An integrated aluminum alloy hollow subframe and a liquid die forging method thereof

Abstract

The present application relates to a kind of integral aluminum alloy hollow subframe and its liquid die forging method, wherein the liquid die forging method of the integral aluminum alloy hollow subframe adopts the compound liquid die forging process of vertical injection, horizontal pressurization and center pouring, radiation type multi-inlet gate outlet is combined, inorganic sand core and its preheating under core technology are combined, effectively solve the problem that sand core is easily crushed and serious sand sticking, simultaneously, through multi-stage pressurization curve optimization feeding process, the smoothness of product cavity inner wall reaches 0.2mm, eutectic silicon is refined to 5~10 μm, α dendrite secondary dendrite spacing is less than 20 μm, the strength deviation of obtained product is less than 15MPa, the elongation deviation is less than 1.5%, X-ray flaw detection reaches 1~2 levels, process yield is 60~80%, successfully overcome the defects of existing liquid die forging process for preparing integral aluminum alloy hollow subframe, such as sand core easily crushed, serious sand sticking, large performance deviation and low process yield.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy liquid forging technology, specifically to an integral aluminum alloy hollow subframe and its liquid forging method. Background Technology

[0002] Aluminum alloy hollow subframes are crucial components for achieving automotive lightweighting, and their manufacturing process has long faced the dual challenges of performance and cost. While traditional gravity casting and low-pressure casting processes can achieve product forming, they struggle to simultaneously meet the requirements of thin-walled lightweighting and high performance. Gravity casting, due to its process characteristics, requires a minimum wall thickness of 5mm or more, severely limiting weight reduction. Furthermore, the organic binder-coated sand cores used to form the hollow structure have significant defects: the vibration-induced sand shedding rate is only 40-50%, requiring high-temperature sand calcination at 400-450℃ for removal, increasing energy consumption and cost while also causing environmental pollution. Simultaneously, the high gas generation of the coated sand cores significantly increases the risk of porosity defects. While low-pressure casting can reduce the wall thickness to 4mm... However, due to insufficient filling pressure (only about 0.1MPa), the internal microstructure of the product is coarse (eutectic silicon is fibrous or needle-like, with an average size of 25μm; the average spacing of α dendrite secondary dendrites is 35μm). There are significant performance differences in different parts, with strength deviations as high as 20~50MPa and elongation deviations as high as 3-5 percentage points. There are uncertain weak performance areas, and the fatigue resistance is low. Moreover, due to the high mold temperature, thick coating layer, and thick material cake, the production cycle is as long as 8 minutes or more, and the process yield is only 40~50%, which seriously restricts the mass production efficiency.

[0003] While liquid forging (also known as extrusion casting) technology has demonstrated advantages in the manufacture of other aluminum alloy structural parts and has been applied in the manufacture of open-type (solid, such as existing patent document CN117483711A) and split subframes, it faces significant technical obstacles in the application of integrated hollow subframes. Firstly, existing liquid forging processes use horizontal liquid forging mills with single-sided injection, resulting in long flow paths, large temperature drops, and high flow resistance, frequently leading to incomplete forming of defective products and weakening of distal performance. Secondly, the filling speed is limited to <500mm / s, which, while reducing air entrapment, exacerbates the risk of cold shuts, resulting in a yield rate of less than 50%. Thirdly, localized pressure compensation lacks scientific basis; premature pressure application cannot eliminate shrinkage defects, while delayed pressure application fails due to insufficient liquid metal quantity. More importantly, hollow aluminum alloy subframes require the use of sand cores to form cavities. Existing liquid forging processes must address three core challenges: the sand core must maintain its strength under high pressure to prevent crushing, while also being easily collapsible and cleanable; high-speed filling is necessary to accommodate thin walls and large gaps, while avoiding air and slag entrapment; and high-pressure feeding ensures density while preventing liquid metal from seeping into the sand core and causing sand adhesion. While existing technologies employ multi-stage injection speed and pressure settings, parameter settings rely on trial and error based on experience, lacking theoretical support, resulting in poor process stability. Their pressurization regime often involves rapid pressure increase to holding pressure after V / P conversion, easily causing sand core crushing. Furthermore, while the large ingate outlet design of existing technologies facilitates feeding, it leads to overheating in the ingate outlet area, exacerbating sand adhesion defects. These factors collectively result in low yield and inconsistent performance of one-piece hollow aluminum alloy subframes produced by existing liquid forging processes, failing to meet mass production and usage requirements, and currently remaining a gap in the technology. Therefore, overcoming the shortcomings of existing liquid forging processes in preparing one-piece aluminum alloy hollow subframes, such as easy crushing of sand cores, severe sand adhesion, large performance differences, and low process yield, has become a key technical bottleneck restricting the development of the industry. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the existing liquid forging process for preparing one-piece aluminum alloy hollow subframes, such as easy crushing of the sand core, serious sand adhesion, large performance deviation and low process yield. Thus, the present invention provides a one-piece aluminum alloy hollow subframe and its liquid forging method to solve the above problems.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] In a first aspect, the present invention provides a liquid forging method for an integral aluminum alloy hollow subframe, comprising:

[0007] S1. Obtain the aluminum alloy liquid and inorganic sand core, use the preheated inorganic sand core as the core of the mold cavity and close the mold (install the preheated sand core in the inner cavity of the lower mold to complete the mold closing).

[0008] S2. Casting and Filling: Molten aluminum alloy is poured into the central pressure chamber located at the center of the mold. The main pressure head moves axially along the central pressure chamber, applying pressure to the molten aluminum alloy and pushing it axially away from the drive end of the main pressure head. After reaching the end of the central pressure chamber, the flow direction of the molten aluminum alloy is changed by the flow divider cone structure, changing it from axial flow to horizontal flow. The changed flow direction of the molten aluminum alloy enters the mold cavity through several ingates radially distributed around the flow divider cone to complete the filling process. The specific process includes:

[0009] S2.1 Slow injection and low-pressure casting: Start the main pressure head and push the molten aluminum alloy in the central pressure chamber into the slag collection ring and the inner gating at an injection speed of 100~200mm / s.

[0010] S2.2 Rapid pressurization filling: When the aluminum alloy liquid reaches the preset position before the outlet of the inner gate, the motion control mode of the main pressure head is changed from speed control to pressure control, and the pressure is rapidly increased to pressure P1, so that the aluminum alloy liquid quickly fills the mold cavity under pressure P1. P1 is 20~40MPa, and the pressure building time is no more than 12 milliseconds.

[0011] S2.3, Pressurized slag discharge and pressure-holding solidification shell: When the aluminum alloy liquid completely covers the surface of the sand core and fills the inner cavity of the mold to 90~95% of the volume, the main pressure head continues to pressurize to the slag discharge pressure P2, the pressure P2 is 60~70MPa, the pressure build-up time is less than 10 milliseconds, and it is held at this pressure for a duration T1, T1 is 0.2~0.5 seconds, so that the aluminum alloy liquid in contact with the surface of the sand core forms a dense solidification shell of 0.1~0.3mm, effectively preventing sand adhesion defects;

[0012] S2.4 High-Pressure Overall Compensation and Local Extrusion Compensation: The main pressure head rapidly increases the pressure to the overall compensation pressure P3, which is 120~150MPa. The pressure build-up time is no more than 10 milliseconds, and the pressure holding time T2 (seconds) = 1.665 × H 2 In the formula, H is the thickness of the material cake, in cm, with a value ranging from 3 to 5. Simultaneously, at locations on the subframe where solidification is slower than the surrounding metal (e.g., hot spots), localized extrusion and compensation are implemented using independently controlled pressure heads. The localized extrusion and compensation pressure P4 (P4 is the ratio of the pressure applied by the pressure head to the corresponding cross-sectional area of ​​the pressure head) is 2 to 3 times the overall compensation pressure P3, with a pressure build-up time of less than 20 milliseconds. The start time T3 (T3 is the delay time from the establishment of the overall compensation pressure P3 to the initiation of localized extrusion and compensation) and the holding time T4 (T4 is the duration of the localized extrusion and compensation pressure P4) are calculated using the following formulas:

[0013] T3 (seconds) = (0.3~0.6) × M2 (1);

[0014] T4 (seconds) = (5.5~6.5) × M 2 (2);

[0015] Where M is the ratio of the volume of the locally compressed and shrunken area to its surface area, in centimeters;

[0016] The above intelligent pressurization curve and multi-stage casting system achieve their core function through multi-stage precision pressure control. Specifically:

[0017] Slow injection and low-pressure casting: The appropriate flow rate is ensured by the injection speed of 100~200mm / s, which can reduce the temperature drop in the central pressure chamber and the flow channel, and avoid violent fluctuations in the liquid level in the pressure chamber, effectively preventing air entrapment and slag entrapment.

[0018] The pressure build-up and holding times at each stage must be strictly controlled within the set range; otherwise, the expected process effect cannot be achieved. Specifically:

[0019] If the pressure build-up time of P1 exceeds 12 milliseconds, fluid flow will be interrupted, leading to blockage of the ingate outlet and cold shut-off.

[0020] If the pressure build-up time of P2 is greater than 10 milliseconds, the liquid flow will cause the filling process to be stuck or interrupted, and the scum and oxide inclusions at the front end of the liquid flow will hinder the flow, resulting in incomplete subframe forming.

[0021] The holding time T1 of P2 is used to form a dense solidified shell on the surface of the sand core to prevent the aluminum liquid from penetrating and causing sand sticking defects under subsequent high pressure conditions;

[0022] The holding time T2 (P3) overcomes the plastic deformation resistance of the pre-crystallized shell generated inside the barrel and the flow resistance of the molten aluminum between dendrites by applying high pressure. This ensures that the molten alloy can pass through the pores between dendrites to fully compensate for shrinkage, achieving microstructural densification and complete solidification. If the time is insufficient, the unsolidified portion will develop shrinkage defects due to insufficient feeding pressure; if the time is too long, it will reduce production efficiency and may lead to grain coarsening.

[0023] The timing of local pressurization, T3, is crucial to the feeding effect. If it is too early, the temperature of the feeding area will be too high and the shrinkage will be too large, making it impossible to achieve sufficient feeding; if it is too late, the solidified layer in contact with the pressure head will be too thick, which will consume too much feeding aluminum alloy liquid and make it difficult to effectively feed due to increased deformation resistance.

[0024] The local pressure holding time T4 is similar to that of T2 in terms of its mechanism. If the time is insufficient, premature pressure release will prevent the remaining liquid phase from solidifying and shrinking, thus failing to compensate for the pressure loss. If the time is too long, it will easily lead to overpressure, causing grain growth or microcracks.

[0025] S3, Depressurization and Mold Opening: The main pressure head and the sub-pressure head are depressurized and returned to their original positions, the mold is opened, the internal sand core is removed, and the cast aluminum alloy hollow subframe is obtained.

[0026] S4. Post-processing: The cast aluminum alloy hollow subframe is heat-treated for strengthening and then machined to obtain a one-piece aluminum alloy hollow subframe. Optionally, the wall thickness of the one-piece aluminum alloy hollow subframe can be 3~4mm.

[0027] Furthermore, the preheating process for the inorganic sand core before core setting is as follows: holding at 120~200℃ for 15~45 minutes; the purpose of preheating the inorganic sand core before core setting is to prevent cold shuts. However, if the temperature is below this range, the strength of the sand core will decrease, which may lead to breakage during the core setting process; if the temperature is below this range, cold shuts will occur, and the core cannot be completely formed. And / or, the inorganic sand core includes an inorganic binder, a nano-silica powder reinforcing agent, and raw sand; and / or, the preparation of the inorganic sand core includes: sand injection molding of the core sand material at a mold temperature of 150~200℃, curing with hot air at 150~200℃, and after demolding, applying an anti-erosion coating or covering with aluminum foil while hot in the inner sprue outlet area of ​​the inorganic sand core (if the coating is not applied while hot, moisture will penetrate into the sand core, forming a high-moisture, zero-strength zone, which will significantly reduce the strength of the sand core or cause the coating to peel off during the subsequent drying process), and then placing the treated inorganic sand core in an environment with humidity below 30% to cool to room temperature to obtain the finished sand core. Optionally, the inorganic binder is composed of 95 wt% silicate and 5 wt% phosphate; wherein, the phosphate is used to improve the hot strength of the sand core to prevent it from breaking; the amount of inorganic binder added is 2.2 to 3.2% based on 100% of the original sand mass, and the amount of nano-silica powder reinforcing agent added is 40 to 60% of the inorganic binder mass; the original sand includes, but is not limited to, at least one of scrubbed sand, calcined sand, and ceramsite sand (e.g., pearl sand).

[0028] Furthermore, in step S2, an inert gas curtain is used to protect the molten aluminum alloy during pouring; and / or, the pouring speed of the molten aluminum alloy into the central pressure chamber is 6~10 kg / s; and / or, the mass of the molten aluminum alloy poured into the central pressure chamber is 1.2~1.5 times the mass of the cast aluminum alloy hollow subframe. The inert gas curtain includes, but is not limited to, a nitrogen or argon gas curtain.

[0029] Further, the slag collecting ring is an annular groove surrounding the flow divider cone; and / or, the ingate is a channel connecting the slag collecting ring and the mold cavity; and / or, the ratio of the cross-sectional area of ​​the central pressure chamber (the cross-section in the direction of movement of the main pressure head), the cross-sectional area of ​​the slag collecting ring flow channel (the annular cross-section in the direction of horizontal flow of the aluminum alloy liquid in the ring), to the total cross-sectional area of ​​all ingate outlets (the cross-section in the direction of injection of aluminum alloy liquid into the cavity) is (6~10):(12~15):1, and the flow rate is controlled by the gradual change of the cross-sectional area from the central pressure chamber to the ingate outlet; and / or, the ratio of the outlet thickness of the ingate to the wall thickness of the cast aluminum alloy hollow subframe body is controlled to be 1.2~1.5:1; and / or, during the filling process, the flow rate of the aluminum alloy liquid at the ingate outlet is 0.6~2.0m / s.

[0030] Furthermore, the preset position is 3-8 mm from the front end of the aluminum alloy liquid to the outlet of the inlet gating system.

[0031] Furthermore, during the liquid forging process, the mold temperature control system independently controls the cooling or heating of different areas within the mold cavity to regulate the solidification process of the aluminum alloy liquid and achieve synchronous solidification of the aluminum alloy liquid; optionally, the mold temperature control system includes cooling water channels, heating oil channels, and quenching inserts (e.g., water-cooled beryllium copper inserts).

[0032] And / or, in step S2.4, enhanced cooling is applied to the subframe at locations where the localized metal solidifies more slowly than the surrounding metal.

[0033] Furthermore, the preparation process of the aluminum alloy liquid includes: using cast aluminum alloy (which can be alloy liquid or alloy ingot, with no specific limitation on the form) as raw material, adding one or more microalloying elements for microalloying treatment; adding a modifier for modification treatment; and then performing refining and degassing treatment to finally obtain a high-purity aluminum alloy liquid with a hydrogen content ≤0.1ml / 100g and an inclusion content K value ≤0.1. The refining and degassing treatment temperature is 710~730℃.

[0034] Further, the cast aluminum alloy is an aluminum-silicon-magnesium alloy (e.g., A356 series aluminum alloy, ZL101 series aluminum alloy), an aluminum-copper alloy, or an aluminum-zinc alloy; and / or, the microalloying element includes at least one of manganese, titanium, and rare earth elements (selected from one or more of lanthanum (La), cerium (Ce), scandium (Sc), erbium (Er), and europium (Eu)); and / or, the modifier includes at least one of strontium and antimony, preferably strontium. Optionally, when the cast aluminum alloy is an A356 series aluminum alloy or / and a ZL101 aluminum alloy, based on 100wt% of the mass of the final high-purity aluminum alloy liquid, 0.10~0.20wt% Mn, 0.10~0.15wt% Ti, 0.05~0.15wt% La and / or Ce are added for microalloying; and 0.002~0.010wt% Sr is added for modification treatment. The chemical composition of the obtained aluminum alloy liquid is as follows: Si 6.5~7.5wt%, Mg 0.30~0.45wt%, Ti 0.10~0.15wt%, Mn 0.10~0.20wt%, Cu 0.07~0.10wt%, Zn 0.05~0.1wt%, Fe ≤0.15wt%, and the total amount of other impurities is less than 0.5wt%.

[0035] Furthermore, after depressurization and mold opening, the cast aluminum alloy hollow subframe is subjected to pressure shaping and residual material punching in sequence;

[0036] And / or, the heat treatment strengthening process includes: slow heating, heat treatment solution holding, rapid quenching, and aging treatment performed sequentially. When the cast aluminum alloy is A356 series aluminum alloy or / and ZL101 aluminum alloy (different alloys require different heat treatment process parameters; that is, if other non-A356 series aluminum alloys or / and ZL101 aluminum alloys are used, the heat treatment process should be adjusted as needed), the slow heating rate is 2~5℃ / min; the heat treatment solution holding temperature is 525~535℃, and the duration is 60~90min; in the rapid quenching step, the time from opening the furnace door to entering the water is ≤12 seconds, and the water temperature is 40~50℃; in the aging treatment step, the time from exiting the water to loading the aging furnace is less than 2h, the heating rate is 10~15℃ / min, the holding temperature is 175~190℃, and the holding time is 4~6h.

[0037] Secondly, the present invention also provides an integral aluminum alloy hollow subframe, which is prepared by the liquid forging method of the aforementioned integral aluminum alloy hollow subframe.

[0038] Furthermore, in the metallographic structure of the integrated aluminum alloy hollow subframe, the eutectic silicon is granular with an average size of 5~10μm and the α-dendritic secondary dendrite spacing is less than 20μm; the tensile strength deviation of the integrated aluminum alloy hollow subframe is <15MPa, the elongation deviation is <1.5%, the X-ray flaw detection reaches level 1~2, and the surface finish of the cavity inner wall is ≤0.2mm.

[0039] The technical solution of this invention has the following advantages:

[0040] This invention overcomes the shortcomings of existing liquid forging processes for preparing one-piece hollow aluminum alloy subframes, such as easy crushing of sand cores, severe sand adhesion, large performance deviations, and low process yield. By adopting a multi-stage pressure casting liquid forging process that combines vertical injection, horizontal pressurization, and center gating with radial multi-inner gate outlets, along with inorganic sand cores and their preheating core technology, the overall forming of high-performance hollow aluminum alloy subframes has been successfully achieved, resulting in a breakthrough in process performance and product quality.

[0041] Specifically, this invention solves three major core problems: First, by adopting inorganic sand cores and their preheating core technology, it completely solves the environmental problems of severe porosity defects and the need for high-temperature sand burning in traditional organic sand cores, as well as the problems of crushing, sand adhesion, displacement, and poor collapsibility caused by insufficient sand core strength; Second, based on rheology, engineering heat transfer, and the principle of metal solidification, a scientific process model is established, and an intelligent pressurization curve and multi-stage casting system are designed, solving the problems of repeated trial and error and high scrap rate caused by the lack of scientific basis for process parameters; Third, through the coordinated design of vertical injection, horizontal pressurization, and central gating and radial multi-ingate outlets, the problems of long process flow, large temperature drop, large filling resistance, and weak performance areas caused by single-sided gating are effectively eliminated. The intelligent pressurization curve and multi-stage casting system play a core role through the following multi-stage precision control: In the slow-injection, low-pressure casting stage, an injection speed of 100-200 mm / s ensures appropriate flow velocity, reduces temperature drop, and prevents air and slag entrapment; in the rapid pressurization and filling stage, 20-40 MPa pressure is established within 12 milliseconds to avoid flow blockage; in the pressurization and slag discharge stage, 60-70 MPa pressure is established within 10 milliseconds and maintained for 0.2-0.5 seconds, pushing the slag at the front of the flow into the slag collection bag, forming an effective solidified shell on the sand core surface to prevent sand adhesion; in the high-pressure overall feeding stage, 120-150 MPa pressure is used and the flow is controlled according to T2=1.665×H. 2 The formula controls the holding time to ensure complete densification and solidification; during the local extrusion and feeding stage, a pressure of 2 to 3 times P3 is used, and the pressure is calculated according to T3 = (0.3 to 0.6) × M. 2 And T4 = (5.5~6.5) × M 2 The formula precisely controls the timing and duration of pressurization, enabling accurate compensation of thick, localized areas.

[0042] By combining the above technical means, this invention increases the process yield from approximately 40% of existing liquid forging technology to 60-80%, controls the tensile strength deviation within 15 MPa, and the elongation deviation less than 1.5 percentage points, ensuring a high degree of consistency in the performance of all parts of the product. Simultaneously, the surface finish of the product's cavity inner wall reaches 0.2 mm, the eutectic silicon is uniformly distributed with fine particles of 5-10 micrometers, the α-dendritic secondary dendrite spacing is less than 20 micrometers, and the X-ray flaw detection of internal defects (porosity, inclusions, shrinkage cavities) reaches level 1-2, fully meeting the stringent requirements of automotive lightweight components for high strength, high precision, and excellent fatigue performance. Attached Figure Description

[0043] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0044] Figure 1 This is a top view schematic diagram of the internal cavity structure of the liquid forging die for the integrated aluminum alloy hollow subframe of the present invention;

[0045] Figure 2 This is a cross-sectional schematic diagram of the internal cavity structure of the liquid forging die for the integrated aluminum alloy hollow subframe of the present invention;

[0046] Figure 3 This is a schematic diagram of the process of liquid forging the one-piece aluminum alloy hollow subframe of the present invention;

[0047] Figure 4 This is a schematic diagram of the intelligent pressurization curve of the liquid forging of the integrated aluminum alloy hollow subframe of the present invention.

[0048] Explanation of reference numerals in the attached diagram: 1-Inorganic sand core, 2-Pressure head, 3-Slag collection bag, 4-Inner gate, 5-Central pressure chamber, 6-Slag collection ring, 7-Sand outlet hole, 8-Main pressure head, 9-Aluminum alloy liquid, 10-Lower mold, 11-Upper mold, 12-Exhaust block, 13-Diverter cone, 14-Inner gate outlet, 15-Sand core head. Detailed Implementation

[0049] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0050] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0051] In the following examples and comparative examples, the process yield (acceptance rate) = (the weight of the cast aluminum alloy hollow subframe after punching / the total weight of the poured aluminum alloy liquid) × 100%;

[0052] Production cycle time refers to the total time from the pouring of molten aluminum alloy to the complete solidification and removal of the mold from the cast hollow aluminum alloy subframe.

[0053] Strength deviation refers to the difference between the maximum and minimum values ​​of a series of tensile strength values ​​obtained after taking samples from different parts of the same aluminum alloy hollow subframe product and conducting tensile tests.

[0054] Elongation deviation refers to the difference between the maximum and minimum values ​​of a series of elongation values ​​after fracture obtained by taking samples from different parts of the same aluminum alloy hollow subframe product and conducting tensile tests.

[0055] The test method for tensile testing is GB / T 228.1-2021;

[0056] The testing method for X-ray flaw detection is GB / T 11346-2018 "Classification of defects in radiographic inspection of aluminum alloy castings".

[0057] Example 1

[0058] This embodiment provides a liquid forging method for an integrated aluminum alloy hollow subframe (4mm wall thickness, 22kg weight). A top view of the liquid forging die's internal cavity structure is shown below. Figure 1 As shown, the sectional schematic structure is as follows Figure 2 As shown, the process flow diagram of liquid forging is as follows: Figure 3 As shown in the figure, the intelligent pressurization curve of liquid forging is illustrated in the figure below. Figure 4 As shown, the specific steps are as follows:

[0059] (1) Alloy smelting: Using A356.2 aluminum alloy liquid as the base, based on the mass of the final high-purity aluminum alloy liquid as 100wt%, 0.10wt% Mn, 0.10wt% Ti and 0.05wt% La were added for microalloying treatment, and 0.002wt% Sr was added for modification treatment. Then, it was refined and degassed at 710℃ to finally obtain a high-purity aluminum alloy liquid with an inclusion content K value of 0.08 and a hydrogen content of 0.09ml / 100g. The chemical composition of the obtained aluminum alloy liquid is 6.5wt% Si, 0.30wt% Mg, 0.10wt% Ti, 0.10wt% Mn, 0.05wt% La, 0.12wt% Fe, 0.08wt% Cu, 0.06wt% Zn, and the total of other impurities is 0.38wt%.

[0060] (2) Sand core preparation and installation: The core sand material is shot into the core using a hot core box sand shot machine. The temperature of the sand core mold is controlled at 150℃. The core is formed at this temperature and then cured with 150℃ hot air. After curing, an inorganic sand core is obtained. After demolding, an anti-erosion coating (the specific coating is a commercially available anti-erosion water-based diatomaceous earth coating, the same below) is applied to the outlet of the inner sprue of the inorganic sand core while it is still hot. Then, the sand core coated with the anti-erosion coating is placed in an environment with humidity below 30% to cool to room temperature. The prepared sand core is placed in a microwave oven. After being preheated at 120℃ for 45 minutes by microwave, it is installed in the inner cavity of the lower mold. After the mold is closed, a complete cavity is formed (vertical indirect liquid forging, horizontal parting surface, upper and lower parting). The core sand material is composed of inorganic binder, nano-silica powder reinforcing agent and granulated sand. The inorganic binder is composed of 95wt% silicate and 5wt% phosphate. Based on the original sand mass of 100%, the amount of inorganic binder added is 2.2%, and the amount of nano-silica powder reinforcing agent added is 40% of the mass of inorganic binder.

[0061] (3) Protective casting and filling: Under the protection of argon gas curtain (to prevent the aluminum liquid from being exposed to air and being oxidized and entangled), the high-purity aluminum alloy liquid is rapidly injected into the vertical central pressure chamber at a casting speed of 6 kg / s. The central pressure chamber has a diameter of 200 mm and is fixed at the center of the lower mold plate. The mass of the injected aluminum alloy liquid is 1.2 times the standard amount required for the cast aluminum alloy hollow subframe. The main pressure head, moving axially along the central pressure chamber, applies pressure to the molten aluminum alloy. The molten aluminum alloy moves at a speed of 100 mm / s axially away from the drive end of the main pressure head. Upon reaching the end of the central pressure chamber, the flow direction of the molten aluminum alloy is changed by a flow divider cone structure fixed to the upper mold, changing it from axial flow to horizontal flow. Subsequently, the molten aluminum alloy is sequentially pushed into the slag collecting ring (an annular groove surrounding the flow divider cone) and eight radiating inlet runners (channels connecting the slag collecting ring and the mold cavity). Just before reaching the inlet runner outlet (3 mm from the front of the molten aluminum alloy at the inlet runner outlet, this is the preset position), the main pressure head... The motion control mode of the head is changed to pressure control (i.e., V / P conversion), and the pressure is rapidly increased to the set pressure P1, so that the aluminum alloy liquid fills the inner cavity of the subframe mold under pressure, wraps the sand core, and achieves uniform filling of the radial multi-ingate outlet; the set pressure P1 is the ratio of the thrust of the main pressure head to the cross-sectional area of ​​the pressure chamber. In this embodiment, P1 is 20MPa, and the pressure build-up time to reach P1 is 10 milliseconds; the ratio of the cross-sectional area of ​​the central pressure chamber, the cross-sectional area of ​​the slag collection annular channel and the total cross-sectional area of ​​all ingate outlets is 6:12:1; the ratio of the thickness of the ingate outlet to the wall thickness of the cast aluminum alloy hollow subframe body is controlled at 1.2:1; during the filling process, the flow velocity of the aluminum alloy liquid at the ingate outlet is 0.8m / s. During the liquid forging process, the mold temperature control system (including cooling water channels, heating oil channels and quenching inserts (water-cooled beryllium copper inserts)) independently controls the cooling or heating of different areas inside the mold cavity to regulate the solidification process of the aluminum alloy liquid and achieve synchronous solidification of the aluminum alloy liquid.

[0062] (4) Pressurization and slag discharge and pressure holding solidification: When the aluminum alloy liquid of the subframe completely covers the surface of the sand core and fills the inner cavity of the mold to 90%, the main pressure head pressurizes to the slag discharge pressure of 60MPa (P2) within 9 milliseconds of pressure building time, so that the cold material and slag at the front end of the aluminum alloy liquid quickly enter the slag bag; maintain this pressure (slag discharge pressure P2) for 0.2 seconds (T1) so that the aluminum alloy liquid in contact with the surface of the sand core forms a dense solidification shell of 0.1mm, which effectively prevents sand adhesion defects;

[0063] (5) High-pressure overall compensation and local control (local pressure boosting and local rapid cooling): After holding pressure for T1 time, the pressure is rapidly increased again to the overall compensation pressure of 120MPa (P3) within 10 milliseconds. The main pressure head compresses the material cake and pushes the aluminum alloy liquid to perform overall compensation of the aluminum alloy liquid of the entire subframe; the holding pressure time is set to T2 (seconds) = 1.665 × H 2 The calculation determines (where H is the thickness of the material cake in cm, and is set to 5); after reaching the compensation pressure P3, at a location on the subframe where solidification is slower than the surrounding metal, local compression compensation is implemented using an independently controlled pressure-distributing head. The process of local compression compensation is as follows: local compression compensation is performed by applying pressure with the pressure-distributing head. The local compression compensation pressure P4 is equal to twice P3, the pressure build-up time is 16 milliseconds, and the local compression compensation start time T3 is calculated according to the formula: T3 (seconds) = 0.6 × M 2 The calculation shows that the local compression and pressure holding time T4 is calculated using the formula: T4 (seconds) = 6.5 × M 2 The calculation is performed, where M is the ratio of the volume of the locally extruded and compensated area to its surface area, in centimeters. Simultaneously with the locally extruded and compensated portion, local rapid cooling is implemented to accelerate the solidification of this area. The local rapid cooling process involves: activating the cooling water supply to the water-cooled beryllium copper insert (which has internal circulating cooling channels) to accelerate local cooling and solidification, thereby promoting the simultaneous solidification of the molten aluminum within the mold cavity.

[0064] (6) Post-processing and finishing: After the cast aluminum alloy hollow subframe is completely cured and formed, pressure is released and the mold is opened. Pressure release and mold opening include: depressurizing the sub-pressure head and the main pressure head, opening the mold and ejecting the cast aluminum alloy hollow subframe. After the cast aluminum alloy hollow subframe is air-cooled to room temperature, the sand core is removed using a vibrating sand removal machine. Subsequently, the hollow subframe is pressure-shaped and punched using a press to break off the process residue such as the inner sprue and slag bag, thus obtaining the cast aluminum alloy hollow subframe. The cast aluminum alloy hollow subframe was strengthened by heat treatment. The heat treatment strengthening steps were as follows: slow heating (heating rate 2℃ / min), heat treatment solution (heating temperature 525℃, holding time 90min, so that the compounds in the microstructure of the subframe dissolve into the matrix and the eutectic silicon is rounded), rapid furnace quenching (time from opening the furnace door to water immersion 10 seconds, water temperature 45±5℃), and aging treatment (time from water immersion to furnace loading 1h, heating rate 10℃ / min, holding temperature 175℃, holding time 6h). Finally, a one-piece aluminum alloy hollow subframe with a wall thickness of 4mm and a weight of 22kg was obtained by machining. Its performance test results are shown in Tables 1 and 2.

[0065] In this embodiment, the core collapse rate after vibration and sand removal reached 98%, there were no sand adhesion defects on the inner cavity surface, and no core crushing or displacement occurred during the entire high-pressure filling and feeding process; the inner wall smoothness of the product cavity reached 0.2mm, and the internal quality showed a defect level of 1 to 2 by X-ray flaw detection; the microstructure showed that the eutectic silicon was uniformly distributed in fine particles with an average size of 7μm and the α-dendritic secondary dendrite spacing was 18μm; the mechanical properties showed high consistency, with the tensile strength deviation of only 14MPa and the elongation deviation of only 1.5% in different parts (6 key parts of the aluminum alloy hollow subframe tested (one of each of the four beams on the front, rear, left, and right sides, and one of each of the front and rear bushing holes, the same below); the process yield increased to 65%, fully meeting the stringent requirements of automotive lightweight components for high strength, high precision, excellent collapse resistance, and anti-sand adhesion performance.

[0066] Example 2

[0067] This embodiment provides a liquid forging method for a one-piece aluminum alloy hollow subframe (3mm wall thickness, 20kg weight), using the same mold as in Embodiment 1. The specific steps are as follows:

[0068] (1) Alloy smelting: Using A356.2 aluminum alloy liquid as the base, based on the mass of the final high-purity aluminum alloy liquid as 100wt%, 0.20wt% Mn, 0.15wt% Ti and 0.15wt% Ce were added for microalloying treatment, and 0.010wt% Sr was added for modification treatment. Then, it was refined and degassed at 730℃ to finally obtain a high-purity aluminum alloy liquid with an inclusion content K value of 0.09 and a hydrogen content of 0.08ml / 100g. The chemical composition of the obtained aluminum alloy liquid is 7.5wt% Si, 0.45wt% Mg, 0.15wt% Ti, 0.20wt% Mn, 0.15wt% Ce, 0.10wt% Fe, 0.07wt% Cu, 0.05wt% Zn, and the total of other impurities is 0.38wt%.

[0069] (2) Sand core preparation and installation: The core sand material is shot into the core using a hot core box sand shooting machine. The mold temperature is controlled at 200℃. The core is formed at this temperature and then cured with 200℃ hot air. After curing, an inorganic sand core is obtained. After demolding, an anti-erosion coating is applied to the inner sprue outlet of the inorganic sand core while it is still hot. The sand core coated with the anti-erosion coating is then placed in an environment with humidity below 30% to cool to room temperature. The prepared sand core is placed in a microwave oven and preheated at 200℃ for 15 minutes. Then it is installed in the inner cavity of the lower mold. After the mold is closed, a complete cavity is formed (vertical indirect liquid forging, horizontal parting surface, upper and lower parting). The core sand material is composed of inorganic binder, nano-silica powder reinforcing agent and pearl sand. The inorganic binder is composed of 95wt% silicate and 5wt% phosphate. The amount of inorganic binder added is 3.2% based on the original sand mass of 100%. The amount of nano-silica powder reinforcing agent added is 60% of the inorganic binder mass.

[0070] (3) Protective casting and filling: Under the protection of argon gas curtain (to prevent the aluminum liquid from being exposed to air and being oxidized and entangled), the high-purity aluminum alloy liquid is rapidly injected into the vertical central pressure chamber at a casting speed of 10 kg / s. The central pressure chamber has a diameter of 250 mm and is fixed at the center of the lower mold plate. The mass of the injected aluminum alloy liquid is 1.5 times the standard amount required for the cast aluminum alloy hollow subframe. The main pressure head, moving axially along the central pressure chamber, applies pressure to the molten aluminum alloy. The molten aluminum alloy moves at a speed of 200 mm / s, propelling it away from the drive end of the main pressure head along the central pressure chamber axis. Upon reaching the end of the central pressure chamber, the flow direction of the molten aluminum alloy is changed to horizontal by a flow divider cone structure fixed to the upper mold. Subsequently, the molten aluminum alloy is pushed sequentially into the slag collecting ring (an annular groove surrounding the flow divider cone) and eight radiating inlet runners (channels connecting the slag collecting ring and the mold cavity). Just before reaching the inlet runner outlet (8 mm from the front of the molten aluminum alloy at the inlet runner outlet, this is a preset position), the main pressure head... The motion control mode was changed to pressure control (i.e., V / P conversion), and the pressure was rapidly increased to the set pressure P1, so that the aluminum alloy liquid filled the inner cavity of the subframe mold under pressure, wrapped the sand core, and achieved uniform filling of the radial multi-ingate outlet; the set pressure P1 is the ratio of the thrust of the main pressure head to the cross-sectional area of ​​the pressure chamber. In this embodiment, P1 is 40MPa, and the pressure build-up time to reach P1 is 11 milliseconds; the ratio of the cross-sectional area of ​​the central pressure chamber, the cross-sectional area of ​​the slag collection annular channel and the total cross-sectional area of ​​all ingate outlets is 10:15:1; the ratio of the thickness of the ingate outlet to the wall thickness of the cast aluminum alloy hollow subframe body is controlled at 1.5:1; during the filling process, the flow velocity of the aluminum alloy liquid at the ingate outlet is 2.0m / s. During the liquid forging process, the mold temperature control system (including cooling water channels, heating oil channels and quenching inserts (water-cooled beryllium copper inserts)) independently controls the cooling or heating of different areas inside the mold cavity to regulate the solidification process of the aluminum alloy liquid and achieve synchronous solidification of the aluminum alloy liquid.

[0071] (4) Pressurized slag discharge and pressure-holding solidification: When the aluminum alloy liquid of the subframe completely covers the surface of the sand core and fills the inner cavity of the mold to 95%, the main pressure head pressurizes to the slag discharge pressure of 70MPa (P2) within 9 milliseconds of pressure building time, so that the cold material and slag at the front end of the aluminum alloy liquid quickly enter the slag bag; maintain this pressure (slag discharge pressure P2) for 0.5 seconds (T1) so that the aluminum alloy liquid in contact with the surface of the sand core forms a dense solidification shell of 0.3mm, effectively preventing sand adhesion defects;

[0072] (5) High-pressure overall compensation and local control (local pressure boosting and local rapid cooling): After holding pressure for T1 time, the pressure is rapidly increased to 150MPa (P3) overall compensation pressure within 10 milliseconds. The main pressure head compresses the material cake and pushes the aluminum alloy liquid to perform overall compensation of the aluminum alloy liquid of the entire subframe; the holding pressure time is set to T2 (seconds) = 1.665 × H 2 The calculation determines (where H is the thickness of the material cake in cm, and is taken as 3); after reaching the compensation pressure P3, local extrusion compensation is implemented at a location on the subframe where the solidification is slower than the surrounding metal, using an independently controlled pressure-distributing head. The local extrusion compensation process is as follows: local extrusion compensation is performed using a pressure-distributing head, the local extrusion compensation pressure P4 (the ratio of the pressure exerted by the pressure-distributing head to the corresponding cross-sectional area of ​​the pressure-distributing head) is equal to 3 times P3, the pressure build-up time is 18 milliseconds, and the local extrusion compensation start time T3 (the delay time from the establishment of the overall compensation pressure P3 to the start of local extrusion compensation) is calculated using the formula: T3 (seconds) = 0.3 × M 2 The calculation shows that the duration of local compression and pressure holding, T4 (the duration of the local compression and pressure holding force P4), is calculated using the formula: T4 (seconds) = 5.5 × M. 2 The calculation is performed, where M is the ratio of the volume of the locally extruded and compensated area to its surface area, in centimeters. Simultaneously with the locally extruded and compensated portion, local rapid cooling is implemented to accelerate the solidification of this area. The local rapid cooling process involves: activating the cooling water supply to the water-cooled beryllium copper insert (which has internal circulating cooling channels) to accelerate local cooling and solidification, thereby promoting the simultaneous solidification of the molten aluminum within the mold cavity.

[0073] (6) Post-processing and finishing: After the cast aluminum alloy hollow subframe is completely cured and formed, pressure is released and the mold is opened. Pressure release and mold opening include: depressurizing the sub-pressure head and the main pressure head, opening the mold and ejecting the cast aluminum alloy hollow subframe. After the cast aluminum alloy hollow subframe is air-cooled to room temperature, the sand core is removed using a vibrating sand removal machine. Subsequently, the hollow subframe is pressure-shaped and punched using a press to break off the process residue such as the inner sprue and slag bag, thus obtaining the cast aluminum alloy hollow subframe. The cast aluminum alloy hollow subframe was strengthened by heat treatment. The heat treatment strengthening steps were as follows: slow heating (heating rate 5℃ / min), heat treatment solution (heating temperature 535℃, holding time 60min, so that the compounds in the microstructure of the subframe dissolve into the matrix and the eutectic silicon is rounded), rapid furnace quenching (time from opening the furnace door to water immersion 11 seconds, water temperature 45±5℃), and aging treatment (time from water immersion to furnace loading 1.5h, heating rate 15℃ / min, holding temperature 190℃, holding time 4h). Finally, a one-piece aluminum alloy hollow subframe with a wall thickness of 3mm and a weight of 20kg was obtained by machining. The performance test results are shown in Tables 1 and 2.

[0074] In this embodiment, the core collapse rate after vibration and sand removal reaches 95%, there are no sand adhesion defects on the inner cavity surface, and no core crushing or displacement occurs during the entire high-pressure filling and feeding process; the inner wall smoothness of the product cavity reaches 0.2mm, and the internal quality shows a defect level of 1 to 2 according to X-ray flaw detection; the microstructure shows that the eutectic silicon is uniformly distributed in fine particles with an average size of 5μm and the α-dendritic secondary dendrite spacing is 16μm; the mechanical properties show high consistency, with the tensile strength deviation of different parts controlled within 13.5MPa and the elongation deviation only 2%; the process yield is increased to 75%, fully meeting the stringent requirements of automotive lightweight components for high strength, high precision, excellent collapse resistance, and anti-sand adhesion performance.

[0075] Example 3

[0076] This embodiment provides a liquid forging method for a one-piece aluminum alloy hollow subframe (wall thickness 3.5mm, weight 24kg), using the same mold as in Embodiment 1. The specific steps are as follows:

[0077] (1) Alloy smelting: Using A356.2 aluminum alloy liquid as the base, based on the mass of the final high-purity aluminum alloy liquid as 100wt%, 0.15wt% Mn, 0.12wt% Ti and 0.10wt% La were added for microalloying treatment, and 0.006wt% Sr was added for modification treatment. Then, it was refined and degassed at 720℃ to finally obtain a high-purity aluminum alloy liquid with an inclusion content K value of 0.1 and a hydrogen content of 0.1ml / 100g. The chemical composition of the obtained aluminum alloy liquid is 7.0wt% Si, 0.37wt% Mg, 0.12wt% Ti, 0.12wt% Mn, 0.10wt% La, 0.15wt% Fe, 0.1wt% Cu, 0.1wt% Zn, and the total of other impurities is 0.49wt%.

[0078] (2) Sand core preparation and installation: The core sand material is shot into the core using a hot core box sand shooting machine. The mold temperature is controlled at 175℃. The core is formed at this temperature and then cured with 175℃ hot air. After curing, an inorganic sand core is obtained. After demolding, an anti-erosion coating is applied to the inner sprue outlet of the inorganic sand core while it is still hot. Then, the sand core coated with the anti-erosion coating is placed in an environment with humidity below 30% to cool to room temperature. The prepared sand core is placed in a microwave oven and preheated at 160℃ for 30 minutes. Then, it is installed in the inner cavity of the lower mold. After the mold is closed, a complete cavity is formed (vertical indirect liquid forging, horizontal parting surface, upper and lower parting). The core sand material is composed of inorganic binder, nano-silica powder reinforcing agent and pearl sand. The inorganic binder is composed of 95wt% silicate and 5wt% phosphate. The amount of inorganic binder added is 2.7% based on the original sand mass of 100%. The amount of nano-silica powder reinforcing agent added is 50% of the inorganic binder mass.

[0079] (3) Protective casting and filling: Under the protection of argon gas curtain (to prevent the aluminum liquid from being exposed to air and being oxidized and entangled), the high-purity aluminum alloy liquid is rapidly injected into the vertical central pressure chamber at a casting speed of 8 kg / s. The central pressure chamber has a diameter of 230 mm and is fixed at the center of the lower mold plate. The mass of the injected aluminum alloy liquid is 1.35 times the standard amount required for the cast aluminum alloy hollow subframe. The main pressure head, moving axially along the central pressure chamber, applies pressure to the molten aluminum alloy. The molten aluminum alloy moves at a speed of 150 mm / s, propelling it away from the drive end of the main pressure head along the central pressure chamber axis. Upon reaching the end of the central pressure chamber, the flow direction of the molten aluminum alloy is changed to horizontal by a flow divider cone structure fixed to the upper mold. Subsequently, a slag-collecting ring (an annular groove surrounding the flow divider cone) and eight radiating inlet runners (channels connecting the slag-collecting ring and the mold cavity) are sequentially pushed in. Just before reaching the inlet runner outlet (5 mm from the front of the molten aluminum alloy at the inlet runner outlet, this is the preset position), the main pressure head... The dynamic control mode is changed to pressure control (i.e., V / P conversion), and the pressure is rapidly increased to the set pressure P1, so that the aluminum alloy liquid fills the inner cavity of the subframe mold under pressure, wraps the sand core, and achieves uniform filling of the radial multi-ingate outlet; the set pressure P1 is the ratio of the thrust of the main pressure head to the cross-sectional area of ​​the pressure chamber. In this embodiment, P1 is 30MPa, and the pressure build-up time to reach P1 is 11 milliseconds; the ratio of the cross-sectional area of ​​the central pressure chamber, the cross-sectional area of ​​the slag collection annular channel and the total cross-sectional area of ​​all ingate outlets is 8:13:1; the ratio of the thickness of the ingate outlet to the wall thickness of the cast aluminum alloy hollow subframe body is controlled at 1.4:1; during the filling process, the flow velocity of the aluminum alloy liquid at the ingate outlet is 1.5m / s. During the liquid forging process, the mold temperature control system (including cooling water channels, heating oil channels and quenching inserts (water-cooled beryllium copper inserts)) independently controls the cooling or heating of different areas inside the mold cavity to regulate the solidification process of the aluminum alloy liquid and achieve synchronous solidification of the aluminum alloy liquid.

[0080] (4) Pressurized slag discharge and pressure-holding solidification: When the aluminum alloy liquid of the subframe completely covers the surface of the sand core and fills the inner cavity of the mold to 92%, the main pressure head pressurizes to 65MPa (P2) slag discharge pressure within 10 milliseconds, so that the cold material and slag at the front end of the aluminum alloy liquid quickly enter the slag bag; maintain this pressure (slag discharge pressure P2) for 0.3 seconds (T1) so that the aluminum alloy liquid in contact with the surface of the sand core forms a 0.2mm dense solidification shell, effectively preventing sand adhesion defects;

[0081] (5) High-pressure overall compensation and local control (local pressure boosting and local rapid cooling): After holding pressure for T1 time, the pressure is rapidly increased again to 135MPa (P3) overall compensation pressure within 9 milliseconds. The main pressure head compresses the material cake and pushes the aluminum alloy liquid to perform overall compensation of the aluminum alloy liquid of the entire subframe; the holding pressure time is set to T2 (seconds) = 1.665 × H 2 The calculation determines (where H is the thickness of the material cake in cm, and is set to 4); after reaching the compensation pressure P3, local extrusion compensation is implemented at a location on the subframe where the solidification is slower than the surrounding metal, using an independently controlled pressure-distributing head. The local extrusion compensation process is as follows: local extrusion compensation is performed using a pressure-distributing head, with the local extrusion compensation pressure P4 (the ratio of the pressure exerted by the pressure-distributing head to the corresponding cross-sectional area of ​​the pressure-distributing head) equal to 2.5 times P3. The pressure build-up time is 17 milliseconds, and the local extrusion compensation start time T3 (the delay time from the establishment of the overall compensation pressure P3 to the initiation of local extrusion compensation) is calculated using the formula: T3 (seconds) = 0.45 × M 2 The calculation shows that the duration of local compression and pressure holding, T4 (the duration of the local compression and pressure holding force P4), is calculated using the formula: T4 (seconds) = 6.0 × M 2 The calculation is performed, where M is the ratio of the volume of the locally extruded and compensated area to its surface area, in centimeters. Simultaneously with the locally extruded and compensated portion, local rapid cooling is implemented to accelerate the solidification of this area. The local rapid cooling process involves: activating the cooling water supply to the water-cooled beryllium copper insert (which has internal circulating cooling channels) to accelerate local cooling and solidification, thereby promoting the simultaneous solidification of the molten aluminum within the mold cavity.

[0082] (6) Post-processing and finishing: After the cast aluminum alloy hollow subframe is completely cured and formed, pressure is released and the mold is opened. Pressure release and mold opening include: depressurizing the sub-pressure head and the main pressure head, opening the mold and ejecting the cast aluminum alloy hollow subframe. After the cast aluminum alloy hollow subframe is air-cooled to room temperature, the sand core is removed using a vibrating sand removal machine. Subsequently, the hollow subframe is pressure-shaped and punched using a press to break off the process residue such as the inner sprue and slag bag, thus obtaining the cast aluminum alloy hollow subframe. The cast aluminum alloy hollow subframe was strengthened by heat treatment. The heat treatment strengthening steps were as follows: slow heating (heating rate 3.5℃ / min), heat treatment solution (heating temperature 530℃, holding time 75min, so that the compounds in the microstructure of the subframe dissolve into the matrix and the eutectic silicon is rounded), rapid furnace quenching (time from opening the furnace door to water immersion 12 seconds, water temperature 45±5℃), and aging treatment (time from water immersion to furnace loading 1.5h, heating rate 12.5℃ / min, holding temperature 185℃, holding time 5h). Finally, a one-piece aluminum alloy hollow subframe with a wall thickness of 3.5mm and a weight of 24kg was obtained by machining. The performance test results are shown in Tables 1 and 2.

[0083] In this embodiment, the core collapse rate after vibration and sand removal reached 97%, with no sand adhesion defects on the inner cavity surface, and no core crushing or displacement occurred during the entire high-pressure filling and feeding process; the inner wall smoothness of the product cavity reached 0.2mm, and the internal quality was shown by X-ray flaw detection to be grade 1 to 2; the microstructure showed that the eutectic silicon was uniformly distributed in fine particles with an average size of 6μm and the α-dendritic secondary dendrite spacing was 17μm; the mechanical properties showed high consistency, with the tensile strength deviation in different parts controlled at 14.5MPa and the elongation deviation at only 1.5%; the process yield was increased to 73%, fully meeting the stringent requirements of automotive lightweight components for high strength, high precision, excellent collapse resistance, and anti-sand adhesion performance.

[0084] Comparative Example 1

[0085] This comparative example provides a method for preparing hollow aluminum alloy subframes using low-pressure casting, the specific steps of which are as follows:

[0086] (1) Aluminum alloy smelting: The formula and process are the same as in Example 1;

[0087] (2) Sand core preparation and core setting: The composition of the sand core material is the same as in Example 1, but no preheating treatment is performed before mold closing. The sand core at room temperature (25°C) is used directly for core setting; the coating on the sand core surface is the same as in Example 1.

[0088] (3) Low-pressure filling and solidification: A constant pressure of 80 kPa is applied to the aluminum alloy liquid surface using a low-pressure casting pneumatic control system, so that the molten metal fills the mold cavity through 8 riser pipes. After holding the pressure for 4 minutes, the pressure is released, the mold is opened and the part is taken out.

[0089] (4) Post-processing: The gating system was removed using a cutting saw, followed by heat treatment with the same process parameters as in Example 1, to obtain an integrated aluminum alloy hollow subframe. The performance test results are shown in Tables 1 and 2.

[0090] While this comparative example can achieve the integral forming of the A356.2 aluminum alloy hollow subframe, the sand core collapse rate after vibration and sand removal is 90%, and there are local sand adhesion defects on the inner cavity surface. In addition, sand core displacement and breakage occur occasionally during production. The surface finish of the inner wall of the product cavity is only 0.35mm, and the internal quality is grade 2 to 3 as shown by X-ray flaw detection. The eutectic silicon in the microstructure is fibrous with an average size of 25μm, and the average spacing between the α dendrites and secondary dendrites is 35μm. The mechanical properties are inconsistent, with tensile strength deviations of up to 35MPa and elongation deviations of 3% (maximum value 5.5%, minimum value 2.5%) in different parts (the detection points are the same as in Example 1, which are 6 key parts). The process yield is only 46%, which cannot meet the stringent requirements of high strength, high precision, clean inner cavity, and high performance consistency for lightweight automotive components.

[0091] Comparative Example 2

[0092] This comparative example provides a liquid forging method for a one-piece hollow aluminum alloy subframe. The difference from Example 1 is that no preheating treatment is performed before mold closing; instead, a sand core at room temperature (25°C) is used directly for the core-setting operation, while other conditions remain the same as in Example 1. As a result, the temperature drop during the molten metal filling process was too large, leading to numerous cold shut defects and preventing complete molding.

[0093] Comparative Example 3

[0094] This comparative example provides a liquid forging method for an integral aluminum alloy hollow subframe. The difference between this method and Example 1 is that the injection speed of the main indenter in step (3) is changed to 50 mm / s, while other conditions remain the same as in Example 1. The results show that due to the low injection speed, a large number of cold shut defects exist in the product, and it cannot be completely formed.

[0095] Comparative Example 4

[0096] This comparative example provides a liquid forging method for an integral aluminum alloy hollow subframe. The difference between this method and Example 1 is that the injection speed of the main indenter in step (3) is changed to 400 mm / s, while other conditions remain the same as in Example 1. The results show that complete forming is possible, but a large number of porosity and inclusion defects appear. After heat treatment, a large number of blistering defects appear, and the performance is significantly reduced. The performance test results are shown in Tables 1 and 2.

[0097] Comparative Example 5

[0098] This comparative example provides a liquid forging method for a one-piece hollow aluminum alloy subframe. The difference between this method and Example 1 is that the pressure build-up time (P1) is 20 milliseconds, while other conditions remain the same as in Example 1. The results show that a cold shut defect occurred, and the far end of the subframe failed to be fully filled and thus failed to form.

[0099] Comparative Example 6

[0100] This comparative example provides a liquid forging method for a one-piece hollow aluminum alloy subframe. The difference between this method and Example 1 is that the holding time T1 (P2) is only 0.1 seconds, while other conditions remain the same as in Example 1. Results: Because a solidified shell was applied before the sand core formed, severe sand adhesion defects occurred, which could not be cleaned, leading to scrap. Furthermore, sand adhesion caused a certain degree of local performance degradation and increased performance deviation. The performance test results are shown in Tables 1 and 2.

[0101] Comparative Example 7

[0102] This comparative example provides a liquid forging method for a one-piece hollow aluminum alloy subframe. The difference between this method and Example 1 is that the local extrusion and feeding start time T3 is calculated using the following formula: T3 (seconds) = 0.2 × M 2In the formula, M is the ratio of the volume of the locally compressed and shrunken area to its surface area, in centimeters. Other conditions are the same as in Example 1. The results show that shrinkage porosity defects occurred, and the flaw detection level could only reach 4. The performance test results are shown in Tables 1 and 2.

[0103] Comparative Example 8

[0104] This comparative example provides a liquid forging method for a one-piece hollow aluminum alloy subframe. The difference between this method and Example 1 is that the local extrusion and feeding start time T3 is calculated using the following formula: T3 (seconds) = 1.0 × M 2 In the formula, M is the ratio of the volume of the locally compressed and shrunken area to its surface area, in centimeters. Other conditions are the same as in Example 1. The results show that severe shrinkage porosity defects occurred, and the flaw detection level could only reach 4. The performance test results are shown in Tables 1 and 2.

[0105] Comparative Example 9

[0106] This comparative example provides a liquid forging method for a one-piece hollow aluminum alloy subframe. The difference between this method and Example 1 is that the local extrusion and pressure holding time T4 is calculated using the following formula: T4 (seconds) = 3.0 × M 2 In the formula, M is the ratio of the volume of the locally compressed and shrunken area to its surface area, in centimeters. Other conditions are the same as in Example 1. The results show that shrinkage defects appeared at the locally compressed location, and the performance deviation increased significantly, failing to meet the requirements; the performance test results are shown in Tables 1 and 2.

[0107] Comparative Example 10

[0108] This comparative example provides a liquid forging method for a one-piece hollow aluminum alloy subframe. The difference between this method and Example 1 is that the local extrusion and feeding holding time T4 is calculated using the following formula: T4 (seconds) = 8.0 × M 2 In the formula, M is the ratio of the volume of the locally compressed area to its surface area, in centimeters. Other conditions are the same as in Example 1. The results show that crack defects appeared in the locally compressed area, and the performance deviation increased significantly; the performance test results are shown in Tables 1 and 2.

[0109] Comparative Example 11

[0110] This comparative example provides a liquid forging method for a one-piece hollow aluminum alloy subframe. The difference from Example 1 is that the local extrusion and feeding pressure P4 is equal to one times P3; that is, the local extrusion and feeding pressure is the same as the overall feeding pressure, and no local extrusion and feeding operation is performed. As a result, shrinkage defects appeared in the thicker areas, the flaw detection level reached level 4, and the performance deviation increased significantly. Other conditions are the same as in Example 1. The performance test results are shown in Tables 1 and 2.

[0111] Table 1

[0112]

[0113] Table 2

[0114]

[0115] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A liquid forging method for an integral aluminum alloy hollow subframe, characterized in that, include: S1. Obtain aluminum alloy liquid and inorganic sand core, use the preheated inorganic sand core as the core of the mold cavity and close the mold. S2. Pouring and Filling: Molten aluminum alloy is poured into the central pressure chamber located at the center of the mold. The main pressure head moves along the axial direction of the central pressure chamber, applying pressure to the molten aluminum alloy inside and pushing it to move away from the driving end of the main pressure head along the axial direction of the central pressure chamber. After the molten aluminum alloy reaches the end of the central pressure chamber, the flow direction of the molten aluminum alloy is changed by the flow divider cone structure, changing it from flowing along the axial direction of the central pressure chamber to flowing horizontally. The molten aluminum alloy with the changed flow direction enters the inner cavity of the mold through several ingates that are radially distributed around the flow divider cone to complete the filling. Its specific process includes: S2.1 Slow injection and low-pressure casting: Start the main pressure head and push the molten aluminum alloy in the central pressure chamber into the slag collection ring and the inner gating at an injection speed of 100~200mm / s. S2.2 Rapid pressurization filling: When the aluminum alloy liquid reaches the preset position before the outlet of the inner gate, the motion control mode of the main pressure head is changed from speed control to pressure control, and the pressure is rapidly increased to pressure P1, so that the aluminum alloy liquid quickly fills the mold cavity under pressure P1. P1 is 20~40MPa, and the pressure building time is no more than 12 milliseconds. S2.3, Pressurization and Slag Removal and Pressure Holding for Shell Solidification: When the aluminum alloy liquid completely covers the surface of the sand core and fills the inner cavity of the mold to 90~95% of its volume, the main pressure head continues to pressurize to the slag removal pressure P2, which is 60~70MPa, with a pressure build-up time of less than 10 milliseconds, and maintains this pressure for a duration of T1, which is 0.2~0.5 seconds. S2.4 High-Pressure Overall Compensation and Local Extrusion Compensation: The main pressure head rapidly increases the pressure to the overall compensation pressure P3, which is 120~150MPa. The pressure holding time T2 (seconds) = 1.665 × H 2 In the formula, H represents the thickness of the material cake in cm, with a value ranging from 3 to 5. Simultaneously, at locations on the subframe where solidification is slower than the surrounding metal, localized compression and feeding are implemented using an independently controlled pressure-reducing head. The localized compression and feeding pressure P4 applied by the pressure-reducing head is 2 to 3 times the overall feeding pressure P3, with a pressure build-up time of less than 20 milliseconds. The start time T3 and holding time T4 of the localized compression and feeding are calculated using the following formulas: T3 (seconds) = (0.3~0.6) × M 2 (1); T4 (seconds) = (5.5~6.5) × M 2 (2); Where M is the ratio of the volume of the locally compressed and shrunken area to its surface area, in centimeters; S3, Depressurization and Mold Opening: Depressurize the main pressure head and the secondary pressure head, open the mold, remove the internal sand core, and obtain the cast aluminum alloy hollow subframe; S4. Post-processing: The cast aluminum alloy hollow subframe is heat-treated for strengthening and machined to obtain a one-piece aluminum alloy hollow subframe finished product.

2. The liquid forging method for an integrated aluminum alloy hollow subframe according to claim 1, characterized in that, The preheating process for the inorganic sand core before core placement is as follows: heat preservation at 120~200℃ for 15~45 minutes; And / or, the inorganic sand core includes an inorganic binder, a nano-silica powder reinforcing agent, and raw sand; And / or, the preparation of the inorganic sand core includes: shooting the core sand material into shape at a mold temperature of 150~200℃, and curing it with hot air at 150~200℃. After demolding, while still hot, applying an anti-erosion coating or covering it with aluminum foil to the outlet area of ​​the inner sprue of the inorganic sand core, and then placing the treated inorganic sand core in an environment with humidity below 30% to cool it to room temperature to obtain the finished sand core.

3. The liquid forging method for the integrated aluminum alloy hollow subframe according to claim 1, characterized in that, In step S2, an inert gas curtain is used to protect the molten aluminum alloy during casting; and / or, the rate at which the molten aluminum alloy is poured into the central pressure chamber is 6~10 kg / s; and / or, the mass of the molten aluminum alloy poured into the central pressure chamber is 1.2~1.5 times the mass of the cast aluminum alloy hollow subframe.

4. The liquid forging method for an integrated aluminum alloy hollow subframe according to claim 1, characterized in that, The slag collecting ring is an annular groove surrounding the flow divider cone; and / or, the ingate is a channel connecting the slag collecting ring and the inner cavity of the mold; and / or, the ratio of the cross-sectional area of ​​the central pressure chamber, the cross-sectional area of ​​the slag collecting ring flow channel, and the total cross-sectional area of ​​all ingate outlets is (6~10):(12~15):1; and / or, the ratio of the outlet thickness of the ingate to the wall thickness of the cast aluminum alloy hollow subframe body is controlled to be 1.2~1.5:1; and / or, during the filling process, the flow velocity of the aluminum alloy liquid at the outlet of the ingate is 0.6~2.0m / s; And / or, the preset position is the position where the front end of the aluminum alloy liquid is 3~8mm away from the outlet of the inlet gate.

5. The liquid forging method for an integrated hollow aluminum alloy subframe according to claim 1, characterized in that, During the liquid forging process, the mold temperature control system independently controls the cooling or heating of different areas inside the mold cavity to regulate the solidification process of the aluminum alloy liquid; optionally, the mold temperature control system includes cooling water channels, heating oil channels and quenching inserts. And / or, in step S2.4, enhanced cooling is applied to the subframe at locations where the localized metal solidifies more slowly than the surrounding metal.

6. The liquid forging method for an integrated hollow aluminum alloy subframe according to claim 1, characterized in that, The preparation process of the aluminum alloy liquid includes: using cast aluminum alloy as raw material, adding one or more microalloying elements for microalloying treatment; adding modifiers for modification treatment; and then refining and degassing treatment to finally obtain a high-purity aluminum alloy liquid with hydrogen content ≤0.1ml / 100g and inclusion content K value ≤0.

1.

7. The liquid forging method for an integrated hollow aluminum alloy subframe according to claim 6, characterized in that, The cast aluminum alloy is an aluminum-silicon-magnesium, aluminum-copper, or aluminum-zinc cast aluminum alloy; and / or, the microalloying element includes at least one of manganese, titanium, and rare earth elements; and / or, the modifier includes at least one of strontium and antimony, preferably strontium.

8. The liquid forging method for an integrated hollow aluminum alloy subframe according to claim 1, characterized in that, After depressurization and mold opening, the cast aluminum alloy hollow subframe is pressure-corrected and the remaining material is punched out in sequence. And / or, the heat treatment strengthening process includes: slow heating, heat preservation solution treatment, rapid furnace quenching and aging treatment performed sequentially.

9. A one-piece hollow aluminum alloy subframe, characterized in that, It is prepared by the liquid forging method of the one-piece aluminum alloy hollow subframe as described in any one of claims 1 to 8.

10. The integrated aluminum alloy hollow subframe according to claim 9, characterized in that, In the metallographic structure of the integrated aluminum alloy hollow subframe, the eutectic silicon is granular with an average size of 5~10μm and the α-dendritic secondary dendrite spacing is less than 20μm. The tensile strength deviation of the integrated aluminum alloy hollow subframe is <15MPa, the elongation deviation is <1.5%, the X-ray flaw detection reaches level 1~2, and the surface finish of the cavity inner wall is ≤0.2mm.

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