Al-cu-mn-ca alloy and method for producing the same

Abstract

The application provides an Al-Cu-Mn-Ca alloy and a preparation method thereof. The raw material of the alloy comprises, in percentage by mass: Cu: 4-5%, Mn: 0.5-1%, Ca: 0.5-1%, Ti: 0.1-0.3%, and the balance of Al; and the total amount of impurities Fe, Si and Mg is less than 0.2%. The alloy provided by the application can increase the casting performance of the alloy by adding a proper amount of Ca element to the Al-Cu-Mn alloy, can improve the strength of the aluminum alloy material by fully utilizing the precipitation strengthening of the Al2Cu phase under the premise of ensuring the good casting performance of the alloy, and can manufacture the high-strength and high-toughness casting aluminum alloy with excellent casting performance by adopting the extrusion casting process.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to an Al-Cu-Mn-Ca alloy and its preparation method. Background Technology

[0002] Aluminum alloys, as lightweight materials, have received widespread attention in aerospace, automotive, and shipbuilding industries. It is well known that Al-Cu alloys possess low density, good heat resistance, ease of machining, and can be strengthened through heat treatment; therefore, the strongest cast aluminum alloys currently available are developed based on the Al-Cu system. However, Al-Cu alloys have a high susceptibility to hot cracking and poor fluidity, resulting in poor casting performance and severely limiting their applications. Because Al-Si alloys contain a large amount of eutectic structure, they possess excellent fluidity and casting performance, but their overall mechanical properties are generally average, especially their elongation, which is difficult to exceed 8%. The automotive industry typically requires structural components to have an elongation of no less than 10%, therefore, traditional Al-Si alloys struggle to meet the stringent requirements of modern manufacturing.

[0003] In recent years, Ca has been increasingly recognized as a promising low-cost element for the preparation of aluminum-based light alloys. It has been reported that Ca alloying has the following advantages: (1) Ca forms an ultrafine eutectic (Al)Al4Ca with Al, with a volume fraction greater than 30%, which is three times that of the Al-Si eutectic; (2) Ca is abundant and inexpensive, which can significantly reduce alloy costs; and (iii) Ca has a density of 1.542 g / cm³. 3 This can further reduce the weight of aluminum alloys. (iv) Al-Ca alloys have good corrosion resistance. However, currently cast aluminum-calcium alloys generally suffer from the contradiction of being "strong but not tough" and "strong and tough but not castable," making it difficult to expand their applications. Therefore, it is urgent to develop aluminum alloys with excellent casting properties and high strength / toughness to expand their practical applications. Summary of the Invention

[0004] The purpose of this invention is to overcome the deficiencies of the prior art and provide an Al-Cu-Mn-Ca alloy and its preparation method.

[0005] An Al-Cu-Mn-Ca alloy, the raw materials of which, by mass percentage, comprise:

[0006] Cu: 4%–5%, Mn: 0.5%–1%, Ca: 0.5%–1%, Ti: 0.1%–0.3%, balance Al.

[0007] A method for preparing the Al-Cu-Mn-Ca alloy as described above, comprising:

[0008] S1. Pure Al is added into the resistance melting furnace according to the calculated weight and melted. After it is completely melted, the temperature of the melt is maintained at 750℃. Then it is left to stand for 4 hours to remove the precipitate and slag, and finally pure molten aluminum is obtained.

[0009] S2. Dry the calculated weights of the intermediate alloys Al-20Cu and Al-10Mn;

[0010] S3. Place the baked and dried intermediate alloys Al-20Cu and Al-10Mn into the pure molten aluminum liquid, while raising the solution temperature to 780°C and stirring for 5 minutes every 20 minutes to ensure that the elements are evenly diffused in the solution. Then let it stand for 1 hour to remove precipitates and slag again.

[0011] S4. Lower the solution temperature to 730℃, add pure Ca granules in batches until all the calculated weight of Ca has been added. Stir immediately after each addition of pure Ca granules.

[0012] S5. Adjust the solution temperature to 750℃, then add the calculated weight of intermediate alloy Al-5Ti-B. After the intermediate alloy Al-5Ti-B has completely melted, use a slag removal and degassing device to purify the melt.

[0013] S6. After slag removal and degassing, the oxide layer and slag on the surface of the melt are removed, and the smelted alloy solution is finally obtained.

[0014] S7. Use extrusion casting equipment to cast the molten alloy solution. The extrusion casting process is as follows: mold temperature 200℃, solution temperature 750℃, extrusion pressure 70MPa.

[0015] S8, filling type;

[0016] S9, Pressure holding;

[0017] S10, Open the mold and remove the parts;

[0018] S11. Perform a two-stage solution aging treatment on the alloy removed from the mold.

[0019] Furthermore, in the preparation method of the Al-Cu-Mn-Ca alloy as described above, the particle size of the pure Ca particles is 0.3-0.8 cm; and the amount of pure Ca particles added each time does not exceed 0.5 kg.

[0020] Furthermore, in the preparation method of the Al-Cu-Mn-Ca alloy as described above, the gas introduced during slag removal in step S4 is CCl4, and the time is 20 minutes.

[0021] Furthermore, in the preparation method of the Al-Cu-Mn-Ca alloy as described above, the secondary solution aging treatment includes:

[0022] The first-stage solution treatment was carried out at a temperature of 535℃ for 10 hours, and the second-stage solution treatment was carried out at a temperature of 555℃ for 4 hours.

[0023] Furthermore, in the preparation method of the Al-Cu-Mn-Ca alloy as described above, after the secondary solution aging treatment, the alloy is quenched in water at 20°C, and then aged at 165°C for 6 hours.

[0024] This invention, by controlling the Ca content to 0.5%–1%, enables the prepared alloy to possess excellent mechanical and casting properties, with a tensile strength of 343 MPa and an elongation of 32%, far exceeding those of currently commercially available cast aluminum alloys. Furthermore, by controlling the Ca content to above 0.5% before casting and extrusion, this invention generates a large amount of nanoscale ultrafine eutectic Al4Ca phase at the grain boundaries, resulting in an alloy with excellent plastic deformation coordination and significantly increased elongation. Conversely, when Ca content exceeds 1%, a large amount of blocky primary Al4Ca phase appears, impairing the alloy's strength and ductility. Therefore, by controlling the Ca content to 0.5%–1% before casting and extrusion in the aluminum alloy preparation process, this invention enables the alloy to possess both good castability and excellent mechanical properties.

[0025] The design theory for adding elements to high-strength and high-toughness cast aluminum alloys provided by this invention is as follows:

[0026] Cu (Cu) is the most important alloying element in Al-Cu cast aluminum alloys. The as-cast microstructure of Al-Cu binary alloys contains two phases: α-Al and θ (Al₂Cu). These two phases form a binary eutectic (α+Al₂Cu) at the grain boundaries. The maximum solubility of copper in the α phase is approximately 5.65% at the binary eutectic temperature (548℃), but drops to below 0.1% at room temperature. Alloys with such drastic solubility changes can undergo solution hardening followed by artificial aging. During aging, Al-Cu alloys acquire a large number of dispersed GP zones, θ" and θ' strengthening phases. The precipitation of these transition phases distorts the crystal lattice of the α solid solution and hinders dislocation slip, thereby strengthening the alloy. Experiments show that alloys with a Cu content of 4.6–5.6% can guarantee the maximum quenching effect. Once the equilibrium solid solubility of Cu exceeds 5.7 wt.%, the ductility of the as-cast Al-Cu alloy decreases. At this point, brittleness and micron-sized θ-Al₂Cu precipitates form at the grain boundaries, leading to crack initiation and reducing the alloy's elongation. The malleability of the alloy is such that a Cu content above 5.7% offers no benefit to the alloy's strength, as excess Cu cannot be dissolved and therefore cannot be used for θ'-Al₂Cu precipitation strengthening. Al-Cu alloys have a wide solid-liquid solidification range and a severe tendency towards porosity. The Al₂Cu phase in the eutectic exhibits very low plasticity near its melting point and is easily torn during solidification shrinkage, thus readily leading to hot cracking. While increasing the copper content significantly improves the alloy's casting properties, it also noticeably reduces its mechanical properties. To maximize the age-hardening effect, this invention controls the Cu content within the range of 4% to 5%.

[0027] Mn element: Adding Mn to Al-Cu binary alloys can significantly improve the room temperature and high temperature mechanical properties of the alloys, while also improving their casting properties. The grain boundaries of Al-Cu-Mn ternary alloys contain α-Al, θ(Al₂Cu), and T(Al₂O₃) elements. 20A ternary eutectic of Cu2Mn3 phase. During solution aging of this alloy, firstly, in the second-stage solution aging process, the T phase in the ternary eutectic formed by non-equilibrium solidification dissolves into α-Al, with excess T phase distributed discontinuously in a network at the grain boundaries. Then, during aging, nano-sized T phases are dispersed and precipitated in the matrix. The T phase and the aluminum matrix form a coherent interface, exhibiting a strong strengthening effect. The T phase not only has a complex composition and crystallization lattice with minimal solubility variation, but it is also relatively stable at high temperatures, does not easily agglomerate and grow, and possesses high hot hardness. The added Mn, besides partially forming the heat-resistant T phase, also partially dissolves into the matrix, playing a certain role in solid solution strengthening. Mn belongs to the transition group and has an incomplete outer electron shell. When Mn atoms enter the lattice, they cause electron redistribution, significantly increasing the interatomic bonding force and hindering atomic diffusion. Simultaneously, Mn is a surface-active element in solid solutions, accumulating near grain boundaries and strongly inhibiting diffusion at these boundaries. Furthermore, due to the low Fe content in the alloy, sticking to the mold is likely to occur. Adding Mn can replace Fe to reduce sticking. Mn can also alter the morphology of the Fe-rich phase and neutralize the harmful effects of Fe impurities. For these reasons, this invention adds 0.5–1% Mn to the Al-Cu alloy.

[0028] Ca (Ca) forms an ultrafine eutectic with aluminum (Al)+Al4Ca, with a eutectic fraction exceeding 30% (vol.), three times that of the (Al)+(Si) eutectic. The (Al)+Al4Ca eutectic structure is located between grains, effectively reducing the alloy's hot-cracking tendency and increasing the casting performance of Al-Cu-Mn alloys. Furthermore, the (Al)+Al4Ca eutectic possesses nanoscale lamellae, which can effectively coordinate matrix deformation and greatly increase the alloy's plasticity.

[0029] Ti: Ti is an effective grain refiner. Ti forms nanoscale Al3Ti particles with Al, which can greatly increase the nucleation sites of Al grains, thereby generating more grains. However, if the Ti content exceeds 0.3 wt.%, a blocky primary Al3Ti phase will form in the material. This not only consumes Ti atoms used for nucleation, but the brittle primary phase will also become a crack initiation site, thus degrading the material's performance. Therefore, the Ti content in the high-strength aluminum alloy material provided by this invention shall not exceed 0.3 wt.%.

[0030] The alloy provided by this invention can increase the casting performance of the alloy by appropriately adding trace amounts of Ca to the Al-Cu-Mn alloy. Under the premise of ensuring good casting performance, the precipitation strengthening of the Al2Cu phase is fully utilized to improve the strength of the aluminum alloy material, and a high-strength and high-toughness cast aluminum alloy with excellent casting performance is manufactured by extrusion casting process.

[0031] This invention improves the casting performance of an alloy by adding 5% Cu and less than 1 wt.% Ca, so that the prepared alloy can simultaneously have two precipitated phases, Al4Ca and Al2Cu, with a volume fraction ratio of Al2Cu:Al4Ca = 1:9.

[0032] In addition, in order to avoid the influence of impurities such as Fe, Si, and Mg on the overall performance of the aluminum alloy material of the present invention, their total amount needs to be controlled, that is, the total amount of impurities in the alloy shall not exceed 0.2 wt.%.

[0033] Squeeze casting is a casting method that applies high pressure to the melt, causing the molten alloy to solidify under pressure and using pressure to force feeding. It combines the strength of forging with the flexibility of casting, and can produce high-performance castings with dense structures.

[0034] The preparation method provided by this invention employs a two-stage solution treatment followed by a single-stage aging process. The first-stage solution treatment aims to dissolve the network-like Al2Cu phase at the grain boundaries into the aluminum matrix. DSC thermal analysis revealed that the dissolution temperature of the Al2Cu phase is 540℃. Considering a 5℃ error in the heat treatment furnace, the first-stage solution treatment temperature is set at 535℃. To ensure complete dissolution of the Al2Cu phase into the aluminum matrix, a reasonable solution time needs to be determined. Therefore, an alloy with a solution time of 10 hours exhibits optimal mechanical properties, hence the first-stage solution time is set at 10 hours. The second-stage solution treatment aims to spheroidize the lamellar or rod-shaped Al4Ca eutectic phase into granular particles, further increasing the alloy's strength and ductility. If the second-stage solution time is too short, the Al4Ca eutectic phase spheroidization effect is poor; if the second-stage solution time is too long, the Al4Ca eutectic phase tends to grow after spheroidization, deteriorating the alloy's properties. The single-stage aging process aims to uniformly precipitate the dissolved Al2Cu phase at the nanoscale.

[0035] The alloy preparation method provided by this invention forms a microstructure through a casting and extrusion process. This microstructure includes α(Al) solid solution and fine precipitates. The precipitates consist of Al₂Cu, Al₄Ca, and Al₂O₃. 12 Cu3Mn2, (Al,Cu)4Ca and Al 20At least one of Cu2Mn3, the precipitated phase morphologically includes nanoclusters, regular GP regions, and a multiphase ultrafine eutectic structure with nanoplatelet spacing. The multiphase ultrafine eutectic structure with nanoplatelet spacing is located between Al grains. Due to its low melting point, the eutectic structure is usually the last to solidify, thus increasing melt fluidity during solidification, facilitating timely feeding, and reducing the tendency of Al-Cu alloys to hot crack during casting. Furthermore, the nanoscale ultrafine eutectic structure possesses both high strength and high toughness, not only providing a certain degree of eutectic strengthening but also acting as a stress carrier, deforming along with the Al grains, thereby coordinating the plastic deformation of Al grains and greatly increasing the alloy's plasticity. Moreover, the interlayer spacing of this multiphase ultrafine eutectic structure with nanoplatelet spacing is approximately 200 nm, and the mechanical properties of the eutectic structure mainly depend on the spacing of the eutectic lamellae.

[0036] The preparation method provided by this invention results in an alloy comprising a second phase and precipitated phases. Specifically, this invention forms an Al4Ca eutectic phase (second phase) by adding Ca and forms nano-reinforcing precipitates by adding Cu and Mn. The purpose of the second phase is to improve the casting properties of the alloy; the purpose of the precipitates is to strengthen the alloy. Since the precipitates form a composite structure of at least two fine reinforcing phases, they possess both good strengthening effect and thermal stability. Therefore, this is beneficial for ensuring that the aluminum alloy material has both good natural aging stability and comprehensive mechanical properties. Moreover, after T6 heat treatment, the large number of precipitates in the alloy material can also significantly improve the strength of the material.

[0037] The preparation method provided by this invention enables the uniform distribution of precipitated phases, thereby imparting a certain strength to the alloy. Specifically, the multiphase ultrafine eutectic structure with nanosheet spacing is uniformly distributed between grains, which can effectively coordinate grain deformation, delay crack propagation by changing crack paths, and thus greatly improve the plasticity of the alloy (see...). Figure 4 (In-situ tensile diagram). The precipitated phase is uniformly dispersed in the matrix and effectively pins dislocations during deformation of the aluminum alloy, thereby significantly improving the strength of the cast aluminum alloy, especially after T6 heat treatment, the strength of the aluminum alloy is increased by 100 MPa.

[0038] The preparation method provided by this invention can control the area ratio of multiphase ultrafine eutectic structure with nanosheet interlayer spacing to microstructure at 8.3-16.8%, thereby endowing the alloy with excellent flow properties and low thermal tearing tendency.

[0039] The preparation method provided by this invention, through pressure holding at 100MPa and two-stage solution treatment and aging, can control the interlamellar spacing to 200nm, thereby simultaneously improving the strength and plasticity of the alloy.

[0040] The preparation method provided by this invention involves solution treatment and aging of the alloy extracted from the mold to form precipitated phases, including granular TMn phase and acicular Al2Cu phase precipitated during the solution treatment process. The granular TMn phase has an equivalent circle diameter of approximately 100 nanometers, while the acicular Al2Cu phase has a length of approximately 2-3 μm and a width of approximately several hundred nanometers. The equivalent circle diameter refers to the diameter of a circle with the same area as an irregular geometric shape. These granular TMn and acicular Al2Cu phases enable the alloy prepared by this method to possess good castability and excellent mechanical properties.

[0041] The preparation method provided by this invention, through T6 heat treatment, produces an aluminum alloy with a strength of not less than 300 MPa, comparable to commercially available Al-Si cast alloys. Its elongation at break reaches 30%, far exceeding most existing cast alloys (Al-Si, Al-Cu, Al-Mg, etc.). This cast aluminum alloy is suitable for manufacturing lightweight automotive parts requiring high strength and plasticity.

[0042] In summary, by controlling the mass percentages of each raw material in this invention to be Cu: 4%–5%, Mn: 0.5%–1%, Ca: 0.5%–1%, Ti: 0.1%–0.3%, with the balance being Al; and ensuring that the total amount of impurities such as Fe, Si, and Mg is below 0.2%, the prepared alloy has the following advantages:

[0043] 1. Ca does not react with Cu and Mn to form intermetallic compounds and instead consumes each other.

[0044] 2. Ca and Al undergo a eutectic reaction to form Al4Ca colonies with nanoscale structure. The formation of this eutectic structure can not only improve the casting performance of Al-Cu alloy, but also greatly improve the plasticity of the alloy.

[0045] 3. Cu and Al combine to form an Al2Cu eutectic structure with a network structure. This structure can precipitate nano-reinforcing phases after T6 heat treatment. These nano-reinforcing phases generally have a coherent relationship with the Al grains and exhibit a strong dispersion strengthening effect. Therefore, ultrafine eutectic Al4Ca colonies and nano-aged Al2Cu precipitates can synergistically enhance the strength and plasticity of the alloy. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the casting steps for casting aluminum alloys according to the present invention;

[0047] Figure 2 Scanning electron microscope images of the intermetallic phase morphology of aluminum alloy castings with different calcium contents;

[0048] Figure 3 Figure showing the changes in microstructure of aluminum alloy castings with different calcium contents after in-situ stretching by 1000 μm.

[0049] Figure 4 Mechanical tensile curves for the addition of 0.5 wt.% Ca. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention are described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0051] Figure 1 A schematic diagram of the aluminum alloy casting process, as shown below. Figure 1 As shown, including Figure 1 (a) Figure 1 (b) Figure 1 (c) Figure 1 (d) Four-step diagram, in which, Figure 1 (a) is a diagram showing a certain amount of molten alloy being poured into the injection sleeve using a ladle. Figure 1 (b) Diagram showing the upward die-casting of molten alloy using an injection sleeve. Figure 1 (c) is a diagram of the alloy liquid filling under pressure. Figure 1 (d) is a diagram showing the holding pressure after the alloy liquid filling process is completed.

[0052] Example 1:

[0053] The Al-Cu-Mn-Ca alloy provided in this embodiment comprises the following raw materials, calculated by mass percentage:

[0054] Cu: 4%, Mn: 1%, Ca: 1%, Ti: 0.1%, balance Al.

[0055] The Al-Cu-Mn-Ca alloy was prepared according to the above proportions using the following preparation method:

[0056] S1. Add pure Al to the resistance melting furnace according to the calculated weight and melt it. After it is completely melted, keep the melt temperature at 750℃ and let it stand for 4 hours to ensure that the sludge settles and the slag floats.

[0057] S2. Place the calculated weights of intermediate alloys Al-20Cu and Al-10Mn in a machine-side oven and bake for 20 minutes to ensure the intermediate alloys are completely dry.

[0058] S3. Slowly place the baked and dried intermediate alloys Al-20Cu and Al-10Mn into the molten aluminum using a large spoon. At the same time, raise the solution temperature to 780℃ and stir for 5 minutes every 20 minutes to ensure that the elements are evenly diffused in the solution. Let it stand for 1 hour to ensure that the sludge settles and the slag floats to the surface.

[0059] S4. To avoid loss of Ca, lower the solution temperature to 730℃. Use a large spoon to add pure Ca particles with a diameter of about 0.5cm in several batches. Since Ca is relatively reactive, the amount added each time should not exceed 0.5kg. Stir with a large spoon for 2 minutes immediately after each addition until all the calculated weight of Ca has been added. Then stir with a large spoon for 5 minutes to ensure that the Ca is completely diffused in the solution.

[0060] S5. Adjust the solution temperature to 750℃, then add the calculated weight of Al-5Ti-B master alloy. After the Al-5Ti-B master alloy has completely melted, use a slag removal and degassing device to purify the melt. The gas introduced for slag removal is CCl4, and the time is 20 minutes.

[0061] S6. After slag removal and degassing, use a large spoon to completely remove the oxide layer and slag from the surface of the melt to ensure the purity of the melt.

[0062] S7. Use extrusion casting equipment to cast the molten solution. The extrusion casting process is as follows: the die casting machine tonnage is 400t, the mold temperature is 200℃, the solution temperature is 750℃, and the extrusion pressure is 70MPa.

[0063] S8, filling type;

[0064] S9. Hold the pressure at 100MPa for 30s;

[0065] S10, Open the mold and remove the parts;

[0066] S11. Perform a two-stage solution treatment and aging on the alloy removed from the mold. The first stage solution treatment temperature is 535℃ and the time is 10 hours. The second stage solution treatment temperature is 555℃ and the time is 4 hours. After solution treatment, quench the alloy in water at 20℃ and then age it at 165℃ for 6 hours.

[0067] Example 2:

[0068] The difference between this embodiment and Embodiment 1 is that the raw materials, calculated by mass percentage, include:

[0069] Cu: 5%, Mn: 0.5%, Ca: 0.5%, Ti: 0.3%, balance Al.

[0070] Example 3:

[0071] The difference between this embodiment and Embodiment 1 is that the raw materials, calculated by mass percentage, include:

[0072] Cu: 4.5%, Mn: 0.8%, Ca: 0.7%, Ti: 0.2%, balance Al.

[0073] Figure 2 Scanning electron microscope (SEM) images of the intermetallic phase morphology of aluminum alloy castings with different calcium contents. Figure 2 (a) shows the microstructure of the calcium-free alloy; Figure 2 (b) shows the microstructure of the alloy with 0.5% calcium addition; Figure 2 Image (c) shows the microstructure of the alloy with 1% calcium addition. Figure 2 Image (d) is a magnified view of the microstructure of the calcium-free alloy. Figure 2 (e) is a magnified view of the microstructure of the alloy with 0.5% calcium addition; Figure 2 Image (f) is a magnified view of the microstructure of a 1% calcium-added alloy; through Figure 2 It can be seen that the morphology and quantity of grain boundary eutectic phases in the microstructure of aluminum alloy castings with different calcium contents vary considerably. The impact on casting performance is as follows: In calcium-free alloys, the grain boundary eutectic phase is less abundant, making casting defects more likely; the eutectic phase is brittle and prone to cracking and debonding during tensile testing, leading to strain concentration. Alloys with 0.5% and 1% calcium addition exhibit a greater distribution of ultrafine eutectic phases at the grain boundaries. These ultrafine eutectic phases help suppress shear localization, thereby stabilizing and promoting uniform overall plastic deformation.

[0074] Figure 3 The diagram shows the changes in microstructure of aluminum alloy castings with different calcium contents after in-situ tensile stretching of 1000 μm. Figure 3 (a) is a scanning electron microscope image of the calcium-free alloy under in-situ tensile stress at a displacement of 300 μm;

[0075] Figure 3 (b) is a scanning electron microscope image of the calcium-free alloy under in-situ tensile displacement of 600 μm. Figure 3 Image (c) is a scanning electron microscope image of the calcium-free alloy under in-situ tensile displacement of 900 μm. Figure 3 (d) is a 300µm displacement scanning electron microscope image of an alloy with 0.5% calcium addition under in-situ tensile stress. Figure 3 (e) is a scanning electron microscope image of in-situ stretching with a displacement of 600 μm for 0.5% calcium addition. Figure 3 (f) is a scanning electron microscope image of in-situ stretching at 900 μm with 0.5% calcium added; via Figure 3 It can be seen that in the calcium-free alloy, the eutectic phase at the grain boundaries is prone to debonding and cracking, resulting in poor mechanical properties. In contrast, the 0.5% calcium-added alloy exhibits numerous slip lines within the grains, with deformation evenly distributed across all grains, and no significant change in the ultrafine eutectic structure at the grain boundaries.

[0076] Figure 4 Comparison of mechanical tensile curves for calcium-free alloys and those with 0.5 wt.% Ca, through... Figure 4 It can be seen that, compared with the calcium-free alloy, the room temperature plasticity of the alloy increased by 3 times, reaching 31.1%, after adding 0.5 wt.% Ca.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an Al-Cu-Mn-Ca alloy, characterized in that, Its raw materials, calculated as a percentage by mass, include: Cu: 4%–5%, Mn: 0.5%–1%, Ca: 0.5%–1%, Ti: 0.1%–0.3%, balance Al; Its preparation method includes the following steps: S1. Pure Al is added into the resistance melting furnace according to the calculated weight and melted. After it is completely melted, the temperature of the melt is maintained at 750℃. Then it is left to stand for 4 hours to remove the precipitate and slag, and finally pure molten aluminum is obtained. S2. Dry the calculated weights of the intermediate alloys Al-20Cu and Al-10Mn; S3. Place the baked and dried intermediate alloys Al-20Cu and Al-10Mn into the pure molten aluminum liquid, while raising the solution temperature to 780°C and stirring for 5 minutes every 20 minutes to ensure that the elements are evenly diffused in the solution. Then let it stand for 1 hour to remove precipitates and slag again. S4. Lower the solution temperature to 730℃, add pure Ca granules in batches until all the calculated weight of Ca has been added. Stir immediately after each addition of pure Ca granules. S5. Adjust the solution temperature to 750℃, then add the calculated weight of intermediate alloy Al-5Ti-B. After the intermediate alloy Al-5Ti-B has completely melted, use a slag removal and degassing device to purify the melt. S6. After slag removal and degassing, the oxide layer and slag on the surface of the melt are removed, and the smelted alloy solution is finally obtained. S7. Use extrusion casting equipment to cast the molten alloy solution. The extrusion casting process is as follows: the die casting machine tonnage is 400t, the mold temperature is 200℃, the solution temperature is 750℃, and the extrusion pressure is 70MPa. S8, filling type; S9. Hold the pressure at 100MPa for 30s; S10, Open the mold and remove the parts; S11. Perform a two-stage solution aging treatment on the alloy removed from the mold. The pure Ca particles have a particle size of 0.3-0.8 cm; the amount of pure Ca particles added each time does not exceed 0.5 kg; In step S5, the gas introduced for slag removal is CCl4, and the time is 20 minutes. The secondary solution aging treatment includes: First-stage solution treatment: 535℃ for 10 hours; Second-stage solution treatment: 555℃ for 4 hours. After a two-stage solution treatment, the alloy was quenched in water at 20°C and then aged at 165°C for 6 hours.

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