Preparation method of heat-resistant cast Al-Si-Cu-Mg alloy

Abstract

The invention discloses a preparation method of a heat-resistant cast Al-Si-Cu-Mg alloy, and relates to the technical field of aluminum alloy materials. The preparation method specifically comprises the following steps that raw materials of pure Al, Al-Si intermediate alloy, Al-Cu intermediate alloy, pure Mg, Al-Mn intermediate alloy, Al-Sc intermediate alloy, Al-V intermediate alloy and Al-Ti intermediate alloy are weighed in proportion; the preparation method comprises the following steps: uniformly smelting alloy raw materials to obtain alloy melt; cooling the alloy melt, refining, degassing, deslagging, preserving heat and standing; the alloy melt obtained after heat preservation and standing is cooled and then poured into a mold to be solidified and formed, and a cast ingot is obtained; and the cast ingot is firstly subjected to high-temperature aging regression, then subjected to low-temperature re-aging treatment and then cooled, and the heat-resistant cast Al-Si-Cu-Mg alloy is obtained. According to the Al-Si-Cu-Mg alloy and the preparation method thereof, by controlling the content of all the elements, grain refinement is achieved, the type and size of a precipitated phase are regulated and controlled through the synergistic effect of the aging regression heat treatment process, and the obtained Al-Si-Cu-Mg alloy has excellent room-temperature and high-temperature tensile strength and ductility and is wide in application prospect.

Description

Technical Field

[0001] This invention relates to a method for preparing a heat-resistant castable Al-Si-Cu-Mg alloy, belonging to the field of aluminum alloy material technology. Background Technology

[0002] With the urgent demand for lightweight, high-temperature resistant structural materials in the aerospace, automotive, and energy equipment industries, cast aluminum alloys have become a research hotspot for key materials due to their excellent specific strength, casting performance, and cost controllability. However, traditional cast aluminum alloys generally face significant degradation of mechanical properties under high-temperature service environments (>200℃). The fundamental reason lies in the reduced grain boundary strength, coarsening of precipitated phases (such as Mg2Si and θ-Al2Cu), and intensified dislocation movement of the aluminum alloy matrix at high temperatures, making it difficult for the material's high-temperature strength and creep resistance to meet long-term service requirements. Taking a typical Al-Si-Cu-Mg alloy as an example, its tensile strength at 250℃ is usually less than 50% of its room temperature strength, severely restricting its application in high-temperature components such as engine pistons and turbocharger housings.

[0003] Microalloying is an effective method to improve the properties of aluminum alloys. Related techniques include using a three-step heat treatment to enhance the segregation of Sc at the θ' / Al interface, suppressing the coarsening of θ'-Al2Cu, and ultimately significantly improving the creep resistance of Al-Cu alloys at 300°C. There are also studies using multi-step homogeneous heat treatment to promote the formation of Al3(Sc,Zr) particles in Al-Cu-Sc-Zr-Mn alloys, thereby improving alloy strength. Furthermore, during high-temperature thermal exposure, Sc and Zr elements tend to segregate at the θ' / Al interface, increasing the thermal stability of the θ'-Al2Cu phase.

[0004] However, Al-Si-Cu-Mg alloys contain both low-melting-point and high-melting-point precipitates. Cu and Mg diffuse rapidly in the aluminum matrix, resulting in low precipitation temperatures for Al₂Cu and Mg₂Si (<200℃); while rare earth elements diffuse more slowly, leading to relatively higher precipitation temperatures (>300℃). Traditional single-stage aging typically only precipitates the θ'-Al₂Cu phase, resulting in fewer nuclei in the GP zone that tend to grow rapidly or directly precipitate coarse, stable phases, leading to a decrease in strength. Therefore, optimizing the precipitation characteristics of the alloy is crucial for further improving its overall performance. Designing and developing a cost-effective, high-performance, heat-resistant Al-Si-Cu-Mg alloy preparation method to address its insufficient high-temperature performance has become a critical issue urgently needing resolution in materials science. Summary of the Invention

[0005] One objective of this invention is to provide a heat-resistant castable Al-Si-Cu-Mg alloy, wherein the elemental composition of the heat-resistant castable Al-Si-Cu-Mg alloy, by mass percentage, comprises: 6.5-11.0% Si, 1.5-5.5% Cu, 0.1-0.5% Mg, 0.05-0.25% Mn, 0.05-0.35% Sc, 0.05-0.25% V, 0.05-0.25% Ti, with the balance being Al and unavoidable impurities; wherein the mass percentage relationship between Cu and Mg satisfies 4.6≤0.49Cu+10Mg≤5.2, and the mass percentage of Sc, V, and Ti satisfies Sc:V:Ti=(1.0~1.2):(0.8~1.0):(0.8~1.0).

[0006] The second objective of this invention is to provide a method for preparing a heat-resistant castable Al-Si-Cu-Mg alloy, specifically including the following steps: (1) Batching: Weigh out pure Al, Al-Si master alloy, Al-Cu master alloy, pure Mg, Al-Mn master alloy, Al-Sc master alloy, Al-V master alloy and Al-Ti master alloy as alloy raw materials according to the proportion.

[0007] (2) Melting: First, pure Al, Al-Si master alloy and Al-Cu master alloy are added to the melting device and heated to melt evenly. Then, Al-Mn master alloy, Al-Sc master alloy, Al-V master alloy and Al-Ti master alloy are added and melted evenly. Then, the temperature is lowered and pure Mg is added and melted evenly to obtain the alloy melt.

[0008] (3) Refining and degassing: Cool the alloy melt, then add refining agent for refining, then degas (preferably high-purity argon as carrier gas), remove slag, and then keep it warm and stand.

[0009] (4) Casting: After the alloy melt has been kept at a constant temperature, it is cooled down and then poured into a mold to solidify and form an ingot.

[0010] (5) Heat treatment: The ingot is first subjected to high temperature aging and then low temperature re-aging treatment, followed by cooling to obtain heat-resistant cast Al-Si-Cu-Mg alloy.

[0011] Preferably, in step (2), the melting temperature of pure Al, Al-Si master alloy, and Al-Cu master alloy is 680-720℃; the melting temperature of Al-Mn master alloy, Al-Sc master alloy, Al-V master alloy, and Al-Ti master alloy is 740-800℃; and the melting temperature of pure Mg is 740℃.

[0012] Preferably, in step (3), the alloy melt is cooled to 720-740℃; the mass percentage of the added refining agent is 0.2-0.5% of the mass of the alloy melt; the refining agent is added to the bottom of the alloy melt; after the refining agent has completely reacted, it is stirred rapidly for 3-5 minutes; the refining conditions are: after the refining agent has completely reacted and it has been stirred rapidly, it is kept at 720-740℃ for 10-15 minutes.

[0013] More preferably, the refining agent in step (3) is a fluorine-based refining agent.

[0014] Preferably, the degassing treatment time in step (3) is 6-10 min; the heat preservation and standing time is 10-15 min.

[0015] Preferably, in step (4), the alloy melt after heat preservation and standing is cooled to 700-720℃.

[0016] Preferably, the conditions for high-temperature aging regression in step (5) are: aging at 300-350℃ for 10-40h, and then regression at 500-540℃ for 2-4h; the conditions for low-temperature re-aging are: low-temperature re-aging at 170-220℃ for 4-8h.

[0017] Mechanism of the invention: This invention provides a method for preparing a heat-resistant castable Al-Si-Cu-Mg alloy. Through the synergistic effect of alloy composition and preparation process, the micro-alloying effect of Mn, Sc, V, and Ti elements is fully utilized. This synergistic effect promotes the nucleation and growth of the heat-resistant Al3Sc precipitate, allows the low-melting-point θ-Al2Cu precipitates to dissolve back into the matrix, and promotes the spheroidization and discontinuous distribution of the eutectic silicon phase. Simultaneously, it induces the precipitation of high-density nano-precipitates, significantly improving the room-temperature and high-temperature strength of the Al-Si-Cu-Mg alloy to meet the demands of modern industry for high-performance aluminum alloy materials. This multi-scale strengthening mechanism of "precipitate pinning + eutectic phase support + interface synergistic strengthening" overcomes the limitations of traditional single strengthening techniques and provides a novel technical route for developing a new generation of heat-resistant castable aluminum alloys.

[0018] The beneficial effects of this invention are: (1) Through the synergistic effect of composite microalloying and heat treatment, the tensile strength of the alloy at room temperature can reach 400-450MPa and the elongation can reach 3-6%; at a high temperature of 250℃, the tensile strength can still be maintained at 250-300MPa, which is significantly better than the room temperature and high temperature strength of traditional AlSiCuMg alloys, and can better meet the needs of aerospace and automotive manufacturing for high-performance aluminum alloy materials.

[0019] (2) This invention effectively refines alloy grains through the synergistic effect of high-temperature aging re-heat treatment, low-temperature re-aging heat treatment and alloy raw material regulation, while promoting the formation of high thermal stability nano θ'-Al2Cu phase, Q-Al5Cu2Mg8Si6 phase and AlTiVSc phase; refines AlCuSc and AlSiMnFe primary phases, enabling them to pin dislocations and grain boundaries at high temperatures, effectively inhibiting the growth of the alloy structure at high temperatures, and ensuring that the alloy still has good mechanical properties at high temperatures.

[0020] (3) The preparation method of the present invention is simple, easy to operate and control, and the alloy has excellent high-temperature mechanical properties without the use of cerium group and yttrium group rare earth elements. The production cost is low and it is suitable for large-scale industrial production. Attached Figure Description

[0021] Figure 1 The image shows the DSC curve of the heat-resistant cast Al-Si-Cu-Mg alloy prepared in Example 1 of this invention.

[0022] Figure 2 This is a SEM image of the heat-resistant cast Al-Si-Cu-Mg alloy prepared in Example 1 of the present invention.

[0023] Figure 3 The image shown is a TEM image of the heat-resistant cast Al-Si-Cu-Mg alloy prepared in Example 1 of this invention. Detailed Implementation

[0024] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0025] Unless otherwise specified, all chemical reagents used in the embodiments and comparative examples of this invention are commercially available analytical grade reagents. The intermediate alloy raw materials used in this invention are commercially available raw materials.

[0026] Example 1 A method for preparing a heat-resistant castable Al-Si-Cu-Mg alloy, specifically including the following steps: (1) Batching: Weigh out the raw materials of high-purity aluminum ingot, Al-20Si master alloy, Al-50Cu master alloy, high-purity magnesium ingot, Al-20Mn master alloy, Al-5Sc master alloy, Al-10V master alloy and Al-10Ti master alloy according to the proportion. The raw material composition includes 11% Si, 2.5% Cu, 0.4% Mg, 0.1% Mn, 0.12% Sc, 0.1% V and 0.1% Ti by mass percentage, with the balance being Al and unavoidable impurities (where the mass fraction relationship of Cu, Mg, Sc, V and Ti is 0.49Cu+10Mg=5.2, Sc:V:Ti=1.2:1:1).

[0027] (2) Melting: High-purity aluminum ingots, Al-20Si master alloy and Al-50Cu master alloy are added to the graphite crucible of the resistance furnace and heated to 720°C to melt evenly. Then the temperature is raised to 800°C and Al-20Mn master alloy, Al-5Sc master alloy, Al-10V master alloy and Al-10Ti master alloy are added and melted evenly. Then the temperature is lowered to 740°C and high-purity magnesium ingot is added. Then the mixture is stirred quickly and melted evenly and the slag is removed to obtain the alloy melt.

[0028] (3) Refining and degassing: Cool the alloy melt to 730°C, then add the fluorine-based refining agent to the bottom of the alloy melt for refining. The amount of fluorine-based refining agent added to the alloy melt is 0.5% by mass. After the refining agent has reacted completely, stir quickly for 5 minutes, then keep it at 730°C for 10 minutes; remove the slag, then use high-purity argon to degas the alloy melt for 10 minutes, and then keep it at 730°C for 15 minutes.

[0029] (4) Casting: The alloy melt, after being kept at a constant temperature, is cooled to 720°C and then poured into a mold to solidify and form an ingot.

[0030] (5) Heat treatment: The ingot is first subjected to high temperature aging treatment at 320℃ for 24h, then restored at 500℃ for 4h, and then subjected to low temperature re-aging treatment at 170℃ for 8h. After cooling, heat-resistant casting Al-Si-Cu-Mg alloy is obtained.

[0031] Differential scanning calorimetry (DSC) was performed on the heat-resistant cast Al-Si-Cu-Mg alloy prepared in this embodiment. The relationship between the heat flux or thermal power difference between the sample end and the reference end under nitrogen atmosphere and programmed temperature was measured as a function of temperature and time. The results are as follows: Figure 1 As shown in the diagram, four endothermic peaks can be observed from the DSC image. Analysis reveals that the melting point of Al₂Cu is 512℃, the melting point of the Q-Al₅Cu₂Mg₈Si₆ phase is 521℃, the melting point of the eutectic Si is 578℃, and the melting point of the α-Al matrix is ​​591℃. Therefore, to ensure the eutectic phase is dissolved back into the aluminum matrix, the temperature range for the reversion treatment is set at 500-540℃.

[0032] The surface morphology, composition, and structure of the alloy samples were analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the results are as follows: Figure 2 and Figure 3 As shown. From Figure 2 SEM analysis revealed the presence of an α-Al matrix, a eutectic Si phase, an AlCuSc phase, a Q-Al5Cu2Mg8Si6 phase, and an AlSiMnFe phase. Figure 3The TEM images revealed nanoscale θ'-Al2Cu phase, Q-Al5Cu2Mg8Si6 phase, and AlTiVSc phase. Among them, the thermally stable AlCuSc phase, Q-Al5Cu2Mg8Si6 phase, and AlSiMnFe phase effectively pinned grain boundaries, while the AlTiVSc phase pinned dislocations at high temperatures, inhibiting microstructure growth and recrystallization at high temperatures, improving the high-temperature microstructure stability of the alloy, and ensuring that the alloy still has good mechanical properties at high temperatures.

[0033] The heat-resistant castable Al-Si-Cu-Mg alloy prepared in this embodiment has good mechanical properties. Its tensile properties at room temperature (25℃) and 250℃ are shown in Table 1. As can be seen from Table 1, the heat-resistant castable Al-Si-Cu-Mg alloy prepared in this embodiment has a tensile strength of 412±5MPa and an elongation after fracture of 4.0±1.5% at 25℃, and a tensile strength of 273±11MPa and an elongation after fracture of 7.7±2.1% at 250℃.

[0034] In summary, this embodiment utilizes the synergistic effect of microalloying of Sc, V, and Ti in Al-Si-Cu-Mg-based alloys and aging treatment to induce reinforcing phases in the alloy, significantly improving the room temperature and high temperature strength of Al-Si-Cu-Mg alloys. This overcomes the limitations of traditional single strengthening techniques and has broad application prospects.

[0035] Example 2 A method for preparing a heat-resistant castable Al-Si-Cu-Mg alloy, specifically including the following steps: (1) Batching: Weigh out the raw materials of high-purity aluminum ingot, Al-20Si master alloy, Al-50Cu master alloy, high-purity magnesium ingot, Al-20Mn master alloy, Al-5Sc master alloy, Al-10V master alloy and Al-10Ti master alloy according to the proportion. The raw material composition includes 7.5% Si, 5.5% Cu, 0.25% Mg, 0.15% Mn, 0.24% Sc, 0.2% V and 0.2% Ti by mass percentage, with the balance being Al and unavoidable impurities (where the mass fraction relationship of Cu, Mg, Sc, V and Ti is 0.49Cu+10Mg=5.2, Sc:V:Ti=1.2:1:1).

[0036] (2) Melting: High-purity aluminum ingots, Al-20Si master alloy and Al-50Cu master alloy are added to the graphite crucible of the resistance furnace and heated to 710°C to melt evenly. Then, the temperature is raised to 780°C and Al-20Mn master alloy, Al-5Sc master alloy, Al-10V master alloy and Al-10Ti master alloy are added and melted evenly. Then, the temperature is lowered to 740°C and high-purity magnesium ingot is added. Then, the mixture is quickly stirred and melted evenly, and the slag is removed to obtain the alloy melt.

[0037] (3) Refining and degassing: At 740℃, fluorine-based refining agent is added to the bottom of the alloy melt for refining. The amount of fluorine-based refining agent added to the alloy melt is 0.5% by mass. After the refining agent has reacted completely, it is stirred rapidly for 5 minutes, and then kept at 740℃ for 10 minutes. The slag is removed, and then the alloy melt is degassed with high-purity argon for 10 minutes, and then kept at 740℃ for 15 minutes.

[0038] (4) Casting: The alloy melt, after being kept at a constant temperature, is cooled to 700°C and then poured into a mold to solidify and form an ingot.

[0039] (5) Heat treatment: The ingot is first subjected to high temperature aging treatment at 345℃ for 12h, then restored at 510℃ for 3h, and then subjected to low temperature re-aging treatment at 200℃ for 6h. After cooling, heat-resistant casting Al-Si-Cu-Mg alloy is obtained.

[0040] The surface morphology, composition, and structure of the heat-resistant cast Al-Si-Cu-Mg alloy prepared in this embodiment were analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM images revealed that the heat-resistant cast Al-Si-Cu-Mg alloy of this embodiment contains an α-Al matrix, eutectic Si phase, AlCuSc phase, Q-Al5Cu2Mg8Si6 phase, and AlSiMnFe phase. TEM images showed that the heat-resistant cast Al-Si-Cu-Mg alloy of this embodiment contains nano-θ'-Al2Cu phase, Q-Al5Cu2Mg8Si6 phase, and AlTiVSc phase. The thermally stable AlCuSc, Q-Al5Cu2Mg8Si6, and AlSiMnFe phases effectively pin grain boundaries, while the AlTiVSc phase can pin dislocations at high temperatures, inhibiting microstructure growth and recrystallization at high temperatures, improving the high-temperature microstructure stability of the alloy, and ensuring that the alloy still possesses good mechanical properties at high temperatures.

[0041] The heat-resistant castable Al-Si-Cu-Mg alloy prepared in this embodiment has good mechanical properties. Its tensile properties at room temperature (25℃) and 250℃ are shown in Table 1. As can be seen from Table 1, the heat-resistant castable Al-Si-Cu-Mg alloy prepared in this embodiment has a tensile strength of 437±4MPa and an elongation after fracture of 3.4±1.8% at 25℃, and a tensile strength of 284±9MPa and an elongation after fracture of 7.1±1.1% at 250℃.

[0042] In summary, this embodiment utilizes the synergistic effect of microalloying of Sc, V, and Ti in Al-Si-Cu-Mg-based alloys and aging treatment to induce reinforcing phases in the alloy, significantly improving the room temperature and high temperature strength of Al-Si-Cu-Mg alloys. This overcomes the limitations of traditional single strengthening techniques and has broad application prospects.

[0043] Example 3 A method for preparing a heat-resistant castable Al-Si-Cu-Mg alloy, specifically including the following steps: (1) Batching: Weigh out the raw materials of high-purity aluminum ingot, Al-20Si master alloy, Al-50Cu master alloy, high-purity magnesium ingot, Al-20Mn master alloy, Al-5Sc master alloy, Al-10V master alloy and Al-10Ti master alloy according to the proportion. The raw material composition includes 10.5% Si, 4% Cu, 0.3% Mg, 0.2% Mn, 0.06% Sc, 0.05% V and 0.05% Ti by mass percentage, with the balance being Al and unavoidable impurities (where the mass fraction relationship of Cu, Mg, Sc, V and Ti is 0.49Cu+10Mg=4.96, Sc:V:Ti=1.2:1:1).

[0044] (2) Melting: High-purity aluminum ingots, Al-20Si master alloy and Al-50Cu master alloy are added to the graphite crucible of the resistance furnace and heated to 720°C to melt evenly. Then the temperature is raised to 800°C and Al-20Mn master alloy, Al-5Sc master alloy, Al-10V master alloy and Al-10Ti master alloy are added and melted evenly. Then the temperature is lowered to 740°C and high-purity magnesium ingot is added. Then the mixture is stirred quickly and melted evenly and the slag is removed to obtain the alloy melt.

[0045] (3) Refining and degassing: At 740℃, fluorine-based refining agent is added to the bottom of the alloy melt for refining. The amount of fluorine-based refining agent added to the alloy melt is 0.5% by mass. After the refining agent has reacted completely, it is stirred rapidly for 5 minutes, and then kept at 740℃ for 10 minutes. The slag is removed, and then the alloy melt is degassed with high-purity argon for 10 minutes, and then kept at 740℃ for 15 minutes.

[0046] (4) Casting: The alloy melt, after being kept at a constant temperature, is cooled to 710°C and then poured into a mold to solidify and form an ingot.

[0047] (5) Heat treatment: The ingot is first subjected to high temperature aging treatment at 300℃ for 40h, then subjected to aging treatment at 525℃ for 2h, and then subjected to low temperature re-aging treatment at 220℃ for 4h, and then cooled to obtain heat-resistant cast Al-Si-Cu-Mg alloy.

[0048] The surface morphology, composition, and structure of the heat-resistant cast Al-Si-Cu-Mg alloy prepared in this embodiment were analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM images revealed that the heat-resistant cast Al-Si-Cu-Mg alloy of this embodiment contains an α-Al matrix, eutectic Si phase, AlCuSc phase, Q-Al5Cu2Mg8Si6 phase, and AlSiMnFe phase. TEM images showed that the heat-resistant cast Al-Si-Cu-Mg alloy of this embodiment contains nano-θ'-Al2Cu phase, Q-Al5Cu2Mg8Si6 phase, and AlTiVSc phase. The thermally stable AlCuSc, Q-Al5Cu2Mg8Si6, and AlSiMnFe phases effectively pin grain boundaries, while the AlTiVSc phase can pin dislocations at high temperatures, inhibiting microstructure growth and recrystallization at high temperatures, improving the high-temperature microstructure stability of the alloy, and ensuring that the alloy still possesses good mechanical properties at high temperatures.

[0049] The heat-resistant castable Al-Si-Cu-Mg alloy prepared in this embodiment has good mechanical properties. Its tensile properties at room temperature (25℃) and 250℃ are shown in Table 1. As can be seen from Table 1, the heat-resistant castable Al-Si-Cu-Mg alloy prepared in this embodiment has a tensile strength of 424±2MPa and an elongation after fracture of 5.4±0.7% at 25℃, and a tensile strength of 271±2MPa and an elongation after fracture of 8.6±2.5% at 250℃.

[0050] In summary, this embodiment utilizes the synergistic effect of microalloying of Sc, V, and Ti in Al-Si-Cu-Mg-based alloys and aging treatment to induce reinforcing phases in the alloy, significantly improving the room temperature and high temperature strength of Al-Si-Cu-Mg alloys. This overcomes the limitations of traditional single strengthening techniques and has broad application prospects.

[0051] Example 4 A method for preparing a heat-resistant castable Al-Si-Cu-Mg alloy, specifically including the following steps: (1) Batching: Weigh out the raw materials of high-purity aluminum ingot, Al-20Si master alloy, Al-50Cu master alloy, high-purity magnesium ingot, Al-20Mn master alloy, Al-5Sc master alloy, Al-10V master alloy and Al-10Ti master alloy according to the proportion. The raw material composition includes 6.5% Si, 3.27% Cu, 0.3% Mg, 0.05% Mn, 0.35% Sc, 0.25% V and 0.25% Ti by mass percentage, with the balance being Al and unavoidable impurities (where the mass fraction relationship of Cu, Mg, Sc, V and Ti is 0.49Cu+10Mg=4.6, Sc:V:Ti=1.2:0.857:0.857).

[0052] (2) Melting: High-purity aluminum ingots, Al-20Si master alloy and Al-50Cu master alloy are added to the graphite crucible of the resistance furnace and heated to 680°C to melt evenly. Then, the temperature is raised to 760°C and Al-20Mn master alloy, Al-5Sc master alloy, Al-10V master alloy and Al-10Ti master alloy are added and melted evenly. Then, the temperature is lowered to 740°C and pure magnesium ingot is added to continue melting. Then, the mixture is quickly stirred and melted evenly, and the slag is removed to obtain the alloy melt.

[0053] (3) Refining and degassing: At 740℃, fluorine-based refining agent is added to the bottom of the alloy melt for refining. The amount of fluorine-based refining agent added to the alloy melt is 0.2% by mass. After the refining agent has reacted completely, it is stirred rapidly for 3 minutes, and then kept at 720℃ for 12 minutes. The slag is removed, and then the alloy melt is degassed with high-purity argon for 6 minutes, and then kept at 720℃ for 12 minutes.

[0054] (4) Casting: The alloy melt, after being kept at a constant temperature, is cooled to 710°C and then poured into a mold to solidify and form an ingot.

[0055] (5) Heat treatment: The ingot is first subjected to high temperature aging treatment at 350℃ for 10h, then subjected to 540℃ for 2h, and then subjected to low temperature re-aging treatment at 220℃ for 4h, and then cooled to obtain heat-resistant cast Al-Si-Cu-Mg alloy.

[0056] The surface morphology, composition, and structure of the heat-resistant cast Al-Si-Cu-Mg alloy prepared in this embodiment were analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM images revealed that the heat-resistant cast Al-Si-Cu-Mg alloy of this embodiment contains an α-Al matrix, eutectic Si phase, AlCuSc phase, Q-Al5Cu2Mg8Si6 phase, and AlSiMnFe phase. TEM images showed that the heat-resistant cast Al-Si-Cu-Mg alloy of this embodiment contains nano-θ'-Al2Cu phase, Q-Al5Cu2Mg8Si6 phase, and AlTiVSc phase. The thermally stable AlCuSc, Q-Al5Cu2Mg8Si6, and AlSiMnFe phases effectively pin grain boundaries, while the AlTiVSc phase can pin dislocations at high temperatures, inhibiting microstructure growth and recrystallization at high temperatures, improving the high-temperature microstructure stability of the alloy, and ensuring that the alloy still possesses good mechanical properties at high temperatures.

[0057] The heat-resistant castable Al-Si-Cu-Mg alloy prepared in this embodiment has good mechanical properties. The tensile strength of the heat-resistant castable Al-Si-Cu-Mg alloy prepared in this embodiment is 451±7MPa at 25℃ and the elongation after fracture is 3.1±0.5%. The tensile strength at 250℃ is 295±4MPa and the elongation after fracture is 7.8±1.1%.

[0058] In summary, this embodiment utilizes the synergistic effect of microalloying of Sc, V, and Ti in Al-Si-Cu-Mg-based alloys and aging treatment to induce reinforcing phases in the alloy, significantly improving the room temperature and high temperature strength of Al-Si-Cu-Mg alloys. This overcomes the limitations of traditional single strengthening techniques and has broad application prospects.

[0059] Example 5 A method for preparing a heat-resistant castable Al-Si-Cu-Mg alloy, specifically including the following steps: (1) Batching: Weigh out the raw materials of high-purity aluminum ingot, Al-20Si master alloy, Al-50Cu master alloy, high-purity magnesium ingot, Al-20Mn master alloy, Al-5Sc master alloy, Al-10V master alloy and Al-10Ti master alloy according to the proportion. The raw material composition includes 11% Si, 1.5% Cu, 0.39% Mg, 0.25% Mn, 0.06% Sc, 0.05% V and 0.05% Ti by mass percentage, with the balance being Al and unavoidable impurities (where the mass fraction relationship of Cu, Mg, Sc, V and Ti is 0.49Cu+10Mg=4.6, Sc:V:Ti=1.2:1:1).

[0060] (2) Melting: High-purity aluminum ingots, Al-20Si master alloy, and Al-50Cu master alloy are added to the graphite crucible of the resistance furnace and heated to 710°C to melt evenly. Then, the temperature is further increased to 740°C, and Al-20Mn master alloy, Al-5Sc master alloy, Al-10V master alloy, high-purity magnesium ingot and Al-10Ti master alloy are added and melted evenly. Then, the mixture is quickly stirred and melted evenly, and the slag is removed to obtain the alloy melt.

[0061] (3) Refining and degassing: Cool the alloy melt to 720°C, add fluoride-based refining agent to the bottom of the alloy melt for refining, wherein the amount of fluoride-based refining agent added to the alloy melt is 0.3% by mass. After the refining agent has reacted completely, stir quickly for 4 minutes, then keep it at 730°C for 15 minutes; remove the slag, and then use high-purity argon gas to degas the alloy melt for 8 minutes, and then keep it at 730°C for 10 minutes.

[0062] (4) Casting: The alloy melt, after being kept at a constant temperature, is cooled to 710°C and then poured into a mold to solidify and form an ingot.

[0063] (5) Heat treatment: The ingot is first subjected to high temperature aging treatment at 350℃ for 10h, then subjected to aging treatment at 500℃ for 4h, and then subjected to low temperature re-aging treatment at 220℃ for 4h, and then cooled to obtain heat-resistant cast Al-Si-Cu-Mg alloy.

[0064] The surface morphology, composition, and structure of the heat-resistant cast Al-Si-Cu-Mg alloy prepared in this embodiment were analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM images revealed that the heat-resistant cast Al-Si-Cu-Mg alloy of this embodiment contains an α-Al matrix, eutectic Si phase, AlCuSc phase, Q-Al5Cu2Mg8Si6 phase, and AlSiMnFe phase. TEM images showed that the heat-resistant cast Al-Si-Cu-Mg alloy of this embodiment contains nano-θ'-Al2Cu phase, Q-Al5Cu2Mg8Si6 phase, and AlTiVSc phase. The thermally stable AlCuSc, Q-Al5Cu2Mg8Si6, and AlSiMnFe phases effectively pin grain boundaries, while the AlTiVSc phase can pin dislocations at high temperatures, inhibiting microstructure growth and recrystallization at high temperatures, improving the high-temperature microstructure stability of the alloy, and ensuring that the alloy still possesses good mechanical properties at high temperatures.

[0065] The heat-resistant castable Al-Si-Cu-Mg alloy prepared in this embodiment has good mechanical properties. The tensile strength of the heat-resistant castable Al-Si-Cu-Mg alloy prepared in this embodiment is 427±5MPa at 25℃ and the elongation after fracture is 3.3±0.9%. The tensile strength at 250℃ is 268±5MPa and the elongation after fracture is 6.6±0.4%.

[0066] In summary, this embodiment utilizes the synergistic effect of microalloying of Sc, V, and Ti in Al-Si-Cu-Mg-based alloys and aging treatment to induce reinforcing phases in the alloy, significantly improving the room temperature and high temperature strength of Al-Si-Cu-Mg alloys. This overcomes the limitations of traditional single strengthening techniques and has broad application prospects.

[0067] The room temperature and 250℃ high temperature tensile properties of the heat-resistant cast Al-Si-Cu-Mg alloys of Examples 1-3 of this invention are shown in Table 1.

[0068] Table 1 Comparative Example 1 A method for preparing an Al-Si-Cu-Mg alloy specifically includes the following steps: (1) Batching: Weigh out the raw materials of high-purity aluminum ingot, Al-20Si master alloy, Al-50Cu master alloy, high-purity magnesium ingot, Al-20Mn master alloy, Al-5Sc master alloy, Al-10V master alloy and Al-10Ti master alloy according to the proportion. The raw material composition includes 11% Si, 2.5% Cu, 0.4% Mg, 0.1% Mn, 0.12% Sc, 0.1% V and 0.1% Ti by mass percentage, with the balance being Al and unavoidable impurities (where the mass fraction relationship of Cu, Mg, Sc, V and Ti is 0.49Cu+10Mg=5.2, Sc:V:Ti=1.2:1:1).

[0069] (2) Melting: High-purity aluminum ingots, Al-20Si master alloy and Al-50Cu master alloy are added to the graphite crucible of the resistance furnace and heated to 720°C to melt evenly. Then the temperature is raised to 800°C and Al-20Mn master alloy, Al-5Sc master alloy, Al-10V master alloy and Al-10Ti master alloy are added and melted evenly. Then the temperature is lowered to 740°C and high-purity magnesium ingot is added. Then the mixture is stirred quickly and melted evenly and the slag is removed to obtain the alloy melt.

[0070] (3) Refining and degassing: Cool the alloy melt to 730°C, then add the fluorine-based refining agent to the bottom of the alloy melt for refining. The amount of fluorine-based refining agent added to the alloy melt is 0.5% by mass. After the refining agent has reacted completely, stir quickly for 5 minutes, then keep it at 730°C for 10 minutes; remove the slag, then use high-purity argon to degas the alloy melt for 10 minutes, and then keep it at 730°C for 15 minutes.

[0071] (4) Casting: The alloy melt, after being kept at a constant temperature, is cooled to 720°C and then poured into a mold to solidify and form an ingot.

[0072] (5) Heat treatment: The ingot is aged at 320℃ for 36 hours to obtain Al-Si-Cu-Mg alloy.

[0073] The surface morphology, composition, and structure of the Al-Si-Cu-Mg alloy prepared in this comparative example were analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM images showed that the Al-Si-Cu-Mg alloy in this comparative example contained an α-Al matrix, a eutectic Si phase, and large-sized bulk Al2Cu phase, AlCuSc phase, Q-Al5Cu2Mg8Si6 phase, and AlSiMnFe phase. TEM images showed that the Al-Si-Cu-Mg alloy in this comparative example contained nano-AlTiVSc phase, Q-Al5Cu2Mg8Si6 phase, and θ-Al2Cu phase with a size greater than 1 μm.

[0074] The Al-Si-Cu-Mg alloy prepared in this comparative example has a tensile strength of 405±13MPa and an elongation after fracture of 1.7±0.5% at 25℃, and a tensile strength of 243±4MPa and an elongation after fracture of 4.5±1.1% at 250℃.

[0075] In summary, this comparative example, due to its aging treatment at only 320℃ for 36 hours, resulted in a low volume fraction of the precipitated θ'-Al2Cu and Q-Al5Cu2Mg8Si6 phases, which underwent severe coarsening or partial dissolution. The large θ-Al2Cu phases were incoherent with the aluminum matrix, offering little effect in hindering dislocation movement. Furthermore, the bulky eutectic phases (AlCuSc, Q-Al5Cu2Mg8Si6, and AlSiMnFe phases) failed to dissolve back into the matrix, remaining relatively large and becoming stress concentration points under stress, which is detrimental to the alloy's plasticity.

[0076] Comparative Example 2 A method for preparing an Al-Si-Cu-Mg alloy specifically includes the following steps: (1) Batching: Weigh out the raw materials of high-purity aluminum ingot, Al-20Si master alloy, Al-50Cu master alloy, high-purity magnesium ingot, Al-20Mn master alloy, Al-5Sc master alloy and Al-10Ti master alloy according to the proportion. The raw material composition includes 11% Si, 2.5% Cu, 0.4% Mg, 0.1% Mn, 0.12% Sc and 0.1% Ti by mass percentage, with the balance being Al and unavoidable impurities (where the mass fraction relationship of Cu, Mg, Sc and Ti is 0.49Cu+10Mg=5.2, Sc:Ti=1.2:1).

[0077] (2) Melting: High-purity aluminum ingots, Al-20Si master alloy and Al-50Cu master alloy are added to the graphite crucible of the resistance furnace and heated to 720°C to melt evenly. Then the temperature is raised to 800°C and Al-20Mn master alloy, Al-5Sc master alloy and Al-10Ti master alloy are added and melted evenly. Then the temperature is lowered to 740°C and high-purity magnesium ingot is added. Then the mixture is stirred quickly and melted evenly and the slag is removed to obtain the alloy melt.

[0078] (3) Refining and degassing: Cool the alloy melt to 730°C, then add the fluorine-based refining agent to the bottom of the alloy melt for refining. The amount of fluorine-based refining agent added to the alloy melt is 0.5% by mass. After the refining agent has reacted completely, stir quickly for 5 minutes, then keep it at 730°C for 10 minutes; remove the slag, then use high-purity argon to degas the alloy melt for 10 minutes, and then keep it at 730°C for 15 minutes.

[0079] (4) Casting: The alloy melt, after being kept at a constant temperature, is cooled to 720°C and then poured into a mold to solidify and form an ingot.

[0080] (5) Heat treatment: The ingot is first subjected to high temperature aging treatment at 320℃ for 24h, then subjected to aging treatment at 500℃ for 4h, and then subjected to low temperature re-aging treatment at 170℃ for 8h, and then cooled to obtain Al-Si-Cu-Mg alloy.

[0081] The surface morphology, composition, and structure of the Al-Si-Cu-Mg alloy prepared in this comparative example were analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM images showed that the Al-Si-Cu-Mg alloy in this comparative example contained an α-Al matrix, a eutectic Si phase, an AlCuSc phase, a Q-Al5Cu2Mg8Si6 phase, an AlSiMnFe phase, and an acicular Al3Ti phase. TEM images showed that the Al-Si-Cu-Mg alloy in this comparative example contained nano-Q-Al5Cu2Mg8Si6 phase and θ-Al2Cu phase.

[0082] The Al-Si-Cu-Mg alloy prepared in this comparative example has a tensile strength of 385±5MPa and an elongation after fracture of 4.5±0.8% at 25℃, and a tensile strength of 220±6MPa and an elongation after fracture of 8.8±1.2% at 250℃.

[0083] In summary, the comparative example failed to precipitate the nano-AlTiVSc phase due to the absence of V, resulting in a weakened precipitation strengthening effect. The newly formed needle-like Al3Ti phase cuts through the aluminum matrix, easily becoming stress concentration zones under stress and inducing microcracks. Therefore, both the room temperature and high temperature strength of the alloy decreased.

[0084] Comparative Example 3 A method for preparing an Al-Si-Cu-Mg alloy specifically includes the following steps: (1) Batching: Weigh high-purity aluminum ingots, Al-20Si master alloy, Al-50Cu master alloy, high-purity magnesium ingots, Al-20Mn master alloy, and Al-5Sc master alloy raw materials according to the proportion. The raw material composition includes 11% Si, 2.5% Cu, 0.4% Mg, 0.1% Mn, and 0.12% Sc by mass percentage, with the balance being Al and unavoidable impurities (where the mass fraction relationship between Cu and Mg is 0.49Cu + 10Mg = 5.2).

[0085] (2) Melting: High-purity aluminum ingots, Al-20Si master alloy and Al-50Cu master alloy are added to the graphite crucible of the resistance furnace and heated to 720°C to melt evenly. Then the temperature is raised to 800°C and Al-20Mn master alloy and Al-5Sc master alloy are added and melted evenly. Then the temperature is lowered to 740°C and high-purity magnesium ingot is added. Then the mixture is stirred quickly and melted evenly. Slag is removed to obtain the alloy melt.

[0086] (3) Refining and degassing: Cool the alloy melt to 730°C, then add the fluorine-based refining agent to the bottom of the alloy melt for refining. The amount of fluorine-based refining agent added to the alloy melt is 0.5% by mass. After the refining agent has reacted completely, stir quickly for 5 minutes, then keep it at 730°C for 10 minutes; remove the slag, then use high-purity argon to degas the alloy melt for 10 minutes, and then keep it at 730°C for 15 minutes.

[0087] (4) Casting: The alloy melt, after being kept at a constant temperature, is cooled to 720°C and then poured into a mold to solidify and form an ingot.

[0088] (5) Heat treatment: The ingot is first subjected to high temperature aging treatment at 320℃ for 24h, then subjected to aging treatment at 500℃ for 4h, and then subjected to low temperature re-aging treatment at 170℃ for 8h, and then cooled to obtain Al-Si-Cu-Mg alloy.

[0089] The surface morphology, composition, and structure of the Al-Si-Cu-Mg alloy prepared in this comparative example were analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM images showed that the Al-Si-Cu-Mg alloy in this comparative example contained an α-Al matrix, a eutectic Si phase, an AlCuSc phase, a Q-Al5Cu2Mg8Si6 phase, and an AlSiMnFe phase. TEM images showed that the Al-Si-Cu-Mg alloy in this comparative example contained nano-Q-Al5Cu2Mg8Si6 phase and θ-Al2Cu phase.

[0090] The Al-Si-Cu-Mg alloy prepared in this comparative example has a tensile strength of 402±5 MPa and an elongation after fracture of 1.2±0.4% at 25℃, and a tensile strength of 257±9 MPa and an elongation after fracture of 5.0±0.5% at 250℃.

[0091] In summary, this comparative example, due to the addition of Mn and Sc for microalloying but without the addition of V and Ti, exhibits low solid solubility of Mn and Sc in the aluminum matrix. Mn promotes the transformation of the impurity Fe phase into a more rounded and finer AlSiMnFe phase. Although Mn can improve the Fe phase, the resulting AlSiMnFe phase becomes excessively coarse. These coarse primary phases can become crack initiation sites under stress, thus reducing the alloy's ductility. Furthermore, it was found that Sc cannot form the ideal nanoscale Al3Sc strengthening phase, instead forming coarse composite phases with other elements (such as Cu), leading to a weakening of the traditional precipitation strengthening effect.

[0092] Comparative Example 4 A method for preparing an Al-Si-Cu-Mg alloy specifically includes the following steps: (1) Batching: Weigh out the raw materials of high-purity aluminum ingot, Al-20Si master alloy, Al-50Cu master alloy, high-purity magnesium ingot, Al-20Mn master alloy, Al-10V master alloy and Al-10Ti master alloy according to the proportion. The raw material composition includes 11% Si, 2.5% Cu, 0.4% Mg, 0.1% Mn, 0.1% V and 0.1% Ti by mass percentage, with the balance being Al and unavoidable impurities (where the mass fraction relationship of Cu, Mg, V and Ti is 0.49Cu+10Mg=5.2, V:Ti=1:1).

[0093] (2) Melting: High-purity aluminum ingots, Al-20Si master alloy and Al-50Cu master alloy are added to the graphite crucible of the resistance furnace and heated to 720°C to melt evenly. Then, the temperature is raised to 800°C and Al-20Mn master alloy, Al-10V master alloy and Al-10Ti master alloy are added and melted evenly. Then, the temperature is lowered to 740°C and high-purity magnesium ingot is added. Then, the mixture is quickly stirred and melted evenly and the slag is removed to obtain the alloy melt.

[0094] (3) Refining and degassing: Cool the alloy melt to 730°C, then add the fluorine-based refining agent to the bottom of the alloy melt for refining. The amount of fluorine-based refining agent added to the alloy melt is 0.5% by mass. After the refining agent has reacted completely, stir quickly for 5 minutes, then keep it at 730°C for 10 minutes; remove the slag, then use high-purity argon to degas the alloy melt for 10 minutes, and then keep it at 730°C for 15 minutes.

[0095] (4) Casting: The alloy melt, after being kept at a constant temperature, is cooled to 720°C and then poured into a mold to solidify and form an ingot.

[0096] (5) Heat treatment: The ingot is first subjected to high temperature aging treatment at 320℃ for 24h, then subjected to aging treatment at 500℃ for 4h, and then subjected to low temperature re-aging treatment at 170℃ for 8h, and then cooled to obtain Al-Si-Cu-Mg alloy.

[0097] The surface morphology, composition, and structure of the Al-Si-Cu-Mg alloy prepared in this comparative example were analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM images revealed that the Al-Si-Cu-Mg alloy in this comparative example contained an α-Al matrix, a eutectic Si phase, a Q-Al5Cu2Mg8Si6 phase, an AlSiMnFe phase, and an Al3Ti phase. TEM images showed that the Al-Si-Cu-Mg alloy in this comparative example contained nano-Q-Al5Cu2Mg8Si6 and θ-Al2Cu phases. The Al-Si-Cu-Mg alloy prepared in this comparative example has a tensile strength of 394±5 MPa and an elongation after fracture of 1.9±1.0% at 25℃, and a tensile strength of 257±10 MPa and an elongation after fracture of 4.2±0.9% at 250℃.

[0098] In summary, the comparative example, due to the absence of Sc, exhibited a weakened grain refinement effect, resulting in a larger grain size in the alloy. Furthermore, Al2Cu exhibited lower heat resistance than AlCuSc, and the θ'-Al2Cu phase tended to coarsen and grow at high temperatures, failing to pin dislocations and inhibiting microstructure growth and recrystallization at high temperatures. The newly formed acicular Al3Ti phase would cut into the aluminum matrix, easily becoming stress concentration zones under stress conditions, initiating microcracks, and resulting in poor alloy plasticity.

[0099] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A heat-resistant castable Al-Si-Cu-Mg alloy, characterized in that, The elemental composition of the heat-resistant castable Al-Si-Cu-Mg alloy, by mass percentage, includes: 6.5-11.0% Si, 1.5-5.5% Cu, 0.1-0.5% Mg, 0.05-0.25% Mn, 0.05-0.35% Sc, 0.05-0.25% V, and 0.05-0.25% Ti, with the balance being Al and unavoidable impurities; wherein the mass percentage relationship between Cu and Mg satisfies 4.6≤0.49Cu+10Mg≤5.2, and the mass percentage of Sc, V, and Ti satisfies Sc:V:Ti=(1.0~1.2):(0.8~1.0):(0.8~1.0).

2. The method for preparing the heat-resistant castable Al-Si-Cu-Mg alloy according to claim 1, characterized in that, Specifically, the following steps are included: (1) Batching: Weigh out pure Al, Al-Si master alloy, Al-Cu master alloy, pure Mg, Al-Mn master alloy, Al-Sc master alloy, Al-V master alloy and Al-Ti master alloy as alloy raw materials according to the proportion; (2) Melting: First, pure Al, Al-Si master alloy and Al-Cu master alloy are added to the melting device and heated and melted evenly. Then, Al-Mn master alloy, Al-Sc master alloy, Al-V master alloy and Al-Ti master alloy are added and melted evenly. Then, the temperature is lowered and pure Mg is added and melted evenly to obtain the alloy melt. (3) Refining and degassing: Cool the alloy melt, then add refining agent for refining, then degas and remove slag, and then keep it warm and stand. (4) Casting: After the alloy melt has been kept at a constant temperature, it is cooled down and then poured into a mold to solidify and form an ingot. (5) Heat treatment: The ingot is first subjected to high temperature aging and then low temperature re-aging treatment, followed by cooling to obtain heat-resistant cast Al-Si-Cu-Mg alloy.

3. The method for preparing the heat-resistant castable Al-Si-Cu-Mg alloy according to claim 2, characterized in that, In step (2), the melting temperature of pure Al, Al-Si master alloy, and Al-Cu master alloy is 680-720℃; the melting temperature of Al-Mn master alloy, Al-Sc master alloy, Al-V master alloy, and Al-Ti master alloy is 740-800℃; and the melting temperature of pure Mg is 740℃.

4. The method for preparing the heat-resistant castable Al-Si-Cu-Mg alloy according to claim 2, characterized in that, In step (3), the alloy melt is cooled to 720-740℃; the mass percentage of the added refining agent is 0.2-0.5% of the alloy melt, the refining agent is added to the bottom of the alloy melt, and after the refining agent has reacted completely, it is stirred rapidly for 3-5 minutes; the refining conditions are: after the refining agent has reacted completely and is stirred rapidly, it is kept at 720-740℃ for 10-15 minutes.

5. The method for preparing the heat-resistant castable Al-Si-Cu-Mg alloy according to claim 2, characterized in that, The degassing process in step (3) takes 6-10 minutes; the heat preservation and settling time is 10-15 minutes.

6. The method for preparing the heat-resistant castable Al-Si-Cu-Mg alloy according to claim 2, characterized in that, In step (4), the alloy melt after being kept at a constant temperature is cooled to 700-720℃.

7. The method for preparing the heat-resistant castable Al-Si-Cu-Mg alloy according to claim 2, characterized in that, The conditions for high-temperature aging regression in step (5) are: aging at 300-350℃ for 10-40h, and then regression at 500-540℃ for 2-4h; the conditions for low-temperature re-aging are: low-temperature re-aging at 170-220℃ for 4-8h.

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