Investigation of microstructure and mechanical properties of friction stir welded AA6016-T4 and DC04 alloy joints

  • Krishna Komerla
  • Andreas Naumov
  • Chris Mertin
  • Ulrich Prahl
  • Wolfgang Bleck


In this study, the microstructure and mechanical properties of dissimilar friction stir welded aluminum and steel joints were investigated, in order to understand the role of tool offset in the enhancement of weld properties. Conventional techniques like light-optical microscopy, electron back scatter diffraction, energy dispersive spectroscopy, and indentation tests were utilized to characterize the joints. Tool offset resulted in a mode of welding where minimal shear strain accumulation in steel and complete dynamic recrystallization of aluminum were achieved. Additionally, macroscopically defect and inter-metallic compound free joints were obtained, with only a small fraction of Fe chips embedded in the aluminum matrix. Through plastic deformation and thermal effects, significant differences in grain size and micro-hardness were observed in the various regions of the welded joint. Due to high temperatures and strain rates, dynamic recrystallization was activated in aluminum. The kernel average misorientation map revealed the lack of stored deformation energy in the microstructure, indicating the presence of fully recrystallized grains. Due to its high thermal stability, steel did not recrystallize but, exhibited marginal grain growth in both thermo-mechanically affected zone and heat-affected zone. It also contained a highly refined grain structure in the weld zone. The texture maps plotted for the weld zone of Fe alloy showed weak shear texture indicating minimal shear strain accumulation. A good correlation between the experimental and predicted hardness was observed in steel. In the aluminum alloy, however, prediction was overestimation as the additional softening due to dynamic recrystallization and dissolution or coarsening of precipitates was not taken into account by the model.


Friction stir welding Electron back scatter diffraction (EBSD) Micro-hardness Grain size Shear texture Dynamic recrystallization 


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The authors would like to thank the German Research Foundation DFG for their continued support of our research within the Cluster of Excellence “Integrative Technologies for High Wage Countries”.


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Copyright information

© Springer-Verlag London Ltd. 2017

Authors and Affiliations

  • Krishna Komerla
    • 1
  • Andreas Naumov
    • 2
  • Chris Mertin
    • 3
  • Ulrich Prahl
    • 1
  • Wolfgang Bleck
    • 1
  1. 1.Steel Institute IEHKRWTH Aachen UniversityAachenGermany
  2. 2.Welding and Joining Institute ISFRWTH Aachen UniversityAachenGermany
  3. 3.Institute of Metal Forming IBFRWTH Aachen UniversityAachenGermany

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