A liquid die-casting method for an integrated subframe

Abstract

The application relates to the technical field of automobile manufacturing, and discloses a liquid die forging method for an integrated auxiliary frame, which comprises the following steps: alloy melting, determination of pouring weight and pouring temperature, multi-stage pressure injection, rapid pressure boosting, dynamic pressure keeping, local pressure boosting, pressure releasing and mold opening, mold ejection and cooling, and T5 heat treatment forming. Compared with the prior art, the integrated auxiliary frame formed by using the liquid die forging method adopts low-pressure high-speed pressure injection and high-pressure slow feeding, the finished product is complete in forming and smooth in appearance; the added local pressure boosting process in the process flow makes the finished product compact inside and free of shrinkage defects; the design of a single inner gate makes the finished product free of shrinkage defects, inclusions and porosity defects; and the T5 heat treatment process makes the finished product's bearing capacity and safety and reliability simultaneously improved.

Description

Technical Field

[0001] This invention relates to the field of automobile manufacturing technology, and in particular to a liquid forging method for an integrated subframe. Background Technology

[0002] As a key safety structural component of the chassis system, the subframe needs to withstand the weight of the vehicle itself and the impact load from the road surface. Its safety, durability and reliability have received widespread attention and importance. It requires high load-bearing capacity, as well as a low yield strength ratio and high elongation to ensure its high safety and reliability.

[0003] To address the above issues, existing technologies employ extrusion casting to prepare integrated subframes made of aluminum alloy. Specifically, Chinese patent application CN112517884A discloses an extrusion casting method for aluminum alloy subframes. However, subframes prepared using this method cannot simultaneously achieve both safety and load-bearing capacity. When the strength exceeds 300 MPa and the yield strength ratio is as high as 0.89, the plasticity is only 7%, resulting in insufficient safety. When the elongation reaches 8%, the strength is only 280 MPa, leading to insufficient load-bearing capacity. The root cause of the excessively high yield strength ratio and insufficient plasticity lies in the reliance on T6 heat treatment for dispersion strengthening to increase strength, which inevitably leads to an excessively high yield strength ratio and reduced plasticity. The root cause of insufficient strength lies in the air and slag entrapment during the existing extrusion casting process, resulting in inclusions and porosity defects within the subframe.

[0004] Therefore, how to improve existing construction methods to simultaneously ensure the structural strength and plasticity of the subframe is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems, the purpose of this invention is to provide a liquid forging method for an integrated subframe to ensure both structural strength and plasticity of the integrated subframe.

[0006] Based on this, the present invention provides a liquid forging method for an integrated subframe, which includes the following steps:

[0007] S1. Alloy melting: Based on alloy ingots with an iron content of less than 0.12%, rare earth elements are added for purification, followed by Al-10Sr modifier for modification, and non-toxic refining agent is added for refining and degassing. An electric resistance furnace is set up to maintain the raw material temperature.

[0008] S2. Determine the casting weight and casting temperature. The mass of the raw material injected into the mold cavity is 130%-160% of the predetermined mass of the subframe, and the casting temperature in the mold cavity is 675-700℃.

[0009] S3, multi-stage injection, sets 3-6 different injection parameters for injection filling of molten metal poured into the mold cavity;

[0010] S4. Rapid pressurization: rapidly increases the pressure inside the mold cavity at a rate of 20-50 bar / s, increasing the pressure inside the mold cavity to 100-120 bar within 1-3 seconds.

[0011] S5. Dynamic pressure holding: The pressure value in the mold cavity is maintained at 150-210 bar. The main pressure head increases the pressure in real time according to the solidification shrinkage rate of the aluminum alloy subframe, and always maintains the set pressure. The pressure fluctuation is less than ±0.5 bar, and the pressure holding time is 25-40 seconds.

[0012] S6. Local pressure boosting: After 1-5 seconds of dynamic pressure holding, use an auxiliary pressure head to locally boost the mounting boss of the subframe and the intersection of the left and right longitudinal beams and the front crossbeam. The boosting pressure is 160-210 bar, which will locally generate a pressure of 120MPa-200MPa in the aluminum alloy liquid.

[0013] S7. Depressurize and open the mold, opening the mold cavity and releasing the pressure inside the mold cavity;

[0014] S8. Demolding and cooling: Remove the pre-formed subframe from the mold cavity and let it stand to reduce the temperature of the subframe.

[0015] For S9 and T5 heat treatment, the workpiece is placed in a heating furnace and heated to 510-535℃. After holding at that temperature for 8-16 hours, it is immersed in water at 30-50℃ for 3-5 seconds to cool down. After cooling, it is taken out and reheated to 130-150℃ within 2 hours. After holding at that temperature for 8-16 hours, it is taken out of the furnace and cooled to room temperature to form an integrated subframe.

[0016] In some embodiments of this application, the rare earth content used for purification in step S1 is 0.02-0.1%.

[0017] In some embodiments of this application, the content of the deteriorating agent used for deterioration treatment in step S1 is 0.05-0.1%.

[0018] In some embodiments of this application, the non-toxic refining agent is added in step S1 by gas rotary blowing or vortex blowing.

[0019] In some embodiments of this application, a mold with a cavity is used, wherein the mold has only one ingate, and the ratio of the cross-sectional area of ​​the ingate to the cross-sectional area of ​​the injection hammer is 0.2-0.6.

[0020] In some embodiments of this application, the mold is provided with a plurality of slag collection bags and venting channels, the ratio of the cross-sectional area of ​​the venting channel to the cross-sectional area of ​​the ingate is 0.2-0.5, and the volume of the slag collection bags is 5-10% of the volume of the mold cavity.

[0021] The liquid forging method for an integrated subframe provided in this invention has the following advantages compared with the prior art:

[0022] 1. Complete forming and smooth surface. Existing liquid forging technology emphasizes low speed and high pressure. However, for this type of one-piece subframe, low-speed injection is difficult to form completely, while high-speed injection is prone to porosity defects. This invention uses low-pressure high-speed injection and high-pressure slow-speed feeding, which can not only form completely but also fully feed the material, resulting in a subframe with a smooth surface and complete forming.

[0023] 2. Dense internal structure, free from shrinkage defects. The process flow of this invention incorporates localized pressurization, which allows for high-pressure compensation of isolated hot spots, eliminating shrinkage defects.

[0024] 3. Free from inclusions and porosity defects. This invention employs a single gating system with an ingate cross-sectional area to hammer cross-sectional area ratio of 0.2-0.5 (large gating, small hammer). This slows down the filling speed of the molten metal, allows for rapid filling to prevent excessive cooling, and reduces the risk of air and slag entrapment. The venting area to ingate cross-sectional area ratio is also 0.2-0.5, and the slag collection bag volume is 5-10% of the subframe mold cavity volume. Based on the flow characteristics of the alloy liquid and gas, this ensures smooth gas removal from the mold cavity without causing material spraying (aluminum liquid escape).

[0025] 4. Simultaneous improvement in load-bearing capacity and safety reliability. This invention employs a T5 heat treatment process instead of T6, namely solution treatment + incomplete aging, to achieve high strength, a low yield strength ratio, and high elongation. Sampling of the subframe from this application revealed an ultimate strength of 310-330 MPa, a yield strength of 220-240 MPa, a yield strength ratio of only 0.71-0.73 (less than 75%), and an elongation greater than 11%. The T5 heat treatment process ensures both load-bearing capacity and safety reliability. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the integrated subframe structure according to some embodiments of the present invention;

[0027] Figure 2 This is a schematic diagram of the internal structure of the mold cavity used to manufacture an integrated subframe according to some embodiments of the present invention.

[0028] In the diagram, 1. Front crossbeam; 2. Rear crossbeam; 3. Left longitudinal beam; 4. Right longitudinal beam; 5. Mounting boss; 6. Swing arm mounting lug bracket; 7. Front swing arm support; 8. Anti-collision beam mounting seat; 9. Mold cavity; 10. Inner runner; 11. Slag collection bag; 12. Venting channel; 13. Injection hammer. Detailed Implementation

[0029] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0030] It should be understood that the terms "before," "after," etc., are used in this invention to describe various types of information, but this information should not be limited to these terms. These terms are only used to distinguish information of the same type from each other. For example, "before" information can also be called "after" information, and "after" information can also be called "before" information, without departing from the scope of this invention.

[0031] like Figure 1 and Figure 2 As shown, an integrated subframe includes a front crossbeam 1, a rear crossbeam 2, a left longitudinal beam 3, a right longitudinal beam 4, a mounting boss 5, a control arm mounting lug bracket 6, a front control arm support 7, and a crash beam mounting seat 8. Based on the above structural design, this invention provides a liquid forging method for an integrated subframe, comprising the following steps:

[0032] S1. Alloy melting: Based on alloy ingots with an iron content of less than 0.12%, 0.02-0.1% rare earth is added for purification treatment, followed by 0.05-0.1% Al-10Sr modifier for modification treatment. Non-toxic refining agent is added for refining and degassing by rotary blowing or vortex blowing, and an electric resistance furnace is set up to maintain the raw material temperature.

[0033] S2. Determine the casting weight and casting temperature. The mass of the raw material injected into the mold cavity 9 is 130%-160% of the predetermined mass of the subframe, and the casting temperature in the mold cavity 9 is 675-700℃.

[0034] S3, Multi-stage injection: Set 3-6 different injection parameters for the molten metal poured into the mold cavity 9 for injection filling;

[0035] S4. Rapid pressurization: Rapidly increase the pressure inside the mold cavity 9 at a pressurization rate of 20-50 bar / s, increasing the pressure inside the mold cavity 9 to 100-120 bar within 1-3 seconds.

[0036] S5. Dynamic pressure holding: The pressure value in the mold cavity 9 is maintained at 150-210 bar. The main pressure head increases the pressure in real time according to the solidification shrinkage rate of the aluminum alloy subframe, and always maintains the set pressure. The pressure fluctuation is less than ±0.5 bar, and the pressure holding time is 25-40 seconds.

[0037] S6. Local pressure boosting: After 1-5 seconds of dynamic pressure holding, use an auxiliary pressure head to locally boost the mounting boss of the subframe and the intersection of the left and right longitudinal beams and the front crossbeam. The boosting pressure is 160-210 bar, which will locally generate a pressure of 120MPa-200MPa in the aluminum alloy liquid.

[0038] S7. Depressurize and open the mold, open the mold cavity 9 and release the pressure inside the mold cavity 9;

[0039] S8. Demolding and cooling: Remove the pre-formed subframe from the mold cavity 9 and let it stand to reduce the temperature of the subframe.

[0040] For S9 and T5 heat treatment, the workpiece is placed in a heating furnace and heated to 510-535℃. After holding at that temperature for 8-16 hours, it is immersed in water at 30-50℃ for 3-5 seconds to cool down. After cooling, it is taken out and reheated to 130-150℃ within 2 hours. After holding at that temperature for 8-16 hours, it is taken out of the furnace and cooled to room temperature to form an integrated subframe.

[0041] The beneficial effects of this invention are as follows:

[0042] 1. Complete forming and smooth surface. Existing liquid forging technology emphasizes low speed and high pressure. However, for this type of one-piece subframe, low-speed injection is difficult to form completely, while high-speed injection is prone to porosity defects. This invention uses low-pressure high-speed injection and high-pressure slow-speed feeding, which can not only form completely but also fully feed the material, resulting in a subframe with a smooth surface and complete forming.

[0043] 2. Dense internal structure, free from shrinkage defects. The process flow of this invention incorporates localized pressurization, which allows for high-pressure compensation of isolated hot spots, eliminating shrinkage defects.

[0044] 3. Free from inclusions and porosity defects. This invention employs a single gating system with an ingate cross-sectional area to hammer cross-sectional area ratio of 0.2-0.5 (large gating and small hammer). This slows down the filling speed of the molten metal, allows for rapid filling to prevent excessive cooling, and reduces the risk of air and slag entrapment. The venting area to ingate cross-sectional area ratio is also 0.2-0.5, and the volume of the slag collection bag 11 is 5-10% of the volume of the subframe mold cavity 9. Based on the flow characteristics of the alloy liquid and gas, this ensures smooth gas removal from the mold cavity 9 without material spraying (aluminum liquid escape).

[0045] 4. Simultaneous improvement in load-bearing capacity and safety reliability. This invention employs a T5 heat treatment process instead of T6, namely solution treatment followed by incomplete aging, to achieve high strength, a low yield strength ratio, and high elongation. Samples of the subframe body of this invention show an ultimate tensile strength of 310-330 MPa, a yield strength of 220-240 MPa, a yield strength ratio of only 0.71-0.73 (less than 75%), and an elongation greater than 11%. This ensures both load-bearing capacity and safety reliability.

[0046] Optionally, for the liquid forging method of the integrated subframe of this application, the mold used to prepare the integrated subframe has only one ingate 10, and the ratio of the cross-sectional area of ​​the ingate 10 to the cross-sectional area of ​​the injection hammer 13 is 0.2-0.6. The prior art uses a multi-ingate 10 scheme, while the present invention uses a single ingate 10, which can prevent air entrapment and slag entrapment defects caused by the convergence of multiple streams due to multiple ingates 10; the above arrangement can also ensure that the speed at which the molten metal fills the mold cavity 9 is moderate, without jetting or severe turbulence, thereby avoiding air entrapment and slag entrapment defects.

[0047] Furthermore, the mold is equipped with several slag collection bags 11 and venting channels 12. The ratio of the cross-sectional area of ​​the venting channel 12 to the cross-sectional area of ​​the ingate is 0.2-0.5, and the volume of the slag collection bags 11 is 5-10% of the volume of the mold cavity 9. This feature ensures that the gas in the mold cavity 9 is discharged as quickly as possible, and the oxide inclusions at the front end of the liquid flow are effectively collected, effectively preventing inclusions and porosity defects.

[0048] To more clearly describe the preparation method of this application, the present invention provides the following embodiments.

[0049] Example 1

[0050] Specifically, Embodiment 1 provides an integral subframe prepared using the above-described liquid forging method. The integral subframe has dimensions of 920mm*600mm*128mm, a single weight of 9.5kg, a minimum wall thickness of 3mm, and is made of A356.2 aluminum alloy. The subframe is vertically formed, with the rear crossbeam at the bottom, using a horizontal parting line and a vertical downward injection molding process in the middle section.

[0051] In this embodiment, the alloy melting uses A356.2 alloy ingots with an iron content of less than 0.12% as raw materials, adds 0.02% rare earth for purification treatment, adds 0.1% Al-10Sr modifier for modification treatment, and uses gas rotary blowing and vortex addition of non-toxic refining agent for refining and degassing, and keeps the furnace warm.

[0052] During the quantitative and temperature-controlled casting stage, the casting volume is 1.6 times the weight of the subframe, and the casting temperature is 700℃. It should be noted that insufficient casting volume leads to inadequate shrinkage compensation and shrinkage defects; excessive casting volume results in a longer casting cake and increased pressure attenuation, also causing shrinkage defects. Excessively high casting temperatures lead to severe shrinkage defects and increased shrinkage; excessively low temperatures can cause cold shuts, making molding difficult.

[0053] In this embodiment, the molten metal poured into the barrel is injected using three different injection parameters. The first-level parameters are as follows: pressure 140 bar, speed 140 mm / s, position 110 mm; the second-level parameters are as follows: pressure 75 bar, speed 80 mm / s, position 450 mm; and the third-level parameters are as follows: pressure 85 bar, speed 130 mm / s, position 590 mm. This graded injection ensures that the molten metal smoothly and continuously fills the mold cavity 9, preventing defects such as cold shuts, air entrapment, and slag entrapment.

[0054] During the rapid pressurization phase, the pressurization rate is 35 bar / s, and the pressure is increased to 120 bar within 1 second.

[0055] During the dynamic pressure holding stage, the preset pressure holding value is 210 bar. The main pressure head increases the pressure in real time according to the solidification and shrinkage rate of the aluminum alloy subframe, and always maintains the set pressure. The pressure fluctuation is less than ±0.5 bar, and the pressure holding time is 25 seconds.

[0056] In this embodiment, localized pressurization involves a 1-second delay after the start of dynamic pressure holding, followed by the application of an auxiliary pressure head to locally pressurize the mounting bosses of the subframe and the intersections of the left and right longitudinal beams with the front crossbeam. The pressurization pressure is 160 bar, creating a localized pressure of 120 MPa in the molten aluminum alloy. Due to the complex structure of the subframe, the mounting bosses and the intersections of the left and right longitudinal beams with the front crossbeam cool slowly, making it difficult to maintain unobstructed feeding channels between them and the gating system. While these feeding channels solidify, the components themselves are not yet solidified. Applying localized pressure at these locations allows for pressure-based feeding, eliminating shrinkage defects in these areas.

[0057] The heat treatment stage is T5 treatment, which is solution treatment plus under-aging treatment. The workpiece is placed in a heating furnace and heated to 510-535℃, held for 8-16 hours, and then immersed in 30-50℃ water for 3-5 seconds to cool. After removal, it is reheated to 130-150℃ within 2 hours and held for 8-16 hours before being removed from the furnace and cooled to room temperature. This treatment produces fine and appropriate amounts of precipitates, which can achieve high strength, reduce the yield strength ratio, improve plasticity, and enhance the safety and reliability of the auxiliary workshop.

[0058] In this embodiment, the mold still uses a single ingate 10, which is located in the middle section of the rear crossbeam. The ratio of the cross-sectional area of ​​the ingate 10 to the cross-sectional area of ​​the injection hammer 13 is 0.2. Furthermore, in this embodiment, the ratio of the cross-sectional area of ​​the venting channel 12 to the cross-sectional area of ​​the ingate is 0.5, and the volume of the slag collection bag 11 is 5% of the volume of the subframe mold cavity 9. Based on the above structure, it can be ensured that the gas in the subframe mold cavity 9 is discharged as soon as possible, and the oxide inclusions at the front end of the liquid flow are effectively collected, effectively preventing inclusions and porosity defects.

[0059] The entire manufacturing process was smooth and free of aluminum spraying. The resulting unibody subframe had no welded joints, was perfectly formed, and had a smooth surface. Flaw detection revealed a dense internal structure with no shrinkage defects, inclusions, or porosity. Samples of the unibody subframe, after T5 heat treatment, showed an ultimate tensile strength of 310 MPa, a yield strength of 220 MPa, a yield-to-tensile ratio of only 0.71 (less than 75%), and an elongation of 11.5%. This ensured both load-bearing capacity and high safety and reliability.

[0060] Example 2

[0061] Furthermore, in Embodiment 2 of this application, an integral subframe prepared using the above-mentioned liquid forging method is provided. The integral subframe has an outline dimension of 920mm*610mm*130mm, a single weight of 10.5kg, a minimum wall thickness of 4mm, and is made of A356.2 aluminum alloy.

[0062] In the alloy melting stage, A356.2 alloy ingots with an iron content of less than 0.11% are used as raw materials. 0.06% rare earth is added for purification treatment, and 0.075% Al-10Sr modifier is added for modification treatment. Non-toxic refining agents are added for refining and degassing by gas rotary blowing and vortex blowing. The electric resistance furnace is kept warm.

[0063] In this embodiment, the casting volume is 1.45 times the weight of the subframe, and the casting temperature is 685℃.

[0064] In the multi-stage injection stage, the molten metal poured into the barrel is injected with four different injection parameters for molding. The parameters for stage 1 are as follows: pressure 135 bar, speed 135 mm / s, position 115 mm; the parameters for stage 2 are as follows: pressure 130 bar, speed 130 mm / s, position 385 mm; the parameters for stage 3 are as follows: pressure 85 bar, speed 55 mm / s, position 480 mm; and the parameters for stage 4 are as follows: pressure 70 bar, speed 110 mm / s, position 600 mm.

[0065] During the rapid pressurization phase, the pressurization rate is 25 bar / s, and the pressure increases to 120 bar within 2 seconds.

[0066] The preset pressure value for dynamic pressure holding is 180 bar. The main pressure head increases the pressure in real time according to the solidification and shrinkage rate of the aluminum alloy subframe, and always maintains the set pressure. The pressure fluctuation is less than ±0.5 bar, and the pressure holding time is 32 seconds.

[0067] Local pressurization involves delaying the start of dynamic pressure holding for 3 seconds, then using an auxiliary pressure head to locally pressurize the mounting bosses of the subframe and the intersection of the left and right longitudinal beams with the front crossbeam. The pressurization pressure is 180 bar, which locally generates a pressure of 160 MPa in the molten aluminum alloy.

[0068] The heat treatment stage is T5 treatment, which is solution treatment + under-aging treatment. The workpiece is placed in a heating furnace and heated to 510-535℃. After holding at that temperature for 8-16 hours, it is immersed in water at 30-50℃ for 3-5 seconds to cool down and then taken out. It is then reheated to 130-150℃ within 2 hours and held at that temperature for 8-16 hours before being taken out of the furnace and cooled to room temperature.

[0069] In this embodiment, the ratio of the cross-sectional area of ​​the ingate 10 to the cross-sectional area of ​​the injection hammer 13 is 0.4; the ratio of the cross-sectional area of ​​the vent 12 to the cross-sectional area of ​​the ingate is 0.35; and the volume of the slag collection bag 11 is 7.5% of the volume of the subframe mold cavity 9.

[0070] Sampling of the integrated subframe of this embodiment yielded an ultimate strength of 320 MPa, a yield strength of 230 MPa, a yield ratio of only 0.72 (less than 75%), and an elongation of 11.5%.

[0071] Example 3

[0072] Furthermore, Embodiment 3 of this application provides an integral subframe prepared using the above-described liquid forging method. The integral subframe has an outline dimension of 920mm*610mm*128mm, a single weight of 11.5kg, a minimum wall thickness of 5mm, and is made of A356.2 aluminum alloy.

[0073] In the alloy melting stage, A356.2 alloy ingots with an iron content of less than 0.10% are used as raw materials. 0.1% rare earth is added for purification treatment, and 0.1% Al-10Sr modifier is added for modification treatment. Non-toxic refining agents are added for refining and degassing by gas rotary blowing or vortex blowing. The electric resistance furnace is kept warm.

[0074] In this embodiment, the casting volume is 1.3 times the weight of the subframe, and the casting temperature is 675°C.

[0075] In the multi-stage injection stage, the molten metal poured into the barrel is injected with six different injection parameters for molding. The parameters for stage 1 are as follows: pressure 140 bar, speed 140 mm / s, position 110 mm; the parameters for stage 2 are as follows: pressure 130 bar, speed 110 mm / s, position 380 mm; the parameters for stage 3 are as follows: pressure 75 bar, speed 80 mm / s, position 450 mm; the parameters for stage 4 are as follows: pressure 80 bar, speed 50 mm / s, position 480 mm; the parameters for stage 5 are as follows: pressure 50 bar, speed 110 mm / s, position 565 mm; and the parameters for stage 6 are as follows: pressure 60 bar, speed 120 mm / s, position 610 mm.

[0076] During the rapid pressurization phase, the pressurization rate is 20 bar / s, and the pressure increases to 120 bar within 3 seconds.

[0077] In this embodiment, the preset pressure value for dynamic pressure holding is 150 bar. The main pressure head increases the pressure in real time according to the solidification and shrinkage rate of the aluminum alloy subframe, and always maintains the set pressure. The pressure fluctuation is less than ±0.5 bar, and the pressure holding time is 40 seconds.

[0078] Local pressurization involves delaying for 5 seconds after the start of dynamic pressure holding, then using an auxiliary pressure head to locally pressurize the mounting bosses of the subframe and the intersection of the left and right longitudinal beams with the front crossbeam. The pressurization pressure is 180 bar, which locally generates a pressure of 200 MPa in the molten aluminum alloy.

[0079] The heat treatment stage is T5 treatment, which is solution treatment + under-aging treatment. The workpiece is placed in a heating furnace and heated to 510-535℃. After holding at that temperature for 8-16 hours, it is immersed in water at 30-50℃ for 3-5 seconds to cool down and then taken out. It is then reheated to 130-150℃ within 2 hours and held at that temperature for 8-16 hours before being taken out of the furnace and cooled to room temperature.

[0080] In this embodiment, the ratio of the cross-sectional area of ​​the ingate 10 to the cross-sectional area of ​​the injection hammer 13 is 0.6, the ratio of the cross-sectional area of ​​the vent 12 to the cross-sectional area of ​​the ingate is 0.5, and the volume of the slag collection bag 11 is 5% of the volume of the subframe mold cavity 9.

[0081] Sampling of the integrated subframe of this embodiment yielded an ultimate strength of 330 MPa, a yield strength of 230 MPa, a yield ratio of only 0.73 (less than 75%), and an elongation of 11.2%.

[0082] In summary, this invention provides a liquid forging method for an integrated subframe, comprising steps such as alloy melting, determining the casting weight and pouring temperature, multi-stage injection, rapid pressurization, dynamic pressure holding, local pressurization, pressure release and mold opening, mold cooling, and T5 heat treatment forming. Compared with existing technologies, the integrated subframe formed using this liquid forging method employs low-pressure high-speed injection and high-pressure slow-speed shrinkage compensation, resulting in a complete forming and smooth surface of the finished product. The added local pressurization process in the process flow makes the finished product internally dense and free of shrinkage defects. The single ingate design ensures that the finished product is free of shrinkage defects, inclusions, and porosity defects. The T5 heat treatment process simultaneously improves the load-bearing capacity and safety reliability of the finished product.

[0083] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A liquid forging method for an integrated subframe, characterized in that, Includes the following steps: S1. Alloy melting: Based on alloy ingots with an iron content of less than 0.12%, rare earth elements are added for purification, followed by Al-10Sr modifier for modification, and non-toxic refining agent is added for refining and degassing. An electric resistance furnace is set up to maintain the raw material temperature. S2. Determine the casting weight and casting temperature. The mass of the raw material injected into the mold cavity is 130%-160% of the predetermined mass of the subframe, and the casting temperature in the mold cavity is 675-700℃. S3, multi-stage injection, sets 3-6 different injection parameters for injection filling of molten metal poured into the mold cavity; S4. Rapid pressurization: rapidly increases the pressure inside the mold cavity at a rate of 20-50 bar / s, increasing the pressure inside the mold cavity to 100-120 bar within 1-3 seconds. S5. Dynamic pressure holding: The pressure value in the mold cavity is maintained at 150-210 bar. The main pressure head increases the pressure in real time according to the solidification shrinkage rate of the aluminum alloy subframe, and always maintains the set pressure. The pressure fluctuation is less than ±0.5 bar, and the pressure holding time is 25-40 seconds. S6. Local pressure boosting: After 1-5 seconds of dynamic pressure holding, use an auxiliary pressure head to locally boost the mounting boss of the subframe and the intersection of the left and right longitudinal beams and the front crossbeam. The boosting pressure is 160-210 bar, which will locally generate a pressure of 120MPa-200MPa in the aluminum alloy liquid. S7. Depressurize and open the mold, opening the mold cavity and releasing the pressure inside the mold cavity; S8. Demolding and cooling: Remove the pre-formed subframe from the mold cavity and let it stand to reduce the temperature of the subframe. For S9 and T5 heat treatment, the workpiece is placed in a heating furnace and heated to 510-535℃. After holding at that temperature for 8-16 hours, it is immersed in water at 30-50℃ for 3-5 seconds to cool down. After cooling, it is taken out and reheated to 130-150℃ within 2 hours. After holding at that temperature for 8-16 hours, it is taken out of the furnace and cooled to room temperature to form an integrated subframe.

2. The liquid forging method for an integrated subframe according to claim 1, characterized in that, In step S1, the rare earth content used for purification is 0.02-0.1%.

3. The liquid forging method for an integrated subframe according to claim 1, characterized in that, In step S1, the content of the deteriorating agent used for the deterioration treatment is 0.05-0.1%.

4. The liquid forging method for an integrated subframe according to claim 1, characterized in that, In step S1, a non-toxic refining agent is added by gas rotary jetting or vortex jetting.

5. The liquid forging method for an integrated subframe according to claim 1, characterized in that, A mold with a cavity is used, and the mold has only one ingate. The ratio of the cross-sectional area of ​​the ingate to the cross-sectional area of ​​the injection hammer is 0.2-0.

6.

6. The liquid forging method for an integrated subframe according to claim 5, characterized in that, The mold is provided with several slag collection bags and venting channels. The ratio of the cross-sectional area of ​​the venting channel to the cross-sectional area of ​​the ingate is 0.2-0.

5. The volume of the slag collection bag is 5-10% of the volume of the mold cavity.

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