A method for additive manufacturing of CNTs-reinforced WE43 composite materials based on annular laser spot

Abstract

The present invention discloses a method for preparing an additively reinforced WE43 composite material based on an annular laser spot CNTs, wherein the CNTs are CNTs coated with surface metal, and the coating metal is copper. After the copper coating, the copper accounts for 35wt.% of the total amount of the coated CNTs, and the particle size is 10-20nm. The Cu layer has a low laser absorptivity, and the CNTs structure damage caused by direct laser irradiation is improved. At the same time, the CNTs / α-Mg interface bonding strength can be improved by means of the good interface wetting and metallurgical reaction of Mg-Cu. The laser spot used is annular, the spot outer diameter is about 5.5mm, and the inner hole diameter is about 1.7mm. The annular spot energy is relatively uniform, which is beneficial to protect the CNTs structure from being destroyed. The cladding parameters are: the copper-coated CNTs / WE43 mixed powder feeding rate is 2r / min, the powder feeding gas flow rate is 5L / min, the laser cladding power is 1500W, the scanning speed is 4mm / s, the shielding gas flow rate is 22.5L / min, and the stay between each pass is 6s.

Description

Technical Field

[0001] The invention belongs to the field of material processing, and specifically relates to a method for additively preparing a CNTs-reinforced WE43 composite material. Background Art

[0002] In the field of high-tech, magnesium alloys have become a research hotspot in the field of metal-based composites due to their abundant reserves, low density, high specific strength, and excellent damping properties. However, the shortcomings of magnesium alloys, such as low tensile strength, low hardness, and poor wear resistance, limit their widespread application. Carbon nanotubes (CNTs) are tubular nanoscale graphite crystals. Due to their excellent comprehensive mechanical properties, high aspect ratio, and light weight, CNTs are currently one of the most ideal fiber reinforcement materials for magnesium alloys. Casting and powder metallurgy preparation processes for CNT-reinforced magnesium-based composites have been widely researched and applied. However, less research has been conducted on the use of laser additive manufacturing processes to manufacture CNT-reinforced magnesium-based composites.

[0003] In the preparation process of CNTs-reinforced magnesium-based composites, CNTs need to be mixed with magnesium alloys, and ball milling is a relatively common and efficient method. Studies have found that the ball milling process has a significant impact on the mixed powder. The ball milling process parameters include: ball-to-material ratio, stirring shaft speed, ball milling time, etc. When the ball ratio is large, the stirring shaft speed is fast, and the ball milling time is long, the magnesium powder particles will be broken and the CNTs structure will be destroyed, affecting the molding of the magnesium alloy additive and the reinforcement effect of the CNTs; conversely, when the ball ratio is small, the stirring shaft speed is slow, and the ball milling time is short, the CNTs will agglomerate, and the magnesium alloy and CNTs cannot be fully and evenly mixed. Therefore, the ball milling process is very important for the preparation of high-quality magnesium alloy composite additives.

[0004] Currently, the fabrication of CNTs-reinforced magnesium-based composites by laser cladding faces the following major challenges: poor wettability between CNTs and the magnesium matrix, a lack of chemical reaction, and significant differences in density and thermal expansion coefficient, resulting in low CNT-α(Mg) interfacial bonding strength. Direct laser irradiation of CNTs can lead to structural transformations, such as merging, recombination, and aggregation. Furthermore, high temperatures can easily lead to oxidation, significantly diminishing their unique and superior properties. Therefore, optimizing fabrication methods to enhance the strength and toughness of CNTs / Mg composites is essential. Kang et al. compared the effects of laser irradiation and heating on the structure of CNTs at 350°C in vacuum and air. Their results showed that CNTs were more susceptible to oxidation and ablation in air. Huang et al. investigated the morphological and structural changes of CNTs during high-temperature annealing and heat treatment in vacuum. Their results showed that high-temperature treatment in vacuum did not damage the CNT structure but rather eliminated impurities and purified the CNTs. In addition to thermal oxidation and ablation, the effects of laser irradiation on carbon nanotubes have also been investigated. Hwang et al. studied the preparation of carbon nanotube-reinforced nickel-based composites by laser cladding and powder addition. Their results showed that compared with the as-received multi-walled carbon nanotube powder, the resulting composites exhibited a higher number of defects and smaller domain (or bundle) size. It has also been reported that during laser welding of CNT-reinforced magnesium-based composites, the majority of the CNTs were transformed into locally aggregated nanoscale and submicron carbon particles. Electroless nickel coating of CNTs improves their wettability and provides effective shielding between the CNTs and the laser beam during laser cladding. Results indicate that nickel coating can reduce structural damage to CNTs under laser irradiation. Compared to other metals, copper has a lower absorption rate for 1064 nm laser light, making it a suitable coating metal to minimize structural damage to CNTs caused by direct laser irradiation. However, the effect of Cu coating on the microstructural evolution of carbon nanotubes has been little studied to date. Summary of the Invention

[0005] The purpose of the present invention is to provide a laser additive manufacturing method for CNTs-reinforced WE43 composite materials based on CNTs modification, which is used to realize laser additive manufacturing of CNTs-reinforced WE43 composite materials.

[0006] The technical solutions for achieving the purpose of the present invention are:

[0007] A laser manufacturing method for CNTs reinforced WE43 composite material comprises the following steps:

[0008] Step 1: Prepare copper-coated CNTs by chemical plating, where copper accounts for 35 wt.% of the total amount of the coated CNTs and the particle size is 10-20 nm.

[0009] Step 2: Mix copper-coated CNTs / WE43 powder, with copper-coated CNTs accounting for 0.5 wt.% of the total weight of CNTs / WE43 powder.

[0010] Step 3: Add CNTs / WE43 mixed powder into the powder feeder. The powder feeding rate of the mixed powder is 2 r / min, the powder feeding gas flow rate is 5 L / min, and the substrate is WE43 magnesium alloy with a thickness of 10 mm.

[0011] Step 4: Use coaxial powder feeding to laser clad the CNTs / WE43 mixed powder to form a uniform cladding layer. The laser spot used is annular, with an outer diameter of about 5.5 mm and an inner hole diameter of about 1.7 mm. The laser cladding power is 1500 W, the scanning rate is 4 mm / s, the shielding gas flow rate is 22.5 L / min, and the dwell time between each pass is 6 s.

[0012] Compared with existing technologies, this invention offers significant advantages: by coating the CNTs with Cu, the Cu layer's low laser absorption rate is exploited to mitigate structural damage to the CNTs caused by direct laser irradiation. Furthermore, the excellent interfacial wetting and metallurgical reaction between Mg and Cu enhances the CNT / α-Mg interface bonding strength. The laser spot used is annular, with relatively uniform energy distribution, which helps protect the CNT structure from damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a preparation process diagram of the annular spot laser additive preparation method of CNTs reinforced WE43 composite material of the present invention.

[0014] Figure 2 This is a preparation flow chart of the annular spot laser additive preparation method of CNTs reinforced WE43 composite materials of the present invention.

[0015] Figure 3 SEM images of the CNTs / WE43 mixed powder after ball milling in the annular spot laser additive preparation method for CNTs-reinforced WE43 composite materials. (a) Magnified image of a mixed powder particle, 500x magnification, 100μm; (b) Magnified image of a single particle surface, 30,000x magnification, 1μm; (c) Magnified image of a single particle surface, 100,000x magnification, 500nm.

[0016] Figure 4 These are the appearance diagrams of samples prepared using the annular spot laser additive manufacturing method for CNTs-reinforced WE43 composite materials. (a) Top view of the additive sample; (b) Cross-sectional view of the additive sample.

[0017] Figure 5This is a macroscopic metallographic image of the CNTs-reinforced WE43 composite material after cladding in the annular spot laser additive preparation method of the present invention.

[0018] Figure 6 Ramam spectra obtained for Cu-CNTs with different copper coating thicknesses at 600W laser power during the annular spot laser additive preparation method for CNT-reinforced WE43 composites. (a) CNTs, (b) 35wt.% Cu-CNTs, (c) 45wt.% Cu-CNTs.

[0019] Figure 7 These are SEM images of the CNTs-reinforced WE43 composite material after cladding in the annular spot laser additive manufacturing method of the present invention. (a) 50 μm; (b) 500 nm; (c) 5 μm. DETAILED DESCRIPTION

[0020] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] The laser additive manufacturing method for annular spot of CNTs-reinforced WE43 composite material of the present invention is specifically implemented according to the following steps:

[0022] Step 1: Prepare copper-coated CNTs by chemical plating, where copper accounts for 35 wt.% of the total amount of the coated CNTs and the particle size is 10-20 nm.

[0023] Step 2: Weigh CNTs and WE43 powders by weight, and use argon-protected ball milling to mix copper-coated CNTs / WE43 powders. The particle size of WE43 powder is 100-200 mesh. The argon is filled in by opening the air inlet and outlet of the ball mill, and then filling argon from the air inlet for 1 minute, and then closing the air inlet and outlet. The speed of the ball mill is 200 r / min, and the ball milling time is 3 hours. The diameters of the grinding balls in the ball mill are 6 mm and 10 mm, respectively, and the ratio of large and small balls is 10:3.

[0024] Step 3: Add CNTs / WE43 mixed powder into the powder feeder. The powder feeding rate of the mixed powder is 2 r / min, the powder feeding gas flow rate is 5 L / min, and the substrate is magnesium alloy with a thickness of 10 mm.

[0025] Step 4: Use coaxial powder feeding to laser clad the CNTs / WE43 mixed powder to form a uniform cladding layer. The laser spot used is annular, with an outer diameter of about 5.5 mm and an inner hole diameter of about 1.7 mm. The laser cladding power is 1500 W, the scanning rate is 4 mm / s, the shielding gas flow rate is 22.5 L / min, and the dwell time between each pass is 6 s.

[0026] Example 1

[0027] Preparation of 0.5 wt.% CNTs / WE43 composite material was carried out according to the following steps:

[0028] Step 1: Prepare copper-coated CNTs by chemical plating, where copper accounts for 35 wt.% of the total amount of the coated CNTs and the particle size is 10-20 nm.

[0029] Step 2: Weigh 0.25g CNTs and 49.75g WE43 magnesium alloy powder, and use argon protection ball milling to mix copper-coated CNTs / WE43 powder. The particle size of WE43 powder is 100-200 mesh. The argon is filled in by opening the air inlet and outlet of the ball mill, and then filling argon from the air inlet for 1 minute, and then closing the air inlet and outlet. The speed of the ball mill is 200r / min, and the ball milling time is 3h. The diameters of the grinding balls in the ball mill are 6mm and 10mm, respectively, and the ratio of large and small balls is 10:3.

[0030] Step 3: Add CNTs / WE43 mixed powder into the powder feeder. The powder feeding rate of the mixed powder is 2 r / min, the powder feeding gas flow rate is 5 L / min, and the substrate is magnesium alloy with a thickness of 10 mm.

[0031] Step 4: Use coaxial powder feeding to laser clad the CNTs / WE43 mixed powder to form a uniform cladding layer. The laser spot used is annular, with an outer diameter of about 5.5 mm and an inner hole diameter of about 1.7 mm. The laser cladding power is 1500 W, the scanning rate is 4 mm / s, the shielding gas flow rate is 22.5 L / min, and the dwell time between each pass is 6 s.

[0032] Example 2

[0033] A 1.0 wt.% CNTs / WE43 composite material was prepared by the following steps:

[0034] Step 1: Prepare copper-coated CNTs by chemical plating, where copper accounts for 35 wt.% of the total amount of the coated CNTs and the particle size is 10-20 nm.

[0035] Step 2: Weigh 0.50g CNTs and 49.50g WE43 magnesium alloy powder, and use argon protection ball milling to mix copper-coated CNTs / WE43 powder. The particle size of WE43 powder is 100-200 mesh. The argon is filled in by opening the air inlet and outlet of the ball mill, and then filling argon from the air inlet for 1 minute, and then closing the air inlet and outlet. The speed of the ball mill is 200r / min, and the ball milling time is 3h. The diameters of the grinding balls in the ball mill are 6mm and 10mm, respectively, and the ratio of large and small balls is 10:3.

[0036] Step 3: Add CNTs / WE43 mixed powder into the powder feeder. The powder feeding rate of the mixed powder is 2 r / min, the powder feeding gas flow rate is 5 L / min, and the substrate is magnesium alloy with a thickness of 10 mm.

[0037] Step 4: Use coaxial powder feeding to laser clad the CNTs / WE43 mixed powder to form a uniform cladding layer. The laser spot used is annular, with an outer diameter of about 5.5 mm and an inner hole diameter of about 1.7 mm. The laser cladding power is 1500 W, the scanning rate is 4 mm / s, the shielding gas flow rate is 22.5 L / min, and the dwell time between each pass is 6 s.

[0038] Example 3

[0039] A 1.5 wt.% CNTs / WE43 composite material was prepared by the following steps:

[0040] Step 1: Prepare copper-coated CNTs by chemical plating, where copper accounts for 35 wt.% of the total amount of the coated CNTs and the particle size is 10-20 nm.

[0041] Step 2: Weigh 0.75g CNTs and 49.25g WE43 magnesium alloy powder, and use argon protection ball milling to mix copper-coated CNTs / WE43 powder. The particle size of WE43 powder is 100-200 mesh. The argon is filled in by opening the air inlet and outlet of the ball mill, and then filling argon from the air inlet for 1 minute, and then closing the air inlet and outlet. The speed of the ball mill is 200r / min, and the ball milling time is 3h. The diameters of the grinding balls in the ball mill are 6mm and 10mm, respectively, and the ratio of large and small balls is 10:3.

[0042] Step 3: Add CNTs / WE43 mixed powder into the powder feeder. The powder feeding rate of the mixed powder is 2 r / min, the powder feeding gas flow rate is 5 L / min, and the substrate is magnesium alloy with a thickness of 10 mm.

[0043] Step 4: Use coaxial powder feeding to laser clad the CNTs / WE43 mixed powder to form a uniform cladding layer. The laser spot used is annular, with an outer diameter of about 5.5 mm and an inner hole diameter of about 1.7 mm. The laser cladding power is 1500 W, the scanning rate is 4 mm / s, the shielding gas flow rate is 22.5 L / min, and the dwell time between each pass is 6 s.

[0044] Figure 3 This is the SEM image of the CNTs / WE43 mixed powder after ball milling. It can be seen from the figure that the mixed powder has good dispersion, and the CNTs are distributed on the surface of the WE43 particles and are evenly dispersed. Figure 5This macroscopic metallographic image shows the absence of macroscopic defects such as pores and cracks in the cross-sectional structure. Both the matrix and the additive material exhibit equiaxed grains. The blue box in the metallographic image represents the magnified area of the matrix, the yellow box represents the magnified area at the bottom of the additive material, and the green box represents the magnified area at the top of the additive material. The grains in the additive material are clearly refined, significantly increasing the hardness. Figure 6 Ramam spectra of Cu-CNTs with different copper coating thicknesses obtained at 600W laser power. By comparison, the I D / I G The value is 1.01, the ratio is large, and there are more defects. As the copper plating thickness increases, I D / I G The ratio of becomes smaller and smaller, and the defects gradually decrease, indicating that the copper plating on the surface of CNTs can reflect laser and improve the damage of CNTs structure caused by direct laser irradiation. Figure 7 The morphology of the CNTs after cladding is observed under high magnification SEM. The CNTs are clearly entangled and long, demonstrating that the CNTs remain intact and well-dispersed after ball milling and laser cladding. They also exhibit no agglomeration and a close interface with the magnesium alloy, showing no defects. Table 1 shows the Vickers hardness test results for magnesium alloy cladding layers with varying CNT content.

[0045] Table 1 Vickers hardness of magnesium alloy cladding layers with different CNTs contents

[0046]

[0047] By comparing the rolled magnesium alloy with the same composition and Examples 1-3, it was found that the Vickers hardness of Examples 1-3 was close to or even higher than that of the rolled magnesium alloy with the same composition.

Claims

1. A method for additively preparing WE43 composite materials based on annular laser spot CNTs reinforcement, characterized in that: The method comprises the following specific steps: Step 1: Preparation of copper-coated CNTs by electroless plating; Step 2: Mixing copper-coated CNTs / WE43 powder; Step 3: Add CNTs / WE43 mixed powder into the powder feeder; Step 4: Laser cladding the CNTs / WE43 mixed powder to form a uniform cladding layer using a coaxial powder feeding method. The laser spot used is annular. Copper accounts for 35 wt.% of the total amount of coated CNTs, and the particle size is 10-20 nm; The laser spot is annular, with an outer diameter of 5.5mm and an inner diameter of 1.7mm; The cladding parameters are as follows: copper-coated CNTs / WE43 mixed powder feeding rate of 2 r / min, powder feeding gas flow rate of 5 L / min, laser cladding power of 1500 W, scanning speed of 4 mm / s, shielding gas flow rate of 22.5 L / min, and a dwell time of 6 s between each pass.

2. The additive manufacturing method for CNTs-enhanced WE43 composite materials based on annular laser spot according to claim 1, characterized in that: The mixed copper-coated CNTs / WE43 powder can be mixed by argon-protected ball milling. The speed of the ball mill is 200 r / min, the ball milling time is 3 h, the diameters of the grinding balls in the ball mill are 6 mm and 10 mm, respectively, and the ratio of large and small balls is 10:

3.

3. The additive manufacturing method for CNTs-reinforced WE43 composite material based on annular laser spot according to claim 1, characterized in that: The copper-coated CNTs accounted for 0.5 wt.% of the total weight of CNTs / WE43 powder.

4. The additive preparation method for CNTs-reinforced WE43 composite materials based on annular laser spot according to claim 1, characterized in that: The powder feeding rate of the mixed powder is 2 r / min, the powder feeding gas flow rate is 5 L / min, and the substrate is WE43 magnesium alloy with a thickness of 10 mm.

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