A high-strength and high-toughness aluminum alloy formulation and preparation method for automotive exterior parts

Abstract

This invention discloses a high-strength and high-toughness aluminum alloy formula and preparation method for automotive exterior parts. The aluminum alloy uses aluminum as the matrix and is precisely proportioned with Si, Mg, Mn, Cu, Zr, Ti, and trace rare earth elements Y. The mass ratio of each component is strictly controlled. Through a proprietary preparation process of gradient melting, refining and impurity removal, directional solidification, and two-stage aging and shaping, the alloy grains are refined and the distribution of the second phase is optimized. This invention effectively balances the ultra-high strength and excellent toughness of the aluminum alloy. The material has a tensile strength ≥380MPa, an elongation after fracture ≥18%, and is crack-free and has a high surface smoothness. It is suitable for precision machining of various exterior parts such as automotive door trim, bumpers, and rearview mirror housings. It also has excellent weather resistance and structural stability, and has extremely high industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy material technology, specifically relating to a high-strength and high-toughness aluminum alloy formula and preparation method for automotive exterior parts. Background Technology

[0002] After years of development, the aluminum alloy materials and manufacturing processes used in automotive exterior parts have formed a standardized production system. Currently, commercial vehicle exterior parts mostly use conventional grades of aluminum alloys, such as 6061 and 6063. These alloys, with their excellent extrusion molding and surface treatment properties, occupy a mainstream position in the automotive exterior parts market and can meet the basic usage needs of ordinary passenger car exterior parts.

[0003] However, existing conventional aluminum alloy materials for automotive exteriors have core technical problems: the imbalance between strength and toughness leads to poor precision forming performance of the material. During the stamping, bending, and cutting of automotive exterior parts, micro-cracks, wrinkles, and deformation defects are very likely to occur. Moreover, the structural stability of the formed components is insufficient, and they are prone to deformation failure during long-term outdoor service, which cannot meet the precision processing and durability requirements of high-end automotive exterior parts.

[0004] Specifically, existing mainstream 6061 and 6063 aluminum alloys use general-purpose formulations with a wide range of Si and Mg main strengthening elements ratios without precise coupling control. Furthermore, trace refining and modifying elements are added singly or absently. When increasing alloy strength, the Si and Mg content needs to be increased, which easily leads to coarse agglomeration of the Mg2Si strengthening phase, significantly reducing the material's plasticity and toughness. Conversely, when ensuring toughness and formability, the strengthening element content needs to be reduced, which results in insufficient alloy strength and poor structural rigidity. At the same time, existing alloys do not specifically control the impurity content and element ratios. Fe impurities easily form needle-like brittle intermetallic compounds, and the unreasonable ratios of Zr, Ti, and rare earth refining elements fail to effectively refine grains and eliminate microstructure segregation, further exacerbating the imbalance between strength and toughness. Therefore, it is necessary to develop entirely new alloy formulations to solve these core technical problems. Summary of the Invention

[0005] This invention addresses the core technical problems of imbalanced strength and toughness in existing automotive exterior aluminum alloys, as well as the susceptibility to cracking and deformation during precision forming. It innovatively designs a precisely coupled multi-element alloy formulation system, coupled with a proprietary preparation process involving gradient melting, directional solidification, and dual-stage aging. Through precise proportioning of main strengthening elements, composite refinement of trace elements, extreme control of impurities, and precise adaptation of process parameters, it achieves ultra-fine alloy grains and uniformly dispersed strengthening phases. This completely solves the technical bottleneck of traditional alloys where strength and toughness cannot be simultaneously achieved, and poor formability. The result is an automotive exterior aluminum alloy that combines ultra-high strength, high toughness, high surface quality, and high dimensional stability.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A high-strength and high-toughness aluminum alloy formula for automotive exterior parts is composed of the following components by mass percentage: Si: 0.85-1.05%, Mg: 0.90-1.10%, Mn: 0.35-0.50%, Cu: 0.15-0.25%, Zr: 0.12-0.18%, Ti: 0.08-0.12%, rare earth Y: 0.008-0.015%, Fe≤0.10%, single impurity≤0.03%, total impurities≤0.15%, and the balance being high-purity aluminum.

[0008] A preferred embodiment of the present invention comprises the following components by mass percentage: Si: 0.90–1.00%, Mg: 0.95–1.05%, Mn: 0.40–0.45%, Cu: 0.18–0.22%, Zr: 0.14–0.16%, Ti: 0.09–0.11%, rare earth Y: 0.010–0.013%, Fe ≤ 0.08%, single impurity ≤ 0.02%, total impurities ≤ 0.12%, and the balance being high-purity aluminum with a purity ≥ 99.95%.

[0009] In a preferred embodiment of the present invention, the mass ratio of Si to Mg is 1:0.95 to 1:1.15. Controlling this ratio can stably generate the Mg2Si strengthening phase, avoid material embrittlement caused by the enrichment of a single strengthening phase, and ensure the strength of the alloy while retaining its plasticity and toughness.

[0010] In a preferred embodiment of the present invention, the mass ratio of Mn to Cu is 2:1 to 2.8:1. Through the synergistic effect of the two elements, the grains are refined, grain boundary segregation is suppressed, and the fatigue resistance and structural uniformity of the alloy are improved.

[0011] In a preferred embodiment of the present invention, the mass ratio of Zr to Ti is 1.2:1 to 1.8:1, which refines the grains, eliminates dendritic segregation in the as-cast structure, and reduces stress concentration sites during the forming process.

[0012] In a preferred embodiment of the present invention, the single impurity is one element from Zn, Cr, Pb, Sn, Ni, V, P, and S, and the total impurity is the sum of the masses of all impurity elements Zn, Cr, Pb, Sn, Ni, V, P, and S.

[0013] A method for preparing a high-strength and high-toughness aluminum alloy for automotive exterior parts, comprising the following steps: Step S1, raw material pretreatment: Select high-purity aluminum ingots, aluminum-silicon master alloys, aluminum-magnesium master alloys, aluminum-manganese master alloys, aluminum-copper master alloys, aluminum-zirconium master alloys, aluminum-titanium master alloys and rare earth yttrium, remove oxide scale and oil stains from the surface of the raw materials, dry them for later use, drying temperature 120~150℃, heat preservation time 2~3h. Step S2, gradient melting: High-purity aluminum ingots are put into the melting furnace and heated to 680-700℃ for complete melting. The temperature is held for 15-20 minutes. Aluminum silicon, aluminum manganese, and aluminum copper master alloys are added in sequence. The temperature is raised to 710-720℃ and held for 20-25 minutes. Then aluminum magnesium, aluminum zirconium, and aluminum titanium master alloys are added. Finally, rare earth element Y is added. The temperature is raised to 725-735℃ and held for 30-40 minutes. High-purity argon gas is introduced for protection throughout the process. Step S3, refining and impurity removal: Add 0.2-0.4 wt% of aluminum-titanium-boron refining agent to the molten alloy liquid, stir for 5-8 min, let stand for 15-20 min, remove oxide inclusions and gas impurities in the melt, and obtain pure alloy melt after filtration; Step S4, Directional solidification ingot: Pure alloy melt is injected into a metal mold preheated to 280-320°C. A gradient cooling process is adopted, with the bottom of the mold cooling rate at 8-12°C / min, the sidewall cooling rate at 4-6°C / min, and the top naturally and slowly cooled to obtain an aluminum alloy ingot. Step S5, homogenization heat treatment: Heat the aluminum alloy ingot to 540-560℃, hold for 4-6 hours, cool it in the furnace to 300℃, and then remove it from the furnace and air cool it to eliminate the internal stress and compositional segregation in the casting state. Step S6, extrusion molding: Heat the heat-treated ingot to 480-500℃, hold for 1.5-2.5h, and extrude it with an extrusion pressure of 18-22MPa and an extrusion speed of 1.2-1.8m / min to obtain aluminum alloy profiles; Step S7, two-stage aging treatment: first-stage aging temperature 120-130℃, holding for 2-3 hours; second-stage aging temperature 170-180℃, holding for 4-5 hours; remove from the furnace and air-cool to room temperature to complete the preparation.

[0014] In a preferred embodiment of the present invention, in step S3, during the refining and impurity removal process, the argon purity is ≥99.99%, the gas flow rate is 15-20 L / min, the stirring speed is 300-400 r / min, and a 200-mesh ceramic filter plate is used for filtration to thoroughly remove micron-sized inclusions and impurities.

[0015] In a preferred embodiment of the present invention, in step S6, the straightness deviation of the profile after extrusion molding is ≤0.5mm / m, and the surface roughness Ra is ≤0.8μm; in step S7, after the two-stage aging treatment, the Mg2Si strengthening phase inside the alloy is uniformly dispersed, the particle size is controlled at 20-50nm, and there are no agglomerated coarse phases.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. Innovative Formula: Breaking through the traditional wide-range ratio design of general-purpose aluminum alloys, it adopts an original formula system with precise coupling ratio of multiple elements, trace rare earth composite modification, and extreme control of impurities. By limiting the pairwise ratio of core elements, it precisely controls the type, size and distribution of strengthening phases, and for the first time achieves the simultaneous optimal matching of strength, toughness, formability and surface quality of aluminum alloys for automotive exteriors, overcoming the technical bias of traditional formulas that cannot achieve both strength and toughness.

[0017] 2. Technological Innovation: The innovative gradient melting, directional solidification, and two-stage aging synergistic process overturns the traditional general process mode of isothermal melting, natural solidification, and single-stage aging. It precisely controls the microstructure evolution of the alloy in the entire process of melting, solidification, and heat treatment, completely eliminating defects such as microstructure segregation, internal stress, and strengthening phase agglomeration, and maximizing the release of material performance potential.

[0018] 3. Significant performance advantages: The aluminum alloy prepared by this invention has a tensile strength ≥380MPa and an elongation after fracture ≥18%. Compared with the traditional 6063 aluminum alloy (tensile strength 210MPa, elongation 12%), the strength is increased by more than 80% and the toughness is increased by more than 50%. Precision stamping and bending are performed without cracks or deformation, and the forming qualification rate is ≥99.5%. The material has low surface roughness, excellent weather resistance and fatigue resistance, and can be adapted to complex outdoor working conditions for a long time.

[0019] 4. Strong industrial applicability: The raw materials of this invention are readily available and the process is compatible with existing aluminum alloy mass production equipment. It does not require major modifications to the production line and can achieve large-scale industrial production. It is widely applicable to various precision automotive exterior parts, combining economy and high-end compatibility, and has broad market application prospects. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments or prior art, the drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the component ratio of a high-strength and high-toughness aluminum alloy formulation for automotive exterior parts, provided by an embodiment of the present invention.

[0022] Figure 2 This invention provides a flowchart of a method for preparing a high-strength and high-toughness aluminum alloy for automotive exterior parts.

[0023] Figure 3 This is a comparison diagram of the microstructure of the aluminum alloy of the present invention and the traditional 6063 aluminum alloy in the as-cast state.

[0024] Figure 4This is a TEM microstructure diagram of the strengthening phase distribution after the two-stage aging treatment of aluminum alloy according to the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0026] like Figure 1 As shown, this embodiment of the invention provides a high-strength and high-toughness aluminum alloy formulation for automotive exterior parts, composed of the following components by mass percentage: Si: 0.85–1.05%, Mg: 0.90–1.10%, Mn: 0.35–0.50%, Cu: 0.15–0.25%, Zr: 0.12–0.18%, Ti: 0.08–0.12%, rare earth Y: 0.008–0.015%, Fe ≤ 0.10%, single impurity ≤ 0.03%, total impurities ≤ 0.15%, with the balance being high-purity aluminum; preferably, the purity of the high-purity aluminum is ≥ 99.95%.

[0027] Si and Mg are the core strengthening elements of the alloy, which can react to form nano-sized Mg2Si strengthening phases, dispersed in the aluminum matrix, significantly improving the strength and rigidity of the alloy. Mn can refine grains, inhibit grain boundary slip, and improve the toughness and fatigue resistance of the alloy. Cu assists in strengthening, optimizes the crystal structure, and improves the uniformity of the alloy structure. The addition of Zr and Ti can doubly refine the as-cast grains, eliminate dendritic segregation, and reduce the stress concentration sites during forming. Trace amounts of rare earth Y can purify the melt, remove oxide inclusions, refine the second-phase particles, and improve the surface quality and weather resistance of the material. Strictly limiting the content of Fe and total impurities prevents the formation of needle-like brittle phases, thus avoiding material embrittlement and cracking at the source. This formula solves the technical problem of existing automotive exterior aluminum alloys being unable to balance strength and toughness, and prone to cracking and deformation during precision forming, by precisely controlling the ratio of the main strengthening elements Si and Mg and the composite refinement modification of trace amounts of Zr, Ti, and rare earth Y, and by precisely controlling single impurities and total impurities.

[0028] Among them, a single impurity refers to any unavoidable trace metallic or non-metallic impurity element in the alloy system other than the elements specified above. The mass percentage of a single impurity shall not exceed 0.03% to prevent the enrichment of a single impurity to form a local brittle phase and cause stress concentration cracking. The total impurity is the sum of the mass of all single trace impurity elements. The total impurity content is controlled within 0.15% to control the overall purity of the alloy and avoid the accumulation of multiple impurities that cause the matrix structure to become loose and the formability and weather resistance to decrease.

[0029] In some embodiments, the preferred formulation of the high-strength and high-toughness aluminum alloy for automotive exterior parts is an optimal range formulation, consisting of the following components by mass percentage: Si: 0.90–1.00%, Mg: 0.95–1.05%, Mn: 0.40–0.45%, Cu: 0.18–0.22%, Zr: 0.14–0.16%, Ti: 0.09–0.11%, rare earth Y: 0.010–0.013%, Fe≤0.08%, single impurity≤0.02%, total impurities≤0.12%, with the balance being high-purity aluminum with a purity ≥99.95%.

[0030] In some embodiments, the mass ratio of Si to Mg is 1:0.95 to 1:1.15. Controlling this ratio can stably generate the Mg2Si reinforcing phase, avoid material embrittlement caused by the enrichment of a single reinforcing phase, and ensure the strength of the alloy while retaining its plasticity and toughness.

[0031] In some embodiments, the mass ratio of Mn to Cu is 2:1 to 2.8:1. Through the synergistic effect of the two elements, the grains are refined, grain boundary segregation is suppressed, and the fatigue resistance and structural uniformity of the alloy are improved.

[0032] In some embodiments, the mass ratio of Zr to Ti is 1.2:1 to 1.8:1, which refines the grains, eliminates dendritic segregation in the as-cast structure, and reduces stress concentration sites during the forming process.

[0033] In some embodiments, the specific mass addition of rare earth Y is 0.008-0.015%. This trace amount is the optimal narrow range for adapting to the high-strength and tough aluminum alloy system of the present invention. When it is below 0.008%, the rare earth doping amount is insufficient, and it cannot effectively play the role of melt purification and second phase refinement. The inclusions and micropore defects inside the alloy cannot be effectively eliminated. When it is above 0.015%, rare earth Y undergoes element enrichment and segregation, which easily forms coarse rare earth intermetallic compounds, interrupting the continuity of the aluminum matrix, causing a significant decrease in alloy toughness and formability, and increasing raw material costs. This precise trace amount range can efficiently adsorb oxygen and hydrogen gas impurities and oxide inclusions in the melt without changing the main component system of the alloy matrix or generating harmful rare earth phases. It can uniformly refine coarse second phase particles in the matrix, reduce alloy porosity and structural defect rate, and significantly improve the density of the material matrix, surface smoothness and outdoor weather resistance, which is suitable for the high surface precision processing requirements of automotive exterior parts anodizing, coating and other processes.

[0034] In some embodiments, the single impurity is one element from Zn, Cr, Pb, Sn, Ni, V, P, and S, and the total impurity is the sum of the masses of all impurity elements Zn, Cr, Pb, Sn, Ni, V, P, and S.

[0035] In some embodiments, Fe is a major harmful impurity in aluminum alloys. Excessive Fe will react with Al and Si to form acicular AlFeSi brittle phases, disrupting the continuity of the matrix and significantly reducing the toughness of the material. This invention strictly limits the mass percentage of Fe impurities in the alloy to ≤0.10%, which avoids the formation of acicular brittle phases by Fe and Al and Si, completely eliminating the problems of material cracking and reduced toughness caused by brittle phases.

[0036] like Figure 2 As shown in the figure, this invention also provides a method for preparing a high-strength and high-toughness aluminum alloy for automotive exterior parts, characterized by comprising the following steps: Step S1, raw material pretreatment: Select high-purity aluminum ingots, aluminum-silicon master alloys, aluminum-magnesium master alloys, aluminum-manganese master alloys, aluminum-copper master alloys, aluminum-zirconium master alloys, aluminum-titanium master alloys and rare earth yttrium, remove oxide scale and oil stains from the surface of the raw materials, dry them for later use, drying temperature 120~150℃, heat preservation time 2~3h. Step S2, gradient melting: High-purity aluminum ingots are put into a melting furnace and heated to 680-700℃ for complete melting. The temperature is held for 15-20 minutes. Aluminum silicon, aluminum manganese, and aluminum copper master alloys are added in sequence. The temperature is raised to 710-720℃ and held for 20-25 minutes. Then aluminum magnesium, aluminum zirconium, and aluminum titanium master alloys are added. Finally, rare earth element Y is added. The temperature is raised to 725-735℃ and held for 30-40 minutes. High-purity argon gas is introduced for protection throughout the process. Step S3, refining and impurity removal: Add 0.2-0.4 wt% of aluminum-titanium-boron refining agent to the molten alloy liquid, stir for 5-8 min, let stand for 15-20 min, remove oxide inclusions and gas impurities in the melt, and obtain pure alloy melt after filtration; Step S4, Directional solidification ingot: Pure alloy melt is injected into a metal mold preheated to 280-320°C. A gradient cooling process is adopted, with the bottom of the mold cooling rate at 8-12°C / min, the sidewall cooling rate at 4-6°C / min, and the top naturally and slowly cooled to obtain an aluminum alloy ingot. Step S5, homogenization heat treatment: Heat the aluminum alloy ingot to 540-560℃, hold for 4-6 hours, cool it in the furnace to 300℃, and then remove it from the furnace and air cool it to eliminate the internal stress and compositional segregation in the casting state. Step S6, extrusion molding: Heat the heat-treated ingot to 480-500℃, hold for 1.5-2.5h, and extrude it with an extrusion pressure of 18-22MPa and an extrusion speed of 1.2-1.8m / min to obtain aluminum alloy profiles; Step S7, two-stage aging treatment: first-stage aging temperature 120-130℃, holding for 2-3 hours; second-stage aging temperature 170-180℃, holding for 4-5 hours; remove from the furnace and air-cool to room temperature to complete the preparation.

[0037] In step S3, during the refining and impurity removal process, the argon purity is ≥99.99%, the gas flow rate is 15–20 L / min, the stirring speed is 300–400 r / min, and a 200-mesh ceramic filter plate is used for filtration to thoroughly remove micron-sized inclusions. In step S6, after extrusion molding, the straightness deviation of the profile is ≤0.5 mm / m, and the surface roughness Ra is ≤0.8 μm. In step S7, after the two-stage aging treatment, the Mg2Si strengthening phase inside the alloy is uniformly dispersed, with a particle size controlled at 20–50 nm, and no agglomerated coarse phases.

[0038] The gradient melting process, compared to traditional one-time melting, enables the step-by-step stable melting of elements with different melting points, effectively avoiding the burn-off of low-melting-point elements and the agglomeration of high-melting-point elements, ensuring uniform dispersion of all elements. Argon gas is used for full-process protection during melting to prevent oxidation and gas absorption in the melt, reducing oxidation inclusion defects. The directional gradient cooling solidification process precisely controls the cooling rate of different areas of the ingot, achieving orderly grain refinement and eliminating as-cast internal stress. Homogenization heat treatment eliminates component segregation and stabilizes the matrix structure. Controllable extrusion molding ensures the dimensional accuracy and surface quality of the profile. Compared to traditional single-stage aging, two-stage aging enables the step-by-step precipitation and uniform dispersion of strengthening phases, avoiding coarse agglomeration of strengthening phases, and simultaneously improving the strength and toughness of the alloy, solving the problems of uneven structure, performance fluctuations, and forming defects caused by traditional processes.

[0039] like Figure 3 As shown, the traditional 6063 aluminum alloy has obvious coarse dendrites, severe grain boundary segregation, a large number of needle-like brittle phases, and loose areas. The aluminum alloy of the present invention has uniform and fine grains, completely eliminates dendritic structure, has clear and regular grain boundaries, no brittle inclusions or compositional segregation, and has a dense and uniform structure, which directly reflects the optimization effect of composite refining elements and impurity control on the metallographic structure.

[0040] like Figure 4 As shown in the transmission electron microscope (TEM) microstructure image, the uniformly dispersed nanoscale Mg2Si reinforcing phase in the aluminum alloy matrix of this invention can be clearly observed. The particle size of the reinforcing phase is concentrated in the range of 20-50 nm, with no agglomeration or coarse precipitates. The phase is uniformly distributed within the grains and at the grain boundaries, with no obvious defects. This verifies that the two-stage aging process of this invention can precisely control the precipitation state of the reinforcing phase, achieving a high-strength and high-toughness matching effect in the alloy.

[0041] Example 1 A high-strength and high-toughness aluminum alloy formula for automotive exterior parts is composed of the following components by mass percentage: Si: 0.95%, Mg: 1.00%, Mn: 0.42%, Cu: 0.20%, Zr: 0.15%, Ti: 0.10%, rare earth Y: 0.012%, Fe: 0.07%, single impurity ≤0.02%, total impurities ≤0.12%, and the balance being high-purity aluminum with a purity of 99.95%.

[0042] The preparation method includes the following steps: Step S1, raw material pretreatment: Select the corresponding high-purity aluminum ingots and various intermediate alloys and rare earth elements, mechanically remove the surface oxide scale and oil stains, place them in a drying oven at 135℃ for 2.5h, and thoroughly dry the moisture for later use. Step S2, gradient melting: High-purity aluminum ingots are put into a resistance melting furnace, heated to 690℃ for complete melting, and held for 18 minutes; aluminum-silicon, aluminum-manganese, and aluminum-copper master alloys are added in sequence, heated to 715℃ and held for 22 minutes; then aluminum-magnesium, aluminum-zirconium, and aluminum-titanium master alloys are added, and finally rare earth element Y is added, heated to 730℃ and held for 35 minutes, with 99.99% high-purity argon gas purging throughout the process at a flow rate of 18 L / min; Step S3, refining and impurity removal: Add 0.3wt% aluminum-titanium-boron refining agent, stir at 350r / min for 6min, let stand for 18min, and filter the melt using a 200-mesh ceramic filter plate to remove impurities and gases; Step S4, Directional solidification ingot: Pour the pure melt into a metal mold preheated to 300°C, with a bottom cooling rate of 10°C / min, a side wall cooling rate of 5°C / min, and a top natural slow cooling, to obtain an aluminum alloy ingot after complete solidification. Step S5, homogenization heat treatment: The ingot is heated to 550℃ and held for 5 hours, then cooled to 300℃ in the furnace and air-cooled. Step S6, extrusion molding: The ingot is heated to 490℃ and held for 2 hours, and then extruded using an extrusion pressure of 20MPa and an extrusion speed of 1.5m / min to obtain an aluminum alloy profile; Step S7, two-stage aging treatment: first-stage aging at 125℃ for 2.5h, second-stage aging at 175℃ for 4.5h, then air-cooled to room temperature after removal from the furnace to complete the preparation.

[0043] Example 2 A high-strength and high-toughness aluminum alloy formula for automotive exterior parts is composed of the following components by mass percentage: Si: 0.90%, Mg: 0.95%, Mn: 0.40%, Cu: 0.18%, Zr: 0.14%, Ti: 0.09%, rare earth Y: 0.010%, Fe: 0.06%, single impurity ≤ 0.02%, total impurities ≤ 0.12%, and the balance being high-purity aluminum with a purity of 99.95%.

[0044] The preparation method is the same as in Example 1, with each process parameter finely adjusted within the specified range. The melting and holding temperature fluctuates by 5°C, and the aging and holding time fluctuates by 0.2h.

[0045] Example 3 A high-strength and high-toughness aluminum alloy formula for automotive exterior parts is composed of the following components by mass percentage: Si: 1.00%, Mg: 1.05%, Mn: 0.45%, Cu: 0.22%, Zr: 0.16%, Ti: 0.11%, rare earth Y: 0.013%, Fe: 0.08%, single impurity ≤0.02%, total impurities ≤0.12%, and the balance being high-purity aluminum with a purity of 99.95%.

[0046] The preparation method is the same as in Example 1, and the process parameters are adjusted according to the optimal range.

[0047] Comparative Example 1 (Traditional 6063 Aluminum Alloy) Commercially available 6063 aluminum alloy is used, with the following formula: Si: 0.4-0.8%, Mg: 0.4-0.7%, Fe≤0.35%, and the balance being aluminum. It is prepared using conventional smelting and single-stage aging processes.

[0048] Comparative Example 2 (Formula without rare earth modification) The rare earth element Y is removed from the formulation of this invention, and the remaining components and preparation process are completely consistent with those in Example 1.

[0049] Comparative Example 3 (Single-stage aging process) The formula is the same as in Example 1, and the preparation process adopts the traditional single-stage aging (175℃ for 7 hours), with the remaining steps unchanged.

[0050] Mechanical properties, formability, and surface quality of the aluminum alloys in each embodiment and comparative example were tested. The testing standards were based on GB / T 228.1-2021 Standard for Tensile Testing of Metallic Materials and Standard for Forming Testing of Automotive Aluminum Alloy Exterior Parts. The performance test results are as follows: The aluminum alloys prepared in Examples 1-3 have tensile strengths of 385MPa, 382MPa, and 388MPa, respectively, elongation after fracture of 18.6%, 18.2%, and 18.9%, respectively, surface roughness Ra≤0.6μm, no cracks or deformation when stamped and bent at 180°, and a forming qualification rate of 100%.

[0051] Comparative Example 1: Traditional 6063 aluminum alloy has a tensile strength of 212 MPa, an elongation after fracture of 12.1%, and is prone to micro-cracks when bent in thin-walled form, with a forming qualification rate of 85%.

[0052] Comparative Example 2: A rare earth-free aluminum alloy with a tensile strength of 356 MPa, an elongation after fracture of 15.3%, a small amount of inclusions in its microstructure, and a poor surface finish.

[0053] Comparative Example 3: Single-stage aging aluminum alloy with a tensile strength of 362 MPa and an elongation after fracture of 14.8%. The strengthening phase is coarse, the forming stress concentration is obvious, and it is prone to slight deformation.

[0054] Based on the above test results, this invention effectively solves the core technical problems of imbalance between strength and toughness and easy cracking and deformation in precision forming of existing aluminum alloys through original precise formula and exclusive preparation process. The comprehensive performance of the material is far superior to traditional commercial alloys and comparative solutions, and it has outstanding technical advantages and creativity.

[0055] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A high-strength and high-toughness aluminum alloy formula for automotive exterior parts, characterized in that, Composed of the following components by mass percentage composition: Si: 0.85–1.05%, Mg: 0.90–1.10%, Mn: 0.35–0.50%, Cu: 0.15–0.25%, Zr: 0.12–0.18%, Ti: 0.08–0.12%, rare earth Y: 0.008–0.015%, Fe≤0.10%, single impurity≤0.03%, total impurities≤0.15%, balance is high-purity aluminum.

2. The high-strength and high-toughness aluminum alloy formulation for automotive exterior parts according to claim 1, characterized in that, Composed of the following components by mass percentage composition: Si: 0.90~1.00%, Mg: 0.95~1.05%, Mn: 0.40~0.45%, Cu: 0.18~0.22%, Zr: 0.14~0.16%, Ti: 0.09~0.11%, rare earth Y: 0.010~0.013%, Fe≤0.08%, single impurity≤0.02%, total impurities≤0.12%, with the balance being high-purity aluminum with a purity ≥99.95%.

3. The high-strength and high-toughness aluminum alloy formulation for automotive exterior parts according to claim 1, characterized in that, The mass ratio of Si to Mg is 1:0.95 to 1:1.

15. Controlling this ratio can stably generate the Mg2Si strengthening phase, avoid material embrittlement caused by the enrichment of a single strengthening phase, and ensure the strength of the alloy while retaining its plasticity and toughness.

4. The high-strength and high-toughness aluminum alloy formulation for automotive exterior parts according to claim 1, characterized in that, The mass ratio of Mn to Cu is 2:1 to 2.8:

1. Through the synergistic effect of the two elements, the grains are refined, grain boundary segregation is suppressed, and the fatigue resistance and structural uniformity of the alloy are improved.

5. The high-strength and high-toughness aluminum alloy formulation for automotive exterior parts according to claim 1, characterized in that, The mass ratio of Zr to Ti is 1.2:1 to 1.8:1, which refines the grains, eliminates dendritic segregation in the as-cast structure, and reduces stress concentration sites during the forming process.

6. The high-strength and high-toughness aluminum alloy formulation for automotive exterior parts according to claim 1, characterized in that, A single impurity is one of the elements Zn, Cr, Pb, Sn, Ni, V, P, and S. The total impurity is the sum of the masses of all impurity elements Zn, Cr, Pb, Sn, Ni, V, P, and S.

7. A method for preparing a high-strength and high-toughness aluminum alloy for automotive exterior parts, used to prepare the aluminum alloy according to any one of claims 1-6, characterized in that, Includes the following steps: Step S1, raw material pretreatment: Select high-purity aluminum ingots, aluminum-silicon master alloys, aluminum-magnesium master alloys, aluminum-manganese master alloys, aluminum-copper master alloys, aluminum-zirconium master alloys, aluminum-titanium master alloys and rare earth yttrium, remove oxide scale and oil stains from the surface of the raw materials, dry them for later use, drying temperature 120~150℃, heat preservation time 2~3h. Step S2, gradient melting: High-purity aluminum ingots are put into the melting furnace and heated to 680-700℃ for complete melting. The temperature is held for 15-20 minutes. Aluminum silicon, aluminum manganese, and aluminum copper master alloys are added in sequence. The temperature is raised to 710-720℃ and held for 20-25 minutes. Then aluminum magnesium, aluminum zirconium, and aluminum titanium master alloys are added. Finally, rare earth element Y is added. The temperature is raised to 725-735℃ and held for 30-40 minutes. High-purity argon gas is introduced for protection throughout the process. Step S3, refining and impurity removal: Add 0.2-0.4 wt% of aluminum-titanium-boron refining agent to the molten alloy liquid, stir for 5-8 min, let stand for 15-20 min, remove oxide inclusions and gas impurities in the melt, and obtain pure alloy melt after filtration; Step S4, Directional solidification ingot: Pure alloy melt is injected into a metal mold preheated to 280-320°C. A gradient cooling process is adopted, with a cooling rate of 8-12°C / min at the bottom of the mold, a cooling rate of 4-6°C / min at the sidewalls, and natural slow cooling at the top, to solidify and obtain an aluminum alloy ingot. Step S5, homogenization heat treatment: Heat the aluminum alloy ingot to 540-560℃, hold for 4-6 hours, cool it in the furnace to 300℃, and then remove it from the furnace and air cool it to eliminate the internal stress and composition segregation in the casting state. Step S6, extrusion molding: Heat the heat-treated ingot to 480-500℃, hold for 1.5-2.5h, and extrude it with an extrusion pressure of 18-22MPa and an extrusion speed of 1.2-1.8m / min to obtain aluminum alloy profiles; Step S7, two-stage aging treatment: first-stage aging temperature 120-130℃, holding for 2-3 hours; second-stage aging temperature 170-180℃, holding for 4-5 hours; remove from the furnace and air-cool to room temperature to complete the preparation.

8. The method for preparing high-strength and high-toughness aluminum alloy for automotive exterior parts according to claim 7, characterized in that, In step S3, during the refining and impurity removal process, the argon purity is ≥99.99%, the gas flow rate is 15~20L / min, the stirring speed is 300~400r / min, and a 200-mesh ceramic filter plate is used for filtration to thoroughly remove micron-sized inclusions and impurities.

9. The method for preparing high-strength and high-toughness aluminum alloy for automotive exterior parts according to claim 7, characterized in that, In step S6, the straightness deviation of the extruded profile is ≤0.5mm / m and the surface roughness Ra is ≤0.8μm; in step S7, after the two-stage aging treatment, the Mg2Si strengthening phase inside the alloy is uniformly dispersed, with the particle size controlled between 20 and 50nm, and there are no agglomerated coarse phases.

Images