TC6 alloy is a martensitic α-β two-phase titanium alloy with good comprehensive properties. Its composition is Ti-6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si, containing α-stabilizing element Al, isomorphous β-stabilizing element Mo and eutectoid β-stabilizing elements Cr, Fe and Si, and β-stability coefficient Kp is 0.6. This alloy is used in the annealed state and can also be subjected to appropriate strengthening heat treatments.
Chemical composition of TC6 titanium alloy (%)
Performance characteristics of TC6 titanium alloy
TC6 titanium alloy has many excellent performance characteristics! Not only does it have higher room temperature strength, it is also stronger than TC4 alloy, up to 85MPa. In addition, it exhibits excellent thermal strength performance below 450°C. This makes TC6 alloy very advantageous for applications in high temperature environments.
Regarding processing performance, TC6 alloy also shows good characteristics. It has low deformation resistance and high plasticity, which makes it easier to thermal and mechanical processing. At the same time, it can also be connected by welding and other methods.
TC6 alloy is mainly used to manufacture key parts such as compressor discs and blades of aerospace engines. It can work stably under long-term high temperature conditions, such as more than 6,000 hours below 400°C, and less than 2,000 hours at 450°C. This heat resistance makes TC6 alloy of important application value in the aviation field.
Heat treatment system of TC6 titanium alloy
The heat treatment systems of TC6 titanium alloy are as follows:
1 Ordinary annealing: Heat treatment at 800-850°C for 1-2 hours, and then cool naturally.
2 Isothermal annealing: Select the annealing temperature in the range of 870-950°C. The typical regime is heat treatment at 870°C for 1-2 hours, and then quickly cool the material to 550-650°C, or transfer it to another temperature Furnace at 550-650°C, keep there for 2 hours, and finally cool naturally. This system is generally applicable to materials with cross-sectional dimensions less than or equal to 50mm.
3Double annealing: Select the annealing temperature within the range of 870-950℃. The typical system is to first conduct heat treatment at 880℃ for 1-2 hours, then naturally cool, and then conduct heat treatment at 550-600℃ for 2-5 hours. , and finally cool naturally again. This system is generally applicable to materials with cross-sectional dimensions greater than 50mm.
- Solid solution treatment: Select the solution treatment temperature within the range of 840-900°C. The typical system is heat treatment at 850°C for 1 hour, followed by rapid water quenching.
- Aging treatment: Select an aging temperature in the range of 500-620°C. The typical system is heat treatment at 550°C for 1-4 hours, and then natural cooling.
These heat treatment regimes can be selected and adapted according to specific needs and cross-sectional dimensions of the material.
Smelting and casting process of TC6 titanium alloy
- Smelting of ingots: Ingots used for manufacturing bars and forgings should be smelted in vacuum consumable electrode arc furnaces more than twice. Use grade 0-1 small particle sponge titanium with an oxygen content of no more than 0.08% as the raw material, and add an Al-Mo master alloy with a molybdenum content of 50% and an Al-Si master alloy with a silicon content of 10%. Industrial grade iron wire or iron particles.
- Distribution of electrode blocks: Special attention needs to be paid to the way the electrode blocks are distributed to ensure the uniform distribution of various alloying elements in the electrode blocks. The consumable electrodes are welded using argon shielded plasma welding method, and tungsten electrode argon arc welding is strictly prohibited.
3 Vacuum melting: During a vacuum melting, the absolute pressure should not be greater than 1.3Pa.
4 Remelting: The last remelting can be performed in vacuum or in an argon atmosphere.
- Thermal capping operation: Before the end of melting, the thermal capping operation must be performed to ensure the quality of the molten pool.
Antioxidation properties of TC6 titanium alloy
Under long-term high temperature exposure, especially at 400°C, a thin golden oxide film will form on the surface of TC6 alloy. This oxide film can protect the metal surface and prevent further oxidation.
As the temperature increases, the oxide film will gradually become thicker. When the temperature exceeds 550°C, the oxidation phenomenon will become more obvious, and oxygen begins to diffuse into the metal, resulting in the formation of a hardened layer (α layer) on the surface.
In summary, the oxidation resistance of TC6 titanium alloy is relatively good below 400°C and can form a protective oxide film. However, after the temperature exceeds 550°C, the oxidation phenomenon of the alloy will intensify, and appropriate measures need to be taken to protect the alloy surface from the effects of oxidation.
Corrosion resistance of TC6 titanium alloy
TC6 alloy will only react in higher concentrations of sulfuric acid, hydrochloric acid and orthophosphoric acid, and is relatively sensitive to these acidic environments.
In a nitric acid environment, TC6 alloy reacts very weakly and shows high corrosion resistance.
TC6 alloy shows strong corrosion resistance in seawater and is not susceptible to the corrosive effects of seawater.
However, in hydrofluoric acid, even at very low concentrations, TC6 alloys are still susceptible to reaction and corrosion.
To sum up, TC6 titanium alloy shows high corrosion resistance in various corrosive environments, which is better than stainless steel. However, for acidic media with higher concentrations and strong corrosive agents such as hydrofluoric acid, TC6 alloy still needs to be carefully protected and used.
Welding performance of TC6 titanium alloy
TC6 alloy is suitable for welding structures. Commonly used welding methods include tungsten inert gas welding (TIG welding) and electron beam welding (EB welding).
Since TC6 alloy is a highly alloyed α-β titanium alloy, the welding thermal cycle has a greater impact on it, which may lead to adverse structural and performance changes in the weld and surrounding areas.
In order to eliminate or reduce the effects of this change, a common practice is to use specialized heat treatment methods. Commonly used heat treatment methods include heat treatment annealing, solution treatment and aging treatment. The specific method chosen depends on the requirements of the welded structure and the conditions of the material.
Heat treatment can adjust the organizational structure of the welding area, improve the strength and toughness of the welded joint, and reduce the impact of post-weld deformation.
Main uses of TC6 titanium alloy
TC6 titanium alloy has a wide range of applications. Its main uses include but are not limited to:
Aerospace industry: TC6 alloy is a medium-strength alloy that is widely used in the aerospace field to manufacture aircraft bulkheads, joints and other load-bearing structural parts as well as fasteners for different purposes. It has excellent strength and lightweight properties and meets the material performance and weight requirements of the aviation industry. In addition, this alloy can also produce semi-finished products including rods, forgings and die forgings.