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Effect of dwell time on joint interface microstructure and strength of dissimilar friction stir spot-welded al-5083 and st-12 alloy sheets

Fereiduni, E ; Sharif University of Technology | 2017

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  1. Type of Document: Article
  2. DOI: 10.1007/s11661-017-3971-7
  3. Publisher: Springer Boston , 2017
  4. Abstract:
  5. Joining of Al-5083 alloy sheet to St-12 steel sheet was performed using a new friction stir spot welding (FSSW) technique in which the tool pin tip did not enter lower steel sheet. Effect of dwell time on the microstructure and mechanical properties of the joints was studied by various methods including microhardness measurements, shear test, stereo and light microscopy as well as scanning and transmission electron microscopy (SEM and TEM). Results indicated that compared to the conventional FSSW process, stronger joints can be achieved by this FSSW technique. Cross-sectional observation of the failed specimens indicated the occurrence of final fracture from the circumference of the tool pin where the Al sheet thickness was decreased as a result of the tool pin penetration. However, microhardness measurements introduced these fracture locations as the hardest regions of the Al part of welds. In addition to the Al3Fe and Al5Fe2 intermetallic compounds reported in the literature to form at the interface of dissimilar Al/steel joints, a third layer of AlFe intermetallic compound was also identified adjacent to the steel side of welds. Enhancement of the dwell time from 5 to 15 seconds increased the intermetallic layer thickness from ~1.7 to ~3 µm and resulted in the formation of harder stirred zone. This consequently increased the strength of the weld. © 2017, The Minerals, Metals & Materials Society and ASM International
  6. Keywords:
  7. Alloy steel ; Fracture ; Friction ; Friction stir welding ; High resolution transmission electron microscopy ; Intermetallics ; Iron compounds ; Microhardness ; Microstructure ; Scanning electron microscopy ; Shear flow ; Soldering alloys ; Spot welding ; Steel sheet ; Transmission electron microscopy ; Welding ; Welds ; Cross-sectional observations ; Fracture location ; Friction stir spot welding ; Intermetallic layer ; Joint interfaces ; Microhardness measurement ; Microstructure and mechanical properties ; Scanning and transmission electron microscopy ; Aluminum
  8. Source: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 48, Issue 4 , 2017 , Pages 1744-1758 ; 10735623 (ISSN)
  9. URL: https://link.springer.com/article/10.1007/s11661-017-3971-7