A heat treatment free aluminum alloy and its extrusion casting preparation method

Abstract

The application relates to a heat treatment-free aluminum alloy and an extrusion casting preparation method thereof, and belongs to the technical field of non-ferrous metal alloys, solves the problems that the heat treatment-free aluminum alloy in the prior art has low strength, poor corrosion resistance and is difficult to meet the use requirements of large thin-wall aluminum alloy castings, and realizes preparation of the heat treatment-free aluminum alloy with high strength.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of non-ferrous metal alloys, in particular to a heat treatment-free aluminum alloy and an extrusion casting preparation method thereof. BACKGROUND

[0002] With the rapid development of the transportation industry, the lightweight requirement of the transportation tools is increasingly strong. Aluminum alloys are widely used in automobile structural parts due to their low density, high strength, corrosion resistance and other excellent properties. In order to achieve the purpose of lightweight, higher requirements are put forward for the performance and size of aluminum alloy castings.

[0003] Generally, in order to obtain high-strength aluminum alloy castings, high-temperature heat treatment process is required. However, for large thin-walled aluminum alloy castings, high-temperature heat treatment process not only increases the time and cost, but also easily causes deformation of the large thin-walled aluminum alloy castings. In the later stage, multiple corrections are required before use. Severe deformation will directly cause the castings to be scrapped, ultimately leading to a significant reduction in the yield of large thin-walled aluminum alloy castings and a significant increase in production costs.

[0004] In recent years, research and development of heat treatment-free aluminum alloys have become a hot topic, among which Al-Si, Al-Si-Mg, and Al-Si-Cu-Mg systems are mainly used. Al-Si has low strength and poor corrosion resistance, which cannot meet the performance requirements of high strength and high corrosion resistance. Although Mg and Cu elements in Al-Si-Mg and Al-Si-Cu-Mg systems improve the strength of the alloy, the presence of Mg elements forms Mg2Si phase, resulting in a decrease in the elongation of the alloy, and the addition of Cu elements adversely affects the corrosion resistance of the aluminum alloy. SUMMARY

[0005] In view of the above analysis, the present application aims to provide a heat treatment-free aluminum alloy and an extrusion casting preparation method thereof, to solve at least one of the problems of the existing heat treatment-free aluminum alloy, such as low strength, poor corrosion resistance, and difficulty in meeting the use requirements of large thin-walled aluminum alloy castings.

[0006] On the one hand, the present application provides a heat treatment-free aluminum alloy, the components of which are as follows in terms of mass percentage: Mg: 2.5-4.0%, Mn: 0.8-1.5%, Zn: 0.5-1.2%, RE: 0.05-0.3%, single impurity ≤0.05%, total impurities ≤0.15%, and the balance being Al.

[0007] On the other hand, the present application also provides an extrusion casting preparation method of a heat treatment-free aluminum alloy, for preparing the aluminum alloy, comprising the following steps:

[0008] S1: batching: weighing the raw materials according to the designed element mass percentage of the aluminum alloy;

[0009] S2: smelting the raw materials to obtain an aluminum alloy smelting liquid;

[0010] S3: extrusion casting;

[0011] S4: aging treatment to obtain an aluminum alloy product.

[0012] Specifically, in step S1, the raw materials include pure Mg, Al-10Mn intermediate alloy, Al-60Zn intermediate alloy, and rare earth RE.

[0013] Further, in step S2, the smelting process includes:

[0014] S2a: after melting pure Al and rare earth RE at 780-800℃, sequentially adding Al-10Mn intermediate alloy and Al-60Zn intermediate alloy, keeping for 30 min after complete melting to obtain a primary smelting liquid;

[0015] S2b: cooling the primary smelting liquid to 680-700℃, adding pure Mg wrapped with aluminum foil, stirring after complete melting, keeping for 20 min to obtain a secondary smelting liquid;

[0016] S2c: adding a deslagging agent to the secondary smelting liquid, keeping for 20 min, and refining and degassing by argon blowing, standing for 30-60 min, and deslagging to obtain an aluminum alloy smelting liquid.

[0017] Specifically, the extrusion casting process in step S3 is to extrusion cast the aluminum alloy smelting liquid obtained in step S2 into a cast rod at a certain temperature.

[0018] Exemplarily, during extrusion casting, the temperature of the aluminum alloy smelting liquid is 740-780℃, and the mold temperature is 250-280℃.

[0019] Preferably, during extrusion casting, the injection speed is 0.2-0.5 m / s, the injection force is 120-150 MPa, and the injection time is 10-15 s.

[0020] Further, the process conditions of the aging treatment in step S4 are: aging temperature 25-50℃, aging time 1-5 days, and air cooling.

[0021] Specifically, the deslagging agent is a composite inorganic salt.

[0022] It should be noted that the room temperature tensile strength of the aluminum alloy product is >320 MPa, the yield strength is >240 MPa, and the elongation after fracture is >11%.

[0023] Compared with the prior art, the present application can at least achieve one of the following beneficial effects:

[0024] 1. The Si-free heat treatment-free aluminum alloy has high strength and high corrosion resistance compared with Si-containing heat treatment-free aluminum alloy materials, and the corrosion resistance of the heat treatment-free aluminum alloy material is improved.

[0025] 2. In the Si-free heat treatment-free aluminum alloy, Mg and Zn elements are introduced to play a solid solution strengthening role, and MgZn2 is precipitated during natural aging to improve the strength of the alloy, and an appropriate amount of RE elements are added to further refine the grain, and a high-strength aluminum alloy material can be obtained only by natural aging.

[0026] Compared with Si-containing heat treatment-free aluminum alloy materials, it has high strength and high corrosion resistance; compared with A356 aluminum alloy and other cast strengthening aluminum alloy materials, high strength and high elongation after fracture can be ensured without complex heat treatment process.

[0027] 3. In the prior art, the heat treatment-free aluminum alloy contains silicon, and the heat treatment-free aluminum alloy designed in the present application does not contain Si. Based on this, in view of the poor flowability of Si-free aluminum liquid, the present application uses reasonable casting temperature (higher than the existing aluminum-silicon alloy 700 DEG C casting temperature) and selects extrusion casting process, and uses the characteristics of low-speed filling and high-pressure solidification of extrusion casting to partially compensate for the problem of insufficient flowability of aluminum liquid, to obtain a casting with more compact structure and fine grains, thereby further improving the strength of the alloy.

[0028] 4. The present application obtains an aluminum alloy with high strength and excellent corrosion resistance by optimizing the alloy element composition, the room temperature tensile strength is > 320 MPa, the yield strength is > 240 MPa, and the elongation after fracture is > 11%.

[0029] In the present application, the above technical solutions can be combined with each other to realize more preferred combination schemes. Other features and advantages of the present application will be described in the subsequent specification, and some advantages will become apparent from the specification, or will be understood by implementing the present application. The purpose and other advantages of the present application can be achieved and obtained from the contents specifically pointed out in the specification and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0030] The accompanying drawings are only for the purpose of illustrating specific embodiments and are not considered as limiting the present application, and in the whole drawings, the same reference signs represent the same parts.

[0031] Figure 1 SEM structure diagram of the aluminum alloy prepared for the present application example 4;

[0032] Figure 2 SEM structure diagram of the aluminum alloy prepared for the present application comparative example 1;

[0033] Figure 3 This is a schematic diagram of the SEM microstructure of the aluminum alloy prepared in Comparative Example 2 of the present invention. Detailed Implementation

[0034] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0035] In one specific embodiment of the present invention, a heat-free aluminum alloy is disclosed, the composition of which, by mass percentage, is: Mg: 2.5-4.0%, Mn: 0.8-1.5%, Zn: 0.5-1.2%, RE: 0.05-0.3%, individual impurities ≤0.05%, total impurities ≤0.15%, and the balance being Al.

[0036] This invention improves mechanical properties by introducing strengthening phases and rare earth element grain refiners through changes in alloy composition. Grain refinement has a positive effect on significantly improving yield strength, tensile strength, and elongation after fracture. The rare earth element RE is a mixture of La and Ce, with La and Ce having the same effect and their proportions are not limited.

[0037] The following details the function and dosage selection of the components contained in this invention:

[0038] Mg: Most of the Mg element is dissolved in the aluminum alloy matrix, playing a role in solid solution strengthening and improving yield strength. A portion of Mg combines with Zn to form the MgZn2 phase, which precipitates during subsequent artificial or natural aging, further increasing the strength of the aluminum alloy. Furthermore, the potential difference between Mg and Al is small, so the addition of Mg has minimal impact on the corrosion resistance of the aluminum alloy. Too low a Mg content will not achieve the above effects, so the lower limit for Mg content is 2.5%. However, excessive Mg will lead to poor alloy fluidity and easily cause defects during casting; therefore, the upper limit for Mg content is preferably 4%.

[0039] Mn: The main mechanism by which Mn affects alloy properties is that it combines with Al atoms to form Al6Mn compounds, i.e., dispersed particles. The recrystallization process may be delayed or even stopped due to the presence of these particles, thus increasing the recrystallization temperature. In addition, this compound can react with Fe atoms to form a new intermetallic compound, Al6MnFe, which reduces the adverse effects of Fe on alloy properties. The potential of Al-Mn compounds is comparable to that of Al, improving the alloy's corrosion resistance. Too low a Mn content will not achieve the above effects, so the lower limit for Mg content is 0.8%. However, excessive Mn will lead to the formation of coarse Al-Mn particles in the alloy, resulting in reduced toughness. Therefore, the upper limit for Mn content is preferably 1.5%.

[0040] Zn: Part of the Zn element is dissolved in the aluminum alloy matrix, playing a solid solution strengthening role. Another part of Zn will form the MgZn2 phase with Mg, which will precipitate during subsequent artificial or natural aging, thereby improving the strength of the aluminum alloy. If the Zn content is too low, the above effects will not be achieved, so the lower limit of Zn content is 0.5%. However, excessive Zn will lead to a decrease in the corrosion resistance of the alloy, so the upper limit of Zn content is preferably 1.2%.

[0041] RE: RE is mainly a mixture of La and Ce. It is mainly used as a grain refiner to refine the grains and improve the strength of the alloy. Moreover, its price is low and will not significantly increase the cost. However, excessive addition of RE can also cause adverse effects such as reduced toughness and hot cracking of the alloy.

[0042] On the other hand, a specific embodiment of the present invention also discloses a method for preparing aluminum alloy by extrusion casting without heat treatment, comprising the following steps:

[0043] S1: Ingredients: Weigh the raw materials according to the mass percentage of the aluminum alloy design elements;

[0044] S2: Melt the raw materials to obtain aluminum alloy molten liquid;

[0045] S3: Extrusion casting;

[0046] S4: Timeliness processing.

[0047] Specifically, in step S1, the raw materials used are pure Mg, Al-10Mn master alloy, Al-60Zn master alloy, and rare earth RE (a mixture of La and Ce);

[0048] Furthermore, in step S2, the smelting process includes:

[0049] S2a: Pure Al and rare earth RE (a mixture of La and Ce) are melted at 780-800℃, and Al-10Mn master alloy and Al-60Zn master alloy are added in sequence. After all the alloy is melted, it is kept at the temperature for 30 minutes to obtain a primary smelting liquid.

[0050] S2b: Cool the primary molten liquid to 680-700℃, add pure Mg wrapped in aluminum foil, stir after it is completely melted, and keep it at the temperature for 20 minutes to obtain the secondary molten liquid;

[0051] S2c: Add a slag remover to the secondary smelting liquid and keep it warm for 20 minutes. Then, argon gas is introduced for refining and degassing. Let it stand for 30 to 60 minutes, remove the slag, and obtain the aluminum alloy smelting liquid.

[0052] It should be noted that, in order to reduce Mg burn-off, pure Mg is added later in the secondary smelting process and wrapped in aluminum foil.

[0053] For example, in the three-stage smelting process, the slag remover is added before degassing to prevent gas from being introduced during stirring; the slag remover is a composite inorganic salt.

[0054] In one possible design, the composite inorganic salt is sodium chloride and potassium chloride, specifically 55% sodium chloride (NaCl) and 45% potassium chloride (KCl).

[0055] Melting in three stages can avoid a long melting time for the alloy and is beneficial for controlling the temperature of the molten liquid.

[0056] Furthermore, the extrusion casting process described in step S3 involves extruding the aluminum alloy molten liquid obtained in step S2 into a casting rod at a certain temperature.

[0057] Squeeze casting is characterized by low-speed filling and high-pressure solidification, which can produce castings with a denser structure and finer grains, thereby further improving the strength of the alloy, reducing internal defects and improving the microstructure, and effectively improving the strength and overall performance of aluminum alloys.

[0058] Specifically, during extrusion casting, the temperature of the aluminum alloy molten liquid is 740–780°C, such as 745°C, 750°C, 755°C, 760°C, 765°C, 770°C, or 775°C, and the mold temperature is 250–280°C, such as 255°C, 260°C, 265°C, 270°C, or 275°C.

[0059] Too low a mold temperature can lead to difficulties in product molding, defects such as weld lines and rough product surfaces, as well as defects in casting holes and cold walls. Too high a mold temperature can cause defects such as surface bubbles, sticking to the mold, and shrinkage cavities in castings, while also reducing the life of the mold.

[0060] During squeeze casting, the injection speed is 0.2–0.5 m / s, such as 0.2 m / s, 0.3 m / s, 0.4 m / s, and 0.5 m / s; the injection force is 120–150 MPa, such as 120 MPa, 130 MPa, 140 MPa, and 150 MPa; and the injection time is 10–15 s, such as 11 s, 12 s, 13 s, 14 s, and 15 s.

[0061] Appropriate injection speed ensures smooth flow of molten aluminum alloy, facilitates venting, and reduces porosity and inclusions inside the casting. If the injection speed is too fast, a large amount of gas may be entrained in the molten aluminum, leading to defects such as porosity in the casting. Appropriate injection pressure promotes the filling and feeding of molten aluminum, reduces porosity and shrinkage defects in the casting, and improves the density of the casting. Insufficient injection pressure will prevent the molten aluminum from filling the mold cavity, while excessive injection pressure will lead to accelerated mold wear and cracks on the surface of the casting. Appropriate injection time ensures that the molten aluminum fully fills the mold cavity and receives good feeding, thereby reducing defects in the casting and improving the density and mechanical properties of the casting.

[0062] Furthermore, the aging process conditions described in step S4 are as follows: aging temperature 25-50℃, such as 25-30℃, 30-40℃, or 40-50℃, aging time 1-5 days, and air cooling.

[0063] It should be noted that the aging temperature of 25℃ is room temperature, i.e., natural aging; in order to shorten the production period, the material can be placed in a low-temperature furnace at no more than 50℃ to accelerate the aging process; through artificial aging or natural aging, some Zn will precipitate the MgZn2 phase formed by Zn and Mg elements, thereby improving the strength of the aluminum alloy.

[0064] The precipitation of the MgZn2 phase can be controlled by adjusting the aging temperature and time. When the aging temperature is low, the aging time can be appropriately extended, and when the aging temperature is high, the aging time can be shortened.

[0065] In summary, this invention enhances the strength of the alloy by introducing Mg and Zn elements for solid solution strengthening and precipitating MgZn2 during natural aging. Furthermore, the addition of appropriate amounts of RE elements further refines the grain size, resulting in a high-strength aluminum alloy material that can be obtained through natural aging alone. By optimizing the alloy element composition, a high-strength and corrosion-resistant aluminum alloy is obtained, exhibiting a room temperature tensile strength >320 MPa, a yield strength >240 MPa, and an elongation after fracture >11%. Finally, the use of extrusion casting further improves the alloy's strength by producing castings with a denser microstructure and finer grains.

[0066] The following examples and comparative examples demonstrate the performance of aluminum alloy products prepared by different casting processes.

[0067] Example 1

[0068] This embodiment provides a heat-free aluminum alloy and its extrusion casting preparation method.

[0069] The chemical composition and mass percentage of the aluminum alloy are as follows: Mg 3.0%, Mn 1.2%, Zn 0.8%, RE 0.1%, individual impurities ≤0.05%, total impurities ≤0.15%, and the balance is Al, as shown in Table 1.

[0070] The preparation steps are as follows:

[0071] S1: Ingredients: Weigh out pure Al, rare earth RE (a mixture of La and Ce), pure Mg, Al-10Mn master alloy, and Al-60Zn master alloy as raw materials according to the mass percentage of each element.

[0072] S2a: Pure Al and rare earth RE (a mixture of La and Ce) are melted at 780-790℃, and Al-10Mn master alloy and Al-60Zn master alloy are added in sequence. After all the alloy is melted, it is kept at the temperature for 30 minutes to obtain a primary smelting liquid.

[0073] S2b: Cool the primary molten liquid to 680-700℃, add pure Mg wrapped in aluminum foil, stir after it is completely melted, and keep it at the temperature for 20 minutes to obtain the secondary molten liquid;

[0074] S2c: Add 55% sodium chloride (NaCl) and 45% potassium chloride (KCl) composite inorganic salt to the secondary smelting liquid as a slag remover and keep it at a constant temperature for 20 minutes. Then, argon gas is introduced for refining and degassing. After standing for 30 minutes, the slag is removed to obtain the aluminum alloy smelting liquid.

[0075] S3: Extrusion casting: Extrusion casting is carried out at an aluminum alloy melt temperature of 750℃ and a mold temperature of 270℃ to obtain a cast rod;

[0076] The extrusion process parameters are as follows: injection speed is 0.3 m / s, injection force is 120 MPa, and injection time is 15 s.

[0077] S4: Aging treatment: The casting rod obtained in step S3 is subjected to aging treatment at an aging temperature of 40-50℃ for 1 day, followed by air cooling to obtain the aluminum alloy product.

[0078] The properties of the obtained aluminum alloy products are shown in Table 2.

[0079] Example 2

[0080] This embodiment provides a heat-free aluminum alloy and its extrusion casting preparation method.

[0081] The chemical composition and mass percentage of the aluminum alloy are as follows: Mg 3.2%, Mn 1.2%, Zn 0.8%, RE 0.1%, individual impurities ≤0.05%, total impurities ≤0.15%, and the balance is Al, as shown in Table 1.

[0082] The preparation steps and conditions are the same as in Example 1.

[0083] The properties of the obtained aluminum alloy products are shown in Table 2.

[0084] Example 3

[0085] This embodiment provides a heat-free aluminum alloy and its extrusion casting preparation method.

[0086] The chemical composition and mass percentage of the aluminum alloy are as follows: Mg 3.5%, Mn 1.2%, Zn 0.8%, RE 0.1%, individual impurities ≤0.05%, total impurities ≤0.15%, and the balance is Al, as shown in Table 1.

[0087] The preparation steps and conditions are the same as in Example 1.

[0088] The properties of the obtained aluminum alloy products are shown in Table 2.

[0089] Example 4

[0090] This embodiment provides a heat-free aluminum alloy and its extrusion casting preparation method.

[0091] The chemical composition and mass percentage of the aluminum alloy are as follows: Mg 3.2%, Mn 1.2%, Zn 1.0%, RE 0.1%, individual impurities ≤0.05%, total impurities ≤0.15%, and the balance is Al, as shown in Table 1.

[0092] The preparation steps and conditions are the same as in Example 1.

[0093] The properties of the obtained aluminum alloy products are shown in Table 2.

[0094] Example 5

[0095] This embodiment provides a heat-free aluminum alloy and its extrusion casting preparation method.

[0096] The chemical composition and mass percentage of the aluminum alloy are as follows: Mg 3.2%, Mn 1.2%, Zn 1.2%, RE 0.1%, individual impurities ≤0.05%, total impurities ≤0.15%, and the balance is Al, as shown in Table 1.

[0097] The preparation steps and conditions are the same as in Example 1.

[0098] The properties of the obtained aluminum alloy products are shown in Table 2.

[0099] Example 6

[0100] This embodiment provides a heat-free aluminum alloy and its extrusion casting preparation method.

[0101] The chemical composition of the aluminum alloy is the same as that in Example 4, and the main preparation steps and conditions are the same as those in Example 1. The difference is that the extrusion casting process parameters are different.

[0102] The extrusion process parameters are: injection speed of 0.5 m / s, injection force of 150 MPa, and injection time of 15 s;

[0103] The properties of the obtained aluminum alloy products are shown in Table 2.

[0104] Example 7

[0105] This embodiment provides a heat-free aluminum alloy and its extrusion casting preparation method.

[0106] The chemical composition of the aluminum alloy is the same as that in Example 4, and the main preparation steps and conditions are the same as those in Example 1. The difference is that the aging process parameters are different.

[0107] Aging temperature 25-30℃, aging time 3 days, air cooling.

[0108] The properties of the obtained aluminum alloy products are shown in Table 2.

[0109] Comparative Example 1

[0110] This embodiment provides a heat-free aluminum alloy and its gravity preparation method.

[0111] The chemical composition and mass percentage of the aluminum alloy are as follows: Mg 3.2%, Mn 1.2%, Zn 1.0%, RE 0.1%, individual impurities ≤0.05%, total impurities ≤0.15%, and the balance is Al, as shown in Table 1.

[0112] The preparation steps are as follows:

[0113] S1: Ingredients: Weigh out pure Al, rare earth RE (a mixture of La and Ce), pure Mg, Al-10Mn master alloy, and Al-60Zn master alloy as raw materials according to the mass percentage of each element.

[0114] S2: The raw materials are smelted to obtain an aluminum alloy molten liquid. Specifically, the smelting process involves melting pure Al and rare earth RE (a mixture of La and Ce) at 790℃, then sequentially adding Al-10Mn master alloy and Al-60Zn master alloy. After complete melting, the mixture is held at this temperature for 30 minutes to obtain a primary molten liquid. Subsequently, the molten liquid is cooled to 700℃, and pure Mg wrapped in aluminum foil is added. After complete melting, the mixture is stirred and held at this temperature for 20 minutes to obtain a secondary molten liquid. Then, a slag remover is added and the mixture is held at this temperature for 20 minutes, while argon gas is introduced for refining and degassing. After standing for 30 minutes, the slag is removed to obtain a tertiary molten liquid.

[0115] S3: Gravity casting: The temperature of the molten aluminum is 750℃, and the temperature of the mold is 260℃;

[0116] S4: Aging treatment: The obtained material is subjected to aging treatment at an aging temperature of 40-50℃ for 1-2 days to obtain the aluminum alloy.

[0117] The properties of the obtained aluminum alloy products are shown in Table 2.

[0118] Comparative Example 2

[0119] This embodiment provides a heat-free aluminum alloy and its gravity preparation method.

[0120] The chemical composition and mass percentage of the aluminum alloy are as follows: Mg 3.2%, Mn 1.2%, Zn 1.0%, RE 0%, individual impurities ≤0.05%, total impurities ≤0.15%, and the balance is Al, as shown in Table 1.

[0121] The preparation steps and conditions were the same as those in Comparative Example 1.

[0122] The properties of the obtained aluminum alloy products are shown in Table 2.

[0123] Table 1 Alloy composition table for examples and comparative examples

[0124] No. Mg Mn Zn RE Al Example 1 3.0 1.2 0.8 0.1 Balance Example 2 3.2 1.2 0.8 0.1 Balance Example 3 3.5 1.2 0.8 0.1 Balance Example 4 3.2 1.2 1.0 0.1 Balance Example 5 3.2 1.2 1.2 0.1 Balance Example 6 3.2 1.2 1.0 0.1 Balance Example 7 3.2 1.2 1.0 0.1 Balance Comparative Example 1 3.2 1.2 1.0 0.1 Balance Comparative Example 2 3.2 1.2 1.0 - Balance

[0125] Table 2. Performance Comparison of Examples and Comparative Examples

[0126] Example Tensile strength (MPa) Yield strength (MPa) Elongation at break (%) Example 1 335 261 14.3 Example 2 358 278 12.9 Example 3 346 242 11.6 Example 4 372 289 13.5 Example 5 361 274 12.4 Example 6 375 248 12.1 Example 7 322 246 11.3 Comparative Example 1 206 163 6.8 Comparative Example 2 188 142 7.2

[0127] The aluminum alloy obtained through the above steps has room temperature mechanical properties as shown in Table 2, which were measured according to the national standard GB / T228.1-2010 Metallic Materials - Room Temperature Tensile Test.

[0128] Data comparison shows that the mechanical properties of the aluminum alloys prepared by the preparation method disclosed in this invention in Examples 1-7 are significantly improved compared with those prepared by the prior art in Comparative Examples 1-2.

[0129] Examples 1-3 are identical except for the Mg content. As the Mg content increases, the mechanical properties of the alloy first increase and then decrease. Mg will form the MgZn2 phase with Zn, which will improve the mechanical properties of the alloy. However, the addition of Mg will also reduce the fluidity of the alloy, making it easy to produce casting defects, resulting in a decrease in mechanical properties and a decrease in elongation after fracture.

[0130] Examples 2, 4, and 5 are identical except for the Zn content. As the Zn content increases, the mechanical properties of the alloy first increase and then decrease. Zn will form the MgZn2 phase with Mg, which will improve the mechanical properties of the alloy. However, the addition of excessive Zn will lead to a decrease in mechanical properties and also a decrease in the corrosion resistance of the alloy.

[0131] Examples 4, 6, and 7 have the same alloy composition but different preparation processes. In Example 6, the injection speed and injection force during extrusion casting are higher than those in Example 4. As shown in Table 2, the mechanical properties of the products from both examples are similar. In Example 7, the aging temperature is lower than that of Example 4, so the aging time needs to be extended appropriately. The mechanical properties of the product from Example 7 are still slightly lower than those from Example 4.

[0132] Example 4 and Comparative Example 1 have the same alloy composition but different preparation processes. The alloy prepared by the squeeze casting process in Example 4 has significantly improved mechanical properties compared to the alloy prepared by gravity casting in Comparative Example 1. Figure 1 , Figure 2 The images shown are SEM microstructure diagrams of Example 4 and Comparative Example 1 of the present invention, respectively. As can be seen from the SEM image of Example 4, the aluminum alloy material prepared therefrom has a denser microstructure than that of Comparative Example 1, with no casting defects such as shrinkage cavities, and the grains are finer. Higher performance materials can be obtained through extrusion casting process.

[0133] Comparative Examples 1 and 2: Comparative Example 1 included RE elements, while Comparative Example 2 did not. Figure 2 , Figure 3 The images shown are SEM microstructure diagrams of Comparative Example 1 and Comparative Example 2 of this invention. Compared with Comparative Example 2, Comparative Example 1 still has some casting defects, but due to the addition of mixed rare earth element RE, Comparative Example 1 has fewer defects and finer grains. Therefore, Comparative Example 2 has lower performance, indicating that RE element plays a role in refining grains and improving alloy strength.

[0134] In summary, this invention enhances the strength of the alloy by introducing Mg and Zn elements for solid solution strengthening and precipitating MgZn2 during natural aging. Furthermore, the addition of appropriate amounts of RE elements further refines the grain size, allowing for the production of high-strength aluminum alloys through natural aging alone. By optimizing the alloy element composition, a high-strength aluminum alloy with excellent corrosion resistance is obtained, exhibiting a room temperature tensile strength >320 MPa, a yield strength >240 MPa, and an elongation after fracture >11%. Finally, the use of extrusion casting further improves the alloy's strength by producing castings with a denser microstructure and finer grains.

[0135] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A heat-treat-free aluminum alloy characterized by, The components are in mass percentage: Mg: 2.5~3.5%, Mn: 0.8~1.5%, Zn: 1.0~1.2%, RE: 0.05~0.3%, single impurity ≤0.05%, total impurities ≤0.15%, the balance being Al; The aluminum alloy preparation method comprises the following steps: S1: batching: according to the mass percentage of the designed elements of the aluminum alloy, the raw materials are weighed; S2: the raw materials are melted to obtain an aluminum alloy melting liquid; S2a: after the pure Al and the rare earth RE are melted at 780~800℃, the Al-10Mn intermediate alloy and the Al-60Zn intermediate alloy are sequentially added, after complete melting, the temperature is kept for 30min to obtain a primary melting liquid; S2b: the primary melting liquid is cooled to 680~700℃, the pure Mg wrapped by aluminum foil is added, after complete melting, the temperature is kept for 20min to obtain a secondary melting liquid; S2c: the secondary melting liquid is added with a deslagging agent and kept for 20min, and argon is introduced for refining and degassing, and after standing for 30min~60min, the slag is removed to obtain the aluminum alloy melting liquid; S3: extrusion casting; the aluminum alloy melting liquid obtained in step S2 is extrusion cast into a casting rod at a certain temperature; during the extrusion casting, the temperature of the aluminum alloy melting liquid is 740~780℃, and the mold temperature is 250~280℃; The injection speed is 0.2~0.5m / s, which ensures the smooth flow of the aluminum alloy melting liquid, is beneficial to exhaust, and reduces the pores and inclusions in the casting; The injection force is 120~150MPa, which promotes the filling and shrinkage of the aluminum liquid, reduces the pores and shrinkage defects in the casting, and improves the compactness of the casting; The injection time is 10~15s, which ensures the sufficient filling of the aluminum liquid in the cavity and good shrinkage, thereby reducing the defects in the casting and improving the compactness and mechanical properties of the casting; S4: aging treatment, so that part of the Zn and the Mg element form MgZn2 phase and precipitate, and the aluminum alloy product is obtained; The aluminum alloy product has a room temperature tensile strength of >320MPa, a yield strength of >240MPa, and an elongation after fracture of >11%.

2. A method of producing a heat-treatable aluminium alloy by extrusion casting for producing the aluminium alloy of claim 1, characterised in that, Comprise the following steps: S1: batching: according to the mass percentage of the designed elements of the aluminum alloy, the raw materials are weighed; S2: the raw materials are melted to obtain an aluminum alloy melting liquid; S2a: after the pure Al and the rare earth RE are melted at 780~800℃, the Al-10Mn intermediate alloy and the Al-60Zn intermediate alloy are sequentially added, after complete melting, the temperature is kept for 30min to obtain a primary melting liquid; S2b: the primary melting liquid is cooled to 680~700℃, the pure Mg wrapped by aluminum foil is added, after complete melting, the temperature is kept for 20min to obtain a secondary melting liquid; S2c: the secondary melting liquid is added with a deslagging agent and kept for 20min, and argon is introduced for refining and degassing, and after standing for 30min~60min, the slag is removed to obtain the aluminum alloy melting liquid; S3: extrusion casting; the aluminum alloy melting liquid obtained in step S2 is extrusion cast into a casting rod at a certain temperature; during the extrusion casting, the temperature of the aluminum alloy melting liquid is 740~780℃, and the mold temperature is 250~280℃; The injection speed is 0.2-0.5 m / s, which ensures the stable flow of the aluminum alloy smelting liquid, is beneficial to exhaust, and reduces the pores and inclusions in the castings; The injection force is 120-150 MPa, which promotes the filling and shrinkage of the aluminum liquid, reduces the pores and shrinkage defects in the castings, and improves the compactness of the castings; The injection time is 10-15 s, which ensures the sufficient filling of the aluminum liquid in the cavity and good shrinkage, thereby reducing the defects in the castings and improving the compactness and mechanical properties of the castings; S4: aging treatment, part of Zn will form MgZn2 phase with Mg element, and an aluminum alloy product is obtained.

3. The preparation method according to claim 2, characterized in that, In step S1, the raw materials are pure Mg, Al-10Mn intermediate alloy, Al-60Zn intermediate alloy, and rare earth RE.

4. The preparation method according to claim 2, characterized in that, In step S2, the smelting process comprises: S2a: after melting pure Al and rare earth RE at 780-800℃, sequentially adding Al-10Mn intermediate alloy and Al-60Zn intermediate alloy, and after complete melting, keeping warm for 30 min, a primary smelting liquid is obtained; S2b: cooling the primary smelting liquid to 680-700℃, adding pure Mg wrapped with aluminum foil, after complete melting, stirring, and keeping warm for 20 min, a secondary smelting liquid is obtained; S2c: adding a deslagging agent to the secondary smelting liquid, keeping warm for 20 min, and refining and degassing by argon blowing, and after standing for 30-60 min, slagging, an aluminum alloy smelting liquid is obtained.

5. The preparation method according to claim 2, characterized in that, The extrusion casting process in step S3 is to extrusion cast the aluminum alloy smelting liquid obtained in step S2 into a cast rod at a certain temperature.

6. The preparation method according to claim 5, characterized in that, During extrusion casting, the temperature of the aluminum alloy smelting liquid is 740-780℃, and the mold temperature is 250-280℃.

7. The preparation method according to claim 5, characterized in that, During extrusion casting, the injection speed is 0.2-0.5 m / s, the injection force is 120-150 MPa, and the injection time is 10-15 s.

8. The preparation method according to claim 2, characterized in that, The process conditions of the aging treatment in step S4 are: aging temperature 25-50℃, aging time 1-5 days, and air cooling.

9. The preparation method according to claim 4, characterized in that, The deslagging agent is a composite inorganic salt.

10. The method of claim 2, wherein, The aluminum alloy product has a room temperature tensile strength of >320 MPa, a yield strength of >240 MPa, and an elongation after fracture of >11%.

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