TC4 titanium alloy has excellent comprehensive properties, and the output accounts for more than 50% of the entire titanium alloy products, and more than 80% of the total amount of titanium alloy products is used in the aerospace industry. It is mainly used as load-bearing components of aircraft, which accounts for approximately the amount of titanium alloy used for load-bearing components. 70% to 80% of the total. At present, some countries in the world have mature technologies for preparing large-scale titanium alloy materials and have formulated corresponding specifications. For example, the thickness of Ti-6Al-4V (TC4) titanium alloy sheets in the American Standard AMS 4911L can reach 100mm. However, due to the limitations of the preparation process and the level of use, the preparation of high-performance large-size TC4 titanium alloy thick plates (thickness greater than 40mm and width greater than 2000mm) in China still faces many challenges.
As the thickness and width of the TC4 titanium alloy sheet increase, the difficulty of controlling the uniformity of the structure and maintaining its strong plastic matching will also increase. The use of suitable hot working methods is effective for preparing large-size TC4 titanium alloy thick plates. way. The researchers used the thermal processing map obtained by the thermal simulation test as a reference to explore the deformation amount, rolling temperature and other process parameters, and successfully prepared a large-size TC4 with good plate shape and uniform structure on a 2800mm four-high hot rolling mill. titanium rectangular rod alloy thick plate.
The TC4 titanium alloy ingot used in the experiment was smelted by vacuum consumable arc three times, with a mass of 5t. After peeling the ingots, samples were taken at the upper, middle, and lower parts of the ingot and analyzed for composition. From the analysis results, it can be seen that the main elements Al, V and the impurity elements Fe and O are evenly distributed on the upper, middle, and lower parts of the ingot without segregation. Fully meet the requirements of preparing large-size TC4 titanium alloy thick plates.
The riser and the bottom of the ingot are removed after ultrasonic testing, and then forged into a slab by multi-directional forging on a large-tonnage fast forging machine. A sample was taken from the cross section of the slab head to observe the microstructure in the middle of the thickness direction. Simultaneously cut a Φ10mm compression sample on the cross section of the slab head, and conduct a thermal simulation test on the Gleeble1500 thermal simulation test machine. Among them, the deformation temperature is set to 800, 850, 900, 950, 1000, 1050°C, and the strain rate is set to 0.01, 0.1, 1, 10, and 20s-1.
Next, the slab is heated, reversing hot rolling, ordinary annealing, and surface treatment to obtain a 40-70mm thick TC4 Titanium Capillary Pipe alloy sheet. Use the MTS testing machine to test the room temperature tensile properties of the plate; use the Olympus microscope to observe the metallographic structure.
the result shows:
(1) The hot rolling process developed by the thermal simulation test results successfully produced large-size TC4 titanium alloy thick plates with excellent comprehensive properties. The key process parameters of TC4 thick plate rolling and its suitable control range are heating temperature 900～980℃, strain rate 5～12s-1, and the maximum deformation rate of the last fire pass is not less than 15%～20%.
(2) The microstructure of the prepared TC4 titanium alloy thick plate is a two-state structure, composed of equiaxed primary α phase, elongated secondary α phase and intercrystalline β phase with an average grain size of 25μm. The tensile strength is 925～960MPa, the yield strength is 870～910MPa, and the elongation is 12.0%～14.5%.
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