A magnesium-based composite material with heterogeneous structure plasticization, preparation method and application

Abstract

The present invention belongs to the field of metal material science and technology, and specifically relates to a magnesium-based composite material with heterogeneous structure plasticization, a preparation method and an application. A preparation method of a magnesium-based composite material with heterogeneous structure plasticization, comprising the following steps: S1: mixing AZ61 magnesium alloy powder, pure titanium carbide and stearic acid, performing low-speed and high-speed ball milling to obtain a mixed powder, and then cooling the powder to perform powder filling and cold pressing; S2: performing a vacuum hot pressing process with gradient temperature increase and exhaust on the powder after cold pressing in S1, and cooling to perform thermal deformation to obtain a magnesium-based composite material with heterogeneous structure plasticization. The plasticity of the magnesium-based composite material prepared by the present invention is significantly improved, which expands the potential for application of magnesium-based composite materials in the industrial field.

Description

Technical Field

[0001] The present invention belongs to the field of metal material science and technology, and specifically relates to a heterogeneous structure plasticized magnesium-based composite material, a preparation method and an application thereof. Background Technology

[0002] With the increasing demand for energy conservation and emission reduction, the development of lightweight structural materials has received widespread attention. Nano-enhanced magnesium-based composite materials have the advantages of low density, high specific strength, specific stiffness, and vibration and noise reduction, and have broad application prospects in aerospace, transportation, and national defense.

[0003] Although the addition of nano-reinforcements can maximize the strength of magnesium alloys without significantly losing plasticity. Since nano-reinforcements are difficult to disperse in the metal matrix, the full play of the strengthening effect of the composite material is affected, and the plasticity of magnesium-based composite materials is often low, which largely restricts the application of such materials. The traditional idea of ​​preparing metal-based composite materials is to disperse the reinforcements as evenly as possible, but this idea still makes it difficult to break the common phenomenon of strength-plasticity inversion in composite materials. Therefore, the development of a preparation method for magnesium-based composite materials with high strength-plasticity synergy is of great practical significance and can greatly expand the application field of magnesium-based materials. SUMMARY OF THE INVENTION

[0004] Aiming at the problems and shortcomings of the prior art, the present invention provides a method for preparing a heterogeneous structure plasticized magnesium-based composite material, comprising the following steps:

[0005] S1: Mix AZ61 magnesium alloy powder, pure titanium carbide and stearic acid, perform low-speed and high-speed ball milling to obtain mixed powder, and then cool the powder for powder filling and cold pressing;

[0006] S2: The powder after cold pressing in S1 is subjected to a vacuum hot pressing process with gradient temperature increase and exhaust, and then cooled for thermal deformation to obtain a magnesium-based composite material with heterogeneous structure plasticization.

[0007] Furthermore, the mass ratio of pure titanium carbide and stearic acid described in S1 is 0.53-1.18:1.

[0008] Furthermore, the mass percentage of pure titanium carbide in S1 is 0.8-1.3wt.%, the mass percentage of stearic acid is 1.1-1.5wt.%, and the remainder is AZ61 magnesium alloy.

[0009] Further, the low-speed ball milling time in S1 is 20 h, the high-speed ball milling time is 1 h, the low-speed ball milling speed is 100 - 200 rpm, the high-speed ball milling speed is 280 - 320 rpm, and the low-speed ball milling pauses for 5 min every 15 min and the ball milling tank needs to be taken out and hand-cranked every 45 min, and the high-speed ball milling pauses for 5 min every 10 min.

[0010] Further, the pressure in the cold pressing process in S1 is set to 2.5 MPa.

[0011] Further, the vacuum hot pressing process in S2 includes first raising the temperature to 300 °C and maintaining it at this temperature for 15 min, then raising the temperature to 450 °C and maintaining it at this temperature for 15 min, further raising the temperature to 475 °C for exhaust and maintaining it for 30 min, and after the exhaust is completed, insulating at 520 °C for 1 h while applying a pressure of 50 MPa.

[0012] Further, the hot deformation process in S2 uses hot extrusion, the extrusion temperature is set to 300 - 350 °C, the extrusion ratio is 15 - 20:1, and the extrusion speed is 2.5 - 3.5 mm / s.

[0013] A heterogeneous structure - plasticized magnesium - based composite material, the magnesium - based composite material has heterogeneous structure characteristics, and the magnesium - based composite material also contains added nano - reinforcement particles TiC and self - generated micron - sized β - Mg 17 Al 12 second phase.

[0014] An application of a heterogeneous structure - plasticized magnesium - based composite material, the magnesium - based composite material is applied in the preparation of aerospace materials.

[0015] Technical effects

[0016] (1) Through a heterogeneous structure - plasticized magnesium - based composite material provided by the present invention, compared with traditional homogeneous fine - grained magnesium - based composite materials, the plasticity can be nearly doubled while maintaining the high - strength characteristics of traditional magnesium - based materials, which is crucial for improving the application performance of materials in complex environments. In terms of performance, the compressive strength of the heterogeneous structure magnesium - based composite material reaches 419 ± 6 MPa, and the true strain is as high as 7.3 ± 0.2%. Microcracks are likely to appear during the processing of composite materials, especially when the content of reinforcement particles is relatively high. The present invention effectively solves this problem by introducing a heterogeneous structure. The introduction of the heterogeneous structure not only maintains the high strength of the material but also significantly improves the plasticity, making the composite material easier to form during processing and reducing the generation of microcracks, thus providing practical value for the wide application of composite materials.

[0017] (2) By using the preparation method of a heterogeneous structure - plasticized magnesium - based composite material provided by the present invention and adopting the vacuum hot - pressing method, the oxidation phenomenon of the magnesium - based composite material can be prevented, thereby preventing the embrittlement of the composite material. This method can synchronize heating and pressurization, which is beneficial to the densification of powder metallurgy materials, especially for composite materials. In addition, through this hot - pressing process, high - density composite materials can be prepared with relatively small pressure. This is because on the one hand, the vacuum environment reduces the participation of gas, making it easier to achieve powder densification. On the other hand, under the action of thermal activation effect and pressure, heating can increase the thermal energy of powder particles, improve their diffusion rate and plastic deformation ability, thus promoting the bonding and diffusion of powder particles under lower pressure.

[0018] (3) By using the preparation method of a heterogeneous structure - plasticized magnesium - based composite material provided by the present invention, the vacuum hot - pressing method allows for precise control of the size of bimodal grains, which directly affects the densification and properties of the material. By precisely regulating the grain size, the composite material of the present invention realizes a significant improvement in plasticity while maintaining high strength, which is of great significance for improving the overall performance and processing formability of the material. The hot - deformation step of the present invention cleverly utilizes the multi - scale particle distribution characteristics of the material and realizes precise regulation of the double - heterogeneous structure through precise process control. This step is not only extremely simple in operation but also easy to implement, providing a solid technical foundation for the industrial production of the material.

[0019] (4) Through the application of a heterogeneous structure - plasticized magnesium - based composite material provided by the present invention, the properties of the material obtained by this preparation method are enhanced, expanding the application potential of magnesium - based composite materials in the industrial field. Brief Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings. In the drawings:

[0021] Figure 1 It is the EBSD map and the corresponding geometrically necessary dislocation density distribution map of the AZ61 - TiC magnesium - based composite material of the present invention;

[0022] Figure 2 It is the SEM map of the heterogeneous magnesium - based composite material AZ61 - TiC of the present invention and the corresponding EDS area scan maps of different elements.

[0023] Figure 3Compressive mechanical property curve of heterogeneous and homogeneous magnesium-based composite AZ61-TiC. Detailed implementation mode

[0024] The following will combine Example 1 of the present invention and the attached Figures 1 to 3 , and clearly and completely describe the technical solutions of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0025] Example 1

[0026] S1: Mix magnesium alloy powder AZ61 (purity greater than 99.9%), titanium carbide TiC (purity greater than 98%), and 1.3 wt.% stearic acid, then perform low-speed ball milling for 20 h and then high-speed ball milling for 1 h. During low-speed ball milling, it pauses for 5 min every 15 min and the ball milling tank needs to be taken out and shaken by hand every 45 min to prevent sticking to the wall or caking; during high-speed ball milling, it pauses for 5 min every 10 min to prevent overheating and is taken out and shaken by hand to obtain a mixed powder; after the ball milling is completed, the powder is placed in a vacuum glove box and taken out for powder loading after cooling. After manual compaction, it is quickly taken out for cold pressing; the mold is placed on a 200-ton vertical hydraulic press for cold pressing, the main cylinder pressure is set to 2.5 MPa, and once the set pressure is reached during the downward pressing process, this pressure is maintained for 5 min. After the pressure holding time ends, the pressure of the hydraulic press is slowly released to avoid damage to the material or mold caused by too fast pressure release;

[0027] S2: Put the cold-pressed mold into a vacuum hot press for hot pressing, exhaust at 475 °C for 30 min, keep the temperature at 520 °C for 1 h while applying a pressure of 50 MPa after the exhaust is completed, and then cool with the furnace; perform plastic deformation on the material treated by vacuum hot pressing, set the extrusion temperature to 350 °C, the extrusion ratio to 19:1, and the extrusion rod speed to 3.5 mm / s; obtain a heterogeneous structure plasticized magnesium-based composite material.

[0028] This method realizes large plastic deformation of the initial powder by combining long-time low-speed ball milling and high-speed ball milling technologies. This process causes almost all powder particles to be pressed into flat shapes, providing sufficient driving force for the growth of grains during the subsequent sintering process. During the sintering process, the grains in the powder have undergone significant growth, forming coarse grains with uniform sizes.

[0029] The magnesium-based composite material prepared by the present invention has heterogeneous structure characteristics, which exist in two aspects. On the one hand, the grain size of the magnesium alloy matrix shows a bimodal distribution, where the size of the coarse grains is about 10 - 15 μm, and the size of the fine grains is about 1 - 4 μm. On the other hand, the composite material also contains multi-scale particles (externally added nano-reinforcement particles TiC and self-generated micron β-Mg 17 Al 12 second phase), and these particles also show non-uniform distribution. Specifically, these particles are sparse in the coarse grain region and enriched in the fine grain region.

[0030] The components and their mass percentages of the magnesium-based composite material designed above are titanium carbide TiC 0.8 - 1.3 wt.%, stearic acid 1.1 - 1.5 wt.%, and the balance is AZ61 magnesium alloy. In a further optimized scheme, the components and their mass percentages are titanium carbide TiC 1 wt.%, stearic acid 1.3 wt.%, and the balance is AZ61 magnesium alloy.

[0031] After the vacuum hot pressing process, a coarse grain structure is formed in the bulk material, laying a foundation for subsequent hot deformation; a gradient heating exhaust process is introduced during the vacuum hot pressing process. In this process, the temperature is first raised to 300 °C and held at this temperature for 15 min, then raised to 450 °C and held at this temperature for 15 min, and then the temperature is further raised to 475 °C and also held for 30 min. Keeping the temperature at a lower level for heat preservation, since the temperature has not reached the melting point of the magnesium alloy, no liquid phase will be formed, and at the same time, the premature occurrence of metallurgical reactions is avoided. The low-temperature heat preservation at this stage is particularly beneficial for removing air and volatile impurities in the material, providing a guarantee for the smooth progress of the subsequent metallurgical process. Finally, the temperature is continuously raised to the target temperature of 520 °C. At this stage, since the gas has been effectively removed during the aforementioned exhaust process, the small pores between the powder particles begin to be filled with the metal liquid, promoting the metallurgical bonding of the powder particles. Compared with directly heating to the target temperature, the gradient heating exhaust technology adopted by the present invention is more conducive to ensuring the high density and uniformity of the material.

[0032] The hot deformation step plastically deforms the compacted material subjected to vacuum hot pressing through precisely controlled hot extrusion or hot rolling processes to achieve a dual heterogeneous structure of the magnesium-based composite. The parameter settings in Example 1 are based on a deep understanding of the material properties and deformation mechanisms to ensure that the material can achieve the target heterogeneous structure during hot deformation. Hot deformation is the key to forming a special structure. In this process, by superimposing the effects of multi-scale particles through appropriate hot deformation methods, part of the material undergoes dynamic recrystallization while part does not, thus forming a dual-structured composite material. Dual structure means that on the one hand, a bimodal grain structure distribution is presented at the grain scale of the matrix, and on the other hand, the multi-scale particles are also non-uniformly distributed in the composite material. In particular, the externally added nano-particles and micron-sized second phases are enriched in the fine-grained region and sparse in the coarse-grained region. The externally added nano-TiC particles are enriched in some regions but uniformly distributed within these regions. Their presence also promotes the nucleation of the β-Mg 17 Al 12 phase. These micron-sized β-Mg 17 Al 12 phases promote dynamic recrystallization during hot deformation. A large number of nano-TiC particles can also pin the grains, so finally a fine-grained region rich in particles is formed. At the same time, the strength and stability of the material are further enhanced. In the region where the nano-TiC particles are sparse, the micron-sized β-Mg 17 Al 12 phases are also scarce. Due to the lack of the excitation nucleation of the second-phase particles, dynamic recrystallization is relatively difficult to occur. Only when the dislocations accumulate to a certain amount can the threshold of dynamic recrystallization be reached. In addition, due to the lack of pinning of nano-particles, the grains in this region are prone to grow, and finally a coarse-grained region sparse in particles is formed. This dual-structured characteristic formed by the hot deformation process endows the magnesium-based composite with excellent comprehensive properties.

[0033] Combined Figure 1 The microstructure of the extruded magnesium-based composite AZ61-TiC observed by electron backscatter diffraction (EBSD) technology reveals its unique bimodal structure grain characteristics. Among them, the average size of the coarse grains is about 10 - 15 μm, while the average size of the fine grains is about 1 - 4 μm. As Figure 1 (a) shows. In particular, Figure 1A large number of geometrically necessary dislocations (GNDs), and even substructures, exist in the coarse grains in (b). In contrast, the GND density is lower in the fine-grained region. This phenomenon can be attributed to the fact that the large grains formed during the sintering process accumulated a large amount of GNDs after hot extrusion. When the GNDs accumulated to a certain extent, the dislocations rearranged to form substructures, and the substructures continuously absorbed dislocations and evolved into large-angle grain boundaries, thus forming fine grains. Therefore, the fine grains are new grains formed by dynamic recrystallization, and the GND density in the fine-grained region is low. In the coarse-grained region, due to insufficient dynamic recrystallization during the hot deformation process, a large number of dislocations remained, so a high density of GNDs was shown.

[0034] Figure 2 The secondary electron scanning image of the magnesium matrix composite AZ61-TiC is shown. Figure 2 Figure a is the SEM image of the heterogeneous magnesium matrix composite AZ61-TiC. Figure 2 Figure b is the EDS area scan image corresponding to different elements. Figure 2 Figures c - 2f are the EDS area scan images of Mg, Al, Ti, and C respectively. Among them Figure 2 Figure a clearly reveals that most of the second phases are distributed at the grain boundaries, and its corresponding area scan image further confirms that the particle enrichment region is rich in TiC particles, as Figure 2 shown in Figure b. These second phases and nanoparticles located in the fine-grained region play a role in dispersion strengthening and enhance the microstructural stability of the material. In addition, the synergistic effect of the fine-grain strengthening mechanism significantly improves the strength of the fine-grained region, thus greatly improving the overall strength of the composite material.

[0035] Figure 3 The compressive mechanical properties of the heterogeneous and homogeneous magnesium matrix composites AZ61-TiC were compared. The true strain of the homogeneous magnesium matrix composite was 3.8 ± 0.1%, while the true strain of the heterogeneous structure magnesium matrix composite of the present invention was significantly increased to 7.3 ± 0.2%, which was increased by about 92% compared with the homogeneous structure. This significant improvement confirms that the introduction of the heterogeneous structure can greatly enhance the plasticity of the material. Although the compressive strength of the heterogeneous structure magnesium matrix composite is 419 ± 6 MPa, which is 37 ± 10 MPa lower than that of the homogeneous composite, it only decreased by 8%. This indicates that the composite material of the present invention significantly improves the plasticity while maintaining a relatively high strength, achieving an excellent balance between strength and plasticity.

[0036] A magnesium-based composite material with heterogeneous structure plasticization provided by the present invention has a high density of dislocations in the coarse-grained region of the magnesium-based composite material. Therefore, it can also provide strength. On the basis of maintaining the high-strength characteristics of traditional magnesium-based materials, the plasticity is significantly enhanced. The introduction of the heterogeneous structure makes the composite material easier to form during the processing and reduces the generation of microcracks. The magnesium-based composite material described in the present invention has heterogeneous structure characteristics, which exist in two aspects. On the one hand, the grain size of the magnesium alloy matrix shows a bimodal distribution, where the size of the coarse grains is about 10-15 μm and the size of the fine grains is about 1-4 μm. On the other hand, the composite material also contains multi-scale particles (externally added nano-reinforcement particles TiC and self-generated micron β-Mg 17 Al 12 second phase), and these particles also show non-uniform distribution. Specifically, these particles are sparse in the coarse-grained region and enriched in the fine-grained region.

[0037] A preparation method of a magnesium-based composite material with heterogeneous structure plasticization provided by the present invention, through ball milling, vacuum hot pressing, hot extrusion, and adjusting the hot extrusion speed to control the microstructure, so that it has a double heterogeneous structure, enabling the composite material to obtain high strain hardening and excellent passivation crack performance, and improving its toughness and plasticity while maintaining the high strength of the alloy.

[0038] An application of a magnesium-based composite material with heterogeneous structure plasticization provided by the present invention, through this preparation method and structure, broadens the potential of the magnesium-based composite material in the industrial field and provides practical value for the wide application of the composite material.

Claims

1. A method for preparing a heterogeneous structure plasticized magnesium-based composite material, characterized in that: The following steps are involved: S1: AZ61 magnesium alloy powder, pure titanium carbide and stearic acid are mixed, and low-speed ball milling and high-speed ball milling are performed to obtain mixed powder, and the powder is cooled and then charged and cold pressed; S2: The powder after cold pressing in S1 is subjected to a vacuum hot pressing process with gradient temperature increase and exhaust, and then cooled for thermal deformation to obtain a magnesium-based composite material with heterogeneous structure plasticization; The low-speed ball milling time described in S1 is 20 hours, the high-speed ball milling time is 1 hour, the low-speed ball milling speed is 100-200 rpm, the high-speed ball milling speed is 280-320 rpm, and the low-speed ball milling is paused for 5 minutes every 15 minutes, the ball milling jar needs to be taken out and hand-cranked every 45 minutes, and the high-speed ball milling process is paused for 5 minutes every 10 minutes; The vacuum hot pressing process described in S2 includes first raising the temperature to 300°C and maintaining it at this temperature for 15 minutes, then raising the temperature to 450°C and maintaining it at this temperature for 15 minutes, and then raising the temperature to 475°C for exhaust and maintaining it for 30 minutes. After the exhaust is completed, the temperature is maintained at 520°C for 1 hour while applying a pressure of 50MPa; The mass percentage of pure titanium carbide in S1 is 0.8-1.3wt.%, the mass percentage of stearic acid is 1.1-1.5wt.%, and the balance is AZ61 magnesium alloy powder; The pressure in the cold press described in S1 is set to 2.5 MPa; The thermal deformation described in S2 adopts hot extrusion, the extrusion temperature is set to 300~350℃, the extrusion ratio is 15~20:1, and the extrusion speed is 2.5~3.5mm / s.

2. The method for preparing a heterogeneous structure plasticized magnesium-based composite material according to claim 1, characterized in that: The mass ratio of pure titanium carbide and stearic acid described in S1 is 0.53~1.18:

1.

3. A heterogeneous structure plasticized magnesium-based composite material obtained by the preparation method according to any one of claims 1 to 2, characterized in that: The magnesium-based composite material is characterized by a heterogeneous structure, and the magnesium-based composite material also contains an external nano-reinforcement particle TiC and a self-generated micronized β-Mg 17 Al 12 Second phase.

4. The use of a heterogeneous structure plasticized magnesium-based composite material according to claim 3, wherein The characteristic lies in that the magnesium-based composite material is used in the preparation of aerospace materials.

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