Flame-retardant nickel-coated aluminum composite powder for metal additive and preparation method thereof

Abstract

This invention discloses a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing and its preparation method, belonging to the field of metal additive manufacturing technology. First, a silica barrier layer is constructed in situ on the surface of aluminum powder, followed by the in-situ growth of an aminocobalt-based MOF layer, resulting in modified aluminum powder loaded with aminocobalt-based MOF. This imparts the powder with rigid heat-resistant barrier and energy-absorbing buffering capabilities. Simultaneously, 2-carboxyethylphenylphosphine is used as an organophosphine ligand to coordinate with lanthanum and cerium bimetallic ions to form a lanthanum-cerium bimetallic organophosphophosphate. Finally, using the modified aluminum powder as a substrate, a chemical nickel plating process is employed to achieve uniform co-deposition of the nickel-phosphorus alloy layer and the lanthanum-cerium bimetallic organophosphophosphate on the powder surface, thus obtaining the flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing. The composite powder prepared by this invention possesses excellent flame-retardant and thermal runaway resistance properties, laser forming compatibility, and stable mechanical properties, meeting the application requirements of high-end metal additive manufacturing in the aerospace field.

Description

Technical Field

[0001] This invention belongs to the field of metal additive manufacturing technology, specifically a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing and its preparation method. Background Technology

[0002] Metal additive manufacturing (commonly known as metal 3D printing) has been widely used in the aerospace lightweighting field due to its extremely high degree of design freedom. Aluminum alloys, with their advantages of low density and high specific strength, have become the most promising core materials in this field. However, aluminum itself is a highly reactive metal, and micron-sized aluminum powder has a low auto-ignition temperature and poor thermal stability. This serious lack of thermal stability makes the powder prone to transient thermal overload and thermal runaway when exposed to high-energy laser beams during 3D printing. This not only causes severe molten pool splashing and damages the stability of the printing process, but also directly leads to the performance failure of the formed component.

[0003] To address the issues of flammability and thermal runaway in aluminum powder, existing technologies typically employ internal multi-element alloying to enhance the overall thermal stability of the aluminum powder. Chinese patent application CN112620649A discloses an aluminum alloy material and laser 3D printed aluminum alloy components based on this material. The alloy powder is prepared by mixing and melting Al, Mn, Ti, and Mg and then atomizing it. The introduction of transition elements with higher melting points, such as Ti and Mn, improves the high-temperature structural stability of the aluminum matrix and endows the alloy powder with basic flame-retardant properties for thermal protection.

[0004] In the above technical solutions, elements such as Ti and Mn are all solid-dissolved within the aluminum matrix, failing to form an effective thermal barrier on the powder surface to block or buffer high-energy lasers. In actual 3D printing, due to the extremely low Gibbs free energy of the reaction between aluminum and oxygen to form alumina, the highly reactive aluminum atoms are prone to undergoing an exothermic oxidation reaction, releasing enormous amounts of additional heat, further exacerbating local thermal overload. This causes the liquid aluminum to boil and vaporize, generating rapidly expanding metal vapors inside the molten pool. Consequently, due to the rapid solidification characteristic of 3D printing, these metal vapors cannot escape from the liquid molten pool in time and are captured and sealed in situ by the rapidly solidified matrix within the component body. This results in the component being densely packed with micropores, which, when the component is under load during service, evolve into highly destructive stress concentration sources, causing a significant decrease in the mechanical properties of the material, failing to meet the stringent application requirements of high-reliability metal components in the aerospace field. Summary of the Invention

[0005] The purpose of this invention is to provide a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing and its preparation method. By constructing a rigid silica barrier layer in situ on the surface of aluminum powder, modifying it by growing an amino-cobalt-based MOF functional layer in situ, and anchoring it at the interface with lanthanum-cerium bimetallic organophosphorus, and preparing a dense nickel-phosphorus alloy coating layer by chemical nickel plating, the flame-retardant and thermal runaway resistance of the aluminum-based composite powder is significantly improved, meeting the core requirements of material reliability for high-end metal additive manufacturing in the aerospace field.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] This invention provides a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing, which is prepared through the following steps:

[0008] Step 1: Using aluminum powder as raw material, a nano-silica layer is first constructed in situ on the surface of the aluminum powder using the sol-gel method to obtain silica composite aluminum powder. Subsequently, polyvinylpyrrolidone is introduced as a surfactant to anchor cobalt ions on the silica composite aluminum powder. Under solvothermal conditions, the cobalt metal center undergoes a coordination assembly reaction with 2-aminoterephthalic acid and terephthalic acid dual ligands to obtain aluminum powder modified with amino-cobalt-based MOF.

[0009] Step 2: Using 2-carboxyethylphenylphosphino acid as a phosphorus-containing organic ligand, and lanthanum nitrate hexahydrate and cerium nitrate hexahydrate as rare earth metal sources, under hydrothermal conditions, the strong coordination ability of rare earth metal ions is utilized to undergo coordination polymerization with the organic ligand to obtain lanthanum-cerium bimetallic organophosphophosphate.

[0010] Step 3: Construct an acidic electroless nickel plating system with nickel sulfate as the main salt, sodium hypophosphite as the reducing agent and phosphorus source, and sodium citrate and lactic acid as dual complexing agents. Modified aluminum powder loaded with amino-cobalt-based MOF and lanthanum-cerium bimetallic organic hypophosphite are co-dispersed in this system. Under constant temperature heating, hypophosphite undergoes an autocatalytic redox reaction, depositing a dense amorphous nickel-phosphite alloy layer in situ on the surface of the modified aluminum powder. Simultaneously, the lanthanum-cerium bimetallic organic hypophosphite is mechanically encapsulated by the continuously growing alloy layer and co-deposited, yielding a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing.

[0011] This invention also provides a method for preparing a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing, comprising the following steps:

[0012] Nickel sulfate, sodium citrate, lactic acid, and deionized water were placed in a reactor under a nitrogen atmosphere and stirred at 25-35℃ for 1-2 hours. Sodium hypophosphite was added, and the reaction was continued for 10-20 minutes. Ammonia solution with a concentration of 0.5 mol / L was added to adjust the pH of the reaction solution to 4.5-5.5. Lanthanum-cerium bimetallic organic hypophosphite was added, and the mixture was ultrasonically dispersed for 30-60 minutes. The reaction was continued for 20-40 minutes. Aluminum powder modified with amino-cobalt-based MOF was added, and the mixture was reacted at 75-85℃ for 40-60 minutes. The mixture was filtered, washed, vacuum dried to constant weight, mechanically dispersed, and sieved to obtain a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing.

[0013] Furthermore, the ratio of nickel sulfate, sodium citrate, lactic acid, deionized water, sodium hypophosphite, lanthanum-cerium bimetallic organic hypophosphite, and aluminum powder modified with amino-cobalt-based MOF is 150-250g: 80-150g: 100-200g: 5-8L: 150-300g: 5-15g: 100-200g.

[0014] Furthermore, the preparation process of lanthanum-cerium bimetallic organophosphophosphate is as follows:

[0015] 2-Carboxyethylphenylphosphino acid, lanthanum nitrate hexahydrate, cerium nitrate hexahydrate, and deionized water were placed in a reaction vessel and stirred at 25-35℃ for 1-2 h. The mixture was then heated to 110-130℃ and reacted for 22-26 h. After filtration, washing, and vacuum drying to constant weight, lanthanum-cerium bimetallic organophosphophosphate was obtained.

[0016] Furthermore, the ratio of 2-carboxyethylphenylphosphonic acid, lanthanum nitrate hexahydrate, cerium nitrate hexahydrate, and deionized water is 16-32g:10-20g:10-20g:3-5L.

[0017] Furthermore, the preparation process of aluminum powder modified with amino-cobalt-based MOF is as follows:

[0018] Silica composite aluminum powder, polyvinylpyrrolidone, and deionized water were placed in a reaction vessel and ultrasonically dispersed for 20-40 min. The mixture was stirred at 25-35℃ for 10-12 h. Cobalt nitrate hexahydrate was added, and stirring was continued at the same temperature for 10-12 h. 2-Aminoterephthalic acid and terephthalic acid were dissolved in anhydrous ethanol and added to the reaction vessel. The mixture was reacted at 150-160℃ for 12-14 h. The mixture was filtered, washed, and vacuum dried to constant weight to obtain aluminum powder modified with amino cobalt-based MOF.

[0019] Furthermore, the ratio of silica composite aluminum powder, polyvinylpyrrolidone, deionized water, cobalt nitrate hexahydrate, anhydrous ethanol, 2-aminoterephthalic acid and terephthalic acid is 200-300g: 3-5g: 800-1500mL: 400-800mL: 2-6g: 1-3g.

[0020] Furthermore, the preparation process of silica-alumina composite powder is as follows:

[0021] Aluminum powder and anhydrous ethanol were placed in a reaction vessel under a nitrogen atmosphere and stirred at 30-40℃ for 20-40 min. Tetraethyl orthosilicate solution, 0.5 mol / L ammonia water and deionized water were added dropwise, and the mixture was reacted at the same temperature for 4-6 h. The mixture was then filtered, washed, and vacuum dried to constant weight to obtain silica composite aluminum powder.

[0022] Furthermore, the ratio of aluminum powder, anhydrous ethanol, tetraethyl orthosilicate solution, ammonia, and deionized water is 300-400g: 1500-2500mL: 15-25mL: 30-60mL: 40-80mL.

[0023] The beneficial effects of this invention are:

[0024] 1. The flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing prepared in this invention forms a composite protective structure that combines rigid heat-resistant barrier and energy absorption buffer by constructing a silica layer and a loaded amino-cobalt-based MOF layer in situ on the surface of aluminum powder. The silica layer is a high-melting-point inorganic barrier layer that can form a stable heat insulation and flame-retardant foundation for the aluminum substrate. Under the transient irradiation of high-energy lasers in metal additive manufacturing, the organic ligands of the amino-cobalt-based MOF layer can undergo endothermic decomposition and in-situ carbonization. The decomposition process can effectively absorb and consume laser energy, playing a heat buffering role. At the same time, the decomposition of residual cobalt-based metal nodes and carbonization layer together build a thermal protection barrier, effectively blocking the direct contact between the high-energy laser beam and the highly reactive aluminum substrate, effectively curbing the boiling and vaporization phenomenon caused by instantaneous overheating of liquid aluminum, reducing the generation of metal vapor pores inside the formed component, and laying a solid core foundation for the stability of the printing process.

[0025] 2. The flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing prepared in this invention forms a composite protection system with interfacial anchoring co-deposition and biphase synergistic flame retardancy through the interfacial coordination between an amino-cobalt-based MOF layer and lanthanum-cerium bimetallic organic hypophosphite. The amino groups on the MOF framework act as strong nucleophilic coordination sites, enabling efficient adsorption and firm anchoring of the lanthanum-cerium bimetallic organic hypophosphite. This allows it to be uniformly deposited on the powder surface along with the nickel-phosphorus layer during electroless nickel plating, achieving a high-density and stable loading of the lanthanum-cerium bimetallic organic hypophosphite and improving the basic flame retardant and thermal oxidation resistance of the composite powder. Under the instantaneous high temperature of laser, lanthanum and cerium rare earth ions can catalyze coking, promoting the formation of a dense, rare earth-rich, antioxidant coke layer on the powder surface, constructing a continuous and stable condensed-phase flame-retardant barrier, and providing a reliable flame-retardant protection foundation for the stable operation of the printing process.

[0026] 3. The flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing prepared by this invention forms a dense nickel-phosphorus alloy coating layer on the outermost layer of the powder through a chemical nickel plating process. Due to the excellent absorption characteristics of nickel for laser, this nickel-phosphorus alloy layer can preferentially absorb laser energy and melt rapidly under the instantaneous high temperature of laser in metal additive manufacturing, reducing the critical laser power required for powder melting. At the same time, the inorganic heat insulation and flame-retardant barrier pre-constructed on the surface of the aluminum powder can effectively buffer the transfer of laser heat to the aluminum matrix, allowing the aluminum matrix, which is prone to boiling, to melt smoothly within a mild and controlled thermodynamic window. This promotes the in-situ deep metallurgical reaction between molten nickel and aluminum, generating a densely distributed high-strength dispersed reinforcing phase, reducing the internal micropores caused by the violent expansion of metal vapor, and ensuring the stability of the material's mechanical properties. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1: This example provides a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing, prepared through the following steps:

[0029] S1: Place 300g of aluminum powder and 1500mL of anhydrous ethanol in a reaction vessel under a nitrogen atmosphere, stir at 200r / min for 20min at 30℃, add 15mL of tetraethyl orthosilicate solution (obtained by mixing tetraethyl orthosilicate and anhydrous ethanol at a volume ratio of 1:5), 30mL of 0.5mol / L ammonia water and 40mL of deionized water dropwise, and react at the same temperature and stirring rate for 4h. After the reaction is completed, filter, wash the filter cake twice with anhydrous ethanol, and vacuum dry at 60℃ to constant weight to obtain silica composite aluminum powder.

[0030] S2: 200g of silica composite aluminum powder, 3g of polyvinylpyrrolidone and 800mL of deionized water were placed in a reaction vessel and ultrasonically dispersed for 20min. The mixture was stirred at 200r / min for 10h at 25℃. 6g of cobalt nitrate hexahydrate was added, and stirring was continued for 10h at the same temperature and stirring rate. 2g of 2-aminoterephthalic acid and 1g of terephthalic acid were dissolved in 400mL of anhydrous ethanol and added to the reaction vessel. The mixture was reacted at 150℃ with the same stirring rate for 12h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed twice with anhydrous ethanol and vacuum dried at 60℃ to constant weight to obtain aluminum powder modified with aminocobalt-based MOF.

[0031] S3: 16g of 2-carboxyethylphenylphosphinoic acid, 10g of lanthanum nitrate hexahydrate, 10g of cerium nitrate hexahydrate and 3L of deionized water were placed in a reaction vessel and stirred at 200r / min for 1h at 25℃. The temperature was then raised to 110℃ and the reaction was continued at the same stirring rate for 22h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed twice with deionized water and dried under vacuum at 60℃ to constant weight to obtain lanthanum-cerium bimetallic organophosphophosphate.

[0032] S4: 150g nickel sulfate, 80g sodium citrate, 100g lactic acid and 5L deionized water were placed in a reactor under a nitrogen atmosphere and stirred at 200r / min for 1h at 25℃. 150g sodium hypophosphite was added and reacted at the same temperature and stirring rate for 10min. Ammonia solution with a concentration of 0.5mol / L was added to adjust the pH of the reaction solution to 4.5. 5g lanthanum-cerium bimetallic organic hypophosphite was added and ultrasonically dispersed for 30min. The reaction was carried out at the same temperature and stirring rate for 20min. 100g of aluminum powder modified with amino-cobalt-based MOF was added and reacted at 75℃ at the same stirring rate for 40min. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed twice with deionized water and anhydrous ethanol. It was then vacuum dried at 100℃ to constant weight, mechanically dispersed and sieved through a 300-mesh sieve to obtain flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing.

[0033] Example 2: This example provides a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing, prepared through the following steps:

[0034] S1: Place 350g of aluminum powder and 2000mL of anhydrous ethanol in a reaction vessel under a nitrogen atmosphere, stir at 250r / min for 30min at 35℃, add 20mL of tetraethyl orthosilicate solution (obtained by mixing tetraethyl orthosilicate and anhydrous ethanol at a volume ratio of 1:5), 45mL of 0.5mol / L ammonia water and 60mL of deionized water dropwise, and react at the same temperature and stirring rate for 5h. After the reaction is completed, filter, wash the filter cake three times with anhydrous ethanol, and vacuum dry at 70℃ to constant weight to obtain silica composite aluminum powder.

[0035] S2: 250g of silica composite aluminum powder, 4g of polyvinylpyrrolidone and 1200mL of deionized water were placed in a reaction vessel and ultrasonically dispersed for 30min. The mixture was stirred at 250r / min at 30℃ for 11h. 9g of cobalt nitrate hexahydrate was added, and stirring was continued for 11h at the same temperature and stirring rate. 4g of 2-aminoterephthalic acid and 2g of terephthalic acid were dissolved in 600mL of anhydrous ethanol and added to the reaction vessel. The mixture was reacted at 155℃ at the same stirring rate for 13h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed three times with anhydrous ethanol. The cake was then vacuum dried at 70℃ to constant weight to obtain aluminum powder modified with aminocobalt-based MOF.

[0036] S3: 24g of 2-carboxyethylphenylphosphinoic acid, 15g of lanthanum nitrate hexahydrate, 15g of cerium nitrate hexahydrate and 4L of deionized water were placed in a reaction vessel and stirred at 250r / min for 1.5h at 30℃. The temperature was then raised to 120℃ and the reaction was continued at the same stirring rate for 24h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed three times with deionized water and dried under vacuum at 70℃ to constant weight to obtain lanthanum-cerium bimetallic organophosphophosphate.

[0037] S4: 200g nickel sulfate, 120g sodium citrate, 150g lactic acid, and 7L deionized water were placed in a reactor under a nitrogen atmosphere and stirred at 250r / min for 1.5h at 30℃. 230g sodium hypophosphite was added, and the reaction was carried out at the same temperature and stirring rate for 15min. Ammonia solution with a concentration of 0.5mol / L was added to adjust the pH of the reaction solution to 5. 10g lanthanum-cerium bimetallic organic hypophosphite was added, and the mixture was ultrasonically dispersed for 45min. The reaction was carried out at the same temperature and stirring rate for 30min. 150g of aluminum powder modified with amino-cobalt-based MOF was added, and the reaction was carried out at 70℃ with the same stirring rate for 50min. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed three times with deionized water and anhydrous ethanol. The cake was vacuum dried at 110℃ to constant weight, mechanically dispersed, and sieved through a 350-mesh sieve to obtain flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing.

[0038] Example 3: This example provides a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing, prepared through the following steps:

[0039] S1: 400g of aluminum powder and 2500mL of anhydrous ethanol were placed in a reaction vessel under a nitrogen atmosphere and stirred at 300r / min for 40min at 40℃. Then, 25mL of tetraethyl orthosilicate solution (obtained by mixing tetraethyl orthosilicate and anhydrous ethanol at a volume ratio of 1:5), 60mL of 0.5mol / L ammonia water and 80mL of deionized water were added dropwise. The reaction was carried out at the same temperature and stirring rate for 6h. After the reaction was completed, the mixture was filtered, and the filter cake was washed 4 times with anhydrous ethanol and dried under vacuum at 80℃ to constant weight to obtain silica composite aluminum powder.

[0040] S2: 300g of silica composite aluminum powder, 5g of polyvinylpyrrolidone and 1500mL of deionized water were placed in a reaction vessel and ultrasonically dispersed for 40min. The mixture was stirred at 300r / min at 35℃ for 12h. 12g of cobalt nitrate hexahydrate was added and stirred for another 12h at the same temperature and stirring rate. 6g of 2-aminoterephthalic acid and 3g of terephthalic acid were dissolved in 800mL of anhydrous ethanol and added to the reaction vessel. The mixture was reacted at 160℃ at the same stirring rate for 14h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed four times with anhydrous ethanol. The cake was then vacuum dried at 80℃ to constant weight to obtain aluminum powder modified with aminocobalt-based MOF.

[0041] S3: 32g of 2-carboxyethylphenylphosphonic acid, 20g of lanthanum nitrate hexahydrate, 20g of cerium nitrate hexahydrate and 5L of deionized water were placed in a reaction vessel and stirred at 300r / min for 2h at 35℃. The temperature was then raised to 130℃ and the reaction was continued at the same stirring rate for 26h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed 4 times with deionized water and dried under vacuum at 80℃ to constant weight to obtain lanthanum-cerium bimetallic organophosphophosphate.

[0042] S4: 250g nickel sulfate, 150g sodium citrate, 200g lactic acid, and 8L deionized water were placed in a reactor under a nitrogen atmosphere and stirred at 300r / min for 2h at 35℃. 300g sodium hypophosphite was added, and the reaction was carried out at the same temperature and stirring rate for 20min. Ammonia solution with a concentration of 0.5mol / L was added to adjust the pH of the reaction solution to 5.5. 15g lanthanum-cerium bimetallic organic hypophosphite was added, and the mixture was ultrasonically dispersed for 60min. The reaction was carried out at the same temperature and stirring rate for 40min. 200g of aluminum powder modified with amino-cobalt-based MOF was added, and the reaction was carried out at 85℃ with the same stirring rate for 60min. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed four times with deionized water and anhydrous ethanol. The cake was vacuum dried at 120℃ to constant weight, mechanically dispersed, and sieved through a 400-mesh sieve to obtain flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing.

[0043] The flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing prepared in Examples 1-3 above involves: first, dispersing aluminum powder in an alcohol-water mixture; then, utilizing the hydrolysis and condensation reaction of tetraethyl orthosilicate under alkaline catalysis with ammonia to form a nano-silica protective layer on the aluminum powder surface, resulting in silica composite aluminum powder; subsequently, through the surface modification and adsorption of polyvinylpyrrolidone, cobalt ions are coordinated with 2-aminoterephthalic acid and terephthalic acid in a high-temperature solvothermal system to form an amino-containing cobalt-based metal-organic framework on the silica composite aluminum powder, thus obtaining amino-containing cobalt-based MOF-modified aluminum powder; finally, using rare earth metal ions from lanthanum nitrate and cerium nitrate and 2-carboxyethylphenylphosphine... A complexation and coordination reaction occurs to obtain lanthanum-cerium bimetallic organic hypophosphite. Finally, the lanthanum-cerium bimetallic organic hypophosphite and aluminum powder modified with amino-cobalt-based MOF are dispersed in an acidic chemical plating solution with nickel sulfate as the nickel source, sodium citrate, and lactic acid as the complexing agent. The free amino groups on the MOF surface coordinate with the lanthanum-cerium bimetallic organic hypophosphite and undergo interfacial adsorption. Under heating conditions, sodium hypophosphite is used as a reducing agent to react with the phosphorus source in a redox reaction, reducing the complexed nickel ions in the solution. In-situ deposition of nickel-phosphorus alloy occurs on the surface of the modified aluminum powder. During the deposition process, the lanthanum-cerium bimetallic organic hypophosphite is physically encapsulated and co-deposited into the alloy layer, resulting in a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing.

[0044] Comparative Example 1: The difference from Example 2 is that in step S2, an equal amount of terephthalic acid is used instead of 2-aminoterephthalic acid, while the other steps remain unchanged, to prepare a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing.

[0045] Comparative Example 2: The difference from Example 2 is that in step S4, the silica composite aluminum powder prepared in step S1 is used instead of the aluminum powder loaded with amino cobalt-based MOF modified in step S2, while the other steps remain unchanged, to prepare a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing.

[0046] Comparative Example 3: The difference from Example 2 is that the lanthanum-cerium bimetallic organic hypophosphite prepared in step S3 is removed in step S4, while the other steps remain unchanged, and a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing is prepared.

[0047] The aluminum powder purchased in the above examples and comparative examples was produced by Zhongnuo New Materials (Beijing) Technology Co., Ltd. It is spherical pure aluminum powder with an average particle size of 30-50μm, and is used after being washed and dried with anhydrous ethanol; the polyvinylpyrrolidone was produced by Sinopharm Chemical Reagent Co., Ltd., with an average molecular weight of 40,000.

[0048] The flame-retardant nickel-coated aluminum composite powders for metal additive manufacturing prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests, and the test results are shown in Table 1.

[0049] Sample preparation: The composite powders prepared in the above examples and comparative examples were placed in a selective laser melting device and 3D forming was performed according to the preset process parameters to prepare cubic samples with a size of 10mm×10mm×10mm for densification performance testing, and dumbbell-shaped tensile samples conforming to the national standard GB / T 228.1-2021 were prepared for mechanical property testing.

[0050] Flame retardant properties: The flame retardant nickel-coated aluminum composite powder for metal additive manufacturing prepared in the examples and comparative examples was heated in air at a rate of 10℃ / min using a synchronous thermal analyzer. The oxidation initiation temperature of the powder was recorded. The higher the oxidation initiation temperature, the better the powder’s resistance to thermal runaway and flame retardant protection.

[0051] Mechanical properties: Referring to standard GB / T 228.1-2021, the specimen was placed on a universal testing machine for tensile testing. The tensile speed was set to 1.0 mm / min until the specimen broke. The tensile strength and elongation after fracture were recorded. The higher the tensile strength and elongation after fracture of the specimen, the better the mechanical properties of the specimen.

[0052] Density performance: The actual density of the above cubic sample was measured using the Archimedes displacement method, and the ratio of its density to the theoretical density was calculated to obtain the relative density. The higher the relative density, the better the density of the sample.

[0053] Table 1 Performance Test Table for Flame-Retardant Nickel-Clad Aluminum Composite Powder for Metal Additive Manufacturing

[0054] project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Oxidation initiation temperature / (°C) 692 705 698 620 545 640 Tensile strength (MPa) 372 382 376 315 265 342 Elongation after fracture (%) 9.6 10.2 9.8 6.2 3.1 8.0 Relative density (%) 99.2 99.6 99.4 98.1 96.5 98.8

[0055] As shown in Table 1, the flame-retardant nickel-coated aluminum composite powders for metal additive manufacturing prepared in Examples 1-3 all exhibit superior performance compared to the comparative examples. This indicates that the present invention, by sequentially constructing a silica barrier layer and an amino-cobalt-based MOF modification layer on the surface of aluminum powder, combined with the synergistic flame retardancy of lanthanum-cerium bimetallic organic hypophosphite and the dense coating of nickel-phosphorus alloy, forms a multi-layer synergistic protection system. This system may effectively suppress the oxidation and thermal runaway of the aluminum matrix under the instantaneous high temperature of laser, thereby enabling the composite powder to possess excellent flame-retardant protection performance, high forming density, and stable mechanical properties.

[0056] The mechanical properties and density of the composite powder in Comparative Example 1 showed a significant decrease, possibly due to the lack of amino active sites on the MOF framework. During the chemical composite plating stage, the system lost its strong nucleophilic adsorption capacity for lanthanum-cerium bimetallic organophosphophosphate in the liquid phase, which may have resulted in a low loading rate and loose bonding of the flame retardant component on the powder surface. This made it prone to peeling off during subsequent 3D printing powder spreading and laser shock, leading to a deterioration in the density and mechanical properties of the sample. At the same time, during the continuous heating test in the simultaneous thermal analysis, the powder may have undergone an earlier oxidation reaction due to incomplete coverage of the surface flame retardant, thus reducing the flame retardant effect.

[0057] The composite powder in Comparative Example 2 showed a significant decrease in all properties, possibly because the amino-cobalt-based MOF layer was directly removed. On the one hand, the thermal buffering effect of the endothermic decomposition and in-situ carbonization of the organic ligands in the MOF layer was lost. On the other hand, without the MOF layer to provide uniform nucleation sites for the nickel-phosphorus coating, the coating is prone to uneven coating and incomplete coating, and cannot form a complete physical oxygen barrier to protect the aluminum powder, resulting in premature and severe oxidation of the powder. In subsequent 3D printing, the liquid aluminum may boil on a large scale and emit metal vapor due to the failure of the protective structure, forming severe porosity defects inside the matrix, which greatly weakens the mechanical properties of the sample.

[0058] The oxidation initiation temperature of the composite powder in Comparative Example 3 was significantly lower than that in the Example. This may be because the lanthanum-cerium bimetallic organic hypophosphite was removed during the preparation process. In the powder flame retardant performance test, although the system still retained silica, MOF framework and dense nickel-phosphorus shell to maintain the basic oxidation temperature, the powder may not be able to build a flame retardant defense at higher temperatures due to the lack of the chemical mechanism of rare earth ion catalysis to carbonization, which reduces the basic flame retardant protection capability of the powder.

[0059] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing, characterized in that, Prepared by the following steps: Step 1: Using aluminum powder as raw material, a nano-silica layer is first constructed in situ on the surface of the aluminum powder using the sol-gel method to obtain silica composite aluminum powder; cobalt ions are anchored on the silica composite aluminum powder using polyvinylpyrrolidone; under solvothermal conditions, the cobalt metal center undergoes a coordination assembly reaction with 2-aminoterephthalic acid and terephthalic acid dual ligands to obtain aluminum powder modified with amino-cobalt-based MOF. Step 2: Using 2-carboxyethylphenylphosphino acid as a phosphorus-containing organic ligand, and lanthanum nitrate hexahydrate and cerium nitrate hexahydrate as rare earth metal sources, coordination polymerization was carried out under hydrothermal conditions to obtain lanthanum-cerium bimetallic organophosphophosphate. Step 3: Construct an acidic electroless nickel plating system with nickel sulfate as the main salt, sodium hypophosphite as the reducing agent and phosphorus source, and sodium citrate and lactic acid as dual complexing agents. Modified aluminum powder loaded with amino-cobalt-based MOF and lanthanum-cerium bimetallic organic hypophosphite are co-dispersed in the acidic electroless nickel plating system. Under constant temperature heating, hypophosphite undergoes an autocatalytic redox reaction, depositing a dense amorphous nickel-phosphite alloy layer in situ on the surface of the modified aluminum powder. Simultaneously, the lanthanum-cerium bimetallic organic hypophosphite is mechanically encapsulated by the continuously growing alloy layer and co-deposited, yielding a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing.

2. The method for preparing a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing according to claim 1, characterized in that, The lanthanum-cerium bimetallic organophosphophosphate described in step two is prepared through the following steps: 2-Carboxyethylphenylphosphino acid, lanthanum nitrate hexahydrate, cerium nitrate hexahydrate, and deionized water were placed in a reaction vessel and stirred at 25-35℃ for 1-2 h. The mixture was then heated to 110-130℃ and reacted for 22-26 h. After filtration, washing, and vacuum drying to constant weight, lanthanum-cerium bimetallic organophosphophosphate was obtained.

3. The method for preparing a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing according to claim 2, characterized in that, The ratio of 2-carboxyethylphenylphosphonic acid, lanthanum nitrate hexahydrate, cerium nitrate hexahydrate, and deionized water is 16-32g: 10-20g: 10-20g: 3-5L.

4. The method for preparing a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing according to claim 1, characterized in that, The aluminum powder supported on amino-cobalt-based MOF modified aluminum powder described in step one is prepared through the following steps: Silica composite aluminum powder, polyvinylpyrrolidone, and deionized water were placed in a reaction vessel and ultrasonically dispersed for 20-40 min. The mixture was stirred at 25-35℃ for 10-12 h. Cobalt nitrate hexahydrate was added, and stirring was continued at the same temperature for 10-12 h. 2-Aminoterephthalic acid and terephthalic acid were dissolved in anhydrous ethanol and added to the reaction vessel. The mixture was reacted at 150-160℃ for 12-14 h. The mixture was filtered, washed, and vacuum dried to constant weight to obtain aluminum powder modified with amino cobalt-based MOF.

5. The method for preparing a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing according to claim 4, characterized in that, The ratio of the amounts of silica composite aluminum powder, polyvinylpyrrolidone, deionized water, cobalt nitrate hexahydrate, anhydrous ethanol, 2-aminoterephthalic acid, and terephthalic acid is 200-300g: 3-5g: 800-1500mL: 400-800mL: 2-6g: 1-3g.

6. The method for preparing a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing according to claim 5, characterized in that, The silica-aluminum composite powder is prepared through the following steps: Aluminum powder and anhydrous ethanol were placed in a reaction vessel under a nitrogen atmosphere and stirred at 30-40℃ for 20-40 min. Tetraethyl orthosilicate solution, 0.5 mol / L ammonia water and deionized water were added dropwise, and the mixture was reacted at the same temperature for 4-6 h. The mixture was then filtered, washed, and vacuum dried to constant weight to obtain silica composite aluminum powder.

7. The method for preparing a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing according to claim 6, characterized in that, The ratio of aluminum powder, anhydrous ethanol, tetraethyl orthosilicate solution, ammonia, and deionized water is 300-400g: 1500-2500mL: 15-25mL: 30-60mL: 40-80mL.

8. The method for preparing a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing according to claim 1, characterized in that, The flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing described in step three is prepared through the following steps: Nickel sulfate, sodium citrate, lactic acid, and deionized water were placed in a reactor under a nitrogen atmosphere and stirred at 25-35℃ for 1-2 hours. Sodium hypophosphite was added, and the reaction was continued for 10-20 minutes. Ammonia solution with a concentration of 0.5 mol / L was added to adjust the pH of the reaction solution to 4.5-5.

5. Lanthanum-cerium bimetallic organic hypophosphite was added, and the mixture was ultrasonically dispersed for 30-60 minutes. The reaction was continued for 20-40 minutes. Aluminum powder modified with amino-cobalt-based MOF was added, and the mixture was reacted at 75-85℃ for 40-60 minutes. The mixture was filtered, washed, vacuum dried to constant weight, mechanically dispersed, and sieved to obtain a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing.

9. The method for preparing a flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing according to claim 8, characterized in that, The ratio of nickel sulfate, sodium citrate, lactic acid, deionized water, sodium hypophosphite, lanthanum-cerium bimetallic organic hypophosphite, and aluminum powder modified with amino-cobalt-based MOF is 150-250g: 80-150g: 100-200g: 5-8L: 150-300g: 5-15g: 100-200g.

10. A flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing, characterized in that, The flame-retardant nickel-coated aluminum composite powder for metal additive manufacturing, as described in any one of claims 1-9, is prepared by the method described in any one of claims 1-9.