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Materials processing and joining

Which statement correctly describes the features of friction stir welding (FSW)?

  1. AA rotating tool's frictional heat softens the material below its melting point to stir and join it, so pores and solidification cracks are rare
  2. BIt is a type of arc welding in which the joint is heated above its melting point and filler metal is added while a rotating tool stirs the molten weld pool
  3. CA high-energy electron beam melts the material locally and penetrates deeply into it, so the joining can only be done inside a large vacuum chamber
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Answer: A. A rotating tool's frictional heat softens the material below its melting point to stir and join it, so pores and solidification cracks are rare

In friction stir welding, a tool with a protrusion (probe) at its tip is rotated and plunged into the abutting joint, the material softened by frictional heat is made to flow plastically and mix, and the tool then travels along the joint line. Because it is solid-state joining in which the material does not melt, the porosity and solidification cracking that are problems in fusion welding do not occur, and the joint consists of fine recrystallized grains. It can join 2000- and 7000-series aluminum alloys, which are prone to hot cracking in fusion welding, and it is used for railway car and ship members. The descriptions of arc welding, which heats above the melting point, and of electron beam welding belong to other joining methods. Using it on high-melting steels or titanium requires tool materials that resist wear at high temperature.

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