FSW: Multiple Choice

A set of questions on friction stir welding to prepare for your exam

Answering the following multiple choice questions will help you to assess your level of knowledge about friction stir welding, e.g. when you prepare yourself for an exam. Only one of the four answers is correct.


Examples of right-handed threads, neutral threads or left-handed threads in combi­nation with the welding direction and the recommended direction of the tool rotation.

© AluStir


Which type of threads is generally preferred? Please, press one of the four buttons.

Tool Offset from the Centreline

Cross-sectional macrostructures of Al-Cu friction stir welds made using various offsets

© Nima Eslami, Yannik Hischer, Alexander Harms, Dennis Lauterbach and Stefan Böhm, CC BY 4.0


Which offset should be used for welding dissimilar materials? Please, press one of the four buttons.


FSW AA6061/AA6061 + 40 vol% SiC Plates at Cenim-CSIC, DTU and AIMEN. Optical micrograph (a) and schematic illustration (b) of the cross-section. Dark-gray and light-gray regions correspond to the MMC and the AA6061 alloy, respectively. Intermediate shading corresponds to the area which appears to be one broad band close to the plate bottom and which splits into two narrower individual bands on the advancing side. Dashed lines indicate the approximate location of the pin during FSW.

© S Señorís-Puentes, RF Serrano, G González-Doncel, JH Hattel; OV Mishin, CC BY 4.0


If you look at the flash on the left-hand-side and on the right-hand-side of a friction stir weld, you will note that...

Plasticised Material underneath the Tool

A certain amount of plasticised material should be visible underneath a tool that is tilted by 2.5° 

© AluStir


If the the FSW tool, which is tilted by 2.5°, has been plunged at the correct tool heel plunge depth, the following amount of plasticised material should be visible:

Onion Rings

Onions on Flish and Chips

© AluStir


The mixture of the workpiece materials causes a refined microstructure in the nuggets, which some metallurgists describe colloquially as "onion rings", should be as follows:  


FSW of Copper to Steel

The FSW tool is commonly offset towards the copper for FSW of copper to steel

© AluStir


For friction stir welding of copper to steel, the offset of the FSW tool towards the copper should be set as follows:  


2D-Non-Linear Welds

Friction stir welding of non-linear welds

© AluStir


If you have a non-linear weld with tight curves, you should consider the following:[2]



An anonymised Google Analytics survey in November 2021 showed:

  • Contestants: 239
  • Right: 123
  • Wrong: 84
  • No answer: 32


  1. Wenya Li, Qian Yang, Zhihan Zhang and Dalu Gao: Effect of weld curvature radius and tool rotation direction on joint microstructure in friction stir welding casting alloys. Materials & Design, Volume 53, 2014, ISSN 0261-3069. Pages 124-128.