Method for the superplastic forming of a multilayer as-cast metal sheet and metal component

Abstract

The application provides a multilayer as-cast metal plate superplastic forming preparation method and a metal component, and the preparation method comprises the following steps: preparing at least two as-cast metal plates to be spliced and performing friction stir processing on the superplastic forming area of each plate, then stacking each plate upside down, and performing friction stir splicing on each splicing area; placing each plate spliced into one body in a superplastic die, heating to a preset temperature, then filling inert gas into each superplastic deformation area, and obtaining the target metal component by controlling the gas pressure. The application adopts the friction stir processing+friction stir splicing+superplastic forming process to directly prepare a multilayer metal complex component, the process is shorter than that of a traditional preparation method, the splicing efficiency can be improved, and the time consumption of the whole preparation process is reduced; while realizing reliable splicing of the as-cast metal plates, the splicing area can also form fine grain / superfine grain structure, the structure is more uniform, and the probability of cracks at the junction of the superplastic deformation area and the splicing area is reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of material processing technology, and particularly relates to a method for preparing a multilayer as-cast metal plate by superplastic forming and a metal component. BACKGROUND

[0002] The superplastic forming / diffusion bonding technology is a forming technology for obtaining a complex structural part by combining superplastic forming and diffusion welding. The superplastic forming / diffusion bonding technology has the advantages of weight reduction, small deformation resistance, near-net forming, forming of complex structural parts, and low cost, and has been widely applied in the fields of mold manufacturing, electronic instruments, instruments, light industry, and aerospace. Especially with the development of science and technology, the superplastic forming / diffusion bonding technology has been widely applied in key parts such as airplanes, missiles, and aircraft structures.

[0003] However, one of the important factors limiting the development of the superplastic forming / diffusion bonding technology is the high forming / bonding temperature and low production efficiency. Specifically, the temperature of the conventional superplastic forming and diffusion bonding is about 900-920℃, and the conventional diffusion bonding is mainly volume diffusion, which is slow in welding speed. This process often needs tens of minutes to tens of hours to achieve diffusion bonding, resulting in that the existing superplastic forming / diffusion bonding technology is time-consuming at high temperature, the production efficiency of the forming process is low, the grains of the formed component are severely coarsened, and the performance is severely degraded.

[0004] At present, there are patents that improve the traditional superplastic forming / diffusion bonding technology. For example, the patent with application number 202210590851.0 discloses an aluminum alloy / aluminum-lithium alloy hollow stiffener skin forming method and mold, which uses friction stir welding + superplastic forming process on rolled plate to obtain a hollow stiffener skin with high reliability. Since friction stir welding is used instead of traditional diffusion bonding, the production efficiency of the forming process can be greatly improved. However, this patent must use rolled plate as the forming raw material, which greatly increases the forming process flow, forming time and raw material cost compared with cast plate. In addition, during the friction stir lap welding of aluminum alloy, hook-shaped crack defects are prone to occur. Due to the great difference between the microstructure of the rolled plate and the friction stir welding, the crack propagation will be aggravated during the superplastic forming process, which will affect the quality of the formed component. In addition, although this patent uses friction stir lap welding at room temperature instead of high-temperature diffusion welding, the raw material used is the traditional rolled plate, and the superplastic forming temperature has not been reduced compared with the traditional aluminum alloy superplastic forming high temperature. Therefore, the superplastic forming temperature of this patent is still relatively high. In addition, this patent only involves aluminum alloy, which has a low melting point, low material strength, and good forming ability. It is relatively easy to achieve effective connection of aluminum alloy using friction stir welding method. However, for high-melting-point alloys such as titanium alloy and high-entropy alloy, the melting point is high, the strength is high, the chemical activity is strong, and the thermal conductivity is low. The selection of welding tool material and shape and size is extremely harsh, the process window is very narrow, and defects are prone to occur. The welding difficulty is greatly increased. The friction stir welding process used for aluminum alloy cannot be applied to high-melting-point materials such as titanium alloy and high-entropy alloy. Therefore, the method used in this patent cannot be replicated for high-melting-point alloys such as titanium alloy and high-entropy alloy.

[0005] For the superplasticity of titanium alloy friction stir welding, the patent inventors disclosed a processing method for realizing high superplasticity of titanium alloy welded joints in prior application numbers 2019101220069 and 202110259444.7, and a friction stir welding process and superplastic forming process for realizing overall uniform superplastic forming of titanium alloy welded joints. The two processes are characterized by using friction stir welding to butt joint the titanium alloy plates in two dimensions, thereby splicing small-sized plates into large-sized plates in two dimensions, and obtaining uniform structure of the titanium alloy plates in two dimensions, realizing uniform superplastic forming of the overall spliced plates. Therefore, the patent is a superplastic forming method for single-layer metal plate components, but does not involve the splicing and superplastic forming of multi-layer plates in the thickness direction. In addition, the patent with application number 2023100602289 discloses a low-cost short-process preparation method for large complex components. The process prepares large-sized bulk plates in two dimensions by multi-pass friction stir processing and friction stir welding, and realizes superplastic forming of the large-sized bulk plates. The patent is also a superplastic forming method for single-layer metal plate components, but does not involve the splicing and superplastic forming of multi-layer plates in three dimensions.

[0006] Therefore, it is urgent to invent a short-process high-efficiency forming process for multi-layer metal plate complex components using as-cast plates as raw materials. SUMMARY

[0007] Therefore, the present application provides a multi-layer as-cast metal plate superplastic forming preparation method and a metal component to solve the problems of high raw material cost, long superplastic forming / diffusion bonding time, low forming process production efficiency, and defects in the splicing area in the related art.

[0008] To solve the above problems, the present application provides a multi-layer as-cast metal plate superplastic forming preparation method, comprising the following steps:

[0009] Plate preparation step: preparing at least two as-cast metal plates to be spliced;

[0010] Plate processing step: determining the splicing area and the superplastic deformation area of each as-cast metal plate, and performing friction stir processing on the superplastic deformation area of each as-cast metal plate;

[0011] Plate stacking step: stacking the metal plates after friction stir processing (at this time, the metal plates are no longer as-cast metal plates due to the friction stir processing, and the same applies below) on top of each other, and ensuring that the positions of the splicing areas of each as-cast metal plate correspond to each other;

[0012] Welding and splicing step: performing friction stir splicing on each splicing area;

[0013] a superplastic forming step of placing the metal plates welded together in a superplastic mold, heating to a predetermined temperature, filling inert gas into each of the superplastic deformation regions, and obtaining a target metal member by controlling the gas pressure of the superplastic forming.

[0014] In some embodiments,

[0015] The superplastic deformation region of each of the metal plates after the friction stir processing of the superplastic deformation region is a uniform ultra-fine grain / fine grain region.

[0016] In some embodiments,

[0017] The process parameters of the friction stir welding of the lap region are the same as the process parameters of the friction stir processing of the superplastic deformation region, so that the structures of the superplastic deformation region and the lap region are equivalent.

[0018] In some embodiments,

[0019] The process parameters include: the rotation speed of the stirring head, the welding speed.

[0020] In some embodiments,

[0021] The cast metal plate is one of a titanium alloy plate, a high-entropy alloy plate, and a steel plate, the rotation speed of the stirring head is 200-600 rpm, and the welding speed is 25-200 mm / min, so that the local region of the superplastic forming has a fine equiaxed structure with a high proportion of high-angle grain boundaries; and / or, the greater the thickness of the cast metal plate to be processed, the greater the rotation speed of the stirring head.

[0022] In some embodiments,

[0023] The gas pressure is 0.1-10 MPa.

[0024] In some embodiments,

[0025] After the friction stir processing of the superplastic deformation region of each of the cast metal plates, before the plate stacking step, further comprising:

[0026] Applying a flux to the respective opposite superplastic deformation regions of the two metal plates that are lapped together.

[0027] In some embodiments,

[0028] In the superplastic forming step, a flux is applied to the region where the superplastic mold and the metal plate can contact.

[0029] In some embodiments,

[0030] In the welding step, an air passage is left during the friction stir welding of the overlapping area, and in the superplastic forming step, the inert gas is filled into the superplastic deformation area through the air passage.

[0031] The application also provides a metal component prepared by the above-mentioned multi-layer as-cast metal plate superplastic forming preparation method.

[0032] Compared with the prior art, the application uses as-cast plate as the raw material for friction stir processing, directly forms fine grains / ultra-fine grains, has a short process flow, and uses the friction stir welding method to realize reliable welding of the corresponding overlapping areas of the upper and lower metal sheets. On the one hand, compared with the traditional diffusion connection method, the friction stir welding in the application has a short time consumption, can improve the connection efficiency, and thus reduce the time consumption of the entire preparation process. On the other hand, while realizing reliable welding of the upper and lower metal sheets, the friction stir welding can also form fine grain / ultra-fine grain structure in the overlapping area. Since the friction stir processing and friction stir welding have the same processing mechanism, the superplastic forming area and the upper and lower plate overlapping area have the same grain size, so the entire multi-layer plate has more uniform grain structure. This can effectively reduce the probability of cracks at the junction of the superplastic deformation area and the overlapping area during the superplastic forming process, and thus improve the effect of superplastic forming. In addition, compared with the traditional diffusion connection which needs to be carried out at high temperature (for example, the superplastic forming and diffusion temperature of titanium alloy is about 900-920℃), the friction stir welding in the application is carried out at room temperature, and the connection is not limited by temperature. In addition, the high proportion of high-angle grain boundaries of the fine grains prepared by friction stir processing can greatly reduce the superplastic forming temperature compared with the low proportion of high-angle grain boundaries of the traditional rolling plate. Therefore, the overall superplastic forming temperature is greatly reduced when forming the multi-layer component. The multi-layer as-cast metal plate superplastic forming preparation method in the application is especially suitable for three-dimensional scale forming of complex components of multi-layer (two or more) plates.

[0033] Therefore, the application provides a short-flow multi-layer metal plate superplastic forming preparation method and a metal component using as-cast plate as the raw material, which can obtain uniform microstructure, improve production efficiency, reduce the probability of crack generation, and reduce the superplastic forming temperature, and can short-flow prepare a multi-layer complex component in three-dimensional scale. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 FIG. 1 is a step schematic diagram of a multi-layer as-cast metal plate superplastic forming preparation method according to an embodiment of the application;

[0035] Figure 2 FIG. 2 is a state schematic diagram of a multi-layer as-cast metal plate superplastic forming preparation method according to an embodiment of the application, which shows the state of the as-cast metal plate corresponding to each preparation method step.

[0036] Figure 3 Multi-pass processing map for local superplastic forming area of as-cast metal plate when the as-cast metal plate is a titanium alloy as-cast plate;

[0037] Figure 4 Friction stir lap joint map for two-layer titanium alloy as-cast plate;

[0038] Figure 5 Wherein a is a microstructure map of friction stir processing, and b is a microstructure map of friction stir lap joint. DETAILED DESCRIPTION

[0039] For reference Figures 1 to 5 As shown in the drawings, according to an embodiment of the present application, a method for preparing a multi-layer as-cast metal plate by superplastic forming is provided, comprising the following steps:

[0040] Plate preparation step: preparing at least two as-cast metal plates to be lap jointed (for example, plate 1 and plate 2 in the drawings, preferably, each as-cast metal plate has the same material); Figure 2 Plate processing step: determining the lap joint area (for example, the lap joint area indicated in the drawings) and the superplastic deformation area (for example, the superplastic forming area indicated in the drawings) of each as-cast metal plate, as shown in the drawings, the lap joint area and the superplastic deformation area are arranged separately and successively on the same as-cast metal plate, and the specific arrangement mode can be matched according to the purpose of forming the component, and the superplastic deformation area of each as-cast metal plate is subjected to friction stir processing (single-pass / multi-pass friction stir processing) to obtain a fine grain / ultra-fine grain area with uniform structure;

[0041] Figure 2 Plate stacking step: stacking each metal plate upside down, and ensuring that the positions of the lap joint areas of each metal plate correspond to each other upside down; Figure 2 Figure 1 Welding and lap joint step: performing friction stir lap joint on each lap joint area, so as to form a reliable and sealed lap joint between each metal plate stacked upside down;

[0042] Superplastic forming step: placing each metal plate welded into one body in a superplastic mold (for example, the mold in the drawings), heating to a preset temperature, filling inert gas into each superplastic deformation area, and making the superplastic deformation area locally superplastically deform by controlling the gas pressure of superplastic forming, so as to obtain a target metal component (for example, the component in the drawings);

[0043] Superplastic forming step: placing each metal plate welded into one body in a superplastic mold (for example, the mold in the drawings), heating to a preset temperature, filling inert gas into each superplastic deformation area, and making the superplastic deformation area locally superplastically deform by controlling the gas pressure of superplastic forming, so as to obtain a target metal component (for example, the component in the drawings);

[0044] Superplastic forming step: placing each metal plate welded into one body in a superplastic mold (for example, the mold in the drawings), heating to a preset temperature, filling inert gas into each superplastic deformation area, and making the superplastic deformation area locally superplastically deform by controlling the gas pressure of superplastic forming, so as to obtain a target metal component (for example, the component in the drawings); Figure 2 Figure 2 Superplastic forming step: placing each metal plate welded into one body in a superplastic mold (for example, the mold in the drawings), heating to a preset temperature, filling inert gas into each superplastic deformation area, and making the superplastic deformation area locally superplastically deform by controlling the gas pressure of superplastic forming, so as to obtain a target metal component (for example, the component in the drawings);​​It can be understood that the preset temperature is reasonably selected according to the material of the metal plate, and is not particularly limited here. Specifically, the superplastic forming temperature of different materials is different, and the selection of the temperature is related to the material. Normally, the superplastic deformation temperature is greater than 0.5 times the melting point (Kelvin temperature) of the material. For example, when the cast metal plate is a titanium alloy plate, the superplastic forming temperature range is generally 600-1000℃. Normally, the higher the superplastic deformation temperature, the smaller the gas pressure.

[0045] In the technical solution, the reliable lap joint of the corresponding lap joint areas of the upper and lower metal sheets is realized by using the friction stir lap joint method. On the one hand, compared with the traditional diffusion connection method, the process flow of the friction stir lap joint method in the application is shorter, which can improve the connection efficiency and thus reduce the time consumption of the entire preparation process. On the other hand, while realizing the reliable lap joint of the upper and lower metal sheets, the friction stir lap joint can also form fine equiaxed ultrafine grain structures in the lap joint area, and the grain structure is more uniform, which can effectively reduce the probability of defects (such as cracks) at the junction of the superplastic deformation area and the lap joint area during superplastic forming, thereby improving the effect of superplastic forming. It can be understood that the multi-layer cast metal plate superplastic forming preparation method in the application is especially suitable for three-dimensional forming of complex components by using multi-layer (two or more) plates.

[0046] In order to improve the deformation effect of superplastic deformation, generally, at least the necessary processing of each superplastic deformation area is needed to improve the grain size and uniformity of the area. The commonly used method in the prior art is to roll the plate. Generally, the cast metal plate is processed by cold rolling. On the one hand, the process of preparing the plate by cold rolling is complicated and the process flow is long, which increases the time consumption of the overall preparation process. On the other hand, the grain structure at the lap joint area is quite different from the previous one, and the plate with large difference is prone to cracks at the junction of the lap joint area and the superplastic forming area during superplastic deformation. However, before the plate stacking step, the present application only needs to perform single / multi-pass friction stir processing on the superplastic deformation area of each cast metal plate, so that the superplastic deformation area has a uniform ultrafine grain / fine grain structure. In this way, combined with the friction stir lap joint of the lap joint area as described above, the grain size and uniformity of the lap joint area and the superplastic deformation area are consistent, which eliminates the disadvantages of the complicated process and long process flow of the cold rolling method for preparing the cast metal plate, and effectively reduces the probability of defects (such as cracks) at the junction of the superplastic deformation area and the lap joint area, thereby further improving the quality of the superplastic deformation prepared metal component.

[0047] In a preferred embodiment, the process parameters of the friction stir lap joint of the lap joint region are the same as the process parameters of the friction stir processing of the superplastic deformation region, and the process parameters can specifically be the rotation speed of the stir head and the welding speed, so as to further ensure the homogenization degree of the microstructure grains in the lap joint region and the superplastic deformation region. It needs to be particularly pointed out that, for the same cast metal plate, the lap joint region and the superplastic deformation region constitute the entire region of the cast metal plate, both regions are processed (or welded) by the friction stir process, and the process parameters of the two regions are kept consistent, so that the two regions have nearly the same deformation ability, and the metal component prepared has better forming effect. It needs to be particularly pointed out that the same parameters of the friction stir processing and the friction stir lap joint can obtain similar microstructures. Although the friction stir lap joint is not a superplastic forming zone, the lap joint region as a sealing edge will also deform to a certain extent, and the advantage of using the same parameters is that the lap joint region can better deform in the superplastic deformation process due to the same microstructure and deformation zone, and the stress concentration at the sealing edge after forming is reduced.

[0048] In some embodiments, the cast metal plate is one of a titanium alloy plate, a high-entropy alloy plate or a steel plate, the rotation speed of the stir head during the friction stir processing and the lap joint process is 200-600 rpm, and the welding speed is 25-200 mm / min, so that the microstructure of the superplastic forming local region (i.e., the superplastic forming region) of the titanium alloy plate, the high-entropy alloy plate and the steel plate is a fine equiaxed structure with a high-angle grain boundary (a misfit angle not less than 15 degrees) with a proportion higher than 85%. The greater the thickness of the cast metal plate to be processed, the greater the rotation speed of the stir head, so as to improve the efficiency and homogenization effect of the friction stir processing.

[0049] The gas pressure of the inert gas is 0.1-10 MPa. When the gas pressure is lower than 0.1 MPa, the superplastic forming rate of the alloy is relatively low, which leads to serious microstructure coarsening and greatly reduced performance of the complex component during the forming process. When the gas pressure is higher than 10 MPa, the superplastic forming rate is relatively high, which leads to defects of the complex component.

[0050] In some embodiments, after the superplastic deformation region of each cast metal plate is processed by the friction stir processing, before the plate stacking step, the method further comprises:

[0051] The two metal plates that are to be lapped each have a relative superplastic deformation region, and a flux is coated on the superplastic deformation region. For the same reason, during the superplastic forming step, a flux is coated on the region where the superplastic die and the metal plate can contact, so as to facilitate the deformation of the two metal plates of the superplastic deformation region away from each other or facilitate the smooth separation of the metal component and the die.

[0052] In some embodiments, during the welding lap step, an air channel is provided during the friction stirring lap process of the lap area, and during the superplastic forming step, inert gas is introduced into the superplastic deformation area through the air channel.

[0053] According to an embodiment of the present invention, a metal component is also provided, which is prepared by the above-described method for superplastic forming of multilayer cast metal plates.

[0054] The superplastic forming preparation method of the aforementioned multilayer cast metal plate of this application is described below with reference to several embodiments and comparative examples.

[0055] Example 1

[0056] A 2mm thick cast titanium alloy sheet (hereinafter referred to as the titanium alloy sheet) was fixed on the welding machine plane. A tungsten-rhenium alloy stirring tool with a shoulder diameter of 11mm was used to perform single-pass / multi-pass friction stir processing on the localized area requiring superplastic forming. The stirring pin speed was 300 rpm, and the welding speed was 50 mm / min. The same processing parameters were used to perform single-pass / multi-pass friction stir processing on another titanium alloy sheet for a localized area requiring superplastic forming. Figure 3 As shown; after applying a weld nugget to the locally superplastic forming areas of two single-pass / multi-pass processed titanium alloy plates, they are stacked together and fixed on the welding machine plane. A tungsten-rhenium alloy stirring tool with a shoulder diameter of 11 mm is used to perform friction stir bonding in the areas where the two / multi-layer plates need to overlap. The stirring needle speed is 300 rpm and the welding speed is 50 mm / min. Figure 4 As shown, the prepared sheet material is placed in a mold and heated to 800°C. Superplastic forming is then performed under a gas pressure of 3.61 MPa to finally obtain a complex component with localized forming.

[0057] Technical Results: A uniform microstructure with a high-angle grain boundary ratio of 93% and an average grain size of 0.6 micrometers was successfully obtained in the local superplastic forming region. Figure 5 As shown in Figure a, the friction stir lap region also successfully obtained a microstructure with a high-angle grain boundary ratio of 94% and a grain size of 0.7 micrometers, as shown in Figure a. Figure 5 As shown in b, the microstructures of the two are quite similar.

[0058] It should be noted that due to the slight systematic error in each EBSD (electron backscatter diffraction) test, it is normal for there to be some differences in the microstructure of different regions. This difference can be ignored in engineering, thus proving that the microstructure of the superplastic forming area and the overlapping area are consistent.

[0059] Comparative Example 1

[0060] A 2mm titanium alloy plate is fixed on the welding machine plane, and a tungsten-rhenium alloy stirring tool with a shoulder diameter of 11mm is used to perform single / multi-pass friction stir processing on the local area that needs to be superplastic formed, the stirring needle rotation speed is 300rpm, and the welding speed is 50mm / min; another titanium alloy plate is processed by single / multi-pass friction stir processing on the local area that needs to be superplastic formed, as shown in Figure 3 ; the two single / multi-pass processed titanium alloy plates are stacked together after the local superplastic formed areas are coated with a flux, and are fixed on the welding machine plane, and a tungsten-rhenium alloy stirring tool with a shoulder diameter of 11mm is used to perform friction stir lap joining in the area where the two layers / multi-layers of plates need to be overlapped, the stirring needle rotation speed is 400rpm, and the welding speed is 40mm / min, as shown in Figure 4 . The prepared plate is placed in a mold and heated to 800℃, and superplastic forming is performed under a gas pressure of 3.61MPa, and finally a locally formed complex component is obtained, and cracks appear at the junction of the superplastic forming area and the lap joint area.

[0061] Technical effects and analysis: This is because the superplastic forming area has a uniform structure with a high-angle grain boundary proportion of 93% and an average grain size of 0.6 microns, while the friction stir lap joint area has a high-angle grain boundary proportion of 91% and a grain size of 2.4 microns, and the inconsistent grain size leads to different flow stresses during deformation, resulting in uneven deformation and cracks at the junction. Therefore, the uniformity of the structure of the superplastic forming area and the lap joint area is an important factor in obtaining a defect-free complex component.

[0062] Specifically, because the stirring speed and welding speed of the lap joint area are different from those of the superplastic deformation area, the difference in structure increases the probability of cracks at the junction of the superplastic deformation area and the lap joint area. The same friction stir processing parameters of the superplastic deformation area and the lap joint area are more conducive to the final result of superplastic forming. If they are not the same, cracks may occur (the probability of cracks increases).

[0063] Comparative Example 2

[0064] Two 2mm titanium alloy plates are prepared by a multi-pass rolling and annealing process. The two plates are coated with a flux at the position that needs to be superplastic formed, and after detecting the tightness, the sealed plate is heated to the diffusion welding temperature, and the outer surface of the sealed plate is pressurized, and diffusion welding is achieved under high temperature and pressure. After heating to 900℃, superplastic forming is performed under a gas pressure of 0.8MPa, and finally a locally formed complex component is obtained.

[0065] Technical effects and analysis: The traditional superplastic forming / diffusion bonding technology is complex and cumbersome, which reduces the efficiency of superplastic forming sheet preparation and assembly. Diffusion welding requires welding at high temperature, and the welding rate is slow, the efficiency is low, and the microstructure obtained by diffusion welding is coarse, with a grain size of 30 microns, and the performance of the formed part is poor. The single / multi-pass friction stir processing and friction stir lap joint process has a short process flow, can obtain high-proportion high-angle grain boundary equiaxed fine grain / superfine grain structure, and can reduce the superplastic forming temperature. In addition, the process is efficient, and the material obtains uniform fine-grained structure. Therefore, the process can significantly improve the efficiency of superplastic forming sheet preparation and assembly, has excellent superplastic performance, reduces the superplastic forming temperature, and is more conducive to the application of superplastic forming technology in industrial production.

[0066] Example 2

[0067] A 2mm titanium alloy sheet was fixed on the welding machine plane, a tungsten-rhenium alloy stirring tool with a shoulder diameter of 11mm was used to perform single / multi-pass friction stir processing on the local area requiring superplastic forming, the stirring pin rotation speed was 200r / min, and the welding speed was 25mm / min. Another titanium alloy sheet was subjected to single / multi-pass friction stir processing on the local area requiring superplastic forming using the same processing parameters. The two single / multi-pass processed titanium alloy sheets were stacked together after the local superplastic forming area was coated with a stop flux, and were fixed on the welding machine plane. A tungsten-rhenium alloy stirring tool with a shoulder diameter of 11mm was used to perform friction stir lap joint on the area requiring lap joint of the two / multi-layer sheets, the stirring pin rotation speed was 200r / min, and the welding speed was 25mm / min. The prepared sheet was placed in the mold and heated to 800℃, and superplastic forming was performed under a gas pressure of 1.5MPa.

[0068] Technical effects: A uniform microstructure with a high-angle grain boundary proportion of 92% and an average grain size of 0.42 microns was successfully obtained in the local superplastic forming area, and a high-angle grain boundary proportion of 90% and a grain size of 0.46 microns were successfully obtained in the friction stir lap joint area. A complex component was finally obtained by local forming.

[0069] Comparative Example 3

[0070] A 2mm titanium alloy plate was fixed on the welding machine plane, and a tungsten-cobalt alloy stirring tool with a shoulder diameter of 11mm was used to perform single / multi-pass friction stir processing on the local area that needed superplastic forming, with a stirring pin rotation speed of 150rpm and a welding speed of 20mm / min. Another titanium alloy plate was processed in the same way. The two single / multi-pass processed titanium alloy plates were stacked together after the local superplastic forming area was coated with a stop welding agent, and were fixed on the welding machine plane. A tungsten-cobalt alloy stirring tool with a shoulder diameter of 11mm was used to perform friction stir lap welding on the area that needed to be overlapped between the two layers / multi-layers, with a stirring pin rotation speed of 150rpm and a welding speed of 20mm / min. The prepared plate was placed in a mold and heated to 800℃, and superplastic forming was performed under a gas pressure of 1.5MPa.

[0071] Technical effects and analysis: Lower rotation speed and welding speed result in tunnel defects in the processing and welding areas, so complex components cannot be formed.

[0072] Comparative Example 4

[0073] A 2mm titanium alloy plate was fixed on the welding machine plane, and a tungsten-cobalt alloy stirring tool with a shoulder diameter of 11mm was used to perform single / multi-pass friction stir processing on the local area that needed superplastic forming, with a stirring pin rotation speed of 200rpm and a welding speed of 25mm / min. Another titanium alloy plate was processed in the same way. The two single / multi-pass processed titanium alloy plates were stacked together after the local superplastic forming area was coated with a stop welding agent, and were fixed on the welding machine plane. A tungsten-cobalt alloy stirring tool with a shoulder diameter of 11mm was used to perform friction stir lap welding on the area that needed to be overlapped between the two layers / multi-layers, with a stirring pin rotation speed of 200rpm and a welding speed of 25mm / min. The prepared plate was placed in a mold and heated to 800℃ and 900℃, and superplastic forming was performed under a gas pressure of 0.05MPa.

[0074] Technical effects and analysis: Smaller gas pressure makes the superplastic forming rate of the alloy too low, and the forming time is too long, resulting in serious grain coarsening of complex components during the forming process, and a significant decrease in component performance. Therefore, the regulation of gas pressure directly affects the final forming quality of the alloy.

[0075] Example 3

[0076] A 2mm titanium alloy plate was fixed on the welding machine plane, and a tungsten-rhenium alloy stirring tool with a shoulder diameter of 11mm was used to perform single / multi-pass friction stirring on the local area that needed superplastic forming, the stirring needle rotation speed was 600rpm, and the welding speed was 200mm / min. Another titanium alloy plate was processed by single / multi-pass friction stirring on the local area that needed superplastic forming using the same processing parameters. The two titanium alloy plates after single / multi-pass processing were stacked together after coating the local superplastic forming area with a welding inhibitor, and were fixed on the welding machine plane. A tungsten-rhenium alloy stirring tool with a shoulder diameter of 11mm was used to perform friction lap joint on the area that needed lap joint of the two / multi-layer plates, the stirring needle rotation speed was 600rpm, and the welding speed was 200mm / min. The prepared plate was placed in the mold and heated to 900℃, and superplastic forming was performed under a gas pressure of 10MPa.

[0077] Technical effects: In the local superplastic forming area, a high-angle grain boundary proportion of 87% and a lamellar structure width of 180nm, a length-diameter ratio of 8 were successfully obtained, and in the friction lap joint area, a high-angle grain boundary proportion of 89% and a lamellar structure width of 200nm, a length-diameter ratio of 7.5 were successfully obtained, and finally a complex component with local forming was obtained.

[0078] Comparative Example 5

[0079] A 2mm titanium alloy plate was fixed on the welding machine plane, and a tungsten-rhenium alloy stirring tool with a shoulder diameter of 11mm was used to perform single / multi-pass friction stirring on the local area that needed superplastic forming, the stirring needle rotation speed was 700rpm, and the welding speed was 250mm / min. Another titanium alloy plate was processed by single / multi-pass friction stirring on the local area that needed superplastic forming using the same processing parameters. The two titanium alloy plates after single / multi-pass processing were stacked together after coating the local superplastic forming area with a welding inhibitor, and were fixed on the welding machine plane. A tungsten-rhenium alloy stirring tool with a shoulder diameter of 11mm was used to perform friction lap joint on the area that needed lap joint of the two / multi-layer plates, the stirring needle rotation speed was 700rpm, and the welding speed was 250mm / min.

[0080] Technical effects and analysis: Higher rotation speed and welding speed result in tunnel defects in the processing area and the welding area, so complex components cannot be formed.

[0081] Comparative Example 6

[0082] A 2mm titanium alloy plate was fixed on the welding machine plane, and a tungsten-cobalt alloy stirring tool with a shoulder diameter of 11mm was used to perform single / multi-pass friction stir processing on the local area that needed superplastic forming, with a stirring needle speed of 600rpm and a welding speed of 200mm / min. Another titanium alloy plate was processed in the same way. The two single / multi-pass processed titanium alloy plates were stacked together after the local superplastic forming area was coated with a stop welding agent, and were fixed on the welding machine plane. A tungsten-cobalt alloy stirring tool with a shoulder diameter of 11mm was used to perform friction stir lap joining in the area where the two layers / multi-layers needed to be joined, with a stirring needle speed of 600rpm and a welding speed of 200mm / min. The prepared plate was placed in the mold and heated to 900℃, and superplastic forming was performed under a gas pressure of 12MPa.

[0083] Technical effects: A larger gas pressure makes the superplastic deformation rate too fast, resulting in cracks in the plastic forming area, so complex components cannot be formed.

[0084] Example 4

[0085] A 2mm CoCrFeNiMn high-entropy alloy plate (as-cast, same below) was fixed on the welding machine plane, and a tungsten-cobalt alloy stirring tool with a shoulder diameter of 11mm was used to perform single / multi-pass friction stir processing on the local area that needed superplastic forming, with a stirring needle speed of 400rpm and a welding speed of 50mm / min. Another CoCrFeNiMn high-entropy alloy plate was processed in the same way. The two single / multi-pass processed CoCrFeNiMn high-entropy alloy plates were stacked together after the local superplastic forming area was coated with a stop welding agent, and were fixed on the welding machine plane. A tungsten-cobalt alloy stirring tool with a shoulder diameter of 11mm was used to perform friction stir lap joining in the area where the two layers / multi-layers needed to be joined, with a stirring needle speed of 400rpm and a welding speed of 50mm / min. The prepared plate was placed in the mold and heated to 675℃, and superplastic forming was performed under a gas pressure of 4MPa.

[0086] Technical effects: A fine-grained structure with a high-angle grain boundary proportion of 92% and an average grain size of 2 microns was successfully obtained in the local superplastic forming area. A fine-grained structure with a high-angle grain boundary proportion of 93% and a grain size of 2.2 microns was also successfully obtained in the friction stir lap joining area. A complex component was finally obtained by local forming.

[0087] Comparative Example 7

[0088] A 2mm CoCrFeNiMn high-entropy alloy plate was fixed on the welding machine plane, and a tungsten-cobalt alloy stirring tool with a shoulder diameter of 11 mm was used to perform single / multi-pass friction stirring on the local area that needed to be superplastic formed. The stirring pin rotation speed was 400 rpm, and the welding speed was 50 mm / min. Another CoCrFeNiMn high-entropy alloy plate was subjected to single / multi-pass friction stirring on the local area that needed to be superplastic formed using the same processing parameters. The two single / multi-pass processed CoCrFeNiMn high-entropy alloy plate local superplastic forming areas were coated with a stop flux and then stacked together and fixed on the welding machine plane. A tungsten-cobalt alloy stirring tool with a shoulder diameter of 11 mm was used to perform friction lap joining in the area where the two layers / multi-layers needed to be joined. The stirring pin rotation speed was 800 rpm, and the welding speed was 50 mm / min. The prepared plate was placed in the mold and heated to 675°C, and superplastic forming was performed under a gas pressure of 4 MPa. Finally, a locally formed complex component was obtained, and cracks appeared at the junction of the superplastic forming area and the lap joint area.

[0089] Technical effects and analysis: This is because the high-angle grain boundary proportion in the superplastic forming area is 92% and the average grain size is 2 microns, while the high-angle grain boundary proportion in the friction lap joint area is 95% and the grain size is 4.5 microns. The inconsistency in grain size leads to different flow stresses during deformation, resulting in uneven deformation and causing cracks at the junction. Therefore, the uniformity of the structure in the superplastic forming area and the lap joint area is an important factor in obtaining a defect-free complex component.

[0090] Example 5

[0091] A 2mm CoCrFeNiMn high-entropy alloy plate was fixed on the welding machine plane, and a tungsten-cobalt alloy stirring tool with a shoulder diameter of 11 mm was used to perform single / multi-pass friction stirring on the local area that needed to be superplastic formed. The stirring pin rotation speed was 200 rpm, and the welding speed was 25 mm / min. Another CoCrFeNiMn high-entropy alloy plate was subjected to single / multi-pass friction stirring on the local area that needed to be superplastic formed using the same processing parameters. The two single / multi-pass processed CoCrFeNiMn high-entropy alloy plate local superplastic forming areas were coated with a stop flux and then stacked together and fixed on the welding machine plane. A tungsten-cobalt alloy stirring tool with a shoulder diameter of 11 mm was used to perform friction lap joining in the area where the two layers / multi-layers needed to be joined. The stirring pin rotation speed was 200 rpm, and the welding speed was 25 mm / min. The prepared plate was placed in the mold and heated to 650°C, and superplastic forming was performed under a gas pressure of 0.1 MPa.

[0092] Technical effects: Fine grain structure with high angle grain boundary fraction of 87% and average grain size of 1.3 microns is successfully obtained in the locally superplastic formed zone. Fine grain structure with high angle grain boundary fraction of 90% and grain size of 1.4 microns is also successfully obtained in the friction stir lap zone. A locally formed complex component is finally obtained.

[0093] Comparative Example 8

[0094] A 2mm CoCrFeNiMn high-entropy alloy plate is fixed on the welding machine plane, and a tungsten-cobalt alloy stirring tool with a shoulder diameter of 11mm is used to perform single / multi-pass friction stir processing on the local area that needs to be superplastically formed, with a stirring pin rotation speed of 100rpm and a welding speed of 20mm / min. Another CoCrFeNiMn high-entropy alloy plate is processed in the same way. The locally superplastically formed areas of the two single / multi-pass processed CoCrFeNiMn high-entropy alloy plates are coated with a stop flux and then stacked together and fixed on the welding machine plane. A tungsten-cobalt alloy stirring tool with a shoulder diameter of 11mm is used to perform friction stir lap joining in the area where the two layers / multiple layers need to be joined, with a stirring pin rotation speed of 100rpm and a welding speed of 20mm / min.

[0095] Technical effects: Technical effects and analysis: Lower rotation speed and welding speed result in tunnel defects in the processed area and the welding area, so complex components cannot be formed.

[0096] Comparative Example 9

[0097] A 2mm CoCrFeNiMn high-entropy alloy plate is fixed on the welding machine plane, and a tungsten-cobalt alloy stirring tool with a shoulder diameter of 11mm is used to perform single / multi-pass friction stir processing on the local area that needs to be superplastically formed, with a stirring pin rotation speed of 200rpm and a welding speed of 25mm / min. Another CoCrFeNiMn high-entropy alloy plate is processed in the same way. The locally superplastically formed areas of the two single / multi-pass processed CoCrFeNiMn high-entropy alloy plates are coated with a stop flux and then stacked together and fixed on the welding machine plane. A tungsten-cobalt alloy stirring tool with a shoulder diameter of 11mm is used to perform friction stir lap joining in the area where the two layers / multiple layers need to be joined, with a stirring pin rotation speed of 200rpm and a welding speed of 25mm / min. The prepared plate is placed in a mold and heated to 650°C, and superplastic forming is performed under a gas pressure of 0.05MPa.

[0098] Technical effects: Smaller gas pressure makes the alloy superplastic forming rate too low, superplastic forming time too long, resulting in serious grain coarsening of complex components during forming process, and the performance of components is greatly reduced. Therefore, the regulation of gas pressure directly affects the final forming quality of the alloy.

[0099] Example 6

[0100] A 2mm CoCrFeNiMn high-entropy alloy plate was fixed on the welding machine plane, and a tungsten-rhenium alloy stirring tool with a shoulder diameter of 11mm was used to stir the local area needing superplastic forming in single / multi-pass friction stir processing, the stirring needle speed was 600rpm, and the welding speed was 200mm / min. Another CoCrFeNiMn high-entropy alloy plate was processed in the same way. The two single / multi-pass processed CoCrFeNiMn high-entropy alloy plates were stacked together after the local superplastic forming area was coated with a soldering inhibitor, and were fixed on the welding machine plane. A tungsten-rhenium alloy stirring tool with a shoulder diameter of 11mm was used to stir the area needing lap joint in two / multi-layer plates, the stirring needle speed was 600rpm, and the welding speed was 200mm / min. The prepared plate was placed in the mold and heated to 700℃, and then superplastic forming was carried out under a gas pressure of 10MPa.

[0101] Technical effects: Fine-grained structure with high-angle grain boundary ratio of 94% and average grain size of 2.4 microns was successfully obtained in the local superplastic forming area. Fine-grained structure with high-angle grain boundary ratio of 95% and grain size of 2.6 microns was also successfully obtained in the friction stir lap joint area. Finally, a complex component was obtained by local forming.

[0102] Comparative Example 10

[0103] A 2mm CoCrFeNiMn high-entropy alloy plate was fixed on the welding machine plane, and a tungsten-cobalt alloy stirring tool with a shoulder diameter of 11 mm was used to perform single / multi-pass friction stirring on the local area that needed to be superplastically formed. The stirring needle rotation speed was 700 rpm, and the welding speed was 250 mm / min. Another CoCrFeNiMn high-entropy alloy plate was subjected to single / multi-pass friction stirring on the local area that needed to be superplastically formed using the same processing parameters. The two single / multi-pass processed CoCrFeNiMn high-entropy alloy plate local superplastic forming areas were coated with a stop flux and stacked together, and then fixed on the welding machine plane. A tungsten-cobalt alloy stirring tool with a shoulder diameter of 11 mm was used to perform friction lap joining on the areas that needed to be lap joined in the two layers / multi-layers of plates. The stirring needle rotation speed was 700 rpm, and the welding speed was 250 mm / min. The prepared plate was placed in the mold and heated to 700°C, and then superplastic forming was performed under a gas pressure of 10 MPa. Cracks occurred during the deformation process.

[0104] Technical effects: In the local superplastic forming area, a fine-grained structure with a high-angle grain boundary proportion of 94% and an average grain size of 3 microns was successfully obtained. In the friction lap joining area, a fine-grained structure with a high-angle grain boundary proportion of 95% and a grain size of 3.4 microns was also successfully obtained. The larger grain size makes the CoCrFeNiMn high-entropy alloy plate not have superplastic deformation capability.

[0105] Comparative Example 11

[0106] A 2mm CoCrFeNiMn high-entropy alloy plate was fixed on the welding machine plane, and a tungsten-cobalt alloy stirring tool with a shoulder diameter of 11 mm was used to perform single / multi-pass friction stirring on the local area that needed to be superplastically formed. The stirring needle rotation speed was 600 rpm, and the welding speed was 200 mm / min. Another CoCrFeNiMn high-entropy alloy plate was subjected to single / multi-pass friction stirring on the local area that needed to be superplastically formed using the same processing parameters. The two single / multi-pass processed CoCrFeNiMn high-entropy alloy plate local superplastic forming areas were coated with a stop flux and stacked together, and then fixed on the welding machine plane. A tungsten-cobalt alloy stirring tool with a shoulder diameter of 11 mm was used to perform friction lap joining on the areas that needed to be lap joined in the two layers / multi-layers of plates. The stirring needle rotation speed was 600 rpm, and the welding speed was 200 mm / min. The prepared plate was placed in the mold and heated to 700°C, and then superplastic forming was performed.

[0107] Technical effects: The larger gas pressure leads to too fast a superplastic deformation rate, which causes cracks in the plastic forming area.

[0108] From the above examples and comparative examples, it can be seen that the single / multi-pass friction stir processing and friction stir lap joining technology is an improvement on the traditional superplastic forming / diffusion bonding technology. Unlike the traditional method, the process improves the structure of the superplastic forming area of the plate and combines the friction stir lap joining process to join the double / multi-layer plate. On the one hand, the process can significantly improve the efficiency of superplastic forming. On the other hand, the superplastic forming area and the lap joining area are both fine-grained / ultra-fine-grained structures, so that the material as a whole has uniform superplastic deformation capability, thereby obtaining a complex component with a multi-layer structure and excellent performance through superplastic forming at high temperature. Therefore, the process can further promote the application of alloy superplastic forming technology to complex components.

[0109] It is easily understood by those skilled in the art that the advantageous technical features of each mode described above can be freely combined and superimposed without conflict.

[0110] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application. The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of manufacturing a multilayer as-cast metal sheet superplastic formed, characterized in that, The method comprises the following steps: a plate preparation step of preparing at least two cast metal plates to be overlapped in the thickness direction of the metal plates; a plate processing step of determining the overlapping area and the superplastic deformation area of each of the cast metal plates, and stir-friction processing the superplastic deformation area of each of the cast metal plates; a plate stacking step of stacking the stir-friction processed metal plates on top of each other, and ensuring that the overlapping areas of each of the metal plates correspond to each other; a welding and overlapping step of stir-friction welding and overlapping the overlapping areas of each of the metal plates at room temperature outside the superplastic mold; a superplastic forming step of placing the metal plates welded together in the superplastic mold, heating to a preset temperature, filling inert gas into the superplastic deformation area, and obtaining a target metal component in three dimensions by controlling the gas pressure of the superplastic forming; the superplastic deformation area of each of the metal plates after stir-friction processing is a uniform ultra-fine grain / fine grain area; the process parameters of the stir-friction welding and overlapping of the overlapping areas are the same as the process parameters of the stir-friction processing of the superplastic deformation area, so that the structures of the superplastic deformation area and the overlapping area are equivalent, the process parameters include the rotation speed of the stir head and the welding speed, the cast metal plate is one of a titanium alloy plate, a high-entropy alloy plate, and a steel plate, the rotation speed of the stir head is 200-600 rpm, and the welding speed is 25-200 mm / min, so that the local area of the superplastic forming is a small equiaxed structure with a high proportion of high-angle grain boundaries.

2. The method according to claim 1, wherein the greater the thickness of the cast metal plate to be processed, the greater the rotation speed of the stir head.

3. The method according to claim 1, wherein the gas pressure is 0.1-10 MPa.

4. The method according to claim 1, wherein after the stir-friction processing of the superplastic deformation area of each of the cast metal plates, before the plate stacking step, the method further comprises: applying a flux to the opposite superplastic deformation areas of the two metal plates to be overlapped.

5. The method according to claim 1, wherein in the superplastic forming step, a flux is applied to the area where the superplastic mold and the metal plate can contact.

6. The method according to claim 1, wherein in the welding and overlapping step, an air passage is left during the stir-friction welding and overlapping of the overlapping areas, and in the superplastic forming step, the inert gas is filled into the superplastic deformation area through the air passage.

7. A metal member characterized by The method is prepared by the method according to any one of claims 1-6.

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