Laser additive manufacturing magnesium alloy and preparation method and application thereof

Abstract

The invention belongs to the technical field of alloys, and particularly relates to a laser additive manufacturing magnesium alloy and a preparation method and application thereof. The invention provides a magnesium alloy laser additive manufacturing method which comprises the following steps: mixing magnesium alloy powder and a high-melting-point reinforcing phase to obtain a mixed material; the melting point of the high-melting-point reinforced phase is 2800-3900 DEG C; and the mixed material is subjected to laser additive manufacturing and then subjected to heat treatment, and the magnesium alloy is obtained. Magnesium alloy powder and high-melting-point reinforcing phases are used as raw materials for laser additive manufacturing, the high-melting-point reinforcing phases are distributed in a microscopic structure or at a grain boundary of a formed alloy in the laser additive manufacturing process, and in the subsequent heat treatment process, the dispersed reinforcing phases can generate a pinning effect to hinder migration of the grain boundary and generate resistance to the grain boundary, so that the grain boundary is prevented from being damaged. Therefore, the abnormal grain coarsening behavior of the magnesium alloy in the subsequent heat treatment process is inhibited, the microscopic structure of the magnesium alloy is improved, and the mechanical property of the magnesium alloy is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of alloys, and particularly relates to a laser additive manufacturing magnesium alloy and a preparation method and application thereof. BACKGROUND

[0002] Lightweight is an important development direction of aerospace structural parts, magnesium alloy has the advantages of light weight, high specific strength and specific stiffness, etc., and is widely used in aircraft, missiles, rockets, satellites, spaceships and other aerospace vehicles, which not only improves the maneuverability of the aircraft, but also reduces the launch cost of the spacecraft. The traditional preparation method of magnesium alloy aerospace components is mainly plastic deformation (rolling, extrusion and forging, etc.) and casting forming. The magnesium alloy components formed by plastic deformation method can obtain fine grain structure and have excellent mechanical properties, while the casting forming method can realize the overall forming of complex structure, and has the advantages of low production cost and short production cycle. With the rapid development of the aerospace industry and the increasing maturity of the research and development of high-performance magnesium alloy materials, the forming technology is also rapidly developing towards large-scale and integration, but the traditional plastic forming and casting forming process cannot meet the development needs of magnesium alloy aerospace components.

[0003] In recent years, the laser additive manufacturing technology developed can provide an integrated solution for the efficient, short-cycle and net forming manufacturing of high-performance and complex structure metal components, and has great development potential in the preparation of aerospace magnesium alloy components. In order to improve the organization and enhance the mechanical properties, the magnesium alloy prepared by laser additive manufacturing is usually heat treated. However, the existing heat treatment process will cause the abnormal coarsening of the internal organization of the magnesium alloy laser additive manufacturing component, forming abnormal coarse alpha-Mg grains. The formation of abnormal coarse grains in the magnesium alloy laser additive component after heat treatment will directly reduce the mechanical properties of the material, so that the heat treatment process adopted will have the opposite effect. In order to promote the improvement of the mechanical properties of the magnesium alloy laser additive component, it is necessary to take certain measures to inhibit the abnormal coarsening of the grains after heat treatment. SUMMARY

[0004] Therefore, the application provides a laser additive manufacturing magnesium alloy and a preparation method and application thereof. The magnesium alloy prepared by the method provided by the application has a small grain size, which improves the mechanical properties of the magnesium alloy on the basis of ensuring lightweight.

[0005] In order to solve the above technical problems, the application provides a method for laser additive manufacturing of magnesium alloy, comprising the following steps: Mixing magnesium alloy powder and high melting point reinforcing phase to obtain a mixture; the melting point of the high melting point reinforcing phase is 2800-3900 DEG C; the mixture is subjected to laser additive manufacturing and then heat treated to obtain a magnesium alloy.

[0006] Preferably, the high-melting-point reinforcing phase comprises one or more of SiC, TiC, graphene, and carbon nanotubes; The morphology of the high-melting-point reinforcing phase comprises fibers or particles; The particle size of the particles is 10-100 μm, and the length of the fibers is 5-20 μm.

[0007] Preferably, the magnesium alloy powder comprises ZM5 magnesium alloy powder, ZM6 magnesium alloy powder, or AZ91D magnesium alloy powder; The magnesium alloy powder comprises a magnesium alloy powder for laser powder bed melting or a magnesium alloy powder for laser directed energy deposition; The particle size of the magnesium alloy powder for laser powder bed melting ranges from 15 to 53 μm; The particle size of the magnesium alloy powder for laser directed energy deposition ranges from 75 to 150 μm.

[0008] Preferably, the mass percentage of the high-melting-point reinforcing phase in the mixed material is less than or equal to 30%.

[0009] Preferably, the mixing method comprises ball milling at a speed of 50-150 r / min for 2-6 h. After the mixing, the mixed material is further dried to obtain the mixed material, wherein the drying temperature is 80-150 °C, and the drying time is 2-8 h.

[0010] Preferably, the laser additive manufacturing comprises a laser powder bed melting process or a laser directed energy deposition process. The conditions of the laser powder bed melting process comprise a laser power of 50-200 W, a powder layer thickness of 0.02-0.05 mm, a scanning interval of 50-150 μm, a scanning speed of 100-500 mm / s, a spot diameter of 0.08-0.1 mm, and argon protection. The conditions of the laser directed energy deposition process comprise a laser power of 1000-1400 W, a powder feeding rate of 0.4-0.8 g / min, a scanning interval of 1.0-1.5 mm, a scanning speed of 3-7 mm / s, and argon protection.

[0011] Preferably, the heat treatment comprises annealing or solid solution treatment.

[0012] Preferably, the annealing temperature is 270-350 °C, the temperature rising rate to the annealing temperature is 10-50 °C / min, the annealing holding time is 60-90 min, and the cooling mode is furnace cooling. The solution treatment temperature is 420~540℃, the heating rate to the required solution treatment temperature is 28~32℃ / min, the holding time of the solution treatment is 4~12h, and the cooling method of the solution treatment is water cooling.

[0013] The present invention also provides a magnesium alloy prepared by the method described in the above technical solution, wherein the average grain size of the magnesium alloy is 22~23μm.

[0014] The present invention also provides the application of the magnesium alloy described in the above technical solution in the aerospace field.

[0015] This invention provides a method for laser additive manufacturing of magnesium alloys, comprising the following steps: mixing magnesium alloy powder and a high-melting-point reinforcing phase to obtain a mixture; the high-melting-point reinforcing phase has a melting point of 2800~3900℃; and subjecting the mixture to laser additive manufacturing followed by heat treatment to obtain a magnesium alloy. This invention uses magnesium alloy powder and a high-melting-point reinforcing phase as raw materials for laser additive manufacturing. During the laser additive process, the high-melting-point reinforcing phase does not participate in or partially participates in the metallurgical reaction, ultimately distributing within the microstructure or at grain boundaries of the formed alloy. During subsequent heat treatment, these dispersed reinforcing phases exhibit a "pinning effect," hindering grain boundary migration and creating resistance to grain boundary movement. This suppresses abnormal grain coarsening behavior in the magnesium alloy during subsequent heat treatment, thereby improving the microstructure of the laser-added magnesium alloy and promoting enhanced mechanical properties. Attached Figure Description

[0016] Figure 1 The diagrams show the grain size changes during the laser additive manufacturing of magnesium alloys with and without the addition of a high-melting-point reinforcing phase. (a1) to (a2) are the grain size changes during the laser additive manufacturing of magnesium alloys without the addition of a high-melting-point reinforcing phase, and (b1) to (b2) are the grain size changes during the laser additive manufacturing of magnesium alloys with the addition of a high-melting-point reinforcing phase. Figure 2 This is a diagram showing the result of laser-directed energy deposition of the product obtained in step 2 of Comparative Example 1. Figure 3 This is a diagram showing the result of the laser-added magnesium alloy component obtained in step 3 of Comparative Example 1. Figure 4 The result diagram is shown in step 3 of Example 1, depicting the magnesium alloy. Figure 5 The tensile property curves are for the laser-directed energy deposition product obtained in step 2 of Comparative Example 1, the laser additive magnesium alloy component obtained in step 3 of Comparative Example 1, and the magnesium alloy obtained in step 3 of Example 1. Detailed Implementation

[0017] This invention provides a method for laser additive manufacturing of magnesium alloys, comprising the following steps: Magnesium alloy powder and a high-melting-point reinforcing phase are mixed to obtain a mixture; the melting point of the high-melting-point reinforcing phase is 2800~3900℃; The mixture is subjected to laser additive manufacturing followed by heat treatment to obtain a magnesium alloy.

[0018] In this invention, unless otherwise specified, all materials are conventional commercially available products.

[0019] This invention involves mixing magnesium alloy powder with a high-melting-point reinforcing phase to obtain a mixture. In this invention, the high-melting-point reinforcing phase has a melting point of 2800~3900℃; the high-melting-point reinforcing phase may include one or more of SiC, TiC, graphene, and carbon nanotubes, specifically SiC, TiC, graphene, or carbon nanotubes; the melting point of SiC is 2827℃, the melting point of TiC is 3880℃, the melting point of graphene is 4227℃, and the melting point of carbon nanotubes is 3550℃; the morphology of the high-melting-point reinforcing phase may include fibers or particles; the particle size may be 10~100μm; and the length of the fibers may be 5~20μm.

[0020] In one specific embodiment of the present invention, the magnesium alloy powder may include ZM5 magnesium alloy powder, ZM6 magnesium alloy powder, or AZ91D magnesium alloy powder; the magnesium alloy powder may include magnesium alloy powder for laser powder bed melting or magnesium alloy powder for laser directed energy deposition; the particle size range of the magnesium alloy powder for laser powder bed melting may be 15~53μm; the particle size range of the magnesium alloy powder for laser directed energy deposition may be 75~150μm. In another specific embodiment of the present invention, the mass percentage of the high-melting-point reinforcing phase in the mixture may be less than 30%, or may be 0.5~28%, specifically 1%, 5%, 10%, 15%, 20%, or 25%.

[0021] In one specific embodiment of the present invention, the mixing method may include ball milling, wherein the rotation speed of the ball milling may be 50~150 r / min, specifically 60 r / min, 70 r / min, 80 r / min, 90 r / min, 100 r / min, 110 r / min, 120 r / min, 130 r / min or 140 r / min; and the ball milling time may be 2~6 h, specifically 3 h, 4 h or 5 h.

[0022] As a specific embodiment of the present invention, the mixing process may further include: drying the mixed materials to obtain the mixed material; the drying temperature may be 80~150℃ or 100~140℃; the drying time may be 2~8h or 3~5h.

[0023] After obtaining the mixture, the present invention performs laser additive manufacturing on the mixture followed by heat treatment to obtain a magnesium alloy. As a specific embodiment of the present invention, the laser additive manufacturing includes a laser powder bed melting process or a laser directional energy deposition process. As a specific embodiment of the present invention, the conditions of the laser powder bed melting process may include: laser power of 50~200W, powder layer thickness of 0.02~0.05mm, scanning spacing of 50~150μm, scanning speed of 100~500mm / s, spot diameter of 0.08~0.1mm, and argon protection; or laser power of 100~150W, powder layer thickness of 0.03~0.04mm, scanning spacing of 80~120μm, scanning speed of 200~400mm / s, spot diameter of 0.09~0.1mm, and argon protection. As a specific embodiment of the present invention, the conditions of the laser directional energy deposition process may include: laser power of 1000~1400W, powder feed rate of 0.4~0.8g / min, scanning spacing of 1.0~1.5mm, scanning speed of 3~7mm / s, and argon protection; or it may be: laser power of 1000~1300W, powder feed rate of 0.5~0.7g / min, scanning spacing of 1.1~1.4mm, scanning speed of 4~6mm / s, and argon protection.

[0024] In one specific embodiment of the present invention, the heat treatment may include annealing or solution treatment. In another specific embodiment, the annealing temperature may be 270~350℃, specifically 300℃, 320℃, or 340℃; the heating rate to the required annealing temperature may be 10~50℃ / min, specifically 20℃ / min, 30℃ / min, or 40℃ / min; the holding time for the annealing may be 60~90min, specifically 65min, 70min, 75min, or 80min; and the cooling method for the annealing may be furnace cooling. In one specific embodiment of the present invention, the solution treatment temperature can be 420~540℃, specifically 450℃, 480℃, 500℃, 525℃ or 535℃; the heating rate to the required solution treatment temperature can be 28~32℃ / min, specifically 30℃ / min; the holding time of the solution treatment can be 4~12h, specifically 5h, 8h or 10h; the cooling method of the solution treatment can be water cooling.

[0025] This invention suppresses abnormal coarsening behavior of magnesium alloys during heat treatment by adding a high-melting-point reinforcing phase to magnesium alloy powder for laser additive manufacturing and utilizing its distribution at the grain boundaries of the microstructure of the laser additive magnesium alloy.

[0026] Figure 1 This diagram illustrates the grain size changes in magnesium alloys during laser additive manufacturing with and without the addition of a high-melting-point reinforcing phase. (a1)~(a2) show the grain size changes without the addition of a high-melting-point reinforcing phase, while (b1)~(b2) show the grain size changes with the addition of a high-melting-point reinforcing phase. Laser additive manufacturing technology is characterized by high energy input, large temperature gradient, and fast solidification rate. Under this non-equilibrium solidification state, magnesium alloys will preferentially grow into a non-uniform, relatively fine dendritic structure with high internal energy. Furthermore, during cyclic deposition, some structures will remelt, leading to inhomogeneous interlayer structures and a reduced second-phase content, such as... Figure 1 As shown in (a1). Therefore, during the subsequent heat treatment process, the internal structure of laser additive manufacturing of magnesium alloys will undergo abnormal coarsening, forming irregularly shaped, abnormally large grains, such as... Figure 1 As shown in (a2), the mechanical properties of heat-treated magnesium alloys are severely reduced. This invention adds a certain amount of high-melting-point reinforcing phase material to magnesium alloy powder for laser additive manufacturing. During the laser additive manufacturing process, as the molten pool flows and solidifies, this material is uniformly distributed within the magnesium alloy microstructure, such as... Figure 1 As shown in (b1), it plays a role in refining and homogenizing the microstructure and stabilizing grain boundaries. Therefore, during subsequent heat treatment, the pinning effect of the high melting point reinforcement relative to the grain boundaries suppresses abnormal grain coarsening behavior, such as... Figure 1 As shown in (b2), it promotes the improvement of the mechanical properties of magnesium alloy.

[0027] The present invention also provides a magnesium alloy prepared by the method described above, wherein the average grain size of the magnesium alloy is 22~23μm, specifically 22.7μm.

[0028] The present invention also provides the application of the magnesium alloy described in the above technical solution in the aerospace field.

[0029] The method provided by this invention can suppress abnormal grain coarsening in laser-added magnesium alloys after heat treatment, and has the following advantages: Firstly, by introducing a high-melting-point reinforcing phase, this invention hinders grain boundary migration during heat treatment, suppresses abnormal grain coarsening, improves the microstructure of the heat-treated laser-added magnesium alloy, and promotes enhanced mechanical properties. Secondly, the high-melting-point reinforcing phase can improve the mechanical properties of the deposited laser-added magnesium alloy through grain refinement, dispersion strengthening, second-phase strengthening, and dislocation strengthening. This invention overcomes the problems of low absolute strength and stiffness, and poor load-bearing capacity in traditional laser-added magnesium alloys through the synergistic effect between the magnesium alloy matrix and the high-melting-point reinforcing phase.

[0030] In this invention, the introduction of the high-melting-point reinforcing phase into the magnesium alloy composite powder can reduce the laser energy directly acting on the surface of the alloy powder by improving the surface state of the magnesium alloy powder, thereby improving the stability of the interaction between the laser and the powder, and increasing the melt viscosity to cause the liquid phase to aggregate and reduce its surface deformation, thereby improving the forming accuracy and forming quality of the magnesium alloy laser additive component.

[0031] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0032] Example 1 Step 1: Select SiC particles with a particle size of 10~100μm as the reinforcing phase, and mix them with ZM6 alloy spherical powder (particle size of 75~150μm) at a mass ratio of 1:99. Place them in a micro omnidirectional planetary ball mill for ball milling at a speed of 100r / min for 5h. After ball milling, place the mixed powder in a drying oven and dry it at 100℃ for 5h to obtain the mixture. Step 2: Place the mixture into a laser additive manufacturing equipment for laser directional energy deposition. The process parameters are as follows: laser power 1000W, powder feed rate 0.6g / min, scanning spacing 1.2mm, scanning speed 5mm / s, and argon protection. Step 3: Place the product after laser-directed energy deposition into a heat treatment furnace for solution treatment to obtain a magnesium alloy; the solution treatment temperature is 525℃, the heating rate is 30℃ / min, the holding time is 8h, and it is water-cooled.

[0033] Comparative Example 1 Magnesium alloy components were prepared according to the method in Example 1, except that no reinforcing phase was added during the preparation process. The specific steps are as follows: Step 1: Using ZM6 alloy spherical powder (particle size 75~150μm) as raw material, place it in a drying oven and dry it at 100℃ for 5 hours; Step 2: Place ZM6 alloy spherical powder into a laser additive manufacturing equipment for laser directional energy deposition. The process parameters are as follows: laser power 1000W, powder feed rate 0.6g / min, scanning spacing 1.2mm, scanning speed 5mm / s, and argon protection. Step 3: Place the laser-directed energy deposition product into a heat treatment furnace for solution treatment (solution treatment temperature is 525℃, heating rate is 30℃ / min, holding time is 8h, water cooling) to obtain laser additive magnesium alloy components.

[0034] Magnesium alloys prepared in Example 1 and Comparative Example 1 were cut using a wire cutting machine to prepare metallographic samples. These samples were then polished sequentially using 200-3000 grit sandpaper at varying magnifications, from low to high. The polished metallographic samples were then examined using an optical microscope (OM), scanning electron microscope (SEM), and electron backscatter diffractometer (EBSD) to observe the internal grain size. The results are as follows: Figures 2-4 As shown, where, Figure 2 This is the result of the laser-directed energy deposition product obtained in step 2 of Comparative Example 1. Figure 3 The result is the laser-added magnesium alloy component obtained in step 3 of Comparative Example 1. Figure 4 The result is the magnesium alloy obtained in step 3 of Example 1.

[0035] Depend on Figure 2 It can be seen that the average grain size of the laser-added ZM6 alloy (the laser-directed energy deposition ZM6 alloy obtained in step 2 of Comparative Example 1) is 17.3 μm, and the maximum grain size is 29.8 μm; from Figure 3 It can be seen that after solution treatment, the laser additive manufacturing of ZM6 alloy (comparative Example 1, step 3, laser-directed energy deposition of ZM6 alloy after heat treatment) showed abnormal grain coarsening, with an average grain size of 28.6 μm and a maximum grain size of 377.7 μm; Figure 4 It can be seen that after solution treatment, the laser additive manufacturing of ZM6 / SiC alloy (laser-directed energy deposition ZM6 alloy obtained in step 3 of Example 1) did not show abnormal grain coarsening, with an average grain size of 22.7 μm and a maximum size of 61.5 μm.

[0036] Tensile tests were conducted at room temperature (25°C) on the laser-directed energy deposited ZM6 alloy obtained in step 2 of Comparative Example 1, the heat-treated laser-directed energy deposited ZM6 alloy obtained in step 3 of Comparative Example 1, and the heat-treated laser-directed energy deposited ZM6 alloy obtained in step 3 of Example 1, using a tensile testing machine according to GB / T 228.1 standard. The results are as follows: Figure 5 As shown, the strain rate is 0.5 mm / min.

[0037] Depend on Figure 5 It can be seen that the average tensile strength of the deposited laser additive ZM6 alloy is 173.7 MPa and the average yield strength is 119.4 MPa. After solution treatment, due to the formation of abnormally coarse grains, the tensile strength decreases significantly, with the average tensile strength dropping to 155.8 MPa and the average yield strength dropping to 73.9 MPa. By adding a high-melting-point reinforcing phase, the abnormal coarsening of grains is effectively suppressed. Combined with the second-phase strengthening effect, the tensile strength of the alloy is effectively improved, with the average tensile strength reaching 179.3 MPa and the average yield strength reaching 103.9 MPa.

[0038] The above test results prove that the preparation method provided by the present invention can effectively suppress grain coarsening during heat treatment and obtain a laser additive manufacturing alloy with good mechanical properties.

[0039] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method of laser additive manufacturing of a magnesium alloy, characterized in that, The method comprises the following steps: mixing a magnesium alloy powder and a high-melting-point reinforcing phase to obtain a mixed material; the high-melting-point reinforcing phase has a melting point of 2800-3900 ℃; and the mixed material is subjected to laser additive manufacturing and then heat treatment to obtain a magnesium alloy.

2. The method of laser additive manufacturing of a magnesium alloy according to claim 1, characterized in that The high-melting-point reinforcing phase comprises one or more of SiC, TiC, graphene and carbon nanotubes. The high-melting-point reinforcing phase has a morphology comprising fibers or particles. The particles have a particle size of 10-100 μm, and the fibers have a length of 5-20 μm.

3. The method of laser additive manufacturing of a magnesium alloy according to claim 1, characterized in that The magnesium alloy powder comprises a ZM5 magnesium alloy powder, a ZM6 magnesium alloy powder or an AZ91D magnesium alloy powder. The magnesium alloy powder comprises a laser powder bed fusion magnesium alloy powder or a laser directed energy deposition magnesium alloy powder. The laser powder bed fusion magnesium alloy powder has a particle size range of 15-53 μm. The laser directed energy deposition magnesium alloy powder has a particle size range of 75-150 μm.

4. The method of laser additive manufacturing of a magnesium alloy according to any one of claims 1 to 3, characterized in that The mixed material has a mass percentage of the high-melting-point reinforcing phase of 30% or less.

5. The method of laser additive manufacturing of a magnesium alloy according to claim 4, characterized in that The mixing method comprises ball milling at a rotation speed of 50-150 r / min for 2-6 h. The mixed material is dried to obtain the mixed material; the drying is performed at a temperature of 80-150 ℃ for 2-8 h.

6. The method of laser additive manufacturing of a magnesium alloy according to claim 1, wherein, The laser additive manufacturing comprises a laser powder bed fusion process or a laser directed energy deposition process. The laser powder bed fusion process has a laser power of 50-200 W, a powder layer thickness of 0.02-0.05 mm, a scanning interval of 50-150 μm, a scanning speed of 100-500 mm / s, a light spot diameter of 0.08-0.1 mm and argon protection. The laser directed energy deposition process has a laser power of 1000-1400 W, a powder feeding rate of 0.4-0.8 g / min, a scanning interval of 1.0-1.5 mm, a scanning speed of 3-7 mm / s and argon protection.

7. The method of laser additive manufacturing of a magnesium alloy according to claim 1, wherein, The heat treatment comprises annealing treatment or solid solution treatment.

8. The method of laser additive manufacturing of a magnesium alloy according to claim 7, characterized in that The annealing treatment has a temperature of 270-350 ℃, a temperature rising rate of 10-50 ℃ / min, a holding time of 60-90 min and furnace cooling. The solid solution treatment has a temperature of 420-540 ℃, a temperature rising rate of 28-32 ℃ / min, a holding time of 4-12 h and water cooling.

9. The magnesium alloy produced according to the method of any one of claims 1 to 8, characterized in that, The magnesium alloy has an average grain size of 22-23 μm.

10. Use of the magnesium alloy of claim 9 in the field of aerospace.

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