Fasteners, as an important general-purpose basic component, play a crucial role in industry. According to their application fields, fasteners are classified into general-purpose fasteners and aerospace fasteners. In the aviation field, the connection method of aircraft is still mainly mechanical connection, and the connection assembly of aircraft relies on a large number of various fasteners. In the aerospace field, the connection between aircraft sections also relies on fasteners. With the development of equipment lightweighting, more and more aerospace fasteners are favoring titanium alloy materials.
Advantages of using titanium materials
Low density: The density of titanium alloy is significantly lower than that of steel materials, so titanium alloy fasteners are lighter in material weight than steel fasteners.
High specific strength: Titanium alloy is a metal material with relatively high specific strength among common metal materials. Taking advantage of its high specific strength, titanium alloy can also be used to replace the lighter aluminum alloy material. Under the same external load, the geometric dimensions of titanium alloy parts are smaller, which can effectively save space. This material utilization concept is of great significance to the aerospace field.
High melting point: The melting point of titanium alloy is significantly higher than that of steel materials, so the heat resistance of titanium alloy fasteners is better than that of steel fasteners. The coefficient of thermal expansion and elastic modulus are small.
Titanium alloy materials commonly used for fasteners
TC4 titanium alloy
TC4 titanium alloy is a medium-strength two-phase titanium alloy and is also the most studied and applied titanium alloy material. Most titanium alloy materials used in fasteners are TC4 titanium alloy. When TC4 titanium alloy is used to manufacture fasteners, only hot heading can be adopted, and specialized hot heading equipment and heating equipment must be used. This not only affects production efficiency but also results in a relatively low material utilization rate. For high-strength fasteners, the strength of TC4 titanium alloy fasteners cannot meet the requirements. The tensile strength of the alloy after solution aging can reach up to 1,100 MPa, and the shear strength is around 650 MPa. Due to the poor hardenability of TC4 titanium alloy, the cross-sectional size of TC4 titanium alloy fasteners is generally below 19 mm during solution aging. TC4 titanium alloy fasteners include bolts, high-lock bolts, studs, screws and ring slot rivets, etc. Among them, most TC4 bolts have been widely applied in domestic aircraft, engines, airborne equipment, aerospace vehicles and satellites.
TC6 titanium alloy
TC6 titanium alloy is a martensitic (α+β) type duplex titanium alloy with excellent comprehensive performance. Its nominal composition is Ti-6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si. This alloy is generally used in the annealed state and can also be strengthened through heat treatment. It also has good oxidation resistance.
TC16 titanium alloy
TC16 titanium alloy is a typical two-phase titanium alloy strengthened by solution aging, with a nominal composition of Ti-3Al-5Mo-4.5V. After solution treatment, this alloy has high room-temperature plasticity, so it has good cold heading performance, with a upsetting ratio reaching 1:4. In the manufacturing of fasteners, TC16 titanium alloy can be directly formed by cold heading or by hot heading. At present, TC16 titanium alloy fasteners include bolts, screws and self-locking nuts, etc.
Future development trend
With the development of the aerospace industry, the connection technology level adopted by new aircraft and space vehicles is constantly improving, and new requirements are also put forward for new fasteners. One of the future development trends is to develop ultra-high strength titanium alloy fasteners with tensile strength ranging from 1,200 to 1,500 MPa and shear strength ≥750 MPa in the future.
Titanium fasteners, these seemingly tiny components, are actually a microcosm of the progress in aerospace technology. From reducing the weight of aircraft to ensuring structural safety, from high-temperature resistance and corrosion resistance to electromagnetic compatibility, titanium alloy fasteners, with the posture of "all-round players", support humanity's dream of exploring the sky. In the future, with the deep integration of materials science and manufacturing technology, titanium fasteners are bound to write more breakthrough chapters in the aerospace field and become a lasting driving force for the performance revolution of aircraft.
