Heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy and preparation method thereof

Abstract

The invention provides a heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy and a preparation method thereof. The alloy comprises the following elements in percentage by mass: 6.5%-7.5% of Si, 0.45%-0.6% of Mg, 0.3%-0.6% of Cu, 0.5%-5.5% of Ni, 0.1%-0.2% of Ti and the balance of Al and other inevitable impurities. According to the method, the room-temperature tensile strength and the high-temperature tensile strength of the alloy are improved by adjusting the content of Si, Mg, Cu, Ni and Ti in the aluminum alloy and carrying out different heat treatment, the room-temperature tensile strength of the aluminum alloy obtained through two-stage solid solution and single-stage aging treatment reaches 280-315 MPa, and the high-temperature instantaneous tensile strength at the temperature of 270 DEG C is kept to be 210 MPa or above; after two-stage solid solution and two-stage aging treatment, the room-temperature tensile strength reaches 315-340 MPa, the high-temperature instantaneous tensile strength at 150-250 DEG C still keeps 85%-90% of the room-temperature tensile strength, but the tensile strength is kept above 120 MPa after the temperature is higher than 300 DEG C, and therefore the prepared aluminum alloy can be applied to production of large complex castings such as engine boxes and cylinder covers.

Description

Technical Field

[0001] The invention relates to a heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy and a preparation method thereof, belonging to the field of industrial aluminum alloys and their manufacture. Background Art

[0002] Aluminum alloys have been widely used in automobile production due to their advantages such as low density, high strength, high recovery rate and good impact resistance, and have become an ideal material for automobile production. Al-Si alloy has good casting processability. By adding elements such as Cu and Mg to strengthen it, it can be used in the production of large and complex castings such as engine cases and cylinder heads. In diesel engines, Al-6Si aluminum alloy is often used to produce its cylinder head through sand casting. As the cylinder pressure of the diesel engine increases and as required by the new national standard, the operating temperature of the cylinder head increases from 150°C to 200°C during operation, resulting in cracks in the engine cylinder head and oil leakage and other engine failures under excessive pressure and temperature operating conditions. Therefore, it is necessary to optimize the design of the traditional aluminum alloy, improve its casting performance, and improve the heat treatment process so that it can meet the performance of high-temperature and pressure operating conditions.

[0003] The present invention provides a heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy and a preparation method thereof. By improving the proportion of alloy elements, the tensile strength of the cast alloy at high temperatures is improved, and the problem of low alloy performance under high-temperature working environments is solved. The cast alloy in the invention can be used in the production of large and complex castings such as engine cases and cylinder heads, providing greater possibilities for the development of the automotive industry. Summary of the invention

[0004] In order to solve the shortcomings of existing aluminum alloy materials, one of the purposes of the present invention is to provide a heat-resistant and high-strength cast Al-Si-Cu-Ni aluminum alloy, which includes the following substances, calculated by mass percentage: 6.5% to 7.5% Si, 0.45% to 0.6% Mg, 0.3% to 0.6% Cu, 0.5% to 5.5% Ni, 0.1% to 0.2% Ti, and the remainder is Al and other inevitable impurities, wherein the sum of the mass percentages of Si, Mg, Cu, Ni, Ti, the remainder Al and other inevitable impurities is 100%.

[0005] Preferably, the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy includes the following substances, calculated by mass percentage: 7.0% Si, 0.5% Mg, 0.5% Cu, 3.69% Ni, 0.1% Ti, and the remainder is Al and other inevitable impurities, wherein the sum of the mass percentages of Si, Mg, Cu, Ni, Ti, the remainder Al and other inevitable impurities is 100%.

[0006] Another object of the present invention is to provide a method for preparing a heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy, the specific steps of which are as follows:

[0007] (1) Prepare raw materials according to the percentage of elements contained in the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy.

[0008] (2) Add the weighed raw materials with higher melting points into the smelting furnace at the same time until the raw materials are completely melted to obtain an alloy solution.

[0009] (3) Adding a refining agent (any refining agent may be used) to the alloy solution obtained in step (2) for refining, and performing a slag removal treatment after heat preservation to obtain a refined alloy solution.

[0010] (4) Al-Ti master alloy is added to the refined alloy solution for modification. Ar gas is introduced for stirring and degassing to obtain a uniform modified Al-Si alloy melt.

[0011] (5) When the temperature of the Al-Si alloy melt drops to 700-750°C, the Mg-containing raw material is added, stirred and allowed to stand for 30 minutes, and when the temperature drops to 690-710°C, it is cast into an Al-Si-Cu-Ni aluminum alloy material.

[0012] (6) The obtained Al-Si-Cu-Ni aluminum alloy material is placed in a heat treatment furnace for double-stage solution treatment and then water-cooled to room temperature.

[0013] (7) The Al-Si-Cu-Ni aluminum alloy material treated in step (6) is subjected to double aging treatment and then air-cooled to room temperature to obtain product A. Product A is suitable for a high temperature working environment of 150° C. to 250° C.

[0014] The Al-Si-Cu-Ni aluminum alloy material prepared in step (6) is subjected to a single-stage aging treatment and then air-cooled to room temperature to obtain product B. Product B is suitable for a high-temperature working environment of 250°C to 300°C.

[0015] Preferably, the raw materials in step (1) include: Al-Si alloy, Ni-containing raw material, Cu-containing raw material, Mg-containing raw material, Al-Ti master alloy, wherein the Ni-containing raw material is: Al-Ni master alloy or pure Ni, the Cu-containing raw material is: Al-Cu master alloy or pure Cu, and the Mg-containing raw material is: Al-Mg master alloy or pure Mg.

[0016] Preferably, the raw material with a high melting point in step (2) is: Al-Si alloy, Ni-containing raw material, Cu-containing raw material.

[0017] Preferably, the smelting conditions in step (2) are: 780-820° C., and the holding time is 1 h.

[0018] Preferably, the insulation time in step (3) is 5 to 10 minutes.

[0019] Preferably, the conditions for the double-stage solution treatment in step (6) are: first, keep the temperature at 490-510° C. for 2 hours and then continue to heat up to 530-540° C. and keep the temperature for 4-6 hours.

[0020] Preferably, the conditions for the double aging treatment in step (7) are: first keep at 160-170°C for 8-12 hours, air cool to room temperature, and then keep at 170-180°C for 4-8 hours.

[0021] Preferably, it is characterized in that the conditions of the single-stage aging treatment in step (7) are: keeping warm at 160-180° C. for 8-16 hours.

[0022] Beneficial effects of the present invention

[0023] (1) The present invention improves the room temperature and high temperature tensile strength of the alloy by adjusting the contents of Si, Mg, Cu, Ni and Ti in the aluminum alloy and performing a double-stage solid solution treatment + a single-stage aging treatment or a double-stage solid solution treatment + a double-stage aging treatment. The room temperature tensile strength of the aluminum alloy obtained by the double-stage solid solution treatment + a single-stage aging treatment reaches 280 to 315 MPa, the instantaneous tensile strength at 120°C is 250 to 290 MPa, the instantaneous tensile strength at 170°C is 220 to 280 MPa, and the instantaneous tensile strength at 270°C is 210 to 230 MPa. The high temperature instantaneous tensile strength of the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy at 250°C to 300°C still retains 85% to 90% of the room temperature tensile strength, so it is suitable for use at 250°C to 300°C. High temperature working environment, fields requiring high temperature strength and stability; after double-stage solid solution + double-stage aging treatment, the room temperature tensile strength reaches 315-340MPa, the instantaneous tensile strength at 150℃ is 260-310MPa, the instantaneous tensile strength at 200℃ is 240-290MPa, and the instantaneous tensile strength at 300℃ is 130-155MPa. After this heat treatment, the high-temperature instantaneous tensile strength of the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy at 150℃-250℃ still retains 85%-90% of the room temperature tensile strength, but after the temperature is higher than 250℃, it can only retain 45%-60% of the room temperature tensile strength. Therefore, it is suitable for high temperature working environment of 150℃-250℃, and fields with higher requirements for room temperature performance and certain high temperature performance.

[0024] (2) The present invention prepares Al-Si-Cu-Ni aluminum alloy suitable for different high-temperature environments through different heat treatment methods. The casting alloy in the present invention can be used in the production of large and complex castings such as engine cases and cylinder heads, providing greater possibilities for the development of the automotive industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the SEM image of the heat-resistant and high-strength Al-Si-Cu-Ni aluminum alloy prepared in Example 1 after single-stage aging.

[0026] Figure 2 This is the SEM image of the heat-resistant and high-strength Al-Si-Cu-Ni aluminum alloy prepared in Example 2 after single-stage aging.

[0027] Figure 3 This is the SEM image of the heat-resistant and high-strength Al-Si-Cu-Ni aluminum alloy prepared in Example 3 after single-stage aging.

[0028] Figure 4 This is the SEM image of the heat-resistant and high-strength Al-Si-Cu-Ni aluminum alloy prepared in Example 4 after single-stage aging.

[0029] Figure 5 This is the SEM image of the heat-resistant and high-strength Al-Si-Cu-Ni aluminum alloy prepared in Example 1 after double-stage aging.

[0030] Figure 6 This is the SEM image of the heat-resistant and high-strength Al-Si-Cu-Ni aluminum alloy prepared in Example 2 after double-stage aging.

[0031] Figure 7 This is the SEM image of the heat-resistant and high-strength Al-Si-Cu-Ni aluminum alloy prepared in Example 3 after double-stage aging.

[0032] Figure 8 This is the SEM image of the heat-resistant and high-strength Al-Si-Cu-Ni aluminum alloy prepared in Example 4 after double-stage aging. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. However, the following embodiments are merely simple examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0034] The present invention provides a heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy, whose chemical composition mass percentage is: 6.5%-7.5% Si, 0.45%-0.6% Mg, 0.3%-0.6% Cu, 0.5%-5.5% Ni, 0.1%-0.5% Fe, 0.1%-0.2% Ti, and the balance is Al and other inevitable impurities, wherein the sum of the mass percentages of Si, Mg, Cu, Ni, Ti, Fe, the balance Al and other inevitable impurities is 100%, and the amount of each substance in each embodiment is shown in Table 1.

[0035] Table 1 Amount of each substance used in each embodiment

[0036] Serial number Si Cu Mg Ni Ti Al and other unavoidable impurities Example 1 6.96 0.51 0.51 1.02 0.12 margin Example 2 6.82 0.51 0.53 1.95 0.11 margin Example 3 7.00 0.50 0.50 3.69 0.10 margin Example 4 7.10 0.54 0.61 5.13 0.11 margin

[0037] Example 1

[0038] This embodiment provides a method for preparing a heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy

[0039] (1) According to Table 1, Al-Si alloy is used as raw material, Al-Ni master alloy, Al-Cu master alloy, Al-Mg master alloy and Al-Ti master alloy are used as raw materials, and the corresponding weights are weighed according to the proportions of each element in the alloy composition.

[0040] (2) Add the Al-Ni master alloy, Al-Cu master alloy and Al-Si alloy raw materials containing high melting point alloy elements in the raw materials weighed above into a smelting furnace at the same time, heat to 800° C. until the raw materials are completely melted, and keep the temperature for 1 hour to obtain an alloy solution.

[0041] (3) After adding a refining agent to the alloy melt for refining, the alloy melt is kept warm for 5 minutes and slag is removed to obtain a refined alloy solution.

[0042] (4) Adding Al-Ti master alloy to the refined alloy solution for modification, introducing inert gas Ar gas for stirring and degassing treatment, and obtaining a uniform modified Al-Si alloy melt.

[0043] (5) When the temperature of the Al-Si alloy melt drops to 700°C, the Al-Mg intermediate alloy is added, stirred and allowed to stand for 30 minutes, and when the temperature drops to 700°C, it is cast into a heat-resistant and high-strength cast Al-Si-Cu-Ni aluminum alloy material.

[0044] (6) placing the obtained heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy or casting in a heat treatment furnace, heating it to 495° C. and keeping it for 2 h, then continuing to heat it to 535° C. and keeping it for 6 h, performing a two-stage solution treatment, and then water cooling it to room temperature;

[0045] (7) The heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy casting treated in step (6) is kept at 160° C. for 8 h and then air-cooled to room temperature, and then kept at 170° C. for 4 h. After double-stage aging treatment, it is air-cooled to room temperature to obtain product A.

[0046] The heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy casting treated in step (6) is kept at 170°C for 16 hours, subjected to a single-stage aging treatment, and then air-cooled to room temperature to obtain product B.

[0047] According to relevant tests, the room temperature tensile strength of product A prepared in this embodiment is 315 MPa, the instantaneous tensile strength at 150°C is 259 MPa, the instantaneous tensile strength at 200°C is 247 MPa, and the instantaneous tensile strength at 300°C is 140 MPa.

[0048] According to relevant tests, the room temperature tensile strength of product B prepared in this embodiment is 280 MPa, the instantaneous tensile strength at 120°C is 251 MPa, the instantaneous tensile strength at 170°C is 224 MPa, and the instantaneous tensile strength at 270°C is 210 MPa.

[0049] The SEM image of the double-stage aging product A prepared in this example is as follows Figure 5 As shown in the figure, it can be seen that a large number of white skeletons, a small amount of blocky nickel-rich phases and strip-shaped gray eutectic silicon are distributed among the α-Al matrix, and the size of the gray eutectic silicon decreases and gradually spheroidizes.

[0050] The SEM image of the product B prepared in this example after single-stage aging is as follows Figure 1 As shown in the figure, it can be seen that a small amount of white skeleton-like, a large amount of blocky nickel-rich phase and network gray eutectic silicon are distributed among the α-Al matrix, and the dark gray crystals are relatively coarse.

[0051] Example 2

[0052] The preparation method of this embodiment is the same as that of Example 1. The contents of various elements in the prepared heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy are shown in Table 1.

[0053] According to relevant tests, the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy prepared in this embodiment has a room temperature tensile strength of 283 MPa after single-stage aging treatment, an instantaneous tensile strength of 269 MPa at 120°C, an instantaneous tensile strength of 240 MPa at 170°C, and an instantaneous tensile strength of 213 MPa at 270°C.

[0054] The SEM image of the heat-resistant high-strength Al-Si-Cu-Ni aluminum alloy prepared in this embodiment after single-stage aging is as follows: Figure 2As shown in the figure, it can be seen that a small amount of white skeletal nickel-rich phase is distributed among the α-Al matrix, a large number of strip-like nickel-rich phases increase, and the network-like gray eutectic silicon decreases slightly and gradually spheroidizes.

[0055] According to relevant tests, the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy prepared in this embodiment has a room temperature tensile strength of 325 MPa after double-stage aging treatment, an instantaneous tensile strength of 276 MPa at 150°C, an instantaneous tensile strength of 254 MPa at 200°C, and an instantaneous tensile strength of 136 MPa at 300°C.

[0056] The SEM image of the heat-resistant high-strength Al-Si-Cu-Ni aluminum alloy prepared in this embodiment after double-stage aging is as follows: Figure 6 As shown in the figure, it can be seen that a large number of white skeletal and strip-shaped nickel-rich phases distributed between the α-Al matrix increase, and the network-like gray eutectic silicon gradually spheroidizes.

[0057] Example 3

[0058] The preparation method of this embodiment is the same as that of embodiment 1, and the contents of each element in the prepared heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy are shown in Table 1. Al-Si alloy is used as raw material, Al-Ni master alloy, pure Cu wire, pure Mg sheet, Al-Ti master alloy, etc. are used as raw materials, and the corresponding weights are weighed according to the proportions of each element in the alloy composition;

[0059] According to relevant tests, the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy prepared in this embodiment has a room temperature tensile strength of 315 MPa after single-stage aging treatment, an instantaneous tensile strength of 277 MPa at 120°C, an instantaneous tensile strength of 234 MPa at 170°C, and an instantaneous tensile strength of 220 MPa at 270°C.

[0060] The SEM image of the heat-resistant high-strength Al-Si-Cu-Ni aluminum alloy prepared in this embodiment after single-stage aging is as follows: Figure 3 As shown in the figure, it can be seen that the white skeletal nickel-rich phase between the α-Al matrix is ​​reduced, the blocky nickel-rich phase is significantly increased, the network gray eutectic silicon is obviously spheroidized, and the dark gray crystals are obviously finer.

[0061] According to relevant tests, the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy prepared in this embodiment has a room temperature tensile strength of 340 MPa after double-stage aging treatment, an instantaneous tensile strength of 283 MPa at 150°C, an instantaneous tensile strength of 253 MPa at 200°C, and an instantaneous tensile strength of 147 MPa at 300°C.

[0062] The SEM image of the heat-resistant high-strength Al-Si-Cu-Ni aluminum alloy prepared in this embodiment after double-stage aging is as follows: Figure 7As shown in the figure, it can be seen that the white nickel-rich phase between the α-Al matrix is ​​obviously spheroidized and more evenly distributed, the skeletal second phase disappears, the gray eutectic silicon spheroidizes and becomes finer, and the dark gray unit cell size is significantly reduced.

[0063] Example 4

[0064] The preparation method of this embodiment is the same as that of Example 1. The contents of various elements in the prepared heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy are shown in Table 1.

[0065] According to relevant tests, the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy prepared in this embodiment has a room temperature tensile strength of 306 MPa after single-stage aging treatment, an instantaneous tensile strength of 290 MPa at 120°C, an instantaneous tensile strength of 280 MPa at 170°C, and an instantaneous tensile strength of 230 MPa at 270°C.

[0066] The SEM image of the heat-resistant high-strength Al-Si-Cu-Ni aluminum alloy prepared in this embodiment after single-stage aging is as follows: Figure 4 As shown in the figure, it can be seen that the white nickel-rich phase is in the form of blocks and fine spheres and is concentrated in the α-Al matrix. The spherical gray eutectic silicon increases and becomes finer, and the dark gray unit cell becomes significantly smaller.

[0067] According to relevant tests, the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy prepared in this embodiment has a room temperature tensile strength of 335 MPa after double-stage aging treatment, an instantaneous tensile strength of 304 MPa at 150°C, an instantaneous tensile strength of 287 MPa at 200°C, and an instantaneous tensile strength of 152 MPa at 300°C.

[0068] The SEM image of the heat-resistant high-strength Al-Si-Cu-Ni aluminum alloy prepared in this embodiment after double-stage aging is as follows: Figure 8 As shown in the figure, it can be seen that the white nickel-rich phase is gathered in the α-Al matrix in a fishbone and strip shape, and the spherical gray eutectic silicon increases but is relatively coarse.

[0069] Comparative Example 1

[0070] For comparison, the only difference between the comparative example and the present embodiment 1 is that the content of each alloy element is different from that of the embodiment 1, and the content of each alloy element of the comparative example 1 is shown in Table 2. The preparation method of the comparative example is exactly the same as that of the embodiment 1, but the room temperature tensile strength of the comparative example is 150 MPa lower than that of the embodiment 1, and the instantaneous tensile strength at 300°C is 85 MPa lower than that of the embodiment 1.

[0071] Comparative Example 2

[0072] For comparison, the only difference between the comparative example and the present embodiment 1 is that the content of each alloy element is different from that of the embodiment 1, and the content of each alloy element of the comparative example 1 is shown in Table 2. The preparation method of the comparative example is exactly the same as that of the embodiment 2, but the room temperature tensile strength of the comparative example is 70.2 MPa lower than that of the embodiment 2, and the instantaneous tensile strength at 300°C is 49.4 MPa lower than that of the embodiment 2.

[0073] Comparative Example 3

[0074] For comparison, the only difference between the comparative example and the present embodiment 1 is that the content of each alloy element is different from that of the embodiment 1, and the content of each alloy element of the comparative example 1 is shown in Table 2. The preparation method of the comparative example is exactly the same as that of the embodiment 1, but the room temperature tensile strength of the comparative example is 50 MPa lower than that of the embodiment 1, and the instantaneous tensile strength at 300°C is 46.5 MPa lower than that of the embodiment 1.

[0075] Comparative Example 4

[0076] For comparison, the only difference between the comparative example and the present embodiment 1 is that the content of each alloy element is different from that of the embodiment 1, and the content of each alloy element of the comparative example 1 is shown in Table 2. The preparation method of the comparative example is exactly the same as that of the embodiment 1, but the room temperature tensile strength of the comparative example is 41 MPa lower than that of the embodiment 1, and the instantaneous tensile strength at 300°C is 48 MPa lower than that of the embodiment 1.

[0077] Table 2 Amount of each substance in each comparative example

[0078] Serial number Si Cu Mg Ni Ti Al and other unavoidable impurities Comparative Example 1 12.00 0.50 0.50 1.00 0.10 margin Comparative Example 2 7.50 2.63 0.50 1.93 0.10 margin Comparative Example 3 7.50 0.50 1.01 1.00 0.10 margin Comparative Example 4 6.88 0.55 0.50 0.01 0.10 margin

[0079] It can be seen from the performance of the above four groups of example alloys and comparative alloys that the alloy prepared by the present invention has significantly improved hardness and strength compared with the existing Al-Si-Cu-Ni aluminum alloy. By adding a suitable Ni content and a suitable heat treatment process, Ni forms a Ni-rich phase in the α-Al matrix, wherein the nickel element reacts eutectic with the aluminum element to generate a high-temperature stable ε-Al3Ni phase, which is segregated at the grain boundary to inhibit the expansion of alloy cracks. Iron is an impurity element in common aluminum-silicon alloys. When the iron content is greater than the silicon content, an intermetallic compound α-AlFeSi phase is formed. When the silicon content is greater than the iron content, a β-AlFeSi phase is formed, wherein the β-AlFeSi phase reduces the tensile properties. After adding a suitable nickel element in the present invention, the harmful β-AlFeSi phase is transformed into an α-AlFeSi phase and a heat-resistant Al9FeNi phase that are beneficial to the alloy properties. The Al9FeNi phase has both dispersion strengthening effects and can hinder dislocation climb at high temperatures, thereby improving the high-temperature strength and hardness of the alloy without reducing its linear expansion coefficient. As the nickel content increases, the ε-Al3Ni phase and the Al9FeNi phase also increase significantly after heat treatment.

[0080] After the single-stage aging treatment, the room temperature tensile strength of the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy reaches 280-315MPa, and the high-temperature instantaneous tensile strength at 250°C-300°C still retains 85%-90% of the room temperature tensile strength, so it is suitable for a high-temperature working environment of 250°C-300°C; after the double-stage aging treatment, the room temperature tensile strength of the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy reaches 315-340MPa, and the high-temperature instantaneous tensile strength of the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy at 150°C-250°C still retains 85%-90% of the room temperature tensile strength, but after the temperature is higher than 250°C, only 45%-60% of the room temperature tensile strength can be retained, so it is suitable for a high-temperature working environment of 150°C-250°C.

Claims

1. A heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy, characterized in that: The heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy includes the following elements in percentage by mass: 6.5% to 7.5% Si, 0.45% to 0.6% Mg, 0.3% to 0.6% Cu, 0.5% to 5.5% Ni, 0.1% to 0.2% Ti, and the remainder is Al and other inevitable impurities, wherein the sum of the mass percentages of Si, Mg, Cu, Ni, Ti, Fe, Al and other inevitable impurities is 100%.

2. The method for preparing the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy according to claim 1, characterized in that: The specific steps include: (1) preparing raw materials according to the percentage of elements contained in the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy; (2) adding the raw materials with higher melting points among the weighed raw materials into the smelting furnace at the same time, and then keeping the temperature until the raw materials are completely melted to obtain an alloy solution; (3) adding a refining agent to the alloy solution obtained in step (2) for refining, and performing a slag removal treatment after heat preservation to obtain a refined alloy solution; (4) adding the Al-Ti master alloy to the refined alloy solution for modification, introducing Ar gas for stirring and degassing, and obtaining a uniformly modified Al-Si alloy melt; (5) When the temperature of the Al-Si alloy melt drops to 700-750°C, the raw material containing Mg is added, stirred and allowed to stand for 30 minutes, and when the temperature drops to 690-710°C, the Al-Si-Cu-Ni aluminum alloy material is cast; (6) placing the obtained Al-Si-Cu-Ni aluminum alloy material into a heat treatment furnace for double-stage solution treatment and then water cooling to room temperature; (7) performing double aging treatment on the Al-Si-Cu-Ni aluminum alloy material treated in step (6) and then air cooling to room temperature to obtain product A, which is suitable for a high temperature working environment of 150° C. to 250° C.; The Al-Si-Cu-Ni aluminum alloy material prepared in step (6) is subjected to a single-stage aging treatment and then air-cooled to room temperature to obtain product B. Product B is suitable for a high-temperature working environment of 250°C to 300°C.

3. The method for preparing the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy according to claim 2, characterized in that: The raw materials in step (1) include: Al-Si alloy, Ni-containing raw material, Cu-containing raw material, Mg-containing raw material, Al-Ti master alloy, wherein the Ni-containing raw material is: Al-Ni master alloy or pure Ni, the Cu-containing raw material is: Al-Cu master alloy or pure Cu, and the Mg-containing raw material is: Al-Mg master alloy or pure Mg.

4. The method for preparing the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy according to claim 3, characterized in that: The raw materials with high melting points in step (2) are: Al-Si alloy, Ni-containing raw materials, and Cu-containing raw materials.

5. The method for preparing the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy according to claim 2, characterized in that: The smelting conditions in step (2) are: 780-820° C., and the holding time is 1 h.

6. The method for preparing the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy according to claim 2, characterized in that: The insulation time in step (3) is 5 to 10 minutes.

7. The method for preparing the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy according to claim 2, characterized in that: The conditions of the double-stage solution treatment in step (6) are: first, keep the temperature at 490-510°C for 2 hours and then continue to heat up to 530-540°C and keep the temperature for 4-6 hours.

8. The method for preparing the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy according to claim 2, characterized in that: The conditions of the double aging treatment in step (7) are: first keep at 160-170°C for 8-12 hours, air cool to room temperature, and then keep at 170-180°C for 4-8 hours.

9. The method for preparing the heat-resistant high-strength cast Al-Si-Cu-Ni aluminum alloy according to claim 2, characterized in that: The conditions of the single-stage aging treatment in step (7) are: keeping warm at 160-180° C. for 8-16 hours.

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