Aluminum alloy cold extrusion forming TWIP steel die and preparation method thereof

Abstract

The present application belongs to the field of mold processing, and relates to a heat treatment free TWIP steel mold for aluminum alloy cold extrusion precision forming and a preparation method thereof. The present application adopts TWIP steel as the mold material, first obtains a blank material with high yield strength (>=800MPa) through medium temperature plastic processing, then processes the cold extrusion mold semi-finished product by using the blank material, and then performs multiple extrusion processing on the semi-finished product mold under the press by using an aluminum alloy bar, so that the material on the inner cavity surface of the mold is hardened by a small amount of plastic deformation, and the inner cavity of the mold no longer occurs plastic deformation under the action of the extrusion pressure. Finally, the inner cavity and the outer surface of the mold are finished to the final size and precision through wire cutting and grinding and the like processing. The TWIP steel mold has significantly enhanced high pressure resistance and brittle fracture resistance, and the service life is obviously increased, and the production cost of the aluminum alloy extrusion product is obviously reduced, thereby providing a new material and a new process for solving the problems of the aluminum alloy high pressure cold extrusion forming mold, such as easy cracking, short service life and high cost.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of aluminum alloy plastic forming die processing, and particularly relates to a heat treatment-free TWIP steel die for aluminum alloy cold extrusion precision forming and a preparation method thereof. BACKGROUND

[0002] Cold extrusion is an important part of precision plastic volume forming technology. During cold extrusion, the metal blank to be processed is first placed in the cold extrusion die, and then the punch on the press is used to apply pressure to the blank at room temperature, so that the metal blank is plastically deformed to fill the die cavity, thereby obtaining an extruded part with the required shape, size and mechanical properties. Because it does not need to be heated, the extrusion pressure is large, and the filling speed is fast, cold extrusion forming has the advantages of high precision, high efficiency, high quality and low consumption, and is one of the most widely used technologies in plastic forming processing of metal materials, especially non-ferrous metal materials. For aluminum alloy cold extrusion forming, because of the high pressure in the cavity, the aluminum alloy has strong adhesion and low flowability, in order to ensure that all details on the part can be precisely formed, a material with high strength and toughness should be used to make the die to withstand high pressure and impact without breaking, and toughness is one of the performance indicators that need to be considered first.

[0003] At present, the die materials for aluminum alloy cold extrusion precision forming mainly include H13 and DC53. The former is H13 air-quenching hardened hot work die steel introduced from the United States, with a brand of 4Cr5MoSiV1 and a hardness of HRC56~58; the latter is a cold work die steel improved on the basis of Japanese SKD11 (Cr12MoV), with a hardness of HRC62~63 and a toughness twice that of Cr12MoV. Although these two materials have good effects when used in general and precision dies, they are prone to cracking when extruding some aluminum alloy parts with fine structures due to the large forming pressure, and the service life of the die is very short. In order to solve this problem, many manufacturers adjust the heat treatment process to appropriately reduce the hardness and improve the toughness, but the effect is very limited, and die cracking problems still occur frequently. Therefore, finding a suitable die material to improve the high-pressure cracking resistance of the die is one of the difficult problems to be solved in this field. SUMMARY

[0004] One of the purposes of the present application is to provide a preparation method of a heat treatment-free TWIP steel die for aluminum alloy cold extrusion precision forming. The TWIP steel with high strength and toughness is used as the die material, the semi-finished cold extrusion die is rough machined after medium temperature fixed ratio forging, 4~6 extrusion treatments are performed on the semi-finished cold extrusion die with the same aluminum alloy bar, a small amount of plastic deformation and hardening occur on the inner cavity surface of the die, and finally the inner cavity and outer surface of the die are finished to the final size and precision through wire cutting and grinding and other processes. The die processing technology is simple, the result is easy to control, the cost is greatly reduced, and the die has the advantages of high toughness and long service life.

[0005] In order to achieve the above object, the present application adopts the following technical scheme: a preparation method of TWIP steel mold for aluminum alloy cold extrusion forming, comprising the following steps:

[0006] S1, melting; according to the formula of TWIP steel, weighing the elemental raw materials and intermediate alloy V-Fe and N-Cr and adding them into the melting furnace, pouring into steel ingot after melting under argon protection; the chemical composition of the TWIP steel is as follows according to mass percentage: C: 0.06-1.0; Mn: 17.0-30.0; Al: 0.1-3.0; Si: 0.4-0.8; P≤0.05; S≤0.01; V: 0.15-0.30; N: 0.10-0.5; the rest is Fe;

[0007] S2, high temperature forging; first heat the steel ingot to 1000-1100℃, and keep for 3-4h, and forge into square billet with section 200-300mm square and length≥400mm by one or more fires;

[0008] S3, medium temperature forging; reheat the above square billet to 650-750℃, keep for 1.5-2.0h, forge into round billet of φ120×600mm by one fire, and cut off the riser for standby;

[0009] S4, rough machining of mold; process the forged round billet into cold extrusion mold semi-finished product with internal spline, and the inner cavity size is 0.10-0.15mm smaller than the actual size.

[0010] S5, cold extrusion hardening treatment: put the aluminum alloy bar of appropriate specification into the cavity of the above rough machining mold, and fill the cavity with the aluminum alloy bar by cold extrusion process under the pressure of 50-60 tons, keep for 5-8s, then eject the aluminum alloy extrusion part, measure the inner cavity size of the mold, and repeat the above extrusion process 4-6 times until the inner cavity size of the cold extrusion mold semi-finished product no longer changes;

[0011] S6, finishing; finish the cold extrusion mold semi-finished product after hardening treatment, process the mold inner cavity to the required size accuracy and roughness, and obtain the final TWIP steel mold for aluminum alloy cold extrusion forming.

[0012] Further improvement of the preparation method of TWIP steel mold for aluminum alloy cold extrusion forming:

[0013] Preferably, the TWIP steel belongs to Fe-Mn-Al-Si system.

[0014] Preferably, the mechanical properties of the TWIP steel in forged state are as follows: yield strength R P0.2 :≥800MPa; tensile strength R m: >= 1150 MPa; elongation A after fracture: >= 30%.

[0015] Preferably, the TWIP steel preferably has the following chemical composition in terms of mass percentage: (1) high toughness type: C: 0.06-0.08; Mn: 28.0-30.0; Al: 3.0-3.2; Si: 3.0-3.2; P: <= 0.01; S: <= 0.01; V: 0.15-0.20; N: 0.10-0.20; and the rest is Fe; (2) high strength type: C: 0.6-0.9; Mn: 18.0-20.0; Al: 0.1-0.2; Si: 0.4-0.6; P: <= 0.05; S: <= 0.005; V: 0.15-0.30; N: 0.10-0.5; and the rest is Fe.

[0016] Preferably, in step S1, the elemental raw materials are Fe, Mn, Al, Si and C.

[0017] Preferably, in step S1, the elemental Mn, Al and Si are added after all other raw materials are completely melted, and the power of the electric furnace is increased to the maximum to rapidly melt them.

[0018] Preferably, in step S2, when multiple forging is performed, annealing treatment at 850-1100 DEG C for 1-2 hours is performed between every two times of forging.

[0019] Preferably, in step S4, turning or wire cutting processing means is used to process the forged round billet into a cold extrusion die semi-finished product with internal splines.

[0020] Preferably, in step S6, wire cutting slow wire cutting or precision grinding is used to finish process the cold extrusion die semi-finished product after hardening treatment.

[0021] The second object of the present application is to provide an aluminum alloy cold extrusion forming TWIP steel die prepared by the preparation method of the aluminum alloy cold extrusion forming TWIP steel die.

[0022] The present application has the following beneficial effects compared with the prior art:

[0023] 1) The present application aims to provide a heat treatment-free, high strength and toughness TWIP steel die for aluminum alloy cold extrusion precision forming and a preparation method thereof, which has high-pressure fracture resistance and belongs to Fe-Mn-Al-Si TWIP steel. P0.2 : 800-900 MPa; R m: 1150~1250MPa; A: 25~35%, with high yield strength (≥ 800MPa). Then the blank material is processed into a semi-finished cold extrusion die, the inner cavity size of which is 0.10~0.15mm smaller than the actual size. Before the formal extrusion of aluminum alloy products, 4~6 extrusion treatments are carried out on the semi-finished cold extrusion die with the same aluminum alloy bar, so that the inner cavity surface of the die is slightly deformed and hardened, and the inner cavity size of the die no longer changes. Finally, the inner cavity and outer surface of the die are finished to the final size and precision through wire cutting and grinding and other processes. After nearly ten thousand extrusion tests, it is proved that under the same die, extruded products and extrusion conditions, the TWIP steel die is intact without any cracks.

[0024] Compared with the conventional die steel, the TWIP steel die deformed and strengthened by cold extrusion has significantly enhanced high-pressure resistance and brittle fracture resistance, the forming efficiency and size precision of the aluminum alloy cold extruded product are significantly improved, and the production cost is significantly reduced, which provides a new material and new process for solving the problems of easy cracking, low service life and high cost of aluminum alloy high-pressure cold extrusion forming die. The present application improves the hardness of the inner cavity surface of the die by work hardening method, forms the gradient distribution of the hardness in the thickness direction of the die, and thus ensures that the die has high high-pressure resistance and fracture resistance. After work hardening, the hardness of the inner cavity surface of the TWIP steel die is ≥HRC35, and the thickness of the hardened layer is ≥5mm.

[0025] 2) The preferred TWIP steel composition of the present application aims to reduce the stacking fault energy of the TWIP steel from the general 35mJ / m 2 to 30mJ / m 2The following, alloy plastic deformation process twinning and stacking fault density increases, the microstructure of the capacity to accept dislocation, especially the immobile dislocation increases, thus the alloy work hardening ability is enhanced, a small amount of plastic deformation can produce significant strengthening and hardening effect. Because the deformation and hardening only occur in the surface of the inner cavity of the mold during extrusion, the rest of the material still maintains the original hardness and toughness. After the completion of the extrusion treatment, the hardness of the inner surface of the mold is increased to HRC 34.5, and the hardness of the other parts is HRC 17.0. Although the inner surface hardness is lower than that of the traditional mold steel, it has extremely high deformation resistance due to hardening. Therefore, when the inner cavity of the mold is subjected to high pressure, the high hardness material near the inner surface layer can resist the pressure and not deform, at the same time, the high stress is transmitted to the subsurface layer. The material outside the subsurface layer has high toughness, so the stress concentration can be reduced, thereby inhibiting the initiation of cracks. The gradient distribution of strength and toughness along the thickness direction of the mold makes the mold show excellent characteristics of high pressure resistance and no cracking, which is very suitable for aluminum alloy extrusion forming production. In addition, the mold material of the TWIP steel used in the present application only needs to be subjected to a small number of extrusion treatments to meet the use requirements, and does not need to be heat treated. Therefore, the mold machining process is simple, the result is easy to control, and the cost is greatly reduced. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creating laborious work.

[0027] Figure 1 For the cold extrusion hardening treatment of step S5 of example 1, the microhardness distribution of the mold from the inner cavity surface to the thickness direction of the mold.

[0028] Figure 2 The aluminum alloy cold extrusion forming mold part drawing of the TWIP steel mold for aluminum alloy cold extrusion forming prepared in example 1.

[0029] Figure 3 The tensile stress-strain curve of the TWIP steel mold blank in the as-forged state for aluminum alloy cold extrusion forming prepared in example 1.

[0030] Figure 4 The tensile stress-strain curve of the TWIP steel mold blank in the as-forged state for aluminum alloy cold extrusion forming prepared in example 2.

[0031] Figure 5 The tensile stress-strain curve of the TWIP steel mold blank in the as-forged state for aluminum alloy cold extrusion forming prepared in example 3. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application is further described in detail below in combination with embodiments, and all other embodiments obtained by those skilled in the art without creative labor on the basis of the embodiments in the present application belong to the protection scope of the present application.

[0033] Embodiment 1

[0034] The present embodiment provides a preparation method of a heat treatment-free TWIP steel mold for cold extrusion precision forming of an aluminum alloy, and the specific implementation steps are as follows:

[0035] S1, smelting: according to the composition (wt.%) of TWIP steel: C: 0.9; Mn: 19; Al: 2.8; Si: 0.7; P: ≤0.01; S: ≤0.01; V: 0.15; N: 0.20; the rest is Fe. Weigh the raw materials such as carbon, manganese, aluminum, silicon, iron, vanadium iron and nitrogen chromium alloy, and add them into a vacuum induction furnace for smelting under argon protection. The elemental Mn, Al, Si and C must be added after all other raw materials are completely melted, the power of the electric furnace is increased to the maximum to rapidly melt the raw materials, and after the smelting is completed, the steel ingot of about 160 kg is poured.

[0036] S2, high temperature forging: heat the steel ingot to 1050℃, homogenize for 2h, and then forge into a square billet with a section of 300mm square and a length of about 500mm in two fires, wherein the first fire is elongated along the axis of the steel ingot, and the forging ratio is 4; the second fire is upset, and the forging ratio is 9;

[0037] S3, medium temperature forging: reheat the above square billet to 700℃ and keep for 3 hours, and elongate it into two φ120×600mm round billets in one fire, and cut off the riser for standby;

[0038] S4, rough machining mold: using wire cutting processing means, the TWIP steel round billet is turned to the rough machining outer diameter to the drawing calibration value, and the inner cavity is wire cut to the inner cavity size processing to be smaller than the drawing calibration value by 0.15mm, to obtain a cold extrusion mold semi-finished product;

[0039] S5, cold extrusion hardening treatment: put the aluminum alloy rod of the appropriate specification into the cavity of the above rough machining mold, and use cold extrusion process to fill the aluminum alloy rod into the cavity under the pressure of 60 tons. After keeping pressure for 7s, the aluminum alloy extruded part is ejected, the inner cavity size of the mold is measured, and the above extrusion process is repeated for 5 times until the inner cavity size of the cold extrusion mold semi-finished product no longer changes;

[0040] S6, finishing: the semi-finished cold extrusion die after hardening treatment is finished by wire cutting slow wire feeding, the die cavity is processed to the required dimensional accuracy and roughness, and finally the TWIP steel die for aluminum alloy cold extrusion forming is obtained.

[0041] The appearance of cracking of H13 and DC53 dies is observed when the extruded aluminum alloy product with splines is observed, at this time the forming pressure is 60 tons, and the extruded aluminum alloy product is less than 1000 pieces. It can be seen that the H13 and DC53 dies have both been fractured and the cracks have penetrated through the entire die, showing typical brittle fracture characteristics. It shows that under high pressure extrusion conditions, both of the two die materials cannot meet the production requirements.

[0042] The state of the TWIP steel die for aluminum alloy cold extrusion forming prepared in Example 1 after nearly ten thousand times of extrusion test is observed, which proves that under the same die, extruded product and extrusion conditions, the TWIP steel die is intact and no cracks are generated.

[0043] The change of the center hole diameter of the cold extrusion die semi-finished product prepared in step S4 of Example 1 with the number of extrusions is shown in Table 1; and the microhardness distribution of the die from the inner cavity surface to the thickness direction of the die after cold extrusion hardening treatment in step S5 of Example 1 is shown in Table 2. Figure 1 Figure 1 It can be seen from Table 1 and

[0044] Table 1 Change of inner cavity diameter of TWIP steel die during extrusion hardening treatment (pressure: 60 tons)

[0045]

[0046]

[0047] Figure 2 The aluminum alloy cold extrusion forming die part drawing of the TWIP steel die for aluminum alloy cold extrusion forming prepared in Example 1.

[0048] The stress-strain curve of the forged round billet in step S3 of Example 1 is shown in Table 3. Figure 3 Figure 3 ​​It can be seen that, after medium temperature forging, the average values of yield strength and tensile strength of the TWIP steel have reached 850 MPa and 1250 MPa respectively, while maintaining a very high ductility, and the average value of elongation after fracture is still as high as 30%.

[0049] Embodiment 2

[0050] The embodiment provides a preparation method of an aluminum alloy cold extrusion precision forming heat treatment-free TWIP steel mold, and specifically comprises the following steps:

[0051] S1, melting: according to the composition (wt.%) of the TWIP steel: C: 0.06; Mn: 30; Al: 3.0; Si: 3.0; P: ≤0.01; S: ≤0.01; V: 0.15; N: 0.20; and the rest is Fe. The raw materials such as carbon, manganese, aluminum, silicon, iron, vanadium iron and nitrogen chromium alloy are weighed and added into a vacuum induction furnace for melting under the protection of argon. The elemental Mn, Al, Si and C must be added after all other raw materials are completely melted, the power of the electric furnace is increased to the maximum to rapidly melt the raw materials, and after the melting is completed, a round ingot with a weight of about 160 kg is poured.

[0052] S2, high temperature forging: the ingot is heated to 1050℃, homogenized for 2h, and then forged into a square billet with a section of 300mm square and a length of about 500mm in two fires, wherein the first fire is elongated along the axis of the ingot, and the forging ratio is 6.3; the second fire is upset, and the forging ratio is 9;

[0053] S3, medium temperature forging: the above square billet is reheated to 750℃ and kept for 4 hours, and then elongated into two round billets with a diameter of 120mm and a length of 600mm in one fire, and the round billets are reserved after the riser is cut off;

[0054] S4, rough machining of the mold; the TWIP steel round billet is rough machined to the outer diameter of the drawing specification by wire cutting processing, and the inner cavity is processed to be smaller than the drawing specification by 0.15mm, to obtain a cold extrusion mold semi-finished product;

[0055] S5, cold extrusion hardening treatment: the aluminum alloy rod with an appropriate specification is placed in the cavity of the rough machining mold, and the cold extrusion process is adopted to fill the cavity with the aluminum alloy rod under the pressure of 60 tons, and after keeping the pressure for 7s, the aluminum alloy extruded part is ejected, the inner cavity size of the mold is measured, and the above extrusion process is repeated for 5 times until the inner cavity size of the cold extrusion mold semi-finished product no longer changes;

[0056] S6, finishing: the cold extrusion mold semi-finished product after the hardening treatment is finished by wire cutting slow wire feeding, the inner cavity of the mold is processed to the required size precision and roughness, and finally the TWIP steel mold for aluminum alloy cold extrusion forming is obtained.

[0057] The stress-strain curve of the round billet after forging in step S3 of Embodiment 2 is as followsFigure 4 Compared with Example 1, the yield strength of the TWIP steel of the present example is slightly decreased, but the tensile strength and the elongation at break are improved, the average yield strength is 820 MPa, the average tensile strength reaches 1265 MPa, and the average elongation at break is as high as 43%.

[0058] Example 3

[0059] The present example provides a preparation method of a heat treatment-free TWIP steel mold for aluminum alloy cold extrusion precision forming, which specifically comprises the following steps:

[0060] S1, melting: according to the composition (wt.%) of TWIP steel: C: 0.8; Mn: 20; Al: 0.2; Si: 0.4; P: ≤0.01; S: ≤0.01; V: 0.20; N: 0.30; the rest is Fe. Weigh the raw materials such as carbon, manganese, aluminum, silicon, iron, vanadium iron and nitrogen chromium alloy, and add them into a vacuum induction furnace for melting under argon protection. The elemental Mn, Al, Si and C must be added after all other raw materials are completely melted, the power of the electric furnace is increased to the maximum to rapidly melt the raw materials. After the melting is completed, pour into a round ingot with a weight of about 160 kg.

[0061] S2, high temperature forging: heat the ingot to 1050℃, homogenize for 2h, and then forge into a square billet with a section of 300mm square and a length of about 500mm in two fires, wherein the first fire is elongated along the axis of the ingot, and the forging ratio is 6.3; the second fire is upset, and the forging ratio is 9;

[0062] S3, medium temperature forging: reheat the above square billet to 650℃ and keep for 5 hours, elongate into two φ120×600mm round billets in one fire, and cut off the riser for standby;

[0063] S4, rough machining of the mold; using wire cutting machining means, the TWIP steel round billet is turned to the rough machining outer diameter to the drawing calibration value, and the inner cavity is wire cut to be 0.15mm smaller than the drawing calibration value, to obtain a cold extrusion mold semi-finished product;

[0064] S5, cold extrusion hardening treatment: put the aluminum alloy rod of the appropriate specification into the cavity of the above rough machining mold, use cold extrusion process to make the aluminum alloy rod fill the cavity under the pressure of 60 tons, after keeping pressure for 7s, eject the aluminum alloy extruded part, measure the inner cavity size of the mold, and repeat the above extrusion process for 5 times until the inner cavity size of the cold extrusion mold semi-finished product no longer changes;

[0065] S6, finishing: through wire cutting slow wire feeding, the cold extrusion mold semi-finished product after hardening treatment is finished to process the mold inner cavity to the required size accuracy and roughness, and finally obtain the TWIP steel mold for aluminum alloy cold extrusion forming.

[0066] The stress-strain curve of the round billet after forging in step S3 of Example 3 is shown in Figure 5 As can be seen from Figure 5 Compared with Example 1, the strength of the TWIP steel in this example is significantly improved, and the ductility is slightly decreased. The average yield strength is 1283 MPa, the average tensile strength is as high as 1515 MPa, and the average elongation after fracture is still nearly 30%.

[0067] It can be seen from the observation of the appearance of the finally prepared TWIP steel die for cold extrusion forming of aluminum alloy that the TWIP steel die after pre-press hardening does not have any cracks after use, and can meet the production of aluminum alloy extruded parts.

[0068] Those skilled in the art should understand that the above description is only several specific embodiments of the present application, not all embodiments. It should be noted that many modifications and improvements can also be made by those skilled in the art, and all modifications and improvements that do not exceed the scope of the claims should be considered as the protection scope of the present application.

Claims

1. A method for producing a TWIP steel die for cold extrusion forming of an aluminum alloy, characterized by, It comprises the following steps: S1, smelting; according to the formula of TWIP steel, weighing the elemental raw materials and intermediate alloy V-Fe and N-Cr and adding them into a smelting furnace, smelting under argon protection and pouring into an ingot; the chemical composition of the TWIP steel is as follows according to mass percentage: C: 0.06-1.0; Mn: 17.0-30.0; Al: 0.1-3.5; Si: 0.4-3.5; P≤0.05; S≤0.01; V：0.15～0.30； N: 0.10-0.5; the rest is Fe; S2, high-temperature forging; first heat the ingot to 1000-1100℃, keep for 3-4h, forge into a square billet with a section of 200-300mm square and a length of ≥400mm by one or more fires; S3, medium-temperature forging; reheat the square billet to 650-750℃, keep for 1.5-2.0h, forge into a round billet of φ120×600mm by one fire, and cut off the riser for standby; S4, rough machining mold; process the forged round billet into a cold extrusion mold semi-finished product with internal splines, and the inner cavity size is 0.10-0.15mm smaller than the actual size; S5, cold extrusion hardening treatment; put the aluminum alloy rod of appropriate specification into the cavity of the above rough machining mold, adopt cold extrusion process, extrude the aluminum alloy rod under a pressure of 50-60 tons to fill the cavity, keep pressure for 5-8s, eject the aluminum alloy extruded part, measure the inner cavity size of the mold, and repeat the above extrusion process 4-6 times until the inner cavity size of the cold extrusion mold semi-finished product no longer changes; S6, finishing; finish the cold extrusion mold semi-finished product after hardening treatment to process the mold inner cavity to the required size accuracy and roughness, and obtain the final TWIP steel mold for aluminum alloy cold extrusion forming.

2. The method of producing an aluminum alloy cold extrusion forming TWIP steel die according to claim 1, characterized by, The TWIP steel belongs to Fe-Mn-Al-Si system.

3. The method of claim 1, wherein the TWIP steel die for cold extrusion forming of an aluminum alloy is prepared by the steps of: The mechanical properties of the TWIP steel in the as-forged state are as follows: yield strength R P0.2 : > 800 MPa; tensile strength R m : > 1150 MPa; elongation at break A: > 30%. ​ 4. The method of producing an aluminum alloy cold extrusion forming TWIP steel die according to claim 1 or 2, characterized by, The chemical composition of the TWIP steel is divided into two types according to mass percentage: (1) high toughness type: C: 0.06-0.08; Mn: 28.0-30.0; Al: 3.0-3.2; Si: 3.0-3.2; P: ≤0.01; S：≤0.01； V：0.15～0.20； N: 0.10-0.20; the rest is Fe; (2) high strength type: C: 0.6-0.9; Mn: 18.0-20.0; Al：0.1～0.2； Si: 0.4-0.6; P：≤0.05； S：≤0.005； V：0.15～0.30； N: 0.10-0.5; the rest is Fe.

5. The method of claim 1, wherein the TWIP steel die for cold extrusion forming of an aluminum alloy is prepared by the steps of: In step S1, the elemental raw materials are Fe, Mn, Al, Si and C. ​ 6. The method of producing an aluminum alloy cold extrusion forming TWIP steel die according to claim 5, characterized by, In step S1, the elemental Mn, Al and Si must be added after all other raw materials are completely melted, and at the same time, the power of the electric furnace is increased to the maximum to make them melt quickly.

7. The method of claim 1, wherein the TWIP steel die for cold extrusion forming of an aluminum alloy is prepared by the steps of: In step S2, when multiple fire forging is performed, annealing treatment is performed between every two fires at 850-1100℃ for 1-2h. ​ 8. The method of claim 1, wherein the TWIP steel die for cold extrusion forming of an aluminum alloy is prepared by the steps of: In step S4, the forged round billet is processed into a cold extrusion mold semi-finished product with internal splines by turning or wire cutting means. ​ 9. The method of claim 1, wherein the TWIP steel die for cold extrusion forming of an aluminum alloy is prepared by the steps of: In step S6, the cold extrusion mold semi-finished product after hardening treatment is finished by wire cutting slow wire feeding or precision grinding. ​ 10. An aluminum alloy cold extrusion forming TWIP steel mold prepared by the method of any one of claims 1-9.

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