the surface interface optimized ceramic particles account for 0.1-40% of the mass of the magnesium-based alloy.

3. The method of claim 1, wherein, In step (1), when preparing ceramic particles with an oxide layer on the surface, the non-oxide ceramic particles are pre-oxidized by heating at a temperature above 800°C to form an oxide layer on their surface.

4. The method of claim 1, wherein, The pre-oxidation temperature in step (1) is 800-950℃, and the pre-oxidation time is 1-3 h.

5. The method of claim 1, wherein, The aluminum-coated ceramic particles in step (1) are prepared by molten aluminum impregnation, physical vapor deposition, mechanical ball milling, or thermal spraying. The thickness of the aluminum coating on the aluminum-coated ceramic particles is 0.1-100 μm.

6. The method of claim 1, wherein, Step (2) Heat the magnesium-based alloy particles together with the ceramic particles with optimized interface from step (1) at a temperature of 650-700℃ to melt the magnesium-based alloy and obtain a mixed melt.

7. The method of claim 1, wherein, The particle size of the prefabricated composite particles in step (3) is 2-20 mm.

8. A ceramic particle-reinforced magnesium-based composite material, characterized by, Obtained by means of any one of claims 1-7.

9. A system for producing a ceramic particle-reinforced magnesium-based composite material as claimed in claim 8, characterized in that Includes premixing equipment and semi-solid die-casting equipment; The premixing device is used to realize the heating, premixing, cooling and crushing of magnesium-based alloy particles and interface-optimized ceramic particles. It includes a heating premixing unit, a cooling unit and a crushing unit. The heating premixing unit includes a heating furnace (1), a slurry container (2) placed in the heating furnace (1), a graphite ultrasonic probe (3) inserted below the liquid surface of the slurry container (2), a temperature sensor (5) and a temperature controller (6). The graphite ultrasonic probe (3) is hollow and has a through-hole design, which is used to introduce inert gas into the slurry container (2) to perform gas stirring and ultrasonic stirring of the melt in the slurry container (2) to obtain a uniformly mixed melt. The temperature sensor (5) is used to detect the temperature in the heating furnace (1), and the temperature controller (6) is used to control the temperature of the heating furnace (1). The cooling unit is connected to the slurry container (2) and is used to cool the uniformly mixed melt to obtain a solid intermediate alloy. The crushing unit is connected to the cooling unit and is used to crush the solid intermediate alloy to obtain pre-made composite particles. The semi-solid die-casting device is used to die-cast the pre-made composite particles using a semi-solid die-casting process, thereby producing a magnesium-based composite material reinforced with ceramic particles.

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