Method for regulating and controlling microscopic structure of TC6 titanium alloy bar for aviation

Abstract

The invention discloses a method for regulating and controlling the microstructure of a TC6 titanium alloy bar for aviation. The method comprises the following steps: 1, carrying out upsetting and drawing blooming forging on a TC6 cast ingot; 2, surface coping and damage inspection and blanking are carried out; 3, drawing-out, secondary-heating forging, surface coping and damage inspection are carried out; 4, drawing-out, third-fire forging, surface coping and damage inspection are carried out; 5, carrying out primary fire rolling to obtain an intermediate bar billet; 6, surface grinding and damage inspection; 7, performing secondary fire rolling to obtain a semi-finished bar blank; and 8, carrying out heat treatment and machining on the product to obtain the finished TC6 titanium alloy bar. According to the method, the original structure of the TC6 blank is effectively crushed and refined through reasonable design of the machining procedures and limitation of technological parameters in combination with design of a heat treatment system, the content of the primary alpha phase in the microscopic structure and the uniformity of the structure are remarkably improved, the microscopic structure meeting the special standard is obtained, the product stability of the TC6 titanium alloy bar is improved, and the quality of the TC6 titanium alloy bar is improved. Meanwhile, production efficiency is improved, and production cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of aviation technology, and particularly relates to a method for regulating the microstructure of TC6 titanium alloy bars for aviation. Background Art

[0002] Aerospace technology is a highly integrated modern science and technology and is also one of the manifestations of a country's highest industrial level. In recent years, China's large aircraft, space station, and lunar exploration projects will generate a large demand for aerospace titanium alloys. Especially in the large aircraft project, the application of aerospace titanium alloys will gradually increase. The launch of major projects in the aviation industry is both an opportunity and a challenge for China's titanium industry. From the current development trend of materials used in aerospace parts in Western developed countries, titanium alloy materials with high specific strength and low density will still be the main metal materials used in aerospace for a long time. As a new type of structural material, titanium alloys are endowed with excellent comprehensive properties, such as high specific strength, low density, good crack propagation resistance, fatigue strength, and processing performance. They can serve in environments from room temperature to medium and high temperatures and are important materials for the application of aerospace parts. Titanium alloys are mainly used in production components such as engine compressor disks, pipe plates, turbine disks, and cabin plates, as well as structural components such as large aircraft landing tools, external sheets, fusion plates, and incubators, hydraulic systems, and rear fusion component parts.

[0003] TC6 titanium alloy is a new type of martensitic (α + β) two-phase heat-resistant titanium alloy independently developed in China. It not only has good hot working performance but also has relatively ideal comprehensive mechanical properties. It can be subjected to annealing heat treatment, has heat resistance and thermal stability, and its room temperature strength is 85 MPa higher than that of TC4 titanium alloy. It can work for a long time at 400°C - 450°C and is mainly used to manufacture aviation engine blades, fasteners, and turbine disks, etc., and mainly in the form of blades in China.

[0004] During the hot plastic deformation process of TC6 titanium alloy, the microstructure is relatively sensitive to process parameters such as deformation temperature, strain rate, deformation degree, and heat treatment method. The problems existing in the existing processing methods such as forging, rolling, and heat treatment of TC6 titanium alloy bars are: they cannot meet the requirements of special standards for macro and microstructures, and it is difficult to find a suitable atlas corresponding in the rating atlas for the high-magnification microstructure many times; the content of primary α phase in the microstructure is less than 20%; the first-pass yield rate of similar products is only 73%; the production cycle is nearly one month; and the production cost is relatively high. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for regulating the microstructure of TC6 titanium alloy bars for aviation in view of the deficiencies of the above-mentioned prior art. The method effectively crushes and refines the original structure of the TC6 billet by rationally designing the processing procedures and limiting the process parameters, combined with the design of the heat treatment system, significantly improves the primary α phase content and the uniformity of the microstructure in the microstructure, obtains a microstructure that meets special standards, improves the product stability of the TC6 titanium alloy bars, and at the same time improves production efficiency and reduces production costs, solving the problems of no appropriate atlas corresponding to the microstructure of TC6 titanium alloy bars for aviation, low yield, long production cycle and high cost.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for microstructure control of TC6 titanium alloy bars for aviation, characterized in that the method comprises the following steps:

[0007] Step 1: Forging: Use a fast forging machine to upset and elongate the TC6 ingot to obtain a square bar blank;

[0008] Step 2, surface grinding, flaw inspection and cutting: the square bar blank obtained in step 1 is subjected to surface grinding to remove local cracks, and after inspection, there are no defects visible to the naked eye on the surface, and the grinding part has a smooth transition, and then it is evenly divided and cut to obtain square bar blank segments;

[0009] Step 3, two-fire forging: using a fast forging machine to lengthen the square bar blank obtained in step 2 to obtain a two-fire forging blank, and then performing the surface grinding and flaw inspection process in step 2;

[0010] Step 4, three-fire forging: using a fast forging machine to stretch the two-fire forging billet after surface grinding and flaw inspection in step 3 to obtain a three-fire forging billet, and then performing the surface grinding and flaw inspection process in step 2;

[0011] Step 5, one-fire rolling: using a pass rolling mill to perform one-fire rolling on the three-fire forging billet after surface grinding and flaw inspection in step 4 to obtain an intermediate billet;

[0012] Step 6: Surface grinding and flaw inspection: The intermediate bar blank obtained in step 5 is subjected to surface grinding to remove surface and deeper cracks, and after inspection, there are no visible defects on the surface, and the grinding part has a smooth transition;

[0013] Step 7, two-stage rolling: a groove rolling mill is used to perform two-stage rolling on the intermediate bar billet after surface grinding and flaw inspection in step 6 to obtain a semi-finished bar billet;

[0014] Step 8. Product heat treatment and machining: The semi-finished bar obtained in step 7 is placed in a heat treatment furnace for heat treatment and residual heat straightening, and then machined by a CNC machining center to within the target product diameter tolerance range, and the end face is flattened and polished to obtain a finished TC6 titanium alloy bar.

[0015] The above method for regulating the microstructure of TC6 titanium alloy bars for aviation is characterized in that the cogging forging in step one includes two upsetting and two drawing processes, and the deformation amount of single upsetting and single drawing is more than 25%, the total deformation amount of cogging forging is greater than 65%, and the relative feed amount during the cogging forging process is 0.5 - 0.7; the heating system for the cogging forging is: first keep warm at 800°C - 850°C for 120 min - 150 min, then heat up in the furnace to 1130°C - 1170°C and keep warm for 210 min - 240 min, and the final forging temperature is not less than 850°C.

[0016] The above method for regulating the microstructure of TC6 titanium alloy bars for aviation is characterized in that the surface grinding process in step two is as follows: first, use a hanging grinding wheel to perform overall surface grinding on the surface of the square bar blank, and then use a handheld grinding wheel to perform local point grinding on the places that the hanging grinding wheel did not grind cleanly; the length range difference of the square bar blank segments obtained after equal division and cutting does not exceed 30 mm, and the ingot section numbers are marked on the obtained square bar blank segments in the order from the head to the tail for convenient later material management and traceability.

[0017] The above method for regulating the microstructure of TC6 titanium alloy bars for aviation is characterized in that the total deformation amount of the second forging in step three is greater than 65%, and the total deformation amount from the cogging forging in step one to the second forging in step three exceeds 85%; the heating system for the second forging is: select to keep warm at 10°C - 80°C below the phase transformation point for 140 min - 200 min, and the final forging temperature is not less than 800°C.

[0018] The above method for regulating the microstructure of TC6 titanium alloy bars for aviation is characterized in that the total deformation amount of the third forging in step four is greater than 60%; the heating system for the third forging is: select to keep warm at 10°C - 80°C below the phase transformation point for 80 min - 140 min, and the final forging temperature is not less than 800°C.

[0019] The above method for regulating the microstructure of TC6 titanium alloy bars for aviation is characterized in that the total deformation amount of the first rolling in step five is greater than 73%, a total of 10 passes of rolling are performed, and the deformation amount of a single pass of rolling is 20%; the heating system for the first rolling is: keep warm at 900°C - 940°C for 90 min - 120 min, and the final rolling temperature is less than 890°C.

[0020] The above method for regulating the microstructure of TC6 titanium alloy bars for aviation is characterized in that the surface grinding in step six is as follows: first, use a centerless lathe to peel the surface of the intermediate bar blank to remove surface cracks, and then use a grinding machine to grind the intermediate bar blank after peeling to remove deep cracks and deep sticking pits.

[0021] The above-mentioned method for microstructure control of TC6 titanium alloy bars for aviation is characterized in that the total deformation of the two-pass rolling in step seven is greater than 74%, a total of 6 rolling passes are performed, and the deformation of a single rolling pass is 15% to 20%; the heating system of the two-pass rolling is: keeping warm at 850°C to 880°C for 50min to 80min.

[0022] The above-mentioned method for microstructure control of TC6 titanium alloy bars for aviation is characterized in that the heat treatment described in step eight adopts isothermal annealing heat treatment, and the isothermal annealing heat treatment system is: after keeping at 870°C for 90min to 120min, furnace cooling to 650°C and keeping for 120min, and air cooling; after the heat treatment, an online multi-roll straightening machine is used to perform residual heat straightening on the semi-finished bar blank to ensure the straightness of the finished bar, which is beneficial to subsequent machining.

[0023] The above-mentioned method for microstructure control of TC6 titanium alloy rods for aviation is characterized in that the surface of the finished TC6 titanium alloy rod described in step eight is smooth and uniform, without traces of grinding, and without visible delamination, cracks, fissures, pores, metal and non-metal inclusions and other defects visible to the naked eye.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] 1. The present invention realizes the regulation of the microstructure of TC6 titanium alloy bars by sequentially performing forging, rolling and heat treatment processes on TC6 ingots, combined with the optimization of the forging times and rolling times, so as to meet the requirements of the prior art for aviation bars, while significantly reducing the process steps, improving production efficiency (increased by 12%) and reducing costs (reduced by 17%).

[0026] 2. The present invention controls the structure of the forging blank by reasonably allocating the deformation parameters and the relative feed amount in the forging process, effectively crushes and refines the original structure of the TC6 ingot, significantly improves the uniformity of the transverse and longitudinal structure and performance of the forging blank, and provides a good raw material basis for the subsequent rolling process.

[0027] 3. The present invention significantly reduces defects such as folding and ears in the billet during the rolling process through the reasonable design of the rolling process and the reasonable distribution of the number of rolling passes and the deformation amount of each rolling pass, thereby effectively improving the processing yield of the billet and significantly reducing the raw material cost of TC6 titanium alloy bars for aviation.

[0028] 4. The present invention significantly increases the content of primary α phase in the microstructure after deformation by single-fire rolling by controlling the heating temperature of single-fire rolling. At the same time, by controlling the final rolling temperature, the precipitation of secondary α phase from β phase is reduced, thereby preliminarily achieving the purpose of significantly increasing the content of primary α phase by single-fire rolling.

[0029] 5. By reasonably setting the heating temperature of two-stage rolling, the intermediate billet is continuously deformed at a lower temperature, and the precipitated lamellar secondary α-phase undergoes dynamic recrystallization to form a new primary α-phase with a smaller size, further increasing the content of the primary α-phase in the microstructure, so that the content of the primary α-phase after two-stage rolling can reach 60% - 70%.

[0030] 6. By performing isothermal annealing heat treatment on the semi-finished billet obtained after forging and rolling, the smaller-sized α-phase precipitated by the previous deformation grows and deforms, and the purpose of increasing the content of the primary α-phase is achieved again. Thus, the content of the primary α-phase in the microstructure of the TC6 titanium alloy bar after isothermal annealing heat treatment can reach 80%, far meeting the requirements for the content of the primary α-phase in the special standard of the TC6 titanium alloy bar for aviation use.

[0031] The technical solution of the present invention will be further described in detail below with reference to the drawings and embodiments. Description of the Drawings

[0032] Figure 1 It is a reference rating atlas of the macrostructure of the TC6 titanium alloy bar for aviation use in the prior art.

[0033] Figure 2 It is a reference rating atlas of the microstructure of the TC6 titanium alloy bar for aviation use in the prior art.

[0034] Figure 3 It is the longitudinal macrostructure metallographic diagram of the finished TC6 titanium alloy bar prepared in Example 1 of the present invention

[0035] Figure 4 It is the longitudinal microstructure metallographic diagram of the finished TC6 titanium alloy bar prepared in Example 1 of the present invention.

[0036] Figure 5 It is the longitudinal macrostructure metallographic diagram of the finished TC6 titanium alloy bar prepared in Example 2 of the present invention

[0037] Figure 6 It is the longitudinal microstructure metallographic diagram of the finished TC6 titanium alloy bar prepared in Example 2 of the present invention. Detailed Embodiments

[0038] The requirements for the microstructure and properties of the TC6 titanium alloy bar for aviation use in the prior art are as follows:

[0039] (1) The room-temperature mechanical properties of the bar should meet the requirements of Table 1 below.

[0040] Table 1 Longitudinal room-temperature mechanical properties of the annealed bar

[0041]

[0042] (2) The high-temperature mechanical properties of the bar shall meet the requirements in Table 2 below.

[0043] Table 2 Longitudinal High-Temperature Mechanical Properties of Annealed Bars

[0044]

[0045] In Table 2, σ represents the creep strength, and τ represents the duration at 400 °C.

[0046] (3) Macrostructure: Obvious and clearly visible grains to the naked eye are not allowed in the macrostructure of the bar; layering, cracks, pores, segregation, metallic or non-metallic inclusions, and other metallurgical defects visible to the naked eye are not allowed in the macrostructure; the macro grain size is evaluated according to the atlas and shall meet the requirements of Grades 1 to 4 shown in Figure 1 shown in.

[0047] (4) Microstructure: The high-magnification microstructure of the bar shall be a uniform structure processed through the α + β two-phase region, and all original β grains shall be fully broken. The microstructure after annealing is evaluated according to the atlas and shall meet the requirements of Grades 1 to 5 shown in Figure 2 shown in.

[0048] In the embodiments of the present invention, "□" represents the cross-sectional side length of the square bar blank, which is equivalent to the width and thickness of the square bar blank.

[0049] Example 1

[0050] This example includes the following steps:

[0051] Step 1: Ingot forging: Use a quick forging machine to perform two upsetting and two drawing operations on a TC6 ingot with a diameter of φ610 mm. Upset it to a diameter × length of φ750 mm × L, then draw it to a side length × length of □560 mm × L, then upset it to a diameter × length of φ650 mm × L, and then draw it to a side length × length of □310 mm × L. The relative feed rate is 0.5 to obtain a square bar blank. The heating system for ingot forging is as follows: First, hold at 800 °C ± 10 °C for 120 min, then slowly heat up to 1130 °C ± 10 °C in the furnace and hold for 210 min, and the final forging temperature is 870 °C;

[0052] Step 2: Surface grinding, defect inspection, and blanking: First, use a hanging grinder to perform overall surface grinding on the square bar blank obtained in Step 1, and then use a handheld grinder to perform local point grinding on the areas not cleaned by the hanging grinder to remove local cracks. After inspection, there are no defects visible to the naked eye on the surface, and the grinding parts are smoothly transitioned. Then, perform six-equal division blanking to obtain square bar blank segments; the length range of the square bar blank segments obtained after six-equal division blanking does not exceed 30 mm, and the square bar blank segments obtained are marked with ingot section numbers in the order from the head to the tail for convenient later material management and traceability;

[0053] Step 3. Two-stage forging: Use a quick forging machine to stretch the square bar blank obtained in Step 2 to obtain a two-stage forged blank with a side length × length of □180 mm × L. The heating regime for two-stage forging is: select 970°C ± 10°C for heat preservation for 140 min, the final forging temperature is 850°C, cut in half from the middle, and then perform the surface grinding and flaw inspection process in Step 2 on the two-stage forged blank after cutting in half;

[0054] Step 4. Three-stage forging: Use a quick forging machine to stretch the two-stage forged blank after surface grinding and flaw inspection in Step 3 to obtain a three-stage forged blank with a side length × length of □110 mm × L. The heating regime for three-stage forging is: select 970°C ± 10°C for heat preservation for 80 min, and the final forging temperature is 850°C, cut in half from the middle, and then perform the surface grinding and flaw inspection process in Step 2 on the three-stage forged blank after cutting in half;

[0055] Step 5. First-stage rolling: Use a pass mill to perform first-stage rolling on the three-stage forged blank after surface grinding and flaw inspection in Step 4. A total of 10 passes of rolling are carried out, and the single-pass rolling deformation is 20%. The heating regime for first-stage rolling is: heat preservation at 930°C ± 10°C for 90 min, and the final rolling temperature is 880°C to obtain an intermediate bar blank with a diameter of φ65 mm;

[0056] Step 6. Surface grinding and flaw inspection: First, use a centerless lathe to peel the surface of the intermediate bar blank obtained in Step 5 to remove surface cracks, and then use a grinding machine to grind the peeled intermediate bar blank to remove deep cracks and deep sticking pits. After inspection, there are no visible defects on the surface, and the ground parts are smoothly transitioned;

[0057] Step 7. Second-stage rolling: Use a pass mill to perform second-stage rolling on the intermediate bar blank after surface grinding and flaw inspection in Step 6. A total of 6 passes of rolling are carried out, and the single-pass rolling deformation is 15% - 25%. The heating regime for second-stage rolling is: heat preservation at 850°C ± 10°C for 50 min, and the final rolling temperature is 770°C to obtain a semi-finished bar blank with a diameter of φ35 mm;

[0058] Step 8. Product heat treatment and machining: Place the semi-finished bar blank obtained in Step 7 in a heat treatment furnace for isothermal annealing heat treatment. The isothermal annealing heat treatment regime is: heat preservation at 870°C ± 10°C for 90 min, then furnace cooling to 650°C for heat preservation for 120 min, air cooling, and use an online multi-roll straightening machine to straighten the semi-finished bar blank with residual heat to ensure the straightness of the finished bar, which is beneficial for subsequent machining. Then, machine it to within the target product diameter tolerance range through a CNC machining center, and flatten and turn the end face to obtain a finished TC6 titanium alloy bar with a diameter of φ32 ±0.8 mm. The surface of the finished TC6 titanium alloy bar is smooth and uniform, without grinding marks, and there are no visible delamination, cracks, fissures, pores, metal and non-metal inclusions, and other visible defects to the naked eye.

[0059] Figure 3 This is the longitudinal macrostructure metallographic diagram of the finished TC6 titanium alloy bar prepared in this example. From Figure 3 it can be seen that there are no obvious and clearly visible grains to the naked eye in the macrostructure of this bar, no delamination, cracks, pores, segregation, metallic or non-metallic inclusions, and other metallurgical defects visible to the naked eye. The macro grain size is evaluated according to the atlas and meets Figure 1 Grade 2.

[0060] Figure 4 This is the longitudinal high-magnification microstructure metallographic diagram of the finished TC6 titanium alloy bar prepared in this example. From Figure 4 it can be seen that the microstructure of this bar is a uniform structure processed in the α+β two-phase region. All the original β grains are fully fragmented. The microstructure after annealing is evaluated according to the atlas and meets Figure 2 Grade 2.

[0061] Samples were taken from the finished TC6 titanium alloy bar prepared in this example for performance and composition testing. The test results are shown in Table 3 below.

[0062] Table 3 Performance test results of the finished TC6 titanium alloy bar prepared in Example 1

[0063]

[0064] By comparing the performance test results of the finished TC6 titanium alloy bar in Table 3 with the performance requirements of the TC6 titanium alloy bar in the prior art in Tables 1-2, it can be seen that the macrostructure, high-magnification microstructure, room-temperature mechanical properties, and high-temperature mechanical properties of the TC6 titanium alloy bar prepared in this example all meet the requirements of the prior art.

[0065] Example 2

[0066] This example includes the following steps:

[0067] Step 1: Blooming forging: Use a quick forging machine to perform two upsetting and two drawing operations on a TC6 ingot with a diameter of φ610mm. Upset it to a diameter×length of φ750mm×L, then draw it to a side length×length of □560mm×L, then upset it to a diameter×length of φ650mm×L, and then draw it to a side length×length of □310mm×L. The relative feed rate is 0.7 to obtain a square bar billet. The heating system for blooming forging is as follows: First, hold at 850°C±10°C for 150 min, then heat up to 1170°C±10°C in the furnace and hold for 240 min, and the final forging temperature is 850°C;

[0068] Step 2. Surface grinding, defect inspection and blanking: First, use a hanging grinding wheel machine to perform overall surface grinding on the square bar blank obtained in Step 1. Then, use a handheld grinding wheel machine to perform local point grinding on the areas not cleaned by the hanging grinding wheel machine, remove local cracks, and after inspection, there are no visible defects on the surface. The grinding parts are smoothly transitioned. Then, perform six-equal-part blanking to obtain square bar blank segments; the length range of the square bar blank segments obtained after the six-equal-part blanking does not exceed 30 mm, and the square bar blank segments obtained are marked with ingot section numbers in the order from the head to the tail for convenient later material management and traceability;

[0069] Step 3. Second-stage forging: Use a quick forging machine to elongate the square bar blank segments obtained in Step 2 to obtain a second-stage forged blank with a side length × length of □180 mm × L. The total deformation amount of the second-stage forging is 66%, and the total deformation amount from the initial blank forging to the second-stage forging is 89%. And the heating system for the second-stage forging is: select 900 °C ± 10 °C for heat preservation for 200 min, the final forging temperature is 800 °C, perform middle blanking, and then perform the surface grinding and defect inspection process in Step 2 on the second-stage forged blank after blanking;

[0070] Step 4. Third-stage forging: Use a quick forging machine to elongate the second-stage forged blank after surface grinding and defect inspection in Step 3 to obtain a third-stage forged blank with a side length × length of □110 mm × L. And the heating system for the third-stage forging is: select 900 °C ± 10 °C for heat preservation for 140 min, and the final forging temperature is 800 °C, perform middle blanking, and then perform the surface grinding and defect inspection process in Step 2 on the third-stage forged blank after blanking;

[0071] Step 5. First-stage rolling: Use a pass mill to perform first-stage rolling on the third-stage forged blank after surface grinding and defect inspection in Step 4. A total of 10 passes of rolling are carried out, the single-pass rolling deformation amount is 20%, and the total deformation amount is 77%. And the heating system for the first-stage rolling is: heat preservation at 940 °C ± 10 °C for 120 min, and the final rolling temperature is 880 °C to obtain an intermediate bar blank with a diameter of φ59 mm;

[0072] Step 6. Surface grinding and defect inspection: First, use a centerless lathe to perform surface peeling on the intermediate bar blank obtained in Step 5 to remove surface cracks. Then, use a grinding machine to grind the intermediate bar blank after peeling to remove deep cracks and deep sticking pits, and after inspection, there are no visible defects on the surface. The grinding parts are smoothly transitioned;

[0073] Step 7. Second-stage rolling: Use a pass mill to perform second-stage rolling on the intermediate bar blank after surface grinding and defect inspection in Step 6. A total of 6 passes of rolling are carried out, and the single-pass rolling deformation amount is 15% - 25%. The heating system for the second-stage rolling is: heat preservation at 880 °C ± 10 °C for 80 min, and the final rolling temperature is 850 °C to obtain a semi-finished product bar blank with a diameter of φ22 mm;

[0074] Step 8. Product heat treatment and machining: Place the semi-finished billet obtained in Step 7 in a heat treatment furnace for isothermal annealing heat treatment. The isothermal annealing heat treatment regime is as follows: Insulate at 870°C ± 10°C for 120 min, then cool in the furnace to 650°C and insulate for 120 min, and then air cool. Use an online multi-roll straightening machine to straighten the semi-finished billet with residual heat to ensure the straightness of the finished bar, which is beneficial for subsequent machining. Then, machine it to within the target product diameter tolerance range through a CNC machining center, and flatten and turn the end face to obtain a finished TC6 titanium alloy bar with a diameter of φ20 ±0.8 mm. The surface of the finished TC6 titanium alloy bar is smooth and uniform, without grinding marks, and there are no visible layering, cracks, fissures, pores, metal and non-metal inclusions, and other visible defects to the naked eye.

[0075] Figure 5 is the longitudinal macrostructure metallographic diagram of the finished TC6 titanium alloy bar prepared in this example. From Figure 5 it can be seen that there are no obvious and visible clear grains in the macrostructure of the bar, no layering, cracks, pores, segregation, metal or non-metal inclusions, and other visible metallurgical defects. The macro grain size is evaluated according to the atlas and meets Figure 1 Grade 2.

[0076] Figure 6 is the longitudinal microstructure metallographic diagram of the finished TC6 titanium alloy bar prepared in this example. From Figure 6 it can be seen that the microstructure of the bar is a uniform structure processed through the α + β two-phase region. All the original β grains are fully fragmented. The microstructure after annealing is evaluated according to the atlas and meets Figure 2 Grade 3.

[0077] Samples of the finished TC6 titanium alloy bar prepared in this example are taken for performance and composition testing, and the test results are shown in Table 4 below.

[0078] Table 4 Performance test results of the finished TC6 titanium alloy bar prepared in Example 2

[0079]

[0080] By comparing the performance test results of the finished TC6 titanium alloy bar in Table 4 with the performance requirements of the existing technology for TC6 titanium alloy bars in Tables 1 - 2, it can be seen that the macrostructure, microstructure, room temperature mechanical properties, and high temperature mechanical properties of the TC6 titanium alloy bar prepared in this example all meet the requirements of the existing technology.

[0081] The above are only the preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent variations made to the above embodiments according to the technical essence of the invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for controlling the microstructure of TC6 titanium alloy bars for aviation, characterized in that, The method includes the following steps: Step 1, bloom forging: Upsetting and drawing out a TC6 ingot using a quick forging machine to obtain a square bar blank. Step 2, surface grinding for inspection and blanking: Surface grinding the square bar blank obtained in Step 1 to remove local cracks, and after inspection, there are no visible defects to the naked eye on the surface, the ground parts are smoothly transitioned, and then it is evenly divided and cut to obtain square bar blank segments. Step 3, second heat forging: Drawing out the square bar blank segments obtained in Step 2 using a quick forging machine to obtain second heat forged blanks, and then performing the surface grinding and inspection process in Step 2. Step 4, third heat forging: Drawing out the second heat forged blanks after surface grinding and inspection in Step 3 using a quick forging machine to obtain third heat forged blanks, and then performing the surface grinding and inspection process in Step 2. Step 5, first heat rolling: Performing first heat rolling on the third heat forged blanks after surface grinding and inspection in Step 4 using a pass mill to obtain intermediate bar blanks. Step 6, surface grinding for inspection: Surface grinding the intermediate bar blanks obtained in Step 5 to remove surface and deeper cracks, and after inspection, there are no visible defects to the naked eye on the surface, the ground parts are smoothly transitioned. Step 7, second heat rolling: Performing second heat rolling on the intermediate bar blanks after surface grinding and inspection in Step 6 using a pass mill to obtain semi-finished bar blanks. Step 8, product heat treatment and machining: Placing the semi-finished bar blanks obtained in Step 7 into a heat treatment furnace for heat treatment, and performing residual heat straightening, then machining to within the target product diameter tolerance range using a CNC machining center, and flattening and turning the end faces to obtain finished TC6 titanium alloy bars.

2. A method for controlling the microstructure of TC6 titanium alloy bars for aviation according to claim 1, characterized in that, The bloom forging in Step 1 includes two upsetting and two drawing out operations, and the deformation amount of single upsetting and single drawing out is more than 25% each, the total deformation amount of bloom forging is greater than 65%, and the relative feed amount during the bloom forging process is 0.5 - 0.7; the heating system for the bloom forging is: first insulating at 800°C - 850°C for 120 min - 150 min, then heating up in the furnace to 1130°C - 1170°C and insulating for 210 min - 240 min, and the final forging temperature is not less than 850°C.

3. A method for controlling the microstructure of TC6 titanium alloy bars for aviation according to claim 1, characterized in that, The surface grinding process in Step 2 is: first performing overall surface grinding on the surface of the square bar blank using a hanging grinding wheel, and then performing local point grinding on the places not cleaned by the hanging grinding wheel using a hand-held grinding wheel; the length range of the square bar blank segments obtained after the even division and cutting does not exceed 30 mm, and the ingot section numbers are marked on the obtained square bar blank segments in the order from the head to the tail for convenient later material management and traceability.

4. A method for controlling the microstructure of TC6 titanium alloy bars for aviation according to claim 1, characterized in that, The total deformation amount of the second heat forging in Step 3 is greater than 65%, and the total deformation amount from the bloom forging in Step 1 to the second heat forging in Step 3 exceeds 85%; the heating system for the second heat forging is: selecting to insulate at 10°C - 80°C below the phase transformation point for 140 min - 200 min, and the final forging temperature is not less than 800°C.

5. A method for controlling the microstructure of TC6 titanium alloy bars for aviation according to claim 1, characterized in that, The total deformation amount of the third heat forging in Step 4 is greater than 60%; the heating system for the third heat forging is: selecting to insulate at 10°C - 80°C below the phase transformation point for 80 min - 140 min, and the final forging temperature is not less than 800°C.

6. A method for controlling the microstructure of TC6 titanium alloy bars for aviation according to claim 1, characterized in that, The total deformation of the one-fire rolling described in Step 5 is greater than 73%, and it goes through 10 passes of rolling, with the deformation per pass being 20%; the heating regime of the one-fire rolling is: holding at 900°C - 940°C for 90 min - 120 min, and the finishing rolling temperature is less than 890°C.

7. A method for controlling the microstructure of TC6 titanium alloy bars for aviation according to claim 1, characterized in that The surface grinding described in Step 6 is as follows: first, centerless turning is used to peel the surface of the intermediate billet to remove surface cracks, and then a grinding machine is used to grind the peeled intermediate billet to remove deep cracks and deep sticking pits.

8. A method for controlling the microstructure of TC6 titanium alloy bars for aviation according to claim 1, characterized in that, The total deformation of the two-fire rolling described in Step 7 is greater than 74%, and it goes through 6 passes of rolling, with the deformation per pass being 15% - 20%; the heating regime of the two-fire rolling is: holding at 850°C - 880°C for 50 min - 80 min.

9. A method for controlling the microstructure of TC6 titanium alloy bars for aviation according to claim 1, characterized in that, The heat treatment described in Step 8 uses isothermal annealing heat treatment, and the isothermal annealing heat treatment regime is: holding at 870°C for 90 min - 120 min and then furnace cooling to 650°C and holding for 120 min, followed by air cooling; after the heat treatment, an online multi-roll straightening machine is used to straighten the semi-finished billet with residual heat to ensure the straightness of the finished bar, which is beneficial for subsequent machining.

10. A method for controlling the microstructure of TC6 titanium alloy bars for aviation according to claim 1, characterized in that, The surface of the finished TC6 titanium alloy bar described in Step 8 is smooth and uniform, without grinding marks, and without visible layering, cracks, fissures, pores, metallic and non-metallic inclusions, and other visible defects to the naked eye.

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