A method for preparing a chopped carbon fiber reinforced magnesium matrix composite containing an LPSO phase

Abstract

The application discloses a preparation method of a chopped carbon fiber reinforced magnesium matrix composite material containing an LPSO phase, and comprises the following steps: 1, placing chopped carbon fibers into a water solution containing a dispersant and stirring, and then performing negative pressure suction filtration to obtain a chopped carbon fiber preform; 2, melting metal raw materials to obtain an alloy liquid, and the metal raw materials contain magnesium for forming the LPSO phase; 3, placing the chopped carbon fiber preform into a mold and preheating; 4, under the protection of argon, pouring the alloy liquid into the mold, then preheating a sealing block and placing the sealing block on the top of the mold to seal the mold; 5, infiltrating the alloy liquid by pressing the sealing block under low pressure, and then pressurizing under high pressure to obtain a densified block; 6, immediately demolding and air cooling the densified block. The application combines rheocasting with liquid-solid high-pressure forming process, and demolds and cools under high temperature, so that the LPSO structure is formed in the chopped carbon fiber reinforced magnesium matrix composite material, and the application is suitable for the field of aerospace.

Description

Technical Field

[0001] This invention belongs to the field of metal matrix composite technology, and in particular relates to a method for preparing magnesium matrix composite material reinforced with short-cut carbon fibers containing LPSO phase. Background Technology

[0002] Short-cut carbon fiber reinforced magnesium matrix (C sf Mg / Mg composites are considered important candidate materials for achieving structural lightweighting in major national strategic fields such as aerospace, low-altitude economy, and high-end equipment manufacturing due to their low density, high specific strength, low coefficient of thermal expansion, good damping, and creep resistance. However, currently, commercially available Mg-Al alloys such as pure magnesium and AZ91 are used to prepare C... sf When C / Mg composites are manufactured, the matrix generally lacks characteristic microstructures capable of coordinating deformation. Combined with the presence of hard carbon fibers and imperfect carbon-magnesium interfacial bonding, these composites often exhibit extremely poor plasticity, which has become a significant obstacle to C / Mg composites. sf One of the important issues in the promotion and application of Mg / Mg composite materials.

[0003] In recent years, the long-period stacked ordered (LPSO) structure formed in the Mg-Y-Zn alloy system has been considered an important microstructure for achieving the strengthening and toughening of magnesium alloys due to its unique layered atomic structure and excellent deformation compatibility. This phase readily forms serrated kink bands under stress, which can improve alloy plasticity through the kinking effect. It has attracted widespread attention in the research and application of rare-earth magnesium alloys, but its introduction into C... sf Research on C / Mg composites is scarce. Therefore, there is an urgent need to investigate a method for preparing C containing the LPSO phase. sf The preparation method of Mg / Mg composite material is proposed to ensure that the LPSO phase precipitation is not affected by the fiber distribution and can be appropriate and uniform. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing chopped carbon fiber reinforced magnesium matrix composites containing the LPSO phase. This method combines rheological casting with liquid-solid high-pressure forming, and demolds and cools the densified bulk material while maintaining a high temperature, thereby achieving the formation of the LPSO structure within the chopped carbon fiber reinforced magnesium matrix composite and solving the problem of poor plasticity in chopped carbon fiber reinforced magnesium matrix composites.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing magnesium-based composite materials reinforced with short-cut carbon fibers containing LPSO phase, characterized by comprising the following steps: Step 1: Place the chopped carbon fibers into an aqueous solution containing a dispersant and stir. Then filter under negative pressure to obtain the chopped carbon fiber preform. Step 2: Melt the metal raw materials to obtain an alloy liquid; the metal raw materials include magnesium that forms the LPSO phase; Step 3: Place the chopped carbon fiber preform obtained in Step 1 into the mold, and preheat the mold and the chopped carbon fiber preform. Step 4: Under argon protection, pour the molten alloy obtained in Step 2 into the preheated mold in Step 3, and then place the preheated sealing block on top of the mold to seal the mold. Step 5: Press down the sealing block placed on top of the mold in Step 4 with low pressure to allow the alloy liquid to gradually penetrate into the short-cut carbon fiber preform. After the penetration is completed, maintain the pressure under high pressure to obtain a densified block. Step 6: Immediately demold the densified block obtained in Step 5, and after air cooling, obtain a magnesium matrix composite material with short-cut carbon fiber containing LPSO phase.

[0006] This invention utilizes low pressure to gradually impregnate a molten alloy into a short-cut carbon fiber preform. After impregnation, high pressure is applied for pressure holding. At this point, the semi-solid molten alloy still has a certain shrinkage compensation capacity under high pressure. Densification is then completed through pressure holding. Subsequently, the densified block is immediately demolded. At this time, the densified block itself maintains a high temperature, which can reduce the friction between the densified block and the mold wall while preventing grain growth, making demolding easier. Furthermore, the high-temperature demolding and air cooling can give the densified block a high cooling rate, effectively promoting the formation and uniform precipitation of the LPSO (long-period stacked ordered) phase, and achieving the refinement and dispersion distribution of the LPSO phase in the matrix.

[0007] The above-mentioned method for preparing a magnesium matrix composite material reinforced with short-cut carbon fibers containing LPSO phase is characterized in that the length of the short-cut carbon fibers in step one is 100μm~300μm.

[0008] The above-mentioned method for preparing a short-cut carbon fiber reinforced magnesium matrix composite material containing LPSO phase is characterized in that the metal raw materials in step two include metallic Mg, metallic Zn and Mg-Y master alloy.

[0009] This invention introduces an LPSO structure for the first time on the basis of fiber reinforcement using Mg-Y-Zn alloy as the matrix. By giving full play to the torsional strengthening effect of the structure, the deformation coordination ability of the matrix is ​​improved. In addition, the short carbon fiber itself has high load-bearing capacity and stiffness. The combination of the two ultimately gives the composite material high strength and stiffness, while maintaining a certain plasticity.

[0010] The above-mentioned method for preparing a magnesium matrix composite material reinforced with short-cut carbon fibers containing LPSO phase is characterized in that the atomic ratio of Y to Zn in the metal raw material is (2.5~4.5):1.

[0011] Since Y tends to accumulate at the interface between carbon fiber and magnesium alloy, it is necessary to appropriately increase the amount of Y to ensure that the Y consumed at the interface does not affect the formation of the LPSO phase. This invention controls the atomic ratio of Y to Zn to be (2.5~4.5):1, which is about 1.5 times larger than the Y / Zn atomic ratio of (1.3~3.3):1 required for the formation of the LPSO phase in magnesium alloy without considering interface consumption, thus ensuring the formation of the LPSO phase.

[0012] The above-mentioned method for preparing a short-cut carbon fiber reinforced magnesium matrix composite material containing LPSO phase is characterized in that the melting method in step two is as follows: under argon protection, metallic magnesium is placed in a crucible and heated to 730℃~735℃ and held at that temperature. After the metallic magnesium is completely melted, Mg-Y master alloy and metallic Zn are added in sequence, and the mixture is kept at that temperature and stirred evenly.

[0013] The above-mentioned method for preparing a magnesium matrix composite material reinforced with LPSO phase by short-cut carbon fiber is characterized in that the preheating temperature of the mold and the short-cut carbon fiber preform in step three is 500℃~530℃, and the preheating temperature of the sealing block in step four is 730℃~735℃.

[0014] This invention increases the wettability of the carbon-magnesium interface by preheating the mold and the short-cut carbon fiber preform to 500°C, which is beneficial for magnesium liquid impregnation. On the other hand, it can prevent premature solidification of magnesium liquid during the impregnation process. At the same time, by setting the preheating temperature of the sealing block to be consistent with the pouring temperature of the alloy liquid, the temperature of the alloy liquid is not reduced when it comes into contact with the alloy liquid.

[0015] The above-mentioned method for preparing a magnesium matrix composite material reinforced with short-cut carbon fibers containing LPSO phase is characterized in that the low pressure in step five is 5MPa~10MPa, the high pressure is 180MPa~200MPa, and the holding time of the high pressure is 5min~10min.

[0016] This invention employs low-pressure assisted impregnation at 5MPa~10MPa to avoid damaging the structural integrity of the short-cut carbon fiber preform due to excessive pressure; by holding the preform at 180MPa~200MPa for 5min~10min, the solidification shrinkage phenomenon can be compensated to achieve densification, which also helps to prevent premature debonding of the interface caused by the shrinkage stress of magnesium near the interface.

[0017] The above-mentioned method for preparing a short-cut carbon fiber reinforced magnesium matrix composite material containing LPSO phase is characterized in that the temperature of the densified block during demolding in step six is ​​430℃~450℃.

[0018] Compared with the prior art, the present invention has the following advantages: 1. This invention uses a combination of rheological casting and liquid-solid high-pressure forming processes to obtain rare earth magnesium alloys containing LPSO phase. By reducing the temperature gradient and liquid shrinkage during the flow of the alloy melt through semi-solid rheological structure, it is beneficial to improve the wetting ability of magnesium liquid on short carbon fiber preforms and realize the stable forming of short carbon fiber reinforced magnesium matrix composites.

[0019] 2. During the preparation process of this invention, the demolding temperature is controlled to enable the densified bulk material to have a high cooling rate, which can effectively promote the formation and uniform precipitation of the LPSO phase in the Mg-Y-Zn system, and realize the refinement and dispersion distribution of the LPSO phase in the matrix; at the same time, it can also affect the element segregation behavior at the carbon-magnesium interface, and can change the structural characteristics of the traditional carbon-magnesium interface through in-situ reaction, effectively improve the interfacial bonding strength, and reduce the tendency of interfacial debonding.

[0020] 3. The process of this invention is simple, the forming efficiency is high, and it can achieve near-net-shape forming. It has good prospects for engineering applications and is suitable for the preparation of large-size and complex structures of lightweight high-performance magnesium-based composite materials.

[0021] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0022] Figure 1 The above are process flow diagrams of the preparation methods in Examples 1-3 of this invention.

[0023] Figure 2 This is a diagram showing the distribution of short-cut carbon fibers inside the short-cut carbon fiber reinforced magnesium matrix composite material in Example 1 of the present invention.

[0024] Figure 3 This is a diagram showing the LPSO phase distribution inside the short-cut carbon fiber reinforced magnesium matrix composite material in Example 1 of the present invention.

[0025] Figure 4 This is a diagram of the carbon-magnesium interface inside the short-cut carbon fiber reinforced magnesium matrix composite material in Example 1 of the present invention.

[0026] Figure 5 This is a tensile stress-strain curve of the short-cut carbon fiber reinforced magnesium matrix composite material in Example 1 of the present invention.

[0027] Figure 6 This is a microstructure diagram of the short-cut carbon fiber reinforced magnesium matrix composite material in Example 2 of the present invention.

[0028] Figure 7 This is a microstructure diagram of the short-cut carbon fiber reinforced magnesium matrix composite material in Comparative Example 1 of the present invention.

[0029] Figure 8This is a microstructure diagram of the short-cut carbon fiber reinforced magnesium matrix composite material in Comparative Example 2 of the present invention. Detailed Implementation

[0030] Example 1 like Figure 1 As shown, the preparation method of this embodiment includes the following steps: Step 1: Place 40g of short carbon fibers with a length of 100μm~300μm into an aqueous solution containing a dispersant and stir. Then, remove the liquid by vacuum filtration under negative pressure using a vacuum pump. Control the height of the short carbon fiber preform by adjusting the pressure of the pressure bar to obtain a short carbon fiber preform with uniform fiber distribution. Step 2: Place 260g of Mg into a crucible, heat the melting furnace to 730℃ under an argon atmosphere and hold for 20 minutes. After the Mg has completely melted, add 60g of Mg-30%Y master alloy and 5g of Zn in sequence, hold for another 15 minutes, and then stir evenly with a stirrer to obtain an alloy liquid. Then let the alloy liquid stand and remove slag. The atomic ratio of Y to Zn is 2.5:1. Step 3: Place the chopped carbon fiber preform obtained in Step 1 into the mold, and preheat the mold and the chopped carbon fiber preform together to 500°C using a heating furnace (equipped with a temperature sensor); the mold is an extrusion cylinder, and the lower end of the extrusion cylinder is equipped with a concave mold and an ejector pin for quick demolding; Step 4: Under argon protection, pour the molten alloy obtained in Step 2 into the preheated mold in Step 3 using a pouring ladle. Then, place the sealing block, which has been preheated to 730°C, on top of the mold to seal it. Step 5: Turn on the press and press down the sealing block placed on top of the mold in step 4. Use a low pressure of 5MPa to gradually impregnate the alloy liquid into the short-cut carbon fiber preform. After impregnation, the pressure is instantly increased to a high pressure of 200MPa and held for 5 minutes to obtain a dense block. Then the press head is retracted. Step 6: Demold the densified bulk material obtained in Step 5 at a temperature of 440℃, and air-cool it to obtain a magnesium matrix composite material with short-cut carbon fiber containing LPSO phase.

[0031] Microscopic analysis was performed on the short-cut carbon fiber reinforced magnesium matrix composite material prepared in this embodiment. The internal fiber distribution is as follows: Figure 2 As shown, the short-cut carbon fiber reinforced magnesium matrix composite material has no pores or infiltration defects, has a dense structure, good forming quality, and the short-cut carbon fibers are evenly distributed. LPSO phase distribution as follows Figure 3As shown, numerous striped precipitates appeared in the matrix region. The striped precipitates were not directly related to the fiber distribution and their direction showed obvious random orientation. Further analysis showed that the stripes in some areas were parallel to each other, which is a typical LPSO phase distribution feature. This also indicates that the short-cut carbon fiber reinforced magnesium matrix composite containing LPSO phase was successfully prepared in this embodiment. Carbon-magnesium interface such as Figure 4 As shown, there is a white precipitate layer mainly composed of Y elements at the carbon-magnesium interface, and at the same time... Figure 4 As indicated by the middle arrow, there are rod-shaped phases growing into the matrix on the outer side of the interface layer, which easily form a pinning effect during load transfer, thereby improving the interface's load-bearing capacity. The tensile stress-strain results of the short-cut carbon fiber reinforced magnesium matrix composite are as follows: Figure 5 As shown, the strength reached 181 MPa and the elongation reached 4.6%, indicating that the short-cut carbon fiber reinforced magnesium matrix composite has good mechanical properties.

[0032] Example 2 The difference between this embodiment and Embodiment 1 is as follows: In step two, the furnace temperature is increased to 735°C, and the weight of the Mg-30Y master alloy is increased to 83g, at which point the atomic ratio of Y to Zn is 3.5:1; in step three, the preheating temperature of both the mold and the chopped carbon fiber preform is increased to 530°C; in step four, the preheating temperature of the sealing block is 735°C; in step five, a low pressure of 10MPa is used to gradually impregnate the alloy liquid, and after impregnation, the pressure is instantly increased to a high pressure of 200MPa and held for 10 minutes; in step six, the temperature of the densified block is 430°C during demolding.

[0033] The microstructure of the short-cut carbon fiber reinforced magnesium matrix composite material prepared in this embodiment is as follows: Figure 6 As shown, there are more distinct strip-shaped LPSO phases in the magnesium matrix, and the size of these strip-shaped phases is also larger than that in Example 1; the elongation of the short-cut carbon fiber reinforced magnesium matrix composite material was found to be 4.7%.

[0034] Example 3 The difference between this embodiment and Embodiment 2 is as follows: in step two, the mass of metallic Zn is kept constant, and the weight of the Mg-30Y master alloy is increased so that the atomic ratio of Y to Zn is 4.5:1; in step five, the alloy liquid is gradually impregnated under a low pressure of 8MPa, and after impregnation is completed, the pressure is instantly increased to a high pressure of 180MPa and held for 8 minutes; in step six, the temperature of the densified block is 450℃ when demolding.

[0035] Upon inspection, it was found that the matrix of the short-cut carbon fiber reinforced magnesium matrix composite prepared in this embodiment contained obvious strip-shaped LPSO phase, and the elongation of the short-cut carbon fiber reinforced magnesium matrix composite reached 4.4%.

[0036] Comparative Example 1 The difference between this comparative example and Example 2 is that: in step five, a low pressure of 10 MPa is used to gradually impregnate the alloy liquid, and after impregnation, the pressure is instantly increased to a high pressure of 150 MPa and held for 5 minutes; in step six, the temperature of the densified block during demolding is 480°C.

[0037] The microstructure of the short-cut carbon fiber reinforced magnesium matrix composite prepared in this comparative example is as follows: Figure 7 As shown, minute shrinkage defects appeared in the structure (as indicated by the circle in the figure); this is the result of the combined effect of the relatively low high pressure, short holding time, and high demolding temperature in this comparative example; this shows that the present invention can obtain a defect-free composite material structure by designing a coordinated match between high pressure, holding time, and demolding temperature.

[0038] Comparative Example 2 The difference between this comparative example and Example 3 is that in step two, the mass of metallic Zn is kept constant, and the weight of the Mg-30Y master alloy is increased so that the atomic ratio of Y to Zn is 5.0:1.

[0039] The microstructure of the short-cut carbon fiber reinforced magnesium matrix composite prepared in this comparative example is as follows: Figure 8 As shown, compared with Example 3, due to the increase of Y element, a large amount of Y-rich phase precipitates at the carbon-magnesium interface; although the composite material was successfully prepared, the relatively high density of Y element leads to a significant increase in the mass of the sample in this comparative example, which will be detrimental to the lightweight properties of magnesium-based composite materials; indicating that by designing the range of Y to Zn atomic ratio, the present invention can bring out the lightweight properties of magnesium-based composite materials on the basis of forming LPSO phase.

[0040] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a magnesium matrix composite material reinforced with short-cut carbon fibers containing LPSO phase, characterized in that, Includes the following steps: Step 1: Place the chopped carbon fibers into an aqueous solution containing a dispersant and stir. Then filter under negative pressure to obtain the chopped carbon fiber preform. Step 2: Melt the metal raw materials to obtain an alloy liquid; the metal raw materials include magnesium that forms the LPSO phase; Step 3: Place the chopped carbon fiber preform obtained in Step 1 into the mold, and preheat the mold and the chopped carbon fiber preform. Step 4: Under argon protection, pour the molten alloy obtained in Step 2 into the preheated mold in Step 3, and then place the preheated sealing block on top of the mold to seal the mold. Step 5: Press down the sealing block placed on top of the mold in Step 4 with low pressure to allow the alloy liquid to gradually penetrate into the short-cut carbon fiber preform. After the penetration is completed, maintain the pressure under high pressure to obtain a densified block. Step 6: Immediately demold the densified block obtained in Step 5, and after air cooling, obtain a magnesium matrix composite material with short-cut carbon fiber containing LPSO phase.

2. The method for preparing a magnesium matrix composite material reinforced with LPSO phase according to claim 1, characterized in that, The length of the short-cut carbon fiber mentioned in step one is 100μm~300μm.

3. The method for preparing a magnesium matrix composite material reinforced with LPSO phase according to claim 1, characterized in that, The metal raw materials mentioned in step two include metallic Mg, metallic Zn, and Mg-Y master alloy.

4. The method for preparing a magnesium matrix composite material reinforced with LPSO phase according to claim 3, characterized in that, The atomic ratio of Y to Zn in the metal raw material is (2.5~4.5):

1.

5. The method for preparing a magnesium matrix composite material reinforced with LPSO phase according to claim 3, characterized in that, The smelting method described in step two is as follows: under argon protection, metallic magnesium is placed in a crucible and heated to 730℃~735℃ and held at that temperature. After the metallic magnesium is completely melted, Mg-Y master alloy and metallic Zn are added in sequence, and the mixture is kept at that temperature and stirred evenly.

6. The method for preparing a magnesium matrix composite material reinforced with LPSO phase according to claim 1, characterized in that, The preheating temperature of the mold and the chopped carbon fiber preform in step three is 500℃~530℃, and the preheating temperature of the sealing block in step four is 730℃~735℃.

7. The method for preparing a magnesium matrix composite material reinforced with LPSO phase according to claim 1, characterized in that, The low pressure mentioned in step five is 5MPa~10MPa, the high pressure is 180MPa~200MPa, and the holding time of the high pressure is 5min~10min.

8. The method for preparing a magnesium matrix composite material reinforced with LPSO phase according to claim 1, characterized in that, The temperature of the densified block during demolding in step six is ​​430℃~450℃.

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