High-strength die-cast aluminum alloy and preparation and die-casting process thereof

Abstract

The application discloses a high-strength die-casting aluminum alloy and a preparation and die-casting process thereof, and belongs to the technical field of aluminum alloy manufacturing technology. The aluminum alloy contains the following components in percentage by weight: Si: 8-12%, Mg: 0.2-0.6%, Fe: less than or equal to 0.8%, Mn: less than or equal to 0.3%, Cu: less than or equal to 0.1%, Zn: less than or equal to 0.05%, trace elements: Sr: 0.02-0.05%, Ti: 0.1-0.3%, the balance being Al and impurities, and the total amount of the impurities being less than or equal to 0.15%. The application can solve the problems of strength-toughness imbalance and stress sensitivity of the existing aluminum alloy.

Description

A high-strength die-cast aluminum alloy and its preparation and die-casting process Technical Field

[0001] This invention belongs to the field of aluminum alloy production technology, specifically relating to a high-strength die-cast aluminum alloy and its preparation and die-casting process. Background Technology

[0002] Die-cast aluminum alloys are a class of lightweight materials formed under high pressure and high speed, widely used in automobiles, aerospace, and electronic devices. They are primarily represented by Al-Si alloys, possessing good fluidity, corrosion resistance, and high specific strength. Traditional die-cast aluminum alloys improve casting performance by adding elements such as Si, Mg, and Cu, but this has significant drawbacks: high Fe content easily forms hard and brittle intermetallic compounds, such as β-Al5FeSi; and uneven cooling leading to coarse grains and shrinkage cavities further limits the improvement of mechanical properties. With industrial development, the demand for high strength, high toughness, and fatigue resistance in aluminum alloys is increasing, especially in applications such as new energy vehicle structural components and 5G communication housings, where traditional alloys are no longer sufficient. Existing die-cast aluminum alloys, such as Al-Si alloys, while possessing good casting performance, still have the following shortcomings: in composition design, traditional alloys rely on high Fe and Mn content to suppress heat generation, but this easily forms coarse brittle β-Al5FeSi phases, leading to decreased mechanical properties and failing to meet the high mechanical stress requirements under complex working conditions. Furthermore, traditional cooling processes employ uniform temperature control, which can easily lead to internal stress concentration, further exacerbating the failure risk of castings under dynamic loads. Therefore, there is an urgent need to provide a high-strength die-cast aluminum alloy and its preparation and die-casting process to solve the problems of strength-toughness imbalance and stress sensitivity in existing aluminum alloys. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a high-strength die-cast aluminum alloy and its preparation and die-casting process, which can solve the above-mentioned technical problems.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] This invention discloses a high-strength die-cast aluminum alloy, which, by weight percentage, comprises the following components:

[0006] Si:8-12%, Mg:0.2-0.6%, Fe≤0.8%, Mn≤0.3%, Cu≤0.1%, Zn≤0.05%,

[0007] Trace elements: Sr: 0.02-0.05%, Ti: 0.1-0.3%,

[0008] The balance consists of Al and impurities, with the total amount of impurities ≤ 0.15%.

[0009] A preparation and die-casting process for a high-strength die-cast aluminum alloy, wherein the aluminum alloy is the aforementioned high-strength die-cast aluminum alloy, includes the following steps:

[0010] (1) Melting stage: Aluminum alloy is melted at 720-740℃, protected by Ar+SF6 mixed gas, and the Sr and Ti contents are monitored in real time;

[0011] (2) Dynamic feeding: When the Sr content is lower than the target value of 0.01wt%, Al-10Sr master alloy is automatically added; the Sr / Ti content of the smelting is monitored in real time, and the cooling parameters are dynamically adjusted according to the current Sr / Ti addition amount;

[0012] (3) Die casting stage: High pressure and high speed are used for die casting, with a filling speed of 4-6m / s and an internal pressure of 120-150MPa.

[0013] (4) Demolding.

[0014] Furthermore, in step (2), the dynamic adjustment of cooling parameters based on the current Sr / Ti content includes correcting the cooling rate by adjusting the actual and baseline amounts of Sr and Ti added, wherein the corrected cooling rate...

[0015] V c =V0·[1+k sr (C sr -C0)+k Ti (C Ti -C1)]

[0016] V0 is the base cooling rate;

[0017] K sr K Ti These are the empirical coefficients for Sr and Ti, respectively;

[0018] C sr C Ti These represent the actual amounts of Sr and Ti added, respectively.

[0019] C0 and C1 are the baseline addition amounts of Sr and Ti, respectively.

[0020] Furthermore, it also includes step (3.5), which includes: during the aluminum alloy die casting process, the Sr content inside the aluminum alloy is detected simultaneously to detect whether there is a Sr agglomeration zone. If the detection result is negative, step (4) is executed after the die casting is completed; if the detection result is positive, the state of the aluminum alloy is determined. When the aluminum alloy is in a molten state, ultra-low temperature spraying is performed on the Sr agglomeration zone, and the cooling rate of the surrounding area is reduced by 20-30% simultaneously until the Sr agglomeration zone disappears. The Sr agglomeration zone is a region where the local Sr content is greater than the preset first Sr content threshold. When the aluminum alloy is in a solid state, the aluminum alloy is restarted to a molten state, and after ultrasonic stirring for a period of time, step (1-3.5) is repeated.

[0021] Furthermore, the following method is used to perform cryogenic spraying on the Sr segregation region: a thermal barrier region is formed in the target molten region by using an alternating magnetic field, so that the thermal barrier region is contained within the Sr segregation region, and a cooling medium is simultaneously pulsedly sprayed into the thermal barrier region, so that the cooling rate of the target region is ≥200℃ / s and the cooling rate of the surrounding region is ≤50℃ / s.

[0022] Furthermore, the cooling medium for cryogenic spraying is liquid nitrogen, and the magnetic field frequency in the thermal barrier zone is 10-50kHz with an intensity of 0.5-1.5T.

[0023] Furthermore, ultra-low temperature cooling medium is sprayed into the thermal barrier zone through a pipe. The main material of the pipe is silicon nitride, and the outside of the pipe is coated with an isolation layer.

[0024] The beneficial effects of this invention are as follows:

[0025] This invention discloses a high-strength die-cast aluminum alloy and its preparation and die-casting process, which enables the formed aluminum alloy to possess high strength and high toughness, effectively coping with mechanical stress under various complex working conditions. The above process is simple and can improve the production efficiency of aluminum alloys while ensuring their strength.

[0026] Other advantages, objectives, and features of the invention will be set forth in the following description and will be apparent to those skilled in the art in some respects, or may be learned by practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0027] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following figures are provided for illustration:

[0028] Figure 1 is a flowchart of the preparation and die-casting process of the present invention;

[0029] Figure 2 is a schematic diagram showing the location of the Sr segregation region in this invention. Detailed Implementation

[0030] A high-strength die-cast aluminum alloy, comprising the following components by weight percentage:

[0031] Si:8-12%, Mg:0.2-0.6%, Fe≤0.8%, Mn≤0.3%, Cu≤0.1%, Zn≤0.05%,

[0032] Trace elements: Sr: 0.02-0.05%, Ti: 0.1-0.3%,

[0033] The balance consists of Al and impurities, with the total amount of impurities ≤ 0.15%.

[0034] Table 1 shows the effect of Sr and Ti content on the properties of die-cast aluminum alloys.

[0035]

[0036] This invention refines the eutectic Si phase in aluminum alloys by adding trace amounts of Sr, reducing its size from the conventional 15-20 μm to 3-5 μm, significantly improving toughness. Specifically, Sr atoms can selectively adsorb onto the crystal planes of the eutectic Si crystal, inhibiting its anisotropic growth and forcing Si to transform from a lamellar to a fibrous or granular structure. Sr reduces Si twinning, promotes high-density twinning, and restricts the growth of the Si phase in multiple directions, ultimately refining its size from 15-20 μm to 3-5 μm.

[0037] By adding Ti, a TiB2 / Al3Ti heterogeneous nucleation core is formed, refining the α-Al grains to achieve a dendrite arm spacing of ≤30μm and increasing the tensile strength to over 450MPa. Specifically, since TiB2 has a lattice mismatch of only 4.3% with α-Al, it can serve as a highly efficient nucleation substrate, while Al3Ti, with a mismatch of 5.1% with α-Al, also promotes nucleation.

[0038] In the aluminum alloy of this invention, limiting the Fe content avoids the formation of the brittle β-Al5FeSi phase, reduces crack initiation sites, and controlling the Zn content prevents intergranular corrosion, thereby improving the environmental durability of the alloy.

[0039] As shown in Figure 1, a high-strength die-casting aluminum alloy is prepared and die-cast using the aforementioned aluminum alloy, including the following steps:

[0040] (1) Melting stage: Aluminum alloys are melted at 720-740℃ to avoid Sr volatilization caused by high temperature, while ensuring full homogenization of the alloy. Ar+SF6 mixed gas is used for protection to effectively reduce Sr oxidation loss, reducing the loss rate from 30% to <5%, ensuring compositional stability, and monitoring Sr and Ti content in real time;

[0041] (2) Dynamic feeding: When the Sr content is lower than the target value of 0.01wt%, Al-10Sr master alloy is automatically added; the Sr / Ti content of the smelting is monitored in real time, and the cooling parameters are dynamically adjusted according to the current Sr / Ti addition amount; through dynamic feeding, the final composition deviation is ensured to be ≤3%, and the problem of eutectic Si coarsening caused by Sr burn-off is avoided.

[0042] (3) Die casting stage: High pressure and high speed are used for die casting, with a filling speed of 4-6m / s and an in-mold pressure of 120-150MPa. Using the above pressure can reduce air entrapment defects and promote rapid solidification to form a fine-grained structure.

[0043] In step (2), the cooling parameters are dynamically adjusted based on the current Sr / Ti content, including correcting the cooling rate by adjusting the actual and baseline amounts of Sr and Ti. The corrected cooling rate is then...

[0044] V c =V0·[1+k sr (C sr -C0)+k Ti (C Ti -C1)]

[0045] V0 is the base cooling rate;

[0046] K sr K Ti These are the empirical coefficients for Sr and Ti, respectively; here, we take K. sr -1.2, K Ti It is +0.8;

[0047] C sr C Ti These represent the actual amounts of Sr and Ti added, respectively.

[0048] C0 and C1 are the baseline addition amounts of Sr and Ti, respectively, which are 0.01 wt% and 0.1 wt% here.

[0049] Because Sr lowers the eutectic temperature, cooling needs to be slowed down to avoid overcooling, while Ti raises the nucleation temperature, requiring accelerated cooling to refine the grains. Therefore, the aforementioned cooling rate needs to be modified to ensure the performance of the aluminum alloy. The dynamically modified cooling rate stabilizes the eutectic Si size at 3-5 μm and the α-Al dendrite arm spacing at ≤30 μm, avoiding the microstructure inhomogeneity problems caused by traditional fixed cooling processes.

[0050] As a further improvement of the present invention, the preparation and die-casting process of the present invention further includes step (3.5), which includes: during the die-casting process of aluminum alloy, the Sr content inside the aluminum alloy is detected simultaneously to detect whether there is a Sr agglomeration region. When the detection result is negative, after the die-casting is completed, step (4) is executed; when the detection result is positive, the state of the aluminum alloy is determined by directly observing the flow state of the aluminum alloy. When the aluminum alloy is in a molten state, ultra-low temperature spraying is performed on the Sr agglomeration region, and the cooling rate of the surrounding area is reduced by 20-30% simultaneously until the Sr agglomeration region disappears. The Sr agglomeration region is a region where the local Sr content is greater than the preset first Sr content threshold.

[0051] The first Sr content threshold of this invention is set at 650°C. When the aluminum alloy is in a solid state, the aluminum alloy is restarted to a molten state, and after ultrasonic stirring for a period of time, steps (1-3.5) are repeated.

[0052] When a Sr agglomeration region is detected, cryogenic spraying is applied to that region, while simultaneously reducing the cooling rate of the surrounding area by 20-30%. The cryogenic spraying of liquid nitrogen instantly freezes the agglomeration region, forcibly interrupting the diffusion of Sr atoms and breaking the agglomerates into nanoscale particles. Simultaneously reducing the cooling rate of the surrounding area can prevent thermal stress cracking, while allowing Sr atoms to diffuse to the surrounding area, thus achieving compositional homogenization.

[0053] In this embodiment, as shown in Figure 2, the cryogenic spraying of the Sr segregation region is performed using the following method: a thermal barrier zone is formed in the target molten area using an alternating magnetic field. A thermal barrier refers to a localized heat flow barrier region artificially created in the melt by an external energy field (such as an alternating magnetic field). Through electromagnetic eddy currents or other effects, a "thermal isolation zone" is formed around the target area to prevent heat from the surrounding high-temperature melt from entering.

[0054] The thermal barrier zone is contained within the Sr segregation zone, and a cooling medium is simultaneously pulsed into the thermal barrier zone, resulting in a cooling rate of ≥200℃ / s for the target area and ≤50℃ / s for the surrounding area. By using an alternating magnetic field to form the thermal barrier zone, heat leakage from the target area can be blocked, ensuring that cooling (such as liquid nitrogen injection) is localized and preventing rapid dilution of the cold energy by the surrounding melt. The temperature difference ΔT between the target area and the surrounding area can be increased from 50℃ in traditional methods to over 200℃, providing a precise operating environment for cold sources such as liquid nitrogen. This technology is particularly suitable for solving problems such as Sr segregation and localized overcooling in molten aluminum alloys. In practical applications, the magnetic field parameters can be optimized to balance energy consumption and effectiveness.

[0055] The electromagnetic coil is divided into multiple independent sectors along the circumference of the crucible. Multiple electromagnetic coils within the same sector are distributed axially. The current and frequency of each electromagnetic coil in each sector can be adjusted independently. Rotating the crucible can be used to assist in adjusting the circumferential position of the thermal barrier region, and the radial position can be adjusted by translating the crucible. Specifically, the crucible is rotatably mounted on a base, and the base is slidably mounted on a planar moving platform. The crucible can rotate around its own axis on the base, and the base can move on the planar moving platform. By marking the detection position of the Sr segregation region, the thermal barrier region can be included within the Sr segregation region.

[0056] In this embodiment, the cooling medium for cryogenic injection is liquid nitrogen, and the magnetic field frequency in the thermal barrier region is 10-50 kHz with an intensity of 0.5-1.5 T. This ensures the stability of the thermal barrier region formation. The cryogenic cooling medium is injected into the thermal barrier region through a pipe. The main material of the pipe is silicon nitride, and the outer side of the pipe is coated with an isolation layer. The isolation layer is a BN coating or an Al2O3 coating, and the density of the isolation layer can be further improved through surface modification.

[0057] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A preparation and die-casting process for a high-strength die-cast aluminum alloy, wherein the aluminum alloy, by weight percentage, comprises the following components: Si: 8-12%, Mg: 0.2-0.6%, Fe≤0.8%, Mn≤0.3%, Cu≤0.1%, Zn≤0.05%, trace elements: Sr: 0.02-0.05%, Ti: 0.1-0.3%, with the balance being Al and impurities, and the total amount of impurities ≤0.15%, characterized in that: The process includes the following steps: (1) Melting stage: aluminum alloy is melted at 720-740℃, protected by Ar+SF6 mixed gas, and the Sr and Ti contents are monitored in real time; (2) Dynamic feeding: when the Sr content is lower than the target value of 0.01wt%, Al-10Sr master alloy is automatically added; the Sr / Ti content of the melt is monitored in real time, and the cooling parameters are dynamically adjusted by the current Sr / Ti addition amount; (3) Die casting stage: high pressure and high speed are used for die casting, the filling speed is 4-6m / s, and the mold pressure is 120-150MPa; (4) Demolding; In step (2), the dynamic adjustment of the cooling parameters by the current Sr / Ti content includes correcting the cooling rate by the actual addition amount and the reference addition amount of Sr and Ti, wherein the corrected cooling rate ； Based on the cooling rate; ， These are the empirical coefficients for Sr and Ti, respectively; ， These represent the actual amounts of Sr and Ti added, respectively. ， The reference addition amounts of Sr and Ti are respectively; it also includes step (3.5), which includes: during the die casting process of aluminum alloy, the Sr content inside the aluminum alloy is detected simultaneously to detect whether there is a Sr agglomeration zone. When the detection result is negative, after the die casting is completed, step (4) is executed; when the detection result is positive, the state of the aluminum alloy is determined. When the aluminum alloy is in a molten state, ultra-low temperature spraying is performed on the Sr agglomeration zone, and the cooling rate of the surrounding area is reduced by 20-30% simultaneously until the Sr agglomeration zone disappears. The Sr agglomeration zone is a region where the local Sr content is greater than the preset first Sr content threshold. When the aluminum alloy is in a solid state, the aluminum alloy is restarted to a molten state. After ultrasonic stirring for a period of time, step (1-3.5) is repeated. The ultra-low temperature spraying of the Sr agglomeration zone is performed by the following method: a thermal barrier zone is formed in the target molten area by an alternating magnetic field, so that the thermal barrier zone is contained in the Sr agglomeration zone, and a cooling medium is pulsedly sprayed into the thermal barrier zone simultaneously, so that the cooling rate of the target area is ≥200℃ / s and the cooling rate of the surrounding area is ≤50℃ / s.

2. The preparation and die-casting process of a high-strength die-cast aluminum alloy according to claim 1, characterized in that: The cooling medium for cryogenic injection is liquid nitrogen, and the magnetic field frequency in the thermal barrier zone is 10-50kHz with an intensity of 0.5-1.5T.

3. The preparation and die-casting process of a high-strength die-cast aluminum alloy according to claim 2, characterized in that: The ultra-low temperature cooling medium is injected into the thermal barrier zone through a pipe. The main material of the pipe is silicon nitride, and the outside of the pipe is coated with an isolation layer.

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