Lightweight hydraulic shell and low-pressure casting method thereof

Abstract

The invention belongs to the technical field of metal casting, and relates to a lightweight hydraulic shell which is made of ZL101 aluminum alloy, and at least two boss structures are arranged on the bottom face of the hydraulic shell. The casting structure comprises a pouring gate located between the bosses and an integrated rectangular feeding structure connected with the bosses, and the pouring gate is arranged at the midpoint of the connecting line of the circle centers of the two bosses. The invention further discloses a low-pressure casting method which comprises the steps of smelting and refining the ZL101 aluminum alloy, preheating a mold, arranging a cooling water path, controlling low-pressure casting parameters to carry out liquid lifting, mold filling and pressure maintaining, and carrying out T6 heat treatment and processing on a casting. Through collaborative optimization of materials and a structural process, the problems that a traditional hydraulic shell is large in weight and poor in corrosion resistance and the defect rate is high due to uneven temperature or insufficient feeding in the casting process are solved, and unification of light weight, good comprehensive performance and low-defect-rate casting of the shell is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal casting, and relates to low-pressure casting, in particular to a lightweight hydraulic shell and a low-pressure casting method thereof. BACKGROUND

[0002] The hydraulic shell is a core bearing and protection component of the hydraulic system, mainly used for packaging and protecting hydraulic elements (such as valves, pumps, motors, etc.), while providing oil passage and mounting interface. The hydraulic shell is a core basic component of the hydraulic system, used for packaging hydraulic elements, building oil passage and providing mounting interface. In the fields sensitive to weight such as new energy vehicles and aerospace, the lightweight of the shell is crucial.

[0003] The material selection of the hydraulic shell needs to consider factors such as strength, pressure resistance, corrosion resistance, processing performance and cost. Common materials include carbon steel (such as 45 steel, Q345, 42CrMo, with excellent mechanical strength and high pressure resistance, but need surface treatment (such as galvanizing, phosphating) to prevent rust), stainless steel (such as 304, 316, with strong corrosion resistance but high cost), aluminum alloy (such as ZL105, ZL101, with outstanding lightweight advantage, and good heat dissipation and processing performance) and the like. The mainstream material on the market is cast iron, with the advantages of excellent mechanical strength and low cost, but due to the development of new energy, the demand for lightweight is increasing, so the use of aluminum alloy is increasing. The existing hydraulic shell materials are mainly carbon steel (such as 45 steel, Q345) and cast iron, which have the advantages of high strength (carbon steel tensile strength ≥600MPa), but have two major defects:

[0004] 1. Poor lightweight adaptability: the density of carbon steel is 7.85g / cm 3 In the scenarios sensitive to weight such as new energy vehicles and aerospace, it will cause the overall energy consumption of the equipment to increase and the load redundancy to increase, which cannot meet the lightweight design requirements;

[0005] 2. High maintenance cost and poor heat dissipation: carbon steel is prone to rust and needs to be regularly treated with galvanizing, phosphating and other surface corrosion prevention treatments, with an annual maintenance cost 30-50% higher than that of aluminum alloy; at the same time, its thermal conductivity is only about 50W / (m·K), and the heat dissipation capacity is poor, which easily leads to performance degradation due to high oil temperature in high-power hydraulic systems.

[0006] Although some application scenarios try to use aluminum alloy, such as ZL105, the advantage of which is that the addition of Cu in the alloy composition makes the room temperature performance better and the wear resistance better, but ZL105 has obvious short boards due to the presence of Cu (1.0-1.5%): poor corrosion resistance (additional surface treatment is required in a humid environment), weak high-temperature performance (tensile strength at 200℃ is only 40-50% of that at room temperature, and the upper limit of the long-term use temperature is ≤100℃), and cannot adapt to medium and low temperature working conditions above 100℃ and environments with slight corrosion.

[0007] Low-pressure casting is a common forming method for hydraulic housings. For a hydraulic housing with two bosses (such as a stepped circle) structure on the bottom surface, the traditional pouring scheme faces challenges. If a double-gate design is used, the two gates are close together, and a flow divider package needs to be set in the mold, resulting in a long residence time of the molten metal in the flow divider package, causing the local temperature of the mold to be too high (exceeding 280℃), disturbing the solidification sequence, and the porosity defect rate of the casting can be as high as 25% or more. If a single-gate design is used, the long flow path of the molten metal and the decay of the feeding pressure make the remote area prone to porosity due to insufficient feeding, and the defect rate is still 20-22%.

[0008] Therefore, the prior art lacks a comprehensive solution that can ensure the lightweight of the hydraulic housing while having good medium and low temperature strength, corrosion resistance, and low casting defect rate. SUMMARY

[0009] In view of the insufficient material and process adaptability in the prior art, the purpose of the present application is to disclose a lightweight hydraulic housing and a low-pressure casting method thereof.

[0010] Technical solution

[0011] A lightweight hydraulic housing made of a silico-magnesium series casting aluminum alloy, the bottom surface of which is provided with at least two bosses arranged at intervals; the casting structure of the hydraulic housing includes a gate located between the bosses, and an integrated feeding structure connecting each boss; wherein the gate is arranged at the midpoint of the connecting line of the centers of the two boss structures; the integrated feeding structure is a rectangular structure arranged between the boss structures, and the inner side of the rectangular feeding structure smoothly transitions with the outer wall of the boss structure.

[0012] In a preferred embodiment of the present application, the silico-magnesium series casting aluminum alloy is ZL101 aluminum alloy, and the chemical composition of the ZL101 aluminum alloy includes, by mass percentage: 6.5-7.5% of Si and 0.25-0.45% of Mg, with the balance being aluminum and unavoidable impurities.

[0013] In a preferred embodiment of the present invention, the ZL101 aluminum alloy, after being subjected to T6 heat treatment, has the following mechanical properties: tensile strength ≥220MPa, yield strength ≥180MPa, elongation ≥3%, and hardness 80-100HB.

[0014] In a preferred embodiment of the present invention, the boss structure is a stepped circle, the diameter of the two stepped circles is 55-65mm, and the center distance is 100-110mm.

[0015] In a preferred embodiment of the present invention, the diameter of the gate is 55-60 mm and the length is 30-40 mm.

[0016] In a preferred embodiment of the present invention, the rectangular compensation structure has a length of 100-110mm, a width of 55-65mm, and a height of 15-25mm.

[0017] In a preferred embodiment of the present invention, the radius of the fillet at the transition between the rectangular compensation structure and the stepped circle is 3-8 mm.

[0018] A second objective of this invention is to disclose a low-pressure casting method for the aforementioned lightweight hydraulic housing.

[0019] A low-pressure casting method for a lightweight hydraulic housing includes the following steps:

[0020] S1. Material smelting: Smelt ZL101 aluminum alloy ingots and refine them to obtain an alloy liquid with a gas content ≤0.15mL / 100g;

[0021] S2. Mold preparation: The mold is made of mold steel, the surface of the mold cavity is polished to Ra0.8μm, the mold is preheated to 200-250℃, and cooling water channels are arranged on both sides of the mold cavity;

[0022] S3. Low-pressure casting: The alloy liquid is cooled to 680-720℃, and compressed air is introduced for liquid raising, mold filling and pressure holding; wherein, the mold filling pressure is 0.03-0.05MPa, the mold filling time is 8-12s; the pressure holding pressure is 0.05-0.07MPa, the pressure holding time is 30-60s, and then the pressure is reduced to 0MPa at a rate of 0.005MPa / s. After cooling for 40-50s, the mold is opened and the casting is taken out.

[0023] S4. Post-treatment: The casting is subjected to T6 heat treatment, then the gate and flash are removed, and then machining and surface treatment are performed.

[0024] In a preferred embodiment of the present invention, in step S1, the melting temperature is 730-750℃; the refining process involves adding 0.1-0.2% hexachloroethane by mass of the alloy liquid and holding it at that temperature for 15-20 minutes.

[0025] In a preferred embodiment of the present invention, in step S2, the mold steel is H13 hot work mold steel; the diameter of the cooling water channel is 8mm, and the distance between the cooling water channel and the surface of the mold cavity is 15-20mm; cooling water with a temperature of 20-30℃ and a flow rate of 4-6L / min is introduced into the cooling water channel.

[0026] In a preferred embodiment of the present invention, in step S3, the initial liquid pressure is 0.02-0.03 MPa and the pressure increase rate is 0.01 MPa / s; after the pressure holding is completed, the pressure is reduced to 0 MPa at a rate not greater than 0.005 MPa / s, and the mold is opened after cooling for 40-50 seconds.

[0027] In a preferred embodiment of the present invention, step S4, the T6 heat treatment includes: solution treatment at 535-545℃ for 6-8 hours, followed by water quenching; and then aging treatment at 150-160℃ for 8-10 hours.

[0028] In a preferred embodiment of the present invention, in step S4, when machining the casting using a CNC milling machine, the machining accuracy is controlled at IT8 level.

[0029] This invention simplifies the casting system from a dual-gate to a single-gate design by modifying the blank structure and casting method. In terms of development costs, the simplified mold structure (eliminating the riser tank) reduces mold costs; in terms of the casting process, the reduction of a gate lowers the bottom mold temperature, improves process control, and increases the yield rate; and in terms of the product, the product weight is reduced by approximately 0.5 kg, further reducing costs.

[0030] Beneficial effects

[0031] This invention, by selecting ZL101 aluminum alloy and optimizing the heat treatment process, enables the shell to achieve medium strength (tensile strength 220-260MPa) while reducing weight by approximately 65% ​​compared to carbon steel parts of the same size. It also exhibits excellent corrosion resistance and a long-term operating temperature limit of 150℃, with overall product performance meeting target operating conditions. The innovative design of a single gate combined with an integrated rectangular feeding structure ensures smooth molten metal flow and sufficient feeding, effectively solving the porosity problem caused by localized overheating in dual-gate systems or insufficient feeding in a single gate. This reduces the internal defect rate of castings from over 20% in the prior art to below 5%, resulting in a low casting defect rate. The simplified mold structure (eliminating the runner) combined with precisely controlled cooling water channels ensures a uniform and stable mold temperature field with minimal fluctuations, guaranteeing fine grains and stable mechanical properties in the castings. This increases the product qualification rate to over 90% and enhances process stability. The simplified mold structure reduces manufacturing costs, shortens production cycle time, and improves production efficiency. Furthermore, the material's excellent corrosion resistance eliminates the need for additional surface treatment processes, reducing the overall cost over the entire product lifecycle. Attached Figure Description

[0032] Figure 1 Schematic diagram of the bottom structure of a traditional hydraulic housing;

[0033] Figure 2 Schematic diagram of the bottom structure of the lightweight hydraulic housing;

[0034] Figure 3 A schematic diagram of the cross-sectional structure of a traditional hydraulic housing mold;

[0035] Figure 4 Schematic diagram of the cross-sectional structure of a lightweight hydraulic housing mold. Detailed Implementation

[0036] The present invention will be described in detail below with reference to embodiments, so that those skilled in the art can better understand the present invention, but the present invention is not limited to the following embodiments.

[0037] Example 1

[0038] Manufacturing of hydraulic housing for new energy vehicles

[0039] 1. Raw material preparation

[0040] ZL101 aluminum alloy ingots conforming to GB / T 1173-2013 standard were selected, with the following chemical composition: Si 7.0%, Mg 0.35%, Fe 0.2%, Cu 0.05%, Mn 0.03%, and the remainder being Al. The aluminum alloy ingots were placed in a 500kg resistance furnace and heated to 740℃ for melting. 0.15% hexachloroethane refining agent was added, and the mixture was stirred for 10 minutes, held at that temperature for 18 minutes, and allowed to stand for 12 minutes. The gas content of the molten alloy was measured to be 0.12mL / 100g, which meets the requirements.

[0041] 2. Mold preparation

[0042] The mold is made of H13 steel, and the cavity size is designed based on the finished product size (200mm long × 150mm wide × 80mm high), with a 1.3% allowance for casting shrinkage. The gate is located at the midpoint of the connecting line of two stepped circles (60mm in diameter and 105mm in center distance) on the bottom surface, with a diameter of 58mm and a length of 35mm. The shrinkage compensation structure is a rectangle with a length of 105mm, a width of 60mm, and a height of 20mm, and a corner radius of R5mm. The mold is preheated to 230℃, and the cooling water channel is circulated (25℃, flow rate 5L / min).

[0043] 3. Low-pressure casting process

[0044] Liquid Lifting: The temperature of the alloy liquid is reduced to 700℃, compressed air is introduced, the initial liquid lifting pressure is 0.025MPa, the pressure increase rate is 0.01MPa / s, and the molten metal enters the gate through the liquid lifting pipe, which takes 5s.

[0045] Filling: The pressure is continuously increased to 0.04 MPa, and the molten metal fills the cavity. The filling time is 9 seconds.

[0046] Pressure holding: The pressure is increased to 0.055MPa and held for 40 seconds to ensure sufficient compression.

[0047] Pressure reduction and mold opening: Reduce the pressure to 0 MPa at a rate of 0.005 MPa / s, cool for 50 seconds, then open the mold and remove the casting.

[0048] 4. Post-processing and testing

[0049] T6 heat treatment: solution heat treatment at 540℃ for 7 hours, water quenching; aging heat treatment at 155℃ for 9 hours, cooling to room temperature;

[0050] Machining: Remove gates (5mm allowance) using CNC milling machine, machine oil passage holes (10mm diameter, tolerance H7) and mounting thread holes (M12), with an accuracy of IT8 grade;

[0051] Performance testing:

[0052] Mechanical properties: tensile strength 242MPa, yield strength 203MPa, elongation 5.2%, hardness 88HB, meeting design requirements;

[0053] Defect detection: X-ray flaw detection (GB / T 6417.1-2005) shows that the casting has no porosity or shrinkage cavities, and the defect level is ≤1.

[0054] Air tightness test: 0.8MPa compressed air is introduced and the pressure is maintained for 30s. The leakage rate is ≤0.01MPa / min, which meets the sealing requirements of the hydraulic system.

[0055] Corrosion resistance test: Neutral salt spray test (GB / T10125-2021) 48h, no rust on the surface, corrosion rate 0.008mm / year.

[0056] Example 2

[0057] Manufacturing of hydraulic control housing for construction machinery

[0058] 1. Raw material preparation

[0059] ZL101 aluminum alloy ingots were selected, with the following chemical composition: Si 6.8%, Mg 0.40%, Fe 0.18%, Cu 0.04%, Mn 0.02%, and the remainder being Al. The aluminum alloy ingots were placed in an 800kg resistance furnace and heated to 735℃ for melting. 0.12% hexachloroethane refining agent was added, and the mixture was stirred for 12 minutes, held at that temperature for 16 minutes, and allowed to stand for 10 minutes. The gas content of the molten alloy was measured to be 0.10 mL / 100g.

[0060] 2. Mold preparation

[0061] The mold is made of H13 steel, and the cavity size is designed based on the finished product size (250mm long × 200mm wide × 100mm high), with a 1.3% allowance for casting shrinkage. The gate is located at the midpoint of the connecting line of two stepped circles (65mm in diameter and 110mm in center distance) on the bottom surface, with a diameter of 60mm and a length of 40mm. The shrinkage compensation structure is a rectangle with a length of 110mm, a width of 65mm, and a height of 25mm, and a corner radius of R8mm. The mold is preheated to 240℃, and the cooling water channel is circulated (22℃, flow rate 6L / min).

[0062] 3. Low-pressure casting process

[0063] Liquid raising: The temperature of the alloy liquid is reduced to 710℃, compressed air is introduced, the initial liquid raising pressure is 0.028MPa, the pressure raising rate is 0.01MPa / s, the metal liquid enters the gate, and the time is 6s;

[0064] Filling: The pressure is continuously increased to 0.045MPa, and the molten metal fills the cavity. The filling time is 11s.

[0065] Pressure holding: The pressure is raised to 0.065 MPa and held for 50 seconds;

[0066] Pressure reduction and mold opening: Reduce the pressure to 0 MPa at a rate of 0.004 MPa / s, cool for 45 seconds, then open the mold and remove the casting.

[0067] 4. Post-processing and testing

[0068] T6 heat treatment: solution heat treatment at 542℃ for 7.5 hours, followed by water quenching; aging heat treatment at 158℃ for 8.5 hours, followed by cooling to room temperature;

[0069] Machining: Remove the gate (6mm allowance) using CNC milling machine, machine the oil passage hole (12mm diameter, tolerance H7) and the mounting thread hole (M16) with an accuracy of IT8 grade;

[0070] Performance testing:

[0071] Mechanical properties: tensile strength 238MPa, yield strength 195MPa, elongation 4.8%, hardness 92HB;

[0072] Defect detection: X-ray inspection showed that the casting had no porosity or shrinkage cavities, and the defect level was ≤1.

[0073] Air tightness test: 1.0MPa compressed air is introduced and the pressure is maintained for 30s. The leakage rate is ≤0.01MPa / min.

[0074] Corrosion resistance test: After 48 hours of neutral salt spray test, no rust was found on the surface, and the corrosion rate was 0.007 mm / year.

[0075] Comparative Example

[0076] In contrast, a ZL105 aluminum alloy shell with the same structure was cast using a traditional dual-gating scheme (with gating points set at the center of two stepped circles). The results showed that due to localized overheating of the mold, the porosity defect rate of the casting was as high as 28%; and because ZL105 has poor high-temperature performance, its strength at 150℃ is only about 45% of its room temperature strength, which cannot meet the requirements of the working conditions.

[0077] This comparative example strongly demonstrates the significant progress made by this invention in the synergistic optimization of materials and processes.

[0078] The above embodiments fully demonstrate that the lightweight hydraulic housing and its low-pressure casting method provided by the present invention can effectively solve the problems raised in the background art and achieve the expected technical effects.

[0079] The embodiments described above are merely specific implementations of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A lightweight hydraulic housing, characterized in that: The hydraulic housing is made of silicon-magnesium cast aluminum alloy, and its bottom surface has at least two spaced boss structures. The casting structure of the hydraulic housing includes a gate located between the boss structures and an integrated feeding structure connecting each boss. The gate is located at the midpoint of the line connecting the centers of the two boss structures. The integrated feeding structure is a rectangular structure located between the boss structures, and the inner side of the rectangular feeding structure smoothly transitions to the outer wall of the boss structure.

2. The lightweight hydraulic housing according to claim 1, characterized in that: The silicon-magnesium based cast aluminum alloy is ZL101 aluminum alloy. The chemical composition of the ZL101 aluminum alloy, by mass percentage, includes: 6.5-7.5% Si and 0.25-0.45% Mg, with the balance being aluminum and unavoidable impurities.

3. The lightweight hydraulic housing according to claim 2, characterized in that, After T6 heat treatment, the ZL101 aluminum alloy has the following mechanical properties: tensile strength ≥220MPa, yield strength ≥180MPa, elongation ≥3%, and hardness 80-100HB.

4. The lightweight hydraulic housing according to claim 1, characterized in that: The boss structure is a stepped circle, and the diameter of the two stepped circles is 55-65mm, with a center distance of 100-110mm.

5. The lightweight hydraulic housing according to claim 1, characterized in that: The diameter of the gate is 55-60mm and the length is 30-40mm.

6. The lightweight hydraulic housing according to claim 1, characterized in that: The rectangular compensation structure has a length of 100-110mm, a width of 55-65mm, and a height of 15-25mm.

7. The lightweight hydraulic housing according to claim 1, characterized in that: The radius of the fillet at the transition between the rectangular compensation structure and the stepped circle is 3-8mm.

8. A low-pressure casting method for manufacturing a lightweight hydraulic housing as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Material smelting: Smelt ZL101 aluminum alloy ingots and refine them to obtain an alloy liquid with a gas content ≤0.15mL / 100g; S2. Mold preparation: The mold is made of mold steel, the surface of the mold cavity is polished to Ra0.8μm, the mold is preheated to 200-250℃, and cooling water channels are arranged on both sides of the mold cavity; S3. Low-pressure casting: The alloy liquid is cooled to 680-720℃, and compressed air is introduced for liquid raising, mold filling and pressure holding; wherein, the mold filling pressure is 0.03-0.05MPa, the mold filling time is 8-12s; the pressure holding pressure is 0.05-0.07MPa, the pressure holding time is 30-60s, and then the pressure is reduced to 0MPa at a rate of 0.005MPa / s. After cooling for 40-50s, the mold is opened and the casting is taken out. S4. Post-treatment: The casting is subjected to T6 heat treatment, then the gate and flash are removed, and then machining and surface treatment are performed.

9. The low-pressure casting method for the lightweight hydraulic housing according to claim 8, characterized in that: In step S1, the melting temperature is 730-750℃; the refining process involves adding 0.1-0.2% hexachloroethane by mass of the alloy liquid and holding it at that temperature for 15-20 minutes. In step S2, the mold steel is H13 hot work mold steel; the diameter of the cooling water channel is 8mm, and the distance between the cooling water channel and the surface of the mold cavity is 15-20mm; cooling water with a temperature of 20-30℃ and a flow rate of 4-6L / min is introduced into the cooling water channel.

10. The low-pressure casting method for the lightweight hydraulic housing according to claim 8, characterized in that: In step S3, the initial liquid pressure is 0.02-0.03 MPa, and the pressure increase rate is 0.01 MPa / s; after the pressure holding is completed, the pressure is reduced to 0 MPa at a rate not exceeding 0.005 MPa / s, and the mold is opened after cooling for 40-50 seconds. In step S4, the T6 heat treatment includes: solution treatment at 535-545℃ for 6-8 hours, followed by water quenching; and then aging treatment at 150-160℃ for 8-10 hours. In step S4, when the casting is machined using a CNC milling machine, the machining accuracy is controlled at IT8 level.

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