Dy-modified heat-treatment-free high-strength high-toughness die-casting aluminum-magnesium-silicon alloy and preparation method thereof

Abstract

The invention belongs to the technical field of metal materials, and particularly relates to a Dy metamorphic heat-treatment-free high-strength high-toughness die-casting aluminum-magnesium-silicon (Al-Mg-Si) alloy and a preparation method thereof. 2.5%-4% of Si; 0.3 to 0.5 percent of Mn; 0.01 to 0.2 percent of Dy; 0.1 to 0.5 percent of Zn; be: 0.002% to 0.003%; the total content of impurities is less than or equal to 0.2%; and the balance of Al. The alloy has good casting performance, a die-cast sample does not need to be subjected to heat treatment, the high-strength and high-toughness characteristics are achieved at different cooling speeds, and the application requirements of large-wall-thickness-difference automobile body structural parts of new energy automobiles are completely met.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of metal materials, in particular to a Dy-modified heat-treatment-free high-strength and high-toughness die-casting Al-Mg-Si alloy and a preparation method thereof. BACKGROUND

[0002] With the rapid development of new energy vehicles, aerospace, rail transportation, 3C electronics and other industries, thin-walled, integrated and functionally integrated designs are adopted, which leads to a sharp increase in the demand for thin-walled, complex cavity, high dimensional accuracy and good surface quality metal parts. Although traditional gravity casting, sand casting and other processes are mature and widely applicable, they are difficult to meet the requirements of modern industry for high quality and high reliability in terms of filling capacity, forming efficiency, dimensional stability and batch production consistency.

[0003] High-pressure casting (referred to as die casting) technology refers to a near-net forming technology in which liquid metal fills the mold cavity in the form of high speed and high pressure, and solidifies under pressure. High-pressure casting technology can well solve the above-mentioned needs, and can also reduce the pressure faced by enterprises in cost control and energy saving and emission reduction, and can realize near-net shaping, reduce machining allowance and shorten production cycle. However, due to the rapid filling of die casting technology, the structure of the part is thin, and after heat treatment, it will produce a large deformation, which seriously affects the yield of the part. Therefore, it is crucial to develop heat-treatment-free high-strength and high-toughness die-casting aluminum alloy.

[0004] Heat-treatment-free die-casting aluminum alloy is mainly of the Al-Mg-Si system. Mg element can significantly increase the tensile strength, hardness and corrosion resistance of the alloy die casting, and Mg and Si elements can form Mg2Si phase to improve the tensile strength and yield strength of the alloy. Germany Rhein Company developed a Magsimal-59 (Al5Mg2SiMn) alloy which can achieve a yield strength of 160 MPa, a tensile strength of 300 MPa and an elongation of 15-17% in as-cast state, but the yield strength and tensile strength of the alloy cannot meet the mechanical performance requirements of modern new energy vehicle structural parts.

[0005] The Chinese patent application No. 202511545670.6 discloses a die-casting aluminum alloy material and a preparation method thereof. The die-casting aluminum alloy material comprises, by mass fraction: Si 8.7-9.5%, Cu 0.5-1.0%, Ti 0.5-0.7%, Zn 0.5-0.8%, Mn 0.3-0.6%, Mg 0.2-0.4%, Co 0.17-0.35%, B 0.15-0.25%, Ni 0.2-0.3%, Fe≤0.3%, the total amount of unavoidable impurity elements≤0.3%, and the balance of Al. The aluminum alloy adopts a step-by-step adding AlTi10 and an ultrasonic-electromagnetic-ultrasonic treatment mode, so as to accurately control the process parameters, and the die-casting aluminum alloy material with high strength obtained in this way has a yield strength of 220 MPa, a tensile strength of 340 MPa, and an elongation of 5%. It can be seen that although the die-casting aluminum alloy does not need to be heat treated, it can still obtain good mechanical properties, but the following defects exist: the step-by-step adding AlTi10 and the ultrasonic-electromagnetic-ultrasonic treatment mode are needed, and the process is relatively complex, which is not suitable for industrial batch production. In addition, the tensile strength and elongation of the alloy cannot meet the industrial production needs of new energy vehicles.

[0006] The Chinese patent application No. 202511075874.8 discloses a high-strength and high-toughness die-casting aluminum alloy for vehicles and a preparation method thereof. The die-casting aluminum alloy material comprises, by mass fraction: Si 7.0-9.5%, Fe 0.3%, Cu 0.2-0.8%, Mn 0.3-0.8%, Mg 0.1-0.6%, Cr 0.04-0.15%, Zn 0.05-0.20%, Ti 0.1%, Sr 0.015-0.045%, Mo 0.01-0.06%, RE 0.01-0.08%, and the balance of Al and impurities, wherein the total content of impurities is 0.25%. The alloy effectively reduces the defects caused by the die-casting process, avoids the subsequent alloy heat treatment process, and enables the die-casting aluminum alloy prepared to have high strength and toughness and good hot cracking resistance in the as-cast state, with a yield strength of 140 MPa, a tensile strength of 270 MPa, and an elongation of 13%. However, the following defects exist: the strength of the alloy is limited to improve, deformation easily occurs on vehicle parts, and the degassing process is complex.

[0007] Therefore, how to develop a die-casting aluminum alloy material that is free of heat treatment, has high strength and toughness, and has a simple process has become a problem to be solved. SUMMARY

[0008] The application aims to provide a Dy-modified heat treatment-free high-strength and high-toughness die-casting Al-Mg-Si alloy and a preparation method thereof.

[0009] To achieve the above-mentioned purposes, the application adopts the following specific technical solutions:

[0010] In a first aspect, the application provides a Dy-modified heat treatment-free high-strength and high-toughness die-casting Al-Mg-Si alloy, wherein the weight percentage of each component is as follows: Mg: 6.5-8.5%; Si: 2.5-4%; Mn: 0.3-0.5%; Dy: 0.01-0.2%; Zn: 0.1-0.5%; Be: 0.002-0.003%; the total content of impurities is less than or equal to 0.2% (wherein Fe≤0.1% and Cu≤0.1%); and the rest is Al.

[0011] The selected alloy system of the application is an Al-Mg-Si alloy system, which is different from die-casting Al-Si alloy. The main strengthening phase of the die-casting Al-Mg-Si alloy is eutectic Mg2Si structure, and the size and morphology of the eutectic Mg2Si will significantly affect the mechanical properties and casting properties of the alloy. Therefore, the element contents of the main alloying elements Mg and Si, and the modification of the eutectic Mg2Si structure through micro-alloying are particularly important. When the Mg content is relatively high, the morphology of Mg2Si in the eutectic structure will change from rod-like or flake-like to curved Mg2Si particles. With the increase of the Si content, the eutectic point temperature, the eutectic growth rate and the volume fraction of Mg2Si in the eutectic group will increase, and the Mg2Si will be rod-like or lamellar. When the Mg content is 6.5-8.5% and the Si content is 2.5-4%, the eutectic Mg2Si in the die-casting aluminum alloy is short rod-like, which is the best Mg2Si morphology in terms of mechanical properties according to the literature. In addition, the Mg / Si ratio should be greater than 1.6 and less than or equal to 2.6. When the Mg / Si ratio is greater than 2.6, too much Mg will be left in the aluminum alloy, increasing the tendency of hot cracking. When the Mg / Si ratio is less than or equal to 1.6, a large amount of primary Si will be generated in the alloy, which is not conducive to the mechanical properties of the alloy.

[0012] Rare earth elements are frequently introduced into alloy systems as modifiers. In this alloy system, preliminary experiments and phase diagram calculations screened out Dy, a high-quality rare earth element for modifying eutectic Mg2Si. When added at a content of 0.01 wt.%, the size of the eutectic Mg2Si in the alloy significantly decreased; rod-shaped Mg2Si shortened to short rods or dots. Simultaneously, the size and number of eutectic clusters also decreased, resulting in a significant improvement in the alloy's tensile strength and plasticity. Microstructural observation revealed that Dy combined with Al to form the Al2Dy3 phase, primarily enriched around the eutectic clusters. It is speculated that the modification mechanism involves inhibiting eutectic cluster growth, leading to more uniform growth of eutectic Mg2Si within the alloy. Mechanical property testing showed that the alloy's tensile strength increased to a maximum of 370 MPa, and the elongation increased to approximately 16%. However, excessive Dy reduced the alloy's overall mechanical properties. A large amount of the Al2Dy3 phase was observed in the microstructure, resulting in a slight increase in yield strength but a significant decrease in elongation. Based on gradient experiments, it was found that the best denaturation effect was achieved when the Dy element content was 0.01~0.2 wt.%.

[0013] In aluminum alloys, Zn plays a role in coordinating deformation. By adding 0.1~0.5 wt.% Zn, the elongation of the alloy can be increased without reducing the yield strength. When the Dy content is 0.02 wt.% and the Zn content is 0.3 wt.%, the alloy achieves the best mechanical properties. The contributions of Dy and Zn to the elongation have an additive effect and can be added simultaneously.

[0014] Increasing the Fe content leads to the formation of brittle phases, reducing the alloy's plasticity; while adding Mn can alter the acicular or plate-like iron-rich phase, forming a blocky Al(Fe,Mn) phase, thus improving the alloy's properties. Be can reduce the burn-off of Mg. Therefore, 0.3~0.5 wt.% Mn and 0.002~0.003 wt.% Be are added to the alloy.

[0015] Secondly, the present invention provides a method for preparing the Dy-modified heat-free high-strength and high-toughness die-cast Al-Mg-Si alloy, comprising the following steps:

[0016] S1. Material preparation: Prepare materials according to the above aluminum alloy composition and weight percentage; among them, Al, Zn, and Mg are prepared in the form of industrial pure Al, pure Zn, and pure Mg, and Mn, Si, Dy, and Be are prepared in the form of aluminum-containing master alloys Al-10Mn, Al-20Si, Al-10Dy, and Al-2Be.

[0017] S2. Melting: First, melt the pure aluminum. The prepared pure aluminum (99.97% purity) is placed in the melting furnace and heated to 300℃, then gradually increased to 740-760℃ in 100℃ increments. Next, add Al-10Mn, Al-20Si, Al-2Be, and Al-10Dy master alloys and stir until homogeneous. After melting, cool to 710-720℃, add pure Zn, and stir until homogeneous. Then, when the melt cools to 670-690℃, add pure Mg and press it into the bottom area of ​​the crucible for melting (pure Mg must not come into contact with air; it must be fully immersed in the molten aluminum for 15 minutes, and after complete melting, stir steadily in one direction).

[0018] S3. Refining: Heat the melt from step S2 to 720~730℃, sprinkle refining agent powder into the melt for spray refining and slag removal treatment, let it stand for 15~30 minutes, and then skim off the slag on the surface of the melt.

[0019] S4. Die casting: The melt after refining and slag removal in step S3 is subjected to high pressure casting using a die casting machine to obtain die castings.

[0020] Preferably, step S1 further includes a step of preheating the prepared raw materials to 180~240°C for drying.

[0021] Preferably, step S2 further includes the following steps: after the final melting and stirring are uniform, the mixture is allowed to stand and a pre-furnace composition analysis is performed to detect the composition content of the alloy melt. For melts with deviations in content, additional material is added or diluted to bring the composition to the required level.

[0022] Preferably, in step S3, the refining agent is a salt flux containing potassium (K).

[0023] Preferably, in step S4, when producing die-cast parts in high-pressure casting, the pouring temperature is 690~710℃.

[0024] Preferably, in step S4, when producing die-cast parts in high-pressure casting, the high-speed speed (during injection) of the die-casting machine is set to 2.5~3.2 m / s.

[0025] Preferably, in step S4, when die-casting is carried out in high pressure casting, the casting pressure range is 80~150MPa.

[0026] In terms of process, this invention adopts high-pressure die casting technology. The advantages of high-pressure die casting in preparing aluminum alloys are mainly reflected in high efficiency and high integration: its high-speed filling and forced cooling make the forming and solidification process extremely fast, which facilitates highly automated mass production; under high pressure, the aluminum liquid has a strong ability to fill thin-walled, deep-cavity and complex rib structures, which can obtain near-net-shape parts with high dimensional accuracy and good repeatability, and the surface quality is also more stable, thereby significantly reducing subsequent machining and assembly welding processes and reducing the overall manufacturing cost; at the same time, rapid solidification and pressure feeding are often conducive to the refinement of the microstructure and the reduction of shrinkage tendency, so that the parts have better overall consistency and engineering applicability while ensuring appearance and geometric quality.

[0027] Furthermore, this invention employs a combination of physical and chemical modification. The high cooling rate (typically greater than 100 K / s) during high-pressure casting constitutes physical modification, while the addition of the rare earth element Dy reduces the size of the eutectic Mg2Si, constituting chemical modification. The advantage of this combination is that when the die-cast part has a thick wall, the cooling rate of the core decreases, making physical modification alone insufficient to meet the alloy's performance requirements. In this case, chemical modification becomes particularly important, refining the long and coarse eutectic Mg2Si structure into short rod-like structures, thereby improving the material's overall mechanical properties.

[0028] Aluminum alloys prepared according to the formula and die-casting process of this invention do not require heat treatment after die casting. The mechanical properties of the resulting die-cast aluminum alloys can reach a yield strength of 175~200MPa, a tensile strength of 350~370MPa, and an elongation of 13~16.2%.

[0029] The present invention has the following beneficial effects:

[0030] 1. This invention improves the strength of die-cast aluminum alloys by adding Mg and Si elements to form a eutectic Mg2Si strengthening phase, rationally controlling the Mg and Si element ratio to reduce the material's tendency for hot cracking while maintaining good casting performance. By adding Dy and Zn elements, the eutectic Mg2Si structure is modified during the solidification process of the aluminum alloy melt, refining the eutectic Mg2Si size and improving the overall mechanical properties of the material.

[0031] 2. This invention uses high-pressure die casting process to produce aluminum alloy die castings. By adjusting the high speed, the optimal process parameters are obtained. High strength and toughness can be obtained without long-term temperature homogenization, strengthening solution treatment and aging treatment. The process is simpler, the production cost is reduced, and it is suitable for industrial mass production.

[0032] 3. The heat-free die-cast aluminum alloy obtained by this invention has high toughness and high strength. The yield strength of the die-cast aluminum alloy in the die-cast state is 175~200MPa, the tensile strength is 350~370MPa, and the elongation is 13~16.2%, which fully meets the application requirements of new energy vehicle body structural parts with large wall thickness difference. Attached Figure Description

[0033] Figure 1 The SEM structure of the high-pressure die-cast aluminum alloy part in Embodiment 1 of the present invention.

[0034] Figure 2 These are comparison images of the SEM microstructure of high-pressure die-cast aluminum alloy parts from Embodiment 1 (top) and Comparative Example 1 (bottom) of the present invention at the same magnification.

[0035] Figure 3 The mechanical property curves of the high-pressure die-cast aluminum alloys in Comparative Example 1 and Example 1 of this invention are shown. Detailed Implementation

[0036] The present invention will now be described in detail with reference to specific embodiments. Unless otherwise specified, all materials involved in the following embodiments are commercially available conventional materials, and all operations involved are conventional operations in the art unless otherwise specified.

[0037] Example 1

[0038] This embodiment provides a Dy-modified, heat-toughened-free, high-strength, high-toughness die-cast Al-Mg-Si alloy. The weight percentages of the components in this aluminum alloy are: Mg: 7.2%; Si: 3.0%; Mn: 0.33%; Zn: 0.25%; Dy: 0.08%; Be: 0.002%, with total impurities ≤0.2%, and the balance being Al. This aluminum alloy is prepared according to the following steps:

[0039] S1. Material preparation: Prepare materials according to the aluminum alloy composition and weight percentage; among which, Al, Zn, and Mg are prepared in the form of industrial pure Al, pure Zn, and pure Mg, and Mn, Si, Dy, and Be are prepared in the form of aluminum-containing master alloys; preheat the prepared raw materials to 200℃.

[0040] S2. Melting: First, melt the pure aluminum. Place the prepared pure aluminum (99.97% purity) into the melting furnace and heat it to 300℃ initially, then increase the temperature in increments of 100℃ to 740~760℃. Next, add Al-10Mn, Al-20Si, Al-2Be, and Al-10Dy master alloys and stir until homogeneous. After melting, cool to 710~720℃, add pure Zn, and stir until homogeneous. Then, when the melt cools to 670~690℃, add pure Mg and press it into the bottom area of ​​the crucible for melting (pure Mg must not come into contact with air; it must be fully immersed in the molten aluminum for 15 minutes, and after complete melting, stir steadily in one direction).

[0041] S3. Refining: Heat the melt from step S2 to 720~730℃, sprinkle refining agent powder into the melt for spray refining and slag removal treatment, let it stand for 15~30 minutes, and then skim off the slag on the surface of the melt.

[0042] S4. High-pressure casting: The melt after refining and slag removal in step S3 is die-cast. The die-casting conditions are: casting pressure 100MPa, pouring temperature 700~710℃, and high speed 2.5m / s.

[0043] Example 2

[0044] This embodiment provides a Dy-modified, heat-free, high-strength, high-toughness die-cast Al-Mg-Si alloy. The weight percentages of each component in this aluminum alloy are: Mg: 8.5%; Si: 4.0%; Mn: 0.5%; Zn: 0.1%; Dy: 0.05%; Be: 0.003%, with a total impurity content of ≤0.2% and the balance being Al.

[0045] The preparation steps of this aluminum alloy are basically the same as in Example 1, except that the die casting conditions are: casting pressure 105MPa, pouring temperature 700~710℃, and high speed 2.7m / s.

[0046] Example 3

[0047] This embodiment provides a Dy-modified, heat-free, high-strength, high-toughness die-cast Al-Mg-Si alloy. The weight percentages of the components in this aluminum alloy are: Mg: 6.5%; Si: 2.5%; Mn: 0.42%; Zn: 0.36%; Dy: 0.1%; Be: 0.002%, with total impurities ≤0.2% and the balance being Al.

[0048] The preparation steps of this aluminum alloy are basically the same as in Example 1, except that the die casting conditions are: casting pressure 90MPa, pouring temperature 700~710℃, and high speed 2.6m / s.

[0049] Example 4

[0050] This embodiment provides a Dy-modified, heat-free, high-strength, high-toughness die-cast Al-Mg-Si alloy. The weight percentages of the components in this aluminum alloy are: Mg: 6.8%; Si: 2.8%; Mn: 0.36%; Zn: 0.5%; Dy: 0.2%; Be: 0.003%, with total impurities ≤0.2% and the balance being Al.

[0051] The preparation steps of this aluminum alloy are basically the same as those in Example 1, except that the die casting conditions are: casting pressure 110MPa, pouring temperature 700~710℃, and high speed 3.0m / s.

[0052] Example 5

[0053] This embodiment provides a Dy-modified, heat-free, high-strength, high-toughness die-cast Al-Mg-Si alloy. The weight percentages of the components in this aluminum alloy are: Mg: 7.5%; Si: 3.5%; Mn: 0.3%; Zn: 0.22%; Dy: 0.17%; Be: 0.003%, with a total impurity content of ≤0.2% and the balance being Al.

[0054] The preparation steps of this aluminum alloy are basically the same as those in Example 1, except that the die casting conditions are: casting pressure 130MPa, pouring temperature 700~710℃, and high speed 3.2m / s.

[0055] Example 6

[0056] This embodiment provides a Dy-modified, heat-free, high-strength, high-toughness die-cast Al-Mg-Si alloy. The weight percentages of each component in this aluminum alloy are: Mg: 8.0%; Si: 3.8%; Mn: 0.45%; Zn: 0.15%; Dy: 0.17%; Be: 0.003%, with a total impurity content of ≤0.2% and the balance being Al.

[0057] The preparation steps of this aluminum alloy are basically the same as in Example 1, except that the die casting conditions are: casting pressure 100MPa, pouring temperature 700~710℃, and high speed 2.8m / s.

[0058] Example 7

[0059] This embodiment provides a Dy-modified, heat-free, high-strength, high-toughness die-cast Al-Mg-Si alloy. The weight percentages of each component in this aluminum alloy are: Mg: 7.0%; Si: 3.2%; Mn: 0.3%; Zn: 0.18%; Dy: 0.01%; Be: 0.002%, with total impurities ≤0.2% and the balance being Al.

[0060] The preparation steps of this aluminum alloy are basically the same as in Example 1, except that the die casting conditions are: casting pressure 150MPa, pouring temperature 700~710℃, and high speed 3.0m / s.

[0061] Example 8

[0062] This embodiment provides a Dy-modified, heat-free, high-strength, high-toughness die-cast Al-Mg-Si alloy. The weight percentages of the components in this aluminum alloy are: Mg: 7.8%; Si: 3.4%; Mn: 0.38%; Zn: 0.4%; Dy: 0.03%; Be: 0.003%, with a total impurity content of ≤0.2% and the balance being Al.

[0063] The preparation steps of this aluminum alloy are basically the same as in Example 1, except that the die casting conditions are: casting pressure 120MPa, pouring temperature 700~710℃, and high speed 3.2m / s.

[0064] Comparative Example 1

[0065] This embodiment provides a heat-free, high-strength, high-toughness die-cast Al-Mg-Si alloy, which is basically the same as Example 1, except that the modifier Dy is not added in this comparative example.

[0066] Comparative Example 2

[0067] This comparative example provides a Dy-modified, heat-free, high-strength, high-toughness die-cast Al-Mg-Si alloy, which is basically the same as Example 1, except that the amount of Dy added in this comparative example is 0.5 wt.%.

[0068] The alloys obtained in the above embodiments and comparative examples were subjected to the following performance tests:

[0069] 1. Characterization

[0070] The die-cast aluminum alloy parts in the examples have good microstructure and morphology. Figure 1 Taking the microstructure diagram of the alloy in Example 1 as an example, it can be seen that the microstructure has no obvious defects, the eutectic Mg2Si size is less than 2 μm, and the shape is short rod-shaped or approximately dot-shaped. High-brightness, fine Al2Dy3 phases are formed in the alloy and enriched near the eutectic Mg2Si. A comparison diagram of the microstructures of Example 1 and Comparative Example 1 is shown below. Figure 2 As shown, Comparative Example 1, without the addition of Dy element, has a longer eutectic Mg2Si structure compared to Example 1.

[0071] 2. Component analysis

[0072] The composition of the die-cast aluminum alloy parts obtained in each embodiment and comparative example, and the composition test results are summarized in Table 1. The composition test was conducted according to the method in GB_T 20975.25-2020 "Chemical Analysis Methods for Aluminum and Aluminum Alloys - Part 25: Determination of Element Content by Inductively Coupled Plasma Atomic Emission Spectrometry". The measured results were basically consistent with the expected composition.

[0073] Table 1. Alloy composition analysis (wt.%) for each example and comparative example

[0074]

[0075] Note: Bal. in the table indicates the balance; among impurities, Fe≤0.1% and Cu≤0.1%.

[0076] 3. Strength and toughness

[0077] Figure 3 The mechanical property curves of the high-pressure die-cast aluminum alloys of Comparative Example 1 and Example 1 are shown. The performance test results of the die-cast aluminum alloy parts obtained from each example and comparative example are summarized in Table 2. The room temperature tensile properties were tested according to the methods in GB / T 228.1-2021 "Metallic Materials - Tensile Testing - Part 1: Room Temperature Test Method". It can be seen that the alloys in the examples all have high strength (yield strength above 175 MPa, tensile strength above 353 MPa) and toughness (elongation above 13.0%). The addition of Dy improves both strength and toughness, but excessive addition (more than 0.2%) will decrease toughness.

[0078] Table 2. Strength and toughness test data of alloys in various embodiments and comparative examples

[0079]

[0080] In summary, through formulation design and optimized preparation methods, the alloy of this invention successfully modifies and reduces the size of the eutectic Mg2Si, making it more suitable for use in thick-walled parts. The alloy of this invention utilizes a high-pressure die-casting process to achieve more precise casting shapes and superior mechanical properties, while simultaneously reducing production costs and energy consumption. It possesses excellent mechanical properties, meeting the application requirements of complex structural components in the lightweight industry.

[0081] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. Any changes made by those skilled in the art after reading the specification of the present invention, as long as they are within the scope of the claims of the present invention, will be protected by patent law.

Claims

1. A Dy-modified, heat-toughening-free, high-strength, high-toughness die-cast Al-Mg-Si alloy, characterized in that, The weight percentages of the components in this alloy are: Mg: 6.5~8.5%; Si: 2.5~4%; Mn: 0.3~0.5%; Dy: 0.01~0.2%; Zn: 0.1~0.5%; Be: 0.002~0.003%; total impurities ≤0.2%; the remainder is Al.

2. The Dy-modified, heat-toughened-free, high-strength, high-toughness die-cast Al-Mg-Si alloy according to claim 1, characterized in that, The ratio of Mg to Si is greater than 1.6 and less than or equal to 2.

6.

3. The Dy-modified, heat-free, high-strength, high-toughness die-cast Al-Mg-Si alloy according to claim 1, characterized in that, The Dy element content is 0.02 wt.%, and the Zn element content is 0.3 wt.%.

4. The Dy-modified, heat-toughened-free, high-strength, high-toughness die-cast Al-Mg-Si alloy according to claim 1, characterized in that, The die-cast aluminum alloy has a yield strength of 175~200MPa, a tensile strength of 350~370MPa, and an elongation of 13~16.2% in the die-cast state.

5. The method for preparing the Dy-modified, heat-free, high-strength, high-toughness die-cast Al-Mg-Si alloy according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Material preparation: Prepare materials according to the aluminum alloy composition and weight percentage; among them, Al, Zn, and Mg are prepared in the form of industrial pure Al, pure Zn, and pure Mg, while Mn, Si, Dy, and Be are prepared in the form of aluminum-containing master alloys Al-10Mn, Al-20Si, Al-10Dy, and Al-2Be. S2. Melting: First, melt the pure aluminum. Put the prepared pure aluminum into the melting furnace and heat it to 740~760℃ to melt it. Then add Al-10Mn, Al-20Si, Al-2Be, and Al-10Dy master alloys and stir evenly. After melting, cool down to 710~720℃, add pure Zn and stir evenly. Then, when the melt cools down to 670~690℃, add pure Mg, press it into the bottom area of ​​the crucible to melt, and stir evenly. S3. Refining: Heat the melt from step S2 to 720~730℃, sprinkle refining agent powder into the melt for spray refining and slag removal treatment, let it stand for 15~30 minutes, and then skim off the slag on the surface of the melt. S4. Die casting: The melt after refining and slag removal in step S3 is subjected to high pressure casting using a die casting machine to obtain die castings.

6. The method for preparing Dy-modified heat-free high-strength and high-toughness die-cast Al-Mg-Si alloy according to claim 5, characterized in that, Step S1 also includes a step of preheating the prepared raw materials to 180~240℃ and drying them.

7. The method for preparing Dy-modified heat-free high-strength and high-toughness die-cast Al-Mg-Si alloy according to claim 5, characterized in that, Step S2 also includes the following steps: after the final melting and stirring are uniform, the mixture is allowed to stand and a pre-furnace composition analysis is performed to detect the composition content of the alloy melt. For melts with deviations in content, additional material is added or diluted to bring the composition to the required level.

8. The method for preparing Dy-modified, heat-free, high-strength, high-toughness die-cast Al-Mg-Si alloy according to claim 5, characterized in that, In step S4, when producing die-cast parts in high pressure casting, the pouring temperature is 690~710℃.

9. The method for preparing Dy-modified, heat-free, high-strength, high-toughness die-cast Al-Mg-Si alloy according to claim 5, characterized in that, In step S4, when producing die-cast parts in high-pressure die casting, the high-speed setting of the die-casting machine is 2.5~3.2m / s.

10. The method for preparing Dy-modified heat-free high-strength and high-toughness die-cast Al-Mg-Si alloy according to claim 5, characterized in that, In step S4, when die-casting is carried out in high pressure casting, the casting pressure range is 80~150MPa.

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