Method for reducing micro porosity in secondary aluminum alloys and investment casting method

Abstract

The present application relates to the technical field of investment casting, in particular to a method for reducing micro porosity of secondary aluminum alloy and an investment casting method. The method for reducing micro porosity of secondary aluminum alloy comprises the following steps: pouring secondary aluminum alloy liquid into a mold shell, cooling and solidifying after pouring to obtain a casting; pressurizing a pouring chamber where the mold shell is located at the beginning of pouring until the metal liquid is cooled to 400 DEG C and the pressurizing is stopped; in the pressurizing, a pressure is applied to make the initial pressure P0 of the pouring chamber 1.2-4 times of the standard atmospheric pressure. In the method, a certain pressure is applied during the pouring of the secondary aluminum alloy liquid, which can greatly reduce the micro porosity on the surface and inside of the secondary aluminum alloy casting and greatly improve the yield of the casting.

Description

Technical Field

[0001] This invention relates to the field of investment casting technology, and in particular to a method for reducing microporousness in di-series aluminum alloys and an investment casting method. Background Technology

[0002] Diaryl aluminum alloys (Al-Cu series) are widely used in the manufacture of high-strength components in aerospace, automotive, and other fields due to their excellent mechanical properties and heat resistance. However, during the casting process, due to the wide crystallization temperature range of diaryl aluminum alloys, they are prone to forming a paste-like solidification. The pre-formed solid dendrites divide the residual liquid metal into multiple isolated small regions, leading to the formation of tiny pores between grains during crystallization. This ultimately results in microporosity, severely affecting the integrity and mechanical properties of the casting, shortening its service life, and even causing it to be scrapped. Therefore, how to effectively control microporosity defects in the casting process of diaryl aluminum alloys has always been a key technical problem that urgently needs to be solved in the casting and related fields.

[0003] Chinese patent application CN105728654A describes a process for reducing surface microporosity in dihedral aluminum alloy castings through dispersed casting, cold shell casting, and forced cooling. However, this process is cumbersome and costly; furthermore, it only addresses surface microporosity and cannot eliminate microporosity within the casting.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for reducing the micro porosity of binary aluminum alloys and an investment casting method. In the process of casting binary aluminum alloys, this invention applies a certain pressure to significantly reduce the micro porosity of binary aluminum alloys, which can greatly improve the yield of castings.

[0006] To achieve the above-mentioned objective of the present invention, the first aspect of the present invention provides a method for reducing the micro porosity of a binary aluminum alloy, comprising the following steps: pouring molten binary aluminum alloy into a mold shell, and cooling and solidifying the casting after pouring to obtain a casting. At the start of pouring, the pouring chamber containing the mold shell is pressurized until the molten metal cools down to 400°C and then the pressurization is stopped. During the pressurization process, pressure is applied so that the initial pressure P0 of the casting chamber is 1.2 to 4 times the standard atmospheric pressure.

[0007] In a specific embodiment of the present invention, the initial pressure P0, the contour dimension X of the casting, and the thickness W of the casting satisfy the following: When the outline dimension X of the casting is less than 1m or the thickness W of the casting is less than 10mm, the initial pressure P0 satisfies: 1.2P s≤P0<1.5P s ; When the outline dimension of the casting is 1m ≤ X < 5m or the thickness of the casting is 10mm ≤ W < 100mm, the initial pressure P0 satisfies: 1.5P s ≤P0<2P s ; When the outline dimension X of the casting is ≥ 5m or the thickness W of the casting is ≥ 100mm, the initial pressure P0 satisfies: 2P s ≤P0≤4P s ; Among them, P s Standard atmospheric pressure.

[0008] In a specific embodiment of the present invention, during the pressurization, in addition to the initial pressure P0, the remaining pressure P in the casting chamber increases as the superheat ΔT of the molten metal decreases.

[0009] In a specific embodiment of the present invention, the remaining pressure P in the casting chamber and the superheat ΔT of the molten metal satisfy the following equation: P = k / ΔT + C; where k = 5 × 10⁻⁶. 4 ~6×10 6 C represents the initial pressure P0.

[0010] The second aspect of the present invention provides a method for investment casting of a binary aluminum alloy, including the method for reducing the micro porosity of the binary aluminum alloy provided in the first aspect of the present invention.

[0011] In a specific embodiment of the present invention, a three-dimensional modeling software is used to perform structural analysis on the structure of the casting to be formed, and the outline dimension X of the casting to be formed is obtained.

[0012] In a specific embodiment of the present invention, a wax model is prepared according to the structure of the casting to be formed, and the wax models are combined to obtain a wax model assembly; the wax model assembly is used to make a shell to obtain a mold shell; and the mold shell is used for casting.

[0013] In a specific embodiment of the present invention, the binary aluminum alloy includes at least one of ZL201, ZL201A, ZL205, ZL205A and ZL208.

[0014] In a specific embodiment of the present invention, the pouring temperature of the molten aluminum alloy is 700-720°C.

[0015] In a specific embodiment of the present invention, the temperature of the mold shell is 200–350°C.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: In the method of this invention, applying a certain pressure during the pouring of molten aluminum alloy significantly reduces the microporousness on the surface and inside of the aluminum alloy casting, greatly improving the casting yield. Furthermore, the method of this invention is simple and easy to operate, not only with low production costs but also improving the first-pass yield of castings. In addition, the method of this invention is highly adaptable to aluminum alloy castings. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 The DR test results are for the casting obtained in Example 1 of this invention. Figure 2 The DR test results are for the casting prepared in Comparative Example 1 of this invention. Figure 3 The DR test results are for the casting prepared in Comparative Example 2 of this invention. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0020] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0021] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] The first aspect of the present invention provides a method for reducing the micro porosity of a binary aluminum alloy, comprising the following steps: pouring molten binary aluminum alloy into a mold shell, and cooling and solidifying the molten alloy after pouring to obtain a casting; At the start of pouring, the pouring chamber containing the mold shell is pressurized until the molten metal cools down to 400°C and then the pressurization is stopped. During pressurization, pressure is applied to make the initial pressure P0 of the casting chamber 1.2 to 4 times the standard atmospheric pressure.

[0023] In the method of the present invention, applying a certain pressure during the pouring process of the molten aluminum alloy can significantly reduce the micro porosity on the surface and inside of the aluminum alloy casting, thereby greatly improving the yield of the casting.

[0024] In different implementations, during pressurization, a certain pressure is applied so that the initial pressure P0 of the casting chamber is within the range of 1.2 times, 1.4 times, 1.5 times, 1.8 times, 2 times, 2.5 times, 3 times, 3.5 times, 4 times, or any combination thereof. During solidification, the dendritic network in the mushy region generates significant resistance; under low pressure, the molten metal cannot overcome this resistance to compensate for shrinkage cavities and porosity. By adjusting the initial pressure P0 to meet the above conditions, these dendritic channels can be "forcibly opened," forcing the molten metal into the shrinkage cavity region, achieving forced feeding, while ensuring the elimination of micro-porosity in the casting and avoiding damage to the container and waste of resources.

[0025] Furthermore, in the method of the present invention, pressure is applied throughout the entire process from the start of casting until the molten metal cools to 400°C, which is beneficial for the molten metal to fully fill each micro-region during the casting and solidification process; and at the end of solidification, the continuous pressure will squeeze the residual liquid structure that has not yet fully solidified, causing the dendrites to move closer to each other and avoiding the formation of looseness.

[0026] In a specific embodiment of the present invention, the initial pressure P0, the contour dimension X of the casting, and the thickness W of the casting satisfy the following: When the casting's outline dimension X < 1m or the casting's thickness W < 10mm, the initial pressure P0 satisfies: 1.2P s≤P0<1.5P s ; When the outline dimension of the casting is 1m ≤ X < 5m or the thickness of the casting is 10mm ≤ W < 100mm, the initial pressure P0 satisfies: 1.5P s ≤P0<2P s ; When the outline dimension X of the casting is ≥ 5m or the thickness W of the casting is ≥ 100mm, the initial pressure P0 satisfies: 2P s ≤P0≤4P s ; Among them, P s Standard atmospheric pressure.

[0027] This invention adjusts the applied pressure based on the casting's outline dimensions and thickness. Specifically, when the casting's outline dimensions are small or its thickness is thin, the applied pressure is adjusted to keep the initial pressure P0 in the pouring chamber relatively small, such as 1.2P. s 1.25P s 1.3P s 1.35P s 1.4P s 1.45P s 1.49P s This range, or any combination of both, ensures stable filling of the molten metal and eliminates microporous structures, while avoiding other defects caused by excessive pressure and reducing the requirements for containers, etc. When the casting's outline dimensions or thickness increase, the applied pressure is adjusted to relatively increase the initial pressure P0 of the pouring chamber, such as to 1.5P. s 1.55P s 1.6P s 1.65P s 1.7P s 1.75P s 1.8P s 1.85P s 1.9P s 1.95P s 1.99P s Or a range consisting of any two of these conditions, under which the molten metal can complete filling of a longer distance with greater flow resistance before cooling and solidification, and the filling time can be shortened, the temperature drop during the filling process reduced, and good fluidity maintained. When the outline dimensions of the casting further increase or the thickness of the casting further increases, the applied pressure is adjusted to further increase the initial pressure P0 of the pouring chamber, such as 2P. s 2.2P s 2.5P s 2.8P s 3Ps 3.2P s 3.5P s 3.8P s 4P s Or a range consisting of any two of them.

[0028] In a specific embodiment of the present invention, during pressurization, apart from the initial pressure P0, the remaining pressure P in the casting chamber increases as the superheat ΔT of the molten metal decreases.

[0029] The superheat ΔT of the molten metal refers to the difference between the actual temperature of the molten aluminum alloy and the liquidus temperature. As pouring proceeds, the actual temperature of the molten metal changes, and the superheat ΔT changes accordingly.

[0030] In a specific embodiment of the present invention, the remaining pressure P in the casting chamber and the superheat ΔT of the molten metal satisfy the following equation: P = k / ΔT + C; where k = 5 × 10⁻⁶. 4 ~6×10 6 C represents the initial pressure P0. The unit of the molten metal superheat ΔT is °C, the unit of C is Pa, and the unit of P is Pa. When calculating the remaining pressure P, the values ​​of ΔT in °C and C in Pa are used.

[0031] k is a process parameter, positively correlated with flow channel resistance and casting complexity. An ideal filling speed is preset through simulation or experience. Based on equipment parameters and the flow channel, the theoretical pressure required to achieve the preset filling speed is calculated using conventional simulation. A suitable k is obtained based on the difference between the theoretical pressure and the initial pressure. The inventors discovered in their research that when k is controlled within 5 × 10... 4 ~6×10 6 This is more conducive to balancing the filling speed and reducing the porosity of the casting. Specifically, k can be 5×10 4 6×10 4 7×10 4 8×10 4 9×10 4 1×10 5 2×10 5 5×10 5 8×10 5 1×10 6 2×10 6 4×10 6 5×10 6 6×10 6 Or any value between any two of its endpoints, preferably 5 × 10 6 ~6×10 6 .

[0032] In a specific embodiment of the present invention, pressurizing the casting chamber includes introducing argon and / or nitrogen into the casting chamber.

[0033] In a specific embodiment of the present invention, the casting chamber includes a housing, a crucible, a resistance heating wire, and a lid. The housing is used to hold the mold shell, and the lid is movably connected to the housing to open or close the casting chamber. The crucible is used to store molten metal, and the resistance heating wire heats the crucible. Further, it includes a gas inlet and a gas outlet disposed on the side wall of the housing, with a positive pressure source and a negative pressure source externally connected to the gas inlet and outlet, respectively. Gas is injected into or drawn out of the casting chamber through the positive pressure source and / or the negative pressure source to regulate the pressure within the casting chamber. Specifically, the pressure can be regulated using conventional components such as solenoid valves. The positive pressure source may include an argon gas cylinder.

[0034] The second aspect of the present invention provides a method for investment casting of a binary aluminum alloy, including the method for reducing the micro porosity of the binary aluminum alloy provided in the first aspect of the present invention.

[0035] In the investment casting method of the present invention, the preparation of the wax pattern and the mold shell can be carried out according to existing processes, and the control of the pouring temperature and the cooling method after pouring can also adopt existing processes. Unless otherwise specified in the present invention, any step in the preparation process of investment casting of two-dimensional aluminum alloy castings should be understood as using a well-known and mature process in the art.

[0036] In a specific embodiment of the present invention, three-dimensional modeling software is used to perform structural analysis on the structure of the casting to be formed, and the outline dimension X of the casting to be formed is obtained.

[0037] In a specific embodiment of the present invention, a wax model is prepared according to the structure of the casting to be formed, and the wax models are combined to obtain a wax model assembly; the wax model assembly is used to make a shell to obtain a mold shell; and the mold shell is used for casting.

[0038] In a specific embodiment of the present invention, the binary aluminum alloy includes at least one of ZL201, ZL201A, ZL205, ZL205A and ZL208.

[0039] In a specific embodiment of the present invention, the pouring temperature of the molten aluminum alloy is 700–720°C. Further, the temperature of the mold shell is 200–350°C.

[0040] Example 1 This embodiment provides a method for investment casting of ZL201A aluminum alloy castings, including the following steps: (1) Use three-dimensional modeling software to perform structural analysis on the structure of the casting to be formed. The corresponding contour dimension X is 391mm and the casting thickness W < 10mm.

[0041] (2) The ZL201A alloy was melted, mold shell was prepared and baked according to the conventional process of degassing after refining. The mold shell preparation and baking were carried out with reference to the method of improving the porosity of large thin-walled cylindrical castings in investment casting (Example 1 in CN 116117078 A).

[0042] (3) Connect an argon gas cylinder to the casting chamber containing the mold shell, then ventilate the casting chamber to preheat the mold shell to 350°C, and control the initial pressure of the casting chamber to 1.35 × 10⁻⁶. 5 Pa, pour the metal liquid at 720℃ into the mold shell, and set k=5.7×10 6 According to P=5.7×10 6 / ΔT+1.35×10 5 Pressurize the casting chamber until the molten metal cools to 400°C; stop pressurizing and restore the pressure in the casting chamber to atmospheric pressure through the gas outlet. Remove the mold shell and clean the shell using water pressure. Cut the cleaned casting and use a DR (Digital Radiography) to observe the porosity of the casting. Figure 1 As shown in the figure, there is no microporous structure in the casting.

[0043] Example 2 This embodiment refers to the method of embodiment 1, the only difference being that the outline dimension X of the casting is different in step (1) and the initial pressure of the pouring chamber is different in step (3).

[0044] In this embodiment, the outline dimension X of the casting in step (1) is 1260mm; the initial pressure of the pouring chamber in step (3) is controlled to be 1.75×10 5 Pa.

[0045] Example 3 This embodiment refers to the method of embodiment 1, the only difference being that the outline dimension X of the casting is different in step (1) and the initial pressure of the pouring chamber is different in step (3).

[0046] In this embodiment, the outline dimension X of the casting in step (1) is 5260mm; the initial pressure of the pouring chamber in step (3) is controlled to be 3.0×10. 5 Pa.

[0047] Example 4 This embodiment refers to the method of embodiment 1, the only difference being that the initial pressure of the casting chamber in step (3) is different.

[0048] In this embodiment, the initial pressure of the casting chamber in step (3) is controlled to be 1.22 × 10⁻⁶. 5 Pa.

[0049] Example 5 This embodiment refers to the method of embodiment 1, the only difference being that the initial pressure of the casting chamber in step (3) is different.

[0050] In this embodiment, the initial pressure of the casting chamber in step (3) is controlled to be 1.51 × 10⁻⁶. 5 Pa.

[0051] Example 6 This embodiment refers to the method of embodiment 1, the only difference being that the value of k is different in step (3).

[0052] In this embodiment, k is set to 5 × 10 4 According to P=5×10 4 / ΔT+1.35×10 5 Pressurize the casting chamber.

[0053] Example 7 This embodiment refers to the method of embodiment 1, the only difference being that the value of k is different in step (3).

[0054] In this embodiment, k is set to 6 × 10 6 According to P=6×10 6 / ΔT+1.35×10 5 Pressurize the casting chamber.

[0055] Example 8 This embodiment refers to the method of embodiment 1, the only difference being that the value of k is different in step (3).

[0056] In this embodiment, k is set to 4 × 10 4 According to P=4×10 4 / ΔT+1.35×10 5 Pressurize the casting chamber.

[0057] Example 9 This embodiment refers to the method of embodiment 1, the only difference being that the value of k is different in step (3).

[0058] In this embodiment, k is set to 6.5 × 10 6 According to P=6.5×10 6 / ΔT+1.35×10 5 Pressurize the casting chamber.

[0059] Comparative Example 1 Comparative Example 1 follows the method of Example 1, except that the pressure in the casting chamber is different in step (3).

[0060] Throughout the entire pouring and cooling process of Comparative Example 1, the pressure in the pouring chamber was 101325 Pa.

[0061] The DR inspection results of the casting obtained in Comparative Example 1 are as follows: Figure 2 As shown in the figure, microporous structures exist in the casting.

[0062] Comparative Example 2 Comparative Example 2 follows the same method as Comparative Example 1, except that the initial pressure in the casting chamber is different.

[0063] In Comparative Example 2, the initial pressure in the casting chamber during the entire pouring and cooling process was 1.1 × 10⁻⁶. 5 Pa.

[0064] The DR inspection results of the casting obtained in Comparative Example 2 are as follows: Figure 3 As shown in the figure, microporous structures exist in the casting.

[0065] Experimental Example The castings obtained from different embodiments and comparative examples were tested for metallurgical quality and mechanical properties in accordance with the HB963-2005 standard. The test results are shown in Table 1.

[0066] Table 1 Test results of different castings

[0067] The test results above show that, in the method of the present invention, applying a certain pressure during the pouring of the molten aluminum alloy can significantly reduce the microporousness on the surface and inside of the aluminum alloy casting, thereby greatly improving the yield of the casting. Furthermore, the method of the present invention is simple and easy to operate, not only with low production costs but also by improving the first-pass yield of the casting.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for investment casting of di-series aluminum alloys, characterized in that, The process includes the following steps: pouring molten aluminum alloy into a mold shell, cooling and solidifying the poured metal after pouring to obtain a casting; the temperature of the mold shell is 200-350℃. At the start of pouring, the pouring chamber containing the mold shell is pressurized until the molten metal cools down to 400°C and then the pressurization is stopped. During the pressurization process, pressure is applied so that the initial pressure P0 of the casting chamber is 1.2 to 4 times the standard atmospheric pressure. The initial pressure P0, the contour dimension X of the casting, and the thickness W of the casting satisfy the following: When the outline dimension X of the casting is less than 1m or the thickness W of the casting is less than 10mm, the initial pressure P0 satisfies: 1.2P s ≤P0<1.5P s ; When the outline dimension of the casting is 1m ≤ X < 5m or the thickness of the casting is 10mm ≤ W < 100mm, the initial pressure P0 satisfies: 1.5P s ≤P0<2P s ; When the outline dimension X of the casting is ≥ 5m or the thickness W of the casting is ≥ 100mm, the initial pressure P0 satisfies: 2P s ≤P0≤4P s ; Among them, P s Standard atmospheric pressure; During the pressurization, except for the initial pressure P0, the remaining pressure P in the casting chamber increases as the superheat ΔT of the molten metal decreases. The remaining pressure P in the casting chamber and the superheat ΔT of the molten metal satisfy the following equation: P = k / ΔT + C; where k = 5 × 10⁻⁶. 4 ~6×10 6 C represents the initial pressure P0.

2. The method according to claim 1, characterized in that, The structure of the casting to be formed is analyzed using 3D modeling software to obtain the outline dimension X of the casting to be formed.

3. The method according to claim 2, characterized in that, A wax model is prepared according to the structure of the casting to be formed, and the wax models are combined to obtain a wax model assembly; the wax model assembly is used to make a shell to obtain a mold shell; the mold shell is used for casting.

4. The method according to claim 1, characterized in that, The binary aluminum alloy includes at least one of ZL201, ZL201A, ZL205, ZL205A and ZL208.

5. The method according to claim 3, characterized in that, During the casting process, the casting temperature of the molten aluminum alloy is 700–720°C.

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