Application of Imaging Techniques to Determine the Post-Yield Behaviour of the Heterogeneous Microstructure of Friction Stir Welds

S Ramachandran*, A.K. Lakshminarayanan, P.A.S. Reed, Janice M Dulieu-Barton

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

4 Citations (Scopus)
37 Downloads (Pure)

Abstract

Background
Friction Stir Welding (FSW) causes intense plastic deformation and consequent thermomechanical interactions resulting in a localised heterogeneous microstructure. To understand the weld mechanical behaviour, it is necessary to identify each microstructural sub-region in the weld.

Objective
Determine the relationship between the local microstructure and mechanical behaviour of the different microstructural regions in a FSW.

Methods
Scanning electron microscopy (SEM) identified the microstructural sub-regions of an FSW joint. A novel High-Resolution Digital Image Correlation (HR-DIC) methodology enabled the determination of full-field strain response to provide the mechanical behaviour of the FSW sub-regions. X-ray computed tomography (CT) identified the geometry of the FSW and material composition.

Results
The grain morphology in the FSW varied in the stir zone with a fine grain structure in the weld nugget and larger grains in the thermomechanical affected zone (TMAZ); the grains were larger in the retreating side (RS) compared to the advancing side (AS). Tungsten deposits were found in the weld nugget and attributed to tool wear. The mechanical properties of the weld subregions showed that the material in the stir zone had a greater yield strength than the base material and the RS of the FSW was much more ductile than the weld nugget and the AS side. The tungsten distributions in the stir zone correlated with the local mechanical behaviour.

Conclusions
A novel methodology is developed that combines microstructural observations with HR-DIC enabling, for the first time, the FSW sub-region mechanical behaviour, to be related to the local grain morphology and inclusions caused by tool wear.
Original languageEnglish
Pages (from-to)1045-1063
Number of pages19
JournalExperimental Mechanics
Volume61
DOIs
Publication statusPublished - 21 Apr 2021

Bibliographical note

Funding Information:
The authors like to acknowledge the funding support provided by the Engineering and Physical Sciences Research Council (EPSRC) through a research grant (EPSRC Reference: EP/R031711/1). The experimental work described in the paper was conducted in the Testing and Structures Research Laboratory (TSRL) at the University of Southampton (https://www.southampton.ac.uk/engineering/research/facilities/tsrl.page ). The authors are grateful for the support received from Andrew Robinson, the TSRL Principal Experimental Officer. The authors also thank the Department of Mechanical Engineering, Sri Sivasubramaniya Nadar College of Engineering (Autonomous), Tamilnadu, India for supplying the FSW test specimens.

Funding Information:
The authors like to acknowledge the funding support provided by the Engineering and Physical Sciences Research Council (EPSRC) through a research grant (EPSRC Reference: EP/R031711/1). The experimental work described in the paper was conducted in the Testing and Structures Research Laboratory (TSRL) at the University of Southampton ( https://www.southampton.ac.uk/engineering/research/facilities/tsrl.page ). The authors are grateful for the support received from Andrew Robinson, the TSRL Principal Experimental Officer. The authors also thank the Department of Mechanical Engineering, Sri Sivasubramaniya Nadar College of Engineering (Autonomous), Tamilnadu, India for supplying the FSW test specimens.

Publisher Copyright:
© 2021, The Author(s).

Keywords

  • Stainless steel
  • Friction stir welding
  • Digital image correlation

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