Microstructure evolution and high cycle fatigue failure behavior of friction stir-welded Ti–6Al–4 V at varying welding speeds

Peter Madindwa Mashinini, Isaac Dinaharan, Danie Gerhardus Hattingh, Jebaraj David Raja Selvam

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)

Abstract

Ti–6Al–4V sheets of 3 mm thickness were joined via friction stir welding (FSW) technique using industrial purpose I-STIR machine. Since the welding speed is a key parameter in production, it was varied from 40 to 200 mm/min in steps of 40 mm/min. Sound joints were obtained without macroscopic defects using a lanthanated tungsten tool. The microstructure, hardness, and residual stress of the joints were evaluated. Stir zone encountered phase transformation and the microstructure of the base metal transformed into a lamellar structure resembling a widmanstätten structure. There was a marginal improvement in hardness subsequent to welding. Tensile kind of residual stresses were recorded along the longitudinal direction of the weld seam. Compressive stresses were observed outside the weld region. Fatigue tests were carried in as welded and polished condition at a stress ratio of 0.1. All specimens failed at the stir zone irrespective of the surface condition and the welding speed. Shoulder formed striation marks served as crack initiation sites for as welded specimens. Slip bands within the lamellar structure or root flaws act as crack initiators in case of polished specimens. The microstructural variation influenced the fatigue strength to a certain degree. The increase in welding speed lowered the fatigue strength.

Original languageEnglish
Pages (from-to)4041-4054
Number of pages14
JournalInternational Journal of Advanced Manufacturing Technology
Volume122
Issue number9-10
DOIs
Publication statusPublished - Oct 2022

Keywords

  • Fatigue
  • Friction stir welding
  • Lamellar structure
  • Residual stress
  • Titanium alloy

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Software
  • Mechanical Engineering
  • Computer Science Applications
  • Industrial and Manufacturing Engineering

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