Production method of main reducer bottom cover die forging of engine for helicopter

Abstract

The invention discloses a production method of a main reducer bottom cover die forging of an engine for a helicopter, and belongs to the field of aluminum alloy structural part manufacturing. The problem that an existing helicopter engine main reducer bottom cover die forging is poor in bearing capacity and toughness is solved. The method comprises: forging a forging cake blank; carrying out pre-pressing forming, corrosive washing and damage repairing, and carrying out die forging forming to obtain a die forging; machining rib turning and corrosive washing damage repairing are carried out, and a die forging A is obtained; performing four-time die forging forming to obtain a die forging B; and carrying out corrosive wash damage repairing and heat treatment to obtain the helicopter engine main reducer bottom cover die forging. The bearing capacity, toughness and the like of the die forging are improved, the service life of parts is prolonged, and the development requirements of the aerospace industry in China are met. The die forging meets the standard requirement, the overall use performance of the main reducer bottom cover is improved, the strength and fracture toughness of a military main reducer bottom cover are improved, the service life of main reducer bottom cover parts is prolonged, and the requirement of the high-performance 2014 aluminum alloy main reducer bottom cover die forging for aviation is met.

Description

Technical Field

[0001] The invention belongs to the field of aluminum alloy structural parts manufacturing, and in particular relates to a production method of a main reducer bottom cover die forging for a helicopter engine. Background Art

[0002] With the rapid development of my country's aerospace industry, the performance requirements for ultra-high-strength aluminum alloy structural parts are getting higher and higher. The engine casing forgings are stress-bearing structural parts. The stability of the structural parts' performance plays an important role in the entire engine and even the entire aircraft. The engine die forgings are mainly made of ultra-high-strength aluminum alloys. At present, the main reducer bottom cover die forgings have problems with poor bearing capacity and toughness. The main reason is that the die forgings have the problem of low-multiple streamline irregularities and the strength and fracture toughness of the engine main reducer bottom cover need to be improved. In this way, the overall performance of the main reducer bottom cover can be improved, so as to reduce the probability of cracking of engine structural parts during flight. Summary of the invention

[0003] The purpose of the present invention is to solve the problems of poor load-bearing capacity and toughness of existing helicopter engine main reducer bottom cover die forgings, and to provide a production method of helicopter engine main reducer bottom cover die forgings.

[0004] A method for producing a die forging of a main reducer bottom cover for a helicopter engine, which is carried out according to the following steps:

[0005] 1. Forging and blank making:

[0006] A cylindrical aluminum alloy ingot with a size of Φ162×390 mm is heated to 460-480° C., the start forging temperature is 450° C., and the blank is forged on a 5000-ton vertical free forging hydraulic press. The flat anvil temperature during forging is 350° C.-400° C., and the blank is forged into an elliptical forging cake with a height of H=30 mm by a one-time multi-directional forging process to obtain a forging cake blank;

[0007] 2. Pre-pressing, etching, repairing and die forging:

[0008] The forging cake blank is heated to 450°C-480°C, the first piece forging temperature is 430°C-450°C, the first piece final forging temperature is 410°C-430°C, the final piece forging temperature is 420°C-440°C, the final piece final forging temperature is 400°C-430°C, the die temperature is 360°C-400°C, and a pre-pressed forging is obtained, and then etching and cleaning are performed to repair the damage, and then the first die forging is performed to obtain a die forging;

[0009] 3. Machining, turning and corrosion repair:

[0010] The die forging is placed on a machining milling machine, and the annular ribs on the die forging are all machined off, and then the forging is etched and repaired, and then the defects on the die forging are checked and removed to obtain a die forging A;

[0011] 4. Four-step die forging:

[0012] The die forging A is placed in a heating furnace for forgings to heat up. When it comes out of the furnace, the start forging temperature and the final forging temperature of the first and last pieces of each horizontal material tray are 400°C to 450°C. It is die-formed on a 5000-ton vertical free forging hydraulic press. The forging is die-formed four times in total, and lubrication and pressing are performed twice during the final pressing. Then, the car is lifted and deflated before pressing again to ensure the forming. The burrs are then cut off on a sawing machine to obtain the die forging B.

[0013] 5. Etching, repairing and heat treatment:

[0014] The die forging B is etched and repaired, and then pre-fire inspection is carried out. The qualified die forgings are erected in a quenching basket, kept warm for 60 minutes at a quenching temperature of 493°C to 499°C, the temperature of the water used for quenching is 50°C to 70°C, the quenching transfer time is ≤15s, and the quenching basket is reciprocated and lifted in the water for 15 to 25 times, and then hoisted out of the water after staying in the water for 15 minutes, and loaded into an aging furnace after quenching furnace number, with a placement interval of ≥50mm, and then kept warm for 12 hours at an aging temperature of 168°C to 175°C, to obtain a helicopter engine main reducer bottom cover die forging, and the manufacturing is completed.

[0015] Furthermore, the mass percentages of elements in the aluminum alloy ingot in step one are Si 0.5% to 1.2%, Fe ≤0.7%, Cu 3.9% to 5.0%, Mn 0.40% to 1.2%, Mg 0.20% to 0.8%, Cr ≤0.10%, Zn ≤0.25%, Ti ≤0.15%, individual impurities ≤0.05%, total impurities ≤0.15%, and the rest is Al.

[0016] Furthermore, in the first die forging in step 2, the pre-pressed forging after etching and repair is heated to 450°C-480°C, the first piece start forging temperature is 420°C-450°C, the first piece final forging temperature is 400°C-430°C, the last piece start forging temperature is 410°C-430°C, the last piece final forging temperature is 400°C-420°C, and the die temperature is 360°C-400°C.

[0017] Furthermore, in the four die forging processes described in step 4, before die forging, the dirt in the die cavity of the die should be cleared with compressed air, and lubricant should be applied after the upper and lower dies are installed.

[0018] Furthermore, the lubricant is composed of a mixture of sand ingot oil and graphite in a volume ratio of 1:10.

[0019] Furthermore, in step 4, the burr removal is as follows: 0<the residual amount of the burr after removal≤2mm.

[0020] Furthermore, the etching, cleaning and repairing processes described in steps two, three and five are all the same, specifically as follows: the machined die forgings are erected in a stainless steel basket, and are etched and degreased for 5 to 20 minutes in an alkaline bath having a temperature of 50°C to 70°C and a mass fraction of 10% to 20% NaOH, and then the alkaline solution is washed off in a cold water tank at room temperature, and then neutralized and washed for 3 to 8 minutes in an acid tank having a mass fraction of 20% to 40% HNO3 at room temperature, and then the acid solution is washed off in a cold water tank at room temperature, and finally rinsed in a hot water tank at a water temperature of 50 to 80°C.

[0021] Furthermore, the pre-fire inspection in step 5 is as follows: the die forging B after etching and repair is taken out and placed on a repair site with an aluminum pad on the ground for pre-fire inspection.

[0022] In the present invention, after the die forging is pre-pressed, etched and repaired, it is subjected to the first die forging, and then the annular ribs filled and formed on the die forging are all machined off on a machining milling machine, and then etched and repaired, and then four final die forgings are performed on a hydraulic press. After the annular ribs of the die forging formed by the first die forging are machined off, during the second die forging, part of the metal fills the cavity, and part flows to the web. Since the metal fills the cavity again, there is no resistance in the cavity part, but resistance is encountered when filling the web. The metal easily fills the annular rib cavity and can no longer take a shortcut to flow to the web. The streamline of the metal is completely along the direction of the cavity, achieving the best effect. When the die forging produced by the technical solution is subjected to macroscopic structural comparison and analysis, it is obtained that the macroscopic structure of the die forging does not have streamline irregularity defects, thereby achieving the purpose of improving the bearing capacity and service life of the parts. The alloy has the characteristics of compact structure, high specific strength and hardness, and high toughness, and is widely used in the aerospace field. The stable performance of the die forgings will enable my country to gradually master similar technologies and reduce the probability of cracking of engine structural parts during flight. This technology has broad promotion and application value in the aviation industry.

[0023] Advantages of the present invention:

[0024] The present invention improves the bearing capacity and toughness of the die forging, increases the service life of the parts, and meets the development needs of my country's aerospace industry. It can be used in the actual production of similar annular rib die forgings to solve the problem of low-multiple streamline irregularity of the die forging. It not only meets the standard requirements, but also improves the overall performance of the main reducer bottom cover, improves the strength and fracture toughness of the military main reducer bottom cover, increases the service life of the main reducer bottom cover parts, and meets the requirements of high-performance 2014 aluminum alloy main reducer bottom cover die forgings for aviation.

[0025] The invention is suitable for producing die forgings of main reducer bottom cover of helicopter engine. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a physical picture of the die forging of the main reducer bottom cover of the helicopter engine in the embodiment. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is not limited to the specific implementation modes listed below, but also includes any combination of the specific implementation modes.

[0028] Specific implementation method 1: This implementation method is a production method of a helicopter engine main reducer bottom cover die forging, which is carried out in the following steps:

[0029] 1. Forging and blank making:

[0030] A cylindrical aluminum alloy ingot with a size of Φ162×390 mm is heated to 460-480° C., the start forging temperature is 450° C., and the blank is forged on a 5000-ton vertical free forging hydraulic press. The flat anvil temperature during forging is 350° C.-400° C., and the blank is forged into an elliptical forging cake with a height of H=30 mm by a one-time multi-directional forging process to obtain a forging cake blank;

[0031] 2. Pre-pressing, etching, repairing and die forging:

[0032] The forging cake blank is heated to 450°C-480°C, the first piece forging temperature is 430°C-450°C, the first piece final forging temperature is 410°C-430°C, the final piece forging temperature is 420°C-440°C, the final piece final forging temperature is 400°C-430°C, the die temperature is 360°C-400°C, and a pre-pressed forging is obtained, and then etching and cleaning are performed to repair the damage, and then the first die forging is performed to obtain a die forging;

[0033] 3. Machining, turning and corrosion repair:

[0034] The die forging is placed on a machining milling machine, and the annular ribs on the die forging are all machined off, and then the forging is etched and repaired, and then the defects on the die forging are checked and removed to obtain a die forging A;

[0035] 4. Four-step die forging:

[0036] The die forging A is placed in a heating furnace for forgings to heat up. When it comes out of the furnace, the start forging temperature and the final forging temperature of the first and last pieces of each horizontal material tray are 400°C to 450°C. It is die-formed on a 5000-ton vertical free forging hydraulic press. The forging is die-formed four times in total, and lubrication and pressing are performed twice during the final pressing. Then, the car is lifted and deflated before pressing again to ensure the forming. The burrs are then cut off on a sawing machine to obtain the die forging B.

[0037] 5. Etching, repairing and heat treatment:

[0038] The die forging B is etched and repaired, and then pre-fire inspection is carried out. The qualified die forgings are erected in a quenching basket, kept warm for 60 minutes at a quenching temperature of 493°C to 499°C, the temperature of the water used for quenching is 50°C to 70°C, the quenching transfer time is ≤15s, and the quenching basket is reciprocated and lifted in the water for 15 to 25 times, and then hoisted out of the water after staying in the water for 15 minutes, and loaded into an aging furnace after quenching furnace number, with a placement interval of ≥50mm, and then kept warm for 12 hours at an aging temperature of 168°C to 175°C, to obtain a helicopter engine main reducer bottom cover die forging, and the manufacturing is completed.

[0039] The one-time multi-directional forging process in step 1 of this embodiment adopts one-time upsetting and one-time drawing forging treatment.

[0040] The defects on the forging described in step three of this embodiment are folding and bumping defects.

[0041] In step 5 of this embodiment, when punching the quenching furnace number, it must be punched to the position set on the drawing and must be clear.

[0042] The placement interval described in step 5 of this embodiment is ≥50mm, the purpose of which is to ensure uniform and rapid heating and facilitate smooth circulation of air.

[0043] Specific embodiment 2: This embodiment is different from specific embodiment 1 in that the mass percentage of elements in the aluminum alloy ingot in step 1 is Si 0.5% to 1.2%, Fe ≤0.7%, Cu 3.9% to 5.0%, Mn 0.40% to 1.2%, Mg 0.20% to 0.8%, Cr ≤0.10%, Zn ≤0.25%, Ti ≤0.15%, single impurity ≤0.05%, total impurity ≤0.15%, and the rest is Al. Other steps and parameters are the same as those in specific embodiment 1.

[0044] Specific implementation method three: This implementation method is different from specific implementation method one in that, in step two, the first die forging is as follows: the pre-pressed forging piece after etching and repair is heated to 450°C to 480°C, the first piece start forging temperature is 420°C to 450°C, the first piece final forging temperature is 400°C to 430°C, the last piece start forging temperature is 410°C to 430°C, the last piece final forging temperature is 400°C to 420°C, and the die temperature is 360°C to 400°C. Other steps and parameters are the same as those in specific implementation method one.

[0045] Specific implementation method 4: This implementation method is different from specific implementation method 1 in that, in step 4, the four die forgings are performed, and before die forging, the dirt in the die cavity of the die is cleared with compressed air, and lubricant is applied after the upper and lower dies are installed. The other steps and parameters are the same as those of specific implementation method 1.

[0046] Specific embodiment 5: This embodiment is different from specific embodiment 4 in that the lubricant is composed of a mixture of sand ingot oil and graphite in a volume ratio of 1:10. Other steps and parameters are the same as those of specific embodiment 4.

[0047] Specific implementation method 6: This implementation method is different from the specific implementation method 1 in that, in step 4, the burr removal is: 0<the residual amount of the burr after removal≤2mm. The other steps and parameters are the same as those in the specific implementation method 1.

[0048] Specific implementation example 7: This implementation example is the same as the specific implementation example in that the start forging temperature and the final forging temperature of the first and last piece of each horizontally arranged material tray when it is taken out of the furnace in step 4 are 420° C. The other steps and parameters are the same as those of the specific implementation example 1.

[0049] Specific embodiment eight: This embodiment is the same as the specific embodiment in that the etching and repairing processes described in steps two, three and five are all the same, specifically as follows: the die forging after machining is erected in a stainless steel material basket, and is etched and degreased for 5 to 20 minutes in an alkaline bath solution with a temperature of 50°C to 70°C and a mass fraction of 10% to 20% NaOH, then the alkaline solution is washed off in a cold water tank at room temperature, then neutralized and washed for 3 to 8 minutes in an acid tank with a mass fraction of 20% to 40% HNO3 at room temperature, the acid solution is washed off in a cold water tank at room temperature, and finally rinsed in a hot water tank with a water temperature of 50 to 80°C. Other steps and parameters are the same as those of specific embodiment one.

[0050] In this embodiment, the purpose of standing upright in the stainless steel basket is to prevent the liquid from flowing in and out of the inner cavity of the forging, so that the etching and washing are not thorough; the alkali solution washing in the cold water tank at room temperature must be fully washed with water; the time for etching, degreasing and neutralization and whitening must be controlled within the specified range to prevent inadequate corrosion or excessive corrosion.

[0051] Specific embodiment 9: This embodiment differs from specific embodiment 1 in that the pre-fire inspection in step 5 is: the die forging B after etching and repair is taken out and placed on the repair site with an aluminum pad on the ground for pre-fire inspection. Other steps and parameters are the same as those in specific embodiment 1.

[0052] Specific embodiment 10: This embodiment differs from specific embodiment 1 in that in step 5, the quenching temperature is kept at 495°C for 60 minutes, the temperature of the water used for quenching is 65°C, the quenching transfer time is ≤15s, and the quenching basket is lifted and lowered 20 times in the water, and then lifted out of the water after staying in the water for 15 minutes. The other steps and parameters are the same as those of specific embodiment 1.

[0053] The beneficial effects of the present invention are verified by the following examples:

[0054] Example:

[0055] A method for producing a die forging of a main reducer bottom cover for a helicopter engine, which is carried out according to the following steps:

[0056] 1. Forging and blank making:

[0057] A cylindrical aluminum alloy ingot with a size of Φ162×390 mm was heated to 470°C, the start forging temperature was 450°C, and the blank was forged on a 5000-ton vertical free forging hydraulic press. The flat anvil temperature during forging was 380°C. The blank was forged into an elliptical forging cake with a height of H=30 mm by a one-time multi-directional forging process to obtain a forging cake blank;

[0058] 2. Pre-pressing, etching, repairing and die forging:

[0059] The forging cake blank is heated to 470°C, the first piece forging temperature is 440°C, the first piece final forging temperature is 420°C, the final piece forging temperature is 420°C, the final piece final forging temperature is 430°C, and the die temperature is 380°C to obtain a pre-pressed forging, which is then etched and cleaned for repairing, and then subjected to the first die forging to obtain a die forging;

[0060] 3. Machining, turning and corrosion repair:

[0061] The die forging is placed on a machining milling machine, and the annular ribs on the die forging are all machined off, and then the forging is etched and repaired, and then the defects on the die forging are checked and removed to obtain a die forging A;

[0062] 4. Four-step die forging:

[0063] The die forging A is placed in a heating furnace for forgings to heat up. The start forging temperature and the final forging temperature of the first and last pieces of each horizontal material tray are 430°C when they are taken out of the furnace. The forgings are die-pressed on a 5000-ton vertical free forging hydraulic press. The forgings are die-pressed four times in total, and two lubrication presses are performed during the final press. Then, the car is lifted and deflated before pressing again to ensure the forming. The burrs are then cut off on a sawing machine to obtain the die forging B.

[0064] 5. Etching, repairing and heat treatment:

[0065] The die forging B is etched and repaired, and then pre-fire inspection is carried out. The qualified die forgings are erected in a quenching basket and kept warm for 60 minutes at a quenching temperature of 495°C. The temperature of the water used for quenching is 65°C, the quenching transfer time is ≤15s, and the quenching basket is reciprocated and lifted 20 times in the water, and then hoisted out of the water after staying in the water for 15 minutes. After marking the quenching furnace number, it is loaded into an aging furnace with a placement interval of ≥50mm, and then kept warm for 12 hours at an aging temperature of 170°C to obtain a helicopter engine main reducer bottom cover die forging, and the manufacturing is completed.

[0066] The defects on the forging described in step three of this embodiment refer to folding and bumping defects.

[0067] When punching the quenching furnace number in step 5 of this embodiment, it must be punched to the position set on the drawing and must be clear.

[0068] The placement interval described in step 5 of this embodiment is ≥50mm, the purpose of which is to ensure uniform and rapid heating and facilitate smooth circulation of air.

[0069] The mass percentages of elements in the aluminum alloy ingot described in step 1 of this embodiment are Si: 0.8%, Fe: ≤0.7%, Cu: 4.2%, Mn: 1.0%, Mg: 0.6%, Cr: ≤0.10%, Zn: ≤0.25%, Ti: ≤0.15%, individual impurities: ≤0.05%, total impurities: ≤0.15%, and the rest is Al.

[0070] The first die forging in step 2 of this embodiment: the pre-pressed forging after etching and repair is heated to 470°C, the first piece start forging temperature is 420°C, the first piece final forging temperature is 425°C, the last piece start forging temperature is 430°C, the last piece final forging temperature is 420°C, and the die temperature is 380°C.

[0071] In the four die forging processes described in step 4 of this embodiment, compressed air is used to clear away dirt in the die cavity before die forging, and lubricant is applied after the upper and lower dies are installed; the lubricant is composed of a mixture of sand ingot oil and graphite in a volume ratio of 1:10.

[0072] In step 4 of this embodiment, the burrs are removed: 0<the residual amount of burrs after removal≤2mm.

[0073] The etching and repairing processes described in steps 2, 3 and 5 of this embodiment are all consistent, and are specifically as follows: the machined die forgings are erected in a stainless steel material basket, and are etched and degreased in an alkaline bath solution with a temperature of 65°C and a mass fraction of 15% NaOH for 15 minutes, and then the alkaline solution is washed off in a cold water tank at room temperature, and then neutralized and washed in an acid tank with a mass fraction of 30% HNO3 at room temperature for 6 minutes, and the acid solution is washed off in a cold water tank at room temperature, and finally rinsed in a hot water tank with a water temperature of 70°C.

[0074] The purpose of standing upright in the stainless steel basket in this embodiment is to prevent the liquid from flowing in and out of the inner cavity of the forging, so that the etching and washing are not thorough; the alkali solution washing in the cold water tank at room temperature must be fully washed; the time for etching, degreasing and neutralization and whitening must be controlled within the specified range to prevent inadequate corrosion or excessive corrosion.

[0075] The pre-fire inspection in step 5 of this embodiment is as follows: the die forging B after etching, cleaning and repair is taken out and placed on a repair site with an aluminum pad on the ground for pre-fire inspection.

[0076] The helicopter engine main reducer bottom cover die forging manufactured in this embodiment has an aluminum alloy grade of 2014. The obtained 2014 aluminum alloy main reducer bottom cover die forging not only meets the standard requirements, but also improves the overall performance of the main reducer bottom cover, improves the strength and fracture toughness of the military main reducer bottom cover, and the specific performance data are shown in Tables 1 and 2; the service life of the main reducer bottom cover parts is increased, and the service life is 10 years; it meets the requirements of high-performance 2014 aluminum alloy main reducer bottom cover die forgings for aviation, and the actual product is as follows: Figure 1 As shown, the forging has uniform structure and the streamlines are distributed along the shape of the inspected section.

[0077] Table 1 Mechanical properties data

[0078] Sampling direction Tensile strength(MPa) Yield strength (MPa) Relative elongation Vertical 477.2 418.5 10.3 469.8 403.7 10.6 Horizontal 474.1 425.4 11.6 495.4 455.9 11.8

[0079] Table 2 Fracture toughness data

[0080] Sampling direction Kic(MPa.m∧1 / 2) LT 26.77 LT 30.41 LT 30.71 LT 30.34

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for producing a die forging of a main reducer bottom cover for a helicopter engine, characterized in that It proceeds as follows:

1. Forging and blank making: A cylindrical aluminum alloy ingot with a size of Φ162×390 mm is heated to 460-480° C., the start forging temperature is 450° C., and the blank is forged on a 5000-ton vertical free forging hydraulic press. The flat anvil temperature during forging is 350° C.-400° C., and the blank is forged into an elliptical forging cake with a height of H=30 mm by a one-time multi-directional forging process to obtain a forging cake blank; 2. Pre-pressing, etching, repairing and die forging: The forging cake blank is heated to 450°C-480°C, the first piece forging temperature is 430°C-450°C, the first piece final forging temperature is 410°C-430°C, the final piece forging temperature is 420°C-440°C, the final piece final forging temperature is 400°C-430°C, the die temperature is 360°C-400°C, and a pre-pressed forging is obtained, and then etching and cleaning are performed to repair the damage, and then the first die forging is performed to obtain a die forging; 3. Machining, turning and corrosion repair: The die forging is placed on a machining milling machine, and the annular ribs on the die forging are all machined off, and then the forging is etched and repaired, and then the defects on the die forging are checked and removed to obtain a die forging A; 4. Four-step die forging: The die forging A is placed in a heating furnace for forgings to heat up. When it comes out of the furnace, the start forging temperature and the final forging temperature of the first and last pieces of each horizontal material tray are 400°C to 450°C. It is die-formed on a 5000-ton vertical free forging hydraulic press. The forging is die-formed four times in total, and lubrication and pressing are performed twice during the final pressing. Then, the car is lifted and deflated before pressing again to ensure the forming. The burrs are then cut off on a sawing machine to obtain the die forging B.

5. Etching, repairing and heat treatment: The die forging B is etched and repaired, and then pre-fire inspection is carried out. The qualified die forgings are erected in a quenching basket, kept warm for 60 minutes at a quenching temperature of 493°C to 499°C, the temperature of the water used for quenching is 50°C to 70°C, the quenching transfer time is ≤15s, and the quenching basket is reciprocated and lifted in the water for 15 to 25 times, and then hoisted out of the water after staying in the water for 15 minutes, and loaded into an aging furnace after quenching furnace number, with a placement interval of ≥50mm, and then kept warm for 12 hours at an aging temperature of 168°C to 175°C, to obtain a helicopter engine main reducer bottom cover die forging, and the manufacturing is completed.

2. The method for producing a helicopter engine main reducer bottom cover die forging according to claim 1, characterized in that The mass percentages of elements in the aluminum alloy ingot in step 1 are Si 0.5% to 1.2%, Fe ≤0.7%, Cu 3.9% to 5.0%, Mn 0.40% to 1.2%, Mg 0.20% to 0.8%, Cr ≤0.10%, Zn ≤0.25%, Ti ≤0.15%, single impurities ≤0.05%, total impurities ≤0.15%, and the rest is Al.

3. The method for producing a helicopter engine main reducer bottom cover die forging according to claim 1, characterized in that The first die forging in step 2: the pre-pressed forging after etching and repair is heated to 450°C-480°C, the first piece start forging temperature is 420°C-450°C, the first piece final forging temperature is 400°C-430°C, the last piece start forging temperature is 410°C-430°C, the last piece final forging temperature is 400°C-420°C, and the die temperature is 360°C-400°C.

4. The method for producing a helicopter engine main reducer bottom cover die forging according to claim 1, characterized in that In step 4, the four die forgings are performed. Before die forging, compressed air should be used to remove the dirt in the die cavity, and lubricant should be applied after the upper and lower dies are installed.

5. The method for producing a helicopter engine main reducer bottom cover die forging according to claim 4, characterized in that The lubricant is composed of a mixture of sand ingot oil and graphite in a volume ratio of 1:

10.

6. The method for producing a helicopter engine main reducer bottom cover die forging according to claim 1, characterized in that The burr removal described in step 4: 0<the residual amount of burr after removal≤2mm.

7. The method for producing a helicopter engine main reducer bottom cover die forging according to claim 1, characterized in that In step 4, the starting forging temperature and the final forging temperature of the first and last piece of each horizontal row of material trays when they are taken out of the furnace are 420°C.

8. The method for producing a helicopter engine main reducer bottom cover die forging according to claim 1, characterized in that The etching, cleaning and repairing processes described in steps two, three and five are all the same, specifically as follows: the machined die forgings are erected in a stainless steel basket, and are etched and degreased for 5 to 20 minutes in an alkaline bath containing 10% to 20% NaOH by mass at a temperature of 50°C to 70°C, and then the alkaline solution is washed off in a cold water tank at room temperature, and then neutralized and washed for 3 to 8 minutes in an acid tank containing 20% ​​to 40% HNO3 by mass at room temperature, and then the acid solution is washed off in a cold water tank at room temperature, and finally rinsed in a hot water tank at a water temperature of 50 to 80°C.

9. The method for producing a helicopter engine main reducer bottom cover die forging according to claim 1, characterized in that Pre-fire inspection as described in step 5: The die forging B after etching and repair is taken out and placed on the repair site with an aluminum pad on the ground for pre-fire inspection.

10. The method for producing a die forging of a main reducer bottom cover for a helicopter engine according to claim 1, characterized in that In step 5, the quenching temperature is kept at 495°C for 60 minutes, the temperature of the water used for quenching is 65°C, the quenching transfer time is ≤15s, and the quenching basket is reciprocated and lifted in the water for 20 times, and then hung out of the water after staying in the water for 15 minutes.

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