A manufacturing process of TC4 titanium alloy bolts for aerospace

Abstract

The invention discloses a manufacturing process of TC4 titanium alloy bolts for aerospace, and belongs to the technical field of aerospace fastener manufacturing. The surface fluorine-boration lubrication treatment method in the process includes the following steps: step one, removing oil stains on the surface of parts; step two, removing the oxide layer on the surface of parts; step three, performing fluorine-boration treatment on parts to form a lubricating film layer on the surface of parts. Before hot upsetting the parts, the outer circle of the parts is first turned and ground, and then the surface is subjected to fluorine-boration lubrication treatment to form a dark gray or gray-black dense protective film on the surface of the parts, which is the lubricating film layer. The lubricating film layer can improve the surface hardness and wear resistance of the parts, so as to effectively solve the problem of bonding between the hot upsetting parts and the mold when hot upsetting the heads of the titanium alloy bolts, and avoid wrinkling and poor folding of the heads and the fillets under the heads of the hot upsetting parts, thereby significantly improving the processing quality and yield rate of the TC4 titanium alloy bolts.

Description

Technical Field

[0001] The invention relates to a manufacturing process of a TC4 titanium alloy bolt for aerospace, and belongs to the technical field of aerospace fastener manufacturing. Background Art

[0002] In the field of aerospace fastener technology, the application ratio of titanium alloy materials has increased year by year. Due to the characteristics of high strength-to-yield ratio and low specific gravity, titanium alloy bolts can achieve reliable connection and weight reduction. Titanium alloy materials have excellent hardenability, and the mechanical properties of bolt parts made of them are stable. In addition, titanium alloy materials have excellent corrosion resistance, and titanium alloy bolts can be used for fastening connections in high-strength acidic environments. The head of the TC4 titanium alloy MJ threaded bolt with a strength grade of 1100MPa needs to be formed by upsetting, and cannot be obtained by mechanical processing, punching, casting, etc., to ensure that the metal grain streamlines of the bolt head, the fillet under the head, and the screw are continuous and complete. In addition, the TC4 titanium alloy material has high tensile strength and a lower elongation than that of carbon steel and austenitic stainless steel. Its elongation is less than 50% of the elongation of stainless steel; its elastic modulus is low, and its elastic modulus E is about 110GPa, which is about 1 / 2 of the elastic modulus E of steel.

[0003] A Chinese patent document with publication number CN110421318A discloses a processing technology for aviation titanium alloy high-locking bolts. Qualified raw materials are screened and forged into blanks. In the subsequent upsetting process, the head of the high-locking bolt, the step rod diameters with different rod diameters, the head angle and the R angle under the head are formed at one time through continuous upsetting by an upsetting machine and using a mold of corresponding specifications, thereby ensuring the continuity of the internal grain structure of the blank and guaranteeing the performance of the product.

[0004] However, TC4 titanium alloy material has its own particularity. It is easy to produce elastic deformation, has a large friction coefficient, has strong chemical affinity, and is very easy to combine with other metals. During the process of upsetting bolts, it is severely bonded to the mold, the surface of the formed blank is rough, and the bolt head and the fillet under the head are prone to wrinkling, folding and other undesirable phenomena. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a manufacturing process of TC4 titanium alloy bolts for aerospace.

[0006] The present invention is achieved through the following technical solutions:

[0007] A manufacturing process of TC4 titanium alloy bolts for aerospace uses the following process route: blanking, turning the outer circle, chamfering, grinding the outer circle, surface fluorine boronization lubrication treatment, hot upsetting, alkali cleaning, heat treatment, sandblasting, turning the outer shape, chamfering, deburring, drilling the locking thread hole, rolling the bolt head fillet R, thread rolling, intermediate inspection, 100% fluorescent flaw detection, titanium alloy blue anodizing, general inspection, and packaging and warehousing;

[0008] The surface fluorine boronization lubrication treatment method comprises the following steps:

[0009] Step 1: Remove oil stains from the surface of parts;

[0010] Step 2: Remove the oxide layer on the surface of the parts;

[0011] Step 3: Performing fluorine-boration treatment on the parts to form a lubricating film layer on the surface of the parts;

[0012] The hot upsetting comprises the following steps:

[0013] Step A: Use high-frequency induction heating to heat the part to 600°C ± 10°C within 5s to 8s, with an oscillation coefficient of 300 to 500, and a heating length on the part of L1;

[0014] Step B, using a mold and a press to upset the head of the part that has been heated in step A to obtain a hot upset part;

[0015] Step C, performing metallographic inspection on the first hot-forged part;

[0016] The mold comprises a lower mold and an upper mold, wherein the lower mold is mounted on a lower mold frame of a press, and the upper mold is mounted at the bottom of an upper mold frame of the press and is located directly above the lower mold;

[0017] The lower die comprises a lower die seat and a positioning ejector rod, the lower die seat is coaxially provided with a through hole A, and the lower die seat is coaxially provided with a blind hole at the lower end of the through hole A, and a hard alloy ring A is coaxially embedded at the upper end of the through hole A, the inner hole of the hard alloy ring A is circular, and is clearance-matched with the part after the surface fluorine-borated lubrication treatment, the positioning ejector rod is clearance-matched with the through hole A, and the upper end of the positioning ejector rod is located in the through hole A, and the lower end is located in the blind hole;

[0018] The upper die comprises an upper die seat, a die seat cushion block, a hexagonal pressure rod, a cushion block and a cushion sleeve. A carbide ring B is coaxially embedded on the inner side of the upper die seat. The thickness of the carbide ring B is consistent with that of the upper die seat, and the inner hole of the carbide ring B is a regular hexagon. The die seat cushion block is placed on the upper die seat. A through hole B is coaxially provided on the die seat cushion block, and the diameter of the through hole B is larger than the outer diameter of the carbide ring A. The cushion sleeve is located in the through hole B, and is gapped with the through hole B and contacts with the carbide ring A. The lower end of the hexagonal pressure rod passes through the cushion sleeve and extends into the carbide ring B, and is gapped with the inner hole of the carbide ring B. The cushion block is placed on the hexagonal pressure rod.

[0019] The hexagonal pressure rod comprises a hexagonal section and a pressure rod head, one end of the pressure rod head is connected to one end of the hexagonal section, and the diameter of the pressure rod head is between the inner diameter and the outer diameter of the cushion sleeve.

[0020] The method for removing oil stains on the surface of parts in step 1 comprises the following steps:

[0021] Step 1: Soak the parts in a water-based cleaning agent LCX-52 at a temperature of 40°C to 60°C for 15 to 25 minutes, and shake the parts every 3 to 5 minutes. The mass of the solute in 1L of water-based cleaning agent LCX-52 is 40g to 60g.

[0022] Step 2: Soak the parts in water at a temperature of 40°C to 60°C for 0.5min to 1min;

[0023] Step 3: Rinse the parts with clean water at room temperature for 10s to 15s;

[0024] Step 4: Perform water film test on the parts. If the water film does not break within 30 seconds, the parts are qualified.

[0025] The method for removing the oxide layer on the surface of the parts in step 2 is: first immerse the parts in a mixture of hydrofluoric acid and nitric acid for 3s~5s, and then rinse the parts with clean water at room temperature for 10s~15s; 1L of the mixture of hydrofluoric acid and nitric acid contains 30ml~40ml of hydrofluoric acid with a concentration of 40%, 300ml~400ml of nitric acid with a concentration of 68%, and the rest is clean water.

[0026] The method for performing fluorine boron treatment on the parts in step 3 comprises the following steps:

[0027] Step a, soak the parts in a mixture of potassium fluoroborate, ammonium nitrate and barium chloride at a temperature of 90°C to 95°C for 15min to 25min, and shake the parts every 3min to 5min. 1L of the mixture of potassium fluoroborate, ammonium nitrate and barium chloride contains 60g to 80g of potassium fluoroborate, 30g to 40g of ammonium nitrate and 60g to 80g of barium chloride;

[0028] Step b, soak the parts in water at a temperature of 40°C to 60°C for 0.5min to 1min;

[0029] Step c: Rinse the parts with clean water at room temperature for 10s to 15s;

[0030] Step d: Use compressed air to blow dry the parts, then place the parts in a drying oven to dry, and then take out the parts and place them in a plastic box.

[0031] The positioning push rod and the hexagonal pressure rod are both made of 6542 high-speed steel.

[0032] The alkali washing method comprises the following steps:

[0033] Step I: Soak the hot forged part in a mixture of sodium hydroxide and sodium nitrite at a temperature of 120° C. to 140° C. for 30 min to 120 min, wherein 1 L of the mixture of sodium hydroxide and sodium nitrite contains 500 g to 700 g of sodium hydroxide and 150 g to 250 g of sodium nitrite;

[0034] Step II: Soak the hot forged parts in water at a temperature of 40°C to 60°C for 0.5min to 1min, and then rinse the hot forged parts with clean water at room temperature for 10s to 15s;

[0035] Step III, soak the hot forged piece in a mixture of hydrofluoric acid and nitric acid for 3s to 5s, wherein 1L of the mixture of hydrofluoric acid and nitric acid contains 30ml to 40ml of hydrofluoric acid with a concentration of 40%, 300ml to 400ml of nitric acid with a concentration of 68%, and the rest is clean water;

[0036] Step IV: Rinse the hot forged parts with clean water at room temperature for 10s to 15s;

[0037] Step V: Repeat steps I to IV until the oxide layer on the surface of the hot forged part is completely removed.

[0038] The heat treatment includes solution treatment and aging treatment. The solution treatment method is: ultrasonically clean the hot upsetting piece and dry it, place it in a vacuum water quenching furnace and heat it to 800°C~820°C, preheat it for 30min~40min, then heat it to 910°C±10°C, and keep it warm for 60min~70min, the vacuum degree in the furnace is not greater than 0.067Pa, then take the hot upsetting piece out of the furnace for water cooling, the transfer time of the hot upsetting piece is not greater than 10s, the water temperature is not greater than 40°C, and finally ultrasonically clean the hot upsetting piece again and blow it dry with compressed air;

[0039] The aging treatment method is: heat the hot forged parts to 510℃±10℃ in a vacuum tempering furnace, keep the temperature for 480min~500min, and the vacuum degree in the furnace is not greater than 0.067Pa. Then, argon gas is passed into the furnace to cool the hot forged parts to room temperature until the pressure in the furnace rises to (1~1.4)×10 5 Pa, mechanical properties test of hot upsetting parts treated in the same furnace, tensile strength σ b =1100±100MPa is qualified.

[0040] The beneficial effects of the present invention are:

[0041] 1. Before hot upsetting the parts, first turn and grind the outer circle of the parts, and then perform fluorine boron lubrication treatment on the surface to form a dark gray or gray-black dense protective film on the surface of the parts, which is the lubricating film layer. The lubricating film layer can improve the surface hardness and wear resistance of the parts, so as to effectively solve the problem of adhesion between the hot upsetting parts and the mold when hot upsetting the heads of titanium alloy bolts, and avoid wrinkling and poor folding of the heads and fillets under the heads of the hot upsetting parts, which significantly improves the processing quality and yield rate of TC4 titanium alloy bolts.

[0042] 2. Before fluorinating and boronizing the surface of the parts, first use chemical degreasing to effectively remove the oil on the surface of the parts, and then activate the parts with a mixture of hydrofluoric acid and nitric acid to remove the extremely thin oxide film on the surface of the titanium alloy parts, exposing the fresh metal surface, so that the lubricating film layer that is well bonded to the substrate can be better obtained later.

[0043] 3. The cemented carbide ring B is protected by the cushion sleeve to prevent the head of the pressure rod from directly squeezing and impacting the cemented carbide ring B, so as to extend the service life of the cemented carbide ring B. A cushion block is set at the upper end of the hexagonal pressure rod to adjust the stroke of the hexagonal pressure rod forging parts by increasing or reducing its thickness, ensuring that the height size of the head of the hot forging part meets the TC4 titanium alloy bolt drawing and process requirements.

[0044] 4. Remove the coating and oxide layer on the surface of the hot forging parts by alkali washing to ensure the heat treatment effect of the hot forging parts in the next process.

[0045] 5. After completing the hot upsetting of the parts to obtain the hot upsetting parts, the hot upsetting parts are alkali washed, and then the TC4 titanium alloy bolts are subjected to solid solution treatment + aging treatment to meet the strength requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a schematic diagram of the structure of TC4 titanium alloy bolt;

[0047] Figure 2 It is a schematic diagram of the structure of the parts;

[0048] Figure 3 It is a schematic diagram of the main structure of the hot upsetting part;

[0049] Figure 4 for Figure 3 Left view of;

[0050] Figure 5 It is a structural schematic diagram of the lower die, upper die, lower die frame and upper die frame of the present invention when hot upsetting a part to obtain a hot upsetting piece;

[0051] Figure 6 It is a structural schematic diagram of the lower die and the upper die pair of the present invention when hot upsetting a part to obtain a hot upsetting piece;

[0052] Figure 7 It is a schematic diagram of the main structure of the hexagonal pressure rod of the present invention;

[0053] Figure 8 for Figure 7 Bottom view of

[0054] Fig. 9 In order to adopt the original process route, the outer circle of the part is turned, and after the lubricating oil is applied on the surface of the part, it is directly hot-forged to obtain the hot-forged part. When the metallographic inspection is finally carried out, it is found that the head of the hot-forged part has a folded metallographic picture;

[0055] Fig.10 In order to adopt the original process route, the outer circle of the part is turned, and after the lubricating oil is applied on the surface of the part, it is directly hot-forged to obtain the hot-forged part. When the metallographic inspection is finally carried out, it is found that the fillet of the head of the hot-forged part has a folded metallographic picture;

[0056] Fig.11 This is a metallographic diagram of the head of the hot forging piece after hot forging according to the present invention. No overheating occurs, and no folding of the head of the hot forging piece and the fillet under the head occurs.

[0057] In the figure: 1-TC4 titanium alloy bolt, 2-lower die, 20-lower die base, 200-through hole A, 201-blind hole, 21-positioning push rod, 22-carbide ring A, 3-upper die, 30-upper die base, 31-die base pad, 310-through hole B, 32-hexagonal pressure rod, 320-hexagonal section, 321-pressure rod head, 33-pad, 34-shim, 35-carbide ring B, 4-lower die frame, 5-upper die frame, 6-parts, 7-hot upsetting parts. DETAILED DESCRIPTION

[0058] The technical solution of the present invention is further described below, but the scope of protection claimed is not limited to the description.

[0059] like Figures 1 to 11 As shown, the manufacturing process of TC4 titanium alloy bolts for aerospace use described in the present invention adopts the following process route: blanking, turning the outer circle, chamfering, grinding the outer circle, surface fluorine boron lubrication treatment, hot upsetting, alkali cleaning, heat treatment, sandblasting, turning the shape, chamfering, deburring, drilling the locking thread hole, rolling the bolt head fillet R, thread rolling, intermediate inspection, 100% fluorescent flaw detection, titanium alloy blue anodizing, general inspection, and packaging and warehousing;

[0060] The surface fluorine boronization lubrication treatment method comprises the following steps:

[0061] Step 1: Remove oil stains from the surface of part 6;

[0062] Step 2: removing the oxide layer on the surface of part 6;

[0063] Step 3: Perform fluorine boron treatment on the part 6 to form a lubricating film layer on the surface of the part 6.

[0064] The hot upsetting comprises the following steps:

[0065] Step A, using high-frequency induction heating to heat part 6 to 600°C ± 10°C within 5s to 8s, with an oscillation coefficient of 300 to 500, and a heating length on part 6 of L1;

[0066] Step B, using a mold and a press to upset the head of the part 6 that has been heated in step A to obtain a hot upset part 7;

[0067] Step C: performing metallographic inspection on the first hot-forged part 7.

[0068] Since the elongation of TC4 titanium alloy is small, the cold-forged bolt head material is very easy to crack, so the part 6 is properly heated before forging to increase its forgeability. The first hot-forged part 7 is subjected to metallographic inspection, and overheating is not allowed.

[0069] The mold includes a lower mold 2 and an upper mold 3, the lower mold 2 is installed on a lower mold frame 4 of the press, and the upper mold 3 is installed at the bottom of an upper mold frame 5 of the press and is located directly above the lower mold 2;

[0070] The lower die 2 includes a lower die base 20 and a positioning ejector 21. The lower die base 20 is coaxially provided with a through hole A200, and a blind hole 201 is coaxially opened at the lower end of the through hole A200 on the lower die base 20. A hard alloy ring A22 is coaxially embedded at the upper end of the through hole A200. The inner hole of the hard alloy ring A22 is circular and has a clearance fit with the part 6 after the surface fluorine boron lubrication treatment. The positioning ejector 21 has a clearance fit with the through hole A200, and the upper end of the positioning ejector 21 is located in the through hole A200, and the lower end is located in the blind hole 201.

[0071] The upper die 3 comprises an upper die base 30, a die base cushion block 31, a hexagonal pressure rod 32, a cushion block 33 and a cushion sleeve 34. A carbide ring B35 is coaxially embedded on the inner side of the upper die base 30. The thickness of the carbide ring B35 is consistent with the thickness of the upper die base 30, and the inner hole of the carbide ring B35 is a regular hexagon. The die base cushion block 31 is placed on the upper die base 30. A through hole B310 is coaxially provided on the die base cushion block 31. The diameter of the through hole B310 is larger than the outer diameter of the carbide ring A22. The cushion sleeve 34 is located in the through hole B310, with a clearance fit with the through hole B310, and in contact with the carbide ring A22. The lower end of the hexagonal pressure rod 32 passes through the cushion sleeve 34 and extends into the carbide ring B35, and with a clearance fit with the inner hole of the carbide ring B35. The cushion block 33 is placed on the hexagonal pressure rod 32.

[0072] The hexagonal pressure rod 32 includes a hexagonal section 320 and a pressure rod head 321 . One end of the pressure rod head 321 is connected to one end of the hexagonal section 320 , and the diameter of the pressure rod head 321 is between the inner diameter and the outer diameter of the cushion sleeve 34 .

[0073] A through hole B310 is coaxially arranged on the die base pad 31, and the diameter of the through hole B310 is larger than the outer diameter of the carbide ring A22. The cushion sleeve 34 is located in the through hole B310, and is in clearance with the through hole B310 and in contact with the carbide ring A22. The diameter of the pressure rod head 321 is between the inner diameter and the outer diameter of the cushion sleeve 34; the carbide ring B35 is protected by the cushion sleeve 34 to prevent the pressure rod head 321 from directly squeezing and impacting the carbide ring B35, so as to extend the service life of the carbide ring B35. A cushion block 33 is arranged at the upper end of the hexagonal pressure rod 32, so as to adjust the stroke of the hexagonal pressure rod 32 for upsetting the part 6 by increasing or decreasing its thickness, and ensure that the height dimension of the head of the hot upsetting part 7 meets the drawing and process requirements of the TC4 titanium alloy bolt 1.

[0074] The method of using a mold and a press to upset the head of the part 6 that has been heated in step A to obtain a hot upsetting part 7 is as follows: insert the lower end of the part 6 into the carbide ring A22 until the lower end face of the part 6 abuts against the upper end face of the positioning push rod 21. At this time, the volume of the part 6 extending out of the carbide ring A22 is 1.1 times the volume of the formed bolt head. Then the press drives the hexagonal pressure rod 32 to move downward, and cooperates with the regular hexagonal inner hole of the carbide ring B35 and the positioning push rod 21 to upset the head of the part 6 to obtain the hot upsetting part 7. Next, the press drives the upper die frame 5 and the upper die 3 to move upward. After moving up to a certain height, the punching rod of the upper die frame 5 hits the hexagonal pressure rod 32 under the action of gravity and inertia to achieve automatic blanking.

[0075] The method for removing oil stains on the surface of the part 6 in step 1 comprises the following steps:

[0076] Step 1: Soak part 6 in a water-based cleaning agent LCX-52 at a temperature of 40°C to 60°C for 15 to 25 minutes, and shake part 6 every 3 to 5 minutes. The mass of the solute in 1L of the water-based cleaning agent LCX-52 is 40g to 60g.

[0077] Step 2: Soak the component 6 in water at a temperature of 40°C to 60°C for 0.5min to 1min;

[0078] Step 3: Rinse the parts with clean water at room temperature for 610s to 15s;

[0079] Step 4: Perform water film test on part 6. If the water film does not break within 30 seconds, it is qualified.

[0080] The method for removing the oxide layer on the surface of part 6 in step 2 is: first soak part 6 in a mixture of hydrofluoric acid and nitric acid for 3s~5s, and then rinse part 6 with clean water at room temperature for 10s~15s; 1L of the mixture of hydrofluoric acid and nitric acid contains 30ml~40ml of hydrofluoric acid with a concentration of 40%, 300ml~400ml of nitric acid with a concentration of 68%, and the rest is clean water. When in use, it is necessary to strictly control the immersion time of part 6 in the mixture of hydrofluoric acid and nitric acid, and it is strictly forbidden to have excessive corrosion; the part 6 is activated by the mixture of hydrofluoric acid and nitric acid to remove the extremely thin oxide film on the surface of the titanium alloy part 6, exposing the fresh metal surface, so as to obtain a plating (or coating) layer that is well bonded to the substrate, that is, a lubricating film layer, in the future.

[0081] The method for performing fluorine boron treatment on the part 6 in step 3 comprises the following steps:

[0082] Step a, soaking the component 6 in a mixture of potassium fluoroborate, ammonium nitrate and barium chloride at a temperature of 90°C to 95°C for 15min to 25min, and shaking the component 6 every 3min to 5min. 1L of the mixture of potassium fluoroborate, ammonium nitrate and barium chloride contains 60g to 80g of potassium fluoroborate, 30g to 40g of ammonium nitrate and 60g to 80g of barium chloride;

[0083] Step b, soak the component 6 in water at a temperature of 40°C to 60°C for 0.5min to 1min;

[0084] Step c: Rinse the parts with clean water at room temperature for 610s to 15s;

[0085] Step d: Use compressed air to blow dry the part 6, then place the part 6 in a drying box for drying, and then take out the part 6 and place it in a plastic box.

[0086] After the fluorine boron treatment, the surface of the part 6 is uniformly dark gray or gray-black. Slight discoloration or local slight white spots on the surface of the part 6 due to different states are allowed, but film shedding and large white spots are not allowed. The dark gray or gray-black dense protective film formed on the surface of the part 6 is the lubricating film layer, which can improve the surface hardness and wear resistance of the part 6, so as to effectively solve the problem of adhesion between the hot forging part 7 and the mold when hot forging the head of the titanium alloy bolt, and avoid wrinkling and poor folding of the head and the fillet under the head of the hot forging part 7, which significantly improves the processing quality and yield rate of the TC4 titanium alloy bolt.

[0087] The positioning push rod 21 and the hexagonal pressure rod 32 are made of 6542 high-speed steel. When the part 6 is hot-forged, the positioning push rod 21 and the hexagonal pressure rod 32 are the main force-bearing components, so the material is selected to be 6542 high-speed steel so that they can withstand greater impact force.

[0088] The alkali washing method comprises the following steps:

[0089] Step I: soak the hot upsetting piece 7 in a mixture of sodium hydroxide and sodium nitrite at a temperature of 120° C. to 140° C. for 30 min to 120 min, wherein 1 L of the mixture of sodium hydroxide and sodium nitrite contains 500 g to 700 g of sodium hydroxide and 150 g to 250 g of sodium nitrite;

[0090] Step II, soak the hot upsetting piece 7 in water at a temperature of 40°C to 60°C for 0.5min to 1min, and then rinse the hot upsetting piece 7 with clean water at room temperature for 10s to 15s;

[0091] Step III, soak the hot forging piece 7 in a mixture of hydrofluoric acid and nitric acid for 3s to 5s, wherein 1L of the mixture of hydrofluoric acid and nitric acid contains 30ml to 40ml of hydrofluoric acid with a concentration of 40%, 300ml to 400ml of nitric acid with a concentration of 68%, and the rest is clean water;

[0092] Step IV: Rinse the hot forged parts with clean water at room temperature for 710s to 15s;

[0093] Step V: Repeat steps I to IV until the oxide layer on the surface of the hot forging piece 7 is completely removed.

[0094] During use, since the oxide layer on the surface of the hot forging piece 7 is relatively thick after hot forging, one alkali washing cannot completely remove the oxide layer, so it is necessary to repeat steps I to IV until the oxide layer on the surface of the hot forging piece 7 is completely removed. The coating and oxide layer on the surface of the hot forging piece 7 are removed by the above alkali washing method.

[0095] The heat treatment includes solution treatment and aging treatment. The solution treatment method is: ultrasonically clean the hot upsetting piece 7 and dry it, place it in a vacuum water quenching furnace and heat it to 800°C~820°C, preheat it for 30min~40min, then heat it to 910°C±10°C, and keep it warm for 60min~70min, the vacuum degree in the furnace is not greater than 0.067Pa, then take the hot upsetting piece 7 out of the furnace for water cooling, the transfer time of the hot upsetting piece 7 is not greater than 10s, the water temperature is not greater than 40°C, and finally ultrasonically clean the hot upsetting piece 7 again and blow it dry with compressed air;

[0096] The aging treatment method is as follows: the hot upsetting piece 7 is placed in a vacuum tempering furnace and heated to 510°C ± 10°C, and kept warm for 480min~500min. The vacuum degree in the furnace is not greater than 0.067Pa. Then, argon gas is passed into the furnace to cool the hot upsetting piece 7 to room temperature until the pressure in the furnace rises to (1~1.4)×10 5 Pa, the mechanical properties test of the hot upsetting piece 7 heat treated in the same furnace, the tensile strength σ b =1100±100 MPa is qualified.

[0097] After the hot-forged part 7 is alkali-washed, the TC4 titanium alloy bolt 1 is subjected to solution treatment and aging treatment to achieve the strength requirement.

Claims

1. A manufacturing process of TC4 titanium alloy bolts for aerospace, characterized by: The following process routes are adopted: cutting, turning the outer circle, chamfering, grinding the outer circle, surface fluorine boron lubrication treatment, hot upsetting, alkali cleaning, heat treatment, sandblasting, turning the outer shape, chamfering, deburring, drilling the locking thread hole, rolling the bolt head fillet R, thread rolling, intermediate inspection, 100% fluorescent flaw detection, titanium alloy blue anodizing, general inspection, and packaging and warehousing; The surface fluorine boronization lubrication treatment method comprises the following steps: Step 1: Remove oil stains from the surface of the part (6); Step 2, removing the surface oxide layer of the part (6); Step 3: performing a fluorine-boration treatment on the part (6) to form a lubricating film layer on the surface of the part (6); The hot upsetting comprises the following steps: Step A, using high-frequency induction heating to heat the part (6) to 600°C±10°C within 5s to 8s, with an oscillation coefficient of 300 to 500, and a heating length L1 on the part (6); Step B, using a mold and a press to upset the head of the part (6) that has been heated in step A to obtain a hot upset part (7); Step C, performing metallographic inspection on the first hot-forged piece (7); The mold comprises a lower mold (2) and an upper mold (3), the lower mold (2) being mounted on a lower mold frame (4) of a press, and the upper mold (3) being mounted at the bottom of an upper mold frame (5) of the press and being located directly above the lower mold (2); The lower die (2) comprises a lower die base (20) and a positioning push rod (21); a through hole A (200) is coaxially provided on the lower die base (20); a blind hole (201) is coaxially opened on the lower die base (20) at the lower end of the through hole A (200); a hard alloy ring A (22) is coaxially embedded at the upper end of the through hole A (200); the inner hole of the hard alloy ring A (22) is circular and is clearance-matched with the part (6) after the surface fluorine-boron lubrication treatment; the positioning push rod (21) is clearance-matched with the through hole A (200); the upper end of the positioning push rod (21) is located in the through hole A (200), and the lower end is located in the blind hole (201); The upper die (3) comprises an upper die seat (30), a die seat cushion block (31), a hexagonal pressure rod (32), a cushion block (33) and a cushion sleeve (34); a hard alloy ring B (35) is coaxially embedded in the inner side of the upper die seat (30); the thickness of the hard alloy ring B (35) is consistent with that of the upper die seat (30); and the inner hole of the hard alloy ring B (35) is a regular hexagon; the die seat cushion block (31) is placed on the upper die seat (30); and a through hole is coaxially provided on the die seat cushion block (31). The through hole B (310) has a diameter larger than the outer diameter of the hard alloy ring B (35); the washer (34) is located in the through hole B (310), is gap-matched with the through hole B (310), and is in contact with the hard alloy ring B (35); the lower end of the hexagonal pressure rod (32) passes through the washer (34) and then extends into the hard alloy ring B (35), and is gap-matched with the inner hole of the hard alloy ring B (35); the cushion block (33) is placed on the hexagonal pressure rod (32); The hexagonal pressure rod (32) comprises a hexagonal section (320) and a pressure rod head (321), one end of the pressure rod head (321) is connected to one end of the hexagonal section (320), and the diameter of the pressure rod head (321) is between the inner diameter and the outer diameter of the cushion sleeve (34); The method of performing fluorine-boration treatment on the part (6) in step 3 comprises the following steps: Step a, soaking the component (6) in a mixture of potassium fluoroborate, ammonium nitrate and barium chloride at a temperature of 90° C. to 95° C. for 15 to 25 minutes, and shaking the component (6) every 3 to 5 minutes, wherein 1 L of the mixture of potassium fluoroborate, ammonium nitrate and barium chloride contains 60 g to 80 g of potassium fluoroborate, 30 g to 40 g of ammonium nitrate and 60 g to 80 g of barium chloride; Step b, soaking the component (6) in water at a temperature of 40°C to 60°C for 0.5 min to 1 min; Step c: Rinse the parts (6) with clean water at room temperature for 10s to 15s; Step d, using compressed air to blow dry the part (6), then placing the part (6) in a drying oven for drying, and then taking out the part (6) and placing it in a plastic box; The heat treatment comprises a solution treatment and an aging treatment. The solution treatment method comprises: ultrasonically cleaning the hot upsetting piece (7) and drying it, placing it in a vacuum water quenching furnace and heating it to 800°C~820°C, preheating it for 30min~40min, then heating it to 910°C±10°C and keeping it warm for 60min~70min, the vacuum degree in the furnace is not greater than 0.067Pa, then taking the hot upsetting piece (7) out of the furnace and water cooling it, the transfer time of the hot upsetting piece (7) is not greater than 10s, the water temperature is not greater than 40°C, and finally ultrasonically cleaning the hot upsetting piece (7) again and blowing it dry with compressed air; The aging treatment method is as follows: the hot forged piece (7) is placed in a vacuum tempering furnace and heated to 510°C ± 10°C, and kept at this temperature for 480 min to 500 min. The vacuum degree in the furnace is not greater than 0.067 Pa. Then, argon gas is passed into the furnace to cool the hot forged piece (7) to room temperature until the pressure in the furnace rises to 1×10 5 Pa~1.4×10 5 Pa, the mechanical properties test of the hot upsetting piece (7) heat treated in the same furnace, the tensile strength σ b =1100±100 MPa is qualified.

2. The manufacturing process of TC4 titanium alloy bolts for aerospace as claimed in claim 1, characterized in that: The method for removing oil stains from the surface of the part (6) in step 1 comprises the following steps: Step 1, soak the part (6) in a water-based cleaning agent LCX-52 at a temperature of 40°C to 60°C for 15 minutes to 25 minutes, and shake the part (6) every 3 minutes to 5 minutes. The mass of the solute in 1L of the water-based cleaning agent LCX-52 is 40g to 60g; Step 2, soak the component (6) in water at a temperature of 40°C to 60°C for 0.5 min to 1 min; Step 3: Rinse the parts (6) with clean water at room temperature for 10 to 15 seconds; Step 4: Perform a water film test on the part (6). If the water film does not break within 30 seconds, it is qualified.

3. The manufacturing process of TC4 titanium alloy bolts for aerospace as claimed in claim 1, characterized in that: The method for removing the oxide layer on the surface of the component (6) in step 2 is: first, immerse the component (6) in a mixture of hydrofluoric acid and nitric acid for 3s to 5s, and then rinse the component (6) with clean water at room temperature for 10s to 15s; 1L of the mixture of hydrofluoric acid and nitric acid contains 30ml to 40ml of hydrofluoric acid with a concentration of 40%, 300ml to 400ml of nitric acid with a concentration of 68%, and the rest is clean water.

4. The manufacturing process of TC4 titanium alloy bolts for aerospace as claimed in claim 1, characterized in that: The positioning push rod (21) and the hexagonal pressure rod (32) are both made of 6542 high-speed steel.

5. The manufacturing process of TC4 titanium alloy bolts for aerospace as claimed in claim 1, characterized in that: The alkali washing method comprises the following steps: Step I: soak the hot forged part (7) in a mixture of sodium hydroxide and sodium nitrite at a temperature of 120° C. to 140° C. for 30 min to 120 min, wherein 1 L of the mixture of sodium hydroxide and sodium nitrite contains 500 g to 700 g of sodium hydroxide and 150 g to 250 g of sodium nitrite; Step II, soak the hot forged piece (7) in water at a temperature of 40°C to 60°C for 0.5 min to 1 min, and then rinse the hot forged piece (7) with clean water at room temperature for 10 s to 15 s; Step III, soaking the hot forged piece (7) in a mixture of hydrofluoric acid and nitric acid for 3s to 5s, wherein 1L of the mixture of hydrofluoric acid and nitric acid contains 30ml to 40ml of hydrofluoric acid with a concentration of 40%, 300ml to 400ml of nitric acid with a concentration of 68%, and the rest is clean water; Step IV: Rinse the hot forged part (7) with clean water at room temperature for 10s to 15s; Step V, repeating steps I to IV until the oxide layer on the surface of the hot forged part (7) is completely removed.

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