A die-casting thermal cracking-resistant heat treatment-free aluminum alloy and its preparation method

Abstract

The present invention relates to the technical field of aluminum alloy materials, and in particular to a die-casting aluminum alloy that resists thermal cracking and does not require heat treatment, and a preparation method thereof. The aluminum alloy comprises the following raw materials in percentage by mass: 6-10% Mg, 1.2-2.8% Li, 0.05-0.15% Cu, 0.4-0.5% Mn, 0.05-0.08% Ti, 0.01-0.03% Sr, 0.75-0.8% composite refiner, and 0.25-0.35% modifier. Each element is added in the form of an industrial pure metal or alloy, wherein the element Li is added in the form of a Mg-Li alloy, the element Ti is added in the form of an Al-Ti alloy, the element Sr is added in the form of an Al-Sr alloy, and the balance is metallic Al. The die-casting aluminum alloy that resists thermal cracking and does not require heat treatment prepared by the present invention not only has good thermal cracking resistance, but also has excellent tensile strength, thereby effectively ensuring its quality.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy materials, in particular to a die-casting aluminum alloy that resists thermal cracking and does not require heat treatment, and a preparation method thereof. Background Art

[0002] Die-cast aluminum alloys have a wide range of applications in modern industry, especially in the automotive, aerospace and electronics fields.

[0003] With the development of industry, the performance requirements for die-cast aluminum alloys are becoming increasingly stringent, while the control of production costs and production efficiency is also becoming more stringent. In the automotive industry, to achieve lightweighting goals, improve fuel efficiency, and reduce exhaust emissions, a large number of high-performance aluminum alloy components are required. The aerospace field, on the other hand, has extremely high requirements for material strength, toughness, heat resistance, and corrosion resistance, while also requiring components to have high reliability and stability.

[0004] Traditional die-cast aluminum alloys, which rely on heat treatment to improve their performance, are no longer able to meet these demands. Therefore, developing a die-cast aluminum alloy that is heat-resistant and heat-treatment-free, which can avoid heat cracking during the die-casting process while achieving excellent overall performance without heat treatment, has become an important topic in the current aluminum alloy material research field. Summary of the Invention

[0005] The purpose of the present invention is to provide a die-casting aluminum alloy that is resistant to thermal cracking and does not require heat treatment, and a preparation method thereof. The prepared die-casting aluminum alloy that is resistant to thermal cracking and does not require heat treatment not only has good thermal cracking resistance, but also has excellent tensile strength, effectively ensuring its quality.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The first aspect of the present invention provides a die-casting heat-cracking-resistant heat-treatment-free aluminum alloy, which includes the following raw materials in percentage by mass: Mg 6-10%, Li 1.2-2.8%, Cu 0.05-0.15%, Mn 0.4-0.5%, Ti 0.05-0.08%, Sr 0.01-0.03%, composite refiner 0.75-0.8%, and modifier 0.25-0.35%. Each element is added in the form of an industrial pure metal or alloy, wherein the element Li is added in the form of a Mg-Li alloy, the element Ti is added in the form of an Al-Ti alloy, the element Sr is added in the form of an Al-Sr alloy, and the balance is metallic Al.

[0008] The present invention is further configured as follows: the composite refiner is formed by mixing the first refiner and the second refiner in a mass ratio of 1:0.22-0.34.

[0009] The present invention is further configured as follows: the preparation process of the first refiner is as follows:

[0010] Weigh 2.5% Ti, 2.5% B, and 0.3% C according to the following mass percentages, with the balance being Al. Dry the resulting mixture in a vacuum drying oven at 110-120°C for 120-140 minutes.

[0011] After cooling, the mixture was placed in a vacuum planetary ball mill, and stearic acid was added thereto. The mixture was ball-milled for 40 to 50 minutes at a speed of 310 to 350 r / min and a ball-to-material ratio of 10:1. The milled powder was pre-pressed into small round blocks with a diameter of 35 μm and a thickness of 7 mm. The mixture was placed in a tube furnace under vacuum atmosphere and heated, and then kept warm for 110 to 120 minutes.

[0012] The sintered powder is ball-milled for the second time under vacuum conditions to obtain the first refining agent.

[0013] The present invention is further configured as follows: the added amount of the stearic acid is 1.2-1.4% of the mass of the mixture.

[0014] The present invention is further configured as follows: the temperature is raised to 450-470° C. at a rate of 10-15° C. / min.

[0015] The present invention is further configured as follows: the rotation speed of the secondary ball milling is 280-300 r / min, and the ball milling time is 22-24 h.

[0016] The present invention is further configured as follows: the preparation process of the second refiner is as follows:

[0017] Al powder, Nb powder and graphene powder were mixed uniformly in a vacuum planetary ball mill at a mass ratio of 38-40:1:1;

[0018] The ball-milled powder was taken out and pre-pressed into small round blocks with a diameter of 35 μm and a thickness of 7 mm. The blocks were placed in a tube furnace under vacuum atmosphere and heated for 110 to 120 minutes.

[0019] The sintered powder is subjected to a second ball milling under vacuum conditions to obtain a second refining agent;

[0020] Among them, the ball milling speed is 300-310 r / min, the time is 80-100 min, and the ball-to-material ratio is 10:1;

[0021] The temperature is raised to 500-510°C at a rate of 8-10°C / min;

[0022] The rotation speed of the secondary ball milling is 320-340 r / min, and the ball milling time is 18-20 h.

[0023] The present invention is further configured as follows: the preparation process of the modifier is as follows:

[0024] Al-10Sb and Al-10La were placed in a resistance furnace at a mass ratio of 5:1 and melted at 860°C.

[0025] After complete melting, the covering agent is evenly sprinkled on the surface of the melt, and then the melt is kept warm for 30 minutes. After the end of the insulation, the melt is poured into a mold preheated to 250°C, cooled, crushed, and ball-milled to obtain a modifier.

[0026] The present invention is further configured as follows: the added amount of the covering agent is 1% of the mass of the melt, and the covering agent is formed by mixing sodium chloride and potassium chloride in a mass ratio of 1:1.

[0027] The second aspect of the present invention further provides a method for preparing the above-mentioned die-casting heat-cracking resistant heat-treatment-free aluminum alloy, comprising the following steps:

[0028] Step 1: Accurately weigh the raw materials required for preparing the aluminum alloy, preheat the Al material to 160-180°C, then place it in a melting furnace and melt it at 760-780°C. After it is completely melted, keep it warm for 30-40 minutes;

[0029] Step 2: After heating to 860°C, add the remaining raw materials under an inert atmosphere, melt them completely, then cool to 840°C and keep warm for 12 to 15 minutes;

[0030] Step 3: After heat preservation, heat it to 860℃ for the second time, then degas and refine it, and keep it warm for 10-15 minutes. Cast the obtained alloy melt into an ingot at a pouring temperature of 740-800℃ and a cooling rate of 50-100℃ / s to obtain an aluminum alloy product.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] In the present invention, Mg, Li, Cu, Mn, Ti, Sr, a composite refiner, a modifier, and Al are used as raw materials, wherein each element is added in the form of an industrial pure metal or alloy, the element Li is added in the form of a Mg-Li alloy, the element Ti is added in the form of an Al-Ti alloy, and the element Sr is added in the form of an Al-Sr alloy. The raw materials required for preparing the aluminum alloy are accurately weighed, and the Al material is preheated, then placed in a smelting furnace for melting, and then heated. After heating, the remaining raw materials are added thereto under an inert atmosphere. After all are melted, the temperature is lowered and kept warm. After keeping warm, the temperature is raised for a second time, and then degassing and refining are carried out, and then keeping warm. The resulting alloy melt is cast into an ingot to obtain an aluminum alloy product. The die-casting heat-resistant and heat-treatment-free aluminum alloy prepared by the present invention not only has good heat cracking resistance, but also has excellent tensile strength, effectively ensuring its quality and quality. The die-casting heat-resistant and heat-treatment-free aluminum alloy and its preparation method provided by the present invention have a broader market prospect and are more suitable for promotion. DETAILED DESCRIPTION

[0033] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0034] Example 1

[0035] This embodiment provides a die-cast, thermal crack-resistant, heat-treatment-free aluminum alloy, comprising the following raw materials in percentage by mass: 6% Mg, 1.2% Li, 0.05% Cu, 0.4% Mn, 0.05% Ti, 0.01% Sr, 0.75% composite refiner, and 0.25% modifier. Each element is added in the form of an industrially pure metal or alloy, wherein the element Li is added in the form of a Mg-Li alloy, the element Ti is added in the form of an Al-Ti alloy, and the element Sr is added in the form of an Al-Sr alloy, with the remainder being metallic Al.

[0036] The composite refiner is prepared by mixing the first refiner and the second refiner in a mass ratio of 1:0.22.

[0037] Furthermore, the preparation process of the first refiner is as follows:

[0038] Ti 2.5%, B 2.5%, C 0.3% were weighed according to the following mass percentages, and the balance was Al. The resulting mixture was placed in a vacuum drying oven at 110°C and dried for 120 minutes;

[0039] After cooling, the product was placed in a vacuum planetary ball mill, and stearic acid was added thereto. The product was ball-milled for 40 min at 310 r / min and a ball-to-material ratio of 10:1. The milled powder was pre-pressed into small round blocks with a diameter of 35 μm and a thickness of 7 mm. The ball was placed in a tube furnace under vacuum atmosphere and heated for 110 min.

[0040] The sintered powder is ball-milled for the second time under vacuum conditions to obtain the first refining agent.

[0041] Furthermore, the amount of stearic acid added is 1.2% by weight of the mixture.

[0042] The temperature was raised to 450°C at a rate of 10°C / min.

[0043] The rotation speed of the secondary ball milling was 280 r / min, and the ball milling time was 22 h.

[0044] In addition, the preparation process of the second refiner is as follows:

[0045] Al powder, Nb powder and graphene powder were mixed uniformly in a vacuum planetary ball mill at a mass ratio of 38:1:1;

[0046] The ball-milled powder was taken out and pre-pressed into a small round block with a diameter of 35 μm and a thickness of 7 mm. The block was placed in a tube furnace under vacuum atmosphere and heated for 110 min.

[0047] The sintered powder is subjected to a second ball milling under vacuum conditions to obtain a second refining agent;

[0048] The ball milling speed was 300 r / min, the time was 80 min, and the ball-to-material ratio was 10:1;

[0049] The temperature was raised to 500 °C at a rate of 8 °C / min;

[0050] The rotation speed of the secondary ball milling was 320 r / min, and the ball milling time was 18 h.

[0051] The preparation process of the modifier is as follows:

[0052] Al-10Sb and Al-10La were placed in a resistance furnace at a mass ratio of 5:1 and melted at 860°C.

[0053] After complete melting, the covering agent is evenly sprinkled on the surface of the melt, and then the melt is kept warm for 30 minutes. After the end of the insulation, the melt is poured into a mold preheated to 250°C, cooled, crushed, and ball-milled to obtain a modifier.

[0054] Furthermore, the amount of the covering agent added is 1% of the mass of the melt, and the covering agent is prepared by mixing sodium chloride and potassium chloride in a mass ratio of 1:1.

[0055] In addition, this embodiment also provides a method for preparing the above-mentioned die-casting heat-cracking-resistant heat-treatment-free aluminum alloy, comprising the following steps:

[0056] Step 1: Accurately weigh the raw materials required for preparing the aluminum alloy, preheat the Al material to 160°C, then place it in a melting furnace and melt it at 760°C. After it is completely melted, keep it warm for 30 minutes;

[0057] Step 2: After heating to 860°C, add the remaining raw materials under an inert atmosphere, melt them completely, then cool to 840°C and keep warm for 12 minutes;

[0058] Step 3: After heat preservation, the temperature is raised to 860°C for the second time, and then degassing and refining are carried out, and the heat preservation is continued for 10 minutes. The obtained alloy melt is poured into an ingot with a pouring temperature of 740°C and a cooling rate of 50°C / s to obtain an aluminum alloy product.

[0059] Example 2

[0060] The preparation method of the die-casting thermal cracking resistant heat treatment-free aluminum alloy provided in this embodiment is basically the same as that of Example 1, except that the specific raw material composition and the specific preparation method of the die-casting thermal cracking resistant heat treatment-free aluminum alloy provided in this embodiment are different. The specific raw material composition and the specific preparation method of the die-casting thermal cracking resistant heat treatment-free aluminum alloy provided in this embodiment are as follows:

[0061] This embodiment provides a die-cast, thermal crack-resistant, heat-treatment-free aluminum alloy, comprising the following raw materials in percentage by mass: Mg 8%, Li 2%, Cu 0.15%, Mn 0.5%, Ti 0.06%, Sr 0.02%, a composite refiner 0.77%, and a modifier 0.3%. Each element is added in the form of an industrially pure metal or alloy, wherein the element Li is added in the form of a Mg-Li alloy, the element Ti is added in the form of an Al-Ti alloy, and the element Sr is added in the form of an Al-Sr alloy, with the balance being metallic Al.

[0062] The composite refiner is prepared by mixing the first refiner and the second refiner in a mass ratio of 1:0.28.

[0063] Furthermore, the preparation process of the first refiner is as follows:

[0064] Ti 2.5%, B 2.5%, C 0.3% were weighed according to the following mass percentages, and the balance was Al. The resulting mixture was placed in a vacuum drying oven at 115°C and dried for 130 minutes;

[0065] After cooling, the product was placed in a vacuum planetary ball mill, and stearic acid was added thereto. The product was ball-milled for 45 min at 330 r / min and a ball-to-material ratio of 10:1. The milled powder was pre-pressed into small round blocks with a diameter of 35 μm and a thickness of 7 mm. The ball was placed in a tube furnace under vacuum atmosphere and heated for 115 min.

[0066] The sintered powder is ball-milled for the second time under vacuum conditions to obtain the first refining agent.

[0067] Furthermore, stearic acid is added in an amount of 1.3% by weight of the mixture.

[0068] The temperature was raised to 460°C at a rate of 12°C / min.

[0069] The rotation speed of the secondary ball milling was 290 r / min, and the ball milling time was 23 h.

[0070] In addition, the preparation process of the second refiner is as follows:

[0071] Al powder, Nb powder and graphene powder were mixed uniformly in a vacuum planetary ball mill at a mass ratio of 39:1:1;

[0072] The ball-milled powder was taken out and pre-pressed into a small round block with a diameter of 35 μm and a thickness of 7 mm. The block was placed in a tube furnace under vacuum atmosphere and heated for 115 min.

[0073] The sintered powder is subjected to a second ball milling under vacuum conditions to obtain a second refining agent;

[0074] The ball milling speed was 305 r / min, the time was 90 min, and the ball-to-material ratio was 10:1;

[0075] The temperature was raised to 505°C at a rate of 9°C / min;

[0076] The rotation speed of the secondary ball milling was 330 r / min, and the ball milling time was 19 h.

[0077] The preparation process of the modifier is as follows:

[0078] Al-10Sb and Al-10La were placed in a resistance furnace at a mass ratio of 5:1 and melted at 860°C.

[0079] After complete melting, the covering agent is evenly sprinkled on the surface of the melt, and then the melt is kept warm for 30 minutes. After the end of the insulation, the melt is poured into a mold preheated to 250°C, cooled, crushed, and ball-milled to obtain a modifier.

[0080] Furthermore, the amount of the covering agent added is 1% of the mass of the melt, and the covering agent is prepared by mixing sodium chloride and potassium chloride in a mass ratio of 1:1.

[0081] In addition, this embodiment also provides a method for preparing the above-mentioned die-casting heat-cracking resistant heat-treatment-free aluminum alloy, comprising the following steps:

[0082] Step 1: Accurately weigh the raw materials required for preparing the aluminum alloy, preheat the Al material to 170°C, then place it in a melting furnace and melt it at 770°C. After it is completely melted, keep it warm for 35 minutes;

[0083] Step 2: After heating to 860°C, add the remaining raw materials under an inert atmosphere, melt them completely, then cool to 840°C and keep warm for 13 minutes;

[0084] Step 3: After holding, heat up to 860°C for the second time, then degas and refine, and hold for 12 minutes. The resulting alloy melt is poured into an ingot at a pouring temperature of 760°C and a cooling rate of 70°C / s to obtain an aluminum alloy product.

[0085] Example 3

[0086] The preparation method of the die-casting thermal cracking resistant heat treatment-free aluminum alloy provided in this embodiment is basically the same as that of Example 1, except that the specific raw material composition and the specific preparation method of the die-casting thermal cracking resistant heat treatment-free aluminum alloy provided in this embodiment are different. The specific raw material composition and the specific preparation method of the die-casting thermal cracking resistant heat treatment-free aluminum alloy provided in this embodiment are as follows:

[0087] This embodiment provides a die-cast, thermal crack-resistant, heat-treatment-free aluminum alloy, comprising the following raw materials in percentage by mass: Mg 10%, Li 2.8%, Cu 0.15%, Mn 0.5%, Ti 0.08%, Sr 0.03%, a composite refiner 0.8%, and a modifier 0.35%. Each element is added in the form of an industrially pure metal or alloy, wherein the element Li is added in the form of a Mg-Li alloy, the element Ti is added in the form of an Al-Ti alloy, and the element Sr is added in the form of an Al-Sr alloy, with the remainder being metallic Al.

[0088] The composite refiner is prepared by mixing the first refiner and the second refiner in a mass ratio of 1:0.22 to 0.34.

[0089] Furthermore, the preparation process of the first refiner is as follows:

[0090] Ti 2.5%, B 2.5%, C 0.3% were weighed according to the following mass percentages, and the balance was Al. The resulting mixture was placed in a vacuum drying oven at 120°C and dried for 140 minutes;

[0091] After cooling, the product was placed in a vacuum planetary ball mill, and stearic acid was added thereto. The product was ball-milled for 50 min at 350 r / min and a ball-to-material ratio of 10:1. The milled powder was pre-pressed into small round blocks with a diameter of 35 μm and a thickness of 7 mm. The ball was placed in a tube furnace under vacuum atmosphere and heated for 120 min.

[0092] The sintered powder is ball-milled for the second time under vacuum conditions to obtain the first refining agent.

[0093] Furthermore, stearic acid is added in an amount of 1.4% by weight of the mixture.

[0094] The temperature was raised to 470°C at a rate of 15°C / min.

[0095] The rotation speed of the secondary ball milling was 300 r / min, and the ball milling time was 24 h.

[0096] In addition, the preparation process of the second refiner is as follows:

[0097] Al powder, Nb powder and graphene powder were mixed uniformly in a vacuum planetary ball mill at a mass ratio of 40:1:1;

[0098] The ball-milled powder was taken out and pre-pressed into small round blocks with a diameter of 35 μm and a thickness of 7 mm. The blocks were placed in a tube furnace under vacuum atmosphere and heated for 120 min.

[0099] The sintered powder is subjected to a second ball milling under vacuum conditions to obtain a second refining agent;

[0100] The ball milling speed was 310 r / min, the time was 100 min, and the ball-to-material ratio was 10:1;

[0101] The temperature was raised to 510°C at a rate of 10°C / min;

[0102] The rotation speed of the secondary ball milling was 340 r / min, and the ball milling time was 20 h.

[0103] The preparation process of the modifier is as follows:

[0104] Al-10Sb and Al-10La were placed in a resistance furnace at a mass ratio of 5:1 and melted at 860°C.

[0105] After complete melting, the covering agent is evenly sprinkled on the surface of the melt, and then the melt is kept warm for 30 minutes. After the end of the insulation, the melt is poured into a mold preheated to 250°C, cooled, crushed, and ball-milled to obtain a modifier.

[0106] Furthermore, the amount of the covering agent added is 1% of the mass of the melt, and the covering agent is prepared by mixing sodium chloride and potassium chloride in a mass ratio of 1:1.

[0107] In addition, this embodiment also provides a method for preparing the above-mentioned die-casting heat-cracking resistant heat-treatment-free aluminum alloy, comprising the following steps:

[0108] Step 1: Accurately weigh the raw materials required for preparing the aluminum alloy, preheat the Al material to 180°C, then place it in a melting furnace and melt it at 780°C. After it is completely melted, keep it warm for 40 minutes;

[0109] Step 2: After heating to 860°C, add the remaining raw materials under an inert atmosphere, melt them completely, then cool to 840°C and keep warm for 15 minutes;

[0110] Step 3: After heat preservation, the temperature is raised to 860°C for the second time, and then degassing and refining are carried out, and heat preservation is continued for 15 minutes. The obtained alloy melt is poured into an ingot with a pouring temperature of 800°C and a cooling rate of 100°C / s to obtain an aluminum alloy product.

[0111] Comparative Example 1: The difference from Example 1 is that this example does not contain a composite refiner.

[0112] Comparative Example 2: The difference from Example 1 is that in this example, an equal amount of the first refining agent is used instead of the composite refining agent.

[0113] Comparative Example 3: The difference from Example 1 is that in this example, an equal amount of a second refiner is used instead of the composite refiner.

[0114] Comparative Example 4: The difference from Example 1 is that this example does not contain a modifier.

[0115] Performance test: The aluminum alloy samples provided in Examples 1 to 3 and Comparative Examples 1 to 4 are marked as Examples 1 to 3 and Comparative Examples 1 to 4, respectively; and the relevant properties of the aluminum alloys provided in Examples 1 to 3 and Comparative Examples 1 to 4 are tested as follows:

[0116] 1. Thermal crack resistance test: The test method is based on the test standard JB / T4022.2-1999.

[0117] 2. Tensile strength test: The test method is to use the American Instron3369 mechanical testing machine with a tensile rate of 2mm / min.

[0118] The obtained test data are recorded in Table 1 and Table 2 below:

[0119] Table 1 Test results of thermal cracking resistance of each group of aluminum alloys

[0120] Group Thermal crack resistance value (N) Example 1 group 712 Example 2 group 708 Example 3 group 711 Comparison group 1 635 Comparison of 2 groups 647 Comparison of 3 groups 658 Comparison of 4 groups 674

[0121] Table 2 Tensile strength test results of each group of aluminum alloys

[0122] Group Tensile strength (MPa) Example 1 group 301 Example 2 group 296 Example 3 group 297 Comparison group 1 261 Comparison of 2 groups 265 Comparison of 3 groups 270 Comparison of 4 groups 283

[0123] Comparing and analyzing the relevant data in Tables 1 and 2, it can be seen that the die-cast, thermal crack-resistant, heat-treatment-free aluminum alloy prepared by the present invention not only has good thermal cracking resistance but also excellent tensile strength, effectively ensuring its quality and quality. This shows that the die-cast, thermal crack-resistant, heat-treatment-free aluminum alloy and its preparation method provided by the present invention have broader market prospects and are more suitable for promotion.

[0124] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0125] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A die-casting aluminum alloy that resists thermal cracking and does not require heat treatment, characterized in that: The aluminum alloy comprises the following raw materials in mass percentage: Mg 6-10%, Li 1.2-2.8%, Cu 0.05-0.15%, Mn 0.4-0.5%, Ti 0.05-0.08%, Sr 0.01-0.03%, composite refiner 0.75-0.8%, and modifier 0.25-0.35%, wherein each element is added in the form of industrial pure metal or alloy, wherein Li is added in the form of Mg-Li alloy, Ti is added in the form of Al-Ti alloy, Sr is added in the form of Al-Sr alloy, and the balance is metallic Al; The composite refiner is formed by mixing the first refiner and the second refiner in a mass ratio of 1:0.22 to 0.34; The preparation process of the first refiner is as follows: Weigh 2.5% Ti, 2.5% B, and 0.3% C according to the following mass percentages, with the balance being Al. Dry the resulting mixture in a vacuum drying oven at 110-120°C for 120-140 minutes. After cooling, the mixture was placed in a vacuum planetary ball mill, and stearic acid was added thereto. The mixture was ball-milled for 40 to 50 minutes at a speed of 310 to 350 r / min and a ball-to-material ratio of 10:

1. The milled powder was pre-pressed into small round blocks with a diameter of 35 μm and a thickness of 7 mm. The mixture was placed in a tube furnace under vacuum atmosphere and heated, and then kept warm for 110 to 120 minutes. The sintered powder is subjected to secondary ball milling under vacuum conditions to obtain a first refining agent; The preparation process of the second refiner is as follows: Al powder, Nb powder and graphene powder were mixed uniformly in a vacuum planetary ball mill at a mass ratio of 38-40:1:1, wherein the ball milling speed was 300-310 r / min, the time was 80-100 min, and the ball-to-material ratio was 10:1; The ball-milled powder was taken out and pre-pressed into a small round block with a diameter of 35 μm and a thickness of 7 mm. The block was placed in a tube furnace under vacuum atmosphere and heated for 110 to 120 minutes. The temperature was raised to 500 to 510°C at a rate of 8 to 10°C / min. The sintered powder is subjected to a secondary ball milling under vacuum conditions, wherein the secondary ball milling speed is 320-340 r / min and the ball milling time is 18-20 h to obtain a second refining agent; The preparation process of the modifier is as follows: Al-10Sb and Al-10La were placed in a resistance furnace at a mass ratio of 5:1 and melted at 860°C. After complete melting, the covering agent is evenly sprinkled on the surface of the melt, and then the melt is kept warm for 30 minutes. After the end of the insulation, the melt is poured into a mold preheated to 250°C, cooled, crushed, and ball-milled to obtain a modifier.

2. The die-casting heat-cracking resistant heat-treatment-free aluminum alloy according to claim 1, characterized in that: The added amount of the stearic acid is 1.2-1.4% of the mass of the mixture.

3. The die-casting heat-cracking resistant heat-treatment-free aluminum alloy according to claim 1, characterized in that: During the preparation of the first refining agent, the temperature is raised to 450-470° C. at a rate of 10-15° C. / min.

4. The die-casting heat-cracking resistant heat-treatment-free aluminum alloy according to claim 1, characterized in that: During the preparation of the first refining agent, the rotation speed of the secondary ball milling is 280-300 r / min, and the ball milling time is 22-24 h.

5. The die-casting heat-cracking resistant heat-treatment-free aluminum alloy according to claim 1, characterized in that: The added amount of the covering agent is 1% of the mass of the melt, and the covering agent is prepared by mixing sodium chloride and potassium chloride in a mass ratio of 1:

1.

6. The method for preparing a die-casting heat-cracking-resistant heat-treatment-free aluminum alloy according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1: Accurately weigh the raw materials required for preparing the aluminum alloy, preheat the Al material to 160-180°C, then place it in a melting furnace and melt it at 760-780°C. After it is completely melted, keep it warm for 30-40 minutes; Step 2: After heating to 860°C, add the remaining raw materials under an inert atmosphere, melt them completely, then cool to 840°C and keep warm for 12 to 15 minutes; Step 3: After heat preservation, heat it to 860℃ for the second time, then degas and refine it, and keep it warm for 10-15 minutes. Cast the obtained alloy melt into an ingot at a pouring temperature of 740-800℃ and a cooling rate of 50-100℃ / s to obtain an aluminum alloy product.