Crack-resistant high-toughness rare earth aluminum alloy and preparation method, aluminum alloy part and additive manufacturing method, and application

Abstract

This disclosure discloses a crack-resistant, high-strength, and high-toughness rare-earth aluminum alloy, its preparation method, aluminum alloy parts, additive manufacturing method, and applications, belonging to the field of laser additive manufacturing technology. The crack-resistant, high-strength, and high-toughness rare-earth aluminum alloy comprises 5.0-8.5% Zn, 1.2-3.5% Mg, 1.5-3.0% Cu, 0.1-0.6% Sc, 0.05-0.4% Er, 0.1-0.5% Zr, 0.1-0.4% Si, 0.05-0.1% Mn, 0.15-0.3% Ti, and 0.02-0.04% Cr, with the balance being Al and unavoidable impurities. The mass ratio of Sc to (Er+Zr) is 0.9 ≤ Sc / (Er+Zr) ≤ 1.2. Composite microalloying of Sc, Er, and Zr is beneficial for forming the L12 structure of Al3(Sc, Er, Zr) nanophase, inducing the formation of equiaxed-columnar composite structure, reducing the hot cracking sensitivity of 7xxx series aluminum alloys in additive manufacturing process, and is suitable for the preparation of complex thin-walled structural parts.

Description

Technical Field

[0001] This disclosure belongs to the field of laser additive manufacturing technology, specifically relating to a crack-resistant, high-strength, and tough rare-earth aluminum alloy suitable for selective laser melting, its preparation method, aluminum alloy parts, additive manufacturing method, and applications. Background Technology

[0002] With the rapid development of aerospace, new energy vehicles, and high-end industrial equipment towards lightweight, high load-bearing capacity, integrated structure, and precision thin-walled construction, complex thin-walled structural components have become the mainstream design direction for core and critical parts such as aircraft fuselage ribs, vehicle battery housings, chassis load-bearing components, and industrial precision housings. Currently, the mainstream material systems for manufacturing high-strength and tough complex thin-walled structural components are Al-Si series casting alloys, 2xxx (Al-Cu), and 7xxx (Al-Zn-Mg-Cu) series high-strength aluminum alloys. Among them, 7xxx series aluminum alloys, as one of the highest-strength commercial aluminum alloys currently available, possess excellent room-temperature comprehensive properties.

[0003] Secondly, for the aforementioned mainstream material systems, the current mainstream preparation processes mainly include casting, extrusion, and machining. These processes include smelting, stepwise feeding of intermediate alloys, long-term refining, semi-continuous casting, multi-stage homogenization, hot extrusion / rolling / forging, and multi-stage heat treatment. These processes are typically carried out at low cooling rates (10...). 1 -10 2 At K / s, the production cycle is long, the precipitated phase has sufficient time to nucleate and grow, and the sensitivity to element ratio is low. However, the current technology has a wide range of element ratios, which cannot reduce the lattice mismatch between the Al3(Sc,Er,Zr) phase and the Al matrix. This results in an excessively long nucleation and incubation period, which is not enough time for precipitation at the solidification front of the molten pool. As a result, the transformation from columnar crystals to equiaxed crystals (CET) cannot be triggered, and hot cracks will still occur. Furthermore, the melting method is prone to element segregation and severe system burn-off. Trace elements such as Zr, Ti, and rare earth elements are difficult to dissolve uniformly. Thin-walled components are prone to microcracks and performance fluctuations due to uneven composition, which in turn affects strength and other properties, and cannot meet the requirements of high-strength and tough complex thin-walled structural components. In addition, selective laser melting (SLM) additive manufacturing can currently be used to integrally form arbitrarily complex hollow, lattice, and thin-walled irregular structures without the need for molds. However, due to the high laser reflectivity and strong thermal conductivity of aluminum alloys, and the wide solidification temperature range of 7xxx series aluminum alloys, the extremely high temperature gradient and cooling rate (10) of SLM can lead to problems. 4 -10 6At K / s, the residual liquid phase cannot fill the tiny voids caused by thermal stress in time, resulting in extremely high susceptibility to hot cracking. More importantly, driven by directional heat dissipation, traditional aluminum alloys are prone to forming coarse epitaxial columnar grains that penetrate multiple molten pools under additive manufacturing conditions. These straight grain boundaries further exacerbate the tendency of crack propagation, severely limiting their practical application in high-end additive manufacturing.

[0004] To address the hot cracking problem of 7xxx series aluminum alloys in the SLM process, various alloying modification methods have been explored. For example, some studies have disclosed the use of mechanical mixing to incorporate submicron-sized Si powder into 7075 aluminum alloy powder; others have employed the addition of Zr particles alone or a combination of Si and Zr. However, simply adding Si easily forms brittle, low-melting-point eutectics at grain boundaries, while the addition of Zr alone, without crystallographic matching optimization, struggles to form a sufficiently dense density of effective nucleation sites at extremely high cooling rates. Related test results show that while these modification methods have somewhat refined the microstructure, micropores remain in the samples, and the highest tensile strength is only 468 MPa, with a yield strength of only 385 MPa. This means that traditional modification methods severely sacrifice the ultra-high strength potential inherent in 7xxx series alloys, making it difficult to achieve a perfect balance between crack-free forming and excellent comprehensive mechanical properties.

[0005] Therefore, in response to the problem of the inability to simultaneously achieve both hot cracking and strong crack resistance in additive manufacturing of 7xxx series high-strength aluminum alloys, the inventors, through long-term research, discovered that by using a low-cost, precisely proportioned composite microalloying design of rare earth and transition elements, combined with optimized laser printing parameters and heat treatment processes, the hot cracking problem of 7xxx series aluminum alloys in additive manufacturing can be solved to a certain extent. This also creates a unique bimodal grain structure, breaking through the bottleneck of the existing technology where "strength and crack resistance cannot be achieved simultaneously," and obtaining excellent comprehensive mechanical properties with extremely high yield strength ratio, high tensile strength, and excellent elongation. Summary of the Invention

[0006] This disclosure aims to at least solve one of the technical problems existing in the prior art, and to provide a crack-resistant, high-strength and tough rare earth aluminum alloy and its preparation method, aluminum alloy parts and additive manufacturing method, and applications.

[0007] One aspect of this disclosure provides a crack-resistant, high-strength, and high-toughness rare-earth aluminum alloy, comprising, by mass percentage: 5.0-8.5% Zn, 1.2-3.5% Mg, 1.5-3.0% Cu, 0.1-0.6% Sc, 0.05-0.4% Er, 0.1-0.5% Zr, 0.1-0.4% Si, 0.05-0.1% Mn, 0.15-0.3% Ti, 0.02-0.04% Cr, with the balance being Al and unavoidable impurities. In the unavoidable impurities, the mass percentage of a single impurity element is ≤0.05%, and the total mass percentage of impurities is ≤0.15%. The mass ratio of Sc to (Er+Zr) is 0.9≤Sc / (Er+Zr)≤1.2.

[0008] Optionally, the mass ratio of Sc to (Er+Zr) is 1.0≤Sc / (Er+Zr)≤1.1.

[0009] In another aspect of this disclosure, a method for preparing the crack-resistant, high-strength, and tough rare-earth aluminum alloy described above is provided, the method comprising: Using high-purity aluminum ingots, pure metal ingots, and aluminum-based master alloys as raw materials; The raw materials are subjected to vacuum induction gradient melting under a protective atmosphere to form a liquid alloy melt with uniform composition. The liquid alloy melt is subjected to degassing and refining treatment to obtain a pure alloy liquid; The pure alloy liquid is atomized into powder, and then sieved to obtain crack-resistant, high-strength and tough rare earth aluminum alloy spherical powder.

[0010] Optionally, the particle size distribution of the crack-resistant, high-strength and tough rare earth aluminum alloy spherical powder is 15-53 µm, the Hall flow rate is ≤35 s / 50 g, and the sphericity is ≥95%.

[0011] Optionally, the step of performing vacuum induction gradient melting on the raw materials under a protective atmosphere to form a homogeneous liquid alloy melt includes: The high-purity aluminum ingot and the aluminum-based master alloy are held at 900-950 ℃ for 20-40 min to obtain a melt; then the melt is cooled to 720-750 ℃, a pure metal ingot is added, and the melt is held at 700-950 ℃ for 10-20 min under electromagnetic stirring. The degassing and refining process includes: Add refining agent at 750-800 ℃ and hold for heat preservation and degassing for 10-20 min; The atomization pressure of the gas atomization powder is 2.0-5.0 MPa, and the flow rate of the molten metal is controlled by a guide tube with an inner diameter of 3.0-4.0 mm.

[0012] In another aspect of this disclosure, an additive manufacturing method for aluminum alloy parts is provided, the additive manufacturing method comprising: Selective laser melting technology was used to form the crack-resistant, high-strength and tough rare-earth aluminum alloy spherical powder described above, resulting in a shaped part. The formed part is subjected to heat treatment, which includes solution treatment and two-stage aging treatment, to obtain an aluminum alloy part.

[0013] Optionally, the process parameters of the selective laser melting technology are set as follows: laser power 400-450 W, scanning speed 700-800 mm / s, scanning spacing 0.08-0.1 mm, and layer thickness 0.03 mm. The solution treatment temperature is 460-480 ℃, and the solution is held for 30-60 min followed by water cooling. The first stage of the two-stage aging process is carried out at a temperature of 100-120 ℃ for 4-8 h, and the second stage is carried out at a temperature of 150-170 ℃ for 8-12 h.

[0014] In another aspect of this disclosure, an aluminum alloy part is provided, which is manufactured using the additive manufacturing method described above.

[0015] Optionally, the aluminum alloy part has a primary nanoscale Al3(Sc,Er,Zr) phase with an L12 structure and an average particle size ≤100 nm; and a bimodal grain structure induced by the L12 phase, the bimodal grain structure including fine equiaxed crystal regions located in the boundary region of the molten pool and columnar crystals located in the center region of the molten pool; The aluminum alloy parts have a room temperature tensile strength ≥580 MPa, a yield strength ≥540 MPa, and an elongation after fracture ≥9.0% along the XY and Z directions.

[0016] Another aspect of this disclosure proposes an aluminum alloy part, as described above, for use in the manufacture of high-strength, tough, complex thin-walled structural parts in the aerospace, automotive, or industrial fields.

[0017] Optionally, the complex thin-walled structural component includes aerospace load-bearing components, automotive lightweight structural components, battery housings, precision instrument housings, or lattice structural components.

[0018] This disclosure presents a crack-resistant, high-strength, and tough rare-earth aluminum alloy, its preparation method, aluminum alloy parts, additive manufacturing method, and applications, which have the following advantages compared to the prior art: (1) This invention designs a 7xxx series aluminum alloy composition with rare earth (Sc, Er) elements and transition metal (Mn, Cr, Ti, etc.) elements in composite microalloying. Utilizing the extremely high cooling rate characteristic of laser additive manufacturing, a large number of dispersed nanoscale strengthening phases are formed in situ in the aluminum matrix. In particular, by compositely adding inexpensive Er and Zr to replace part of the expensive Sc, not only is the material cost significantly reduced, but also coherent composite nanoprecipitates with L12 structures, such as Al3(Sc, Er, Zr), are precipitated, strongly suppressing microstructure coarsening during solidification and significantly reducing the tendency of traditional 7xxx series aluminum alloys to generate hot cracks and micropore defects during additive manufacturing.

[0019] (2) This invention locks in the deep coupling of Sc / (Er+Zr) with additive forming and heat treatment processes through a specific mass ratio, effectively triggering the columnar-to-equiaxed crystal transformation (CET) at the extremely high cooling rate of SLM. The dense equiaxed crystal region at the melt pool boundary can effectively passivate the crack tip, while the columnar crystals in the center ensure strength. This synergistic deformation mechanism of the equiaxed / columnar bimodal structure improves the matching relationship between strength, toughness and crack resistance.

[0020] (3) The rare earth aluminum alloy material of the present invention exhibits excellent near-isotropic mechanical characteristics at room temperature, overcoming the bottleneck that traditional additive manufacturing parts often suffer from a significant performance drop in the vertical direction (Z direction) due to weak interlayer bonding and severe epitaxial growth.

[0021] (4) The rare earth aluminum alloy material for laser additive manufacturing of the present invention has excellent mechanical properties such as excellent formability, no obvious cracks, and high strength and toughness, which can meet the industrial demand for high strength, lightweight and complex structure aluminum alloys. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the method for preparing crack-resistant, high-strength, and tough rare-earth aluminum alloys according to a specific embodiment of this disclosure. Figure 2 This is a flowchart illustrating the additive manufacturing method for aluminum alloy parts according to a specific embodiment of this disclosure. Figure 3 This is a scanning electron microscope image of the crack-resistant, high-strength, and tough rare-earth aluminum alloy powder of Embodiment 1 of this disclosure; Figure 4 This is an optical microscope image of the printed corrosion metallographic structure of the rare earth aluminum alloy part of Embodiment 1 of this disclosure; Figure 5 This is a scanning electron microscope image of the metallographic structure of the rare earth aluminum alloy part in the printed state of Embodiment 1 of this disclosure. Figure 6 This is a phase distribution diagram of the rare earth aluminum alloy part after corrosion according to Embodiment 1 of this disclosure; Figure 7This is a diagram showing the morphology and distribution of the strengthening phase after corrosion of a rare earth aluminum alloy part according to Embodiment 1 of this disclosure. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solutions of this disclosure, the disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain this disclosure and represent a part of the embodiments of this disclosure, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the protection scope of this disclosure.

[0024] One aspect of this disclosure provides a crack-resistant, high-strength, and high-toughness rare-earth aluminum alloy suitable for selective laser melting. The crack-resistant, high-strength, and high-toughness rare-earth aluminum alloy comprises, by mass percentage: 5.0-8.5% Zn, 1.2-3.5% Mg, 1.5-3.0% Cu, 0.1-0.6% Sc, 0.05-0.4% Er, 0.1-0.5% Zr, 0.1-0.4% Si, 0.05-0.1% Mn, 0.15-0.3% Ti, 0.02-0.04% Cr, with the balance being Al and unavoidable impurities. In the unavoidable impurities, the mass percentage of a single impurity element is ≤0.05%, and the total mass percentage of impurities is ≤0.15%. The mass ratio of Sc to (Er+Zr) is 0.9 ≤ Sc / (Er+Zr) ≤ 1.2.

[0025] It should be noted that the crack-resistant, high-strength, and tough rare-earth aluminum alloy provided in this embodiment is a spherical powder, which is an additive manufacturing raw material designed based on selective laser melting (SLM) technology. Because the cooling rate of SLM is as high as 10... 4 -10 6 K / s, the molten pool exists for only milliseconds. Thermodynamically and kinetically, the nucleation barrier is proportional to the square of the lattice mismatch. If the mismatch in SLM is not low enough, the nucleation incubation period will be longer than the molten pool solidification time, resulting in the L12 phase not having enough time to precipitate before the aluminum matrix solidifies into coarse columnar crystals and cracks. Therefore, this embodiment uses Al-Zn-Mg-Cu as the toughening matrix. By precisely controlling the synergistic addition of Sc, Er, and Zr elements and a specific mass ratio (0.9≤Sc / (Er+Zr)≤1.2), a very narrow range of 1.0-1.10 is more preferred. In this way, the rapid solidification of SLM forming (10 K / s) is achieved. 4 -10 6Under extreme non-equilibrium solidification conditions (K / s), the Sc / (Er+Zr) mass ratio is an engineering batching and composition control parameter. Its corresponding atomic ratio range is favorable for the composite occupancy of Sc, Er, and Zr in the Al3X type L12 phase, thereby reducing the lattice mismatch between the Al3(Sc,Er,Zr) phase and the Al matrix. In other words, the composite addition of Sc, Er, and Zr is beneficial for the in-situ formation of a nanoscale Al3(Sc,Er,Zr) phase with an L12 structure. This phase can act as heterogeneous nucleation sites, promoting the transformation of columnar crystals to equiaxed crystals (CET), forming fine equiaxed crystal regions at the melt pool boundary, while retaining columnar crystals in the center, constructing a unique bimodal microstructure. This structure, to some extent, eliminates the extremely high high-temperature hot cracking sensitivity of 7xxx series aluminum alloys. While significantly reducing the cost of Sc, it endows the formed parts with excellent room-temperature strength and plasticity synergy (room-temperature tensile strength ≥580 MPa, elongation after fracture ≥9.0). This technology (%) solved the bottleneck problem of "the inability to achieve both strength and crack resistance" in additive manufacturing of high-strength aluminum alloys.

[0026] It should be noted that the inventors have creatively discovered that when the mass ratio of Sc / (Er+Zr) is controlled within the range of 0.9 ≤ Sc / (Er+Zr) ≤ 1.2, especially within the range of 1.0-1.10, it is beneficial to promote the composite occupancy of Er and Zr atoms in the Al3(Sc,Er,Zr) nanophase and reduce the lattice mismatch between this phase and the Al matrix, thereby forming a highly coherent L12 phase with extremely low lattice mismatch with the aluminum matrix in situ within the matrix. This coherent relationship allows the precipitated phase to lower the heterogeneous nucleation barrier and promote nucleation, constructing a unique "equiaxed shell-columnar core" bimodal structure at the melt pool boundary. Furthermore, this specific ratio of composite phase endows the material with excellent high-temperature stability, which is impossible to achieve in conventional 7xxx series alloys that rely solely on η' phase strengthening.

[0027] In some preferred embodiments, the preferred mass percentages of the components are: 5.8-7.3% Zn, 1.7-2.7% Mg, 1.9-2.6% Cu, 0.35-0.45% Sc, 0.15-0.25% Er, 0.2-0.3% Zr, 0.2-0.4% Si, 0.09-0.1% Mn, 0.15-0.2% Ti, and 0.03-0.04% Cr. This content ensures that the total Zn / Mg / Cu content is sufficiently high to form a high-density η' phase after aging, effectively providing the strength of the 7-series aluminum alloy; the Sc / Er / Zr content enables the in-situ formation of a high-density, nanoscale L12-Al3(Sc,Er,Zr) phase under SLM ultrafast cooling conditions, maximizing grain refinement and resistance to hot cracking. Furthermore, the aforementioned optimal Si content significantly improves the fluidity of the alloy melt. Through the backfilling effect of the Si-rich eutectic liquid film at the end of solidification, it further passivates and closes thermal stress micropores, while the precipitation of nano-Mg2Si phase after heat treatment provides auxiliary strengthening. Secondly, trace amounts of Mn and Cr can combine with impurity elements, purifying grain boundaries and effectively suppressing the segregation of low-melting-point eutectic phases under the rapid solidification conditions of SLM. They also form dispersed intermetallic compounds that pin grain boundaries, improving the alloy's toughness and resistance to stress corrosion cracking. Moreover, Ti can form the Al3Ti phase with Al, serving as an additional nucleation core to aid in grain refinement, while simultaneously improving the thermal stability of the melting and SLM forming processes.

[0028] In some other preferred embodiments, the mass ratio of Sc to (Er+Zr) is preferably 1.0-1.10. This ratio range allows the lattice constant compensation effect of Er and Zr on Sc to be optimal, forming a coherent L12 phase with extremely low lattice mismatch with the aluminum matrix, resulting in better nucleation efficiency and hot crack suppression.

[0029] In this embodiment, on the one hand, the L12 nanophase achieves grain refinement and forms an ultrafine equiaxed grain structure; on the other hand, the Zn-Mg-Cu main strengthening phase precipitates uniformly within the grains and forms a bimodal grain structure, which not only ensures strength but also improves toughness, avoids the formation of brittle grain boundary phases, achieves high density and crack-free SLM formed parts, and solves the forming defect problem of traditional 7-series aluminum alloys in additive manufacturing.

[0030] like Figure 1 As shown, in another aspect of this disclosure, a method S100 for preparing the crack-resistant, high-strength, and tough rare-earth aluminum alloy described above is proposed, specifically including the following steps S110-S140: S110 uses high-purity aluminum ingots, pure metal ingots, and aluminum-based master alloys as raw materials.

[0031] In step S110, the pure metal ingots include pure zinc ingots and pure magnesium ingots, and the aluminum-based master alloys include Al-Cu, Al-Sc, Al-Er, Al-Zr, Al-Si, Al-Mn, Al-Ti, and Al-Cr master alloys.

[0032] In step S110, a step-by-step batching process is adopted to divide the raw materials into a high-melting-point element group (including high-purity aluminum ingots and intermediate alloys other than Zn and Mg) and a volatile element group (pure zinc ingots and pure magnesium ingots) for separate preparation, so as to achieve precise composition control in subsequent smelting steps.

[0033] S120. The raw materials are subjected to vacuum induction gradient melting under a protective atmosphere to form a liquid alloy melt with uniform composition.

[0034] In step S120, high-purity aluminum ingots and aluminum-based master alloys are placed in a crucible of a vacuum induction furnace and heated to 900-950 °C under high-purity argon protection and held for 20-40 min to obtain a melt. This ensures sufficient diffusion and atomic-level solid solution of high-melting-point elements (Sc, Er) and transition elements (Zr) in the aluminum matrix, and effectively suppresses the high-temperature burn-off of volatile elements (Zn, Mg) using the high-purity argon environment. Subsequently, the melt is cooled to 720-750 °C, and pure zinc and magnesium ingots are pressed into the lower part of the melt and held for 10-20 min under electromagnetic stirring. The electromagnetic stirring breaks the compositional gradient inside the melt, ultimately obtaining a highly homogeneous liquid alloy melt.

[0035] S130. The liquid alloy melt is degassed and refined to remove gases and inclusions, resulting in a pure alloy melt.

[0036] In step S130, the degassing and refining process includes: adjusting the melt temperature to 750-800 ℃ after the feeding is completed, adding refining agent and holding for degassing for 10-20 min.

[0037] In some preferred embodiments, the refining agent is a sodium-free refining agent, such as a sodium-free compound flux composed of magnesium chloride, potassium chloride, etc., and its addition amount is 0.1-0.3 wt% of the alloy melt mass.

[0038] The smelting process in this embodiment adopts a two-stage smelting method of "high-temperature alloying + cooling and degassing". It is preferred to melt at a higher temperature and hold it at a higher temperature to ensure that the rare earth phase is completely dissolved. Then, the temperature is lowered and a sodium-free refining agent is added for degassing treatment to cut off the generation of hydrogen pores from the source.

[0039] S140. The pure alloy liquid is atomized into powder and then sieved to obtain crack-resistant, high-strength and tough rare earth aluminum alloy spherical powder.

[0040] In step S140, the atomization pressure of the gas atomization powder is 2.0-5.0 MPa, and the flow rate of the molten metal is controlled by a guide tube with an inner diameter of 3.0-4.0 mm.

[0041] In step S140, the particle size distribution of the crack-resistant, high-strength and tough rare earth aluminum alloy spherical powder is 15-53 µm, the Hall flow rate is ≤35 s / 50 g, and the sphericity is ≥95%.

[0042] This embodiment preferably uses a 3.5 mm guide tube and 2.0-5.0 MPa high-pressure argon gas atomization to prepare high-quality powder with a particle size of 15-53 μm, sphericity ≥95%, and Hall flow rate ≤35 s / 50 g, which provides a foundation for efficient laser absorption and dense forming.

[0043] like Figure 2 As shown, in another aspect of this disclosure, an additive manufacturing method S200 for aluminum alloy parts is proposed, which includes S210-S220: S210. Selective laser melting technology is used to form the crack-resistant, high-strength, and tough rare-earth aluminum alloy spherical powder described above, to obtain the formed part.

[0044] In step S210, the crack-resistant, high-strength, and tough rare-earth aluminum alloy spherical powder prepared above is used as the raw material for additive manufacturing. Selective laser melting technology is used to melt and shape it. The process parameters of selective laser melting technology are set as follows: laser power 400-450 W, scanning speed 700-800 mm / s, scanning spacing 0.08-0.1 mm, layer thickness 0.03 mm, and interlayer rotation angle of 67° or 90° for printing.

[0045] This embodiment employs a high laser power of 400-450 W matched with a scanning speed of 700-800 mm / s. This specific energy density window precisely controls the temperature gradient (G) and solidification rate (V) of the molten pool, ensuring sufficient solidification of high-melting-point elements such as Sc / Zr while maintaining the thermodynamic conditions required to trigger a bimodal microstructure. Furthermore, the interlayer rotation angle of 67° or 90° allows for misaligned overlapping of the melt channels, effectively dispersing residual thermal stress between the high-strength alloy layers.

[0046] S220. The formed part is subjected to heat treatment, which includes solution treatment and two-stage aging treatment.

[0047] In step S220, the solution treatment temperature is 460-480 ℃, and the solution is held for 30-60 min followed by water cooling. Then, without intermediate rolling deformation, a two-stage aging treatment is performed sequentially. The first-stage aging treatment temperature is 100-120 ℃, held for 4-8 h, and the second-stage aging treatment temperature is 150-170 ℃, held for 8-12 h.

[0048] It should be noted that the heat treatment object in this embodiment is an Al-Zn-Mg-Cu-Sc-Er-Zr alloy forming part after selective laser melting. This forming part has a molten pool structure formed by rapid solidification, high residual stress, and L12 structure Al3(Sc,Er,Zr) nanophase induced by Sc, Er, and Zr composite microalloying. Based on this structure, this embodiment, without intermediate rolling deformation, first promotes the formation of GP regions by solute atoms through a first-stage low-temperature aging, and then promotes the dispersion precipitation of the η′ phase through a second-stage medium-temperature aging. At the same time, it is beneficial to retain the grain boundary pinning effect of the L12 structure Al3(Sc,Er,Zr) phase, thereby achieving a synergistic effect of residual stress release, precipitation strengthening, and stabilization of the thermal crack resistance structure.

[0049] This embodiment employs a solution treatment at 460-480 ℃ for 30-60 min followed by water cooling, combined with a specific two-stage aging process (the first stage is held at 100-120 ℃ for 4-8 h, and the second stage is held at 150-170 ℃ for 8-12 h). The first-stage low-temperature aging promotes the formation of high-density, uniformly dispersed GP regions (atomic-rich regions) within the alloy, serving as precursors for subsequent phase transformations. The second-stage high-temperature aging promotes the in-situ transformation of the GP regions into extremely fine η' primary strengthening phases and dispersed fine copper-containing auxiliary strengthening phases. This heat treatment regime simultaneously eliminates residual stress from printing while preserving the pinning effect of the L12 phase, achieving multi-phase synergistic strengthening. In other words, the aforementioned solution temperature not only ensures sufficient remelting of the high-content primary strengthening phase, but more importantly, under the extremely high residual stress characteristic of SLM, this temperature, combined with an extremely narrow proportion of L12 phase, effectively avoids grain boundary remelting, providing a suitable supersaturated solid solution for subsequent two-stage aging.

[0050] In particular, the unique two-stage aging process of 100-120℃ and 150-170℃ disclosed herein is specifically designed to alleviate the residual stress unique to SLM and match the precipitation kinetics of microalloyed phases. The first stage, low-temperature aging treatment (100-120℃), utilizes the extremely high supersaturation vacancies and dislocations within the SLM formed part to promote high-density aggregation of solute atoms to form GP regions. The second stage, medium-temperature aging treatment (150-170℃), relies on the L12 nanophase retained from the previous solid solution treatment as "non-uniform nucleation sites," promoting the dispersion and precipitation of the η' phase around the L12 phase and at high-density dislocations. Compared with some traditional heat treatment processes for wrought aluminum alloys, this disclosure employs a lower-temperature two-stage aging process to avoid excessive coarsening of the nano-strengthening phase in the SLM formed part. Therefore, the heat treatment process of this disclosure successfully balances residual stress release with the synergistic strengthening of the L12 and η' phases. In other words, based on the bimodal microstructure formed by the specific microalloying ratio disclosed in this paper, the two-stage aging not only does not lead to a significant decrease in strength, but also promotes the uniform nucleation of high-density GP regions in a matrix with extremely high dislocation density through the first stage of low temperature, and the second stage of medium temperature causes extremely dispersed fine η' phase to precipitate inside the matrix, while retaining the pinning effect of the L12 coherent phase generated in situ during SLM solidification.

[0051] This embodiment, through the composite addition of Sc, Er, and Zr and the limitation of the Sc / (Er+Zr) content, and by employing gas atomization powder preparation, SLM forming, solution treatment, and two-stage aging synergistic treatment, produces an aluminum alloy part with a unique bimodal grain structure. The molten pool boundary is mainly composed of fine equiaxed crystals induced by nano-scale L12 structure Al3(Sc,Er,Zr) particles, while the center of the molten pool is composed of columnar crystals. Furthermore, Al3(Sc,Er,Zr) maintains a coherent relationship with the aluminum matrix, and its average particle size is ≤100 nm. This solves the problem of high hot cracking sensitivity and the inability to simultaneously achieve strength, toughness, and crack resistance in additive manufacturing of 7xxx series high-strength aluminum alloys.

[0052] In another aspect of this disclosure, an aluminum alloy part is provided, which is manufactured using the additive manufacturing method described above.

[0053] In some preferred embodiments, the rare-earth aluminum alloy parts disclosed herein possess excellent near-isotropic mechanical properties. At room temperature, the tensile strength in both the horizontal (XY) and vertical (Z) directions is ≥580 MPa, the yield strength is ≥540 MPa, and the elongation is ≥9.0%.

[0054] In another aspect of this disclosure, an aluminum alloy part described above is proposed for use in the manufacture of high-strength, high-toughness, complex thin-walled structural parts in the aerospace, automotive, or industrial fields.

[0055] In some preferred embodiments, the complex thin-walled structural component includes aerospace load-bearing components, automotive lightweight structural components, battery housings, precision instrument housings, or lattice structural components.

[0056] It should be emphasized that the rare earth aluminum alloy material disclosed herein belongs to the 7xxx series aluminum alloys, and its internal microscopic synergistic regulation mechanism of alloying elements is as follows: 1. Matrix strengthening elements (Zn, Mg, Cu, Si) Zn and Mg: Both are core elements for precipitation strengthening in alloys during aging. Under specific heat treatments, Zn and Mg combine in the aluminum matrix to precipitate a high-density η' phase (MgZn2). Appropriately increasing the Zn content can enhance the precipitation strengthening response; however, to avoid inducing extremely high susceptibility to high-temperature hot cracking and the formation of coarse, insoluble T phases (AlZnMgCu), this invention optimizes the Zn / Mg ratio, improving the melt solidification path while ensuring high strength. Furthermore, the addition of Mg effectively refines the grains and reduces the tendency for intergranular corrosion.

[0057] Cu: On the one hand, Cu combines with Mg and Al to precipitate S phase (Al2CuMg) and metastable fine θ' phase (Al2Cu), which provide auxiliary strengthening through modulus strengthening and dislocation bypass mechanism (Orowan mechanism), further improving the yield strength of the material and giving the material good plastic deformation coordination ability; on the other hand, Cu can narrow the solidification range of the alloy, and its enriched liquid phase provides a certain backfilling effect at the end of SLM solidification, which helps to reduce the sensitivity to hot cracking.

[0058] Si: Strictly controlled at a low level of 0.1-0.4%. An appropriate amount of Si can effectively reduce the coefficient of thermal expansion of aluminum alloys and significantly reduce melt viscosity, improve the liquid phase fluidity under the extremely high cooling rate of SLM, and suppress porosity and incomplete fusion defects; at the same time, it precipitates dispersed nano-Mg2Si particles during heat treatment, providing auxiliary solid solution and precipitation strengthening.

[0059] 2. Core crack resistance and microstructure evolution elements (Sc, Er, Zr) The core innovation of this invention lies in achieving a significant reduction in material costs and a substantial improvement in crack resistance by locking in a specific mass ratio of Sc / (Er+Zr) (preferably 1.0-1.10). Sc and Er: As core rare earth strengthening elements, they form Al3Sc / Al3Er nanoprecipitates with Al with an L12 structure, strongly pinning grain boundaries and dislocations, inhibiting grain growth, and resulting in a finer and more uniform microstructure; they also increase the recrystallization temperature. In addition, the purifying effect of Sc / Er (removing impurities such as oxygen and hydrogen from the melt) can further improve the density and corrosion resistance of the alloy.

[0060] Zr: As an important transition metal microalloying element, its role is similar to that of Sc / Er. It can form the Al3Zr phase, which helps to refine grains and resist recrystallization.

[0061] 3. Auxiliary microalloying elements (Mn, Ti, Cr) Mn: It forms high-melting-point Al6Mn dispersed particles, which not only strongly pin the subgrain boundaries after solidification, but also help to break the continuous grain boundary precipitation network and delay recrystallization nucleation.

[0062] Unlike traditional forging or semi-solid die casting processes, SLM exhibits an extremely high cooling rate. The addition of trace amounts of Ti and Cr in this invention does not serve a conventional corrosion-resistant or simple grain-refining function. Under the extremely high temperature gradient of SLM, an appropriate amount of Cr effectively suppresses the segregation of the rapidly solidified low-melting-point eutectic phase at grain boundaries. This is achieved through the in-situ precipitation of dispersed intermetallic compounds, resulting in a strong multi-scale synergistic pinning effect on grain boundaries and dislocations. Furthermore, Ti not only forms Al3Ti to aid grain refinement but also undergoes strong multi-element coupling with the composite-added Sc, Er, and Zr, further reducing the nucleation undercooling of the L12 structure Al3(Sc,Er,Zr) composite nanophase. This multi-scale grain boundary pinning mechanism, specifically designed for the rapid solidification of SLM, is neither achievable nor necessary in conventional slow solidification processes (such as die casting or ingot forging).

[0063] 4. Deep coupling between preparation and forming processes The rare earth aluminum alloy preparation method disclosed herein includes selective laser melting (SLM) with specific parameters and heat treatment process. The two-stage aging treatment is designed to eliminate the residual stress unique to SLM and match the precipitation kinetics of microalloyed phases. The heat treatment process successfully takes into account both residual stress release and synergistic strengthening of L12 phase and η' phase.

[0064] The preparation method of rare earth aluminum alloy spherical powder raw material and aluminum alloy parts will be further explained below with reference to specific embodiments.

[0065] Example 1 This embodiment provides a rare earth aluminum alloy spherical powder. By mass percentage, the composition of the rare earth aluminum alloy spherical powder includes: 7.16% Zn, 2.46% Mg, 2.33% Cu, 0.37% Si, 0.094% Mn, 0.38% Sc, 0.15% Er, 0.2% Zr, 0.18% Ti, 0.038% Cr, with the balance being Al and unavoidable impurities.

[0066] Calculations show that the mass ratio of Sc / (Er+Zr) in this embodiment is 1.086, which meets the ratio requirement for promoting efficient heterogeneous nucleation in this invention.

[0067] This embodiment also provides a method for preparing the rare earth aluminum alloy, including the following steps: The preparation process of rare earth aluminum alloy raw material powder is as follows: (1) Raw material ratio: According to the composition ratio, high-purity aluminum ingots, pure zinc ingots, pure magnesium ingots, and Al-Cu, Al-Sc, Al-Er, Al-Zr, Al-Si, Al-Mn, Al-Ti, and Al-Cr intermediate binary alloys are used as raw materials.

[0068] (2) Vacuum induction gradient melting: First, high-purity aluminum ingots and the above-mentioned intermediate binary alloys (excluding Zn and Mg) are placed in the crucible of a vacuum induction furnace and heated to 950 °C under argon protection. After all the materials have melted, the temperature is held for 30 min to allow the high-melting-point rare earth and transition elements to fully diffuse and alloy in the aluminum melt. Then, the alloyed melt is cooled to 750 °C, and pure zinc and pure magnesium ingots are wrapped in aluminum foil and pressed into the lower part of the melt. Electromagnetic stirring is used to fully melt and alloy them, and the temperature is held for 15 min.

[0069] (3) Degassing and refining: At 750 °C, add 0.2% of the total mass of the aluminum alloy-specific sodium-free refining agent to the melt and continue to hold for degassing for 15 min. This step aims to suppress the high-temperature burn-off of volatile elements while removing hydrogen and oxide inclusions inside the melt to obtain a high-purity molten metal.

[0070] (4) Atomization powder making: The refined high-purity metal melt is transferred into the atomization tank and discharged through the guide tube with an inner diameter of 3.5 mm. Argon gas at a pressure of 2.5 MPa is used to atomize the melt into powder. (5) Powder sieving: The particle size of the powder was tested using a Mastersizer 3000 / MS2000 Malvern laser particle size analyzer, and crack-resistant high-strength and tough rare earth aluminum alloy powder with a particle size range of 15-53 µm was obtained. The Hall flow rate of the crack-resistant high-strength and tough rare earth aluminum alloy powder was 35 s / 50 g, and the sphericity was 97%.

[0071] Furthermore, the crack-resistant, high-strength, and tough rare-earth aluminum alloy powder prepared above is used as a raw material for preparing aluminum alloy parts. The manufacturing process of these aluminum alloy parts is as follows: S1. Draw the part model to be printed on the 3D design software, add supports and slice the 3D model, and put the rare earth aluminum alloy raw material powder into the 3D printing equipment for selective laser melting (SLM) additive manufacturing; wherein the SLM laser is 1070 nm infrared light, the substrate preheating temperature is 150 ℃, the laser power is 435 W, the scanning speed is 800 mm / s, the scanning spacing is 0.1 mm, the layer thickness is 0.03 mm, and the rotation angle is 90.

[0072] S2. The formed part is subjected to solution treatment and two-stage aging treatment. The heating rate of the solution treatment is 10 ℃ / min, the holding temperature is 470 ℃, the holding time is 40 min, and then it is water cooled. The first stage of the two-stage aging treatment is held at 110 ℃ for 6 h, and the second stage is held at 160 ℃ for 10 h.

[0073] like Figure 3 As shown, the crack-resistant, high-strength, and tough rare-earth aluminum alloy prepared in this embodiment is a spherical powder.

[0074] like Figure 4 and Figure 5 As shown, the aluminum alloy formed part prepared in this embodiment has very few holes and no obvious defects such as cracks.

[0075] like Figure 6 As shown, the aluminum alloy material has a refined bimodal grain structure, with the molten pool boundary being an equiaxed grain region and the molten pool center being a columnar grain region.

[0076] like Figure 7 As shown, the distribution of the aluminum alloy reinforcing phase along the boundary and center of the molten pool.

[0077] Furthermore, the aluminum alloy parts of this embodiment 1 were subjected to room temperature tensile mechanical property tests. The test method was performed in accordance with GB / T 228.1-2021. The results are shown in Table 1 below. In Table 1, XY is the direction parallel to the substrate, and Z is the deposition direction, i.e., the direction perpendicular to the substrate.

[0078] Table 1. Room temperature tensile mechanical properties of aluminum alloy material in Example 1 along the XY and Z directions.

[0079] As shown in Table 1 above, this embodiment 1, while maintaining high tensile strength and yield strength, exhibits significantly improved elongation after fracture and excellent near-isotropic mechanical characteristics. The tensile strength of the printed sample along the horizontal direction (XY direction) reaches over 582 MPa, and the elongation exceeds 11%; the tensile strength of the printed sample along the vertical direction (Z direction) remains above 580 MPa, and the elongation remains above 9%. This indicates that, based on the Sc / (Er+Zr) mass ratio being within the range specified in this disclosure, further control of the Si content and the combination of solution-two-stage aging treatment are beneficial to improving the molten pool microstructure and precipitate distribution, enhancing the material's plasticity coordination, and thus achieving a comprehensive balance of strength, plasticity, and crack resistance. Simultaneously, it overcomes the bottleneck of traditional additive manufacturing parts where the performance in the vertical direction (Z direction) often declines significantly due to weak interlayer bonding and severe epitaxial growth.

[0080] In summary, the technical solution of this embodiment 1, through specific component design, aluminum alloy preparation process and aluminum alloy raw material properties, enables the prepared rare earth aluminum alloy parts to have excellent mechanical strength such as excellent formability, no obvious cracks and high strength. It can well meet the industrial demand for high strength and toughness, lightweight and complex structure aluminum alloys, and solve the problems of cracks and poor strength that occur in traditional aluminum alloy materials during additive manufacturing.

[0081] Comparative Example 1 This comparative example provides a rare earth aluminum alloy spherical powder, which, by mass percentage, comprises: 7.26% Zn, 2.66% Mg, 2.34% Cu, 0.069% Si, 0.094% Mn, 0.30% Sc, 0.23% Er, 0.22% Zr, 0.24% Ti, 0.033% Cr, with the balance being Al and unavoidable impurities.

[0082] Calculations show that the mass ratio of Sc / (Er+Zr) in this comparative example is 0.667, which is lower than the range of 0.9≤Sc / (Er+Zr)≤1.2 defined in the claims of this disclosure.

[0083] The powder preparation process, selective laser melting forming process, and solid solution-two-stage aging treatment process in this comparative example are basically the same as those in Example 1.

[0084] Compared to Example 1, although this comparative example still contains Sc, Er, and Zr, the Sc / (Er+Zr) mass ratio is lower than the range specified in this disclosure. Therefore, the effective nucleation effect of Sc in the Al3(Sc,Er,Zr) type L12 phase is insufficient, and the synergistic occupancy effect of Sc, Er, and Zr in the L12 structured composite nanophase is difficult to fully exert. This results in a weakened induction effect of the L12 structured Al3(Sc,Er,Zr) nanophase on the transformation from columnar to equiaxed crystals, reduced continuity of the fine equiaxed crystal region at the melt pool boundary, and an increased tendency for columnar crystal growth, making it difficult to form the stable and continuous equiaxed-columnar composite structure as in Example 1.

[0085] Furthermore, the aluminum alloy parts obtained in this comparative example were subjected to room temperature tensile mechanical property tests. The test methods were performed according to GB / T 228.1-2021, and the test results are shown in Table 2. Here, XY represents the direction parallel to the substrate, and Z represents the deposition direction, i.e., perpendicular to the substrate.

[0086] Table 2 shows that although the aluminum alloy parts obtained in Comparative Example 1 have high tensile strength and yield strength, their elongation after fracture is low, with an elongation of 3.5% in the XY direction and 5.5% in the Z direction, significantly lower than that in Example 1. These results indicate that when the Sc / (Er+Zr) mass ratio is below the range specified in this disclosure, the material tends towards high strength characteristics, but lacks sufficient plasticity coordination, making it difficult to simultaneously achieve strength, plasticity, and crack resistance. Therefore, controlling the Sc / (Er+Zr) mass ratio within the range of 0.9 ≤ Sc / (Er+Zr) ≤ 1.2 is beneficial for forming a stable L12 structure Al3(Sc,Er,Zr) nanophase and equiaxed-columnar composite microstructure, thereby achieving a comprehensive balance between strength, plasticity, and crack resistance.

[0087] Table 2. Results of room temperature tensile mechanical properties of the aluminum alloy material in Comparative Example 1 along the XY and Z directions.

[0088] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of this disclosure, and this disclosure is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this disclosure, and these modifications and improvements are also considered to be within the scope of protection of this disclosure.

Claims

1. A crack-resistant, high-strength, and high-toughness rare-earth aluminum alloy, characterized in that, By mass percentage, the crack-resistant, high-strength, and tough rare-earth aluminum alloy comprises: 5.0-8.5% Zn, 1.2-3.5% Mg, 1.5-3.0% Cu, 0.1-0.6% Sc, 0.05-0.4% Er, 0.1-0.5% Zr, 0.1-0.4% Si, 0.05-0.1% Mn, 0.15-0.3% Ti, 0.02-0.04% Cr, with the balance being Al and unavoidable impurities. In the unavoidable impurities, the mass percentage of a single impurity element is ≤0.05%, and the total mass percentage of impurities is ≤0.15%. The mass ratio of Sc to (Er+Zr) is 0.9≤Sc / (Er+Zr)≤1.

2.

2. The crack-resistant, high-strength, and tough rare-earth aluminum alloy according to claim 1, characterized in that, The mass ratio of Sc to (Er+Zr) is 1.0≤Sc / (Er+Zr)≤1.

1.

3. A method for preparing a crack-resistant, high-strength, and tough rare-earth aluminum alloy as described in any one of claims 1-2, characterized in that, The method includes: Using high-purity aluminum ingots, pure metal ingots, and aluminum-based master alloys as raw materials; The raw materials are subjected to vacuum induction gradient melting under a protective atmosphere to form a liquid alloy melt with uniform composition. The liquid alloy melt is subjected to degassing and refining treatment to obtain a pure alloy liquid; The pure alloy liquid is atomized into powder, and then sieved to obtain crack-resistant, high-strength and tough rare earth aluminum alloy spherical powder.

4. The method according to claim 3, characterized in that, The crack-resistant, high-strength, and tough rare-earth aluminum alloy spherical powder has a particle size distribution of 15-53 µm, a Hall flow rate ≤35 s / 50 g, and a sphericity ≥95%.

5. The method according to claim 3, characterized in that, The raw materials are subjected to vacuum induction gradient melting under a protective atmosphere to form a homogeneous liquid alloy melt, comprising: The high-purity aluminum ingot and the aluminum-based master alloy are held at 900-950 ℃ for 20-40 min to obtain a melt; then the melt is cooled to 720-750 ℃, a pure metal ingot is added, and the melt is held at 700-950 ℃ for 10-20 min under electromagnetic stirring. The degassing and refining process includes: Add refining agent at 750-800 ℃ and hold for heat preservation and degassing for 10-20 min; The atomization pressure of the gas atomization powder is 2.0-5.0 MPa, and the flow rate of the molten metal is controlled by a guide tube with an inner diameter of 3.0-4.0 mm.

6. An additive manufacturing method for aluminum alloy parts, characterized in that, The additive manufacturing method includes: Selective laser melting technology is used to form the crack-resistant, high-strength and tough rare earth aluminum alloy spherical powder prepared by any one of claims 3-5 into a shaped part. The formed part is subjected to heat treatment, which includes solution treatment and two-stage aging treatment, to obtain an aluminum alloy part.

7. The additive manufacturing method according to claim 6, characterized in that, The process parameters for the selective laser melting technology are set as follows: laser power 400-450 W, scanning speed 700-800 mm / s, scanning spacing 0.08-0.1 mm, and layer thickness 0.03 mm. The solution treatment temperature is 460-480 ℃, and the solution is held for 30-60 min followed by water cooling. The first stage of the two-stage aging process is carried out at a temperature of 100-120 ℃ for 4-8 h, and the second stage is carried out at a temperature of 150-170 ℃ for 8-12 h.

8. An aluminum alloy part, characterized in that, The aluminum alloy part is manufactured using the additive manufacturing method described in claim 6 or 7.

9. The aluminum alloy part according to claim 8, characterized in that, The aluminum alloy part has a nanoscale Al3(Sc,Er,Zr) phase with an L12 structure and an average particle size ≤100 nm; and a bimodal grain structure induced by the L12 phase, the bimodal grain structure including fine equiaxed crystal regions located in the boundary region of the molten pool and columnar crystals located in the center region of the molten pool. The aluminum alloy parts have a room temperature tensile strength ≥580 MPa, a yield strength ≥540 MPa, and an elongation after fracture ≥9.0% along the XY and Z directions.

10. An aluminum alloy part as described in claim 8 or 9 is used in the manufacture of high-strength, high-toughness, complex thin-walled structural parts in the aerospace, automotive, or industrial fields.

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