Method for additive manufacturing of ultrahigh-strength aluminum alloy

Abstract

The invention discloses an ultra-high-strength aluminum alloy for additive manufacturing, and belongs to the field of aluminum alloy manufacturing. Selective laser melting (LPBF) has become an important technology for manufacturing aluminum alloy parts. At present, commercial alloys such as an Al-Si system are relatively low in mechanical property. Compared with the prior art, the advanced aluminum alloy modified by adding rare or expensive elements (such as Sc and Zr) has high mechanical performance, but the industrial popularization of the aluminum alloy is limited by high cost. According to the invention, only Co and Si elements are added into an aluminum matrix as strengthening elements, an alloy with the mass ratio of Al-(4.8-5.5%) Co-(4.8-5.5%) Si is designed, a laser powder bed melting process is adopted, and printing process parameters are controlled, so that a fine equiaxed crystal structure can be obtained, and a large number of nano-sized short rod-shaped Al9Co2 phases can be formed in the matrix. The compressive strength of the alloy is improved through cooperation of fine grain strengthening, second phase strengthening and back stress strengthening, the compressive strength of the final alloy reaches 978.34 + / -4.7 MPa, the strain is 31.36 + / -0.2%, and the performance of the alloy is higher than that of an additive manufacturing aluminum alloy reported at present.

Description

Technical Field

[0001] A method for additive manufacturing of ultra-high strength aluminum alloys, belonging to the field of aluminum alloy manufacturing. Background Technology

[0002] Aluminum alloys, renowned for their low density, high specific strength, and excellent corrosion resistance, are critical materials in industries such as automotive, aerospace, and transportation, where weight reduction and performance optimization are paramount. In recent years, the application of laser powder bed melting (LPBF) technology in aluminum alloys has increased significantly. Leveraging its high forming flexibility, near-net-shape forming of complex parts, and rapid solidification, LPBF overcomes the limitations of traditional processing methods, such as coarse microstructure or poor mechanical properties, and has become an important technology for manufacturing aluminum alloy parts. However, developing high-performance aluminum alloys suitable for LPBF remains challenging. Current commercial alloys, such as the Al-Si series (e.g., AlSi10Mg, AlSi12), are widely used in LPBF due to their excellent printability. However, these alloys have relatively low mechanical properties, with ultimate tensile strength (UTS) below 3870 MPa and elongation below 6%. In contrast, advanced aluminum alloys modified with rare or expensive elements (such as Sc, Zr) offer enhanced mechanical properties, but their high cost limits their industrial adoption. Summary of the Invention

[0003] This invention solves the problems of high cost, complex alloy element design, and still needing further improvement in strength of aluminum alloys used in additive manufacturing.

[0004] A method for additive manufacturing of ultra-high strength aluminum alloys is characterized by: firstly, using gas atomization powder preparation technology to prepare alloy powder with the composition of Al-(4.8-5.5%)Co-(4.8-5.5%)Si, then sieving the atomized powder and selecting powder with a size of 15-53 microns for laser powder bed melting and forming of printed parts, and after printing, performing post-processing on the parts including surface cleaning and polishing, finally obtaining clean parts.

[0005] Furthermore, the specific parameters for the laser powder bed melting and forming are as follows: layer thickness 25-35μm, scanning spacing 100-120μm, substrate preheating temperature set to 150-200℃, laser scanning strategy using stripe scanning with interlayer rotation of 67°, laser power 240-260W, and scanning speed 1300-1500mm / s.

[0006] Furthermore, in the laser powder bed melting and forming process, after each layer of material is scanned by the laser for the first time, it is not immediately spread into powder, but is instead scanned a second time for remelting; the parameters and scanning strategy of the remelting laser are consistent with those of the initial laser.

[0007] The strengthening mechanism of the alloy of this invention is as follows: (1) By controlling the process parameters, especially by remelting, Al9Co2 particles preferentially precipitate during the solidification of the molten pool and act as heterogeneous nucleation points, inhibiting excessive grain growth and transforming columnar crystals into fine equiaxed crystals; (2) After remelting, nanoscale short rod-shaped Al9Co2 phases are formed in the matrix. The α-Al soft phase and the Al9Co2 hard phase generate plastic strain differences during deformation, generating and accumulating a large number of geometrically necessary dislocations (GNDs) at the interface. Strain mismatch generates back stress, significantly improving the strength of the alloy; (3) The nanoscale short rod-shaped Al9Co2 phase, as a hard phase, forces dislocations to bypass or accumulate through the Orowan strengthening mechanism, increasing the resistance to dislocation movement. In addition, after remelting, the continuous cellular structure walls are destroyed, avoiding brittle fracture. Under the synergistic effect of the three strengthening mechanisms of grain refinement strengthening, Orowan strengthening, and back stress strengthening induced by heterogeneous deformation, the alloy achieves ultra-high mechanical properties. The final alloy achieved a compressive strength of 978.34±4.7MPa and a strain of 31.36±0.2%, which is higher than the performance of all additively manufactured aluminum alloys reported to date.

[0008] In addition, we conducted extensive experimental research during the invention process and found that alloying elements such as molybdenum, vanadium, titanium, and tungsten cannot form an effective reinforcing phase with Si. Under the same additive manufacturing process conditions, it is impossible to produce aluminum alloy products with similar strength and high compression ratio by combining molybdenum, vanadium, titanium, tungsten, etc. with Si. Only by combining Co and Si can aluminum alloy products with excellent performance be prepared.

[0009] This invention designs a novel composition, adding only Co and Si elements as reinforcing elements to an aluminum matrix, with a designed mass ratio of Al-(4.8–5.5%)Co-(4.8–5.5%)Si. Employing a laser powder bed melting process, and by controlling the printing process parameters, a fine equiaxed grain structure can be obtained. Furthermore, two reinforcing phases are distributed within the matrix: 100-200 nm short rod-shaped Al9Co2 intermetallic compounds and 100 nm Si particles. The fine grain reinforcement, second-phase reinforcement, and back stress reinforcement synergistically improve the compressive strength of the alloy, ultimately achieving a compressive strength of 978.34 ± 4.7 MPa and a strain of 31.36 ± 0.2%, exceeding the performance of currently reported additively manufactured aluminum alloys. Attached Figure Description

[0010] Figure 1 These are typical transmission electron microscopy (TEM) images of the aluminum alloys prepared according to this invention. Figure 2 This is a typical compressive stress-strain curve for the aluminum alloy prepared by this invention. Detailed Implementation

[0011] (1) Preparation of Al-5%Co-5%Si ultra-high strength aluminum alloy based on LPBF process

[0012] First, alloy powder was prepared using gas atomization. The alloy composition was Al-5%Co-5%Si. Powder with a particle size of 15-53 micrometers was sieved and used for laser powder bed melting and forming. The forming parameters were: layer thickness 25 μm, scanning spacing 100 μm, substrate preheating temperature set to 200℃, laser scanning strategy using stripe scanning with interlayer rotation of 67°, laser power 240W, and scanning speed 1300 mm / s. After the first laser scan, each layer of material was not immediately spread into powder but instead underwent a second scan for remelting. The parameters and scanning strategy of the remelting laser were consistent with the initial laser scan. Parts were printed according to the above process parameters. After printing, the parts underwent post-processing, including surface cleaning and polishing, to obtain clean parts. After mechanical property testing, the compressive strength reached 978 MPa, and the compression ratio was 31.36%.

[0013] (2) Preparation of Al-5.5%Co-5.5%Si ultra-high strength aluminum alloy based on LPBF process

[0014] First, alloy powder was prepared using gas atomization. The alloy composition was Al-5.5%Co-5.5%Si. Powder with a particle size of 15-53 micrometers was sieved for laser powder bed melting and forming. The forming parameters were: layer thickness 35μm, scanning spacing 120μm, substrate preheating temperature set to 200℃, laser scanning strategy using stripe scanning with interlayer rotation of 67°, laser power 260W, and scanning speed 1500mm / s. After the first laser scan, each layer of material was not immediately spread; instead, it underwent a second scan for remelting. The parameters and scanning strategy of the remelting laser were consistent with the initial laser scan. Parts were printed according to the above process parameters. After printing, the parts underwent post-processing, including surface cleaning and polishing, to obtain clean parts. Mechanical property testing showed a compressive strength of 983MPa and a compression ratio of 31.16%.

Claims

1. A method for additive manufacturing of ultra-high strength aluminum alloy, characterized in that: First, alloy powder is prepared using gas atomization powder preparation technology. Its composition is Al-(4.8-5.5%)Co-(4.8-5.5%)Si. Then, the atomized powder is sieved, and powder with a size of 15-53 microns is selected for laser powder bed melting and forming of printed parts. After printing, the parts are post-processed, including surface cleaning and polishing, to finally obtain clean parts.

2. The method for additive manufacturing of ultra-high strength aluminum alloy according to claim 1, characterized in that, The specific parameters for the laser powder bed melting and forming are as follows: layer thickness 25-35μm, scanning spacing 100-120μm, substrate preheating temperature set to 150-200℃, laser scanning strategy using stripe scanning with interlayer rotation of 67°, laser power 240-260W, and scanning speed 1300-1500mm / s.

3. The method for additive manufacturing of ultra-high strength aluminum alloy according to claim 1, characterized in that, The laser powder bed is melted and shaped. After the first laser scan, each layer of material is not immediately spread into powder, but is remelted by a second scan. The parameters and scanning strategy of the remelting laser are the same as those of the initial laser.

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