CN112743092B - Method for refining 3D printing aluminum alloy crystal grains and improving thermal conductivity of aluminum alloy crystal grains - Google Patents

Abstract

The invention discloses a method for refining 3D printing aluminum alloy crystal grains and improving its thermal conductivity. The steps of the method are as follows: (1) subjecting the MXene two-dimensional nanosheet material to high temperature heat treatment; (2) subjecting the heat-treated MXene and ball milling media to ball milling; (3) subjecting the ball milled MXene to aluminum alloy spherical powder colloid mixing; (4) grinding and sieving after drying, to obtain composite powder for selective laser melting and forming; (5) using the composite powder in step (4) to perform selective laser melting and forming of aluminum alloy, after forming, natural cooling Then the aluminum alloy formed parts are obtained. In the invention, the MXene two-dimensional nano-layer sheet material is used as a nano-additive to promote the refinement of crystal grains; at the same time, the thermal conductivity of the alloy is improved by utilizing the characteristics of high thermal conductivity and large adhesion area of the sheet structure.

Description

A method to refine 3D printed aluminum alloy grains and improve their thermal conductivity

technical field

The invention belongs to the technical field of metal material 3D printing, and in particular relates to a method for refining 3D printing aluminum alloy grains and improving its thermal conductivity.

Background technique

With the strong growth in demand for lightweight, structural and functional integration, aluminum alloys are becoming more and more widely used. Especially in the fields of electronic communication, aerospace and other fields, the requirements for thermal conductivity and comprehensive mechanical properties of aluminum alloy materials are also getting higher and higher. However, for some special-shaped parts and complex thin-walled structural parts, traditional processing methods are difficult to prepare. Selective Laser Melting (SLM) technology uses a focused laser beam to selectively melt metal or alloy powder layer by layer to form a metallurgically bonded, densely organized entity. Due to the simple process and high dimensional accuracy of the formed parts, laser selective melting forming technology is the most promising new method for preparing aluminum alloy parts.

However, due to the high reflectivity of the aluminum alloy to the laser, many elements that are easy to burn, and the solidification temperature range is wide, the laser printing is difficult to form, and it is easy to form coarse columnar crystals and thermal cracks. In a literature study (JH Martin, BDYahata, JMHundley, et al. Nature, 549 (2017) 365-369), the HRL laboratory at the University of California, USA, introduced ZrH into _Al7075 powder by electrostatic assembly technology to refine SLM-shaped 7075 aluminum Alloy grains. Although the problem of hot cracking is solved to a certain extent, due to the existence of many pores in the formed parts, the mechanical properties are relatively low, and the highest tensile strength is only 417MPa, which is far lower than the 7075 aluminum prepared by the traditional ingot metallurgy method. The tensile strength of the alloy material (above 550MPa). At the same time, this method has no obvious effect on the improvement of thermal conductivity.

On the other hand, the thermal conductivity of ordinary aluminum alloys is low, ranging from 96W/(m·K) of commonly used ADC12 to 175W/(m·K) of AlSi6, which still cannot meet the needs of industrial development. In order to improve the thermal conductivity of aluminum alloys, most of the high thermal conductivity aluminum alloy materials on the market improve the thermal conductivity by controlling the element content and forming process. Patent CN109022856 A discloses a process for producing aluminum alloy ingots with high thermal conductivity. Through the steps of controlling melting temperature, adding refining agent, and light treatment, aluminum alloy products with high thermal conductivity are prepared. However, this method is complex and not suitable for 3D printing technology.

Therefore, it is difficult for the existing 3D printed aluminum alloys to meet the requirements of grain refinement and thermal conductivity improvement at the same time.

SUMMARY OF THE INVENTION

In order to solve the above technical problems, the present invention provides a method for refining 3D printed aluminum alloy grains and improving its thermal conductivity.

For realizing the above-mentioned purpose of the invention, the technical scheme adopted in the present invention is as follows:

A method for refining 3D printed aluminum alloy grains and improving its thermal conductivity, the steps are as follows:

(1) The MXene two-dimensional nanosheet material is subjected to high temperature heat treatment;

(2) Ball milling the heat-treated MXene two-dimensional nanosheet material with a ball milling medium;

(3) mixing the ball-milled MXene two-dimensional nanosheet material with the dispersant solution in a certain proportion and performing ultrasonic dispersion treatment to obtain a suspension;

(4) adding the aluminum alloy powder to the suspension and ultrasonically vibrating, stirring and leaving it to stand;

(5) the mixed solution obtained in step (4) is filtered and washed, dried, then ground and sieved to obtain composite powder for selective laser melting and forming;

(6) Using the composite powder to form an aluminum alloy by selective laser melting, and after the forming is completed, an aluminum alloy formed part is obtained after natural cooling.

Further, in step (1), the number of layers of the MXene two-dimensional nanosheet material is within 5 layers.

Further, in step (1), the heat treatment is specifically: heating to 1200°C at a rate of 10°C/min-20°C/min, then keeping for 2-4 hours, and then naturally cooling to room temperature.

Further, in step (2), the mass ratio of the ball-milling medium to the MXene two-dimensional nano-layer material is 5:1, the rotational speed of the ball-milling treatment is 100-500r/min, and the ball-milling treatment time is 1-48h.

Further, in step (3), the dispersant solution is prepared as a dispersant solution by using a liquid dispersant or by mixing a solid dispersant and an organic solvent, and the organic solvent is anhydrous ethanol.

Further, in step (3), the ratio of the MXene two-dimensional nanolayer sheet material to the dispersant solution is 1-2 g: 200 ml.

Further, in step (4), the aluminum alloy powder particles are spherical or nearly spherical, and the particle size of the powder is 15-63 μm.

Further, in step (4), the aluminum alloy powder is added to the suspension at a mass ratio of 90 to 99:1 to the material of the MXene two-dimensional nanolayer sheet.

Further, in step (4), the ultrasonic vibration time is 30-60min, and the electric stirrer is used for stirring, the stirring speed is 2000-3000rpm, the stirring time is 15-30min, and the standing time is 24-48h.

Further, in step (5), the grinding time was 30min, and sieved with a 250M screen.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

(1) Compared with other existing 3D printing aluminum alloys, the MXene two-dimensional nanomaterial is introduced into the alloy used in the method of the present invention to act as a nucleating agent, so that the original coarse dendrites are transformed into equiaxed crystals with higher thermal crack resistance. , which has the effect of refining the grains of the alloy and reducing cracks during the forming process. And because of the grain refinement strengthening, the performance of the formed parts has been enhanced to a certain extent.

(2) Compared with the general MXene two-dimensional material, the MXene two-dimensional material used in the method of the present invention undergoes a high-temperature heat treatment process. Thermal conductivity value.

(3) MXene two-dimensional nanomaterials are introduced into the alloys used in the method of the present invention. Compared with general grain refining alloys containing heterogeneous nucleating agents, such as carbon tubes, the reaction of MXene two-dimensional materials with the matrix during SLM forming Smaller, it can retain its shape, increase the contact area with the powder, and form a thermal conductive network under a certain amount, which plays a role in enhancing the thermal conductivity of the alloy. The general grain refiner does not have the effect of enhancing thermal conductivity.

(4) The aluminum alloy composite powder used in the method of the present invention is prepared by colloidal mixing. Compared with the existing mechanical mixing method, the agglomeration can be removed well and the wetting between MXene and powder particles can be facilitated. The particle size of the original powder did not increase significantly.

Description of drawings

FIG. 1 is a flowchart of the method provided in Embodiment 1 of the present invention.

FIG. 2 is the morphology of the Ti ₂ C-MXene after ball milling prepared in Example 1 of the present invention.

FIG. 3 is the macroscopic morphology of the 7075 aluminum alloy powder provided in Example 2 of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. The exemplary embodiments of the present invention and their descriptions are only used to explain the present invention, and are not intended to limit the present invention.

The invention provides a method for refining 3D printing aluminum alloy grains and improving its thermal conductivity, using 3D printing aluminum alloy powder and MXene two-dimensional nano-layer material. MXene is a new type of two-dimensional lamellar material. Because of its surface properties, it has the advantages of fast ion migration and extremely high thermal conductivity. It acts as heterogeneous nucleating particles in 3D printing laser beam melts, which can effectively achieve refinement. grains and improve mechanical properties. However, the surface functional groups such as -OH and -F introduced by the preparation process will significantly reduce its actual thermal conductivity. Therefore, the MXene two-dimensional material used in the present invention is subjected to high temperature heat treatment to remove free water, adsorbed gas molecules and hydroxyl groups on its surface at high temperature, thereby improving the actual thermal conductivity; Remove surface functional groups. At the same time, the colloidal mixing method is used to prepare the mixed powder, which can well remove the agglomeration and help the wetting between the MXene and the powder particles, so that the particle size of the composite powder does not increase significantly compared with the original powder.

The concrete steps of the inventive method are as follows:

(1) Put the MXene two-dimensional nanosheet material (the number of layers is less than or equal to five layers) into a vacuum tube furnace for high temperature heat treatment, heat up to 1200 °C at a rate of 10 °C/min, then keep it for 2 hours, and then naturally cool to room temperature .

(2) The heat-treated MXene two-dimensional nanosheet material and the ball-milling medium are put into a vacuum ball-milling jar under the protection of inert gas, sealed and ball-milled, and the MXene two-dimensional MXene two-dimensional The nanosheet material is ground into smaller discrete nanosheets;

(3) Mix the MXene two-dimensional nanosheet material after ball milling treatment with the dispersant solution in a certain proportion and carry out ultrasonic dispersion treatment, and the ultrasonic time is 30min;

(4) The aluminum alloy powder (in spherical or nearly spherical shape, the particle size of the powder is 15-63 μm) is added to the suspension liquid in a certain proportion and ultrasonically oscillated, stirred with an electric stirrer, and then allowed to stand;

(5) filter and wash the mixed solution obtained in step (4) and put it into a vacuum drying oven to dry, then grind and sieve to obtain a composite powder for selective laser melting and forming;

(6) Under the protection of argon gas with a purity of 99.99%, the composite powder obtained in step (5) is used for selective laser melting to ensure that the oxygen content in the working chamber is less than 300ppm, and after natural cooling, an aluminum alloy refined by MXene is obtained. member.

Example 1

As shown in Figure 1, the specific steps of this embodiment are as follows:

(1) Select spherical aluminum alloy powder with a particle size in the range of 15-63 μm.

(2) Spread the Ti ₂ C-MXene two-dimensional nanosheet material evenly in the crucible and place it in a vacuum tube furnace. After vacuuming, the temperature is raised to 1200 °C at a rate of 10 °C/min, and then kept for 2 h, and then cooled to room temperature naturally. .

(3) The Ti ₂ C-MXene two-dimensional nanosheet material obtained by heat treatment and the ball milling medium were put into a vacuum ball mill under the protection of inert gas, sealed and ball milled. The ball milling speed was 120r/min, and the ball milling treatment time was 4h. The mass ratio of pellets is 5:1. The Ti ₂ C-MXene two-dimensional material was ground into discrete nano-sheets with smaller volume as shown in Fig.

(4) Mix the ball-milled Ti ₂ C-MXene two-dimensional nanosheet material with the liquid dispersant methyl pyridine ketone (NMP) in a ratio of 1 g: 100 ml and carry out ultrasonic dispersion treatment to obtain a suspension, ultrasonically The time is 30 minutes.

(5) adding the aluminum alloy powder of step (1) to the prepared suspension in a mass ratio of 99:1 to the MXene two-dimensional nanolayer material, and performing ultrasonic vibration for 30 minutes. Stir at a speed of 2000 rpm for 20 min to make the Ti ₂ C-MXene two-dimensional nanosheet material evenly dispersed and adhere to the aluminum alloy matrix powder, and then stand for 24 h.

(6) After mixing evenly, filter the mixed solution and wash the solid obtained by filtration with absolute ethanol, put it in a vacuum drying oven to dry at 60°C for 20h, take out and grind for 30min and sieve the powder below 250M for selective laser melting take shape.

Example 2

The concrete steps of this embodiment are as follows:

(1) Select spherical 7075 aluminum alloy powder with a particle size in the range of 15-63 μm, and its macroscopic morphology is shown in Figure 3.

(2) Spread the Ti ₃ C ₂ -MXene two-dimensional nanosheet material evenly in the crucible and place it in a vacuum tube furnace. After evacuation, the temperature is raised to 1200 ℃ at a rate of 10 ℃/min, and then kept for 2 hours, and then naturally cooled to room temperature.

(3) The Ti ₃ C ₂ -MXene two-dimensional nanosheet material obtained by heat treatment and the ball-milling medium were put into a vacuum ball-milling tank under the protection of inert gas to seal and carry out ball-milling treatment. The ball-milling speed was 120r/min and the ball-milling treatment time was 4h. , the mass ratio of pellets is 5:1. The Ti ₃ C ₂ -MXene two-dimensional nanosheet material was ground into discrete nanosheets with smaller volume during the repeated impact with the grinding ball and the inner wall of the ball mill.

(4) Mix the ball-milled Ti ₃ C ₂ -MXene two-dimensional nanosheet material with the solid dispersant polyvinylpyridine (PVP) mixture in a ratio of 1 g: 100 ml and carry out ultrasonic dispersion treatment to obtain a suspension solution, the ultrasonic time is 30min, and the solid dispersant mixture is obtained by mixing and dissolving 25ml absolute ethanol and 0.1g PVP.

(5) adding the aluminum alloy powder of step (1) to the suspension in the prepared suspension at a mass ratio of 99:1 to the MXene two-dimensional nanolayer material, and performing ultrasonic oscillation for 30 minutes, while using an electric motor The stirrer was stirred at a speed of 2000 rpm for 20 min to make the Ti ₃ C ₂ -MXene two-dimensional nanosheet material uniformly dispersed and attached to the aluminum alloy base powder, and then left to stand for 24 h.

(6) After mixing evenly, filter the mixed solution and wash the solid obtained by filtration with absolute ethanol, put it in a vacuum drying oven to dry at 60°C for 20h, take out and grind for 30min and sieve the powder below 250M for selective laser melting take shape.

In order to demonstrate the effect of the method of the present invention, the steps of Example 1 are repeated as a comparative example, but the raw material is AlSi10Mg aluminum alloy powder, and the MXene two-dimensional nano-layer material is not added.

The aluminum alloy composite powder prepared in Examples 1 and 2 and the composite powder prepared in the comparative example were processed and formed by a suitable 3D printing process on a laser selective melting forming equipment, and the forming process was carried out under the protection of argon gas with a purity of 99.99%. , to ensure that the oxygen content in the working cavity is less than 300ppm during forming. The printed samples were processed into samples, and their thermal conductivity, tensile strength and elongation were tested. The results are shown in Table 1:

Table 1 Results of Thermal Conductivity, Tensile Strength and Elongation

Thermal conductivity (W/m*k) Tensile strength (MPa) Elongation(%) Example 1 216 493 9.8 Example 2 235 510 11.2 Comparative example 119 412 6.3

It can be seen from the results in Table 1 that compared with the aluminum alloy 3D printed parts of the comparative example without the addition of MXene two-dimensional nanosheet material, the aluminum alloy of the present invention has better thermal conductivity, and at the same time, due to grain refinement, it has Higher tensile strength and elongation.

The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not intended to limit the scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (9)

1. A method for refining 3D printing aluminum alloy grains and improving the thermal conductivity of the aluminum alloy grains is characterized by comprising the following steps:

(1) carrying out high-temperature heat treatment on the MXene two-dimensional nano-layer sheet material;

(2) performing ball milling treatment on the MXene two-dimensional nano-layer sheet material subjected to heat treatment and a ball milling medium;

(3) mixing the MXene two-dimensional nano-layer sheet material subjected to ball milling treatment with a dispersing agent solution in a ratio of 1-2 g: mixing 200ml of the mixture and performing ultrasonic dispersion treatment to obtain suspension;

(4) adding aluminum alloy powder into the suspension, carrying out ultrasonic oscillation, stirring and standing;

(5) filtering and washing the mixed solution obtained in the step (4), drying, grinding and screening to obtain composite powder for selective laser melting forming;

(6) and carrying out selective laser melting on the composite powder to form the aluminum alloy, and naturally cooling after forming to obtain an aluminum alloy formed part.

2. The method for refining the grains and improving the thermal conductivity of the 3D printed aluminum alloy according to the claim 1, wherein the number of MXene two-dimensional nano-layer sheets in step (1) is within 5.

3. The method for refining the crystal grains and improving the thermal conductivity of the 3D printed aluminum alloy as claimed in claim 1, wherein in the step (1), the heat treatment is specifically as follows: heating to 1200 ℃ at the speed of 10-20 ℃/min, preserving the heat for 2-4h, and naturally cooling to room temperature.

4. The method for refining the 3D printing aluminum alloy crystal grains and improving the thermal conductivity thereof as claimed in claim 1, wherein in the step (2), the mass ratio of the ball milling medium to the MXene two-dimensional nano-layer sheet material is 5:1, the rotation speed of the ball milling treatment is 100-.

5. The method for refining the crystal grains of the 3D printed aluminum alloy and improving the thermal conductivity of the crystal grains of the 3D printed aluminum alloy as claimed in claim 1, wherein in the step (3), the dispersant solution is prepared by adopting a liquid dispersant or mixing a solid dispersant with an organic solvent, and the organic solvent is absolute ethyl alcohol.

6. The method for refining the grains and improving the thermal conductivity of 3D printed aluminum alloy as claimed in claim 1, wherein in step (4), the aluminum alloy powder particles are spherical or nearly spherical, and the particle diameter of the powder is 15-63 μm.

7. The method for refining the crystal grains and improving the thermal conductivity of the 3D printed aluminum alloy according to claim 1, wherein in the step (4), the mass ratio of the aluminum alloy powder to the MXene two-dimensional nano-layer sheet material is 90-99: 1 was added to the suspension.

8. The method for refining the 3D printing aluminum alloy grains and improving the thermal conductivity thereof as claimed in claim 1, wherein in the step (4), the ultrasonic oscillation time is 30-60min, an electric stirrer is adopted for stirring, the stirring speed is 2000-3000rpm, the stirring time is 15-30min, and the standing time is 24-48 h.

9. The method for refining the grains and improving the thermal conductivity of the 3D printed aluminum alloy as claimed in claim 1, wherein in the step (5), the grinding time is 30min and the grains are sieved by a 250M screen.

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