High-strength and thermal-stability aluminum alloy casting and casting and rapid production method thereof

Abstract

The invention 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, and the aluminum alloy casting comprises the following alloy components 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, less than or equal to 0.03 wt% of inevitable 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 an aluminum alloy casting with high strength and thermal stability, the room-temperature yield strength of the aluminum alloy casting is larger than or equal to 220 MPa, the room-temperature tensile strength of the aluminum alloy casting is larger than or equal to 400 MPa, and the room-temperature elongation at break of the aluminum alloy casting is larger than or equal to 12%; the tensile strength is greater than or equal to 320 MPa and the attenuation rate is less than or equal to 20% during high-temperature stretching at 100-150 DEG C; wherein the tensile strength is larger than or equal to 360 MPa and the attenuation rate is smaller than or equal to 10% during 100-DEG C high-temperature stretching, and the tensile strength is larger than or equal to 320 MPa and the attenuation rate is smaller than or equal to 20% during 150-DEG C high-temperature stretching

Description

Technical Field

[0001] This invention belongs to the field of high-performance alloy die casting manufacturing, specifically relating to high-strength and thermally stable aluminum alloy castings and their casting and rapid production methods. Background Technology

[0002] Integrated castings can reduce the number of parts and assembly steps, improve structural strength and rigidity, and achieve lightweighting, cost reduction, and efficiency improvement. Aluminum alloys, as a major force in lightweighting, are a key material driving integrated castings due to their excellent specific strength, light weight, and easy recyclability. Currently, aluminum alloys are mainly used in castings with relatively low strength requirements, such as the rear floor and battery casing of new energy vehicles. With the further increase in lightweighting demands, this will expand to complex, high-load-bearing castings such as the front engine compartment and electric drive housing. However, integrated castings are difficult to process due to their large size, complexity, and thin walls. Conventional heat treatment (long-term solution treatment and aging treatment) can cause localized deformation and blistering, and the strength of the casting cannot be further improved through large deformation methods such as extrusion and rolling. Existing technologies often add high content or multiple rare earth elements (such as Ce, La, etc.) to improve the strength of the casting, but the increase in strength is accompanied by a decrease in elongation; the two cannot be achieved simultaneously. Therefore, the room temperature yield strength of existing commercial aluminum alloy castings is generally ≤160 MPa, room temperature tensile strength is ≤300 MPa, and room temperature elongation at break is <10%, which makes it difficult to meet the performance requirements of products such as front engine compartments and battery casings.

[0003] Meanwhile, castings need to withstand cyclic use at 100-150 °C, requiring the material to maintain a low attenuation rate over a wide temperature range. However, due to factors such as softening of precipitated phases and grain boundary sliding in high-temperature environments, the strength attenuation rate of conventional aluminum alloy castings will be ≥30%. Existing technologies typically add high amounts of rare earth elements (such as Ce, La, Y, etc.) and elements like Ni and Fe to Al-Si alloys to form high-melting-point phases that suppress high-temperature softening. Although this reduces the high-temperature attenuation rate of aluminum alloy castings, it significantly increases costs. Additionally, Al-Mg alloys require the addition of Si to form the Mg2Si phase to improve high-temperature strength, but the brittle Mg2Si phase is prone to becoming a crack initiation point under stress, leading to a decrease in room-temperature plasticity. Therefore, existing technologies struggle to synergistically improve either room-temperature plasticity or high-temperature thermal stability (reducing the strength attenuation rate), let alone all three. Therefore, how to avoid the addition of rare earth elements to achieve low cost, simplified process, accelerated production process, and efficient simultaneous improvement of room temperature strength and plasticity and high temperature thermal stability of aluminum alloy castings (reducing strength decay rate) and realize industrial production is a technical problem that urgently needs to be solved. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention provides a high-strength and thermally stable aluminum alloy casting. 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 2The 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%.

[0005] Further, by mass percentage, the alloy composition of the aluminum alloy casting 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.

[0006] Further, 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 by mass percentage. After polishing, the mixture is heated to 180~230 ℃. Then, the pure aluminum, Al-24.4Si master alloy, and Al-10Mn master alloy are melted at 780~790 ℃, and 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.

[0007] Further, 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 conversion, voltage conversion and current conversion pulse treatments, and water cooling to room temperature to obtain a high-strength and thermally stable aluminum alloy casting; 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 conversion, voltage conversion and current conversion 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 7 ~2.5×10 9 A / m 2 The processing time is 4~10 seconds.

[0008] The advantages of this invention compared to existing technologies are as follows: Because it is difficult to further improve the strength of integrated castings through high-temperature, long-term heat treatment, extrusion, rolling, and other processes, existing technologies often add high content or multiple rare earth elements (such as Ce, La, etc.) and elements such as Ni, Fe, and Si, which leads to a significant increase in cost. Furthermore, these technologies can only improve the room temperature strength, plasticity, or high-temperature thermal stability of aluminum alloy castings individually, making it difficult to achieve all three properties. For example, while room temperature strength of aluminum alloy castings may increase, room temperature plasticity may decrease; and while high-temperature degradation may decrease, room temperature strength and plasticity may also decrease. Compared with existing technologies, this invention rapidly improves the room temperature strength, plasticity, and high-temperature thermal stability of aluminum alloy castings through the interaction, proportioning, process, and synergistic control of process parameters. The advantages of this invention include: firstly, it achieves solidification structure control and refinement without adding any rare earth elements, reducing production costs and improving room temperature strength, plasticity, and high-temperature thermal stability. Secondly, from a microscopic perspective, this technology breaks away from the existing needle-like micron-sized eutectic Mg2Si phase and forms nanoscale spherical eutectic Mg2Si (size 50~100 nm), increasing nucleation sites and refining the matrix grains (10~50 μm). This effectively accelerates solute diffusion and enrichment, promoting high-density Mg-Si clusters (density 1~5×10⁻⁶). 23 m -3 (4-6 nm in size), nano-sized β-Mg2Si (50-100 nm in size) and T-Mg 32 (Al, Zn, Cu) 49 Phase (size 5~50 nm) precipitates.

[0009] Compared to existing technologies that produce needle-like and micron-sized eutectic Mg2Si, making it difficult to simultaneously improve the strength and ductility of room-temperature alloys, and whose softening of single precipitates and grain boundary sliding lead to significant high-temperature strength degradation, this invention utilizes spheroidized eutectic Mg2Si, high-density Mg-Si clusters, and high-temperature stable β-Mg2Si and T-Mg... 32(Al, Zn, Cu) 49 The synergistic effect of multiple nanophases significantly improves the room temperature strength and ductility, and high-temperature thermal stability of aluminum alloy castings (reducing the high-temperature performance degradation rate), far exceeding the strength, ductility, and high-temperature thermal stability of aluminum alloys obtained by existing technologies. The high-strength and thermally stable aluminum alloy castings obtained by this invention have a room temperature yield strength ≥220 MPa, a room temperature tensile strength ≥400 MPa, and a room temperature elongation at break ≥12%. Under high-temperature tensile testing at 100~150℃, the tensile strength is ≥320 MPa with a degradation rate ≤20%; specifically, under high-temperature tensile testing at 100℃, the tensile strength is ≥360 MPa with a degradation rate ≤10%, and under high-temperature tensile testing at 150℃, the tensile strength is ≥320 MPa with a degradation rate ≤20%. Attached Figure Description

[0010] Figure 1 This is a transmission electron microscope (TEM) image of the eutectic Mg2Si phase in the high-strength and thermally stable aluminum alloy casting 1 obtained in Example 1 of the present invention. Figure 2 Transmission electron microscopy (TEM) images of the β-Mg2Si phase and Mg-Si clusters in the high-strength and thermally stable aluminum alloy casting 1 obtained in Example 1 of this invention. Figure 3 T-Mg in the high-strength and thermally stable aluminum alloy casting 1 obtained in Embodiment 1 of the present invention 32 (Al, Zn, Cu) 49 Transmission electron microscope image of the phase; Figure 4 This is a light microscope image of the matrix grains in the high-strength and thermally stable aluminum alloy casting 1 obtained in Embodiment 1 of the present invention; Figure 5 This is a transmission electron microscope (TEM) image of the eutectic Mg2Si phase in the aluminum alloy casting obtained in Comparative Example 1 of this invention. Figure 6 This is a light microscope image of the matrix grains in the aluminum alloy casting obtained in Comparative Example 1 of the present invention. Detailed Implementation

[0011] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention will be described in detail below with reference to specific embodiments. These embodiments are merely preferred implementations of this invention and are not intended to limit the invention.

[0012] The purity 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.

[0013] Example 1 The alloy composition of the aluminum alloy casting, by weight percentage, includes: 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; 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 to 183 ℃. Then heat the pure aluminum, Al-24.4Si master alloy and Al-10Mn master alloy to 785 ℃ and melt them. Then add pure copper. Hold at 713 ℃. Under the protection of SF6 and CO2 mixed gas with a volume ratio of 1.7:98.3, add pure magnesium, pure zinc, Mg-30Bi master alloy, Mg-30Sn master alloy, Al-10Ti master alloy and Al-5Zr master alloy in sequence. Raise the temperature to 750 ℃, add refining agent and hold for 12 min. After stirring for 2 min and slag removal, use high-purity argon gas in conjunction with graphite rod for degassing. After min, the alloy melt is obtained; The refining agent is a mixture of C2Cl6 and KF, with a mass ratio of C2Cl6 to KF of 2.7:1, and the mass ratio of the refining agent to the alloy melt is 0.6%:1. (2) After the alloy melt obtained in step (1) is kept at 712 °C, it is subjected to constant speed variable pressure vacuum high pressure die casting, three frequency conversion, voltage conversion and current conversion pulse treatments, and water cooling to room temperature to obtain a high strength and thermal stability aluminum alloy casting 1. The constant-speed variable-pressure vacuum high-pressure die casting method has a vacuum level of 4 kPa, an injection speed of 1.6 m / s, and a casting pressure of 105 MPa. The frequency, voltage, and current pulse processing for each cycle is as follows: the first pulse current processing has a frequency of 52 Hz, a voltage of 5.5 V, and a current density of 5.7 × 10⁻⁶. 7 A / m 2 The processing time was 5 seconds; the frequency of the second pulse current processing was 55 Hz, the voltage was 5.4 V, and the current density was 5.5 × 10⁻⁶. 7 A / m 2 The processing time was 4 seconds; the frequency of the third pulse current processing was 54 Hz, the voltage was 6.4 V, and the current density was 6.5 × 10⁻⁶. 7 A / m 2 The processing time is 6 seconds.

[0014] The high-strength and thermally stable aluminum alloy casting 1 has a room temperature yield strength of 222 MPa, a tensile strength of 405 MPa, and a fracture elongation of 13.8%; under high temperature tension at 100 ℃, the tensile strength is 366 MPa with a decay rate of 9.6%; under high temperature tension at 150 ℃, the tensile strength is 327 MPa with a decay rate of 19.2%.

[0015] from Figure 1-4 It can be seen from the data that the density and size of Mg-Si clusters in the high-strength and thermally stable aluminum alloy casting 1 are 2×10⁻⁶. 23 m -3 And 5 nm, eutectic Mg2Si, β-Mg2Si and T-Mg 32 (Al, Zn, Cu) 49 The phase sizes are 72, 53, and 25 nm, respectively, and the matrix grain size is 32 μm.

[0016] Example 2 The alloy composition of the aluminum alloy casting, by weight percentage, includes: 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 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 to 196 ℃. Then heat the pure aluminum, Al-24.4Si master alloy and Al-10Mn master alloy to 790 ℃ and melt them. Then add pure copper. Hold at 718 ℃. Under the protection of SF6 and CO2 mixed gas with a volume ratio of 2.1:97.9, add pure magnesium, pure zinc, Mg-30Bi master alloy, Mg-30Sn master alloy, Al-10Ti master alloy and Al-5Zr master alloy in sequence. Raise the temperature to 753 ℃, add refining agent and hold for 11 min. After stirring for 3 min and slag removal, use high-purity argon gas with graphite rod for degassing. After min, the alloy melt is obtained; 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 0.5%:1. 2) After the alloy melt obtained in step (1) is kept at 710 ℃, it is subjected to constant speed variable pressure vacuum high pressure die casting, 4 frequency conversion, pressure conversion and current conversion pulse treatments, and water cooling to room temperature to obtain high strength and thermal stability aluminum alloy casting 2. The constant-speed variable-pressure vacuum high-pressure die casting method has the following parameters: vacuum level of 5 kPa, injection speed of 2.1 m / s, and casting pressure of 113 MPa. The frequency, voltage, and current pulse processing for each step is as follows: the first pulse current processing has a frequency of 64 Hz, a voltage of 6.3 V, and a current density of 6.7 × 10⁻⁶. 7 A / m 2 The processing time was 8 seconds; the frequency of the second pulse current processing was 65 Hz, the voltage was 6.1 V, and the current density was 6.3 × 10⁻⁶. 7 A / m 2 The processing time was 10 seconds; the frequency of the third pulse current processing was 61 Hz, the voltage was 6.2 V, and the current density was 6.5 × 10⁻⁶. 8 A / m 2 The processing time was 9 seconds; the frequency of the fourth pulse current processing was 60 Hz, the voltage was 5.9 V, and the current density was 6.4 × 10⁻⁶. 7 A / m 2 The processing time is 7 seconds.

[0017] The high-strength and thermally stable aluminum alloy casting 2 has a room temperature yield strength of 233 MPa, a tensile strength of 403 MPa, and a fracture elongation of 13.6%; under high temperature tension at 100 ℃, the tensile strength is 368 MPa with a decay rate of 8.7%; under high temperature tension at 150 ℃, the tensile strength is 324 MPa with a decay rate of 19.6%.

[0018] The density and size of Mg-Si clusters in the high-strength and thermally stable aluminum alloy casting 2 are 2.5 × 10⁻⁶. 23 m -3 And 4nm, eutectic Mg2Si, β-Mg2Si and T-Mg 32 (Al, Zn, Cu) 49 The phase sizes are 65, 43 and 32 nm, respectively, and the matrix grain size is 26 μm.

[0019] Comparative Example 1 The alloy composition of the aluminum alloy casting, by weight percentage, includes: 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 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 92 ℃. Then heat the pure aluminum, Al-24.4Si master alloy and Al-10Mn master alloy to 735 ℃ and melt them. Then add pure copper. Hold at 752 ℃ 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 5.5:94.5. After stirring for 6 min and removing slag, the alloy melt is obtained. (2) After the alloy melt obtained in step (1) is kept at 735 °C, it is subjected to vacuum high pressure die casting, pulse treatment once, and water cooling to room temperature to obtain aluminum alloy castings. The constant-speed variable-pressure vacuum high-pressure die casting method has the following characteristics: vacuum degree of 12 kPa, injection speed of 5.2 m / s, and casting pressure of 75 MPa; the pulse processing frequency is 65 Hz, voltage is 7.3 V, and current density is 3.4 × 10⁻⁶. 7 A / m 2 The processing time is 1 second; 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%; when stretched at 100 ℃, the tensile strength is 275 MPa with a decay rate of 22.3%; and when stretched at 150 ℃, the tensile strength is 253 MPa with a decay rate of 28.6%.

[0020] from Figure 5-6 It can be seen that Mg-Si clusters, β-Mg2Si, and T-Mg were not found in the aluminum alloy castings. 32 (Al, Zn, Cu) 49 The eutectic Mg2Si phase has a size of 575 nm, and the matrix grain size is 85 μm.

[0021] In summary, this invention achieves solidification structure control and refinement, promotes the precipitation of multiple nanophases, and simultaneously improves the room temperature strength and ductility and high temperature thermal stability (i.e., high temperature performance degradation rate) of aluminum alloy castings. The high-strength and thermally stable aluminum alloy castings exhibit a room temperature yield strength ≥220 MPa, a room temperature tensile strength ≥400 MPa, and a room temperature elongation at break ≥12%. Under high-temperature tensile testing at 100~150 ℃, the tensile strength is ≥320 MPa with a degradation rate ≤20%; specifically, under high-temperature tensile testing at 100 ℃, the tensile strength is ≥360 MPa with a degradation rate ≤10%, and under high-temperature tensile testing at 150 ℃, the tensile strength is ≥320 MPa with a degradation rate ≤20%.

[0022] Comparative Example 1 has similar composition and process to Examples 1 and 2, and the alloy composition ratio and process parameters are not within the scope of protection of the claims of this invention. The aluminum alloy casting obtained in Comparative Example 1 has lower room temperature strength and higher temperature thermal stability than that of Examples 1 and 2 (as shown in Tables 1 and 2), and no Mg-Si clusters, β-Mg2Si, and T-Mg were found in the aluminum alloy casting. 32 (Al, Zn, Cu) 49 The eutectic Mg2Si phase and the matrix grain size are both larger than those in Examples 1 and 2. This indicates that the composition ratio and process parameters of the present invention can only achieve the simultaneous improvement of room temperature strength and high temperature thermal stability of aluminum alloy castings, as well as the promotion of solidification, refinement of multiple microstructures, and precipitation of multiple nanophases, within the scope of the claims of the present invention. This breaks through the limitations of existing technologies that solve the problems faced by aluminum alloys by forming a single microstructure, and the difficulty of existing technologies in solving the problems of either strength and plasticity or high temperature thermal stability, let alone solving all three problems simultaneously. The present invention improves the strength and plasticity of alloys and high temperature thermal stability by forming multiple microstructures in a synergistic manner. In addition, the composition ratio and process parameters of each embodiment of the present invention are different, and the obtained performance and attenuation rate are also different. This shows that the significant improvement effect obtained by the present invention is not determined by a certain component or process, but is achieved through the synergistic regulation of component interaction, ratio, process, and process parameters.

[0023] Table 1 shows the room temperature mechanical properties of the alloys obtained in Examples 1-2 and Comparative Example 1.

[0024] Table 2 shows the high-temperature mechanical properties of the alloys obtained in Examples 1-2 and Comparative Example 1.

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.

Images