A green and energy-saving extrusion casting method and apparatus that combines liquid phase retention and forced feeding sequential solidification

Abstract

This invention discloses a green and energy-saving extrusion casting method and apparatus that combines liquid phase retention and forced feeding sequential solidification. The method includes the following steps: melting a pre-proportioned metal to obtain a basic alloy melt; degassing and refining followed by the addition of an intermediate alloy to obtain an intermediate alloy melt; lowering the temperature to obtain a finished alloy melt; during casting, adjusting the ingate temperature between the solid and liquid phases of the finished alloy melt; and activating a multi-point positioning cooling device to locally force-cool areas with large wall thicknesses. This invention, by precisely controlling the ingate temperature between the solid and liquid phases of the alloy melt, ensures that the alloy melt at the ingate is in a solid-liquid mixed state during pressure holding solidification. The liquid alloy melt can smoothly pass through the gap between the primary solid phases and flow into the shrinkage cavities of the casting body during pressure holding solidification, achieving further forced feeding of the liquid during the pressure holding process of alloy melt extrusion casting. This results in high-quality castings with high microstructure density, few shrinkage cavities and porosity defects, and excellent strength and elongation.

Description

Technical Field

[0001] This invention relates to a green and energy-saving extrusion casting method and apparatus that combines liquid phase retention and forced feeding sequential solidification. Background Technology

[0002] High-quality integral forming of large structural components is a challenge in the field of parts manufacturing. Extrusion casting (also known as liquid forging) solves the problems of low feeding efficiency and shrinkage defects in gravity casting by integral rheological feeding, and overcomes the limitations of solid forging technology and equipment with its good rheological filling ability, thus becoming a new choice for high-quality integral forming manufacturing of large structural components.

[0003] Because the molten metal fills the mold cavity at high speed during the squeeze casting process, its flow pattern is turbulent. Therefore, casting defects such as air entrapment, shrinkage cavities, and porosity are inevitable in die castings. Especially when the structure of large castings becomes more complex, the molten alloy often cannot flow smoothly and cannot completely fill the complex shape and small structure of the mold, resulting in defects such as incomplete filling or voids in the product. These defects not only affect the appearance of the product but also reduce its mechanical properties and durability. In addition, in die casting production, it is common to encounter situations where the cavity volume of some thick parts of the casting body is large. Because a lot of molten metal accumulates in the thick parts after filling, a lot of heat is also accumulated. Therefore, the molten metal inside the casting dissipates heat and solidifies more slowly. The thickness of the ingate in squeeze casting mold is generally about 1 / 3 to 1 / 2 of the casting thickness, and the solidification rate is faster. The high-temperature aluminum alloy melt enters the cavity through the ingate and is then cooled by the cooling system to form the aluminum alloy product. As the molten aluminum alloy in the mold cavity gradually cools, the ingate area often solidifies faster than the casting itself, blocking the feeding channel of the molten metal and causing shrinkage cavities inside the casting, thus reducing the strength and quality of the die casting. To improve the quality of die castings, the die casting machine maintains a continuous pressure at the gate of the die casting mold during the die casting process to compensate for the shrinkage caused by cooling. While this method can improve the shrinkage problem of die castings to some extent and is beneficial to improving the quality of die castings, when the molten aluminum in the mold cavity cools, the thinner parts cool faster than the thicker parts. When the thinner part at the ingate area has basically solidified, the thicker part inside the casting is still not completely solidified. When the die casting machine completes the filling and pressurization and enters the holding pressure stage, the pressure acting on the ingate of the die casting mold cannot be transmitted to the thicker parts. During the cooling process of this part, the aluminum alloy at the ingate cannot be replenished, which can easily lead to shrinkage depressions on the surface of the die casting or shrinkage cavities inside the die casting, thus affecting the strength and quality of the die casting.

[0004] Furthermore, in traditional die casting, the sprue, ingate, and excess material remain in the injection barrel, ingate, and runner after each die casting. This residue often accounts for 1 / 3 to 1 / 2 of the workpiece's weight, and even more in some thin-walled or small parts. For example, in a typical aluminum alloy die casting, the workpiece itself weighs 200g, while the sprue and ingate area can weigh 100g to 200g, representing 33% to 50% of the total weight. This portion of metal must be removed and remelted as scrap in traditional processes. While the scrap can be reused, each remelting requires heating the metal from room temperature to above the liquidus line, significantly increasing energy consumption, causing severe oxidation and burn-off, increasing inclusions, and severely degrading quality. Each die casting requires injecting a complete volume of molten metal (casting + sprue + ingate) into the injection barrel, necessitating sufficient time for feeding and injection, limiting further increases in cycle time. In multi-cavity die casting or complex runner designs, the proportion of excess material further increases, leading to even more significant material waste. Summary of the Invention

[0005] The main objective of this invention is to provide a green and energy-saving extrusion casting method and apparatus that combines liquid phase retention and forced feeding sequence solidification, in order to solve the problems mentioned in the background above.

[0006] The objective of this invention can be achieved by adopting the following technical solution:

[0007] A green and energy-saving extrusion casting method that combines liquid phase retention and forced feeding sequential solidification includes the following steps:

[0008] Step S1: According to the requirements, the metal elements are proportioned and the proportioned metal elements are melted at 100~200℃ above the alloy liquidus line to prepare a basic alloy melt.

[0009] Step S2: Degassing and refining the prepared basic alloy melt;

[0010] Step S3: Add intermediate alloy to the base alloy melt, melt and stir at 100~200℃ above the alloy liquidus line to obtain intermediate alloy melt;

[0011] Step S4: Lower the temperature of the intermediate alloy melt to 25~50°C above the alloy liquidus line, keep it at the temperature and let it stand, then remove the surface slag to obtain the finished alloy melt.

[0012] Step S5: Heat the sprue and the ingate. The heating temperature is between the solid and liquid phases of the finished alloy melt, so that the finished alloy melt at the ingate is in a solid-liquid mixed state during pressure holding and solidification, thus ensuring the fluidity of the finished alloy melt.

[0013] Step S6: Pour the liquid finished alloy melt with a temperature of 25~50℃ above the liquidus line into the mold cavity, and squeeze the finished alloy melt through the injection cylinder for casting.

[0014] Step S7: During the pouring and solidification process, the multi-point positioning cooling device is turned on to force cooling the parts of the casting with a larger wall thickness than other locations, ensuring that the area of ​​the casting that is finally solidified is at the ingate.

[0015] Step S8: Continuously heat the sprue and the ingate position. The heating temperature is between the solid and liquid phases of the finished alloy melt. After the finished alloy melt fills the cavity, pressure holding and solidification are performed. At this time, the alloy melt at the ingate is maintained in the liquidus temperature range or the semi-solid range.

[0016] Step S9: After the casting solidifies, separate the casting from the ingate and remove it. The sprue and part of the ingate metal remain at the front end of the injection cylinder, remaining in a liquid or semi-solid state.

[0017] Step S10: The injection punch retracts, and the liquid or semi-solid metal in the sprue and inlet area remains in the injection barrel as part of the metal source for the next injection.

[0018] Step S11: Based on the amount of metal required for the casting, add new molten metal to the injection cylinder and mix it with the recycled molten metal retained in the spool to achieve continuous recycling of the molten metal in the spool.

[0019] Preferably, in step S1, the ratio is the metal element ratio of the Al-8Si alloy, specifically: the Si content is 8.0 wt.%, and the remainder is Al;

[0020] Alternatively, the metal element composition of A356 aluminum alloy is as follows: Si content is 6.5wt.%~7.5wt.%, Mg content is 0.20wt.%~0.40wt.%, and the remainder is Al;

[0021] The metal element composition of AZ91D magnesium alloy is as follows: Al content is 8.5wt.%-9.5wt.%, zinc content is 0.45wt.%-0.9wt.%, manganese content is 0.17wt.%-0.4wt.%, and the remainder is Mg.

[0022] Preferably, in step S2, the gas used for degassing and refining is anhydrous nitrogen or anhydrous argon, and the degassing and refining time is 15-20 min. In step 4, the settling time is 15-45 min. In step 8, the pressure holding and solidification time is 3-10 s.

[0023] Preferably, in steps S5 and S8, the section from the sprue to the ingate is heated by a temperature gradient, with a temperature difference of ≥60℃ from the sprue to the ingate and a temperature difference of ≥100℃ from the sprue to the cavity.

[0024] Preferably, in step S5, the liquid phase fraction in the finished alloy melt in the solid-liquid mixed state is >40%.

[0025] Preferably, in step S8, the liquid phase fraction of the alloy melt at the ingate is >40%.

[0026] Preferably, in step S3, a deteriorating and refining agent is added and the mixture is stirred.

[0027] Preferably, in step S7, thermocouples are used to collect the real-time temperature of the mold points at various parts of the casting. Based on the feedback of the collected real-time temperature, when the cooling rate of the thick part of the casting is lower than that of the thin part, the multi-point positioning cooling device is activated to accelerate and force-cool the thick part of the casting.

[0028] A green and energy-saving extrusion casting forming device that combines liquid phase retention and forced feeding sequential solidification includes an outer mold and an inner mold. The inner mold has a cavity for casting and an ingate. Below the ingate, a sprue and a feed port are arranged in sequence. The outer rings of the ingate and the sprue are respectively equipped with a first heating device and a second heating device. An injection cylinder is arranged outside the feed port. The inner mold has a multi-point positioning cooling device on the outside of the cavity. The multi-point positioning cooling device is located on the part of the cavity with a larger wall thickness than other positions. A slag bag is arranged outside the cavity, and an exhaust channel is provided on the slag bag.

[0029] Preferably, the first heating device and the second heating device are any one of electromagnetic induction coil heating, resistance coil heating, steam heating and dielectric heating. When the first heating device and the second heating device are electromagnetic induction coil heating, a graphite heating sleeve is provided outside the electromagnetic induction coil.

[0030] Compared with the prior art, the beneficial technical effects of the present invention are:

[0031] 1. This invention precisely controls the temperature of the ingate between the solid and liquid phases of the alloy melt, so that the alloy melt at the ingate is in a solid-liquid mixed state during pressure holding and solidification. During the pressure holding and solidification process, the liquid alloy melt can smoothly pass through the gap between the primary solid phases and flow into the shrinkage porosity of the casting body. This achieves further forced feeding of the liquid during the pressure holding process of alloy melt extrusion casting, resulting in high-quality castings with high microstructure density, few shrinkage cavities and porosity defects, and excellent strength and elongation.

[0032] 2. This invention achieves precise control of the mold temperature field, forced cooling of thick parts, and forced heating of the ingate position, effectively reducing the difficulty of disrupting the sequential solidification temperature field of large-sized castings due to many dynamic changing factors, realizing gradient sequential solidification of castings, reducing shrinkage porosity and shrinkage defects formed in thicker parts, reducing casting defects, and reducing the shrinkage porosity defect rate of metal castings by more than 30% compared with traditional preparation processes.

[0033] 3. The present invention has a metal molten material reuse rate of ≥90%, reduces the amount of material added in each die casting by 40% to 50%, eliminates the material molten material remelting step, saves about 30% to 40% of energy, and can open the mold without waiting for the material molten material to solidify, thus reducing energy consumption and shortening the process flow.

[0034] 3. The temperature control method for the two-phase zone of the in-mold gate and sprue proposed in this invention, compared with the traditional process, allows the liquid metal to pass smoothly through the gap between the primary solid phases during the pressure holding and solidification process by controlling the heating temperature of the in-mold gate in conjunction with multi-point cooling. This solves the flow channel blockage phenomenon during the pressure feeding of castings in the traditional process, avoids the problem of the continuous weakening of fluidity caused by the cooling of the aluminum liquid at the end of solidification, and particularly solves the problem of dense porosity caused by cooling shrinkage during the final pressure holding and molding process of the product, thus greatly improving the product qualification rate. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the extrusion casting apparatus of the present invention;

[0036] Figure 2 This is a schematic diagram showing the position of the positioning cooling device of the present invention;

[0037] Figure 3 This is a diagram of the shrinkage cavity in the casting of Comparative Example 1 of the present invention;

[0038] Figure 4 This is a diagram of the shrinkage cavity in the casting according to Embodiment 1 of the present invention;

[0039] Figure 5 This is a metallographic image of the casting in the as-cast state of Comparative Example 1 of the present invention;

[0040] Figure 6 This is a metallographic image of the casting in the as-cast state according to Embodiment 1 of the present invention;

[0041] Figure 7 This is a metallographic image of the casting in the heat-treated state of Comparative Example 2 of the present invention;

[0042] Figure 8 This is a metallographic image of the casting in the heat-treated state according to Embodiment 2 of the present invention.

[0043] In the diagram: 1. Outer mold; 2. Inner mold; 3. Cavity; 4. Inner gate; 5. Sprue; 6. Inlet; 7. First heating device; 8. Second heating device; 9. Injection cylinder; 10. Multi-point positioning cooling device; 11. Slag bag; 12. Venting channel; 13. Graphite heating sleeve. Detailed Implementation

[0044] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0045] Please see Figures 1 to 8 One embodiment provided by the present invention:

[0046] A green and energy-saving extrusion casting method that combines liquid phase retention and forced feeding sequential solidification includes the following steps:

[0047] Step S1: According to the requirements, the metal elements are proportioned and the proportioned metal elements are melted at 100~200℃ above the alloy liquidus line to prepare a basic alloy melt.

[0048] Step S2: Degassing and refining the prepared basic alloy melt;

[0049] Step S3: Add intermediate alloy to the base alloy melt, melt and stir at 100~200℃ above the alloy liquidus line to obtain intermediate alloy melt;

[0050] Step S4: Lower the temperature of the intermediate alloy melt to 25~50°C above the alloy liquidus line, keep it at the temperature and let it stand, then remove the surface slag to obtain the finished alloy melt.

[0051] Step S5: Heat the sprue 5 and the inner gate 4. The heating temperature is between the solid and liquid two-phase regions of the finished alloy melt, so that the finished alloy melt at the inner gate 4 is in a solid-liquid mixed state during pressure holding and solidification, thus ensuring the fluidity of the finished alloy melt.

[0052] Step S6: Pour the liquid finished alloy melt with a temperature of 25~50℃ above the liquidus line into the mold cavity 3, and squeeze the finished alloy melt through the injection cylinder 9;

[0053] Step S7: During the pouring and solidification process, the multi-point positioning cooling device 10 is turned on to force cooling the parts of the casting with a larger wall thickness than other locations, ensuring that the area of ​​the casting that is finally solidified is at the ingate 4.

[0054] Step S8: Continuously heat the material handle 5 and the ingate 4. The heating temperature is between the solid and liquid phases of the finished alloy melt. After the finished alloy melt fills the cavity 3, pressure holding and solidification are performed. At this time, the alloy melt at the ingate 4 is maintained in the liquidus temperature range or the semi-solid range.

[0055] Step S9: After the casting solidifies, the casting is separated from the ingate 4 and removed. The sprue 5 and part of the metal from the ingate 4 remain at the front end of the injection cylinder 9, remaining in a liquid or semi-solid state.

[0056] Step S10: The injection punch retracts, and the liquid or semi-solid metal in the area of ​​the sprue 5 and the inner gate 4 remains in the injection cylinder 9, serving as part of the metal source for the next injection.

[0057] Step S11: Based on the amount of metal required for the casting, add new molten metal to the injection cylinder 9 and mix it with the recycled molten metal retained in the slurry 5 to achieve continuous recycling of the molten metal in the slurry 5. Each die casting only requires the amount of metal required for the casting, and the slurry 5 no longer becomes waste.

[0058] Furthermore, in step 1, the metal element ratio of the Al-8Si alloy is as follows: Si content is 8.0 wt.%, and the remainder is Al;

[0059] Alternatively, the metal element composition of A356 aluminum alloy is as follows: Si content is 6.5wt.%~7.5wt.%, Mg content is 0.20wt.%~0.40wt.%, and the remainder is Al;

[0060] The metal element composition of AZ91D magnesium alloy is as follows: Al content is 8.5wt.%-9.5wt.%, zinc content is 0.45wt.%-0.9wt.%, manganese content is 0.17wt.%-0.4wt.%, and the remainder is Mg.

[0061] The aforementioned alloys all have a relatively wide solid-liquid two-phase region, generally greater than 50°C. The alloys require a relatively long time to completely solidify from the liquidus to the solidus. For such alloys, the casting method of this application can more effectively compensate for defects, reduce porosity, and significantly improve the performance of the castings.

[0062] Furthermore, in step S2, the gas used for degassing and refining is anhydrous nitrogen or anhydrous argon, and the degassing and refining time is 15-20 min. In step 4, the settling time is 15-45 min. In step 8, the pressure holding and solidification time is 3-10 s.

[0063] Furthermore, in steps S5 and S8, the area from the sprue 5 to the ingate 4 is heated by a temperature-controlled gradient. The temperature difference from the sprue 5 to the ingate 4 is ≥60℃, and the temperature difference from the sprue 5 to the cavity 3 is ≥100℃. Through temperature control, the casting has solidified, while the sprue 5 and the ingate 4 area remain liquid or semi-solid and are not completely solidified. Since the sprue 5 and the ingate 4 area are continuously heated and remain liquid or semi-solid, during the solidification and shrinkage process of the casting, the molten metal in the sprue 5 can be continuously fed sequentially to the thicker parts of the casting through the ingate 4, which significantly reduces shrinkage cavities and porosity defects.

[0064] Furthermore, in step S5, the liquid phase fraction in the finished alloy melt in the solid-liquid mixed state is >40%, ensuring pressure transmission while maintaining the fluidity of the finished alloy melt.

[0065] Furthermore, in step S8, the liquid phase fraction of the alloy melt at the four inlet gates is >40%.

[0066] Furthermore, in step S3, a modifier is added and stirred to make the intermediate alloy easier to dissolve.

[0067] Furthermore, in step S7, thermocouples are used to collect the real-time temperature of the mold points at various parts of the casting. Based on the feedback of the collected real-time temperature, when the cooling rate of the thick part of the casting is lower than that of the thin part, the multi-point positioning cooling device 10 is activated to accelerate the forced cooling of the thick part of the casting, reduce local uneven solidification, realize the overall sequential solidification of the casting, and cast a casting with refined structure and improved density.

[0068] A green and energy-saving extrusion casting forming device that combines liquid phase retention and forced feeding sequential solidification includes an outer mold 1 and an inner mold 2. The inner mold 2 has a cavity 3 for casting inside. An ingate 4 is provided on the inner mold 2. A sprue 5 and a feed port 6 are arranged in sequence below the ingate 4. A first heating device 7 and a second heating device 8 are respectively provided on the outer ring of the ingate 4 and the sprue 5. An injection cylinder 9 is provided outside the feed port 6. A multi-point positioning cooling device 10 is provided on the outside of the cavity 3 inside the inner mold 2. The multi-point positioning cooling device 10 is located on the part of the cavity 3 with a larger wall thickness than other positions. A slag bag 11 is provided outside the cavity 3. An exhaust channel 12 is provided on the slag bag 11.

[0069] Furthermore, the first heating device 7 and the second heating device 8 can be any one of electromagnetic induction coil heating, resistance coil heating, steam heating and dielectric heating. When the first heating device 7 and the second heating device 8 are electromagnetic induction coil heating, a graphite heating sleeve 13 is provided outside the electromagnetic induction coil, which can improve heating efficiency, protect the coil and make the heating more uniform.

[0070] Example 1

[0071] Forced feeding sequence solidification extrusion casting of Al-8Si aluminum alloy compressor intermediate shell:

[0072] The solidus and liquidus temperatures of Al-8Si aluminum alloy were measured to be 560℃ and 620℃, respectively. The Al-8Si aluminum alloy raw material was melted at 800℃ to prepare a basic Al-8Si aluminum alloy melt. The prepared basic alloy melt was subjected to degassing and refining treatment for 15 minutes. Al-Sr master alloy and Al-Ti-Nb-B master alloy were added to the basic alloy melt, along with a modifier and refiner. The melt was then melted and stirred at 780℃ to obtain a master alloy melt. The temperature of the master alloy melt was lowered to 645℃, held at that temperature, and allowed to stand for 30 minutes before removing the surface slag to obtain the finished alloy melt.

[0073] The first heating device 7 and the second heating device 8 on the outside of the ingate 4 and the sprue 5 are turned on. The temperature of the ingate 4 is adjusted to 590°C through gradient temperature control, so that the finished alloy melt at the ingate 4 is in a solid-liquid mixed state during pressure solidification. The temperature of the sprue 5 is 650°C. 2kg of liquid finished alloy melt at 645°C is poured into the mold. The finished alloy melt is squeezed and cast through the injection cylinder 9. During the pouring and solidification process, the multi-point positioning cooling device 10 is turned on to force-cool the parts of the casting with a larger wall thickness than other positions, ensuring that the area of ​​the casting that is finally solidified is at the ingate 4. After the finished alloy melt fills the cavity 3, pressure solidification is carried out.

[0074] Maintain a gradient heating state between the sprue 5 and the ingate 4. After the casting solidifies, separate the casting from the ingate 4, remove the casting and weigh it. The weight of the casting is 1 kg. Perform solution aging treatment.

[0075] The sprue 5 and part of the ingate 4 remain at the front end of the injection cylinder 9, in a liquid or semi-solid state. As the injection punch retracts, the liquid or semi-solid metal in the sprue 5 and ingate 4 area remains in the injection cylinder 9, serving as a source of metal for the next injection. Based on the required amount of metal for the casting, 1.1 kg of new molten metal is added to the injection cylinder 9 and mixed with the recycled molten metal retained in the sprue 5, achieving continuous recycling of the molten metal in the sprue 5.

[0076] Comparative Example 1

[0077] Conventional extrusion casting of Al-8Si aluminum alloy compressor intermediate housing:

[0078] Al-8Si alloy raw material was melted at 800℃ to prepare a basic Al-8Si alloy melt. The prepared basic alloy melt was degassed and refined for 15 minutes. Al-Sr master alloy and Al-Ti-Nb-B master alloy were added to the basic alloy melt, along with a modifier and refiner. The melt was then melted and stirred at 780℃ to obtain a master alloy melt. The temperature of the master alloy melt was lowered to 645℃, held at that temperature, and allowed to stand for 30 minutes before removing surface slag to obtain the finished alloy melt. 2 kg of the melt was directly poured into a mold for conventional extrusion casting. After solidification, the formed casting was removed and subjected to solution aging treatment.

[0079] Table 1 Mechanical properties of castings from Example 1 and Comparative Example 1

[0080] Yield strength (MPa) Tensile strength (MPa) Elongation (%) Example 1 370 420 6.5 Comparative Example 1 352 402 3.8

[0081] As shown in Table 1, Example 1 has a higher yield strength, higher tensile strength, and greater elongation compared to Comparative Example 1.

[0082] Figure 3 Shrinkage cavity diagram of the ingate of the casting in Comparative Example 1 Figure 4 The diagram shows the shrinkage cavities of the ingate in Example 1. It is clear that there are many shrinkage cavities on the surface of the ingate in Comparative Example 1, while there are no shrinkage cavities on the surface of the ingate in Example 1.

[0083] Figure 5 The image shows the as-cast metallographic image of the casting in Comparative Example 1. Figure 6 The metallographic image of the casting in Example 1 clearly shows that the casting in Comparative Example 1 has obvious pores and inclusions with a size of about 100 μm, while the casting in Example 1 does not have obvious pores.

[0084] Therefore, Example 1 has better mechanical properties.

[0085] Example 2

[0086] Forced feeding sequence solidification extrusion casting of A356 aluminum alloy steering knuckle:

[0087] The solidus and liquidus temperatures of A356 aluminum alloy were measured to be 555℃ and 620℃, respectively. The A356 aluminum alloy raw material was melted at 780℃ to prepare a basic A356 aluminum alloy melt. The prepared basic alloy melt was subjected to degassing and refining treatment for 15 minutes. Al-Sr master alloy and Al-Ti-Nb-B master alloy were added to the basic alloy melt, along with a modifier and refiner. The melt was then melted and stirred at 760℃ to obtain a master alloy melt. The temperature of the master alloy melt was lowered to 645℃, held at that temperature, and allowed to stand for 30 minutes before removing the surface slag to obtain the finished alloy melt.

[0088] The first heating device 7 and the second heating device 8 on the outside of the ingate 4 and the sprue 5 are turned on. The temperature of the ingate 4 is adjusted to 590°C through gradient temperature control, so that the finished alloy melt at the ingate 4 is in a solid-liquid mixed state during pressure holding and solidification. The temperature of the sprue 5 is 650°C. 2.4 kg of liquid finished alloy melt at 645°C is poured into the mold. The finished alloy melt is squeezed and cast through the injection cylinder 9. During the pouring and solidification process, the multi-point positioning cooling device 10 is turned on to force-cool the parts of the casting with a larger wall thickness than other positions, ensuring that the area of ​​the casting that is finally solidified is at the ingate 4. After the finished alloy melt fills the cavity 3, pressure holding and solidification are carried out.

[0089] Maintain a gradient heating state between the sprue 5 and the ingate 4. After the casting solidifies, separate the casting from the ingate 4, remove the casting and weigh it. The weight of the casting is 1.2 kg. Perform solution aging treatment.

[0090] The sprue 5 and part of the ingate 4 remain at the front end of the injection cylinder 9, in a liquid or semi-solid state. As the injection punch retracts, the liquid or semi-solid metal in the sprue 5 and ingate 4 areas remains in the injection cylinder 9, serving as a source of metal for the next injection. Based on the required amount of metal for the casting, 1.3 kg of new molten metal is added to the injection cylinder 9 and mixed with the recycled molten metal retained in the sprue 5, achieving continuous recycling of the molten metal in the sprue 5.

[0091] Comparative Example 2

[0092] Conventional extrusion casting of A356 aluminum alloy steering knuckle:

[0093] A356 aluminum alloy raw material is melted at 780℃ to prepare a basic A356 aluminum alloy melt. The prepared basic alloy melt is then degassed and refined for 15 minutes. Al-Sr master alloy and Al-Ti-Nb-B master alloy are added to the basic alloy melt, along with a modifier and refiner. The melt is then stirred at 760℃ to obtain a master alloy melt. The temperature of the master alloy melt is lowered to 645℃, held at that temperature, and allowed to stand for 30 minutes before removing surface slag to obtain the finished alloy melt. This melt is then directly poured into a mold for conventional extrusion casting. After solidification, the formed casting is removed and subjected to solution aging treatment.

[0094] Table 2 Mechanical properties of Example 2 and Comparative Example 2

[0095] Yield strength (MPa) Tensile strength (MPa) Elongation (%) Example 2 305 213 10.2 Comparative Example 2 276 185 6.7

[0096] As shown in Table 2, Example 2 has a higher yield strength, higher tensile strength, and greater elongation compared to Comparative Example 2.

[0097] Figure 7 The image shows the metallographic structure of the heat-treated casting in Comparative Example 2. Figure 8 The metallographic image of the casting in Example 2 after heat treatment shows that the casting in Comparative Example 2 has a large number of micropores with a size of 3-9 μm that have developed after solution treatment and aging. These micropores are numerous and dense, which will reduce the fatigue life of the casting and affect its mechanical properties.

[0098] The castings of Example 2 showed no obvious micropores after solution treatment and aging, thus exhibiting better mechanical properties.

[0099] Example 3

[0100] The AZ91D magnesium alloy differential bracket is formed by forced feeding sequence solidification extrusion casting:

[0101] The solidus and liquidus temperatures of AZ91D magnesium alloy were measured to be 470℃ and 595℃, respectively. The alloy was melted at 700℃ to prepare a basic AZ91D alloy melt. The prepared basic alloy melt was then subjected to degassing and refining treatment for 15 minutes. The temperature of the basic alloy melt was lowered to 620℃, held at that temperature, and allowed to stand for 25 minutes before removing the surface slag to obtain the finished alloy melt.

[0102] The first heating device 7 and the second heating device 8 on the outside of the ingate 4 and the sprue 5 are turned on. The temperature of the ingate 4 is adjusted to 555℃ through gradient temperature control so that the finished alloy melt at the ingate 4 is in a solid-liquid mixed state during pressure holding and solidification. The temperature of the sprue 5 is 625℃. 2.8 kg of liquid finished alloy melt at 620℃ is poured into the mold. The finished alloy melt is squeezed and cast through the injection cylinder 9. During the pouring and solidification process, the multi-point positioning cooling device 10 is turned on to force cooling the parts of the casting with a larger wall thickness than other positions, ensuring that the area of ​​the casting that is finally solidified is at the ingate 4. After the finished alloy melt fills the cavity 3, pressure holding and solidification are carried out.

[0103] Maintain a gradient heating state between the sprue 5 and the ingate 4. After the casting solidifies, separate the casting from the ingate 4, remove the casting and weigh it. The weight of the casting is 1.5 kg. Perform solution aging treatment.

[0104] The sprue 5 and part of the ingate 4 remain at the front end of the injection cylinder 9, in a liquid or semi-solid state. As the injection punch retracts, the liquid or semi-solid metal in the sprue 5 and ingate 4 area remains in the injection cylinder 9, serving as a source of metal for the next injection. Based on the required amount of metal for the casting, 1.4 kg of new molten metal is added to the injection cylinder 9 and mixed with the recycled molten metal retained in the sprue 5, achieving continuous recycling of the molten metal in the sprue 5.

[0105] Comparative Example 3

[0106] Conventional extrusion casting of the AZ91D magnesium alloy differential bracket:

[0107] The alloy was melted at 700℃ to prepare a basic AZ91D alloy melt. The prepared basic alloy melt was then degassed and refined for 15 minutes. The temperature of the basic alloy melt was then lowered to 620℃, held at that temperature, and allowed to stand for 25 minutes before removing the surface slag to obtain the finished alloy melt. This melt was then directly poured into a mold for conventional extrusion casting. After solidification, the formed casting was removed and subjected to solution aging treatment.

[0108] Table 3 Mechanical properties of Example 3 and Comparative Example 3

[0109] Yield strength (MPa) Tensile strength (MPa) Elongation (%) Example 3 286 178 19.6 Comparative Example 3 261 164 11.2

[0110] As shown in Table 3, Example 3 has a higher yield strength, higher tensile strength, and greater elongation compared to Comparative Example 3.

[0111] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A green and energy-saving extrusion casting method that combines liquid phase retention and forced feeding sequential solidification, characterized in that: Includes the following steps: Step S1: According to the requirements, the metal elements are proportioned and the proportioned metal elements are melted at 100~200℃ above the alloy liquidus line to prepare a basic alloy melt. Step S2: Degassing and refining the prepared basic alloy melt; Step S3: Add intermediate alloy to the base alloy melt, melt and stir at 100~200℃ above the alloy liquidus line to obtain intermediate alloy melt; Step S4: Lower the temperature of the intermediate alloy melt to 25~50°C above the alloy liquidus line, keep it at the temperature and let it stand, then remove the surface slag to obtain the finished alloy melt. Step S5: Heat the sprue (5) and the ingate (4) at a temperature between the solid and liquid phases of the finished alloy melt, so that the finished alloy melt at the ingate (4) is in a solid-liquid mixed state during pressure holding and solidification, thus ensuring the fluidity of the finished alloy melt. Step S6: Pour the liquid finished alloy melt with a temperature of 25~50℃ above the liquidus line into the mold cavity (3), and squeeze the finished alloy melt through the injection cylinder (9); Step S7: During the pouring and solidification process, the multi-point positioning cooling device (10) is turned on to force cooling the part of the casting with a larger wall thickness than other positions, so as to ensure that the area of ​​the casting that is finally solidified is at the ingate (4). Step S8: Continuously heat the material handle (5) and the ingate (4) at the position of the material handle (5). The heating temperature is between the solid and liquid phases of the finished alloy melt. After the finished alloy melt fills the cavity (3), it is pressure-held and solidified. At this time, the alloy melt at the ingate (4) is maintained in the liquidus temperature range or the semi-solid range. Step S9: After the casting solidifies, the casting is separated from the ingate (4) and removed. The sprue (5) and part of the metal from the ingate (4) remain at the front end of the injection cylinder (9) and remain in a liquid or semi-solid state. Step S10: The injection punch retracts, and the liquid or semi-solid metal in the sprue (5) and inner gate (4) area remains in the injection barrel (9) as part of the metal source for the next injection. Step S11: Based on the amount of metal required for the casting, add new molten metal to the injection cylinder (9) and mix it with the recycled molten metal retained in the material handle (5) to achieve continuous recycling of the molten metal in the material handle (5).

2. The green and energy-saving extrusion casting method according to claim 1, which combines liquid phase retention and forced feeding sequential solidification, is characterized in that: In step S1, the temperature difference between the solid and liquid phases of the alloy composed of the metal elements is greater than 50°C, and the specific proportions of the metal elements are as follows: The specified ratio is the metal element ratio of the Al-8Si alloy, specifically: Si content is 8.0 wt.%, the remainder is Al; Alternatively, the metal element composition of A356 aluminum alloy is as follows: Si content is 6.5wt.%~7.5wt.%, Mg content is 0.20wt.%~0.40wt.%, and the remainder is Al; The metal element composition of AZ91D magnesium alloy is as follows: Al content is 8.5wt.%-9.5wt.%, zinc content is 0.45wt.%-0.9wt.%, manganese content is 0.17wt.%-0.4wt.%, and the remainder is Mg.

3. The green and energy-saving extrusion casting method according to claim 1, which combines liquid phase retention and forced feeding sequential solidification, is characterized in that: In step S2, the gas used for degassing and refining is anhydrous nitrogen or anhydrous argon, and the degassing and refining time is 15-20 min. In step S4, the settling time is 15-45 min. In step S8, the pressure holding and solidification time is 3-10 s.

4. The green and energy-saving extrusion casting method according to claim 1, which combines liquid phase retention and forced feeding sequential solidification, is characterized in that: In steps S5 and S8, the temperature gradient heating is used in the section from the sprue (5) to the ingate (4), the temperature drop from the sprue (5) to the ingate (4) is ≥60℃, and the temperature drop from the sprue (5) to the cavity (3) is ≥100℃.

5. The green and energy-saving extrusion casting method according to claim 1, which combines liquid phase retention and forced feeding sequential solidification, is characterized in that: In step S5, the liquid phase fraction in the finished alloy melt in the solid-liquid mixed state is >40%.

6. The green and energy-saving extrusion casting method according to claim 1, which combines liquid phase retention and forced feeding sequential solidification, is characterized in that: In step S8, the liquid phase fraction of the alloy melt at the inner gate (4) is >40%.

7. The green and energy-saving extrusion casting method according to claim 1, which combines liquid phase retention and forced feeding sequential solidification, is characterized in that: In step S3, a refining agent is added and the mixture is stirred.

8. The green and energy-saving extrusion casting method according to claim 1, which combines liquid phase retention and forced feeding sequential solidification, is characterized in that: In step S7, thermocouples are used to collect the real-time temperature of the mold points at various parts of the casting. Based on the feedback of the collected real-time temperature, when the cooling rate of the thick part of the casting is lower than that of the thin part, the multi-point positioning cooling device (10) is activated to accelerate the forced cooling of the thick part of the casting.

9. A green and energy-saving extrusion casting apparatus that combines liquid phase retention and forced feeding sequential solidification, the apparatus being based on the extrusion casting method according to any one of claims 1-8, characterized in that: The mold includes an outer mold (1) and an inner mold (2). The inner mold (2) has a cavity (3) for casting. The inner mold (2) has an ingate (4). Below the ingate (4), a sprue (5) and a feed port (6) are arranged in sequence. The outer rings of the ingate (4) and the sprue (5) are respectively provided with a first heating device (7) and a second heating device (8). The feed port (6) is provided with an injection cylinder (9). The inner mold (2) has a multi-point positioning cooling device (10) outside the cavity (3). The multi-point positioning cooling device (10) is located in a part outside the cavity (3) with a larger wall thickness than other positions. The cavity (3) has a slag bag (11) outside. The slag bag (11) has an exhaust channel (12).

10. The green and energy-saving extrusion casting forming device with both liquid phase retention and forced feeding sequential solidification as described in claim 9, characterized in that: The first heating device (7) and the second heating device (8) are any one of electromagnetic induction coil heating, resistance coil heating, steam heating and dielectric heating. When the first heating device (7) and the second heating device (8) are electromagnetic induction coil heating, a graphite heating sleeve (13) is provided outside the electromagnetic induction coil.

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