The Role of Fasteners in Aircraft Structures
A modern airliner contains hundreds of thousands of fasteners, and their total weight is significant enough that fastener selection directly affects fuel burn and payload. Titanium fasteners weigh about 56 percent of equivalent steel fasteners, so replacing steel bolts, rivets and screws with titanium saves tens of kilograms per aircraft. In high-performance military aircraft the savings are even more valuable, which is why titanium fastening has been standard practice for decades.
Weight is not the only driver. Titanium fasteners eliminate galvanic corrosion concerns when used in aluminium and composite structures, and their fatigue strength suits the cyclic loading of pressurised fuselages, wing skins and control surfaces. Unlike aluminium fasteners, titanium does not require protective plating for corrosion resistance in most airframe environments.
Alloys and Specifications
The dominant aerospace fastener alloy is Ti-6Al-4V, supplied to AMS 4967 for bar stock and used for bolts with minimum tensile strength of 895 MPa in the annealed condition, rising above 1100 MPa in the heat-treated condition. For shear applications, Ti-6Al-4V is used in rivets, and beta alloys such as Ti-3Al-8V-6Cr-4Mo-4Zr, known as Beta-C, are specified where higher strength, around 1240 MPa, is needed for large structural bolts.
Fastener specifications control the whole product, not just the alloy. AMS 4967 defines the bar chemistry, tensile properties and microstructural cleanliness, while AMS 5739 and related documents cover bolts, and NAS and MS standards define dimensions, threads and tolerances. Cadmium plating was historically applied to steel fasteners for corrosion control; titanium needs no cadmium, which also removes a toxic process from the supply chain.
Manufacturing of Titanium Fasteners
Titanium fasteners are manufactured by heading, rolling or machining from bar. Heading at elevated temperature forms the head without cutting away material, preserving grain flow, and threads are rolled rather than cut so that the thread roots carry compressive residual stress, which improves fatigue life. After forming, fasteners are solution treated and aged for high-strength grades, then straightened and inspected.
Surface treatments are applied for lubrication and corrosion control. Anodising produces a thin oxide that resists galling, and dry film lubricants such as molybdenum disulfide coatings are applied to threads to control friction during installation. Because titanium-to-titanium contact can gall and seize, the lubricant and controlled surface roughness are as important as the geometry itself.
Applications Across the Airframe
Titanium fasteners join fuselage skin panels, wing-to-fuselage attachments, engine mounts, landing gear fittings, flap and slat tracks, and composite structure joints. In graphite-epoxy structures, titanium is the preferred fastener metal because its potential is close to that of carbon fibre, minimising galvanic coupling, and its thermal expansion behaviour is compatible with composite panels.
Engine areas use titanium fasteners for their temperature capability and resistance to the corrosive products of combustion. Fasteners in the pylon and nacelle must hold preload at operating temperatures of several hundred degrees Celsius, where aluminium would lose strength and steel would add unacceptable weight. The fatigue performance of rolled-thread titanium bolts is the reason these joints remain tight for the life of the engine installation.
Installation and Quality Control
Installation practice for titanium fasteners is controlled by the airframe builder's process specifications. Hole preparation, fastener-to-hole clearance and the application of sealant and lubricant are prescribed, and installation torque is set to achieve the designed preload without galling. Inspection after installation checks flushness for countersunk fasteners and correct protrusion for protruding-head types.
Quality control during manufacture includes tensile testing of sample bolts from each lot, metallographic examination for microstructure, and non-destructive testing for surface cracks. Dimensional inspection of thread form and head geometry ensures interchangeability with the millions of fasteners already in service, and full material traceability is maintained from the bar heat to the finished lot.
Frequently Asked Questions
Q: Why use titanium fasteners in aircraft?
A: Titanium fasteners weigh about 44 percent less than steel equivalents, resist corrosion without plating, and offer high fatigue strength, reducing airframe weight and maintenance.
Q: Which titanium alloys are used for aerospace fasteners?
A: Ti-6Al-4V covers the majority of bolts and rivets, and higher-strength beta alloys such as Ti-3Al-8V-6Cr-4Mo-4Zr are used for large structural bolts.
Q: How are titanium fastener threads made?
A: Threads are rolled rather than cut, which imparts compressive residual stress at the thread roots and significantly improves fatigue life.
Q: Do titanium fasteners corrode in contact with carbon fibre composites?
A: No, titanium's electrochemical potential is close to carbon fibre, so galvanic corrosion is minimal, which is why it is preferred for composite structure joints.
Q: What lubricant is used when installing titanium fasteners?
A: Dry film lubricants such as molybdenum disulfide coatings are applied to threads, because unlubricated titanium-to-titanium contact can gall and seize.
