Lightweight aluminum alloy automobile transmission case shell and production process thereof

Abstract

The application belongs to the technical field of aluminum alloy automobile parts, and particularly relates to a lightweight aluminum alloy automobile gearbox shell and a production process thereof. The lightweight aluminum alloy automobile gearbox shell is integrally formed through a composite die casting process; the chemical composition of the lightweight aluminum alloy material is as follows in terms of mass percentage: Si 8.5-11.5%, Cu 1.5-3.5%, Mg 0.25-0.55%, Mn 0.4-0.8%, Fe 0.6-1.2%, Zn <=0.5%, Ti 0.05-0.25%, Sr 0.01-0.06%, Zr 0.05-0.20%, V 0.03-0.12%, and the balance of Al and inevitable impurities, wherein the mass ratio of Mn / Fe is 0.4-0.8:1. The lightweight aluminum alloy automobile gearbox has high strength, high toughness, good casting performance and corrosion resistance, and a preparation method thereof is also provided.

Description

Technical Field

[0001] This invention belongs to the technical field of aluminum alloy automotive parts, specifically relating to lightweight aluminum alloy automotive transmission housings and their manufacturing processes. Background Technology

[0002] Aluminum alloys have become the mainstream material for automotive transmission housings due to their advantages such as low density, good thermal conductivity, high specific strength, and strong ability to form complex structures. As a core structural component of the automotive transmission system, the transmission housing houses gears, bearings, clutches, hydraulic control systems, and lubrication systems, while also providing positioning accuracy, rigid support, heat dissipation, and sealing protection for power transmission components. Currently, aluminum alloy transmission housings are widely used in manual transmissions (MT), automatic transmissions (AT), dual-clutch transmissions (DCT), continuously variable transmissions (CVT), hybrid power transmissions (DHT), and reducers and electric drive systems in new energy vehicles.

[0003] Currently, the main manufacturing processes for aluminum alloy gearbox housings include high-pressure die casting, low-pressure casting, squeeze casting, gravity casting, and vacuum die casting. Among these, high-pressure die casting has become the mainstream process for mass production of complex, thin-walled gearbox housings due to its high production efficiency, good dimensional accuracy, and excellent surface quality. Low-pressure casting offers stable filling, good feeding effect, and high casting density, making it suitable for housing parts with high mechanical performance requirements. Squeeze casting combines the advantages of forging and casting, effectively reducing casting defects. Vacuum die casting, by extracting gas from the mold cavity during the die casting process, can significantly reduce porosity defects and improve the microstructure. In recent years, with the development of computer simulation technology, CAE software-based prediction of filling, solidification, and defects has become an important means of process optimization. Furthermore, semi-solid die casting, as an emerging process, has also been explored for application in gearbox housing manufacturing; research shows that it offers more stable and uniform filling and effectively avoids air entrapment.

[0004] Commonly used aluminum alloy materials for gearbox housings include ADC12, A380, A383, AlSi9Cu3, and AlSi. 10 Die-cast aluminum alloys such as Mg. Among them, ADC12 / A383 is widely used due to its good fluidity and suitability for complex thin-walled die-casting parts; A380 is also a common automotive die-casting aluminum alloy; AlSi7Mg 0.3 Materials such as AlSi9Cu3 are used in gravity casting and low-pressure casting processes. These aluminum alloys use aluminum as the base material, with added elements such as silicon, copper, and magnesium to improve casting performance, strength, and wear resistance. In recent years, heat-treatable die-cast aluminum alloys have also begun to attract attention, with tensile strength reaching 260 MPa, yield strength 140 MPa, and elongation exceeding 12%.

[0005] Despite significant advancements in aluminum alloy gearbox housing technology, the following prominent issues remain with current technology: First, casting defects are difficult to eliminate completely. The gearbox housing has a complex structure and uneven wall thickness, making it highly susceptible to defects such as porosity, shrinkage cavities, and cold shuts during die casting. Defects such as air entrapment and shrinkage cavities are also common in low-pressure casting. These internal defects severely affect the housing's airtightness, mechanical properties, and service life.

[0006] Secondly, heat treatment deformation is a significant problem. Due to the thin walls of the gearbox housing, the tortuous internal oil passages, and the numerous weight-reduction holes, thermal and structural stresses cannot be evenly released during heat treatment. This easily leads to stress concentration and uneven distribution, causing severe housing deformation, and even preventing the front and rear housings from closing, making subsequent correction extremely difficult. Traditional aluminum alloy die-castings must undergo heat treatment to meet performance requirements, but thin-walled castings are highly susceptible to deformation or even scrap during heat treatment, significantly reducing the yield rate.

[0007] Third, aluminum alloy materials have limitations in performance. Commonly used die-cast aluminum alloys have relatively low strength and hardness, making them prone to deformation in critical components such as bearing housings under high torque conditions. Furthermore, silicon segregation is easily generated during the alloy production process, which can seriously affect the safety of parts.

[0008] Fourth, the finishing process is difficult. Aluminum alloys have a large coefficient of linear expansion, which makes them prone to sticking to the cutting tool and generating built-up edge during machining, affecting dimensional accuracy and surface roughness; changes in ambient temperature can also easily cause instability in the machining quality of aluminum shells.

[0009] In summary, existing aluminum alloy gearbox housing technology still has many shortcomings in terms of casting defect control, heat treatment deformation suppression, material performance improvement, and precision machining. There is an urgent need to develop new material systems and processing methods to overcome these technical bottlenecks. For example, Chinese patent CN110317983A discloses a composite extrusion casting method for high-quality aluminum alloy automotive gearbox housings, using extrusion casting to replace traditional die casting and improving the mechanical properties of the housing by optimizing the aluminum alloy composition, melting process, and heat treatment regime. However, extrusion casting equipment requires large investments and has relatively low production efficiency, making it difficult to meet the needs of mass production. Although low-pressure casting can reduce porosity defects, improper control of process parameters can still easily lead to defects such as air entrapment and shrinkage porosity. Numerical simulations of the filling and solidification processes of the original low-pressure casting process for gearbox housings have revealed that castings are prone to air entrapment and shrinkage porosity defects in specific areas. Furthermore, due to its complex structure and uneven wall thickness, the gearbox housing is difficult to release thermal and structural stresses evenly during heat treatment, making it highly susceptible to deformation and causing difficulties in subsequent processing. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a lightweight aluminum alloy automotive transmission housing with high strength, high toughness, good casting performance and corrosion resistance, which meets the requirements of lightweight automotive transmissions. The present invention also provides a method for its preparation.

[0011] This invention provides a lightweight aluminum alloy shell material, the chemical composition of which, by mass percentage, is: Si 8.5~11.5%, Cu 1.5~3.5%, Mg 0.25~0.55%, Mn 0.4~0.8%, Fe 0.6~1.2%, Zn ≤0.5%, Ti 0.05~0.25%, Sr 0.01~0.06%, Zr 0.05~0.20%, V 0.03~0.12%, with the balance being Al and unavoidable impurities, wherein the mass ratio of Mn / Fe is 0.4~0.8:1.

[0012] This invention optimizes the proportions of the main elements Si, Cu, and Mg, ensuring excellent casting properties and age-hardening effects in the alloy. The addition of Mn effectively suppresses the formation of acicular β-AlFe phases, transforming the iron-rich phase into fine, blocky phases, thereby improving the alloy's plasticity. Sr acts as a modifier to refine the eutectic silicon phase. The combined addition of Zr and V forms fine, dispersed phases, improving the alloy's high-temperature strength and creep resistance. Ti acts as a grain refiner to refine α-Al grains. The synergistic effect of these elements allows the alloy to achieve excellent mechanical properties in the as-cast state, eliminating the need for heat treatment strengthening and fundamentally avoiding heat treatment deformation problems.

[0013] The gearbox housing of the present invention is integrally formed from the above-mentioned aluminum alloy material through a composite die casting process. The housing wall thickness is 2.5~6.0mm, the maximum wall thickness difference is no more than 30mm, and the external dimensions are 400~500mm×350~430mm×200~260mm.

[0014] The bearing housing is equipped with an annular reinforcing boss, with a height of 5-15mm and a width of 8-20mm, which can effectively improve the load-bearing capacity and deformation resistance of the bearing housing. The oil passage area of ​​the housing is equipped with multiple heat dissipation fins distributed along the oil passage direction, with a height of 2-6mm and a spacing of 10-25mm, which ensures heat dissipation effect without excessively increasing the weight of the housing.

[0015] The shell surface is coated with a micro-arc oxidation ceramic layer with a thickness of 10-50 μm and a surface hardness ≥ HV 400, which significantly improves the shell's wear resistance and corrosion resistance. The inner wall of the oil passage is coated with a laser cladding reinforcement layer with a thickness of 0.3-1.0 mm, made of Al-Si-Cu alloy powder, which effectively improves the wear resistance and sealing performance of the inner wall of the oil passage.

[0016] This invention provides a manufacturing process for a lightweight aluminum alloy automotive transmission housing, comprising the following steps: (1) Batching and smelting: Batching is carried out according to the above chemical composition. Aluminum ingots, silicon, copper, magnesium, manganese and other raw materials are added to the smelting furnace and smelted at 720~780℃. After refining and degassing, the mixture is allowed to stand for 20~40 minutes to obtain aluminum alloy melt.

[0017] (2) Vacuum die casting filling: The molten aluminum alloy is poured into a mold preheated to 180-250°C at 680-720°C. Vacuum die casting filling is carried out under the conditions of injection speed of 2.0-4.5 m / s, injection pressure of 60-120 MPa, and mold cavity vacuum degree ≤5 kPa. The mold gating system is a ring gating system, including a central sprue and 4-8 radially distributed transverse runners. The ring gating system can ensure that the molten metal fills evenly from the center to the periphery, avoiding the problems of long molten metal flow path and unstable filling in traditional gating systems.

[0018] (3) Local extrusion and shrinkage compensation: Within 0.5 to 3.0 seconds after the filling is completed, start the local extrusion device to apply an extrusion pressure of 50 to 150 MPa to the bearing seat, thick boss and oil passage intersection of the housing, and hold the pressure for 3 to 10 seconds. Local extrusion can effectively eliminate defects such as shrinkage cavities and porosity by applying directional pressure to specific areas.

[0019] (4) Zoned Temperature Controlled Solidification: The cooling rate of different areas of the shell is controlled by a zoned temperature control system installed in the mold. The zoned temperature control system includes heating pipes installed in the thick areas of the mold and cooling channels installed in the thin-walled areas of the mold. The heating pipes heat the thick areas in the early stage of solidification, while the cooling channels force-cool the thin-walled areas in the middle and late stages of solidification. This allows the thin-walled areas of the shell to cool rapidly at a rate of 8~15℃ / s, while the thick areas cool slowly at a rate of 2~6℃ / s. The temperature gradient of each part of the shell is controlled to be ≤50℃, so that the shell solidifies in the order of "thin-walled areas solidify first, thick areas solidify later". This sequential solidification method can effectively avoid shrinkage porosity defects.

[0020] (5) Demolding and post-processing: After solidification, the mold is opened and the casting is removed, and the burrs and flash are removed.

[0021] (6) Micro-arc oxidation treatment: Place the cleaned shell in a silicate-based or phosphate-based electrolyte and perform micro-arc oxidation treatment for 10 to 40 minutes under the conditions of voltage 400~650V and current density 5~20A / dm², and control the electrolyte temperature at 15~40℃.

[0022] (7) Laser cladding of oil passages: The inner wall of the oil passages of the shell is strengthened by laser cladding process. The laser power is 1.5~3.5kW, the scanning speed is 5~20mm / s, the powder feeding rate is 8~25g / min, the overlap rate is 30~60%, the protective gas is argon, and the flow rate is 8~20L / min.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) By optimizing the alloy composition, the present invention enables the shell to obtain excellent mechanical properties (tensile strength ≥280MPa, yield strength ≥150MPa, elongation ≥8%) in the cast state, without the need for T6 heat treatment, thus fundamentally avoiding the problem of deformation of thin-walled shells during heat treatment.

[0024] (2) The present invention effectively eliminates casting defects such as porosity, shrinkage porosity and shrinkage cavity by using a composite process of vacuum die casting, local extrusion and zoned temperature-controlled solidification, and the shell density is significantly improved.

[0025] (3) The tensile strength of the gearbox housing of the present invention can reach 280~320MPa, yield strength 150~185MPa, and elongation 8~14%, which is significantly better than the traditional ADC12 die-cast aluminum alloy (tensile strength about 240MPa and elongation about 3%).

[0026] (4) Since the present invention does not require heat treatment, it avoids dimensional deformation during the heat treatment process, and the flatness of the shell can be controlled within 0.05mm / 300mm.

[0027] (5) The micro-arc oxidation ceramic layer of the present invention makes the surface hardness of the shell reach HV 400 or more, and significantly improves the wear resistance and corrosion resistance; the laser cladding layer of the oil passage effectively improves the wear resistance and sealing of the inner wall of the oil passage.

[0028] (6) The heat dissipation fin design in the oil passage area of ​​the housing of the present invention and the good thermal conductivity of the micro-arc oxidation ceramic layer improve the heat dissipation efficiency of the gearbox by more than 15%.

[0029] (7) The heat-free process of the present invention eliminates heat treatment processes such as solution treatment, quenching, and aging, which greatly shortens the production cycle and reduces energy consumption and production costs. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments and comparative examples. The raw materials used in the following embodiments and comparative examples are all commercially available products.

[0031] Example 1 A manufacturing process for a lightweight aluminum alloy automotive transmission housing includes the following steps: (1) Batching and smelting: The raw materials such as aluminum ingots, silicon, copper, magnesium, and manganese are added to the smelting furnace according to the above chemical composition and smelted at 750°C. After refining and degassing, the mixture is allowed to stand for 30 minutes to obtain aluminum alloy melt. In this embodiment, the chemical composition of the aluminum alloy material by mass percentage is as follows: Si 10.2%, Cu 2.8%, Mg 0.42%, Mn 0.65%, Fe 0.85%, Zn 0.3%, Ti 0.15%, Sr 0.04%, Zr 0.12%, V 0.08%, the mass ratio of Mn / Fe is 0.76:1, and the balance is Al and unavoidable impurities.

[0032] (2) Vacuum die casting filling: The molten aluminum alloy is poured into a mold preheated to 220°C at 700°C. Vacuum die casting filling is carried out under the conditions of injection speed of 3.5 m / s, injection pressure of 90 MPa, and vacuum degree of 3 kPa in the mold cavity. The gating system of the mold is a ring gating system, including a central sprue and 6 radially distributed horizontal runners.

[0033] (3) Local extrusion and shrinkage: Within 1.5s after the filling is completed, start the local extrusion device to apply an extrusion pressure of 100MPa to the bearing seat, thick boss and oil passage intersection of the shell, and hold the pressure for 6s.

[0034] (4) Zoned temperature control solidification: The cooling rate of different areas of the shell is controlled by a zoned temperature control system installed in the mold. The zoned temperature control system includes heating pipes installed in the thick areas of the mold and cooling water channels installed in the thin-walled areas of the mold. The heating pipes heat the thick areas in the early stage of solidification, and the cooling water channels force-cool the thin-walled areas in the middle and late stages of solidification, so that the thin-walled areas of the shell are cooled rapidly at a rate of 12℃ / s and the thick areas are cooled slowly at a rate of 4℃ / s, controlling the temperature gradient of each part of the shell to be 40℃, so that the shell solidifies in the order of "thin-walled areas solidify first and thick areas solidify later".

[0035] (5) Demolding and post-processing: After solidification, the mold is opened and the casting is removed, and the burrs and flash are removed.

[0036] (6) Micro-arc oxidation treatment: The cleaned shell is placed in a silicate-based electrolyte and subjected to an oxidation process at a voltage of 520V and a current density of 12A / dm³. 2 Micro-arc oxidation was performed for 25 minutes under the following conditions, with the electrolyte temperature controlled at 25℃.

[0037] (7) Laser cladding of oil passages: The inner wall of the oil passages of the shell is strengthened by laser cladding process. The laser power is 2.5kW, the scanning speed is 12mm / s, the powder feeding rate is 16g / min, the overlap rate is 45%, the protective gas is argon, and the flow rate is 15L / min.

[0038] Example 2 A manufacturing process for a lightweight aluminum alloy automotive transmission housing includes the following steps: (1) Batching and smelting: Batching is carried out according to the above chemical composition. Aluminum ingots, silicon, copper, magnesium, manganese and other raw materials are added to the smelting furnace and smelted at 730°C. After refining and degassing, the mixture is allowed to stand for 25 minutes to obtain aluminum alloy melt. In this embodiment, the chemical composition of the aluminum alloy material by mass percentage is as follows: Si 9.0%, Cu 2.0%, Mg 0.30%, Mn 0.45%, Fe 0.70%, Zn 0.2%, Ti 0.08%, Sr 0.02%, Zr 0.07%, V 0.05%, Mn / Fe mass ratio is 0.64:1, and the balance is Al and unavoidable impurities.

[0039] (2) Vacuum die casting filling: The molten aluminum alloy is poured into a mold preheated to 190°C at 685°C. Vacuum die casting filling is carried out under the conditions of injection speed of 2.5m / s, injection pressure of 70MPa, and vacuum degree of 4kPa in the mold cavity. The gating system of the mold is a ring gating system, including a central sprue and four radially distributed horizontal runners.

[0040] (3) Local extrusion and shrinkage: Within 2.0s after the filling is completed, start the local extrusion device to apply an extrusion pressure of 70MPa to the bearing seat, thick boss and oil passage intersection of the shell, and hold the pressure for 5s.

[0041] (4) Zoned temperature control solidification: The cooling rate of different areas of the shell is controlled by a zoned temperature control system installed in the mold. The zoned temperature control system includes heating pipes installed in the thick areas of the mold and cooling channels installed in the thin-walled areas of the mold. The heating pipes heat the thick areas in the early stage of solidification, and the cooling channels force-cool the thin-walled areas in the middle and late stages of solidification, so that the thin-walled areas of the shell are cooled rapidly at a rate of 10℃ / s and the thick areas are cooled slowly at a rate of 3℃ / s, controlling the temperature gradient of each part of the shell to be 45℃, so that the shell solidifies in the order of "thin-walled areas solidify first and thick areas solidify later".

[0042] (5) Demolding and post-processing: After solidification, the mold is opened and the casting is removed, and the burrs and flash are removed.

[0043] (6) Micro-arc oxidation treatment: The cleaned shell is placed in a phosphate-based electrolyte and subjected to an oxidation process at a voltage of 450V and a current density of 8A / dm³. 2 Micro-arc oxidation was performed for 30 minutes under the following conditions, with the electrolyte temperature controlled at 20℃.

[0044] (7) Laser cladding of oil passages: The inner wall of the oil passages of the shell is strengthened by laser cladding process. The laser power is 2.0kW, the scanning speed is 10mm / s, the powder feeding rate is 12g / min, the overlap rate is 35%, the protective gas is argon, and the flow rate is 12L / min.

[0045] Example 3 A manufacturing process for a lightweight aluminum alloy automotive transmission housing includes the following steps: (1) Batching and smelting: Batching is carried out according to the above chemical composition. Aluminum ingots, silicon, copper, magnesium, manganese and other raw materials are added to the smelting furnace and smelted at 770°C. After refining and degassing, the mixture is allowed to stand for 35 minutes to obtain aluminum alloy melt. In this embodiment, the chemical composition of the aluminum alloy material by mass percentage is as follows: Si 11.0%, Cu 3.2%, Mg 0.50%, Mn 0.75%, Fe 1.10%, Zn 0.4%, Ti 0.22%, Sr 0.05%, Zr 0.18%, V 0.11%, Mn / Fe mass ratio is 0.68:1, and the balance is Al and unavoidable impurities.

[0046] (2) Vacuum die casting filling: The molten aluminum alloy is poured into a mold preheated to 240°C at 715°C. Vacuum die casting filling is carried out under the conditions of injection speed of 4.2m / s, injection pressure of 110MPa, and mold cavity vacuum degree of 2kPa. The mold gating system is a ring gating system, including a central sprue and 8 radially distributed horizontal runners.

[0047] (3) Local extrusion and shrinkage: Within 1.0s after the filling is completed, start the local extrusion device to apply an extrusion pressure of 130MPa to the bearing seat, thick boss and oil passage intersection of the shell, and hold the pressure for 8s.

[0048] (4) Zoned temperature control solidification: The cooling rate of different areas of the shell is controlled by a zoned temperature control system installed in the mold. The zoned temperature control system includes heating pipes installed in the thick areas of the mold and cooling water channels installed in the thin-walled areas of the mold. The heating pipes heat the thick areas in the early stage of solidification, and the cooling water channels force-cool the thin-walled areas in the middle and late stages of solidification, so that the thin-walled areas of the shell are cooled rapidly at a rate of 14℃ / s and the thick areas are cooled slowly at a rate of 5℃ / s, controlling the temperature gradient of each part of the shell to be 35℃, so that the shell solidifies in the order of "thin-walled areas solidify first and thick areas solidify later".

[0049] (5) Demolding and post-processing: After solidification, the mold is opened and the casting is removed, and the burrs and flash are removed.

[0050] (6) Micro-arc oxidation treatment: The cleaned shell is placed in a silicate-based electrolyte and subjected to an oxidation process at a voltage of 600V and a current density of 18A / dm³.2 Micro-arc oxidation was performed for 15 minutes under the following conditions, with the electrolyte temperature controlled at 35℃.

[0051] (7) Laser cladding of oil passages: The inner wall of the oil passages of the shell is strengthened by laser cladding process. The laser power is 3.2kW, the scanning speed is 18mm / s, the powder feeding rate is 22g / min, the overlap rate is 55%, the protective gas is argon, and the flow rate is 18L / min.

[0052] Example 4 A manufacturing process for a lightweight aluminum alloy automotive transmission housing includes the following steps: (1) Batching and smelting: The raw materials such as aluminum ingots, silicon, copper, magnesium, and manganese are added to the smelting furnace according to the above chemical composition and smelted at 750°C. After refining and degassing, the mixture is allowed to stand for 30 minutes to obtain aluminum alloy melt. In this embodiment, the chemical composition of the aluminum alloy material by mass percentage is as follows: Si 10.2%, Cu 2.8%, Mg 0.42%, Mn 0.65%, Fe 0.85%, Zn 0.3%, Ti 0.15%, Sr 0.04%, Zr 0.12%, V 0.08%, the mass ratio of Mn / Fe is 0.76:1, and the balance is Al and unavoidable impurities.

[0053] (2) Vacuum die casting filling: The molten aluminum alloy is poured into a mold preheated to 220°C at 700°C. Vacuum die casting filling is carried out under the conditions of injection speed of 3.5m / s, injection pressure of 90MPa, and mold cavity vacuum degree of 3kPa. The mold gating system is a ring gating system, including a central sprue and 6 radially distributed horizontal runners. The total cross-sectional area of ​​the ingate is 1500mm².

[0054] (3) Local extrusion and shrinkage: Within 1.5s after the filling is completed, start the local extrusion device to apply an extrusion pressure of 100MPa to the bearing seat, thick boss and oil passage intersection of the shell, and hold the pressure for 6s.

[0055] (4) Zoned temperature control solidification: The cooling rate of different areas of the shell is controlled by a zoned temperature control system installed in the mold. The zoned temperature control system includes heating pipes installed in the thick areas of the mold and cooling water channels installed in the thin-walled areas of the mold. The heating pipes heat the thick areas in the early stage of solidification, and the cooling water channels force-cool the thin-walled areas in the middle and late stages of solidification, so that the thin-walled areas of the shell are cooled rapidly at a rate of 12℃ / s and the thick areas are cooled slowly at a rate of 4℃ / s, controlling the temperature gradient of each part of the shell to be 40℃, so that the shell solidifies in the order of "thin-walled areas solidify first and thick areas solidify later".

[0056] (5) Demolding and post-processing: After solidification, the mold is opened and the casting is removed, and the burrs and flash are removed.

[0057] (6) Micro-arc oxidation treatment: The cleaned shell is placed in a silicate-based electrolyte and subjected to an oxidation process at a voltage of 520V and a current density of 12A / dm³. 2 Micro-arc oxidation was performed for 25 minutes under the following conditions, with the electrolyte temperature controlled at 25℃.

[0058] (7) Laser cladding of oil passages: The inner wall of the oil passages of the shell is strengthened by laser cladding process. The laser power is 2.5kW, the scanning speed is 12mm / s, the powder feeding rate is 16g / min, the overlap rate is 45%, the protective gas is argon, and the flow rate is 15L / min.

[0059] Example 5 A manufacturing process for a lightweight aluminum alloy automotive transmission housing includes the following steps: (1) Batching and smelting: The raw materials such as aluminum ingots, silicon, copper, magnesium, and manganese are added to the smelting furnace according to the above chemical composition and smelted at 750°C. After refining and degassing, the mixture is allowed to stand for 30 minutes to obtain aluminum alloy melt. In this embodiment, the chemical composition of the aluminum alloy material by mass percentage is as follows: Si 10.2%, Cu 2.8%, Mg 0.42%, Mn 0.65%, Fe 0.85%, Zn 0.3%, Ti 0.15%, Sr 0.04%, Zr 0.12%, V 0.08%, the mass ratio of Mn / Fe is 0.76:1, and the balance is Al and unavoidable impurities.

[0060] (2) Vacuum die casting filling: The molten aluminum alloy is poured into a mold preheated to 220°C at 700°C. Vacuum die casting filling is carried out under the conditions of injection speed of 3.5 m / s, injection pressure of 90 MPa, and vacuum degree of 3 kPa in the mold cavity. The gating system of the mold is a ring gating system, including a central sprue and 6 radially distributed horizontal runners.

[0061] (3) Local extrusion and shrinkage: Within 1.5s after the filling is completed, start the local extrusion device to apply an extrusion pressure of 100MPa to the bearing seat, thick boss and oil passage intersection of the shell, and hold the pressure for 6s.

[0062] (4) Zoned Temperature Controlled Solidification: The cooling rate of different areas of the shell is controlled by a zoned temperature control system installed in the mold. The zoned temperature control system includes heating pipes installed in the thick areas of the mold and cooling water channels installed in the thin-walled areas of the mold. The heating pipes heat the thick areas in the early stage of solidification, while the cooling water channels force-cool the thin-walled areas in the middle and late stages of solidification. This results in the thin-walled areas of the shell cooling rapidly at a rate of 12℃ / s, while the thick areas cool slowly at a rate of 4℃ / s. The temperature gradient of each part of the shell is controlled to be 40℃, so that the shell solidifies in the order of "thin-walled areas solidifying first, thick areas solidifying later". In this embodiment, the heating pipe power of the zoned temperature control system is 6kW, and the flow rate of cooling water in the cooling water channels is 15L / min.

[0063] (5) Demolding and post-processing: After solidification, the mold is opened and the casting is removed, and the burrs and flash are removed.

[0064] (6) Micro-arc oxidation treatment: The cleaned shell is placed in a silicate-based electrolyte and subjected to an oxidation process at a voltage of 520V and a current density of 12A / dm³. 2 Micro-arc oxidation was performed for 25 minutes under the following conditions, with the electrolyte temperature controlled at 25℃.

[0065] (7) Laser cladding of oil passages: The inner wall of the oil passages of the shell is strengthened by laser cladding process. The laser power is 2.5kW, the scanning speed is 12mm / s, the powder feeding rate is 16g / min, the overlap rate is 45%, the protective gas is argon, and the flow rate is 15L / min.

[0066] Example 6 A manufacturing process for a lightweight aluminum alloy automotive transmission housing includes the following steps: (1) Batching and smelting: The raw materials such as aluminum ingots, silicon, copper, magnesium, and manganese are added to the smelting furnace according to the above chemical composition and smelted at 750°C. After refining and degassing, the mixture is allowed to stand for 30 minutes to obtain aluminum alloy melt. In this embodiment, the chemical composition of the aluminum alloy material by mass percentage is as follows: Si 10.2%, Cu 2.8%, Mg 0.42%, Mn 0.65%, Fe 0.85%, Zn 0.3%, Ti 0.15%, Sr 0.04%, Zr 0.12%, V 0.08%, the mass ratio of Mn / Fe is 0.76:1, and the balance is Al and unavoidable impurities.

[0067] (2) Vacuum die casting filling: The molten aluminum alloy is poured into a mold preheated to 220°C at 700°C. Vacuum die casting filling is carried out under the conditions of injection speed of 3.5m / s, injection pressure of 90MPa, and mold cavity vacuum degree of 3kPa. The mold gating system is a ring gating system, including a central sprue and 6 radially distributed horizontal runners. The total cross-sectional area of ​​the ingate is 1500mm².

[0068] (3) Local extrusion and shrinkage: Within 1.5s after the filling is completed, start the local extrusion device to apply an extrusion pressure of 100MPa to the bearing seat, thick boss and oil passage intersection of the shell, and hold the pressure for 6s.

[0069] (4) Zoned Temperature Controlled Solidification: The cooling rate of different areas of the shell is controlled by a zoned temperature control system installed in the mold. The zoned temperature control system includes heating pipes installed in the thick areas of the mold and cooling water channels installed in the thin-walled areas of the mold. The heating pipes heat the thick areas in the early stage of solidification, while the cooling water channels force-cool the thin-walled areas in the middle and late stages of solidification. This results in the thin-walled areas of the shell cooling rapidly at a rate of 12℃ / s, while the thick areas cool slowly at a rate of 4℃ / s. The temperature gradient of each part of the shell is controlled to be 40℃, so that the shell solidifies in the order of "thin-walled areas solidifying first, thick areas solidifying later". In this embodiment, the heating pipe power of the zoned temperature control system is 6kW, and the flow rate of cooling water in the cooling water channels is 15L / min.

[0070] (5) Demolding and post-processing: After solidification, the mold is opened and the casting is removed, and the burrs and flash are removed.

[0071] (6) Micro-arc oxidation treatment: The cleaned shell is placed in a silicate electrolyte and micro-arc oxidation treatment is carried out for 25 minutes under the conditions of voltage 520V and current density 12A / dm², and the electrolyte temperature is controlled at 25℃.

[0072] (7) Laser cladding of oil passages: The inner wall of the oil passages of the shell is strengthened by laser cladding process. The laser power is 2.5kW, the scanning speed is 12mm / s, the powder feeding rate is 16g / min, the overlap rate is 45%, the protective gas is argon, and the flow rate is 15L / min.

[0073] Comparative Example 1 The aluminum alloy automotive gearbox housing in this comparative example differs from that in Example 1 in that: Material composition: The material is a conventional ADC12 aluminum alloy, and its chemical composition by mass percentage is: Si 9.6~12.0%, Cu 1.5~3.5%, Fe≤1.3%, Mn≤0.5%, Mg≤0.3%, Zn≤1.0%, Ni≤0.5%, Sn≤0.3%, with the balance being Al and unavoidable impurities.

[0074] The production process includes the following steps: (1) Batching and smelting: Batching is carried out according to the conventional ADC12 chemical composition. Aluminum ingots, silicon, copper and other raw materials are added to the smelting furnace and smelted at 750°C. After refining and degassing, the mixture is allowed to stand for 30 minutes to obtain aluminum alloy melt.

[0075] (2) Traditional die casting filling: The aluminum alloy melt is poured into a mold preheated to 220°C at 700°C, and die casting filling is carried out under the conditions of injection speed of 3.5m / s and injection pressure of 90MPa. The mold gating system of this comparative example is a traditional side gate gating system (instead of a ring gating system), and no vacuum pumping device is set (that is, the mold cavity is not in a vacuum state, and vacuum die casting filling is not performed).

[0076] (3) Solidification and cooling: After the filling is completed, no local extrusion device is started (i.e., no local extrusion and shrinkage is performed) and no zone temperature control system is set up (i.e., no zone temperature control solidification is performed). Instead, the casting is allowed to cool naturally in the mold until it is completely solidified.

[0077] (4) Demolding and post-processing: After solidification, the mold is opened and the casting is removed, and the burrs and flash are removed.

[0078] (5) T6 heat treatment: The cleaned shell is subjected to T6 heat treatment, which includes: solution treatment, holding at 495℃ for 4 hours, followed by quenching in water at 60~80℃; followed by aging treatment, holding at 175℃ for 6 hours, and air cooling to room temperature.

[0079] (6) Surface treatment: This comparative example does not undergo micro-arc oxidation treatment or oil channel laser cladding treatment.

[0080] Comparative Example 2 The aluminum alloy automotive gearbox housing in this comparative example differs from that in Example 1 in that: Material composition: The aluminum alloy material of Example 1 of this invention is used, and its chemical composition by mass percentage is: Si 10.2%, Cu 2.8%, Mg 0.42%, Mn 0.65%, Fe 0.85%, Zn 0.3%, Ti 0.15%, Sr 0.04%, Zr 0.12%, V 0.08%, the mass ratio of Mn / Fe is 0.76:1, and the balance is Al and unavoidable impurities.

[0081] The production process includes the following steps: (1) Batching and smelting: Batching is carried out according to the above chemical composition. Aluminum ingots, silicon, copper, magnesium, manganese and other raw materials are added to the smelting furnace and smelted at 750°C. After refining and degassing, the mixture is allowed to stand for 30 minutes to obtain aluminum alloy melt.

[0082] (2) Traditional die casting filling: The aluminum alloy melt is poured into a mold preheated to 220°C at 700°C, and die casting filling is carried out under the conditions of injection speed of 3.5m / s and injection pressure of 90MPa. The mold gating system of this comparative example is a traditional side gate gating system (instead of a ring gating system), and no vacuum pumping device is set (that is, the mold cavity is not in a vacuum state, and vacuum die casting filling is not performed).

[0083] (3) Solidification and cooling: After the filling is completed, no local extrusion device is started (i.e., no local extrusion and shrinkage is performed) and no zone temperature control system is set up (i.e., no zone temperature control solidification is performed). Instead, the casting is allowed to cool naturally in the mold until it is completely solidified.

[0084] (4) Demolding and post-processing: After solidification, the mold is opened and the casting is removed, and the burrs and flash are removed.

[0085] (5) Post-treatment: This comparative example does not perform T6 heat treatment on the casting (i.e. the casting is kept in the as-cast state and does not undergo solution treatment and aging treatment), nor does it undergo micro-arc oxidation treatment or oil channel laser cladding treatment.

[0086] Comparative Example 3 The aluminum alloy automotive gearbox housing in this comparative example differs from that in Example 1 in that: Material composition: The material is a conventional ADC12 aluminum alloy, and its chemical composition by mass percentage is: Si 9.6~12.0%, Cu 1.5~3.5%, Fe≤1.3%, Mn≤0.5%, Mg≤0.3%, Zn≤1.0%, Ni≤0.5%, Sn≤0.3%, with the balance being Al and unavoidable impurities.

[0087] The production process includes the following steps: (1) Batching and smelting: Batching is carried out according to the conventional ADC12 chemical composition. Aluminum ingots, silicon, copper and other raw materials are added to the smelting furnace and smelted at 750°C. After refining and degassing, the mixture is allowed to stand for 30 minutes to obtain aluminum alloy melt.

[0088] (2) Vacuum die casting filling: The molten aluminum alloy is poured into a mold preheated to 220°C at 700°C. Vacuum die casting filling is carried out under the conditions of injection speed of 3.5 m / s, injection pressure of 90 MPa, and mold cavity vacuum of 3 kPa. The mold gating system is a ring gating system, including a central sprue and six radially distributed transverse runners. The ring gating system can ensure that the molten metal fills evenly from the center to the periphery, avoiding the problems of long molten metal flow path and unstable filling in traditional gating systems.

[0089] (3) Local extrusion and shrinkage compensation: Within 1.5 seconds after the filling is completed, the local extrusion device is started to apply an extrusion pressure of 100MPa to the bearing seat, thick boss and oil passage intersection of the shell, and hold the pressure for 6 seconds. Local extrusion can effectively eliminate defects such as shrinkage cavities and porosity by applying directional pressure to specific areas.

[0090] (4) Zoned Temperature Controlled Solidification: The cooling rate of different areas of the shell is controlled by a zoned temperature control system installed in the mold. The zoned temperature control system includes heating pipes installed in the thick areas of the mold and cooling channels installed in the thin-walled areas of the mold. The heating pipes heat the thick areas in the early stage of solidification, while the cooling channels force-cool the thin-walled areas in the middle and late stages of solidification. This results in the thin-walled areas of the shell cooling rapidly at a rate of 12℃ / s, while the thick areas cool slowly at a rate of 4℃ / s. The temperature gradient of each part of the shell is controlled at 40℃, so that the shell solidifies in the order of "thin-walled areas solidifying first, thick areas solidifying later". This sequential solidification method can effectively avoid shrinkage porosity defects.

[0091] (5) Demolding and post-processing: After solidification, the mold is opened and the casting is removed, and the burrs and flash are removed.

[0092] (6) T6 heat treatment: The cleaned shell is subjected to T6 heat treatment, which includes: solution treatment, holding at 495℃ for 4 hours, followed by quenching in water at 60~80℃; followed by aging treatment, holding at 175℃ for 6 hours, and air cooling to room temperature.

[0093] (7) Surface treatment: This comparative example does not undergo micro-arc oxidation treatment or oil channel laser cladding treatment.

[0094] Comparative Example 4 The aluminum alloy automotive gearbox housing in this comparative example differs from that in Example 1 in that: Material composition: The aluminum alloy material of Example 1 of this invention is used, and its chemical composition by mass percentage is: Si 10.2%, Cu 2.8%, Mg 0.42%, Mn 0.65%, Fe 0.85%, Zn 0.3%, Ti 0.15%, Sr 0.04%, Zr 0.12%, V 0.08%, the mass ratio of Mn / Fe is 0.76:1, and the balance is Al and unavoidable impurities.

[0095] The production process includes the following steps: (1) Batching and smelting: Batching is carried out according to the above chemical composition. Aluminum ingots, silicon, copper, magnesium, manganese and other raw materials are added to the smelting furnace and smelted at 750°C. After refining and degassing, the mixture is allowed to stand for 30 minutes to obtain aluminum alloy melt.

[0096] (2) Vacuum die casting filling: The molten aluminum alloy is poured into a mold preheated to 220°C at 700°C. Vacuum die casting filling is carried out under the conditions of injection speed of 3.5 m / s, injection pressure of 90 MPa, and vacuum degree of 3 kPa in the mold cavity. The gating system of the mold is a ring gating system, including a central sprue and 6 radially distributed horizontal runners.

[0097] (3) Local extrusion and shrinkage: Within 1.5s after the filling is completed, start the local extrusion device to apply an extrusion pressure of 100MPa to the bearing seat, thick boss and oil passage intersection of the shell, and hold the pressure for 6s.

[0098] (4) Natural solidification and cooling: This comparative example does not have a zoned temperature control system (i.e., it does not perform zoned temperature control solidification). Instead, after local extrusion is completed, the casting is naturally cooled in the mold until it is completely solidified (i.e., the entire area is solidified under the same natural cooling conditions, without distinguishing between different cooling rates for thin-walled and thick-walled areas).

[0099] (5) Demolding and post-processing: After solidification, the mold is opened and the casting is removed, and the burrs and flash are removed.

[0100] (6) Post-treatment: This comparative example does not perform T6 heat treatment on the casting (i.e. the casting is kept in the as-cast state), nor does it perform micro-arc oxidation treatment or oil channel laser cladding treatment.

[0101] Comparative Example 5 The aluminum alloy automotive gearbox housing in this comparative example differs from that in Example 1 in that: Material composition: The aluminum alloy material of Example 1 of this invention is used, and its chemical composition by mass percentage is: Si 10.2%, Cu 2.8%, Mg 0.42%, Mn 0.65%, Fe 0.85%, Zn 0.3%, Ti 0.15%, Sr 0.04%, Zr 0.12%, V 0.08%, the mass ratio of Mn / Fe is 0.76:1, and the balance is Al and unavoidable impurities.

[0102] The production process includes the following steps: (1) Batching and smelting: Batching is carried out according to the above chemical composition. Aluminum ingots, silicon, copper, magnesium, manganese and other raw materials are added to the smelting furnace and smelted at 750°C. After refining and degassing, the mixture is allowed to stand for 30 minutes to obtain aluminum alloy melt.

[0103] (2) Vacuum die casting filling: The molten aluminum alloy is poured into a mold preheated to 220°C at 700°C. Vacuum die casting filling is carried out under the conditions of injection speed of 3.5 m / s, injection pressure of 90 MPa, and vacuum degree of 3 kPa in the mold cavity. The gating system of the mold is a ring gating system, including a central sprue and 6 radially distributed horizontal runners.

[0104] (3) Solidification and cooling: After the filling is completed, this comparative example does not start any local extrusion device (i.e., no local extrusion and shrinkage compensation is performed).

[0105] (4) Zoned temperature control solidification: The cooling rate of different areas of the shell is controlled by a zoned temperature control system installed in the mold. The zoned temperature control system includes heating pipes installed in the thick areas of the mold and cooling water channels installed in the thin-walled areas of the mold. The heating pipes heat the thick areas in the early stage of solidification, and the cooling water channels force-cool the thin-walled areas in the middle and late stages of solidification, so that the thin-walled areas of the shell are cooled rapidly at a rate of 12℃ / s and the thick areas are cooled slowly at a rate of 4℃ / s, controlling the temperature gradient of each part of the shell to be 40℃, so that the shell solidifies in the order of "thin-walled areas solidify first and thick areas solidify later".

[0106] (5) Demolding and post-processing: After solidification, the mold is opened and the casting is removed, and the burrs and flash are removed.

[0107] (6) Post-treatment: This comparative example does not perform T6 heat treatment on the casting (i.e. the casting is kept in the as-cast state), nor does it perform micro-arc oxidation treatment or oil channel laser cladding treatment.

[0108] The products prepared in the above embodiments and comparative examples were subjected to mechanical testing, casting result testing, dimensional accuracy and deformation testing, wear resistance and corrosion resistance testing, and the test results are shown in Table 1.

[0109] Table 1 Mechanical Test Results

[0110] Table 2 Product Casting Inspection Results

[0111] Table 3 Comparison of dimensional accuracy and deformation between each embodiment and the comparative example

[0112] Table 4 Comparison of wear resistance and corrosion resistance between the embodiments and comparative examples

Claims

1. A lightweight aluminum alloy automotive gearbox housing, characterized in that, It is integrally formed from lightweight aluminum alloy material through a composite die-casting process; the chemical composition of the lightweight aluminum alloy material, by mass percentage, is: Si 8.5~11.5%, Cu 1.5~3.5%, Mg 0.25~0.55%, Mn 0.4~0.8%, Fe 0.6~1.2%, Zn≤0.5%, Ti 0.05~0.25%, Sr 0.01~0.06%, Zr 0.05~0.20%, V 0.03~0.12%, with the balance being Al and unavoidable impurities, wherein the mass ratio of Mn / Fe is 0.4~0.8:1; The composite die casting process includes: melting the lightweight aluminum alloy material into an aluminum alloy melt, first performing vacuum die casting to fill the mold, and immediately starting a local extrusion device to extrude and compress the thick parts of the shell after the filling is completed. During the solidification process, the temperature gradient of the shell is controlled by a zoned temperature control system so that each part of the shell solidifies in a preset order.

2. The lightweight aluminum alloy automotive gearbox housing according to claim 1, characterized in that, The wall thickness of the gearbox housing is 2.5~6.0mm, with a maximum wall thickness difference of no more than 30mm, and the external dimensions of the housing are 400~500mm×350~430mm×200~260mm.

3. The lightweight aluminum alloy automotive gearbox housing according to claim 1, characterized in that, The bearing seat of the gearbox housing is provided with an annular reinforcing boss, the height of which is 5~15mm and the width of which is 8~20mm; the oil passage area of ​​the housing is provided with multiple heat dissipation fins distributed along the direction of the oil passage, the height of which is 2~6mm and the spacing of which is 10~25mm.

4. The lightweight aluminum alloy automotive gearbox housing according to claim 1, characterized in that, The surface of the gearbox housing is provided with a micro-arc oxidation ceramic layer, the thickness of which is 10~50μm and the surface hardness is ≥HV400.

5. The lightweight aluminum alloy automotive gearbox housing according to claim 1, characterized in that, The inner wall of the oil passage of the gearbox housing is provided with a laser cladding reinforcement layer, the thickness of which is 0.3~1.0mm and the material is Al-Si-Cu alloy powder.

6. A manufacturing process for a lightweight aluminum alloy automotive transmission housing as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Batching and smelting: Batching is carried out according to the chemical composition. Aluminum ingots, silicon, copper, magnesium, manganese and other raw materials are added to the smelting furnace and smelted at 720~780℃. After refining and degassing, the mixture is allowed to stand for 20~40 minutes to obtain aluminum alloy melt. (2) Vacuum die casting filling: The aluminum alloy melt obtained in step (1) is poured into a mold preheated to 180~250℃ at 680~720℃. Vacuum die casting filling is carried out under the conditions of injection speed of 2.0~4.5m / s, injection pressure of 60~120MPa, and mold cavity vacuum degree ≤5kPa. (3) Local extrusion and shrinkage: Within 0.5 to 3.0 seconds after the filling is completed, start the local extrusion device to apply an extrusion pressure of 50 to 150 MPa to the bearing seat, thick boss and oil passage intersection of the shell, and hold the pressure for 3 to 10 seconds; (4) Zoned temperature control solidification: The cooling rate of different areas of the shell is controlled by the zoned temperature control system set in the mold, so that the thin-walled area of ​​the shell is cooled rapidly at a rate of 8~15℃ / s, and the thick area is cooled slowly at a rate of 2~6℃ / s, and the temperature gradient of each part of the shell is controlled to be ≤50℃ until the shell is completely solidified. (5) Demolding and post-processing: After solidification, the mold is opened and the casting is removed, and the burrs and flash are removed. (6) Micro-arc oxidation treatment: Place the cleaned shell in the electrolyte and apply the oxidation at a voltage of 400~650V and a current density of 5~20A / dm³. 2 Under these conditions, micro-arc oxidation is performed for 10-40 minutes to form a ceramic layer on the shell surface; (7) Laser cladding of oil passages: The inner wall of the oil passages of the shell is strengthened by laser cladding process with laser power of 1.5~3.5kW, scanning speed of 5~20mm / s and powder feeding rate of 8~25g / min.

7. The manufacturing process for the lightweight aluminum alloy automotive gearbox housing according to claim 6, characterized in that, The gating system of the mold in step (2) is a ring gating system, including a central sprue and 4 to 8 radially distributed horizontal sprues. The end of each horizontal sprue is connected to an ingate, and the total cross-sectional area of ​​the ingate is 800 to 2000 mm².

8. The manufacturing process for the lightweight aluminum alloy automotive gearbox housing according to claim 6, characterized in that, The partitioned temperature control system in step (4) includes a heating pipe installed in the thick area of ​​the mold and a cooling water channel installed in the thin-walled area of ​​the mold. The heating pipe heats and replenishes the temperature of the thick area in the early stage of solidification, and the cooling water channel forces the thin-walled area to cool in the middle and late stages of solidification, so that the shell solidifies in the order of "thin-walled area solidifies first, thick area solidifies later".

9. The manufacturing process for the lightweight aluminum alloy automotive gearbox housing according to claim 6, characterized in that, The electrolyte in step (6) is a silicate-based or phosphate-based electrolyte, and the electrolyte temperature is controlled at 15~40℃ during the micro-arc oxidation process.

10. The manufacturing process for the lightweight aluminum alloy automotive gearbox housing according to claim 6, characterized in that, The overlap rate of the laser cladding in step (7) is 30-60%, the protective gas is argon, and the gas flow rate is 8-20 L / min.

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