A heat-treatable-free die-casting aluminum alloy, its preparation method and application

Abstract

The present invention discloses a heat-treatable-free die-casting aluminum alloy and its preparation method and application. The die-casting aluminum alloy is composed of the following components by mass percentage: 10-13% Si, 0.05-0.15% Mg, 0.35-0.65% Fe, 0.2-0.45% Mn, 0.16-0.32% trace elements, and the balance is impurity elements and Al; the trace elements include the following components by mass percentage: 0.08-0.15% Zr, 0.012-0.03% Sr, 0.02-0.09% RE, 0-0.05% Ti, and the Sr and RE are added in the form of an Al-Sr-RE master alloy; the sum of the mass percentages of Mn and Fe is 0.75-0.9%. Based on the Al-Si alloy, the present invention finally obtains a heat-treatable-free die-casting aluminum alloy with both castability and high strength and toughness by adjusting the contents of various components.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal materials, and particularly relates to a die-casting aluminum alloy that can be free of heat treatment, and a preparation method and application thereof. Background Art

[0002] While automobiles bring convenience to people's lives, they also bring energy consumption and environmental pollution. In order to cope with the global energy and environmental crises, traditional fuel vehicles are gradually being replaced by new energy vehicles. Limited by the battery energy density, the weight increase of the current battery is 15 - 30% higher than that of fuel vehicles of the same level, which becomes one of the obstacles to the endurance of new energy vehicles. Therefore, the lightweighting of new energy vehicles is more urgent than that of fuel vehicles.

[0003] In recent years, the die-casting integrated forming technology has become one of the effective ways to achieve the lightweighting of automobiles, but the corresponding materials cannot improve their strength through heat treatment, and it is urgent to carry out research on high-strength and tough die-casting aluminum alloy materials that are non / heat-treatment-free.

[0004] CN115125420A discloses a cast aluminum alloy for high-performance structural parts that can be free of heat treatment. This alloy contains Si: 6.0% - 8.5%, Mg: 0.05% - 0.40%, Cu: 0.50% - 0.85%, Cr: 0.20% - 0.60%, Er: 0.01% - 0.10%, Mn: 0.45% - 0.75%, Zn: 0.1% - 3.0%, V: 0.04% - 0.14%, Ni: 0.01% - 0.1%, Ba ≤ 0.1%, Y ≤ 0.1%, Fe ≤ 0.16%, and the balance is Al. By adding specific contents of Cu, Mg, and Si elements, strengthening phases such as Al2Cu, Mg2Si, and Al-Si-Cu-Mg are formed, significantly improving the strength of the casting. The tensile strength of the casting reaches 290 MPa, but the elongation is less than 10%.

[0005] CN115961183A discloses a heat-treatment-free high-strength and tough die-casting aluminum alloy, which consists of 7.0 - 10.0% silicon, no more than 0.05% copper, no more than 0.4% magnesium, 0.3 - 0.7% manganese, no more than 0.2% iron, no more than 0.07% zinc, no more than 0.2% titanium, 0.015 - 0.03% strontium, 0.01 - 0.1% vanadium, and 0.01 - 0.1% zirconium. By regulating the contents of Mg and Zr, the tensile strength and elongation reach 260 MPa and more than 15.5% respectively. However, the yield strength is only about 120 MPa.

[0006] CN116287891A discloses a heat-treatable die-casting aluminum alloy, which contains 6.5 - 8.3% Si, 0.2 - 0.4% Mg, 0.25 - 0.50% Cu, 0.09 - 0.25% Fe, 0.5 - 0.8% Mn, 0.05 - 0.20% Ti, 0.02 - 0.04% Sr, 0.01 - 0.1% Zr, Hf less than or equal to 0.05%, Zn less than or equal to 0.25%, rare earth elements less than or equal to 0.1%, other impurity elements less than or equal to 0.05% and the balance Al; wherein, the rare earth elements include at least one of La, Ce and Y; the ratio of the total weight of Cu and Mg to the total weight of Zr and Hf is less than or equal to 22. By introducing Hf, Zr, and RE elements to control the grains, second phases, and precipitation phases, the properties of the aluminum alloy are improved. The tensile strength, yield strength, and elongation of the casting reach 276 MPa, 133 MPa, and more than 10.7% respectively, but the alloy contains a low Fe content and a rare and precious metal Hf content, resulting in a high cost. Summary of the Invention

[0007] In order to overcome at least one of the above-mentioned problems existing in the prior art, one of the objectives of the present invention is to provide a heat-treatable die-casting aluminum alloy, which is a heat-treatable die-casting alloy with both good castability and high strength and toughness.

[0008] Another objective of the present invention is to provide a preparation method for the above die-casting aluminum alloy.

[0009] Another objective of the present invention is to provide an application of the above die-casting aluminum alloy in the automotive field.

[0010] In order to achieve the above objectives, the technical solutions adopted by the present invention are as follows:

[0011] In the first aspect of the present invention, a heat-treatable die-casting aluminum alloy is provided, which is composed of the following components by mass percentage: 10 - 13% Si, 0.05 - 0.15% Mg, 0.35 - 0.65% Fe, 0.2 - 0.45% Mn, 0.16 - 0.32% trace elements, and the balance is impurity elements and Al; the trace elements include the following components by mass percentage: 0.08 - 0.15% Zr, 0.012 - 0.03% Sr, 0.02 - 0.09% RE, 0 - 0.05% Ti, and the Sr and RE are added in the form of an Al-Sr-RE master alloy; the sum of the mass percentages of Mn and Fe is 0.75 - 0.9%.

[0012] The present invention is based on an Al-Si alloy. The Si content is designed to be near its eutectic point to maximize the fluidity of the alloy. The Mg content is designed within its solid solubility range to improve the strength of the alloy through solid solution strengthening. Both Fe and Mn can effectively reduce sticking to the mold. On the one hand, through total amount control, the optimization of non-sticking to the mold is achieved. On the other hand, the morphology of the iron-rich phase is regulated by the relative contents of Si, Fe, and Mn to reduce the harm of the iron-rich phase and improve the plasticity of the alloy. When the Si content is relatively high, the Fe content is relatively high and the Mn content is relatively low, and vice versa. The formation temperature ranges of α-Al, Al-Si eutectic, and iron-rich phase are accurately analyzed using thermodynamic calculations, and the contents of Mn and Fe are optimized according to the Si content. Adding an appropriate amount of trace elements is beneficial to improving the strength and plasticity of the alloy. Among them, adding a small amount of Zr can refine the grains, especially when the Si content is relatively low, there is still a small amount of primary α-Al formed. Adding an Al-Sr-RE master alloy as a composite modifier can deeply modify the eutectic silicon, refine the size of the eutectic silicon, and improve the plasticity of the alloy. Ti is an optional additive component. Adding an appropriate amount of Ti can refine the grains to a certain extent, which is beneficial to improving the plasticity and strength of the alloy.

[0013] Preferably, in the composition of the die-cast aluminum alloy, the mass percentage of Si is 10.5 - 13%; non-limiting examples are 11%, 11.5%, 12%, or 12.5%.

[0014] Preferably, in the composition of the die-cast aluminum alloy, the mass percentage of Mg is 0.08 - 0.15%; non-limiting examples are 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, or 0.14%.

[0015] Preferably, in the composition of the die-cast aluminum alloy, the mass percentage of Fe is 0.35 - 0.55%; non-limiting examples are 0.4%, 0.42%, 0.45%, 0.48%, or 0.5%.

[0016] Preferably, in the composition of the die-cast aluminum alloy, the mass percentage of Mn is 0.3 - 0.45%; non-limiting examples are 0.32%, 0.35%, 0.37%, 0.4%, or 0.42%.

[0017] Preferably, in the composition of the die-cast aluminum alloy, the sum of the mass percentages of Mn and Fe is 0.8 - 0.87%; non-limiting examples are 0.81%, 0.82%, 0.83%, 0.84%, 0.85%, or 0.86%.

[0018] Preferably, in the composition of the die-cast aluminum alloy, the mass percentage of trace elements is 0.16 - 0.232%; non-limiting examples are 0.17%, 0.18%, 0.19%, 0.2%, 0.21%, 0.22% or 0.23%.

[0019] In the composition of the trace elements, non-limiting examples of the mass percentage of Zr are 0.09%, 0.1%, 0.11%, 0.12%, 0.13% or 0.14%.

[0020] In the composition of the trace elements, non-limiting examples of the mass percentage of Sr are 0.008%, 0.01%, 0.012%, 0.015% or 0.018%.

[0021] In the composition of the trace elements, non-limiting examples of the mass percentage of RE are 0.03%, 0.04%, 0.05%, 0.06%, 0.07% or 0.08%.

[0022] In the composition of the trace elements, non-limiting examples of the mass percentage of Ti are 0.01%, 0.02%, 0.03% or 0.04%.

[0023] Preferably, the die-cast aluminum alloy is composed of the following components by mass percentage: 10.5 - 13% Si, 0.08 - 0.15% Mg, 0.35 - 0.55% Fe, 0.3 - 0.45% Mn, 0.16 - 0.232% trace elements, and the balance is impurity elements and Al; the trace elements are composed of the following components by mass percentage: 0.08 - 0.15% Zr, 0.012 - 0.02% Sr, 0.02 - 0.09% RE, 0 - 0.05% Ti; the sum of the mass percentages of Mn and Fe is 0.8 - 0.87%.

[0024] Preferably, in the composition of the die-cast aluminum alloy, the mass percentage of impurity elements < 0.5%; more preferably, among the impurity elements, the mass percentage of a single impurity element < 0.1%.

[0025] Preferably, the RE is a mixture of La and Ce.

[0026] Preferably, in the RE, the mass ratio of La to Ce is 0.2 - 0.5.

[0027] Preferably, the tensile strength of the die-cast aluminum alloy is 280 - 320 MPa; more preferably 295 - 310 MPa.

[0028] Preferably, the yield strength of the die-cast aluminum alloy is 135 - 160 MPa; more preferably 140 - 155 MPa.

[0029] Preferably, the elongation of the die-casting aluminum alloy is 12-20%; more preferably 12.5-18.5%.

[0030] Preferably, the die-casting aluminum alloy contains spherical eutectic silicon grains.

[0031] Preferably, the average particle size of the eutectic silicon is 0.5-5 μm; more preferably 0.5-3 μm; even more preferably 0.5-2 μm.

[0032] The second aspect of the present invention provides a method for preparing a die-casting aluminum alloy as described in the first aspect of the present invention, comprising the following steps: melting an initial raw material containing target components, performing a first refining, adjusting the contents of other components except Mg, Sr, and RE to target contents, performing a second refining, adjusting the contents of Mg, Sr, and RE to target contents, and casting to obtain the die-casting aluminum alloy.

[0033] By performing two refinings, the purity and strength-toughness of the alloy can be improved. And since Mg, Sr, and RE are easily burned-out elements, their contents are adjusted after the second refining, and finally a die-casting aluminum alloy containing various target contents and target components is obtained, and a heat-treatment-free die-casting alloy with both castability and strength-toughness is prepared.

[0034] Preferably, the initial raw material includes at least one of Al-Si, Al-Mn, Al-Si-Mg, Al-Mg-Mn-Fe, or Al-Mg-Mn series alloys.

[0035] In some specific embodiments of the present invention, the initial raw material is selected from aluminum alloy scraps; in some more specific embodiments of the present invention, the mass percentage of the aluminum alloy scraps in all the raw materials of the die-casting aluminum alloy is ≥50%; non-limiting examples are 60%, 70%, 80%, 90%, or 100%.

[0036] Since in the die-casting aluminum alloy of the present invention, in addition to Si, it also contains a certain amount of elements such as Mg, Fe, Mn, Ti, Sr, etc., this provides a prerequisite for the addition of aluminum alloy scraps. Through appropriate ratios, the mass ratio of the scraps can be up to more than 50%. If the composition of the aluminum alloy scraps is reasonably adjusted to meet the requirements of the composition of each component in the die-casting aluminum alloy, the usage amount of the aluminum alloy scraps can reach 100%.

[0037] When the present invention uses aluminum alloy waste as the initial raw material, it actually provides a method for upgrading and recycling aluminum alloy waste, and finally produces a die-casting aluminum alloy with both casting formability and high strength and toughness that can be heat-treated free. The method of the present invention can use more than 50% of aluminum alloy waste as raw materials, which can greatly reduce carbon emissions and energy consumption during alloy preparation, and at the same time can offset the cost brought by adding trace rare earth elements, and the obtained alloy has good casting formability and high strength and toughness.

[0038] In some specific embodiments of the present invention, the way to adjust the component content is to add a regulating raw material; the regulating raw material includes at least one of a simple substance, an intermediate alloy or a compound containing this component.

[0039] In some specific embodiments of the present invention, when adjusting the contents of Sr and RE, the regulating raw material used is an Al-Sr-RE intermediate alloy.

[0040] Preferably, the melting temperature is 700 - 750 °C.

[0041] Preferably, the temperature of the first refining is 700 - 750 °C.

[0042] Preferably, the temperature of the second refining is 700 - 750 °C.

[0043] Preferably, the first refining and the second refining are carried out in the presence of a refining agent and a protective gas.

[0044] Preferably, the refining agent includes chlorides, fluorides or a combination thereof; more preferably, the refining agent is selected from the combination of chlorides and fluorides.

[0045] Preferably, the protective gas includes at least one of nitrogen, argon or helium.

[0046] Preferably, the casting is specifically as follows: After the melt is allowed to stand for 15 - 30 min, the slag is skimmed off, and then the casting is carried out under the condition of a covering agent.

[0047] Preferably, the covering agent is selected from chlorides. The chlorides can protect the melt and are beneficial to the casting process.

[0048] The third aspect of the present invention provides an application of the die-casting aluminum alloy as described in the first aspect of the present invention in the automotive field.

[0049] Preferably, the vehicle is a lightweight vehicle; more preferably, the lightweight vehicle is a new energy vehicle.

[0050] The beneficial effects of the present invention are as follows: Based on the Al-Si alloy, by adjusting the content of Mg, it is beneficial to grain refinement and deep modification of eutectic silicon to refine the microstructure. The contents of Fe and Mn are designed through thermodynamic calculations to control the type, morphology and distribution of iron-rich phases, and specific contents of trace elements including Zr, Sr, RE and optional Ti are added to improve the strength and plasticity of the alloy. Finally, a heat-treatment-free die-casting aluminum alloy with both castability and high strength and toughness is prepared, which has wide applications in the automotive field, especially in the field of lightweighting.

[0051] More specifically, compared with the prior art, the present invention has the following advantages:

[0052] 1. The die-casting aluminum alloy of the present invention has good castability, and does not stick to the mold during the alloy preparation process. In the present invention, the eutectic point of Si is about 12.6% (mass percentage). By designing the content of Si near the eutectic point, the fluidity of the alloy is maximally improved; in addition, both Fe and Mn can effectively reduce mold sticking, and through total amount control, the optimization of non-sticking to the mold is achieved.

[0053] 2. The die-casting aluminum alloy of the present invention has good strength and toughness. Regarding strength, mainly by designing the content of Mg within the solid solubility range, the strength of the alloy is improved through solid solution strengthening. Regarding toughness and plasticity, mainly through the following aspects: First, by adding a small amount of Zr to refine the grains, especially to ensure that a small amount of primary α-Al still forms when the Si content is relatively low; second, by adding an Al-Sr-RE composite modifier to deeply modify the eutectic silicon and refine the size of the eutectic silicon; finally, by the relative contents of Si, Fe, and Mn to control the morphology of the iron-rich phase and reduce the harm of the iron-rich phase, thereby improving the plasticity of the alloy.

[0054] 3. The die-casting aluminum alloy of the present invention can use aluminum alloy scrap as the initial raw material. Through appropriate proportioning, the mass ratio of the scrap can be up to more than 50% at most. This provides a method for grade-preserving recycling of aluminum alloy scrap, which can greatly reduce carbon emissions and energy consumption during the alloy preparation process, and at the same time can offset the cost brought by adding trace rare earth elements, and the obtained alloy has good castability and strength and toughness. Description of the Drawings

[0055] Figure 1 It is the metallographic atlas of the die-casting aluminum alloy of Example 1 of the present invention.

[0056] Figure 2 It is the metallographic atlas of the die-casting aluminum alloy of Comparative Example 1 of the present invention. Detailed Embodiments

[0057] The content of the present invention will be further described in detail through specific embodiments below. It should also be understood that the following embodiments are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the principles described in the present invention all fall within the protection scope of the present invention. The specific process parameters and the like in the following examples are also only an example within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description in this article, rather than being limited to the specific data in the following examples. The raw materials, reagents or devices used in the following examples and comparative examples can be obtained from conventional commercial channels or can be obtained by existing known methods without special instructions.

[0058] It should be noted that in the following examples and comparative examples, RE is a mixture of La and Ce, and the mass ratio of La to Ce is 0.2 - 0.5; the temperatures of the first refining and the second refining are the same as the melting temperature, the time and pressure adopt conventional processes, the refining agent is chloride and a small amount of fluoride; the covering agent is chloride for protecting the melt; the way to adjust the component content is to add regulating raw materials, and the regulating raw materials include at least one of the simple substance, master alloy or compound containing this component.

[0059] Example 1

[0060] A die-casting aluminum alloy that can be heat-treated-free is composed of the following components by mass percentage:

[0061] Si 10.5%, Mg 0.15%, Fe 0.55%, Mn 0.3%, Zr 0.15%, Sr 0.01%, RE 0.03%, and the rest are impurity elements and Al. RE is a mixture of La and Ce, and the mass ratio of La to Ce is 0.5.

[0062] The preparation process of this die-casting aluminum alloy is as follows:

[0063] (1) Scrap sorting: Using a portable composition tester, select Al-Si, Al-Mn, Al-Si-Mg, Al-Mg-Mn-Fe, Al-Mg-Mn series scraps, and determine the addition ratio of various scraps according to the scraps and the target components;

[0064] (2) Melting: Add the scraps to the melting furnace in sequence. Before adding the materials, the scraps with small size (<10mm) and large specific surface area need to be pressed, and the temperature is raised to 720°C;

[0065] (3) First refining: After the raw materials are melted, blow high-purity argon / nitrogen carrying the refining agent into the melt to purify the melt;

[0066] (4) Composition adjustment: After holding the temperature for 20 min, take a sample to test the alloy composition, and make the first adjustment according to the alloy composition (except for Mg, Sr, and RE elements). Subsequently, perform the second refining, and the refining process is the same as the first one;

[0067] (5) Modification: Take a sample to test the alloy composition, and add Mg and Al-Sr-RE master alloy as needed;

[0068] (6) Casting: After the melt stands still for 20 min, skim the slag, and then sprinkle a layer of covering agent; the aluminum melt is transferred through a launder to a holding furnace and directly supplied to a casting forming device or an ingot production line; a rotary degassing device and a double-layer ceramic filter plate are installed on the launder to obtain a clean aluminum alloy melt and ingots.

[0069] Example 2

[0070] A die-casting aluminum alloy that can be free of heat treatment is composed of the following components by mass percentage:

[0071] Si 13%, Mg 0.08%, Fe 0.35%, Mn 0.45%, Zr 0.08%, Ti 0.01%, Sr 0.02%, RE 0.05%, and the balance is impurity elements and Al. RE is a mixture of La and Ce, and the mass ratio of La to Ce is 0.25.

[0072] The preparation process of the die-casting aluminum alloy is as follows:

[0073] (1) Scrap sorting: Use a portable composition tester to select Al-Si, Al-Mn, Al-Si-Mg, Al-Mg-Mn-Fe, and Al-Mg-Mn series scraps, and determine the addition ratio of each scrap according to the scraps and the target composition;

[0074] (2) Melting: Add the scraps to the melting furnace in sequence. Before adding the materials, it is necessary to press the scraps with small size (<10 mm) and large specific surface area, and heat up to 730 °C;

[0075] (3) First refining: After the raw materials are melted, blow high-purity argon / nitrogen carrying a refining agent into the melt to purify the melt;

[0076] (4) Composition adjustment: After holding the temperature for 15 min, take a sample to test the alloy composition, and make the first adjustment according to the alloy composition (except for Mg, Sr, and RE elements). Subsequently, perform the second refining, and the refining process is the same as the first one;

[0077] (5) Modification: Take a sample to test the alloy composition, and add Mg and Al-Sr-RE master alloy as needed;

[0078] (6) Casting: After the melt is static for 30 min, skim the slag, and then sprinkle a layer of covering agent; the aluminum melt is transferred through a launder to a holding furnace and directly supplied to a casting forming device or an ingot production line; a rotary degassing device and a double-layer ceramic filter plate are installed on the launder to obtain a clean aluminum alloy melt and ingots.

[0079] Example 3

[0080] A die-casting aluminum alloy that can be free of heat treatment is composed of the following components by mass percentage:

[0081] Si 12%, Mg 0.13%, Fe 0.45%, Mn 0.40%, Zr 0.10%, Ti 0.03%, Sr 0.006%, RE 0.09%, and the balance are impurity elements and Al. RE is a mixture of La and Ce, and the mass ratio of La to Ce is 0.2.

[0082] The preparation process of the die-casting aluminum alloy is as follows:

[0083] (1) Scrap sorting: Use a portable composition tester to select Al-Si, Al-Mn, Al-Si-Mg, Al-Mg-Mn-Fe, and Al-Mg-Mn series scraps, and determine the addition ratio of each scrap according to the scraps and the target composition;

[0084] (2) Melting: Add the scraps to a melting furnace in sequence. Before feeding, the scraps with small size (<10 mm) and large specific surface area need to be pressed, and the temperature is raised to 700 °C;

[0085] (3) First refining: After the raw materials are melted, blow high-purity argon / nitrogen carrying a refining agent into the melt to purify the melt;

[0086] (4) Composition adjustment: After holding for 25 min, sample and test the alloy composition, and make the first adjustment (except for Mg, Sr, and RE elements) according to the alloy composition. Then carry out the second refining, and the refining process is the same as the first one;

[0087] (5) Modification: Sample and test the alloy composition, and add Mg and Al-Sr-RE master alloy as needed;

[0088] (6) Casting: After the melt is static for 15 min, skim the slag, and then sprinkle a layer of covering agent; the aluminum melt is transferred through a launder to a holding furnace and directly supplied to a casting forming device or an ingot production line; a rotary degassing device and a double-layer ceramic filter plate are installed on the launder to obtain a clean aluminum alloy melt and ingots.

[0089] Example 4

[0090] A die-casting aluminum alloy that can be free of heat treatment is composed of the following components by mass percentage:

[0091] Si 11.5%, Mg 0.10%, Fe 0.50%, Mn 0.37%, Zr 0.12%, Ti 0.05%, Sr 0.015%, RE 0.02%, and the rest are impurity elements and Al. RE is a mixture of La and Ce, and the mass ratio of La to Ce is 0.4.

[0092] The preparation process of this die-casting aluminum alloy is as follows:

[0093] (1) Scrap sorting: Using a portable composition tester, select Al-Si, Al-Mn, Al-Si-Mg, Al-Mg-Mn-Fe, and Al-Mg-Mn series scraps, and determine the addition ratio of various scraps according to the scraps and the target composition;

[0094] (2) Melting: Add the scraps to the melting furnace in sequence. Before adding the materials, the scraps with small size (<10mm) and large specific surface area need to be pressed, and the temperature is raised to 750 °C;

[0095] (3) First refining: After the raw materials are melted, blow high-purity argon / nitrogen carrying a refining agent into the melt to purify the melt;

[0096] (4) Composition adjustment: After holding for 25 minutes, take samples to test the alloy composition, and make the first adjustment (except for Mg, Sr, and RE elements) according to the alloy composition. Then carry out the second refining, and the refining process is the same as the first time;

[0097] (5) Modification: Take samples to test the alloy composition, and add Mg and Al-Sr-RE master alloy as needed;

[0098] (6) Casting: After the melt stands for 20 minutes, skim the slag, and then sprinkle a layer of covering agent; the aluminum melt is transferred through a launder to a holding furnace and directly supplied to a casting equipment or an ingot production line; a rotary degassing device and a double-layer ceramic filter plate are installed on the launder to obtain a clean aluminum alloy melt and ingots.

[0099] Comparative Example 1

[0100] A die-casting aluminum alloy that can be heat-treated free, different from Example 1 in that the composition of Comparative Example 1 does not contain RE element, and other components, their contents, and the alloy preparation process are the same as those of Example 1.

[0101] Comparative Example 2

[0102] A die-casting aluminum alloy that can be heat-treated free, different from Example 2 in that the composition of Comparative Example 2 does not contain Sr element, and other components, their contents, and the alloy preparation process are the same as those of Example 2.

[0103] Comparative Example 3

[0104] A die-casting aluminum alloy that can be heat-treated free, which is different from Example 3 in that the composition of Comparative Example 3 does not contain Zr element, and the other components, their contents and the alloy preparation process are the same as those in Example 3.

[0105] Comparative Example 4

[0106] A die-casting aluminum alloy that can be heat-treated free, which is different from Example 4 in that the composition of Comparative Example 4 does not contain Ti element, and the other components, their contents and the alloy preparation process are the same as those in Example 4.

[0107] Select the aluminum alloy die-castings prepared in Examples 1 to 4 and Comparative Examples 1 to 4, and detect their tensile mechanical properties respectively. The tests are carried out in accordance with GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature". The results are shown in Table 1.

[0108] Table 1 Composition (unit: mass percentage %) and mechanical properties of die-casting aluminum alloys in Examples 1 to 4 and Comparative Examples 1 to 4

[0109]

[0110]

[0111] Analyze Table 1. Comparing Examples 1 to 2 with Comparative Examples 1 to 2, it can be seen that when Sr and RE are both contained, the elongation rate of the die-casting parts is significantly improved compared with when Sr or RE is added alone; comparing Examples 3 to 4 with Comparative Examples 3 to 4, it can be seen that the addition of Zr and Ti is beneficial to the significant improvement of the plasticity of the castings, and the alloy strength is also slightly improved; and from the comparison between Example 1 and Comparative Example 4, it can be seen that adding appropriate amounts of trace elements (including Zr, Ti, Sr, RE) is beneficial to improving the strength and plasticity of the material.

[0112] Perform a microscopic morphology analysis on the structure obtained in Example 1. The results are as Figure 1 shown. The grayish-black ones are eutectic silicon, and the white ones are aluminum matrix. It can be seen that the eutectic silicon obtained in Example 1 is evenly distributed, with small size, an average particle size of about 2 μm, and high sphericity. Perform a microscopic morphology analysis on the structure obtained in Comparative Example 1. The results are as Figure 2 shown. It can be seen that the eutectic silicon obtained in Comparative Example 1 is in the form of plate-like and Chinese character-like, unevenly distributed, and has low sphericity.

[0113] As can be seen from the above, the die-casting aluminum alloy of the embodiment of the present invention has good castability and does not stick to the mold during the alloy preparation process. In the embodiment of the present invention, the eutectic point of Si is about 12.6% (mass percentage). By designing the content of Si near the eutectic point, the fluidity of the alloy is maximally improved; in addition, both Fe and Mn can effectively reduce mold sticking, and through total amount control, the optimization of non-sticking to the mold is achieved.

[0114] The die-casting aluminum alloy of the embodiment of the present invention has good strength and toughness. Regarding strength, it is mainly by designing the content of Mg within the solid solubility range to improve the strength of the alloy through solid solution strengthening. Regarding toughness and plasticity, it is mainly through the following aspects: First, adding a small amount of Zr to refine the grains, especially ensuring that a small amount of primary α-Al is formed even when the Si content is relatively low; second, adding an Al-Sr-RE composite modifier to deeply modify the eutectic silicon and refine the size of the eutectic silicon; finally, regulating the morphology of the iron-rich phase by the relative contents of Si, Fe, and Mn to reduce the harm of the iron-rich phase, thereby improving the plasticity of the alloy.

[0115] The die-casting aluminum alloy of the embodiment of the present invention can use aluminum alloy scraps as the initial raw material. Through appropriate ratios, the mass ratio of the scraps can be up to more than 50% at most. This provides a method for the grade-preserving recycling of aluminum alloy scraps, which can greatly reduce the carbon emissions and energy consumption during the alloy preparation process, and at the same time can offset the cost brought by adding a small amount of rare earth elements, and the obtained alloy has good castability and strength and toughness.

[0116] In summary, the present invention is based on the Al-Si alloy. By adjusting the content of Mg, it is beneficial to grain refinement and deep modification and refinement of the eutectic silicon structure. Using thermodynamic calculations to design the contents of Fe and Mn to regulate the type, morphology, and distribution of the iron-rich phase, and adding specific contents of trace elements, including Zr, Sr, RE, and optional Ti, to improve the strength and plasticity of the alloy. Finally, a die-casting aluminum alloy with both castability and strength and toughness that can be heat-treated-free is prepared, which has a wide range of applications in the automotive field, especially in the lightweight field.

Claims

1. A die-casting aluminum alloy that can be heat-treated free, characterized in that, It consists of components with the following mass percentages: 11.5 - 13% Si, 0.05 - 0.15% Mg, 0.35 - 0.65% Fe, 0.2 - 0.45% Mn, 0.16 - 0.32% trace elements, and the balance being impurity elements and Al; the trace elements consist of components with the following mass percentages: 0.08 - 0.15% Zr, 0.012 - 0.03% Sr, 0.02 - 0.09% RE, 0.03 - 0.05% Ti, and the Sr and RE are added in the form of an Al - Sr - RE master alloy; the sum of the mass percentages of Mn and Fe is 0.75 - 0.9%; the die - casting aluminum alloy contains spherical eutectic silicon grains; The average particle size of the eutectic silicon is 0.5 - 5 μm; The tensile strength of the die - casting aluminum alloy is 300 - 320 MPa; the yield strength of the die - casting aluminum alloy is 140 - 160 MPa; The elongation of the die - casting aluminum alloy is 16 - 20%; The heat - treatable - free die - casting aluminum alloy is obtained by a method including the following steps: melting the initial raw materials containing the target components, conducting the first refining, adjusting the contents of other components except Mg, Sr, and RE to the target contents, conducting the second refining, adjusting the contents of Mg, Sr, and RE to the target contents, and casting to obtain the die - casting aluminum alloy; the initial raw materials are selected from aluminum alloy scraps; the mass percentage of the aluminum alloy scraps in all the raw materials of the die - casting aluminum alloy is ≥50%.

2. The die-cast aluminum alloy according to claim 1, characterized in that, The RE is a mixture of La and Ce.

3. The die-cast aluminum alloy according to claim 2, wherein The mass ratio of La to Ce is 0.2 - 0.

5.

4. A preparation method of the die-casting aluminum alloy according to any one of claims 1 to 3, characterized in that, It includes the following steps: Melting the initial raw materials containing the target components, conducting the first refining, adjusting the contents of other components except Mg, Sr, and RE to the target contents, conducting the second refining, adjusting the contents of Mg, Sr, and RE to the target contents, and casting to obtain the die - casting aluminum alloy; the initial raw materials are selected from aluminum alloy scraps; the mass percentage of the aluminum alloy scraps in all the raw materials of the die - casting aluminum alloy is ≥50%.

5. The preparation method according to claim 4, characterized in that, The initial raw materials include at least one of Al - Si, Al - Mn, Al - Si - Mg, Al - Mg - Mn - Fe, or Al - Mg - Mn series alloys.

6. The preparation method according to claim 4, wherein The melting temperature is 700 - 750 °C; And / or, the temperature of the first refining is 700 - 750 °C; And / or, the temperature of the second refining is 700 - 750 °C.

7. The preparation method according to claim 4, characterized in that, The first refining and the second refining are carried out in the presence of a refining agent and a protective gas.

8. Application of a die - casting aluminum alloy as described in any one of claims 1 - 3 in the automotive field.

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