TC16 titanium alloy is a type of titanium alloy material with good process plasticity developed in China in the early 21st century based on the composition design of the Russian BT16 titanium alloy. It belongs to the α+β two-phase titanium alloy, with a nominal composition of Ti-3Al-5Mo-4.5V, a phase transformation point between 840 and 880 °C, and a β stability coefficient of 0.83. It possesses high plasticity, high strength, good hardenability, excellent cold heading formability, as well as good anti-fatigue and weldability, with low sensitivity to stress concentration.
The total weight of fasteners used in a medium-sized aircraft (such as the domestic C919) can account for 5% to 6% of the aircraft's total weight, amounting to 2 to 3 million pieces[3]. Figure 1 shows the TC16 titanium alloy fasteners and the C919 aircraft.
TC16 titanium alloy is commonly strengthened through cold heading and heat treatment, hence the material is required to have good plasticity in the annealed state and higher strength in the solution-treated and aged state. Compared to the Russian BT16 titanium alloy, the domestically produced TC16 titanium alloy has comparable mechanical properties and process plasticity, but the cold heading process is not yet mature enough to achieve mass production. Studies have shown that the cold heading deformation ability of the material is related to plasticity, shear strength, and microstructure.
Different annealing and solution-aging processes have a significant impact on the microstructure and properties of the alloy[4]. Therefore, this paper investigates the effects of different annealing and solution-aging processes on the microstructure and properties of TC16 alloy bars, providing technical support for the localization and mass production of TC16 alloy fasteners.
To improve the maturity of the cold heading process for TC16 titanium alloy, the study first conducted a systematic annealing treatment on the TC16 titanium alloy. By adjusting the annealing temperature and time, we observed changes in the microstructure and macroscopic properties of the alloy. The study found that as the annealing temperature increased and the holding time extended, the grain size of the TC16 titanium alloy gradually increased, and plasticity improved. However, it is also necessary to control the excessive growth of grains to avoid affecting the subsequent cold heading formability.
Based on the optimized annealing process, we conducted solution and aging treatments on the TC16 titanium alloy. Solution treatment can further enhance the strength of the alloy, while aging treatment helps to precipitate strengthening phases, improving the overall properties of the alloy. By adjusting the solution temperature, holding time, aging temperature, and time, we obtained a series of TC16 titanium alloy samples with different microstructures and properties.
Experimental results show that within the solution treatment temperature range of 780°C to 820°C, the strength and plasticity of the TC16 titanium alloy reached a good level. Controlling the holding time between 1 to 2 hours ensures that the alloy elements are fully dissolved, laying the foundation for subsequent aging treatment. Within the aging treatment temperature range of 530°C to 580°C, the strength and toughness of the alloy were significantly improved. With aging time between 4 to 8 hours, the performance of the alloy reached its optimal state.
Through mechanical property testing of the TC16 titanium alloy under different process parameters, we found that the optimized annealing and solution-aging processes could increase the yield strength of the TC16 titanium alloy by over 20% and the tensile strength by over 15%, while maintaining good plasticity. In addition, cold heading experiments indicate that the TC16 titanium alloy treated with the optimized process has good cold heading formability, laying the foundation for mass production.
To further verify the performance of TC16 titanium alloy fasteners in practical applications, we applied them to simulated tests on the C919 aircraft. The test results show that the fasteners made from TC16 titanium alloy meet the aircraft's operational requirements in terms of fatigue life, tensile strength, and weldability, and exhibit good anti-fatigue performance in stress concentration areas.
The study also discussed the mass production of TC16 titanium alloy fasteners. By optimizing the production line layout, improving cold heading forming equipment and die design, we achieved efficient and stable production of TC16 titanium alloy fasteners. At the same time, strict control over the quality during the production process ensured the product quality of the fasteners.
In summary, through the study of the annealing and solution-aging processes of the TC16 titanium alloy, we have provided strong technical support for the localization and mass production of TC16 alloy fasteners for aviation use. This not only helps to reduce aircraft manufacturing costs and enhance the international competitiveness of China's aviation manufacturing industry but also lays a solid foundation for the application and development of titanium alloy materials in our country. In the future, we will continue to delve into the performance optimization and process improvement of TC16 titanium alloy to meet
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