High-elongation aluminum alloy for automobile lightweight parts and method for preparing the same

Abstract

This invention discloses a high-elongation aluminum alloy for lightweight automotive components and its preparation method, relating to the field of aluminum alloy material technology. It features a hierarchical porous structure with surface micron-sized closed pores and a core nano-sized through-pore. The Ti and Mn elements synergistically form an Al-Ti-Mn martensitic phase transformation core region with Al, and the Cr element precisely controls the martensitic phase transformation initiation temperature to room temperature, ensuring stable triggering of the austenite-to-martensitic phase transformation and energy absorption during room-temperature collisions. This invention achieves initial impact buffering and gradual collapse energy absorption through a hierarchical porous structure with surface micron-sized closed pores and a core nano-sized through-pore. This dual energy absorption mechanism significantly improves the material's strength-ductility product, far exceeding that of traditional aluminum alloys.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy materials technology, and in particular to high elongation aluminum alloys for lightweight automotive components and their preparation methods. Background Technology

[0002] As the automotive industry rapidly advances towards energy conservation and safety, lightweighting and crash safety have become the core contradictions in automotive design. Lightweight automotive components must reduce their own weight while possessing excellent energy absorption and plastic deformation capabilities to protect occupants during a collision.

[0003] Among the existing aluminum alloy materials used in automobiles, traditional high-elongation aluminum alloys are mostly dense structures, which are prone to local necking fractures during collisions and have limited energy absorption efficiency; while porous aluminum alloys can achieve lightweighting, they generally have problems such as insufficient strength and easy brittle fracture during deformation, making it difficult to meet the requirements of safety components.

[0004] To improve energy absorption performance, some technologies attempt to introduce a martensitic phase transformation mechanism. However, aluminum alloys themselves struggle to form a stable martensitic phase transformation core region, and the phase transformation initiation temperature is difficult to precisely control within the range of normal automotive operating temperatures, resulting in unstable phase transformation energy absorption. Furthermore, the pore walls of existing porous aluminum alloys are mostly homogeneous structures, failing to balance initial strength with the requirements of continuous plastic deformation, further limiting their application in automotive safety components.

[0005] Furthermore, existing preparation techniques struggle to achieve the synergistic construction of hierarchical porous structures and phase change core regions. Either the pore structure has poor uniformity, or the phase change elements are unevenly distributed, making it difficult to simultaneously improve the material's strength-plasticity synergy and energy absorption capacity, thus failing to meet the extreme requirements of lightweight safety components for automobiles. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a high-elongation aluminum alloy for lightweight automotive components and a method for its preparation. The technical solution is as follows:

[0007] High-elongation aluminum alloy for lightweight automotive components features a hierarchical porous structure with surface micron-sized closed pores and core nano-sized through pores; the high-elongation aluminum alloy composition and weight ratio are as follows:

[0008] Mg: 4.0wt%-5.5wt%, Ti: 0.8wt%-1.2wt%, Mn: 1.5wt%-2.0wt%, Sc: 0.15wt%-0.25wt%, Zr: 0.10wt%-0.20wt%, Cr: 0.05wt%-0.15wt%, Fe: 0.08wt%-0.12wt%; Si: 0.01wt%-0.02wt%; balance Al;

[0009] The Ti and Mn work together with Al to form the Al-Ti-Mn martensitic phase transformation core region. The Cr element precisely controls the martensitic phase transformation initiation temperature to room temperature to ensure that the austenite to martensitic phase transformation energy absorption is stably triggered during room temperature collision.

[0010] The surface micron-sized closed pores and the core nano-sized through pores form an integrated gradient heterogeneous structure. The surface layer consists of ultrafine equiaxed crystals, while the core layer contains Al6Mn and Fe-Al pseudo-precipitated phases, which work together with the martensitic phase transformation to achieve continuous plastic deformation and energy absorption.

[0011] Optionally, Fe-Al pseudo-precipitate phases are diffusely distributed in the pore walls and core of the surface micron-closed pores and the core nano-through pores. The Fe-Al pseudo-precipitate phases are distributed in a gradient by double-sided differential temperature heat treatment and exogenous Fe element diffusion technology, and the content of Fe-Al pseudo-precipitate phases gradually increases from the surface of the pore wall to the core.

[0012] The gradient heterogeneous pore wall structure induces stress through heterogeneous deformation, so that the pore wall does not undergo brittle fracture during collision deformation, but can also induce continuous plastic deformation through the Fe-Al pseudo-precipitation phase in the core. This synergistic effect of hierarchical porous structure and martensitic phase transformation achieves a synergistic improvement in strength and plasticity.

[0013] Optionally, the martensitic phase transformation initiation temperature controlled by the Cr element is 0℃-20℃, and the temperature range is fully adapted to the normal temperature use environment of automobiles, ensuring that the phase transformation trigger response time during a collision is less than or equal to 5ms.

[0014] Optionally, the porosity of the surface micron-sized closed pores is 9%-11%, and the pore size is 30μm-50μm; the porosity of the core nano-sized through pores is 16%-18%, the pore size is 8-10nm, and the three-dimensional connectivity of the through pores is greater than or equal to 90%.

[0015] Optionally, the Al6Mn phase in the core of the pore wall is composed of nano-sized particles with a particle size of 50nm-100nm, which are alternately dispersed with the Fe-Al pseudo-precipitate phase to form a dual-phase synergistic reinforcement structure.

[0016] Optionally, the Fe-Al pseudo-precipitate phase has a particle size of 20-50 nm, a content gradient from the pore wall surface to the core of 0.5% / μm-1.0% / μm, and a maximum volume fraction of less than or equal to 8% in the core.

[0017] Optionally, the pore wall thickness of the hierarchical porous structure is 5-15 μm, and the pore wall thickness of the surface micron-sized closed pores is greater than the pore wall thickness of the core nano-sized through pores.

[0018] A method for preparing high-elongation aluminum alloys for lightweight automotive components, comprising the following steps:

[0019] Step 1: Mix high-purity aluminum powder, Al-50Mg master alloy powder, Al-10Ti, Al-20Mn, Al-2Sc, Al-10Zr, and Al-5Cr powders according to the formula ratio, and control the powder particle size to be less than or equal to 50μm.

[0020] Step 2: High-energy ball milling for 12-15 hours under argon protection, ball-to-material ratio (9-10):1, rotation speed 300 r / min, so that Ti and Mn synergistically form nanoscale dispersed pre-phase change cores of Al, to obtain composite powder;

[0021] Step 3: Mix the composite powder with the soluble salt template at a mass ratio of (7-8):3, and add 5% water-soluble binder to granulate;

[0022] Step 4: Use material extrusion molding process to 3D print the surface layer and core according to the set thickness to form a preform with a preset multi-layered porous structure.

[0023] Step 5: After degreasing and pre-curing, the green body is sintered under a set vacuum condition to obtain a sintered green body;

[0024] Step 6: The sintered green body is immersed in 5% hydrochloric acid solution at room temperature for 7-8 hours to dissolve the template. After cleaning and drying, it is subjected to double-sided differential temperature heat treatment, with the surface layer at 450℃-480℃ and the core at 360℃-380℃ for 3-5 minutes, followed by water quenching.

[0025] Step 7: After low-temperature tempering and warm rolling at 250°C, the thickness is reduced by 5% to obtain the finished product.

[0026] Optionally, the soluble salt template mentioned in step 3 is a sodium chloride-potassium chloride composite salt template, and is configured according to the surface and core regions:

[0027] The soluble salt template with a particle size of 30μm-50μm corresponds to the micron-closed pores on the surface, and the soluble salt template with a particle size of 6nm-10nm corresponds to the nano-pores in the core. The two types of soluble salt templates are mixed with the composite powder at a volume ratio of 1:(1.2-1.5) between the surface and the core.

[0028] The specific process parameters for 3D printing in step 4 are as follows: surface printing layer thickness 0.08-0.12mm, core printing layer thickness 0.04-0.06mm, printing speed 4mm / s-6mm / s, nozzle temperature 170℃-190℃, and the printing path adopts differentiated planning of surface honeycomb and core mesh to ensure that the surface layer forms a closed-cell structure and the core forms a three-dimensional interconnected through-cell structure.

[0029] Optionally, the specific process parameters for step 5 are as follows:

[0030] Degreasing treatment: Place the 3D printed blank in a forced-air drying oven and heat it to 110℃-130℃ at a rate of 5℃ / min. Hold it at this temperature for 3-4 hours to completely remove the water-soluble binder and avoid residual impurities affecting the pore structure.

[0031] Pre-curing treatment: After degreasing, heat to 280℃-320℃ at a rate of 10℃ / min and hold for 2-3 hours to allow the composite powder particles to initially form a metallurgical bond and prevent the pore structure from collapsing during subsequent sintering.

[0032] Sintering treatment: The pre-cured green body is placed in a vacuum sintering furnace, and the vacuum degree is controlled to be less than or equal to 1. The temperature is increased to 600℃-620℃ at a rate of 8℃ / min and held for 2.5-3.5 hours to ensure that the powder particles are fully fused without damaging the pre-set porous template.

[0033] In summary, the present invention has at least one of the following beneficial technical effects:

[0034] This invention provides a high-elongation aluminum alloy for lightweight automotive components and its preparation method. By using Ti and Mn in synergy with Al to form an Al-Ti-Mn martensitic phase transformation core region, and by precisely controlling the phase transformation initiation temperature with Cr, the austenite-to-martensitic phase transformation is stably triggered during room temperature collisions, directly capturing a large amount of collision energy during the phase transformation process. At the same time, the hierarchical porous structure of micron-sized closed pores on the surface and nano-sized open pores in the core achieves initial impact buffering and gradual collapse energy absorption. This dual energy absorption mechanism significantly improves the strength-ductility product of the material, far exceeding that of traditional aluminum alloys.

[0035] The pore wall adopts an integrated gradient structure with ultrafine equiaxed crystals on the surface and heterogeneous phases in the core. The fine crystals on the surface strengthen the initial structural integrity and impact resistance, while the gradient distribution of Al6Mn and Fe-Al pseudo-precipitated phases in the core induces continuous plastic deformation, avoiding brittle fracture of the pore wall upon impact, thus achieving a synergistic improvement in strength and elongation.

[0036] The hierarchical porous structure reduces the material density by 8%-12%, significantly improving the lightweight effect; while the synergistic effect of martensitic phase transformation and gradient pore walls ensures that the material is lightweight while improving the collision energy absorption efficiency by more than 60%, fully meeting the dual requirements of automotive safety components for lightweighting and safety.

[0037] The process employs a combination of high-energy ball milling, 3D printing, and double-sided differential temperature heat treatment to precisely control the formation of the phase change core region, the construction of hierarchical porous structures, and the preparation of gradient pore walls. The process parameters are within a reasonable range, have strong repeatability, and are suitable for industrial mass production.

[0038] The material combines high specific strength, high elongation and high energy absorption capacity, and has good isotropy. It can be widely used in a variety of lightweight automotive safety components such as door anti-collision beams, bumpers, energy-absorbing boxes, and seat frames, and is suitable for complex stress scenarios. Attached Figure Description

[0039] Figure 1 This is a schematic flowchart of the method for preparing high elongation aluminum alloy for lightweight automotive components according to the present invention. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to the accompanying drawings.

[0041] This invention discloses a high elongation aluminum alloy for lightweight automotive components and its preparation method.

[0042] Reference Figure 1 Example 1: A high-elongation aluminum alloy for lightweight automotive components, possessing a hierarchical porous structure with surface micron-sized closed pores and core nano-sized through pores; the high-elongation aluminum alloy composition and weight ratio are as follows:

[0043] Mg: 4.0wt%-5.5wt%, Ti: 0.8wt%-1.2wt%, Mn: 1.5wt%-2.0wt%, Sc: 0.15wt%-0.25wt%, Zr: 0.10wt%-0.20wt%, Cr: 0.05wt%-0.15wt%, Fe: 0.08wt%-0.12wt%; Si: 0.01wt%-0.02wt%; balance Al;

[0044] The Ti and Mn work together with Al to form the Al-Ti-Mn martensitic phase transformation core region. The Cr element precisely controls the martensitic phase transformation initiation temperature to room temperature to ensure that the austenite to martensitic phase transformation energy absorption is stably triggered during room temperature collision.

[0045] The surface micron-sized closed pores and the core nano-sized through pores form an integrated gradient heterogeneous structure. The surface layer consists of ultrafine equiaxed crystals, while the core layer contains Al6Mn and Fe-Al pseudo-precipitated phases, which work together with the martensitic phase transformation to achieve continuous plastic deformation and energy absorption.

[0046] By employing the above technical solution, the aluminum matrix itself has a face-centered cubic structure, making it difficult for martensitic phase transformation to occur at room temperature. Titanium and manganese have atomic radii close to aluminum, allowing them to form a stable ternary solid solution. This solid solution exhibits a stable austenitic structure during high-temperature sintering, transforming into a metastable state upon cooling to room temperature. When the instantaneous stress generated by a car collision acts on the material, the free energy of the metastable austenite is higher than that of the martensite. This stress becomes the phase transformation trigger condition, driving the austenite to rapidly transform into martensite through lattice shear. This phase transformation process is accompanied by a significant enthalpy change, directly capturing a large amount of collision energy and preventing energy from being transferred to the passenger compartment as impact loads.

[0047] The martensitic transformation initiation temperature is determined by the lattice distortion energy and chemical composition of the alloy system. Chromium, as a transition metal, undergoes localized lattice contraction due to differences in atomic radii when dissolved in an Al-Ti-Mn ternary solid solution, lowering the free energy barrier required for the phase transformation. By precisely controlling the chromium content, the phase transformation initiation temperature can be stabilized within the ambient temperature range, perfectly adapting to automotive operating environments in most regions globally. Simultaneously, the addition of chromium does not affect the ability of titanium and manganese to form the phase transformation core region, ensuring a rapid response to collision stress and meeting the millisecond-level stress loading requirements of automotive collisions.

[0048] The porosity and pore size design of the surface micron-sized closed-pore structure allow it to buffer impact loads and disperse stress concentration during the initial stage of collision through elastic deformation and slight plastic collapse of the pore walls. The core nanopores are three-dimensional interconnected structures that undergo progressive collapse along the stress direction during collision, forming a continuous structural energy absorption process. The difference in porosity and pore size between the surface closed pores and the core nanopores constructs a buffer-collapse hierarchical energy absorption path, avoiding the problem of discontinuous energy absorption or local failure of a single porous structure, while reducing the overall density of the material and achieving the goal of lightweighting.

[0049] The ultrafine equiaxed grains on the pore wall surface enhance structural integrity through a grain refinement strengthening effect. Their high-density grain boundaries hinder crack initiation and propagation, ensuring the pore wall does not undergo brittle fracture in the initial collision phase. The Al6Mn phase distributed in the pore wall core serves as a nanoscale reinforcing phase, alternately dispersed with the Fe-Al pseudo-precipitate phase, forming a synergistic two-phase structure. The Fe-Al pseudo-precipitate phase generates heterogeneous deformation-induced stress through its gradient distribution, causing continuous strain hardening of the pore wall during deformation. This avoids necking fracture while inducing stable plastic deformation. This gradient structure, combined with martensitic phase transformation and hierarchical porous structure, enables the material to absorb a large amount of energy while maintaining excellent elongation and structural stability.

[0050] Upon impact, the closed pores on the surface initially buffer stress, which is then transferred to the core, triggering a martensitic phase transformation. Energy absorption from this phase transformation occurs simultaneously with energy absorption from the collapse of the through-pores. The gradient heterogeneous structure of the pore walls ensures the material does not fracture under high stress, further absorbing energy through continuous plastic deformation. These mechanisms work together to form a complete energy absorption chain: buffering, phase transformation, collapse, and continuous deformation, ultimately achieving a synergistic balance between lightweight design, high elongation, and high energy absorption capacity.

[0051] Example 2: Fe-Al pseudo-precipitate phase is diffusely distributed in the pore walls and core of the surface micron-closed pores and the core nano-through pores. The Fe-Al pseudo-precipitate phase is distributed in a gradient by double-sided differential temperature heat treatment and exogenous Fe element diffusion technology, and the content of Fe-Al pseudo-precipitate phase gradually increases from the surface of the pore wall to the core.

[0052] The gradient heterogeneous pore wall structure induces stress through heterogeneous deformation, so that the pore wall does not undergo brittle fracture during collision deformation, but can also induce continuous plastic deformation through the Fe-Al pseudo-precipitation phase in the core. This synergistic effect of hierarchical porous structure and martensitic phase transformation achieves a synergistic improvement in strength and plasticity.

[0053] By employing the above technical solution, exogenous Fe element is uniformly mixed in the composite powder in the form of alloy powder, providing the material basis for the formation of Fe-Al pseudo-precipitate phase. Double-sided differential temperature heat treatment constructs a directional temperature gradient through the temperature difference between the surface and the core. The surface is heated to a higher temperature, with sufficient atomic diffusion kinetic energy, making it easier for Fe atoms to dissolve into the aluminum matrix and difficult to form precipitates. The core is heated to a lower temperature, slowing down the atomic diffusion rate, limiting the diffusion distance between Fe and Al atoms, making them more likely to accumulate and react at grain boundaries and defects, forming Fe-Al pseudo-precipitate phase. The difference in diffusion kinetics caused by the temperature gradient causes the amount of Fe-Al pseudo-precipitate phase to gradually increase from the surface of the pore wall to the core, ultimately forming a continuous gradient distribution. This distribution matches the stress requirements of the pore wall, achieving a precise fit between structure and performance.

[0054] The surface layer of the pore wall consists of ultrafine equiaxed crystals, exhibiting high strength and hardness. In the core, due to the gradient distribution of the Fe-Al pseudo-precipitate phase, strength and hardness gradually increase from the surface to the core, creating a significant heterogeneity in mechanical properties. When impact loads are applied to the pore wall, the deformation capabilities of the surface and core differ: the surface tends towards elastic deformation and a small amount of plastic deformation, while the core, under the influence of the Fe-Al pseudo-precipitate phase, undergoes deformation accompanied by dislocation slip and phase interface displacement. This heterogeneity in mechanical properties leads to deformation incoordination, resulting in internal stress in the transition region between the surface and core—i.e., heterogeneous deformation-induced stress. This stress effectively inhibits crack initiation and propagation, preventing brittle fracture of the pore wall during deformation.

[0055] The Fe-Al pseudo-precipitate phase is a nanoscale dispersed second phase that interacts with the aluminum matrix. When the pore walls are subjected to impact stress, the Fe-Al pseudo-precipitate phase acts as a "hindrance point" to dislocation motion, causing dislocations to accumulate at the phase interface. This triggers the initiation of multiple slip systems, promoting continuous plastic deformation. Simultaneously, the gradient distribution of the Fe-Al pseudo-precipitate phase allows deformation stress to be gradually transferred from the surface to the core, preventing deformation interruption caused by localized stress concentration. This gradient-induced continuous plastic deformation effectively dissipates impact energy, compensating for the insufficient energy absorption during deformation of a single structure.

[0056] The gradient heterogeneous pore wall structure, hierarchical porous structure, and martensitic phase transformation work synergistically. The hierarchical porous structure achieves initial energy absorption through buffering and collapse, while the martensitic phase transformation captures a large amount of energy through phase transformation enthalpy change. The gradient heterogeneous pore wall provides structural support for the first two mechanisms. The surface fine-grained reinforcement of the pore wall ensures the integrity of the porous structure in the early stages of collision, preventing premature collapse of the pores. The Fe-Al pseudo-precipitate phase in the core induces continuous plastic deformation, allowing the strengthening effect of the martensitic phase transformation to be fully utilized, preventing the material from becoming brittle due to phase transformation strengthening. The three work together to solve the problem of insufficient strength in porous materials and overcome the limitation of limited plasticity in traditional phase transformation materials, ultimately achieving a simultaneous improvement in strength-plasticity synergy and energy absorption efficiency.

[0057] In Example 3, the martensitic phase transformation initiation temperature controlled by the Cr element is 0℃-20℃. This temperature range is fully adapted to the normal temperature use environment of automobiles, ensuring that the phase transformation trigger response time during a collision is less than or equal to 5ms.

[0058] In Example 4, the porosity of the surface micron-sized closed pores is 9%-11%, and the pore size is 30μm-50μm; the porosity of the core nano-sized through pores is 16%-18%, the pore size is 8-10nm, and the three-dimensional connectivity of the through pores is greater than or equal to 90%.

[0059] In Example 5, the Al6Mn phase in the core of the pore wall is composed of nano-sized particles with a particle size of 50nm-100nm, which are alternately dispersed with the Fe-Al pseudo-precipitate phase to form a dual-phase synergistic reinforcement structure.

[0060] In Example 6, the Fe-Al pseudo-precipitate phase has a particle size of 20-50 nm, and the content gradient from the surface of the pore wall to the core is 0.5% / μm-1.0% / μm, with the highest volume fraction in the core being less than or equal to 8%.

[0061] In Example 7, the pore wall thickness of the hierarchical porous structure is 5-15 μm, and the pore wall thickness of the surface micron-closed pores is greater than the pore wall thickness of the core nano-through pores.

[0062] By employing the above technical solution, after Cr is dissolved into the Al-Ti-Mn ternary solid solution, local lattice contraction is induced by the difference in atomic radii, precisely controlling the phase transition free energy barrier. When the Cr content is in the range of 0.05wt%-0.15wt%, the phase transition initiation temperature is stably locked at 0℃-20℃. This range completely covers the normal temperature range of daily automotive use in most parts of the world, avoiding the problem of phase transition failing to trigger due to excessively high temperatures or occurring prematurely due to excessively low temperatures, regardless of whether the environment is extremely cold or mild.

[0063] Martensitic phase transformation is a diffusionless phase transformation, relying on lattice shear to complete at an extremely fast rate. The addition of Cr further lowers the stress threshold for phase transformation initiation, while the Al3(Sc,Zr) nanoparticles formed by Sc and Zr act as heterogeneous nucleation sites, significantly shortening the phase transformation incubation period. The synergistic effect of both elements keeps the phase transformation trigger response time within 5ms, perfectly matching the millisecond-level stress loading process of a car collision, ensuring that collision energy can be captured in a timely manner.

[0064] The porosity of the surface micron-sized closed pores is set at 9%-11%, and the pore size is 30μm-50μm. This combination of parameters ensures both the lightweight effect of the material and the buffering of the initial impact through elastic deformation and slight plastic collapse of the pore walls. The closed-pore structure with a pore size of 30μm-50μm has moderate strength, preventing excessive deformation or collapse in the early stages of impact, effectively dispersing stress concentration, and laying the foundation for subsequent energy absorption in the core.

[0065] The porosity of the core nanopores is increased to 16%-18%, and the pore size is reduced to 8nm-10nm. The higher porosity provides greater deformation space, and the nanoscale pore size makes the pore walls thinner, which facilitates gradual collapse and continuously consumes collision energy. The three-dimensional connectivity rate ≥90% ensures that the through-pores form continuous deformation channels, avoiding deformation interruption caused by local isolated pores, and making the core collapse uniform and stable.

[0066] The difference in pore parameters between the surface and the core creates a buffer-depth collapse hierarchical energy absorption system. The low porosity and large pore size of the surface ensure structural stability, while the high porosity and small pore size of the core enhance energy absorption efficiency. The two work together to achieve a balance between lightweight and energy absorption capacity.

[0067] During high-temperature sintering, Mn and Al undergo a chemical reaction to form Al6Mn nanoparticles with a particle size controlled between 50nm and 100nm. This size is sufficient to hinder dislocation movement through the Orowan mechanism and improve the material strength, while avoiding stress concentration due to excessively large particles, which would affect plasticity.

[0068] Al6Mn and Fe-Al pseudo-precipitate phases are alternately dispersed, forming a synergistically strengthening dual-phase structure. The Al6Mn phase has higher hardness, focusing on improving the load-bearing capacity of the pore walls and core; the Fe-Al pseudo-precipitate phase has better toughness, focusing on inducing sustained plastic deformation. The alternating distribution of the two phases ensures that dislocation movement is both hindered and strengthened by the Al6Mn phase, and that multiple slip systems are activated under the influence of the Fe-Al pseudo-precipitate phase, avoiding excessive local deformation that could lead to necking, thus achieving a synergistic improvement in both strength and plasticity.

[0069] The Fe-Al pseudo-precipitate phase particle size is set to 20nm-50nm. Particles of this size can be uniformly dispersed in the aluminum matrix and tightly bonded to the matrix interface. This effectively hinders dislocation slip and does not increase brittleness due to particle agglomeration.

[0070] The design, with a content gradient of 0.5% / μm-1.0% / μm, precisely matches the stress gradient of the pore walls. The surface layer of the pore walls needs to maintain deformation flexibility; a low Fe-Al pseudo-precipitate content does not affect the deformation capacity of the fine grains on the surface. From the surface to the core, the stress gradually concentrates, and the Fe-Al pseudo-precipitate content gradually increases, strengthening the core's ability to induce plastic deformation. The maximum volume fraction in the core is ≤8% because excessive Fe-Al pseudo-precipitate leads to an increase in phase interfaces, easily initiating crack initiation. This upper limit balances the strengthening effect with plasticity retention, preventing brittle fracture of the pore walls.

[0071] The overall thickness of the pore wall is controlled between 5μm and 15μm. This range ensures the structural integrity of the pore wall and the stability of the multi-layered porous structure, without sacrificing the lightweight effect due to excessive thickness. Too thin a thickness will result in insufficient pore wall strength, making it prone to fracture in the initial impact phase; too thick a thickness will increase the overall density of the material, weakening the lightweight advantage.

[0072] The surface micron-sized closed pores have a thicker pore wall than the core nano-sized open pores, a design based on the functional division of labor between the two. The surface layer needs to directly withstand the initial impact, and the thicker pore wall can improve impact resistance and prevent premature collapse of the surface closed pores. The core's core function is progressive collapse and energy absorption. The thinner pore wall is more prone to plastic deformation and can reduce deformation resistance, making the collapse process continuous and stable. This forms a "strong support-high deformation" functional synergy with the thicker pore wall of the surface layer, ensuring a continuous and efficient overall energy absorption process.

[0073] Example 8, a method for preparing high elongation aluminum alloy for lightweight automotive components, comprising the following steps:

[0074] Step 1: Mix high-purity aluminum powder, Al-50Mg master alloy powder, Al-10Ti, Al-20Mn, Al-2Sc, Al-10Zr, and Al-5Cr powders according to the formula ratio, and control the powder particle size to be less than or equal to 50μm.

[0075] Step 2: High-energy ball milling for 12-15 hours under argon protection, ball-to-material ratio (9-10):1, rotation speed 300 r / min, so that Ti and Mn synergistically form nanoscale dispersed pre-phase change cores of Al, to obtain composite powder;

[0076] Step 3: Mix the composite powder with the soluble salt template at a mass ratio of (7-8):3, and add 5% water-soluble binder to granulate;

[0077] Step 4: Use material extrusion molding process to 3D print the surface layer and core according to the set thickness to form a preform with a preset multi-layered porous structure.

[0078] Step 5: After degreasing and pre-curing, the green body is sintered under a set vacuum condition to obtain a sintered green body;

[0079] Step 6: The sintered green body is immersed in 5% hydrochloric acid solution at room temperature for 7-8 hours to dissolve the template. After cleaning and drying, it is subjected to double-sided differential temperature heat treatment, with the surface layer at 450℃-480℃ and the core at 360℃-380℃ for 3-5 minutes, followed by water quenching.

[0080] Step 7: After low-temperature tempering and warm rolling at 250°C, the thickness is reduced by 5% to obtain the finished product.

[0081] By adopting the above technical solution and selecting high-purity aluminum powder and master alloy powders of various alloying elements, the impurity content can be precisely controlled, avoiding excessive harmful impurities such as Si from affecting material performance. Controlling the particle size of all powders to ≤50μm increases the specific surface area of ​​the powder, shortens the element diffusion distance during subsequent ball milling, and ensures that functional elements such as Ti, Mn, and Cr can be uniformly dispersed and fully dissolved. The selection of different master alloy powders is based on the solid solution characteristics of each element. Pre-alloying reduces the difficulty of solid solution of elements in the aluminum matrix, laying a material foundation for the subsequent formation of a uniform phase transformation core region and strengthening phase.

[0082] Argon gas protection isolates the powder from air, preventing oxidation during ball milling and avoiding the oxide film from affecting element diffusion and subsequent metallurgical bonding. A ball-to-powder ratio of 9-10:1 and a rotation speed of 300 r / min generate sufficient impact and shear forces to induce severe plastic deformation, breakage, and bonding of the powder particles. A ball milling time of 12-15 hours ensures that elements such as Ti and Mn overcome solid solubility limitations, forcibly dissolving into the aluminum lattice at the nanoscale, while simultaneously forming numerous lattice distortions and nanograin boundaries. These structural defects, along with the nanoscale dispersed Ti-Mn enrichment regions, collectively constitute the pre-transformation nucleus for martensitic transformation, providing the necessary structural conditions for subsequent stress-induced phase transformation.

[0083] The composite powder and soluble salt template are mixed at a mass ratio of 7-8:3. This ratio ensures that the subsequently formed porous structure meets the requirements for lightweighting and energy absorption, while also ensuring that the pore walls have sufficient thickness to support structural stability. The soluble salt template, acting as a "sacrificial skeleton" for the pores, directly determines the subsequent pore size through its particle size distribution, providing a pre-set template for the formation of surface micron-sized closed pores and core nano-sized through pores. Adding 5% water-soluble binder enhances the adhesion between the powder and the template, preventing the particles from becoming loose after granulation and ensuring the formability of the green body during 3D printing. Simultaneously, the binder is easily soluble in water and can be completely removed during the subsequent debinding process, leaving no impurities.

[0084] Material extrusion molding technology can precisely control the output and stacking morphology of printing material, adapting to the differentiated design requirements of multi-layered porous structures. Printing the surface layer and core separately according to a set thickness, through differentiated control of the printing path and parameters, results in a dense honeycomb-like stacking on the surface and a loose mesh-like stacking in the core, laying the macroscopic morphological foundation for subsequent formation of closed-cell and open-cell structures. During printing, the presence of a binder ensures that the powder particles are tightly bonded to the template, ensuring that the preform does not collapse during subsequent processing, achieving precise prefabrication of multi-layered porous structures.

[0085] The core of the degreasing process is to remove the water-soluble binder. This is achieved by gradually increasing the temperature, allowing the binder to slowly evaporate or dissolve, thus preventing rapid heating that could cause cracking of the green body. Pre-curing is performed at 280℃-320℃, at which point slight diffusion and bonding occur on the surface of the powder particles, forming preliminary metallurgical nodules. This prevents the green body structure from becoming loose and collapsing during subsequent sintering due to the presence of the template. The sintering process under vacuum avoids powder oxidation, while the sintering temperature of 600℃-620℃ ensures sufficient diffusion and solid solution of the aluminum matrix and alloying elements, forming Al-Ti-Mn solid solutions and reinforcing phases such as Al6Mn, without prematurely decomposing the soluble salt template, thus ensuring the integrity of the porous template.

[0086] Immersion in a 5% hydrochloric acid solution at room temperature for 7-8 hours rapidly dissolves the soluble salt template. Simultaneously, the hydrochloric acid solution has weak corrosiveness to the aluminum matrix and will not damage the pore wall structure, ultimately forming a hierarchical porous structure consistent with the template morphology. Double-sided differential temperature heat treatment creates a directional temperature gradient through the temperature difference between the surface (450℃-480℃) and the core (360℃-380℃). The high surface temperature ensures sufficient atomic diffusion kinetic energy, allowing more Fe to dissolve into the matrix, forming ultrafine equiaxed crystals. The low core temperature restricts Fe diffusion, causing it to react with Al to form a Fe-Al pseudo-precipitate phase, with its content gradually increasing from the surface to the core, forming a gradient heterogeneous pore wall. Holding at this temperature for 3-5 minutes ensures sufficient phase transformation and precipitation reactions, followed by water quenching to rapidly freeze the gradient structure and metastable austenite state, preserving conditions for subsequent stress-induced phase transformation.

[0087] The purpose of low-temperature tempering is to eliminate the internal stress generated during water quenching, preventing cracking of the billet due to internal stress, and further stabilizing the martensitic transformation initiation temperature to ensure the stability of the phase transformation at room temperature. Warm rolling at 250℃ reduces the thickness by 5%. This slight plastic deformation compacts the hole walls, improving their density and structural integrity. Simultaneously, deformation strengthening further refines the grains, increasing material strength. During warm rolling, the gradient heterogeneous structure of the hole walls is not destroyed; instead, the slight deformation makes the Fe-Al pseudo-precipitate phase distribution more uniform, enhancing the synergistic strengthening effect of the two phases, ultimately resulting in a finished product with excellent strength-plasticity synergy and energy absorption properties.

[0088] Example 9, the soluble salt template mentioned in step 3 is a sodium chloride-potassium chloride composite salt template, and it is configured according to the surface and core regions:

[0089] The soluble salt template with a particle size of 30μm-50μm corresponds to the micron-closed pores on the surface, and the soluble salt template with a particle size of 6nm-10nm corresponds to the nano-pores in the core. The two types of soluble salt templates are mixed with the composite powder at a volume ratio of 1:(1.2-1.5) between the surface and the core.

[0090] The specific process parameters for 3D printing in step 4 are as follows: surface printing layer thickness 0.08-0.12mm, core printing layer thickness 0.04-0.06mm, printing speed 4mm / s-6mm / s, nozzle temperature 170℃-190℃, and the printing path adopts differentiated planning of surface honeycomb and core mesh to ensure that the surface layer forms a closed-cell structure and the core forms a three-dimensional interconnected through-cell structure.

[0091] By employing the above technical solution, both sodium chloride and potassium chloride are water-soluble inorganic salts, readily soluble in hydrochloric acid solution at room temperature. They can be quickly removed without residue during subsequent template etching, preventing corrosion of the aluminum matrix and pore wall structure. The composite salt template formed by these two salts has a higher melting point than the single salts, maintaining morphological stability during the subsequent sintering process (600℃-620℃) and avoiding premature melting that could lead to pore structure collapse. The composite salt has a regular crystal structure and good particle formability, allowing for precise control of particle size distribution through sieving, providing stable template support for the accurate preparation of surface micron-sized closed pores and core nano-sized through pores.

[0092] The preset pore size for the surface micron-sized closed pores is 30μm-50μm, therefore the corresponding template particle size is set to 30μm-50μm. The template particle size directly matches the final pore particle size, ensuring that the closed pore size formed after etching meets the design requirements. The preset pore size for the core nano-sized through pores is 8nm-10nm, paired with a template particle size of 6nm-10nm. This ensures accurate through-pore size while avoiding agglomeration caused by excessively small template particle size, which would affect pore uniformity.

[0093] The volume ratio of the surface layer to the core template is set at 1:1.2-1.5, which is based on the difference in porosity between the two: the core porosity (16%-18%) is higher than that of the surface layer (9%-11%), requiring a larger volume of template to create sufficient pore space. This volume ratio ensures that the surface layer pore walls have sufficient thickness to support structural stability, while the core has sufficient interconnected pores to achieve gradual collapse, avoiding insufficient porosity or pore wall strength due to an imbalance in template usage.

[0094] The surface printing layer is 0.08-0.12 mm thick. This thicker layer allows for sufficient and tight packing of the composite powder and the large-diameter template, reducing interparticle voids and ensuring a closed honeycomb structure after etching, preventing interconnected pores. The core printing layer is 0.04-0.06 mm thick. This thinner layer facilitates the formation of a mesh-like stacking of small-diameter templates, leaving natural interconnected channels between particles. Subsequent etching naturally forms a three-dimensional interconnected nanoporous structure. This differentiated layer thickness design directly adapts to the porosity requirements of the surface and core layers, achieving precise molding of the hierarchical structure.

[0095] A printing speed of 4mm / s-6mm / s is the optimal range for balancing forming efficiency and accuracy: too high a speed will cause the powder and template to accumulate loosely, resulting in a non-dense blank structure that is prone to cracking later; too low a speed will cause the binder to over-cur at the nozzle, affecting the continuity of material output.

[0096] A nozzle temperature of 170℃-190℃ maintains the water-soluble binder's appropriate fluidity, ensuring thorough wetting and bonding of the composite powder and template particles. This prevents excessively high temperatures from causing binder decomposition and volatilization, or excessively low temperatures from resulting in insufficient adhesion and fragmentation of the preform. This temperature range matches the thermal stability of the composite salt template, preventing premature melting or deformation and ensuring the integrity of the template's shape.

[0097] The surface layer employs a honeycomb printing path, with each honeycomb unit being a closed polygon. As powder and template are deposited along this path, the units are tightly connected. After the template is etched away, an independent closed-cell structure is formed, effectively buffering the initial impact of a collision. The core layer uses a mesh printing path, with the mesh structure composed of interwoven lines. As particles accumulate, continuous interconnected channels are formed. After the template is etched away, a three-dimensional interconnected network of pores is created, providing deformation space for progressive collapse during collisions. This differentiated planning of the two paths, combined with the template's partitioned configuration and layered thickness design, precisely achieves a hierarchical porous structure of "surface closed pores + core open pores," laying the structural foundation for the subsequent energy absorption mechanism.

[0098] Example 10, the specific process parameters for step 5 are as follows:

[0099] Degreasing treatment: Place the 3D printed blank in a forced-air drying oven and heat it to 110℃-130℃ at a rate of 5℃ / min. Hold it at this temperature for 3-4 hours to completely remove the water-soluble binder and avoid residual impurities affecting the pore structure.

[0100] Pre-curing treatment: After degreasing, heat to 280℃-320℃ at a rate of 10℃ / min and hold for 2-3 hours to allow the composite powder particles to initially form a metallurgical bond and prevent the pore structure from collapsing during subsequent sintering.

[0101] Sintering treatment: The pre-cured green body is placed in a vacuum sintering furnace, and the vacuum degree is controlled to be less than or equal to 1. The temperature is increased to 600℃-620℃ at a rate of 8℃ / min and held for 2.5-3.5 hours to ensure that the powder particles are fully fused without damaging the pre-set porous template.

[0102] By adopting the above technical solution, the temperature is slowly increased by 5℃ / min to avoid the rapid volatilization of the binder and cracking of the blank. The water-soluble binder can be completely volatilized by holding at 110℃-130℃ for 3-4 hours, preventing residual impurities from clogging the pores or affecting the cleanliness of the pore walls.

[0103] The 10℃ / min heating rate balances efficiency and structural stability, while the 280℃-320℃ holding temperature allows for slight diffusion and welding of the powder particles, forming a preliminary metallurgical bond that provides structural support for subsequent sintering and prevents the collapse of the porous template.

[0104] Less than or equal to High vacuum isolation prevents powder oxidation; heating at 8℃ / min reduces thermal stress and avoids cracking of the green body; holding at 600℃-620℃ for 2.5-3.5 hours ensures that the powder is fully fused to form the target phase, and because the temperature is lower than the melting point of the composite salt template, it ensures that the porous template is completely preserved.

[0105] The following specific embodiments illustrate the implementation principle of the present invention:

[0106] Alloy formulation (by weight percentage):

[0107] Mg: 5.0%, Ti: 1.0%, Mn: 1.8%, Sc: 0.20%, Zr: 0.15%, Cr: 0.10%, Fe: 0.10%, Si: 0.015%, balance Al.

[0108] 2. Preparation process parameters

[0109] Step 1: Mix high-purity aluminum powder, Al-50Mg master alloy powder, Al-10Ti, Al-20Mn, Al-2Sc, Al-10Zr, and Al-5Cr powders, with the powder particle size controlled to 40μm.

[0110] Step 2: High-energy ball milling for 14 hours under argon protection, ball-to-material ratio 9.5:1, rotation speed 300 r / min.

[0111] Step 3: Mix the composite powder with the sodium chloride-potassium chloride composite salt template at a mass ratio of 7.5:3, add 5% water-soluble binder for granulation; the surface template particle size is 40μm, the core template particle size is 8nm, and the template volume ratio is 1:1.3.

[0112] Step 4: 3D print the surface layer with a thickness of 0.10mm, the core layer with a thickness of 0.05mm, the printing speed is 5mm / s, the nozzle temperature is 180℃, the surface layer has a honeycomb pattern, and the core layer has a mesh pattern.

[0113] Step 5: Degreasing: Heat to 120℃ at 5℃ / min and hold for 3.5 hours; Pre-curing: Heat to 300℃ at 10℃ / min and hold for 2.5 hours; Sintering vacuum degree 3×10 -4 Pa, heated to 610℃ at 8℃ / min, and held for 3 hours.

[0114] Step 6: Soak in 5% hydrochloric acid solution at room temperature for 7.5 hours, then perform double-sided differential temperature heat treatment at 460°C for the surface and 370°C for the core, hold for 4 minutes, and then quench in water.

[0115] Step 7: After low-temperature tempering, the thickness is reduced by 5% by warm rolling at 250°C to obtain the finished product.

[0116] The performance test results of the finished product are shown in Table 1:

[0117] Table 1

[0118]

[0119] The performance comparison results of the finished product and the traditional product are shown in Table 2:

[0120] Table 2

[0121]

[0122] The product of this invention surpasses traditional automotive aluminum alloys in all core performance aspects. The strength-ductility product is increased by 310%, 289%, and 198% respectively compared to traditional 6061, 7075, and 5052 aluminum alloys, while the energy absorption efficiency is increased by 183%, 143%, and 196%, achieving a synergistic breakthrough in high strength and high elongation.

[0123] Compared to 6061 and 7075 aluminum alloys, the density is reduced by 1.9% and 5.7% respectively. Combined with a hierarchical porous structure, it offers significant lightweight advantages. The newly added martensitic phase transformation energy absorption mechanism, combined with gradient heterogeneous pore walls and a hierarchical porous structure, enables the material to respond quickly and continuously absorb energy during room temperature collisions. This solves the pain points of traditional aluminum alloys, which are either insufficient in strength or have low elongation and poor energy absorption, making it fully suitable for the use of lightweight safety components in automobiles.

[0124] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A high-elongation aluminum alloy for lightweight automotive components, characterized in that, A hierarchical porous structure with surface micron-sized closed pores and core nano-sized open pores; high elongation aluminum alloy composition and weight ratio: Mg: 4.0wt%-5.5wt%, Ti: 0.8wt%-1.2wt%, Mn: 1.5wt%-2.0wt%, Sc: 0.15wt%-0.25wt%, Zr: 0.10wt%-0.20wt%, Cr: 0.05wt%-0.15wt%, Fe: 0.08wt%-0.12wt%; Si: 0.01wt%-0.02wt%; balance Al; The Ti and Mn work together with Al to form the Al-Ti-Mn martensitic phase transformation core region. The Cr element precisely controls the martensitic phase transformation initiation temperature to room temperature to ensure that the austenite to martensitic phase transformation energy absorption is stably triggered during room temperature collision. The surface micron-sized closed pores and the core nano-sized through pores form an integrated gradient heterogeneous structure. The surface layer consists of ultrafine equiaxed crystals, while the core layer contains Al6Mn and Fe-Al pseudo-precipitated phases, which work together with the martensitic phase transformation to achieve continuous plastic deformation and energy absorption.

2. The high elongation aluminum alloy for lightweight automotive components according to claim 1, characterized in that, Fe-Al pseudo-precipitate phases are diffusely distributed in the pore walls and core of the surface micron-closed pores and the core nano-through pores. The Fe-Al pseudo-precipitate phases are distributed in a gradient by double-sided differential temperature heat treatment and exogenous Fe element diffusion technology, and the content of Fe-Al pseudo-precipitate phases gradually increases from the surface of the pore wall to the core. The gradient heterogeneous pore wall structure induces stress through heterogeneous deformation, so that the pore wall does not undergo brittle fracture during collision deformation, but can also induce continuous plastic deformation through the Fe-Al pseudo-precipitation phase in the core. This synergistic effect of hierarchical porous structure and martensitic phase transformation achieves a synergistic improvement in strength and plasticity.

3. The high elongation aluminum alloy for lightweight automotive components according to claim 2, characterized in that, The martensitic phase transformation initiation temperature controlled by the Cr element is 0℃-20℃, and the temperature range is fully adapted to the normal temperature use environment of automobiles, ensuring that the phase transformation trigger response time is less than or equal to 5ms during a collision.

4. The high elongation aluminum alloy for lightweight automotive components according to claim 3, characterized in that, The porosity of the surface micron-closed pores is 9%-11%, and the pore size is 30μm-50μm; the porosity of the core nano-through pores is 16%-18%, the pore size is 8-10nm, and the three-dimensional connectivity of the through pores is greater than or equal to 90%.

5. The high elongation aluminum alloy for lightweight automotive components according to claim 4, characterized in that, The Al6Mn phase in the core of the pore wall consists of nano-sized particles with a particle size of 50nm-100nm, which are alternately dispersed with the Fe-Al pseudo-precipitate phase to form a dual-phase synergistic reinforcement structure.

6. The high elongation aluminum alloy for lightweight automotive components according to claim 5, characterized in that, The Fe-Al pseudo-precipitate phase has a particle size of 20-50 nm, and the content gradient from the surface of the pore wall to the core is 0.5% / μm-1.0% / μm, with the highest volume fraction in the core being less than or equal to 8%.

7. The high elongation aluminum alloy for lightweight automotive components according to claim 6, characterized in that, The pore wall thickness of the hierarchical porous structure is 5-15 μm, and the pore wall thickness of the surface micron-closed pores is greater than that of the core nano-through pores.

8. A method for preparing high-elongation aluminum alloys for lightweight automotive components, characterized in that: The method for preparing the high elongation aluminum alloy for lightweight automotive components as described in claim 7 comprises the following steps: Step 1: Mix high-purity aluminum powder, Al-50Mg master alloy powder, Al-10Ti, Al-20Mn, Al-2Sc, Al-10Zr, and Al-5Cr powders according to the formula ratio, and control the powder particle size to be less than or equal to 50μm. Step 2: High-energy ball milling for 12-15 hours under argon protection, ball-to-material ratio (9-10):1, rotation speed 300 r / min, so that Ti and Mn synergistically form nanoscale dispersed pre-phase change cores of Al, to obtain composite powder; Step 3: Mix the composite powder with the soluble salt template at a mass ratio of (7-8):3, and add 5% water-soluble binder to granulate; Step 4: Use material extrusion molding process to 3D print the surface layer and core according to the set thickness to form a preform with a preset multi-layered porous structure. Step 5: After degreasing and pre-curing, the green body is sintered under a set vacuum condition to obtain a sintered green body; Step 6: The sintered green body is immersed in 5% hydrochloric acid solution at room temperature for 7-8 hours to dissolve the template. After cleaning and drying, it is subjected to double-sided differential temperature heat treatment, with the surface layer at 450℃-480℃ and the core at 360℃-380℃ for 3-5 minutes, followed by water quenching. Step 7: After low-temperature tempering and warm rolling at 250°C, the thickness is reduced by 5% to obtain the finished product.

9. The method for preparing high elongation aluminum alloy for lightweight automotive components according to claim 8, characterized in that: The soluble salt template mentioned in step 3 is a sodium chloride-potassium chloride composite salt template, and it is configured according to the surface and core regions: The soluble salt template with a particle size of 30μm-50μm corresponds to the micron-closed pores on the surface, and the soluble salt template with a particle size of 6nm-10nm corresponds to the nano-pores in the core. The two types of soluble salt templates are mixed with the composite powder at a volume ratio of 1:(1.2-1.5) between the surface and the core. The specific process parameters for 3D printing in step 4 are as follows: surface printing layer thickness 0.08-0.12mm, core printing layer thickness 0.04-0.06mm, printing speed 4mm / s-6mm / s, nozzle temperature 170℃-190℃, and the printing path adopts differentiated planning of surface honeycomb and core mesh to ensure that the surface layer forms a closed-cell structure and the core forms a three-dimensional interconnected through-cell structure.

10. The method for preparing high elongation aluminum alloy for lightweight automotive components according to claim 9, characterized in that: The specific process parameters for step 5 are as follows: Degreasing treatment: Place the 3D printed blank in a forced-air drying oven and heat it to 110℃-130℃ at a rate of 5℃ / min. Hold it at this temperature for 3-4 hours to completely remove the water-soluble binder and avoid residual impurities affecting the pore structure. Pre-curing treatment: After degreasing, heat to 280℃-320℃ at a rate of 10℃ / min and hold for 2-3 hours to allow the composite powder particles to initially form a metallurgical bond and prevent the pore structure from collapsing during subsequent sintering. Sintering treatment: The pre-cured green body is placed in a vacuum sintering furnace, and the vacuum degree is controlled to be less than or equal to 1. The temperature is increased to 600℃-620℃ at a rate of 8℃ / min and held for 2.5-3.5 hours to ensure that the powder particles are fully fused without damaging the pre-set porous template.

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