Electron beam selective melting additive manufacturing method for Al-Si-Mg alloys

Abstract

This invention discloses a method for electron beam selective melting additive manufacturing of Al-Si-Mg alloys, comprising: providing Al-Si-Mg alloy powder for 3D printing; loading a forming base plate into an electron beam 3D printing device and adjusting the height of the base plate; preheating the base plate to no more than 480°C under vacuum conditions and holding at that temperature; uniformly spreading the Al-Si-Mg alloy powder onto the preheated base plate, and performing electron beam printing including the following processes: preheating before the powder bed – selective melting – postheating after the powder bed; repeating the process of lowering the base plate height, spreading powder, and electron beam printing until all layers are printed. This invention achieves stable and high-quality forming of Al-Si-Mg aluminum alloys by designing the matching between powder characteristics and process parameters in electron beam selective melting additive manufacturing of Al-Si-Mg alloys.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, and specifically to a method for selective electron beam melting additive manufacturing of Al-Si-Mg alloys. Background Technology

[0002] Additive manufacturing (or 3D printing) technology based on layer-by-layer selective melting of metal powder beds can rapidly form high-performance structural parts with complex shapes, and has great application prospects in aerospace, rail transportation and biomedicine.

[0003] Selective laser melting (SLM) and electron beam selective melting (EBSM) use high-energy lasers and electron beams as energy sources, respectively, to selectively melt metal powder into tiny molten pools along a preset scanning path. The process scans layer by layer from bottom to top, ultimately obtaining a near-net-shape part. The printing process generates an extremely fast cooling rate (10⁻⁶ m / s). 3 ~10 7 The extremely high temperature gradient (K / S) and repeated thermal cycling can lead to large residual stress inside the material, causing the printed alloy to be prone to cracking.

[0004] Compared to SLM technology, the high vacuum environment and preheating of the powder bed in EBSM effectively avoid the problems faced by SLM-printed aluminum alloys, such as easy oxidation, high laser reflectivity, high residual stress, and easy cracking. At the same time, the high energy utilization of the electron beam allows for rapid melting of metal powder, significantly improving manufacturing efficiency. However, currently, only 2XXX series (Al-Cu series) aluminum alloys and AlSi10Mg from the cast Al-Si series are suitable for EBSM printing. In Al-Si-Mg series aluminum alloys, the addition of Mg strengthens the alloy, resulting in a narrow solidification temperature range, good fluidity, and low heat transfer tendency.

[0005] In EBSM technology, the higher energy density of the electron beam leads to faster forming efficiency, but it also causes the evaporation (elemental loss) of low-boiling-point elements (such as Al and Mg) in the aluminum alloy. This results in less precipitation of the Mg2Si strengthening phase during subsequent heat treatment, leading to a decrease in material strength. Furthermore, while the preheating process of the powder bed can effectively reduce stress accumulation during forming and slightly sinter the powder, inappropriate preheating parameters can cause abnormal changes in the powder bed state (such as powder blowing due to insufficient sintering or peeling due to excessive energy). This further leads to problems with forming during the melting stage. For the melting stage, the electron beam energy input plays a decisive role in the alloy's formability. Too low an energy level easily leads to defects such as porosity and cracks, while too high an energy level easily leads to deformations such as bulging and warping. These are all key issues in forming Al-Si-Mg alloys using EBSM technology, affecting the further engineering applications of this alloy.

[0006] [Patent Application 202310087790.0] Complex compositional modification of aluminum alloy powder is required to ensure its EBSM formability.

[0007] [Patent Application 202311842243.5] focuses on local preheating of the powder bed to ensure the stability of the printing process. This patent is an EBSM forming method for the entire aluminum alloy category, with the embodiments focusing on AlZnMgCu alloys, but it does not provide suitable process parameters for the entire printing process.

[0008] Therefore, it is necessary to comprehensively design the entire process method for EBSM printing of Al-Si-Mg alloys in order to achieve high-quality forming and expand the application range of high-performance aluminum alloy structural parts with complex shapes. Summary of the Invention

[0009] To address the aforementioned technical problems and shortcomings in this field, this invention provides an electron beam selective melting additive manufacturing method for Al-Si-Mg alloys. By designing the matching between powder characteristics and process parameters in the electron beam selective melting additive manufacturing of Al-Si-Mg alloys, and by combining appropriate processes such as base plate preheating, powder bed preheating, and selective melting according to the characteristics of the metal powder, the method ensures stable sintering between powders during preheating, guarantees stable evolution of the molten pool during melting, and avoids abnormalities such as powder blowing, peeling, powder pushing, bulging, and warping during the printing process, thereby achieving stable and high-quality forming of Al-Si-Mg aluminum alloys.

[0010] The specific technical solutions are as follows:

[0011] A method for electron beam selective melting additive manufacturing of Al-Si-Mg alloys, comprising:

[0012] Provided Al-Si-Mg alloy powder for 3D printing; the composition of the Al-Si-Mg alloy powder by mass percentage is Si: 6% to 20%, Mg: 0.2% to 3%, Fe: <0.7%, with the balance being Al and unavoidable impurities;

[0013] The forming base plate is installed into the electron beam 3D printing equipment, the height of the base plate is adjusted, and the pre-lowering amount of the base plate is set to 3 to 10 times the thickness of the slice layer to compensate for the expansion of the base plate during preheating.

[0014] Preheat the base plate to no more than 480°C (e.g., 200°C, 300°C, etc.) under vacuum conditions and keep it at that temperature to ensure that the powder can quickly sinter together during the preheating process;

[0015] The Al-Si-Mg alloy powder was uniformly spread onto a preheated substrate and then subjected to electron beam printing, which included the following processes: preheating before the powder bed, selective melting, and postheating after the powder bed. The parameters for preheating before and after the powder bed included: accelerating voltage of 60 kV and volume energy density of 0.1–2 J / mm². 3 (e.g., 0.5 J / mm) 3 The preheating time is 5–50 s (e.g., 18 s), and the postheating time is 0–50 s; the parameters for selective melting include: accelerating voltage of 60 kV and solid energy density of 15–70 J / mm³. 3 (e.g., 16.8 J / mm) 3 18.1 J / mm 3 39.2J / mm 3 (etc.), the energy density of the contour volume is 7–20 J / mm. 3 (e.g., 12.5J / mm) 3 (etc.), the amount of powder taken is 1.1 to 1.8 times the thickness of the slice layer (e.g., 1.2 times, etc.);

[0016] Repeat the process of lowering the base plate height, spreading powder, and electron beam printing until all layers are printed.

[0017] In this invention, the surface of the printed component is an outline, while the rest is a solid.

[0018] To avoid collision between the base plate and the squeegee used for powder spreading caused by thermal expansion during preheating, the base plate needs to be lowered a certain height beforehand. However, excessive lowering can lead to poor contact between the first few layers of formed solids and the base plate, resulting in warping. This can affect the forming quality or even terminate printing. Preferably, the pre-lowering amount of the base plate is set to 3 to 10 times the thickness of the slice layer, for example, 4 times, depending on the base plate preheating temperature.

[0019] The preheating process before and after printing of the powder bed in this invention ensures slight sintering between powder particles before printing and maintains the optimal temperature of the powder bed after printing, avoiding abnormalities such as powder blowing or peeling. The electron beam used for preheating can be either defocused or focused.

[0020] The electron beam selective melting additive manufacturing method for Al-Si-Mg alloys described above has an Al-Si-Mg alloy powder with a particle size range of 0.035–0.15 mm, and more specifically 0.04–0.1 mm, which can meet the requirements for powder layer thickness.

[0021] The electron beam selective melting additive manufacturing method for Al-Si-Mg alloys, in order to further improve the Mg-related reinforcing phase in the EBSM-printed alloy and reduce the hot cracking tendency of the alloy, specifies that, by mass percentage, the Si content in the Al-Si-Mg alloy powder is near the eutectic composition point, preferably 9% to 13%, more preferably 11% to 12%, such as 11.82%, and the Mg content is preferably 0.4% to 3%, more preferably 2% to 3%, such as 2.3%.

[0022] The electron beam selective melting additive manufacturing method for Al-Si-Mg alloys described above, wherein the vacuum conditions are achieved through the following operation: the vacuum degree of the forming chamber reaches 2.5 × 10⁻⁶. -2 Pa (preferred 10) -3 Pa can further ensure that the vacuum degree and oxygen content of the forming chamber are below 0.15-0.2 Pa. Inert gas is filled in to stabilize the vacuum degree in the range of 0.15-0.2 Pa.

[0023] In this invention, inert gas refers to a gas that does not participate in the reaction, such as helium, argon, and other rare gases.

[0024] In the electron beam selective melting additive manufacturing method for Al-Si-Mg alloys, after the base plate is preheated to no more than 480°C, the base plate can be kept warm with a current of 1-5mA (or even 1-3mA) for at least 5 minutes.

[0025] The electron beam selective melting additive manufacturing method for Al-Si-Mg alloys described above allows for a slice layer thickness of 0.03–0.12 mm, and more specifically 0.05–0.08 mm.

[0026] In the electron beam selective melting additive manufacturing method for Al-Si-Mg alloys, the interlayer rotation angle during electron beam printing can be 90°, 67°, or 30°.

[0027] The electron beam selective melting additive manufacturing method for Al-Si-Mg alloys can employ defocused electron beam selective melting, and the defocusing amount can be negative, and further, it can be -0.5V.

[0028] The electron beam selective melting additive manufacturing method for Al-Si-Mg alloys can also employ focused electron beam selective melting.

[0029] In this invention, the volume energy density (VED) can be calculated based on the electron beam accelerating voltage U, current I, scanning speed V, slice thickness L, and scanning spacing H. The calculation formula is: VED = (UI) / (VLH).

[0030] The electron beam selective melting additive manufacturing method for Al-Si-Mg alloys produces Al-Si-Mg alloy 3D parts with a density greater than the theoretical density of the alloy (2.68 g / cm³). 3 98%, preferably greater than the theoretical density of the alloy (2.68 g / cm³). 3 99%.

[0031] Compared with the prior art, the beneficial effects of this invention are as follows:

[0032] This invention fills the technological gap in the selective electron beam melting (EBSM) additive manufacturing of Al-Si-Mg alloys. The selection of suitable powder and process parameters avoids common anomalies during EBSM printing, such as powder blowing, warping, bulging, and peeling, ensuring a stable forming process and high-quality results. Simultaneously, the optimization of the alloy composition expands the range of aluminum alloys suitable for EBSM printing. Adjusting the Si content in the powder ensures excellent casting properties; increasing the Mg content guarantees a Mg balance in the printed alloy, improving the strength of the aluminum alloy. This has significant practical implications for the further application of complex-shaped aluminum alloy structural components. Attached Figure Description

[0033] Figure 1 This is a photograph of the Al-Si-Mg alloy bulk sample printed by EBSM in Example 1.

[0034] Figure 2 This is a typical microstructure photograph of the Al-Si-Mg system printed alloy in Example 1.

[0035] Figure 3 This is a typical room temperature tensile curve of the printed alloy in Example 1.

[0036] Figure 4 This is a photograph of the tensile fracture morphology of the printed alloy in Example 1.

[0037] Figure 5 These are photographs of bulk alloy samples printed by EBSM under different bulk energy densities in Example 2.

[0038] Figure 6 This is a relative density diagram of the EBSM-printed alloy under different physical energy densities in Example 2.

[0039] Figure 7 This is a photograph of the powder bed sintering process in Comparative Example 1.

[0040] Figure 8 The image shows the surface morphology of the printed alloy in Comparative Example 2. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer.

[0042] Example 1:

[0043] This embodiment provides a stable forming method for electron beam selective melting additive manufacturing of Al-Si-Mg alloys, including the following steps:

[0044] S1. Composition Design. To reduce the cracking tendency of Al-Si-Mg alloys during EBSM printing and narrow the solidification temperature range of the alloy, the Si content was fixed near the eutectic point. At the same time, to improve the strength of the alloy in the printed state and after heat treatment, the Mg content in the printed alloy was increased. By mass percentage, the Si content in the aluminum alloy powder was 11.82%, the Mg content was 2.30%, the Fe content was <0.7%, and the balance was Al and unavoidable impurities.

[0045] S2. Screen the aluminum alloy powder particle size to meet the requirements for powder layer thickness. The particle size range of aluminum alloy powder used in EBSM is 0.04~0.1mm.

[0046] S3. EBSM Pre-printing Processing. Determine the placement of the parts to be printed in any pre-modeling software; input parameters such as slice layer thickness and electron beam scanning path planning in the slicing software corresponding to the EBSM device to obtain the printing project file.

[0047] S4. Powder loading and base plate leveling. Stainless steel is selected as the forming base plate. The sieved aluminum alloy powder and the forming base plate are loaded into the printing equipment. The base plate is leveled and lowered a certain height to compensate for the thermal expansion during the preheating of the base plate.

[0048] To avoid collision between the preheated base plate and the scraper caused by thermal expansion, the forming base plate needs to be lowered by a certain height. Based on the preheating temperature of the base plate, the pre-lowering amount of the base plate is set to 4 times the layer thickness.

[0049] S5. Evacuate the equipment. Wait for the vacuum level in the forming chamber to reach 10. -3 Below Pa, fill with inert gas and maintain for 3-5 minutes. Helium is used as the inert gas. Wait until the vacuum degree reaches 1.5 × 10⁻⁶ Pa.-1 After the voltage stabilizes near Pa, turn on the high-voltage power supply.

[0050] S6. Preheat the forming base plate. Preheat the forming base plate to the preset temperature of 300℃ and hold it at that temperature for 5 minutes using a current of 1-3mA.

[0051] S7. Powder bed preheating. Based on the size of the formed base plate and the state of the powder bed after preheating, the accelerating voltage is 60kV, and the volume energy density is 0.5J / mm². 3 The preheating time is 18 seconds to ensure the sintering of the powder particles. In this embodiment, a focused electron beam is used to preheat the substrate.

[0052] S8. Selective Melting. Input the forming process parameters into the EBSM printing equipment, which then performs selective melting on the forming base plate according to the preset parameters.

[0053] To ensure successful forming and high printing quality of Al-Si-Mg alloys using EBSM printing, the preferred process parameters are: accelerating voltage 60kV and bulk energy density 18.1J / mm². 3 The energy density of the contour volume is 12.5 J / mm². 3 The powder amount is 1.2 times the slice thickness, and defocused electron beam selective melting is used with a defocusing amount of -0.5V.

[0054] S9. Repeat steps S7 and S8 until printing is complete, then perform post-processing. Remove the printed sample from the oven, clean it, and characterize its microstructure and properties.

[0055] The morphology of the block sample printed according to this embodiment is as follows: Figure 1 As shown, EBSM-printed Al-Si-Mg alloys lack the Si network structure found in SLM-formed alloys of the same type. Figure 2 As shown, this structure is detrimental to the alloy's plasticity. The printed alloy was then subjected to a stretching machine at 10... -3 S -1 Uniaxial tensile strain at a given strain rate yielded the room temperature tensile curve as shown below. Figure 3 As shown, the yield strength is 90.5 MPa, the tensile strength is 164.9 MPa, and the elongation is 10.7%. Tensile fracture morphology (e.g.) Figure 4 The presence of numerous dimples in the fracture indicates that the fracture mode is ductile fracture.

[0056] Example 2:

[0057] The alloy powder composition in Example 2 is the same as that in Example 1, and the printing process is basically the same.

[0058] The difference lies in the energy density of the solid material used in the selective melting process of step S8. The energy densities of the solid materials are 16.8, 18.1, 18.8, 23.5, 24.9, 25.1, and 26.14 J / mm², respectively. 3 And repeat the printing process. The morphology of the printed alloy at different volume energy densities is as follows: Figure 5 As shown, the alloy can be formed within this range, indicating that the printing method (process parameters) ensures the basic formability of the alloy. The forming quality can be judged based on the surface morphology of the printed alloy; under different process parameters, different types of defects exist, such as spheroidization and bulging. The energy density is 18.1 J / mm². 3 The printing effect is optimal at this time. It is also suitable for a wider range of solid volume energy densities (16.8–39.2 J / mm²). 3 Within the specified range, the corresponding printed alloy (theoretical density of the alloy is 2.68 g / cm³) 3 The relative density change trend is as follows: Figure 6 As shown, under different parameters, the relative density of the printed alloy reached over 98%, with some areas approaching 99.9% (fully dense), demonstrating the effectiveness of the method.

[0059] Comparative Example 1:

[0060] Comparative Example 1 has the same alloy powder composition as that in Example 1, and the printing process is basically the same.

[0061] The difference lies in the preheating temperature of the base plate in step S6: 500℃; and the preheating temperature of the powder bed in step S7: the volumetric energy density is 2.2 J / mm². 3 The preheating time is 30 seconds; the solid melting parameters for step S8 are: solid energy density of 65 J / mm³. 3 The high preheating temperature of the substrate (500℃), combined with the high powder bed preheating and solid energy density, prevents EBSM from forming. After printing several layers, severe powder agglomeration occurs in the substrate, hindering its descent. Figure 7 As shown, selecting an inappropriate combination of process parameters will prevent the formation of a block sample.

[0062] Comparative Example 2:

[0063] The difference between Comparative Example 2 and Example 1 is that the contour volume energy density in step S8 was not set, and the morphology of the printed alloy block is as follows: Figure 8 As shown. Due to the lack of appropriate contour process parameters, although the block sample can be effectively formed, it cannot achieve precise forming, resulting in poor printing quality.

[0064] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for electron beam selective melting additive manufacturing of Al-Si-Mg alloys, characterized in that, include: Provides Al-Si-Mg alloy powder for 3D printing; the composition of the Al-Si-Mg alloy powder by mass percentage is Si: 6%~20%, Mg: 0.2%~3%, Fe: <0.7%, with the balance being Al and unavoidable impurities; The forming base plate is installed into the electron beam 3D printing equipment. The height of the base plate is adjusted, and the pre-lowering amount of the base plate is set to 3 to 10 times the slice layer thickness; the slice layer thickness is 0.03 to 0.12 mm. Preheat the base plate to no more than 480°C under vacuum conditions and maintain the temperature. The Al-Si-Mg alloy powder was uniformly spread onto a preheated substrate and then subjected to electron beam printing, which included the following processes: preheating before the powder bed, selective electron beam melting, and postheating after the powder bed. The parameters for both preheating before and after the powder bed included: accelerating voltage of 60 kV and volume energy density of 0.1~2 J / mm². 3 The preheating time before the powder bed is 5~50 s, and the preheating time after the powder bed is 0~50 s; the parameters for selective electron beam melting include: accelerating voltage 60 kV, and solid energy density of 15~70 J / mm. 3 The volumetric energy density is 7~20 J / mm. 3 The amount of powder taken is 1.1 to 1.8 times the thickness of the slice layer; defocused electron beam selective melting is used, and the defocusing amount is negative; Repeat the process of lowering the base plate height, spreading powder, and electron beam printing until all layers are printed.

2. The electron beam selective melting additive manufacturing method for Al-Si-Mg alloys according to claim 1, characterized in that, The particle size range of the Al-Si-Mg alloy powder is 0.035~0.15 mm.

3. The electron beam selective melting additive manufacturing method for Al-Si-Mg alloys according to claim 1, characterized in that, The Al-Si-Mg alloy powder, by mass percentage, contains 9% to 13% Si and 0.4% to 3% Mg.

4. The electron beam selective melting additive manufacturing method for Al-Si-Mg alloys according to claim 1, characterized in that, The vacuum conditions are achieved through the following operation: the vacuum degree of the forming chamber reaches 2.5 × 10⁻⁶. -2 Below Pa, inert gas is introduced to stabilize the vacuum level within the range of 0.15~0.2 Pa.

5. The electron beam selective melting additive manufacturing method for Al-Si-Mg alloys according to claim 1, characterized in that, After preheating the base plate to no more than 480°C, keep the base plate warm for at least 5 minutes with a current of 1~5 mA.

6. The electron beam selective melting additive manufacturing method for Al-Si-Mg alloys according to claim 1, characterized in that, The thickness of the slice layer is 0.05~0.08 mm.

7. The electron beam selective melting additive manufacturing method for Al-Si-Mg alloys according to claim 1, characterized in that, During electron beam printing, the interlayer rotation angle is 90°, 67°, or 30°.

8. The electron beam selective melting additive manufacturing method for Al-Si-Mg alloys according to claim 1, characterized in that, The defocusing amount is -0.5 V.

Images