A four-needle-like zinc oxide whisker reinforced magnesium-based composite material and a preparation method thereof

Abstract

The application discloses a kind of four needle-shaped zinc oxide whisker reinforced magnesium-based composite material and preparation method thereof, it is related to alloy-based composite material preparation technical field;The preparation method includes the following steps: (1) magnesium matrix is added to alcohol, then four needle-shaped zinc oxide whisker is added, is dispersed by mechanical stirring and ultrasonic, filtration, and wet mixed powder is obtained;(2) the wet mixed powder obtained in step (1) is dried under argon environment, then is filled into graphite mould and is pounded solid, is placed on the medium-frequency induction equipment with copper coil and is applied micro-pressure, heat pressure sintering is preserved, finally, cooling to room temperature, demoulding, and magnesium-based composite material is obtained.The magnesium-based composite material with high strength, high elastic modulus, good corrosion resistance, high temperature resistance, wear resistance and isotropic mechanical properties is prepared, effectively solve the problems such as low strength and elastic modulus of magnesium and its alloy, poor high temperature resistance and wear resistance and serious mechanical property anisotropy in the prior art.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of alloy-based composite material preparation, in particular to a four-needle-shaped zinc oxide whisker reinforced magnesium-based composite material and a preparation method thereof. BACKGROUND

[0002] Magnesium and its alloys, as the lightest structural metal materials, have potential research and application value in the fields of aviation, aerospace, automobile industry and biomedical materials due to their high specific strength, specific stiffness, good electromagnetic shielding and damping performance. However, magnesium alloys have not been widely applied due to their low elastic modulus and strength, poor high-temperature stability, wear resistance and corrosion resistance. In addition, due to the poor symmetry of the close-packed hexagonal crystal structure of magnesium itself, the mechanical properties of magnesium and its alloys exhibit mechanical property anisotropy. This further limits the application of magnesium and its alloys in structural parts that simultaneously bear tensile stress and compressive stress. Therefore, seeking a breakthrough in the problems of low strength and elastic modulus, poor high-temperature resistance and wear resistance, and serious mechanical property anisotropy of magnesium and its alloys is the focus of attention and research of many domestic and foreign scholars. A large number of studies have shown that introducing reinforcing bodies into magnesium and its alloys to prepare new magnesium-based composite materials is one of the effective ways to improve the comprehensive mechanical properties of magnesium and its alloys.

[0003] The preparation of magnesium-based composites often involves the introduction of reinforcements through external addition. These reinforcements are generally required to have excellent load-bearing capacity and wettability, as well as to be non-reactive or moderately reactive with the matrix. Granular and rod-shaped whisker-like reinforcements are often the primary materials used. Current research on magnesium-based composites uses commonly used reinforcements such as SiC, B4C, TiC, Al2O3, SiO2, ZrO2, TiB2, Si3N4, and Al3N4 particles, as well as whiskers such as SiC, Si3N4, Al2O3, and Mg2B2O5, along with novel reinforcements such as GNPs (graphene flakes) and CNTs (carbon nanotubes). These reinforcements are mostly zero-dimensional and one-dimensional, with only flake-shaped GNPs belonging to the two-dimensional category. Currently, the size of zero-dimensional granular reinforcements is generally moving toward the nanoscale, which in turn increases the production cost of these granular reinforcements by a factor of two, significantly hindering the development of magnesium-based composites. In addition, since nano-sized particle reinforcements are difficult to disperse, it is not easy to add too much, so their improvement on the elastic modulus, high temperature resistance and wear resistance, and anisotropy of mechanical properties of the matrix alloy is minimal. For one-dimensional whiskers and two-dimensional plate-like reinforcements, although they have a good effect on improving the room temperature and high temperature mechanical properties and elastic modulus of the matrix alloy, the existence of anisotropy of their enhanced mechanical properties is also one of the limiting factors. Based on this, zinc oxide (ZnO) whiskers with good comprehensive mechanical properties and low preparation cost exhibit a unique four-dimensional spatial structure, which provides a new idea for the development of magnesium-based composite materials with good comprehensive properties. The core of the four-needle ZnO whisker extends four needle-like crystals in the radial direction. Each needle-like crystal is a single crystal microfiber. The angle between any two needles is 109°. Its four-needle structure has a completely isotropic reinforcement effect. Furthermore, their needles exhibit small dislocations, low defects, and high purity. Their tensile strength and elastic modulus reach 10 GPa and 350 GPa, respectively, approaching theoretical strengths. Furthermore, they can withstand temperatures approaching 1720°C, demonstrating excellent high-temperature resistance. Their comprehensive strengthening effect is irreplaceable by other zero-dimensional, one-dimensional, and two-dimensional reinforcements. Therefore, tetrapod-shaped ZnO whiskers are a potential reinforcement for magnesium-based composites. However, research on tetrapod-shaped ZnO whisker-reinforced magnesium-based composites has been reported.

[0004] Based on the above, the introduction of tetrapod-shaped ZnO whiskers into magnesium and its alloys is expected to improve their overall performance, leading to the development of magnesium-based composites with high strength, high elastic modulus, good corrosion resistance, high temperature resistance, wear resistance, and isotropic mechanical properties. This will lay the foundation for the widespread application of magnesium-based composites in fields such as aviation, aerospace, machinery, and automobiles.

[0005] In the preparation process of magnesium-based composite, how to add a large amount of four-needle ZnO whisker reinforcement into the matrix and uniformly disperse is currently two major difficulties in the preparation process of metal matrix composites. The commonly used preparation methods are mainly divided into liquid method and solid method. The liquid method is mainly based on stirring casting method, which has the advantages of simple process, good quality, low cost and is suitable for mass production. However, due to the large surface tension and poor wettability of the whisker reinforcement, the reinforcement often produces welding, deposition or floating, so that the reinforcement is difficult to be added in a large amount into the magnesium alloy matrix, and cannot be uniformly dispersed. In addition, when the four-needle ZnO whisker is added by the preform block method in the smelting process, the mixture of four-needle ZnO whisker and powder will be crushed into a preform block, and the four needle-shaped whiskers extending in the radial direction of the core will be crushed, thereby destroying the unique four-dimensional space structure. Furthermore, even if the four-needle ZnO whisker is added into the melt, it will also be replaced by the magnesium solution for a long time, which will destroy the unique space structure. The powder metallurgy and hot isostatic pressing method are the most typical in the solid method. Although these two methods can easily disperse the magnesium alloy powder and the whisker reinforcement, and the prepared composite material has ultra-fine grains and high strength, stiffness and other mechanical properties, but in the preparation process of magnesium-based composite, the mixture of reinforcement and magnesium alloy powder needs to be hot pressed and sintered, and further extruded to obtain a dense magnesium-based composite, which can easily destroy the four-dimensional space structure of the four-needle ZnO whisker.

[0006] Therefore, in view of the three difficulties encountered in the preparation process of four-needle ZnO whisker reinforced magnesium-based composite, such as the difficulty of adding a large amount of reinforcement and uniformly dispersing, and the four-dimensional space structure being easily destroyed, a new preparation process needs to be developed by combining the advantages of powder metallurgy and stirring casting method to solve the above problems. SUMMARY

[0007] In order to solve the above technical problems, the purpose of the present application is to provide a four-needle zinc oxide whisker reinforced magnesium-based composite and a preparation method thereof, which introduces four-needle ZnO whisker with unique four-dimensional space structure into magnesium and its alloy, and solves the key technologies of adding a large amount of reinforcement, uniform dispersion and four-dimensional space structure being easily destroyed, and obtains magnesium-based composite with high strength, high elastic modulus, good corrosion resistance, high temperature resistance, wear resistance and mechanical properties isotropy, which effectively solves the problems of low strength and elastic modulus, poor high temperature resistance and wear resistance, and serious mechanical property anisotropy in the prior art.

[0008] The technical scheme for solving the above technical problems of the present application is as follows: a preparation method of four-needle zinc oxide whisker reinforced magnesium-based composite is provided, which comprises the following steps:

[0009] (1) adding a magnesium matrix into alcohol, then adding tetrapod-shaped zinc oxide whiskers, mechanically stirring and ultrasonically dispersing, and filtering to obtain a wet mixed powder;

[0010] (2) The wet mixed powder obtained in step (1) is dried under an argon environment, then placed in a graphite grinder and pounded, and then placed on a medium-frequency induction device with a copper coil to apply micro-pressure, hot-pressed and sintered for heat preservation, and finally cooled to room temperature and demolded to obtain a magnesium-based composite material reinforced with four-needle zinc oxide whiskers.

[0011] Furthermore, in step (1), the magnesium matrix is ​​one of pure magnesium powder, magnesium alloy AZ31, magnesium alloy AZ61, magnesium alloy AZ91 and magnesium alloy ZK60.

[0012] Furthermore, in step (1), the particle size of the magnesium matrix is ​​≥200 mesh, and the size of the four-needle zinc oxide whiskers is 5-200 μm.

[0013] Furthermore, in the magnesium-based composite material reinforced with tetrapod-shaped zinc oxide whiskers, the addition amount of the tetrapod-shaped zinc oxide whiskers is 1-30 wt %.

[0014] Furthermore, in step (1), mechanical stirring is performed at 200-400 r / min for 20-40 min.

[0015] Furthermore, in step (1), ultrasonic dispersion is performed at 30-60 kHz for 20-40 min.

[0016] Furthermore, in step (2), drying is performed at a temperature of 30-80° C. for 20-40 min, and the argon gas flow rate is 1-5 L / min.

[0017] Furthermore, in step (2), hot pressing and sintering are carried out at 450-700° C. and 5-15 kW for 5-30 min, with a heating rate of 80-100° C. / min.

[0018] Furthermore, in step (2), during hot pressing and sintering, the pressure is less than 10 MPa.

[0019] Furthermore, in step (2), cooling is performed at room temperature.

[0020] Furthermore, the preparation method of the four-needle zinc oxide whisker reinforced magnesium-based composite material produces a four-needle zinc oxide whisker reinforced magnesium-based composite material.

[0021] The present invention has the following beneficial effects:

[0022] 1. The present invention introduces four-needle ZnO whiskers with a unique four-dimensional spatial structure into magnesium and its alloys, focusing on solving key technologies such as large-scale addition, uniform dispersion and easy destruction of the four-dimensional spatial structure of the reinforcement, thereby producing a magnesium-based composite material with high strength, high elastic modulus, good corrosion resistance, high temperature resistance, wear resistance and isotropic mechanical properties, effectively solving the problems of low strength and elastic modulus, poor high temperature resistance and wear resistance, and severe anisotropy of mechanical properties of magnesium and its alloys in the prior art.

[0023] 2. In the preparation process of the four-needle zinc oxide whisker reinforced magnesium-based composite material of the present invention, the four-needle zinc oxide whiskers and magnesium alloy powder are first mixed in anhydrous ethanol and stirred and ultrasonically dispersed evenly. Then, after filtering through filter paper, the mixed powder is placed in a drying oven and dried under an Ar gas protection environment. This solves the problem that the reinforcement is difficult to add and disperse in large quantities, and the argon environment also prevents the powder from oxidizing. Subsequently, the dried mixed powder is loaded into a grinding tool, and the grinding tool is placed on a medium-frequency induction device with a copper coil to apply micro-pressure for rapid sintering and micro-melting of the matrix. Finally, cooling is performed to obtain a magnesium-based composite material reinforced with four-needle zinc oxide whiskers. Under micro-pressure, the unique four-dimensional spatial structure of the four-needle zinc oxide whiskers is preserved, and finally a magnesium-based composite material reinforced with four-needle ZnO whiskers is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a microstructure diagram of the magnesium-based composite material obtained in Example 1;

[0025] Figure 2 The mechanical properties test results of the magnesium-based composite material obtained in Example 1 are as follows;

[0026] Figure 3 This is a microstructure diagram of the magnesium-based composite material obtained in Example 2;

[0027] Figure 4 The mechanical properties test results of the magnesium-based composite material obtained in Example 2;

[0028] Figure 5 This is a microstructure diagram of the magnesium-based composite material obtained in Example 3;

[0029] Figure 6 These are the mechanical property test results of the magnesium-based composite material obtained in Example 3. DETAILED DESCRIPTION

[0030] The principles and features of the present invention are described below. The examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. In the examples, where specific conditions are not specified, conventional conditions or manufacturer-recommended conditions were used. Reagents or instruments used where the manufacturer is not specified are commercially available conventional products.

[0031] Example 1

[0032] A magnesium-based composite material reinforced with tetrapod-shaped zinc oxide whiskers, the preparation method of which comprises the following steps:

[0033] (1) Pure magnesium powder with a particle size of 200 mesh was added to alcohol, and then 50 μm tetrapod-shaped zinc oxide whiskers (Mg:ZnO=70:30) were added. The mixture was mechanically stirred at 300 r / min for 30 min, ultrasonically dispersed at 35 kHz for 35 min, and filtered to obtain a wet mixed powder.

[0034] (2) The wet mixed powder obtained in step (1) was dried at 50°C for 30 min under an argon environment (gas flow rate 3 L / min), then placed in a graphite grinder and pounded, and then placed on a medium-frequency induction device with a copper coil to apply a micro-pressure of 1 MPa, and heated to 650°C at a rate of 100°C / min to slightly melt the matrix, kept warm for 8 min, and finally cooled to room temperature and demolded to obtain a magnesium-based composite material reinforced with four-needle zinc oxide whiskers.

[0035] The microstructure of the obtained four-needle zinc oxide whisker reinforced magnesium matrix composite material is as follows: Figure 1 As shown; under the conditions of test force of 0.1kgf and dwell time of 10s, four points are randomly selected and the hardness distribution of the material is measured as follows Figure 2 As shown, the average value is 118.8Hv.

[0036] Example 2

[0037] A magnesium-based composite material reinforced with tetrapod-shaped zinc oxide whiskers, the preparation method of which comprises the following steps:

[0038] (1) 300-mesh magnesium alloy AZ31 powder was added to alcohol, followed by 20 μm tetrapod-shaped zinc oxide whiskers (AZ31:ZnO=90:10), mechanically stirred at 350 rpm for 25 min, ultrasonically dispersed at 40 kHz for 30 min, and filtered to obtain a wet mixed powder.

[0039] (2) The wet mixed powder obtained in step (1) was dried at 60°C for 30 min under an argon environment (gas flow rate 3 L / min), then placed in a graphite grinder and pounded, and then placed on a medium-frequency induction device with a copper coil to apply a micro-pressure of 3 MPa, and the temperature was raised to 550°C at a rate of 90°C / min to slightly melt the matrix, and the temperature was kept for 15 min. Finally, it was cooled to room temperature and demolded to obtain a magnesium-based composite material reinforced with four-needle zinc oxide whiskers.

[0040] The microstructure of the obtained four-needle zinc oxide whisker reinforced magnesium matrix composite material is as follows: Figure 3As shown; under the conditions of test force of 0.1kgf and dwell time of 10s, four points are randomly selected and the hardness distribution of the material is measured as follows Figure 4 As shown, the average value is 115.9Hv.

[0041] Example 3

[0042] A magnesium-based composite material reinforced with tetrapod-shaped zinc oxide whiskers, the preparation method of which comprises the following steps:

[0043] (1) Magnesium alloy ZK60 powder with a particle size of 400 mesh was added to alcohol, and then 100 μm tetrapod-shaped zinc oxide whiskers (ZK60:ZnO=95:5) were added. The mixture was mechanically stirred at 350 r / min for 30 min, ultrasonically dispersed at 50 kHz for 30 min, and filtered to obtain a wet mixed powder.

[0044] (2) The wet mixed powder obtained in step (1) was dried at 70°C for 20 min under an argon environment (gas flow rate 3 L / min), then placed in a graphite grinder and pounded, and then placed on a medium-frequency induction device with a copper coil to apply a micro-pressure of 8 MPa, and heated to 500°C at a rate of 80°C / min to slightly melt the matrix, kept warm for 30 min, and finally cooled to room temperature and demolded to obtain a magnesium-based composite material reinforced with four-needle zinc oxide whiskers.

[0045] The microstructure of the obtained four-needle zinc oxide whisker reinforced magnesium matrix composite material is as follows: Figure 5 As shown; under the conditions of test force of 0.1kgf and dwell time of 10s, four points are randomly selected and the hardness distribution of the material is measured as follows Figure 6 As shown, the average value is 106.9Hv.

[0046] According to the hardness-strength empirical formula: Hv≈3·R m (Hv-hardness, R m - tensile strength) and composite material stiffness stress model: E = f r E r +(1-f r )E m (f r -Reinforcement volume fraction, %; E r - Elastic modulus of reinforcement, GPa; E m - matrix elastic modulus, GPa) Comparative Examples 1-3 show that:

[0047] (1) The magnesium-based composite material prepared by hot pressing and sintering process using magnesium / magnesium alloy as the matrix and zinc oxide mixed powder as the raw material can effectively retain the unique three-dimensional four-needle structure of zinc oxide whiskers.

[0048] (2) Generally, the hardness values of pure magnesium, AZ31 and ZK60 are 36Hv, 49Hv and 70-95Hv respectively, while the hardness values of zinc oxide reinforced magnesium matrix composites are all greater than 100Hv; it can be inferred from the hardness-strength empirical formula that zinc oxide can significantly improve the strength of the material.

[0049] (3) It can be seen from Example 1 and Example 3 that the hardness values of pure magnesium and ZK60 are 36Hv and 70-95Hv respectively, but the hardness value of the composite material with 30% ZnO added to the pure magnesium matrix is higher than that of the composite material with 5% ZnO added to the ZK60 matrix; it can be inferred from the hardness-strength empirical formula that the coordination of the matrix composition and the amount of zinc oxide added can prepare high-strength magnesium matrix composites.

[0050] (4) It can be seen from the comparison of Examples 1-3 that the elastic modulus of zinc oxide is much greater than that of the matrix, and it can be inferred from the stiffness stress model of the composite material that the elastic modulus of the magnesium matrix composite material is significantly improved with the increase of the content of the reinforcing phase ZnO.

[0051] In summary, the present application introduces four-needle-shaped ZnO whiskers with a unique four-dimensional space structure into magnesium and its alloys, and focuses on solving the key technologies of large-scale addition, uniform dispersibility and easy destruction of the four-dimensional space structure of the reinforcing body, and prepares magnesium matrix composites with high strength, high elastic modulus, good corrosion resistance, high temperature resistance, wear resistance and isotropic mechanical properties, effectively solving the problems of low strength and elastic modulus, poor high temperature resistance and wear resistance and serious anisotropy of mechanical properties of magnesium and its alloys in the prior art.

[0052] The above only describes the preferred embodiments of the present application and is not intended to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a magnesium-based composite material reinforced with four-needle zinc oxide whiskers, characterized in that: The following steps are involved: (1) Adding magnesium matrix to alcohol, then adding tetrapod-shaped zinc oxide whiskers, mechanically stirring and ultrasonically dispersing, filtering, and obtaining wet mixed powder; (2) drying the wet mixed powder obtained in step (1) under an argon environment, then placing it in a graphite grinder and pounding it, then placing it on a medium-frequency induction device with a copper coil to apply micro-pressure, hot-pressing and sintering, and finally cooling it to room temperature and demolding it to obtain a magnesium-based composite material reinforced with four-needle zinc oxide whiskers; In the magnesium-based composite material reinforced with tetrapod-shaped zinc oxide whiskers, the addition amount of tetrapod-shaped zinc oxide whiskers is 1-30wt%; in step (2), hot pressing and sintering are performed at 450-700°C and 5-15KW for 5-30min, the heating rate is 80-100°C / min, and the pressure during hot pressing and sintering is less than 10MPa.

2. The method for preparing a magnesium-based composite material reinforced with four-needle zinc oxide whiskers as claimed in claim 1, wherein: In step (1), the magnesium matrix is ​​one of pure magnesium powder, magnesium alloy AZ31, magnesium alloy AZ61, magnesium alloy AZ91 and magnesium alloy ZK60.

3. The method for preparing a magnesium-based composite material reinforced with four-needle zinc oxide whiskers according to claim 1, wherein: In step (1), the particle size of the magnesium matrix is ​​≥200 mesh, and the size of the four-needle zinc oxide whiskers is 5-200 μm.

4. The method for preparing a magnesium-based composite material reinforced with four-needle zinc oxide whiskers according to claim 1, wherein: In step (1), mechanical stirring is performed at 200-400 r / min for 20-40 min.

5. The method for preparing a magnesium-based composite material reinforced with four-needle zinc oxide whiskers according to claim 1, wherein: In step (1), ultrasonic dispersion is performed at 30-60 kHz for 20-40 min.

6. The method for preparing a magnesium-based composite material reinforced with four-needle zinc oxide whiskers according to claim 1, wherein: In step (2), drying is performed at a temperature of 30-80° C. for 20-40 min, with an argon gas flow rate of 1-5 L / min.

7. A tetrapod-like zinc oxide whisker-reinforced magnesium-based composite material obtained by the method for preparing a tetrapod-like zinc oxide whisker-reinforced magnesium-based composite material according to any one of claims 1 to 6.

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