High-strength and high-toughness Al-Cu-Mg series cast aluminum alloy and preparation method thereof

Abstract

The invention discloses a high-strength and high-toughness Al-Cu-Mg series cast aluminum alloy and a preparation method of the high-strength and high-toughness Al-Cu-Mg series cast aluminum alloy. The alloy comprises the following components in percentage by mass: 3.5%-5.5% of Cu; 2.0% to 2.5% of Mg; 0.15% to 0.25% of Si; mn: 0.5%-1.0%; 0.05% to 0.15% of Cr; 0.08%-0.15% of V, and 0.10%-0.20% of Ti; 0.02% to 0.06% of La; 0.02% to 0.06% of Ce; 0.01% to 0.03% of Sr; fe: less than or equal to 0.25%; and the balance of Al and other inevitable impurities. According to the invention, through collaborative optimization of a process route of chemical component design, smelting casting molding control, multi-stage solution treatment and staged aging, the elongation after fracture is effectively maintained and even improved while the tensile strength and the specified plastic extension strength are remarkably improved, so that the synchronous improvement of the strength and the toughness in a casting system is realized.

Description

Technical Field

[0001] This invention belongs to the field of alloy material preparation technology, and specifically relates to a high-strength and high-toughness Al–Cu–Mg cast aluminum alloy and its preparation method. Background Technology

[0002] In recent years, Al-Cu-Mg aluminum alloys have gradually become an important component of high-performance structural materials due to their high specific strength and low density. These alloys maintain high mechanical strength even under medium- and high-temperature conditions, significantly improving the stability and reliability of critical components in automobiles and other applications under extreme temperature conditions. Therefore, they have gained widespread attention and application in fields with stringent material performance requirements, such as aerospace and automotive lightweighting. Furthermore, appropriately increasing the magnesium content not only helps enhance the precipitation strengthening effect and overall mechanical properties but also reduces the unit cost while meeting performance requirements, making the material more economical while maintaining excellent comprehensive performance. Based on these advantages, Al-Cu-Mg alloys show broad application prospects in high-end fields such as aerospace and automotive lightweighting.

[0003] For example, patent CN115652154A provides a casting aluminum alloy material with the following chemical composition: Cu 5.3–6.4%, Mg 0.05–0.40%, Mn 0.10–0.50%, Ti 0.02–0.10%, Zr 0.10–0.25%, Yb 0.20–0.40%, Sc 0.30–0.80%, unavoidable impurities, and the balance Al. By adding higher contents of rare earth elements such as zirconium, scandium, and ytterbium, the grains are refined and the formation of Al3(Sc,Zr) / Al3Sc precipitates is promoted, thereby significantly improving the strength and toughness of the alloy.

[0004] Based on production practices and literature reviews, while existing patents have improved the strength of Al-Cu-Mg alloys to some extent, their effect on improving elongation after fracture is limited, and the cost of the elements used is high. This leads to increased production costs, making it difficult to meet the demands of industrialized aluminum alloy production and large-scale applications.

[0005] Therefore, there is an urgent need to develop a new Al-Cu-Mg cast aluminum alloy to simultaneously meet the dual performance challenges of high strength and high toughness. Summary of the Invention

[0006] To address the aforementioned problems and deficiencies, this invention provides a high-strength and high-toughness Al–Cu–Mg cast aluminum alloy.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A high-strength and high-toughness Al–Cu–Mg cast aluminum alloy, with the following chemical composition by mass percentage: Cu: 3.5%–5.5%; Mg: 2.0%–2.5%; Si: 0.15%–0.25%; Mn: 0.5%–1.0%; Cr: 0.05%–0.15%; V: 0.08%–0.15%; Ti: 0.10%–0.20%; La: 0.02%–0.06%; Ce: 0.02%–0.06%; Sr: 0.01%–0.03%; Fe: ≤0.25%; the balance being Al and other unavoidable impurities.

[0008] The functions of each element in this invention are as follows: Cu and Mg form S-series phases with the chemical formula Al2CuMg during the "solution treatment-quenching-aging" process. The precipitation sequence is: supersaturated solid solution → Cu–Mg copolymer clusters / GPB region (Guinier–Preston–Bagaryatsky region) → coherent lamellae S″ → semi-coherent lamellae S′ → equilibrium phase S. Among these, the coherent lamellae S″ / semi-coherent lamellae S′ exhibit good coherent or semi-coherent interfacial relationships and high interfacial stress, effectively pinning and bending dislocations and inhibiting slip system initiation, thus significantly improving the specified ductile elongation strength and tensile strength of the material. Under the synergistic effect of high Cu content (3.5%–5.5%) and high Mg content (2.0%–2.5%), the semi-coherent lamellae S′ become the dominant precipitate phase during the aging stage, achieving high strength while maintaining good toughness and ensuring a stable process window. Within the Cu content range of 3.5%–5.5%, Cu significantly improves the strength of the alloy through its synergistic effect with Mg. The addition of Cu leads to the formation of S-series phases, namely Al₂CuMg, in the alloy. These precipitates effectively pin and bend dislocations, inhibiting slip system initiation and thus enhancing the tensile strength and yield strength of the material. Excessive Cu content can result in overly large precipitates, causing the alloy to become brittle and affecting toughness. Therefore, a Cu content of 3.5%–5.5% ensures both strengthening and good toughness. The Mg content is selected between 2.0% and 2.5% to optimize the precipitation behavior of the S′ phase, thereby improving the alloy's strength. Within this range, Mg and Cu work together to promote the formation of the S′ phase and effectively improve the alloy's tensile strength. Too low a Mg content results in insufficient S′ phase precipitation and an insignificant strengthening effect; while excessively high Mg content leads to coarsening of the precipitates, reducing the alloy's plasticity. By controlling the Mg content between 2.0% and 2.5%, an alloy with high strength and good toughness can be obtained.

[0009] The Si content setting of 0.15%–0.25% balances filling performance and precipitation path control: within the aforementioned Mg content range, only a limited and dispersed distribution of Mg2Si forms, providing auxiliary precipitation strengthening for strength; simultaneously, an appropriate amount of Si helps suppress the formation of the metastable phase Q′ / equilibrium phase Q (Al5Cu2Mg8Si) continuous network and coarse eutectic Mg2Si phase, avoiding the diversion and consumption of Mg elements, weakening the strengthening effect of the S′ phase, and reducing forming efficiency. The selection of Si content between 0.15% and 0.25% is mainly to control the formation of precipitates while ensuring the aluminum alloy's filling performance, thereby optimizing the material's strength and processing performance. An appropriate amount of Si helps improve the alloy's fluidity and enhance its filling ability, while avoiding excessive Mg2Si precipitation and maintaining the alloy's toughness. In addition, the intermetallic compounds formed by the reaction of Si with impurity Fe can reduce the negative impact of Fe, thereby improving the overall performance of the alloy. This invention achieves an optimal balance between material strength and manufacturability by precisely controlling the Si content and coordinating with appropriate heat treatment processes to encourage Mg to preferentially participate in the S-system precipitation process and suppress interphase competition mechanisms.

[0010] The synergistic effect of Mn (0.5%–1.0%) and Cr (0.05%–0.15%) can promote the transformation of brittle needle-like or plate-like β-AlFeSi phases in the as-cast state into blunt, rounded α-Al(Fe,Mn,Cr)Si phases, thereby significantly reducing stress concentration and crack susceptibility. Furthermore, Al6Mn and Al2O3 phases will precipitate during heat treatment. 12 (Fe,Mn)3Si and a small amount of Al7Cr / Al 13 High-melting-point dispersed phases such as Cr2 exert a Zener pinning effect on dislocations, subgrain boundaries, and grain boundaries, effectively suppressing recrystallization and grain growth, thereby improving the stability and consistency of microstructure and mechanical properties in thick-section and thin-walled parts. It is particularly noteworthy that the Fe phase not only changes from needle-like or plate-like morphology to blunt rounded shape, but its particle size also becomes finer and more uniformly distributed, thus transforming from a potential crack initiation phase into a stable precipitate that facilitates dispersed pinning.

[0011] The addition of 0.10%–0.20% Ti and 0.08%–0.15% V introduces compositional supercooling at the solidification front, increasing the nucleation rate and reducing the grain growth rate, thereby obtaining a fine and uniform equiaxed grain structure. The trace amounts of B (≤0.01%) introduced by the grain refiner used with Ti further promote heterogeneous nucleation behavior through TiB2 / Al3Ti nuclei, enhancing the grain refinement effect. Furthermore, the addition of V to the alloy improves its high-temperature properties, particularly enhancing creep resistance and thermal stability, allowing the alloy to better maintain its mechanical properties at high temperatures. V, through synergistic effects with elements such as Ti and Cr, forms a stable Al3(Ti,V,Cr) dispersed precipitate. This phase continuously pins dislocations and subgrain boundaries during subsequent heat treatment and provides heterogeneous nucleation sites for S′, thereby improving precipitation density and nucleation stability, achieving a dual strengthening mechanism of grain refinement and dispersion strengthening. The selection range of V (0.08%–0.15%) mainly promotes the formation and stabilization of the precipitate through synergistic effects with Ti and Cr, thereby enhancing the overall properties of the alloy. This range ensures that V enhances the mechanical properties and thermal stability of the alloy while maintaining good processability and toughness. La (0.02%–0.06%) and Ce (0.02%–0.06%) generate fine rare earth-aluminum compounds, such as Al, in the aluminum matrix. 11 (RE)3 and Al2(RE), where RE represents La and Ce, have a significant modifying and purifying effect on brittle eutectic phases and oxide inclusions in the as-cast microstructure, effectively refining the secondary dendrite arm spacing and reducing potential crack initiation sites. During aging treatment and service, these particles have a stabilizing effect on phase boundary migration and atomic diffusion processes, delaying over-aging softening behavior and improving the thermal stability of the microstructure. Controlling rare earth elements within a narrow range helps avoid the precipitation of coarse rare earth phases, thus mitigating their adverse effects on toughness. At the microscale, the fine α-Al(Fe,Mn,Cr)Si phase, rare earth-aluminum compounds, and Al3(Ti,V,Cr) dispersed precipitates commonly found in this alloy are adjacent or coexisting in local micro-regions, forming "fine-grained composite strengthening units". On the one hand, this unit acts as an unshearable barrier and Zener pinning source (referring to the physical barrier effect of certain small particles on grain boundaries or dislocations, which restricts grain growth or dislocation movement), effectively suppressing dislocation movement and substructure evolution; on the other hand, it provides heterogeneous nucleation sites for S′ precipitation, synergistically improving precipitation density and stability, thereby achieving comprehensive optimization of material strength and toughness.

[0012] Furthermore, Sr, at 0.01%–0.03%, acts as an effective modifier, significantly regulating the morphology of the small amount of eutectic Si phase present during solidification: the originally needle-like or blocky Si phase is refined into a dispersed fibrous structure, thereby effectively reducing stress concentration and crack sensitivity. Simultaneously, Sr can also delay the eutectic solidification process, improve the alloy's filling and feeding properties, and thus reduce shrinkage porosity and hot cracking tendency. Given that the Si content in this alloy is strictly controlled within a narrow compositional range of 0.15%–0.25%, Sr can still fully exert its modifying effect in the limited eutectic structure, forming a synergistic enhancement effect with the modification effect of Mn / Cr on the Fe phase. Further research shows that the introduction of Sr helps reduce the ineffective consumption of Mg, inhibits the formation of coarse Mg2Si eutectic phase, promotes Mg preferential participation in the S-system precipitation reaction, and ensures the precipitation pathway dominated by the S′ phase. Therefore, in the system of this invention, Sr not only improves casting process performance, such as filling performance and resistance to hot cracking, at the macroscopic level, but also indirectly improves the stability of material mechanical properties through microstructure optimization.

[0013] Furthermore, the mass ratio of Cu to Mg is controlled between 1.6 and 2.5, that is, 1.6≤Cu / Mg≤2.5.

[0014] By controlling the Cu / Mg mass ratio within the range of 1.6 to 2.5, it can be ensured that the reserves of Cu and Mg elements are sufficient without being redundant.

[0015] Furthermore, the total mass percentage of Mn and Cr is 0.65% to 0.95%.

[0016] Furthermore, the total mass percentage of Ti and V is 0.25% to 0.3%.

[0017] Furthermore, the total mass percentage of La and Ce is 0.06% to 0.1%.

[0018] This invention provides a method for preparing a high-strength and high-toughness Al–Cu–Mg cast aluminum alloy, comprising the following steps: (1) Raw material preparation and preheating; Prepare industrial pure aluminum, master alloys Al–Mn, Al–V, Al–Cr, Al–Cu, Al–Si, Al–Ti–B, Al–La, Al–Ce, Al–Sr with a purity ≥99.7%, and pure magnesium ingots with a purity ≥99.9%. All raw materials and smelting tools should be thoroughly dried and preheated to 100℃~150℃.

[0019] (2) Smelting and alloying; After preheating, the alloy melt is obtained by sequentially smelting, refining and removing impurities.

[0020] Furthermore, in step (2) of this application, the aluminum material is heated to 740°C to 760°C to completely melt it, then the slag is removed, and then the temperature of the melt is raised to 750°C to 780°C and held for 5 min to 10 min.

[0021] Furthermore, in step (2) of this application, Al–Mn→Al–V→Al–Cr→Al–Cu→Al–Si→Al–Sr→pure magnesium ingot→Al–La→Al–Ce→Al–Ti–B are added sequentially.

[0022] Furthermore, in step (2) of this application, the Al–Mn, Al–V, and Al–Cr master alloys are added in stages. After each addition, the mixture is stirred at an outer edge linear velocity of 0.8 m / s to 1.2 m / s for 2 min to 5 min. The overall heat preservation time during the alloy addition stage is 8 min to 15 min.

[0023] Furthermore, in step (2) of this application, after adding the Al–Cu and Al–Si master alloys, the mixture is stirred for 2 to 3 minutes to ensure complete melting.

[0024] Furthermore, in step (2) of this application, the aluminum liquid is refined by using a refining agent at 740℃~750℃ for three refining processes. The amount of refining agent used in each process is 0.08%~0.12% of the melt mass, and the refining time for each process is 15min~20min. An inert gas is introduced during refining, and the mixture is allowed to stand for 10min~20min after refining.

[0025] Furthermore, an Al–Sr master alloy was added at a temperature range of 730℃ to 740℃ and gently stirred for 1 to 2 minutes.

[0026] Furthermore, in step (2) of this application, the melt temperature is adjusted to 720℃~740℃, pure magnesium ingots preheated to 200℃~250℃ are added, and the mixture is slowly stirred for 1min~2min under inert gas protection, and then left to stand for 2min~3min.

[0027] After adding pure magnesium ingots, degassing is performed: use an inert gas rotor to degas for 6 to 10 minutes, and then let it stand for 5 to 10 minutes.

[0028] Furthermore, in step (2) of this application, Al–La and Al–Ce master alloys are added, stirred slightly for about 1 min to 2 min, and then left to stand for 2 min to 3 min, and it is ensured that the time interval from the addition of rare earth to casting does not exceed 10 min.

[0029] Furthermore, in step (2) of this application, the Al–Ti–B master alloy grain refiner is added 5-8 minutes before casting, and gently stirred for 0.5-1 minutes. Then, the slag is removed and the mixture is allowed to stand until casting. The time interval between the addition of rare earth elements La and Ce to the casting process should be controlled within 10 minutes, and the time interval between the addition of the Al–Ti–B master alloy and the completion of the standing process and casting should be controlled within 5-8 minutes.

[0030] (3) Casting: The treated aluminum alloy melt is kept at 720℃~740℃ and formed by gravity casting using a metal mold. The metal mold is preheated to 200℃~250℃ and coated with a refractory coating with a thickness controlled between 0.15mm and 0.25mm. It is recommended to use a stable and continuous bottom-pouring method to reduce turbulence and reduce inclusion content.

[0031] This invention also provides a heat treatment method suitable for cast aluminum alloy castings. Its core feature lies in employing a "staged solution treatment + online rapid quenching" and a "three-stage artificial aging process of low-temperature nucleation—medium-temperature strengthening—high-temperature stabilization" to fully leverage the synergistic effect of multiple strengthening mechanisms. The method includes the following steps: The solution is subjected to two stages: the first stage is at a temperature of 440℃~455℃ and a holding time of 60min~120min; the second stage is at a temperature of 460℃~470℃ and a holding time of 30min~60min.

[0032] After the solution treatment is completed, the casting is transferred to warm water at 40℃-80℃ within 30 seconds for quenching.

[0033] Multi-stage time treatment: after quenching, the following three-stage aging treatment is carried out within 2 hours: the first stage is held at 110℃~120℃ for 4h~6h, the second stage is held at 165℃~175℃ for 6h~8h, and the third stage is held at 185℃~195℃ for 2h~4h.

[0034] Compared with the prior art, the beneficial effects of this application are as follows: (1) By synergistically setting the content of Cu to 3.5%–5.5% and Mg to 2.0%–2.5%, and controlling the content of Si to 0.15%–0.25% within a narrow range, while introducing a small amount of Sr to 0.01%–0.03%, and combining it with microalloying elements such as Mn to 0.5%–1.0%, Cr to 0.05%–0.15%, V to 0.08%–0.15%, Ti to 0.10%–0.20%, La to 0.02%–0.06%, and Ce to 0.02%–0.06%, a precipitation strengthening mechanism dominated by S′(Al2CuMg) is constructed. Among them, Sr can modify the finite eutectic Si and inhibit the formation of coarse eutectic Mg2Si / continuous Q′ / Q network, thereby reducing the ineffective consumption of Mg and making it preferentially participate in the S-system precipitation reaction, significantly enhancing the stability of the S′-dominated precipitation path. Furthermore, through the pinning effect of dispersed phases such as Al3(Ti,V,Cr), AlMn, and α–Al(Fe,Mn,Cr)Si, combined with the purification effect of rare earth elements and the modification effect of Sr on the morphology of Si phase, a composite strengthening system of "precipitation + dispersion strengthening + fine grain strengthening + purification" is finally formed, achieving synergistic optimization of high strength, high toughness and consistent performance of thick sections in the material.

[0035] (2) Under the synergistic effect of Mn / Cr, the needle-like / plate-like β-AlFeSi in the as-cast state is effectively transformed into fine, uniformly dispersed, blunt-rounded α-Al(Fe,Mn,Cr)Si, significantly reducing stress concentration and generating a continuous Zener pinning effect on dislocation movement and subgrain boundaries. Simultaneously, rare-earth aluminum compounds Al... 11 RE3 and Al2RE (RE=La, Ce) and Al3 (Ti, V, Cr, La, Ce) dispersed phases are adjacent to or coexist with refined Fe-containing components at the microscale, collectively forming fine-grained composite reinforcing units. These units not only act as shear-independent barriers to suppress dislocation slip but also provide heterogeneous nucleation sites for S′ (Al2CuMg) precipitation, thereby improving precipitation density and stability. Further research shows that the added elements not only participate in strengthening in the form of precipitated phases, but also, after solution treatment, Cu, Mg, Mn, Cr, and small amounts of Ti / V enter the α-Al matrix, increasing lattice frictional stress and generating a solute dragging effect, further enhancing the material properties.

[0036] (3) A heat treatment regime of two-stage solution treatment (460℃~475℃) → (478℃~485℃) + rapid quenching (water temperature 20℃~60℃, transfer time ≤30s) + three-stage artificial aging (110℃~120℃) × (4h~6h) → (165℃~175℃) × (6h~8h) → (185℃~195℃) × (2h~4h) is adopted. The first stage mainly forms Cu / Mg enriched clusters and GPB regions. The second stage generates high-density fine lamellar S′ precipitates. The third stage stabilizes the precipitate interface and improves the resistance to softening by light over-aging.

[0037] (4) The Al–Cu–Mg series cast aluminum alloy provided by the present invention has excellent comprehensive mechanical properties, with a tensile strength ≥460MPa, a specified plastic elongation strength ≥440MPa, and an elongation after fracture ≥12%. Attached Figure Description

[0038] Figure 1 This is a scanning electron microscope image of the cast aluminum alloy in Example 1; Figure 2 This is a transmission electron microscope image of Example 1; Figure 3 These are high-magnification scanning electron microscope images and area scan element photographs of Example 1. Detailed Implementation

[0039] The present invention can be further understood through the specific embodiments and comparative embodiments given below. However, these are not intended to limit the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0040] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this invention can be purchased commercially.

[0041] Example 1 This invention provides an Al–Cu–Mg series cast aluminum alloy with high strength and high toughness, the chemical composition of which is expressed as follows by mass percentage: 4.2%Cu, 2.3%Mg, 0.19%Si, 0.75%Mn, 0.09%Cr, 0.11%V, 0.16%Ti, 0.035%La, 0.035%Ce, 0.02%Sr, 0.14%Fe; the balance is Al.

[0042] The key component control parameters are: Cu / Mg mass ratio of 1.83; total Mn+Cr content of 0.84%; total Ti+V content of 0.27%; and total La+Ce content of 0.07%.

[0043] The specific preparation method is as follows: (1) Raw material and mold preheating: According to the composition and mass percentage of the aluminum alloy, 2.104 kg of copper wire with a purity of 99.8%, 1.153 kg of magnesium ingot with a purity of 99.8%, 0.475 kg of Al-20Si alloy, 1.875 kg of Al-20Mn alloy, 0.225 kg of Al-20Cr alloy, 0.55 kg of Al-10V alloy, 1.60 kg of Al-Ti-B refining agent, 0.0875 kg of Al-20La alloy, 0.0875 kg of Al-20Ce alloy, 0.05 kg of Al-20Sr alloy, and 45.84 kg of aluminum ingot with a purity of 99.7% were selected as raw materials for batching. The raw materials were thoroughly dried and preheated to 125°C; the metal mold was preheated to 215°C and coated with refractory coating, with the coating thickness controlled between 0.15 mm and 0.25 mm.

[0044] (2) Melting and alloying: The aluminum material was melted at 752℃ and the slag was removed. Then the temperature was raised to 768℃ and held for 10 min. Al–Mn→Al–V→Al–Cr master alloys were added in sequence. After each addition, the mixture was stirred at a speed of 1 m / s at the outer edge of the stirrer for 3 min. The temperature was held for a total of 12 min. Then Al–Cu and Al–Si master alloys were added and stirred for 3 min each until completely melted.

[0045] (3) Refining: Refining was carried out three times at 747℃ using a refining agent. The amount of refining agent used each time was 0.11 wt.% and the refining time was 20 min. Argon gas was introduced throughout the process at a flow rate of 0.85 L / min. After each refining was completed, the mixture was left to stand for 20 min.

[0046] (4) Sr modification treatment: Add Al–Sr master alloy at 734℃ and stir gently for 1.5 min.

[0047] (5) Addition of magnesium and secondary degassing: The melt temperature was reduced to 730°C, pure magnesium ingots preheated to 225°C were added, and the mixture was slowly stirred for 1.8 min under an argon protective atmosphere and allowed to stand for 3 min. Then, an inert gas rotor was used for degassing for 8 min, and the mixture was allowed to stand for 6 min after degassing.

[0048] (6) Rare earth element addition: Add Al–La and Al–Ce intermediate alloy, stir gently for 1.2 min and let stand for 3 min; the time interval from the completion of rare earth element addition to casting should be controlled within 10 min.

[0049] (7) Grain refinement treatment: Add Al–Ti–B master alloy 6 minutes before casting, stir gently for 1 minute and let stand until casting.

[0050] (8) Gravity casting: The melt temperature is maintained at 730℃ during the casting process. The bottom casting method of metal mold is adopted to ensure a stable casting process.

[0051] (9) Heat treatment process: Double solution treatment is adopted, namely 448℃ for 95min and 466℃ for 48min; after the solution treatment is completed, it is transferred to 62℃ warm water for quenching within 30s; after quenching, a three-stage aging process is carried out within 2h, namely 116℃×5h, 171℃×7.5h and 191℃×3h, and finally air-cooled.

[0052] The Al–Cu–Mg cast aluminum alloy prepared in Example 1 has excellent mechanical properties, with a tensile strength of 482 MPa, a specified plastic elongation strength of 442 MPa, and an elongation after fracture of 14.6%.

[0053] Example 2 The chemical composition, expressed as a percentage by mass, is: 3.5% Cu, 2.5% Mg, 0.25% Si, 1% Mn, 0.15% Cr, 0.15% V, 0.2% Ti, 0.02% La, 0.02% Ce, 0.01% Sr, 0.25% Fe; the balance is Al.

[0054] The key component control parameters are: Cu / Mg mass ratio = 1.40; Mn + Cr = 1.15%; Ti + V = 0.35%; La + Ce = 0.04%.

[0055] The preparation method is basically the same as in Example 1, with the following differences: Based on the composition and mass percentage of the aluminum alloy, the following raw materials were selected for batching: 1.754 kg of copper wire with a purity of 99.8%, 1.253 kg of magnesium ingot with a purity of 99.8%, 0.625 kg of Al-20Si master alloy, 2.500 kg of Al-20Mn master alloy, 0.375 kg of Al-20Cr master alloy, 0.750 kg of Al-10V master alloy, 2.000 kg of Al-Ti-B refining agent (calculated based on Al-5Ti-1B), 0.050 kg of Al-20La master alloy, 0.050 kg of Al-20Ce master alloy, 0.025 kg of Al-20Sr master alloy, and 40.62 kg of aluminum ingot with a purity of 99.7%. The raw materials are preheated to 130°C; the aluminum material is melted at 755°C and then heated to 770°C; refining is carried out at 748°C with a refining agent dosage of 0.11% and argon gas is introduced for protection at a flow rate of 0.9 L / min; Al–Sr master alloy is added at 735°C; pure magnesium ingots preheated to 230°C are added at 735°C and immediately subjected to rotor degassing treatment for 8 min, and then allowed to stand for 6 min after degassing; Al–Ti–B master alloy is added 6 min before casting; the metal mold is preheated to 220°C.

[0056] Gravity casting: The melt temperature is maintained at 720℃~740℃ during the casting process, and a bottom-pouring method with a metal mold is adopted to ensure a stable casting process.

[0057] Heat treatment process: Two-stage solution treatment is adopted, namely 450℃×100min and 468℃×40min; after the solution treatment is completed, the solution is transferred to 70℃ warm water for quenching within ≤30s; after quenching, a three-stage aging process is implemented within 2h, namely 118℃×5h, 172℃×7h and 192℃×3h.

[0058] The cast aluminum alloy prepared in Example 2 has excellent mechanical properties, with a tensile strength of 470 MPa, a specified plastic elongation strength of 428 MPa, and an elongation after fracture of 12.1%.

[0059] Example 3 The chemical composition, expressed as a percentage by mass, is: 5.5% Cu, 2.0% Mg, 0.15% Si, 0.50% Mn, 0.05% Cr, 0.08% V, 0.10% Ti, 0.06% La, 0.06% Ce, 0.03% Sr, 0.20% Fe; the balance is Al.

[0060] The key component control parameters are: Cu / Mg mass ratio = 2.75; Mn + Cr = 0.55%; Ti + V = 0.18%; La + Ce = 0.12%.

[0061] The preparation method is basically the same as in Example 1, with the following differences: Based on the composition and mass percentage of the aluminum alloy, 2.756 kg of copper wire with a purity of 99.8%, 1.002 kg of magnesium ingot with a purity of 99.8%, 0.375 kg of Al-20Si master alloy, 1.250 kg of Al-20Mn master alloy, 0.125 kg of Al-20Cr master alloy, 0.400 kg of Al-10V master alloy, 1.000 kg of Al-Ti-B refining agent (calculated based on Al-5Ti-1B), 0.150 kg of Al-20La master alloy, 0.150 kg of Al-20Ce master alloy, 0.075 kg of Al-20Sr master alloy, and 42.72 kg of aluminum ingot with a purity of 99.7% were selected as raw materials for batching. The raw materials are preheated to 140℃; the aluminum material is melted at 760℃, and then heated to 775℃; refining is carried out at 750℃ with a refining agent dosage of 0.09%, and argon gas is introduced for protection at a flow rate of 0.7L / min; Al–Sr master alloy is added at 736℃, corresponding to a Sr content of 0.03%; pure magnesium ingots preheated to 240℃ are added at 740℃ and immediately subjected to rotor degassing treatment for 6-8 minutes, and then allowed to stand for 6 minutes after degassing; Al–Ti–B master alloy is added 5 minutes before casting; the metal mold preheating temperature is 200℃.

[0062] Gravity casting: The melt temperature is maintained at 730℃ during the casting process, and a bottom-pouring method with a metal mold is used to ensure a stable casting process.

[0063] Heat treatment process: Two-stage solution treatment is adopted, namely 445℃×80min and 462℃×50min; after the solution treatment is completed, the solution is transferred to 50℃ warm water for quenching within ≤30s; after quenching, a three-stage aging process is carried out within 2 hours, namely 112℃×6h, 168℃×8h and 188℃×4h.

[0064] The aluminum alloy prepared in Example 3 has excellent mechanical properties, with a tensile strength of 466 MPa, a specified ductile elongation of 424 MPa, and an elongation after fracture of 12.9%.

[0065] Example 4 The chemical composition, expressed as a percentage by mass, is: 4% Cu, 2.5% Mg, 0.22% Si, 0.8% Mn, 0.15% Cr, 0.15% V, 0.10% Ti, 0.05% La, 0.05% Ce, 0.01% Sr, 0.20% Fe; the balance is Al.

[0066] The key component control parameters are: Cu / Mg=1.6; Mn+Cr=0.95%; Ti+V=0.25%; La+Ce=0.10%.

[0067] The preparation method is basically the same as in Example 1, with the following differences: 2.004 kg of copper wire with a purity of 99.8%, 1.253 kg of magnesium ingot with a purity of 99.8%, 0.550 kg of Al-20Si master alloy, 2.000 kg of Al-20Mn master alloy, 0.375 kg of Al-20Cr master alloy, 0.750 kg of Al-10V master alloy, 1.000 kg of Al-Ti-B refining agent, 0.125 kg of Al-20La master alloy, 0.125 kg of Al-20Ce master alloy, 0.025 kg of Al-20Sr master alloy, and 41.793 kg of aluminum ingot with a purity of 99.7% were selected as raw materials for batching according to the composition and mass percentage of the aluminum alloy. The raw materials are preheated to 125℃; the aluminum material is melted at 745℃, and then the temperature is raised to 760℃; refining is carried out at 742℃ with a refining agent dosage of 0.12% and argon gas is introduced for protection at a flow rate of 1.0L / min; Al–Sr master alloy is added at 732℃-734℃; pure magnesium ingots preheated to 210℃ are added at 725℃ and immediately subjected to rotor degassing treatment for 8-10 minutes, and then allowed to stand for 6-8 minutes after degassing; Al–Ti–B master alloy is added 7 minutes before casting; the metal mold preheating temperature is 230℃.

[0068] Gravity casting: During the casting process, the melt temperature is maintained within the range of 720℃~740℃. In this example, it is controlled at 725℃-735℃. The bottom pouring method of metal mold is adopted to ensure a stable casting process.

[0069] Heat treatment process: Two-stage solution treatment is adopted, namely 455℃×110min and 470℃×30min; after the solution treatment is completed, the solution is transferred to 80℃ warm water for quenching within ≤30s; after quenching, a three-stage aging process is carried out within 2h, namely 120℃×4h, 175℃×6h and 195℃×2h.

[0070] The cast aluminum alloy prepared in Example 4 has excellent mechanical properties, with a tensile strength of 471 MPa, a specified plastic elongation strength of 432 MPa, and an elongation after fracture of 13.3%.

[0071] Example 5 The chemical composition, expressed as a percentage by mass, is: 5.0% Cu, 2.0% Mg, 0.15% Si, 0.60% Mn, 0.05% Cr, 0.15% V, 0.15% Ti, 0.03% La, 0.03% Ce, 0.02% Sr, 0.22% Fe; the balance is Al.

[0072] The key component control parameters are: Cu / Mg mass ratio = 2.50; Mn + Cr = 0.65%; Ti + V = 0.30%; La + Ce = 0.06%.

[0073] The preparation method is basically the same as in Example 1, with the following differences: 2.505 kg of copper wire with a purity of 99.8%, 1.002 kg of magnesium ingot with a purity of 99.8%, 0.375 kg of Al-20Si master alloy, 1.500 kg of Al-20Mn master alloy, 0.125 kg of Al-20Cr master alloy, 0.750 kg of Al-10V master alloy, 1.500 kg of Al-Ti-B refining agent (calculated based on Al-5Ti-1B), 0.075 kg of Al-20La master alloy, 0.075 kg of Al-20Ce master alloy, 0.050 kg of Al-20Sr master alloy, and 42.043 kg of aluminum ingot with a purity of 99.7% were selected as raw materials for batching according to the composition and mass percentage of the aluminum alloy. The raw materials are preheated to 135℃; the aluminum material is melted at 752℃ and then heated to 768℃; refining is carried out at 746℃ with a refining agent dosage of 0.10% and argon gas is introduced for protection at a flow rate of 0.85L / min; Al–Sr master alloy is added at 734℃~736℃; pure magnesium ingots preheated to 225℃ are added at 732℃ and immediately subjected to rotor degassing treatment for 8 minutes, and then allowed to stand for 6 minutes after degassing; Al–Ti–B master alloy is added 5 minutes before casting; the metal mold preheating temperature is 215℃.

[0074] Gravity casting: During the casting process, the melt temperature is maintained within the range of 720℃~740℃, and in this example, it is controlled at 725℃~735℃. The bottom pouring method of metal mold is adopted to ensure a stable casting process.

[0075] Heat treatment process: Two-stage solution treatment is adopted, namely 440℃×120min and 460℃×60min; after the solution treatment is completed, the solution is transferred to 40℃ warm water for quenching within ≤30s; after quenching, a three-stage aging process is implemented within 2h, namely 110℃×6h, 165℃×8h and 185℃×4h.

[0076] The cast aluminum alloy prepared in Example 5 has excellent mechanical properties, with a tensile strength of 480 MPa, a specified plastic elongation strength of 439 MPa, and an elongation after fracture of 14.2%.

[0077] Comparative Example Comparative Example 1 The chemical composition, expressed as a percentage by mass, is: 2.8% Cu, 2.2% Mg, 0.20% Si, 0.70% Mn, 0.08% Cr, 0.10% V, 0.15% Ti, 0.03% La, 0.03% Ce, 0.02% Sr, 0.18% Fe; the balance is Al.

[0078] The key component control parameters are: Cu / Mg mass ratio = 1.27; Mn + Cr = 0.78%; Ti + V = 0.25%; La + Ce = 0.06%.

[0079] Preparation method: According to the composition and mass percentage of the aluminum alloy, the following raw materials are selected for batching: 1.402 kg of copper wire with a purity of 99.8%, 1.102 kg of magnesium ingot with a purity of 99.8%, 0.50 kg of Al-20Si alloy, 1.75 kg of Al-20Mn alloy, 0.20 kg of Al-20Cr alloy, 0.50 kg of Al-10V alloy, 1.50 kg of Al-Ti-B refining agent (providing 0.075 kg of titanium), 0.075 kg of Al-20La alloy, 0.075 kg of Al-20Ce alloy, 0.05 kg of Al-20Sr alloy, and 46.98 kg of aluminum ingot with a purity of 99.7%. The preparation process is the same as in Example 1, and the heat treatment process is also carried out in accordance with Example 1. During the gravity casting process, it is carried out in accordance with Example 1, the melt holding temperature is controlled at 720℃~740℃, and the bottom pouring stable casting method is adopted.

[0080] The cast aluminum alloy prepared in Comparative Example 1 has the following mechanical properties: tensile strength of 385 MPa, specified plastic elongation strength of 350 MPa, and elongation after fracture of 10.5%.

[0081] Comparative Example 2 The chemical composition, expressed as a percentage by mass, is: 6.5% Cu, 2.3% Mg, 0.22% Si, 0.80% Mn, 0.10% Cr, 0.12% V, 0.18% Ti, 0.04% La, 0.04% Ce, 0.02% Sr, 0.20% Fe; the balance is Al.

[0082] The key component control parameters are: Cu / Mg mass ratio = 2.83; Mn+Cr = 0.90%; Ti+V = 0.30%; La+Ce = 0.08%.

[0083] Preparation method: According to the composition and mass percentage of the aluminum alloy, the following raw materials were selected for batching: 3.26 kg of copper wire with a purity of 99.8%, 1.153 kg of magnesium ingot with a purity of 99.8%, 0.55 kg of Al-20Si alloy, 2.00 kg of Al-20Mn alloy, 0.25 kg of Al-20Cr alloy, 0.60 kg of Al-10V alloy, 1.80 kg of Al-Ti-B refining agent, 0.10 kg of Al-20La alloy, 0.10 kg of Al-20Ce alloy, 0.05 kg of Al-20Sr alloy, and 44.91 kg of aluminum ingot with a purity of 99.7%. The preparation process and heat treatment process were the same as in Example 2; during gravity casting, the process was carried out as in Example 1, with the melt holding temperature controlled at 720℃~740℃, and a bottom-pouring stable casting method was adopted.

[0084] The cast aluminum alloy prepared in Comparative Example 2 has the following mechanical properties: tensile strength of 485 MPa, specified ductile elongation of 445 MPa, and elongation after fracture of 6.5%.

[0085] Comparative Example 3 The chemical composition, expressed as a percentage by mass, is: 4.5% Cu, 1.5% Mg, 0.20% Si, 0.70% Mn, 0.08% Cr, 0.10% V, 0.15% Ti, 0.03% La, 0.03% Ce, 0.02% Sr, 0.18% Fe; the balance is Al.

[0086] The key component control parameters are: Cu / Mg mass ratio = 3.00; Mn + Cr = 0.78%; Ti + V = 0.25%; La + Ce = 0.06%.

[0087] Preparation method: According to the composition and mass percentage of the aluminum alloy, the following raw materials were selected for batching: 2.254 kg of copper wire with a purity of 99.8%, 0.752 kg of magnesium ingot with a purity of 99.8%, 0.50 kg of Al-20Si alloy, 1.75 kg of Al-20Mn alloy, 0.20 kg of Al-20Cr alloy, 0.50 kg of Al-10V alloy, 1.50 kg of Al-Ti-B refining agent (providing 0.075 kg of titanium), 0.075 kg of Al-20La alloy, 0.075 kg of Al-20Ce alloy, 0.05 kg of Al-20Sr alloy, and 46.07 kg of aluminum ingot with a purity of 99.7%. The preparation process and heat treatment process are the same as in Example 1; during gravity casting, the process is carried out as in Example 1, the melt holding temperature is controlled at 720℃~740℃, and a bottom-pouring stable casting method is adopted.

[0088] The cast aluminum alloy prepared in Comparative Example 3 has the following mechanical properties: tensile strength of 415 MPa, specified plastic elongation strength of 270 MPa, and elongation after fracture of 11.0%.

[0089] Comparative Example 4 The chemical composition, expressed as a percentage by mass, is: 4.0% Cu, 2.2% Mg, 0.18% Si, 0.30% Mn, 0.03% Cr, 0.10% V, 0.15% Ti, 0% La, 0% Ce, 0.02% Sr, 0.35% Fe; the balance is Al.

[0090] The key component control parameters are: Cu / Mg mass ratio = 1.82; Mn + Cr = 0.33%; Ti + V = 0.25%; La + Ce = 0.

[0091] Preparation method: According to the composition and mass percentage of the aluminum alloy, the following raw materials were selected for batching: 2.004 kg of copper wire with a purity of 99.8%, 1.102 kg of magnesium ingot with a purity of 99.8%, 0.50 kg of Al-20Si alloy, 1.75 kg of Al-20Mn alloy, 0.25 kg of Al-20Cr alloy, 0.50 kg of Al-10V alloy, 1.50 kg of Al-Ti-B refining agent, 0.075 kg of Al-20La alloy, 0.075 kg of Al-20Ce alloy, 0.05 kg of Al-20Sr alloy, and 45.65 kg of aluminum ingot with a purity of 99.7%. The preparation process and heat treatment process were the same as in Example 1; during gravity casting, the process was carried out as in Example 1, with the melt holding temperature controlled at 720℃~740℃, and a bottom-pouring stable casting method was adopted.

[0092] The cast aluminum alloy prepared in Comparative Example 4 has the following mechanical properties: tensile strength of 410 MPa, specified plastic elongation strength of 380 MPa, and elongation after fracture of 8.0%.

[0093] Comparative Example 5 The chemical composition, expressed as a percentage by mass, is: 4.2% Cu, 2.3% Mg, 0.20% Si, 0.75% Mn, 0.10% Cr, 0.11% V, 0.16% Ti, 0.12% La, 0.10% Ce, 0.02% Sr, 0.16% Fe; the balance is Al.

[0094] The key component control parameters are: Cu / Mg mass ratio = 1.83; Mn + Cr = 0.85%; Ti + V = 0.27%; La + Ce = 0.22%.

[0095] Preparation method: According to the composition and mass percentage of the aluminum alloy, the following raw materials were selected for batching: 2.104 kg of copper wire with a purity of 99.8%, 1.153 kg of magnesium ingot with a purity of 99.8%, 0.50 kg of Al-20Si alloy, 1.875 kg of Al-20Mn alloy, 0.25 kg of Al-20Cr alloy, 0.55 kg of Al-10V alloy, 1.60 kg of Al-Ti-B refining agent, 0.30 kg of Al-20La alloy, 0.25 kg of Al-20Ce alloy, 0.05 kg of Al-20Sr alloy, and 45.84 kg of aluminum ingot with a purity of 99.7%. The preparation process and heat treatment process were the same as in Example 1; during gravity casting, the process was carried out as in Example 1, with the melt holding temperature controlled at 720℃~740℃, and a bottom-pouring stable casting method was adopted.

[0096] The cast aluminum alloy prepared in Comparative Example 5 has the following mechanical properties: tensile strength of 430 MPa, specified plastic elongation strength of 390 MPa, and elongation after fracture of 9.0%.

[0097] Comparative Example 6 The chemical composition is the same as in Example 1, specifically 4.2% Cu, 2.3% Mg, 0.19% Si, 0.75% Mn, 0.09% Cr, 0.11% V, 0.16% Ti, 0.035% La, 0.035% Ce, 0.02% Sr, and 0.14% Fe; the balance is Al.

[0098] The key component control parameters are: Cu / Mg mass ratio of 1.83; total Mn+Cr content of 0.84%; total Ti+V content of 0.27%; and total La+Ce content of 0.07%.

[0099] Preparation method: The preparation process is the same as in Example 1; the gravity casting process is performed in accordance with Example 1, the melt holding temperature is controlled at 720℃~740℃, and a bottom-pouring stable casting method is adopted; the heat treatment adopts a process combining ordinary single-stage solution treatment and single-stage aging: the solution temperature is 495℃, the holding time is 2h, and then water quenching is performed at room temperature; the aging treatment temperature is 175℃, and the holding time is 8h.

[0100] The cast aluminum alloy prepared in Comparative Example 6 has the following mechanical properties: tensile strength of 435 MPa, specified ductile elongation of 395 MPa, and elongation after fracture of 10.2%.

[0101] Table 1 Tensile properties of Al-Cu-Mg alloys provided in the examples and comparative examples <![CDATA[Tensile strength R m / MPa]]> <![CDATA[Specified plastic extension strength R p0.2 / MPa]]> Elongation after fracture / % Example 1 482 442 14.6 Example 2 470 428 12.1 Example 3 466 424 12.9 Example 4 471 432 13.3 Example 5 480 439 14.2 Comparative Example 1 385 350 10.5 Comparative Example 2 485 445 6.5 Comparative Example 3 415 270 11 Comparative Example 4 410 380 8.0 Comparative Example 5 430 390 9.0 Comparative Example 6 435 395 10.2 As can be seen from the mechanical property data of Examples 1–5 and Comparative Examples 1–6 in Table 1, Examples 1–5 all achieved the technical indicators of tensile strength ≥450MPa, specified plastic elongation strength ≥420MPa, and elongation after fracture ≥12%. Compared with the comparative examples, the examples have a better match between strength and toughness, which fully verifies the rationality and applicability of the composition range and process route set by the present invention, namely gravity casting combined with graded heat treatment, and can meet the stringent performance requirements of cast structural parts for high-strength and high-toughness aluminum alloys.

[0102] The comparison between the examples and Comparative Examples 1–3 shows that the Cu content and Cu / Mg mass ratio have a decisive influence on the performance. In Comparative Example 1, the Cu content was 2.8%, lower than the 3.5%–5.5% of the present invention, and the Cu / Mg mass ratio was 1.27, lower than the 1.40–2.75 of the present invention, resulting in insufficient precipitation of solid solution and S phase (S′ / Al2CuMg), and a tensile strength of only 385 MPa. In Comparative Example 2, the Cu content was as high as 6.5%, and the Cu / Mg mass ratio was 2.83, both exceeding the recommended range of the present invention. Although the tensile strength reached 485 MPa, the formation of more brittle second phase led to a significant decrease in elongation after fracture to 6.5%, and an increased tendency for hot cracking during casting. In Comparative Example 3, the Mg content was 1.5%, lower than the 2.0%–2.5% of the present invention, and the Cu / Mg mass ratio was 3.00, exceeding the range of the present invention. This resulted in a weakened S-phase strengthening effect and uneven microstructure, causing the tensile strength, specified plastic extension strength, and elongation after fracture to all fail to meet the standards, which were 415 MPa, 270 MPa, and 11%, respectively. Therefore, controlling the Cu content to 3.5–5.5%, the Mg content to 2.0%–2.5%, and the Cu / Mg mass ratio to 1.40–2.75 are the key component windows for achieving a synergistic effect of high strength and high toughness.

[0103] The comparison between the examples and Comparative Example 4 illustrates that the addition of Mn / Cr composites plays a crucial role in refining and stabilizing the microstructure. In Comparative Example 4, the Mn content was 0.30% and the Cr content was 0.03%, both lower than the range of this invention. The total Mn+Cr content was 0.33%, lower than 0.55%–1.15%, making it difficult for the Fe phase to effectively transform into the rounded α-Al(Fe,Mn,Cr)Si phase. The grain refinement effect and dispersion pinning effect were insufficient, resulting in a tensile strength of only 410 MPa. In contrast, the total Mn+Cr content in the examples was controlled within the range of 0.65%–1.05%, enabling the formation of finely dispersed precipitates, such as Al6Mn and Al... 12 The presence of (Fe,Mn)3Si and a small amount of Cr phase effectively stabilizes the Fe phase morphology, significantly improving the alloy's strength and cross-sectional microstructure consistency. Therefore, controlling the total Mn+Cr content between 0.55% and 1.15% is a necessary condition for achieving grain refinement and dispersion strengthening.

[0104] There is an optimal range for the addition of rare earth elements. In Comparative Example 4, the contents of La and Ce were both 0, lower than the 0.02%–0.06% of this invention, while the Fe content was 0.35%, exceeding the 0.25% of this invention. This lack of rare earth purification and stabilization effects, coupled with the formation of coarse, needle-like iron-rich phases, resulted in substandard tensile strength, specified ductile elongation, and elongation after fracture. In Comparative Example 5, the La content was 0.12%, the Ce content was 0.10%, and the total La+Ce content was 0.22%, exceeding the 0.12% of this invention. Excessive rare earth promoted the formation of coarse compounds and triggered segregation, becoming potential crack initiators, while simultaneously inhibiting the S′ strengthening effect, leading to a simultaneous decrease in strength and toughness. Therefore, controlling the La and Ce contents to 0.02–0.06%, and the total La+Ce content not exceeding 0.12%, represents the optimal addition range for achieving rare earth purification and modification effects. Simultaneously, the Fe content should be controlled to ≤0.25% to avoid the formation of harmful needle-like phases.

[0105] Ti / V microalloying exhibits a significant synergistic effect. Examples show that when the Ti content is 0.10%–0.20%, the V content is 0.08%–0.15%, and the total Ti+V content is controlled at 0.20%–0.35%, fine Al3(Ti,V,Cr) dispersed phases can be formed. These phases synergize with the TiB2 / Al3Ti heteronucleation introduced by the grain refiner, achieving a dual strengthening mechanism of grain refinement and dispersion pinning. This results in excellent overall performance in all examples, effectively verifying the feasibility and practicality of this microalloying strategy.

[0106] Taking Example 1 as an example, Figure 1This is a scanning electron microscope (SEM) image of the cast aluminum alloy from Example 1. The white particles shown in the image are the S′(Al2CuMg) phase. Furthermore, the grain refinement effect of the material can be observed from the image, which is characterized by smaller and more uniform grains. Figure 2 These are transmission electron microscopy (TEM) images of Example 1. The upper left image shows the HAADF morphology, and the remaining images show the elemental distributions of Al, Cu, Mg, Si, Mn, Sr, Cr, V, Ti, La, and Ce. The HAADF image shows a bright band / tongue-shaped phase and an equiaxed polygonal particle surrounded by the matrix. Al is darker in these locations, indicating that they belong to a non-Al secondary phase. The banded phase is strongly bright in both the Cu and Mg images, while the Si signal is not significant, indicating that this phase is a Cu- and Mg-enriched Al₂CuMg. This morphology and co-enrichment characteristic are consistent with the strengthening route of this alloy: "Cu 4.2% + Mg 2.3%, Cu / Mg ≈ 1.83, with S′ as the dominant precipitation component after solution treatment, quenching, and aging." The coherent / semi-coherent interface of S″ / S′ effectively pins dislocations, providing the main source of strength. Granular Si and Mg are enhanced simultaneously on the graph, while the Cu signal is very weak, indicating that it is Mg2Si rather than a Cu-containing phase. The small number and discrete distribution of these particles indicate that the low Si design of 0.15%–0.25% combined with Sr modification effectively suppresses the formation of continuous network-like Q′ / Q and coarse eutectic Mg2Si, thereby avoiding ineffective Mg diversion and ensuring the precipitation path dominated by S′. The graphs of Mn, Cr, V, and Ti show a uniform fine dot distribution with slight enhancement at individual particles, indicating that they are mainly in the form of Al6Mn and Al 12 Fine, dispersed phases such as (Fe,Mn)3Si and Al3(Ti,V,Cr) exist. These particles not only refine grains and act as Zener pinns during solidification / heat treatment, inhibiting recrystallization and grain growth, but also provide heterogeneous nucleation sites for S′ precipitation, forming a synergistic mechanism of "grain refinement + dispersion strengthening". The distribution of La and Ce is a dense, scattered pattern across the entire field, with no coarse agglomerates observed, indicating that rare earth elements exist in the form of fine Al–RE compounds, which can purify inclusions, refine dendrite spacing, improve the thermal stability of the microstructure, and delay over-aging. The Sr signal is weak and appears as localized dots, which is a common characteristic at a trace level of 0.02%; its main function is to modify small amounts of eutectic Si, improve filling and shrinkage, and indirectly inhibit the formation of coarse Mg2Si.

[0107] Figure 3This is a high-magnification scanning electron microscope (SEM) image and a surface scan elemental image of Example 1. This image shows the distribution of different elements in the aluminum alloy, helping to reveal the microstructural characteristics of the alloy during different heat treatment processes. Cu and Mg are key components of the strengthening phase (Al₂CuMg), and they work together during solution treatment, quenching, and aging to form phases with different precipitation sequences. The distribution of Cu and Mg is clearly visible in the image, indicating that these two elements exist in the alloy in a fine, dispersed form, significantly improving the alloy's specified ductile elongation strength and tensile strength. Especially under the synergistic effect of high Cu and high Mg content, Cu and Mg can promote the precipitation of the S′ phase, further enhancing the material's strength and ductility. Si is uniformly distributed in the image, consistent with its role in the alloy. Si mainly provides auxiliary precipitation strengthening by forming the Mg₂Si phase. Simultaneously, an appropriate amount of Si helps avoid over-aging softening and inhibits the formation of coarse Mg₂Si eutectic phases, ensuring the dominant precipitation of the S′ phase and optimizing the material's mechanical properties. The distribution of Mn and Cr elements demonstrates their synergistic effect in improving the microstructure of aluminum alloys, particularly by altering the morphology of the Fe phase, thereby reducing crack susceptibility and stress concentration effects. These elements also contribute to the precipitation of high-melting-point dispersed phases (Al6Mn and Al...). 12 (Fe,Mn)3Si pins dislocations, subgrain boundaries, and grain boundaries, effectively inhibiting grain growth and improving alloy stability. Sr also plays a significant role in alloy modification, particularly in controlling the morphology of the eutectic Si phase. The introduction of Sr effectively transforms Si from a needle-like or blocky structure into a fibrous structure, reducing potential crack sources and improving crack resistance. Simultaneously, it inhibits the ineffective precipitation of Mg2Si, ensuring Mg participation in the precipitation pathway of the S-series phases and enhancing the overall mechanical properties of the material. Furthermore, the addition of Ti and V promotes grain refinement through nucleation effects, while simultaneously forming a stable Al3(Ti,V,Cr) dispersed phase, which continues to pin dislocations during subsequent heat treatment, further enhancing the grain refinement effect and strength of the material.

[0108] The necessity of the heat treatment route is further highlighted by the comparison between Example 1 and Comparative Example 6. Both have identical compositions, but Comparative Example 6 uses a standard T6 process, i.e., a single-stage solution treatment at 495℃ for 2 hours followed by a single-stage aging process at 175℃ for 8 hours. Due to the high solution temperature, it is prone to localized initial melting or grain boundary melting, and it is difficult to form the optimized precipitation sequence of GPB regions / atom clusters → S″ → S′, resulting in a strength of only 425 MPa / 390 MPa / 10.2%. In contrast, Example 1 uses a dual solution treatment process (448℃ for 95 minutes + 466℃ for 48 minutes) and a three-stage aging process (116℃ for 5 hours + 171℃ for 7.5 hours + 191℃ for 3 hours), resulting in improved performance of 482 MPa / 442 MPa / 14.6%, significantly better than Comparative Example 6. This result indicates that a multi-stage solution treatment combined with a multi-stage aging process plays a crucial role in obtaining high-density, fine-grained S′ and achieving a good balance between strength and toughness.

[0109] In summary, this invention, through a synergistic design of Cu / Mg ratio of 1.4–2.75, Mn+Cr composite addition controlled at 0.55%–1.15%, Ti+V microalloying total amount controlled at 0.20%–0.35%, and appropriate addition of rare earth elements at 0.04%≤La+Ce≤0.12%, combined with an innovative heat treatment process of double solution treatment and three-stage aging, successfully achieved simultaneous improvement in the strength and toughness of cast aluminum alloys, providing a new technical route for the development of high-performance aluminum alloy castings.

[0110] The above description is merely an exemplary embodiment of the present invention and is not intended to limit the scope of patent protection of the present invention. Any equivalent structural improvements or equivalent process changes made on the basis of the present invention, or methods or structures directly or indirectly applied to other related technical fields, should be included within the scope of patent protection of the present invention.

Claims

1. A high-strength and high-toughness Al–Cu–Mg cast aluminum alloy, characterized in that, Its chemical composition by mass percentage Includes: Cu: 3.5%–5.5%; Mg: 2.0%～2.5%； Si: 0.15%–0.25%; Mn: 0.5%–1.0%; Cr: 0.05%–0.15%; V: 0.08%–0.15%; Ti: 0.10%–0.20%; La: 0.02%–0.06%; Ce: 0.02%–0.06%; Sr: 0.01%–0.03%; Fe: ≤0.25%; balance Al and other unavoidable impurities.

2. The Al–Cu–Mg cast aluminum alloy according to claim 1, characterized in that, The mass ratio of Cu to Mg is 1.60 to 2.

50.

3. The Al–Cu–Mg cast aluminum alloy according to claim 1, characterized in that, The total mass percentage of Mn and Cr is 0.65% to 0.95%.

4. The Al–Cu–Mg cast aluminum alloy according to claim 1, characterized in that, The total mass percentage of Ti and V is 0.25% to 0.30%.

5. The Al–Cu–Mg cast aluminum alloy according to claim 1, characterized in that, The total mass percentage of La and Ce is 0.06% to 0.10%.

6. A method for preparing an Al–Cu–Mg cast aluminum alloy according to any one of claims 1-5, characterized in that, Includes the following steps: (1) Raw material preparation and preheating The raw materials are prepared according to the chemical composition of the Al–Cu–Mg series cast aluminum alloy as described in any one of claims 1-5. The raw materials and smelting tools are thoroughly dried and preheated to 100°C to 150°C. (2) Smelting and alloying Industrial pure aluminum with a purity ≥99.7% is heated to 740℃~760℃ and melted. Al-Mn, Al-V, and Al-Cr master alloys are added and stirred. Then Al-Cu and Al-Si master alloys are added and stirred for refining. A refining agent is added and an inert gas is introduced. Al-Sr master alloy is added and stirred. Pure magnesium ingots with a purity ≥99.9% are added and stirred after being preheated to 200℃~250℃. Al-La and Al-Ce master alloys are added and stirred. Finally, Al-Ti-B grain refiner is added, stirred, and allowed to stand until casting. Casting: The treated aluminum alloy melt is kept at 720℃~740℃ and formed by gravity casting using a metal mold; Heat treatment: The casting is subjected to heat treatment. After the heat treatment is completed, the casting is air-cooled to room temperature to obtain the Al–Cu–Mg series cast aluminum alloy.

7. The method for preparing Al–Cu–Mg series cast aluminum alloy according to claim 6, characterized in that, The amount of refining agent used in step (2) is controlled at 0.08% to 0.12% of the melt mass, and the refining time is controlled at 15 min to 20 min, and a total of three refining processes are carried out; the time interval between the addition of Al-La and Al-Ce master alloys in step (2) and the casting is controlled within 10 min; the time interval between the addition of Al-Ti-B grain refiner in step (2) and the casting is 5 min to 8 min; the metal mold in step (3) is preheated to 200℃ to 250℃ and coated with refractory coating with a coating thickness of 0.15 mm to 0.25 mm.

8. The method for preparing Al–Cu–Mg cast aluminum alloy according to claim 7, characterized in that, The heat treatment includes the following steps: (1) Double solution treatment First stage: Keep warm at 440℃~455℃ for 60min~120min; Second stage: Keep warm at 460℃~470℃ for 30min~60min; (2) Quenching treatment After solution treatment, the casting is transferred to warm water at 40℃~80℃ within 30 seconds for quenching. (3) Multi-level timeliness processing After quenching, perform the following three-stage aging treatment within 2 hours: First stage: Keep warm at 110℃~120℃ for 4h~6h; Second stage: Keep warm at 165℃~175℃ for 6h~8h; Third stage: Keep warm at 185℃~195℃ for 2h~4h.

9. An aluminum wheel for vehicles, characterized in that, Made from any one of the Al-Cu-Mg series cast aluminum alloys according to claims 1-5.

10. A method for manufacturing an aluminum wheel for automobiles, characterized in that, Includes the following steps: The aluminum alloy melt is obtained by using the Al-Cu-Mg system casting aluminum alloy preparation method as described in any one of claims 6-8, and the aluminum alloy melt is used to form the automotive aluminum wheel.

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