A method for inhibiting crack initiation of 3D printing laser formed aluminum-copper alloy

Abstract

The application discloses a method for inhibiting crack initiation of 3D printing laser forming Al-Cu alloy, which comprises the following steps: (1) mixing Al-Cu alloy powder with Sc2O3 powder, ball milling to obtain Al-Cu / Sc2O3 mixed powder; (2) laser 3D printing forming on the mixed powder, and controlling the laser scanning speed to be 300-500 mm / s. Through high-speed modification of the original powder and laser 3D printing Al-Cu alloy laser process control, the crack sensitivity problem of laser 3D printing forming Al-Cu series and other precipitation strengthening high-strength aluminum alloys is solved, and high-efficiency and high-quality crack-free forming of laser 3D printing Al-Cu alloy is realized. The method provides a possibility for topological optimization design of aerospace part structures, and the formed parts can be applied to the industries with great demand for light-weight high-strength complex structural parts, such as aerospace and communication transmission, and have strong operability and wide application range.

Description

Technical Field

[0001] This invention relates to a method for suppressing the initiation of cracks in aluminum alloys, and more particularly to a method for suppressing the initiation of cracks in 3D-printed laser-formed aluminum-copper alloys. Background Technology

[0002] Laser 3D printing technology currently focuses on two main directions, one of which is selective laser melting (SLM) technology for precision parts. In SLM, computer software first processes the 3D part model into several 2D slices. During the forming process, a layer of metal powder is evenly spread on the substrate using a precision powder spreading device. A high-energy laser beam, under computer control, selectively melts / solidifies the metal powder according to the 2D information of the slices. Then, the substrate is lowered, and the powder spreading device continues to spread metal powder layers on the solidified layer. The laser melts and solidifies the powder, and this process is repeated until the part is formed. Currently, laser 3D printing technology can form some materials such as titanium alloys, aluminum alloys, nickel-based superalloys, and stainless steel, and has significant application prospects in aerospace, defense, and transportation.

[0003] Currently, laser 3D printing of aluminum alloys mainly faces two bottlenecks: First, the most commonly used alloys in laser 3D printing are cast Al-Si alloys. These alloys are eutectic alloys with a narrow solidification range and good weldability, thus exhibiting good formability for laser 3D printing. However, due to the material properties of this alloy, its strength and toughness are limited. Currently, the tensile strength of laser-printed Al-Si alloys is <400MPa, and the elongation is less than 6%, which is insufficient to meet the performance requirements of aerospace and other fields. Second, for commonly used high-strength aluminum alloys in traditional processing, especially Al-Cu and Al-Zn alloys that are mainly strengthened by precipitation, their solidification range is relatively wide. Because the laser additive manufacturing process involves a high-speed melting / solidification process, the instantaneous cooling rate can reach 1000 kJ / m³. 6 -10 7 K / s, which can easily cause solidification cracks when the liquid phase cannot fill the solidification gap at the solidification end of the solidification of Al-Cu alloys formed by laser 3D printing, and thus cause defects such as cracking and warping, resulting in the failure of laser 3D printed Al-Cu components.

[0004] Aluminum alloys are one of the commonly used materials for components in the aerospace field. However, due to the aforementioned problems, the application of laser 3D printing of aluminum alloys in the aerospace field is severely limited. How to effectively suppress crack initiation during laser 3D printing and form high-quality Al-Cu alloy components has become one of the key technical challenges that urgently need to be solved in the field of laser 3D printing of complex components. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a method that can effectively suppress the initiation of cracks in 3D printed laser-formed aluminum-copper alloys.

[0006] Technical solution: The method for suppressing crack initiation in 3D-printed laser-formed aluminum-copper alloys according to the present invention includes the following steps:

[0007] (1) Al-Cu alloy powder and Sc2O3 powder are mixed and ball-milled to obtain Al-Cu / Sc2O3 mixed powder;

[0008] (2) The mixed powder is laser 3D printed and the laser scanning speed is controlled to be 300-500mm / s.

[0009] In step (1), the Sc2O3 powder accounts for 1-1.5 wt.% of the composite powder by mass.

[0010] In step (1), Al-Cu alloy powder and Sc2O3 powder are mixed by high-speed rotary ball milling under a protective atmosphere to obtain Al-Cu / Sc2O3 mixed raw powder. The particle size of the Al-Cu alloy spherical powder is 15-45 μm; the particle size of the Sc2O3 powder is 2-5 μm. Preferably, a number of corundum balls are placed in the ball mill jar to accelerate mixing. Preferably, the ratio of corundum balls to raw materials is 2:1, the rotation speed is r = 350 r / min, and the ball milling time is t = 4 h.

[0011] In step (2), the forming base plate is preheated during the laser 3D printing process; the preheating temperature is 200-300℃ and remains constant throughout the forming process.

[0012] In step (2), the laser power is controlled at 375W-425W; the laser scanning layer thickness is 30μm; the scanning interval is 70μm; and the oxygen content in the forming cavity is less than or equal to 50ppm. Under these process parameters, the high quality of the laser 3D printed dilute Al-Cu / Sc2O3 mixed powder can be further guaranteed. Compared with the laser 3D printed Al-Si aluminum alloy, the scanning speed is significantly reduced under these process parameters, which can effectively reduce the melt solidification rate and the tendency for hot cracking during melt solidification.

[0013] In step (2), during the forming process, the powder spreading device first spreads the mixed powder evenly on the forming base plate, and the high-energy laser beam selectively melts the powder layer under computer control. Then the forming base plate is lowered by one layer thickness, and the powder spreading device spreads the powder again. The above process is repeated until the specimen is processed.

[0014] Invention Principle: Based on the aforementioned high-speed mixing and modification of the original powder and the limitation of laser process parameters, the tendency of intergranular cracking at the solidification end during laser 3D printing of Al-Cu alloys can be effectively suppressed, significantly improving the laser 3D printing formability of Al-Cu components. Its underlying mechanism is as follows: Figure 2 The main point is to modify the original powder with high-speed Sc2O3 mixing to obtain a uniformly mixed Al-Cu / Sc2O3 powder. During subsequent processing, the extremely high temperature under laser transient action causes Sc2O3 to decompose, producing Sc and O elements in the melt. The Sc element reacts with the molten Al matrix: Al + Sc → Al3Sc. Al3Sc, as a precipitate, acts as a nucleating agent in the Al matrix, significantly refining the grains and transforming coarse columnar crystals into fine equiaxed crystals, reducing the tendency for intergranular cracking. Simultaneously, the decomposed O element can be captured by trace amounts of Mg in the Al-Cu alloy and reacts with the Al matrix to produce Al + Mg + O → Al2MgO4. This precipitate serves both as a nucleating agent for the Al matrix to refine the grains and as a nucleation site for Al3Sc precipitation, promoting the precipitation of the Al3Sc phase. By controlling the laser process at a lower scanning speed while simultaneously supplementing it with a high substrate preheating temperature, it is possible to reduce the melt solidification rate and increase the liquid phase filling solidification gap time. On the other hand, it is possible to reduce the temperature gradient, thereby reducing the tendency of internal stress and inhibiting crack initiation.

[0015] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects: (1) By high-speed mixing and modification of the original powder and laser process control of Al-Cu alloy laser 3D printing, the crack sensitivity problem of precipitation-strengthened high-strength aluminum alloys such as Al-Cu system in laser 3D printing is solved, and efficient, high-quality, crack-free forming of Al-Cu alloy in laser 3D printing is realized. (2) High-quality integrated forming of Al-Cu alloy in laser 3D printing is realized. (3) Compared with traditional casting, forging, powder metallurgy and subtractive machining methods, the present invention makes it possible to form high-strength aluminum alloy components by laser 3D printing, which greatly shortens the forming cycle of parts, improves the design freedom of components, and significantly reduces the waste rate of raw materials. It provides the possibility for the topology optimization design of aerospace parts. The formed parts can be applied to industries such as aerospace and communication transmission that have a great demand for lightweight, high-strength, and complex structural parts. It is highly operable and has a wide range of applications. (4) While making precipitation-strengthened aluminum alloy 3D printing possible, it does not involve major modifications or changes to the forming equipment. It has strong universality for existing commercial laser additive manufacturing 3D printing equipment and can be quickly used in current industrial research and development and production. It is economical, practical and highly scalable. Attached Figure Description

[0016] Figure 1This is a process flow diagram of a method for suppressing crack initiation in Al-Cu alloys in 3D printing laser rapid prototyping, as described in this invention.

[0017] Figure 2 This is a schematic diagram of the process mechanism of the method for suppressing crack initiation in Al-Cu alloys in 3D printing laser rapid prototyping according to the present invention;

[0018] Figure 3 This is an optical image of the microstructure of the 3D-printed laser rapid prototyping Al-Cu alloy obtained in Example 1 of the present invention;

[0019] Figure 4 This is an optical image of the microstructure of the 3D-printed laser rapid prototyping Al-Cu alloy obtained in Example 3 of the present invention;

[0020] Figure 5 This is an optical image of the microstructure of the 3D-printed laser rapid prototyping Al-Cu alloy obtained in Example 5 of the present invention;

[0021] Figure 6 This is an optical image of the microstructure of the 3D-printed laser rapid prototyping Al-Cu alloy obtained in Example 6 of the present invention;

[0022] Figure 7 This is an optical image of the microstructure of the 3D-printed laser rapid prototyping Al-Cu alloy obtained in Example 7 of the present invention;

[0023] Figure 8 This is an optical image of the microstructure of the 3D-printed laser rapid prototyping Al-Cu alloy obtained in Example 10 of the present invention.

[0024] Figure 9 This is an optical image of the microstructure of the 3D-printed laser rapid prototyping Al-Cu alloy obtained in Example 11 of this invention.

[0025] Figure 10 This is an optical image of the microstructure of the 3D-printed laser rapid prototyping Al-Cu alloy obtained in Example 13 of the present invention. Detailed Implementation

[0026] The present invention will now be described in further detail.

[0027] Example 1

[0028] like Figure 1 As shown, the present invention provides a method for suppressing crack initiation in Al-Cu alloys in 3D printing laser rapid prototyping, comprising the following steps:

[0029] (1) The Al-Cu alloy powder prepared by gas atomization was used as the original powder, with a particle size of 15-45 μm. The original Al-Cu alloy powder with a particle size of 15-45 μm was modified by Sc2O3 powder with a particle size of 2-5 μm through high-speed rotary mixing in an Ar atmosphere to obtain a Sc2O3 / Al-Cu mixed powder. The weight percentage of Sc2O3 powder was 0%.

[0030] (2) For laser 3D printing of mixed powder, during the forming process, the powder spreading device first evenly spreads a 30μm thick layer of mixed powder on the forming base plate. Under computer control, the high-energy laser beam selectively melts the powder layer. Then, the forming base plate is lowered by one layer thickness, and the powder spreading device spreads powder again. The above process is repeated until the specimen is processed. The cavity is kept in an argon atmosphere throughout the forming process, with an oxygen content of less than 50ppm. The laser scanning speed is set to 400mm / s, the base plate preheating temperature is 300℃, the laser power is 400W, the powder thickness is 30μm, the scanning interval is 60μm, the forming strategy is a partitioned island scanning, and the laser spot diameter is 70μm.

[0031] At this point, the molded specimen exhibited a severe tendency for microcracks, with a density of 98.5% and a tensile strength of 230.6 MPa, indicating poor mechanical properties. The underlying mechanism of this invention is as follows: Figure 2 As shown.

[0032] Example 2

[0033] Based on Example 1, the difference is that the Sc2O3 content is 0.5 wt.%. At this time, the molded sample showed a serious tendency for microcracks, with a density of 99.2%. The tendency for microcracks was improved compared to Example 1. The tensile strength of the specimen was 120.3 MPa, and the mechanical properties were poor.

[0034] Example 3

[0035] Based on Example 1, the difference is that the Sc2O3 content is 1 wt.%. At this time, the molded sample has no tendency for microcracks, the density is 99.4%, the tensile strength of the specimen is 410.7 MPa, and the mechanical properties are excellent.

[0036] Example 4

[0037] Based on Example 1, the difference is that the Sc2O3 content is 1.5 wt.%. At this time, the molded specimen showed no tendency for microcracks, had a density of 98.7%, and a tensile strength of 322.9 MPa. The mechanical properties were lower than in Example 3. This is because the higher additive content reduced melt fluidity, resulting in more residual porosity inside the molded specimen, which reduced the specimen's density and mechanical properties.

[0038] Example 5

[0039] Based on Example 1, the difference is that the Sc2O3 content is 2 wt.%. At this time, the molded sample has no tendency for microcracks, the density is 98.1%, and the tensile strength of the specimen is 240.3 MPa. The mechanical properties are lower than those of Example 4. This is because the increased content of additives leads to a further increase in the residual porosity inside the molded specimen.

[0040] Figure 3 The image shows an optical image of the molded specimen from Example 1, revealing a clear tendency for cracking.

[0041] Figure 4 The image shows an optical image of the molded specimen from Example 3. It can be seen that microcracks are significantly suppressed at an additive content of 1 wt.%, and the specimen is continuous and dense at this point.

[0042] Figure 5 The image shows an optical image of the formed specimen from Example 5. It can be seen that the porosity of the specimen increases significantly when the content of the additive is too high.

[0043] Based on the above Examples 1-5, it can be found that the initiation of microcracks in the molded specimens is closely related to the content of the additives. When the Sc2O3 additive content is low, at 0 and 0.5 wt.%, the microcracks in the specimens cannot be completely eliminated. When the Sc2O3 additive content is high, at 1.5-2 wt.%, the excessive content leads to an increase in residual porosity inside the specimens and a decrease in mechanical properties. Therefore, 1-1.5 wt.% is a more suitable Sc2O3 additive content.

[0044] Example 6

[0045] Based on Example 3, the difference is that the laser scanning speed is set to 200 mm / s.

[0046] At this point, the specimen showed no obvious tendency for microcracks, with a density of 98.2% and a mechanical property of 360.8 MPa.

[0047] Figure 6 The image shows an optical image of the formed sample from Example 6. It can be seen that there are a few metallurgical defects inside the sample. This is because the laser scanning speed is too slow, resulting in excessive energy input. Some low-melting-point elements in the mixed powder evaporate, leaving pores. At this time, the mechanical properties are not high due to the reduced density.

[0048] Example 7

[0049] Based on Example 3, the difference is that the laser scanning speed was set to 600 mm / s. At this speed, the specimen showed no obvious tendency for microcracks, had a density of 98.3%, and a mechanical property of 310.1 MPa.

[0050] Figure 7 The optical image of the formed sample in Example 7 shows that there are a few microcracks inside the sample. This is because the laser scanning speed is too fast, which leads to the accelerated solidification speed of the melt. The liquid phase does not have enough time to fill the solidification gap, resulting in the initiation of microcracks. At this time, the mechanical properties are not high due to the presence of cracks.

[0051] Example 8

[0052] Based on Example 3, the difference is that the laser scanning speed was set to 300 mm / s. At this speed, the specimen showed no obvious tendency for microcracks, had a density of 99.1%, and a mechanical property of 396.2 MPa.

[0053] Example 9

[0054] Based on Example 3, the difference is that the laser scanning speed was set to 500 mm / s. At this speed, the specimen showed no obvious tendency for microcracks, had a density of 99.0%, and a mechanical property of 402.7 MPa.

[0055] Based on Examples 3, 6, 7, 8, and 9, it can be observed that the laser scanning speed during the forming process significantly affects the crack initiation and mechanical properties of the formed specimen. When the laser scanning speed is too low (200 mm / s), the porosity of the specimen increases due to the evaporation problem caused by excessive energy. When the laser scanning speed is too high (600 mm / s), the liquid phase cannot fill the solidification gap due to the fast solidification speed, resulting in the initiation of microcracks. Therefore, a good crack suppression effect and mechanical properties are obtained when the laser scanning speed is in the range of 300-500 mm / s.

[0056] Example 10

[0057] Based on Example 3, but differing from Example 3, the preheating temperature of the base plate was 0°C, i.e., the base plate preheating function was not used. At this time, the formed specimen showed a severe tendency to crack, with a density of 98.7% and a tensile strength of 190.2 MPa.

[0058] Example 11

[0059] Based on Example 3, but differing from Example 3, the preheating temperature of the base plate was 150°C. At this temperature, the formed specimen exhibited a slight tendency to crack, a density of 99.0%, and a tensile strength of 270.6 MPa.

[0060] Example 12

[0061] Based on Example 3, but differing from Example 3, the preheating temperature of the base plate was 200°C. At this temperature, the formed specimen showed no tendency to crack, had a density of 99.2%, and a tensile strength of 370.6 MPa.

[0062] Example 13

[0063] Based on Example 3, the difference is that the preheating temperature of the base plate is 400℃. At this temperature, the formed specimen shows no tendency to crack, has a density of 98.9%, and a tensile strength of 330.8 MPa.

[0064] Figure 8 The optical image of the formed specimen in Example 10 shows that the specimen has a clear tendency to crack when preheated without a base plate.

[0065] Figure 9 The image shows an optical image of the formed sample from Example 11, which reveals that microcracks still exist even after preheating the base plate at 150°C.

[0066] Figure 10 The image shows an optical image of the formed specimen from Example 13. It can be seen that the porosity of the specimen increases significantly when the preheating temperature of the base plate is too high.

[0067] Based on Examples 3, 10, 11, 12, and 13, it can be observed that the preheating temperature of the substrate plays a crucial role in crack suppression during laser 3D printing of Al-Cu alloys. When there is no substrate preheating or the preheating temperature is too low, the high temperature gradient easily generates significant internal stress in the specimen, accelerating the solidification process and leading to crack initiation. While excessively high substrate preheating temperatures effectively suppress cracking, the high temperatures also make the processing unstable, resulting in numerous pores in the specimen and a decline in mechanical properties. In summary, using a substrate preheating temperature of approximately 200-300℃ yields specimens with good crack suppression and mechanical properties.

[0068] The mechanical properties of the laser 3D printed Al-Cu high-strength aluminum alloys prepared in each embodiment are detailed in Table 1 below.

[0069] Table 1 Mechanical properties of laser-printed Al-Cu high-strength aluminum alloys prepared in different embodiments

[0070]

Claims

1. A method for suppressing crack initiation in 3D-printed laser-formed aluminum-copper alloys, characterized in that, Includes the following steps: (1) Al-Cu alloy powder and Sc2O3 powder are mixed and ball-milled to obtain Al-Cu / Sc2O3 mixed powder; the Sc2O3 powder accounts for 1-1.5 wt.% of the composite powder by mass. (2) The mixed powder is laser 3D printed and the laser scanning speed is controlled to be 300-500 mm / s; During the laser 3D printing process, the forming base plate is preheated; the preheating temperature is 200-300℃.

2. The method for suppressing crack initiation in 3D-printed laser-formed aluminum-copper alloys according to claim 1, characterized in that, In step (2), the laser power is controlled to be 375 W-425 W.

3. The method for suppressing crack initiation in 3D-printed laser-formed aluminum-copper alloys according to claim 1, characterized in that, In step (2), the thickness of the laser scanning layer is controlled to be 30 μm and the scanning interval is 70 μm.

4. The method for suppressing crack initiation in 3D-printed laser-formed aluminum-copper alloys according to claim 1, characterized in that, In step (1), the particle size of the Sc2O3 is 2-5 μm.

5. The method for suppressing crack initiation in 3D-printed laser-formed aluminum-copper alloys according to claim 1, characterized in that, In step (1), the particle size of the Al-Cu alloy powder is 15-45 μm.

6. The method for suppressing crack initiation in 3D-printed laser-formed aluminum-copper alloys according to claim 1, characterized in that, In step (1), Al-Cu alloy powder and Sc2O3 powder are mixed by high-speed rotation under an inert atmosphere to obtain Al-Cu / Sc2O3 mixed powder.

7. The method for suppressing crack initiation in 3D-printed laser-formed aluminum-copper alloys according to claim 1, characterized in that, In step (2), during the forming process, the powder spreading device first evenly spreads the mixed powder on the forming base plate, and the high-energy laser beam selectively melts the powder layer under computer control. Then the forming base plate is lowered by one layer thickness, and the powder spreading device spreads the powder again. The above process is repeated until the specimen is processed.

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