A heat treatment free die casting aluminum alloy and its preparation method and application

Abstract

The application discloses a heat treatment-free die-casting aluminum alloy and a preparation method and application thereof, the aluminum alloy comprises Al, Si, Zn, Mg, Mn, Zr, V and optional Sr, and inevitable impurities, the impurities comprise Fe and other impurities except Fe, and the content of each component is further controlled; during preparation, the constituent metals and / or intermediate alloys of the alloy are melted, then refined, and optionally subjected to modification treatment by using Sr or an intermediate alloy containing Sr, and optionally subjected to degassing treatment, so that a pure melt of the aluminum alloy can be obtained, and the aluminum alloy is further die-cast into an aluminum alloy casting; practice shows that the heat treatment-free die-casting aluminum alloy can at least have the advantages of high tolerance to impurities Fe, non-use of rare earth elements, reduction of the use amount of expensive elements, and still having excellent mechanical properties without heat treatment, and in addition, natural aging and baking strengthening can be realized.

Description

Technical Field

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

[0002] In traditional automobile production, dozens or even hundreds of parts are assembled and welded together. However, the booming new energy vehicle industry is adopting a new lightweight vehicle solution: unibody aluminum alloy die casting. Unibody die casting, using a die casting machine and molds, allows for the casting of specified components in a single process, reducing manufacturing costs, lightening the vehicle body structure, and simplifying the automobile production line and processes. For traditional aluminum alloys, heat treatment is essential to ensure the mechanical properties of die-cast parts. However, unibody die-cast automotive parts are too large, and the heat treatment process is prone to defects such as deformation, dimensional changes, and surface blistering. Although some shaping techniques can improve dimensional accuracy and reduce defects to some extent in practice, they also increase the scrap rate, leading to higher processing costs.

[0003] Based on this, a heat-free die-casting aluminum alloy solution is proposed, which makes the development of large integrated die-cast structural components possible. However, some current solutions have the following problems to varying degrees:

[0004] (1) Not only is the formula complex, but it must also contain precious metals or relatively expensive metals. For example, in patent CN115433856B, a metal formula system with more than 12 kinds of metals is used, which has a relatively high production cost and its yield strength needs to be improved.

[0005] (2) If the Fe content in die-cast aluminum alloys is high, it will significantly reduce the toughness of the material. Therefore, the Fe content is usually strictly controlled. For example, invention patents CN114599806A, CN110402295A, CN105316542A, CN113373351A, CN114438380A, CN109881056B, CN112626390B, CN114411020B all require the Fe mass percentage to be less than 0.2% or even less than 0.05%. Such requirements mean that all raw materials must be high-purity electrolytic aluminum, which increases costs and is not conducive to the production of these alloys using recycled aluminum (the energy consumption per ton of recycled aluminum is only about 5% of that of electrolytic aluminum). The use of large amounts of electrolytic aluminum does not meet the national "dual carbon" target.

[0006] (3) Rare earth elements are used to regulate the structure of the alloy to achieve the purpose of strengthening. For example, invention patent CN115161521A uses La, CN114231799A uses RE (at least one of La, Ce, and Sc), CN104831129B uses RE (La, Ce, Sm, and Nd), CN110029250A uses Sc, CN114411020B also uses RE (at least one of La, Er, and Ce), CN114908275A uses at least one of La, Ce, and Er, CN113373351A uses Y, etc. However, rare earth elements still significantly increase the cost of heat treatment-free die-cast aluminum alloys mainly for automotive lightweighting, and the use of multiple mixed rare earth elements is not conducive to the classification, recycling, and reuse of castings in the later stage.

[0007] Therefore, in general, existing heat-free die-cast aluminum alloys have a low tolerance for Fe impurities, which means that the raw material must be high-purity electrolytic aluminum. This is not conducive to reducing energy consumption and recycling aluminum alloy materials, and also makes the corresponding product costs relatively high. In addition, the automotive industry is a very cost-sensitive industry. A large part of the existing heat-free die-cast aluminum alloys use rare earth elements or precious metals to improve alloy performance, which also directly leads to an increase in costs. At the same time, some aluminum alloy products still cannot achieve ideal mechanical properties. Summary of the Invention

[0008] The purpose of this invention is to overcome one or more shortcomings in the prior art and provide an improved heat-free die-cast aluminum alloy that can at least have the advantages of high tolerance to Fe impurities, no use of rare earth elements, reduced use of expensive elements, and still have excellent mechanical properties without heat treatment. In addition, it can also achieve natural aging and baking strengthening.

[0009] The present invention also provides a method for preparing the above-mentioned heat-free die-cast aluminum alloy.

[0010] The present invention also provides an aluminum alloy casting.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: a heat-free die-cast aluminum alloy, which contains Al, Si, Mg, Mn, selective Sr, and unavoidable impurities. In particular, the aluminum alloy also contains the following element combination: Zn, Zr, and V.

[0012] The impurities include Fe and other impurities besides Fe;

[0013] By mass percentage, this aluminum alloy contains: Si 6%-11%, Mg 0.1%-0.8%, Mn 0.2%-0.8%, Zn 3.5%-6.5%, Zr 0.06%-0.3%, V 0.06%-0.3%, Sr 0-0.04%, Fe less than 0.8%, and the total amount of other impurities besides Fe is less than 0.2%. The Al content is adjusted to make the total amount of the aluminum alloy 100%.

[0014] According to some preferred aspects of the invention, the aluminum alloy contains 8%-11% Si by mass percentage.

[0015] According to some preferred aspects of the invention, the aluminum alloy contains 0.1%-0.6% Mg by mass percentage.

[0016] According to some preferred aspects of the invention, the aluminum alloy contains 0.4%-0.8% Mn by mass percentage.

[0017] According to some preferred aspects of the invention, the aluminum alloy contains, by mass percentage, 3.5%-5.5% Zn, 0.06%-0.2% Zr, 0.06%-0.2% V, and 0-0.03% Sr.

[0018] Furthermore, by mass percentage, the aluminum alloy contains: Si 8%-10%, Mg 0.1%-0.3%, Mn 0.4%-0.7%, Zn 3.5%-5.0%, Zr 0.08%-0.15%, V 0.08%-0.15%, Sr 0-0.03%, Fe less than 0.8%, the total of other impurities besides Fe less than 0.2%, and the balance being Al.

[0019] According to some specific aspects of the present invention, the alloy microstructure of the aluminum alloy includes: α-Al matrix, Al+Si binary eutectic microstructure, Al+Mg2Si binary eutectic microstructure, Al+Si+Mg2Si+π-AlFeMgSi+ other phases multi-phase eutectic microstructure, dispersed phase (Al,Si)3Zr, dispersed phase Al3Zr, and dispersed phase Al3V. 1-X M X The dispersion phase α-Al(Mn,Fe)Si, the dispersion phase α-Al(Mn,V,Fe)Si, and the precipitated phase MgZn2; wherein X is 0-1, and M is Mn and / or Fe.

[0020] Furthermore, after die casting, the volume fraction of the eutectic structure is 30%-50%, and the secondary dendrite arms of the α-Al matrix, which is 85%-95% of the size, are 2-10 μm in size.

[0021] According to some preferred aspects of the present invention, in the Fe phase of the alloy structure of the aluminum alloy, the granular α-Fe phase (also referred to as the blocky α-Fe phase) accounts for more than 90% of the total Fe phase, and the content of the needle-like β-Fe phase is less than 10% of the total Fe phase.

[0022] According to the present invention, in the die-cast state, the aluminum alloy, without heat treatment, has a yield strength of 160 MPa or more, a tensile strength of 280 MPa or more, and an elongation of 9.5% or more at room temperature.

[0023] According to some preferred aspects of the invention, in the die-cast state, the yield strength of the aluminum alloy at room temperature after heat treatment is increased by 20%-30% compared to that without heat treatment.

[0024] In some preferred embodiments of the present invention, in the die-cast state, the aluminum alloy is baked and held at 180-230°C for 30-90 minutes, and the yield strength at room temperature reaches more than 190 MPa.

[0025] According to some preferred aspects of the invention, the aluminum alloy has the flowability for die casting at temperatures above 510°C.

[0026] According to the present invention, in the die-cast state, under the test conditions of a smooth sample, a stress ratio R of -1, a loading frequency of 50 Hz, and 10 million cycles, the fatigue strength of the aluminum alloy reaches more than 110 MPa.

[0027] Another technical solution provided by the present invention: a method for preparing the above-mentioned heat-free die-cast aluminum alloy, wherein when the aluminum alloy does not contain Sr, the method for preparing the heat-free die-cast aluminum alloy includes: weighing each component according to the formula, melting it to obtain a melt, and then refining it to obtain a pure melt of the aluminum alloy.

[0028] When the aluminum alloy contains Sr, the preparation method of the heat-free die-cast aluminum alloy includes:

[0029] Weigh each component according to the formula, and melt the components except for Sr or Sr-containing alloys to obtain a melt;

[0030] Then, the materials are refined and modified using Sr or Sr-containing alloys.

[0031] The aluminum alloy is then degassed to obtain a pure melt.

[0032] In some embodiments of the present invention, during the preparation process, each component in the raw materials can be added in the form of pure metals (such as pure Al, pure Mg, pure Zn), metal additives (such as Mn additives), or intermediate alloys of each component, so as to meet the ingredient ratio and reduce the introduction of impurities.

[0033] In some embodiments of the present invention, during the batching process, pure Al ingots (electrolytic aluminum ingots or recycled aluminum ingots), AlSi master alloy or industrial pure silicon or quick-dissolving silicon, pure Mg ingots, pure Zn ingots or Zn segments, AlMn master alloy or manganese agent, AlZr master alloy, AlV master alloy, AlSr master alloy, and grain refiner are weighed and prepared according to the batching list.

[0034] In some embodiments of the present invention, during smelting, the melt temperature is adjusted to 730-800°C. After pure Al and pure Si, fast-dissolving silicon or Si intermediate alloys are melted, pure Zn and intermediate alloys of Mn, Zr, V, etc. are added in sequence. After complete melting, the temperature is lowered to 710-730°C and pure Mg ingots are added.

[0035] After the pure Mg ingots are melted, the refining agent is weighed at 0.5‰ to 1.5‰ of the total mass of the alloy melt, and refined by blowing with high-purity (e.g., greater than or equal to 99%, preferably greater than or equal to 99.5%, more preferably greater than or equal to 99.99%) nitrogen / argon gas. The refining pressure is 0.1±0.01MPa, and the refining speed is 0.8-1.2kg / min. After refining, the mixture is allowed to stand for 5-15 minutes, and then the slag is removed. After removing the slag, the temperature of the aluminum melt is set to 730-750℃, and the melt is stirred to make the temperature uniform. Then the mixture is allowed to stand and discharged into the tundish (in this process, the alloy can also be prepared directly using high-temperature electrolytic aluminum water above 800℃ in a centralized melting furnace, with the option of using or not using recycled material).

[0036] Modification treatment: The transfer ladle is preheated to 720-740℃ and weighed. After the material is discharged, it is weighed again. AlSr master alloy is added according to the melt quality for modification treatment.

[0037] Degassing and slag removal: Degas using a rotor and add 0.8-1.2‰ refining agent. Degassing time is 5-25 min, degassing pressure is 0.15-0.30 MPa, degassing speed is 450±50 r / min, and degassing temperature is 730±10℃. Add refining agent Al5TiB (0.15%-0.25% of the total melt mass) or TCB (0.4%-0.6% of the total melt mass) 1-5 minutes before the end of the degassing process. Remove slag after degassing.

[0038] Preferably, a pre-furnace inspection can be performed before cooling to obtain the aluminum alloy to further ensure its compliance. Specific steps include:

[0039] Pour the aluminum liquid from the transfer bag into the machine side furnace. Add a filter screen before adding material to the machine side furnace. Take mushroom sample and K mold sample, and take samples to test for hydrogen. If the composition is not qualified, adjust it to be qualified according to the alloy composition. If the K mold sample is not qualified, repeat the slag removal process. If the hydrogen content is not qualified, repeat the rotor degassing process.

[0040] If the test is passed, proceed directly to the next step.

[0041] Another technical solution provided by the present invention: an aluminum alloy casting, the preparation method of which includes: melting the above-mentioned heat-free die-casting aluminum alloy, performing modification treatment, degassing treatment and die casting to obtain the aluminum alloy casting;

[0042] Alternatively, the method for preparing the aluminum alloy casting includes: melting and refining the raw material components of the heat-free die-casting aluminum alloy described above, and subjecting it to modification treatment, degassing treatment, and die casting to obtain the aluminum alloy casting.

[0043] According to some preferred aspects of the present invention, the die-casting process includes: aluminum hydraulic casting temperature of 680℃-710℃; mold vacuum degree controlled below 80mbar; mold temperature of 160-250℃; casting pressure of 40-150MPa; injection speed of 0.1-0.5m / s in the low-speed range and 3-5m / s in the high-speed range; the amount of molten material supplied is adjusted and determined according to the thickness of the sprue being 20%-30% of the diameter of the barrel; and the mold holding pressure time of 1-20s.

[0044] The applications of die-cast products include:

[0045] 1) It does not require heat treatment or other methods, meaning it can still meet ideal mechanical properties without heat treatment, and can be used directly in the as-cast state;

[0046] 2) Depending on the actual performance requirements of the casting application and the assembly process arrangement, the yield strength can be further improved by baking and holding at any temperature in the range of 180℃-230℃ for 30-90 minutes. In some cases, it can be increased by about 30-40MPa.

[0047] According to some specific aspects of the present invention, the heat-free die-cast aluminum alloy of the present invention can meet the requirements of integrated die-casting and can be directly applied to die-cast automotive parts.

[0048] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0049] The aluminum alloy of the present invention can simultaneously meet the following conditions: (1) high tolerance for Fe impurities, with an upper limit of about 0.8%; (2) relatively simple formula, without the use of rare earth elements or precious metal elements, and relatively low cost; (3) able to take into account the strength and ductility of the alloy, and also has natural aging and baking strengthening effects, and can significantly improve the yield strength by more than 20% after low temperature baking; (4) under the premise of taking into account toughness and other properties, the yield strength of the alloy in the as-cast state is significantly improved, and can reach about 185MPa even without heat treatment; (5) under the test conditions of smooth sample, stress ratio R = -1, loading frequency 50Hz, and 10 million cycles, the fatigue strength of the alloy in the as-cast state of the present invention reaches more than 110MPa. Attached Figure Description

[0050] Figure 1 The Scheil solidification process simulation curve of the aluminum alloy used in the aluminum alloy casting of Embodiment 1 of the present invention;

[0051] Figure 2 The image shows the microstructure of the aluminum alloy casting of Embodiment 1 of the present invention in the as-cast state (scale bar is 50 μm);

[0052] Figure 3 The image shows the microstructure of the aluminum alloy casting of Embodiment 1 of the present invention in the as-cast state (scale bar is 10 μm);

[0053] Figure 4 The stress-strain curves of the aluminum alloy castings in the F state of Embodiments 2 and 6 of the present invention are obtained from tensile tests.

[0054] Figure 5 Stress-strain curves of aluminum alloy castings in state F for comparative examples 6 and 7.

[0055] Figure 6 This is a full view of the fracture surface in the tensile fracture surface of the aluminum alloy casting of Embodiment 1 of the present invention, obtained by secondary electron imaging using SEM.

[0056] Figure 7 This is a magnified SEM backscatter image of the fracture location of the brittle Fe phase in the tensile fracture surface of the aluminum alloy casting of Embodiment 1 of the present invention. Detailed Implementation

[0057] The main concepts of this invention include: (1) innovatively using the combination of Zr and V to achieve the formation of dispersed phase and the regulation of Fe phase, thereby achieving a double improvement in alloy strength and plasticity, and at the same time enabling the heat-free die-cast aluminum alloy of this invention to accommodate more impurity element Fe.

[0058] In practice, under the system of this invention, the transition elements V and Zr have low diffusion rates in the α-Al matrix (in practice, the diffusion rates of V and Zr at 400℃ are 4.85 × 10⁻⁶, respectively). -24 m 2 ·s -1 1.20×10 -20 m 2 ·s -1 It is superior to the commonly used dispersed phase initiator Mn (6.24×10⁻⁶). -19 m 2 ·s -1 Therefore, in the heat-free die-cast aluminum alloy system of this invention, the dispersed phase obtained by combining V and Zr will have better anti-coarsening performance. This is also consistent with the Lifshitz, Slyozov and Wagner theory, that is, the ideal dispersed phase should have low interfacial energy (low lattice-matrix mismatch), low diffusivity and solubility limit to prevent coarsening caused by bulk diffusion at high temperature. Furthermore, the addition of Zr can form balanced rod-shaped (Al,Si)3Zr and Al3Zr(DO23) precipitates in Al-Si alloys. At the same time, the V introduced simultaneously can form Al3V or Al3V with low lattice mismatch in the Al matrix. 1-X M X (X is 0-1, M is Mn and / or Fe) In addition to trialuminates, V can also promote the precipitation of α-Al(Mn,V,Fe)Si dispersions by substituting Mn and V in α-Al(Mn,Fe)Si, thus achieving the purpose of changing the Fe phase; it can be seen that the combination of the two additive elements selected in this invention not only improves the strength, but also plays a role in regulating the Fe phase, thereby enabling the alloy to accommodate more impurity Fe (<0.8%).

[0059] (2) This invention utilizes the addition of Zn to lower the solidus temperature of the alloy, improving its fluidity, while simultaneously achieving natural aging and baking strengthening. According to the characteristics of die casting, the alloy melt flows under high pressure. Theoretically, this fluidity can be maintained even with a high solids content, and can continue flowing even before complete solidification. The limit temperature of this fluidity is close to the solidus temperature of the melt; therefore, a lower solidus temperature means that fluidity can be maintained at even lower temperatures. Practice shows that in the system of this invention, adding Zn can significantly lower the solidus temperature of the alloy, especially by controlling the amount of Zn added (preferably greater than or equal to 3.5%), thereby maximizing the improvement of the fluidity of cast Al-Si alloys. Currently, most Al-Si alloys simply increase the Si content to optimize fluidity; however, in practice, increasing the Si content to a certain extent has a very limited effect on improving fluidity and may even reduce the alloy's elongation. This invention improves the alloy's fluidity by adding Zn, altering the alloy's solidification range. The improvement in fluidity by Zn provides sufficient room for adjusting the composition of Si and Mg to achieve an optimized match between strength and elongation.

[0060] Furthermore, in the system of this invention, the addition of Zn does not cause a decrease in elongation or a deterioration in corrosion resistance. In other words, while improving processability, it does not negatively affect other properties of the alloy. In particular, in the system of this invention, when Mg is present, the addition of Zn will combine with Mg to form a certain amount of MgZn2, which will improve the yield strength and enhance the low-temperature baking effect. Specifically, this invention achieves excellent mechanical properties without heat treatment, and also has the effect of further improving the strength of the alloy through baking. The yield strength can be increased by about 20%-30% after low-temperature baking.

[0061] (3) The rational matching and application of the main alloying elements Si and Mg allows the eutectic structure strengthening and Mg2Si strengthening to play a positive role, minimizing the negative impact of excessive Si and Mg content on the decrease in elongation. Increasing Si content can improve fluidity and increase the volume fraction of eutectic structure to improve alloy strength, but excessive Si content will lead to poor alloy plasticity. Mg has a very significant strengthening effect on the Al-Si system, but elongation is also very sensitive to Mg content. This invention improves fluidity by adding Zn, giving Si and Mg more room to play their roles. In order to improve strength, the Mg content can be increased, while the loss of elongation can be compensated by appropriately reducing the Si content, thereby achieving an improvement in both strength and elongation.

[0062] Based on this, the present invention provides a heat-free die-cast aluminum alloy comprising: Al, Si, Mg, Mn, selective Sr, and unavoidable impurities. In particular, the aluminum alloy also comprises the following element combination: Zn, Zr, and V.

[0063] The impurities include Fe and other impurities besides Fe;

[0064] By mass percentage, this aluminum alloy contains: Si 6%-11%, Mg 0.1%-0.8%, Mn 0.2%-0.8%, Zn 3.5%-6.5%, Zr 0.06%-0.3%, V 0.06%-0.3%, Sr 0-0.04%, Fe less than 0.8%, and the total amount of other impurities besides Fe is less than 0.2%. The Al content is adjusted to make the total amount of the aluminum alloy 100%.

[0065] Furthermore, impurities can exist in the starting material or be introduced in one or more steps during the processing and / or manufacturing of aluminum alloys. Generally, the content of impurities should be controlled as much as possible to avoid affecting the properties of the alloy. For example, while Fe is generally understood to prevent sticking to the mold and thus help ensure the dimensional accuracy of the casting, excessive introduction of Fe will significantly affect the ductility of the alloy, that is, the brittleness will be amplified, resulting in undesirable effects. Therefore, in aluminum alloys, especially those used in automotive parts, the Fe content is generally required to be relatively low, even below 0.2% or even less than 0.05%. This will cause adverse effects on the original material. The high requirements for raw materials necessitate the use of high-purity electrolytic aluminum, which increases costs and hinders the production of these alloys from recycled aluminum (the energy consumption per ton of recycled aluminum is only about 5% of that of electrolytic aluminum). Furthermore, the preparation process involves iron tools and molds, making it difficult to completely avoid the introduction of iron. However, the formulation system of this invention, through its overall design, allows the Fe content to reach approximately 0.8%, significantly improving the tolerance for Fe impurities. In other words, the formulation system of this invention not only provides better mold-sticking prevention but also greatly reduces the purity requirements for raw materials, saving substantial costs and facilitating industrial application.

[0066] The above-mentioned solution will be further described below with reference to specific embodiments; it should be understood that these embodiments are used to illustrate the basic principles, main features and advantages of the present invention, and the present invention is not limited to the scope of the following embodiments; the implementation conditions used in the embodiments can be further adjusted according to specific requirements, and the implementation conditions not specified are usually the conditions in conventional experiments.

[0067] Unless otherwise specified in the following examples, all raw materials are commercially available or prepared by conventional methods in the art.

[0068] In the following description, to facilitate the testing of aluminum alloy performance, the aluminum alloy is directly die-cast into an aluminum alloy casting during the forming process and then tested. The difference between the two is that aluminum alloy is formed by directly cooling the refined melt of each component, while aluminum alloy casting is formed by die-casting the refined melt of each component into a predetermined shape after modification and degassing treatment. Therefore, the performance of aluminum alloy casting can be used to reflect the performance of aluminum alloy.

[0069] In this field, the pre-designed quantities during the preparation of aluminum alloy castings may have some error compared with the actual test values ​​in the later stages. The test values ​​after die casting are used as the standard in the following description, and the content of each metal is measured by a direct-reading spectrometer.

[0070] Example 1

[0071] This example provides an aluminum alloy casting and its preparation method, the preparation method including:

[0072] (1) Batching: Batching is done in total of 300kg. According to the calculation values ​​in the batching table, pure Al ingot, AlSi20 master alloy, 95% quick-dissolving silicon, pure Mg ingot, pure Zn ingot, AlMn10 master alloy, AlV5 master alloy, AlZr10 master alloy, AlSr10, and grain refiner TCB master alloy are weighed and set aside.

[0073] (2) Melting: In a 300kg 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 Zn, AlMn10 master alloy, AlV5 master alloy, and AlZr10 master alloy according to the actual alloy composition, and stir evenly with a preheated spoon. After the pure Zn and master alloy are completely melted, lower the temperature to 720℃ and press Mg into the melt below the surface of the liquid using a bell jar. After it is completely melted, stir evenly.

[0074] (3) Modification and Degassing: The melt temperature was lowered to 720℃, and the weighed AlSr10 master alloy was added. The mixture was stirred until completely melted and held at that temperature for 5 minutes. Then, the melt temperature was raised to 725±5℃ to begin degassing. The refining agent (Pyroflux GRDR212 purchased from Pyroflux (Shenzhen) High Temperature Materials Co., Ltd.) was weighed at (0.125±0.015)% of the melt mass and added to the automatic refining agent addition funnel of the rotor degasser. Degassing was performed using the rotor degasser. The refining agent addition speed was 500 r / min, the degassing speed was 400 r / min, the high-purity Ar flow rate of the degasser was 25 L / min, and the degassing time was 25 min. Five minutes before the end of degassing, the grain refiner TCB master alloy (purchased from Shandong Maiaojing New Materials Co., Ltd., at 0.5% of the total melt mass) was added. After degassing, the mixture was allowed to stand for 10 min, and alloy composition samples and reduced pressure solidification gas measurement samples were taken.

[0075] (4) Die casting: After degassing and ensuring the composition is qualified, the melt temperature is adjusted to 700±5℃, 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 60mBar, low-speed injection speed 0.2m / s, high-speed injection speed 3.9m / s, casting pressure 80MPa, and mold holding pressure time 6s.

[0076] The casting components and their mass percentages obtained in this embodiment are shown in Table 1.

[0077] Examples 2-6

[0078] These embodiments are basically the same as Embodiment 1, except that the content of each component is different. The obtained casting components and their mass percentages are shown in Table 1.

[0079] Comparative Examples 1-7

[0080] These comparative examples are basically the same as those in Example 1, except that the types and contents of each component are different. The obtained casting components and their mass percentages are shown in Table 1.

[0081] Table 1

[0082]

[0083]

[0084] Performance testing

[0085] (1) See Figure 1As shown, this is a simulation curve of the Scheil solidification process calculated using Thermo-Calc software. C611 and Castasil-37 are benchmark alloys. The vertical axis represents temperature, and the horizontal axis represents the change in the solid content of the alloy as temperature decreases. The figure shows that the aluminum alloy used in the aluminum alloy casting of Example 1 of this invention has a temperature range of 75°C (585°C-510°C) from the initial appearance of solids to a solid content of 1%, which is higher than the benchmark alloys C611 (50°C (608°C-558°C)) and Castasil-37 (25°C (600°C-575°C)). This means that when the melt cools, the alloy of this invention remains liquid above 510°C, theoretically allowing it to continue flowing under high-pressure casting, while the benchmark alloys completely solidify and become non-flowable below 558°C and 575°C, respectively. Moreover, from the moment the alloy of the present invention begins to solidify, the solid content in the alloy melt at any temperature is less than that of the benchmark alloys C611 and Castasil-37. The lower solid content at the same temperature means higher fluidity and filling capacity.

[0086] (2) See Figures 2-3 As shown, this is the microstructure of the aluminum alloy casting in the die-cast state of Embodiment 1 of the present invention. As can be seen from the figure, apart from the unavoidable pre-crystallization in the barrel during high-pressure casting, the alloy microstructure is fine, with most α-Al dendrites having a size below 20 μm; the eutectic silicon exhibits good modification, with the majority forming a fine network structure; from Figure 2 and Figure 3 No needle-like Fe phase was observed; instead, small particles or lumps were observed, indicating that the Fe phase was almost entirely transformed into a granular α-Fe phase (or blocky α-Fe phase), rather than a needle-like β-Fe phase. Figure 3 The proportion of eutectic structure (volume fraction or area shown in this figure) is approximately 50%, and the spacing between secondary dendrite arms is... Figure 3 The measurable size is mostly between 2-10 μm, accounting for about 90%.

[0087] (3) See Figure 4 As shown, the stress-strain curves of the aluminum alloy castings in state F of Embodiments 2 and 6 of this invention are obtained from tensile testing. The figure shows the tensile properties, specifically the yield strength δ. 0.2 Able to reach over 160MPa, tensile strength δ b It can reach a strength of over 280 MPa and an elongation of over 10% (A%).

[0088] See Figure 5 As shown, the stress-strain curves of the aluminum alloy castings in the F state of Comparative Example 6 and Comparative Example 7 are obtained from tensile tests. The figure shows that the tensile properties of Comparative Example 6 are as follows: yield strength δ 0.2Only 145MPa, tensile strength δ b =290MPa, elongation A% =9.6%; tensile properties of Comparative Example 7: yield strength δ 0.2 Only 127MPa, tensile strength δ b =288MPa, elongation A% =11.2%.

[0089] (4) See Figure 6 and Figure 7 As shown, this is the morphology of the tensile fracture surface of the aluminum alloy casting of Embodiment 1 of the present invention. Figure 6 This is the complete fracture surface image obtained from a secondary electron imaging (SEM) image, showing that the alloy exhibits ductile fracture characteristics. Figure 7 The image is a magnified SEM backscattered image of the fracture location of the brittle Fe phase. It can be seen from the image that the crack extends through the high-modulus Fe phase, rather than from the interface between the Fe phase and the matrix. This shows that the Fe phase in the alloy of the present invention has a high bonding strength with the matrix. The Fe phase not only does not cut the matrix, but also, because it is a high-modulus particle, the crack extends from the center of the Fe phase, which plays a certain role in improving the strength of the alloy.

[0090] (5) The properties of the aluminum alloy castings of the present invention and the benchmark alloys in the as-cast state and after low-temperature aging (200℃ / 60min) are shown in Table 2.

[0091] Table 2

[0092]

[0093] Comparative Example 1 did not add V, but added Mo, with both Zr and Mo controlled at 0.2% in a 1:1 ratio. Table 2 shows that, even with the addition of Mo, the tensile strength δ of Comparative Example 1, without V, is significantly lower than that of the present invention. b The elongation is significantly reduced, and low elongation means that the material fractures before reaching its maximum strength (tensile strength) during the tensile test, resulting in a lower yield strength δ. 0.2 It has decreased to some extent;

[0094] Comparative Example 2 did not add V, but added Mo, with both Zr and Mo controlled at 0.1% in a 1:1 ratio. Table 2 shows that, even with the addition of Mo and adjustments to the Zr and Mo content, the tensile strength δ of Comparative Example 1 remained the same after the absence of V. b The situation has improved somewhat, but compared to this invention, the yield strength δ 0.2 However, it decreased further. Overall, its tensile strength δ b and yield strength δ 0.2 All significantly reduced;

[0095] Comparative Example 3 did not add Zr, but added Mo, with both V and Mo controlled at 0.1% and a ratio of 1:1; as shown in Table 2, its yield strength δ 0.2 Very low, only 138 MPa, and tensile strength δ b It is also poor, and its overall performance is not ideal;

[0096] Comparative Example 4, in addition to adding V and Zr elements, further added Mo element, with Zr, V, and Mo all controlled at 0.1%, and the ratio of the three elements being 1:1:1; as shown in Table 2, compared with the present invention, its tensile strength δ b The decline was severe;

[0097] Comparative Example 5, in addition to adding V and Zr elements, further added Mo element, with Zr, V, and Mo all controlled at 0.2%, and the ratio of the three elements being 1:1:1; as shown in Table 2, compared with the present invention, its tensile strength δ b The decrease was significant; compared to Comparative Example 4, the content of Zr, V, and Mo was further increased when all three were present, which had a significant impact on tensile strength δ. b This has caused serious negative impacts;

[0098] Comparative Example 6 did not contain Zn; as shown in Table 2, compared to the present invention, its yield strength δ is not only higher. 0.2 The temperature drops significantly and it does not have the effect of baking to strengthen the skin.

[0099] Comparative Example 7 is a conventional alloy C611, which does not contain Zn, Zr, or V. As shown in Table 2, its yield strength δ... 0.2 The temperature drops significantly, and it does not have the effect of baking to strengthen the food.

[0100] (6) High-cycle fatigue tests were conducted on the smooth specimens of Examples 2 and 5 of the present invention. The test conditions were: stress ratio R = -1, frequency = 50 Hz, and cycle period = 10. 7 The amplitude (load) of 90MPa, 100MPa, 105MPa, 110MPa, 115MPa and 120MPa can all pass the test, and the probability of passing 110MPa is >90%.

[0101] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

[0102] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A heat-treatable die-cast aluminum alloy, comprising: Al, Si, Mg, Mn, selective Sr, and unavoidable impurities, characterized in that, This aluminum alloy also contains the following elemental combination: Zn, Zr, and V; The impurities include Fe and other impurities besides Fe; By mass percentage, this aluminum alloy contains: Si 6%-11%, Mg 0.18%-0.8%, Mn 0.2%-0.8%, Zn 3.5%-6.5%, Zr 0.06%-0.3%, V 0.06%-0.3%, Sr 0-0.04%, Fe less than 0.8%, and the total amount of impurities other than Fe is less than 0.2%. The Al content is adjusted to make the total amount of the aluminum alloy 100%. In the Fe phase of the alloy structure of this aluminum alloy, the granular α-Fe phase accounts for more than 90% of the total Fe phase, while the acicular β-Fe phase content is less than 10% of the total Fe phase.

2. The heat-free die-cast aluminum alloy according to claim 1, characterized in that, By mass percentage, Si accounts for 8%-11% of this aluminum alloy.

3. The heat-free die-cast aluminum alloy according to claim 1, characterized in that, In this aluminum alloy, Mg accounts for 0.18%-0.6% by mass percentage.

4. The heat-free die-cast aluminum alloy according to claim 1, characterized in that, By mass percentage, Mn accounts for 0.4%-0.8% of this aluminum alloy.

5. The heat-free die-cast aluminum alloy according to any one of claims 1-4, characterized in that, In terms of mass percentage, this aluminum alloy contains 3.5%-5.5% Zn, 0.06%-0.2% Zr, 0.06%-0.2% V, and 0-0.03% Sr.

6. The heat-free die-cast aluminum alloy according to any one of claims 1-4, characterized in that, By mass percentage, this aluminum alloy contains: Si 8%-10%, Mg 0.18%-0.3%, Mn 0.4%-0.7%, Zn 3.5%-5.0%, Zr 0.08%-0.15%, V 0.08%-0.15%, Sr 0-0.03%, Fe less than 0.8%, and the total amount of other impurities besides Fe is less than 0.2%, with the balance being Al.

7. The heat-free die-cast aluminum alloy according to claim 1, characterized in that, The microstructure of this aluminum alloy includes: α-Al matrix, Al+Si binary eutectic structure, Al+Mg2Si binary eutectic structure, Al+Si+Mg2Si+π-AlFeMgSi+other phase multi-phase eutectic structure, dispersed phase (Al,Si)3Zr, dispersed phase Al3Zr, and dispersed phase Al3V. 1-X M X The dispersion phases are α-Al(Mn,Fe)Si, α-Al(Mn,V,Fe)Si, and precipitated phases are MgZn2; where X is 0-1 and M is Mn and / or Fe.

8. The heat-free die-cast aluminum alloy according to claim 1 or 7, characterized in that, After die casting, the volume fraction of the eutectic structure is 30%-50%, and the secondary dendrite arm size of the 85%-95% α-Al matrix is ​​2-10 μm.

9. The heat-free die-cast aluminum alloy according to claim 1, characterized in that, In the die-cast state, without heat treatment, the aluminum alloy has a yield strength of over 160 MPa, a tensile strength of over 280 MPa, and an elongation of over 9.5% at room temperature.

10. The heat-free die-cast aluminum alloy according to claim 9, characterized in that, In the die-cast state, the yield strength of this aluminum alloy at room temperature is increased by 20%-30% after heat treatment compared to the untreated state.

11. The heat-free die-cast aluminum alloy according to claim 9 or 10, characterized in that, In the die-cast state, the aluminum alloy is baked at 180-230℃ for 30-90 minutes, and its yield strength at room temperature reaches more than 190MPa.

12. The heat-free die-cast aluminum alloy according to claim 1, characterized in that, The aluminum alloy has the flowability for die casting at temperatures above 510°C; and / or, in the die-cast state, under the test conditions of a smooth sample, a stress ratio R of -1, a loading frequency of 50 Hz, and 10 million cycles, the fatigue strength of the aluminum alloy reaches above 110 MPa.

13. A method for preparing a heat-free die-cast aluminum alloy according to any one of claims 1-12, characterized in that, When the aluminum alloy does not contain Sr, the preparation method of the heat-free die-cast aluminum alloy includes: weighing each component according to the formula, melting it to obtain a melt, and then refining it to obtain a pure melt of the aluminum alloy. When the aluminum alloy contains Sr, the preparation method of the heat-free die-cast aluminum alloy includes: Weigh each component according to the formula, and melt the components except for Sr or Sr-containing alloys to obtain a melt; Then, the materials are refined and modified using Sr or Sr-containing alloys. The aluminum alloy is then degassed to obtain a pure melt.

14. An aluminum alloy casting, characterized in that, The method for preparing the aluminum alloy casting includes: melting the heat-free die-casting aluminum alloy as described in any one of claims 1-12, performing modification treatment, degassing treatment and die casting to obtain the aluminum alloy casting; Alternatively, the method for preparing the aluminum alloy casting includes: melting and refining the raw material components of the heat-free die-casting aluminum alloy as described in any one of claims 1-12, and subjecting it to modification treatment, degassing treatment, and die casting to obtain the aluminum alloy casting.

15. The aluminum alloy casting according to claim 14, characterized in that, This aluminum alloy casting is an automotive part.

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