High-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloys based on rapid casting and rolling and their preparation method

Abstract

This invention provides a high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling, and its preparation method. The alloy, by mass percentage, consists of the following components: Mg: 0.95-1.96%; Si: 0.50-1.54%; Zn: 2.45-4.54%; Cu: 0.55-1.12%; Mn: 0-0.16%; Zr: 0-0.14%; total alloy content ≤8%; total unavoidable impurities ≤0.15%; balance being Al. The preparation method includes: melting, rapid casting and rolling, homogenization treatment, finish rolling, solution treatment, and aging treatment. The aluminum alloy obtained by this invention maintains high T4-state plasticity (elongation ≥30%) while possessing excellent T6-state room temperature high strength and high-temperature thermal stability: at room temperature, the yield strength is ≥400 MPa, and after heat exposure at 140-170 °C for 600-1200 h, it can still maintain a yield strength ≥380 MPa, with a yield strength decay rate ≤5%, exhibiting high mechanical properties and good thermal stability; moreover, the alloy can be rapidly cast and rolled for efficient production, making it easy to promote and apply.

Description

Technical Field

[0001] This invention relates to the field of metal material preparation technology, and in particular to high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloys based on rapid casting and rolling, and their preparation methods. Background Technology

[0002] Under the core trend of global industrial transformation towards lightweighting, energy conservation, and high performance, high-strength aluminum alloys, with their comprehensive advantages such as low density, high specific strength, good processability and corrosion resistance, as well as abundant resources and strong recyclability, have become core supporting materials in key fields such as aerospace, transportation (automotive, high-speed rail), high-end equipment manufacturing, and the electronics industry. Their application can significantly reduce equipment weight, improve endurance and operating efficiency, and reduce energy consumption and carbon emissions, meeting the needs of modern industrial green development. Currently, the room temperature yield strength of traditional age-hardening Al-Mg-Si alloys is 170-300 MPa, and the yield strength decay rate after heat exposure at ~100 ℃ is 14%-20%. The yield strength decay rate of traditional Al-Zn-Mg alloys after heat exposure at ~100 ℃ is >25%. Existing compositions are difficult to meet the stringent material requirements of high-end equipment. To address the aforementioned technical challenges, existing technologies employ methods such as alloying with multiple precious metals (e.g., introducing strengthening elements like Er, Sc, Cr, Y, and Nb) and optimizing advanced manufacturing processes (e.g., laser additive manufacturing, constant diameter angular extrusion, high-pressure torsion, and cumulative rolling) to solve related problems. While these methods can improve alloy strength, they negatively impact the alloy's long-term thermal stability at high temperatures, and the alloy is prone to cracking during large deformation processes. Furthermore, it is difficult to simultaneously improve the strength and ductility of aluminum alloys obtained using existing technologies. In summary, the urgent technical challenge is to simultaneously improve the room temperature and high temperature strength of alloys (reducing the alloy strength decay rate) and increase the elongation rate, while avoiding the addition of rare earth and other precious metals, simplifying the process, reducing costs, and preventing cracking, and to achieve industrial production. Summary of the Invention

[0003] To solve the above-mentioned technical problems, this invention provides a high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling. Its preparation method includes the following steps: By mass percentage, it consists of the following components: Mg: 0.95-1.96%; Si: 0.50-1.54%; Zn: 2.45-4.54%; Cu: 0.55-1.12%; Mn: 0-0.16%; Zr: 0-0.14%; total alloy content ≤8%; total unavoidable impurities ≤0.15%; balance Al. Its preparation method includes the following steps: (1) Under the protection of a mixed gas of SF6 and CO2 with a volume ratio of 1:12-1:5, Al, Al-Cu master alloy, Al-Si master alloy, Al-Mn master alloy and Al-Zr master alloy are heated and melted at 750-780 °C; then cooled to 670-720 °C and pure Mg and pure Zn are added. After the metal and alloy are completely melted, the mixture is stirred, refined and slag removed in sequence to obtain the alloy melt. (2) After the alloy melt obtained in step (1) is kept at 690-750 ℃ ​​for 10-30 min, it is diverted to the casting and rolling mill for rapid casting and rolling to obtain a slab. The rapid casting and rolling is as follows: the roll gap is 1-10 mm, the roll linear speed is 8-15 m / min, and the gating temperature is 500-700 ℃. (3) The slab obtained in step (2) is subjected to step homogenization, finish rolling, solution treatment and artificial aging to obtain a high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling; the step homogenization is carried out at 400-500℃ for 5-10 h, and then at 500-600℃ for 2-8 h; the finish rolling is carried out in 3-12 passes at room temperature, with a reduction of 10-30% per pass and a total reduction of 60-90%; the solution treatment is carried out at 500-600℃ for 4-30 min; the artificial aging treatment is carried out at 120-200℃ for 3-10 h. The high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling exhibits an elongation ≥30% in the T4 state and a yield strength ≥400 MPa in the T6 state. After heat exposure at 140-170 ℃ for 600-1200 h, it still maintains a yield strength ≥380 MPa with a yield strength decay rate ≤5%. The main precipitated phases of the Al-Zn-Mg-Si aluminum alloy are QP phase, β-type phase, T-type phase, and η-type phase, respectively. The cross-sectional size of all four precipitated phases is less than 5 nm, and the precipitate number density is 0.5 × 10⁻⁶. 24 -1.0×10 24 / m 2 .

[0004] Furthermore, the ratio of SF6 and CO2 mixed gas in step (1) is 1:10-1:6.

[0005] Further, in step (1), Al, Al-Cu master alloy, Al-Si master alloy, Al-Mn master alloy and Al-Zr master alloy are heated and melted at 760-770 °C; then cooled to 680-710 °C and pure Mg and pure Zn are added.

[0006] Furthermore, the rapid casting and rolling described in step (2) is as follows: the roll gap is 2-6 mm, the roll linear speed is 11-13 m / min, and the gating temperature is 560-600 ℃.

[0007] Furthermore, the alloy melt described in step (2) is kept at 700-730 °C for 15-25 min.

[0008] Further, the step homogenization described in step (3) involves holding the temperature at 430-480 ℃ for 6-9 h, and then holding it at 520-580 ℃ for 3-7 h.

[0009] Further, the finishing rolling in step (3) is: 4-11 passes of room temperature rolling, with a reduction of 15-25% per pass and a total reduction of 65-85%.

[0010] Further, the solution treatment in step (3) is: heat treatment at 520-580 ℃ for 5-20 min; the artificial aging treatment is: heat treatment at 140-190 ℃ for 4-9 h.

[0011] Furthermore, the high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling described in step (3) has an elongation of 31-40% in the T4 state and a yield strength of 405-450 MPa in the T6 state. After being exposed to heat at 145-165 ℃ for 650-1150 h, it can still maintain a yield strength of 385-435 MPa and a yield strength decay rate of 0.5-4%.

[0012] Furthermore, the cross-sectional size of the four precipitated phases mentioned in step (3) is 2-4 nm, and the number density of precipitated phases is 0.6 × 10⁻⁶. 24 -0.9×10 24 / m 2 .

[0013] This invention obtains a high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy that can be rapidly cast and rolled through the interaction between alloy components, the proportion of alloy components, the process, and the synergistic control of process parameters.

[0014] 1) This invention, by precisely optimizing the elemental composition and ratio of Al-Zn-Mg-Si alloys, fully leverages the synergistic effects between alloying elements, processes, and process parameters. Compared to traditional technologies that rely on adding various rare earth and other precious metal elements, this invention achieves the following beneficial effects without adding any rare earth or other precious metal elements: on the one hand, it suppresses the harmful effects of impurities, achieves forced supersaturated solid solution of alloying elements, and improves element utilization; on the other hand, it promotes the segregation of added elements at the interface between the strengthening phase and the matrix, laying the foundation for subsequent microstructure optimization and performance improvement, and solving the problems of low element utilization and uneven distribution of precipitated phases in traditional alloys.

[0015] 2) Compared to existing technologies, this invention employs a rapid casting and rolling process to achieve efficient alloy preparation, overcoming the limitations of existing complex multi-step processes. The process achieves short-process production at a high casting and rolling speed of 8-15 m / min, adapting to the needs of large-scale industrial applications. Simultaneously, through the synergistic effect of the process and process parameters with alloy composition and proportions, it effectively solves problems such as coarse solidification structure, casting and rolling cracking, and macroscopic morphological defects that are prone to occur in traditional casting and rolling. Compared to existing technologies, this invention, during the rapid forming process, can ensure a smooth and flat macroscopic morphology of the alloy sheet, avoiding cracking and coarse structure, while also regulating and promoting atomic diffusion, providing favorable conditions for high-density multiphase synergistic strengthening, thus breaking through the technical bottleneck of traditional rapid casting and rolling that makes it difficult to balance forming quality and performance.

[0016] 3) This invention achieves comprehensive optimization of the microstructure through the synergistic effects of component interactions, raw material ratios, and process parameters. Firstly, under rapid casting and rolling conditions, it effectively refines the eutectic phase, suppresses coarse segregation, improves element utilization, and obtains a highly solid-solution supersaturated microstructure. Secondly, it avoids the limitations of single-phase (β-type or η-type) dominant strengthening in traditional alloys: the β-type or η-type phases relied upon by traditional alloys are prone to coarsening, transformation, or dissolution in environments above 100 °C, resulting in a sharp drop in dislocation hindering ability, without any alternative strengthening mechanisms to compensate, ultimately leading to a "cliff-like decline" in material strength, making it unsuitable for long-term high-temperature service. Thirdly, it promotes the formation of a high-density multi-phase synergistic strengthening structure, breaking through the constraints of a single strengthening phase in traditional alloys and significantly improving alloy strength. Fourthly, by adding elements to reduce interfacial energy through interfacial segregation, it effectively suppresses the coarsening phenomenon of the strengthening phase in high-temperature environments. The optimized microstructure mainly consists of QP, β-type, T-type, and η-type precipitates, all with cross-sectional dimensions less than 5 nm and a number density of 0.5 × 10⁻⁶. 24 -1.0×10 24 / m 2The obtained alloy exhibits a room temperature yield strength ≥400 MPa, far exceeding that of traditional alloys (170-300 MPa). Furthermore, it possesses excellent thermal stability. Existing technologies show a yield strength attenuation rate of 14%-20% after 500-1000 hours of heat exposure at ~100 ℃, while this invention maintains a yield strength ≥380 MPa under higher temperatures and longer durations, i.e., after 600-1200 hours of heat exposure at 140-170 ℃, with a yield strength attenuation rate ≤5%. This breakthrough overcomes the technical bottleneck of traditional alloys where the reinforcing phase easily coarsens at ~100 ℃ and exhibits severe strength attenuation upon heat exposure.

[0017] This invention, while controlling production costs, significantly refines the eutectic phase and suppresses segregation through the synergistic regulation of alloy composition interactions, proportions, preparation processes, and parameters. This improves the solid solubility of impurities and alloying elements in the aluminum matrix, avoids the formation of coarse, hard particles, meets the requirements of rapid casting and rolling, and simultaneously enhances element utilization. It constructs a multiphase precipitation structure and element interface segregation, effectively suppressing the coarsening of strengthening phases. Microscopically, the main strengthening precipitates of the alloy are QP, β-type, T-type, and η-type phases, breaking through the technical bottleneck of single-strengthening precipitates in existing technologies. The cross-sectional dimensions of all four precipitates are less than 5 nm, with a number density of 0.5 × 10⁻⁶. 24 -1.0×10 24 / m 2 The alloy has a room temperature yield strength of ≥400 MPa, and after heat exposure at 140-170 ℃ for 600-1200 h, the yield strength can still be ≥380 MPa, with a yield strength decay rate of ≤5%, achieving simultaneous improvement in initial mechanical properties and long-term high-temperature service stability.

[0018] In summary, this invention, while avoiding the addition of rare earth elements and simplifying the process to control production costs, significantly refines the eutectic phase, suppresses segregation, and improves the solid solubility of impurities and alloying elements in the aluminum matrix through the synergistic regulation of interactions between alloy components, proportions, processes, and process parameters. It also inhibits the formation of coarse, hard particles, ensuring the alloy composition meets the requirements for rapid casting and rolling. Simultaneously, it releases more usable elements, significantly improving element utilization, and regulates multiphase precipitation and element interface segregation, effectively suppressing the coarsening of strengthening phases. The main precipitated phases in the microstructure are QP phase, β-type phase, T-type phase, and η-type phase, all with cross-sectional dimensions less than 5 nm and a number density of 0.5 × 10⁻⁶. 24 -1.0×10 24 / m 2While maintaining a high elongation, the alloy exhibits a yield strength ≥400 MPa and excellent thermal stability. After heat exposure at 140-170 ℃ for 600-1200 h, the yield strength remains ≥380 MPa, with a yield strength decay rate ≤5%. This simultaneously improves the material's initial mechanical properties and its mechanical properties under prolonged high-temperature exposure. It overcomes the technical bottleneck of existing technologies that struggle to simultaneously improve room-temperature, high-temperature, and thermal stability properties, and also breaks through the limitation of existing technologies that can only address improvements in room-temperature performance, high-temperature performance, or thermal stability individually. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to the embodiments. Example 1

[0020] Taking Al-3.0Zn-1.0Mg-1.2Si-0.7Cu (by mass percentage: Zn: 3.0%, Mg: 1.0%, Si: 1.2%, Cu: 0.7%, unavoidable impurities ≤ 0.15%, balance Al) as an example, the ingredients are prepared according to the above mass percentages. Its preparation method includes the following steps: (1) Under the protection of a mixed gas of SF6 and CO2 with a volume ratio of 1:10, pure Al, Al-Cu master alloy and Al-Si master alloy are heated and melted at 750 °C; then cooled to 680 °C and pure Mg and pure Zn are added. After the metal and alloy are completely melted, the alloy melt is obtained by stirring, refining and slag removal in sequence. (2) After the alloy melt obtained in step (1) is kept at 750 °C for 10 min, it is diverted to a casting and rolling mill for rapid casting and rolling to obtain a slab. The rapid casting and rolling is as follows: the roll gap is 5 mm, the roll linear speed is 10 m / min, and the gating temperature is 500 °C. (3) The slab obtained in step (2) is subjected to step homogenization, finishing rolling, solution treatment and artificial aging treatment to obtain a high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling; the step homogenization is: holding at 460 ℃ for 8 h, and then holding at 550 ℃ for 4 h; the finishing rolling is: 5 passes of room temperature rolling, with a reduction of 20-30% per pass and a total reduction of 70-80%; the solution treatment is: holding at 560 ℃ for 6 min; the artificial aging treatment is: holding at 180 ℃ for 6 h.

[0021] The alloy finally obtained in Example 1 is a high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy that can be rapidly cast and rolled. This alloy has a T4 elongation of 31.5%, allowing it to be stamped into simple or complex structural parts. After aging, the alloy has a yield strength of 401 MPa. After 1000 h of heat exposure at 150 ℃, it still maintains a yield strength of 387 MPa, with a yield strength decay rate of 3.5%. The main precipitates in the microstructure are QP phase, β-type phase, T-type phase, and η-type phase, all with a cross-sectional size less than 5 nm and a precipitate number density of 0.6 × 10⁻⁶. 24 / m 2 . Example 2

[0022] Taking Al-3.5Zn-1.3Mg-1.4Si-0.9Cu-0.14Mn (by mass percentage: Zn: 3.5%, Mg: 1.3%, Si: 1.4%, Cu: 0.9%, Mn: 0.14%, unavoidable impurities ≤ 0.15%, balance Al) as an example, the ingredients are prepared according to the above mass percentages. Its preparation method includes the following steps: (1) Under the protection of a mixed gas of SF6 and CO2 with a volume ratio of 1:8, pure Al, Al-Cu master alloy, Al-Si master alloy and Al-Mn master alloy are heated and melted at 770 °C; then cooled to 690 °C and pure Mg and pure Zn are added. After the metal and alloy are completely melted, they are stirred, refined and slag removed in sequence to obtain alloy melt. (2) After the alloy melt obtained in step (1) is kept at 730 ℃ for 25 min, it is diverted to the casting and rolling mill for rapid casting and rolling to obtain a slab. The rapid casting and rolling is as follows: the roll gap is 10 mm, the roll linear speed is 8 m / min, and the gating temperature is 700 ℃. (3) The slab obtained in step (2) is subjected to step homogenization, fine rolling, solution treatment and artificial aging treatment to obtain a high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling; the step homogenization is: holding at 470 ℃ for 7 h, and then holding at 540 ℃ for 6 h; the fine rolling is: 12 passes of room temperature rolling, with a reduction of 10-20% per pass and a total reduction of 70-90%; the solution treatment is: holding at 500 ℃ for 30 min; the artificial aging treatment is: holding at 120 ℃ for 10 h.

[0023] The alloy finally obtained in Example 2 is a high-strength, thermally stable Al-Zn-Mg-Si aluminum alloy that can be rapidly cast and rolled. This alloy has a T4 elongation of 32.3%, allowing it to be stamped into simple or complex structural parts. After aging, the alloy has a yield strength of 408 MPa. After heat exposure at 140 °C for 1200 h, it still maintains a yield strength of 391 MPa, with a yield strength decay rate of 4.2%. The main precipitated phases are QP, β-type, T-type, and η-type phases, all with a cross-sectional size less than 5 nm and a precipitate number density of 0.7 × 10⁻⁶. 24 / m 2 . Example 3

[0024] Taking Al-4.0Zn-1.9Mg-0.7Si-1.0Cu (by mass percentage: Zn: 4.0%, Mg: 1.9%, Si: 0.7%, Cu: 1.0%, unavoidable impurities ≤ 0.15%, balance Al) as an example, the ingredients are prepared according to the above mass percentages. Its preparation method includes the following steps: (1) Under the protection of a mixed gas of SF6 and CO2 with a volume ratio of 1:5, pure Al, Al-Cu master alloy and Al-Si master alloy are heated and melted at 750 °C; then cooled to 680 °C and pure Mg and pure Zn are added. After the metal and alloy are completely melted, the alloy melt is obtained by stirring, refining and slag removal in sequence. (2) After the alloy melt obtained in step (1) is kept at 690 °C for 25 min, it is diverted to a casting and rolling mill for rapid casting and rolling to obtain a slab. The rapid casting and rolling is as follows: the roll gap is 1 mm, the roll linear speed is 15 m / min, and the gating temperature is 630 °C. (3) The slab obtained in step (2) is subjected to step homogenization, fine rolling, solution treatment and artificial aging treatment to obtain a high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling; the step homogenization is: holding at 500℃ for 5h, and then holding at 600℃ for 2h; the fine rolling is: 6 passes of room temperature rolling, with a reduction of 15-25% per pass and a total reduction of 60-80%; the solution treatment is: holding at 600℃ for 4min; the artificial aging treatment is: holding at 150℃ for 5h.

[0025] The alloy finally obtained in Example 3 is a high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy that can be rapidly cast and rolled. This alloy has a T4 elongation of 31.2%, allowing it to be stamped into simple or complex structural parts. After aging, the alloy has a yield strength of 412 MPa. After 900 h of heat exposure at 160 ℃, it still maintains a yield strength of 395 MPa, with a yield strength decay rate of 4.1%. The main precipitates are QP, β-type, T-type, and η-type phases, all with a cross-sectional size less than 5 nm and a precipitate number density of 0.9 × 10⁻⁶. 24 / m 2 . Example 4

[0026] Taking Al-2.7Zn-1.6Mg-0.5Si-1.1Cu (by mass percentage: Zn: 2.7%, Mg: 1.6%, Si: 0.5%, Cu: 1.1%, unavoidable impurities ≤ 0.15%, balance Al) as an example, the ingredients are prepared according to the above mass percentages. Its preparation method includes the following steps: (1) Under the protection of a mixed gas of SF6 and CO2 with a volume ratio of 1:8, pure Al, Al-Cu master alloy and Al-Si master alloy are heated and melted at 750 °C; then cooled to 690 °C and pure Mg and pure Zn are added. After the metal and alloy are completely melted, the alloy melt is obtained by stirring, refining and slag removal in sequence. (2) After the alloy melt obtained in step (1) is kept at 720 °C for 20 min, it is diverted to a casting and rolling mill for rapid casting and rolling to obtain a slab. The rapid casting and rolling is as follows: the roll gap is 4 mm, the roll linear speed is 10 m / min, and the gating temperature is 550 °C. (3) The slab obtained in step (2) is subjected to step homogenization, fine rolling, solution treatment and artificial aging to obtain a high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling; the step homogenization is: holding at 400 ℃ for 10 h, and then holding at 500 ℃ for 8 h; the fine rolling is: 4 passes of room temperature rolling, with a reduction of 20-30% per pass and a total reduction of 60-80%; the solution treatment is: holding at 550 ℃ for 15 min; the artificial aging treatment is: holding at 160 ℃ for 6 h.

[0027] The alloy finally obtained in Example 4 is a high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy that can be rapidly cast and rolled. This alloy has a T4 elongation of 33.5%, allowing it to be stamped into simple or complex structural parts. After aging, the alloy has a yield strength of 402 MPa. After 600 h of heat exposure at 165 ℃, it still maintains a yield strength of 384 MPa, with a yield strength decay rate of 4.5%. The main precipitates are QP, β-type, T-type, and η-type phases, all with a cross-sectional size less than 5 nm and a precipitate number density of 0.5 × 10⁻⁶. 24 / m 2 . Example 5

[0028] Taking Al-4.5Zn-1.7Mg-0.6Si-1.0Cu-0.13Zr (by mass percentage: Zn: 4.5%, Mg: 1.7%, Si: 0.6%, Cu: 1.0%, Zr: 0.13%, unavoidable impurities ≤ 0.15%, balance Al) as an example, the ingredients are prepared according to the above mass percentages. Its preparation method includes the following steps: (1) Under the protection of a mixed gas of SF6 and CO2 with a volume ratio of 1:12, pure Al, Al-Cu master alloy, Al-Si master alloy and Al-Zr master alloy are heated and melted at 760 °C; then cooled to 700 °C and pure Mg and pure Zn are added. After the metal and alloy are completely melted, they are stirred, refined and slag removed in sequence to obtain alloy melt. (2) After the alloy melt obtained in step (1) is kept at 730 ℃ for 20 min, it is diverted to the casting and rolling mill for rapid casting and rolling to obtain a slab. The rapid casting and rolling is as follows: the roll gap is 6 mm, the roll linear speed is 12 m / min, and the gating temperature is 620 ℃. (3) The slab obtained in step (2) is subjected to step homogenization, finishing rolling, solution treatment and artificial aging treatment to obtain a high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling; the step homogenization is: holding at 470 ℃ for 8 h, and then holding at 570 ℃ for 4 h; the finishing rolling is: 8 passes of room temperature rolling, with a reduction of 20-30% per pass and a total reduction of 80-90%; the solution treatment is: holding at 520 ℃ for 20 min; the artificial aging treatment is: holding at 200 ℃ for 3 h.

[0029] The final alloy obtained in Example 5 is a high-strength, thermally stable Al-Zn-Mg-Si aluminum alloy that can be rapidly cast and rolled. This alloy has a T4 elongation of 32.1%, allowing it to be stamped into simple or complex structural parts. After aging, the alloy has a yield strength of 418 MPa. After 1000 h of heat exposure at 150 ℃, it still maintains a yield strength of 398 MPa, with a yield strength decay rate of 4.8%. The main precipitates are QP, β-type, T-type, and η-type phases, all with a cross-sectional size less than 5 nm and a precipitate number density of 0.9 × 10⁻⁶. 24 / m 2 . Comparative Example 1

[0030] Journal Name: Materials Science & Engineering A In their paper titled "Microstructural evolution and elevated-temperature strengthening mechanism of super-gravity solidified Al-Ce-Scalloy during cold rolling and aging," published in 2025, Vol. 931, page 148188, Penghui Zhang, Chuandong Wu, et al. used Al-11.63Ce-0.39Sc alloy (by mass percentage: Ce: 11.63%, Sc: 0.39%, Fe: 0.04%, Si: 0.05%, unavoidable impurities ≤ 0.09%, balance Al). The preparation process involved using pure Al (99.9 wt%), Al-30Ce master alloy, and Al-2Sc master alloy as raw materials, mixing them according to their nominal composition, melting them in air at 900 ℃, stirring thoroughly, holding for 40 min, pouring the mixture into a graphite crucible preheated to 200 ℃, air cooling, and then transferring the ingot to a centrifuge at 3000 °C. Solidified under a hypergravity field (corresponding to a rotation speed of 5670 r / min), the alloy was processed into a billet of 28.2×18.2×5.2 mm. After being cold rolled at room temperature using twin rolls, the thickness was reduced from 5 mm to 2.5 mm (50% reduction). Finally, the alloy was isothermally aged in a vacuum environment at 300 ℃ for 2 h and then water quenched. The final peak aged state room temperature yield strength of the alloy was 352±3 MPa.

[0031] Compared with the raw materials of this invention, Comparative Example 1 uses high-cost rare earth elements (Ce, Sc), with a total mass percentage as high as 12.02%, while this invention does not add any rare earth elements. In addition, the maximum alloy addition amount of this invention is ≤8%, which is far lower than the rare earth addition content of Comparative Example 1 (12.02%). Therefore, this invention has a significant cost advantage. Furthermore, this invention and Comparative Example 1 use different processes. Comparative Example 1 requires complex steps such as high gravity solidification (3000g centrifugal field). High gravity solidification requires a special centrifuge (speed 5670 r / min), and subsequent aging treatment in a vacuum environment is also required. The process steps are complicated, the equipment requirements are extremely high, and the overall process takes longer. The energy consumption and production cycle are significantly higher than those of this invention, and the operation is more difficult. In terms of performance, the alloy obtained by this invention has a yield strength ≥400 MPa, and after being exposed to heat at 140-170 ℃ for 600-1200 h, it can still maintain a yield strength ≥380 MPa, with a yield strength decay rate ≤5%. The lowest yield strength at room temperature (400 MPa) of this invention is higher than the highest strength (352±3 MPa) of Comparative Example 1. In addition, Comparative Example 1 does not provide technical inspiration for the alloy to have high temperature thermal stability and high plasticity.

[0032] In summary, compared with existing technologies, this invention reduces raw material costs by using no rare earth elements and with lower element content. It also employs a simpler process and faster casting and rolling speed, simultaneously improving the alloy's room temperature strength, plasticity, and high-temperature thermal stability. This breaks through the bottleneck of existing technologies, which can only achieve room temperature strength, plasticity, or high-temperature strength, and simultaneously improves the alloy's room temperature strength, plasticity, and high-temperature strength (high-temperature thermal stability). Furthermore, the process parameters differ in each embodiment of this invention, resulting in different material properties. This demonstrates that the superior effects obtained by this invention are not determined by a specific component ratio, process, or process parameters, but are achieved through the synergistic regulation of component interactions, ratios, processes, and process parameters. The optimal technical effects can only be achieved within the scope of the claims of this invention.

Claims

1. A high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling, characterized in that: It consists of the following components by weight percentage: Composition: Mg: 0.95-1.96%; Si: 0.50-1.54%; Zn: 2.45-4.54%; Cu: 0.55-1.12%; Mn: 0-0.16%; Zr: 0-0.14%; Total alloy content ≤8%; Total unavoidable impurities ≤0.15%; Balance is Al; Its preparation method includes the following steps: (1) Under the protection of a mixed gas of SF6 and CO2 with a volume ratio of 1:12-1:5, Al, Al-Cu master alloy, Al-Si master alloy, Al-Mn master alloy and Al-Zr master alloy are heated and melted at 750-780 °C; then cooled to 670-720 °C and pure Mg and pure Zn are added. After the metal and alloy are completely melted, the mixture is stirred, refined and slag removed in sequence to obtain the alloy melt. (2) After the alloy melt obtained in step (1) is kept at 690-750 ℃ ​​for 10-30 min, it is diverted to the casting and rolling mill for rapid casting and rolling to obtain a slab. The rapid casting and rolling is as follows: the roll gap is 1-10 mm, the roll linear speed is 8-15 m / min, and the gating temperature is 500-700 ℃. (3) The slab obtained in step (2) is subjected to step homogenization, finish rolling, solution treatment and artificial aging to obtain a high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling; the step homogenization is carried out at 400-500℃ for 5-10 h, and then at 500-600℃ for 2-8 h; the finish rolling is carried out in 3-12 passes at room temperature, with a reduction of 10-30% per pass and a total reduction of 60-90%; the solution treatment is carried out at 500-600℃ for 4-30 min; the artificial aging treatment is carried out at 120-200℃ for 3-10 h. The high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling exhibits an elongation ≥30% in the T4 state and a yield strength ≥400 MPa in the T6 state. After heat exposure at 140-170 ℃ for 600-1200 h, it still maintains a yield strength ≥380 MPa with a yield strength decay rate ≤5%. The main precipitated phases of the Al-Zn-Mg-Si aluminum alloy are QP phase, β-type phase, T-type phase, and η-type phase, respectively. The cross-sectional size of all four precipitated phases is less than 5 nm, and the precipitate number density is 0.5 × 10⁻⁶. 24 -1.0×10 24 / m 2 .

2. The high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling as described in claim 1, characterized in that: The ratio of SF6 and CO2 mixed gas in step (1) is 1:10-1:

6.

3. The high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling as described in claim 1, characterized in that: In step (1), Al, Al-Cu master alloy, Al-Si master alloy, Al-Mn master alloy and Al-Zr master alloy are heated and melted at 760-770 °C; then cooled to 680-710 °C and pure Mg and pure Zn are added.

4. The high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling as described in claim 1, characterized in that: The rapid casting and rolling process described in step (2) is as follows: the roll gap is 2-6 mm, the roll linear speed is 11-13 m / min, and the gating temperature is 560-600 ℃.

5. The high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling as described in claim 1, characterized in that: The alloy melt described in step (2) is kept at 700-730 ℃ for 15-25 min.

6. The high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling as described in claim 1, characterized in that: The step homogenization described in step (3) involves holding the temperature at 430-480 ℃ for 6-9 h, and then holding it at 520-580 ℃ for 3-7 h.

7. The high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling as described in claim 1, characterized in that: The finishing rolling in step (3) is: 4-11 passes of room temperature rolling, with a reduction of 15-25% per pass and a total reduction of 65-85%.

8. The high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling as described in claim 1, characterized in that: The solution treatment in step (3) is to keep the temperature at 520-580 ℃ for 5-20 min; the artificial aging treatment is to keep the temperature at 140-190 ℃ for 4-9 h.

9. The high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling as described in claim 1, characterized in that: The high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling described in step (3) has an elongation of 31-40% in the T4 state and a yield strength of 405-450 MPa in the T6 state. After being exposed to heat at 145-165 ℃ for 650-1150 h, it can still maintain a yield strength of 385-435 MPa and a yield strength decay rate of 0.5-4%.

10. The high-strength, high-thermal-stability Al-Zn-Mg-Si aluminum alloy based on rapid casting and rolling as described in claim 1, characterized in that: The four precipitated phases mentioned in step (3) have a cross-sectional size of 2-4 nm and a precipitated phase number density of 0.6 × 10⁻⁶. 24 -0.9×10 24 / m 2 .