Frictions stir welding is a solid state sintering joining process which is relatively new, energy efficient and environmentally friendly. This welding technique is widely used and hugely appreciated, Mishra states ‘FSW is considered to be the most significant development in metal joining in a decade’ (Mishra, 2005:1).
This welding technique works by using a rotating cylindrical tool, which is made of tool steel, with a probe on the end of it. The tool is plunged onto the work piece which is rigidly clamped down and moved along the surface of the work piece which going to be welded. Welding is achieved by friction from the tool which heats up the material. The weld is then categorized into three zones which are:
- Thermally affected zone – the grain structure is not affected by the welding
- Thermomechanically affected zone – the grains are severely twisted
- Dynamically affected zone – old grains disappear and numerous small grains recrystallize
Heating during the welding can cause considerable loss in strength of the material (Kou, 2003:370).
Figure 1: Diagram of friction stir welding (Taken from Friction Stir Link http://www.frictionstirlink.com/desc.html )
(Kou, 2003:370).
Materials that are friction stir welded
Friction stir welding is used on aluminium alloys such as 2xxx, 5xxx, 6xxx and 7xxx. Some of these aluminium alloys are nearly unweldable by fusion welding techniques. This technique can also join dissimilar metals to make hybrid components. Other materials that can be friction stir welded are non-ferrous materials (Mg, Cu, and Ti etc.), steel and even thermoplastics (Mishra, 2005:48)
Applications of the materials
In the Aerospace industry there is a high demand for high-strength aluminium alloys which are used for different parts on an aircraft. These high-strength alloys are difficult to weld using conventional fusion welding techniques due to hot cracking during welding. The alternate method is friction stir welding which is a successful technique when used on these high-strength alloys, this method is also more cost effective and less complex than riveting (Mishra, 2005:61).
Friction stir welding is used to weld armour for the military as it proves better than MIG welding because it has better resistance to exfoliation corrosion and stress corrosion cracking. Friction stir welded materials will also have better mechanical properties than gas metal arc welded materials and gas tungsten arc welding. This method of welding is better for equipment used by the military because the materials will last longer (Mishra, 2005:62).
Bibliography
Kou, Sindo. (2003) Welding Metallurgy New Jersey, Wiley-Interscience
Mishra, R.S. (2005). Friction stir welding and processing. Materials Science and Engineering, Vol 50, 1-78
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