Heat-treatment-free weldable die-casting aluminum alloy and preparation method and application thereof

Abstract

The invention relates to a heat-treatment-free weldable die-casting aluminum alloy and a preparation method and application thereof, and the heat-treatment-free weldable die-casting aluminum alloy comprises the following components in percentage by mass: 6-11% of Si, less than 0.2% of Fe, 0.2-0.6% of Mg, 0.1-0.7% of Mn, 0.1-1.2% of Cu, 0.1-3% of Zn, 0.01-0.04% of Sr and the balance of Al and inevitable impurities. Wherein Mg / Mn is equal to 1 to 1.5. The die-casting aluminum alloy can achieve the balance of high strength and high toughness, and meanwhile has good welding performance.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloys, specifically to a heat-free, weldable die-cast aluminum alloy, its preparation method, and its applications. Background Technology

[0002] This section is intended to provide background or context for the present invention. The description herein is not intended to imply that it is prior art simply because it is included in this section.

[0003] Driven by the global "dual carbon" strategic goals, lightweighting of automobiles has become a key path to achieving energy conservation and emission reduction. Integrated die-casting technology, by integrating dozens or even hundreds of traditionally stamped and welded parts into a single large structural component, significantly reduces vehicle weight, production costs, and manufacturing cycles, and is gradually becoming an important direction for the transformation of automobile manufacturing processes.

[0004] However, the large-scale application of integrated die-casting technology still faces a series of severe challenges, one of the core bottlenecks being the lack of dedicated aluminum alloy materials with matching performance. Traditional die-casting aluminum alloys (such as EN AC-AlSi10MnMg) require high-temperature solution treatment (T4 / T6 heat treatment) to improve strength. However, when this process is applied to large, thin-walled die-cast parts, it is prone to irreversible thermal deformation and surface blistering due to uneven cooling in different parts, resulting in low yield and high correction costs. Therefore, "heat-free" die-casting aluminum alloys, that is, alloys that have good mechanical properties in the die-cast state and do not require subsequent solution treatment, have become the focus of industry research.

[0005] Currently, the mainstream heat-treatable die-cast aluminum alloys are mainly Al-Si alloys. Although this solves the problem of heat treatment deformation, their overall performance, especially strength, still falls short of the ever-increasing demands for structural safety and further lightweighting. Existing technologies mainly suffer from the following prominent problems: 1. The material strength is relatively low, and strengthening methods are costly. To ensure sufficient casting fluidity and elongation, the content of the strengthening element Mg in traditional heat-free Al-Si alloys is usually limited to a low level (e.g., <0.4%), resulting in a yield strength that generally remains in the range of 120-150 MPa, making it difficult to meet the mechanical performance requirements of key structural components. To overcome the strength bottleneck, some existing solutions (such as CN115094281B) have to rely on adding expensive rare earth elements such as nickel (Ni) and scandium (Sc) for strengthening. This not only significantly increases the cost of raw materials, restricting its application in economy vehicles, but also contradicts the environmental protection concept of utilizing recycled aluminum and achieving a circular economy. Other existing solutions, such as CN119663070A, improve the strength of integrated die-cast aluminum alloys by removing iron elements online through composition design and smelting process control, without using expensive rare earth elements. However, the elongation of the aluminum alloy in this solution still needs to be improved, especially the elongation in the as-cast state.

[0006] 2. High dependence on large-scale die-casting equipment and high production costs. As automotive parts become increasingly integrated, the projected area of ​​integrated die-cast parts continues to grow. Producing such ultra-large structural components requires ultra-large die-casting machines with clamping forces exceeding 6,000 tons or even tens of thousands of tons, placing extremely high demands on the design, manufacturing, and maintenance of the supporting molds. This rigid dependence on ultra-large specialized equipment and molds significantly increases fixed asset investment and production costs, limiting the widespread application of this technology.

[0007] 3. The contradiction between alloy fluidity and the filling requirements of large-size castings. The larger the size of the integrated die casting, the longer the flow path of the alloy molten metal from the gate to the end, which places more stringent requirements on the high-temperature fluidity of the alloy. Although high silicon content can improve fluidity, excessive silicon content will negatively affect toughness and machinability. How to ensure good filling ability while taking into account comprehensive performance is a major challenge in material design.

[0008] In summary, there is an urgent need in this field to develop a novel heat-treatable die-casting aluminum alloy that can achieve significant strength improvements without relying on expensive alloying elements, while also possessing excellent casting fluidity and elongation. More ideally, this material should support a "modular" design approach through excellent weldability. This involves first die-casting medium-sized, optimal-performance components, and then welding them into an integral structural unit using reliable joining techniques. This would reduce reliance on ultra-large die-casting equipment and molds, providing a more economical and feasible new path for integrated die-casting technology. Summary of the Invention

[0009] The purpose of this invention is to provide an improved heat-free, weldable die-cast aluminum alloy and its preparation method, which does not use rare / precious metals, achieves a balance between high strength and high toughness, and has good weldability.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention provides a heat-free, weldable die-cast aluminum alloy, comprising, by mass percentage, 6-11% Si, <0.2% Fe, 0.2-0.6% Mg, 0.1-0.7% Mn, 0.1-1.2% Cu, 0.1-3% Zn, 0.01-0.04% Sr, with the balance being Al and unavoidable impurities; wherein, Mg / Mn = 1-1.5.

[0011] In some implementations, the mass percentage of Si is 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, or 11%, etc. Further, the mass percentage of Si is 7-10%.

[0012] In some implementations, Fe < 0.2%, and further, Fe < 0.16%.

[0013] In some implementations, the mass percentage of Mg is 0.2%, 0.3%, 0.4%, 0.5%, or 0.6%, etc. More specifically, the mass percentage of Mg is 0.2% to 0.5%.

[0014] In some implementations, the mass percentage content of Mn is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, or 0.7%. More specifically, the mass percentage content of Mn is 0.2% to 0.6%. In some implementations, the mass percentage of Cu is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, or 1.2%, etc. Further, the mass percentage of Cu is 0.3% to 1%.

[0015] In some implementations, the Zn mass percentage content is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, or 3%, etc. Further, the Zn mass percentage content is 0.3% to 3%.

[0016] In some implementations, the mass percentage of Sr is 0.01%, 0.02%, 0.03%, or 0.04%, etc.

[0017] In some implementations, Mg / Mn = 1, 1.1, 1.2, 1.3, 1.4 or 1.5, etc.

[0018] In some implementations, Cu / Mg = 0.68~3, for example, Cu / Mg = 0.68, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or 3, etc. Further, Cu / Mg = 1.1~2.

[0019] In some implementations, the Sludge exponent SF ≤ 1.2.

[0020] In some implementations, the composition, by mass percentage, includes Si 7-9%, Fe < 0.16%, Mg 0.3-0.5%, Mn 0.2-0.4%, Cu 0.5-0.8%, Zn 0.3-3%, Sr 0.01-0.04%, with the balance being Al and unavoidable impurities; wherein, Mg / Mn = 1-1.5, Cu / Mg = 1.3-2, and Sludge index SF < 1.2.

[0021] In some embodiments, the die-cast aluminum alloy further includes 0.05-0.5% Cr. For example, the mass percentage of Cr is 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, or 0.5%, etc.

[0022] In some embodiments, the die-cast aluminum alloy further includes 0.05-0.5% Mo. For example, the mass percentage of Mo is 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, or 0.5%, etc.

[0023] In some embodiments, the die-cast aluminum alloy further includes 0.01 to 0.2% Sn. For example, the mass percentage of Sn is 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, or 0.2%, etc.

[0024] In some embodiments, the die-cast aluminum alloy further includes one, two, or three of the following: 0.05-0.5% Cr, 0.05-0.5% Mo, and 0.01-0.2% Sn.

[0025] Furthermore, the die-cast aluminum alloy also includes two of the following: 0.05-0.5% Cr, 0.05-0.5% Mo, and 0.01-0.2% Sn.

[0026] Furthermore, the die-cast aluminum alloy also includes 0.05-0.5% Cr and 0.01-0.2% Sn.

[0027] According to some specific embodiments, the content of the unavoidable impurities is a conventional content in the art, for example, the content of a single unavoidable impurity is <0.1wt%, and the total content of the unavoidable impurities is <0.2wt%.

[0028] According to some specific embodiments, the conditional yield strength δ of the die-cast aluminum alloy in the as-cast state 0.2 ≥140MPa, tensile strength δ b ≥280MPa, elongation ≥10.5%. Furthermore, the conditional yield strength δ of the die-cast aluminum alloy in the as-cast state... 0.2 ≥145MPa, tensile strength δ b ≥285MPa, elongation ≥11%.

[0029] According to some specific embodiments, the conditional yield strength δ of the die-cast aluminum alloy after baking and holding at 180~230℃ for 30~90min 0.2 ≥190MPa, tensile strength δ b ≥300MPa, elongation ≥6.9%.

[0030] Furthermore, the conditional yield strength δ of the die-cast aluminum alloy after baking and holding at 180~230℃ for 30~90 min... 0.2 ≥220MPa, tensile strength δ b ≥320MPa, elongation ≥7%.

[0031] According to some specific embodiments, the conditional yield strength δ of the die-cast aluminum alloy welded joint is... 0.2 ≥140MPa, welding coefficient ≥90%, porosity ≤3%.

[0032] Furthermore, the conditional yield strength δ of the die-cast aluminum alloy welded joint 0.2 ≥145MPa, welding coefficient ≥90%, porosity ≤3%.

[0033] A second aspect of the present invention provides a method for preparing a heat-free, weldable die-cast aluminum alloy as described above, comprising the following steps: (1) Melt Al ingots, Si-containing master alloys, fast-melting silicon, Mn-containing master alloys, Zn and Cu, selectively melt Cr-containing master alloys and Mo-containing master alloys, and then hold at a temperature of 620~640℃ for 20~90min. (2) Add Mg ingots to the melt of step (1), selectively add Sn, and melt; (3) Then, Sr or Sr-containing alloys are used for modification treatment, followed by degassing treatment and die casting to obtain aluminum alloy castings.

[0034] This invention achieves the following through composition design and smelting process control: 1) online removal of harmful Fe elements from molten aluminum; 2) a balance between high strength and high toughness with significant cost advantages; 3) improvement of the limitations of the relative properties of needle-shaped Fe-containing materials; 4) good weldability, meeting the connection performance requirements of castings and providing a material basis for modular manufacturing; and 5) no need for complex high-temperature solution treatment, optimizing process adaptability and improving production efficiency.

[0035] "Selectively" means that the ingredient can be added or omitted as needed.

[0036] According to some specific implementation methods, in step (1), the temperature is controlled at 625~635℃ and kept at that temperature for 30~50 minutes.

[0037] According to some specific implementation methods, in step (2), the melt temperature is first raised to 710~730℃, and then the Mg ingot and Sn particles are added and melted.

[0038] According to some specific embodiments, the preparation method further includes a step of baking and strengthening the aluminum alloy casting, wherein the baking and strengthening temperature is controlled at 180~230℃ and the holding time is 30~90min.

[0039] According to some specific embodiments, the raw material Al used to prepare the die-cast aluminum alloy is electrolytic aluminum ingot or recycled aluminum ingot.

[0040] According to some specific embodiments, the aluminum alloy castings prepared by the present invention can be used directly in the as-cast state, or, depending on the actual performance requirements of the casting application and the assembly process arrangement, can be used after baking to further improve its yield strength to 75-85 MPa.

[0041] A third aspect of the present invention provides an automotive body structural component, which is formed by welding multiple heat-free, weldable die-cast aluminum alloys as described above.

[0042] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art: The die-cast aluminum alloy of this invention does not use rare / precious metal elements and still possesses excellent mechanical properties without heat treatment. These mechanical properties are further enhanced through baking and strengthening. The die-cast aluminum alloy of this invention achieves a balance between high strength and high toughness, while also possessing good weldability. Attached Figure Description

[0043] Figure 1 The image shows the microstructure of the alloy in Comparative Example 1. Figure 2 The image shows the microstructure of the alloy in Comparative Example 3. Figure 3 The macroscopic morphology of the weld seams of the aluminum alloys in Example 1 and Comparative Example 2 is shown. Figure 4 The macroscopic morphology of the weld cross-section of the aluminum alloys in Example 1 and Comparative Example 2 is shown. Detailed Implementation

[0044] To address the shortcomings of existing technologies, this invention provides die-cast aluminum alloys with specific components and proportions, which achieve a balance between strength and toughness without using rare earth elements or precious metal elements, and also have good weldability.

[0045] Specifically, this invention employs a multi-component synergistic solid solution-precipitation strengthening system: This invention innovatively constructs a composite strengthening system with Mg, Cu, Mn, and Zn as its core components. By precisely controlling the ratios of Mg and Mn, Mg and Cu, and the amount of Zn, a supersaturated solid solution is formed during the rapid solidification process of die casting, which then promotes the precipitation of strengthening phases dominated by high-density nanoscale Q-AlCuMgSi and Mg2Si phases during subsequent aging. This design eliminates the dependence on expensive elements such as Ni and rare earth elements, achieving high strength while maintaining excellent cost competitiveness and superior elongation.

[0046] Furthermore, this invention utilizes Sn as a vacancy trap to achieve rapid aging response: To overcome the shortcomings of limited solid solubility in die-cast parts and the tendency for natural aging to weaken the effect of artificial aging, this invention adds trace amounts of Sn. Based on the extremely high binding energy between Sn atoms and vacancies, Sn can act as an effective "vacancy trap," inhibiting the formation of clusters (natural aging) by vacancies combining with Mg and Si solute atoms at room temperature, thereby "retaining" more solute atoms for subsequent artificial aging stages. This mechanism ensures that finer, more dispersed strengthening phases can precipitate during short-time (30-90 min) and low-temperature (180-240℃) baking processes, resulting in a significant improvement in yield strength.

[0047] Furthermore, this invention utilizes precise control of the Fe phase morphology and "online purification" technology based on the SF factor. To resolve the contradiction between the harmful effects of Fe and the sustainability of materials, this invention does not simply limit the Fe content. Instead, it introduces a key control parameter through the combined addition of Mn and Cr elements, with the SF factor (SF = 1×%Fe + 2×%Mn + 3×%Cr) ≤ 1.2. This design allows Fe to preferentially form a high-melting-point, high-specific-gravity primary α-Al(Fe,Mn,Cr)Si phase (Sludge phase) with Mn, Cr, and Si. Then, through a specific low-temperature (630±5℃) holding process, this phase agglomerates, settles into bottom slag, and is removed, achieving "online Fe removal" of the melt. This significantly reduces the risk of forming harmful needle-like π and β phases, thus allowing for the safe use of higher Mg content for strengthening while maintaining high elongation, and improving compatibility with recycled aluminum raw materials.

[0048] This invention combines excellent weldability with support for a modular manufacturing strategy: Through composition optimization and Fe phase control, the alloy of this invention achieves a high laser welding coefficient (>0.8) and low porosity. This characteristic enables a "modular" manufacturing strategy: first, medium-sized sub-components with optimal mechanical properties and casting processability are die-cast, and then integrated through high-quality welding. This strategy effectively reduces reliance on ultra-large die-casting machines and molds, minimizes the manufacturing risk and cost of individual parts, and provides a more flexible and economical path for the widespread application of integrated die-casting technology.

[0049] The roles and synergistic effects of each component in this invention are described below: Si (6-11 wt.%): As a major alloying element, it provides excellent casting fluidity, ensuring the filling capacity of large, integrated die-cast parts. Simultaneously, Si forms a eutectic Si phase during solidification, contributing to the alloy's strength.

[0050] Mn (0.1-0.7 wt.%) and Cr (0.05-0.5 wt.%) or Mo (0.05-0.5%): Mn and Cr are not merely traditional modifiers that neutralize the harmful phase morphology of Fe. Instead, through a specific ratio (reflected in an SF factor ≤ 1.2), they preferentially form high-melting-point primary intermetallic compound phases with Fe and Si in the melt (such as the complex α-Al(Fe,Mn,Cr)Si phase, commonly known as the Sludge phase). This phase has a relatively high density and can agglomerate and settle to the bottom of the furnace as slag during the melt settling process, thus achieving "online Fe removal." This process reduces the content of free Fe in the melt from the source, breaking the vicious cycle of "adding Mg → forming needle-like π-Al9FeMg3Si5 phase → damaging elongation." Mo has a similar effect to Cr, therefore the synergistic effect of Mn and Mo can also improve elongation to a certain extent.

[0051] Mg (0.2-0.6 wt.%) and Cu (0.1-1.2 wt.%): These strengthening elements can be safely added provided that the Fe content is effectively controlled. Mg mainly forms the Mg2Si strengthening phase, while Cu participates in the formation of the Q-AlCuMgSi and Al2Cu phases. By controlling the Cu / Mg mass ratio, the precipitation sequence, quantity, and morphology of these strengthening phases can be optimized to achieve a synergistic strengthening effect, which is the basis for obtaining high as-cast strength and excellent aging response.

[0052] Sn (0.05-0.2 wt.%): Sn mainly acts as an aging regulator. The principle is that the binding energy between Sn atoms and vacancies is much higher than that between Si or Mg atoms and vacancies. Supersaturated vacancies generated during rapid cooling after die casting are preferentially captured and fixed by Sn atoms. This effectively inhibits the formation of clusters by vacancies combining with Mg and Si solute atoms at room temperature (i.e., natural aging), allowing more solute atoms to precipitate during subsequent artificial aging processes, forming finer, more dispersed strengthening phases (such as GP zones and β'' phases). This significantly improves the strengthening response speed and strengthening effect of artificial aging, achieving "rapid aging strengthening."

[0053] Zn (0.1-3 wt.%): It is dissolved in the aluminum matrix, playing a role in solid solution strengthening, and can slightly affect the electrode potential of the alloy, and has a certain impact on corrosion resistance.

[0054] Sr (0.01-0.04 wt.%): As a modifier, it effectively refines the morphology of the eutectic Si phase, changing it from coarse needle-like to fine fibrous, and significantly improves the elongation of the alloy.

[0055] Fe (<0.15 wt.%) and impurity control: Fe is controlled at a low level through the above process. Other impurity elements are strictly controlled to avoid introducing unforeseen negative effects.

[0056] The present invention will be further described below with reference to embodiments. However, the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific applications, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0057] Unless otherwise specified herein, the preparation and testing methods involved in the following examples or comparative examples are based on existing technologies. Unless otherwise specified in the following examples, all raw materials are commercially available or prepared using conventional methods in the art. Example 1

[0058] This example provides a die-cast aluminum alloy and its preparation method, which includes the following steps: (1) Batching: Batching is done according to a total of 200kg. Based on the calculated values ​​in the batching table, pure Al ingots, AlSi20 master alloy, 95% quick-dissolving silicon, AlMn10 master alloy, AlCr10 master alloy, pure Cu wire, Sn granules, pure Mg ingots, pure Zn, AlMo5 master alloy, AlSr10 master alloy, and grain refiner TCB are weighed and set aside. (2) Smelting and online Fe removal: In a 200kg capacity crucible furnace, first add pure Al ingots and AlSi20 master alloy and heat the furnace. After they are completely melted, raise the temperature of the melt to 765℃ and press in 95% quick-melting silicon in batches using a bell jar. After the quick-melting silicon is completely melted, add pure AlMn10 master alloy, AlCr10 master alloy, AlMo5 master alloy, pure Zn, and pure Cu wire according to the actual alloy composition. Stir evenly with a preheated spoon. After complete melting, lower the temperature to 630℃±5℃ and hold for 40min. (3) Add Mg and Sn: Raise the melt temperature again to 720±10℃, add the weighed Mg ingots and Sn particles wrapped in aluminum foil, and stir to make them fully melt; (4) Modification and Degassing: Lower the melt temperature to 710℃, add the weighed AlSr10 master alloy, stir until completely melted, and hold for 5 minutes. Then raise the melt temperature to 720℃±10℃ to begin degassing. Weigh 0.1%-0.15% of the melt mass of refining agent (Pyroflux GRDR212 purchased from Pyroflux (Shenzhen) High Temperature Materials Co., Ltd.) and add it to the automatic refining agent addition funnel of the rotor degasser. Degas using the rotor degasser, with the refining agent addition speed at 600 r / min, the degassing speed at 500 r / min, the high-purity Ar flow rate of the degasser at 25 L / min, and the degassing time at 25 min. 5 min before the end of degassing, add 0.3% of the melt mass of grain refiner TCB. After degassing, let stand for 20 min, remove the surface slag, and cool to the die-casting temperature of 690℃~705℃. Take alloy composition samples and depressurized solidification hydrogen test samples; (5) Die casting: After degassing and ensuring the composition is qualified, the melt temperature is maintained at 690℃-705℃, and die casting is performed on a 400-ton die casting machine. The die casting parameters are: mold temperature 170℃, mold filling degree 33%, vacuum degree 50mBar, low-speed injection speed 0.2m / s, high-speed injection speed 4.0m / s, casting pressure 78MPa, and mold holding pressure time 7s; (6) Demolding and water quenching: After gradually demolding, immediately immerse in room temperature water for quenching; (7) Low temperature aging: Set the temperature of the holding furnace to 200℃. After the temperature reaches the set temperature, put the die casting in and hold it for 40 minutes after the temperature rises back to 200℃.

[0059] The batching table for the die-cast aluminum alloy in this embodiment is shown in Table 1. Examples 2-3 and Comparative Examples 1-4

[0060] The preparation methods of these embodiments and comparative examples are the same as those of Example 1, except that the components and contents in the ingredient lists of each die-cast aluminum alloy are different. The ingredient lists of each embodiment and comparative example are shown in Table 1.

[0061]

[0062] The mechanical properties of the aluminum alloy castings from the above embodiments and comparative examples, as well as the aluminum alloys after low-temperature aging treatment, are shown in Table 2. Among them, the conditional yield strength δ... 0.2 Tensile strength δ b The test standard for elongation (A%) is GB / T228.1-2021.

[0063]

[0064] As shown in Table 2, compared with Comparative Examples 1-3, Examples 1-5 all exhibited significantly improved elongation while maintaining comparable or even superior strength. Specifically, Example 1, without the addition of Cr and Mo, resulted in high strength but only a slight increase in elongation. Example 2, by adding both Mn and Cr, effectively avoided the detrimental effect of Fe on elongation, achieving a significant increase in elongation while maintaining high strength. Example 3, by adding both Mn and Mo, resulted in relatively high elongation of the as-cast aluminum alloy, as Mo has a similar effect to Cr. Example 4, omitting Sn, still achieved a good strengthening effect through the combined effect of a suitable Mg / Cu / Mn / Zn element ratio and the addition of Cr and Mo. Example 5, without the addition of Sn and Mo, resulted in the formation of clusters between vacancies and Mg and Si atoms at room temperature after die casting (natural aging), consuming solute atoms available for the precipitation of strengthening phases. Therefore, after artificial aging (200℃ / 40min), the strengthening effect was significantly reduced (δ0.2 after aging was only 192 MPa, an increase of about 47 MPa), while the increase in Examples 1-4 reached 78-83 MPa (strengthening efficiency >40%).

[0065] In Comparative Example 1, the excessively high Cu content led to the precipitation of large-sized lamellar Al₂Cu phases along the grain boundaries, which fragmented the matrix and reduced elongation. The high Cu / Mg ratio significantly increased the size of the Q phase, affecting the precipitation efficiency of the strengthening phase, resulting in limited strength improvement and decreased toughness. The microstructure of Comparative Example 1 is shown below. Figure 1 As shown.

[0066] In Comparative Example 2, the addition of a high content of Mn resulted in the appearance of a needle-like Fe phase with a high Mn content. This not only failed to improve the morphology of the Fe phase but also had a deteriorating effect, severely reducing the elongation.

[0067] Comparative Example 3, lacking the addition of Mn, Cr, and Mo, failed to effectively improve the Fe phase morphology. Fe directly reacted with Mg and Si to form needle-like β-Al5FeSi and π-Al9FeMg3Si5 phases. These phases persisted during solidification, severely disrupting the matrix continuity and leading to a decrease in elongation. Simultaneously, while the high Si content (10 wt.%) improved fluidity, it exacerbated brittleness, resulting in limited strength improvement. The microstructure of Comparative Example 3 is shown below. Figure 2 As shown.

[0068] Welding properties of aluminum alloys in the as-cast state in Example 1 and Comparative Example 2: Laser welding is used, and the specific welding parameters are as follows: Inner ring power 1300W; welding speed 20mm / s; oscillation diameter 1.0mm; oscillation frequency 100Hz.

[0069] Figure 3 and Figure 4The images show the macroscopic morphology of the weld's front and back sides and cross-section, respectively. No obvious welding cracks were found in the heat-affected zone. Table 3 compares the strength of the welded joint with that of the base metal.

[0070]

[0071] As can be seen from Table 3, the welding performance of the aluminum alloy in Example 1 is significantly better than that in Comparative Example 2.

[0072] In summary, the aluminum alloy of this application has the following advantages: 1. It achieves a balance between high strength and high toughness, with significant cost advantages; 2. It improves the limitations of the relative properties of acicular Fe-containing materials; 3. It has good weldability, meeting the connection performance requirements of castings, providing a material basis for modular manufacturing, and avoiding dependence on extreme manufacturing equipment; 4. It does not require complex high-temperature solution treatment, optimizes process adaptability, and improves production efficiency.

[0073] Furthermore, since the present invention involves online iron removal, it is expected that the iron content in the die-cast aluminum alloy will be lower than the iron content in the ingredient list, while the other components should be equivalent to those in the ingredient list.

[0074] The present invention has been described in detail above, with the aim of enabling those skilled in the art to understand and implement the invention. However, this description should not be construed as limiting the scope of protection of the invention. All equivalent changes or modifications made in accordance with the spirit and essence of the invention should be included within the scope of protection of the invention.

Claims

1. A heat-treatable, weldable die cast aluminium alloy characterised in that: It includes Si 6~11%, Fe <0.2%, Mg 0.2~0.6%, Mn 0.1~0.7%, Cu 0.1~1.2%, Zn 0.1~3%, Sr 0.01~0.04% by mass percentage, and the balance of Al and inevitable impurities; wherein, Mg / Mn = 1~1.

5.

2. The heat treatment free, weldable, die cast aluminium alloy according to claim 1, characterized in that: Cu / Mg = 0.68~3.

3. The heat treatment free, weldable, die cast aluminum alloy of claim 1, wherein: Sludge index SF≤1.

2.

4. The heat treatment free, weldable, die cast aluminum alloy of claim 1 wherein: It includes Si 7~9%, Fe <0.16%, Mg 0.3~0.5%, Mn 0.2~0.4%, Cu 0.5~0.8%, Zn 0.3~3%, Sr 0.01~0.04% by mass percentage, and the balance of Al and inevitable impurities; wherein, Mg / Mn = 1~1.5, Cu / Mg = 1.3~2, and Sludge index SF <1.

2.

5. The heat treatment free, weldable, die cast aluminium alloy according to any one of claims 1 to 4, characterized in that: The die-casting aluminum alloy further includes one, two or three of 0.05~0.5% Cr, 0.05~0.5% Mo and 0.01~0.2% Sn.

6. The heat treatment free, weldable, die cast aluminium alloy according to claim 5, characterized in that: The die-casting aluminum alloy further includes two of 0.05~0.5% Cr, 0.05~0.5% Mo and 0.01~0.2% Sn.

7. The heat treatment free, weldable, die cast aluminum alloy of any one of claims 1 to 4, wherein: The condition yield strength δ of the die-cast aluminum alloy under as-cast condition 0.2 ≥ 140 MPa, the tensile strength δ b ≥ 280 MPa, the elongation ≥ 10.5%; the condition yield strength δ of the die-cast aluminum alloy after baking at 180~230℃ for 30~90min 0.2 ≥ 190 MPa, the tensile strength δ b ≥ 300 MPa, the elongation ≥ 6.9%.

8. The heat treatment free, weldable, die cast aluminum alloy of any one of claims 1 to 4, wherein: The conditional yield strength δ of the die-cast aluminum alloy welded joint 0.2 ≥ 140 MPa, a welding coefficient ≥ 90%, and a porosity ≤ 3%.

9. A process for the production of a heat-treatable, weldable die cast aluminium alloy as claimed in any one of claims 1 to 8 characterised in that: It includes the following steps: (1) melt Al ingot, Si-containing intermediate alloy, fast-acting silicon, Mn-containing intermediate alloy, Zn and Cu, optionally melt Cr-containing intermediate alloy and Mo-containing intermediate alloy, and then control the temperature at 620~640℃ for 20~90min; (2) add Mg ingot to the melt of step (1), optionally add Sn, and melt; (3) then modify with Sr or Sr-containing alloy, and then perform degassing treatment and die-casting to obtain an aluminum alloy casting; (4) optionally perform baking strengthening on the aluminum alloy casting, wherein the temperature of the baking strengthening is controlled at 180~230℃, and the holding time is 30~90min.

10. An automotive body structure member characterized by comprising: It is welded by a plurality of heat-treatment-free and weldable die-casting aluminum alloys as claimed in any one of claims 1 to 8.

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