Eccentric thin-wall structural part, forming cavity combined structure and preparation method

Abstract

The invention relates to the technical field of aluminum-based composite materials, in particular to an eccentric thin-wall structural part, a forming cavity combined structure and a preparation method. The structural member is prepared by the preparation method. The preparation method comprises the following steps: building a forming cavity combined structure; a release agent is sprayed to the inner wall face of the forming cavity; the aluminum alloy powder with the target component proportion is filled into the forming cavity in batches, and a blank is obtained through cold pressing in passes; wherein the aluminum alloy powder comprises a reinforcing phase with the mass percentage of 40%-70%; performing hot pressing sintering treatment to obtain a pre-finished product; and the forming cavity is disassembled, a pre-finished product is taken out, and the eccentric thin-wall structural part is obtained through aftertreatment. According to the method, the eccentric thin-wall structural part with high tensile strength can be obtained, the material utilization rate can be greatly increased, the machining time and the machining cost are remarkably reduced, the problem that cracks and even breakage occur due to the fact that stress concentration is likely to be generated during blank demolding is solved, and the problems that the machining allowance is large and the machining difficulty is large are solved.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum-based composite materials, and in particular to an eccentric thin-walled structural part, a molding cavity combined structure and a preparation method. Background Art

[0002] Aluminum-based composites have been widely used in aerospace, automobile manufacturing, engineering structures and other fields due to their high specific strength, high specific stiffness and excellent corrosion resistance. However, the traditional method of preparing aluminum-based composites has many challenges in achieving high-content reinforced phase aluminum-based composites, especially for the preparation of eccentric thin-walled structural parts, which faces problems such as difficult preparation process and high processing cost.

[0003] At present, the traditional methods for preparing aluminum-based composite materials generally include stirring casting, powder metallurgy, and methods of preparing ingots first and then machining. Among them, the stirring casting method has the problem of reinforcement phase sedimentation. Especially when preparing aluminum-based composite materials with high volume fraction reinforcement phases, the reinforcement phase is difficult to be evenly distributed in the matrix, resulting in unstable material properties and even affecting the service life and reliability of the final product. Compared with the stirring casting method, the powder metallurgy method can achieve a uniform distribution of 70% reinforcement phases in aluminum-based composite materials, thereby effectively improving the mechanical properties, wear resistance and high temperature performance of the material. However, for eccentric thin-walled structural parts (height of 150-300mm, wall thickness of 3-10mm, inner diameter of the hollow part of 100-200mm, length and width of the eccentric part of 100-160mm), the powder metallurgy method is prone to stress concentration and cracks or even breakage when the blank is demolded due to the high height and thin wall thickness of the cold-pressed blank. The method of first preparing the ingot and then machining it, that is, first using a cylindrical cavity to prepare the ingot and then machining it, has problems such as large processing allowance and great processing difficulty. Especially for eccentric thin-walled structural parts with high ceramic content, the processing allowance and processing difficulty are doubled, thereby greatly increasing the processing cost.

[0004] In summary, it is necessary to develop an eccentric thin-walled structural part, a molding cavity combination structure and a preparation method to solve the problems existing in the existing powder metallurgy method and the method of first preparing a round ingot and then machining the molding method. Summary of the invention

[0005] The object of the present invention is to provide an eccentric thin-walled structural part, a molding cavity combined structure and a preparation method. The specific technical scheme is as follows:

[0006] In the first aspect, the present invention provides a combined molding cavity structure for an eccentric thin-walled structural part, including an upper mold detachably arranged at the upper end of a female mold, and a lower mold detachably arranged at the lower end of the female mold; a heating element is circumferentially arranged on the outer side of the female mold; a core column is coaxially arranged in the female mold, and an annular reserved gap is arranged between the two; a plurality of detachable reinforcement rib mold blocks are circumferentially arranged at intervals in the annular reserved gap, and each of the detachable reinforcement rib mold blocks is arranged on the inner wall of the female mold; the two ends of the core column are respectively interference fit with the upper mold and the lower mold; and a molding cavity is surrounded by the female mold, the upper mold, the lower mold, the core column and all the detachable reinforcement rib mold blocks.

[0007] Optionally, the spacing width between each two adjacent detachable reinforcement rib mold blocks is 3-10 mm.

[0008] Optionally, the upper mold includes a main body, a first eccentric side plate and a second eccentric side plate; the main body includes a first arc segment and a second arc segment that are integrally formed, and the two are symmetrically bent toward each other; the first eccentric side plate and the second eccentric side plate are respectively arranged on both sides of the main body, and are both connected to the arc of the main body; the corners of the first eccentric side plate away from the side of the main body are set to chamfers, and the corners of the second eccentric side plate away from the side of the main body are set to chamfers, and the arc degree of each chamfer is R7-R15.

[0009] Optionally, the height of the female mold is 300-500 mm.

[0010] In a second aspect, the present invention provides a method for preparing an eccentric thin-walled structural member, comprising:

[0011] Step S1, assembling the molding cavity assembly structure of the eccentric thin-walled structural member to form a molding cavity;

[0012] Step S2, spraying a release agent onto the inner wall surface of the molding cavity;

[0013] Step S3, after the release agent is dried, the aluminum alloy powder with the target composition ratio is filled into the molding cavity in batches, and a green body is obtained by cold pressing in stages; wherein the aluminum alloy powder includes a reinforcing phase with a mass percentage of 40%-70%;

[0014] Step S4, subjecting the green body in the molding cavity to hot pressing and sintering to obtain a pre-finished product;

[0015] Step S5, disassembling the molding cavity, taking out the pre-finished product, and obtaining a molded eccentric thin-walled structural part through post-processing.

[0016] Optionally, the aluminum alloy powder also includes the following components in percentage by mass: 25%-55% aluminum powder, 2%-4% copper powder, 1%-2% magnesium powder and 0.2%-1% zinc powder; the particle size of the aluminum powder is 10-120 μm, and the particle size of the reinforcing phase is 10-120 μm; the reinforcing phase includes at least one of silicon carbide, titanium carbide and zirconium oxide.

[0017] Optionally, the final pressing pressure used in the stepwise cold pressing is 100-200 MPa, and the holding time is 10-20 s; the cold pressing pressure of each step before the final pressing in the stepwise cold pressing is 50-100 MPa.

[0018] Optionally, the hot pressing pressure used in the hot pressing sintering process is 100-150MPa, the sintering temperature is 560-600°C, and the sintering time is 0.5-1h; the hot pressing pressure is maintained during the sintering stage until the sintering is completed; and the hot pressing sintering process is completed under an inert atmosphere.

[0019] Optionally, the post-processing includes machining; or, the post-processing includes machining and multiple heating and cooling processes.

[0020] In a third aspect, the present invention provides an eccentric thin-walled structural component, which is prepared by using the method for preparing the eccentric thin-walled structural component.

[0021] The application of the technical solution of the present invention has at least the following beneficial effects:

[0022] (1) The present invention provides a molding cavity combination structure for an eccentric thin-walled structural part, which can form a molding cavity for an eccentric thin-walled structural part, thereby solving the problems of large processing allowance and great processing difficulty in the prior art of first preparing a round ingot and then machining the molding method.

[0023] (2) The present invention provides a method for preparing an eccentric thin-walled structural part, which adopts a specific molding cavity combination structure in step S1 to form a detachable molding cavity to avoid the problem of stress concentration, cracks or even breakage when the blank is demolded; adopts step S2 to spray a mold release agent, which, on the one hand, prevents the aluminum alloy powder from reacting with the inner wall of the molding cavity during the hot pressing sintering process, and on the other hand, facilitates the demolding of the pre-finished product; adopts step S3 to limit the aluminum alloy powder to contain 40%-70% by mass of the reinforcing phase, so as to prepare an eccentric thin-walled structural part with a high content of the reinforcing phase. The wall structure part makes the prepared eccentric thin-walled structure part have high tensile strength performance; the operation mode of batch filling and step-by-step cold pressing is adopted, so that when making a blank of a certain height, a female mold that is adapted to the height of the blank can be selected, and there is no need to select a female mold that is too high, thereby reducing the cost of using the female mold; the hot pressing and sintering treatment of step S4 can accelerate the diffusion rate of low-melting-point alloy elements in the blank, so that the interface of the blank pressed in the step-by-step cold pressing stage can achieve metallurgical bonding; the molding cavity is disassembled by step S5, and the molded eccentric thin-walled structure part is obtained by post-processing. The preparation method of the present invention can not only obtain an eccentric thin-walled structure part with high tensile strength performance, but also can greatly improve the material utilization rate, and significantly reduce the processing time and processing cost.

[0024] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0026] Figure 1 is a schematic diagram of the axial cross-sectional structure of a molding cavity assembly structure of an eccentric thin-walled structural member in Example 1;

[0027] Figure 2 is a schematic diagram of a transverse cross-sectional structure of a molding cavity assembly structure of an eccentric thin-walled structural member in Example 1;

[0028] Figure 3 yes Figure 1 Schematic diagram of the structure of the middle and upper mold;

[0029] Figure 4 yes Figure 1 Schematic diagram of the structure of the middle and lower molds;

[0030] Figure 5 yes Figure 1 A schematic diagram of the structure of the detachable reinforcing rib die block;

[0031] Among them, 1. female mold, 2. upper mold, 2.1. main body, 2.2. first eccentric side plate, 2.3. second eccentric side plate, 3. lower mold, 4. core column, 5. detachable reinforcing rib mold block, 5.1. first arc block, 5.2. second arc block. DETAILED DESCRIPTION

[0032] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0033] Embodiment 1:

[0034] See also Figure 1-Figure 5 A molding cavity combination structure for an eccentric thin-walled structural part, comprising: an upper mold 2 (the material of the upper mold 2 is H13 steel) is detachably provided at the upper end of a female mold 1 (the height of the female mold 1 is 300-500 mm, specifically 500 mm can be selected; the material of the female mold 1 is H13 steel); a lower mold 3 (the lower mold 3 is annular, with a thickness of 10-20 mm; the material of the lower mold 3 is H13 steel) is detachably provided at the lower end of the female mold 1; a circumferentially provided outer side of the female mold 1 The heating element (specifically, an electric heating rod) has 8 to 12 heating elements, each of which has the same height as the female mold 1 and is arranged circumferentially and spaced in sequence on the outside of the female mold 1 and connected to a power source; a core column 4 (the core column 4 is made of H13 steel) is coaxially arranged in the female mold 1, and an annular reserved gap is arranged between the two, and the width of the annular reserved gap is 15 to 30 mm; a plurality of detachable reinforcing rib mold blocks 5 (detachable The material of the reinforcing rib mold is H13 steel or 45# steel), and each of the detachable reinforcing rib mold blocks 5 is arranged on the inner wall of the female mold 1 (specifically, a blind hole (aperture 5-10mm, hole depth 6-10mm) is arranged on each of the detachable reinforcing rib mold blocks 5, a through hole adapted to the blind hole is arranged on the female mold 1, the same internal thread structure is arranged on the inner wall surface of the blind hole and the through hole, and an H13 steel rod with an external thread structure adapted to the internal thread structure is inserted and locked in the blind hole and the through hole, so that each of the detachable reinforcing rib mold blocks 5 can be detachably fitted on the inner wall of the female mold 1); the two ends of the core column 4 are respectively interference fit with the upper mold 2 and the lower mold 3 (specifically, mounting through holes adapted to the core column 4 are arranged on the upper mold 2 and the lower mold 3); the female mold 1, the upper mold 2, the lower mold 3, the core column 4 and all the detachable reinforcing rib mold blocks 5 form a molding cavity.

[0035] See also Figure 5, the spacing width between each adjacent two detachable reinforcing rib mold blocks 5 is 10mm; the detachable reinforcing rib mold block 5 includes an integrally formed first arc block 5.1 and a second arc block 5.2, and the two are sequentially arranged in a direction away from the inner wall of the female mold 1; the size of the second arc block 5.2 is smaller than the size of the first arc block 5.1. The number, shape and setting position of the detachable reinforcing rib mold blocks 5 are determined according to the structural conditions of the eccentric thin-walled structural member. Generally, the number of the detachable reinforcing rib mold blocks 5 is 5-12.

[0036] See also Figure 3 The upper mold 2 includes a main body 2.1, a first eccentric side plate 2.2 and a second eccentric side plate 2.3; the main body 2.1 includes a first arc segment and a second arc segment formed in one piece, and the two are symmetrically bent toward each other; the first eccentric side plate 2.2 and the second eccentric side plate 2.3 are respectively arranged on both sides of the main body 2.1, and are both connected to the main body 2.1 in an arc; each corner of the first eccentric side plate 2.2 away from the main body 2.1 is set as a chamfer, and each corner of the second eccentric side plate 2.3 away from the main body 2.1 is set as a chamfer, and the arc degree of each chamfer is R7-R15 (radius unit is mm). The chamfer structure with arc connection and specific arc degree is convenient for demoulding of pre-finished products.

[0037] A method for preparing an eccentric thin-walled structural part, comprising:

[0038] Step S1, assembling the molding cavity assembly structure of the eccentric thin-walled structural member to form a molding cavity;

[0039] Step S2, spraying a release agent (specifically graphite) onto the inner wall surface of the molding cavity, with a spraying thickness of 1-3 mm, on the one hand to prevent the aluminum alloy powder from reacting with the inner wall of the molding cavity during the hot pressing sintering process, and on the other hand to facilitate demolding of the pre-finished product;

[0040] Step S3, after the release agent is dried, the aluminum alloy powder with the target composition ratio is filled into the molding cavity in batches, and a green body is obtained by cold pressing in stages. The operation mode of batch filling and cold pressing in stages is adopted, so that when a green body of a certain height is produced, a female mold 1 that is adapted to the height of the green body can be selected, and there is no need to select a female mold 1 that is too high, thereby reducing the use cost of the female mold 1; wherein the aluminum alloy powder includes a reinforcing phase with a mass percentage of 48%;

[0041] Step S4, subjecting the green body in the molding cavity to hot pressing and sintering to obtain a pre-finished product;

[0042] Step S5, disassembling the molding cavity, taking out the pre-finished product, and obtaining a molded eccentric thin-walled structural part through post-processing.

[0043] The aluminum alloy powder also includes the following components in percentage by mass: 45% aluminum powder, 4% copper powder, 2% magnesium powder and 1% zinc powder; the particle size of the aluminum powder is 10-120 μm (the D50 particle size of the aluminum powder is 30 μm), the particle size of the reinforcing phase is 10-120 μm (the D50 particle size of the reinforcing phase is 70 μm); the reinforcing phase is silicon carbide and titanium carbide, and the mass ratio of silicon carbide to titanium carbide is 5:1. The aluminum alloy powder with a specific composition ratio is convenient for preparing an eccentric thin-walled structural part with a dense structure.

[0044] The final pressing pressure used in the step-by-step cold pressing (a total of 4 steps) is 200MPa, and the holding time is 20s; the cold pressing pressure of each step before the final pressing in the step-by-step cold pressing is 50MPa, and no holding time is required. With the step-by-step cold pressing, the cold pressing pressure of each step before the final pressing is relatively low, so that the density of the green body is relatively low. Under the high pressure of the final pressing, the powders at the interface of the green body can flow to each other, forming a complete formed green body without obvious interfaces.

[0045] The hot pressing pressure used in the hot pressing sintering process is 100MPa, the sintering temperature is 560℃, and the sintering time is 1h; the hot pressing pressure is maintained during the sintering stage until the sintering is completed; the hot pressing sintering process is completed under an inert atmosphere. Specifically, before the hot pressing sintering process, a high-temperature sheath with good airtightness is used to cover the molding cavity combination structure and the pressure head required for hot pressing for heat preservation and the introduction of inert gas; the molding cavity and the high-temperature sheath are connected, and the inert atmosphere is a nitrogen atmosphere. Nitrogen is introduced into the molding cavity and the high-temperature sheath until the dew point reaches -40℃ to ensure the high purity of the inert atmosphere, thereby avoiding oxidation of the blank during the hot pressing sintering process and improving the sintering quality of the blank. The hot pressing sintering process can accelerate the diffusion rate of low-melting-point alloy elements in the blank, so that metallurgical bonding can be achieved at the interface of the blank pressed in the cold pressing stage.

[0046] The post-processing includes machining; or, the post-processing includes machining and multiple heating and cooling. Specifically, a CNC lathe is used to process the interface between the detachable reinforcing rib mold block 5 and the pre-finished product with a width of 2-5 mm, and the detachable reinforcing rib mold block 5 is taken out by knocking; if it is difficult to take out the detachable reinforcing rib mold block 5 by knocking, the pre-finished product embedded in the detachable reinforcing rib mold block 5 is heated multiple times (the heating temperature is 200-400°C, specifically 300°C) and cooled, and the difference in thermal expansion coefficient between the aluminum-based composite material and steel is used to loosen the detachable reinforcing rib mold block 5 and then take it out.

[0047] Comparative Example 1 (preparing the ingot first and then machining it):

[0048] Different from Example 1, in step S1, the molding cavity used is a cylindrical cavity, and the inner diameter of the cylinder is the same as the diameter of the circumscribed circle of the upper mold 2; after demolding in step S5, a cylindrical blank is obtained, and an eccentric thin-walled structural part with the same appearance as Example 1 is obtained by machining.

[0049] Comparative Example 2:

[0050] Different from Comparative Example 1, the sintering temperature is 600° C. and the sintering time is 3 h.

[0051] The processing time, processing cost, material utilization rate and tensile strength data of the eccentric thin-walled structural parts with the same appearance as those of Example 1 and Comparative Examples 1-2 are shown in Table 1. The tensile strength data is obtained as follows: According to GB_T228.1-2021 Metallic Material Tensile Test Part 1: Room Temperature Test Method. In terms of processing time and processing cost data, the data of Comparative Example 1 is used as the benchmark, and the data of Example 1 and Comparative Example 2 are percentage data compared to Comparative Example 1.

[0052] Table 1 Processing time, processing cost, material utilization rate and tensile strength data

[0053]

[0054]

[0055] It can be seen from the data in Table 1 that, compared with Comparative Examples 1-2, the eccentric thin-walled structural component prepared by Example 1 of the present invention not only has high tensile strength performance, but also greatly improves material utilization, and significantly reduces processing time and processing cost.

[0056] In Comparative Example 1, the cylindrical blank is directly processed to form an eccentric thin-walled structural part, which has a large processing allowance, a very low material utilization rate, a long processing time, and a high processing cost, which is not conducive to industrial production. At the same time, compared with Example 1, the tensile strength of the eccentric thin-walled structural part prepared in Comparative Example 1 is lower. The main reason is that the cylindrical blank is heated by the heat transfer method of the mold, and the temperature is lower near the middle part of the cylindrical blank. Moreover, due to the short insulation time, the closer the cylindrical blank is to the center, the more difficult it is to reach the sintering temperature, and the metallurgical bonding at the blank interface cannot be fully achieved, resulting in lower tensile strength.

[0057] Compared with Comparative Example 1, the sintering temperature and sintering time are increased in Comparative Example 2. Although the sintering quality can be improved and the tensile strength of the eccentric thin-walled structural part can be improved, the data gap between the tensile strength of the eccentric thin-walled structural part prepared in Example 1 is large. This is mainly because the green body of Example 1 is almost a near-net-shape green body, and each part is relatively thin. After hot pressing sintering and demolding, the green body cools faster in the air, and more strengthening phases are precipitated, which has a solid solution strengthening effect on the green body, thereby significantly improving the tensile strength performance.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A molding cavity combination structure for an eccentric thin-walled structural part, characterized in that: The invention comprises an upper die (2) detachably arranged at the upper end of a female die (1), and a lower die (3) detachably arranged at the lower end of the female die (1); a heating element is circumferentially arranged on the outer side of the female die (1); a core column (4) is coaxially arranged in the female die (1), and an circumferential reserved gap is arranged between the two; a plurality of detachable reinforcing rib mold blocks (5) are circumferentially arranged at intervals in the circumferential reserved gap, and each of the detachable reinforcing rib mold blocks (5) is arranged on the inner wall of the female die (1); the two ends of the core column (4) are respectively interference-fitted with the upper die (2) and the lower die (3); and a molding cavity is surrounded by the female die (1), the upper die (2), the lower die (3), the core column (4) and all the detachable reinforcing rib mold blocks (5).

2. The molding cavity assembly structure of the eccentric thin-walled structural member according to claim 1, characterized in that: The spacing width between each two adjacent detachable reinforcing rib mold blocks (5) is 3-10 mm.

3. The molding cavity assembly structure of the eccentric thin-walled structural member according to claim 1, characterized in that: The upper mold (2) comprises a main body (2.1), a first eccentric side plate (2.2) and a second eccentric side plate (2.3); the main body (2.1) comprises a first arc segment and a second arc segment which are integrally formed and are symmetrically bent toward each other; the first eccentric side plate (2.2) and the second eccentric side plate (2.3) are respectively arranged on both sides of the main body (2.1) and are both connected to the main body (2.1) in an arc; each corner of the first eccentric side plate (2.2) away from the main body (2.1) is arranged as a chamfer, and each corner of the second eccentric side plate (2.3) away from the main body (2.1) is arranged as a chamfer, and the arc degree of each chamfer is R7-R15.

4. The molding cavity assembly structure of the eccentric thin-walled structural member according to claim 1, characterized in that: The height of the female mold (1) is 300-500 mm.

5. A method for preparing an eccentric thin-walled structural part, characterized in that: include: Step S1, assembling a molding cavity assembly structure of an eccentric thin-walled structural member as described in any one of claims 1 to 4 to form a molding cavity; Step S2, spraying a release agent onto the inner wall surface of the molding cavity; Step S3, after the release agent is dried, the aluminum alloy powder with the target composition ratio is filled into the molding cavity in batches, and a green body is obtained by cold pressing in stages; wherein the aluminum alloy powder includes a reinforcing phase with a mass percentage of 40%-70%; Step S4, subjecting the green body in the molding cavity to hot pressing and sintering to obtain a pre-finished product; Step S5, disassembling the molding cavity, taking out the pre-finished product, and obtaining a molded eccentric thin-walled structural part through post-processing.

6. The method for preparing an eccentric thin-walled structural member according to claim 5, characterized in that: The aluminum alloy powder also includes the following components in percentage by mass: 25%-55% aluminum powder, 2%-4% copper powder, 1%-2% magnesium powder and 0.2%-1% zinc powder; the particle size of the aluminum powder is 10-120 μm, and the particle size of the reinforcing phase is 10-120 μm; the reinforcing phase includes at least one of silicon carbide, titanium carbide and zirconium oxide.

7. The method for preparing an eccentric thin-walled structural member according to claim 5, characterized in that: The final pressing pressure used in the step-by-step cold pressing is 100-200 MPa, and the holding time is 10-20 s; the cold pressing pressure of each step before the final pressing in the step-by-step cold pressing is 50-100 MPa.

8. The method for preparing an eccentric thin-walled structural member according to claim 5, characterized in that: The hot pressing pressure used in the hot pressing sintering process is 100-150MPa, the sintering temperature is 560-600°C, and the sintering time is 0.5-1h; the hot pressing pressure is maintained during the sintering stage until the sintering is completed; the hot pressing sintering process is completed in an inert atmosphere.

9. The method for preparing an eccentric thin-walled structural member according to claim 5, characterized in that: The post-processing includes machining; or, the post-processing includes machining and multiple heating and cooling processes.

10. An eccentric thin-walled structural member, characterized in that: The eccentric thin-walled structural component is prepared by the preparation method of claim 5.

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