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

Abstract

The invention discloses an electron beam selective melting additive manufacturing method for an Al-Si-Mg alloy. The method comprises the steps that Al-Si-Mg alloy powder for 3D printing is provided; a bottom plate for forming is loaded into electron beam 3D printing equipment, and the height of the bottom plate is adjusted; the bottom plate is preheated to the temperature not exceeding 480 DEG C under the vacuum condition, and heat preservation is conducted; al-Si-Mg series alloy powder is evenly spread on a preheated bottom plate, and electron beam printing including the following processes of preheating before a powder bed, selective melting and preheating after the powder bed is carried out; and the bottom plate height lowering, powder laying and electron beam printing are repeated till all layers are printed. Stable and high-quality forming of the Al-Si-Mg series aluminum alloy is achieved by designing the matching property of the powder characteristics and the process parameters in the electron beam selective melting additive manufacturing Al-Si-Mg series alloy.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and in particular to an electron beam selective melting additive manufacturing method for an Al-Si-Mg alloy. Background Art

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

[0003] Selective laser melting (SLM) and electron beam selective melting (EBSM) use high-energy laser and electron beam as energy sources, respectively, to selectively melt metal powder to form a tiny molten pool along a preset scanning path, and then scan layer by layer from bottom to top to finally obtain a near-net-shape component. 3 ~10 7 K / S), extremely high temperature gradients, and reciprocating thermal cycles will cause large residual stresses inside the material, making the printed alloy prone to cracking.

[0004] Compared with SLM technology, the high vacuum environment in EBSM and the preheating of the powder bed can effectively avoid the problems faced by SLM printing of aluminum alloys, such as easy oxidation, high laser reflectivity, large residual stress and easy cracking. At the same time, the energy utilization rate of the electron beam is high, which can quickly melt the metal powder and significantly improve the manufacturing efficiency. However, the only aluminum alloys that can be used for EBSM printing are 2XXX series (Al-Cu series) and AlSi10Mg in cast Al-Si series alloys. Al-Si-Mg series aluminum alloys, adding Mg to Al-Si series alloys plays a role in strengthening the alloy, which has the characteristics of narrow solidification temperature range, good fluidity and low thermal tendency.

[0005] In EBSM technology, the higher energy density of the electron beam brings faster forming efficiency, but it also leads to the evaporation of low-boiling-point elements (such as Al and Mg) in aluminum alloys (element burnout), less precipitation of Mg2Si strengthening phase in subsequent heat treatment, and reduced material strength. In addition, although the preheating process of the powder bed can effectively reduce the accumulation of stress in the printed parts during forming and slightly sinter the powder, inappropriate preheating process parameters cause abnormal changes in the powder bed state (such as powder blowing caused by insufficient sintering or peeling caused by excessive energy), which further leads to the problem of being unable to form in the melting stage; for the melting stage, the input of electron beam energy plays a decisive role in the formability of the alloy. Too low energy is prone to defects such as pores and cracks, and too high energy is prone to deformations such as bulging and warping. The above are all key issues in the forming of Al-Si-Mg alloys using EBSM technology, which affect the further engineering application of the alloy.

[0006] [Patent application 202310087790.0] The EBSM formability of aluminum alloy powder can only be guaranteed after complex composition modification.

[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. The embodiment focuses on AlZnMgCu alloy, but does not provide suitable process parameters for the entire printing process.

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

[0009] In view of the above-mentioned technical problems and the shortcomings in the field, the present invention provides an electron beam selective melting additive manufacturing method for Al-Si-Mg alloys. By designing the matching of powder properties and process parameters in electron beam selective melting additive manufacturing of Al-Si-Mg alloys, according to the characteristics of metal powders, appropriate base plate preheating, powder bed preheating, selective melting and other processes are matched to ensure stable sintering between powders during preheating, ensure stable evolution of the molten pool during melting, avoid abnormalities such as powder blowing, peeling, powder pushing, bulging and warping during the printing process, and achieve stable and high-quality forming of Al-Si-Mg aluminum alloys.

[0010] The specific technical solutions are as follows:

[0011] An electron beam selective melting additive manufacturing method for an Al-Si-Mg alloy, comprising:

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

[0013] Load the forming base plate into the electron beam 3D printing equipment, adjust the base plate height, and set the pre-descent amount of the base plate to 3 to 10 times the slice layer thickness 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 warm to ensure that the powders can be quickly sintered to each other during the preheating process;

[0015] The Al-Si-Mg alloy powder is evenly spread on the preheated base plate, and electron beam printing including the following processes is performed: preheating before the powder bed - selective melting - preheating after the powder bed; the parameters of the preheating before and after the powder bed include: an acceleration voltage of 60 kV, a volume energy density of 0.1-2 J / mm 3 (e.g. 0.5J / mm 3 The preheating time is 5 to 50 seconds (e.g., 18 seconds), and the post-preheating time is 0 to 50 seconds. The parameters of the selective melting process include: an acceleration voltage of 60 kV, a body energy density of 15 to 70 J / mm 3 (e.g. 16.8J / mm 3 、18.1J / mm 3 、39.2J / mm 3 The energy density of the contour body is 7~20J / mm 3 (e.g. 12.5J / mm 3 The amount of powder taken is 1.1 to 1.8 times (e.g. 1.2 times, etc.) the thickness of the slice.

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

[0017] In the present invention, the surface layer of the printed component is the outline, and the rest of the printed component is the entity.

[0018] In order to avoid the thermal expansion of the base plate during preheating, which may cause collision with the scraper used for spreading powder, the base plate needs to be lowered to a certain height in advance. If the lowering amount is too large, it is easy to cause poor contact between the first few layers of the formed entity and the base plate, resulting in warping. This will affect the forming quality and even terminate the printing. Preferably, according to the preheating temperature of the base plate, the pre-lowering amount of the base plate is set to 3 to 10 times the thickness of the slice layer, such as 4 times.

[0019] The present invention adopts a preheating process before and after the powder bed to ensure slight sintering between the powders before printing and the temperature of the powder bed after printing to avoid abnormalities such as powder blowing or peeling. The electron beam used for preheating can be in a defocused or focused state.

[0020] In the electron beam selective melting additive manufacturing method for Al-Si-Mg alloy, the particle size range of the Al-Si-Mg alloy powder can be 0.035-0.15 mm, and further can be 0.04-0.1 mm, which can meet the requirements of powder layer thickness.

[0021] The electron beam selective melting additive manufacturing method of the Al-Si-Mg alloy is to further improve the Mg-related reinforcement phase in the EBSM printed alloy and reduce the thermal cracking tendency of the alloy. In the composition of the Al-Si-Mg alloy powder, the Si content is near the eutectic composition point, preferably 9% to 13%, more preferably 11% to 12%, for example, 11.82%, etc., and the Mg content is preferably 0.4% to 3%, more preferably 2% to 3%, for example, 2.3%, etc.

[0022] The electron beam selective melting additive manufacturing method of Al-Si-Mg alloy, the vacuum condition can be achieved by the following operations: the vacuum degree of the forming chamber reaches 2.5×10 -2 Pa (preferably 10 -3 Pa, which can further ensure the vacuum degree and oxygen content of the forming chamber) is below 0.15 ~ 0.2Pa, and inert gas is filled to make the vacuum degree stable in the range of 0.15 ~ 0.2Pa.

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

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

[0025] In the electron beam selective melting additive manufacturing method for Al-Si-Mg alloy, the slice layer thickness can be 0.03-0.12 mm, and further 0.05-0.08 mm.

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

[0027] The electron beam selective melting additive manufacturing method for the Al-Si-Mg alloy may adopt defocused electron beam selective melting, and the defocusing amount may be a negative value, further may be -0.5V.

[0028] The electron beam selective melting additive manufacturing method for the Al-Si-Mg alloy may also adopt focused electron beam selective melting.

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

[0030] The density of the Al-Si-Mg alloy 3D part obtained by electron beam selective melting additive manufacturing method is greater than the theoretical density of the alloy 2.68g / cm 3 98% of the theoretical density of the alloy, preferably greater than 2.68 g / cm 3 99%.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The present invention fills the technical gap in electron beam selective melting additive manufacturing of Al-Si-Mg alloys. The selection of suitable powders and process parameters avoids common abnormalities such as powder blowing, warping, bulging and peeling during EBSM printing, ensuring a stable forming process and forming quality. At the same time, the optimization of alloy composition has opened up new types of aluminum alloys suitable for EBSM printing. By adjusting the Si content in the powder, its excellent casting performance is ensured; by increasing the Mg content, the Mg surplus in the printed alloy is ensured, and the strength of the aluminum alloy is improved, which has great practical significance for the further application of aluminum alloy structural parts with complex shapes. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a photo 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 printed Al-Si-Mg 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 photos of bulk samples of the alloy printed by EBSM at different solid body energy densities in Example 2.

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

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

[0040] Figure 8 This is a photo of the surface morphology of the printed alloy in Comparative Example 2. DETAILED DESCRIPTION

[0041] The present invention will be further described below in conjunction with the accompanying drawings and specific examples. It should be understood that these examples are only intended to illustrate the present invention and are not intended to limit the scope of the present invention. The operating methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturer.

[0042] Embodiment 1:

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

[0044] S1. Composition design. In order to reduce the cracking tendency of Al-Si-Mg alloys during EBSM printing, narrow the alloy solidification temperature range, and fix the Si content near the eutectic point composition, at the same time, in order to improve the strength of the alloy in the printed state and after heat treatment, increase the Mg content in the printed alloy. In terms of mass percentage, the Si content in the aluminum alloy powder is 11.82%, the Mg content is 2.30%, Fe<0.7%, and the balance is Al and unavoidable impurities.

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

[0046] S3. EBSM printing pre-processing. Determine the placement of the printed parts in any modeling pre-processing software; enter the slice layer thickness and electron beam scanning path planning parameters in the slicing software corresponding to the EBSM device to obtain the machine printing engineering file.

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

[0048] In order to avoid the thermal expansion of the preheated bottom plate causing collision with the scraper, the forming bottom plate needs to be lowered to a certain height. According to the preheating temperature of the bottom plate, the pre-lowering amount of the bottom plate is set to 4 times the layer thickness.

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

[0050] S6. Preheat the formed base plate. Preheat the formed base plate to a preset temperature of 300°C and keep it warm for 5 minutes using a current of 1 to 3 mA.

[0051] S7. Powder bed preheating. According to the size of the formed base plate and the state of the powder bed after preheating, the acceleration voltage is 60kV and the volume energy density is 0.5J / mm 3 The preheating time is 18 seconds to ensure the mutual sintering between the powders. In this embodiment, the bottom plate is preheated by a focused electron beam.

[0052] S8. Selective melting: Forming process parameters are input into the EBSM printing device, and the device selectively melts the forming base plate according to the preset parameters.

[0053] To ensure the successful forming and printing quality of EBSM printing Al-Si-Mg aluminum alloy, the preferred process parameters are: acceleration voltage 60kV, solid body energy density 18.1J / mm 3 , the energy density of the contour body is 12.5J / mm 3 The powder amount is 1.2 times the slice thickness, and defocused electron beam selective melting is used with a defocus amount of -0.5V.

[0054] S9. Repeat the steps of lowering the base plate height and S7 and S8 until printing is completed and post-processing is performed. Take out the printed sample, clean it, and characterize its structure and performance.

[0055] The morphology of the block sample printed according to this embodiment is as follows Figure 1 As shown in Figure 2. EBSM printed Al-Si-Mg aluminum alloys do not have the Si network structure of similar alloys formed by SLM, such as Figure 2 As shown in the figure, this structure is not good for the plasticity of the alloy. -3 S -1 The room temperature tensile curve is obtained by uniaxial stretching at a strain rate of Figure 3 As shown, the yield strength is 90.5MPa, the tensile strength is 164.9MPa, and the elongation is 10.7%. Figure 4 There are a lot of dimples in the fracture surface, indicating that the fracture mode is ductile fracture.

[0056] Embodiment 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 is that in the selective melting of step S8, different entity energy densities are used. The entity energy densities are 16.8, 18.1, 18.8, 23.5, 24.9, 25.1, and 26.14 J / mm 3 The printed alloy morphology under different volume energy densities is as follows: Figure 5 As shown in the figure, within this range, the alloy can be formed, 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 such as spheroidization and bulging exist. The energy density is 18.1 J / mm 3 The printing effect is best when the energy density of the solid body (16.8~39.2J / mm 3 ) range, the corresponding printed alloy (theoretical density of the alloy is 2.68g / cm 3 )'s relative density variation trend is as follows Figure 6 Under different parameters, the relative density of the printed alloys reached more than 98%, and some were close to 99.9% for full density, indicating the effectiveness of this method.

[0059] Comparative Example 1:

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

[0061] The difference is that the base plate preheating temperature in step S6 is 500°C; the powder bed preheating in step S7: the body energy density is 2.2J / mm 3 , the preheating time is 30s; the solid melting parameters of step S8: the energy density of the solid body is 65J / mm 3 The high base plate preheating temperature (500℃) combined with the high powder bed preheating and solid body energy density makes EBSM unable to form. The powder of the base plate after printing a few layers is seriously agglomerated, which hinders the base plate from descending. Figure 7 As shown in the figure, if the inappropriate process parameter combination is selected, the block sample cannot be formed.

[0062] Comparative Example 2:

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

[0064] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. An electron beam selective melting additive manufacturing method for Al-Si-Mg alloy, characterized in that: include: Provide Al-Si-Mg alloy powder for 3D printing; the composition of the Al-Si-Mg alloy powder is Si: 6% to 20%, Mg: 0.2% to 3%, Fe: <0.7%, and the balance is Al and unavoidable impurities, in terms of mass percentage; Load the forming base plate into the electron beam 3D printing equipment, adjust the base plate height, and set the pre-descent amount of the base plate to 3 to 10 times the slice layer thickness; Preheat the bottom plate to no more than 480°C under vacuum conditions and keep it warm; The Al-Si-Mg alloy powder is evenly spread on the preheated base plate, and electron beam printing including the following processes is performed: preheating before the powder bed - selective melting - preheating after the powder bed; the parameters of the preheating before and after the powder bed include: an acceleration voltage of 60 kV, a volume energy density of 0.1-2 J / mm 3 , the preheating time is 5 to 50 seconds, and the post-preheating time is 0 to 50 seconds; the parameters of the selective melting include: the acceleration voltage is 60 kV, the energy density of the solid body is 15 to 70 J / mm 3 , the energy density of the contour body is 7~20J / mm 3 , the amount of powder taken is 1.1 to 1.8 times the thickness of the slice; Repeat the steps 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 of Al-Si-Mg alloy according to claim 1, characterized in that: The particle size of the Al-Si-Mg alloy powder is in the range of 0.035 to 0.15 mm.

3. The electron beam selective melting additive manufacturing method of Al-Si-Mg alloy according to claim 1, characterized in that: In terms of mass percentage, the Al-Si-Mg alloy powder comprises 9% to 13% Si and 0.4% to 3% Mg.

4. The electron beam selective melting additive manufacturing method of Al-Si-Mg alloy according to claim 1, characterized in that: The vacuum condition is achieved by the following operations: the vacuum degree of the forming chamber reaches 2.5×10 -2 Pa, fill with inert gas to stabilize the vacuum degree in the range of 0.15 ~ 0.2Pa.

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

6. The electron beam selective melting additive manufacturing method of Al-Si-Mg alloy according to claim 1, characterized in that: The slice thickness is 0.03 to 0.12 mm, and further 0.05 to 0.08 mm.

7. The electron beam selective melting additive manufacturing method of Al-Si-Mg alloy according to claim 1, characterized in that: During electron beam printing, the inter-layer rotation angle was 90°, 67°, or 30°.

8. The electron beam selective melting additive manufacturing method of Al-Si-Mg alloy according to claim 1, characterized in that: Defocused electron beam selective melting is used, and the defocus amount is negative, further to -0.5V.

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