Thermomechanical treatment method for improving mechanical property of aluminum-lithium alloy special-shaped transition cabin section

Abstract

The invention relates to a thermomechanical treatment method for improving the mechanical property of an aluminum-lithium alloy special-shaped transition cabin section, in the method, in the forging cogging stage, an isothermal low-speed deformation mode is adopted for multidirectional forging cogging, casting defects are eliminated, and a coarse crystal phase and a grain structure are refined; in the forming stage, high-temperature isothermal forming is adopted for restraining recrystallized grain growth, and meanwhile the forming load can be reduced; in-mold local cold compression is adopted after solid solution heat treatment, uniform cold deformation can be obtained through local cold compression, quenching residual stress can be reduced, and strengthened compact precipitation can be promoted. Therefore, through cooperation and regulation and control of a full-process deformation treatment process, a coarse crystal phase can be fully refined, a uniform and fine grain structure and a compact precipitation strengthening phase are obtained, and therefore the high-performance complex special-shaped transition cabin section is developed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal material deformation heat treatment, in particular to a deformation heat treatment method for improving the mechanical properties of an aluminum-lithium alloy shaped transition cabin section. BACKGROUND

[0002] The material system of the existing shaped cabin section is mainly 400MPa aluminum-copper alloy. The shaped cabin section has a complex shaped appearance and a high-gusset thin-wall structure, and needs to withstand extremely high aerodynamic axial pressure and impact load during service. Therefore, the mechanical properties and uniformity thereof are required to be extremely high. In order to achieve structural lightweighting, the transition cabin section is manufactured by using aluminum-lithium alloy instead of aluminum-copper alloy, which can reduce the structure by 10% and improve the mechanical properties by 20%. However, the high-quality aluminum-lithium alloy ingot smelting preparation technology for engineering application has shortcomings, and the component forming manufacturing technology suitable therefor is not mature. Therefore, the 500MPa aluminum-lithium alloy with high specific strength and high specific stiffness has not been applied in the material system of the shaped cabin section.

[0003] At present, the aluminum-lithium alloy transition cabin section manufacturing technology is still in the blank stage. The following problems are prone to occur in the forming manufacturing process: 1) the aluminum-lithium alloy has high alloying degree and strong hydrogen absorption capacity. Metallurgical defects such as coarse crystal phase, pores and porosity are easily formed in the original material melting and casting process, which are difficult to be fully eliminated under the conventional process, and seriously restrict the improvement of the subsequent product performance; 2) during the conventional process forming and heat treatment process, the force-thermal energy field of different parts is uneven, and abnormal grain growth is prone to occur at local positions; 3) cold deformation after solid solution heat treatment of the aluminum-lithium alloy is the key to reducing quenching residual stress and promoting the dense precipitation of the main strengthening phase T1 phase. However, the shape of the transition cabin section is complex, and there is a lack of related process technology for obtaining uniform cold deformation. SUMMARY

[0004] Starting from the above-mentioned technical problems, the purpose of the present application is to provide a deformation heat treatment method for improving the mechanical properties of an aluminum-lithium alloy shaped transition cabin section. In the forging breakdown stage, the method adopts isothermal low-speed deformation for multi-directional forging breakdown, eliminates casting defects and refines coarse crystal phase and grain structure; in the forming stage, high-temperature isothermal forming is adopted to inhibit recrystallization grain growth, and the forming load can be reduced; after solid solution heat treatment, local cold compression in the mold is adopted. Local cold compression can obtain uniform cold deformation, reduce quenching residual stress and promote strengthening dense precipitation, and solve the technical problems existing in the forming manufacturing process of the aluminum-lithium alloy transition cabin section in the prior art.

[0005] Specifically, according to one aspect of the present application, a deformation heat treatment method for improving the mechanical properties of an aluminum-lithium alloy shaped transition cabin section is provided, and the method comprises: S100, under a first preset temperature condition, multi-directional forging and blooming of the cast ingot blank is performed based on an isothermal mode, and the deformation rate of the cast ingot blank is controlled to be 5-10 mm / s during the forging and blooming, thereby obtaining a homogeneous forging blank, wherein the first preset temperature is 400±20℃; S200, under a second preset temperature condition, isothermal forging and extrusion compounding is performed on the obtained homogeneous forging blank to shape the homogeneous forging blank, thereby obtaining a shaped special-shaped transition cabin section, wherein the second preset temperature is 460-480℃. S300, the shaped special-shaped transition cabin section is sequentially subjected to solid solution treatment, local cold pressing and aging treatment.

[0006] Preferably, during the multi-directional forging and blooming of the cast ingot blank in step S100, the temperature of the cast ingot blank and the blooming die used for the forging and blooming of the cast ingot blank is controlled to be 400±20℃.

[0007] Preferably, in step S100, the specific operation of multi-directional forging and blooming of the cast ingot blank based on the isothermal mode is to control the temperature of the cast ingot blank and the blooming die to be stable at the first preset temperature condition during the multi-directional forging and blooming, and to perform heading and elongation on the cast ingot blank in three orthogonal directions, wherein each heading and elongation in the three orthogonal directions is one pass, and the multi-directional forging and blooming process needs at most four passes, and the three orthogonal directions refer to a first direction, a second direction and a third direction which are mutually orthogonal.

[0008] Preferably, the heading deformation amount of the cast ingot blank each time is 57-62%.

[0009] Preferably, in step S200, the obtained homogeneous forging blank is placed in a shaping die, and the temperature of the shaping die and the homogeneous forging blank is controlled to be the second preset temperature.

[0010] Preferably, in step S200, during the isothermal forging and extrusion compounding shaping of the obtained homogeneous forging blank, the shaping die is placed in a ring-shaped heating furnace and continuously heated, and the temperature in the ring-shaped heating furnace is controlled to be the second preset temperature.

[0011] Preferably, in step S300, the solid solution treatment is specifically: under the condition that the temperature is 500-510℃, the shaped special-shaped transition cabin section is heat treated for 3.5-4.5h, and then subjected to room temperature water quenching.

[0012] Preferably, in step S300, the local cold pressing is specifically: in the shaping die, thin steel sheets are sequentially pasted on the rib, web, upper end frame and lower end frame positions of the shaped special-shaped transition cabin section after room temperature water quenching, and the positions of the shaped special-shaped transition cabin section to which the thin steel sheets are pasted are subjected to cold pressing treatment, and the process is repeated 2-6 times, wherein the deformation amount of single cold pressing treatment is 1-3%.

[0013] Preferably, the aging treatment in the step S300 is specifically aging treatment at 60±10℃ for 24±2h.

[0014] The deformation heat treatment method for improving the mechanical properties of the aluminum-lithium alloy shaped transition cabin section provided by the application adopts multi-directional open forging by isothermal low-speed deformation in the open forging stage, eliminates casting defects and refines coarse crystalline phases and grain structures; adopts high-temperature isothermal forming in the forming stage to inhibit recrystallization grain growth and reduce forming load; adopts local cold compression in the mold after solid solution heat treatment, and the local cold compression can obtain uniform cold deformation and reduce quenching residual stress and promote strengthening and dense precipitation. Therefore, the application can fully refine coarse crystalline phases, obtain uniform and fine grain structures and dense precipitation strengthening phases by cooperation and regulation of the whole-process deformation treatment process, so as to develop a high-performance complex shaped transition cabin section. BRIEF DESCRIPTION OF DRAWINGS

[0015] In the present application, the drawings are provided to better illustrate the content of the present application, but the present application is by no means limited thereto.

[0016] Figure 1 A flow chart of the deformation heat treatment method for improving the mechanical properties of the aluminum-lithium alloy shaped transition cabin section provided by the present application is shown; Figure 2 A schematic diagram of multi-directional open forging in the present application is shown; Figure 3 A schematic diagram of forging by local cold compression in the present application is shown; Figure 4 A comparative schematic diagram of the internal grain structure of the shaped transition cabin section after forming in Example 1 and Comparative Example 1 is shown; Figure 5 A comparative schematic diagram of the internal grain structure of the shaped transition cabin section after forming in Example 2 and Comparative Example 2 is shown; Figure 6 A comparative schematic diagram of the internal structure of the product in Example 3 and Comparative Example 3 is shown. DETAILED DESCRIPTION

[0017] The present application will be further described in detail below in combination with the drawings and specific embodiments. It will be understood that other embodiments are considered, and these other embodiments can be implemented without departing from the scope or spirit of the present application. Therefore, the following detailed description is non-limiting.

[0018] Unless otherwise specified, all figures used in this specification and claims to indicate feature dimensions, quantities, and physical properties should be understood to be modified by the term "about" in all cases. Therefore, unless stated to the contrary, the numerical parameters listed in the foregoing specification and appended claims are approximations, and those skilled in the art can appropriately modify these approximations to obtain the desired characteristics using the teachings disclosed herein. The use of numerical ranges indicated by endpoints includes all numbers within that range and any range within that range; for example, 1 to 5 includes 1, 1.1, 1.3, 1.5, 2, 2.75, 3, 3.80, 4, and 5, etc.

[0019] like Figures 1-3 As shown, this invention provides a deformation heat treatment method for improving the mechanical properties of irregularly shaped transition sections in aluminum-lithium alloys, the method comprising: S100. Under the first preset temperature condition, the ingot billet is forged in a multi-directional manner based on the isothermal method, and the deformation rate of the ingot billet is controlled to be 5-10 mm / s during the forging process, thereby obtaining a homogeneous forging billet, wherein the first preset temperature is 400±20℃. In step S100, the temperatures of the ingot billet and the blanking mold used for forging the ingot billet are both controlled between the first preset temperature of 400±20℃. Controlling the temperatures of the blanking mold and the ingot billet to be the same can effectively prevent temperature drop. During the casting blanking process, if the temperature is too high, the microstructure will not be refined enough, and if the temperature is too low, cracking is likely to occur. In step S100, the specific operation of multi-directional forging blanking is as follows: The temperature of the ingot billet and the blanking die is controlled to be stable under the first preset temperature condition during the multi-directional forging blanking process. The ingot billet is then upsetting and drawing in three orthogonal directions. Each upsetting and drawing in one of the three orthogonal directions constitutes one pass. The multi-directional forging blanking process requires a maximum of four passes. The three orthogonal directions refer to the first, second, and third mutually orthogonal directions. Figure 2 As shown, specifically, "one pass" refers to sequentially upsetting the ingot billet once in the first direction, drawing it once in the second direction, upsetting it once in the second direction, drawing it once in the third direction, upsetting it once in the third direction, and drawing it once in the first direction. Figure 2 In the diagram, the first direction (direction A) refers to the Z-axis direction, the second direction (direction B) refers to the X-axis direction, and the third direction (direction C) refers to the Y-axis direction. In step S100, the upsetting deformation of each ingot billet is 57-62%. Through large plastic deformation, the coarse crystalline phase can be fully broken and refined, and a dynamic recrystallization structure can be obtained, avoiding casting defects such as compaction and porosity, thereby preparing a homogeneous forging billet.

[0020] S200. Under the second preset temperature condition, the obtained homogeneous forging billet is subjected to isothermal forging and extrusion composite to form the homogeneous forging billet, thereby obtaining the formed irregular transition section, wherein the second preset temperature is 460-480℃. In step S200, the obtained homogeneous forging billet is placed in a forming mold, which is placed in an annular heating furnace and continuously heated. By controlling the temperature inside the annular heating furnace, the temperature of the forming mold and the homogeneous forging billet can be controlled. This operation can ensure the uniformity of the temperature field. Under high temperature conditions, the deformation storage energy can be reduced, the recrystallization grain growth can be suppressed, and a uniform and fine deformed structure can be obtained.

[0021] S300, the formed irregular transition section is subjected to solution treatment, local cold pressing and aging treatment in sequence.

[0022] In step S300, the solution treatment specifically involves: holding the formed irregular transition section at a temperature of 500-510℃ for 3.5-4.5 hours, and then quenching it in water at room temperature. In step S300, the local cold pressing specifically involves: in the forming mold, thin steel sheets (such as...) are sequentially pasted onto the ribs, webs, upper frame, and lower frame positions on the irregularly shaped transition section after room temperature water quenching. Figure 3 , Figure 3 The gaskets in the design are thin steel sheets, and the forgings are irregularly shaped transition sections. Cold pressing is performed on the locations where the thin steel sheets are attached to the irregularly shaped transition sections. The deformation of the ribs, webs, upper frames, and lower frames on the irregularly shaped transition sections during a single cold pressing process is 1-3%. In step S300, the aging treatment specifically involves holding the temperature at 60±10℃ for 24±2 hours. The combined use of solution treatment, local cold pressing, and aging heat treatment promotes the precipitation of the strengthening phase and improves the overall performance of the transition section.

[0023] In the above embodiments, the deformation heat treatment method employs isothermal low-speed deformation for multi-directional forging during the forging stage, eliminating casting defects and refining coarse crystalline phases and grain structure. During the forming stage, high-temperature isothermal forming suppresses recrystallization grain growth and reduces forming load. After solution heat treatment, localized cold compression within the mold is used; this localized cold compression achieves uniform cold deformation, reduces residual quenching stress, and promotes strengthening and dense precipitation. Therefore, this invention, through the coordination and control of the entire deformation treatment process, can fully refine coarse crystalline phases, obtain uniform fine grain structure and dense precipitated strengthening phases, thereby developing high-performance complex irregular-shaped transition sections and completing the deformation heat treatment of the irregular-shaped transition sections' mechanical properties.

[0024] Example

[0025] The application will be described in more detail below with reference to the embodiments. It should be noted that the description and embodiments are intended to facilitate understanding of the present application, and are not intended to limit the present application. The scope of protection of the present application is defined by the appended claims.

[0026] Example 1 (1) The ingot blank is placed in the cogging die for cogging, and the temperature of the ingot blank and the cogging die during the cogging is controlled to be stable at 400°C, the deformation rate of the ingot blank is 8 mm / s, the deformation amount of the ingot blank is 60% for each upsetting, the number of cogging is three passes, and a homogenized forging blank is obtained; (2) The homogenized forging blank is placed in the forming die, the temperature of the homogenized forging blank and the forming die is controlled to be stable at 470°C by the ring heating furnace, and the homogenized forging blank is subjected to combined forging and extrusion forming based on the high-temperature isothermal forming mode, and a shaped special-shaped transition cabin section is obtained, as shown in Figure 4 b, the obtained shaped special-shaped transition cabin section is internally uniform and refined, and the formation of local abnormal coarse grains is effectively avoided; (3) The shaped special-shaped transition cabin section is kept at a temperature of 505°C for 4 hours and then subjected to room temperature water quenching; then, thin steel sheets are pasted on the rib, web, upper end frame and lower end frame positions of the shaped special-shaped transition cabin section in the forming die, and cold pressing is performed on the positions of the shaped special-shaped transition cabin section where the thin steel sheets are pasted, wherein the deformation amount of the rib, web, upper end frame and lower end frame of the shaped special-shaped transition cabin section is 2% for each cold pressing, and the whole local cold pressing operation is repeated for 4 times; finally, the temperature is kept at 60°C for 24 hours.

[0027] The product obtained in Example 1 is subjected to appearance and X-ray detection, no deformation is found in appearance, the size meets the design requirements, and the internal structure of the product is compact.

[0028] Example 2 (1) The ingot blank is placed in the cogging die for cogging, and the temperature of the ingot blank and the cogging die during the cogging is controlled to be stable at 380°C, the deformation rate of the ingot blank is 8 mm / s, the deformation amount of the ingot blank is 57% for each upsetting, the number of cogging is two passes, and a homogenized forging blank is obtained; (2) The homogenized forging blank is placed in the forming die, the temperature of the homogenized forging blank and the forming die is controlled to be stable at 460°C by the ring heating furnace, and the homogenized forging blank is subjected to combined forging and extrusion forming based on the high-temperature isothermal forming mode, and a shaped special-shaped transition cabin section is obtained, as shown in Figure 5 b, the obtained shaped special-shaped transition cabin section realizes the homogenization of the crystalline phase and eliminates the uneven distribution state of the local position crystalline phase aggregation; (3) After the irregular transition section is formed at 500℃, it is kept at room temperature for 3.5h and then water quenched at room temperature. Then, in the forming mold, thin steel sheets are pasted on the ribs, webs, upper frame and lower frame of the irregular transition section in sequence, and cold pressing is performed on the position where the thin steel sheets are pasted on the irregular transition section. The deformation of the ribs, webs, upper frame and lower frame of the irregular transition section in a single cold pressing is 1%, and the entire local cold pressing operation is repeated twice. Finally, it is kept at 50℃ for 22h.

[0029] The product obtained in Example 2 was subjected to appearance and X-ray inspection. No deformation was found in the appearance, the size met the design requirements, and the internal structure of the product was compact.

[0030] Example 3 (1) The ingot billet is placed in the blanking mold for forging and blanking. The temperature of the ingot billet and the blanking mold is controlled to be stable at 420℃ during the forging and blanking process. The deformation rate of the ingot billet is 8mm / s. The deformation amount of the ingot billet in each upsetting is 62%. The number of forging and blanking is four times to obtain a homogeneous forging billet. (2) The homogeneous forging billet is placed in the forming mold, and the temperature of the forming mold and the homogeneous forging billet is controlled at 480°C by the ring heating furnace. The homogeneous forging billet is forged and extruded in combination based on the high temperature isothermal forming method to obtain the irregular transition section after forming. (3) After the irregular transition section is formed at a temperature of 510℃, it is kept at a temperature of 4.5h and then quenched at room temperature. Then, in the forming mold, thin steel sheets are pasted on the ribs, webs, upper frame and lower frame of the irregular transition section in sequence, and cold pressing is performed on the position where the thin steel sheets are pasted on the irregular transition section. The deformation of the ribs, webs, upper frame and lower frame of the irregular transition section in a single cold pressing is 3%, and the entire local cold pressing operation is repeated 6 times. Finally, it is kept at a temperature of 70℃ for 26h.

[0031] The product obtained in Example 3 was subjected to appearance and X-ray inspection. No deformation was found in the appearance, the size met the design requirements, and the internal structure of the product was compact.

[0032] Comparative Example 1 Similar to Example 1, the difference is that in Comparative Example 1, during the forging process in step (1), the deformation rate of the ingot billet is 20 mm / s, and the deformation amount of the ingot billet in each upsetting is 40%.

[0033] The interior of the formed irregular transition section obtained in Example 1 will be inspected, such as... Figure 4 As shown in a, from Figure 4As can be seen in a, there is an abnormal coarse grain phenomenon in some local locations. When the final product obtained by Comparative Example 1 is subjected to appearance and X-ray inspection, the appearance is slightly deformed and the interior of the product is compacted and loose. This is because the single deformation amount of Comparative Example 1 is small and the deformation rate is large, which fails to fully break down and refine the coarse crystals in the workpiece, thus resulting in the compacted and loose interior of the final product and the slight deformation of the product surface.

[0034] Comparative Example 2 Similar to Example 2, the difference is that in Comparative Example 2, the temperature is controlled between 360-480°C during the forging and extrusion composite forming process in step (2).

[0035] The product obtained in Comparative Example 2 underwent appearance and X-ray inspection. The product showed deformation and wrinkling, localized areas of excessive wall thickness, and cracks. This was because the temperature in Comparative Example 2 was not controlled at an isothermal level during the workpiece forming process, leading to a sharp increase in forming load, causing surface deformation and wrinkling, localized excessive wall thickness, and cracks. Figure 5 As shown in Figure a, the crystalline phase aggregates in local locations of the irregularly shaped transition section obtained in Comparative Example 2 exhibit an uneven distribution.

[0036] Comparative Example 3 Similar to Example 3, the difference is that Comparative Example 3 did not perform local steel sheet application during the cold pressing process in step (3), but instead performed overall cold pressing on the entire irregular transition section.

[0037] The product obtained in Comparative Example 3 was subjected to appearance and X-ray inspection. The appearance was severely deformed and the dimensions could not meet the design requirements. This is because Comparative Example 3 adopted an overall cold pressing process. Due to insufficient pressure, it was unable to overcome the material flow resistance and friction to fully fill the cavity, resulting in the final product not being properly formed.

[0038] The internal components of the products obtained in Example 3 and Example 3 will be tested and analyzed, such as... Figure 6 As shown, Figure 6 a shows a schematic diagram of the interior of the product obtained in Comparative Example 3. Figure 6 b shows a schematic diagram of the interior of the product obtained in Example 3, from Figure 6 a and Figure 6 As can be seen from b, compared with Comparative Example 3, the product obtained in Example 3 achieved uniform and dense precipitation of the aluminum-lithium alloy strengthening phase, and the precipitation density was significantly increased.

[0039] In summary, the deformation heat treatment method provided in this application, through the coordination and control of the entire deformation treatment process, can fully refine the coarse crystalline phase, obtain a uniform fine grain structure and a dense precipitated strengthening phase, thereby developing a high-performance complex irregular transition section.

[0040] It should be noted that, in order to solve the technical problems existing in Comparative Examples 2 and 3, in addition to using the heat treatment method provided in this application, large-tonnage forging equipment can also be used. However, large-tonnage forging equipment will significantly increase production costs.

[0041] Obviously, those skilled in the art can make various modifications and variations to this disclosure without departing from its spirit and scope. Therefore, if such modifications and variations fall within the scope of the claims of this invention and their equivalents, this disclosure is also intended to include such modifications and variations.

Claims

1. A deformation heat treatment method for improving the mechanical properties of irregularly shaped transition sections in aluminum-lithium alloys, characterized in that, The method includes: S100. Under the first preset temperature condition, the ingot billet is forged in a multi-directional manner based on the isothermal method, and the deformation rate of the ingot billet is controlled to be 5-10 mm / s during the forging process, thereby obtaining a homogeneous forging billet, wherein the first preset temperature is 400±20℃. S200. Under the second preset temperature condition, the obtained homogeneous forging billet is subjected to isothermal forging and extrusion composite to form the homogeneous forging billet, thereby obtaining the formed irregular transition section, wherein the second preset temperature is 460-480℃. S300, the formed irregular transition section is subjected to solution treatment, local cold pressing and aging treatment in sequence.

2. The method according to claim 1, characterized in that, In the multi-directional forging process of the ingot billet in step S100, the temperature of both the ingot billet and the forging die used to forge the ingot billet is controlled at 400±20℃.

3. The method according to claim 2, characterized in that, In step S100, the specific operation of multi-directional forging of the ingot billet based on isothermal method is as follows: the temperature of the ingot billet and the forging mold is controlled to be stable under the first preset temperature condition during the multi-directional forging process, and the ingot billet is upsetting and drawing in three orthogonal directions. Each upsetting and drawing in the three orthogonal directions is one pass. The multi-directional forging process requires up to four passes. The three orthogonal directions refer to the first direction, the second direction and the third direction that are orthogonal to each other.

4. The method according to claim 3, characterized in that, The upsetting deformation of each ingot billet is 57-62%.

5. The method according to claim 4, characterized in that, In step S200, the obtained homogeneous forging billet is placed in the forming mold, and the temperature of the forming mold and the homogeneous forging billet is controlled to a second preset temperature.

6. The method according to claim 5, characterized in that, In step S200, during the isothermal forging and extrusion process of the obtained homogeneous forging billet, the forming mold is placed in an annular heating furnace and continuously heated, while the temperature inside the annular heating furnace is controlled to a second preset temperature.

7. The method according to claim 6, characterized in that, In step S300, the solution treatment specifically involves: keeping the formed irregular transition section at a temperature of 500-510℃ for 3.5-4.5 hours, and then performing room temperature water quenching.

8. The method according to claim 7, characterized in that, In step S300, the local cold pressing is specifically as follows: in the forming mold, thin steel sheets are sequentially pasted at the positions of the ribs, webs, upper frame and lower frame on the irregularly shaped transition section after room temperature water quenching, and cold pressing is performed on the positions where the thin steel sheets are pasted on the irregularly shaped transition section. This process is repeated 2-6 times, wherein the deformation amount of a single cold pressing is 1-3%.

9. The method according to claim 8, characterized in that, In step S300, the aging process specifically involves maintaining the temperature at 60±10℃ for 24±2 hours.

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