High-strength aluminum alloy complex sheet metal part shape-integration control method

Abstract

This invention provides an integrated control method for the shape and properties of complex sheet metal parts made of high-strength aluminum alloy, belonging to the field of sheet metal forming technology. It addresses the problems of existing technologies for forming complex shapes, low dimensional accuracy, and severe local thinning in high-strength aluminum alloy sheet metal parts. The method includes: Step 1, designing the upper and lower dies used for forming based on the digital model after adding process segments; Step 2, performing finite element simulation on the target part to obtain the upper die pressing stroke H and the equivalent strain ε corresponding to the sheet deformation time. H The relationship is as follows: Step 3, perform multiple pre-forming processes and control the deformation amount of each pre-forming process; Step 4, after solution treatment, the pre-formed part is quickly transferred to a mold for final forming and quenching; Step 5, the part is removed and subjected to aging treatment to obtain a high-strength, high-dimensional-accuracy part. This invention is used to form complex plate-like components of high-strength aluminum alloy and can ensure high strength, dimensional accuracy and uniform wall thickness.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of forming of plate components, and particularly relates to a shape and property integrated control method for a high-strength aluminum alloy complex sheet metal part. BACKGROUND

[0002] High-strength aluminum alloy refers to an aluminum alloy with a tensile strength greater than 480 MPa, mainly 2xxx series of Al-Cu-Mg base and 7xxx series of Al-Zn-Mg-Cu base alloy. High-strength aluminum alloy is widely used in aerospace vehicles due to its small density and high strength, and greatly realizes lightweight. With the further development of new generation aircraft towards lightweight, stealth, high reliability, long life and high speed, the parts show the characteristics of structural integration, thin-walled and size accuracy. Forming thin-walled components with high size accuracy and extremely complex shape brings great challenges to existing forming methods.

[0003] High-strength aluminum alloy needs to be heat treated to achieve states such as T4, T6 and T8 in order to achieve high tensile strength, but the room temperature forming performance under such states is poor, and it is difficult to form complex shape components and has large springback. Hot forming processes such as hot gas bulging, superplastic forming and hot hydraulic forming can improve the deformation performance of the material and reduce the deformation resistance of the material, so as to achieve the purpose of forming complex plate components. When forming under hot state, the strength of the hot formed component decreases due to the softening effect of recovery and recrystallization. Therefore, heat treatment is needed after hot forming to achieve the purpose of strengthening. During the heating and cooling process in the heat treatment process, uneven heating is easy to cause distortion of the component, and the size accuracy cannot meet the use requirements. In addition, when forming under hot state, the hardening capacity of the material decreases sharply, and the deformation is easy to concentrate in some local positions, especially in positions with complex characteristics, which leads to serious local thinning and even rupture, seriously affecting the forming quality of the component.

[0004] In order to solve the problems of existing technology of high-strength aluminum alloy plate components, such as difficulty in forming complex shape, low size accuracy and serious local thinning, a method for forming high-strength aluminum alloy complex plate components and ensuring high strength and size accuracy is needed. SUMMARY

[0005] The application proposes a shape and property integrated control method for a high-strength aluminum alloy complex sheet metal part to solve the problems of existing technology of high-strength aluminum alloy plate components, such as difficulty in forming complex shape, low size accuracy and serious local thinning, which can form high-strength aluminum alloy complex plate components and ensure high strength, size accuracy and wall thickness uniformity.

[0006] In order to solve the above problems, the technical scheme adopted by the application is:

[0007] A shape-property integrated control method of high-strength aluminum alloy complex sheet metal parts, the shape-property integrated control method comprises the following steps:

[0008] 1. Designing a forming die

[0009] 1.1. According to the characteristics of the target part 2-1, add a process section to the target part 2-1 numerical model to obtain a part with a process section 2-2 and obtain its numerical model;

[0010] 1.2. Design the upper die 1 and the lower die 3 used for forming according to the numerical model of the part with the process section 2-2, and the profiles of the two are set according to the profile of the part with the process section 2-2;

[0011] 1.3. Prepare a high-strength aluminum alloy sheet blank according to the numerical model of the part with the process section 2-2.

[0012] 2. Finite element simulation of part forming

[0013] 2.1. Anneal the high-strength aluminum alloy sheet blank at a full annealing temperature T A Under the condition of annealing treatment, obtain an annealed sheet blank, i.e. O-state sheet blank 2;

[0014] 2.2. Test the mechanical properties of the O-state sheet blank 2 through uniaxial tensile test or sheet hydraulic bulging test to obtain the strain ε D and stress-strain relationship when the O-state sheet blank 2 is dispersedly unstable, and fit to obtain the material hardening model:

[0015] σ=K·ε n

[0016] Wherein, σ is the true stress, ε is the true strain, K is the strength coefficient, and n is the strain hardening index, i.e. an index indicating the uniform plastic deformation capacity of the material;

[0017] 2.3. Perform finite element simulation on the material hardening model obtained in step 2.2 to simulate the process of forming the part with the process section 2-2 using the upper die 1 and the lower die 3, obtain the relationship H~ε H between the upper die 1 lower stroke H and the equivalent strain ε H of the O-state sheet blank 2 at the corresponding time of deformation, and obtain the maximum equivalent strain ε max of the O-state sheet blank 2 when the die is closed.

[0018] 3. Preforming of the part

[0019] 3.1. Place the upper die 1 and the lower die 3 on the working platform of the press and fix them with the upper and lower working platforms respectively, and perform opening and closing die test to ensure normal operation;

[0020] 3.2. Calculate the minimum preforming times m needed:

[0021] m=[εmax / ε D ]+1

[0022] wherein, [*] represents rounding integer;

[0023] 3.3. Calculate the allowed deformation amount ε of each preforming A :

[0024] ε A = ε max / m

[0025] 3.4. According to the H~ε relationship of step 2.3, we get: H

[0026] ε H = ε A , the down stroke of the upper die 1 is recorded as H1;

[0027] ε H = 2ε A , the down stroke of the upper die 1 is recorded as H2;

[0028] …

[0029] Thus, ε H = mε A , the down stroke of the upper die 1 is recorded as H m ;

[0030] 3.5. Place the O-state plate blank 2 on the lower die 3 at room temperature and position it, and the upper die 1 is pressed down to perform one preforming, and the down stroke is set according to step 3.4;

[0031] 3.6. Anneal the O-state plate blank 2 obtained by preforming in step 3.5 at a complete annealing temperature T A ;

[0032] 3.7. Repeat steps 3.5 and 3.6, a total of m times of preforming, and finally obtain the process section containing part 2-2.

[0033] 4. Final forming of the part

[0034] 4.1. Place the process section containing part 2-2 after preforming in step 3 in an air furnace for solid solution treatment, the temperature is set to T SHT , and the time is 10-50 minutes;

[0035] Further, spray a heat-conducting coating on the surface of the process section containing part 2-2 after preforming, and then place it in an air furnace for solid solution treatment, and the heat-conducting coating is graphite. In this way, better heat transfer between the part and the mold can be achieved, the cooling speed of the part is improved, and good quenching effect is achieved.

[0036] ​4.2. After solution, the part with process section 2-2 is quickly transferred to the final forming die at room temperature and positioned within 5 seconds, and then the die is quickly closed within 10 seconds.

[0037] The upper and lower dies of the final forming die are the same as the upper die 1 and the lower die 3 in step 3, and a gas flow channel 4 is provided in the upper die 1. The gas flow channel 4 has one inlet opening on the side wall of the upper die 1 and multiple outlets evenly distributed on different parts of the die surface of the upper die 1. After the final forming die is closed, 1-20 MPa of room temperature gas is introduced through the gas flow channel 4 to make the part with process section 2-2 tightly fit on the lower die. The gas is air, nitrogen or argon. The part with process section 2-2 is finally formed and rapidly cooled to achieve the purpose of quenching.

[0038] 5. The final forming die is opened, and the part with process section 2-2 is taken out and subjected to aging treatment. The aging treatment is natural aging or artificial aging. The natural aging is at room temperature, and the artificial aging is at a temperature of 160-180℃ for 6-50 hours. Then the process section is removed to obtain the target part 2-1.

[0039] Further, in step 4.2, the upper die 1 of the final forming die is a room temperature die, and the lower die 3 is set to a temperature of 100-250℃, i.e. a cold-hot combined die is used. In this way, the temperature drop of the blank is slowed down, the cold upper die is quickly cooled, and the thermal distortion is limited, better realizing the integrated control of part precision and microstructure performance.

[0040] Advantages of the present application:

[0041] Firstly, the present application simultaneously performs in-die quenching during final hot forming, and the formed part has high dimensional and shape precision and does not distort;

[0042] Secondly, the present application simultaneously performs in-die quenching during final hot forming, retains the microstructure at high temperature, and can obtain a part with high strength by combining with aging treatment;

[0043] Thirdly, the entire die does not need to be heated, which can reduce energy consumption and greatly improve safety;

[0044] Fourthly, the present application is suitable for manufacturing high-strength aluminum alloy integral complex components with high dimensional precision, surface precision and tensile strength, and has wide application prospects;

[0045] Fifthly, in the present application, the blank gradually cools down from a hot state under the pressure of the upper and lower dies during final forming, and the cooling of each part is relatively uniform, so the part has small residual stress;

[0046] Sixthly, the present application restores the strain hardening capacity through multiple annealing, and avoids the deformation concentration leading to serious wall thickness reduction;

[0047] VII. When the final part of the invention is formed and quenched in the mold, the introduction of pressurized gas can ensure that the part fits more tightly with the mold and achieve a good quenching effect.

[0048] 8. This invention combines finite element simulation to rationally allocate multiple pre-forming processes, simplifying the forming of complex parts into multiple simple part forming processes. Attached Figure Description

[0049] Figure 1 A schematic diagram of the target part;

[0050] Figure 2 This is a schematic diagram of the part containing the process section after it has been formed according to the present invention;

[0051] Figure 3 This is a schematic diagram of the part before forming according to the present invention;

[0052] Figure 4 This is a schematic diagram of the part after it has been formed according to the present invention;

[0053] Figure 5 This is a front view of the mold used during the forming process or the final forming mold of the present invention;

[0054] Figure 6 This is a top view of the mold used in the forming process or the final forming mold of the present invention;

[0055] Figure 7 for Figure 6 Cross-sectional view along line AA;

[0056] Figure 8 for Figure 6 Cross-sectional view along line BB;

[0057] Figure 9 The stress-strain curve is obtained by uniaxial tension of the 2195 aluminum-lithium alloy sheet in Example 1.

[0058] Figure 10 The actual stress-strain curve obtained by uniaxial tensile testing of the 2195 aluminum-lithium alloy sheet in Example 1;

[0059] Figure 11 The equivalent strain ε of the upper die pressing stroke H and the corresponding moment of slab deformation in Example 1 is... H The relationship H ~ ε H .

[0060] In the diagram: 1 Upper mold; 2 O-state slab; 2-1 Target part; 2-2 Part including process section; 3 Lower mold; 4 Gas flow channel. Detailed Implementation

[0061] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described below in conjunction with the accompanying drawings.

[0062] Example 1

[0063] Forming of 2195 aluminum-lithium alloy sheet with 2mm thickness Figure 1 The target part 2-1 is shown.

[0064] 1. Designing forming die

[0065] 1.1. According to the characteristics of the target part 2-1, add process section around the target part 2-1 to obtain the part with process section 2-2 and obtain its numerical model, as shown in Figure 2 .

[0066] 1.2. Design the upper die 1 and the lower die 3 used for forming according to the numerical model of the part with process section 2-2, and the profiles of the two are set according to the profile of the part with process section 2-2;

[0067] 1.3. Prepare high-strength aluminum alloy sheet blank according to the numerical model of the part with process section 2-2.

[0068] 2. Finite element simulation of part forming

[0069] 2.1. Anneal the high-strength aluminum alloy sheet blank at 410℃ for 1 hour to obtain the annealed sheet blank, i.e. the O-state sheet blank 2;

[0070] 2.2. Test the mechanical properties of the O-state sheet blank 2 by using a universal testing machine to obtain the engineering stress-strain curve (as shown in Figure 9 ) and the true stress-strain curve (as shown in Figure 10 ), and obtain the strain ε D = ln(1+0.1926) = 0.1761 at which the dispersion instability occurs, and fit to obtain the material hardening model:

[0071] σ = K·ε n = 415ε 0.261 ;

[0072] 2.3. Input the material hardening model obtained in step 2.2 into the finite element software to simulate the process of forming the part with process section 2-2 using the upper die 1 and the lower die 3, obtain the relationship H~ε H between the upper die 1 downstroke H and the equivalent strain ε H of the O-state sheet blank 2 at the corresponding time of deformation, as shown in Figure 11 , and obtain the maximum equivalent strain ε max = 0.4985 of the part with process section 2-2 when the die is closed.

[0073] 3. Part preforming

[0074] 3.1. Place the upper die 1 and the lower die 3 on the working platform of the press and fix them with the upper and lower working platforms respectively, and perform the opening and closing test to ensure the normal operation;

[0075] 3.2. Calculate the minimum number of pre-forming required as m

[0076] m = [ε max / ε D ]+1 = [0.4985 / 0.1761]+1 = 3

[0077] 3.3. Calculate the allowable deformation amount ε A for each pre-forming:

[0078] ε A = ε max / m = 0.1662

[0079] 3.4. Obtain the following according to the H-ε H relationship in step 2.3:

[0080] ε H = 0.1662, the lower stroke of the upper die 1 is recorded as 188.9 mm;

[0081] ε H = 0.3323, the lower stroke of the upper die 1 is recorded as 258.6 mm;

[0082] ε H = 0.4985, the lower stroke of the upper die 1 is recorded as 343.6 mm;

[0083] 3.5. Place the O-shaped blank 2 at room temperature on the lower die 3 and position it, as shown in Figure 3 , and perform one pre-forming by lowering the upper die 1, as shown in Figure 5 , and the lower stroke is set according to step 3.4;

[0084] 3.6. Anneal the O-shaped blank 2 obtained in step 3.5 at 410℃ for 1 hour;

[0085] 3.7. Repeat steps 3.5 and 3.6, and perform a total of 3 pre-formings, to finally obtain the process section containing part 2-2, as shown in Figure 4 .

[0086] 4. Final forming of the part

[0087] 4.1. Spray a heat-conducting coating on the surface of the process section containing part 2-2 after pre-forming in step 3, and then place it in an air furnace for solid solution treatment, with the temperature set at 520℃ and the time set at 30 minutes;

[0088] 4.2. Quickly transfer the solution-treated part 2-2 containing the process section to the final molding mold at room temperature and position it. The transfer time should be within 5 seconds. Then, quickly close the mold within 10 seconds. Figures 6 to 8 As shown, the upper and lower molds of the final forming mold are the same as the upper mold 1 and lower mold 3 in step 3, respectively. A gas flow channel 4 is provided in the upper mold 1. The inlet of the gas flow channel 4 opens on the side wall of the upper mold 1, and multiple outlets are provided, opening at different parts of the upper mold 1 and evenly distributed. After the mold is closed, 10MPa room temperature nitrogen gas is introduced through the gas flow channel 4 to make the part containing the process section 2-2 fit more tightly with the mold, complete the final forming of the part containing the process section 2-2 and rapidly cool down the part to achieve the purpose of quenching.

[0089] 5. Open the final forming mold, take out part 2-2 containing the process section and perform artificial aging treatment. The artificial aging temperature is 160℃ and the time is 48 hours. Then remove the process section to obtain the target part 2-1.

[0090] The tensile strength of the target part obtained in this embodiment is 581 MPa, and the fit to the tire reaches 0.23 mm.

[0091] Example 2

[0092] This embodiment is basically the same as Embodiment 1, except that natural aging is used in step 5, and the natural aging condition is standing at room temperature. The tensile strength of the target part is 432 MPa, and the fit to the tire reaches 0.21 mm.

[0093] Example 3

[0094] This embodiment is basically the same as Embodiment 1, except that: in step 4.1, a thermally conductive coating is sprayed onto the surface of the pre-formed part 2-2 containing the process section, and then it is placed in an air furnace for solution treatment. The thermally conductive coating is graphite. This setting allows for better heat transfer between the part and the mold, increases the cooling rate of the part, and achieves a good quenching effect.

[0095] Example 4

[0096] This embodiment is basically the same as Embodiment 1, except that: in step 4.2, the upper mold 1 of the final forming mold is a room temperature mold, and the temperature of the lower mold 3 is set to 100℃~250℃, that is, a combination of hot and cold molds is adopted. This setting slows down the temperature drop of the slab, allows for rapid cooling of the cold upper mold, and limits thermal distortion, thereby better achieving integrated control of part accuracy and microstructure properties.

[0097] Example 5

[0098] This embodiment is basically the same as Embodiment 1, except that in step 2.2, the mechanical properties of the O-state slab blank 2 are obtained by hydraulic bulging of the sheet metal. This setting allows for obtaining mechanical properties that are closer to the actual forming stress state of the slab blank, resulting in more accurate results.

[0099] Example 6

[0100] This example is basically the same as Example 1, except that 7B04, 2B06, 2219, and other heat treatable aluminum alloy sheets are used.

[0101] The present application has been disclosed in a preferred embodiment as above, however, not to limit the present application, any skilled person in the art, within the scope of the technical solution of the present application, can make some changes or modifications of the above disclosed structure and technical content as equivalent embodiments, any simple modification, equivalent change and modification of the above embodiments made according to the technical essence of the present application without departing from the technical solution of the present application, still belong to the scope of the technical solution of the present application.

Claims

1. A high-strength aluminum alloy complex sheet metal part shape-property integrated control method, characterized in that the shape-property integrated control method comprises the following steps: Step 1. Forming the upper die (1) and the lower die (3) used for forming according to the numerical model design after the addition process section; 1.

1. According to the characteristics of the target part (2-1), add process segments to the numerical model of the target part (2-1) to obtain a part with process segments (2-2) and its numerical model; 1.

2. According to the numerical model of the part with process segments (2-2), design the upper die (1) and the lower die (3) for forming, and the profiles of the two are set according to the profile of the part with process segments (2-2); 1.

3. According to the numerical model of the part with process segments (2-2), prepare a high-strength aluminum alloy plate blank; Step 2, finite element simulation is performed on the target part (2-1) to obtain the relationship between the lower stroke H of the upper die (1) and the equivalent strain ε of the O-state blank (2) at the corresponding deformation time H . 2.

1. annealing the high-strength aluminum alloy slab at a full annealing temperature T A to obtain an O-state slab (2) under the condition that 2.

2. Test the mechanical properties of the O-state slab (2) to obtain the strain ε of the O-state slab (2) when the dispersion instability occurs D and the stress-strain relationship, and the material hardening model is fitted: σ = K - ε n wherein σ is the true stress, ε is the true strain, K is the strength coefficient, n is the strain hardening index, that is, an index representing the uniform plastic deformation capacity of the material; 2.

3. Perform finite element simulation on the material hardening model obtained in step 2.2 to simulate the process of forming the process section part (2-2) using the upper die (1) and the lower die (3), obtain the relationship H~ε between the upper die (1) pressing stroke H and the equivalent strain ε of the O-state slab (2) at the corresponding time of deformation, and obtain the maximum equivalent strain ε of the O-state slab (2) when the die is closed. H H max ;​​ Step 3, multiple pre-forming is performed and the deformation amount of single pre-forming is controlled; 3.

1. Place the upper die (1) and the lower die (3) on the working platform of the press and fix them on the upper and lower working platforms respectively; 3.

2. Calculate the minimum pre-forming times m required: m=[ε max / ε D ]+1 wherein [ε max / ε D ] is rounded to the nearest integer; 3.

3. Calculate the amount of deformation ε allowed for each preform A : ε A =ε max / m 3.

4. H~s according to step 2.3 H The relationship results in: ε H =ε A When the upper die (1) is pressed down to the lower die (2), the stroke is recorded as H1. ε H =2ε A When the upper die (1) is pressed down to the second position, the stroke is denoted as H2. …… Thus, ε H = mε A When the upper die (1) is pressed down, the stroke is denoted as H m ; 3.

5. Place the O-state plate blank (2) on the lower die (3) at room temperature and position it, then press the upper die (1) to perform one pre-forming, and the pressing stroke is set according to step 3.4; 3.

6. The O-temper slab (2) obtained by preforming in step 3.5 is annealed at a full annealing temperature T A under the conditions. 3.

7. Repeat steps 3.5 and 3.6, a total of m pre-forming, finally obtain the part with process segments (2-2); Step 4, after pre-forming, the part is solid solution treated and quickly transferred to the final forming die for final forming and quenching; Step 5, take out the part and perform aging treatment to obtain the target part (2-1).

2. The high-strength aluminum alloy complex sheet metal part shape and property integrated control method according to claim 1, characterized in that, the step 4. part final forming 4.

1. The preformed process section part (2-2) from step 3 is solution treated in an air furnace at a temperature of T SHT for a time of 10 to 50 minutes. 4.

2. Quickly transfer the part with process segments (2-2) after solid solution to the final forming die at room temperature and position it, the transfer time is within 5 seconds, then quickly close the die, the closing time is within 10 seconds; Step 5. Open the final forming die, take out the part with process segments (2-2) and perform aging treatment, then remove the process segments to obtain the target part (2-1).

3. The method according to claim 2, wherein the method is characterized by: In step 2.2, the mechanical properties of the O-state plate blank (2) are tested by uniaxial tensile test or plate hydraulic bulging test.

4. The method of claim 2, wherein the method is characterized by: In step 4.1, a heat-conducting coating is sprayed on the surface of the part with process segments (2-2) after pre-forming, and then it is placed in an air furnace for solid solution treatment.

5. The method of claim 4, wherein the method is characterized by: The heat-conducting coating is graphite.

6. The method of claim 2, wherein the method is characterized by: In step 4.2, the upper and lower dies of the final forming die are the same as the upper die (1) and the lower die (3) in step 3, and a gas flow channel (4) is provided in the upper die (1), the gas flow channel (4) has one inlet opening on the side wall of the upper die (1) and multiple outlets evenly distributed on different parts of the profile of the upper die (1); after the final forming die is closed, 1-20 MPa of room temperature gas is introduced through the gas flow channel (4) to make the part with process segments (2-2) tightly fit on the lower die, complete the final forming of the part with process segments (2-2) and quickly cool it down to achieve the purpose of quenching.

7. The method of claim 6, wherein the method is characterized by: The gas is air, nitrogen or argon.

8. The method of claim 6, wherein the method is characterized by: The upper die (1) of the final forming die is a room temperature die, and the temperature of the lower die (3) is set to 100-250°C, that is, a cold-hot combined die is used.

9. The method of claim 2, wherein the method is characterized by: In step 5, the aging treatment is natural aging, and the natural aging method is room temperature standing.

10. The method of claim 2, wherein the method is a method of controlling the shape and properties of a complex aluminum alloy sheet metal part with high strength, characterized in that, In step 5, the aging treatment is artificial aging, the artificial aging temperature is 160-180 ℃, and the time is 6-50 hours. In step 5, the aging treatment is artificial aging, the artificial aging temperature is 160-180 ℃, and the time is 6-50 hours.

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