A rare earth-containing Al-Mg-Si alloy and a preparation method thereof

Abstract

This invention relates to a rare-earth Al-Mg-Si alloy and its preparation method, belonging to the field of aluminum alloy material preparation technology. It solves the problems of high quenching sensitivity of existing Al-Mg-Si alloys, easy deformation and cracking of large components under water cooling, and the difficulty in balancing mechanical properties and large-scale production in existing improvement schemes. By mass percentage, the alloy contains Mg: 0.4~0.8%, Si: 0.2~0.6%, La: 0.05~0.2%, Ce: 0.05~0.2%, Y: 0.03~0.15%, Zr: 0.02~0.1%, Fe≤0.15%, Cu≤0.1%, Mn≤0.08%, with the remainder being Al and unavoidable impurities with a total content ≤0.1%. The mass ratio of La, Ce, Y, and Zr is (1~4):(1~4):(0.6~3):(0.4~2), and the mass ratio of Fe to La is ≤1.5. The alloy forms Al3(La,Ce,Y,Zr) nanophases with a size of 5~20 nm. The alloy of this invention utilizes La-Ce-Y-Zr quaternary synergistic microalloying, combined with segmented homogenization and gradient cooling processes, reducing the critical quenching cooling rate to 3~8℃ / s. Air cooling / spray cooling can replace water cooling, achieving a tensile strength ≥280MPa and an elongation ≥15%. It is suitable for high-speed rail car body profiles, new energy vehicle battery trays, and large building structural components.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy material preparation technology, and in particular to a rare earth-containing Al-Mg-Si alloy and its preparation method. Background Technology

[0002] Al-Mg-Si (6xxx series) aluminum alloys, due to their good corrosion resistance, weldability, and moderate strength, have become commonly used structural materials in transportation, new energy, and construction. The strengthening effect of these alloys relies on the Mg2Si nano-strengthening phase formed during aging after solution treatment. If the solution cooling rate is insufficient, Mg and Si are prone to premature precipitation, forming coarse Mg2Si phases, significantly weakening the aging strengthening effect. Therefore, existing Al-Mg-Si alloys have an inherent defect of high quenching sensitivity, requiring rapid cooling methods such as water cooling during production. However, water cooling easily causes internal stress in large and complex components due to temperature differences, leading to deformation and cracking, significantly increasing the scrap rate and restricting its large-scale application in the field of large components.

[0003] To reduce the quenching sensitivity of Al-Mg-Si alloys, numerous attempts have been made in existing technologies, mainly including the addition of rare earth elements, adjustment of composition ratios, and optimization of cooling / heat treatment processes. However, none of these have formed a systematic solution and still have significant shortcomings: the addition of single or dual rare earth elements (La / Ce) can only achieve grain boundary purification and cannot effectively improve the stability of the solid solution, and the critical cooling rate for quenching remains high; some composition ratio improvement schemes either adopt high-Si designs, leading to increased alloy brittleness, or rely on special quenching fluids, increasing raw material and process costs; process optimization schemes mostly rely on special molds and high-precision cooling equipment, resulting in poor versatility, and conventional single-stage homogenization treatment is prone to ingot composition segregation, further exacerbating the tendency of element precipitation during quenching. In addition, existing improvement technologies often fail to ensure the balance of alloy mechanical properties while reducing quenching sensitivity, with elongation and tensile strength under air-cooled conditions generally being low, failing to meet the requirements of high-end applications.

[0004] There is currently no technical solution that can fundamentally reduce the quenching sensitivity of Al-Mg-Si alloys, eliminate the need for special equipment and quenching media, adapt to large-scale production, and ensure the excellent mechanical properties of the alloys. This problem has become a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a rare earth-containing Al-Mg-Si alloy and its preparation method, in order to at least solve one of the technical problems of existing Al-Mg-Si alloys having high quenching sensitivity, large components being prone to deformation and cracking when water-cooled, and existing improved solutions being unable to balance low quenching sensitivity and excellent mechanical properties, and thus unable to adapt to large-scale production.

[0006] On one hand, embodiments of the present invention provide a rare earth Al-Mg-Si alloy, the chemical composition of which, by mass percentage, is as follows: Mg: 0.4~0.8%, Si: 0.2~0.6%, La: 0.05~0.2%, Ce: 0.05~0.2%, Y: 0.03~0.15%, Zr: 0.02~0.1%, Fe≤0.15%, Cu≤0.1%, Mn≤0.08%, the remainder being Al and unavoidable impurities, with total impurity content ≤0.1%; The mass ratio of La, Ce, Y, and Zr is (1~4):(1~4):(0.6~3):(0.4~2); The mass ratio of Fe to La is ≤1.5.

[0007] Furthermore, the La, Ce, Y, and Zr form an Al3(La,Ce,Y,Zr) nanophase in the alloy, and the nanophase size is 5~20 nm.

[0008] Furthermore, the atomic ratio of Mg to Si is 1.2 to 1.5, and satisfies one of the following conditions: When the Mg / Si atomic ratio is 1.2~1.3, the total La+Ce content is ≥0.15%; When the Mg / Si atomic ratio is 1.3~1.5, the total amount of Y+Zr is ≥0.1%.

[0009] Furthermore, the critical cooling rate for quenching of the alloy is 3~8℃ / s.

[0010] Accordingly, this invention proposes a method for preparing the above-mentioned rare earth-containing Al-Mg-Si alloy, comprising the following steps: S1. Batching and smelting; S2. Refining and degassing; the refining agent used in the refining and degassing process is a mixture of Na3AlF6 and KCl in a mass ratio of 2:1, and the mass ratio of Na3AlF6 to Y element in the alloy is (10~20):1; S3. Casting; S4. Segmented homogenization process; S5. Hot-rolled; S6. Solution quenching; S7. Timeliness processing.

[0011] Furthermore, in S4, the segmented homogenization process includes: First stage: Heat to 480~500℃ and keep warm for 4~6 hours; Second stage: Raise the temperature to 560~580℃ and keep it warm for 6~8 hours; After homogenization, the furnace is cooled to room temperature at a rate of ≤5℃ / h.

[0012] Furthermore, in S6, the solution quenching adopts a gradient cooling process: First stage: Cool from 530~550℃ to 300~350℃, with the cooling rate controlled at 6~8℃ / s; Second stage: Cool from 300~350℃ to room temperature, with the cooling rate controlled at 3~5℃ / s; The cooling medium for gradient cooling is either pure air cooling or a mixture of air and atomized water.

[0013] Furthermore, in the gradient cooling process, the cooling rate is controlled by adjusting the atomized water pressure to 0.1~0.3MPa.

[0014] Furthermore, the cooling rate of the gradient cooling process is adapted to the product thickness in the following manner: When preparing plates with a thickness of 6~10mm, the cooling rate in the first stage is 7~8℃ / s, and the cooling rate in the second stage is 4~5℃ / s. When preparing profiles with a thickness of 10~15mm, the cooling rate in the first stage is 6~7℃ / s, and the cooling rate in the second stage is 3~4℃ / s.

[0015] The rare earth-containing Al-Mg-Si alloy described in this invention, and the rare earth-containing Al-Mg-Si alloy obtained by the above preparation method, can be widely used in the preparation of rail transit profiles, new energy vehicle structural components, marine engineering components, or large building structural components.

[0016] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1) This invention utilizes La-Ce-Y-Zr quaternary synergistic microalloying to suppress Mg2Si phase precipitation and maintain supersaturated solid solution stability even under slow cooling conditions as low as 3~8℃ / s. This cooling rate is only 1 / 4 to 1 / 2 of the critical quenching cooling rate (≥12℃ / s) of conventional Al-Mg-Si alloys, yet it achieves a leap from water cooling to pure air / spray cooling, reducing the risk of deformation and cracking in large and complex components due to uneven quenching, and lowering the scrap rate by more than 40%. Compared to existing high-Si (0.9~1.5%) dual rare-earth Al-Mg-Si alloy schemes, this invention has a Si content ≤0.6%, avoiding the brittleness risk caused by high Si while exhibiting lower quenching sensitivity. Compared to existing schemes that refine grains by adding a single Zr element but still require a special quenching fluid, this invention does not require any special quenching fluid, reducing overall manufacturing costs by 30~40%.

[0017] 2) This invention achieves a tensile strength ≥280MPa and an elongation ≥15% under mild cooling conditions of only 3~8℃ / s. This performance level is achieved in existing Al-Mg-Si alloy systems requiring water cooling at speeds above 20℃ / s. Compared to existing Al-Mg-Si alloys containing single or mixed rare earth elements, this invention increases tensile strength by 9~17% and elongation by 15~37% under the same air cooling conditions, breaking through the technical bottleneck of the incompatibility between slow cooling and high strength in 6xxx series aluminum alloys.

[0018] 3) The refining process of this invention strictly limits the mass ratio of Na3AlF6 to Y (10~20):1, reducing the hydrogen content of the melt to 0.12~0.15mL / 100gAl; segmented homogenization reduces the ingot segregation to 5~8%, significantly increasing the precipitation of Al3(La,Ce,Y,Zr) nanophases; gradient cooling reduces the quenching deformation rate of 15mm plates to ≤1.5%. These process improvements require no specialized equipment and can be adapted to conventional aluminum alloy production lines for large-scale stable production, resulting in significant overall cost advantages.

[0019] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0020] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0021] Figure 1 is a transmission electron microscope image of the precipitated phase morphology of the alloy in Example 1 of the present invention; Figure 2 This is the energy spectrum of Al3(La,Ce,Y,Zr) nanoprecipitated phase in the alloy of Example 1 of the present invention. Detailed Implementation

[0022] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0023] To address the high quenching sensitivity of existing Al-Mg-Si alloys and the inherent shortcomings of improvement technologies, this invention provides a rare-earth-containing Al-Mg-Si alloy and its preparation method. This technical solution utilizes La-Ce-Y-Zr quaternary synergistic microalloying, combined with segmented homogenization and gradient cooling processes, to reduce the critical quenching cooling rate of the alloy to 3~8℃ / s. Air cooling / spray cooling can replace water cooling while maintaining excellent performance, making it suitable for the large-scale production of large and complex components.

[0024] A specific embodiment of the present invention discloses a rare earth Al-Mg-Si alloy, the chemical composition of which is as follows by mass percentage: Mg: 0.4~0.8%, Si: 0.2~0.6%, La: 0.05~0.2%, Ce: 0.05~0.2%, Y: 0.03~0.15%, Zr: 0.02~0.1%, Fe≤0.15%, Cu≤0.1%, Mn≤0.08%, the remainder being Al and unavoidable impurities, with a total impurity content ≤0.1%; the mass ratio of La, Ce, Y, and Zr is (1~4):(1~4):(0.6~3):(0.4~2); the mass ratio of Fe to La is ≤1.5 (for example, the Fe / La mass ratio can be: 0.6, 0.75, 0.8, 1.0, 1.2, 1.5).

[0025] The selection of the above composition ranges is based on the strengthening mechanism of 6xxx series aluminum alloys and the synergistic effect of rare earth elements and Zr. Specifically, Mg and Si are the core elements for forming the Mg2Si strengthening phase. If the content is too high, coarse precipitates will easily form; if the content is too low, the strengthening effect will be insufficient. The limited content of La, Ce, Y, and Zr ensures that the quaternary synergistic effect is fully utilized, while avoiding excessive addition that would lead to the formation of coarse intermetallic compounds and a decrease in alloy plasticity. The limitation of impurities such as Fe, Cu, and Mn, as well as the total impurity content, aims to avoid the formation of brittle phases and ensure the balance of the alloy's mechanical properties.

[0026] From the perspective of strengthening mechanism, the traditional strengthening method for Al-Mg-Si alloys is to form Mg2Si nano-strengthening phase by aging after solution treatment. In existing technologies, due to the poor stability of the alloy solid solution, if the cooling rate is insufficient during the solution cooling process, Mg and Si will rapidly precipitate to form coarse Mg2Si phases, resulting in a significant weakening of the subsequent aging strengthening effect. Therefore, rapid water cooling at ≥12℃ / s is required to ensure performance. However, this invention, through the above-mentioned composition design, allows La and Ce to play multiple roles: on the one hand, La and Ce can transform the β-Fe phase in the alloy from needle-like to granular, and at the same time, they can form high-melting-point Al with Fe and Si. 13The Fe4La2 phase prevents the acicular β-Fe from degrading the alloy's plasticity. On the other hand, La and Ce accumulate at the interfaces of the Mg2Si and α-Al(FeMnSi) phases, purifying grain boundaries, inhibiting the segregation of Fe and Si impurities, and reducing the width of the grain boundary non-precipitation zone. Furthermore, trace amounts of La and Ce can effectively adsorb hydrogen and impurity elements in the melt, forming high-melting-point compounds that float to the surface for removal, and altering the growth morphology of the β(Mg2Si) and α-Al(FeMnSi) phases, weakening their sensitivity to quenching rates. It is this synergistic effect of multiple factors that gives the alloy of this invention the fundamental basis for reducing quenching sensitivity through its composition.

[0027] Furthermore, the La, Ce, Y, and Zr form an Al3(La,Ce,Y,Zr) nanophase in the alloy, and the nanophase size is 5~20nm (e.g., 5nm, 8nm, 10nm, 12nm, 15nm, 18nm, 20nm).

[0028] Y, Zr, La, and Ce synergistically form the aforementioned nanophase, with Zr effectively refining the alloy grains. This quaternary nanophase is dispersed throughout the alloy matrix, pinning dislocations and subgrain boundaries, hindering the long-range diffusion of Mg and Si atoms during quenching and cooling, thereby suppressing the precipitation of coarse Mg2Si phases and fundamentally improving the stability of the alloy solid solution. This contrasts with Al formed by single or dual rare earth elements in existing technologies. 11 Unlike coarse intermetallic compounds such as RE3 (typically 50-200 nm in size), the Al3(La,Ce,Y,Zr) nanophase formed in this invention has a size of only 5-20 nm, exhibiting a more significant pinning effect and excellent thermal stability, which can suppress the long-term coarsening of the Mg2Si strengthening phase.

[0029] Regarding impurity control, this invention limits the mass ratio of Fe to La to ≤1.5, so that Fe preferentially forms Al. 13 The Fe4La2 phase, rather than the coarse β-Fe phase, further ensures the stability of the solid solution. If the Fe content exceeds 0.15% and the La content is less than 0.1%, Fe cannot fully form Al. 13 The presence of the Fe4La2 phase will increase the proportion of the β-Fe phase by 15-20%, reduce the elongation of the alloy to below 12%, and severely degrade its plasticity.

[0030] Under the synergistic effect of the aforementioned elements, the alloy can effectively suppress the premature precipitation of the Mg2Si phase and maintain the stability of the supersaturated solid solution even under slow cooling conditions of 3~8℃ / s. This ensures the subsequent aging strengthening effect without the need for rapid water cooling. This cooling rate is only 1 / 4 to 1 / 2 of the critical quenching cooling rate (≥12℃ / s) of conventional Al-Mg-Si alloys, successfully achieving a leap from water cooling to pure air cooling or spray cooling. This reduces the risk of deformation and cracking in large and complex components due to uneven quenching, and lowers the scrap rate by more than 40%.

[0031] Furthermore, the atomic ratio of Mg to Si is 1.2 to 1.5, and satisfies one of the following conditions: When the Mg / Si atomic ratio is 1.2~1.3, the total La+Ce content is ≥0.15%; When the Mg / Si atomic ratio is 1.3~1.5, the total amount of Y+Zr is ≥0.1%.

[0032] Regarding the design of the Mg / Si atomic ratio and the total amount of rare earth elements, this invention synergistically optimizes both. Specifically, the Mg / Si atomic ratio is limited to 1.2~1.5 (e.g., 1.2, 1.25, 1.3, 1.35, 1.4, 1.5). This range represents the optimal ratio for the formation of the Mg2Si strengthening phase. If the atomic ratio is too low, excess Si easily forms a Si-rich phase, leading to increased alloy brittleness. If the atomic ratio is too high, excess Mg easily forms abnormal precipitates such as Al2Mg3Si6, weakening the age-hardening effect.

[0033] Building upon this foundation, the present invention further optimizes the total rare earth content according to different Mg / Si atomic ratio ranges: when the Mg / Si atomic ratio is 1.2~1.3, a small amount of excess Si exists in the system, with the total La+Ce content ≥0.15% (e.g., 0.15%, 0.16%, 0.18%, 0.20%, 0.22%), to enhance grain boundary purification, suppress the segregation of excess Si at grain boundaries, and avoid brittleness caused by Si-rich phases; when the Mg / Si atomic ratio is 1.3~1.5, an excess Mg exists in the system, with the total Y+Zr content ≥0.1% (e.g., 0.10%, 0.12%, 0.15%, 0.18%, 0.20%), effectively suppressing the formation of abnormal precipitates such as Al2Mg3Si6 from excess Mg, ensuring the effective content of Mg and Si in the solid solution. This design enables the alloy to maintain solid solution stability under different Mg / Si ratios through targeted regulation of rare earth elements, thereby improving the stability of the age-hardening effect.

[0034] Furthermore, the critical cooling rate for quenching of the alloy is 3~8℃ / s (e.g., 3℃ / s, 4℃ / s, 5℃ / s, 6℃ / s, 7℃ / s, 8℃ / s).

[0035] Conventional Al-Mg-Si alloys typically require a critical quenching cooling rate of ≥12℃ / s to maintain their performance. If the cooling rate is insufficient, Mg and Si are prone to premature precipitation, forming coarse Mg2Si, leading to a significant decrease in strength. This invention, however, utilizes La-Ce-Y-Zr quaternary synergistic microalloying to reduce the critical quenching cooling rate to 3~8℃ / s, enabling the alloy to maintain the stability of a supersaturated solid solution even under mild conditions such as air cooling or spray cooling.

[0036] Within this cooling rate range, the alloy of this invention exhibits a tensile strength ≥280MPa and an elongation ≥15%. After pure air-cooling quenching, the tensile strength is ≥275MPa with a tensile strength retention rate ≥95%. Compared to existing Al-Mg-Si alloys containing single or mixed rare earth elements, this invention improves tensile strength by 15-20% and elongation by 20-30% under the same air-cooling conditions, successfully overcoming the technical bottleneck of the incompatibility between slow cooling and high strength in 6xxx series aluminum alloys.

[0037] To achieve the performance advantages of the above-mentioned composition design, the present invention also provides a preparation method that is highly compatible with the alloy composition.

[0038] A method for preparing the above-mentioned rare earth-containing Al-Mg-Si alloy includes the following steps: S1. Batching and smelting; S2. Refining and degassing; the refining agent used in the refining and degassing process is a mixture of Na3AlF6 and KCl in a mass ratio of 2:1, and the mass ratio of Na3AlF6 to Y element in the alloy is (10~20):1.

[0039] S3. Casting; S4. Segmented homogenization process; S5. Hot-rolled; S6. Solution quenching; S7. Time-sensitive processing; The preparation method described in this invention is highly compatible with the above alloy composition design, and the process parameters of each step are optimized to fully utilize the quaternary synergistic effect of La-Ce-Y-Zr.

[0040] In the batching and smelting stage (S1), the raw materials used are industrial pure Al (purity ≥99.7%), Al-Mg master alloy, Al-Si master alloy, Al-La master alloy, Al-Ce master alloy, Al-Y master alloy, and Al-Zr master alloy to avoid compositional deviations caused by high-temperature burning of pure metals. The smelting temperature is controlled at 720~750℃ and held for 30~40min. At the same time, argon gas (flow rate 0.3~0.5L / min) is introduced and stirred (speed 50~80r / min) to ensure uniform melt composition.

[0041] In the refining and degassing stage (S2), the refining agent is a mixture of Na3AlF6 and KCl at a mass ratio of 2:1, added at 0.1-0.2% of the melt mass. The mixture is held at this temperature for 15-20 minutes, with an argon degassing flow rate of 0.2-0.4 L / min. The mass ratio of Na3AlF6 to Y in the alloy is limited to (10-20):1, for example, 10:1, 12:1, 14:1, 16:1, 18:1, or 20:1. This is because Na3AlF6 promotes the uniform distribution of Y in the melt, reducing the hydrogen content from 0.25 mL / 100gAl in conventional processes to 0.12-0.15 mL / 100gAl. If Na3AlF6 is insufficient (mass ratio <10:1), Y tends to agglomerate to form the Al2Y phase, preventing Y from effectively participating in the formation of the nanophase, while the hydrogen content rises back to 0.18-0.20 mL / 100gAl.

[0042] In the casting stage (S3), the melt is cooled to 680~700℃ and held for 10~15 minutes before semi-continuous casting. The casting speed is 80~120 mm / min, the cooling water temperature is 25~35℃, and the ingot diameter is 120~200 mm. In the hot rolling stage (S5), the ingot is heated to 450~480℃ and held for 2~3 hours. It is then hot rolled 8~12 times, with a reduction of 8~15% per pass. The final rolling temperature is controlled at 380~420℃. In the aging treatment stage (S7), the aging temperature is 170~180℃, held for 8~12 hours, and then cooled to room temperature in the furnace.

[0043] The process parameters of the above steps work together to ensure the accuracy of alloy composition, the uniformity of microstructure, and the achievement of low quenching sensitivity.

[0044] Furthermore, in S4, the segmented homogenization process includes: First stage: Raise the temperature to 480~500℃ (e.g., 480℃, 485℃, 490℃, 495℃, 500℃), and keep it at that temperature for 4~6 hours (e.g., 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours); Second stage: Raise the temperature to 560~580℃ (e.g., 560℃, 565℃, 570℃, 575℃, 580℃), and keep it warm for 6~8 hours (e.g., 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours); After homogenization, the furnace is cooled to room temperature at a rate ≤5℃ / h (e.g., 1℃ / h, 2℃ / h, 3℃ / h, 4℃ / h, 5℃ / h).

[0045] This segmented homogenization process is specifically designed to address the nucleation requirements of Al3(La,Ce,Y,Zr) quaternary nanophases. The first temperature range effectively dissolves the metastable Al6Mg4Si5 phase. If the temperature is below 480℃ or the holding time is insufficient, the metastable phase residue will be ≥30%, leading to potential cracking during subsequent hot rolling. The second temperature range effectively promotes Al3(La,Ce,Y,Zr) nanophase nucleation. Compared to conventional single-stage homogenization in existing technologies, this segmented homogenization process reduces ingot segregation from 15-20% to 5-8%, and increases the Al3(La,Ce,Y,Zr) nanophase precipitation from less than 60% to ≥85%.

[0046] It should be noted that if the second-stage holding time is less than 6 hours, the nanophase precipitation amount will be less than 60%, and the alloy's quenching sensitivity will increase significantly, making it impossible to achieve the goal of reducing the critical cooling rate to 3~8℃ / s. This invention optimizes the homogenization parameters of the second stage to achieve a nanophase precipitation amount of over 85%, thus fully ensuring the alloy's low quenching sensitivity.

[0047] Furthermore, in S6, the solution quenching adopts a gradient cooling process: The first stage: cooling from 530~550℃ to 300~350℃, with the cooling rate controlled at 6~8℃ / s (e.g., 6℃ / s, 6.5℃ / s, 7℃ / s, 7.5℃ / s, 7.8℃ / s, 8℃ / s). The second stage: cooling from 300~350℃ to room temperature, with the cooling rate controlled at 3~5℃ / s (e.g., 3℃ / s, 3.5℃ / s, 4℃ / s, 4.5℃ / s, 4.8℃ / s, 5℃ / s); The gradient cooling medium uses pure air cooling or a mixture of air and atomized water for cooling. The cooling rate is controlled by adjusting the atomized water pressure from 0.1 to 0.3 MPa (e.g., 0.1 MPa, 0.12 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa).

[0048] The rapid precipitation temperature range for Mg and Si elements is from 530~550℃ to 300~350℃. The first stage uses a cooling rate of 6~8℃ / s to effectively suppress the premature precipitation of the Mg2Si phase in this temperature range. The second stage uses a slower cooling rate of 3~5℃ / s, which ensures the stability of the solid solution and reduces the internal stress generated by excessively rapid cooling. Compared with the existing quenching method using a single cooling rate, this gradient cooling process better matches the precipitation characteristics of Mg and Si elements in different temperature ranges, minimizing the generation of internal stress while ensuring the stability of the solid solution.

[0049] Furthermore, the cooling rate of the gradient cooling process is adapted to the product thickness in the following manner: When preparing plates with a thickness of 6~10mm, the cooling rate in the first stage is 7~8℃ / s, and the cooling rate in the second stage is 4~5℃ / s. When preparing profiles with a thickness of 10~15mm, the cooling rate in the first stage is 6~7℃ / s, and the cooling rate in the second stage is 3~4℃ / s.

[0050] Considering the impact of product thickness on cooling uniformity, this invention further adapts the cooling rate to the thickness. The greater the product thickness, the greater the difference in heat conduction between the core and surface during cooling. If the same cooling rate is used, thicker products are prone to problems such as slow cooling of the core leading to coarse phase precipitation, and excessively rapid cooling of the surface leading to internal stress. Therefore, a slightly slower cooling rate is used for thicker profiles to ensure uniform cooling between the core and surface.

[0051] For example, for a 15mm thick plate, if a cooling rate of 8℃ / s is used, the temperature difference between the core and the surface reaches 45~55℃, and the deformation rate reaches 3~4%. However, when using the cooling rate of 6~7℃ / s adapted by this invention, the temperature difference drops to 20~30℃, and the deformation rate is ≤1.5%. Through the above thickness adaptation, the temperature difference between the core and the surface of a 15mm thick plate can be ≤30℃, the quenching deformation rate can be ≤1.5%, and the tensile strength retention rate after pure air-cooled quenching is ≥95%. In addition, when using spray cooling, the elongation of the alloy of this invention is ≥16%, which is significantly better than the existing Al-Mg-Si alloy containing a single rare earth element (≤13%).

[0052] In summary, this invention achieves a substantial reduction in the quenching sensitivity of Al-Mg-Si alloys through a La-Ce-Y-Zr quaternary synergistic microalloying composition design, combined with segmented homogenization and gradient cooling processes. In the alloys obtained by the above preparation method, rare earth elements La, Ce, Y, and Zr form Al3(La,Ce,Y,Zr) nanophases with a size of 5-20 nm; the critical quenching cooling rate is reduced to 3-8 °C / s; tensile strength ≥280 MPa; yield strength ≥200 MPa; elongation ≥15%; ingot segregation is reduced to 5-8%; hydrogen content is reduced to 0.12-0.15 mL / 100gAl; and the quenching deformation rate of 15mm plate is ≤1.5%.

[0053] The rare earth-containing Al-Mg-Si alloy described in this invention, and the rare earth-containing Al-Mg-Si alloy obtained by the above preparation method, can be widely used in the preparation of rail transit profiles, new energy vehicle structural components, marine engineering components, or large building structural components.

[0054] These components are mostly large and complex cross-sectional profiles. When using existing Al-Mg-Si alloys for preparation, water-cooled quenching is necessary due to their high quenching sensitivity, which easily leads to quenching deformation and cracking, resulting in a high scrap rate. The alloy of this invention reduces the critical cooling rate for quenching to 3~8℃ / s, allowing for the use of pure air cooling or a mixture of air and atomized water cooling instead of water cooling, significantly reducing the risk of quenching deformation and cracking. Furthermore, the preparation process does not require specialized quenching equipment and can be directly adapted to conventional aluminum alloy production lines for large-scale production.

[0055] Specifically, in the rail transit sector, high-speed train body profiles require extremely high dimensional accuracy, and this invention can effectively control quenching deformation to meet assembly accuracy requirements; in the new energy vehicle sector, structural components such as battery trays and anti-collision beams need to balance lightweighting and collision safety, and this invention can still ensure high strength and high elongation even under slow cooling; in the marine engineering sector, low hydrogen content and homogeneous microstructure provide excellent corrosion resistance; and in the large-scale construction sector, a wide process window and low cost advantages facilitate large-scale promotion.

[0056] The present invention will be described in more detail below through specific embodiments. These embodiments are merely descriptions of the best implementation of the invention and do not limit the scope of the invention in any way.

[0057] Example 1 A rare earth Al-Mg-Si alloy has the following chemical composition by mass percentage: Mg: 0.6%, Si: 0.4%, La: 0.1%, Ce: 0.1%, Y: 0.08%, Zr: 0.05%, Fe: 0.12%, Cu: 0.08%, Mn: 0.05%, with the remainder being Al and unavoidable impurities, the total impurity content being ≤0.1%; La:Ce:Y:Zr=2:2:1.6:1, Fe to La mass ratio=1.2, Mg to Si atomic ratio=1.35, and total Y+Zr=0.13%.

[0058] The alloy was observed using transmission electron microscopy, and the results are as follows: Figure 1 As shown. The energy dispersive spectroscopy (EDS) analysis results are as follows. Figure 2 As shown, the precipitated phase contains Al, La, Ce, Y, and Zr elements, and can be identified as an Al3(La,Ce,Y,Zr) nanophase with an average nanophase size of 12 nm.

[0059] The preparation method of the above alloy includes the following steps: S1. Batching and smelting: Add industrial pure Al, Al-Mg master alloy, Al-Si master alloy, Al-La master alloy, Al-Ce master alloy, Al-Y master alloy, and Al-Zr master alloy according to the above component ratio. The purity of industrial pure Al is ≥99.7%. Heat to 730℃ and hold for 35 min. Stir with argon gas at a flow rate of 0.4 L / min and a stirring speed of 60 r / min. S2. Refining and degassing: Add a refining agent of 0.15% of the melt mass. The refining agent is a mixture of Na3AlF6 and KCl in a mass ratio of 2:1. The mass ratio of Na3AlF6 to Y element is 18.75:1. Keep warm for 18 minutes, during which argon gas with a flow rate of 0.3 L / min is introduced to remove bubbles. S3. Casting: Cool the melt to 690℃, let it stand for 12 minutes, and then semi-continuously cast. The casting speed is 100mm / min, the cooling water temperature is 30℃, and the ingot diameter is 160mm. S4. Segmented homogenization treatment: The first stage is heated to 490℃ and held for 5 hours, the second stage is heated to 570℃ and held for 7 hours, and then cooled to room temperature in the furnace at a cooling rate of 4℃ / h. S5. Hot rolling: Heat the ingot to 460℃ and hold for 2.5h, then hot roll 10 times, with a reduction of 10~12% per pass, and a final rolling temperature of 400℃ to roll it into a 10mm thick plate. S6. Solution quenching: Heat the plate to 540℃ and hold for 1.5h. Use gradient cooling process, with a cooling rate of 7.5℃ / s from 540 to 320℃ and a cooling rate of 4.5℃ / s from 320 to room temperature. The cooling medium is a mixture of air and atomized water, with an atomized water pressure of 0.2MPa. S7. Aging treatment: Heat the quenched plate to 175℃ and hold for 10 hours, then cool it to room temperature in the furnace.

[0060] Example 2 A rare earth Al-Mg-Si alloy has the following chemical composition by mass percentage: Mg: 0.4%, Si: 0.2%, La: 0.07%, Ce: 0.08%, Y: 0.03%, Zr: 0.02%, Fe: 0.10%, Cu: 0.05%, Mn: 0.03%, with the remainder being Al and unavoidable impurities, the total impurity content being ≤0.1%; La:Ce:Y:Zr = 3.5:4:1.5:1, Fe to La mass ratio = 1.45, Mg to Si atomic ratio = 1.25, and total La + Ce = 0.15%.

[0061] The preparation method of the above alloy includes the following steps: S1. Batching and smelting: Same as in Example 1; S2. Refining and degassing: Same as in Example 1; S3. Casting: Cool the melt to 690℃, let it stand for 12 minutes, and then semi-continuously cast. The casting speed is 80mm / min, the cooling water temperature is 30℃, and the ingot diameter is 160mm. S4 segmented homogenization treatment: The first stage is heated to 480℃ and held for 4 hours; the second stage is heated to 560℃ and held for 6 hours; then cooled to room temperature in the furnace at a rate of 4℃ / h. S5. Hot rolling: Same as Example 1.

[0062] S6. Solution quenching: Heat the plate to 530℃ and hold for 1 hour. Use a gradient cooling process with a cooling rate of 6.5℃ / s from 530℃ to 300℃ and a cooling rate of 3.5℃ / s from 300℃ to room temperature. The cooling medium is pure air cooling. S7 Aging Treatment: Heat the quenched plate to 170℃ and hold for 8 hours, then cool it to room temperature in the furnace.

[0063] Example 3 A rare earth Al-Mg-Si alloy has the following chemical composition by mass percentage: Mg: 0.8%, Si: 0.6%, La: 0.2%, Ce: 0.2%, Y: 0.15%, Zr: 0.1%, Fe: 0.15%, Cu: 0.10%, Mn: 0.08%, with the remainder being Al and unavoidable impurities, the total impurity content being ≤0.1%; La:Ce:Y:Zr=2:2:1.5:1, Fe to La mass ratio=0.75, Mg to Si atomic ratio=1.4, and total Y+Zr=0.25%.

[0064] The preparation method of the above alloy includes the following steps: S1. Batching and smelting: Same as in Example 1.

[0065] S2. Refining and degassing: Same as in Example 1.

[0066] S3. Casting: Cool the melt to 690℃, let it stand for 12 minutes, and then semi-continuously cast. The casting speed is 120mm / min, the cooling water temperature is 30℃, and the ingot diameter is 160mm.

[0067] S4. Segmented homogenization treatment: The first stage is heated to 500℃ and held for 6 hours, the second stage is heated to 580℃ and held for 8 hours, and then cooled to room temperature in the furnace at a rate of 4℃ / h.

[0068] S5. Hot rolling: Heat the ingot to 460℃ and hold for 2.5 hours. Then hot roll 10 times, with a reduction of 10~12% per pass. The final rolling temperature is 400℃, and the ingot is rolled into a 15mm thick profile.

[0069] S6. Solution quenching: Heat the profile to 550℃ and hold for 2 hours. Use a gradient cooling process with a cooling rate of 6.5℃ / s from 550℃ to 350℃ and a cooling rate of 3.5℃ / s from 350℃ to room temperature. The cooling medium is a mixture of air and atomized water with a pressure of 0.2MPa for the atomized water.

[0070] S7. Aging treatment: Heat the quenched profile to 180℃ and hold for 12 hours, then cool it to room temperature in the furnace.

[0071] Example 4 A rare earth Al-Mg-Si alloy has a chemical composition that is basically the same as that of Example 1, except that the Fe content is adjusted to 0.15% and the mass ratio of Fe to La is 1.5. The other components and proportions are the same as those of Example 1.

[0072] The preparation method of the above alloy is completely consistent with that of Example 1.

[0073] Comparative Example 1 A conventional Al-Mg-Si alloy has the following chemical composition by mass percentage: Mg: 0.6%, Si: 0.4%, Fe: 0.12%, Cu: 0.08%, Mn: 0.05%, with the remainder being Al and unavoidable impurities; no La, Ce, Y, or Zr elements are added.

[0074] The above alloy was prepared using existing conventional processes: melting at 730℃, water-cooled casting, single-stage homogenization at 570℃ for 8 hours, hot rolling at 460℃, solution cooling at 540℃ followed by water cooling (cooling rate 20℃ / s), and aging at 175℃ for 10 hours.

[0075] Comparative Example 2 An Al-Mg-Si alloy containing a single rare earth element has a chemical composition that is basically the same as that of Example 1, except that La is added at 0.2%, and no Ce, Y, or Zr elements are added. The remaining components and proportions are the same as those of Example 1.

[0076] The preparation method of the above alloy is completely consistent with that of Example 1.

[0077] Comparative Example 3 An Al-Mg-Si alloy containing La-Ce-Y-Zr quaternary rare earth elements has a chemical composition that is basically the same as that of Example 1, except that the La:Ce:Y:Zr ratio is adjusted to 5:1:0.5:0.3, while the other components and ratios are the same as those of Example 1.

[0078] The preparation method of the above alloy is completely consistent with that of Example 1.

[0079] Characterization results and analysis The alloy products of the above embodiments and comparative examples were tested, and the results are shown in Table 1 below.

[0080] Table 1

[0081] As can be seen from Table 1, the alloys of Examples 1-4 of this invention all formed Al3(La,Ce,Y,Zr) nanophases of 8~18nm, the critical cooling rate for quenching was reduced to 3~8℃ / s, the tensile strength was ≥280MPa, the yield strength was ≥200MPa, the elongation was ≥15%, the ingot segregation was reduced to 5~8%, the hydrogen content was reduced to 0.12~0.15mL / 100gAl, and the quenching deformation rate of 15mm plate was ≤1.5%.

[0082] In contrast, Comparative Example 1, which did not contain rare earth elements or Zr, and Comparative Example 2, which only added the single rare earth element La, both failed to form the Al3(La,Ce,Y,Zr) nanophase. Although Comparative Example 3 added a quaternary rare earth element, the La:Ce:Y:Zr mass ratio deviated from the range specified in this invention, resulting in a nanophase size that increased to 25 nm, exceeding the 5-20 nm range. The alloys of Comparative Examples 1-3 exhibited a critical quenching cooling rate ≥9℃ / s, an ingot segregation degree ≥13%, a hydrogen content ≥0.18 mL / 100gAl, and a quenching deformation rate ≥2.5% for 15mm plates. Furthermore, their tensile strength, yield strength, and elongation were significantly lower than those of the embodiments of this invention.

[0083] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A rare earth-containing Al-Mg-Si alloy, characterized in that, The chemical composition, by mass percentage, is as follows: Mg: 0.4~0.8%, Si: 0.2~0.6%, La: 0.05~0.2%, Ce: 0.05~0.2%, Y: 0.03~0.15%, Zr: 0.02~0.1%, Fe≤0.15%, Cu≤0.1%, Mn≤0.08%, the remainder being Al and unavoidable impurities, with a total impurity content ≤0.1%; The mass ratio of La, Ce, Y, and Zr is (1~4):(1~4):(0.6~3):(0.4~2); The mass ratio of Fe to La is ≤1.

5.

2. The rare earth-containing Al-Mg-Si alloy according to claim 1, characterized in that, The La, Ce, Y, and Zr form an Al3(La,Ce,Y,Zr) nanophase in the alloy, and the nanophase size is 5~20 nm.

3. The rare earth-containing Al-Mg-Si alloy according to claim 1, characterized in that, The atomic ratio of Mg to Si is 1.2 to 1.5, and one of the following conditions is satisfied: When the Mg / Si atomic ratio is 1.2~1.3, the total La+Ce content is ≥0.15%; When the Mg / Si atomic ratio is 1.3~1.5, the total amount of Y+Zr is ≥0.1%.

4. The rare earth-containing Al-Mg-Si alloy according to claim 1, characterized in that, The critical quenching cooling rate of the alloy is 3~8℃ / s.

5. A method for preparing the rare earth-containing Al-Mg-Si alloy according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Batching and smelting; S2. Refining and degassing; the refining agent used in the refining and degassing process is a mixture of Na3AlF6 and KCl in a mass ratio of 2:1, and the mass ratio of Na3AlF6 to Y element in the alloy is (10~20):1; S3. Casting; S4. Segmented homogenization process; S5. Hot-rolled; S6. Solution quenching; S7. Timeliness processing.

6. The preparation method according to claim 5, characterized in that, In S4, the segmented homogenization process includes: First stage: Heat to 480~500℃ and keep warm for 4~6 hours; Second stage: Raise the temperature to 560~580℃ and keep it warm for 6~8 hours; After homogenization, the furnace is cooled to room temperature at a rate of ≤5℃ / h.

7. The preparation method according to claim 5, characterized in that, In S6, the solution quenching adopts a gradient cooling process: First stage: Cool from 530~550℃ to 300~350℃, with the cooling rate controlled at 6~8℃ / s; Second stage: Cool from 300~350℃ to room temperature, with the cooling rate controlled at 3~5℃ / s; The cooling medium for gradient cooling is either pure air cooling or a mixture of air and atomized water.

8. The preparation method according to claim 7, characterized in that, In the gradient cooling process, the cooling rate is controlled by adjusting the atomized water pressure to 0.1~0.3MPa.

9. The preparation method according to claim 8, characterized in that, The cooling rate of the gradient cooling process is adapted to the product thickness in the following manner: When preparing plates with a thickness of 6~10mm, the cooling rate in the first stage is 7~8℃ / s, and the cooling rate in the second stage is 4~5℃ / s. When preparing profiles with a thickness of 10~15mm, the cooling rate in the first stage is 6~7℃ / s, and the cooling rate in the second stage is 3~4℃ / s.

10. The application of the rare earth-containing Al-Mg-Si alloy according to any one of claims 1-4 or the rare earth-containing Al-Mg-Si alloy obtained by the preparation method according to any one of claims 5-9 in the preparation of rail transit profiles, new energy vehicle structural components, marine engineering components or large building structural components.

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