High strength and heat stable aluminum alloy castings and methods of casting and rapid production thereof

Abstract

The application discloses a high-strength and thermal-stability aluminum alloy casting and a casting and rapid production method thereof, and belongs to the field of high-performance alloy die casting manufacturing. According to the application, the alloy component of the aluminum alloy casting comprises, in percentage by mass, 7.1-9.5 wt% of magnesium, 3.1-4.2 wt% of silicon, 0.05-0.4 wt% of copper, 0.05-1.2 wt% of zinc, 0.6-1.0 wt% of manganese, 0.05-0.2 wt% of bismuth, 0.01-0.2 wt% of tin, 0.01-0.15 wt% of titanium, 0.01-0.2 wt% of zirconium, ≤0.03 wt% of unavoidable impurities, and the balance of aluminum. The alloy is subjected to smelting, refining, stirring, degassing, and variable-frequency, variable-voltage and variable-current pulse treatment to obtain the high-strength and thermal-stability aluminum alloy casting, which has a room-temperature yield strength of ≥220 MPa, a room-temperature tensile strength of ≥400 MPa, and a room-temperature fracture elongation of ≥12%. In high-temperature tensile tests at 100-150 DEG C, the tensile strength is ≥320 MPa, and the attenuation rate is ≤20%. In the high-temperature tensile test at 100 DEG C, the tensile strength is ≥360 MPa, and the attenuation rate is ≤10%. In the high-temperature tensile test at 150 DEG C, the tensile strength is ≥320 MPa, and the attenuation rate is ≤20%.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of high-performance alloy die casting manufacturing, and particularly relates to a high-strength and thermal stability aluminum alloy casting and a casting and rapid production method thereof. BACKGROUND

[0002] Casting integration can reduce the number of parts and assembly links, improve structural strength and rigidity, and achieve lightweight and cost reduction and efficiency improvement. As a lightweight main force, aluminum alloy is a key material for promoting integrated castings due to its excellent specific strength, light weight, and easy recycling. Currently, aluminum alloy is mainly used for new energy vehicle rear floor, battery shell and other castings with low strength requirements. With the further improvement of lightweight demand, in the future, it will be extended to front cabin, electric drive shell and other complex structure high bearing castings. However, integrated castings are difficult to process due to their large size, complexity, thin wall and other characteristics, and local deformation and bubbling will occur during conventional heat treatment (long time solid solution and aging treatment). At the same time, it is not possible to further improve the strength of the casting through extrusion, rolling and other large deformation methods. The existing technology often adds high content or multiple rare earth elements (such as Ce, La, etc.) to improve the strength of the casting, but the strength improvement is accompanied by a decrease in elongation, and both cannot be achieved. Therefore, the existing commercial aluminum alloy castings generally have a room temperature yield strength of ≤160 MPa, a room temperature tensile strength of ≤300 MPa, and a room temperature fracture elongation of <10 %, which is difficult to meet the performance index requirements of front cabin, battery shell and other products.

[0003] At the same time, the casting needs to withstand cyclic use at 100-150 ℃, and the material needs to maintain a low decay rate in a wide temperature range. However, due to factors such as softening of precipitated phase at high temperature and grain boundary sliding, the strength decay rate of conventional aluminum alloy castings will be ≥30 %. In order to reduce the strength decay rate of the alloy, the existing technology usually adds high content of rare earth elements (such as Ce, La, Y, etc.) and Ni, Fe and other elements to form high melting point phases to inhibit high temperature softening. Although the high temperature decay rate of the aluminum alloy casting is reduced, the cost will be greatly increased; in addition, Al-Mg series alloys need to add Si elements to form Mg2Si phases to improve high temperature strength, but the brittle Mg2Si phase is easy to become a crack source when stressed, resulting in a decrease in room temperature plasticity of the alloy. Therefore, the existing technology is difficult to simultaneously improve any two combinations of room temperature strength and plasticity, high temperature thermal stability (reduction of strength decay rate), and even more so for the combination of all three. Therefore, how to avoid the addition of rare earth elements to achieve low cost, simplify the process, speed up the production process, efficiently and simultaneously improve the room temperature strength and plasticity of aluminum alloy castings and high temperature thermal stability (reduction of strength decay rate), and realize industrialized production is a technical problem to be solved at present. SUMMARY

[0004] To solve the above technical problems, the application provides a high-strength and thermal stability aluminum alloy casting, which comprises the following alloy components in percentage by mass: magnesium: 7.1-9.5 wt%, silicon: 3.1-4.2 wt%, copper: 0.05-0.4 wt%, zinc: 0.05-1.2 wt%, manganese: 0.6-1.0 wt%, bismuth: 0.05-0.2 wt%, tin: 0.01-0.2 wt%, titanium: 0.01-0.15 wt%, zirconium: 0.01-0.2 wt%, unavoidable impurities: ≤0.03 wt%, and the balance of aluminum; and a preparation method thereof comprises the following steps:

[0005] (1) pure aluminum, pure magnesium, pure copper, pure zinc, Al-24.4Si intermediate alloy, Al-10Mn intermediate alloy, Mg-30Bi intermediate alloy, Mg-30Sn intermediate alloy, Al-10Ti intermediate alloy and Al-5Zr intermediate alloy are weighed according to percentage by mass, polished, heated at 150-250 DEG C, then the pure aluminum, Al-24.4Si intermediate alloy and Al-10Mn intermediate alloy are heated and melted at 750-800 DEG C, then the pure copper is added; the pure magnesium, pure zinc, Mg-30Bi intermediate alloy, Mg-30Sn intermediate alloy, Al-10Ti intermediate alloy and Al-5Zr intermediate alloy are sequentially added under the protection of SF6 and CO2 mixed gas with a volume ratio of 1-3:97-99 at 700-730 DEG C; a refining agent is added and kept for 10-15 min after the temperature is raised to 740-760 DEG C, and after stirring for 1-5 min and slagging, the alloy melt is obtained by using high-purity argon gas and graphite rod degassing for 1-4 min;

[0006] The refining agent is a mixture of C2Cl6 and KF, and the mass ratio of C2Cl6 to KF is 2-3:1, and the mass ratio of the refining agent to the alloy melt is 0.2-1.2 %:1;

[0007] (2) the alloy melt obtained in step (1) is kept at 700-720 DEG C, and then subjected to constant-speed variable-pressure vacuum high-pressure die casting, 2-10 times of frequency, voltage and current pulse treatment, water cooling to room temperature to obtain the high-strength and thermal stability aluminum alloy casting;

[0008] The constant-speed variable-pressure vacuum high-pressure die casting has a vacuum degree of 2-8 kPa, a shooting speed of 0.1-5 m / s and a casting pressure of 80-150 MPa; and each frequency, voltage and current pulse treatment has a frequency of 40-60 HZ, a voltage of 5-7 V and a current density of 5×10 7 ~3×10 9 A / m 2, the processing time is 2-15 s, the frequency, voltage and current density of each current pulse treatment are different; the high-strength and heat-stable aluminum alloy casting has a room temperature yield strength ≥220 MPa, a room temperature tensile strength ≥400 MPa, and a room temperature elongation at break ≥12 %; in 100-150 ℃ high-temperature tensile test, the tensile strength is ≥320 MPa and the attenuation rate is ≤20 %; in 100 ℃ high-temperature tensile test, the tensile strength is ≥360 MPa and the attenuation rate is ≤10 %; in 150 ℃ high-temperature tensile test, the tensile strength is ≥320 MPa and the attenuation rate is ≤20 %.

[0009] Further, the alloy components of the aluminum alloy casting include, in terms of mass percentage: magnesium: 7.5-8.5 wt%, silicon: 3.3-4.0 wt%, copper: 0.1-0.3 wt%, zinc: 0.2-1.0 wt%, manganese: 0.7-0.9 wt%, bismuth: 0.1-0.15 wt%, tin: 0.05-0.15 wt%, titanium: 0.05-0.12 wt%, zirconium: 0.05-0.15 wt%, unavoidable impurities ≤0.03 wt%, and the balance being aluminum.

[0010] Further, in step (1), the pure aluminum, pure magnesium, pure copper, pure zinc, Al-24.4Si intermediate alloy, Al-10Mn intermediate alloy, Mg-30Bi intermediate alloy, Mg-30Sn intermediate alloy, Al-10Ti intermediate alloy and Al-5Zr intermediate alloy are weighed according to mass percentage, polished, heated at 180-230 ℃, and then the pure aluminum, Al-24.4Si intermediate alloy and Al-10Mn intermediate alloy are heated and melted at 780-790 ℃, and then the pure copper is added; under the protection of SF6 and CO2 mixed gas with a volume ratio of 1.2-2.5:97.5-98.5, the pure magnesium, pure zinc, Mg-30Bi intermediate alloy, Mg-30Sn intermediate alloy, Al-10Ti intermediate alloy and Al-5Zr intermediate alloy are sequentially added at 710-720 ℃; the refining agent is added and held for 11-13 min after the temperature is raised to 745-755 ℃, and after stirring for 2-4 min and slagging, the alloy melt is obtained after degassing with high-purity argon and graphite rod for 2-3 min; the refining agent is a mixture of C2Cl6 and KF, the mass ratio of C2Cl6 to KF is 2.2-2.8:1, and the mass ratio of the refining agent to the alloy melt is 0.5-1.0 %:1.

[0011] Further, the alloy melt obtained in step (2) is kept at 710-715 ℃, then subjected to constant-speed variable-pressure vacuum high-pressure die casting, 3-7 times of variable-frequency, variable-pressure and variable-current pulse treatment, and water cooling to room temperature to obtain high-strength and thermal stability aluminum alloy castings; the constant-speed variable-pressure vacuum high-pressure die casting has a vacuum degree of 3-5 kPa, a injection speed of 0.5-4.5 m / s, and a casting pressure of 90-120 MPa; the variable-frequency, variable-pressure and variable-current pulse treatment has a frequency of 45-55 HZ, a voltage of 5.5-6.5 V, and a current density of 5.5×10 7 ~2.5×10 9 A / m 2 , and a treatment time of 4-10 s.

[0012] Compared with the prior art, the present application has the following advantages:

[0013] Since it is difficult to further improve the strength of the integrated casting by high-temperature and long-time heat treatment, extrusion, rolling and other processes, the prior art often adds high content or multiple rare earth elements (such as Ce, La, etc.) and Ni, Fe, Si and other elements, resulting in a substantial increase in cost, and only a single improvement in the room temperature strength, plasticity or high-temperature thermal stability of the aluminum alloy casting, which is difficult to achieve the above three performances. For example, the room temperature strength of the aluminum alloy casting is improved, but the room temperature plasticity is decreased; the high-temperature decay of the aluminum alloy casting is reduced, but the room temperature strength and plasticity are also decreased. Compared with the prior art, the present application rapidly improves the room temperature strength and plasticity and the high-temperature thermal stability of the aluminum alloy casting through the synergistic regulation of the interaction, ratio, process and process parameters of the components. The advantages of the present application include: first, without adding any rare earth elements, the solidification structure can be regulated and refined, the production cost is reduced, and the room temperature strength and plasticity and the high-temperature thermal stability are improved. Second, from the microstructure, the present application breaks the needle-like micron-sized eutectic Mg2Si phase in the prior art, forms a nanoscale spheroidized eutectic Mg2Si (size of 50-100 nm), increases the nucleation points and refines the matrix grains (10-50 μm), effectively accelerates solute diffusion and enrichment, and promotes the precipitation of high-density Mg-Si clusters (density of 1-5×10 23 m -3 , size of 4-6 nm), nanoscale β-Mg2Si (size of 50-100 nm) and T-Mg 32 (Al, Zn, Cu) 49 phase (size of 5-50 nm).

[0014] Compared with the prior art which produces needle-like and micron-sized eutectic Mg2Si, resulting in difficulty in simultaneous improvement of the room temperature alloy strength and plasticity, and single precipitation phase softening and grain boundary sliding leading to significant high-temperature strength decay, the present application forms spheroidized eutectic Mg2Si, high-density Mg-Si clusters, high-temperature stable β-Mg2Si and T-Mg32 (Al, Zn, Cu) 49 and a plurality of nano phases, significantly improve the room temperature strength and plasticity and high temperature thermal stability (reduce the high temperature performance decay rate) of the aluminum alloy castings, which are much higher than the strength and plasticity and high temperature thermal stability of the aluminum alloy obtained by the prior art. The high strength and thermal stability aluminum alloy castings obtained by the present application have a room temperature yield strength of ≥220 MPa, a room temperature tensile strength of ≥400 MPa, and a room temperature elongation of ≥12 %; in high temperature tensile test at 100-150℃, the tensile strength is ≥320 MPa and the decay rate is ≤20 %; wherein, in high temperature tensile test at 100℃, the tensile strength is ≥360 MPa and the decay rate is ≤10 %, and in high temperature tensile test at 150℃, the tensile strength is ≥320 MPa and the decay rate is ≤20 %. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The transmission electron micrograph of the eutectic Mg2Si phase in the high strength and thermal stability aluminum alloy casting 1 obtained by Example 1 of the present application;

[0016] Figure 2 The transmission electron micrograph of the β-Mg2Si phase and Mg-Si cluster in the high strength and thermal stability aluminum alloy casting 1 obtained by Example 1 of the present application;

[0017] Figure 3 The transmission electron micrograph of the T-Mg 32 (Al, Zn,Cu) 49 phase in the high strength and thermal stability aluminum alloy casting 1 obtained by Example 1 of the present application;

[0018] Figure 4 The optical micrograph of the matrix grain in the high strength and thermal stability aluminum alloy casting 1 obtained by Example 1 of the present application;

[0019] Figure 5 The transmission electron micrograph of the eutectic Mg2Si phase in the aluminum alloy casting obtained by Comparative Example 1 of the present application;

[0020] Figure 6 The optical micrograph of the matrix grain in the aluminum alloy casting obtained by Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical scheme and effect of the present application more clear and explicit, the present application will be described in detail below in combination with specific examples, which are only preferred embodiments of the present application, but not a limitation of the present application.

[0022] The purities of the pure aluminum, pure magnesium, pure copper and pure zinc used in the following examples are 99.99 wt%, 99.9 wt%, 99.9 wt% and 99.995 wt%, respectively.

[0023] Example 1

[0024] The alloy components of the aluminum alloy casting include, in terms of mass percentage: magnesium: 7.5 wt%, silicon: 3.3 wt%, copper: 0.2 wt%, zinc: 0.9 wt%, manganese: 0.7 wt%, bismuth: 0.11 wt%, tin: 0.08 wt%, titanium: 0.11 wt%, zirconium: 0.09 wt%, unavoidable impurities ≤0.03 wt%, and the balance being aluminum; and the preparation method thereof includes the following steps:

[0025] (1) pure aluminum, pure magnesium, pure copper, pure zinc, Al-24.4Si intermediate alloy, Al-10Mn intermediate alloy, Mg-30Bi intermediate alloy, Mg-30Sn intermediate alloy, Al-10Ti intermediate alloy, and Al-5Zr intermediate alloy are weighed according to mass percentage, polished, heated at 183 ℃, and then the pure aluminum, Al-24.4Si intermediate alloy, and Al-10Mn intermediate alloy are heated and melted at 785 ℃, and then pure copper is added; under the protection of SF6 and CO2 mixed gas with a volume ratio of 1.7:98.3, pure magnesium, pure zinc, Mg-30Bi intermediate alloy, Mg-30Sn intermediate alloy, Al-10Ti intermediate alloy, and Al-5Zr intermediate alloy are sequentially added at 713 ℃; a refining agent is added at a temperature of 750 ℃ and the temperature is kept for 12 min, after stirring for 2 min and slagging, the alloy melt is obtained by using high-purity argon gas and graphite rod to degas for 2 min;

[0026] The refining agent is a mixture of C2Cl6 and KF, the mass ratio of C2Cl6 to KF is 2.7:1, and the mass ratio of the refining agent to the alloy melt is 0.6 %:1;

[0027] (2) the alloy melt obtained in step (1) is kept at 712 ℃, and then constant-speed variable-pressure vacuum high-pressure die casting, 3 times of variable-frequency, variable-voltage, and variable-current pulse treatment, and water cooling to room temperature are performed to obtain high-strength and thermal stability aluminum alloy casting 1;

[0028] The constant-speed variable-pressure vacuum high-pressure die casting has a vacuum degree of 4 kPa, a shooting speed of 1.6 m / s, and a casting pressure of 105 MPa; each time of variable-frequency, variable-voltage, and variable-current pulse treatment has the following parameters: the first time of pulse current treatment has a frequency of 52 HZ, a voltage of 5.5 V, a current density of 5.7×10 7 A / m 2 , and a treatment time of 5 s; the second time of pulse current treatment has a frequency of 55 HZ, a voltage of 5.4 V, a current density of 5.5×10 7 A / m 2, the processing time is 4 s; the frequency of the third pulse current processing is 54 HZ, the voltage is 6.4 V, and the current density is 6.5×10 7 A / m 2 , the processing time is 6 s.

[0029] The high-strength and thermal stability aluminum alloy casting 1 has a room temperature yield strength of 222 MPa, a tensile strength of 405 MPa, and an elongation at break of 13.8%; in 100 ℃ high-temperature tensile test, the tensile strength is 366 MPa, and the attenuation rate is 9.6%; in 150 ℃ high-temperature tensile test, the tensile strength is 327 MPa, and the attenuation rate is 19.2%.

[0030] It can be seen from Figures 1-4 that the Mg-Si cluster density and size in the high-strength and thermal stability aluminum alloy casting 1 are 2×10 23 m -3 and 5 nm, respectively, the eutectic Mg2Si, β-Mg2Si and T-Mg 32 (Al, Zn, Cu) 49 phase sizes are 72, 53 and 25 nm, respectively, and the matrix grain size is 32 μm.

[0031] Example 2

[0032] The alloy components of the aluminum alloy casting include, in terms of mass percentage, magnesium: 7.8 wt%, silicon: 3.5 wt%, copper: 0.1 wt%, zinc: 0.8 wt%, manganese: 0.8 wt%, bismuth: 0.14 wt%, tin: 0.12 wt%, titanium: 0.08 wt%, zirconium: 0.11 wt%, unavoidable impurities ≤0.03 wt%, and the balance of aluminum; and the preparation method thereof comprises the following steps:

[0033] (1) pure aluminum, pure magnesium, pure copper, pure zinc, Al-24.4Si intermediate alloy, Al-10Mn intermediate alloy, Mg-30Bi intermediate alloy, Mg-30Sn intermediate alloy, Al-10Ti intermediate alloy and Al-5Zr intermediate alloy are weighed according to mass percentage, polished, heated at 196 ℃, and then the pure aluminum, Al-24.4Si intermediate alloy and Al-10Mn intermediate alloy are heated and melted at 790 ℃, and then the pure copper is added; under the protection of SF6 and CO2 mixed gas with a volume ratio of 2.1:97.9, the pure magnesium, pure zinc, Mg-30Bi intermediate alloy, Mg-30Sn intermediate alloy, Al-10Ti intermediate alloy and Al-5Zr intermediate alloy are sequentially added at 718 ℃; the refining agent is added and kept for 11 min after the temperature is raised to 753 ℃, and after stirring for 3 min and slagging, the alloy melt is obtained by using high-purity argon gas and graphite rod to remove gas for 3 min;

[0034] The refining agent is a mixture of C2Cl6 and KF, the mass ratio of C2Cl6 to KF is 2.3:1, and the mass ratio of the refining agent to the alloy melt is 0.5 %:1;

[0035] 2) after the alloy melt obtained in step (1) is kept at 710 ℃, high-strength and thermal-stability aluminum alloy castings 2 are obtained by constant-speed variable-pressure vacuum high-pressure die casting, 4 times of variable-frequency, variable-voltage and variable-current pulse treatment, and water cooling to room temperature;

[0036] The constant-speed variable-pressure vacuum high-pressure die casting has a vacuum degree of 5 kPa, a injection speed of 2.1 m / s, and a casting pressure of 113 MPa; the each time of variable-frequency, variable-voltage and variable-current pulse treatment has the first time of pulse current treatment with a frequency of 64 HZ, a voltage of 6.3 V, a current density of 6.7×10 7 A / m 2 , and a treatment time of 8 s; the second time of pulse current treatment with a frequency of 65 HZ, a voltage of 6.1 V, a current density of 6.3×10 7 A / m 2 , and a treatment time of 10 s; the third time of pulse current treatment with a frequency of 61 HZ, a voltage of 6.2 V, a current density of 6.5×10 8 A / m 2 , and a treatment time of 9 s; and the fourth time of pulse current treatment with a frequency of 60 HZ, a voltage of 5.9 V, a current density of 6.4×10 7 A / m 2 , and a treatment time of 7 s.

[0037] The high-strength and thermal-stability aluminum alloy castings 2 have a room-temperature yield strength of 233 MPa, a tensile strength of 403 MPa, and an elongation of 13.6 %; a tensile strength of 368 MPa, and an attenuation rate of 8.7 % at 100 ℃ high-temperature tensile test; and a tensile strength of 324 MPa, and an attenuation rate of 19.6 % at 150 ℃ high-temperature tensile test.

[0038] The Mg-Si cluster density and size in the high-strength and thermal-stability aluminum alloy castings 2 are 2.5×10 23 m -3 and 4 nm respectively, the eutectic Mg2Si, β-Mg2Si and T-Mg 32 (Al, Zn, Cu) 49 phase sizes are 65, 43 and 32 nm respectively, and the matrix grain size is 26 μm.

[0039] Comparative Example 1

[0040] The alloy component of the aluminum alloy casting comprises, in percentage by mass: magnesium: 11.3 wt%, silicon: 5.6 wt%, manganese: 0.4 wt%, bismuth: 0.5 wt%, tin: 0.6 wt%, titanium: 0.3 wt%, zirconium: 0.5 wt%, unavoidable impurities ≤0.03 wt%, and the balance of aluminum; and the preparation method thereof comprises the following steps:

[0041] (1) pure aluminum, pure magnesium, pure copper, pure zinc, Al-24.4Si intermediate alloy, Al-10Mn intermediate alloy, Mg-30Bi intermediate alloy, Mg-30Sn intermediate alloy, Al-10Ti intermediate alloy and Al-5Zr intermediate alloy are weighed according to percentage by mass, polished, heated at 92 ℃, and then the pure aluminum, Al-24.4Si intermediate alloy and Al-10Mn intermediate alloy are heated and melted at 735 ℃, and then the pure copper is added; under the protection of SF6 and CO2 mixed gas with a volume ratio of 5.5:94.5, the pure magnesium, pure zinc, Mg-30Bi intermediate alloy, Mg-30Sn intermediate alloy, Al-10Ti intermediate alloy and Al-5Zr intermediate alloy are sequentially added at 752 ℃; after stirring for 6 min and slagging, an alloy melt is obtained;

[0042] (2) the alloy melt obtained in step (1) is kept at 735 ℃, and then vacuum high-pressure die casting, 1-time pulse treatment, water cooling to room temperature are carried out to obtain an aluminum alloy casting;

[0043] The constant-speed variable-pressure vacuum high-pressure die casting has a vacuum degree of 12 kPa, a shooting speed of 5.2 m / s and a casting pressure of 75 MPa; the pulse treatment has a frequency of 65 HZ, a voltage of 7.3 V, a current density of 3.4×10 7 A / m 2 , and a treatment time of 1 s;

[0044] The aluminum alloy casting has a room temperature yield strength of 176 MPa, a tensile strength of 354 MPa and a fracture elongation of 9.5%; in 100 ℃ high-temperature tension, the tensile strength is 275 MPa and the attenuation rate is 22.3%; in 150 ℃ high-temperature tension, the tensile strength is 253 MPa and the attenuation rate is 28.6%.

[0045] It can be seen that: Figures 5-6 In the aluminum alloy casting, no Mg-Si clusters, β-Mg2Si and T-Mg 32 (Al, Zn,Cu) 49 phases are found, the size of eutectic Mg2Si is 575 nm, and the size of the matrix grain is 85 μm.

[0046] In summary, the application realizes solidification tissue regulation and refinement, promotes the precipitation of various nano phases, and improves the room temperature strength and plasticity and high temperature thermal stability (i.e. high temperature performance decay rate) of the aluminum alloy casting. The aluminum alloy casting with high strength and thermal stability has a room temperature yield strength of ≥220 MPa, a room temperature tensile strength of ≥400 MPa, and a room temperature fracture elongation of ≥12%; in high temperature tensile tests at 100-150 ℃, the tensile strength is ≥320 MPa and the decay rate is ≤20%; in the high temperature tensile test at 100 ℃, the tensile strength is ≥360 MPa and the decay rate is ≤10%; and in the high temperature tensile test at 150 ℃, the tensile strength is ≥320 MPa and the decay rate is ≤20%.

[0047] The components and processes of Comparative Example 1 are similar to those of Example 1 and Example 2, and the alloy component proportions and process parameters are not within the protection scope of the claims of the application. The room temperature strength and high temperature thermal stability of the aluminum alloy casting obtained in Comparative Example 1 are lower than those of Example 1 and Example 2 (as shown in Tables 1 and 2), and no Mg-Si clusters, β-Mg2Si and T-Mg 32 (Al, Zn, Cu) 49 phases are found in the aluminum alloy casting, and the size of the eutectic Mg2Si and the size of the matrix grains are both larger than those of Example 1 and Example 2. This shows that the component proportions and process parameters of the application can only realize the simultaneous improvement of the room temperature strength and plasticity and high temperature thermal stability of the aluminum alloy casting, and realize the promotion of the solidification of various tissues and the refinement of various nano phases, only when the component proportions and process parameters are within the protection scope of the claims of the application. This breaks the problem that the prior art solves the problems of the aluminum alloy by forming a single tissue, and the prior art is difficult to solve the problem of either the strength and plasticity or the high temperature thermal stability, not to mention the simultaneous solution of the three problems. The application improves the strength and plasticity and high temperature thermal stability of the alloy by forming various microstructures. In addition, the component proportions and process parameters of each example of the application are different, and the obtained performance and decay rate are also different, which shows that the significant improvement effect obtained by the application is not determined by a certain component or process, but is realized by the synergistic regulation of the component interaction, the proportion, the process and the process parameters.

[0048] Table 1 shows the room temperature mechanical properties of the alloys obtained in Examples 1-2 and Comparative Example 1

[0049]

[0050] Table 2 shows the high temperature mechanical properties of the alloys obtained in Examples 1-2 and Comparative Example 1

[0051]

Claims

1. A high-strength and thermally stable aluminum alloy casting, characterized in that: The alloy composition of the aluminum alloy casting, by weight percentage, includes: magnesium: 7.1~9.5 wt%, silicon: 3.1~4.2 wt%, copper: 0.05~0.4 wt%, zinc: 0.05~1.2 wt%, manganese: 0.6~1.0 wt%, bismuth: 0.05~0.2 wt%, tin: 0.01~0.2 wt%, titanium: 0.01~0.15 wt%, zirconium: 0.01~0.2 wt%, unavoidable impurities ≤0.03 wt%, and the balance being aluminum; its preparation method includes the following steps: (1) Weigh out pure aluminum, pure magnesium, pure copper, pure zinc, Al-24.4Si master alloy, Al-10Mn master alloy, Mg-30Bi master alloy, Mg-30Sn master alloy, Al-10Ti master alloy and Al-5Zr master alloy according to mass percentage. After polishing, heat at 150~250 ℃. Melt the pure aluminum, Al-24.4Si master alloy and Al-10Mn master alloy at 750~800 ℃, and then add pure copper. Hold at 700~730 ℃, and add pure magnesium, pure zinc, Mg-30Bi master alloy, Mg-30Sn master alloy, Al-10Ti master alloy and Al-5Zr master alloy in sequence under the protection of SF6 and CO2 mixed gas with a volume ratio of 1~3:97~99. Raise the temperature to 740~760 ℃, add refining agent and hold for 10~15 min, and stir for 1~5 min. After min and slag removal, high-purity argon gas is used in conjunction with a graphite rod for degassing for 1-4 min to obtain the alloy melt; The refining agent is a mixture of C2Cl6 and KF, with a mass ratio of C2Cl6 to KF of 2~3:1, and the mass ratio of the refining agent to the alloy melt is 0.2~1.2%:

1. (2) After the alloy melt obtained in step (1) is kept at 700~720 ℃, it is subjected to constant speed variable pressure vacuum high pressure die casting, 2~10 frequency, variable pressure and variable current pulse treatments, and water cooling to room temperature to obtain high strength and thermal stability aluminum alloy castings. The constant-speed variable-pressure vacuum high-pressure die casting process features a vacuum level of 2-8 kPa, an injection speed of 0.1-5 m / s, and a casting pressure of 80-150 MPa. The frequency, voltage, and current pulse processing for each cycle includes a frequency of 40-60 Hz, a voltage of 5-7 V, and a current density of 5 × 10⁻⁶. 7 ~3×10 9 A / m 2 The processing time is 2~15 s, and the frequency, voltage and current density of each current pulse are different; the high-strength and thermally stable aluminum alloy casting has a room temperature yield strength ≥220 MPa, a room temperature tensile strength ≥400 MPa, and a room temperature elongation at break ≥12%; when stretched at high temperature of 100~150 ℃, the tensile strength is ≥320 MPa and the attenuation rate is ≤20%; among which, when stretched at high temperature of 100 ℃, the tensile strength is ≥360 MPa and the attenuation rate is ≤10%, and when stretched at high temperature of 150 ℃, the tensile strength is ≥320 MPa and the attenuation rate is ≤20%.

2. The high-strength and thermally stable aluminum alloy casting according to claim 1, characterized in that: The alloy composition of the aluminum alloy casting, by weight percentage, includes: magnesium: 7.5~8.5 wt%, silicon: 3.3~4.0 wt%, copper: 0.1~0.3 wt%, zinc: 0.2~1.0 wt%, manganese: 0.7~0.9 wt%, bismuth: 0.1~0.15 wt%, tin: 0.05~0.15 wt%, titanium: 0.05~0.12 wt%, zirconium: 0.05~0.15 wt%, unavoidable impurities ≤0.03 wt%, and the balance being aluminum.

3. The high-strength and thermally stable aluminum alloy casting according to claim 1, characterized in that: In step (1), pure aluminum, pure magnesium, pure copper, pure zinc, Al-24.4Si master alloy, Al-10Mn master alloy, Mg-30Bi master alloy, Mg-30Sn master alloy, Al-10Ti master alloy, and Al-5Zr master alloy are weighed according to mass percentage. After polishing, the mixture is heated to 180~230 ℃. The pure aluminum, Al-24.4Si master alloy, and Al-10Mn master alloy are then heated to 780~790 ℃ and melted. Then, pure copper is added. The mixture is held at 710~720 ℃ and, under the protection of a mixed gas of SF6 and CO2 with a volume ratio of 1.2~2.5:97.5~98.5, pure magnesium, pure zinc, Mg-30Bi master alloy, Mg-30Sn master alloy, Al-10Ti master alloy, and Al-5Zr master alloy are added sequentially. The temperature is then raised to 745~755 ℃. Add refining agent at ℃ and keep warm for 11-13 min. After stirring for 2-4 min and removing slag, degas with high-purity argon gas and a graphite rod for 2-3 min to obtain alloy melt. The refining agent is a mixture of C2Cl6 and KF, with a mass ratio of C2Cl6 to KF of 2.2-2.8:

1. The mass ratio of the refining agent to the alloy melt is 0.5-1.0%:

1.

4. The high-strength and thermally stable aluminum alloy casting according to claim 1, characterized in that: The alloy melt obtained in step (2) is held at 710~715 ℃, then subjected to constant speed variable pressure vacuum high pressure die casting, 3~7 frequency, voltage and current pulse treatments, and water cooling to room temperature to obtain high-strength and thermally stable aluminum alloy castings. The constant speed variable pressure vacuum high pressure die casting has a vacuum degree of 3~5 kPa, an injection speed of 0.5~4.5 m / s, and a casting pressure of 90~120 MPa. The frequency, voltage and current pulse treatments have a frequency of 45~55 Hz, a voltage of 5.5~6.5 V, and a current density of 5.5×10⁻⁶. 7 ~2.5×10 9 A / m 2 The processing time is 4~10 seconds.

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