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

Abstract

The invention 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, and the aluminum alloy comprises the following components in percentage by weight: 8-12% of Si, 0.2-0.6% of Mg, less than or equal to 0.8% of Fe, less than or equal to 0.3% of Mn, less than or equal to 0.1% of Cu, less than or equal to 0.05% of Zn, 0.02-0.05% of trace elements Sr, 0.1-0.3% of Ti and the balance of Al and impurities, and the total amount of the impurities is less than or equal to 0.15%. The problems of strength-toughness imbalance and stress sensitivity of an existing aluminum alloy can be solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of aluminum alloy production, and particularly relates to a high-strength die-casting aluminum alloy and its preparation and die-casting process. Background Art

[0002] Die-casting aluminum alloy is a kind of lightweight material that is formed by high-pressure and high-speed filling and is widely used in the fields of automobiles, aerospace, and electronic devices. It is mainly represented by Al-Si series alloys, which have good fluidity, corrosion resistance, and relatively high specific strength. Traditional die-casting aluminum alloys improve their casting properties by adding elements such as Si, Mg, and Cu, but there are obvious defects: high Fe content is prone to form hard and brittle intermetallic compounds, such as β-Al5FeSi; and the problems of coarse grains and shrinkage pores caused by uneven cooling further limit the improvement of mechanical properties. With the development of industry, the demand for high strength, high toughness, and anti-fatigue characteristics of aluminum alloys is increasing day by day. Especially in application scenarios such as new energy vehicle structural parts and 5G communication housings, traditional alloys are difficult to meet the requirements. Existing die-casting aluminum alloys, such as Al-Si series alloys, although having good casting properties, still have the following deficiencies: in terms of composition design, traditional alloys rely on high Fe and Mn contents to inhibit hot cracking, but it is easy to form coarse β-Al5FeSi brittle phases, resulting in a decline in mechanical properties and being unable to meet the high mechanical stress requirements under complex working conditions. In addition, the traditional cooling process uses uniform temperature control, which is prone to cause internal stress concentration and further exacerbate the failure risk of castings under dynamic loads. Therefore, there is an urgent need to provide a high-strength die-casting aluminum alloy and its preparation and die-casting process to solve the problems of strength-toughness imbalance and stress sensitivity existing 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-casting aluminum alloy and its preparation and die-casting process, which can solve the above technical problems.

[0004] To achieve the above purpose, the present invention provides the following technical solutions:

[0005] A high-strength die-casting aluminum alloy disclosed by the present invention, 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 is Al and impurities, and the total amount of impurities ≤0.15%.

[0009] Preparation and die-casting process of a high-strength die-casting aluminum alloy. The aluminum alloy is the above-mentioned high-strength die-casting aluminum alloy, and the process includes the following steps:

[0010] (1) Melting stage: Melting the aluminum alloy at 720 - 740 °C, using a mixed gas of Ar + SF6 for protection, and monitoring the Sr and Ti contents in real time;

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

[0012] (3) Die-casting stage: Perform die-casting at high pressure and high speed, with a filling speed of 4 - 6 m / s and an in-mold pressure of 120 - 150 MPa;

[0013] (4) Demolding.

[0014] Furthermore, in step (2), dynamically adjusting the cooling parameters according to the current Sr / Ti content includes correcting the cooling rate based on the actual addition amounts and reference addition amounts of Sr and Ti. Among them, the corrected cooling rate

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

[0016] V0 is the basic cooling rate;

[0017] K sr 、K Ti are the empirical coefficients of Sr and Ti respectively;

[0018] C sr 、C Ti are the actual addition amounts of Sr and Ti respectively;

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

[0020] Further, it further includes step (3.5), and step (3.5) includes: during the aluminum alloy die-casting process, synchronously detecting the Sr content inside the aluminum alloy to detect whether there is an Sr segregation zone. When the detection result is negative, after the die-casting is completed, step (4) is executed; when the detection result is positive, judging the state of the aluminum alloy. When the aluminum alloy is in a molten state, ultra-low temperature spraying is performed on the Sr segregation zone area, and the cooling rate of the surrounding area is synchronously reduced by 20-30%, until the Sr segregation zone disappears, where the Sr segregation zone is an area 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 reheated to the molten state, ultrasonically stirred for a period of time, and then steps (1-3.5) are repeated.

[0021] Further, the following method is adopted for performing ultra-low temperature spraying on the Sr segregation zone area: a thermal barrier zone is formed in the target molten zone through an alternating magnetic field, the thermal barrier zone is included in the Sr segregation zone, and a cooling medium is synchronously pulsed and sprayed into the thermal barrier zone, so that the cooling rate of the target area ≥200°C / s and the cooling rate of the surrounding area ≤50°C / s.

[0022] Further, the cooling medium for ultra-low temperature spraying is liquid nitrogen, the magnetic field frequency of the thermal barrier zone is 10-50 kHz, and the intensity is 0.5-1.5 T.

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

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

[0025] A high-strength die-cast aluminum alloy and its preparation and die-casting process disclosed by the present invention can make the formed aluminum alloy have high strength and high toughness, and can effectively cope with mechanical stresses under various complex working conditions. The above process is simple, and while ensuring the strength of the aluminum alloy, the production efficiency of the aluminum alloy can be improved.

[0026] Other advantages, objectives and features of the present invention will be described in the subsequent specification, and to some extent, they are obvious to those skilled in the art, or those skilled in the art can obtain teachings from the practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the following specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to make the objectives, technical solutions and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration:

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

[0029] Figure 2 It is a schematic diagram of the position of the Sr segregation zone of the present invention. Detailed implementation mode

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

[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 is Al and impurities, and the total amount of impurities ≤0.15%.

[0034] Table 1 shows the influence of Sr and Ti contents on the properties of die-cast aluminum alloy

[0035]

[0036] In the present invention, by adding trace element Sr to the aluminum alloy, the eutectic Si phase can be refined, and it can be reduced from the conventional 15-20 μm to 3-5 μm, significantly improving toughness; specifically, Sr atoms can selectively adsorb on the crystal planes of eutectic Si crystals, inhibit their anisotropic growth, and force Si to change from lamellar to fibrous or granular. Sr reduces the formation of twins in Si, promotes high-density twins, restricts the growth of the Si phase in multiple directions, and finally refines the size from 15-20 μm to 3-5 μm.

[0037] By adding element Ti, TiB2 / Al3Ti heterogeneous nucleation cores are formed to refine the α-Al grains, making their dendrite arm spacing ≤30 μm and increasing the tensile strength to more than 450 MPa. Specifically, since the lattice mismatch degree between TiB2 and α-Al is only 4.3%, it can be used as an efficient nucleation substrate, and the mismatch degree between Al3Ti and α-Al is 5.1%, which also promotes nucleation.

[0038] In the aluminum alloy of the present invention, by restricting the Fe content, the formation of the brittle phase β-Al5FeSi is avoided, the crack sources are reduced, and the Zn content is controlled to prevent intergranular corrosion, improving the environmental durability of the alloy.

[0039] As Figure 1 shown, a preparation and die-casting process of a high-strength die-cast aluminum alloy, using the above aluminum alloy, includes the following steps:

[0040] (1) Melting stage: Melting the aluminum alloy at 720-740 °C, avoiding the volatilization of Sr caused by high temperature, and at the same time ensuring the full homogenization of the alloy. Using an Ar+SF6 mixed gas for protection, effectively reducing the oxidation loss of Sr, reducing the loss rate from 30% to <5%, ensuring the stability of the composition, and monitoring the Sr and Ti contents in real time;

[0041] (2) Dynamic feeding: When the Sr content is lower than the target value of 0.01 wt%, add Al-10Sr master alloy automatically; monitor the Sr / Ti content during melting in real time, and dynamically adjust the cooling parameters according to the current Sr / Ti addition amount; through dynamic feeding, ensure that the final composition deviation ≤ 3%, and avoid the problem of eutectic Si coarsening caused by Sr burning loss.

[0042] (3) Die-casting stage: Carry out die-casting with high pressure and high speed, the filling speed is 4 - 6 m / s, and the in-mold pressure is 120 - 150 MPa. Using the above pressure can reduce the gas entrapment defect, and at the same time promote rapid solidification to form a fine-grained structure.

[0043] In step (2), dynamically adjusting the cooling parameters according to the current Sr / Ti content includes correcting the cooling rate according to the actual addition amount and the reference addition amount of Sr and Ti. Among them, the corrected cooling rate

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

[0045] V0 is the basic cooling rate;

[0046] K sr and K Ti are the empirical coefficients of Sr and Ti respectively. Here, K sr is -1.2 and K Ti is +0.8;

[0047] C sr and C Ti are the actual addition amounts of Sr and Ti respectively;

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

[0049] Since Sr reduces the eutectic temperature, it is necessary to slow down the cooling to avoid undercooling, while Ti increases the nucleation temperature, so it is necessary to accelerate the cooling to refine the grains, thus correcting the above cooling rate to ensure the performance of the aluminum alloy. The dynamically corrected cooling rate makes the eutectic Si size stable at 3 - 5 μm, and the α-Al dendrite arm spacing ≤ 30 μm, avoiding the problem of non-uniform structure caused by the traditional fixed cooling process.

[0050] As a further improvement of the embodiments of the present invention, the preparation and die-casting process of the present invention further includes step (3.5), and step (3.5) includes: during the aluminum alloy die-casting process, synchronously detecting the Sr content inside the aluminum alloy to detect whether there is an Sr segregation 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 judged 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 segregation zone area, and the cooling rate of the surrounding area is synchronously reduced by 20-30%, until the Sr segregation zone disappears, where the Sr segregation zone is an area where the local Sr content is greater than the preset first Sr content threshold.

[0051] In the present invention, the first Sr content threshold is set to 650 °C. When the aluminum alloy is in a solid state, the aluminum alloy is reheated to a molten state, ultrasonically stirred for a period of time, and then steps (1-3.5) are repeated.

[0052] When it is detected that there is an Sr segregation zone, ultra-low temperature spraying is performed on this area, and the cooling rate of the surrounding area is synchronously reduced by 20-30%. The ultra-low temperature spraying of liquid nitrogen instantaneously freezes the segregation zone, the diffusion of Sr atoms is forcibly interrupted, and the segregation clusters are broken into nanoscale particles; synchronously reducing the surrounding cooling rate can avoid thermal stress cracks and at the same time allow Sr atoms to diffuse to the surrounding area to achieve compositional homogenization.

[0053] In this embodiment, as Figure 2 shown, the following method is adopted for ultra-low temperature spraying on the Sr segregation zone area: a thermal barrier zone is formed in the target melting zone through an alternating magnetic field. A thermal barrier refers to a locally heat flow blocking area artificially created in the melt through 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 the heat of the surrounding high-temperature melt from entering.

[0054] Among them, the thermal barrier zone is included in the Sr segregation zone, and a cooling medium is synchronously pulsed into the thermal barrier zone, so that the cooling rate of the target area ≥ 200 °C / s, and the cooling rate of the surrounding area ≤ 50 °C / s. By adopting the method of forming a thermal barrier zone through an alternating magnetic field, the heat leakage of the target area can be blocked, so that the cooling of the target area (such as liquid nitrogen spraying) only acts locally, avoiding the rapid dilution of cold by the surrounding melt. The temperature difference ΔT between the target area and the surrounding area can be increased from 50 °C in the traditional method to more than 200 °C, providing a precise action environment for cold sources such as liquid nitrogen. This technology is particularly suitable for solving problems such as Sr segregation and local supercooling in aluminum alloy melts. When specifically used, the magnetic field parameters can be optimized to balance energy consumption and effect.

[0055] The electromagnetic coils are circumferentially divided into multiple independent sectors along the crucible. The multiple electromagnetic coils in the same sector are axially distributed. Each electromagnetic coil in each sector can be individually adjusted in terms of current and frequency. By rotating the crucible, it can be used to assist in adjusting the circumferential position of the thermal barrier zone, or the crucible can be translated to adjust the radial position. The specific implementation method is as follows: The crucible is rotatably installed on the base, and the base is slidably installed on the 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 zone, the thermal barrier zone can be included in the Sr segregation zone.

[0056] In this embodiment, the cryogenic injection cooling medium is liquid nitrogen. The magnetic field frequency in the thermal barrier zone is 10 - 50 kHz, and the intensity is 0.5 - 1.5 T. To ensure the stability of the formation of the thermal barrier zone. The cryogenic cooling medium is injected into the thermal barrier zone through a pipeline. The main material of the pipeline is silicon nitride, and the outer side of the pipeline is coated with an isolation layer. The isolation layer uses a BN coating or an Al2O3 coating, and the densification 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 restrictive. 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 in terms of form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A high-strength die-cast aluminum alloy, characterized in that: By weight percentage, it contains 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%, The balance is Al and impurities, and the total amount of impurities ≤ 0.15%.

2. A preparation and die-casting process of a high-strength die-casting aluminum alloy, wherein the aluminum alloy is the high-strength die-casting aluminum alloy described in claim 1, and is characterized in that: It includes the following steps: (1) Melting stage: Melting the aluminum alloy at 720 - 740 °C, protected by Ar + SF6 mixed gas, and real-time monitoring the Sr and Ti contents; (2) Dynamic feeding: When the Sr content is lower than the target value of 0.01 wt%, automatically add Al - 10Sr master alloy; real-time monitor the Sr / Ti content during melting, and dynamically adjust the cooling parameters according to the current Sr / Ti addition amount; (3) Die-casting stage: Carry out die-casting with high pressure and high speed, the filling speed is 4 - 6 m / s, and the in-mold pressure is 120 - 150 MPa; (4) Demolding.

3. The preparation and die-casting process of a high-strength die-casting aluminum alloy according to claim 2, characterized in that: In step (2), dynamically adjusting the cooling parameters according to the current Sr / Ti content includes correcting the cooling rate based on the actual addition amounts and reference addition amounts of Sr and Ti. Among them, the corrected cooling rate V c = V0·[1 + k sr (C sr - C0) + k Ti (C Ti - C1)] V0 is the basic cooling rate; K sr and K Ti are the empirical coefficients of Sr and Ti, respectively; C sr and C Ti are the actual addition amounts of Sr and Ti, respectively; C0 and C1 are the reference addition amounts of Sr and Ti respectively.

4. The preparation and die-casting process of a high-strength die-casting aluminum alloy according to claim 3, characterized in that: It also includes step (3.5), and step (3.5) includes: During the die-casting of the aluminum alloy, synchronously detect the Sr content inside the aluminum alloy to detect whether there is a Sr segregation zone. When the detection result is no, after die-casting is completed, execute step (4); when the detection result is yes, judge the state of the aluminum alloy. When the aluminum alloy is in a molten state, perform ultra-low temperature spraying on the Sr segregation zone area, and synchronously reduce the cooling rate of the surrounding area by 20 - 30% until the Sr segregation zone disappears, where the Sr segregation zone is an area where the local Sr content is greater than the preset first Sr content threshold; when the aluminum alloy is in a solid state, restart heating the aluminum alloy to the molten state, stir ultrasonically for a period of time, and then repeat steps (1 - 3.5).

5. The preparation and die-casting process of a high-strength die-casting aluminum alloy according to claim 4, characterized in that: The method of performing ultra-low temperature spraying on the Sr segregation zone area is as follows: Form a thermal barrier zone in the target molten zone through an alternating magnetic field, make the thermal barrier zone included in the Sr segregation zone, and synchronously pulse spray a cooling medium into the thermal barrier zone, so that the cooling rate of the target area ≥ 200 °C / s, and the cooling rate of the surrounding area ≤ 50 °C / s.

6. The preparation and die-casting process of a high-strength die-casting aluminum alloy according to claim 5, characterized in that: The cooling medium for ultra-low temperature spraying is liquid nitrogen, the magnetic field frequency of the thermal barrier zone is 10 - 50 kHz, and the intensity is 0.5 - 1.5 T.

7. The preparation and die-casting process of a high-strength die-casting aluminum alloy according to claim 5, characterized in that: Spray the ultra-low temperature cooling medium into the thermal barrier zone through a pipeline. The main material of the pipeline is silicon nitride, and an isolation layer is coated on the outer side of the pipeline.

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