Graphene reinforced Al-Si composite material system for additive manufacturing and powder preparation method of graphene reinforced Al-Si composite material system

Abstract

The invention discloses a graphene reinforced Al-Si composite material system for additive manufacturing and a powder preparation method of the graphene reinforced Al-Si composite material system. The additive manufacturing aluminum-based composite material with excellent comprehensive performance is developed by taking the good printing manufacturability of the Al-Si alloy and the synergistic effect of the high strength and the high modulus of the graphene nanosheet as the design principle. Graphene is introduced twice in the master ingot preparation process, pre-dispersion is realized in combination with electromagnetic stirring, and graphene modified Al-Si composite material powder is prepared by adopting a gas atomization method. Graphene in the powder prepared through the method is evenly distributed, the sphericity degree of the powder reaches 0.95 or above, the yield strength, the tensile strength and the ductility of the graphene modified Al-Si composite material formed through selective laser melting reach 320-340 MPa, 483-510 MPa and 6.8-8% respectively, and the strength is improved by 18-28% compared with a contrast.

Description

Technical Field

[0001] The present invention relates to a high-strength and high-toughness graphene reinforced Al-Si composite material system for additive manufacturing, and in particular to a high-strength and high-toughness graphene reinforced Al-Si composite material system for additive manufacturing and a powder preparation method thereof. Background Art

[0002] Selective laser melting (SLM), as a 3D printing technology for metal materials, can not only achieve one-time net forming of complex-shaped parts, but also has high forming efficiency and raw material utilization. Al-Si alloy is the most widely used alloy system in selective laser melting aluminum alloys due to its narrow solidification range, good fluidity and low thermal cracking tendency. At present, Al-Si alloy is widely used in additive manufacturing of complex-shaped parts such as crankshafts and impellers. However, compared with high-strength aluminum alloys, the insufficient strength of Al-Si alloy limits the application of this alloy.

[0003] Graphene is a unique two-dimensional material with high strength and high modulus, with an elastic modulus of up to 1TPa and a tensile strength of more than 120GPa. As a reinforcement, it can effectively improve the mechanical properties of Al-Si alloys. Therefore, a graphene-modified Al-Si composite material system is developed based on the design principle of the good fluidity of Al-Si alloys and the synergistic effect of high strength and high modulus of graphene nanosheets. However, the main preparation methods of graphene-modified aluminum-based composite material powders are currently mechanical mixing or chemical coating. For example, CN106825552A discloses a method for preparing a graphene-coated alloy powder composite material for 3D printing, wherein alloy powder is treated with hexadecyltrimethylammonium bromide and reacted with graphene oxide to obtain graphene-coated AlSi10Mg powder.

[0004] However, graphene-modified Al-Si composite powders prepared by mechanical mixing or chemical coating methods have problems such as poor interface bonding between graphene and the matrix and graphene agglomeration, which seriously affect the subsequent selective laser melting processing and lead to deterioration of the mechanical properties of the printed alloy. At the same time, mechanical mixing and chemical coating lead to partial oxidation of the powder, reducing the printing performance. At the same time, the process is complex, the cost is high, and it is not suitable for large-scale industrial production. Summary of the invention

[0005] Aiming at the problem of insufficient strength and plasticity of commercial Al-Si alloy systems, and the problems of poor interface bonding and graphene segregation in preparing graphene-modified Al-Si composite material powders by traditional methods, the present invention develops an Al-Si composite material system modified with graphene nanosheets, adopts a method of adding graphene in batches, and adopts a stirring casting method to prepare a composite material mother ingot to achieve pre-dispersion of graphene, and then adopts an aerosolization method to prepare powders, thereby avoiding the loss of powder sphericity caused by traditional mechanical mixing and chemical coating methods, and fundamentally achieving the preparation of graphene-modified Al-Si composite material powders with uniform graphene dispersion and high sphericity.

[0006] The present invention is achieved through the following technical solutions: A graphene-reinforced Al-Si composite material system for additive manufacturing comprises the following alloy components in percentage by weight: 6.5-7.5% Si, 0.4-0.8% Mg, 0.2-0.5% graphene, and the balance Al.

[0007] During the preparation of the composite material system, graphene is added to the composite system twice, the first time when the composite material system alloy is melted; and the second time when the composite material is cast.

[0008] Preferably, the amount of graphene added during melting of the composite material system is 90-95% of the total mass of the graphene, and the amount of graphene added during casting is 5-10% of the total mass of the graphene.

[0009] The present invention also discloses a method for preparing a graphene-enhanced Al-Si composite material system, comprising the following steps: (A) Preparation of refiner: according to Si 6.5-7.5%, Mg 0.4-0.8%, graphene 0.2-0.5%, and the remainder Al, the mass fraction is calculated, after pure aluminum is completely melted, the temperature is raised to 720℃-750℃, Al-20Si master alloy is added, the temperature is raised to 760℃-800℃, graphene powder is added, and after rapid dispersion, the temperature is lowered to 720℃-750℃, pure magnesium is quickly added to the melt below the liquid surface, and dispersed by electromagnetic stirring; argon gas is used for refining, and the slag is removed and kept at 720℃-750℃ for 5 minutes, metal mold casting is performed to form an ingot, and gas atomization is performed to form a refiner powder; (B) Preparation of composite material system: (1) Calculate the mass fraction according to Si 6.5-7.5%, Mg 0.4-0.8%, graphene 0.2-0.5%, and the balance is Al; (2) When the resistance furnace is heated to 450°C, pure aluminum is loaded into the resistance furnace; (3) After pure aluminum is completely melted, the temperature is raised to 720℃-750℃, and Al-20Si master alloy is added; (4) Raise the temperature to 760°C-800°C, add graphene powder, and quickly disperse the graphene using electromagnetic stirring; (5) Cooling to 720°C-750°C, quickly adding pure magnesium to the melt below the liquid surface, and dispersing it by electromagnetic stirring; (6) Add refiner powder and slag remover in sequence, keep the temperature at 720℃-750℃ for 5 minutes, and then perform slag removal; (7) Performing metal mold casting at a temperature range of 700°C to 720°C to obtain a composite material mother ingot.

[0010] The composite material system mother ingot of the present invention is made into powder or wire. Various powders can be prepared according to the purpose of the powder, which can be used as SLM powder or other powders; the particle size of the powder can also be prepared according to needs, including 1-15μm, 15-53μm, 53-150μm. Wire can be prepared as needed, and arc additive can be obtained by continuous casting, continuous extrusion, etc. φ2-φ9mm.

[0011] When the composite material system mother ingot is made into powder, the method further comprises step (8) of atomizing the composite material system mother ingot obtained in step (7) to prepare powder.

[0012] Preferably, in step (8), the smelting furnace and the atomizing chamber are evacuated and then a protective gas is introduced, and the master ingot alloy is melted and then a high-pressure protective gas is introduced. Under the action of the gas, the melt is dispersed into fine droplets, and the droplets are cooled and solidified to form powder.

[0013] Preferably, in step (8), the temperature of the smelting furnace is 720°C-800°C.

[0014] Preferably, in step (8), the vacuum degree of the atomization chamber is 0.02Pa-0.25Pa.

[0015] Preferably, in step (8), the protective gas used in the atomization process is high-purity argon.

[0016] Preferably, in terms of graphene content: in step (4), the amount of graphene added is 90-95% of the total mass of graphene; in step (6), the amount of graphene added to the refining agent powder is 5-10% of the total mass of graphene.

[0017] Preferably, the particle size of the fine powder prepared by aerosolization in step (A) is 3-15 μm, and the particle size of the powder prepared by aerosolization in step (8) is 15-53 μm.

[0018] Beneficial Effects The invention solves the problems of complex process, high impurity content, graphene agglomeration and loss of powder sphericity in graphene-enhanced Al-Si composite material powder prepared by traditional mechanical mixing and chemical coating methods. By adding graphene in batches, the dispersion problem of graphene is effectively solved, and the refinement problem of refiner is improved at the same time. By combining the advantages of uniform dispersion of the second phase of the stirring casting method and high sphericity of the powder obtained by the gas atomization method, a powder with uniform graphene dispersion and high sphericity is obtained.

[0019] The present invention takes the synergistic effect of good fluidity of Al-Si alloy and high strength and high modulus of graphene nanosheets as design principles, develops a graphene-reinforced Al-Si composite material system, and solves the problem of insufficient strength and plasticity existing in commercial Al-Si alloy systems.

[0020] The present invention adopts a stirring casting method to prepare a graphene / aluminum-silicon composite master ingot alloy, realizes pre-dispersion of graphene in the master ingot alloy, thereby avoiding graphene segregation, and constructs a well-bonded interface between the graphene and the matrix, while producing a significant refinement effect on α-Al dendrites and Si phases.

[0021] The present invention adopts a gas atomization method to prepare graphene / aluminum silicon composite powder. Compared with the traditional graphene and aluminum alloy powder mixed ball milling process, the process adopted by the present invention effectively avoids the introduction of nitrogen and oxygen impurities and the loss of sphericity, thereby obtaining a powder with superior performance, generating greater resistance to dislocations in the composite materials formed by additive manufacturing, and achieving an improvement in the comprehensive mechanical properties.

[0022] The invention adopts a conventional resistance furnace to melt the mother ingot and adopts a conventional vacuum induction melting gas atomization device to prepare the powder, has the advantages of simple process, high production efficiency and low cost, and is suitable for industrial large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a metallographic structure photograph of the mother ingot alloy of Example 2 of the present invention.

[0024] Figure 2 This is the metallographic structure photo of the commercial Al-Si alloy master ingot alloy; Figure 3 This is the dislocation distribution diagram of the printed alloy in Example 2 of the present invention; Figure 4 This is the dislocation distribution diagram of the printed alloy of Comparative Example 2 in the present invention. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0026] Example 1 The composition content of the aluminum alloy is: Si 6.5%, Mg 0.5%, graphene 0.2%, and the balance is Al.

[0027] Preparation method: (A) Preparation of refiner: Calculate the mass fraction according to Si 6.5%, Mg 0.5%, graphene 0.2%, and the remainder Al. After completely melting pure aluminum, heat it to 720°C, add Al-20Si master alloy, heat it to 760°C, add graphene powder, quickly disperse it, refine it with argon, remove slag and keep it at 720°C for 5 minutes, quickly add pure magnesium to the melt below the liquid surface, disperse it by electromagnetic stirring, add slag remover, keep it at 720°C for 5 minutes and then remove slag; cast it in a metal mold at 700°C to make an ingot, evacuate the 720°C melting furnace and the atomizing chamber with a vacuum degree of 0.02Pa, and then introduce argon. After melting the ingot alloy, introduce argon. Under the action of gas, the melt is dispersed into fine droplets, and the droplets are cooled and solidified to form powder. The particle size of the refiner powder is 12μm. (B) Preparation of composite material system: (1) Calculate the mass fraction according to Si 6.5%, Mg 0.5%, graphene 0.2%, and the balance Al; (2) When the resistance furnace is heated to 450°C, pure aluminum is loaded into the resistance furnace; (3) After pure aluminum is completely melted, the temperature is raised to 720°C and Al-20Si master alloy is added; (4) Raise the temperature to 760°C, add graphene powder, and quickly disperse the graphene using electromagnetic stirring; at this time, the amount of graphene powder added is 95% of the total mass of graphene in the final powder; (5) Cooling to 720°C, quickly adding pure magnesium to the melt below the liquid surface, and dispersing it by electromagnetic stirring; (6) Adding refiner powder and slag remover in sequence, keeping the temperature at 720°C for 5 minutes and then performing slag removal; based on the weight of graphene, the amount of graphene added is 5% of the total mass of graphene, and the weight of the required refiner powder is determined; (7) performing metal mold casting at a temperature range of 700° C. to obtain a mother ingot; (8) The mother ingot obtained in step (7) is subjected to gas atomization to prepare powder. The melting furnace at 800° C. and the atomizing chamber with a vacuum degree of 0.02 Pa are evacuated and then argon gas is introduced. After the ingot alloy is melted, argon gas is introduced. Under the action of the gas, the melt is dispersed into fine droplets, which are cooled and solidified to form powder. The particle size of the powder prepared by gas atomization is 15-53 μm.

[0028] Example 2 The composition content of the aluminum alloy is: Si 6.6%, Mg 0.6%, graphene 0.3%, and the balance is Al.

[0029] Preparation method: (A) Preparation of refiner: Calculate the mass fraction according to Si 6.6%, Mg 0.6%, graphene 0.3%, and the remainder Al. After completely melting pure aluminum, heat it to 730°C, add Al-20Si master alloy, heat it to 780°C, add graphene powder, quickly disperse it, refine it with argon, remove slag and keep it at 730°C for 5 minutes, quickly add pure magnesium to the melt below the liquid surface, disperse it by electromagnetic stirring, add slag remover, keep it at 730°C for 5 minutes and then remove slag; cast it in a metal mold at 700°C to make an ingot, evacuate the 730°C melting furnace and the atomizing chamber with a vacuum degree of 0.02Pa, and then introduce argon. After melting the ingot alloy, introduce argon. Under the action of gas, the melt is dispersed into fine droplets, and the droplets are cooled and solidified to form powder. The particle size of the refiner powder is 8μm. (B) Preparation of composite material system: (1) Calculate the mass fraction according to Si 6.6%, Mg 0.6%, graphene 0.3%, and the balance Al; (2) When the resistance furnace is heated to 450°C, pure aluminum is loaded into the resistance furnace; (3) After pure aluminum is completely melted, the temperature is raised to 730°C and Al-20Si master alloy is added; (4) Raise the temperature to 780°C, add graphene powder, and quickly disperse the graphene using electromagnetic stirring; at this time, the amount of graphene powder added is 92% of the total mass of graphene in the final powder; (5) Cooling to 730°C, quickly adding pure magnesium to the melt below the liquid surface, and dispersing it by electromagnetic stirring; (6) Add refiner and slag remover in sequence, keep warm at 730°C for 5 min, and then perform slag removal. The amount of graphene added is 8% of the total mass of graphene, and the weight of the required refiner powder is determined. (7) performing metal mold casting at a temperature range of 700° C. to obtain a mother ingot; (8) The mother ingot obtained in step (7) is subjected to gas atomization to prepare powder. The melting furnace at 730° C. and the atomizing chamber with a vacuum degree of 0.10 Pa are evacuated and then argon gas is introduced. After the ingot alloy is melted, argon gas is introduced. Under the action of the gas, the melt is dispersed into fine droplets, which are cooled and solidified to form powder. The particle size of the powder prepared by gas atomization is 15-53 μm.

[0030] Example 3 The composition content of the aluminum alloy is: Si 7.0%, Mg 0.8%, graphene 0.5%, and the balance is Al.

[0031] Preparation method: (A) Preparation of refiner: Calculate the mass fraction according to Si 7.0%, Mg 0.8%, graphene 0.5%, and the remainder Al. After completely melting pure aluminum, heat it to 750°C, add Al-20Si master alloy, heat it to 800°C, add graphene powder, quickly disperse it, refine it with argon, remove slag and keep it at 750°C for 5 minutes, quickly add pure magnesium under the melt surface, disperse it by electromagnetic stirring, add slag remover, keep it at 750°C for 5 minutes and then remove slag; cast it in a metal mold at 700°C to make an ingot, evacuate the 800°C melting furnace and the atomizing chamber with a vacuum degree of 0.25Pa and then introduce argon, melt the ingot alloy and introduce argon. Under the action of gas, the melt is dispersed into fine droplets, and the droplets are cooled and solidified to form powder. The particle size of the refiner powder is 6μm. (B) Preparation of composite material system: (1) Calculate the mass fraction according to Si 7.0%, Mg 0.8%, graphene 0.5%, and the balance Al; (2) When the resistance furnace is heated to 450°C, pure aluminum is loaded into the resistance furnace; (3) After pure aluminum is completely melted, the temperature is raised to 750°C and Al-20Si master alloy is added; (4) Raise the temperature to 800°C, add graphene powder, and quickly disperse the graphene using electromagnetic stirring; at this time, the amount of graphene powder added is 90% of the total mass of graphene in the final powder; (5) Cooling to 750°C, quickly adding pure magnesium to the melt below the liquid surface, and dispersing it by electromagnetic stirring; (6) Add refiner and slag remover in sequence, keep at 750°C for 5 min, and then remove the slag; based on the weight of graphene, the amount of graphene added is 10% of the total mass of graphene, and the weight of the required refiner powder is determined; (7) performing metal mold casting at a temperature range of 720° C. to obtain a mother ingot; (8) The mother ingot obtained in step (7) is subjected to gas atomization to prepare powder. The melting furnace at 800° C. and the atomizing chamber with a vacuum degree of 0.25 Pa are evacuated and then argon gas is introduced. After the ingot alloy is melted, argon gas is introduced. Under the action of the gas, the melt is dispersed into fine droplets, which are cooled and solidified to form powder. The particle size of the powder prepared by gas atomization is 15-53 μm.

[0032] Comparative Example 1 Preparation of composite material system: (1) Calculate the mass fraction according to Si 6.6%, Mg 0.6%, graphene 0.3%, and the balance Al; (2) When the resistance furnace is heated to 450°C, pure aluminum is loaded into the resistance furnace; (3) After pure aluminum is completely melted, the temperature is raised to 730°C and Al-20Si master alloy is added; (4) Raise the temperature to 780°C, directly add all the required graphene powder, and quickly disperse the graphene using electromagnetic stirring; (5) Cooling to 730°C, quickly adding pure magnesium to the melt below the liquid surface, and dispersing it by electromagnetic stirring; (6) Add slag cleaning agent, keep the temperature at 730℃ for 5 minutes and then carry out slag removal; (7) performing metal mold casting at a temperature range of 700° C. to obtain a mother ingot; (8) The mother ingot obtained in step (7) is subjected to gas atomization to prepare powder. The melting furnace at 730° C. and the atomizing chamber with a vacuum degree of 0.10 Pa are evacuated and then argon gas is introduced. After the ingot alloy is melted, argon gas is introduced. Under the action of the gas, the melt is dispersed into fine droplets, which are cooled and solidified to form powder. The particle size of the powder prepared by gas atomization is 15-53 μm.

[0033] Comparative Example 2 The mass fractions were calculated according to Si 6.6%, Mg 0.6%, graphene 0.3%, and the balance Al; the metal and graphene were mixed by a mechanical mixing ball milling method to obtain graphene-reinforced Al-Si composite material powder.

[0034] The composite powders prepared in the examples and comparative examples were tested: 1. Sphericity: (The morphology of multiple regions of the powder was photographed using a scanning electron microscope (TESCAN MIRA4), and the sphericity was calculated using OpenCV software).

[0035] 2. Yield strength, tensile strength, and elongation (use a CMT5105 tensile testing machine to test the strength and elongation of the material).

[0036] The composite powders prepared in the embodiment and the comparative example were analyzed. The sphericity of the powder prepared in the embodiment was improved by 10% compared with that in the comparative example. It can be seen that the graphene is evenly distributed in the powder prepared by the present invention, and the sphericity of the powder is above 0.95. The yield strength, tensile strength and elongation of the graphene-modified Al-Si composite material formed by selective laser melting are 320-340MPa, 483-510MPa and 6.8-8%, respectively. The yield strength is improved by 20-25% compared with that in comparative example 2, and the tensile strength is improved by 18-28% compared with that in comparative example 2.

[0037] 3. Determine the dislocation distribution of Example 2, Comparative Example 2 and the commercial Al-Si alloy mother ingot metallographic diagram and printed alloy, see Figure 1-Figure 4 ,from Figure 1 It can be seen that the master ingot alloy grains prepared by Example 2 are basically equiaxed, and the Si phase is fine and evenly distributed. Figure 2 It can be seen that the commercial Al-Si alloy grains are dendritic, the Si phase is relatively coarse and presents a network distribution. Figure 3 It can be seen that the printed alloy prepared by Example 2 has a higher dislocation density, indicating that the graphene introduced by the present invention produces a greater resistance to the dislocation movement of the composite material, thereby producing a significant strengthening effect. Figure 4 It can be seen that the dislocation density of the printed alloy prepared by Comparative Example 2 is lower, indicating that the graphene introduced by mechanical mixing has a smaller effect on dislocation hindrance and the resulting strengthening effect is limited.

[0038] In the embodiments, only SLM powder is used as an example, and powders and wires with other particle sizes or uses can be prepared.

Claims

1. A graphene-reinforced Al-Si composite material system for additive manufacturing, characterized in that: The invention comprises the following components in percentage by weight: Si 6.5-7.5%, Mg 0.4-0.8%, graphene 0.2-0.5%, and the balance Al.

2. A method for preparing a graphene-reinforced Al-Si composite material system for additive manufacturing according to claim 1, characterized in that: During the preparation of the composite material system, graphene is added to the composite system twice, the first time when the composite material system alloy is melted; and the second time when the composite material is cast.

3. The method for preparing a graphene-reinforced Al-Si composite material system for additive manufacturing according to claim 2, characterized in that: The amount of graphene added during alloy melting of the composite material system is 90-95% of the total mass of graphene, and the amount of graphene added during casting is 5-10% of the total mass of graphene.

4. The method for preparing a graphene-reinforced Al-Si composite material system for additive manufacturing according to claim 2 or 3, characterized in that: The following steps are involved: (A) Preparation of refiner: according to Si 6.5-7.5%, Mg 0.4-0.8%, graphene 0.2-0.5%, and the remainder Al, the mass fraction is calculated, after pure aluminum is completely melted, the temperature is raised to 720℃-750℃, Al-20Si master alloy is added, the temperature is raised to 760℃-800℃, graphene powder is added, and after rapid dispersion, the temperature is lowered to 720℃-750℃, pure magnesium is quickly added to the melt below the liquid surface, and dispersed by electromagnetic stirring; argon gas is used for refining, and the slag is removed and kept at 720℃-750℃ for 5 minutes, metal mold casting is performed to form an ingot, and gas atomization is performed to form a refiner powder; (B) Preparation of composite material system: (1) Calculate the mass fraction according to Si 6.5-7.5%, Mg 0.4-0.8%, graphene 0.2-0.5%, and the balance is Al; (2) When the resistance furnace is heated to 450°C, pure aluminum is loaded into the resistance furnace; (3) After pure aluminum is completely melted, the temperature is raised to 720℃-750℃, and Al-20Si master alloy is added; (4) Raise the temperature to 760°C-800°C, add graphene powder, and quickly disperse the graphene using electromagnetic stirring; (5) Cooling to 720°C-750°C, quickly adding pure magnesium to the melt below the liquid surface, and dispersing it by electromagnetic stirring; (6) Add refiner powder and slag remover in sequence, keep the temperature at 720℃-750℃ for 5 minutes, and then perform slag removal; (7) Performing metal mold casting in a temperature range of 700°C to 720°C to obtain a composite material system mother ingot.

5. The preparation method according to claim 3, characterized in that: The graphene is added in two steps: the first step is to add directly during casting, and the second step is to introduce the graphene through the refiner powder, which is achieved in step (4) and step (6) respectively; in step (4), the amount of graphene added is 90-95% of the total mass of the graphene; in step (6), the amount of graphene added by the refiner powder is 5-10% of the total mass of the graphene.

6. The preparation method according to claim 3, characterized in that: The composite material system master ingot is made into powder or wire.

7. The preparation method according to claim 3, characterized in that: When the composite material system mother ingot is made into powder, the method further comprises step (8) of atomizing the mother ingot obtained in step (7) to prepare powder.

8. The preparation method according to claim 7, characterized in that: In the step (8), the smelting furnace and the atomizing chamber are evacuated and then a protective gas is introduced, and the master ingot alloy is melted and then a high-pressure protective gas is introduced. Under the action of the gas, the melt is dispersed into fine droplets, and the droplets are cooled and solidified to form powder.

9. The preparation method according to claim 8, characterized in that: The temperature of the smelting furnace is 720℃-800℃; the vacuum degree of the atomization chamber is 0.02Pa-0.25Pa; the protective gas used in the atomization process is high-purity argon.

10. The preparation method according to claim 7, characterized in that: The particle size of the fine powder prepared by aerosolization in step (A) is 3-15 μm, and the particle size of the powder prepared by aerosolization in step (8) is 1-15 μm, 15-53 μm, and 53-150 μm.

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