Laser additive manufacturing method of graphene reinforced metal matrix composite

Abstract

The invention discloses a laser additive manufacturing method of a graphene reinforced metal matrix composite material. The method comprises the following steps: 1, preparing mixed powder of graphene and metal powder by adopting a method of combining ultrasonic and mechanical stirring; secondly, the mixed powder is subjected to preliminary melting through the preliminary melting process parameters, and a preliminary solidification deposition layer is obtained; 3, remelting the preliminary solidification deposition layer by using remelting process parameters to obtain a remelted solidification deposition layer; and fourthly, the second step and the third step are repeated layer by layer, and finally the laser additive manufacturing graphene reinforced metal matrix composite is obtained. According to the method, the mixing uniformity and stability of graphene and metal powder are improved through the ultrasonic and mechanical stirring combined method, graphene agglomeration is avoided, uniform distribution of graphene is promoted through the remelting process, the defect of poor fusion is effectively eliminated, a high-density formed part is obtained, and the product quality is improved. And synchronous improvement of heat conduction and mechanical properties of the laser additive manufacturing graphene reinforced metal matrix composite material is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal additive manufacturing, and in particular relates to a laser additive manufacturing method for a graphene-reinforced metal-based composite material. Background Art

[0002] As a representative technology of metal additive manufacturing, laser selective melting has outstanding advantages in the preparation of high-performance, precise and complex structures, meeting the design and manufacturing needs of lightweight, integrated thermal management structures in aerospace and other fields. However, due to the sharp increase in the power density of the equipment to which the thermal management structure belongs, the low thermal conductivity of conventional metal materials (AlSi10Mg, etc.) formed by laser selective melting can no longer meet the increasingly stringent requirements of thermal management structures. Therefore, it is urgent to develop high thermal conductivity metal materials for laser selective melting technology. Since graphene has excellent thermal conductivity (5000W·m -1 ·K -1 ) and ultimate strength (130GPa). The use of laser selective melting to form graphene-enhanced metal matrix composites can manufacture lightweight, integrated thermal management structures that take into account both thermal conductivity and mechanical properties, and has become a current research hotspot. However, the addition of graphene is very likely to cause poor fusion defects, resulting in a narrow process window and poor formability. On the one hand, graphene has a high surface energy and is prone to agglomeration. When the agglomeration size is too large, its interior cannot be infiltrated by the metal liquid, and poor fusion defects are formed after solidification; on the other hand, graphene increases the thermal conductivity of the formed part, resulting in faster heat dissipation from the molten pool downward, lower molten pool temperature, and greater viscosity, resulting in poor fusion defects. It should be noted that the thermal conductivity of the cavity formed by the poor fusion defect is extremely low, and it is easy to cause stress concentration and lead to premature fracture of the specimen. Therefore, poor fusion will reduce both thermal conductivity and mechanical properties. Therefore, it is urgent to find a method to improve the formability of graphene-enhanced metal matrix composites by laser selective melting, in order to achieve the synergistic improvement of thermal conductivity and mechanical properties of laser additively manufactured graphene-enhanced metal matrix composites. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a laser additive manufacturing method for graphene-enhanced metal-based composite materials in view of the deficiencies of the above-mentioned prior art. The method improves the mixing uniformity and stability of graphene and metal powders through a mixing method combining ultrasound and mechanical stirring, avoids graphene agglomeration, and promotes the uniform distribution of graphene by a remelting process, effectively eliminates poor fusion defects, obtains high-density molded parts, and realizes the simultaneous improvement of thermal conductivity and mechanical properties of laser additively manufactured graphene-enhanced metal-based composite materials, solving the problem of reduced thermal and mechanical properties of formed parts due to poor fusion defects in laser additively manufactured graphene-enhanced metal-based composite materials.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a laser additive manufacturing method for graphene-reinforced metal-based composite materials, characterized in that the method comprises the following steps:

[0005] Step 1: using a mixing method combining ultrasound and mechanical stirring to uniformly adhere graphene to the surface of metal powder to obtain a mixed powder of graphene-reinforced metal-based composite material;

[0006] Step 2: determine the preliminary melting process parameters of laser additive manufacturing, including laser mode, laser spot diameter, substrate preheating temperature, forming atmosphere, laser power, scanning speed, scanning spacing and powder layer thickness, and then use the preliminary melting process parameters to perform preliminary melting on the mixed powder obtained in step 1 to obtain a preliminary solidified deposition layer;

[0007] Step 3: on the basis of the preliminary melting process parameters determined in step 2, setting and optimizing the remelting process parameters, and then remelting the preliminary solidified deposition layer obtained in step 2 using the optimized remelting process parameters to obtain a highly dense remelted solidified deposition layer;

[0008] Step 4: Steps 2 and 3 are then repeated layer by layer, and the initial solidified deposition layers of each layer are obtained by laser additive manufacturing and remelted, and each remelted solidified deposition layer is stacked layer by layer to finally obtain a laser additively manufactured graphene-reinforced metal-based composite material.

[0009] The above-mentioned laser additive manufacturing method of a graphene-enhanced metal-based composite material is characterized in that the mixing method of combining ultrasound and mechanical stirring in step one is: first, graphene is added to an ethanol solution for ultrasound for 2min to 120min, then metal powder is added, ultrasound is continued and mechanical stirring is performed for 2min to 120min. This mixing method ensures that the graphene is fully dispersed in the ethanol solution, and then fully contacts and mixes with the metal powder in a moving state. Usually, graphene generally needs to be stationary for more than 1 day before it can sink to the bottom after ultrasound in an ethanol solution. After the mixing process of combining ultrasound and mechanical stirring in the present invention is completed, the ethanol solution in the upper layer of the container immediately presents a transparent and clear state, and precipitation appears at the bottom, indicating that the graphene has completely adhered to the surface of the metal powder at the bottom of the container, and then the mixed solution system is poured into a suction filtration system for suction filtration to obtain a mixed powder of a graphene-enhanced metal-based composite material.

[0010] The above-mentioned laser additive manufacturing method for graphene-enhanced metal-based composite materials is characterized in that the metal powder in step one is aluminum, aluminum alloy or aluminum-based composite material powder, titanium, titanium alloy or titanium-based composite material powder, copper, copper alloy or copper-based composite material powder, nickel, nickel alloy or nickel-based composite material powder, iron, iron alloy or iron-based composite material powder, and the particle size of the metal powder is 5μm to 180μm.

[0011] The above-mentioned laser additive manufacturing method for graphene-reinforced metal-based composite materials is characterized in that the mass ratio of graphene to metal powder in step one is 1 to 20:1000.

[0012] The above-mentioned laser additive manufacturing method for graphene-reinforced metal-based composite materials is characterized in that the laser additive manufacturing method described in step 2 and step 4 is a laser selective melting method in a powder bed powder laying mode.

[0013] The above-mentioned laser additive manufacturing method of a graphene-reinforced metal-based composite material is characterized in that the preliminary melting in step 2 and the remelting process in step 3 are carried out under the protection of an argon or nitrogen atmosphere.

[0014] The above-mentioned laser additive manufacturing method for a graphene-enhanced metal-based composite material is characterized in that the remelting in step three is to remelt the preliminary solidified deposition layer using remelting process parameters with a laser energy density that is the same as or slightly lower than that of the preliminary melting process of laser additive manufacturing; the laser energy density is the ratio of the laser power divided by the product of the scanning speed, the scanning spacing and the powder layer thickness; the remelting laser power is 100W to 800W, the remelting scanning speed is 100mm / s to 7000mm / s, the remelting scanning spacing is 0.01mm to 0.5mm, and the remelted powder layer thickness is consistent with the preliminary melted powder layer thickness.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] 1. The present invention adopts a mixing method combining ultrasound and mechanical stirring, aiming to utilize mechanical stirring to make graphene and metal powder move and mix, while promoting further uniform mixing of the two through ultrasonic oscillation and cavitation, and graphene is adsorbed on the surface of metal powder, thereby improving the stability of mixed powder, being easier to implement and having high dispersion efficiency, avoiding the problems of metal powder agglomeration, size increase and irregular morphology caused by traditional powder mixing methods (ball milling method, V-type powder mixing method, etc.), while ensuring the integrity of graphene structure, and effectively improving its reinforcing effect on metal powder.

[0017] 2. The present invention adds a remelting process after the laser additive manufacturing forms a preliminary solidified deposition layer, and utilizes the remelting process to promote the convection dispersion of graphene in the molten pool, so that it experiences a longer dispersion time, reduces the size of residual graphene agglomerates, effectively eliminates the poor fusion defects induced by graphene agglomeration, improves the uniformity of graphene dispersion, and obtains a high-density laser additively manufactured graphene-reinforced metal-based composite material with no obvious defects. The present invention is particularly suitable for laser additively manufactured graphene-reinforced metal-based composite materials with high graphene content and poor formability.

[0018] 3. Compared with the non-remelting process, the thermal conductivity, tensile strength and elongation of the graphene-enhanced AlSi7Mg composite material formed by laser selective melting increased from 130.5 W·m to 21.3 W·m -1 ·K -1 , 407.1MPa and 9% increased to 163.6W·m -1 ·K -1 , 440.7MPa and 12%, achieving the simultaneous improvement of thermal conductivity and mechanical properties.

[0019] 4. The present invention can obtain remelting process parameters for remelting by slightly adjusting the initial melting process parameters of laser additive manufacturing. The method is simple and easy to implement, and the manufacturing efficiency is further improved on the basis of ensuring formability.

[0020] 5. The method of the present invention can be extended to other metal additive manufacturing technologies, including electron beam selective melting technology and laser stereo forming technology, further improving the scope of application of the present invention.

[0021] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a comparison diagram of the mixed powder solution obtained by combining ultrasound with mechanical stirring in Example 1 of the present invention and the mixed powder solution obtained by only ultrasound.

[0023] Figure 2 This is a laser scanning path strategy diagram for the remelting process in Example 1 of the present invention.

[0024] Figure 3 This is an optical microscopic comparison of the graphene-reinforced metal-based composite material manufactured by laser additive manufacturing before and after remelting under the same process parameters in Example 1 of the present invention.

[0025] Figure 4 These are optical microscopic comparison images of graphene-reinforced metal-based composite materials manufactured by laser additive manufacturing under different process parameter conditions in Example 2 of the present invention without using a remelting process.

[0026] Figure 5 These are optical microscopic comparison images of graphene-reinforced metal-based composite materials manufactured by laser additive manufacturing using a remelting process under different process parameter conditions in Example 2 of the present invention.

[0027] Figure 6 These are optical microscopic comparison images of graphene-reinforced metal-based composite materials manufactured by laser additive manufacturing under different process parameter conditions in Example 3 of the present invention without using a remelting process.

[0028] Figure 7 These are optical microscopic comparison images of graphene-reinforced metal-based composite materials manufactured by laser additive manufacturing using a remelting process under different process parameter conditions in Example 3 of the present invention. DETAILED DESCRIPTION

[0029] Example 1

[0030] This embodiment includes the following steps:

[0031] Step 1: Using a mixing method combining ultrasound and mechanical stirring, the graphene is uniformly adhered to the AlSi7Mg alloy powder with a particle size of 30 μm to 50 μm to obtain a mixed powder of a graphene-reinforced metal-based composite material; the mixing method combining ultrasound and mechanical stirring is: first, 0.3 g of graphene is added to 500 mL of anhydrous ethanol and ultrasonicated for 10 minutes, then 300 g of AlSi7Mg alloy powder is added, and ultrasound and mechanical stirring are continued for 10 minutes to form a mixed powder solution, such as Figure 1 As shown in (a), the upper transparent liquid in the mixed powder solution is an ethanol solution, and precipitation appears at the bottom, indicating that graphene has completely adhered to the surface of the metal powder at the bottom of the container; Figure 1 (b) is a mixed powder solution obtained by ultrasound without mechanical stirring under the same conditions, in which most of the graphene in the mixed powder solution is still in a suspended state and does not adhere to the surface of the metal powder and precipitate to the bottom of the container together with the metal powder; Figure 1 (a) and Figure 1 The comparison of (b) shows that the mixing method combining ultrasound and mechanical stirring in the present invention promotes uniform mixing of graphene and metal powder;

[0032] Step 2. Determine the preliminary melting process parameters of laser additive manufacturing: The laser additive manufacturing technology is specifically a laser selective melting method of a powder bed powdering method. The selected equipment is BLTS210 of Xi'an Polylite Additive Technology Co., Ltd. The laser mode of the equipment adopts a Gaussian beam, the laser spot diameter is 100μm, the substrate preheating temperature is 200°C, the forming atmosphere is argon, the laser power is 230W, the scanning speed is 1200mm / s, the scanning spacing is 0.1mm~0.2mm, and the powder layer thickness is 30μm. Then, the preliminary melting process parameters of laser selective melting are used to perform preliminary melting on the mixed powder obtained in step 1 to obtain a preliminary solidified deposition layer;

[0033] Step 3: Adjust the laser scanning path based on the initial melting process parameters of laser additive manufacturing determined in step 2, that is, rotate 67° on the basis of the initial melting scanning path to obtain the remelting process scanning path, such as Figure 2 As shown, in order to avoid the tool jamming caused by abnormal protrusions on the surface of the solidified deposition layer during the forming process, the remelting scanning speed is adjusted to 1400 mm / s, and other process parameters including laser mode, laser spot diameter, substrate preheating temperature, forming atmosphere, laser power, scanning spacing and powder layer thickness remain unchanged to obtain the remelting process parameters, and then the remelting process parameters are used to remelt the preliminary solidified deposition layer obtained in step 2 to obtain a highly dense remelted solidified deposition layer;

[0034] Step 4: Steps 2 and 3 are then repeated layer by layer, and the initial solidified deposition layers of each layer are obtained by laser additive manufacturing and remelted, and each remelted solidified deposition layer is stacked layer by layer to finally obtain a laser additively manufactured graphene-reinforced metal-based composite material.

[0035] Figure 3 This is a light microscope comparison of the graphene-enhanced metal matrix composite material manufactured by laser additive manufacturing before and after remelting under the same process parameters in this embodiment. Figure 3 It can be seen that compared with the non-remelting process, the laser additively manufactured graphene reinforced metal matrix composites using the remelting process have almost no poor fusion defects and have better formability.

[0036] The metal powder in step 1 of this embodiment can also be replaced by aluminum or aluminum-based composite powder, titanium, titanium alloy or titanium-based composite powder, copper, copper alloy or copper-based composite powder, nickel, nickel alloy or nickel-based composite powder, iron, iron alloy or iron-based composite powder, and the particle size of the metal powder is 5μm to 180μm.

[0037] Example 2

[0038] The difference between this embodiment and embodiment 1 is that the amount of graphene added in step 1 is 0.9 g, that is, the mass fraction of graphene in the laser additively manufactured graphene-reinforced metal-based composite material obtained in step 4 is 0.3%.

[0039] The process stability of the laser additive manufacturing method of the present invention is studied, and the specific process is as follows: Based on Example 2, while keeping other process parameters unchanged, the laser power is adjusted to 230W, 260W, and 290W respectively, and the scanning speed is gradually increased by 100mm / s from 1100mm / s to 1600mm / s. The optical microscope comparison diagrams of the graphene-reinforced metal-based composite materials manufactured by laser additive manufacturing without and with remelting under different process parameters are shown as follows: Figure 4 and Figure 5 As shown, the results indicate that the remelting process expands the optimal process window of the laser additive manufacturing method and greatly improves the forming process stability of laser additive manufactured graphene reinforced metal matrix composites.

[0040] Example 3

[0041] The difference between this embodiment and embodiment 1 is that the amount of graphene added in step 1 is 1.5 g, that is, the mass fraction of graphene in the laser additively manufactured graphene-reinforced metal-based composite material obtained in step 4 is 0.5%.

[0042] The effect of the remelting process on the amount of graphene added in the laser additive manufacturing method of the present invention was studied. The specific process is as follows: Based on Example 3, while keeping other process parameters unchanged, the laser power was adjusted to 230W, 260W, and 290W respectively, and the scanning speed was gradually increased from 1100mm / s to 1600mm / s by 100mm / s. The optical microscope comparison diagrams of the graphene-reinforced metal-based composite materials manufactured by laser additive manufacturing without and with remelting under different process parameters are shown as follows: Figure 6 and Figure 7 As shown, the results show that when the graphene content is high, if the remelting process is not used, the laser additive manufactured graphene reinforced metal matrix composites will be difficult to form under different process parameters, and the process stability is extremely poor. After the remelting process is used, the laser additive manufactured graphene reinforced metal matrix composites have good formability within the given process parameter range. This shows that the remelting process has a better effect on improving the formability of laser additive manufactured graphene reinforced metal matrix composites with high graphene content.

[0043] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A laser additive manufacturing method for graphene-reinforced metal-based composite materials, characterized in that: The method comprises the following steps: Step 1: using a mixing method combining ultrasound and mechanical stirring to uniformly adhere graphene to the surface of metal powder to obtain a mixed powder of graphene-reinforced metal-based composite material; Step 2: determine the preliminary melting process parameters of laser additive manufacturing, including laser mode, laser spot diameter, substrate preheating temperature, forming atmosphere, laser power, scanning speed, scanning spacing and powder layer thickness, and then use the preliminary melting process parameters to perform preliminary melting on the mixed powder obtained in step 1 to obtain a preliminary solidified deposition layer; Step 3: on the basis of the preliminary melting process parameters determined in step 2, setting and optimizing the remelting process parameters, and then remelting the preliminary solidified deposition layer obtained in step 2 using the optimized remelting process parameters to obtain a highly dense remelted solidified deposition layer; Step 4: Steps 2 and 3 are then repeated layer by layer, and the initial solidified deposition layers of each layer are obtained by laser additive manufacturing and remelted, and each remelted solidified deposition layer is stacked layer by layer to finally obtain a laser additively manufactured graphene-reinforced metal-based composite material.

2. The laser additive manufacturing method of a graphene-reinforced metal-based composite material according to claim 1, characterized in that: The mixing method combining ultrasound and mechanical stirring in step 1 is: firstly, graphene is added to an ethanol solution and ultrasound is applied for 2 to 120 minutes, then metal powder is added, and ultrasound is continued while mechanical stirring is performed for 2 to 120 minutes.

3. The laser additive manufacturing method of a graphene-reinforced metal-based composite material according to claim 1, characterized in that: The metal powder described in step one is aluminum, aluminum alloy or aluminum-based composite powder, titanium, titanium alloy or titanium-based composite powder, copper, copper alloy or copper-based composite powder, nickel, nickel alloy or nickel-based composite powder, iron, iron alloy or iron-based composite powder, and the particle size of the metal powder is 5μm to 180μm.

4. The laser additive manufacturing method of a graphene-reinforced metal matrix composite material according to claim 1, characterized in that: The mass ratio of graphene to metal powder in step 1 is 1 to 20:1000.

5. The laser additive manufacturing method of a graphene-reinforced metal-based composite material according to claim 1, characterized in that: The laser additive manufacturing method described in step 2 and step 4 is a laser selective melting method in a powder bed mode.

6. The laser additive manufacturing method of graphene-enhanced metal-based composite material according to claim 1, characterized in that: The preliminary melting in step 2 and the remelting process in step 3 are carried out under the protection of argon or nitrogen atmosphere.

7. The laser additive manufacturing method of graphene-enhanced metal-based composite material according to claim 1, characterized in that: The remelting described in step three is to remelt the preliminary solidified deposition layer using remelting process parameters with laser energy density equal to or slightly lower than that of the preliminary melting process of laser additive manufacturing; the laser energy density is the ratio of laser power divided by the product of scanning speed, scanning spacing and powder layer thickness; the remelting laser power is 100W~800W, the remelting scanning speed is 100mm / s~7000mm / s, the remelting scanning spacing is 0.01mm~0.5mm, and the remelted powder layer thickness is consistent with the preliminary melted powder layer thickness.

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