A heat-treatment-free high-strength and tough Al-Zn-Si-Ce die-casting aluminum alloy, its preparation method and uses

Abstract

The present invention discloses a heat - treatment - free high - strength and tough Al - Zn - Si - Ce die - casting aluminum alloy, its preparation method and uses, relating to the field of die - casting aluminum alloys. The heat - treatment - free high - strength and tough Al - Zn - Si - Ce die - casting aluminum alloy is composed of 7.0% - 12.5% Si, 6.5% - 13% Zn, 0.8% - 1.9% Mg, 1.2% - 2.0% Cu, 0.12% - 0.95% Ce, 0.2% - 1.0% Mn, 0.1% - 1.0% Fe, Sm ≤ 0.95%, Nb ≤ 0.6%, 0.01% - 0.1% Ti, and the balance Al and other impurities; Mn + Fe: ≥ 0.6%, and the content of other impurities ≤ 0.2%. The heat - treatment - free high - strength and tough Al - Zn - Si - Ce die - casting aluminum alloy of the present application does not require high - temperature heat treatment for strengthening, has a short process, high efficiency, low cost, less carbon emissions, excellent environmental protection, meets the die - casting process forming requirements of complex thin - wall components, has a yield strength ≥ 285 MPa and an elongation ≥ 2.5% under as - cast conditions. The high - strength and tough characteristics bring higher structural safety and provide a new solution for the lightweight upgrading of the industry.

Description

Technical Field

[0001] The present invention relates to the field of die-casting aluminum alloys, and in particular to a heat-treatment-free high-strength and high-toughness Al-Zn-Si-Ce die-casting aluminum alloy, a preparation method thereof, and uses thereof. Background Art

[0002] Aluminum alloy materials have low density and high strength, and are widely used in fields such as 3C electronic consumer products, new energy vehicles, and rail transit. They are one of the important directions for industrial lightweighting, energy conservation, and emission reduction.

[0003] Die-casting aluminum alloy is a one-time net forming process with a short process and high efficiency, and recycled materials can be used, meeting the new environmental protection requirements of green and low-carbon. To achieve the goal of energy conservation and emission reduction, it is necessary to further improve the strength and toughness of die-casting aluminum alloy materials, reduce the amount of materials used, and lower carbon emissions without affecting the reliability of products.

[0004] Among them, Al-Si-based die-casting aluminum alloys are widely used in the preparation of die-castings due to their good casting performance and corrosion resistance. However, the mechanical properties of pure Al-Si-based alloys are relatively low. In scenarios with high structural mechanics requirements, it is necessary to use the T6 high-temperature heat treatment method to improve the strength of the materials. However, the solution quenching process at the T6 high temperature is a rapid cooling environment, and the products are prone to deformation and cannot meet the subsequent assembly requirements, resulting in low yield and high cost. At the same time, the T6 temperature is high, the energy consumption is high, which is not conducive to the requirements of energy conservation and emission reduction.

[0005] Therefore, in recent years, the development and research of heat-treatment-free high-strength and high-toughness alloys have become a hot topic. For example, in the patent application with the publication number of CN116121605A, a heat-treatment-free die-casting aluminum alloy for electric bicycles and a preparation method thereof are disclosed. The alloy includes Si: 7.0wt%-11.0wt%; Mg: 0.8-2.0wt%; Cu: 0.5-1.5wt%; Zn: 2.0-8.0wt%; B: 0.001wt%-0.20wt%; Ti: 0.05-0.2wt%; Mn: 0.1-0.8wt%; Fe: 0.05-0.8wt%; Sr: 0.005-0.5wt%; Zr: <0.1wt%; Cr: <0.1wt%; the sum of the weight percentages of the remaining impurities is controlled below 1.0wt%, and the balance is Al. The above die-casting aluminum alloy has a yield strength of 200-270MPa and an elongation of 2-5% without heat treatment, which preferably meets the production and safety requirements of electric bicycle calipers.

[0006] However, the above die-casting aluminum alloy that does not require heat treatment has a high Zn content. A high Zn content is prone to thermal cracking tendency and it is difficult to meet the die-casting forming requirements of thin-walled components with complex wall thickness changes. Therefore, developing a new type of die-casting aluminum alloy that does not require heat treatment strengthening, has higher strength and toughness, and lower thermal cracking tendency has great value for opening up new markets for die-casting alloys and enhancing the environmental protection competitiveness of enterprises. Summary of the Invention

[0007] In order to improve the problem in the related art that a die-casting aluminum alloy with a high Zn content is prone to thermal cracking tendency and it is difficult to meet the die-casting forming requirements of thin-walled components with complex wall thickness changes, the present application provides a heat-treatment-free high-strength and tough Al-Zn-Si-Ce die-casting aluminum alloy, its preparation method and uses.

[0008] The heat-treatment-free high-strength and tough Al-Zn-Si-Ce die-casting aluminum alloy provided by the present application adopts the following technical solution: A heat-treatment-free high-strength and tough Al-Zn-Si-Ce die-casting aluminum alloy is composed of the following components by weight percentage: Si: 7.0% - 12.5%;

[0009] Zn: 6.5% - 13%;

[0010] Mg: 0.8% - 1.9%;

[0011] Cu: 1.2% - 2.0%;

[0012] Ce: 0.12% - 0.95%;

[0013] Mn: 0.2% - 1.0%;

[0014] Fe: 0.1% - 1.0%;

[0015] Mn + Fe: ≥0.6%;

[0016] Sm: ≤0.95%;

[0017] Nb: ≤0.6%;

[0018] Ti: 0.01% - 0.1%;

[0019] The balance is Al and other impurities, wherein the content of other impurities ≤0.2%.

[0020] In this application, in the Al-Si alloy, by adding elements such as Zn, Mg, Cu, etc. to synergistically strengthen the alloy strength, the yield strength of the alloy can reach more than 290 MPa without heat treatment. At the same time, elements such as Ce are innovatively introduced to significantly refine the solidification structure, and the elongation of the alloy reaches more than 2.5%. The problems of high hot cracking tendency and poor formability caused by high Zn content are greatly improved, and a high-strength and tough die-casting aluminum alloy system with excellent fluidity is developed, which can meet the die-casting process forming requirements of complex thin-walled components with wall thickness changes and no hot cracks are generated. In addition, the high strength and toughness of the Al-Zn-Si-Ce die-casting aluminum alloy bring higher structural safety, which is suitable for the lightweight scenarios of load-bearing components such as the middle plate of 5G mobile phones, electric bicycles, and new energy vehicles, providing a new solution for the lightweight upgrade of the industry and having broad market application prospects.

[0021] The Al-Zn-Si-Ce die-casting aluminum alloy in this application can meet the die-casting process forming requirements of complex thin-walled components with wall thickness changes, specifically manifested as:

[0022] (1) During the processing, no marks are generated on the surface of the thin-walled component, no die-casting cracks are generated, there are few internal pores, and the mechanical properties are excellent;

[0023] (2) No hot cracks are generated at the wall thickness change.

[0024] It should be noted that:

[0025] In the complex thin-walled components with wall thickness changes mentioned in this application, the wall thickness change refers to the wall thickness of the thin-walled component changing from large to small or from small to large. Among them, the minimum wall thickness of the components that can be processed in this application can reach 0.45 mm, and the thickness ratio range of the wall thickness value in the larger wall thickness area to the wall thickness value in the adjacent smaller wall thickness area is 1-18.

[0026] The invention principle of the present invention is as follows:

[0027] The Si element undergoes a eutectic reaction with Al and has excellent solidification fluidity. However, too high Si content is likely to generate primary Si phase, which causes great damage to the toughness of the alloy. In this application, the content range of the Si element is selected to be 7.0% - 12.5%.

[0028] The solubility of Zn element in Al is extremely high. The size of Zn atoms is relatively large. Zn atoms dissolved in Al will cause lattice distortion of the matrix, resulting in a strong solid solution strengthening effect. With too high Zn content, although the alloy can have high strength, the elongation decreases significantly (≤1.5%), and the material is brittle with limited usage scenarios. Further, in this application, based on the Zn element, Mg and Cu elements are added jointly. By increasing the solubility of Mg and Cu elements in Al with the Zn element, while achieving high strength, the alloy maintains high toughness (≥2.5%). However, the melting point of Zn is low. When the Zn content in this application is higher than 13%, it will lead to an increase in the solidification range of the alloy and an increase in the hot cracking tendency of the alloy, unable to meet the structural design requirements of large and complex structures. Therefore, the content range of Zn element in this application is selected as 6.5% - 13%.

[0029] Ce element can combine with Zn to form AlCeZn compounds, reducing the content of Zn in the liquid phase, effectively reducing the problem of the increased solidification temperature range of the alloy caused by the high Zn content, and improving the hot cracking tendency of alloy solidification. At the same time, a large amount of latent heat is released during the above reaction process, which helps to improve the fluidity in the early stage of solidification and enhance the feeding capacity of the alloy melt, further reducing the hot cracking tendency. However, too much Ce will form relatively coarse AlCeZn compounds, blocking the flow of the alloy melt. In addition, due to the extremely low solubility of Ce in Al, even at high temperatures, it is basically insoluble in the Al matrix. Therefore, the crystal phase size of Ce is fine (the particle diameter of the precipitated phase is about 0.1 - 0.5 μm), and the phase structure is a face-centered cubic structure, the same as the matrix alloy, which has the effect of refining the grain structure and improving the toughness of the alloy. In this application, the content range of Ce element is 0.12 - 0.95%.

[0030] Mg element combines with Zn to form MgZn strengthening phases and combines with Si element to form MgSi strengthening phases, playing a major strengthening role. When the content of Mg element is too high, the strengthening phases coarsen, the strengthening effect decreases, and at the same time the elongation decreases significantly. Therefore, the content range of Mg element in this application is 0.8% - 1.9%.

[0031] Cu element combines with Al to form AlCu strengthening phases. When the Cu content is relatively low, it can improve the strength of the alloy, and at the same time the toughness does not decrease significantly. Based on this, the content range of Cu element in this application is 1.2% - 2.0%.

[0032] The Mn element and the Fe element mainly play a role in casting demoulding. Among them, the inventor found based on practical experience that when the sum of the contents of the two elements Mn and Fe ≥ 0.6%, the demoulding property of the alloy is good. At the same time, the Mn element can combine with Fe to form the AlMnFe phase, transform the acicular Fe phase into a short rod shape, and reduce the influence of the Fe element on toughness. However, if the Mn element is too high, it will form a massive AlMn phase with Al, split the matrix, and reduce the elongation. In addition, an excessive amount of the Fe element will reduce the toughness of the alloy. Therefore, it is necessary to control the content ranges of the Mn element and the Fe element not to exceed 1.0%.

[0033] The Nb element and the Sm element. The Nb element mainly plays a role in grain refinement and can further strengthen and purify the melt. It forms a nano-scale AlNb high-temperature phase with Al. The phase structures of the AlNb phase and the α-Al phase are both face-centered cubic types, and their lattice sizes are close, with high coherency. It is an excellent heterogeneous nucleation point for α-Al and can effectively refine the grains. The solubility of the Sm element in Al is low, which causes constitutional supercooling of the alloy, can refine the precipitation phases such as MgZn at the grain boundaries, and can further improve the toughness of the high-alloy content. In addition, the Sm element also has a certain promoting effect on the fluidity of the alloy. This mechanism may be related to the effect of the Sm element on reducing the eutectic temperature of the alloy. However, excessive Nb element and Sm element are likely to form coarse and brittle Al3Nb and Al3Sm phases, the refinement effect significantly decreases, and the elongation of the alloy decreases. Therefore, it is necessary to control the content of the Nb element not to exceed 0.6%, and the content of the Sm element not to exceed 0.95%.

[0034] The addition of the Ti element forms a Ti-rich environment, interacts with the Nb element, and improves the refinement effect. However, if the Ti element is too high, the generated TiAl3 phase is coarse, resulting in a reduction in elongation. Therefore, it is necessary to control the content of the Ti element not to exceed 0.1%.

[0035] Among them, the weight percentage of the Si includes but is not limited to: 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, 10.5%, 11.0%, 11.5%, 12.0%, 12.5%, and is further preferably 9.5% - 11.5%.

[0036] The weight percentage of the Zn includes but is not limited to: 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, 10.5%, 11.0%, 11.5%, 12.0%, 12.5%, 13%, and is further preferably 8.0% - 10.0%.

[0037] The weight percentage of Ce includes, but is not limited to: 0.12%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, and is further preferably 0.15% - 0.60%.

[0038] The weight percentage of Mg includes, but is not limited to: 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, and is further preferably 1.3% - 1.7%.

[0039] The weight percentage of Cu includes, but is not limited to: 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, and is further preferably 1.5% - 1.8%.

[0040] The weight percentage of Mn includes, but is not limited to: 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, and is further preferably 0.3% - 0.7%.

[0041] The weight percentage of Fe includes, but is not limited to: 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, and is further preferably 0.1% - 0.6%.

[0042] The weight percentage of Sm includes, but is not limited to: 0%, 0.15%, 0.25%, 0.35%, 0.45%, 0.55%, 0.65%, 0.75%, 0.85%, 0.95%, and is further preferably 0.08% - 0.45%, such as: 0.08%, 0.18%, 0.28%, 0.38%, 0.45%.

[0043] The weight percentage of Nb includes, but is not limited to: 0%, 0.05%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, and is further preferably 0.05% - 0.26%, such as: 0.05%, 0.10%, 0.15%, 0.20%, 0.26%.

[0044] The weight percentage of Ti includes but is not limited to: 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, and is further preferably 0.02% - 0.07%.

[0045] Preferably, the weight percentage of Si is 9.5% - 11.5%, the weight percentage of Zn is 8.0% - 10.0%, the weight percentage of Mg is 1.3% - 1.7%, the weight percentage of Cu is 1.5% - 1.8%, and the weight percentage of Ce is 0.15% - 0.60%.

[0046] Preferably, the weight percentage of Mn is 0.3% - 0.7%, and the weight percentage of Fe is 0.1% - 0.6%.

[0047] When the weight percentages of Mn element and Fe element are within this range, it can not only effectively improve the demolding performance but also effectively reduce the influence of Fe element on the toughness of the alloy.

[0048] Preferably, the weight percentage of Sm is 0.08% - 0.45%; the weight percentage of Nb is 0.05% - 0.26%.

[0049] When the weight percentages of Sm element and Nb element are within this range, the combination of the two is beneficial to further improve the toughness of the alloy.

[0050] In a second aspect, a preparation method of a heat - treatment - free high - strength and high - toughness Al - Zn - Si - Ce die - casting aluminum alloy provided by the present application adopts the following technical solution:

[0051] A preparation method of a heat - treatment - free high - strength and high - toughness Al - Zn - Si - Ce die - casting aluminum alloy includes the following steps:

[0052] Raw material preparation: Prepare each raw material according to the element composition ratio of the die - casting aluminum alloy;

[0053] Alloying: Melt each raw material evenly to obtain an alloy melt;

[0054] Degassing and filtering: Add a refining agent and a grain refiner to the alloy melt, stir for degassing, skim the slag and filter after standing to obtain a purified alloy melt;

[0055] Die - casting forming: Carry out die - casting forming on the purified alloy melt to obtain a die - casting aluminum alloy.

[0056] Optionally, the raw materials include pure Al ingots, pure Mg ingots, pure Zn ingots, Al - Sm master alloys, Al - Nb master alloys, Al - Ce master alloys, Al - Cu master alloys, Al - Mn master alloys, and elemental silicon.

[0057] In this application, Sm element, Nb element, Ce element, Cu element, and Mn element are preferably added using their respective aluminum alloys, which is beneficial to ensure the full melting and uniform dispersion of Sm element, Nb element, Ce element, Cu element, and Mn element.

[0058] Optionally, the alloying includes the following steps:

[0059] Melting pure Al ingots in a melting furnace, and maintaining the temperature at 710 - 730 °C until the pure Al ingots are completely melted to obtain a first melt;

[0060] Adding Al-Sm master alloy, Al-Nb master alloy, elemental silicon, pure Zn ingots, Al-Cu master alloy, and Al-Mn master alloy to the first melt, and maintaining the temperature at 710 - 730 °C until all the above raw materials are melted to obtain a second melt;

[0061] Pressing pure Mg ingots into the second melt, and maintaining the temperature at 710 - 730 °C until the pure Mg ingots are completely melted to obtain an alloy melt.

[0062] Different from the preparation methods of existing die-casting aluminum alloys, the high-strength and tough Al-Zn-Si-Ce die-casting aluminum alloy in this application does not require T6 high-temperature heat treatment strengthening during preparation, the production process is simpler, and at the same time, the yield rate of die-cast products can be improved.

[0063] Optionally, in the degassing and filtering step, the addition amount of the refining agent is 0.1 - 0.3% of the total mass of the alloy melt; the addition amount of the grain refiner is 0.01 - 0.05% of the total mass of the alloy melt.

[0064] Optionally, the refining agent uses hexachloroethane, and the grain refiner selects Al-Ti-B grain refiner.

[0065] Optionally, in the die-casting forming step, the temperature of the purified alloy melt is 680 - 720 °C, the mold temperature is 220 - 240 °C, the injection speed is 2 - 4 m / s, and the injection pressure is 95 - 105 bar.

[0066] In the third aspect, the present application provides a use of a heat-treatment-free high-strength and tough Al-Zn-Si-Ce die-casting aluminum alloy for preparing thin-walled components with wall thickness changes, bicycle load-bearing structural components, and automobile load-bearing structural components.

[0067] The yield strength of the heat-treatment-free high-strength and tough Al-Zn-Si-Ce die-casting aluminum alloy in this application reaches over 290 MPa, the elongation rate reaches over 2.5%, and it has excellent fluidity. It can meet the die-casting process forming requirements of complex thin-walled components with wall thickness changes, and is suitable for the lightweight scenario requirements of load-bearing components such as the middle plate of 5G mobile phones, electric bicycles, and new energy vehicles, having broad market application prospects.

[0068] In summary, this application at least includes the following beneficial technical effects:

[0069] In the Al-Si alloy of this application, by adding elements such as Zn, Mg, and Cu to synergistically strengthen the alloy strength, the yield strength of the alloy can reach over 290 MPa without heat treatment. At the same time, elements such as Ce are innovatively introduced to significantly refine the solidification structure, and the elongation rate of the alloy reaches over 2.5%. The problems of high hot cracking tendency and poor formability caused by high Zn content are greatly improved, and a high-strength and tough die-casting aluminum alloy system with excellent fluidity is developed, which can meet the die-casting process forming requirements of complex thin-walled components with wall thickness changes and has no thermal cracks. In addition, the high strength and toughness of the Al-Zn-Si-Ce die-casting aluminum alloy bring higher structural safety, are suitable for the lightweight scenario requirements of load-bearing components such as the middle plate of 5G mobile phones, electric bicycles, and new energy vehicles, provide a new solution for the lightweight upgrade of the industry, and have broad market application prospects. Description of the Drawings

[0070] Figure 1 It is the metallographic structure diagram of the die-casting aluminum alloy in Example 2.

[0071] Figure 2 It is the product made of the die-casting aluminum alloy in Example 2.

[0072] Figure 3 It is the metallographic structure diagram of the die-casting aluminum alloy in Comparative Example 1.

[0073] Figure 4 It is the product made of the die-casting aluminum alloy in Comparative Example 1. Detailed Description of the Invention

[0074] The following further details this application with specific experiments in conjunction with the drawings.

[0075] Examples

[0076]

Examples 1-4

[0077] A heat-treatment-free high-strength and tough Al-Zn-Si-Ce die-casting aluminum alloy, and the composition of each component is as shown in Table 1 below:

[0078] Table 1 Composition of the die-casting aluminum alloy in Examples 1-4

[0079]

[0080] In the above Examples 1-4, a preparation method of a heat-treatable high-strength and high-toughness Al-Zn-Si-Ce die-casting aluminum alloy includes the following steps:

[0081] Step A, raw material preparation: Prepare pure Al ingots, pure Mg ingots, pure Zn ingots, Al-Sm master alloy, Al-Nb master alloy, Al-Ce master alloy, Al-Cu master alloy, Al-Mn master alloy, Al-Ti-B master alloy and elemental silicon as raw materials according to the elemental composition ratio of the die-casting aluminum alloy;

[0082] Step B, alloying: Melt the pure Al ingots in a melting furnace, keep them at 720 °C for 2 h, then add Al-Sm master alloy, Al-Nb master alloy, elemental silicon, pure Zn ingots, Al-Cu master alloy, Al-Mn master alloy, keep them at 720 °C for 30 min. After all the above raw materials are melted, press in the pure Mg ingots and keep them at 720 °C for 20 min until the pure Mg ingots are completely melted to obtain an alloy melt;

[0083] Step C, degassing and filtering: Add a refining agent and an Al-Ti-B grain refiner to the melting furnace. The addition amount of the refining agent is 0.2% of the total mass of the alloy melt, and the addition amount of the grain refiner is 0.03% of the total mass of the alloy melt. Stir for degassing, skim the slag and filter after standing;

[0084] Step D, die-casting forming: Use a 300T die-casting machine to carry out die-casting forming on the alloy melt. The temperature of the alloy melt during die-casting forming is kept at 680 °C, the mold temperature is 230 °C, the injection speed is 3 m / s, and the injection pressure is 100 bar to obtain a heat-treatable high-strength and high-toughness Al-Zn-Si-Ce die-casting aluminum alloy.

[0085] Comparative examples

[0086]

Comparative Examples 1-4

[0087] A die-casting aluminum alloy, and the composition of each component is as shown in Table 2 below:

[0088] Table 2 Composition of the die-casting aluminum alloy in Comparative Examples 1-4

[0089]

[0090] The preparation methods of the die-casting aluminum alloys in Comparative Examples 1-4 are also the same as those of the die-casting aluminum alloy in Example 2.

[0091] Performance detection test

[0092] 1. Design the die-casting mold and the size of the tensile bar according to the A-type tensile specimen in GB / T 13822-2017. The diameter of the tensile bar is Φ6.4mm. Then, refer to GB / T 228.1-2010 to test the yield strength and elongation of each tensile bar specimen made of die-cast aluminum alloy in the use examples and comparative examples, and record the results in Table 3 below.

[0093] 2. Use the die-cast aluminum alloy in each example and comparative example to prepare the products shown in Figure 2 、 Figure 4 by the same process, and observe whether there are thermal cracks at the positions where the thickness changes. Among them, there are rib positions on the back of the product, and the setting of the rib positions causes thickness changes in the product. At the positions where the thickness changes, thermal cracks are likely to occur due to the drastic change in thickness.

[0094] Table 3 Mechanical properties and thermal cracking tendency of die-cast aluminum alloy in each example and comparative example

[0095]

[0096] In Examples 1-4, due to the combined strengthening of Zn, Mg, and Cu elements, and the addition of Ce element, the yield strength of the alloy is ≥290 Mpa, the elongation is ≥2.5%, and the alloy has good fluidity and low thermal cracking tendency. Among them, compared with Example 1, in Example 2, Nb and Sm are added in trace amounts on the basis of Example 1. Combining the data in Table 3, it can be seen that the elongation of the die-cast aluminum alloy is improved while the strength remains basically unchanged. In Examples 3 and 4, due to the increase in Zn element and the adjustment of Mg and Cu elements, the strength of the alloy is increased to a certain extent. At the same time, the increase in Ce element content can improve the thermal cracking tendency caused by high Zn content.

[0097] In Comparative Example 1, the addition of Ce element is omitted on the basis of Example 2. Combining the data in Table 3, it can be seen that due to the lack of the refinement effect of Ce element, both the yield strength and elongation of the alloy decrease significantly. At the same time, the thermal cracking tendency of the alloy increases, which is likely to cause cracking during the forming of complex thin-walled components with wall thickness changes.

[0098] In Comparative Example 2, the addition of Mg element is omitted on the basis of Example 2. At the same time, to keep the strength of the alloy above 285 MPa, the contents of Zn element and Cu element are increased. Combining the data in Table 3, it can be seen that when the alloy lacks Mg element and the contents of Zn element and Cu element are increased simultaneously to make the strength of the alloy reach above 285 Mpa, the elongation of the alloy decreases significantly, and the brittleness of the die-cast product is too high to meet the requirements, and it cannot meet the forming requirements of complex thin-walled components with wall thickness changes.

[0099] Comparative Example 3: On the basis of Example 2, the addition of Zn element was omitted. At the same time, in order to maintain the alloy strength above 285 MPa, the contents of Mg and Cu elements were appropriately increased. Combining the data in Table 3, it can be seen that since the alloy does not contain Zn element, the hot cracking tendency of the alloy is small. However, under the condition that the strength of the alloy meets the basic requirements, the elongation rate has a large gap with the target value of 2.5%, and it is difficult to meet the requirements of the lightweight scenario.

[0100] Comparative Example 4: On the basis of Example 4, the Cu element was omitted. At the same time, in order to maintain the alloy strength above 285 MPa, the contents of Zn and Mg elements were appropriately increased on the basis of Example 4 to make up for the strength loss, but the elongation rate still did not meet the mechanical requirement of ≥2.5%. Due to the excessive Zn element content in Comparative Example 2 and Comparative Example 4, the alloy has a slight hot cracking tendency.

[0101] In addition, from Figure 1 it can be seen that the dendritic structure of the metallographic structure in Example 2 was significantly refined, the dendrite length was greatly shortened, which significantly improved the fluidity of the alloy and had a small hot cracking tendency. From Figure 2 it can be seen that the die-cast product prepared in Example 2 had good forming, and no hot cracks occurred under the same forming conditions.

[0102] From Figure 3 it can be seen that obvious dendritic structures can be seen in the metallographic structure of Comparative Example 1. The dendritic structure is large in size and has an obvious influence on the fluidity of the alloy. From Figure 4 it can be seen that under the same forming conditions, there are hot cracks at the thickness change of the die-cast product prepared in Comparative Example 1, that is, the formability of the die-cast aluminum alloy product in Comparative Example 1 is poor.

[0103] This specific embodiment is only an interpretation of the present application, and it does not limit the present application. After reading this specification, those skilled in the art can make modifications without creative contributions to this specific embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A heat-treatment-free high-strength and high-toughness Al-Zn-Si-Ce die-casting aluminum alloy, characterized in that: Consisting of the following components by weight percentage as follows: Si: 7.0% - 12.5%; Zn: 6.5% - 13%; Mg: 0.8% - 1.9%; Cu: 1.2% - 2.0%; Ce: 0.12% - 0.95%; Mn: 0.2% - 1.0%; Fe: 0.1% - 1.0%; Mn + Fe: ≥0.6%; Sm: 0.08% - 0.45%; Nb: 0.05% - 0.26%; Ti: 0.01% - 0.1%; The balance is Al and other impurities, wherein the content of other impurities ≤0.2%; Among them, the yield strength of the heat - treatable - free high - strength and tough Al - Zn - Si - Ce die - casting aluminum alloy reaches above 290 MPa, and the elongation rate reaches above 2.5%.

2. The heat-treatment-free high-strength and high-toughness Al-Zn-Si-Ce die-casting aluminum alloy according to claim 1, characterized in that: The weight percentage of said Si is 9.5% - 11.5%, the weight percentage of said Zn is 8.0% - 10.0%, the weight percentage of said Mg is 1.3% - 1.7%, the weight percentage of said Cu is 1.5% - 1.8%, and the weight percentage of said Ce is 0.15% - 0.60%.

3. The heat-treatment-free high-strength and high-toughness Al-Zn-Si-Ce die-casting aluminum alloy according to claim 1, characterized in that: The weight percentage of said Mn is 0.3% - 0.7%, and the weight percentage of said Fe is 0.1% - 0.6%.

4. The heat-treatment-free high-strength and high-toughness Al-Zn-Si-Ce die-casting aluminum alloy according to claim 1, characterized in that: The weight percentage of said Ti is 0.02% - 0.07%.

5. A preparation method of the heat-treatment-free high-strength and high-toughness Al-Zn-Si-Ce die-casting aluminum alloy according to any one of claims 1-4, characterized in that: Including the following steps: Raw material preparation: Prepare each raw material according to the elemental composition ratio of the die - casting aluminum alloy; Alloying: Melt each raw material evenly to obtain an alloy melt; Degassing and filtering: Add a refining agent and a grain refiner to the alloy melt, stir to remove gas, skim the slag and filter after standing to obtain a purified alloy melt; Die - casting forming: Carry out die - casting forming on the purified alloy melt to obtain a die - casting aluminum alloy.

6. The preparation method of the heat-treatment-free high-strength and high-toughness Al-Zn-Si-Ce die-casting aluminum alloy according to claim 5, characterized in that: The raw materials include pure Al ingots, pure Mg ingots, pure Zn ingots, Al - Sm master alloy, Al - Nb master alloy, Al - Ce master alloy, Al - Cu master alloy, Al - Mn master alloy and elemental silicon.

7. The preparation method of the heat-treatment-free high-strength and high-toughness Al-Zn-Si-Ce die-casting aluminum alloy according to claim 6, characterized in that: The alloying includes the following steps: Melt the pure Al ingot in a melting furnace, keep it at 710 - 730 °C until the pure Al ingot is completely melted to obtain a first melt; Add Al - Sm master alloy, Al - Nb master alloy, elemental silicon, pure Zn ingot, Al - Cu master alloy, Al - Mn master alloy to the first melt, keep it at 710 - 730 °C until all the above raw materials are melted to obtain a second melt; Press the pure Mg ingot into the second melt, keep it at 710 - 730 °C until the pure Mg ingot is completely melted to obtain an alloy melt.

8. The preparation method of a heat-treatment-free high-strength and tough Al-Zn-Si-Ce die-casting aluminum alloy according to claim 5, wherein: In the degassing and filtering step, the addition amount of the refining agent is 0.1 - 0.3% of the total mass of the alloy melt; the addition amount of the grain refiner is 0.01 - 0.05% of the total mass of the alloy melt.

9. The preparation method of a heat-treatment-free high-strength and tough Al-Zn-Si-Ce die-casting aluminum alloy according to claim 5, wherein: In the die - casting forming step, the temperature of the purified alloy melt is 680 - 720 °C, the mold temperature is 220 - 240 °C, the injection speed is 2 - 4 m / s, and the injection pressure is 95 - 105 bar.

10. The use of a heat-treatment-free high-strength and tough Al-Zn-Si-Ce die-casting aluminum alloy according to any one of claims 1-4, wherein: It is used for preparing thin - wall components with wall - thickness changes, bicycle load - bearing structural components and automobile load - bearing structural components.

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