TC2 titanium alloy is a low-strength, high-plasticity near-α titanium alloy, containing 4% α stable element Al and 1.5% β stable element Mn. The alloy is composed of α phase and a small amount of β phase at room temperature equilibrium. The content of β phase is generally 2% to 4%. The alloy has been widely used in the aerospace industry because of its good process plasticity and thermal stability.
TC2 titanium alloy plate is used for aircraft parts by cold forming, so it has high requirements on its structure and performance to prevent the problem of uneven deformation during cold deformation. In order to meet the cold forming requirements of TC2 titanium alloy aircraft parts, the structure is required to be uniform and fine equiaxed.
Using β quenching is an effective method to eliminate the abnormal structure of TC2 titanium alloy sheet. However, in the production practice, when the plate is quenched under the larger size, one end of the plate has been filled with water, and the other end must be delayed for a certain period of time before it can enter the water. In order to investigate the effect of this delay on the quenching structure of the sheet, the researchers studied the quenching process in the production through the method of water quenching + air cooling, and then studied the effect of the cooling rate on the quenching structure of the TC2 titanium alloy sheet.
Using a vacuum consumable arc furnace, using a single vacuum and secondary argon-filled smelting process, a Φ420mm TC2 titanium alloy finished ingot was prepared with a phase transition point of 975±10℃. The ingot is forged on a large-tonnage fast forging machine to form a slab with a thickness of 200 mm, which is then hot-rolled by a 2800 mm hot rolling machine to form a 11 mm thick TC2 titanium alloy sheet. Metallographic samples were taken along the rolling direction of the sheet, and then the sheet was annealed at 760°C. After annealing, the metallographic samples are taken along the rolling direction of the plate, and the water quenched + air-cooled composite treatment samples with a size of 25 mm × 25 mm × 600 mm are taken along the transverse direction of the plate. Then, the plate is quenched by β, and after quenching, it is rolled by subsequent processes to obtain a finished TC2 titanium alloy plate. Then at the end of the finished plate β quenching, the metallographic sample is taken first at the water end and finally at the water end. The water quenching + air cooling composite treatment is to heat the sample to 1000 ℃, keep it for a period of time, the temperature is uniform, and the sample is immersed in water quickly after the heat is penetrated, while the other end of the sample is still cooled in the air. Use Olympus metallographic microscope to observe the microstructure of the hot rolled state of the sheet, the microstructure of the annealed state of 760 ℃, the microstructure of the corresponding parts of the water quenching + air cooling composite treatment sample and the β quenching of the finished plate. Microstructure at the end of the water and at the end of the water. The results showed that:
(1) Martensite transformation occurs in the water quenching + air-cooled composite specimens, but the transformation process is different. As the cooling rate decreases, the amount of intermittent grain boundary α-phase precipitation increases, and the grain boundaries are gradually connected. Clear tissue characteristics cannot be observed under an optical microscope.
(2) The air-cooled part of the water-quenched + air-cooled composite sample is a lamellar structure. As the cooling rate decreases, the α-sheet clusters grow significantly and the width of the α-sheet becomes larger. At the grain boundary, the α flange gradually widens.
(3) The end of the plate that is delayed in water entry during quenching is close to air cooling, and the metallographic structure of the finished plate is uneven, showing a layered distribution; and the structure of the finished plate at the end that enters water faster during quenching is closer to water quenching due to the faster cooling rate. Appears as a uniform and fine isometric structure.

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