Liquid die forging method for complex inner cavity aluminum alloy parts

Abstract

This invention discloses a liquid forging method for complex internal cavity aluminum alloy parts, comprising: Step S1, preparing a sand core, and making the sand core into a spare sand core part adapted to the internal cavity of the workpiece; Step S2, preparing a sand core coating, and uniformly applying the sand core coating to the surface of the spare sand core part; Step S3, drying the spare sand core part, and after drying, placing the spare sand core part into the cavity of the liquid forging die and fixing it, wherein the position of the spare sand core part corresponds to the position of the internal cavity of the workpiece, and then closing the liquid forging die; Step S4, pouring aluminum alloy liquid into the liquid forging die, so that the aluminum alloy liquid fills the cavity and wraps the spare sand core part, and continuing to perform stepped pressure liquid forging on the solidified shell to obtain a liquid forging part; Step S5, opening the die, taking out the liquid forging part with the sand core, breaking the sand core, and obtaining a complex internal cavity aluminum alloy liquid forging part with a smooth internal cavity. This invention can realize the preparation of complex internal cavity workpieces, with a smooth internal cavity, no sand adhesion, and no inclusions or porosity defects.

Description

Technical Field

[0001] The invention relates to the technical field of liquid die forging of aluminum alloy parts, and in particular to a liquid die forging method for aluminum alloy parts with complex inner cavities. Background Art

[0002] Liquid die forging is one of the high-performance forming technologies for metal materials. It has been widely used in the automotive, aviation, rail transportation, power electronics and other industries, and has outstanding advantages in the lightweight invention of replacing steel with aluminum. However, the existing liquid die forging technology cannot produce parts with complex cavities, which greatly limits its application.

[0003] In casting technology, sand cores can be used to form complex inner cavities. However, the strength of the sand cores in the prior art is not high, and they are easily crushed under the high-pressure conditions of liquid die forging. If a high-strength ceramic core is used, it will not be crushed, but its disintegration is poor, and it is difficult to clean after forming. In order to solve the problem that ordinary sand cores have poor disintegration and are difficult to clean, someone invented the soluble core technology, that is, making sand cores with soluble materials, and after the parts are formed, they are placed in water together with the workpiece to dissolve the sand core. However, this soluble core is easy to absorb moisture, which increases the risk of porosity defects in aluminum alloy parts. In addition, this soluble core takes a long time to dissolve, and the production efficiency is low. The workpiece is also prone to corrosion when it is soaked in water for a long time, affecting the apparent quality. Summary of the invention

[0004] The purpose of the present invention is to overcome the above-mentioned defects in the prior art and provide a liquid die forging method for aluminum alloy parts with complex inner cavities, which can overcome the defects of the prior art and realize the preparation of workpieces with complex inner cavities. The inner cavity of the prepared workpiece is smooth, without sand sticking, inclusions and pore defects, and the sand core is easy to remove.

[0005] To achieve the above object, the present invention provides a liquid die forging method for a complex inner cavity aluminum alloy part, comprising:

[0006] Step S1, preparing a sand core, and making the sand core into a spare sand core piece adapted to the inner cavity of the workpiece;

[0007] Step S2, preparing a sand core coating, and evenly applying the sand core coating to the surface of the spare sand core piece;

[0008] Step S3, drying the spare sand core piece, and after drying, placing the spare sand core piece into the cavity of the liquid forging mold and fixing it, wherein the position of the spare sand core piece corresponds to the position of the inner cavity of the workpiece, and then closing the liquid forging mold;

[0009] Step S4, casting aluminum alloy liquid into the liquid forging die, so that the aluminum alloy liquid fills the mold cavity and wraps the spare sand core piece, and after the aluminum alloy liquid forms a solidified shell on the surface of the spare sand core piece, continuing to perform step-by-step pressurized liquid forging on the solidified shell to obtain a liquid forging;

[0010] Step S5, opening the mold, taking out the liquid forging with the sand core, breaking the sand core, and making the sand core flow out of the cavity of the liquid forging to obtain a complex inner cavity aluminum alloy liquid die forging with a smooth inner cavity.

[0011] Furthermore, the sand core in step S1 includes a binder with a weight percentage of 10-20% and an aggregate with a weight percentage of 80-90%, wherein the binder is 2123 resin, the aggregate of the sand core is a mixture of limestone and talcum powder, the mass ratio of the limestone to the talcum powder is 1:(1-5), and the room temperature flexural strength of the sand core is ≥1.2MPa immediately after molding, and the room temperature flexural strength is ≥3MPa after one hour. The sand core prepared by this formula can achieve a room temperature flexural strength of ≥1.2MPa immediately after molding, and a room temperature flexural strength of ≥3MPa after one hour. In the subsequent pressurized liquid forging process, as the pressure increases, a crushing phenomenon will occur, resulting in inclusion defects and Huaxue sand sticking in the workpiece; at the same time, the vibration sand removal of the sand core can also be achieved; the use of 2123 resin can ensure the bonding force and high temperature resistance between the aggregates, and the sand core will not be crushed during use.

[0012] Furthermore, the carrier of the sand core coating in step S2 is an inorganic fluid with a Baume degree of 35-52°Be, and the chemical composition of the inorganic fluid is composed of Na2O and SiO2, and the molar ratio of the two is 1:(3-6), and the balance is water; the sand core coating includes 2-15% by weight of aggregate, and the balance is the inorganic fluid, and the aggregate is refractory clay. The sand core coating obtained by this ratio can ensure that the sand core will not be crushed or fall off during the pressurization process of the method of the present invention to avoid the generation of inclusions; at the same time, the bonding performance of the sand core coating is ensured, and it can be easily coated on the sand core to ensure the thickness of the coating and avoid the generation of pores in the workpiece.

[0013] Furthermore, in step S2, the thickness of the sand core coating is 0.2-0.5mm, the bending strength of the spare sand core at 200°C is ≥23MPa, and the collapse temperature of the spare sand core is ≤400°C. Controlling the thickness of the sand core coating can avoid the generation of pores during the production of the workpiece and improve the quality of the workpiece. The sand core coating can ensure the bending strength of the spare sand core at a specific temperature, avoid the problem of falling off due to too low strength, and the collapse temperature of the spare sand core will not exceed 400, which is convenient for vibration sand removal after the workpiece is processed, and no additional heating process is required, thereby reducing production costs.

[0014] Furthermore, the drying temperature of step S3 is controlled at 150-220° C. and the drying time is 30-120 min. Drying the spare sand core piece can keep the whole piece dry and shaped, which is convenient for assembly in the mold and will not break due to sudden pressure.

[0015] Furthermore, the step-by-step pressurized liquid forging in step S4 includes light-pressure liquid forging and heavy-pressure liquid forging. The pressure of the light-pressure liquid forging is 3-5 MPa, and the pressure holding time is 1-10S. The pressure of the heavy-pressure liquid forging is 30-60 MPa, and the pressure holding time is 15-120S.

[0016] Furthermore, the step-by-step pressurized liquid forging in step S4 includes light-pressure liquid forging and heavy-pressure liquid forging. Specifically, for a workpiece with a wall thickness of less than 5 mm, two-stage pressurized liquid forging, namely, pressurized liquid forging and heavy-pressure liquid forging, can be selected. The pressure of the light-pressure liquid forging is 3-5 MPa, and the pressure is maintained for 1-5 seconds; the pressure of the heavy-pressure liquid forging is 30-50 MPa, and the pressure is maintained for 15-60 seconds.

[0017] Furthermore, the step-pressure liquid forging in step S4 also includes medium-pressure liquid forging, and the pressure of the medium-pressure liquid forging is 6-30 MPa, and the pressure holding time is 2-15S.

[0018] Further, the step-by-step pressurized liquid forging in step S4 includes light pressure liquid forging, medium pressure liquid forging and heavy pressure liquid forging. Specifically, for workpieces with a wall thickness between 5.5 mm and 10 mm, three-stage pressurized liquid forging including pressurized liquid forging, medium pressure liquid forging and heavy pressure liquid forging can be selected. The pressure of the light pressure liquid forging is 3-5 MPa, and the pressure holding time is 3-8 seconds; the pressure of the medium pressure liquid forging is 6-10 MPa, and the pressure holding time is 2-5 seconds. The pressure of the heavy pressure liquid forging is 30-60 MPa, and the pressure holding time is 20-40 seconds.

[0019] Further, the step-by-step pressurized liquid forging in step S4 includes light pressure liquid forging, two medium pressure liquid forgings and heavy pressure liquid forging, wherein the two medium pressure liquid forgings are the first medium pressure liquid forging and the second medium pressure liquid forging respectively. Specifically, for a workpiece with a wall thickness greater than 10 mm, four-stage pressurized liquid forging including pressurized liquid forging, the first medium pressure liquid forging, the second medium pressure liquid forging and heavy pressure liquid forging can be selected. The pressure of the light pressure liquid forging is 3-5 MPa, and the pressure holding time is 3-10 seconds; the pressure of the first medium pressure liquid forging is 6-12 MPa, and the pressure holding time is 5-15 seconds; the pressure of the second medium pressure liquid forging is 15-30 MPa, and the pressure holding time is 5-10 seconds; the pressure of the heavy pressure liquid forging is 30-60 MPa, and the pressure holding time is 30-120S.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1. The method provided by the present invention can realize the preparation of workpieces with complex inner cavities. The sand core has high strength below 300°C and will not be crushed. The liquid forging coating has good coating properties, strong adhesion, and good crusting ability. It can be evenly coated on the sand core and prevent the aluminum alloy liquid from infiltrating. The complex inner cavity of the obtained aluminum alloy liquid forging is smooth and free of sand sticking.

[0022] 2. The sand core is easy to remove. The sand core in the complex inner cavity of the aluminum alloy liquid forging obtained by the method provided by the present invention is easy to remove. No special high-temperature "sand burning" is required. The sand core of the present invention has good collapsibility above 400°C and can be vibrated to remove the sand. The sand core can be removed by using the ordinary vibration sand removal method;

[0023] 3. No inclusion or pore defects. The aluminum alloy liquid forgings obtained by the method provided by the present invention have no inclusion defects caused by sand core sand loss, and no surface pore defects.

[0024] 4. Through high-precision step-by-step pressurization, low-pressure liquid forging is applied only when the aluminum alloy liquid solidifies the shell of the spare sand core, to prevent excessive pressure before the solidification shell is formed, causing the liquid metal to penetrate into the coating and form sticky sand; then high-pressure liquid forging is maintained in the later stage of forming, which will not compress the sand core, but also ensure that the workpiece is fully compensated for shrinkage, thereby improving the forming quality of the workpiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 It is a schematic diagram of the principle of a liquid die forging method for a complex inner cavity aluminum alloy part of the present invention;

[0027] Figure 2 It is a schematic diagram of the structure of the aluminum alloy automobile air spring top seat with a complex inner cavity formed in Example 1 of the present invention;

[0028] Figure 3 It is a schematic structural diagram of another aluminum alloy automobile air spring top seat with a complex inner cavity formed in Example 2 of the present invention;

[0029] Figure 4 It is a schematic structural diagram of another aluminum alloy automobile air spring top seat with a complex inner cavity formed in Example 3 of the present invention; DETAILED DESCRIPTION

[0030] The technical scheme in this embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in this embodiment of the present invention. Obviously, the described embodiment is one embodiment of the present invention, not all embodiments of the present invention. Based on this embodiment of the present invention, all other embodiments of the present invention obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0032] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features.

[0033] like Figure 1 As shown, an embodiment of the present invention provides a liquid die forging method for a complex inner cavity aluminum alloy part, comprising:

[0034] Step S1, preparing a sand core, and making the sand core into a spare sand core piece adapted to the inner cavity of the workpiece;

[0035] Step S2, preparing a sand core coating, and evenly applying the sand core coating to the surface of the spare sand core piece;

[0036] Step S3, drying the spare sand core piece, and after drying, placing the spare sand core piece into the cavity of the liquid forging mold and fixing it, wherein the position of the spare sand core piece corresponds to the position of the inner cavity of the workpiece, and then closing the liquid forging mold;

[0037] Step S4, casting aluminum alloy liquid into the liquid forging die, so that the aluminum alloy liquid fills the mold cavity and wraps the spare sand core piece, and after the aluminum alloy liquid forms a solidified shell on the surface of the spare sand core piece, continuing to perform step-by-step pressurized liquid forging on the solidified shell to obtain a liquid forging;

[0038] Step S5, opening the mold, taking out the liquid forging with the sand core, breaking the sand core, and making the sand core flow out of the cavity of the liquid forging to obtain a complex inner cavity aluminum alloy liquid die forging with a smooth inner cavity.

[0039] Furthermore, the sand core in step S1 includes a binder accounting for 10-20% by weight and an aggregate accounting for 80-90% by weight, the binder is 2123 resin, the aggregate of the sand core is a mixture of limestone and talcum powder, the mass ratio of the limestone to the talcum powder is 1:(1-5), and the molding instant room temperature flexural strength of the sand core is ≥1.2MPa, and the room temperature flexural strength after one hour is ≥3MPa.

[0040] Furthermore, the carrier of the sand core coating in step S2 is an inorganic fluid with a Baume degree of 35-52°Be, the chemical composition of the inorganic fluid is composed of Na2O and SiO2, the molar ratio of the two is 1:(3-6), and the balance is water; the sand core coating includes 2-15% by weight of aggregate, the balance is the inorganic fluid, and the aggregate is refractory clay.

[0041] Furthermore, in the step S2, the coating thickness of the sand core coating is 0.2-0.5 mm, the bending strength of the spare sand core piece at 200°C is ≥23 MPa, and the collapse temperature of the spare sand core piece is ≤400°C.

[0042] Furthermore, the drying temperature of step S3 is controlled at 150-220° C., and the drying time is 30-120 min.

[0043] Furthermore, the step-by-step pressurized liquid forging in step S4 includes light-pressure liquid forging and heavy-pressure liquid forging. The pressure of the light-pressure liquid forging is 3-5 MPa, and the pressure holding time is 1-10S. The pressure of the heavy-pressure liquid forging is 30-60 MPa, and the pressure holding time is 15-120S.

[0044] Furthermore, the step-by-step pressurized liquid forging in step S4 includes light-pressure liquid forging and heavy-pressure liquid forging. Specifically, for a workpiece with a wall thickness of less than 5 mm, two-stage pressurized liquid forging, namely, pressurized liquid forging and heavy-pressure liquid forging, can be selected. The pressure of the light-pressure liquid forging is 3-5 MPa, and the pressure is maintained for 1-5 seconds; the pressure of the heavy-pressure liquid forging is 30-50 MPa, and the pressure is maintained for 15-60 seconds.

[0045] Furthermore, the step-pressure liquid forging in step S4 also includes medium-pressure liquid forging, and the pressure of the medium-pressure liquid forging is 6-30 MPa, and the pressure holding time is 2-15S.

[0046] Further, the step-by-step pressurized liquid forging in step S4 includes light pressure liquid forging, medium pressure liquid forging and heavy pressure liquid forging. Specifically, for workpieces with a wall thickness between 5.5 mm and 10 mm, three-stage pressurized liquid forging including pressurized liquid forging, medium pressure liquid forging and heavy pressure liquid forging can be selected. The pressure of the light pressure liquid forging is 3-5 MPa, and the pressure holding time is 3-8 seconds; the pressure of the medium pressure liquid forging is 6-10 MPa, and the pressure holding time is 2-5 seconds. The pressure of the heavy pressure liquid forging is 30-60 MPa, and the pressure holding time is 20-40 seconds.

[0047] Further, the step-by-step pressurized liquid forging in step S4 includes light pressure liquid forging, two medium pressure liquid forgings and heavy pressure liquid forging, wherein the two medium pressure liquid forgings are the first medium pressure liquid forging and the second medium pressure liquid forging respectively. Specifically, for a workpiece with a wall thickness greater than 10 mm, four-stage pressurized liquid forging including pressurized liquid forging, the first medium pressure liquid forging, the second medium pressure liquid forging and heavy pressure liquid forging can be selected. The pressure of the light pressure liquid forging is 3-5 MPa, and the pressure holding time is 3-10 seconds; the pressure of the first medium pressure liquid forging is 6-12 MPa, and the pressure holding time is 5-15 seconds; the pressure of the second medium pressure liquid forging is 15-30 MPa, and the pressure holding time is 5-10 seconds; the pressure of the heavy pressure liquid forging is 30-60 MPa, and the pressure holding time is 30-120S.

[0048] The following three examples and five comparative examples are given to further illustrate the implementation manner and beneficial effects of the present invention.

[0049] Example 1

[0050] like Figure 2 The embodiment shown in the figure is described by taking the aluminum alloy automobile air spring top seat with a complex inner cavity as an example. The spring top seat has two symmetrical irregular inner cavities, a wall thickness of 5 mm, and is made of ZL101 aluminum alloy with a solidus temperature of 575°C.

[0051] Step S1, preparing a sand core: The sand core of this embodiment includes a binder accounting for 10% by weight and an aggregate accounting for 90% by weight, wherein the binder is 2123 resin, and the aggregate of the sand core is a mixture of limestone and talcum powder, wherein the mass ratio of the limestone to the talcum powder is 1:1, and the 2123 resin and the aggregate are mixed and stirred sufficiently to obtain an initial sand core, and the molding instant room temperature flexural strength of the sand core is 1.2 MPa, and the room temperature flexural strength after one hour is 3 MPa, and then the initial sand core is placed in a mold to make a spare sand core piece adapted to the inner cavity of the workpiece.

[0052] Step S2, preparing sand core coating: the carrier of the sand core coating of this embodiment is an inorganic fluid with a Baume degree of 35°Be, the chemical composition of the inorganic fluid is composed of Na2O and SiO2, the molar ratio of the two is 1:3, and the balance is water; the sand core coating includes 2% by weight of aggregate, the balance is the inorganic fluid, and the aggregate is refractory clay; the inorganic fluid and aggregate of the above proportion are put into a stirring barrel and stirred until the two are fully fused to obtain the sand core coating, and then the sand core coating is evenly applied to the surface of the spare sand core piece, the application thickness of the sand core coating is 0.2mm, the flexural strength of the spare sand core piece at 200°C is 23MPa, and the collapse temperature of the spare sand core piece is 320°C;

[0053] Step S3, placing the spare sand core piece in a drying furnace at 150°C, drying for 30 minutes and then taking it out of the oven. After the drying is completed, the spare sand core piece is placed in the cavity of the liquid forging mold and fixed. The position of the spare sand core piece corresponds to the position of the inner cavity of the workpiece, and then the liquid forging mold is closed;

[0054] Step S4, casting aluminum alloy liquid on the liquid forging die, using the injection mechanism of the liquid die forging machine to push the aluminum alloy liquid to fill the cavity of the liquid forging die, the aluminum alloy liquid wraps the spare sand core part and stays for 1 second, after the aluminum alloy liquid forms a solidified shell on the surface of the spare sand core part, continue to perform step-by-step pressurized liquid forging on the solidified shell to obtain a liquid forging part, in this embodiment, the step-by-step pressurized liquid forging is set twice, including light pressure liquid forging and heavy pressure liquid forging, the pressure of the light pressure liquid forging is 3MPa, and the pressure holding time is 1 second; the pressure of the heavy pressure liquid forging is 30MPa, and the pressure holding time is 15 seconds;

[0055] Step S5, open the mold, take out the liquid forging with the sand core, place it on a vibrating sand-dropping machine for vibration, break the sand core, and make the sand core flow out of the cavity of the liquid forging to obtain a complex inner cavity aluminum alloy liquid die forging with a smooth inner cavity.

[0056] Example 2

[0057] like Figure 3 This embodiment is used to prepare another aluminum alloy automobile air spring top seat (X80 top seat) with a complex inner cavity. The spring top seat has two asymmetric and irregular long inner cavities. The inner cavity of the workpiece is very complex, with a wall thickness of 8mm. The material is ZL101 aluminum alloy, and its solidus temperature is 575℃;

[0058] Step S1, preparing sand core: the sand core of this embodiment includes a binder accounting for 15% by weight and an aggregate accounting for 85% by weight, the binder is 2123 resin, the aggregate of the sand core is a mixture of limestone and talcum powder, the mass ratio of the limestone to the talcum powder is 1:2, and the above 2123 resin and aggregate are mixed and stirred to obtain an initial sand core. The molding instant room temperature flexural strength of the sand core of this embodiment is 1.5MPa, and the room temperature flexural strength after one hour is 4MPa. Then the initial sand core is placed in a mold to make a spare sand core piece adapted to the inner cavity of the workpiece.

[0059] Step S2, preparing sand core coating: the carrier of the sand core coating of this embodiment is an inorganic fluid with a Baume degree of 42°Be, the chemical composition of the inorganic fluid is composed of Na2O and SiO2, the molar ratio of the two is 1:5, and the balance is water; the sand core coating includes 8% by weight of aggregate, the balance is the inorganic fluid, and the aggregate is refractory clay; the inorganic fluid and aggregate of the above proportion are put into a stirring barrel and stirred until the two are fully fused to obtain the sand core coating, and then the sand core coating is evenly applied to the surface of the spare sand core piece, the application thickness of the sand core coating is 0.35mm, the flexural strength of the spare sand core piece at 200°C is 32MPa, and the collapse temperature of the spare sand core piece is 360°C;

[0060] Step S3, placing the spare sand core piece in a drying furnace at 180°C, drying for 60 minutes and then taking it out of the oven. After the drying is completed, the spare sand core piece is placed in the cavity of the liquid forging mold and fixed. The position of the spare sand core piece corresponds to the position of the inner cavity of the workpiece, and then the liquid forging mold is closed;

[0061] Step S4, casting aluminum alloy liquid on the liquid forging die, using the injection mechanism of the liquid die forging machine to push the aluminum alloy liquid to fill the cavity, the aluminum alloy liquid wraps the spare sand core part and stays for 2 seconds, after the aluminum alloy liquid forms a solidified shell on the surface of the spare sand core part, continue to perform step-by-step pressure liquid forging on the solidified shell to obtain a liquid forging part, in this embodiment, the step-by-step pressure liquid forging is set up for three times, including light pressure liquid forging, medium pressure liquid forging and heavy pressure liquid forging, the pressure of the light pressure liquid forging is 5MPa, and the pressure holding time is 3 seconds; the pressure of the medium pressure liquid forging is 8MPa, and the pressure holding time is 3.5 seconds; the pressure of the heavy pressure liquid forging is 40MPa, and the pressure holding time is 30 seconds;

[0062] Step S5, open the mold, take out the liquid forging with the sand core, place it on a vibrating sand-dropping machine for vibration, break the sand core, and make the sand core flow out of the cavity of the liquid forging to obtain a complex inner cavity aluminum alloy liquid die forging with a smooth inner cavity.

[0063] Example 3

[0064] like Figure 4 This embodiment is used to prepare another aluminum alloy automobile air spring top seat (AH8 top seat) with a complex inner cavity. The spring top seat has two asymmetric and irregular inner cavities, of which the left side has a nearly trapezoidal cross-section and the right side has a long strip-shaped cavity. The inner cavity of the workpiece is very complex, with a wall thickness of 15 mm. The material is A356.2 aluminum alloy, and its solidus temperature is 580°C.

[0065] Step S1, preparing sand core: the sand core of this embodiment includes a binder accounting for 20% by weight and an aggregate accounting for 80% by weight, the binder is 2123 resin, the aggregate of the sand core is a mixture of limestone and talcum powder, the mass ratio of the limestone to the talcum powder is 1:3, and the above-mentioned 2123 resin and aggregate are mixed and stirred to obtain an initial sand core. The molding instant room temperature flexural strength of the sand core is 1.8MPa, and the room temperature flexural strength after one hour is 5MPa. Then the initial sand core is placed in a mold to make a spare sand core part adapted to the inner cavity of the workpiece.

[0066] Step S2, preparing sand core coating: the carrier of the sand core coating of this embodiment is an inorganic fluid with a Baume degree of 52°Be, the chemical composition of the inorganic fluid is composed of Na2O and SiO2, the molar ratio of the two is 1:6, and the balance is water; the sand core coating includes 15% by weight of aggregate, the balance is the inorganic fluid, and the aggregate is refractory clay; the inorganic fluid and aggregate of the above proportion are put into a stirring barrel and stirred until the two are fully fused to obtain the sand core coating, and then the sand core coating is evenly applied to the surface of the spare sand core piece, the application thickness of the sand core coating is 0.5mm, the flexural strength of the spare sand core piece at 200°C is 42MPa, and the collapse temperature of the spare sand core piece is 380°C;

[0067] Step S3, placing the spare sand core piece in a drying furnace at 220°C, drying for 120 minutes and then taking it out of the oven, and after the drying is completed, placing the spare sand core piece in the cavity of the liquid forging mold and fixing it, the position of the spare sand core piece corresponds to the position of the inner cavity of the workpiece, and then closing the liquid forging mold;

[0068] Step S4, casting aluminum alloy liquid on the liquid forging die, using the injection mechanism of the liquid die forging machine to push the aluminum alloy liquid to fill the cavity, the aluminum alloy liquid wraps the spare sand core part and stays for 3 seconds, after the aluminum alloy liquid forms a solidified shell on the surface of the spare sand core part, continue to perform step-by-step pressure liquid forging on the solidified shell to obtain a liquid forging part, in this embodiment, the step-by-step pressure liquid forging is provided with four pressure liquid forgings, including light pressure liquid forging, two medium pressure liquid forgings and heavy pressure liquid forging, the two medium pressure liquid forgings are respectively the first medium pressure liquid forging and the second medium pressure liquid forging, the pressure of the light pressure liquid forging is 5MPa, and the pressure holding time is 10 seconds; the pressure of the first medium pressure liquid forging is 12MPa, and the pressure holding time is 12 seconds; the pressure of the second medium pressure liquid forging is 30MPa, and the pressure holding time is 10 seconds; the pressure of the heavy pressure liquid forging is 60MPa, and the pressure holding time is 120S;

[0069] Step S5, open the mold, take out the liquid forging with the sand core, place it on a vibrating sand-dropping machine for vibration, break the sand core, and make the sand core flow out of the cavity of the liquid forging to obtain a complex inner cavity aluminum alloy liquid die forging with a smooth inner cavity.

[0070] Comparative Example 1

[0071] The difference between this comparative example and Example 1 is that the chemical composition of the inorganic fluid in the sand core coating of this comparative example consists of Na2O and SiO2, and the molar ratio of the two is 1:2. The rest is the same as Example 1.

[0072] Comparative Example 2

[0073] The difference between this comparative example and Example 1 is that the chemical composition of the inorganic fluid in the sand core coating of this comparative example consists of Na2O and SiO2, and the molar ratio of the two is 1:7. The rest is the same as Example 1.

[0074] Comparative Example 3

[0075] The difference between this comparative example and Example 1 is that the aggregate of the sand core of this comparative example is a mixture of limestone and talcum powder, the mass ratio of the limestone to the talcum powder is 2:1, and the rest is the same as Example 1.

[0076] Comparative Example 4

[0077] The difference between this comparative example and Example 1 is that the aggregate of the sand core of this comparative example is a mixture of limestone and talcum powder, the mass ratio of the limestone to the talcum powder is 1:6, and the rest is the same as Example 1.

[0078] In order to test the performance of the core sand and the sand core coating, on the basis of Example 1, the specific component parameters of Examples 1-4 are modified, or are less than or greater than the optimal parameters of the present invention, and the sand core and sand core materials obtained by the component parameters of Comparative Examples 1-4 are trial-produced, and Table 1 is obtained:

[0079]

[0080] From the above table, we can see that:

[0081] The sand cores of Examples 1-3 can be effectively formed, and the coating has good coating properties, strong adhesion, and good crusting ability. It can be evenly coated on the sand core and prevent the aluminum alloy liquid from infiltrating. The complex inner cavity of the obtained aluminum alloy liquid forging is smooth and has no sand sticking phenomenon.

[0082] The sand core of the coating comparison example 1 will not be crushed during the pressurized liquid forging process, but it will fall off and produce inclusions; the coating of the sand core of the comparative example 2 is difficult to be coated on the sand core, and it needs to be thickened and repeatedly coated to adhere to the surface of the sand core, resulting in too thick a coating and pores in the workpiece; the sand core of the comparative example 3 will be crushed as the pressure increases during the pressurized liquid forging process, resulting in inclusion defects and Huaxue sand sticking in the workpiece; although the sand core of the comparative example 4 will not be crushed, it is impossible to vibrate the sand off the workpiece;

[0083] In summary, when the molar ratio of Na2O and SiO2 in the carrier inorganic fluid of the sand core coating is less than 1:3, the adhesion between the sand core and the sand core coating is not strong enough, resulting in the sand core falling off during the pressurized liquid forging process. When the molar ratio of Na2O and SiO2 in the inorganic fluid is greater than 1:6, the sand core coating will not be easy to apply on the sand core, resulting in excessive coating thickness, which will cause porosity defects in the workpiece. Therefore, the molar ratio of Na2O and SiO2 is controlled within the range of 1: (3-6), and the effect of the sand core coating can be optimized.

[0084] For the aggregate composition of the sand core, when the mass ratio of limestone to talcum powder is greater than 1:1, the sand core will be crushed when the pressure increases, resulting in inclusion defects and chemical bonding; when the mass ratio of limestone to talcum powder is less than 1:5, although the sand core will not be crushed, the sand cannot be vibrated out of the workpiece. Therefore, when the mass ratio of limestone to talcum powder is within the range of 1: (1-5), the effect of the sand core can be optimized.

[0085] Comparative Example 5

[0086] The difference between this comparative example and Example 1 is that the Na2O in the carrier inorganic fluid of the sand core coating of this comparative example is replaced by calcium oxide, and the same preparation method as Example 1 is adopted, and a solution cannot be formed.

[0087] Comparative Example 6

[0088] The difference between this comparative example and Example 1 is that the SiO2 in the sand core coating of this comparative example is replaced by other oxides, such as iron oxide, and the same preparation method as Example 1 is adopted, and a solution cannot be formed.

[0089] Comparative Example 7

[0090] The difference between this comparative example and Example 1 is that the 2123 resin in this comparative example is replaced by other commercially available resins, such as 2403 resin, both of which are thermoplastic resins, but their bonding strength and high temperature resistance are insufficient and they are crushed during use.

[0091] Comparative Example 8

[0092] The difference between this comparative example and Example 1 is that in this comparative example, the sand core coating is replaced with other commercially available alcohol-based talcum powder coating, resulting in coating peeling and severe sand adhesion.

[0093] Performance Testing

[0094] The samples of Examples 1-3 and Comparative Examples 1-8 were respectively tested for the immediate room temperature flexural strength of the sand core, and the room temperature flexural strength, 200°C flexural strength and collapse temperature after standing for 1 hour, and the testing method was the method of GBT / 4741. Specific data are shown in Table 2

[0095]

[0096] From the above table we can know:

[0097] The materials and material composition ratios of the sand cores and sand core coatings of Examples 1-3 are all within the preferred range values ​​of the present invention. Therefore, the strength of the core sand and the core sand coating meets the requirements of the present invention, that is, the room temperature flexural strength of the sand core immediately after molding is ≥1.2MPa, and the room temperature flexural strength after one hour is ≥3MPa. The flexural strength of the spare sand core parts coated with the sand core coating at 200°C is ≥23MPa, and the collapse temperature of the spare sand core parts is ≤400°C.

[0098] Comparative Examples 5 and 6 cannot form solutions, that is, they cannot prepare corresponding sand core coatings, so there is no need to test them;

[0099] Comparative Examples 7 and 8 both fail to meet the requirement of 200° C. bending strength, and thus may cause problems such as crushing and sand sticking, which do not meet the requirements.

[0100] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A liquid die forging method for a complex inner cavity aluminum alloy part, characterized in that: include: Step S1, preparing a sand core, and making the sand core into a spare sand core piece adapted to the inner cavity of the workpiece; Step S2, preparing a sand core coating, and evenly applying the sand core coating to the surface of the spare sand core piece, wherein the carrier of the sand core coating is an inorganic fluid with a Baume degree of 35-52° Be, the chemical composition of the inorganic fluid is composed of Na2O and SiO2, the molar ratio of the two is 1: (3-6), and the balance is water; the sand core coating includes 2-15% by weight of aggregate, the balance is the inorganic fluid, and the aggregate of the sand core coating is refractory clay; Step S3, drying the spare sand core piece, and after drying, placing the spare sand core piece into the cavity of the liquid forging mold and fixing it, wherein the position of the spare sand core piece corresponds to the position of the inner cavity of the workpiece, and then closing the liquid forging mold; Step S4, casting aluminum alloy liquid into the liquid forging die, so that the aluminum alloy liquid fills the mold cavity and wraps the spare sand core piece, and after the aluminum alloy liquid forms a solidified shell on the surface of the spare sand core piece, continuing to perform step-by-step pressurized liquid forging on the solidified shell to obtain a liquid forging; Step S5, opening the mold, taking out the liquid forging with the sand core, breaking the sand core, and making the sand core flow out of the cavity of the liquid forging to obtain a complex inner cavity aluminum alloy liquid die forging with a smooth inner cavity.

2. The liquid die forging method for a complex inner cavity aluminum alloy part according to claim 1, characterized in that: The sand core comprises a binder accounting for 10-20% by weight and an aggregate accounting for 80-90% by weight, wherein the binder is 2123 resin, the aggregate of the sand core is a mixture of limestone and talcum powder, the mass ratio of the limestone to the talcum powder is 1:(1-5), and the molding instant room temperature flexural strength of the sand core is ≥1.2MPa, and the room temperature flexural strength after one hour is ≥3MPa.

3. The liquid die forging method for a complex inner cavity aluminum alloy part according to claim 1, characterized in that: In the step S2, the coating thickness of the sand core coating is 0.2-0.5 mm, the bending strength of the spare sand core piece at 200°C is ≥23 MPa, and the collapse temperature of the spare sand core piece is ≤400°C.

4. The liquid die forging method for a complex inner cavity aluminum alloy part according to claim 1, characterized in that: The drying temperature of step S3 is controlled at 150-220° C., and the drying time is 30-120 min.

5. The liquid die forging method for a complex inner cavity aluminum alloy part according to claim 1, characterized in that: The step-by-step pressurized liquid forging in step S4 includes light-pressure liquid forging and heavy-pressure liquid forging. The pressure of the light-pressure liquid forging is 3-5 MPa, and the pressure holding time is 1-10 seconds. The pressure of the heavy-pressure liquid forging is 30-60 MPa, and the pressure holding time is 15-120 seconds.

6. The liquid die forging method for a complex inner cavity aluminum alloy part according to claim 5, characterized in that: The step-by-step pressurized liquid forging in step S4 includes light pressure liquid forging and heavy pressure liquid forging. The pressure of the light pressure liquid forging is 3-5 MPa, and the pressure is maintained for 1-5 seconds; the pressure of the heavy pressure liquid forging is 30-50 MPa, and the pressure is maintained for 15-60 seconds.

7. The liquid die forging method for a complex inner cavity aluminum alloy part according to claim 5, characterized in that: The step-pressure liquid forging in step S4 also includes medium-pressure liquid forging, wherein the pressure of the medium-pressure liquid forging is 6-30 MPa and the pressure holding time is 2-15 seconds.

8. The liquid die forging method for a complex inner cavity aluminum alloy part according to claim 7, characterized in that: The step-by-step pressurized liquid forging in step S4 includes light pressure liquid forging, medium pressure liquid forging and heavy pressure liquid forging. The pressure of the light pressure liquid forging is 3-5MPa, and the pressure is maintained for 3-8 seconds; the pressure of the medium pressure liquid forging is 6-10MPa, and the pressure is maintained for 2-5 seconds; the pressure of the heavy pressure liquid forging is 30-60MPa, and the pressure is maintained for 20-40 seconds.

9. The liquid die forging method for a complex inner cavity aluminum alloy part according to claim 7, characterized in that: The step-by-step pressurized liquid forging in step S4 includes light pressure liquid forging, two medium pressure liquid forgings and heavy pressure liquid forging, wherein the two medium pressure liquid forgings are the first medium pressure liquid forging and the second medium pressure liquid forging, respectively. The pressure of the light pressure liquid forging is 3-5MPa, and the pressure holding time is 3-10 seconds; the pressure of the first medium pressure liquid forging is 6-12MPa, and the pressure holding time is 5-15 seconds; the pressure of the second medium pressure liquid forging is 15-30MPa, and the pressure holding time is 5-10 seconds; the pressure of the heavy pressure liquid forging is 30-60MPa, and the pressure holding time is 30-120 seconds.

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