Friction Stir Welding in Defence

Defence platforms combine the hardest joining problems in one place: armour alloys chosen for ballistic performance rather than weldability, structures that must be light and fatigue-tolerant, and hardware where a weld defect is discovered at the worst possible time. FSW’s appeal is that weld properties stop being the limiting factor.

Where FSW is used today

Aluminium armour and hull structure

The high-strength aluminium armour grades (7xxx and 2xxx families) lose a large fraction of their strength — and gain cracking and porosity — when arc welded. FSW of aluminium armour was proven on US amphibious-vehicle programmes in the 2000s and is the reference route where hull welds must approach parent ballistic and fatigue performance without post-weld correction.

Space and launch hardware

Satellite structures, propellant tanks and launch-vehicle stages — shared technology with the aerospace sector, and stir welded for the same reason: fusion welds in high-strength aluminium are the weak link.

Sealed casings and thermal hardware

Munitions and electronics enclosures where a continuous, hermetic, low-distortion weld replaces fasteners and seals, and ruggedised cold plates for radar and directed-energy power electronics (see thermal management).

Where the research is heading

• Armour steels. FSW of rolled homogeneous armour and modern high-hardness grades is an active research field in the UK and US open literature: solid-state welding avoids the softened HAZ and hydrogen-cracking controls that arc welding of quenched-and-tempered armour demands. The engineering questions are tool life and cost per metre.
• Tool materials and assisted processes. PCBN and tungsten-rhenium tools, and induction-assisted preheating to cut plunge forces and abrasive tool wear in hard steels — the economics of steel FSW hinge on this.
• Ballistic and blast performance of stir welds. Building the weld-zone property datasets (hardness mapping, impact toughness, residual stress) that qualification against defence standards requires.
• Solid-state repair. Friction stir deposition to rebuild worn or damaged surfaces on high-value components without a fusion thermal cycle — attractive wherever heat-sensitive parent metallurgy rules out weld repair.