Semi-solid forming process for suspension bracket of automobile chassis

Abstract

The invention relates to the technical field of metal material forming, in particular to an automobile chassis suspension bracket semi-solid forming process which comprises the steps of smelting and refining, multi-physics field coupling pulping, asymmetric mold design, multi-section thixotropic injection, collaborative pressurization and pressure maintaining and aftertreatment. High-quality semi-solid slurry is obtained through mechanical-electromagnetic-pulse ultrasonic composite slurry preparation; synchronous filling of a complex structure is achieved through the asymmetric divergent fan-shaped pouring gate; the technology systematically solves the three bottlenecks of unstable slurry, many filling defects and difficult feeding of a key area in the manufacturing of the high-performance suspension bracket, the obtained part is compact in structure and excellent in mechanical property, the fatigue life of the obtained part is remarkably superior to that of a traditional casting and is comparable with that of a forged piece, and the production cost is reduced. And meanwhile, the near-net forming cost advantage is achieved.

Description

Technical Field

[0001] This invention relates to the field of metal material forming technology, specifically to a semi-solid forming process for automotive chassis suspension brackets. Background Technology

[0002] The chassis suspension bracket is the core load-bearing and connecting component of the vehicle suspension system. Its service conditions are harsh, and it needs to withstand complex multi-directional alternating stress and impact loads. Therefore, it has extremely high requirements for the internal quality, static mechanical properties and high-cycle fatigue performance of the parts.

[0003] Currently, the industry mainly uses the following manufacturing processes:

[0004] 1. Traditional casting process - gravity / low-pressure casting: This type of process has a lower cost and is suitable for forming complex structures, but it has inherent defects. Solidification shrinkage can easily lead to micro-shrinkage porosity, and the trapped gas can form pores. The as-cast structure is coarse. These defects result in insufficient mechanical properties of parts, especially fatigue strength, making it difficult to meet the ever-increasing demands for safety and lightweighting.

[0005] 2. Forging process: It can obtain dense fibrous structure and excellent comprehensive properties. However, this process has low material utilization, requires multiple hot working and a lot of subsequent machining, resulting in high production costs. It is also difficult to directly form bracket-type parts with complex geometric features.

[0006] 3. Ordinary high-pressure die casting process: High production efficiency and good formability, but the high-speed filling of liquid metal will entrain a large amount of gas and trap it in the cavity, resulting in diffuse pores inside the casting. These pores will expand and cause bubbling during heat treatment. Therefore, die castings usually cannot be subjected to solution strengthening heat treatment, and there is a ceiling to performance improvement.

[0007] 4. Conventional semi-solid forming process: As a technology between casting and forging, it utilizes a solid-liquid mixture for forming and has the advantages of low temperature, high viscosity, and stable filling. However, when applied to asymmetrical, multi-stress-point parts such as suspension brackets, it still faces three major technical bottlenecks:

[0008] Unstable slurry quality: Single stirring method - such as electromagnetic stirring or mechanical stirring alone - makes it difficult to continuously obtain a uniform, fine, spherical primary phase structure, resulting in poor batch consistency.

[0009] Defects in filling complex structures: For asymmetrical structures of supports, the general gating system design is prone to causing asynchronous filling of slurry, resulting in cold shuts, flow marks or local air entrapment.

[0010] Insufficient feeding in critical areas: Thick connecting parts of parts, such as mounting hole bosses, are the last to solidify. General pressure holding is insufficient to effectively feed them, which can easily lead to micro-shrinkage porosity, which can become fatigue crack initiation and cause performance fluctuations.

[0011] Therefore, those skilled in the art have provided a semi-solid forming process for automotive chassis suspension brackets to solve the problems mentioned in the background art. Summary of the Invention

[0012] To address the aforementioned technical problems, this invention provides a semi-solid molding process for automotive chassis suspension brackets. This process solves the problem of how to stably obtain high-quality semi-solid slurry through an integrated technical solution, enabling it to smoothly and synchronously fill complex asymmetrical cavities and ensure that key stress areas achieve an extremely dense structure, thereby stably manufacturing suspension bracket products with ultra-high fatigue performance.

[0013] Includes the following steps:

[0014] S1. Smelting and refining: Refining and degassing the molten aluminum alloy;

[0015] S2. Multi-physics field coupled pulping: The refined melt is treated by a composite field of mechanical pre-shearing, electromagnetic stirring and intermittent pulsed ultrasound to prepare a semi-solid slurry with a solid volume fraction of 40%-50%.

[0016] S3. Mold preparation: Use a molding mold with an asymmetrical runner, and pre-set local extrusion mechanisms in the mold corresponding to the key stress areas of the part;

[0017] S4. Multi-segment thixotropic injection: The semi-solid slurry is injected into the cavity of the molding die;

[0018] S5. Synergistic pressurization and pressure holding: After the slurry filling is completed, a global pressure holding pressure and a local extrusion pressure applied by the local extrusion mechanism are applied simultaneously, wherein the local extrusion pressure is higher than the global pressure holding pressure;

[0019] S6. Post-processing: After the pressure holding period is over, the mold is cooled and opened, and the parts are heat-treated.

[0020] Preferably, in step S2, the processing parameters of the intermittent pulse ultrasound are: frequency 18-22kHz, power 1.5-3.5kW, pulse working mode, single pulse working time of 2-5 seconds, and interval time of 1-2 seconds.

[0021] Preferably, step S2 specifically includes: firstly, the melt is subjected to primary pre-shearing and heat dissipation by mechanical spiral stirring, and then the melt is introduced into a secondary chamber, in which electromagnetic stirring and the intermittent pulsed ultrasonic treatment are applied simultaneously, and the intensity of the electromagnetic stirring is 300-500 Gauss.

[0022] Preferably, in the semi-solid slurry prepared in step S2, the average size of the primary α-Al grains is ≤70μm and the shape factor is ≥0.85.

[0023] Preferably, in step S3, the asymmetric gating system is a gradually expanding fan-shaped gating system, which expands in a fan shape along the direction of slurry flow, and the expansion angles on both sides of the gating system are differentiated according to the wall thickness of the corresponding area of ​​the cavity.

[0024] Preferably, in step S3, the molding die is preheated to 220-260°C, and the mold temperature corresponding to the key stress area is controlled by conformal cooling water channels to be 10-20°C higher than the overall mold temperature.

[0025] Preferably, in step S4, the multi-stage thixotropic injection adopts three-stage speed control: the speed of the first-stage low-speed injection is 0.1-0.3 m / s; the speed of the second-stage high-speed injection is 1.5-2.5 m / s; the speed of the third-stage injection is reduced to 0.5-1.0 m / s, and a boost pressure of 50-80 MPa is simultaneously established during the third-stage injection stage.

[0026] Preferably, in step S5, the global holding pressure is 80-100 MPa, the local extrusion pressure is 100-120 MPa, and the time for the combined action of global holding pressure and local extrusion is 5-10 seconds.

[0027] Preferably, in step S1, the refining and degassing treatment adopts a high-purity inert gas rotary degassing method, and the hydrogen content of the melt after treatment is ≤0.15ml / 100gAl;

[0028] The aluminum alloy is an A356 or A357 series aluminum alloy.

[0029] The technical effects and advantages of this invention are as follows:

[0030] This multi-stage composite pulping method combines mechanical pre-shearing, electromagnetic macro-homogenization, and pulsed ultrasonic micro-cavitation. Mechanical stirring achieves initial heat dissipation and shearing; electromagnetic stirring provides gentle laminar vortices to achieve macro-uniform structure; and pulsed ultrasound utilizes its periodic cavitation and acoustic flow effects to powerfully break up dendrites, promote spheroidization, and assist in degassing while avoiding local overheating of the melt. The three work synergistically to ensure high-quality pulp structure and batch stability from the source.

[0031] To address the asymmetrical nature of the suspension support structure, an asymmetrical, gradually expanding fan-shaped gating system was designed. This system intelligently adjusts the flow rate and speed of the slurry to different areas through differentiated expansion angles, enabling it to reach all ends of the cavity simultaneously. This achieves true synchronous and stable filling, completely eliminating defects such as cold shuts and air entrapment caused by asynchronous filling.

[0032] The synergistic shrinkage compensation scheme of global pressure holding and local ultra-high pressure extrusion, while compensating for overall shrinkage with conventional global pressure holding, activates independent, higher-pressure local extrusion pins for key areas such as stress concentration and final solidification mounting holes. This "forging-style" forced shrinkage compensation is applied to these areas at the end of solidification, completely eliminating micro-shrinkage porosity and bringing their density close to the theoretical value.

[0033] The suspension bracket produced by this invention has a tensile strength ≥350MPa, yield strength ≥280MPa, elongation ≥10%, and fatigue limit ≥140MPa (R=0.1, 10^7 cycles). Its performance comprehensively surpasses that of traditional castings and is comparable to that of forgings. At the same time, this process maintains the advantages of near-net-shape forming, high material utilization, and less subsequent processing, achieving the best balance between performance and cost, and possessing outstanding industrial application value and market prospects. Attached Figure Description

[0034] Figure 1 This is an overall flow chart of the semi-solid molding process of the automobile chassis suspension bracket provided in the embodiments of this application;

[0035] Figure 2 This is a schematic diagram of the composite pulping device in the semi-solid molding process of the automobile chassis suspension bracket provided in the embodiments of this application;

[0036] Figure 3 This is a top view of the layout of the asymmetric expanding fan-shaped runner and the bracket cavity in the semi-solid molding process of the automobile chassis suspension bracket provided in the embodiments of this application.

[0037] Figure 4 This is a comparison diagram of the metallographic structure of the slurry obtained by the process of this invention and the comparative process. Detailed Implementation

[0038] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The embodiments of the present invention are given for illustrative and descriptive purposes only, and are not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described to better illustrate the principles and practical application of the invention, and to enable those skilled in the art to understand the invention and design various embodiments with various modifications suitable for a particular purpose.

[0039] Example 1

[0040] Please see Figures 1-4 This embodiment provides a semi-solid forming process for automotive chassis suspension brackets, including the following steps:

[0041] S1. Smelting and refining: A356 or A357 series aluminum alloys are selected. After smelting, high-purity inert gas is used for rotary degassing and refining to control the hydrogen content of the melt to below 0.15ml / 100gAl.

[0042] S2. Multiphysics Coupling Slurry Preparation: The refined melt is transferred to a composite slurry preparation device, where it undergoes a first-stage mechanical spiral pre-shearing cooling process. Then, in a second-stage chamber, electromagnetic eddy current stirring and intermittent pulsed ultrasonic treatment are simultaneously applied to precisely cool the melt to a semi-solid temperature range, yielding a semi-solid slurry with an average primary α-Al grain size ≤70μm and a shape factor ≥0.85. The parameters for the intermittent pulsed ultrasonic treatment are: frequency 18-22kHz, power 1.5-3.5kW, pulse duration 2-5s, interval 1-2s, total processing time 30-60s, and electromagnetic stirring intensity 300-500 Gauss. The solid volume fraction of the semi-solid slurry is 40%-50%.

[0043] S3. Mold preparation: A mold with an asymmetrical gradually expanding fan-shaped runner is adopted. The expansion angle on both sides of the runner is designed asymmetrically according to the wall thickness difference of the corresponding cavity area. In the critical stress area of ​​the mold cavity corresponding to the bracket mounting hole, a conformal cooling water channel and a hydraulically driven local extrusion pin are preset. The mold is preheated to 220-260℃. The mold temperature of the critical stress area is controlled by the conformal cooling water channel to be 10-20℃ higher than the overall mold temperature.

[0044] S4. Multi-stage thixotropic injection: The semi-solid slurry is transferred to the injection chamber and three-stage injection is performed: the first stage is low-speed material stacking, the second stage is high-speed filling of 70%-85% of the cavity, and the third stage is deceleration and pressurization. The first stage low-speed injection speed is 0.1-0.3m / s, the second stage high-speed injection speed is 1.5-2.5m / s, and the third stage injection speed is reduced to 0.5-1.0m / s while simultaneously establishing a pressurization of 50-80MPa.

[0045] S5. Synergistic Pressure Holding: After filling, immediately and simultaneously apply global pressure holding and local ultra-high pressure extrusion in key stress areas. The local extrusion pressure is 30-50 MPa higher than the global pressure holding pressure. They work together until the gate solidifies. The global pressure holding pressure is 80-100 MPa, and the local ultra-high pressure extrusion pressure is 100-120 MPa. The synergistic effect time is 5-10 seconds.

[0046] S6. Post-processing: After the parts have cooled, the mold is opened, and the final product is obtained through T6 heat treatment.

[0047] Implementation:

[0048] Manufacturing of the rear axle lower control arm bracket for SUV models

[0049] 1. Products and Materials

[0050] Part: Rear axle lower control arm bracket, maximum projected area approximately 450cm² 2 The thickest part, the main mounting hole, is 18mm, and the structure is obviously asymmetrical.

[0051] Material: A356 aluminum alloy (Al-7Si-0.3Mg), conforming to GB / T1173 standard.

[0052] 2. Detailed process steps

[0053] S1. Smelting and Refining:

[0054] The A356 alloy ingot was completely melted in a 750°C melting furnace.

[0055] The temperature was lowered to 710℃, and high-purity argon gas (99.999% purity) was used for rotary degassing at a rotor speed of 500 rpm and an argon gas flow rate of 20 L / min for 15 minutes.

[0056] After treatment, the hydrogen content of the melt decreased from the initial 0.35 ml / 100gAl to 0.10 ml / 100gAl.

[0057] S2. Multiphysics Coupled Pulping:

[0058] The refined melt was quickly transferred to a process such as Figure 2 The pulping apparatus shown.

[0059] Primary processing: The melt temperature is reduced to approximately 600°C by using a spiral stirrer at a speed of 350 rpm.

[0060] Secondary composite treatment: The melt enters the secondary chamber, and the 400Gs electromagnetic stirrer is started. At the same time, the pulse ultrasonic device is started with a frequency of 20kHz and a power of 2.5kW. The ultrasonic device operates in a pulse mode of "working for 3 seconds and then pausing for 1.5 seconds", with a total treatment time of 45 seconds.

[0061] During this process, the melt was precisely temperature-controlled to 585°C. Sampling and testing showed that the average size of the nascent α-Al grains in the slurry was 55 μm, with a shape factor of 0.89. In contrast, the slurry stirred electromagnetically with the same parameters had a grain size of 88 μm and a shape factor of 0.74.

[0062] S3. Mold Preparation:

[0063] Mold gating system design such as Figure 3 As shown. Based on simulation analysis and actual wall thickness, the expansion angle of the left runner is set to 12°, and that of the right runner is set to 8°.

[0064] Conformable cooling copper pipes and 10mm diameter hydraulic extrusion pins are arranged at three key locations: two subframe mounting holes and one connecting rod mounting hole.

[0065] The mold is heated to 250°C using a mold temperature controller, and the temperature of the conformal cooling water channels in the three key parts is independently controlled to keep the mold temperature in that area stable at 265°C.

[0066] S4. Multi-segment thixotropic injection:

[0067] Approximately 1.5 kg of slurry was transferred into the injection chamber of a 1000T die-casting machine.

[0068] Injection procedure: First stage speed 0.2 m / s; second stage speed 2.2 m / s; third stage speed reduced to 0.8 m / s, the system applies a boost pressure of 70 MPa.

[0069] S5. Synergistic pressurization and pressure holding:

[0070] After the injection end signal is issued, the die-casting machine immediately applies a global holding pressure of 95 MPa.

[0071] A 0.3-second delay ensures the slurry is fully filled but not yet fully solidified. Three local extrusion pins operate simultaneously, applying an ultra-high pressure of 115 MPa.

[0072] The combined action of global pressure holding and local extrusion lasts for 7 seconds until the gate solidifies.

[0073] S6. Post-processing:

[0074] After holding the pressure and cooling for 35 seconds, open the mold, remove the part, and remove the gating system and risers.

[0075] Perform T6 heat treatment: solution treatment at 535℃ for 2 hours, water quenching at 60℃, and aging at 155℃ for 4 hours.

[0076] 3. Performance Testing and Comparative Analysis

[0077] Samples were taken directly from the thickest and most stressed part of the main mounting hole boss of the finished bracket for testing.

[0078] Mechanical properties (average):

[0079] Tensile strength (UTS): 370MPa

[0080] Yield strength (YS): 298MPa

[0081] Elongation (E1.): 12.5%

[0082] Fatigue performance (axial tension-tension, R=0.1):

[0083] Fatigue limit without fracture after 10^7 cycles: 145 MPa

[0084] Comparison objects:

[0085] Comparison part A (gravity casting + T6): UTS265MPa, fatigue limit ~95MPa, internal X-ray inspection shows shrinkage porosity.

[0086] Comparison part B (conventional semi-solid molding, no local extrusion): UTS335MPa, fatigue limit ~120MPa, microscopic shrinkage and porosity in key parts of the metallography.

[0087] The embodiment of the present invention has superior performance compared to the comparative part. X-ray and metallographic examination shows that the part is dense overall, with no shrinkage or porosity in key areas, and the structure is uniform and fine.

[0088] Conclusion: This embodiment fully presents the implementation process of the present invention. Data proves that through the organic combination of multi-physics field coupled pulping, asymmetric flow channel design and synergistic pressurization and feeding, the present invention successfully manufactures a suspension bracket that meets the requirements of ultra-high performance. Its fatigue life is improved by more than 50% compared with the traditional process, achieving unexpected technical effects and possessing extremely high industrial application value.

[0089] In this solution, unless otherwise explicitly specified and limited, the terms "installation", "setting", "connection", "fixing", "screw connection", etc., should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. Unless otherwise explicitly limited, those skilled in the art can understand the specific meaning of the above terms in this solution according to the specific circumstances.

[0090] In the description of this invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0091] Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art and related fields based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described and explained in the present invention, unless otherwise specified or limited, shall be implemented according to conventional means in the art.

Claims

1. A semi-solid molding process for automotive chassis suspension brackets, characterized in that, Includes the following steps: S1. Smelting and refining: Refining and degassing the molten aluminum alloy; S2. Multi-physics field coupled pulping: The refined melt is treated by a composite field of mechanical pre-shearing, electromagnetic stirring and intermittent pulsed ultrasound to prepare a semi-solid slurry with a solid volume fraction of 40%-50%. S3. Mold preparation: Use a molding mold with an asymmetrical runner, and pre-set local extrusion mechanisms in the mold corresponding to the key stress areas of the part; S4. Multi-segment thixotropic injection: The semi-solid slurry is injected into the cavity of the molding die; S5. Synergistic pressurization and pressure holding: After the slurry filling is completed, a global pressure holding pressure and a local extrusion pressure applied by the local extrusion mechanism are applied simultaneously, wherein the local extrusion pressure is higher than the global pressure holding pressure; S6. Post-processing: After the pressure holding period is over, the mold is cooled and opened, and the parts are heat-treated.

2. The semi-solid forming process for the automotive chassis suspension bracket according to claim 1, characterized in that, In step S2, the processing parameters of the intermittent pulse ultrasound are: frequency 18-22kHz, power 1.5-3.5kW, pulse working mode, single pulse working time of 2-5 seconds, and interval time of 1-2 seconds.

3. The semi-solid forming process for the automotive chassis suspension bracket according to claim 2, characterized in that, Step S2 specifically includes: firstly, the melt is subjected to primary pre-shearing and heat dissipation by mechanical spiral stirring, and then the melt is introduced into a secondary chamber, in which electromagnetic stirring and intermittent pulsed ultrasonic treatment are applied simultaneously, and the intensity of the electromagnetic stirring is 300-500 Gauss.

4. The semi-solid forming process for the automotive chassis suspension bracket according to claim 1, characterized in that, In the semi-solid slurry prepared in step S2, the average size of the primary α-Al grains is ≤70μm and the shape factor is ≥0.

85.

5. The semi-solid forming process for the automotive chassis suspension bracket according to claim 1, characterized in that, In step S3, the asymmetric gating system is a gradually expanding fan-shaped gating system, which expands in a fan shape along the direction of slurry flow, and the expansion angles on both sides of the gating system are differentiated according to the wall thickness of the corresponding area of ​​the cavity.

6. The semi-solid forming process for the automotive chassis suspension bracket according to claim 5, characterized in that, In step S3, the molding die is preheated to 220-260°C, and the mold temperature corresponding to the key stress area is controlled by the conformal cooling water channel to be 10-20°C higher than the overall mold temperature.

7. The semi-solid forming process for the automotive chassis suspension bracket according to claim 1, characterized in that, In step S4, the multi-stage thixotropic injection adopts three-stage speed control: the speed of the first-stage low-speed injection is 0.1-0.3 m / s; the speed of the second-stage high-speed injection is 1.5-2.5 m / s; the speed of the third-stage injection is reduced to 0.5-1.0 m / s, and a boost pressure of 50-80 MPa is simultaneously established during the third-stage injection stage.

8. The semi-solid forming process for the automotive chassis suspension bracket according to claim 1, characterized in that, In step S5, the global holding pressure is 80-100 MPa, the local extrusion pressure is 100-120 MPa, and the time for the combined action of global holding pressure and local extrusion is 5-10 seconds.

9. The semi-solid forming process for the automotive chassis suspension bracket according to claim 1, characterized in that, In step S1, the refining and degassing treatment adopts a high-purity inert gas rotary degassing method, and the hydrogen content of the melt after treatment is ≤0.15ml / 100gAl; The aluminum alloy is an A356 or A357 series aluminum alloy.

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