Preparation method of superfine aluminum carbide-magnesium refining agent

Abstract

The application discloses a preparation method of superfine aluminum-magnesium carbide composite powder, which comprises the following steps: mixing aluminum powder and graphite powder, and grinding the mixture into a first substance in which carbon is in aluminum in a ball mill; adding magnesium powder into the first substance and continuously ball milling to prepare a second substance; and annealing the second substance to obtain the superfine aluminum-magnesium carbide composite powder material. The preparation method solves the problems of the aluminum carbide particles, such as air absorption and poor interface with the magnesium matrix, and makes the aluminum carbide particles have good wettability with the magnesium liquid. The superfine aluminum-magnesium carbide composite powder material solves the problem of high surface energy of the nano particles and easy agglomeration, and makes the aluminum carbide more easily dispersed in the magnesium liquid, so that the mechanical properties of the magnesium alloy are greatly improved. In addition, the ball milling time required by the method is short, and the chemical reaction temperature of carbon and aluminum is low, so that the energy consumption and time consumption of the method are lower than those of the prior art, and the aluminum powder in which carbon is solid-solved is fully converted into aluminum carbide, and the superfine powder is formed.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of materials, and particularly relates to a preparation method of superfine aluminum carbide-magnesium refiner and the superfine aluminum carbide-magnesium refiner prepared by the preparation method. BACKGROUND

[0002] As a close-packed hexagonal crystal structure, magnesium alloy has only three geometric slip systems and two independent slip systems at room temperature, and its plastic deformation ability is poorer than that of body-centered cubic and face-centered cubic crystals. Grain refinement can not only improve the strength of magnesium alloy, but also improve its plasticity and toughness, and is one of the commonly used strengthening methods of magnesium alloy. Al4C3 is a close-packed hexagonal crystal, and its lattice constants are a=0.333 nm and c=0.249 nm, which are different from those of pure magnesium (a=0.320 nm and c=0.520 nm). The mismatch degree of the basal plane of Al4C3 is 3.8%, and according to the metal crystallization theory, the mismatch degree between the nucleation substrate and the magnesium matrix is less than 5%, so Al4C3 can become a crystal nucleus. In addition, the relative density of Al4C3 is 2.36 g / cm 3 , which is similar to that of magnesium alloy, and Al4C3 can become an ideal strengthening phase of magnesium alloy. However, since the melting point of Al4C3 is 2100 DEG C, it is difficult to uniformly disperse in the magnesium melt, and its strengthening effect on the magnesium alloy is restricted. In addition, when Al4C3 is used as a refiner, it is required that the particles of Al4C3 are small, and the interface between Al4C3 and magnesium is well combined or the wettability of Al4C3 with magnesium liquid is good. Therefore, how to manufacture Al4C3 with small particles and good combination with magnesium liquid is the goal pursued by people.

[0003] The preparation methods of Al4C3 powder mainly include metal carbide method, carbothermal reduction method, sol-gel method, microwave synthesis method and mechanical ball milling method. At present, the preparation of aluminum carbide particles has relatively mature technology at home and abroad, but the particles have great limitations in improving the wettability with magnesium liquid. CN109095469A discloses a preparation method of aluminum carbide. First, aluminum powder and graphite powder are uniformly mixed, and then ball milling is carried out under the protection of inert gas, and then sintering is carried out at 600-1000℃ to prepare aluminum carbide powder. The process uses a plasma ball mill to activate and refine the original powder, and introduces cold field plasma into the mechanical ball milling process, which reduces the synthesis temperature of aluminum carbide, but improves the requirements for equipment, and the obtained powder size is relatively large, about 3μm. CN102442668A discloses a method for preparing aluminum carbide from aluminum oxide. Industrial pure aluminum oxide and graphite are mixed, then heated to 1450-1600℃ under a pressure of 1-200Pa for 60-120min, and then cooled to obtain aluminum carbide. The process obtains aluminum carbide with high purity, but has high processing conditions such as low pressure, high vacuum degree and high reaction temperature, high energy consumption, higher requirements for equipment, and larger particle size of the obtained aluminum carbide powder. CN104118878A discloses a preparation method of aluminum carbide. Alumina and graphite are mixed and cold-pressed into a certain size block under certain vacuum conditions, and then heated to 1400-1600℃ for 60-180min, and then cooled to obtain aluminum carbide. The process has high synthesis temperature and long holding time, and needs to be cold-pressed into a certain size block, which makes the process more complex, and further crushing and refining may be needed after sintering.

[0004] Based on the above analysis, a technical scheme capable of preparing ultra-fine aluminum carbide-magnesium powder and solving the poor wettability of ultra-fine aluminum carbide particles with magnesium liquid is urgently needed in the industry. SUMMARY

[0005] In view of the above shortcomings, the present application provides a method for preparing ultra-fine aluminum carbide-magnesium powder by a planetary ball mill, which has the characteristics of simple operation, low cost, low synthesis temperature, small particle size of the synthesized aluminum carbide powder, and the formed aluminum carbide particles in the magnesium powder matrix, which becomes aluminum carbide-magnesium composite powder, to solve the problem of poor wettability of ultra-fine aluminum carbide particles with magnesium liquid.

[0006] To solve the above technical problems, the present application adopts the following technical scheme:

[0007] The present application discloses an ultra-fine aluminum carbide-magnesium composite powder, comprising:

[0008] a first substance composed of aluminum powder and graphite powder; and

[0009] A second substance composed of magnesium powder and aluminum carbide; wherein:

[0010] When forming the first substance, the mass ratio of aluminum powder to graphite powder is (2.75-2.95):1;

[0011] When forming the second substance, the mass ratio of magnesium powder to aluminum carbide is 0.8-1.2:1.

[0012] The application also discloses a preparation method of the ultrafine aluminum carbide-magnesium composite powder material.

[0013] (1) mixing aluminum powder and graphite powder and grinding them into a first substance with carbon in aluminum in a ball mill;

[0014] (2) adding magnesium powder into the first substance and continuing to ball mill to form a second substance;

[0015] (3) annealing the second substance to obtain the ultrafine aluminum carbide-magnesium composite powder material.

[0016] Further, the purity of the aluminum powder, graphite powder and magnesium powder is all greater than 95%;

[0017] Further, the particle size of the aluminum powder and graphite powder is less than 50 μm, and the particle size of the magnesium powder is less than 500 μm.

[0018] Further, the magnesium powder includes but is not limited to pure magnesium, particles processed from magnesium alloy chips such as AZ31, AZ80 and ZK60, and the purity of the argon used is greater than 99.99%.

[0019] Further, the maximum particle size of the aluminum carbide is less than 500 nm.

[0020] Further, the grinding balls in the ball mill are zirconia balls, and the mass ratio of the grinding balls to the material is 35:1-40:1; the ball mill is ball milled under argon protection after being vacuumized, and the purity of the argon is greater than 99.99%.

[0021] Further, the mass ratio of the aluminum powder to the graphite powder is 2.75:1-2.95:1, and the stoichiometric excess of the added graphite relative to the first substance is 0.5%-1.0% as a process control agent.

[0022] Further, the annealing in step (3) is rapidly heated to 650-750 ℃ in a vacuum furnace with a vacuum degree greater than 10 -3 Pa, and then cooled to room temperature after being kept for 20-30 min.

[0023] The application also discloses an ultrafine aluminum carbide-magnesium composite powder material prepared according to any of the above preparation methods.

[0024] The present application has the following advantages:

[0025] The aluminum carbide-magnesium composite powder produced by the method of the present application is produced by solid solution of Al and C elements and then reformation of aluminum carbide in a magnesium matrix, so that the aluminum carbide and magnesium can form a good composite, and the particle size of the aluminum carbide-magnesium composite powder is very small. Thus, the problems of the gettering of the aluminum carbide particles, the poor interface between the aluminum carbide particles and the magnesium matrix, etc. are solved, and the aluminum carbide particles have good wettability with the magnesium liquid; and the problem of the high surface energy of the nanoparticles and easy agglomeration is solved, so that the aluminum carbide is more easily dispersed in the magnesium liquid. To achieve these performances, the preparation process of the aluminum carbide-magnesium composite powder needs to be strictly controlled. The present application can control the size of the generated aluminum carbide particles to be < 500 nm by precise control of the process parameters such as the ball milling medium, the ball-to-material ratio, the ball milling time, the vacuum annealing temperature, the annealing time, and the cooling speed. Since the aluminum carbide particles are fine and have good wettability with the magnesium liquid, the aluminum carbide can be highly dispersed in the magnesium liquid without forming lumps, fully playing its role of dispersion strengthening, and greatly improving the mechanical properties of the magnesium alloy. In addition, the ball milling time required by the method of the present application is short, and the total ball milling time is generally only 7-12 hours, and the temperature at which the chemical reaction of carbon and aluminum occurs is low, only 650-750°C, so the energy and time consumption of the method of the present application are lower than those of the existing methods.

[0026] The first ball milling process of the present application realizes the crushing and fine grinding of the aluminum powder and the graphite powder, and at the same time, the graphite powder is amorphized, a large number of vacancies and dislocations, etc. are generated in the aluminum powder particles, and a large number of new interfaces are continuously refined and generated in the collision process of the aluminum powder and the graphite powder, and the instantaneous temperature rise generated by the collision significantly reduces the diffusion activation energy of carbon atoms in the aluminum lattice, so that carbon enters the aluminum lattice to form a solid solution of carbon in aluminum, and therefore no aluminum carbide is generated in this process. The atomic ratio of aluminum and carbon in aluminum carbide is 4:3, and the stoichiometric amount of graphite powder relative to Al4C3 in the raw materials in the first ball milling process is added in excess, and the excess graphite powder can be used as a process control agent to compensate for the loss of carbon in the ball milling process, and can reduce the agglomeration, wall sticking, caking, and balling of the powder, and reduce the wear of the grinding balls and the grinding cylinder, and can better control the powder composition and improve the powder yield.

[0027] In the second ball milling process of the present application, under the action of external force collision, extrusion, and grinding, the aluminum powder with solid-solved carbon and the magnesium powder are repeatedly crushed, extruded, and cold-welded to form a layered structure, and the layered structure is further refined and curled and overlapped, and finally a composite system of the aluminum powder with solid-solved carbon and the magnesium powder is formed.

[0028] The annealing process of the present application is to heat the composite powder in a quartz glass tube under vacuum atmosphere. Due to the high surface energy and diffusion activation energy of the particles, carbon reacts with aluminum in situ to form aluminum carbide, thereby forming ultra-fine aluminum carbide and magnesium powder composite particles. In this process, the magnesium powder does not react with the carbon and aluminum powder.

[0029] The present application adopts a low-temperature heating and rapid cooling process to ensure that the aluminum powder with dissolved carbon is fully converted to aluminum carbide and forms ultra-fine powder. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 A scanning electron image of the ultra-fine aluminum carbide-magnesium composite powder obtained from Example 1, wherein the magnesium matrix is less than 1 micron and the aluminum carbide particle size is less than 500 nm. DETAILED DESCRIPTION

[0031] The present application will be further described in conjunction with specific examples. It should be understood that all the following examples are only used to illustrate the present application and not to limit the scope of the present application.

[0032] The ball mill used in each example is a BXQM4L planetary ball mill manufactured by Nanjing Telun New Instrument Co., Ltd. The ball mill jar is a stainless steel vacuum jar with a volume of 1 L. The grinding balls are zirconia balls with a diameter of 5 mm, 3 mm and 1 mm, and the total volume of the grinding balls accounts for 50% of the total volume of the jar. and Three kinds can be selected according to actual conditions. The total volume of the grinding balls accounts for 50% of the total volume of the jar.

[0033] Example 1

[0034] Step 1: Mix aluminum powder (purity 99.8%, particle size 300 mesh) and high-purity graphite powder (purity 99.99%, particle size 325 mesh) in a mass ratio of 2.75:1. The amount of graphite powder is 0.5% excess relative to the stoichiometric ratio of the first substance. The excess graphite powder serves as a process control agent. The mixture is loaded into a stainless steel ball mill jar. The ball-to-material ratio (mass ratio of grinding balls to mixed powder) is 30:1. Zirconium carbide grinding balls are added to the ball mill jar. The diameter of the grinding balls is added in a ratio of 30:1. and 200 After the ball mill jar is evacuated, it is filled with argon (purity 99.99%). Then the ball mill jar is installed on the ball mill, and the ball milling is carried out at a speed of 300 r / min for 6 hours.

[0035] Step 2: Add AZ31 magnesium powder (particle size 325 mesh, purity 98%) equal in mass to the sum of the aluminum powder and graphite powder to the ball mill jar of Step 1. After evacuation, it is filled with argon, and the ball milling is continued at a speed of 300 r / min for 1 h.

[0036] Step 3: Take 200g of the powder formed by ball milling and place it in a vacuum furnace with a vacuum degree greater than 10-3 Pa. Heat it to 700℃ within 1 minute, keep it at that temperature for 20 minutes, and then cool it to room temperature within 10 minutes to obtain ultrafine aluminum carbide-magnesium composite powder.

[0037] The obtained ultrafine aluminum carbide-magnesium composite powder contains 50% aluminum carbide by mass.

[0038] Appendix Figure 1 The image shows a scanning electron image of the ultrafine aluminum carbide-magnesium composite powder obtained by this method, wherein the magnesium matrix is ​​less than 1 micrometer and the aluminum carbide particle size is less than 500 nm.

[0039] Example 2

[0040] The differences between this embodiment and Embodiment 1 are as follows:

[0041] Step 1: Mix aluminum powder (99.8% purity, 300 mesh) and high-purity graphite powder (99.99% purity, 325 mesh) at a mass ratio of 2.85:1. The mass ratio of the zirconium carbide grinding balls used to the mixed powder of aluminum powder (300 mesh, 95.0% purity) and graphite powder (300 mesh, 95.0% purity) is 40:1. 40 zirconium carbide grinding balls are used. 150 and 100 The ball milling time is 7 hours.

[0042] Step 2: Add AZ80 (400 mesh, 95.0% purity) to the ball mill jar in Step 1, with a mass equal to 80% of the total mass of aluminum powder and graphite powder. The ball milling time is 2 hours.

[0043] Step 3: Take 200g of the powder formed by ball milling and place it in a vacuum furnace with a vacuum degree greater than 10-3 Pa. Heat it to 650℃ within 1 minute and keep it at that temperature for 15 minutes. Then cool it to room temperature within 6 minutes.

[0044] The obtained ultrafine aluminum carbide-magnesium composite powder contains 55.5% aluminum carbide by mass.

[0045] Example 3

[0046] The differences between this embodiment and Embodiment 1 are as follows:

[0047] Step 1: The ratio of aluminum powder (400 mesh, 97.0% purity) to graphite powder (95.0% purity, 400 mesh) is 2.95:1. The mass ratio of zirconium carbide grinding balls to the mixed powder of aluminum and graphite is 35:1. 40 zirconium carbide grinding balls are used. 200 The ball-milling time was 8 hours.

[0048] Step 2: The same amount of ZK60 magnesium alloy (300 mesh, 97% purity) as the total mass of the aluminum powder and the graphite powder was added into the ball-milling tank of step 1, and then the ball-milling was continued for 1.5 hours at a rotation speed of 300 r / min after vacuumizing and filling with argon.

[0049] The mass percentage of aluminum carbide in the obtained ultrafine aluminum carbide-magnesium composite powder was 50%.

[0050] The above merely illustrates the specific embodiments of the present application and is not intended to limit the present application. 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 ultrafine Al4C3-Mg composite powder, comprising: (1) mixing aluminum powder and graphite powder in a mass ratio of (2.75-2.95):1, and then grinding in a ball mill to form a first substance with carbon in aluminum; (2) adding magnesium powder to the first substance and continuing to grind in the ball mill to form a second substance, the mass ratio of magnesium powder to the first substance being 0.8-1.2:1; (3) heating and annealing the second substance, the annealing being performed in a vacuum degree > 10 -3 heating to 650-750℃ in a vacuum furnace, holding for 20-30min, and then cooling to room temperature, to obtain the superfine aluminum carbide-magnesium composite powder material; wherein: the magnesium powder is a particle processed from pure magnesium chips.

2. The method according to claim 1, wherein: the purity of the aluminum powder, graphite powder and magnesium powder is all >95%; the particle size of the aluminum powder and graphite powder is <50 μm, and the particle size of the magnesium powder is <500 μm.

3. The method according to claim 1, wherein: the maximum particle size of the first substance in step (1) is <500 nm.

4. The method according to claim 1, wherein: the grinding balls in the ball mill are zirconia balls, and the mass ratio of grinding balls to material is 35:1-40:1; the ball mill is operated under argon protection after being vacuumed, and the purity of argon is >99.99%.

5. The method according to claim 1, wherein: the stoichiometric ratio of graphite to the first substance in step (1) is 0.5%-1.0% in excess as a process control agent.

6. An ultrafine Al4C3-Mg composite powder material prepared by the method according to any one of claims 1-5.

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