High-strength aluminum alloy suitable for SLM forming and SLM forming method thereof

Abstract

The invention discloses a high-strength aluminum alloy suitable for SLM forming and an SLM forming method of the high-strength aluminum alloy. The high-strength aluminum alloy is prepared from the following components in percentage by mass: 7.0 to 10.0 percent of Zn, 2.0 to 4.0 percent of Mg, 1.0 to 3.0 percent of Cu, 0.4 to 0.8 percent of Sc, 0.3 to 0.6 percent of Zr, 0.2 to 1.0 percent of Mn and the balance of Al. The SLM forming method of the high-strength aluminum alloy comprises the following steps that (1) raw material powder is prepared, and the particle size distribution range of the obtained mixed powder is 15-53 microns; (2) powder pretreatment: drying the powder in a vacuum or protective atmosphere environment at 100-120 DEG C, and keeping the temperature for 8-12 hours; (3) SLM forming is conducted, layer-by-layer powder laying and selective laser melting are conducted under set technological parameters, subarea scanning is adopted for a laser scanning path, the laser power ranges from 220 W to 270 W, the scanning speed ranges from 700 mm / s to 1200 mm / s, the scanning interval is 0.1 mm, and the deflection angle between every two adjacent scanning layers ranges from 65 degrees to 75 degrees; (4) solution treatment; and (5) aging treatment. According to the method, the problem of hot cracking of 7xxx series aluminum alloy in SLM forming is effectively solved, and the obtained component has high strength and good plasticity.

Description

Technical Field

[0001] This invention relates to a high-strength aluminum alloy suitable for SLM forming and its SLM forming method, belonging to the field of metal additive manufacturing technology. Background Technology

[0002] Selective laser melting (SLM), as one of the core technologies of metal additive manufacturing, has shown broad application prospects in aerospace, precision instruments and other fields due to its advantages such as near-net-shape forming, high design freedom and high material utilization. However, the inherent high-energy beam and rapid melting and solidification characteristics of this technology lead to extremely high cooling rates and significant thermal gradients, posing a severe challenge to the solidification crack sensitivity of materials.

[0003] Traditional 7xxx series (Al-Zn-Mg-Cu series) ultra-high strength aluminum alloys possess excellent strength in the forged and rolled state. However, their wide solidification temperature range and the low-melting-point eutectic phases (such as Mg(Zn,Cu,Al)2) formed at grain boundaries make them typical "difficult-to-weld" materials during SLM forming. The enormous thermal stress generated by rapid solidification easily induces solidification cracks, leading to the formation of a micro-crack network inside the formed part, severely deteriorating its mechanical properties and thus limiting the application of this series of alloys in SLM technology.

[0004] To improve the formability of SLM (Surface Mount Metallurgy) aluminum alloys, existing technologies often employ the addition of elements such as Sc and Zr to form Al3(Sc,Zr) nanoprecipitates, thereby refining grains and suppressing hot cracking. However, the single Sc / Zr microalloying strategy still faces bottlenecks in achieving ultra-high strength in SLM-state aluminum alloys. Therefore, developing a novel aluminum alloy system that can simultaneously achieve excellent SLM formability and ultra-high strength through multi-element alloying and process innovation has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a high-strength aluminum alloy suitable for SLM forming, whose composition is specifically designed for the characteristics of the SLM process, and can effectively overcome the defect of existing 7xxx series aluminum alloys that are prone to solidification cracks in this process.

[0006] Another objective of this invention is to provide an SLM forming and heat treatment method for the above-mentioned aluminum alloy, which, through synergistic optimization of composition and process, yields a formed component with dense microstructure, no cracks, and ultra-high strength.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A high-strength aluminum alloy suitable for SLM forming comprises, by mass percentage, the following components: Zn 7.0-10.0%, Mg 2.0-4.0%, Cu 1.0-3.0%, Sc 0.4-0.8%, Zr 0.3-0.6%, Mn 0.2-1.0%, with the balance being Al and unavoidable impurities.

[0008] A method for SLM forming of the high-strength aluminum alloy includes the following steps: (1) Prepare raw material powder, and the particle size distribution range of the resulting mixed powder is 15-53 μm; (2) Powder pretreatment: Dry the powder in a vacuum or protective atmosphere at 100-120℃ for 8-12 hours. (3) SLM forming: under the set process parameters, layer-by-layer powder spreading and selective laser melting are carried out. The laser scanning path adopts partitioned scanning, the laser power is 220-270W, the scanning rate is 700-1200mm / s, the scanning spacing is 0.1mm, and the deflection angle between adjacent scanning layers is 65°-75°. (4) Solution treatment: After printing and separating the preforms, place them in a heat treatment furnace and perform solution treatment at a temperature range of 460-480℃ for 15-90 minutes. After the heat treatment is completed, quickly immerse the workpieces in room temperature water for quenching. (5) Aging treatment: Artificial aging treatment is performed on the workpiece after solution quenching. The aging temperature is 80-120℃ and the holding time is 12-24h. After aging, the workpiece is cooled to room temperature in still air to obtain the final high-strength aluminum alloy component.

[0009] Preferably, in step (1), pre-alloyed spherical powder is prepared by gas atomization, or mixed powder is prepared by uniformly mixing Al-Zn-Mg-Cu-Sc-Zr alloy powder and Al-Mn alloy powder by mechanical mixing.

[0010] Preferably, in step (3), an aluminum alloy substrate is selected, and acetone and anhydrous ethanol are used in sequence for ultrasonic cleaning to remove oil stains. Then, it is installed and leveled to ensure that it is in the laser focal plane.

[0011] Preferably, in step (3), a digital model of the specimen is designed using 3D modeling software (such as Materialise Magics) and exported as a .stl file. Then, the model is layered using slicing software to generate a processing path file that can be recognized by the SLM equipment.

[0012] Preferably, in step (3), during printing preparation, argon gas with a purity higher than 99.9% is continuously introduced into the forming chamber to expel the oxygen in the forming chamber and keep the oxygen content below 100ppm during the forming process. Then, the substrate preheating system is started to stabilize the substrate temperature at 140±10℃.

[0013] Preferably, in step (3), when spreading powder layer by layer, the thickness of each layer of powder is set to 20-30 μm.

[0014] Preferably, after step (3) is completed, the molded part is cooled to room temperature along with the substrate, and the molded part is separated from the substrate by electrical discharge wire cutting to obtain an aluminum alloy preform.

[0015] The beneficial effects of this invention are: This invention develops a novel aluminum alloy material suitable for SLM process. By adding Sc, Zr and Mn elements for microalloying and optimizing the process, a novel aluminum alloy material with excellent crack resistance, high strength and good plasticity and other static mechanical properties is prepared.

[0016] This invention, through the composite microalloying design of Sc, Zr, and Mn, combined with optimized SLM process parameters, significantly refines the grain structure, suppresses the generation of hot cracks, and enables the formed parts to possess excellent mechanical properties.

[0017] The high-strength aluminum alloy provided by this invention, after SLM forming and solution aging treatment, has a yield strength of up to 637 MPa, a tensile strength of up to 671 MPa, and an elongation of up to 13.5%, with comprehensive performance significantly better than existing SLM-formed 7xxx series aluminum alloys. Attached Figure Description

[0018] Figure 1 This is a scanning electron microscope (SEM) image of the high-strength aluminum alloy powder used in Example 3 of the present invention.

[0019] Figure 2 This is a particle size distribution curve of the high-strength aluminum alloy powder used in Example 3 of the present invention.

[0020] Figure 3 This is an optical microscope (OM) photograph of the cross-section of the alloy specimen after SLM forming in Example 3 of the present invention.

[0021] Figure 4 This is a scanning electron microscope (SEM) image of the cross-section of the alloy specimen after SLM forming in Example 3 of the present invention.

[0022] Figure 5 This is the electron backscatter diffraction (EBSD) grain orientation diagram (IPF diagram) of the alloy specimen after SLM forming in Example 3 of the present invention.

[0023] Figure 6 This is the electron backscatter diffraction (EBSD) grain orientation difference distribution diagram (GOS diagram) of the alloy specimen after SLM forming in Example 3 of the present invention.

[0024] Figure 7 This is a transmission electron microscope (TEM) micrograph of the alloy specimen after SLM forming and heat treatment in Example 3 of the present invention.

[0025] Figure 8 Typical tensile stress-strain curves of high-strength aluminum alloy specimens prepared in Example 3 of this invention at room temperature. Detailed Implementation

[0026] The present invention will be further described in detail below through specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0027] The high-strength aluminum alloy proposed in this invention, suitable for selective laser melting (SLM) forming, comprises the following components by mass percentage: Zn 7.0-10.0%, Mg 2.0-4.0%, Cu 1.0-3.0%, Sc 0.4-0.8%, Zr 0.3-0.6%, Mn 0.2-1.0%, with the balance being Al and unavoidable impurities.

[0028] The high-strength aluminum alloy proposed in this invention has the following advantages: 1. Synergistic Toughening and Strengthening through Multi-element Microalloying: The alloy composition of this invention contains 0.2–1.0 wt.% Mn. Mn atoms in the melt can combine with Al atoms to form an Al6Mn phase. During the rapid solidification process of laser selective melting (SDM), this phase precipitates before α-Al and can act as a heterogeneous nucleation core to promote the formation of equiaxed crystals, significantly refining the grain size and suppressing forming cracks during SDM. The fine grains and uniformly dispersed nanoparticles effectively hinder dislocation movement, significantly improving the yield strength and tensile strength of the material while maintaining or even enhancing its toughness.

[0029] 2. Control of thermal stability of microstructure: Al6Mn particles strongly pin grain boundaries and subgrain boundaries during subsequent heat treatment (such as solution treatment and aging), significantly inhibiting the recovery and recrystallization processes of the alloy. This allows the alloy to retain the fine substructures (such as cellular structures) and work hardening effects generated by SLM forming after high-temperature heat treatment, avoiding grain coarsening and strength loss caused by recrystallization, and helping to maintain high strength. For systems that rely on Al3(Sc,Zr) precipitation strengthening by Sc / Zr, this dual inhibition provides even better results.

[0030] 3. Multi-layered strengthening mechanism: Some Mn atoms can dissolve into the aluminum matrix, producing a solid solution strengthening effect. Furthermore, the addition of Mn may interact with the main alloying elements (such as Cu and Mg), affecting the precipitation kinetics and distribution of the GP zone or the main strengthening phases (such as η'-MgZn2, S'-Al2CuMg). This results in more uniform, fine, and dense precipitates, thereby further optimizing the aging strengthening response on the basis of solid solution strengthening, enabling the material to achieve higher peak hardness and strength.

[0031] The composition of the powder used in Examples 1 to 6 of this invention is shown in Table 1.

[0032] Table 1. Composition of the powders used in the examples The specific process for preparing the high-strength aluminum alloy for laser selective melting proposed in this invention is as follows: Step 1: Prepare powdered raw materials: Pre-alloyed spherical powders with specific compositions were prepared by gas atomization, or aluminum-zinc-magnesium-copper-scandium-zirconium alloy powders were uniformly mixed with aluminum-manganese alloy powders by mechanical mixing to ensure compositional uniformity. The resulting mixed powders had a particle size distribution ranging from 15 to 53 μm.

[0033] Step 2, Powder Pretreatment: The powder is dried in a vacuum or protective atmosphere at 100-120℃ for 8-12 hours to fully remove the moisture and gas adsorbed on the powder surface.

[0034] Step 3, Substrate Preparation: Select a suitable aluminum alloy substrate (such as 7075 aluminum alloy), and use acetone and anhydrous ethanol in sequence for ultrasonic cleaning to remove oil stains. Then install and level it to ensure that it is in the laser focal plane.

[0035] Step 4, 3D model design and slicing: A digital model of the specimen was designed using 3D modeling software (such as Materialise Magics) and exported as a .stl file. Then, slicing software was used to layer the model, generating a processing path file recognizable by the SLM equipment.

[0036] Step 5: Preparing the printing environment: The pretreated powder is loaded into the equipment's powder supply system. After sealing the forming chamber, high-purity (≥99.9%) argon gas is continuously introduced to reduce and maintain the oxygen content inside the chamber below 100 ppm to prevent metal oxidation during printing. Once the oxygen content reaches the target level, the substrate preheating system is activated to stabilize the substrate temperature at 140±10℃.

[0037] Step 6, SLM forming process: Layer-by-layer powder spreading and selective laser melting were performed under the set process parameters. The thickness of each powder layer was set to 30 μm. The laser scanning path adopted a partitioned scanning strategy, and adjacent scanning layers were deflected at a certain angle (preferably 67°). The key SLM process parameters were: laser power 220-270W, scanning rate 700-1200 mm / s, and scanning spacing (track spacing) 0.1 mm. When printing the test piece, the laser power was 220-270W, the scanning rate was 700-1200 mm / s, the track spacing was 0.1 mm, and the interlayer deflection angle was 67°. The SLM forming process parameters in Examples 1-6 are shown in Table 2.

[0038] Table 2 SLM forming process parameters in the embodiments Step 7, Post-processing separation: After printing, once the component has cooled to room temperature along with the substrate, the formed part is separated from the substrate by wire electrical discharge machining or other methods to obtain an aluminum alloy preform.

[0039] Step 8, Solution treatment: The separated preforms were placed in a controlled atmosphere heat treatment furnace and solution treated at 460-480℃ for 15-90 minutes. After the holding time, the workpieces were quickly immersed in room temperature water for quenching. The solution treatment process parameters in Examples 1-6 are shown in Table 3.

[0040] Table 3 shows the solution treatment process parameters in the embodiments. Step 9, Time-sensitive processing: The solution-quenched workpieces were subjected to artificial aging treatment at temperatures ranging from 80 to 120°C for 12 to 24 hours. After aging, the workpieces were cooled to room temperature in still air to obtain the final high-strength aluminum alloy components. The aging process parameters in Examples 1 to 6 are shown in Table 4.

[0041] Table 4 shows the aging treatment process parameters in the embodiments. The powder morphology of the SLM-specific high-strength aluminum alloy used in Example 3 of this invention was observed using a scanning electron microscope (SEM). The obtained SEM image is shown below. Figure 1 As shown. By Figure 1As can be seen, the alloy powder of the present invention has a relatively uniform particle size and a uniform spherical morphology. This excellent sphericity means that the powder has good flowability and high packing density. In the SLM forming process, this ensures that the powder layer thickness is uniform and stable, thus providing the primary material basis for obtaining dense, defect-free formed parts. The uniform particle size distribution also helps to form a uniform molten pool, avoiding process defects caused by powder splashing or local uneven energy density.

[0042] The particle size distribution of the SLM-specific high-strength aluminum-lithium alloy powder used in Example 3 of this invention was tested, and the resulting particle size distribution curve is shown in the figure below. Figure 2 As shown. By Figure 2 It can be seen that the SLM-specific high-strength aluminum alloy powder used in this invention mainly has D10 = 18.01 μm, D50 = 32.15 μm, and D90 = 53.39 μm.

[0043] Metallographic analysis was performed on specimens prepared from the SLM high-strength aluminum alloy powder used in Examples 1-6 of this invention under different SLM forming parameters using an Axiovert 200MAT optical microscope (OM). The distribution of porosity and cracks was observed. No hot cracks or solidification cracks were found in any specimens formed under optimized parameters, indicating that the alloy composition design of this invention effectively suppressed the common hot cracking tendency during SLM forming. Figure 3 The image shown is an optical microscope (OM) photograph of the cross-section of the alloy specimen after SLM forming in Example 3. Figure 3 As can be seen, no cracks or defects were observed; only a small number of isolated spherical pores were observed, with a porosity of less than 0.05% as calculated by image analysis software. This porosity level is far lower than the typical value (usually >0.2%) for conventional SLM-formed aluminum alloys, demonstrating the significant effect of the process parameter combination of the present invention in suppressing porosity and process porosity, and meeting the requirements for the internal quality of key load-bearing components in aerospace and other fields.

[0044] The high-strength aluminum alloy specimen obtained by SLM forming in Example 3 of this invention was subjected to SEM testing using a JSM-7001F electron microscope. The obtained SEM images are shown below. Figure 4 As shown in the image, the main feature is a uniform gray matrix, dotted with a small number of black or grayish-black micropores and inclusions, indicating that the overall quality of the alloy is good; no obvious layered molten pool boundaries or continuous cracks are observed, indicating that the SLM forming parameters (laser power, scanning rate, etc.) are reasonably controlled.

[0045] The high-strength aluminum alloy specimen prepared by SLM forming in Example 3 of this invention was subjected to EBSD testing using an electron backscattering probe equipped with a JSM-7001F electron microscope. The obtained IPF image is shown below. Figure 5As shown, equiaxed and columnar crystals are alternately arranged, with the equiaxed crystal region accounting for nearly 50%. The average grain diameter of the equivalent circle is 3.73 μm, indicating extremely fine grains, which provide a structural basis for the alloy's high strength and good plasticity. The obtained GOS diagram is shown below. Figure 6 As shown in the figure, transversely elongated crystals in the form of stripes or columnar shapes are typical columnar / plate-like crystals growing along the heat flow direction in SLM. The vast majority of the area is dark blue (low GOS), indicating uniform internal grain orientation. This suggests that rapid solidification in SLM leads to a high cooling rate, resulting in low internal grain strain; after T6 or heat treatment, the internal orientation is further homogenized, resulting in recovery and partial recrystallization. Locally, green-yellow-orange grains (medium-high GOS) are present. These grains typically indicate strong strain and high dislocation density; they are often located around pores, melt pool boundaries, and near the second phase; they are associated with coarse precipitates (η / MgZn2 or Sc / Zr-rich particles) in the alloy, indicating the presence of stress concentration areas in the local microstructure. Overall, the microstructure exhibits a composite characteristic of "generally low strain + locally high strain," indicating that the material has good overall structural stability.

[0046] The high-strength aluminum alloy specimen obtained by SLM forming in Example 3 of this invention was subjected to TEM testing using a FEI Tecnai G2 F20 instrument. The obtained TEM images are shown below. Figure 7 As shown, the precipitates are fine in size and uniformly distributed, indicating sufficient aging treatment without significant agglomeration. Slight bright and dark streaks are visible in the matrix region, presumably residual subgrain boundaries or dislocation-dense areas, suggesting that the material retains certain non-equilibrium structural characteristics. No obvious pores or hot cracks were observed, indicating high SLM forming quality. Most of the precipitates in the figure are slender rod-shaped or needle-shaped, approximately 50-150 nm long and 10-20 nm wide, typical of η or η′ phases. In Al-Zn-Mg-Cu alloys, these phases are the main age-strengthening phases; some extremely small, high-brightness, and uniformly distributed nanoparticle precipitates (<10 nm) can be attributed to the L12 structure Al3(Sc,Zr) phase. They mainly function as nucleation sites and inhibit grain growth, forming a highly dispersed distribution under the rapid solidification conditions of SLM.

[0047] The SLM high-strength aluminum alloy specimens of Example 3 of the present invention, after solution treatment and aging, were subjected to tensile tests three times at room temperature, and the stress-strain curves obtained are shown below. Figure 8As shown, its engineering stress-strain curve reveals that the material possesses high yield strength and ultimate tensile strength, exhibiting a broad and stable work hardening plateau after yielding. The specimen enters the yield stage at a strain of approximately 0.01, with the stress rapidly increasing to over 600 MPa; subsequently, it maintains a slowly rising stress level within a large strain range of 0.02–0.12, indicating that the material possesses good uniform plastic deformation capacity and sustained strain hardening characteristics. Fracture finally occurs near approximately 13% of the total elongation, exhibiting a typical steep drop before fracture, reflecting that the material retains a certain degree of ductility even under high strength conditions. Overall test results indicate that this alloy achieves a good balance between high strength and moderate plasticity, making it suitable for engineering applications with high requirements for lightweighting and structural reliability. The components obtained in Examples 1–6 of this invention were subjected to performance tests, and the test results are shown in Table 5.

[0048] Table 5 Performance parameters of the aluminum alloy specimens obtained in the examples The test results above show that the SLM high-strength aluminum alloy provided by this invention, after solution treatment and aging, achieves a yield strength of 637 MPa, a tensile strength of 671 MPa, and an elongation of 13.5%. Traditional forged or extruded 7075-T6 aluminum alloys have a tensile strength of approximately 570 MPa and an elongation of approximately 10%. Other SLM high-strength aluminum alloys disclosed in the prior art generally exhibit tensile strength <600 MPa and elongation <10%. Therefore, the SLM high-strength aluminum alloy provided by this invention not only surpasses the performance of traditional process materials but also achieves an unprecedented combination of strength and plasticity in the SLM additive manufacturing field, fully meeting the stringent requirements of the aerospace industry for lightweight, high-load-bearing structural components.

Claims

1. A high-strength aluminum alloy suitable for SLM forming, characterized in that, By mass percentage, it comprises the following components: Zn 7.0-10.0%, Mg 2.0-4.0%, Cu 1.0-3.0%, Sc 0.4-0.8%, Zr 0.3-0.6%, Mn 0.2-1.0%, with the balance being Al and unavoidable impurities.

2. A method for SLM forming of high-strength aluminum alloy according to claim 1, characterized in that, Includes the following steps: (1) Prepare raw material powder, and the particle size distribution range of the resulting mixed powder is 15-53 μm; (2) Powder pretreatment: Dry the powder in a vacuum or protective atmosphere at 100-120℃ for 8-12 hours. (3) SLM forming: under the set process parameters, layer-by-layer powder spreading and selective laser melting are carried out. The laser scanning path adopts partitioned scanning, the laser power is 220-270W, the scanning rate is 700-1200mm / s, the scanning spacing is 0.1mm, and the deflection angle between adjacent scanning layers is 65°-75°. (4) Solution treatment: After printing and separating the preforms, place them in a heat treatment furnace and perform solution treatment at a temperature range of 460-480℃ for 15-90 minutes. After the heat treatment is completed, quickly immerse the workpieces in room temperature water for quenching. (5) Aging treatment: Artificial aging treatment is performed on the workpiece after solution quenching. The aging temperature is 80-120℃ and the holding time is 12-24h. After aging, the workpiece is cooled to room temperature in still air to obtain the final high-strength aluminum alloy component.

3. The SLM forming method according to claim 2, characterized in that, In step (1), pre-alloyed spherical powder is prepared by gas atomization, or mixed powder is prepared by uniformly mixing Al-Zn-Mg-Cu-Sc-Zr alloy powder and Al-Mn alloy powder by mechanical mixing.

4. The SLM forming method according to claim 2, characterized in that, In step (3), an aluminum alloy substrate is selected, and acetone and anhydrous ethanol are used in sequence for ultrasonic cleaning to remove oil stains. Then, it is installed and leveled to ensure that it is in the laser focal plane.

5. The SLM forming method according to claim 2, characterized in that, In step (3), a digital model of the specimen is designed using 3D modeling software and exported as a .stl file. Then, the model is layered using slicing software to generate a processing path file that can be recognized by the SLM equipment.

6. The SLM forming method according to claim 5, characterized in that, The 3D modeling software is MaterialiseMagics.

7. The SLM forming method according to claim 2, characterized in that, In step (3), during printing preparation, argon gas with a purity higher than 99.9% is continuously introduced into the forming chamber to expel the oxygen in the forming chamber and keep the oxygen content below 100ppm during the forming process. Then, the substrate preheating system is started to stabilize the substrate temperature at 140±10℃.

8. The SLM forming method according to claim 2, characterized in that, In step (3), when spreading powder layer by layer, the thickness of each layer is set to 20-30μm.

9. The SLM forming method according to claim 2, characterized in that, After step (3) is completed, the molded part is cooled to room temperature along with the substrate, and the molded part is separated from the substrate by electrical discharge wire cutting to obtain an aluminum alloy preform.

10. The SLM forming method according to claim 2, characterized in that, In step (3), the heat preservation time for the solution treatment is 30-90 min.

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