Welding of aluminium tank by Friction Stir Welding
Aluminium is increasingly used for the production of tanks, whether in the trucks or in space and aeronautical industries, particularly for the storage of hydrogen, LNG or ergol.
The advantages of FSW for aluminium tank manufacturing
100% LEAK PROOF: No porosity, high quality of Friciton Stir Welding joint, improved corrosion resistance.
SUPERIOR MECHANICAL STRENGTH: High pressure operation, joint efficiency factor between 70 and 100%.
INCREASED LIFETIME: Due to improved fatigue resistance thanks to minimum residual stresses.
EASE OF USE: Friction Stir Welding replaces MIG and TIG (conventional welding processes).
100% leak proof
No porosity, high quality of Friciton Stir Welding joint, improved corrosion resistance.
Superior mechanical strength
High pressure operation, joint efficiency factor between 70 and 100%.
Due to improved fatigue resistance thanks to minimum residual stresses.
Ease of use
Friction Stir Welding replaces MIG and TIG (conventional welding processes).
Which application areas for FSW welded aluminium tanks?
ALUMINIUM HYDROGEN CRYOGENIC TANK WELDED BY FSW
Friction Stir Welding is a welding technique that preserves the mechanical properties of aluminium (joint efficiency coefficient between 70 and 100%). In addition, Friction Stir Welding guarantees a reduced post-weld defect ratio, perfect repeatability, and the possibility of welding high performance aluminium alloys (such as AA2024-T3 or AA2219-T8). Finally, once welded, a cryogenic hydrogen tank will be 100% waterproof, a quality required for this type of application.
To know more about aluminium hydrogen cryogenic tank welded by friction stir welding, click here.
Example of application sectors: aeronautics, space.
FRICTION STIR WELDED SPACE LAUNCHERS
Friction stir welding is used for the circumferential welding of launch vehicle panels and for the welding of domes (butt-welding): the cost of the process is reduced by a factor of 2.
FSW allows the welding of high-performance aluminium alloys, 2xxx and 7xxx series, which are widely used in the manufacture of space launchers but were not previously weldable or very difficult to weld.
In addition, FSW reduces the weight of space launcher by welding lighter stiffened panels:
- Weldable stiffeners of various shapes: cross, triangular, axial and circumferential.
- Stiffeners can be obtained by machining or extrusion.
Sector of applications: space.
LIQUID OXYGEN TANK ASSEMBLED BY FRICTION STIR WELDING
For this application, the advantages of FSW are numerous:
- 100% watertight weld,
- High mechanical properties,
- Excellent repeatability.
Example of application sectors: space, aeronautics.
ZOOM: FSW FOR WELDING TANK STIFFENERS
The stiffening of a tank allows the weight of the tank to be reduced while maintaining equivalent mechanical strength. Friction stir welding is the only welding technology that allows stiffeners to be applied to the tank skin: minimal deformation, minimal residual stresses that improve fatigue life, better corrosion resistance.
FSW welding with a retractable pin: the solution to fill the exit hole
Often a problem in the space or aeronautics sectors, the exit hole of FSW welding can be filled using a retractable pin system. Here is an example:
On the picture above you can see a circumferential FSW weld of a 100mm diameter tank of 2024-T3 aluminium grade and 2.4mm thickness. At the end of the weld, you can see that the exit hole has been filled with the retractable pin principle.
Here you can see a metallographic cross-section of the FSW weld in steady state with no weld defect in accordance with ISO 25239 standard.
In this second metallographic section, we can see that there are no defect in the exit hole of the FSW weld. Indeed, the exit hole is perfectly filled thanks to the retractable pin.
RETRACTABLE PIN PRINCIPLE
Here are the results of YS (yield strength) and UTS (ultimate tensile strength) as a function of the position of the sample on the 3 convex weld sheets. The average UTS is 396 MPa (88% of base metal) with a standard deviation of 18 MPa.
Welding process convex geometry with the stirweld FSW head with retractable pin
Interested in learning more about FSW with retractable pin?
Contact us for a presentation of the Stirweld solution: the FSW head with retractable pin!