A preparation method for improving the heading load performance of hard aluminum alloy rotating sheet metal parts

Abstract

A preparation method for improving the axial load performance of a hard aluminum alloy rotary sheet metal part comprises the following steps: subjecting a circular sheet metal blank to a thickness compression deformation for energy storage at room temperature, so that the fiber grains of the blank are flattened and widened; then, subjecting the blank to a recrystallization heat treatment under double-sided compression, so that the fiber grains are broken into equiaxed fine grains; then, placing the heat-treated blank in a drawing die for plastic limit cold drawing, so that the blank is radially stretched to form a rotary body, and the equiaxed fine grains of the blank are radially elongated into elliptical fine grains; then, the oxidized rotary body is subjected to a thickness hot extrusion through an extrusion die, so that the elliptical fine grains on the annular wall of the rotary body are elongated along the side wall into axial fiber grains; finally, the rotary body is subjected to final heat treatment strengthening by heating for solid solution and quenching and cooling, and then the remaining portion of the rotary body is cut to obtain a finished rotary sheet metal part.

Description

Technical Field

[0001] The present application relates to a sheet metal manufacturing technology in the field of aircraft manufacturing, specifically a preparation method for improving the axial load performance of a hard aluminum alloy rotating sheet metal part. Background Art

[0002] It is well known that metal sheets have various anisotropic properties, and the strength, plasticity, bending and other properties of the sheet along the fiber direction are significantly better than those perpendicular to the fiber direction. The heading load performance is the performance of bearing loads mainly in tension along the flight direction. At present, various aircraft use extruded profiles for parts used in the longitudinal reinforcement structure of the fuselage, such as the long stringers of the aircraft. The reason is that the fiber structure of the extruded profile is consistent with the heading of the aircraft. Hard aluminum alloys such as domestic brand 2A12 and foreign brand 2024 have the significant advantages of light weight and high strength, and are the most widely used materials for sheet metal parts of aircraft. Processing sheet metal parts with a fiber structure consistent with the direction of the main service load is not only beneficial to aircraft weight reduction, but also can significantly increase the service life of the product.

[0003] The applicant's prior patent publication number: CN113787129A, discloses a method for improving the comprehensive mechanical properties of hard aluminum alloy sheet metal parts by means of phase transformation, deformation, and grain refinement. Since metal fibers are formed by flattening or elongating the heat-softened metal grains during hot rolling and extrusion to form a fibrous structure along the flow direction, the formation of metal fiber structure requires that the metal grains are significantly flattened or elongated, which manifests as extremely high plastic deformation on a macro scale. Conventional deformation methods can only change the ratio of longitudinal and transverse grains, so this method cannot form a product with consistent fiber structure and directional load. In particular, hard aluminum alloy rotating sheet metal parts are widely used in the nose, fuselage and other parts of fighter aircraft; the more fiber structures are produced in the parts along the directional direction, the stronger the performance of bearing tensile and bending loads along the directional direction, and the higher the safety factor of the body when the fighter aircraft performs high maneuver acceleration and bears tensile loads along the directional direction. Summary of the Invention

[0004] In order to overcome the defect of the existing technology in which the metal fiber direction of the rotating sheet metal parts cannot be consistent with the axial tensile and bending loads, which affects the service life of the product, the purpose of this application is to provide a preparation method for improving the axial load performance of the rotating sheet metal parts of the duraluminum alloy. The method forms the axial fiber structure of the rotating sheet metal parts through strong cold thick compression deformation, recrystallization heat treatment, high plasticity cold deep drawing, and strong hot thick extrusion along the axial large plastic creep.

[0005] A preparation method for improving the axial load performance of a hard aluminum alloy rotary body sheet metal part, which is characterized by the following: 1) subjecting a circular sheet metal blank to a thickness compression deformation and energy storage at room temperature, so that the thickness of the blank becomes thinner and the fiber grains of the blank are flattened and widened; 2) subjecting the blank after the thickness compression treatment to a recrystallization heat treatment under double-sided compression, so that the flattened and widened fiber grains of the blank are broken into equiaxed fine grains; 3) placing the heat-treated blank in a drawing die for plastic limit cold drawing to form the blank. The material is stretched radially to form a body of revolution, and the equiaxed fine grains of the blank are elongated radially into elliptical fine grains; 4) the body of revolution is cut off and then oxidized; 5) the oxidized body of revolution is hot extruded in the thickness direction through an extrusion die to reduce the wall thickness of the body of revolution, and the elliptical fine grains on the annular wall of the body of revolution are elongated along the side wall into fibrous grains in the longitudinal direction; 6) finally, the body of revolution is subjected to final heat treatment strengthening by heating, solution treatment and quenching and cooling, and the remaining portion of the body of revolution is cut off to obtain a finished sheet metal part of the body of revolution.

[0006] Furthermore, in step 1), the blank is repeatedly cold-rolled and extruded by rollers, so that the blank is perpendicular to the fiber direction as the main deformation direction of thinning and stretching, and the extrusion thinning rate is greater than 30% of the blank thickness.

[0007] Furthermore, in step 2), when the billet is subjected to recrystallization heat treatment in a double-sided compression state, the billet is first pressed on both sides with steel plates, and then the pressed billet is preheated in a temperature environment of 300±20°C, and then the preheated billet is kept warm in a nitrate furnace at a temperature of 420±20°C until the recrystallization ratio of the deformed grains reaches more than 80% and then naturally cooled.

[0008] Furthermore, in step 3), during deep drawing, the blank after heat treatment is mainly deformed in a direction perpendicular to the fiber direction.

[0009] Furthermore, in step 3), the working surface of the lower drawing die of the drawing die is consistent with the inner surface of the rotating sheet metal part, and when the working surfaces of the upper drawing die and the lower drawing die are in the mold closing state, the gap between the upper and lower dies is consistent with the thickness of the blank after heat treatment, and the gap is greater than the theoretical thickness of the rotating sheet metal part.

[0010] Furthermore, in step 5), during thickness extrusion, the rotating body and the lower extrusion die are heated to a temperature of 400±20°C and kept warm, and the upper extrusion die is heated to a temperature of 280±20°C.

[0011] Furthermore, in step 5), the extrusion upper die working surface of the extrusion die is consistent with the inner surface of the rotating sheet metal part, and when the extrusion upper die and the extrusion lower die working surfaces are in the mold closing state, the gap between the upper and lower dies is equal to the theoretical thickness of the rotating sheet metal part, and the extrusion upper die and the extrusion lower die working surfaces are larger than the area of the rotating sheet metal part.

[0012] Furthermore, in step 5), an annular non-working surface is provided on the outer side of the extrusion lower die and the working surface of the extrusion lower die of the extrusion die, and a heat-resistant pressure-bearing block for limiting the mold gap is provided on the annular non-working surface.

[0013] Furthermore, in step 6), when the rotating body is heated for solid solution, the rotating body is first preheated at a temperature of 300±20°C, and then transferred to a salt furnace at 494±5°C for heat preservation and solid solution.

[0014] Furthermore, in step 6), when the rotor is quenched and cooled, the rotor is first placed in a salt furnace at a temperature of 190±10° C. for pre-cooling, and then the pre-cooled rotor is placed in water at room temperature for cooling.

[0015] The beneficial effects of this application are:

[0016] The present application controls the extrusion and extension direction of the blank during the energy storage of the through-thickness compression deformation, so that the equiaxed fine grains are preferentially formed perpendicular to the fiber direction after the recrystallization treatment, and the overall cold plastic forming processability of the material during deep drawing is improved, which is conducive to a larger amount of deep drawing plastic deformation so that more material grains are radially elongated into elliptical shapes, and the number of fiber grains along the heading direction after extrusion is increased. During extrusion, the present application utilizes the high-intensity extrusion creep and easy flow characteristics of the metal in the hot state, and through through-thickness extrusion, the material is dynamically recrystallized and plastically thinned and extended along the heading direction, which can heal the micro cracks generated by deep drawing deformation, improve the material tissue density, and form more fiber grains along the heading direction. Therefore, the rotating sheet metal prepared by the preparation method of the present application not only has a high overall tissue density, but also can form a large number of fiber grains along the heading direction, which can significantly improve the performance of the sheet metal part in bearing tensile loads along the heading direction.

[0017] The present application is further described below with reference to the accompanying drawings and examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the shape of the rotating sheet metal part of this application

[0019] Figure 2 This is a schematic diagram of the energy storage principle of the thick rolling extrusion deformation of the rotating sheet metal blank of this application

[0020] Figure 3 This is a schematic diagram comparing the grain distribution of the rotating sheet metal blank before and after recrystallization heat treatment.

[0021] Figure 4 This is a schematic diagram of deep drawing of the rotating sheet metal part of this application

[0022] Figure 5 This is a schematic diagram of the grain distribution of the rotating sheet metal part after deep drawing

[0023] Figure 6This is a schematic diagram of the thickness extrusion principle of the rotary sheet metal extrusion die of this application

[0024] Explanation of the numbers in the figure: 1. Rotating sheet metal, 2. Heading, 3. Annular wall, 4. Grain, 5. Blank, 6. Roller, 7. Fiber direction, 8. Rotating body, 9. Drawing upper die, 10. Drawing lower die, 11. Extrusion lower die, 12. Extrusion upper die, 13. Annular non-working surface, 14. Pressure block. DETAILED DESCRIPTION

[0025] Refer to the attached Figure 1 To the attached Figure 6 The hard aluminum alloy rotating body sheet metal part 1 involved in this application is as follows Figure 1 As shown, it is a sheet metal part that bears a tensile load along the heading direction 2. The fibrous grains 4 around the annular wall 3 of the rotating body can significantly improve the performance of bearing tensile loads along the heading direction 2. According to the invention scheme of this application, its preparation process is as follows:

[0026] Step 1) The circular sheet metal blank 5 having a thickness greater than that of the rotating sheet metal part 1 is subjected to thickness-wise compression deformation energy storage at room temperature, so that the thickness of the blank 5 becomes thinner, and the blank fiber grains 4 are flattened and widened. The specific operation method is to use a roller 6 to repeatedly cold-roll extrude the blank 5, so that the blank 5 is perpendicular to the fiber direction 7 as the main deformation direction of thinning and extension, and the extrusion thinning rate is greater than 30% of the thickness of the blank 5. Three points need to be supplemented: First, the thickness of the circular blank 5 is greater than the thickness of the rotating sheet metal part 1, the purpose of which is to improve the compression deformation energy storage and the effect of extruding the thinning flow material along the heading 2 to form the heading fiber grains. Second, when the roller 6 is used for repeated cold-rolling extrusion, the local area of the blank 5 is continuously thinned, the force-bearing area is small and the pressure is high, which is conducive to improving the energy storage effect of the blank 5. Third, the main deformation direction of thinning and extension of the blank 5 is perpendicular to the fiber direction 7, that is, the blank 5 is elliptical after extrusion. The purpose is to make the energy storage of the blank 5 have obvious directionality, which can increase the number of equiaxed fine grains 4 perpendicular to the original fiber direction 7 after step 2) recrystallization heat treatment.

[0027] Step 2) The billet 5 after the thickness compression treatment is subjected to recrystallization heat treatment in a double-sided compression state, so that the flattened and widened grains of the billet are broken, and a fiber grain is broken into several equiaxed fine grains 4. Four points need to be supplemented: First, the energy storage of the thickness compression deformation of the billet 5 in step 1) is directional, and it is easy to obtain more and finer equiaxed fine grains 4 at a lower temperature perpendicular to the original fiber direction 7. Second, the billet 5 will expand when heated during the recrystallization heat treatment, and the density of the recrystallized structure in the extruded state is higher. Therefore, the billet 5 is pressed tightly with steel plates on both sides before heat treatment. Third, the size of the recrystallized structure is closely related to the heating temperature and the high-temperature residence time. If the temperature is too high or the holding time is too long, the material will produce some secondary recrystallized coarse grains, which will offset part of the recrystallization refinement effect. Therefore, the compressed blank 5 is first preheated at a temperature of 300±20°C, and then the preheated blank 5 is kept warm in a nitrate furnace at a temperature of 420±20°C until the recrystallization ratio of the deformed grains 4 reaches more than 80% and then cooled naturally. The purpose is to reduce the high temperature residence time to avoid coarsening of the structure and to increase the recrystallization ratio of the deformed grains 4.

[0028] Step 3) The heat-treated blank 5 is placed in a drawing die for plastic limit cold drawing, so that the blank 5 is stretched radially to form a body of revolution 8, and the equiaxed fine grains 4 of the blank 5 are radially elongated into elliptical grains 4. Four additional points need to be explained: First, during deep drawing, the heat-treated blank 5 is mainly deformed in the direction perpendicular to the original fiber direction 7. The reason is that steps 1) and 2) can only make the number of equiaxed fine grains 4 perpendicular to the original fiber direction greater than the original fiber direction, reducing the anisotropy of the blank 5. Taking the direction perpendicular to the original fiber direction 7 as the main deformation direction can not only increase the number of grains 4 radially elongated to form elliptical grains 4, but also change the number of undeformed grains again through deformation, with the purpose of further reducing the anisotropy of the body of revolution material after deep drawing. This can be achieved by increasing the corresponding flange edge resistance. Second, the greater the deformation amount of deep drawing, the more elliptical grains 4 are elongated along the heading 2, so the thinning rate of the maximum thinning zone of deep drawing is controlled to be close to the material equivalent double stretching and bulging thinning rate. Third, the material thickness change in deep drawing is relatively small compared with extrusion. Therefore, the theoretical gap between the working surfaces of the drawing upper die 9 and the drawing lower die 10 of the drawing die in the mold closing state is consistent with the thickness of the blank 5 after the thickness compression treatment. The theoretical gap is greater than the theoretical thickness of the rotating sheet metal part 1.

[0029] Step 4) After cutting the remaining weight of the rotating body 8, an oxidation treatment is performed. Two additional points require clarification: First, the weight of the rotating body 8 after cutting the remaining weight is slightly greater than the theoretical weight of the rotating sheet metal component 1. This is to ensure a balanced extrusion filling rate in step 5) and to increase the through-thickness extrusion pressure, thereby reducing the required equipment tonnage. Second, the oxidation treatment forms a high-temperature resistant oxide film on the surface, which acts as an insulator, preventing the metal from sticking to the die during hot extrusion.

[0030] Step 5) The oxidized rotor 8 is subjected to thick-axis hot extrusion through an extrusion die, reducing the wall thickness of the rotor 8. The elliptical fine grains 4 on the annular wall 3 of the rotor are elongated along the sidewalls to form longitudinal fiber grains 4. Four additional points need to be explained: First, during thick-axis extrusion, the rotor 8 and the lower extrusion die 11 are heated to 400±20°C and kept warm, and the upper extrusion die 12 is heated to 280±20°C. This is to avoid localized coarsening of the microstructure during extrusion heating and to ensure that the material undergoes large plastic expansion along the longitudinal axis during extrusion, resulting in longitudinal fiber grains 4 similar to those formed by hot-rolled sheet metal. Second, the working surface of the upper extrusion die 12 of the extrusion die is consistent with the inner surface of the rotor sheet metal 1. When the working surfaces of the upper extrusion die 12 and the lower extrusion die 11 are closed, the gap between the upper and lower dies is equal to the theoretical thickness of the rotor sheet metal 1. The working surfaces of the upper extrusion die 12 and the lower extrusion die 11 are larger than the area of the rotor sheet metal 1. This is to utilize the thickness difference to increase the number of longitudinal fiber grains 4 formed by extrusion. Third, an annular non-working surface 13 is provided on the outer side of the working surface of the extrusion upper die 12 and the extrusion lower die 11 of the extrusion die, and a heat-resistant pressure block 14 is provided on the annular non-working surface 13 to limit the mold gap. The purpose is to reduce the area of the extrusion die finishing area and ensure uniform wall thickness.

[0031] Step 6) The rotor 8 is subjected to heating, solid solution and quenching cooling to complete the final heat treatment strengthening, and then the remaining portion of the rotor 8 is cut to obtain the finished rotor sheet metal part 1. Two additional points need to be explained: First, when heating and solid solution of the rotor 8, the rotor 8 is first preheated at 300±20°C, and then the rotor 8 is transferred to a 494±5°C salt furnace for heat preservation and solid solution. The purpose is to reduce the high temperature residence time, achieve sufficient solid solution and reduce recrystallization, and retain the heading fiber grains 4 formed by extrusion in step 5) as much as possible. Second, when quenching and cooling the rotor 8, the rotor is first placed in a salt furnace at 190±10°C for pre-cooling, and then the pre-cooled rotor 8 is placed in room temperature water for cooling. There are two purposes: one is to reduce the deformation caused by rapid cooling due to large temperature differences; the other is that the sensitive temperature range of precipitation of the main strengthening phase Al2CuMg of hard aluminum alloy is 300-400℃. Pre-cooling in a salt furnace environment at an artificial aging temperature of 190℃ can increase the precipitation time of the main strengthening phase Al2CuMg and further improve the strengthening effect.

[0032] Finally, in order to facilitate those skilled in the art to understand the content of the invention of this application, this application also needs to supplement the following explanations: Regarding the explanation of the metal fiber direction 7 and the fiber structure, the metal fiber direction usually refers to the direction in which the vast majority of grains are significantly elongated. For most rolled metal plates, linear stripes can generally be seen with the naked eye, but there is no obvious feel. This is a relative concept. The fiber direction referred to in actual production generally refers to the direction of macroscopic stripes visible to the naked eye. In fact, metal plates are similar to multiple layers of superimposed and adhered cotton threads, and the fiber structure is entangled and intertwined in the metal. There will also be a certain proportion of elongated grains 4 perpendicular to the direction of the macroscopic stripes. This is an inherent property of rolled metal plates; therefore, the improvement of the heading load performance described in this application is actually the formation of fibrous grains along the heading that are significantly more elongated than those perpendicular to the heading, and it is not necessary to transform all grain shapes into fiber grains 4 along the heading.

Claims

1. A preparation method for improving the axial load performance of a hard aluminum alloy rotating sheet metal part, which is characterized by The following: 1) A circular sheet metal blank is subjected to a thickness-wise compression deformation and energy storage process at room temperature, thereby thinning the blank and flattening and widening the fiber grains of the blank; 2) the blank after the thickness-wise compression process is subjected to a recrystallization heat treatment under double-sided compression, thereby crushing the flattened and widened fiber grains of the blank into equiaxed fine grains; 3) the heat-treated blank is then placed in a drawing die for plastic limit cold drawing, thereby radially stretching the blank to form a body of revolution, and radially elongating the equiaxed fine grains of the blank into elliptical fine grains; 4) The rotor is cut to the remaining portion and then subjected to oxidation treatment; 5) The oxidized rotor is subjected to thick-axis hot extrusion through an extrusion die to reduce the wall thickness of the rotor, and the elliptical fine grains on the annular wall of the rotor are elongated along the side wall to become axial fiber grains; 6) Finally, the rotor is subjected to final heat treatment strengthening by heating, solution treatment, and quenching and cooling, and the remaining portion of the rotor is then cut to obtain a finished rotor sheet metal part.

2. The method for improving the azimuth load performance of a hard aluminum alloy rotating sheet metal part according to claim 1, wherein: In step 1), the blank is repeatedly cold-rolled and extruded by rollers, so that the blank is perpendicular to the fiber direction as the main deformation direction of thinning and extension, and the extrusion thinning rate is greater than 30% of the blank thickness.

3. The method for improving the azimuth load performance of a hard aluminum alloy rotating sheet metal part according to claim 1, wherein: In step 2), when the billet is subjected to recrystallization heat treatment in a double-sided compression state, the billet is first pressed on both sides with steel plates, and then the pressed billet is preheated in a temperature environment of 300±20°C, and then the preheated billet is kept warm in a nitrate furnace at a temperature of 420±20°C until the recrystallization ratio of the deformed grains reaches more than 80% and then naturally cooled.

4. The method for improving the azimuth load performance of a hard aluminum alloy rotating sheet metal part according to claim 1, wherein: In step 3), during deep drawing, the blank after heat treatment is mainly deformed in a direction perpendicular to the original fiber direction.

5. The method for improving the azimuth load performance of a hard aluminum alloy rotating sheet metal part according to claim 1, wherein: In step 3), the working surface of the lower drawing die of the drawing die is consistent with the inner surface of the rotating sheet metal part. When the working surfaces of the upper drawing die and the lower drawing die are closed, the gap between the upper and lower dies is consistent with the thickness of the blank after heat treatment, and the gap is greater than the theoretical thickness of the rotating sheet metal part.

6. The method for improving the azimuth load performance of a hard aluminum alloy rotating sheet metal part according to claim 1, wherein: In step 5), during thickness extrusion, the rotor and the lower extrusion die are heated to 400±20°C and kept warm, and the upper extrusion die is heated to 280±20°C.

7. The method for improving the azimuth load performance of a hard aluminum alloy rotating sheet metal part according to claim 1, characterized in that: In step 5), the working surface of the extrusion upper die of the extrusion die is consistent with the inner surface of the rotating sheet metal part. When the working surfaces of the extrusion upper die and the extrusion lower die are in the mold closing state, the gap between the upper and lower dies is equal to the theoretical thickness of the rotating sheet metal part, and the working surfaces of the extrusion upper die and the extrusion lower die are larger than the area of the rotating sheet metal part.

8. The method for improving the azimuth load performance of a hard aluminum alloy rotating sheet metal part according to claim 1, wherein: In step 5), an annular non-working surface is further provided on the outer side of the extrusion lower die and the working surface of the extrusion lower die of the extrusion die, and a heat-resistant pressure-bearing block for limiting the mold gap is provided on the annular non-working surface.

9. The method for improving the azimuth load performance of a hard aluminum alloy rotating sheet metal part according to claim 1, wherein: In step 6), when heating and solutionizing the rotating body, the rotating body is first preheated at a temperature of 300±20° C., and then transferred to a salt furnace at 494±5° C. for heat preservation and solutionizing.

10. The method for improving the azimuth load performance of a hard aluminum alloy rotating sheet metal part according to claim 1, wherein: In step 6), when the rotor is quenched and cooled, the rotor is first placed in a salt furnace at 190±10° C. for pre-cooling, and then the pre-cooled rotor is placed in room temperature water for cooling.

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